[Federal Register Volume 89, Number 108 (Tuesday, June 4, 2024)]
[Rules and Regulations]
[Pages 48034-48130]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-11645]



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Vol. 89

Tuesday,

No. 108

June 4, 2024

Part II





 Department of the Interior





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Fish and Wildlife Service





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50 CFR Part 17





Endangered and Threatened Wildlife and Plants; Endangered Species 
Status With Critical Habitat for Guadalupe Fatmucket, Texas Fatmucket, 
Guadalupe Orb, Texas Pimpleback, Balcones Spike, and False Spike, and 
Threatened Species Status With Section 4(d) Rule and Critical Habitat 
for Texas Fawnsfoot; Final Rule

  Federal Register / Vol. 89 , No. 108 / Tuesday, June 4, 2024 / Rules 
and Regulations  

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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R2-ES-2019-0061; FXES1111090FEDR-245-FF09E21000]
RIN 1018-BD16


Endangered and Threatened Wildlife and Plants; Endangered Species 
Status With Critical Habitat for Guadalupe Fatmucket, Texas Fatmucket, 
Guadalupe Orb, Texas Pimpleback, Balcones Spike, and False Spike, and 
Threatened Species Status With Section 4(d) Rule and Critical Habitat 
for Texas Fawnsfoot

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Final rule.

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SUMMARY: We, the U.S. Fish and Wildlife Service (Service), determine 
endangered species status under the Endangered Species Act of 1973 
(Act), as amended, for the Guadalupe fatmucket (Lampsilis bergmanni), 
Texas fatmucket (Lampsilis bracteata), Guadalupe orb (Cyclonaias 
necki), Texas pimpleback (Cyclonaias (=Quadrula) petrina), Balcones 
spike (Fusconaia (=Quincuncina) iheringi), and false spike (Fusconaia 
(=Quincuncina) mitchelli), and threatened species status for the Texas 
fawnsfoot (Truncilla macrodon), seven species of freshwater mussels 
from central Texas. We also issue a rule under section 4(d) of the Act 
for the Texas fawnsfoot that provides measures that are necessary and 
advisable to provide for the conservation of the Texas fawnsfoot. In 
addition, we designate critical habitat for all seven species. In 
total, approximately 1,577.5 river miles (2,538.7 river kilometers) in 
Blanco, Brown, Caldwell, Coleman, Comal, Concho, DeWitt, Gillespie, 
Gonzales, Guadalupe, Hays, Kendall, Kerr, Kimble, Lampasas, Llano, 
Mason, McCulloch, Menard, Mills, Palo Pinto, Parker, Runnels, San Saba, 
Shackelford, Stephens, Sutton, Throckmorton, Tom Green, Travis, and 
Victoria Counties, Texas, fall within the boundaries of the critical 
habitat designation. This rule applies the protections of the Act to 
these species and their designated critical habitats.

DATES: This rule is effective July 5, 2024.

ADDRESSES: This final rule is available on the internet at https://www.regulations.gov. Comments and materials we received, as well as 
supporting documentation we used in preparing this rule, are available 
for public inspection at https://www.regulations.gov at Docket No. FWS-
R2-ES-2019-0061.
    Availability of supporting materials: Supporting materials we used 
in preparing this rule, such as the species status assessment report, 
are available for public inspection at https://www.regulations.gov at 
Docket No. FWS-R2-ES-2019-0061. For the critical habitat designation, 
the coordinates or plot points or both from which the maps are 
generated are included in the decision file and are available at 
https://www.regulations.gov at Docket No. FWS-R2-ES-2019-0061.

FOR FURTHER INFORMATION CONTACT: Karen Myers, Field Supervisor, U.S. 
Fish and Wildlife Service, Austin Ecological Services Field Office, 
1505 Ferguson Lane, Austin, TX 78754; telephone (512) 937-7371. 
Individuals in the United States who are deaf, deafblind, hard of 
hearing, or have a speech disability may dial 711 (TTY, TDD, or 
TeleBraille) to access telecommunications relay services. Individuals 
outside the United States should use the relay services offered within 
their country to make international calls to the point-of-contact in 
the United States.

SUPPLEMENTARY INFORMATION: 

Executive Summary

    Why we need to publish a rule. Under the Act, a species warrants 
listing if it meets the definition of an endangered species (in danger 
of extinction throughout all or a significant portion of its range) or 
a threatened species (likely to become endangered within the 
foreseeable future throughout all or a significant portion of its 
range). If we determine that a species warrants listing, we must list 
the species promptly and designate the species' critical habitat to the 
maximum extent prudent and determinable. We have determined that the 
Guadalupe fatmucket (Lampsilis bergmanni), Texas fatmucket (Lampsilis 
bracteata), Guadalupe orb (Cyclonaias necki), Texas pimpleback 
(Cyclonaias (=Quadrula) petrina), Balcones spike (Fusconaia 
(=Quincuncina) iheringi), and false spike (Fusconaia (=Quincuncina) 
mitchelli) meet the Act's definition of endangered species, and the 
Texas fawnsfoot (Truncilla macrodon) meets the Act's definition of a 
threatened species; therefore, we are listing them as such, finalizing 
a rule under section 4(d) of the Act for the Texas fawnsfoot, and 
designating critical habitat. Both listing a species as an endangered 
or threatened species and designating critical habitat can be completed 
only by issuing a rule through the Administrative Procedure Act 
rulemaking process (5 U.S.C. 551 et seq.).
    What this document does. This rule makes final the listing of the 
Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, Texas pimpleback, 
Balcones spike, and false spike as endangered species, and the Texas 
fawnsfoot as a threatened species with a rule issued under section 4(d) 
of the Act (a ``4(d) rule''). In addition, this rule designates 
critical habitat for all seven central Texas mussel species in 20 units 
(including 32 subunits) totaling 1,577.5 river miles (2,538.7 river 
kilometers (km)) on private, State, and Federal property within 
portions of 31 counties in Texas.
    The basis for our action. Under the Act, we may determine that a 
species is an endangered or threatened species because of any of five 
factors: (A) The present or threatened destruction, modification, or 
curtailment of its habitat or range; (B) overutilization for 
commercial, recreational, scientific, or educational purposes; (C) 
disease or predation; (D) the inadequacy of existing regulatory 
mechanisms; or (E) other natural or manmade factors affecting its 
continued existence; we also take into account conservation efforts, 
such as Candidate Conservation Agreements with Assurances (CCAAs). We 
have determined that increased fine sediment, changes in water quality, 
and altered hydrology in the form of inundation and loss of flow and 
scour of substrate (Factor A), collection (Factor B), predation (Factor 
C), and barriers to fish movement (Factor E) are the primary threats to 
these species. These factors are all exacerbated by the ongoing and 
expected effects of climate change.
    Section 4(a)(3) of the Act requires the Secretary of the Interior 
(Secretary), to designate critical habitat, to the maximum extent 
prudent and determinable, concurrent with listing. Section 3(5)(A) of 
the Act defines critical habitat as (i) the specific areas within the 
geographical area occupied by the species, at the time it is listed, on 
which are found those physical or biological features (I) essential to 
the conservation of the species and (II) which may require special 
management considerations or protections; and (ii) specific areas 
outside the geographical area occupied by the species at the time it is 
listed, upon a determination by the Secretary that such areas are 
essential for the conservation of the species. Section 4(b)(2) of the 
Act states that the Secretary must make the designation on the basis of 
the best scientific data

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available and after taking into consideration the economic impact, the 
impact on national security, and any other relevant impacts of 
specifying any particular area as critical habitat.

Previous Federal Actions

    Please refer to the August 26, 2021, proposed rule (86 FR 47916) 
for a detailed description of previous Federal actions concerning these 
species.

Peer Review

    A species status assessment (SSA) team prepared an SSA report for 
the Guadalupe fatmucket, Texas fatmucket, Texas fawnsfoot, Guadalupe 
orb, Texas pimpleback, and false spike. This SSA report was competed 
prior to the taxonomic divergence of the false spike to reflect the 
recently described Balcones spike (Fusconaia iheringi) (Smith et al. 
2020, entire) (see Summary of Changes from the Proposed Rule, below). 
The SSA team was composed of Service biologists, in consultation with 
other species experts. The SSA report represents a compilation of the 
best scientific and commercial data available concerning the status of 
the species, including the impacts of past, present, and future factors 
(both negative and beneficial) affecting the species.
    In accordance with our joint policy on peer review published in the 
Federal Register on July 1, 1994 (59 FR 34270), and our August 22, 
2016, memorandum updating and clarifying the role of peer review of 
listing actions under the Act, we solicited independent scientific 
review of the information contained in the SSA report. We sent the SSA 
report to eight independent peer reviewers and received six responses. 
Results of this structured peer review process can be found at https://regulations.gov. In preparing the proposed rule, we incorporated the 
results of these peer reviews, as appropriate, into version 1.1 of the 
SSA report, which was the foundation for the proposed rule and this 
final rule. A summary of the peer review comments and our responses can 
be found under Summary of Comments and Recommendations, below.

Summary of Changes From the Proposed Rule

    Based upon our review of the public comments, State agency 
comments, peer review comments, and relevant information that became 
available since the August 26, 2021, proposed rule published, we 
updated information in our SSA report, including:
     Updating the taxonomy of false spike (Fusconaia mitchelli) 
to reflect the divergence from the recently described Balcones spike 
(Fusconaia iheringi) (Smith et al. 2020, entire).
     Updating text to clearly differentiate between the threat 
of sedimentation to freshwater mussels and naturally occurring 
turbidity in a river system; improve consistency in the use of 
``impaired'' when discussing water quality; and further differentiate 
between the threat of sedimentation within a system and the presence of 
turbidity associated with fine organic or inorganic matter, soluble 
organic compounds, algae, or other microscopic organisms.
    We made these and other changes as appropriate in this final rule. 
In addition to minor clarifying edits and incorporation of additional 
information on the species' biology, populations, and threats, this 
final determination differs from the August 26, 2021, proposed rule in 
the following ways:
    (1) We add updated population data for the Texas fatmucket, 
including survey data made available by the Texas Department of 
Transportation since the publication of the proposed rule. Based on the 
presence of Texas fatmucket in Unit TXFM-6b (Upper Onion Creek), this 
unit has now changed from unoccupied to occupied, so we combine the 
Upper and Lower Onion Creek critical habitat units (TXFM-6b and TXFM-
6a, respectively) into one occupied unit (TXFM-6). Therefore, this rule 
differs slightly from the proposed critical habitat designation (86 FR 
47916; August 26, 2021) by unit numbering and occupancy.
    (2) Both the Balcones spike and the false spike are included in 
this final listing rule because the entity known as false spike in the 
August 26, 2021, proposed rule was taxonomically divided into the two 
species. We rename and renumber critical habitat units to reflect the 
updated taxonomy and range of false spike and Balcones spike. We 
renumber proposed critical habitat unit FASP-4 (Guadalupe River Unit) 
as FASP-1; it is now the only critical habitat unit for the false 
spike. The remaining three proposed critical habitat units for the 
false spike are renamed and renumbered for the Balcones spike: unit 
FASP-1 (Little River Unit) is now BASP-1, FASP-2 (San Saba River Unit) 
is now BASP-2, and FASP-3 (Llano River Unit) is now BASP-3.
    (3) For the critical habitat designation, we exclude proposed units 
TXFF-3, TXFF-4, and BASP-1 (previously FASP-1) based on the 
implementation of conservation measures completed by the Brazos River 
Authority (BRA) as part of their candidate conservation agreement with 
assurances (CCAA) for the Balcones spike and Texas fawnsfoot in the 
Brazos River Basin (BRA 2021, pp. 35-51; hereafter, the ``BRA 
Agreement''). We also exclude proposed units TXFF-6 and TXPB-6 based 
upon the implementation of conservation measures completed by the Lower 
Colorado River Authority (LCRA) as part of their CCAA for the Texas 
pimpleback, Texas fawnsfoot, Texas fatmucket, and Balcones spike in the 
Lower Colorado River Basin below O.H. Ivie Reservoir (LCRA 2023, pp. 
45-84; hereafter, the ``LCRA Agreement''). In addition, we exclude 
proposed units TXFF-7 and TXFF-8 based upon the implementation of 
conservation measures completed by the Trinity River Authority (TRA) as 
part of their CCAA for six species in the Trinity River Basin (TRA 
2023, pp. 47-66; hereafter, the ``TRA Agreement'').
    (4) We incorporate minor changes in the length of river miles (and 
kilometers) of occupied stream reaches. We also incorporate minor 
changes in the length of river miles (and kilometers) from the proposed 
critical habitat to reflect those included in the final critical 
habitat unit maps. While we use the same start and end points for all 
final critical habitat unit designations, these minor changes in 
critical habitat designation length are the result of geoprocessing 
tools used in ArcGIS.
    (5) We include short textual descriptions of the designated units 
under Regulation Promulgation in this rule, as under 50 CFR 17.94, 
general descriptions of the location and boundaries of each area may be 
provided to clarify or refine what is included within the boundaries 
depicted on the map, or to explain the exclusion of sites (e.g., paved 
roads, buildings) within the mapped area. These descriptions mirror 
information in the preamble of this rule, which reflects the unit 
description information presented in our August 26, 2021, proposed rule 
as amended by the changes described in this document.
    (6) Based on public comments, we update language in the 4(d) rule 
for the Texas fawnsfoot to clarify and refine the specific prohibitions 
and exceptions to those prohibitions to minimize potential ambiguity. 
Specifically, to qualify for exceptions when conducting channel 
restoration projects, we clarify that the project must meet all 
applicable Federal, State, and local permitting requirements. In 
addition, to allow the Service to make arrangements for surveys and 
potential relocation of any mussels that might be adversely affected 
during channel restoration projects, we add that notice must be 
provided to the Service of the location and nature of the

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proposed work at least 30 days prior to commencing actual construction 
within an area designated as critical habitat for the Texas fawnsfoot. 
In addition, to qualify for exceptions when conducting streambank 
stabilization projects, we specify that: (i) native live stakes, native 
live fascines, or native live brush must be used; (ii) methods that 
include the use of quarried rock (riprap) for more than 25 percent of 
the area within the streambanks or include the use of rock baskets or 
gabion structures do not qualify for this exception; (iii) work using 
these bioengineering methods must be performed at base flow or low 
water conditions and when significant rainfall likely to result in 
significant runoff is not predicted at or upstream of the area where 
work is proposed for a period of at least 3 days after the work is 
scheduled to be undertaken, in order to reduce streambank erosion and 
sedimentation; and (iv) the project must meet all applicable Federal, 
State, and local permitting requirements. Further, to qualify for 
exceptions when conducting soil and water conservation practices, and 
riparian and adjacent upland habitat management activities, we add 
that, to allow the Service to make arrangements for surveys and 
potential relocation of any mussels that might be adversely affected 
during channel restoration projects, notice must be provided to the 
Service of the location and nature of the proposed work at least 30 
days prior to commencing actual construction within an area designated 
as critical habitat for Texas fawnsfoot.
    (7) Based on public comments, we update language to include 
examples of discretionary actions for the central Texas mussels that 
may be subject to consultation procedures under section 7, and more 
clearly define the standards for avoiding jeopardizing the continued 
existence of the species for future section 7 conferences/consultations 
(see Available Conservation Measures, below). In addition, we update 
language to include protective regulations to address the threats to 
the Texas fawnsfoot under section 9, as well as what activities would 
and would not be likely to constitute a violation of section 9 take 
prohibition (see Provisions of the 4(d) Rule, below).
    (8) Based on a public comments, we also make minor, nonsubstantive 
changes and corrections throughout this rule in response to public 
comments. However, the information we received during the public 
comment period on the proposed rule did not change our determination 
that the Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, Texas 
pimpleback, Balcones spike, and false spike meet the Act's definition 
of endangered species, and the Texas fawnsfoot meets the Act's 
definition of a threatened species.

Summary of Comments and Recommendations

    In the proposed rule published on August 26, 2021 (86 FR 47916), we 
requested that all interested parties submit written comments on the 
proposal by October 25, 2021. We also contacted appropriate Federal and 
State agencies, scientific experts and organizations, and other 
interested parties and invited them to comment on the proposal. 
Newspaper notices inviting general public comment were published in the 
Austin Statesman, and we held public hearings on September 14 and 
September 16, 2021. All substantive information we received during the 
comment period has either been incorporated directly into this final 
determination or is addressed below.

Peer Reviewer Comments

    As discussed in Peer Review above, we received comments from six 
peer reviewers on the draft SSA report. We reviewed all comments we 
received from the peer reviewers for substantive issues and new 
information regarding the contents of the SSA report. Peer reviewer 
comments are addressed in the following summary. As discussed above, 
because we conducted this peer review prior to the publication of our 
proposed rule, we had already incorporated all applicable peer review 
comments into version 2.1 of the SSA report, which was the foundation 
for the proposed rule. The peer reviewers generally concurred with our 
methods and conclusions, and provided additional information, 
clarifications, and suggestions to improve the SSA report (Service 
2019b, entire). Peer reviewer comments are addressed in the following 
summary and are incorporated into the SSA report as appropriate.
    (1) Comment: One peer reviewer suggested that, in addition to the 
value limited by the population abundance factor in the overall current 
condition, the ranges used to assign values to the six condition 
factors after averaging should be included in the SSA report.
    Our response: The overall average current condition of the 
populations, not limited by the abundance condition, is not reflective 
of population condition. We chose to limit the overall current 
conditions so they could not exceed abundance because our information 
regarding habitat is not robust enough to outweigh abundance (i.e., a 
mussel population with low abundance but indications of moderate or 
high habitat factors should not be rated to be in moderate or high 
condition). Therefore, reporting the unlimited averages would only 
cause reader confusion that could be derived from presenting multiple 
``overall condition'' values for each population.
    (2) Comment: One peer reviewer suggested, particularly for false 
spike, that the lack of knowledge of host fish could be a factor 
influencing central Texas mussel distribution and abundance if the host 
fish is in fact not a common species.
    Our response: Following the submission of the draft SSA for peer 
review, studies were completed identifying the red shiner (Cyprinella 
lutrensis) and blacktail shiner (Cyprinella venusta) as host fish for 
false spike, and both are common fish species in this area (Dudding et 
al. 2019, p. 16). Host fish for congeners of the mussel species that 
are the subjects of this rule are a suite of typically common fish 
species, and therefore it is unlikely that these mussel species rely 
exclusively on rare fish species to serve as the sole or primary fish 
hosts for reproduction.
    (3) Comment: One peer reviewer and one State commenter stated 
concerns of using 35-millimeter (mm) length to define juveniles, 
especially the use of the threshold for the generally smaller Texas 
fawnsfoot, and they requested that the Service revisit the evidence of 
reproduction criteria, in particular for smaller species.
    Our response: We consulted with regional and national freshwater 
mussel experts from around the United States, and the 35-mm length was 
considered to be an appropriate delineating threshold to use when 
differentiating between adult and juvenile mussels. This conclusion was 
made based on the general consensus amongst those asked that 
individuals below 35 mm in length are not readily detectable during 
field surveys. Without species-specific data identifying the known size 
at age of sexual maturity for the subject species, we found it 
appropriate to consistently use the same cutoff for multiple species if 
no species-specific data were available. As these data become 
available, we will update these criteria as appropriate.

Comments From States

    (4) Comment: One commenter requested that the Service emphasize 
desiccation study data completed at the San Marcos Aquatic Resources 
Center that demonstrate that Texas pimpleback is able to tolerate 32 
days without water and the Texas fatmucket can tolerate about 3 days 
without water.

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    Our response: The desiccation trials mentioned by the commenter 
were conducted in a laboratory growth chamber at 25 degrees Celsius 
([deg]C) (77 degrees Fahrenheit ([deg]F)) and the relative humidity is 
not reported (Bonner et al. 2018, p. 193). Presumably, live freshwater 
mussels experiencing dewatering occurring in the natural environment 
would be exposed to temperatures greater than 25 [deg]C (77 [deg]F), 
especially during summer, when drying events are most likely to occur. 
Additionally, exposed animals would be susceptible to predation. 
Therefore, while we report the results of the desiccation study, 
emphasizing them could erroneously create an inaccurate representation 
of the conditions that exposed mussels would experience and 
artificially inflate the exposure time during which mussels could be 
expected to survive in the wild.
    (5) Comment: The State of Texas disagrees with the finding that 
there are no federalism implications for the designation of critical 
habitat.
    Our response: Federalism is the division and sharing of power 
between the Federal Government and the individual State governments. In 
keeping with Department of the Interior and Department of Commerce 
policy, we requested information from, and coordinated development of, 
the proposed critical habitat designation with appropriate State 
resource agencies throughout central Texas. From a federalism 
perspective, the designation of critical habitat directly affects only 
the responsibilities of Federal agencies. The Act imposes no other 
duties with respect to critical habitat, either for States and local 
governments, or for anyone else. As a result, this final rule does not 
have substantial direct effects either on the States, or on the 
relationship between the national government and the States, or on the 
distribution of powers and responsibilities among the various levels of 
government. In accordance with Executive Order 13132 (Federalism), this 
rule does not have significant federalism effects, and a federalism 
summary impact statement is not required.
    (6) Comment: The State of Texas requested clarification on whether 
the completion of an approved freshwater mussel identification and 
sampling course and proficiency testing will be required for scientists 
with a permit issued under section 10(a)(1)(a) of the Act (a 
``10(a)(1)(a) permit''), and whether the 4(d) rule will allow qualified 
individuals to relocate Texas fawnsfoot.
    Our response: The provision of the 4(d) rule that allows for Texas 
fawnsfoot surveys to be conducted by those who pass an approved Texas 
mussel identification and sampling course is intended for those who are 
sampling for freshwater mussels, in which mussels are collected, 
identified, and returned to the mussel bed from which they came. 
Surveyors who are trained in survey techniques and how to identify the 
various species that occur in Texas will not need a 10(a)(1)(a) permit 
because we expect the effects to the species to be negligible. This 
provision in the 4(d) rule is not intended to replace the 10(a)(1)(a) 
permit process, and those with a 10(a)(1)(a) permit will not be 
required to complete the course. Furthermore, relocation of Texas 
fawnsfoot from one mussel bed to another is not an excepted form of 
take under this 4(d) rule.
    (7) Comment: The State of Texas suggested that naturally occurring 
ambient water quality should be considered in the context of historical 
water quality, and laboratory thresholds reported for temperature, 
salinity, chlorides, and dissolved oxygen should be considered when 
identifying essential water quality thresholds as components of 
critical habitat.
    Our response: The objective use of laboratory-based studies, in 
addition to in situ monitoring, is critical to the understanding of 
physiological and toxicological thresholds for freshwater mussels. Even 
though certain ambient water quality parameters are currently occurring 
in the presence of live freshwater mussels, there is no clear 
indication that these parameters are protective of freshwater mussels, 
as different life stages of the species are more sensitive to water 
quality changes than others (i.e., glochidia and juveniles are more 
sensitive than adults). Freshwater mussel populations throughout the 
State of Texas have declined in recent decades, and the presence of 
reduced or restricted mussel populations should not be used as an 
indicator that instream conditions are adequate for the long-term 
persistence of the population. The completion of laboratory studies can 
provide objective thresholds for individual chemicals, temperatures, or 
other water quality parameters for both lethal and sublethal effects on 
individual freshwater mussel species. When identifying the physical or 
biological features related to water quality for the mussels, we set 
the thresholds at levels that have been objectively identified as 
protective of the mussels. Therefore, laboratory-derived values were 
selected when identifying these components rather than utilizing 
observed ambient values, which, as described above, may not be 
protective of all the covered species life stages.
    (8) Comment: The State of Texas requested clarification on how 
increased extreme precipitation is projected to have divergent effects 
on future high stream flows in different rivers, as the Service has 
predicted for the Llano River and Middle Trinity River.
    Our response: Different river basins experience different 
conditions that affect the future of flows within those basins. For the 
Llano River, while there have been recent significant high flow events, 
recent trends in stream flows in the river have shown an overall 
reduction in flows in the basin. These reductions are expected to 
continue in response to climate change (reduced projected rainfall) and 
expanding development in Texas (groundwater pumping). Conversely, the 
Trinity River is anticipated to experience increases in flows in the 
future due to the growth of the Dallas-Fort Worth metroplex and its 
reliance on surface waters. Water resources that historically would 
have been distributed across the landscape in north Texas have been 
consolidated into an assortment of wastewater treatment and water 
supply system with many return flows feeding into the Trinity River. 
These return flows combine to elevate the baseflows of the Trinity 
River at all times (TRA 2023, pp. 23, 25-27) and can combine with rain 
events, leading to higher high flow events.
    (9) Comment: The State of Texas provided recommendations for 
clarification of the physical or biological features (PBFs) essential 
to the conservation of the central Texas mussels, particularly the PBFs 
concerning the identification of specific elements of the flow regimes 
considered essential, adaptive flexibility in defining host fish for 
the subject mussel species, and the number of sample events required 
(single or multiple) to evaluate the ranges of water quality 
parameters.
    Our response: For the flowing water PBF, we welcome additional 
research on the identification of specific flow regime elements needed 
for the long-term conservation of these mussel species. However, this 
information does not currently exist, and so we could not use specific 
flow rates when developing the PBFs for the species. We are actively 
working with external partners who are researching the role of stream 
flows on Texas fatmucket growth and survival in the Colorado River 
Basin, and we will use these findings as we develop recovery plans for 
the species.
    For the host fish PBF, we must use the best available information 
when

[[Page 48038]]

identifying essential PBFs, and the current science indicates that 
sunfishes (including bluegill (Lepomis macrochirus), green sunfish (L. 
cyanellus), Guadalupe bass (Micropterus treculii), and largemouth bass 
(M. salmoides)), freshwater drum (Aplodinotus grunniens), catfish 
(channel catfish (Ictalurus punctatus), flathead catfish (Pylodictis 
olivarus), and tadpole madtom (Noturus gyrinus)), minnows (family 
Cyprinidae), and shiners (blacktail shiner (Cyprinella venusta) and red 
shiner (C. lutrensis)) are hosts for the central Texas mussel species. 
Additional host fish species identified for these mussels will be 
incorporated into the recovery planning process.
    Finally, for the PBF that relates to water quality, it can be 
challenging to provide specific thresholds for water quality parameters 
because effects to freshwater mussels can range from sublethal to 
lethal depending on the duration of the exposure to conditions as well 
as the time of year, flow rates, and other factors. Currently, species-
specific toxicology studies have not been completed for the species 
included in this rule. Therefore, currently, the Service is using 
surrogate acute water quality standards from other freshwater mussel 
species in the United States to identify physical features for 
designated critical habitat. As the species-specific acute and chronic 
standards are developed for the covered species, the Service will 
revisit and refine the characteristics of these water quality features. 
Once these standards are developed, the Service will work with subject 
matter experts to identify the appropriate sampling techniques to 
evaluate the acceptable thresholds for water quality parameters, and 
work with project proponents to ensure that the most appropriate 
methods will be used to determine effects on listed freshwater mussels 
on a project-by-project basis.
    (10) Comment: The State of Texas and several commenters requested 
that the Service more clearly identify the estimated probability of 
persistence (threshold) that would preclude a listing decision.
    Our response: The ``probability of persistence'' is just one small 
part of our SSA report that informed our analysis and listing decision, 
which also considered the factors identified by the Act (such as a 
species' life history, generation time, current and future threats, and 
trajectory of those threats). There is not a strict probability above 
which we would not list and below which we would list, particularly 
because the information we use to assess the species' persistence is of 
a general nature and does not pinpoint the likelihood of persistence to 
the degree we would require to provide certainty that that the species 
persistence was above or below such a threshold. Therefore, 
``probability of persistence'' alone is not going to result in a 
decision that a species meets the definition of threatened or 
endangered.
    (11) Comment: The State of Texas and several commenters are 
concerned about the economic impact that proposed critical habitat 
would have on private landowners, private property values, and 
wastewater treatment plants (WWTPs), suggesting that the incremental 
effects memo (IEM) only captures baseline costs, and not the total 
costs associated with critical habitat designation. The commenters 
requested that prior to publishing a final rule, the Service conduct a 
new economic analysis, using the coextensive approach.
    Our response: As stated in the economic analysis of the designation 
of critical habitat for the Central Texas mussels, guidelines issued by 
the U.S. Office of Management and Budget (OMB) for the economic 
analysis of regulations direct Federal agencies to measure the costs 
and benefits of a regulatory action against a baseline (i.e., costs and 
benefits that are ``incremental'' to the baseline). The OMB defines the 
baseline as the ``best assessment of the way the world would look 
absent the proposed action.'' (Circular A-4, 2003). In other words, the 
baseline includes any existing regulatory and socio-economic burden 
imposed on landowners, managers, or other resource users affected by 
the designation of critical habitat. The baseline includes the economic 
impacts of listing the species under the Act, even if the listing 
occurs concurrently with critical habitat designation. Impacts that are 
incremental to the baseline (i.e., occurring over and above existing 
constraints) are those that are solely attributable to the designation 
of critical habitat and are the focus of the economic analysis.
    The Service acknowledges that significant debate has occurred 
regarding whether assessing the impact of critical habitat designations 
using the incremental approach is appropriate, with several courts 
issuing divergent opinions. Most recently, the U.S. Ninth Circuit Court 
of Appeals concluded that the incremental approach is appropriate, and 
the U.S. Supreme Court declined to hear the case (Home Builders 
Association of Northern California v. United States Fish and Wildlife 
Service, 616 F.3d 983 (9th Cir. 2010), cert. denied, 179 L. Ed 2d 301, 
2011 U.S. Lexis 1392, 79 U.S.L.W. 3475 (2011); Arizona Cattle Growers 
v. Salazar, 606 F.3d 1160 (9th Cir. 2010), cert. denied, 179 L. Ed. 2d 
300, 2011 U.S. Lexis 1362, 79 U.S. L.W. 3475 (2011)). Subsequently, on 
August 28, 2013, the Service revised its approach to conducting impact 
analyses for designations of critical habitat, specifying that the 
incremental approach should be used (78 FR 53062).

Public Comments

    (12) Comment: A commenter suggested that the reliance on data 
regarding recently dead shell material that are up to 21 years old, 
combined with the difficulty to detect mussels at sites that are not 
visited multiple times, is insufficient to define areas occupied at the 
time of listing and designate those areas as critical habitat for the 
Texas fatmucket, Texas fawnsfoot, and Texas pimpleback.
    Our response: While the Service used the year 2000 as the oldest 
year for ``recent'' survey data, much of the survey data used during 
the review of the species that are the subjects of this rule were 
collected during the increase in sampling efforts following the 2010 
State listing of these species as threatened by the Texas Parks and 
Wildlife Department (TPWD). Therefore, much of the data used for the 
SSA were closer to 10 years old when we were developing the August 26, 
2021, proposed rule. However, in instances in which the data were in 
fact collected approximately 20 years ago, the time gap between the 
data collection and proposed rule would be between 1 and 3 generations 
for these species. Because the Service has not been notified of or 
witnessed rapid, substantial, permanent habitat changes or been 
provided evidence of recent mussel die-offs through the collection of 
large numbers of fresh-dead (shells still attached to soft tissue) or 
recent dead (shells lacking connection to soft tissue but still 
containing a shiny inner shell layer), it is reasonable to conclude 
that these occupied areas would still be occupied by the species at 
some level.
    Much of the freshwater mussel sampling that has been completed in 
Texas to date has consisted of single, opportunistic surveys as part of 
larger research projects or environmental compliance surveys completed 
prior to some form of instream construction rather than monitoring 
events that would require multiple visits to individual sites. While 
multiple visits to a site will provide a clearer picture of population 
abundance and extent, a single visit is often sufficient to

[[Page 48039]]

determine occupancy if the species is present at that time.
    (13) Comment: A commenter stated that the proposed critical habitat 
designation does not include an initial regulatory flexibility analysis 
to satisfy the requirements of the Regulatory Flexibility Act (RFA; 5 
U.S.C. 601 et seq.), and the Service has not prepared an environmental 
impact statement to satisfy the National Environmental Policy Act 
(NEPA; 42 U.S.C. 4321 et seq.).
    Our response: When a species is proposed for listing, the Act's 
section 4(a)(3) requires the Secretary of the Interior (Secretary), to 
the maximum extent prudent and determinable, to designate critical 
habitat for that species. For more information about the considerations 
we must undertake when designating critical habitat, see and 
Consideration of Impacts under Section 4(b)(2) of the Act and 
Regulatory Flexibility Act (5 U.S.C. 601 et seq.), below.
    Under the Regulatory Flexibility Act (RFA), Federal agencies are 
only required to evaluate the potential incremental impacts of a 
rulemaking on directly regulated entities. The regulatory mechanism 
through which critical habitat protections are realized is section 7 of 
the Act, which requires Federal agencies, in consultation with the 
Service, to ensure that any action authorized, funded, or carried by 
the Agency is not likely to adversely modify critical habitat. 
Therefore, only Federal action agencies are directly subject to the 
specific regulatory requirement (avoiding destruction and adverse 
modification) imposed by critical habitat designation. Under these 
circumstances, it is the Service's position that only Federal action 
agencies will be directly regulated by this designation. Therefore, 
because Federal agencies are not small entities, the Service may 
certify that the proposed critical habitat rule will not have a 
significant economic impact on a substantial number of small entities. 
Because certification is possible, no regulatory flexibility analysis 
is required.
    Upon recommendation of the Council on Environmental Quality (CEQ), 
the Service determined that NEPA documents need not be prepared in 
connection with regulations finalizing the listing status for species 
pursuant to section 4(a) of the Act. This critical habitat designation 
is issued concurrently with the listing of the species under section 
4(a). On October 25, 1983, the Service published in the Federal 
Register a notice explaining this decision (48 FR 49244). The Service 
subsequently interpreted this 1983 determination to apply to critical 
habitat designations, based on the decision delivered in a Sixth 
Circuit Court of Appeals case (Pacific Legal Foundation v. Andrus, 657 
F. 2d 829 (1981)) and CEQ's recommendation.
    Based on this interpretation, the Service did not conduct NEPA 
analyses on critical habitat designations between 1983 and 1998. 
However, since the mid-1990s, the question of whether NEPA applies to 
the Federal action of designating critical habitat under the Act has 
been the subject of multiple lawsuits. In Douglas County v. Babbitt, 48 
F.3d 1495 (9th Cir. 1995), the U.S. Court of Appeals for the Ninth 
Circuit upheld the Service's conclusion that critical habitat actions 
are exempt from NEPA compliance. The Service was again challenged on 
this conclusion in Catron County Board of Commissioners v. U.S. Fish 
and Wildlife Service, 75 F.3d 1429 (10th Cir. 1996) (Catron County); 
the U.S. Court of Appeals for the Tenth Circuit ordered the Secretary 
to comply with NEPA when completing critical habitat determinations. 
The DC District Court in Cape Hatteras Access Pres. All. v. U.S. Dep't 
of Interior, 344 F. Supp. 2d 108 (D.D.C. 2004) similarly held that NEPA 
applied to critical habitat designations. However, more recently, the 
Fifth Circuit Court of Appeals agreed with the Ninth Circuit and held 
that NEPA does not apply to critical habitat designations under the Act 
(Markle Interests v. FWS, 827 F.3d 452 (5th Cir. 2016), rev'd on other 
grounds sub nom. Weyerhaeuser v. U.S. Fish and Wildlife Service, 139 S. 
Ct. 361 (2018)). Other district courts have applied this reasoning as 
well (e.g., Otay Mesa Property, LP v. U.S. Department of the Interior, 
144 F. Supp. 3d 35 (D.D.C. 2015)).
    While the Service does not concede that NEPA applies to critical 
habitat designations or revisions under the Act, we agreed to address 
NEPA compliance for critical habitat designations when the range of the 
species occurs within the jurisdiction of the U.S. Court of Appeals for 
the Tenth Circuit, which includes the following States: Colorado, 
Kansas, New Mexico, Oklahoma, Utah, and Wyoming. The central Texas 
mussels' critical habitat designations do not occur within the 
jurisdiction of the U.S. Court of Appeals for the Tenth Circuit, so we 
did not prepare an environmental assessment under NEPA for this 
designation.
    (14) Comment: A commenter requested that proposed critical habitat 
unit TXFM-2 (San Saba River) for the Texas fatmucket be limited to the 
upper section of the San Saba River, as it is the only segment of the 
river that has the PBFs essential to the conservation of the species. 
Because the middle reach of this critical habitat unit lacks an 
adequate hydrologic flow regime, which is an essential PBF, and this 
flow regime is not expected to improve under current predictions of 
increasing periods of drought, and the species does not currently exist 
in the lower reach of the San Saba River, they requested these middle 
and lower reaches of the San Saba River be removed from final critical 
habitat designation.
    Our response: Based on recent survey data, we consider this reach 
to be currently occupied by the species. Despite the anticipated future 
threats to water levels in the middle San Saba River and the Hill 
Country as a whole, live Texas fatmucket have been observed at multiple 
locations in the middle reach of the San Saba River in the last 10 
years. Historical collection records provide evidence that the species 
has also occurred in the past in the lower reach of the San Saba River 
near San Saba, Texas. We acknowledge that the unique geology of the 
middle reach of the San Saba River presents conservation challenges 
concerning flowing water (an essential PBF) in the lower reach of the 
river, but this unit currently contains adequate flowing water, 
suitable substrate, appropriate host fish, and adequate water quality, 
and recovery will entail restoring the species to reaches of habitat 
long enough such that stochastic events do not eliminate the entire 
population. The lower reach of the San Saba does not present these 
geological challenges and contains the essential PBFs needed to support 
the species in this portion of the San Saba River. The middle and lower 
reaches of the San Saba River add approximately 69 river miles (mi) 
(111 river kilometers (km)) of habitat to the population, they would 
increase the overall resiliency of the population.
    (15) Comment: A commenter stated that the Service lacks enough 
species-specific information to designate critical habitat, 
particularly in unoccupied areas, and that the proposed rule fails to 
show that designated critical habitat is determinable.
    Our response: We are required to designate critical habitat based 
on the best scientific data available at the time of designation. We 
considered the best scientific data available regarding the central 
Texas mussels to evaluate potential critical habitat under the Act. We 
have sufficient information to understand the habitat these species 
need and where the species occur, and we solicited peer review on our 
evaluation of that information. The

[[Page 48040]]

listing and critical habitat process does not require perfect 
information; it requires that we use the best available information to 
make our determinations. Therefore, we found that critical habitat was 
determinable in both occupied and unoccupied areas.
    (16) Comment: Several commenters requested that critical habitat 
designation for endangered species be limited to occupied reaches.
    Our response: The Act defines critical habitat under section 
3(5)(A) and allows for the designation of areas within and outside the 
geographical areas occupied by the species at the time of listing. 
There is no statutory requirement to limit critical habitat areas to 
only occupied areas. The Act requires that areas outside the 
geographical area occupied by the species be essential for the 
conservation of the species.
    We have determined that unoccupied units are essential for the 
conservation of the Texas fatmucket and Texas pimpleback because they 
provide for the growth and expansion of the species within portions of 
their historical ranges. We identified areas outside the geographical 
areas currently occupied by the Texas fatmucket and Texas pimpleback as 
critical habitat in order to increase the stream length of critical 
habitat designations adjacent to existing small populations. These 
unoccupied areas are located immediately adjacent to currently occupied 
stream reaches, include one or more of the essential PBFs, and allow 
for expansion of existing populations necessary to improve population 
resiliency, extend physiographic representation, and reduce the risk of 
extinction for the species. The establishment of additional moderately 
healthy to healthy populations across the range of these species would 
reduce their risk of extinction. Improving the resiliency of 
populations in the currently occupied streams, and into identified 
unoccupied areas, will increase species viability. See Criteria Used to 
Identify Critical Habitat, below.
    (17) Comment: Commenters requested that additional unoccupied areas 
be designated as critical habitat. These areas included the upstream 
portions of the Llano River in Edwards County, Texas, lower reaches of 
the Llano River, downstream of the City of Llano in Llano County, 
Texas, and Johnson Creek, which flows into the Guadalupe River in Kerr 
County, Texas.
    Our response: After identifying areas occupied by the species at 
the time of listing, we will identify specific areas outside the 
geographical area occupied by the species at the time of listing that 
the Secretary determines are essential for the conservation of the 
species. We evaluated the upstream portions of the South Llano River 
located in Edwards County and found that this reach of the river does 
not consistently remain wetted and does not provide suitable habitat 
through large portions of the stream in Edwards County and is not 
essential for the conservation of the species. Therefore, we did not 
designate the area as critical habitat. We evaluated the lower reaches 
of the Llano River near the river's confluence with the Little Llano 
River; these reaches are bookended by a dam in the City of Llano used 
for drinking water and a low-head dam which impounds Robinson Lake. Any 
suitable habitat between the two structures would be isolated from 
other existing populations due to stretches of unsuitable habitat and 
impairment of fish passage and therefore is not essential for the 
conservation of either Texas pimpleback or Texas fatmucket. Therefore, 
for the central Texas mussels, other than the unoccupied areas noted in 
this rule (TXFM-1c, TXFF-1b, TXPB-1a, and TXPB-5b),we are not 
designating additional areas outside the geographical area occupied by 
the species because we have not identified any additional unoccupied 
areas that meet the definition of critical habitat at this time.
    (18) Comment: One commenter stated that proposed critical habitat 
unit TXFM-1 does not meet the criteria established for critical habitat 
since it does not contain all the PBFs described in the proposed rule 
as essential to the conservation of the species.
    Our response: In areas occupied at the time of listing a species as 
endangered or threatened, critical habitat is the specific areas on 
which are found the physical or biological features (PBFs) that are 
essential to the conservation of the species and that may require 
special management considerations or protection. It is not required 
that an area contain all PBFs in order to qualify as critical habitat. 
Unit TXFM-1 contains multiple PBFs (e.g., presence of suitable 
substrates, connected instream habitats, and presence of host fish), 
and while the unit may need special management considerations to reduce 
sedimentation, improve water quality, maintain adequate flows, and 
improve habitat connectivity, it meets the definition of critical 
habitat for the Texas fatmucket.
    (19) Comment: A commenter requested that the Service revise its 
discussion of water quality in the lower Colorado River mainstem below 
Austin to state that, according to the Texas Commission on 
Environmental Quality's (TCEQ's) 2020 Integrated Report (TCEQ 2020; 
entire), all water quality parameters being monitored are meeting the 
Texas Surface Water Quality Standards, and there are no impairments.
    Our response: Impairment, as defined through the Texas Surface 
Water Quality Standards, can differ from biological requirements for 
individual species. Because a stream reach meets legal standards for 
water quality parameters does not mean that the water quality meets the 
needs of the species. While we understand that the entire lower 
Colorado River mainstem below Austin may not experience conditions that 
are impacting freshwater mussel growth and survival, we feel that it is 
important to acknowledge that these conditions can exist at times in 
the reach of the river. For example, TCEQ produces an integrated report 
every 2 years that sets the ammonia criterion to denote impairment in 
segments of the Colorado River and includes any exceedances of this 
criteria (TCEQ 2022, entire). Chronic ammonia toxicity studies have 
shown that juvenile freshwater mussel species experience significant 
reductions in growth and survival when exposed to ammonia 
concentrations below these levels (Wang et al. 2007, p. 2054). Data 
presented in the TCEQ 2022 report would place the observed significant 
reductions in growth below the exceedance threshold of 0.33 milligrams 
per liter (mg/L) and reductions in survival near the observed 
exceedance mean value of 0.45 mg/L.
    (20) Comment: Commenters requested more discussion of the threat of 
extended low-flow conditions in the lower Colorado River Basin.
    Our response: There are threats of extended low-flow conditions in 
the lower reaches of the lower Colorado River Basin, and we are 
actively working with the LCRA on the implementation of the LCRA 
Agreement, which includes conservation measures that would help further 
understand, avoid, and minimize the threat of low-flow conditions to 
freshwater mussels in this river basin.
    The 2020 LCRA Water Management Plan (WMP) allocates a portion of 
its ``firm water'' supply to meet environmental flow needs within the 
lower Colorado River Basin (LCRA 2020, pp. ES-2-ES-3). These needs are 
determined through calculated monthly subsistence flow values and are 
based on results of an instream flow study in 2008 (Bio-West 2008, pp. 
69-90) that investigated the flow relationships to aquatic habitat and 
the State-threatened blue sucker (Cycleptus elongatus), and they are 
consistent with the Texas Instream Flow Program methodology

[[Page 48041]]

(LCRA 2020, p. 2-2). While this 2008 study did not specifically focus 
on the habitat needs of freshwater mussels, a subsequent study in 2018 
determined that the subsistence flows standards set by the WMP were 
adequate to protect instream freshwater mussel habitat during the 
periods expected to receive the lowest flow conditions (August; 107 
cubic feet per second at the Wharton U.S. Geological Survey (USGS) 
gauge) (Bonner et al. 2018; entire). The LCRA Agreement states that an 
amendment to the 2020 WMP, which will consider additional information 
regarding flow or temperature needed for freshwater mussels or host 
fish, if available during that amendment process, is expected to occur 
not later than March 1, 2025 (LCRA 2023, pp. 60-63). While these flow 
assurances cannot entirely remove the threat of low flow conditions in 
the lower Colorado River, they can reduce the threat and ameliorate the 
instream conditions during these periods.
    (21) Comment: A commenter stated that candidate conservation 
agreements with assurances (CCAAs) do not provide sufficient certainty 
of benefits to the species because they have limited authority, focus 
on a subset of the threats, allow permittees to withdraw at any time, 
and do not ensure future conditions. The commenter, therefore, requests 
that CCAAs not be used as a basis for critical habitat exclusions in 
the final rule.
    Our response: We evaluate whether an area should be excluded from 
critical habitat based on whether the benefits of exclusion outweigh 
the benefits of inclusion. As outlined in our Policy Regarding 
Implementation of Section 4(b)(2) of the Endangered Species Act (81 FR 
7226), when we undertake a discretionary 4(b)(2) exclusion analysis, we 
will always consider areas covered by a permitted candidate 
conservation agreement with assurances (CCAA) and anticipate 
consistently excluding those areas from a critical habitat designation 
if incidental take caused by the activities in those areas is covered 
by the permit under section 10 of the Act and the CCAA meets all of the 
following conditions: the permittee is properly implementing the 
agreement and is expected to do so for the term of the agreement; the 
species for which critical habitat is being designated is a covered 
species in the agreement; and the agreement specifically addresses the 
habitat of the species for which critical habitat is being designated 
and meets the conservation needs of the species in the planning area.
    We have determined that the BRA Agreement (BRA 2021, entire), LCRA 
Agreement (LCRA 2023, entire), and TRA Agreement (TRA 2023, entire) 
fulfill the above criteria, and we are excluding from this critical 
habitat designation some non-Federal lands covered by these three CCAAs 
that provide for the conservation of the Texas fawnsfoot, Texas 
pimpleback, and Balcones spike. The LCRA Agreement also provides for 
the conservation of Texas fatmucket. However, because no critical 
habitat units for the Texas fatmucket fall within reaches where the 
LCRA Agreement can directly reduce the primary threat of low water 
quantity, we have not excluded any proposed critical habitat for the 
Texas fatmucket based on the LCRA Agreement. Additionally, within the 
BRA and LCRA CCAAs, some non-Federal lands are included in the CCAAs' 
Covered Areas that we did not exclude from designated critical habitat 
(i.e., river miles above Possum Kingdom Reservoir and river miles above 
the Highland lakes in the BRA and LCRA CCAAs respectively). These areas 
were not excluded because while the BRA and LCRA CCAAs provide overall 
net conservation benefits for the covered species, threat reduction 
efforts included as conservation measures within the agreements target 
other locations of their respective basins.
    Possum Kingdom Reservoir represents the most upstream BRA-operated 
infrastructure in the Brazos River Basin. The BRA has no infrastructure 
and limited interests above Possum Kingdom reservoir, and therefore, 
has no way to directly influence freshwater mussel populations or their 
habitats in this portion of the basin (BRA 2021, p. 15). Regarding the 
LCRA CCAA, with the exception of two reservoirs LCRA owns and operates 
for purposes of power plant cooling which are not included in the 
critical habitat designation, LCRA does not own or operate any other 
water infrastructure on any tributaries or on the main stem of the 
Colorado River upstream of Lake Buchanan or on other tributaries or 
river segments that contribute flow to the Highland Lakes or the 
Colorado River within LCRA's broader service area.
    The development and maintenance of effective working partnerships 
with non-Federal partners for the conservation of at-risk species is 
particularly important in areas such as Texas, a State with relatively 
little Federal landownership and many species of conservation concern. 
We find that excluding areas from critical habitat that are receiving 
long-term conservation and management for the purpose of protecting the 
habitat that supports the Texas fawnsfoot, Texas pimpleback, and 
Balcones spike will preserve our external partnerships in Texas and 
will encourage future collaboration towards conservation and recovery 
of listed species.
    Because the agreements are voluntary, they demonstrate the 
commitment of the partners to the conservation actions; the CCAA 
process takes time and effort to put in place, and the agreement must 
result in a net conservation benefit to the species. The partnership 
benefits are significant and outweigh the potential regulatory, 
educational, and ancillary benefits of including the land in the final 
critical habitat designation for these three species; in addition, the 
subject areas are occupied by the species, so there is less incremental 
benefit to the unit being included in the critical habitat designation. 
Therefore, the BRA Agreement, LCRA Agreement, and TRA Agreement provide 
greater protection of habitat for the Texas fawnsfoot, Texas 
pimpleback, and Balcones spike than could be gained through the 
project-by-project analysis under a critical habitat designation.
    (22) Comment: A commenter claimed that our proposed 4(d) rule was 
arbitrary and capricious because we did not assess the costs and 
benefits of the rule and therefore did not establish that the proposed 
4(d) rule was necessary and advisable.
    Our response: The Act clearly prohibits the Service from 
considering economic or similar information when making listing, 
delisting, or reclassification decisions. Congress added this 
prohibition in the 1982 amendments to the Act when it introduced into 
section 4(b)(1) an explicit requirement that all decisions under 
section 4(a)(1) of the Act be based ``solely on the basis of the best 
scientific and commercial data available.'' Congress further explained 
this prohibition in the Conference Report accompanying the 1982 
Amendments: ``The principal purpose of these amendments is to ensure 
that decisions in every phase of the process pertaining to the listing 
or delisting of species are based solely upon biological criteria and 
to prevent non-biological considerations from affecting such decisions. 
These amendments are intended to expedite the decision-making process 
and to ensure prompt action in determining the status of the many 
species which may require the protections of the Act.'' (H.R. Conf. 
Rep. No. 97-835, at 19 (1982).)
    Therefore, following statutory framework and congressional intent, 
we do not conduct or develop economic impact analyses for 
classification decisions. Additionally, 4(d) rules concurrently issued 
with a classification rule are inherently a part of a

[[Page 48042]]

classification decision for a threatened species and therefore, a 
consideration of economic impacts does not apply. If we determine that 
a species meets the Act's definition of a threatened species, part of 
our consideration for completing the listing process is to consider 
what measures are necessary and advisable to provide for the 
conservation of the species under section 4(d) of the Act. We, 
therefore, consider a 4(d) rule to be a necessary phase of the listing 
process to put in place protections for threatened species.
    (23) Comment: Commenters expressed concerns that threatened status 
may be insufficient for the Texas fawnsfoot and recommended it be 
assigned endangered status.
    Our response: The Act defines ``endangered species'' and 
``threatened species'' and mandates five factors for consideration when 
determining a species' status under the Act. We have determined that 
endangered species status under the Act is not appropriate for the 
Texas fawnsfoot because the species maintains multiple, moderately 
resilient populations across its historical range with low risk of 
significant decline in the near term. Further, given its distribution 
and the health of its populations, the Texas fawnsfoot has sufficient 
redundancy and representation to withstand catastrophic events and 
novel changes in its environment in the near term. For these reasons, 
the Texas fawnsfoot is not currently in danger of extinction; it is, 
however, at risk of extinction in the foreseeable future because even 
under the best conditions, and with additional conservation efforts 
undertaken, given the ongoing effects of climate change and human 
activities on altered hydrology and habitat degradation, within 25 to 
50 years, we expect only one population to be in healthy condition, one 
population to remain in moderately healthy condition, four populations 
to be in unhealthy condition, and one population to become functionally 
extirpated. Given the likelihood of increased climate and anthropogenic 
effects in the foreseeable future, as many as three populations are 
expected to become functionally extirpated, leaving no more than four 
unhealthy populations remaining after 25 years. See Determination of 
Status: Texas Fawnsfoot, below.
    (24) Comment: A commenter requested that all species be listed as 
threatened to better promote voluntary habitat conservation.
    Our response: The Act requires us to make a listing determination 
using the best available scientific and commercial data after 
conducting a review of the status of the species. The primary 
difference between an endangered species and a threatened species is 
the timing of the risk of extinction. An ``endangered species'' is one 
that is in danger of extinction throughout all or a significant portion 
of its range. A ``threatened species'' is one that is likely to become 
endangered within the foreseeable future throughout all or a 
significant portion of its range; therefore, it is not currently in 
danger of extinction. After evaluating threats to the central Texas 
mussel species and assessing the cumulative effect of the threats under 
the Act's section 4(a)(1) factors, we found that Guadalupe fatmucket, 
Texas fatmucket, Guadalupe orb, Texas pimpleback, Balcones spike, and 
false spike have declined significantly in overall distribution and 
abundance. At present, most of their known populations exist in very 
low abundances and show limited evidence of recruitment. Furthermore, 
existing available habitats are reduced in quality and quantity, 
relative to historical conditions. We found that, for these six 
species, the threats are currently occurring and result in the species 
being in danger of extinction now. Therefore, a threatened status 
determination for these species would not be appropriate. The 
difference between endangered and threatened does not affect our 
ability to encourage voluntary conservation.
    The listing of a species does not obstruct the development of 
conservation agreements or partnerships to conserve the species. Once a 
species is listed as either endangered or threatened, the Act provides 
many tools to advance the conservation of listed species. Conservation 
of listed species in many parts of the United States is dependent upon 
working partnerships with a wide variety of entities, including the 
voluntary cooperation of non-Federal landowners. Building partnerships 
and promoting cooperation with landowners are essential to 
understanding the status of species on non-Federal lands and may be 
necessary to implement recovery actions, such as reintroduction of 
listed species, habitat restoration, and habitat protection. Once a 
species is listed, for private or other non-Federal property owners, we 
offer voluntary safe harbor agreements that can contribute to the 
recovery of species, habitat conservation plans that allow activities 
(e.g., grazing) to proceed while minimizing effects to species, funding 
through the Partners for Fish and Wildlife Program to help promote 
conservation actions, and grants to the States under section 6 of the 
Act.
    (25) Comment: A commenter stated concerns that the Service focused 
on recent trends when modeling the impacts of climate change and 
disagreed that climate change will exacerbate identified threats in 
central Texas.
    Our response: Experts anticipate that climate change will lead to 
decreased water availability in Texas due to increased frequency and 
intensity of drought conditions in the State. During drought periods, 
pressure on freshwater resources, particularly increased evaporation in 
reservoirs and higher demands on groundwater pumping, in the State will 
lead to a decline in instream flows. Decreased instream flows correlate 
with increases in instream temperatures. In the SSA report, we relied 
upon numerous studies that have identified the effects of increased 
temperature on the growth, fitness, and survival of freshwater mussels 
(Bonner et al. 2018, p. 6; Ganser et al. 2015, p. 1712; Spooner and 
Vaughn 2008, pp. 312-313; Service 2022, p. 10). The combination of 
declines in instream flows and increasing temperatures of the remaining 
flows are anticipated to have a negative impact on remaining freshwater 
mussel populations.
    (26) Comment: A commenter questioned whether mussels are actually 
declining due to human development and suggests that declines may have 
been occurring prior to human contact.
    Our response: While mussel populations surely ebbed and flowed 
prior to human development, it is well established that widespread 
declines of freshwater mussels have occurred in the last 50 to 75 years 
(Haag 2019, p. 43; Haag 2012, pp. 316-390). Through a combination of 
long-term monitoring and evidence in the historical record, it is clear 
that the decline of freshwater mussels is closely tied to advances in 
human infrastructure development (Haag 2012, pp. 316-390). In some 
cases, the ties can be closely pinpointed to the construction of a 
single structure (e.g., large, power-generating hydrodam) and a 
resulting decline and eventual extirpation of an upstream freshwater 
mussel population (e.g., extirpation of the elephant ear (Elliptio 
crassidens) population in the Upper Tennessee Basin following habitat 
fragmentation in tributaries of the Tennessee River (Johnson et al. 
2012a, p. 89)). Regardless of whether declines occurred prior to human 
development, the declines of the central Texas mussel species in the 
recent past are well documented.
    (27) Comment: A commenter requested clarification on whether the 
artificially sustained wastewater effluent flows are beneficial or 
detrimental to the central Texas mussels.

[[Page 48043]]

    Our response: Artificially sustained effluent flows can be 
beneficial to freshwater mussels by providing flow in low-flow and 
drying areas where mussels might otherwise desiccate. However, effluent 
flows can also be detrimental to freshwater mussels if the effluent 
water quality is poor. We consider both water quantity and quality when 
evaluating effluent and its impact on mussels. Parameters for healthy 
water quality and water quantity are defined in the SSA report (Service 
2022, pp. 6-10), and we use these benchmarks as we evaluate the 
species' status now and in the future.
    (28) Comment: A commenter disagreed that pesticides originating 
from agricultural sources are a pollutant of concern at levels 
experienced in the natural environment.
    Our response: Pesticides have been demonstrated to have both lethal 
and non-lethal effects on freshwater organisms, including freshwater 
mussels around the world (Milam et al. 2005, pp. 169-172; Bringolf et 
al. 2007a, p. 2099, 2007b, pp. 2105-2106, 2007c, p. 2092; Chmist et al. 
2019, pp. 439-440). These studies have been completed for multiple, 
freshwater mussel life stages, including glochidia, juveniles, and 
adults, and have documented the harmful effects of a variety of 
herbicides, pesticides, and other chemical compounds. While we support 
and applaud agricultural producers' efforts to target applications and 
reduce run-off into adjacent waterways, it is still necessary to 
acknowledge the threat of the compounds to these mussels, as the 
specific lethal and non-lethal effects are not known for all mussel 
species, and spills, unregulated discharges, and errant applications 
are possible and would have significant negative effects on 
populations.
    (29) Comment: A commenter claimed that the proposed listings are 
unnecessary as Texas already protects the central Texas mussels.
    Our response: In 2007 and 2008, we received petitions requesting 
that we list as endangered or threatened species and designate critical 
habitat for the Texas fatmucket, Texas fawnsfoot, Texas pimpleback, and 
false spike. (See Previous Federal Actions in the August 26, 2021, 
proposed rule (86 FR 47918-47919) for more information.) In 2009, the 
State of Texas listed the Texas fatmucket, Texas fawnsfoot, Texas 
pimpleback, and the false spike as threatened, launching an era of 
freshwater mussel conservation Statewide and bringing attention to this 
faunal group. However, once the Service is petitioned to list a 
species, we are required to complete our regulatory process which takes 
into account conservation efforts and State regulatory efforts in our 
listing determination. Under the requirements of the Act, we must 
conduct the required analysis and list the species if it is found to be 
warranted, and we cannot defer to any State listing. This rule codifies 
our listing determinations for the central Texas mussels.

I. Final Listing Determination

Background

    A thorough review of the taxonomy, life history, and ecology of the 
Guadalupe fatmucket, Texas fatmucket, Texas fawnsfoot, Guadalupe orb, 
Texas pimpleback, Balcones spike, and false spike, referred to as the 
central Texas mussels, is presented in the SSA report (Service 2022, 
pp. 4-44).

Guadalupe Fatmucket

    The Guadalupe fatmucket (Lampsilis bergmanni) was recently 
discovered to be a separate and distinct species from Texas fatmucket 
(Inoue et al. 2018, pp. 5-6; Inoue et al. 2020, entire), and the 
Service now recognizes the Guadalupe fatmucket as a new species that 
occurs only in the Guadalupe River Basin. Because the Guadalupe 
fatmucket is so similar to the Texas fatmucket and better information 
is not yet available, we conclude the Guadalupe fatmucket has similar 
habitat needs (headwater habitats in gravel or bedrock fissures) and 
host fish (sunfishes) as the Texas fatmucket, below.
    The Guadalupe fatmucket is a small to medium-sized freshwater 
mussel (to 4 inches (in) (100 millimeters (mm))) that exhibits sexual 
dimorphism and has a yellow-green-tan shell; it is similar in 
appearance to the Texas fatmucket (a more detailed description of the 
Texas fatmucket is found in Howells et al. 2011, pp. 14-16). Related 
species in the genus Lampsilis from the southeast United States reach a 
maximum age of 13 to 25 years (Haag and Rypel 2010, pp. 4-6), and we 
expect Guadalupe fatmucket to have a similar lifespan.
    Guadalupe fatmucket is currently found in one population, which 
occurs in 52 miles (84 km) of the Guadalupe River Basin in Kendall and 
Kerr Counties, Texas (Randklev et al. 2017c, p. 4) (see table 1, below; 
see also figure 5.11 in Service 2022, p. 118).

                                 Table 1--Current Guadalupe Fatmucket Population
----------------------------------------------------------------------------------------------------------------
                                                                              Occupied reach
            Population               Streams included          Counties         length (mi     Recent collection
                                                                                   (km))        years (numbers)
----------------------------------------------------------------------------------------------------------------
Guadalupe River..................  Guadalupe River;      Kendall and Kerr            52 (84)           2018 (22)
                                    North Fork,           Co., TX.                                 2019 (shells)
                                    Guadalupe River;
                                    Johnson Creek.
----------------------------------------------------------------------------------------------------------------

Texas Fatmucket

    Texas fatmucket has been characterized as a rare Texas endemic 
(Burlakova et al. 2011a, p. 158) and was originally described as the 
species Unio bracteatus by A.A. Gould in 1855 (p. 228) from the 
``Llanos River'' in ``Upper'' Texas. The species is currently 
recognized as Lampsilis bracteata (Williams et al. 2017, pp. 35, 39). 
Recently, individuals that had been known as Texas fatmucket in the 
Guadalupe River Basin were found to be a new species (Inoue et al. 
2020, pp. 93-111); therefore, we now know the Texas fatmucket to only 
occur in the Colorado River Basin.
    The Texas fatmucket is a small to medium-sized freshwater mussel 
(to 4 in (100 mm)) that exhibits sexual dimorphism (males and females 
have different shapes) and has a yellow-green-tan shell (Howells et al. 
2011, pp. 14-16). For a detailed morphological description see Howells 
et al. 1996 (p. 61) and Howells 2014 (p. 41).
    Host fishes for Texas fatmucket are members of the Family 
Centrarchidae (sunfishes) including bluegill (Lepomis macrochirus), 
green sunfish (L. cyanellus), Guadalupe bass (Micropterus treculii), 
and largemouth bass (M. salmoides) (Howells 1997, p. 257; Johnson et 
al. 2012b, p. 148; Howells 2014, p. 41; Ford and Oliver 2015, p. 4; 
Bonner et al. 2018, p. 9).
    Related species can expel conglutinates (packets of glochidia) and 
are known to use mantle lures (Barnhart et al. 2008, pp. 377, 380) to 
attract sight-feeding fishes that attack and rupture the marsupium 
where the glochidia are

[[Page 48044]]

held, thereby becoming infested by glochidia. These species are long-
term brooders (bradytictic), spawning and becoming gravid in the fall 
and releasing glochidia in the spring (Barnhart et al. 2008, p. 384).
    We expect Texas fatmucket has a similar lifespan to related species 
in the genus Lampsilis from the southeast United States, which reach a 
maximum age of 13 to 25 years (Haag and Rypel 2010, pp. 4-6). Texas 
fatmucket occur in firm mud, stable sand, and gravel bottoms, in 
shallow waters, sometimes in bedrock fissures or among roots of bald 
cypress (Taxodium distichum) and other aquatic vegetation (Howells 
2014, p. 41). The species typically occurs in free-flowing rivers but 
can survive in backwater areas, such as in areas upstream of lowhead 
dams (e.g., Llano Park Lake (BioWest, Inc. 2018, pp. 2-3)).
    Texas fatmucket currently occur only in the upper reaches of major 
tributaries within the Colorado River Basin (Randklev et al. 2017c, p. 
4) in five populations: lower Elm Creek, upper/middle San Saba River, 
Llano River, Pedernales River, and Onion Creek (see table 2, below; see 
also figure 5.5 in Service 2022, p. 91). Isolated individuals not 
considered part of larger functioning populations have been found in 
Cherokee Creek, Bluff Creek, and the North Llano River.

                                  Table 2--Current Texas Fatmucket Populations
----------------------------------------------------------------------------------------------------------------
                                                                            Occupied reach   Recent  collection
           Population               Streams included         Counties         length (mi        years (number
                                                                                 (km))           collected)
----------------------------------------------------------------------------------------------------------------
Lower Elm Creek.................  Elm Creek..........  Runnels Co., TX....         12 (19)         2005 (no live
                                                                                                        animals)
                                                                                                        2008 (1)
                                                                                                        2019 (1)
Upper/Middle San Saba River.....  San Saba River.....  Mason, McCulloch,          62 (100)              2005 (2)
                                                        Menard, and San                                 2012 (8)
                                                        Saba Co., TX.                                   2013 (5)
                                                                                                       2016 (29)
                                                                                                       2017 (87)
                                                                                                       2017 (71)
Llano River.....................  Llano River, South   Kimble, Llano, and        127 (204)             2016 (72)
                                   Llano River.         Mason Co., TX.                                 2017 (47)
                                                                                                        2017 (5)
                                                                                                      2018 (635)
                                                                                                        2019 (6)
                                                                                                       2019 (18)
                                                                                                       2021 (99)
Pedernales River................  Pedernales River,    Blanco, Gillespie,         79 (127)              2011 (1)
                                   Live Oak Creek.      and Hays Co., TX.                               2012 (1)
                                                                                                       2017 (18)
Onion Creek.....................  Onion Creek........  Travis Co., TX.....         24 (38)              2010 (3)
                                                                                                        2018 (1)
                                                                                                        2021 (5)
----------------------------------------------------------------------------------------------------------------

Texas Fawnsfoot

    The Texas fawnsfoot was originally described as Unio macrodon 1859 
from a location near Rutersville, Fayette County, Texas (Lea 1859, pp. 
154-155). Texas fawnsfoot is recognized by the scientific community as 
Truncilla macrodon (Williams et al. 2017, pp. 35, 44).
    Texas fawnsfoot is a small- to medium-sized (2.4 in (60 mm)) mussel 
with an elongate oval shell (Howells 2014, p. 111). For a detailed 
description, see Howells et al. 1996 (p. 143) and Howells 2014 (p. 
111).
    Host fish species are not confirmed for the Texas fawnsfoot, but we 
expect they use freshwater drum (Aplodinotus grunniens; Howells 2014, 
p. 111), like other Truncilla species occurring in Texas and elsewhere 
(Ford and Oliver 2015, p. 8). Freshwater drum are molluscivorous 
(mollusk-eating) and become infested with glochidia when they consume 
gravid female mussels (Barnhart et al. 2008, p. 373). This strategy of 
host infestation may limit population size, as reproductively 
successful females are sacrificed (i.e., eaten by freshwater drum). 
Related species are bradytictic, brooding larvae over the winter 
instead of releasing them immediately (Barnhart et al. 2008, p. 384). 
Other species in the genus Truncilla from the Southeast and Midwest 
reach a maximum age ranging from 8 to 18 years (Haag and Rypel 2010, 
pp. 4-6), and we expect the lifespan of Texas fawnsfoot to be similar.
    Texas fawnsfoot are found in medium- to large-sized streams and 
rivers with flowing waters and mud, sand, and gravel substrates 
(Howells 2014, p. 111). Adults are most often found in bank habitats 
and occasionally in backwater, riffle, and point bar habitats, with low 
to moderate velocities that appear to function as flow refuges during 
high flow events (Randklev et al. 2017c, p. 137).
    Texas fawnsfoot occur in the lower reaches of the Colorado and 
Brazos Rivers, and in the Trinity River (Randklev et al. 2017b, p. 4) 
in seven populations: East Fork Trinity River, Middle Trinity River, 
Clear Fork Brazos River, Upper Brazos River, Middle/Lower Brazos River, 
San Saba/Colorado Rivers, and Lower Colorado River (see table 3, below; 
see also figure 5.7 in Service 2022, p. 101). Texas fawnsfoot was 
historically distributed throughout the Colorado and Brazos River 
basins (Howells 2014, pp. 111-112; reviewed in Randklev et al. 2017c, 
pp. 136-137) and in the Trinity River Basin (Randklev et al. 2017b, p. 
11). Texas fawnsfoot historically occurred in the Leon River, but they 
are currently extirpated (Popejoy et al. 2016, p. 477). Randklev et al. 
(2017c, p. 135) surveyed the Llano, San Saba, and Pedernales Rivers and 
found neither live individuals nor dead shells of Texas fawnsfoot. 
Isolated individuals not considered part of functioning populations 
have been found in the Little River.

[[Page 48045]]



                                  Table 3--Current Texas Fawnsfoot Populations
----------------------------------------------------------------------------------------------------------------
                                                                              Occupied reach
            Population               Streams included          Counties         length (mi     Recent collection
                                                                                   (km))        years (numbers)
----------------------------------------------------------------------------------------------------------------
East Fork Trinity River..........  East Fork Trinity     Kaufman Co., TX....         12 (19)           2017 (40)
                                    River.                                                             2018 (12)
Middle Trinity River.............  Trinity River.......  Anderson, Houston,        140 (225)      2016-2017 (59)
                                                          Leon, Madison, and
                                                          Navarro Co., TX.
Clear Fork Brazos River..........  Clear Fork Brazos     Shackelford and             13 (21)            2010 (1)
                                    River.                Throckmorton Co.,                             2018 (0)
                                                          TX.
Upper Brazos River...............  Brazos River........  Palo Pinto and             62 (100)           2017 (23)
                                                          Parker Co., TX.
Middle/Lower Brazos River........  Brazos River........  Austin, Brazos,           346 (557)          2014 (188)
                                                          Burleson, Falls,                             2017 (28)
                                                          Fort Bend, Grimes,                            2021 (1)
                                                          McLennan, Milam,
                                                          Robertson, Waller,
                                                          and Washington
                                                          Co., TX.
San Saba/Colorado Rivers.........  San Saba River,       Mills and San Saba          43 (69)            2017 (0)
                                    Colorado River.       Co., TX.                                      2018 (2)
Lower Colorado River.............  Colorado River......  Colorado,                 109 (175)           2010 (52)
                                                          Matagorda, and                               2015 (10)
                                                          Wharton Co., TX.                              2017 (9)
----------------------------------------------------------------------------------------------------------------

Guadalupe Orb

    Burlakova et al. (2018, entire) recently described the Guadalupe 
orb (Cyclonaias necki) from the Guadalupe River Basin as a separate 
species distinct from Texas pimpleback. The Guadalupe orb occurs only 
in the Guadalupe Basin and is a small-sized mussel with a shell length 
that reaches up to 2.5 in (63 mm) (Burlakova et al. 2018, p. 48). 
Guadalupe orb shells are thinner and more compressed but otherwise 
morphologically similar to the closely related Texas pimpleback. The 
posterior ridge is more distinct and prominent, and the umbo is more 
compressed than in Texas pimpleback (Burlakova et al. 2018, p. 48). 
Individuals collected from the upper Guadalupe River (near Comfort, 
Texas) averaged 1.9 in (48 mm) (Bonner et al. 2018, p. 221). Channel 
catfish (Ictalurus punctatus), flathead catfish (Pylodictis olivarus), 
and tadpole madtom (Noturus gyrinus) are host fish for the Guadalupe 
orb (Dudding et al. 2019, p. 15). Dudding et al. (2019, p. 16) 
cautioned that the apparent clumped distribution of Guadalupe orb (and 
closely related species) in ``strongholds'' could be related to 
observed ongoing declines in native catfishes, including the small and 
rare tadpole madtom, a riffle specialist. The best available 
information leads us to believe that the reproduction, ecological 
interactions, and habitat requirements of Guadalupe orb are similar to 
those of the closely related Texas pimpleback.
    The Guadalupe orb is only known to occur in the Guadalupe River 
Basin in two separate and isolated populations: the upper Guadalupe 
River and the lower Guadalupe River (see table 4, below; see also 
figure 5.13 in Service 2022, p. 125). An isolated individual not 
considered part of a functioning population has been found in the 
Blanco River, a tributary to the San Marcos River (Johnson et al. 2018, 
p. 7).

                                   Table 4--Current Guadalupe Orb Populations
----------------------------------------------------------------------------------------------------------------
                                                                              Occupied reach
            Population               Streams included          Counties         length (mi     Recent collection
                                                                                   (km))        years (numbers)
----------------------------------------------------------------------------------------------------------------
Upper Guadalupe River............  Guadalupe River.....  Comal, Kendall, and        95 (153)            2013 (1)
                                                          Kerr Co., TX.                                2017 (10)
                                                                                                        2018 (2)
Lower Guadalupe River............  Guadalupe River, San  Caldwell, DeWitt,         181 (291)     2014-2015 (893)
                                    Marcos River.         Gonzales,                                    2017 (41)
                                                          Guadalupe, and
                                                          Victoria Co., TX.
----------------------------------------------------------------------------------------------------------------

Texas Pimpleback

    The Texas pimpleback was originally described as Unio petrinus from 
the ``Llanos River'' in ``Upper'' Texas (Gould 1855, p. 228). The 
species is now recognized as Cyclonaias petrina by the scientific 
community (Williams et al. 2017, pp. 35, 37). Burlakova et al. (2018, 
entire) recently described the Guadalupe orb (C. necki) from the 
Guadalupe River Basin as a separate species distinct from Texas 
pimpleback. Texas pimpleback are now considered to occur only in the 
Colorado River Basin of Texas. The Texas pimpleback is a small- to 
medium-sized (up to 4 in (103 mm)) mussel with a moderately inflated, 
yellow, brown, or black shell, occasionally with vague green rays or 
concentric blotches (Howells 2014, p. 93).
    Recent laboratory studies of the closely related Guadalupe orb 
suggest that channel catfish, flathead catfish, and tadpole madtom are 
host fish for the Texas pimpleback (Dudding et al. 2019, p. 2). Related 
species have miniature glochidia and also use catfish as hosts 
(Barnhart et al. 2008, pp. 373, 379). Additionally, related species can 
also produce conglutinates (Barnhart et al. 2008, p. 376) and tend to 
exhibit short-term brooding (tachytictia; releasing glochidia soon 
after the larvae mature) (Barnhart et al. 2008, p. 384). Texas 
pimpleback are reproductively active between April and August (Randklev 
et al. 2017c, p. 110). Related species live as long as 15 to 72 years 
(Haag and Rypel 2010, p. 10).
    Texas pimpleback are known to occur in the Colorado River Basin in 
five isolated populations: Concho River, Upper San Saba River, Lower 
San Saba River/Colorado River, Llano River, and the Lower Colorado 
River (see table 5, below; see also figure 5.9 in Service 2022, p. 
110). Only the Lower San Saba and Llano River populations are known to 
be successfully reproducing. Texas

[[Page 48046]]

pimpleback was historically distributed throughout the Colorado River 
Basin (Howells 2014, pp. 93-94; reviewed in Randklev et al. 2017c, pp. 
109-110).

                                  Table 5--Current Texas Pimpleback Populations
----------------------------------------------------------------------------------------------------------------
                                                                              Occupied reach
            Population               Streams included          Counties         length (mi     Recent collection
                                                                                   (km))        years (numbers)
----------------------------------------------------------------------------------------------------------------
Concho River.....................  Concho River........  Concho Co., TX.....         14 (23)           2008 (47)
                                                                                                        2012 (1)
Upper San Saba River.............  San Saba River......  Menard Co., TX.....         30 (48)            2017 (1)
Lower San Saba/Colorado Rivers...  San Saba River,       Brown, Coleman,           178 (286)          2012 (247)
                                    Colorado River.       McCulloch, Mills,                           2014 (481)
                                                          and San Saba Co.,                            2017 (20)
                                                          TX.                                          2017 (97)
                                                                                                       2018 (42)
                                                                                                       2019 (23)
Llano River......................  Llano River.........  Mason Co., TX......           5 (8)           2012 (10)
                                                                                                        2016 (1)
                                                                                                       2017 (23)
                                                                                                        2018 (1)
                                                                                                       2021 (46)
Lower Colorado River.............  Colorado River......  Colorado and               98 (158)           2014 (49)
                                                          Wharton Co., TX.                              2017 (8)
                                                                                                       2018 (30)
----------------------------------------------------------------------------------------------------------------

Balcones Spike

    The Balcones spike (Fusconaia iheringi) was recently discovered to 
be a separate and distinct species from false spike (Smith et al. 2020, 
entire), and the Service now recognizes the Balcones spike as a new 
species that occurs in the Brazos and Colorado River basins. Because 
the Balcones spike has recently been split from false spike, species-
specific data are not yet available, and so we expect the Balcones 
spike has similar habitat needs (larger creeks and rivers with sand, 
gravel, or cobble substrates, slow to moderate flows) and host fish 
(red shiner (Cyprinella lutrensis) and blacktail shiner (Cyprinella 
venusta)) as the false spike.
    The Balcones spike is a small to medium-sized freshwater mussel (to 
approximately 3.8 inches (in) (96 millimeters (mm))) with a yellow-
green to brown elongate shell, sometimes with greenish rays. While 
similar in appearance to false spike, Balcones spike usually has a 
sharper posterior ridge and shinier periostracum when compared to false 
spike. For a more detailed description, see Smith et al. 2020 (entire). 
Related species in the genus Fusconaia from the southeast United States 
reach a maximum age of 15 to 51 years (Haag and Rypel 2010, pp. 4-6). 
The closely related congener species, false spike, is thought to have a 
maximum age of 15 years (Dudding et al. 2019, p. 167) and to reach 
sexual maturity around 5 years of age (Dudding et al. 2019, p. 167).
    Balcones spike is currently found in three populations in the 
Little River and some tributaries (Brazos River Basin), the lower San 
Saba River (Colorado River Basin), and the Llano River (Colorado River 
Basin) (see table 6, below; see also figure 5.3 in Service 2022, p. 
85).

                                   Table 6--Current Balcones Spike Populations
----------------------------------------------------------------------------------------------------------------
                                                                              Occupied reach   Recent collection
            Population               Streams included          Counties         length (mi      years (numbers
                                                                                   (km))          collected)
----------------------------------------------------------------------------------------------------------------
Little River and tributaries.....  Little River, Brushy  Milam and                   41 (66)           2015 (29)
                                    Creek, San Gabriel    Williamson Co., TX.                          2021 (13)
                                    River.                                                              2021 (1)
Lower San Saba River.............  San Saba River......  San Saba Co., TX...         42 (67)            2012 (3)
Llano River......................  Llano River.........  Mason Co., TX......         <1 (~1)            2017 (1)
                                                                                                       2021 (14)
----------------------------------------------------------------------------------------------------------------

False Spike

    The false spike is native to the Guadalupe Basin in central Texas 
(Howells 2010, p. 4; Randklev et al. 2017c, p. 12). It was thought to 
have historically occurred in the Rio Grande based on the presence of 
fossil and subfossil shells there (Howells 2010, p. 4), but those 
specimens have now been attributed to Sphenonaias taumilapana Conrad 
1855 (no common name; Randklev et al. 2017c, p. 12; Graf and Cummings 
2007, p. 309). Recently, individuals that had been known as false spike 
in the Brazos and Colorado River basins were found to be a new species 
(Smith et al. 2020, entire); therefore, the false spike occurs only in 
the Guadalupe River Basin.
    The false spike was originally described as Unio mitchelli by 
Charles T. Simpson in 1895 from the Guadalupe River in Victoria County, 
Texas (Dall 1896, pp. 5-6). The species was assigned as Quincuncina 
mitchelli by Turgeon et al. (1988, p. 33) and was recognized as such by 
Howells et al. (1996, p. 127), and it was referenced as Quadrula 
mitchelli by Haag (2012, p. 71). Finally, it was recognized as 
Fusconaia mitchelli, its current nomenclature, by Pfeiffer et al. 
(2016, p. 289). False spike is considered a valid taxon by the 
scientific community (Williams et al. 2017, pp. 35, 39).

[[Page 48047]]

    The false spike is a medium-sized freshwater mussel (to 5.2 in (132 
mm)) with a yellow-green to brown or black elongate shell, sometimes 
with greenish rays. For a detailed description, see Howells et al. 1996 
(pp. 127-128) and Howells 2014 (p. 85).
    Based on closely related species, false spike likely brood eggs and 
larvae from early spring to late summer and host fish are expected to 
be minnows (family Cyprinidae) (Pfeiffer et al. 2016, p. 287). 
Confirmed host fish for false spike include blacktail shiner and red 
shiner (Dudding et al. 2019, p. 16).
    Related species in the genus Fusconaia from the southeast United 
States reach a maximum age of 15 to 51 years (Haag and Rypel 2010, pp. 
4-6). False spike is thought to have a maximum age of 15 years (Dudding 
et al. 2019, p. 167) and to reach sexual maturity around 5 years of age 
(Dudding et al. 2019, p. 167).
    False spike occur in larger creeks and rivers with sand, gravel, or 
cobble substrates, and in areas with slow to moderate flows. The 
species is not known from impoundments, nor from deep waters (Howells 
2014, p. 85).
    False spike was once considered common wherever it was found; 
however, beginning in the early 1970s, the species began to be regarded 
as rare throughout its range, based on collection information (Strecker 
1931, pp. 18-19; Randklev et al. 2017c, p. 13). It was considered to be 
extinct until 2011, when the discovery of seven live false spike in the 
Guadalupe River, near Gonzales, Texas, was the first report of living 
individuals in nearly four decades (Howells 2010, p. 4; Randklev et al. 
2011, p. 17). The patchy distribution of false spike could be related 
to host fish relationships (Dudding et al. (2019, pp. 16-17); that is, 
because their host fish have a small home range, have limited dispersal 
ability, and are sensitive to human impacts, distribution of false 
spike could be limited by access to, and movement of, host fish.
    Currently, there is only one known population of false spike in the 
lower Guadalupe River (Guadalupe River Basin) (see table 7, below; see 
also figure 5.2 in Service 2022, p. 81). For more information on this 
population, see the SSA report (Service 2022, pp. 75-82). False spike 
is estimated to have been extirpated from the remainder of its 
historical range throughout the Guadalupe Basin of central Texas 
(reviewed in Randklev et al. 2017c, pp. 12-13).

                                     Table 7--Current False Spike Population
----------------------------------------------------------------------------------------------------------------
                                                                              Occupied reach   Recent collection
            Population               Streams included          Counties         length (mi       years (number
                                                                                   (km))          collected)
----------------------------------------------------------------------------------------------------------------
Lower Guadalupe River............  Guadalupe River.....  DeWitt, Gonzales,         102 (164)     2014-2015 (652)
                                                          and Victoria Co.,
                                                          TX.
----------------------------------------------------------------------------------------------------------------

Regulatory and Analytical Framework

Regulatory Framework

    Section 4 of the Act (16 U.S.C. 1533) and the implementing 
regulations in title 50 of the Code of Federal Regulations set forth 
the procedures for determining whether a species is an endangered 
species or a threatened species, issuing protective regulations for 
threatened species, and designating critical habitat for endangered and 
species. On April 5, 2024, jointly with the National Marine Fisheries 
Service, the Service issued a final rule that revised the regulations 
in 50 CFR 424 regarding how we add, remove, and reclassify endangered 
and threatened species to the lists and the criteria for designating 
listed species' critical habitat (89 FR 24300). On the same day, the 
Service published a final rule revising our protections for endangered 
species and threatened species at 50 CFR 17 (89 FR 23919). These final 
rules are now in effect and are incorporated into the current 
regulations. Our analysis for this decision applied our current 
regulations. Given that we proposed listing and critical habitat for 
these species under our prior regulations (revised in 2019), we have 
also undertaken an analysis of whether our decision would be different 
if we had continued to apply the 2019 regulations and we concluded that 
the decision would be the same. The analyses under both the regulations 
currently in effect and the 2019 regulations are available on https://www.regulations.gov.
    The Act defines an ``endangered species'' as a species that is in 
danger of extinction throughout all or a significant portion of its 
range, and a ``threatened species'' as a species that is likely to 
become an endangered species within the foreseeable future throughout 
all or a significant portion of its range. The Act requires that we 
determine whether any species is an endangered species or a threatened 
species because of any of the following factors:
    (A) The present or threatened destruction, modification, or 
curtailment of its habitat or range;
    (B) Overutilization for commercial, recreational, scientific, or 
educational purposes;
    (C) Disease or predation;
    (D) The inadequacy of existing regulatory mechanisms; or
    (E) Other natural or manmade factors affecting its continued 
existence.
    These factors represent broad categories of natural or human-caused 
actions or conditions that could have an effect on a species' continued 
existence. In evaluating these actions and conditions, we look for 
those that may have a negative effect on individuals of the species, as 
well as other actions or conditions that may ameliorate any negative 
effects or may have positive effects.
    We use the term ``threat'' to refer in general to actions or 
conditions that are known to or are reasonably likely to negatively 
affect individuals of a species. The term ``threat'' includes actions 
or conditions that have a direct impact on individuals (direct 
impacts), as well as those that affect individuals through alteration 
of their habitat or required resources (stressors). The term ``threat'' 
may encompass--either together or separately--the source of the action 
or condition or the action or condition itself.
    However, the mere identification of any threat(s) does not 
necessarily mean that the species meets the statutory definition of an 
``endangered species'' or a ``threatened species.'' In determining 
whether a species meets either definition, we must evaluate all 
identified threats by considering the species' expected response and 
the effects of the threats--in light of those actions and conditions 
that will ameliorate the threats--on an individual, population, and 
species level. We evaluate each threat and its expected effects on the 
species, then analyze the cumulative effect of all of the threats on 
the species as a whole. We also consider the cumulative effect of the 
threats in light of those actions and conditions that will have 
positive effects on the species, such as any

[[Page 48048]]

existing regulatory mechanisms or conservation efforts. The Secretary 
determines whether the species meets the definition of an ``endangered 
species'' or a ``threatened species'' only after conducting this 
cumulative analysis and describing the expected effect on the species 
now and in the foreseeable future.
    The Act does not define the term ``foreseeable future,'' which 
appears in the statutory definition of ``threatened species.'' Our 
implementing regulations at 50 CFR 424.11(d) set forth a framework for 
evaluating the foreseeable future on a case-by-case basis which is 
further described in the 2009 Memorandum Opinion on the foreseeable 
future from the Department of the Interior, Office of the Solicitor (M-
37021, January 16, 2009; ``M- Opinion,'' available online at https://www.doi.gov/sites/doi.opengov.ibmcloud.com/files/uploads/M-37021.pdf). 
The foreseeable future extends as far into the future as the U.S. Fish 
and Wildlife Service and National Marine Fisheries Service (hereafter, 
the Services) can make reasonably reliable predictions about the 
threats to the species and the species' responses to those threats. We 
need not identify the foreseeable future in terms of a specific period 
of time. We will describe the foreseeable future on a case-by-case 
basis, using the best available data and taking into account 
considerations such as the species' life-history characteristics, 
threat-projection timeframes, and environmental variability. In other 
words, the foreseeable future is the period of time over which we can 
make reasonably reliable predictions. ``Reliable'' does not mean 
``certain''; it means sufficient to provide a reasonable degree of 
confidence in the prediction, in light of the conservation purposes of 
the Act.

Analytical Framework

    The SSA report documents the results of our comprehensive 
biological review of the best scientific and commercial data regarding 
the status of the species, including an assessment of the potential 
threats to the species. The SSA report does not represent our decision 
on whether the species should be listed as endangered or threatened 
species under the Act. However, it does provide the scientific basis 
that informs our regulatory decisions, which involve the further 
application of standards within the Act and its implementing 
regulations and policies.
    To assess the viability of the seven central Texas mussels, we used 
the three conservation biology principles of resiliency, redundancy, 
and representation (Shaffer and Stein 2000, pp. 306-310). Briefly, 
resiliency is the ability of the species to withstand environmental and 
demographic stochasticity (for example, wet or dry, warm or cold 
years), redundancy is the ability of the species to withstand 
catastrophic events (for example, droughts, large pollution events), 
and representation is the ability of the species to adapt to both near-
term and long-term changes in its physical and biological environment 
(for example, climate conditions, pathogens). In general, species 
viability will increase with increases in resiliency, redundancy, and 
representation (Smith et al. 2018, p. 306). Using these principles, we 
identified the species' ecological requirements for survival and 
reproduction at the individual, population, and species levels, and 
described the beneficial and risk factors influencing the species' 
viability.
    The SSA process can be categorized into three sequential stages. 
During the first stage, we evaluated each individual species' life-
history needs. The next stage involved an assessment of the historical 
and current condition of the species' demographics and habitat 
characteristics, including an explanation of how the species arrived at 
its current condition. The final stage of the SSA involved making 
predictions about the species' responses to positive and negative 
environmental and anthropogenic influences. Throughout all of these 
stages, we used the best available information to characterize 
viability as the ability of a species to sustain populations in the 
wild over time. We use this information to inform our regulatory 
decision.
    The following is a summary of the key results and conclusions from 
the SSA report; the full SSA report can be found at Docket FWS-R2-ES-
2019-0061 on https://www.regulations.gov and at https://www.fws.gov/office/austin-ecological-services.

Summary of Biological Status and Threats

    In this discussion, we review the biological condition of the 
species and its resources, and the threats that influence the species' 
current and future condition, in order to assess the species' overall 
viability and the risks to that viability.
    Using various timeframes and the current and projected future 
resiliency, redundancy, and representation, we describe the species' 
levels of viability over time. For the central Texas mussels to 
maintain viability, their populations or some portion thereof must be 
sufficiently resilient. A number of factors influence the resiliency of 
central Texas mussel populations, including occupied stream length, 
abundance, and recruitment. While some of the seven species have life-
history adaptations that help them tolerate dewatering and other 
stressors to some extent, each of these stressors diminishes the 
resiliency of populations to some degree and especially in combination. 
Elements of the species' habitat that determine whether central Texas 
mussel populations can grow to maximize habitat occupancy influence 
those factors, thereby increasing the resiliency of populations. These 
resiliency factors and habitat elements are discussed in detail in the 
SSA report and are summarized here.

Species Needs

Occupied Stream Length
    Most freshwater mussels, including the central Texas mussel 
species, are found in aggregations, called mussel beds, that vary in 
size from about 50 to more than 5,000 square meters (m\2\), separated 
by stream reaches in which mussels are absent or rare (Vaughn 2012, p. 
2). We define a mussel population at a larger scale than a single 
mussel bed; it is the collection of mussel beds within a stream reach 
between which infested host fish may travel, allowing for ebbs and 
flows in mussel bed density and abundance over time throughout the 
entirety of the population's occupied reach. Therefore, sufficiently 
resilient mussel populations must occupy stream reaches long enough 
such that stochastic events that affect individual mussel beds do not 
eliminate the entire population, and repopulation by infested fish from 
other mussel beds within the reach can allow the population to recover 
from these events. We consider populations extending more than 50 miles 
(80 kilometers (km)) to be highly resilient to stochastic events 
because a single event is unlikely to affect the entire population. 
Populations occupying reaches between 20 and 49 river mi (32 and 79 
river km) have some resiliency to stochastic events, and populations 
occupying reaches less than 20 miles (32 km) have little resiliency.
Abundance
    Mussel abundance in a given stream reach is a product of the number 
of mussel beds and the density of mussels within those beds. For 
populations of the central Texas mussel species to be healthy (i.e., 
sufficiently resilient), there must be many mussel beds of sufficient 
density such that local stochastic events do not necessarily eliminate 
the bed(s),

[[Page 48049]]

allowing the mussel bed and the overall local population within a 
stream reach to recover from any single event. Mussel abundance is 
indicated by the number of individuals found during a sampling event; 
mussel surveys rarely represent a complete census of the population. 
Instead, density is estimated by the number found during a survey event 
using various statistical techniques. Because we do not have population 
estimates for most populations of the central Texas mussels, nor are 
the techniques directly comparable (i.e., same area size searched, 
similar search time, etc.), we used the number of individuals captured 
as an index over time, presuming relatively similar levels of effort. 
While we cannot precisely determine population abundance at the sites 
using these numbers, we are able to determine if the species is 
dominant at the site or rare and examine this over time if those data 
are available.
Reproduction
    Adequately resilient central Texas mussel populations must also be 
reproducing and recruiting young individuals into the population. 
Population size and abundance reflects previous influences on the 
population and habitat, while reproduction and recruitment reflect 
population trends that may be stable, increasing, or decreasing over 
time. For example, a large, dense mussel population that contains 
mostly old individuals is not likely to remain large and dense into the 
future, as there are few young individuals to sustain the population 
over time (i.e., death rates exceed birth rates and subsequent 
recruitment of reproductive adults resulting in negative population 
growth). Conversely, a population that is less dense but has many young 
and/or gravid individuals may likely grow to a higher density in the 
future (i.e., birth rates and subsequent recruitment of reproductive 
adults exceeds death rates, resulting in positive population growth). 
Detection rates of very young juvenile mussels during routine abundance 
and distribution surveys are extremely low due to sampling bias, as 
sampling for these species involves tactile searches and mussels 
smaller than 35 mm are very difficult to detect (Strayer and Smith 
2003, pp. 47-48).
    Evidence of reproduction is demonstrated by repeated captures of 
small-sized individuals (juveniles and subadults near the low end of 
the detectable range size (about 35 mm); Randklev et al. 2013, p. 9) 
over time and by observing gravid (with eggs in the marsupium, gills, 
or gill pouches) females during the reproductively active time of year. 
While small-sized mussels and gravid females can be difficult to 
detect, it is important that surveyors attempt to detect them, as 
reproduction and subsequent recruitment are important demographic 
parameters that affect growth rates in mussel populations (Berg et al. 
2008, pp. 396, 398-399; Matter et al. 2013, pp. 122-123, 134-135).

Risk Factors for the Central Texas Mussels

    We reviewed the potential risk factors (i.e., threats, stressors) 
that could be affecting the seven central Texas mussels now and in the 
future. In this rule, we will discuss only those factors in detail that 
could meaningfully impact the status of the species. Those risks that 
are not known to have effects on central Texas mussel populations, such 
as disease, are not discussed here but are evaluated in the SSA report. 
Many of the threats and risk factors are the same or similar for each 
of the seven species. Where the effects are expected to be similar, we 
present one discussion that applies to all seven species. Where the 
effects may be unique or different to one species, we will address that 
specifically. The primary risk factors (i.e., threats) affecting the 
status of the central Texas mussels are: (1) Increased fine sediment 
(Factor A from the Act), (2) changes in water quality (Factor A), (3) 
altered hydrology in the form of inundation (Factor A), (4) altered 
hydrology in the form of loss of flow and scour of substrate (Factor 
A), (5) predation and collection (Factor B), and (6) barriers to fish 
movement (Factor E). These factors are all exacerbated by the ongoing 
and expected effects of climate change. Finally, we also reviewed the 
conservation efforts being undertaken for the species.
Increased Fine Sediment
    Juvenile and adult central Texas mussels inhabit microsites that 
have abundant interstitial spaces, or small openings in an otherwise 
closed matrix of substrate, created by gravel, cobble, boulders, 
bedrock crevices, tree roots, and other vegetation. Inhabited 
interstitial spaces have some amount of fine sediment (i.e., clay and 
silt) necessary to provide appropriate shelter. However, excessive 
amounts of fine sediments can reduce the number of appropriate 
microsites in an otherwise suitable mussel bed by filling in these 
interstitial spaces and can smother mussels in place. All seven species 
of the central Texas mussels generally require stable substrates, and 
loose silt deposits do not generally provide for substrate stability 
that can support mussels. Interstitial spaces provide essential habitat 
for juvenile mussels. Juvenile freshwater mussels burrow into 
interstitial substrates, making them particularly susceptible to 
degradation of this habitat feature. When clogged with sand or silt, 
interstitial flow may become reduced (Brim Box and Mossa 1999, p. 100), 
thus reducing juvenile habitat availability and quality. While adult 
mussels can be physically buried by excessive sediment, the main 
impacts of excess sedimentation on unionids (freshwater mussels) are 
often sublethal and include interference with feeding mediated by valve 
closure (Brim Box and Mossa 1999, p. 101). Many land use activities can 
result in excessive erosion, sediment production, and channel 
instability, including, but not limited to, logging, crop farming, 
ranching, mining, and urbanization (Brim Box and Mossa 1999, p. 102).
    Under a natural flow regime, a stream's sediment load is in 
equilibrium such that as sediments are naturally moved downstream from 
one microsite to another, the amount of sediment in the substrate is 
relatively stable, given that different reaches within a river or 
stream may be aggrading (gaining) or degrading (losing) sediment (Poff 
et al. 1997, pp. 770-772). In this context, sedimentation explicitly is 
restricted to increased fine sediments entering a stream system at a 
rate beyond the naturally occurring losing rate and does not replace 
the use of the broader term of turbidity. In addition to increased 
levels of fine sediment, turbidity is also influenced by concentrations 
of fine organic and inorganic matter, soluble organic compounds, algae, 
and other microscopic organisms. Changes in stream turbidity are not 
inherently an indicator of increased sedimentation as turbidity can 
naturally vary from stream to stream in Texas due to unrelated factors 
(e.g., stream primary productivity). Current and past human activities 
result in enhanced sedimentation in river systems, and legacy sediment, 
resulting from past land disturbance and reservoir construction, 
continues to persist and influence river processes and sediment 
dynamics (Wohl 2015, p. 31). These legacy effects can degrade mussel 
habitats. Fine sediments collect on the streambed and in crevices 
during low flow events, and much of the sediment is washed downstream 
during high flow events (also known as cleansing flows) and deposited 
elsewhere. However, increased frequency of low flow events (from 
groundwater extraction, instream surface flow diversions, and drought)

[[Page 48050]]

combined with a decrease in cleansing flows (from reservoir management 
and drought) causes sediment to accumulate. Sediments deposited by 
large-scale flooding or other disturbance may persist for several years 
until adequate cleansing flows can redistribute that sediment 
downstream. When water velocity decreases, which can occur from reduced 
streamflow or inundation, water loses its ability to carry sediment in 
suspension, and sediment falls to the substrate, eventually smothering 
mussels not adapted to soft substrates (Watters 2000, p. 263). Sediment 
accumulation can be exacerbated when there is a simultaneous increase 
in the sources of fine sediments in a watershed.
    In the range of the central Texas mussels, these sources include 
streambank erosion from development, agricultural activities, livestock 
and wildlife grazing and browsing, in-channel disturbances, roads, and 
crossings, among others (Poff et al. 1997, p. 773). In areas with 
ongoing development, runoff can transport substantial amounts of 
sediment from ground disturbance related to construction activities 
with inadequate or absent sedimentation controls. While these 
construction impacts can be transient (lasting only during the 
construction phase), the long-term effects of development are long 
lasting and can result in hydrological alterations as increased 
impervious cover increases runoff and resulting shear stress causes 
streambank instability and additional sedimentation.
    All populations of the central Texas mussels face the risk of fine 
sediment accumulation to varying degrees. Multiple populations of the 
seven central Texas mussel species are experiencing increased 
sedimentation, including, in particular, the Clear Fork Brazos River 
(Texas fawnsfoot), middle and lower Brazos River (Balcones spike and 
Texas fawnsfoot), and lower Colorado River (Texas pimpleback and Texas 
fawnsfoot). In the future, we expect sediment deposition to continue to 
increase across the range of all seven species due to low water levels 
and decreasing frequency of cleansing flows at all populations and for 
longer periods due to climate change and additional human development 
in the watershed.
Changes in Water Quality
    Freshwater mussels and their host fish require water in sufficient 
quantity and quality on a consistent basis to complete their life 
cycles. Urban growth and other anthropogenic activities across Texas 
are placing increased demands on limited freshwater resources that, in 
turn, can have deleterious effects on water quality. Water quality can 
be degraded through contamination or alteration of water chemistry. 
Chemical contaminants are ubiquitous throughout the environment and are 
a major reason for the current declining status of freshwater mussel 
species nationwide (Augspurger et al. 2007, p. 2025). Immature mussels 
(i.e., juveniles and glochidia) are especially sensitive to water 
quality degradation and contaminants (Cope et al. 2008, p. 456; Wang et 
al. 2017, pp. 791-792; Wang et al. 2018, p. 3041).
    Chemicals enter the environment through both point and nonpoint 
source discharges, including hazardous spills, industrial wastewater, 
municipal effluents, and agricultural runoff. These sources contribute 
organic compounds, trace metals, pesticides, and a wide variety of 
newly emerging contaminants (e.g., pharmaceuticals) that comprise some 
85,000 chemicals in commerce today that are released into the aquatic 
environment (EPA 2018, p. 1). The extent to which environmental 
contaminants adversely affect aquatic biota can vary depending on many 
variables such as concentration, volume, and timing of the release. 
Species diversity and abundance consistently rank lower in waters that 
are polluted or otherwise degraded by contaminants. Freshwater mussels 
are not generally found for many miles downstream of municipal WWTPs 
(Gillis et al. 2017, p. 460; Goudreau et al. 1993, p. 211; Horne and 
McIntosh 1979, p. 119). For example, transplanted common freshwater 
mussels (including threeridge (Amblema plicata) and the nonnative Asian 
clam (Corbicula fluminea)) showed reduced growth and survival below a 
WWTP outfall relative to sites located upstream of the WWTP in 
Wilbarger Creek (a tributary to the Colorado River in Travis County, 
Texas); water chemistry was altered by the wastewater flows at 
downstream sites, with elevated constituents in the water column that 
included copper, potassium, magnesium, and zinc (Duncan and Nobles 
2012, p. 8; Nobles and Zhang 2015, p. 11). Contaminants released during 
hazardous spills are also of concern. Although spills are relatively 
short-term localized events, depending on the types of substances and 
volume released, water resources nearby can be severely impacted and 
degraded for years following an incident.
    Ammonia is of particular concern below WWTPs because freshwater 
mussels are particularly sensitive to increased ammonia levels 
(Augspurger et al. 2003, p. 2569). Elevated concentrations (greater 
than 0.2 parts per billion) of un-ionized ammonia (NH3) in 
the interstitial spaces of benthic habitats have been implicated in the 
reproductive failure of other freshwater mussel populations (Strayer 
and Malcom 2012, pp. 1787-1788), and sublethal effects (valve closures) 
have recently been described as total ammonia nitrogen approaches 2.0 
milligrams per liter (mg/L = parts per million (ppm); Bonner et al. 
2018, p. 186). Immature mussels (i.e., juveniles and glochidia) are 
especially sensitive to water quality degradation and contaminants, 
including ammonia (Wang et al. 2007, p. 2055). For pimpleback 
(Cyclonaias pustulosa, a species native to central Texas but not 
included in this listing), the revised Environmental Protection Agency 
ammonia benchmarks are sufficient to protect from short-term effects of 
ammonia on the species' physiological processes (Bonner et al. 2018, p. 
151). However, the long-term effects of chronic exposure (i.e., years 
or decades) to freshwater mussels have yet to be experimentally 
investigated.
    Municipal wastewater contains both ionized and un-ionized ammonia, 
and wastewater discharge permits issued by the Texas Commission on 
Environmental Quality (TCEQ) do not always impose limits on ammonia, 
particularly for smaller volume dischargers. Therefore, at a minimum, 
concentrations of ammonia are likely to be elevated in the immediate 
mixing zone of some WWTP outfalls. Approximately 480 discharge permits 
have been issued for the Brazos River watershed alone from its 
headwaters above Possum Kingdom Lake down to the Gulf of Mexico (TCEQ 
2018, entire), and WWTP outfalls are numerous in other basins 
throughout the ranges of the central Texas mussels. In addition, some 
industrial permits, such as animal processing facilities, have ammonia 
limits in the range of 3 to 4 mg/L or higher, which exceeds levels that 
inhibited growth in juvenile fatmucket (Lampsilis siliquoidea) and 
rainbow mussel (Villosa iris) (Wang et al. 2007, entire).
    An additional type of water quality degradation that affects the 
central Texas mussels is alteration of water quality parameters such as 
dissolved oxygen, temperature, and salinity levels. Dissolved oxygen 
levels may be reduced from increased nutrient inputs or other sources 
of organic matter that increase the biochemical oxygen demand in the 
water column as microorganisms decompose waste. Organic waste can 
originate from storm water or irrigation

[[Page 48051]]

runoff or wastewater effluent, and juvenile mussels seem to be 
particularly sensitive to low dissolved oxygen (with sublethal effects 
evident at 2 ppm and lethal effects evident at 1.3 ppm; Sparks and 
Strayer 1998, pp. 132-133). Increased water temperature (over 30 [deg]C 
(86 [deg]F) and approaching 40 [deg]C (104 [deg]F)) from climate change 
and from low flows during drought can exacerbate low dissolved oxygen 
levels in addition to other drought-related effects on both juvenile 
and adult mussels (Sparks and Strayer 1998, pp. 132-133). Finally, high 
salinity concentrations are an additional concern in certain 
watersheds, where dissolved salts can be particularly limiting to the 
central Texas mussels. Upper portions of the Brazos and Colorado 
Rivers, originating from the Texas High Plains, contain saline water, 
sourced from both natural geological formations and from oil and gas 
development. Salinity in river water is diluted by surface flow, and as 
surface flow decreases, salt concentrations increase, resulting in 
adverse effects to freshwater mussels. Even low levels of salinity (2 
to 4 parts per thousand (ppt)) have been demonstrated to have 
substantial negative effects on reproductive success, metabolic rates, 
and survival of freshwater mussels (Blakeslee et al. 2013, p. 2853). 
The behavioral response of valve closure to high salinity 
concentrations (greater than 2 ppt) is the likely mechanism for reduced 
metabolic rates, reduced feeding, and reduced reproductive success 
based on reported sublethal effects of salinity of more than 2 ppt for 
the Texas pimpleback (Bonner et al. 2018, pp. 155-156).
    Water quality and quantity are interdependent, so reductions in 
surface flow from drought, instream diversion, and groundwater 
extraction serve to concentrate contaminants by reducing flows that 
would otherwise dilute point and non-point source pollution. For 
example, salinity inherently poses a greater risk to aquatic biota 
under low flow conditions as salinity concentrations and water 
temperatures increase. Drought conditions can place additional 
stressors on stream systems beyond reduced flow by exacerbating 
contaminant-related effects to aquatic biota, including the central 
Texas mussels. Not only can temperature be a biological, physical, and 
chemical stressor, the toxicity of many pollutants (e.g., ammonia, 
mercury) to aquatic organisms increases at higher temperatures. We 
foresee threats to water quality increasing into the future as demand 
and competition for limited water resources grows.
Altered Hydrology--Inundation
    All seven central Texas mussels are adapted to flowing water (lotic 
habitats) rather than standing water (lentic habitats) and require 
free-flowing water to survive. Low flow events (including stream 
drying) and inundation can eliminate habitat appropriate for the 
central Texas mussels, and while these species can survive these events 
for a short duration, populations that experience prolonged drying 
events or repeated drying events will not persist over time.
    Inundation has primarily occurred upstream of dams, both large 
(such as the Highland Lakes on the Colorado River and other major flood 
control and water supply reservoirs) and small (low water crossings and 
diversion dams typical of the tributaries and occurring usually on 
privately owned lands throughout central Texas). Inundation causes an 
increase in sediment deposition, eliminating the crevices that many of 
the central Texas mussel species inhabit. Inundation also includes the 
effects of reservoir releases where frequent variation in surface water 
elevation acts to make habitats unsuitable for the central Texas 
mussels. In large reservoirs, deep water is very cold and often devoid 
of oxygen and necessary nutrients. Cold water (less than 11 [deg]C (52 
[deg]F)) stunts mussel growth and delays or hinders spawning. The 
central Texas mussels do not tolerate inundation under large 
reservoirs. Further, deep-water reservoirs with bottom release (like 
Canyon Reservoir) can affect water temperatures several miles 
downriver. The water temperature remains below 21.1 [deg]C for the 
first 3.9 miles (6.3 km) of the 13.8-mile (22.2-km) Canyon Reservoir 
tailrace (TPWD 2007, p. ii), and are cold enough to support a 
recreational nonnative rainbow and brown trout fishery.
    The construction of dams, inundation of reservoirs, and management 
of water releases have significant effects on the natural hydrology of 
a river or stream. For example, dams trap sediment in reservoirs, and 
managed releases typically do not conform to the natural flow regime 
(i.e., higher baseflows, and peak flows of reduced intensity but longer 
duration). Rivers transport not only water but also sediment, which is 
transported mostly as suspended load (held by the water column), and 
most sediment transport occurs during floods as sediment transport 
increases as a power function (greater than linear) of flow (Kondolf 
1997, p. 533). It follows that increased severity of flooding would 
result in greater sediment transport, with important effects on 
substrate stability and benthic habitats for freshwater mussels and 
other organisms dependent on stable benthic habitats. Further, water 
released by dams is usually clear and does not carry a sediment load 
and is considered ``hungry water because the excess energy is typically 
expended on erosion of the channel bed and banks . . . resulting in 
incision (downcutting of the bed) and coarsening of the bed material 
until a new equilibrium is reached'' (Kondolf 1997, p. 535). 
Conversely, depending on how dam releases are conducted, reduced flood 
peaks can lead to accumulations of fine sediment in the riverbed (i.e., 
loss of flushing flows) (Kondolf 1997, pp. 535, 548).
    Operation of flood-control, water-supply, and recreation reservoirs 
results in altered hydrologic regimes, including an attenuation of both 
high- and low-flow events. Flood-control dams store floodwaters and 
then release them in a controlled manner; this extended release of 
flood waters can result in significant scour and loss of substrates 
that provide mussel habitat. Along with this change in the flow of 
water, sediment dynamics are affected as sediment is trapped above and 
scoured below major impoundments. These changes in water and sediment 
transport have negatively affected freshwater mussels and their 
habitats.
    There are numerous dams throughout the range of the central Texas 
mussels. There are now 27 major reservoirs, 16 of which have more than 
50,000 acre-feet of storage, in the Brazos River Basin (BBEST 2012, p. 
33); 31 major reservoirs in the Colorado River Basin, including the 
Highland Lakes (TWDB 2018, p. 1); 9 major reservoirs on the Guadalupe 
River (BBEST 2011, p. 2.2); and 31 major reservoirs in the Trinity 
River Basin (BBEST 2009, p. 10). These reservoirs, subsequent 
inundation, and resulting fragmentation of mussel populations has been 
the primary driver of the current distribution of the central Texas 
mussels. Additional reservoirs are planned for the future, including 
the Cedar Ridge Reservoir, proposed by the City of Abilene on the Clear 
Fork of the Brazos River near the town of Lueders, Texas (see 83 FR 
16061; April 13, 2018), and more than one reservoir is proposed to be 
built off the main channel of the Lower Colorado River in Wharton and 
Colorado Counties, Texas (LCRA 2018, p. 1). The Allens Creek Reservoir 
is proposed for construction on Allens Creek near the City of Wallis, 
to provide water supply and storage for the City of Houston (BRA 2018a, 
p. 1). Water that is planned to be pumped from the Brazos River during 
high flows will be

[[Page 48052]]

stored and released back into the river to meet downstream needs during 
periods of low flow.
Altered Hydrology--Flow Loss and Scour
    Extreme water levels--both low flows and high flows--are threats to 
population persistence of the central Texas mussels. The effects of 
population losses associated with excessively low flows are compounded 
by population losses associated with excessively high flows. Whereas 
persistent low flow during times of drought results in drying of mussel 
habitats and desiccation of exposed mussels, rapid increases in flows 
associated with large-scale rain events and subsequent flooding results 
in scour of the streambed and physical displacement of mussels and 
appropriate substrates. Appropriately sized substrates are moved during 
scouring high flow events, and mussels are transported downstream to 
inappropriate sites or are buried by inappropriately sized materials. 
The central Texas mussels are experiencing a repeating cycle of 
alternating droughts and flooding that, in combination with 
hydrological alterations, impacts population persistence.
    Droughts that have occurred in the recent past have led to 
extremely low flows in several central Texas rivers. Many of these 
rivers have some resiliency to drought because they are spring-fed 
(Colorado River tributaries, Guadalupe River), are very large (lower 
Brazos and Colorado Rivers), or have significant return flows (Trinity 
River), but drought in combination with increased groundwater pumping 
may lead to lower river flows of longer duration than have been 
recorded in the past. Reservoir releases can be managed to some extent 
during drought conditions to prevent complete dewatering below many 
major reservoirs. During the months of July and August 2018, the Clear 
Fork Brazos, Concho, San Saba, Llano, Pedernales, and upper Colorado 
and upper Guadalupe Rivers all had very low flows (USGS 2019, 
unpaginated).
    Streamflow in the Colorado River above the Highland Lakes and 
downstream of the confluence with Concho River has been declining since 
the 1960s as evidenced by annual daily mean streamflow (USGS 2008, pp. 
812, 814, 848, 870, 878, 880), and overall river discharge for the 
Colorado River can be expected to continue to decline due to increased 
drought as a result of climate change, absent significant return flows. 
There are a few exceptions including the Llano River at Llano (USGS 
2008, p. 892), Pedernales River at Fredericksburg (USGS 2008, p. 896), 
Onion Creek near Driftwood, and Onion Creek at Highway 183 (flows 
appear to become more erratic, characteristic of a developing 
watershed) (USGS 2008, pp. 930, 946). In the San Saba River, continuing 
or increasing surface and alluvial aquifer groundwater withdrawals in 
combination with drought are likely to result in reduced streamflow, 
affecting mussels in the future (Randklev et al. 2017c, pp. 10-11).
    Flows have declined due to drought in the Brazos River in recent 
years upstream of Lake Whitney (USGS 2008, pp. 578, 600, 626, 638; BRA 
2018b, p. 6), although baseflows are maintained somewhat due to 
releases from Lake Granbury and other reservoirs in the upper basin 
(USGS 2008, p. 644; BRA 2018b, p. 6). In the middle Brazos, U.S. Army 
Corps of Engineers (USACE) dams have reduced the magnitude of floods on 
the mainstem of the Brazos River downstream of Lake Whitney (USGS 2008, 
pp. 652, 676, 766, 776; BRA 2018b, p. 6), while flows in the lower 
Brazos and Navasota Rivers appear to have higher baseflows due to water 
supply operations in the upper basin that deliver to downstream users 
(USGS 2008, pp. 754, 766, 776; BRA 2018b, p. 6). Lake Limestone 
releases also appear to be contributing to higher base flows in the 
Lower Brazos (BRA 2018b, p. 6). Flows have declined in the upper 
Guadalupe River (USGS 2008, pp. 992, 994, 1000, 1018) but appear 
relatively unchanged at Comfort and Spring Branch and in the San Marcos 
River (USGS 2008, pp. 1004, 1006, 1022), and in the lower Guadalupe 
River (USGS 2008, pp. 1036, 1040). In the lower sections of the 
Colorado River, lower flows and reduced high flow events are more 
common now decades after major reservoirs were constructed (USGS 2008, 
pp. 964, 966). In the Trinity River, low flows are higher (elevated 
baseflows) than they were in the past (USGS 2008, pp. 370, 398, 400, 
430) because of substantial return flows from Dallas area wastewater 
treatment plants.
    Many of the tributary streams (i.e., Concho, San Saba, Llano, and 
Pedernales Rivers) historically received significant groundwater inputs 
from multiple springs associated with the Edwards and other aquifers. 
As spring flows decline due to drought or groundwater lowering from 
pumping, habitat for the central Texas mussels in the tributary streams 
is reduced and could eventually cease to exist (Randklev et al. 2018, 
pp. 13-14). While the central Texas mussels may survive short periods 
of low flow, as low flows persist, mussels face oxygen deprivation, 
increased water temperature, increased predation risk, and ultimately 
stranding, all reducing survivorship, reproduction, and recruitment in 
the population.
    Low-flow events lead to increased risk of desiccation (physical 
stranding and drying) and exposure to elevated water temperature and 
other water quality degradations, such as contaminants, as well as to 
predation. For example, sections of the San Saba River, downstream of 
Menard, Texas, experienced very low flows during the summer of 2015, 
which led to dewatering of occupied habitats as evidenced by 
observations of recent dead shell material of Texas pimpleback and 
Texas fatmucket (TPWD 2015, pp. 2-3; described in detail by Randklev et 
al. 2018, entire). Several USGS stream gauges reported very low flows 
during the 2017-2018 water year, including the Clear Fork of the Brazos 
River, Elm Creek, Concho River at Paint Rock, San Saba River, Colorado 
River at San Saba, Llano River, Pedernales River, and upper Guadalupe 
River (USGS 2018, entire). In 2017, Service, TPWD, and Texas Department 
of Transportation (TxDOT) biologists noted at one site on the Brazos 
River near Highbank, Texas, the presence of 42 dead to fresh dead (with 
tissue intact) Texas fawnsfoot that likely died as a result of recent 
drought or scouring events (Tidwell 2017, entire).
    High flow events lead to increased risk of physical removal, 
transport, and burial (entrainment) of mussels as unstable substrates 
are transported downstream by floodwaters and later redeposited in 
locations that may not be suitable. A site in the lower Colorado River 
near Altair, Texas, suffered significant changes in both mussel 
community structure and bathymetry (measurement of water depths) during 
extensive flooding (and resulting high flows) in August 2017, as a 
result of Hurricane Harvey (Bonner et al. 2018, p. 266). Prior to the 
flooding events, this site held the highest mussel abundance (Bonner et 
al. 2018, pp. 242-243) and represented high-quality habitat within the 
Colorado River Basin. After the flooding events, mussel abundance 
significantly decreased by nearly two orders of magnitude (Bonner et 
al. 2018, p. 266). This location had two of the central Texas mussel 
species (Texas fawnsfoot and Texas pimpleback) present during initial 
surveys in 2017 (Bonner et al. 2018, p. 242). Widespread flooding was 
reported in the Colorado and Guadalupe River Basins of central Texas in 
October 2018.

[[Page 48053]]

    The distribution of mussel beds and their habitats is affected by 
large floods returning at least once during the typical life span of an 
individual mussel (generally from 3 to 30 years). The presence of flow 
refuges mediates the effects of these floods, as shear stress is 
relatively low in flow refuges and where sediments are relatively 
stable, and individual mussels ``must either tolerate high-frequency 
disturbances or be eliminated, and can colonize areas that are 
infrequently disturbed between events'' (Strayer 1999, pp. 468-469). 
Shear stress and relative substrate stability are limiting to mussel 
abundance and species richness (Randklev et al. 2017a, p. 7), and 
riffle habitats may be more resilient to high flow events than littoral 
(bank) habitats.
    The central Texas mussels have historically been, and currently 
remain, exposed to extreme hydrological conditions, including severe 
drought leading to dewatering, and heavy rains leading to damaging 
scour events with movement of mussels and substrate (i.e., ``flash 
flooding''). For example, in 2018, over the span of 69 days, the Llano 
River near Llano, Texas, experienced extreme low flows (0.08 cubic feet 
per second (cfs) on August 8, 2018), and extreme high flows leading to 
severe flooding, which resulted in substantial scour of streambed and 
riparian area habitats (278,000 cfs on October 16, 2018) (LRWA 2019, 
entire). Prolonged drought followed by severe flooding can result in 
failure and collapse of river banks and subsequent sedimentation, as 
demonstrated by slumping and undercutting on the lower Guadalupe River 
(near Cuero, Texas), which is occupied by the false spike and Guadalupe 
orb, in 2015 (Giardino and Rowley 2016, pp. 70-72). The usual drought/
flood cycle in central Texas can be characterized by long periods of 
time without rain interrupted by short periods of heavy rain, resulting 
in often severe flooding. These same patterns led to the development of 
flood control and storage reservoirs throughout Texas in the 20th 
century. It follows that, given the extreme and variable climate of 
central Texas, mussels must have life-history strategies and other 
adaptations that allow them to persist by withstanding severe 
conditions and repopulating during more favorable conditions. However, 
it is also likely that there is a limit to how the mussels might 
respond to increasing variability, frequency, and severity of extreme 
weather events, combined with habitat fragmentation and population 
isolation.
    Sediment deposition may arise from human activities, as well. Sand 
and gravel can be mined from rivers or from adjacent alluvial deposits, 
and instream gravels often require less processing and are thus more 
attractive from a business perspective (Kondolf 1997, p. 541). Instream 
mining directly affects river habitats, and can indirectly affect river 
habitats through channel incision, bed coarsening, and lateral channel 
instability (Kondolf 1997, p. 541). Excavation of pits in or near to 
the channel can create a nickpoint, which can contribute to erosion 
(and mobilization of substrate) associated with head cutting (Kondolf 
1997, p. 541). Off-channel mining of floodplain pits can become 
involved during floods, such that the pits become hydrologically 
connected and thus can affect sediment dynamics in the stream (Kondolf 
1997, p. 545).
Predation and Collection
    Predation on freshwater mussels is a natural phenomenon. Raccoons, 
muskrats, snapping turtles, wading birds, and fish are known to prey 
upon the central Texas mussels. Under natural conditions, the level of 
predation occurring within central Texas mussel populations is not 
likely to pose a significant risk to any given population. However, 
during periods of low flow, terrestrial predators and wading birds have 
increased access to portions of the river that are otherwise too deep 
under normal flow conditions. High levels of predation during drought 
have been observed on the Llano and San Saba Rivers. As drought and low 
flow are predicted to occur more often and for longer periods due to 
the effects of future climate change, the Hill Country tributaries (of 
the Colorado River) in particular are expected to experience additional 
predation pressure into the future, and this may become especially 
problematic in the Llano and San Saba Rivers. Predation is expected to 
be less of a problem for the lower portions of the mainstem river 
populations because the rivers are significantly larger than the 
tributary streams and the central Texas mussels are less likely to be 
found by predators in exposed or very shallow habitats.
    Certain mussel beds within some populations, due to ease of access, 
are vulnerable to overcollection and vandalism. These areas, primarily 
on the Llano and San Saba Rivers, have well-known and well-documented 
mussel beds that have been sampled repeatedly over the past few years 
by multiple researchers and others for a variety of projects (Robertson 
2023, entire).
    Repeated collections and handling can cause disturbance to the 
growth of individual mussels. Freshwater mussels close their shell in 
response to handling, which can lead to the production of a disturbance 
ring in the shell. When closing its shell, it is possible for the 
mussel's mantle-shell margin connection to be disrupted as the mantle 
tissue is retracted. This can result in the production of a growth 
disturbance ring when this mantle-shell connection is re-established in 
a slightly differing location than the original collection causing a 
misalignment of the prismatic layer and periostracum (Haag 2012, p. 
11). Additionally, the closure of the shell during handling can prevent 
feeding (Haag 2012, p. 29), alter respiration rate and heart patterns 
(Haag 2012, pp. 29-30), and require additional energy expenditure to 
retract and then re-establish the foot in substrate to prevent 
dislodgment when returned to stream substrates.
    Handling of freshwater mussels can also have a detrimental impact 
on the reproductive efforts of individual mussels and possibly the 
overall population. It is commonly observed that short-term brooders 
will abort their glochidia due to disturbances or handling (Haag 2012, 
p. 199). In species or individuals that are not able to successfully 
produce multiple broods within a single breeding season, the abortion 
of these glochidia can cause the loss of reproductive output for that 
individual for the year. If many animals have their reproductive output 
curtailed at a single location due to widespread sampling of a site, 
the abortion of glochidia by multiple animals in response to handling 
can lead to an overall reduced reproductive output at a site. If this 
sampling effort is repeated multiple times during a breeding season and 
across multiple years, there is potential for the disturbance of 
multiple years of breeding efforts for many animals at a single 
location. This extended disturbance can lead to multiple years of 
failed recruitment and potentially the loss of multiple age-class 
cohorts within a population at the site.
    Loss of reproductive effort due to handling could be compounded by 
the intentional collection of gravid individuals, especially the 
potential effects on the native populations if an excessive number of 
females are removed, for use as broodstock for propagation or research 
purposes (Jones et al. 2006, p. 531). For example, pulling many gravid 
females from a site may prevent in-situ reproduction from occurring due 
to essentially removing a large percentage of that year's reproducing 
portion of the population from the site.

[[Page 48054]]

Barriers to Fish Movement
    The central Texas mussels historically colonized new areas through 
movement of infested host fish, as newly metamorphosed juveniles would 
excyst from host fish in new locations. Today, the remaining central 
Texas mussel populations are significantly isolated due to habitat 
fragmentation by major reservoirs such that recolonization of areas 
previously extirpated is extremely unlikely, if not impossible, due to 
existing dams creating permanent barriers to host fish movement. There 
is currently no opportunity for interaction among any of the extant 
central Texas mussel populations, as they are isolated from one another 
by major reservoirs.
    The overall distribution of mussels is, in part, a function of host 
fish dispersal (Smith 1985, p. 105). There is limited potential for 
immigration and emigration between populations other than through the 
movement of infected host fish between mussel populations. Small 
populations are more affected by this limited immigration potential 
because they are susceptible to genetic drift, resulting from random 
loss of genetic diversity, and inbreeding depression. At the species 
level, isolated populations that are eliminated due to stochastic 
events cannot be recolonized naturally due to barriers to host fish 
movement, leading to reduced overall redundancy and representation.
    Many of the central Texas mussels' known or assumed primary host 
fish species are common, widespread species in central Texas river 
basins. We know that populations of mussels and their host fish have 
become fragmented and isolated over time following the construction of 
major dams and reservoirs throughout central Texas. We do not currently 
have information demonstrating that the distribution of host fish is a 
factor currently limiting the central Texas mussels' distribution. 
However, a recent study suggested that the currently restricted 
distribution of false spike, Guadalupe orb, and other related species 
could be related to declining abundance of their host fish, 
particularly those fish having small home ranges and specialized 
habitat affinities (Dudding et al. 2019, entire). Further research into 
the relationships between each of the central Texas mussel species and 
their host fish is needed to more fully examine the possible role of 
declining host fish abundance in declining mussel populations.
Effects of Climate Change
    Climate change is already taking place, and continued greenhouse 
gas emissions at or above current rates will cause further warming 
(Intergovernmental Panel on Climate Change (IPCC) 2013, pp. 11-12). 
Warming in Texas is expected to be greatest in the summer (Maloney et 
al. 2014, p. 2236). The number of extremely hot days (high temperatures 
exceeding 95 [deg]F) is expected to double by around 2050 (Kinniburgh 
et al. 2015, p. 83). Western Texas, including portions of the ranges of 
the central Texas mussels, is an area expected to show greater 
responsiveness to the effects of climate change (Diffenbaugh et al. 
2008, p. 3). Changes in stream temperatures are expected to reflect 
changes in air temperature, at a rate of approximately 0.6-0.8 [deg]C 
increase in stream water temperature for every 1 [deg]C increase in air 
temperature (Morrill et al. 2005, pp. 1-2, 15) and with implications 
for temperature-dependent water quality parameters such as dissolved 
oxygen and ammonia toxicity. The central Texas mussels exist at or near 
a climate and habitat gradient in North America, with the eastern 
United States having more rainfall and higher freshwater mussel 
diversity, and the western United States receiving less rainfall and 
having fewer species of freshwater mussels. As such, it is likely that 
the central Texas mussels may be particularly vulnerable to future 
climate changes in combination with current and future stressors 
(Burlakova et al. 2011a, pp. 156, 161, 163; Burlakova et al. 2011b, pp. 
395, 403).
    While projected changes to rainfall in Texas are small (U.S. Global 
Change Research Program (USGCRP) 2017, p. 217), higher temperatures 
caused by anthropogenic factors lead to increased soil water deficits 
because of higher rates of evapotranspiration. This is likely to result 
in increasing drought severity in future climate scenarios just as 
``extreme precipitation, one of the controlling factors in flood 
statistics, is observed to have generally increased and is projected to 
continue to do so across the United States in a warming atmosphere'' 
(USGCRP 2017, p. 231). Even if precipitation and groundwater recharge 
remain at current levels, increased groundwater pumping and resultant 
aquifer shortages due to increased temperatures are nearly certain 
(Lo[aacute]iciga et al. 2000, p. 193; Mace and Wade 2008, pp. 662, 664-
665; Taylor et al. 2013, p. 325). Higher temperatures are also expected 
to lead to increased evaporative losses from reservoirs, which could 
negatively affect downstream releases and flows (Friedrich et al. 2018, 
p. 167). Effects of climate change, such as air temperature increases 
and an increase in drought frequency and intensity, have been shown to 
be occurring throughout the range of the central Texas mussels (USGCRP 
2017, p. 188; Andreadis and Lettenmaier 2006, p. 3), and these effects 
are expected to exacerbate several of the stressors discussed above, 
such as water temperature and flow loss (Wuebbles et al. 2013, p. 16).
    A recent review of future climate projections for Texas concludes 
that both droughts and floods could become more common in central Texas 
and projects that years like 2011 (the warmest on record) could be 
commonplace by the year 2100 (Mullens and McPherson 2017, pp. 3, 6). 
This trend toward more frequent drought is attributed to increases in 
hot temperatures, and the number of days at or above 100 [deg]F are 
projected to ``increase in both consecutive events and the total number 
of days'' (Mullens and McPherson 2017, pp. 14-15). Similarly, floods 
are projected to become more common and severe because of increases in 
the magnitude of extreme precipitation (Mullens and McPherson 2017, p. 
20). Recent `historic' flooding of the Llano River resulted in the 
transport of high levels of silt and debris to Lake Travis, so much so 
that the City of Austin's ability to treat raw water was affected, and 
the City issued a boil water notice and call for water conservation 
(City of Austin 2018, p. 3).
    In the analysis of the future condition of the central Texas 
mussels, we considered climate change to be an exacerbating factor, 
contributing to the increase of fine sediments, changes in water 
quality, loss of flowing water, and predation. Due to the effects of 
ongoing climate change (represented by representative concentration 
pathway (RCP) 4.5), we expect the frequency and duration of cleansing 
flows to decrease, leading to the increase in fine sediments at all 
populations. Many populations will experience increased frequency of 
low flows. More extreme climate change projections (RCP 8.5 and beyond) 
lead to further increases in fine sediment within the populations. 
Similarly, as lower water levels concentrate contaminants and cause 
unsuitable temperature and dissolved oxygen levels, we expect water 
quality to decline to some degree in the future. The SSA report 
includes a detailed analysis of the species' responses to both RCP 4.5 
and 8.5 (Service 2022, pp. 142-145, 149, and appendix C).

Species Current Condition

    Here we discuss the current condition of each known population, 
taking into

[[Page 48055]]

account the risks to those populations that are currently occurring, as 
well as management actions that are currently occurring to address 
those risks. We consider climate change to be currently occurring, 
resulting in changes to the timing and amount of rainfall affecting 
streamflow, increased stream temperatures, and increased accumulation 
of fine sediments. In the SSA report, for each species and population, 
we developed and assigned condition categories for three population 
factors (occupied stream length, abundance, and reproduction) and three 
habitat factors (substrate, flowing water, and water quality) that are 
important for viability of each species. The condition scores for each 
factor were then used to determine an overall condition of each 
population: healthy, moderately healthy, unhealthy, or functionally 
extirpated. These overall conditions translate to our estimated 
probability of persistence of each population, with healthy populations 
having the highest probability of persistence over 20 years (greater 
than 90 percent), moderately healthy populations having a probability 
of persistence that falls between 60 and 90 percent, and unhealthy 
populations having the lowest probability of persistence (between 10 
and 60 percent). Functionally extirpated populations are not expected 
to persist over 20 years or are already extirpated.
Guadalupe Fatmucket
    Overall, there is one known remaining population of Guadalupe 
fatmucket, in the Guadalupe River. Historically, Guadalupe fatmucket 
likely occurred through the Guadalupe River Basin, but it currently 
only occurs in the upper Guadalupe River in an unhealthy population 
with low abundance and little evidence of reproduction or recruitment. 
Very few individuals have been found in recent years. The upper 
Guadalupe River in this reach already experiences very low water 
levels, and these low water events are expected to continue into the 
future; the population is unlikely to rebound from any degraded habitat 
conditions.
Texas Fatmucket
    Overall, there are five known remaining populations of Texas 
fatmucket, all limited to the headwater reaches of the Colorado River 
and its tributaries. Historically, most Texas fatmucket populations 
were likely connected by fish migration throughout the Colorado River 
Basin, but due to impoundments and low water conditions in the Colorado 
River and tributaries, they are currently isolated from one another, 
and repopulation of extirpated locations is unlikely to occur without 
human assistance. Two of the current populations are moderately 
healthy, two are unhealthy, and one is functionally extirpated.
    Lower Elm Creek: The Elm Creek population of Texas fatmucket is 
extremely small and isolated. This population will continue to face 
threats from excessive sedimentation and deterioration of substrate, 
altered hydrology associated with anthropogenic activities and the 
effects of climate change, and water quality degradation. The poor 
habitat conditions and only a single individual found at this site more 
than a decade ago indicate a population that is unlikely to persist and 
may already be extirpated.
    Upper/Middle San Saba River: The population of Texas fatmucket in 
the upper/middle San Saba River is currently moderately healthy. Most 
of the flows in the Upper San Saba River (in Menard County, Texas) are 
from Edwards Formation springs, where the river gains streamflow from 
groundwater except for a reach that loses flow to the aquifer (called a 
losing reach) near the Menard/Mason County line (LBG-Guyton 2002, p. 
3). It is in this losing reach where drought effects are especially 
noticeable, as some flows may percolate downward to the aquifer. Much 
of the middle San Saba River below Menard is reported to have gone dry 
for 10 of the last 16 years by landowners downstream of Menard (Carollo 
Engineers 2015, p. 2). Regardless of the cause, low flows in the San 
Saba River have resulted in significant stream drying, and stranded 
central Texas mussels, including Texas fatmucket and Texas pimpleback, 
have been identified following dewatering as recently as 2015 near and 
below the losing reach (TPWD 2015, p. 3). During the 2011-2013 drought, 
stream flows in the San Saba River were critically low, such that 
several water rights in Schleicher, Menard, and McCulloch Counties were 
suspended by the Texas Commission on Environmental Quality (TCEQ; TCEQ 
2013, entire). These very low flow events are expected to continue into 
the future and put the upper/middle San Saba River population of Texas 
fatmucket at risk of extirpation. Even if the locations of Texas 
fatmucket do not become dry, water quality degradation and increased 
sedimentation associated with low flows is expected.
    Llano River: The Llano River population of Texas fatmucket is 
currently moderately healthy, and collection of the species is frequent 
at this location, although there has been limited evidence that the 
population is successfully reproducing. We expect flows to continue to 
decline and the frequency of extreme flow events to increase, leading 
to increased sedimentation, decreased water quality, and scour. As a 
result, the population of Texas fatmucket is expected to decline.
    Pedernales River: The population of Texas fatmucket in the 
Pedernales River is very small and isolated. The Pedernales River is a 
flashy system, which experiences extreme high flow events, especially 
in the lower reaches in the vicinity of Pedernales Falls State Park and 
below. Occasional, intense thunderstorms can dramatically increase 
streamflow and mobilize large amounts of silt and organic debris (LCRA 
2017, p. 82). The continued increasing frequency of high flow events 
combined with very low Texas fatmucket abundance in the river result in 
a population that is likely to be extirpated and currently is 
unhealthy.
    Onion Creek: Few live individuals of Texas fatmucket have been 
found in Onion Creek since 2010, and we consider this population to be 
functionally extirpated with little chance of persistence. The upper 
reaches of Onion Creek frequently go dry, and several privately owned 
low-head in-channel dams currently exist along upper and lower Onion 
Creek, which further provide barriers to fish passage and mussel 
dispersal, preventing recolonization after low water events. Onion 
Creek is in close proximity to the City of Austin, and continued 
development in the watershed is expected to continue to degrade habitat 
conditions.
Guadalupe Orb
    There are two known remaining populations of the Guadalupe orb, all 
in the Guadalupe River Basin. Historically, Guadalupe orb likely 
occurred throughout the basin with populations connected by fish 
migration, but due to impoundments and low water conditions, they are 
currently isolated from one another, and repopulation of extirpated 
locations is unlikely to occur without human assistance. Both Guadalupe 
orb populations are moderately healthy.
    Upper Guadalupe River: The Guadalupe orb population in the upper 
Guadalupe River occurs over approximately 95 river mi (153 river km), 
and water quantity and quality are in moderate condition. However, the 
population occurs in low numbers, with limited reproduction; this 
population is unhealthy and is expected to become functionally 
extirpated in the near

[[Page 48056]]

future. This stream reach is expected to be sensitive to potential 
changes in groundwater inputs to stream flow. Thus, the stream reach is 
vulnerable to ongoing and future hydrological alterations that reduce 
flows, and thereby result in substrate and water quality degradations, 
during critical conditions.
    San Marcos/Lower Guadalupe Rivers: In the San Marcos and Lower 
Guadalupe River, the Guadalupe orb population currently occupies a 
relatively long stream length, is observed in relatively high 
abundances, and exhibits evidence of reproduction. Significant spring 
complexes contribute substantially to baseflow during dry periods in 
this system and are expected to continue to contribute to baseflows for 
the next 50 years due to conservation measures implemented by the 
Edwards Aquifer Habitat Conservation Plan's partners. These measures 
bolster the resiliency of this population. However, this population is 
subject to extreme high flow events that scour and mobilize the 
substrate, and water quality degradation and sedimentation are threats, 
putting the population at risk of decline.
Texas Pimpleback
    There are five known remaining Texas pimpleback populations, all in 
the Colorado River Basin. Historically, Texas pimpleback likely 
occurred throughout the basin with populations connected by fish 
migration, but due to impoundments and low water conditions, they are 
currently fragmented and isolated from one another, and repopulation of 
extirpated locations is unlikely to occur without human assistance. 
Three of the remaining Texas pimpleback populations are unhealthy and 
are not reproducing, and two of the populations are in moderate 
condition.
    Concho River: The Texas pimpleback population in the Concho River 
is limited by very low levels of flowing water (including periods of 
almost complete dewatering), poor water quality, and poor substrate 
quality associated with excessive sedimentation. The drought of 2011-
2013 resulted in extremely low flows in this river, and only one live 
adult has been found since that time. This population may currently be 
functionally extirpated.
    Middle Colorado/Lower San Saba Rivers: The population of Texas 
pimpleback in the middle Colorado and lower San Saba River is the 
largest known. This population has relatively high abundance but little 
evidence of reproduction, so we expect this population to decline as 
old individuals die and very few young individuals are recruited into 
the reproducing population. The combination of reduced flows, degraded 
water quality, and substrate degradation will reduce the resiliency of 
this population and may cause it to become extirpated. Therefore, this 
population is moderately healthy.
    Upper San Saba River: Similar to other populations of Texas 
pimpleback, the population in the Upper San Saba River is currently 
unhealthy and does not appear to be reproducing. Regardless of the high 
risk of low water levels, the very small population size and lack of 
reproduction will likely result in the extirpation of this population. 
Because of the losing reach near Hext, Texas, that serves to separate 
the upper and lower San Saba River populations, along with differences 
in substrate, this population is isolated and no longer connected to 
the lower San Saba River population.
    Llano River: The population of Texas pimpleback in the Llano River 
occupies a very short stream length, and the population is negatively 
affected by substrate degradation during periods of low flows. This 
population, due to ease of access to the location, is especially 
vulnerable to the threat of overcollection and vandalism. The small 
population size and frequency of low water levels, and flooding with 
scour, cause this population to be unhealthy.
    Lower Colorado River: Currently, the population of Texas pimpleback 
in the lower Colorado River is relatively abundant over a long stream 
length. However, because the species is a riffle specialist, the Texas 
pimpleback is especially sensitive to hydrological alterations leading 
to both extreme drying (dewatering) during low flow events, and to 
extreme high flow events leading to scouring of substrate and movement 
of mature individuals to sites that may or may not be appropriate, as 
evidenced by the August 2017 scouring flood event that substantially 
degraded the quality of the Altair Riffle in the lower Colorado River, 
a formerly robust mussel bed. While this population is in moderate 
condition, we expect this population to be at risk of extirpation due 
to these extreme flow events.
Balcones Spike
    Overall, there are three known remaining populations of Balcones 
spike, comprising less than 3 percent of the species' known historical 
range. Historically, most Balcones spike populations were likely 
connected by fish migration throughout each of the Brazos and Colorado 
River basins, but due to impoundments they are currently fragmented and 
isolated from one another, and repopulation of extirpated locations is 
unlikely to occur without human assistance. Based on our analysis as 
described in the SSA report, the three populations are unhealthy.
    Little River and tributaries: The Little River population is 
considered to have low resiliency currently due to the small size of 
the population. Development in the watershed has reduced water quality 
and substrate conditions currently, and habitat factors are expected to 
continue to decline because of alterations to flows and water quality 
associated primarily with increasing development in the watershed as 
the Austin-Round Rock (Texas) metropolitan area continues to expand. 
Low water levels remain a concern that is mediated somewhat by the 
likelihood that enhanced return flows associated with the development 
and use of alternative water supplies will bolster base flows somewhat. 
The small size of the population combined with continued habitat 
degradation put this population at high risk of extirpation; this 
population is unhealthy.
    Lower San Saba River: The lower San Saba River population is 
currently small and isolated, and therefore has low resiliency and is 
considered unhealthy. The population has low abundance, and a lack of 
reproduction and subsequent recruitment, and we expect it to become 
functionally extirpated in the next 10 years. Future degradation of 
habitat factors is expected as flows continue to be diminished, most 
notably by altered precipitation patterns (that result in dewatering 
droughts and scouring floods) combined with enhanced evaporative 
demands and anthropogenic withdrawals to support existing and future 
demands for municipal and agricultural water.
    Llano River: The Llano River population is currently very small and 
isolated, and therefore has low resiliency. The population occupies an 
extremely small area, and degradation of habitat is expected to 
continue as flows continue to decline due to altered precipitation 
patterns (dewatering droughts and scouring floods) combined with 
enhanced evaporative demands and anthropogenic withdrawals to support 
existing and future demands for municipal and agricultural water. 
Further, this population is well known and easy to access, has 
experienced high collection pressure in recent years, and has not shown 
recent evidence of reproduction. Therefore, this population is 
unhealthy, and we expect the population to become extirpated.

[[Page 48057]]

False Spike
    Overall, there is one known remaining population of false spike, 
comprising approximately 20 percent of the species' known historical 
range. Historically, most false spike populations were likely connected 
by fish migration throughout the Guadalupe River Basin, but due to 
impoundments, the false spike is currently isolated in the lower 
portion of the Guadalupe River and repopulation of extirpated locations 
is unlikely to occur without human assistance. Based on our analysis as 
described in the SSA report, the population is moderately healthy.
    Lower Guadalupe River: The lower Guadalupe River population of 
false spike is the only remaining population of the species and 
considered to have low resiliency. The population has fairly high 
abundance over a long reach, and flow protections afforded by the 
Edwards Aquifer Habitat Conservation Plan have contributed 
substantially to the resiliency of this population by sustaining base 
flows above critical levels. However, despite these base flow 
protections, this population remains vulnerable to changes in water 
quality, sedimentation, and extreme high flow events, such as from 
hurricanes or other strong storms, which scour and deplete mussel beds 
(Strayer 1999, pp. 468-469). Overall, this population is moderately 
healthy.
Texas Fawnsfoot
    There are seven known remaining populations of Texas fawnsfoot, in 
the Trinity, Brazos, and Colorado River basins. Historically, Texas 
fawnsfoot occurred throughout each basin with populations connected by 
fish migration within each basin, but due to impoundments and low water 
conditions, they are currently isolated from one another, and 
repopulation of extirpated locations is unlikely to occur without human 
assistance. Four Texas fawnsfoot populations are moderately healthy, 
and three are unhealthy.
    East Fork Trinity River: The Texas fawnsfoot population in the East 
Fork Trinity River occupies a small stream reach (12 mi (19 km)), 
making it especially vulnerable to a single stochastic event such as a 
spill or flood and changes to water quality. Further, no observations 
of recent reproduction exist for this population; all observed Texas 
fawnsfoot individuals are adults, greater than 35 mm. This population 
is small and isolated from the middle and lower Trinity River 
population by habitat that is unsuitable primarily because of altered 
hydrology, as flows from the Dallas-Fort Worth metro area are too 
flashy to provide suitable habitat for Texas fawnsfoot. Therefore, this 
population is moderately healthy.
    Middle Trinity River: Texas fawnsfoot in the Trinity River have 
experienced improved water quality over the past 30 years due to 
advancements in wastewater treatment technology and facilities, and 
streamflow has been subsidized by return flows originating in part from 
other basins, although water quality degradation and sedimentation are 
still affecting Texas fawnsfoot in this reach. Additionally, the middle 
Trinity River is a relatively long and unobstructed reach of river. 
While habitat may decline, this population is in moderate condition, 
and, therefore, we expect the population of Texas fawnsfoot to persist 
in the middle Trinity River, as we expect that flows will remain within 
a normal range of environmental variation in this reach. Therefore, 
this population is moderately healthy.
    Clear Fork Brazos River: The Texas fawnsfoot population in the 
Clear Fork of the Brazos River is very small and isolated. This 
population likely experienced extensive mortality associated with 
prolonged dewatering during the 2011-2013 drought, combined with 
ambient water quality degradation associated with naturally occurring 
elevated salinity levels from the upper reaches of the river. This 
population is likely functionally extirpated, although more survey 
effort is needed to reach a definitive conclusion. Further, the 
proposed Cedar Ridge Reservoir, if constructed, would result in 
significant hydrologic alterations, which would further degrade the 
overall condition of this population of Texas fawnsfoot. Therefore, 
this population is unhealthy.
    Upper Brazos River: The population of Texas fawnsfoot in the Upper 
Brazos River is characterized by low abundance and lack of evidence of 
reproduction. This reach of the river experiences reduced flows 
associated with continued drought and upstream dam operations. Further, 
water quality degradation associated with naturally occurring salinity 
is expected to continue. This population is at risk of extirpation due 
to its small population size and continued poor habitat conditions. 
Therefore, this population is unhealthy.
    Middle/Lower Brazos River: The population of Texas fawnsfoot in the 
middle and lower Brazos River occupies a fairly long reach of river 
(346 mi (557 km)) and exhibits evidence of reproduction. The lack of 
major impoundments and diversions in the Brazos River below Waco, 
Texas, results in the maintenance of a relatively natural hydrological 
regime. Even so, Texas fawnsfoot surveys have yet to yield the species 
in numbers that would indicate a healthy population, and future habitat 
degradation from reduced flows, increased temperatures, and decreased 
water quality will likely reduce the resiliency of this population. 
Therefore, this population is moderately healthy.
    Lower San Saba River: Texas fawnsfoot in the lower San Saba River 
are found in low abundance with little evidence of reproductive success 
and subsequent recruitment of new individuals to the population. 
Sedimentation is high, due in part to reductions in flowing water over 
time due to a combination of increased water withdrawals and drought. 
We expect this population to become functionally extirpated due to lack 
of water and increased sedimentation. Therefore, this population is 
unhealthy.
    Lower Colorado River: The Texas fawnsfoot population in the lower 
Colorado River is expected to remain extant under current conditions, 
as this reach is expected to remain wetted, although with reduced flow. 
Despite increasing demands for municipal water, we expect that the 
lower Colorado River will continue to flow due to priority downstream 
agricultural and industrial water rights. Similar to the lower Brazos 
River population, Texas fawnsfoot in the Lower Colorado River are 
vulnerable to reduced flows and associated habitat degradation due to 
reductions in flow from upstream tributaries; because the species 
occurs in bank habitats that are likely to become exposed, the species 
will be subjected to desiccation, predation, and increased water 
temperatures as river elevations decline while the river still flows in 
its main channel. Currently, the Lower Colorado River Authority is 
implementing a water management plan that is alleviating this threat by 
providing consistent subsistence flows to the lower Colorado River 
Basin. Therefore, this population is moderately healthy.

Future-Condition Scenarios for the Texas Fawnsfoot

    Because of significant uncertainty regarding if and when flow loss, 
water quality degradations, extreme flooding and scour/substrate 
mobilizing events, or impoundment construction may occur, we have 
forecasted future viability for the Texas fawnsfoot in terms of 
resiliency, redundancy, and representation under four plausible future 
scenarios. Each scenario is projected across up to three time steps

[[Page 48058]]

and considers the biological status of this species' populations and 
habitats in ten, twenty-five, and fifty years. Ten years represents one 
to two generations of mussels, assuming an average reproductive life 
span of five to ten years. Twenty-five years similarly represents two 
to four mussel generations. Fifty years represents five or more 
generations of mussels and corresponds with the current planning 
horizon of the State Water Plans (from 2020 to 2070), a period of time 
for which the human population of the State of Texas is expected to 
grow 88% from 27 million to 51 million (TWDB 2017, p. 3) with much of 
the growth of human population occurring in the watersheds these seven 
species of mussels currently occupy (TWDB 2017, pp. 50-51). Below, we 
provide a brief summary of each plausible future scenario; for more 
detailed information on these models and their projections, please see 
the SSA report (Service 2022, chapter 7).
    Under Scenario 1, which considers a future where the current levels 
of existing degradation as well as existing conservation, current as of 
the preparation of the SSA report, continue for the next 50 years, a 
loss of resiliency, representation, and redundancy is expected. Under 
this scenario, we predicted that the effects of current levels of 
climate change continue to result in low streamflow, which lead to 
increased sedimentation, reduced water quality, and occasional 
desiccation. One population of Texas fawnsfoot remains in moderate 
condition, three populations are considered unhealthy, and three 
populations are functionally extirpated. Those populations in unhealthy 
condition are particularly vulnerable to extirpation.
    Under Scenario 2, which considers a future where ``feasible and 
appropriate conservation plans'' are implemented over the next 50 
years, including Candidate Conservation Agreements with Assurances in 
the Brazos and Colorado River basins that provide coverage for the 
species, Texas fawnsfoot populations generally maintain, or slightly 
improve, resiliency, redundancy, and representation over time as 
conservation measures are implemented to counteract existing stressors. 
Under this scenario, we predict that the effects of current levels of 
climate change continue to result in low stream flows, which lead to 
increased sedimentation, reduced water quality, and occasional 
desiccation, but water conservation measures and riparian improvements 
aid some populations. One population of Texas fawnsfoot is considered 
healthy, three are in moderate condition, two populations are 
considered unhealthy, and one population is functionally extirpated. 
Those populations in unhealthy condition are particularly vulnerable to 
extirpation.
    Under Scenario 3, which considers a future where conditions are no 
better for the species than the status quo Current Conditions, a loss 
of resiliency, representation, and redundancy is expected for the Texas 
fawnsfoot. Under this scenario we predict that intermediate climate 
effects, including more frequent and intense droughts, combined with 
increased ground- and surface-water demands associated with increased 
human demand, reductions in streamflow are expected to occur in all 
streams and rivers, and those effects will be more pronounced in the 
upper basins. Scenario 3 considers additional water projects, such as 
wastewater treatment plant outfalls, only if currently proposed or 
planned. Four populations of Texas fawnsfoot are considered unhealthy, 
three are in moderate condition, two populations are considered 
unhealthy, and three populations are functionally extirpated. Those 
populations in unhealthy condition are particularly vulnerable to 
extirpation.
    Under Scenario 4, which considers a future where conditions are not 
better for the species than the status quo Current Conditions under 
severe climate effects. This scenario considers sever climate effects, 
and we predict more frequent and intense droughts, increased ground- 
and surface-water demands associated with increased human demand, 
additional water projects, like wastewater treatment plant outfalls, as 
well as possible new reservoirs and other construction projects. The 
effects of strong levels of climate change result in even lower stream 
flows, which lead to increased sedimentation, reduced water quality, 
and desiccation. Three populations of Texas fawnsfoot are considered 
unhealthy, and four populations are considered functionally extirpated. 
Those populations in unhealthy condition are particularly vulnerable to 
extirpation.
    As part of the SSA, we also developed three future-condition 
scenarios to capture the range of uncertainties regarding future 
threats and the projected responses by the Guadalupe fatmucket, Texas 
fatmucket, Guadalupe orb, Texas pimpleback, Balcones spike, and false 
spike. Our scenarios assumed a moderate or enhanced probability of 
severe drought, and either propagation or no propagation of the 
species. Because we determined that the current condition of these six 
central Texas mussels is consistent with an endangered species (see 
Determination of Status, below), we are not presenting the results of 
the future scenarios in this final rule. Please refer to the SSA report 
(Service 2022) for the full analysis of future scenarios for these six 
species.
    We note that, by using the SSA framework to guide our analysis of 
the scientific information documented in the SSA report, we have 
analyzed the cumulative effects of identified threats and conservation 
actions on the species. To assess the current and future condition of 
the species, we evaluate the effects of all the relevant factors that 
may be influencing the species, including threats and conservation 
efforts. Because the SSA framework considers not just the presence of 
the factors, but to what degree they collectively influence risk to 
each entire species, our assessment integrates the cumulative effects 
of the factors and replaces a standalone cumulative effects analysis.

Conservation Efforts and Regulatory Mechanisms

    Since 2011, when three of the central Texas mussel species became 
candidates for listing under the Act, many agencies, nongovernmental 
organizations, and other interested parties have been working to 
develop voluntary agreements with private landowners to restore or 
enhance habitats for fish and wildlife in the region, including in the 
watersheds where the central Texas mussels occur. These agreements 
provide voluntary conservation including upland habitat enhancements 
that will, if executed properly, reduce threats to the species while 
improving instream physical habitat and water quality, as well as 
adjacent riparian and upland habitats. Additionally, the Brazos, Lower 
Colorado, and Trinity river authorities have each developed and 
implemented candidate conservation agreements with assurances to 
benefit one or more species of candidate mussels, including the Texas 
fatmucket, Texas fawnsfoot, Texas pimpleback, and Balcones spike in 
their basins (see Private or Other Non-Federal Conservation Plans 
Related to Permits Under Section 10 of the Act, below). Some publicly 
and privately owned lands in the watersheds occupied by the central 
Texas mussels are protected with conservation easements or are 
otherwise managed to support populations of native fish, wildlife, and 
plant populations. The U.S. Department of Agriculture's Natural 
Resources Conservation Service

[[Page 48059]]

(NRCS), along with the Service and State and local partners, is working 
with private landowners to develop and implement comprehensive 
conservation plans to address soil, water, and wildlife resource 
concerns in the lower Colorado River Basin through a Working Lands for 
Wildlife project (NRCS no date, entire).
    There are active efforts to protect, maintain, and improve existing 
water quantity in waters known to be important for mussel populations 
and to reduce threats of flow loss. These efforts include the 
establishment of the Texas Instream Flow Program by the Texas 
Legislature as part of Senate Bill 2 in 2001, and the creation of a 
``comprehensive, statewide process to protect environmental flows'' in 
Senate Bill 3 (SB3) in 2007. Senate Bill 3 also directs the 
Environmental Flows Advisory Group (EFAG) to develop a schedule for 
development of environmental flow regime recommendations and the 
adoption of environmental flow standards within the State. This process 
allows for other groups to develop information on environmental flow 
needs and ways in which those needs can be met for basins for which the 
EFAG has not yet established environmental flow standard schedules 
(Loeffler 2015, entire). The Hydrology-based Environmental Flow Regime 
(HEFR; Opdyke et al. 2014, entire) tool was developed during the SB3 
process and describes flow regimes in terms of subsistence flows, base 
flows, pulse flows, and overbank floods, and it applies the 
``indicators of hydrologic assessment'' (IHA; TNC 2009, entire) to 
determine hydrologic separation and then inform an environmental flow 
recommendation. Environmental flow recommendations have been set for 
each of the river basins occupied by the species that are the subjects 
of this rule.
    The Service has been hosting annual mussel research and 
coordination meetings to help manage and monitor scientific collection 
of mussel populations and encourage collaboration among researchers and 
other conservation partners since 2018 (Service 2018, p. 1; Service 
2019a, p. 1). Additionally, work is under way to evaluate methods of 
captive propagation for the central Texas mussel species at the 
Service's hatchery and research facilities (San Marcos Aquatic Research 
Center, Inks Dam National Fish Hatchery, and Uvalde National Fish 
Hatchery), including efforts to collect gravid females from the wild to 
infest host fish (Bonner et al. 2018, pp. 8, 9, 11).

Determination of Status

    Section 4 of the Act (16 U.S.C. 1533) and its implementing 
regulations (50 CFR part 424) set forth the procedures for determining 
whether a species meets the definition of an endangered species or a 
threatened species. The Act defines an ``endangered species'' as a 
species in danger of extinction throughout all or a significant portion 
of its range, and a ``threatened species'' as a species likely to 
become an endangered species within the foreseeable future throughout 
all or a significant portion of its range. The Act requires that we 
determine whether a species meets the definition of endangered species 
or threatened species because of any of the following factors: (A) The 
present or threatened destruction, modification, or curtailment of its 
habitat or range; (B) overutilization for commercial, recreational, 
scientific, or educational purposes; (C) disease or predation; (D) the 
inadequacy of existing regulatory mechanisms; or (E) other natural or 
manmade factors affecting its continued existence.

Status Throughout All of Its Range

    After evaluating threats to these seven species and assessing the 
cumulative effect of the threats under the Act's section 4(a)(1) 
factors, we found that all seven species of the central Texas mussels 
have declined significantly in overall distribution and abundance. At 
present, most of the known populations exist in very low abundances and 
show limited evidence of recruitment. Furthermore, existing available 
habitats are reduced in quality and quantity, relative to historical 
conditions. Our analysis revealed five primary threats that caused 
these declines and pose a meaningful risk to the viability of the 
species. These threats are primarily related to habitat changes (Factor 
A from the Act): the accumulation of fine sediments, altered hydrology, 
and impairment of water quality, all of which are exacerbated by the 
effects of climate change. Collection (Factor B), and predation (Factor 
C) are also affecting those populations already experiencing low stream 
flow, and barriers to fish movement (Factor E) limit dispersal and 
prevent recolonization after stochastic events.
    Because of historical and ongoing habitat destruction and 
fragmentation, remaining central Texas mussel populations are now 
fragmented and isolated from one another, interrupting the once 
functional metapopulation dynamic that historically made mussel 
populations robust and very resilient to change. The existing 
fragmented and isolated mussel populations are largely in a state of 
chronic degradation due to a number of historical and ongoing stressors 
affecting flows, water quality, sedimentation, and substrate quality. 
Given the high risk of catastrophic events including droughts and 
floods, both of which are exacerbated by climate change, many central 
Texas mussel populations are at a high risk of extirpation.
    Beginning around the turn of the 20th century until 1970, more than 
100 major dams were constructed, creating reservoirs across Texas, 
including several reservoirs in the Brazos and Trinity basins, the 
chain of Highland Lakes on the Lower Colorado River, the Guadalupe 
Valley Hydroelectric Project, and the Canyon Reservoir on the Guadalupe 
River (Dowell 1964, pp. 3-8). The inundation and subsequent altered 
hydrology and sediment dynamics associated with operation of these 
flood-control, hydropower, and municipal water supply reservoirs have 
resulted in irreversible changes to the natural flow regime of these 
rivers. These changes have re-shaped and fragmented these aquatic 
ecosystems and fish and invertebrate communities, including populations 
of the seven species of central Texas mussels, which all depend on 
natural river flows.
    Water quality has benefited from dramatically improved wastewater 
treatment technology in recent years, such that fish populations have 
rebounded but not completely recovered (Perkin and Bonner 2016, p. 97). 
However, water quality degradation continues to affect mussels and 
their habitats, especially as low flow conditions and excessive 
sedimentation interact to diminish instream habitats, and substrate-
mobilizing and mussel-scouring flood events have become more extreme 
and perhaps more frequent.
    Additionally, while host fish may still be adequately represented 
in contemporary fish assemblages, access to fish hosts can be reduced 
during critical reproductive times by barriers such as the many low-
water crossings and low-head dams that now exist and fragment the 
landscape. Diminished access to host fish leads to reduced reproductive 
success just as barriers to fish passage impede the movement of fish, 
and thus compromise the ability of mussels to disperse and colonize new 
habitats following a disturbance (Schwalb et al. 2013, p. 447).
    Populations of each of the seven central Texas mussels face risks 
from declining water quantity in both large and small river segments. 
Low flows lead to dewatering of habitats and desiccation of 
individuals, elevated

[[Page 48060]]

water temperatures, other quality degradations, and increased exposure 
to predation. Finally, direct mortality due to predation and collection 
further limits population sizes of those populations, which are already 
experiencing the stressors discussed above.
    These threats, alone or in combination, are expected to cause the 
extirpation of additional mussel populations, further reducing the 
overall redundancy and representation of each of the seven species of 
central Texas mussels. Historically, each species, with a large range 
of interconnected populations (i.e., having metapopulation dynamics), 
would have been resilient to stochastic events such as drought, 
excessive sedimentation, and scouring floods because even if some 
locations were extirpated by such events, they could be recolonized 
over time by dispersal from nearby survivors and facilitated by 
movements by ``affiliate species'' of host fish (Douda et al. 2012, p. 
536). This connectivity across potential habitats would have made for 
highly resilient species overall, as evidenced by the long and 
successful evolutionary history of freshwater mussels as a taxonomic 
group, and in North America in particular. However, under present 
circumstances, restoration of that connectivity on a regional scale is 
not feasible. As a consequence of these current conditions, the 
viability of the Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, 
Texas pimpleback, Balcones spike, and false spike now primarily depends 
on maintaining and improving the remaining isolated populations and 
potentially restoring new populations where feasible. Additionally, the 
viability of the Texas fawnsfoot into the future depends on maintaining 
connectivity of populations and access to fish hosts within the Brazos, 
Colorado, and Trinity basins.

Guadalupe Fatmucket

    The Guadalupe fatmucket has only one remaining population, and very 
few individuals have been detected and reported in recent years. The 
upper Guadalupe River in this reach already experiences very low water 
levels, putting this population at high risk of extirpation. The 
species has very low viability, with a single population at high risk 
of extirpation, and no additional representation or redundancy. Our 
analysis of the species' current condition, as well as the conservation 
efforts discussed above, shows that the Guadalupe fatmucket is 
currently in danger of extinction throughout all of its range due to 
the severity and immediacy of threats currently impacting the species.

Texas Fatmucket

    Of the five remaining fragmented and isolated populations of Texas 
fatmucket, two are small in abundance and occupied stream length and 
have low to no resiliency (i.e., they are unhealthy), and one 
population is functionally extirpated. The other two current 
populations are moderately healthy. The upper/middle San Saba and Llano 
River populations are larger, with increased abundance and occupied 
stream length, but these populations are vulnerable to stream drying 
and overcollection. These very low flow events are expected to continue 
into the future, and both of these populations of Texas fatmucket are 
at risk of extirpation. Even if the locations of Texas fatmucket do not 
become dry, water quality degradation and increased sedimentation 
associated with low flows is expected. Additionally, the Llano River 
population does not appear to be successfully reproducing, further 
increasing the species' risk of extirpation at this location. The Texas 
fatmucket has no populations that are currently considered healthy. 
Loss of populations at high risk of extirpation leads to low levels of 
redundancy and representation. Overall, these low levels of resiliency, 
redundancy, and representation result in the Texas fatmucket having low 
viability, and the species currently faces a high risk of extinction. 
Our analysis of the species' current condition shows that the Texas 
fatmucket is currently in danger of extinction throughout all of its 
range due to the severity and immediacy of threats currently impacting 
the species.

Guadalupe Orb

    Only two fragmented and isolated populations of Guadalupe orb 
remain, and one of these populations is functionally extirpated. The 
San Marcos/Lower Guadalupe River population is more resilient but is at 
risk of catastrophic events, such as hurricane flooding, that can scour 
and reduce the abundance and distribution of this population. The 
Guadalupe orb has no populations that are considered healthy. Loss of 
populations at high risk of extirpation leads to low levels of 
redundancy and representation, and results in overall low viability. 
The Guadalupe orb currently faces a high risk of extinction. Our 
analysis of the species' current condition, as well as the conservation 
efforts discussed above, shows that the Guadalupe orb is currently in 
danger of extinction throughout all of its range due to the severity 
and immediacy of threats currently impacting the species.

Texas Pimpleback

    Of the five remaining Texas pimpleback populations, three are 
unhealthy and are not reproducing, and two are moderately healthy. The 
populations that are not reproducing are considered functionally 
extirpated, and the two moderately healthy populations are expected to 
continue to decline. The population in the middle Colorado and lower 
San Saba Rivers has very little evidence of reproduction and is 
therefore likely to decline due to a lack of young individuals joining 
the population as the population ages. The lower Colorado River 
population has very recently experienced an extreme high flow event 
(i.e., associated with Hurricane Harvey flooding in August and 
September of 2017) that vastly changed the substrate and mussel 
composition of much of its length, putting this population at high risk 
of extirpation. The Texas pimpleback has no healthy populations, and 
all populations are expected to continue to decline. Loss of 
populations at high risk of extirpation leads to low levels of 
redundancy and representation. Overall, these low levels of resiliency, 
redundancy, and representation result in the Texas pimpleback having 
low viability, and the species currently faces a high risk of 
extinction. Our analysis of the species' current condition, as well as 
the conservation efforts discussed above, shows that the Texas 
pimpleback is currently in danger of extinction throughout all of its 
range due to the severity and immediacy of threats currently impacting 
the species.

Balcones Spike

    The three remaining fragmented and isolated populations of Balcones 
spike are small in abundance and occupied stream length, having low to 
no resiliency. Therefore, the Balcones spike has no populations that 
are currently considered healthy. Loss of populations at high risk of 
extirpation leads to low levels of redundancy and representation. The 
threats identified above are occurring now and are expected to continue 
into the future. Overall, these low levels of resiliency, redundancy, 
and representation result in the Balcones spike having low viability, 
and the species currently faces a high risk of extinction. Our analysis 
of the species' current condition demonstrates that the Balcones spike 
is currently in danger of extinction throughout all of its range due to 
the severity and immediacy of threats currently impacting the species.

[[Page 48061]]

False Spike

    The false spike has only one remaining population that is currently 
in moderately healthy condition. Due the species having a single 
population remaining that is at high risk of extirpation, the false 
spike is considered to have very low viability and no additional 
representation or redundancy. Our analysis of the species' current 
condition, as well as the conservation efforts discussed above, shows 
that the false spike is currently in danger of extinction throughout 
all of its range due to the severity and immediacy of threats currently 
impacting the species.
    Our analysis of the species' current conditions, as well as the 
conservation efforts discussed above, show that the Guadalupe 
fatmucket, Texas fatmucket, Guadalupe orb, Texas pimpleback, false 
spike, and Balcones spike are currently in danger of extinction 
throughout all their ranges due to the severity and immediacy of 
threats currently impacting their populations. The risk of extinction 
is high because the remaining fragmented populations have a high risk 
of extirpation, are isolated, and have limited potential for 
recolonization. We find that a threatened species status is not 
appropriate for Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, 
Texas pimpleback, Balcones spike, and false spike because of their 
currently contracted ranges, because all populations are fragmented and 
isolated from one another, because the threats are occurring across the 
entire range of these species, and because the threats are ongoing 
currently and are expected to continue or worsen into the future. 
Because these species are already in danger of extinction throughout 
their ranges, a threatened status is not appropriate.

Texas Fawnsfoot

    Seven populations of the Texas fawnsfoot remain. Four populations 
are moderately healthy, and three are unhealthy or are functionally 
extirpated. Currently, unlike the other populations of this species, 
two of the moderately healthy populations are not subject to flow 
declines, due to increased flow returns in the Trinity River from 
wastewater treatment facilities and a lack of impoundments on the 
mainstem of the lower Brazos River. In the future, however, as extreme 
flow events become more frequent as rainfall patterns change, and 
increased urbanization results in reduced groundwater levels, we expect 
even these populations to be at an increased risk of extirpation. 
Future higher air temperatures, higher rates of evaporation and 
transpiration, and changing precipitation patterns are expected within 
the range of the Texas fawnsfoot in central Texas (Jiang and Yang 2012, 
pp. 234-239, 242). These future climate changes are expected to lead to 
human responses, such as increased groundwater pumping and surface 
water diversions, associated with increasing demands for and decreasing 
availability of freshwater resources in the State (reviewed in Banner 
et al. 2010, entire). Within 25 to 50 years, even under the best 
conditions and with additional conservation efforts undertaken, given 
the ongoing effects of climate change and human activities on altered 
hydrology and habitat degradation, we expect only one population to be 
in healthy condition, one population to remain in moderately healthy 
condition, four populations to be in unhealthy condition, and one 
population to become functionally extirpated. Given the likelihood of 
increased climate and anthropogenic effects in the foreseeable future, 
as many as three populations are expected to become functionally 
extirpated, leaving no more than four unhealthy populations remaining 
after 25 years. After 50 years, we anticipated that as many as five 
populations are expected to become functionally extirpated, leaving no 
more than three unhealthy populations. In the future, we anticipate 
that the Texas fawnsfoot will have reduced viability, with no highly 
resilient populations and limited representation and redundancy. Thus, 
after assessing the best available information, we determine that the 
Texas fawnsfoot is not currently in danger of extinction but is likely 
to become in danger of extinction within the foreseeable future 
throughout all of its range. Our analysis of the species' current and 
future conditions, as well as the conservation efforts discussed above, 
show that the Texas fawnsfoot is likely to become in danger of 
extinction throughout all or a significant portion of its range within 
the foreseeable future due to increased frequency of drought and 
extremely high flow events, decreased water quality, and decreased 
substrate suitability. We considered whether the Texas fawnsfoot is 
presently in danger of extinction and determined that endangered status 
is not appropriate. The current condition shows two of the populations 
in two of the representative units are not currently subject to 
declining flows or extreme flow events. While threats are currently 
acting on the species and many of those threats are expected to 
continue into the future, we did not find that the species is currently 
in danger of extinction throughout all of its range. According to our 
assessment of plausible future scenarios, the species is likely to 
become an endangered species within the foreseeable future of 25 years 
throughout all of its range. Twenty-five years encompasses about 5 
generations of the Texas fawnsfoot; additionally, models of human 
demand for water (Texas Water Development Board 2017, p. 30) and 
climate change (e.g., Kinniburgh et al. 2015, p. 83) project decreased 
water availability over 25 and 50 years, respectively. As a result, we 
expect increased incidences of low flows followed by scour events as 
well as persistent decreased water quality to be occurring in 25 years. 
Thus, after assessing the best available information, we determine that 
the Texas fawnsfoot is not currently in danger of extinction but is 
likely to become in danger of extinction within the foreseeable future 
throughout all of its range.

Status Throughout a Significant Portion of Its Range: Guadalupe 
Fatmucket, Texas Fatmucket, Guadalupe Orb, Texas Pimpleback, Balcones 
Spike, and False Spike

    Under the Act and our implementing regulations, a species may 
warrant listing if it is in danger of extinction or likely to become so 
in the foreseeable future throughout all or a significant portion of 
its range. We have determined that the Guadalupe fatmucket, Texas 
fatmucket, Guadalupe orb, Texas pimpleback, Balcones spike, and false 
spike are in danger of extinction throughout all of their ranges and, 
accordingly, did not undertake an analysis of whether there are any 
significant portions of these species' ranges. Because the Guadalupe 
fatmucket, Texas fatmucket, Guadalupe orb, Texas pimpleback, Balcones 
spike, and false spike warrant listing as endangered throughout all of 
their ranges, our determination does not conflict with the decision in 
Center for Biological Diversity v. Everson, 435 F. Supp. 3d 69 (D.D.C. 
2020), which vacated the provision of the Final Policy on 
Interpretation of the Phrase ``Significant Portion of Its Range'' in 
the Endangered Species Act's Definitions of ``Endangered Species'' and 
``Threatened Species'' (Final Policy) (79 FR 37578, July 1, 2014) 
providing that if the Services determine that a species is threatened 
throughout all of its range, the Services will not analyze whether the 
species is endangered in a significant portion of its range.

[[Page 48062]]

Status Throughout a Significant Portion of Its Range: Texas Fawnsfoot

    Under the Act and our implementing regulations, a species may 
warrant listing if it is in danger of extinction or likely to become so 
within the foreseeable future throughout all or a significant portion 
of its range. The court in Center for Biological Diversity v. Everson, 
435 F. Supp. 3d 69 (D.D.C. 2020) (Everson), vacated the provision of 
the Final Policy on Interpretation of the Phrase ``Significant Portion 
of Its Range'' in the Endangered Species Act's Definitions of 
``Endangered Species'' and ``Threatened Species'' (Final Policy) (79 FR 
37578; July 1, 2014) that provided if the Service determines that a 
species is threatened throughout all of its range, the Service will not 
analyze whether the species is endangered in a significant portion of 
its range.
    Therefore, we proceed to evaluating whether the species is 
endangered in a significant portion of its range--that is, whether 
there is any portion of the species' range for which both (1) the 
portion is significant; and (2) the species is in danger of extinction 
in that portion. Depending on the case, it might be more efficient for 
us to address the ``significance'' question or the ``status'' question 
first. We can choose to address either question first. Regardless of 
which question we address first, if we reach a negative answer with 
respect to the first question that we address, we do not need to 
evaluate the other question for that portion of the species' range.
    Following the court's holding in Everson, we now consider whether 
there are any significant portions of the species' range where the 
species is in danger of extinction now (i.e., endangered). In 
undertaking this analysis for the Texas fawnsfoot, we choose to address 
the status question first--we consider information pertaining to the 
geographic distribution of both the species and the threats that the 
species faces to identify any portions of the range where the species 
may be endangered.
    We evaluated the range of the Texas fawnsfoot to determine if the 
species is in danger of extinction now in any portion of its range. The 
range of a species can theoretically be divided into portions in an 
infinite number of ways. We focused our analysis on portions of the 
species' range that may meet the definition of an endangered species. 
For Texas fawnsfoot, we considered whether the threats or their effects 
on the species are greater in any biologically meaningful portion of 
the species' range than in other portions such that the species is in 
danger of extinction now in that portion.
    We examined the following threats throughout the range of the 
species: the accumulation of fine sediments, altered hydrology, and 
impairment of water quality (Factor A); collection (Factor B); 
predation (Factor C); and barriers to fish movement (Factor E).
    We identified a portion of the range of the Texas fawnsfoot, the 
upper Brazos River (including the populations in the upper Brazos River 
and Clear Fork Brazos River), that is experiencing a concentration of 
the following threats: altered hydrology and degraded water quality. 
Although these threats are not unique to this area, they are acting at 
a greater intensity here (e.g., populations higher in the watershed and 
that receive less rainfall are more vulnerable to stream drying because 
there is a smaller volume of water in the river), either individually 
or in combination, than elsewhere in the range. In addition, the small 
sizes of each population, coupled with the current condition 
information in the SSA report indicating the two populations in this 
area are unhealthy, leads us to find that this portion provides 
substantial information indicating the populations occurring here may 
be in danger of extinction now.
    We then proceeded to the significance question, asking whether 
there is substantial information indicating that this portion of the 
range (i.e., the upper Brazos River and Clear Fork Brazos River) may be 
significant. As an initial note, the Service's most recent definition 
of ``significant'' within agency policy guidance has been invalidated 
by court order (see Desert Survivors v. U.S. Department of the 
Interior, 321 F. Supp. 3d 1011, 1070-74 (N.D. Cal. 2018)). In 
undertaking this analysis for the Texas fawnsfoot, we considered 
whether the upper Brazos River portion of the species' range may be 
significant based on its biological importance to the overall viability 
of the Texas fawnsfoot. Therefore, for the purposes of this analysis, 
when considering whether this portion may be biologically significant, 
we considered whether the portion may (1) constitute a large geographic 
area relative to the range of the species as a whole; (2) occur in a 
unique habitat or ecoregion for the species; (3) contain high quality 
or high value habitat relative to the remaining portions of the range, 
for the species' continued viability in light of the existing threats; 
or (4) contain habitat that is essential to a specific life-history 
function for the species and that is not found in the other portions 
(for example, the principal breeding ground for the species).
    We evaluated the available information about the portion of the 
range of the Texas fawnsfoot that occupies the upper Brazos River in 
this context, assessing its biological significance in terms of these 
three habitat criteria, and determined the information did not 
substantially indicate it may be significant. Texas fawnsfoot in these 
populations exhibit similar habitat and host fish use to Texas 
fawnsfoot in the remainder of the species' range; thus, there is no 
unique observable environmental usage or behavioral characteristics 
attributable to just this area's populations. The upper Brazos River 
constitutes 40 percent of the range for Texas fawnsfoot, and does not 
constitute a large geographic area relative the range of the species. 
This unit is not essential to any specific life-history function of the 
Texas fawnsfoot that is not found elsewhere in the range. Further, the 
habitat in the upper Brazos River is not of higher quality or higher 
value than the habitat in the remainder of the species' range.
    After reviewing the available information, we did not find that the 
upper Brazos River portion may be significant. Therefore, because we 
could not answer both the status and significance questions in the 
affirmative, we conclude that the upper Brazos River portion of the 
range does not warrant further consideration as a significant portion 
of the range.
    We did not identify any portions of the Texas fawnsfoot's range 
where: (1) the portion is significant; and (2) the species is in danger 
of extinction in that portion. Therefore, we conclude that the Texas 
fawnsfoot is likely to become in danger of extinction within the 
foreseeable future throughout all of its range. This does not conflict 
with the courts' holdings in Desert Survivors v. U.S. Department of the 
Interior, 321 F. Supp. 3d 1011, 1070-74 (N.D. Cal. 2018) and Center for 
Biological Diversity v. Jewell, 248 F. Supp. 3d 946, 959 (D. Ariz. 
2017) because, in reaching this conclusion, we did not apply the 
aspects of the Final Policy, including the definition of 
``significant'' that those court decisions held to be invalid.

Determination of Status: Guadalupe Fatmucket, Texas Fatmucket, 
Guadalupe Orb, Texas Pimpleback, Balcones Spike, and False Spike

    Our review of the best available scientific and commercial 
information indicates that the Guadalupe fatmucket, Texas fatmucket, 
Guadalupe orb, Texas pimpleback, Balcones spike, and false spike meet 
the Act's definition of an

[[Page 48063]]

endangered species. Therefore, we are listing the Guadalupe fatmucket, 
Texas fatmucket, Guadalupe orb, Texas pimpleback, Balcones spike, and 
false spike as endangered species in accordance with sections 3(6) and 
4(a)(1) of the Act.

Determination of Status: Texas Fawnsfoot

    Our review of the best scientific and commercial data available 
indicates that the Texas fawnsfoot meets the Act's definition of a 
threatened species. Therefore, we are listing the Texas fawnsfoot as a 
threatened species in accordance with sections 3(20) and 4(a)(1) of the 
Act.

Available Conservation Measures

    Conservation measures provided to species listed as endangered or 
threatened species under the Act include recognition as a listed 
species, planning and implementation of recovery actions, requirements 
for Federal protection, and prohibitions against certain practices. 
Recognition through listing results in public awareness, and 
conservation by Federal, State, Tribal, and local agencies, private 
organizations, and individuals. The Act encourages cooperation with the 
States and other countries and calls for recovery actions to be carried 
out for listed species. The protection required by Federal agencies, 
including the Service, and the prohibitions against certain activities 
are discussed, in part, below.
    The primary purpose of the Act is the conservation of endangered 
and threatened species and the ecosystems upon which they depend. The 
ultimate goal of such conservation efforts is the recovery of these 
listed species, so that they no longer need the protective measures of 
the Act. Section 4(f) of the Act calls for the Service to develop and 
implement recovery plans for the conservation of endangered and 
threatened species. The goal of this process is to restore listed 
species to a point where they are secure, self-sustaining, and 
functioning components of their ecosystems.
    The recovery planning process begins with development of a recovery 
outline made available to the public soon after a final listing 
determination. The recovery outline guides the immediate implementation 
of urgent recovery actions while a recovery plan is being developed. 
Recovery teams (composed of species experts, Federal and State 
agencies, nongovernmental organizations, and stakeholders) may be 
established to develop and implement recovery plans. The recovery 
planning process involves the identification of actions that are 
necessary to halt and reverse the species' decline by addressing the 
threats to its survival and recovery. The recovery plan identifies 
recovery criteria for review of when a species may be ready for 
reclassification from endangered to threatened (``downlisting'') or 
removal from protected status (``delisting''), and methods for 
monitoring recovery progress. Recovery plans also establish a framework 
for agencies to coordinate their recovery efforts and provide estimates 
of the cost of implementing recovery tasks. Revisions of the plan may 
be done to address continuing or new threats to the species, as new 
substantive information becomes available. When completed, the recovery 
outline, draft recovery plan, and the final recovery plan will be 
available on our website (https://www.fws.gov/program/endangered-species), or from our Austin Ecological Services Field Office (see FOR 
FURTHER INFORMATION CONTACT).
    Implementation of recovery actions generally requires the 
participation of a broad range of partners, including other Federal 
agencies, States, Tribes, nongovernmental organizations, businesses, 
and private landowners. Examples of recovery actions include habitat 
restoration (e.g., restoration of native vegetation), research, captive 
propagation and reintroduction, and outreach and education. The 
recovery of many listed species cannot be accomplished solely on 
Federal lands because their ranges may occur primarily or solely on 
non-Federal lands. To achieve recovery of these species requires 
cooperative conservation efforts on private, State, and Tribal lands.
    Once these species are listed, funding for recovery actions will be 
available from a variety of sources, including Federal budgets, State 
programs, and cost-share grants for non-Federal landowners, the 
academic community, and nongovernmental organizations. In addition, 
pursuant to section 6 of the Act, the State of Texas will be eligible 
for Federal funds to implement management actions that promote the 
protection or recovery of the central Texas mussels. Information on our 
grant programs that are available to aid species recovery can be found 
at: https://www.fws.gov/service/financial-assistance.
    Please let us know if you are interested in participating in 
recovery efforts for the central Texas mussels. Additionally, we invite 
you to submit any new information on these species whenever it becomes 
available and any information you may have for recovery planning 
purposes (see FOR FURTHER INFORMATION CONTACT).
    Section 7 of the Act is titled Interagency Cooperation and mandates 
all Federal action agencies to use their existing authorities to 
further the conservation purposes of the Act and to ensure that their 
actions are not likely to jeopardize the continued existence of listed 
species or adversely modify critical habitat. Regulations implementing 
Section 7 are codified at 50 CFR part 402.
    Section 7(a)(2) states that each Federal action agency shall, in 
consultation with the Secretary, ensure that any action they authorize, 
fund, or carry out is not likely to jeopardize the continued existence 
of a listed species or result in the destruction or adverse 
modification of designated critical habitat. Each Federal agency shall 
review its action at the earliest possible time to determine whether it 
may affect listed species or critical habitat. If a determination is 
made that the action may affect listed species or critical habitat, 
formal consultation is required (50 CFR 402.14(a)), unless the Service 
concurs in writing that the action is not likely to adversely affect 
listed species or critical habitat. At the end of a formal 
consultation, the Service issues a biological opinion, containing its 
determination of whether the Federal action is likely to result in 
jeopardy or adverse modification.
    Examples of discretionary actions for the central Texas mussels 
that may be subject to consultation procedures under section 7 of the 
Act are land management or other landscape-altering activities on 
Federal lands administered by the National Park Service as well as 
actions on State, Tribal, local, or private lands that require a 
Federal permit (such as a permit from the U.S. Army Corps of Engineers 
under section 404 of the Clean Water Act (33 U.S.C. 1251 et seq.) or a 
permit from the Service under section 10 of the Act) or that involve 
some other Federal action (such as funding from the Federal Highway 
Administration, Federal Aviation Administration, or the Federal 
Emergency Management Agency). Federal actions not affecting listed 
species or critical habitat--and actions on State, Tribal, local, or 
private lands that are not federally funded, authorized, or carried out 
by a Federal agency--do not require section 7 consultation. Federal 
agencies should coordinate with the local Service Field Office (see FOR 
FURTHER INFORMATION CONTACT) with any specific questions on section 7 
consultation and conference requirements.

[[Page 48064]]

    The Act and its implementing regulations set forth a series of 
general prohibitions and exceptions that apply to endangered wildlife. 
The prohibitions of section 9(a)(1) of the Act, codified at 50 CFR 
17.21, make it illegal for any person subject to the jurisdiction of 
the United States to commit, to attempt to commit, to solicit another 
to commit or to cause to be committed any of the following: (1) Import 
endangered wildlife into, or export from, the United States; (2) take 
(which includes harass, harm, pursue, hunt, shoot, wound, kill, trap, 
capture, or collect, or to attempt to engage in any such conduct) 
endangered wildlife within the United States or on the high seas; (3) 
possess, sell, deliver, carry, transport, or ship, by any means 
whatsoever, any such wildlife that has been taken illegally; (4) 
deliver, receive, carry, transport, or ship in interstate or foreign 
commerce in the course of commercial activity; or (5) sell or offer for 
sale in interstate or foreign commerce. Certain exceptions to these 
prohibitions apply to employees or agents of the Service, the National 
Marine Fisheries Service, other Federal land management agencies, and 
State conservation agencies.
    We may issue permits to carry out otherwise prohibited activities 
involving endangered wildlife under certain circumstances. Regulations 
governing permits for endangered wildlife are codified at 50 CFR 17.22. 
With regard to endangered wildlife, a permit may be issued: for 
scientific purposes, for enhancing the propagation or survival of the 
species, or for take incidental to otherwise lawful activities. The 
statute also contains certain exemptions from the prohibitions, which 
are found in sections 9 and 10 of the Act.
    It is the policy of the Service, as published in the Federal 
Register on July 1, 1994 (59 FR 34272), to identify to the extent known 
at the time a species is listed, specific activities that will not be 
considered likely to result in violation of section 9 of the Act. To 
the extent possible, activities that will be considered likely to 
result in violation will also be identified in as specific a manner as 
possible. The intent of this policy is to increase public awareness of 
the effect of a listing on proposed and ongoing activities within the 
range of the species.
    Although most of the prohibitions in section 9 of the Act apply to 
endangered species, sections 9(a)(1)(G) and 9(a)(2)(E) of the Act 
prohibit the violation of any regulation under section 4 pertaining to 
any threatened species of fish or wildlife, or threatened species of 
plant, respectively. Section 4(d) of the Act directs the Secretary to 
promulgate protective regulations that are necessary and advisable for 
the conservation of threatened species. As a result, we interpret our 
policy to mean that, when we list a species as a threatened species, to 
the extent possible, we identify activities that will or will not be 
considered likely to result in violation of the protective regulations 
under section 4(d) for that species. For the Texas fawnsfoot, at this 
time, we are unable to identify specific activities that will or will 
not be considered likely to result in violation of section 9 of the Act 
beyond what is already clear from the descriptions of prohibitions and 
exceptions established by protective regulation under section 4(d) of 
the Act.
    Questions regarding whether specific activities would constitute 
violation of section 9 of the Act should be directed to the Ecological 
Services Field Office (see FOR FURTHER INFORMATION CONTACT, above). See 
the discussion below under II. Final Rule Issued Under Section 4(d) of 
the Act, regarding protective regulations under section 4(d) of the Act 
for the Texas fawnsfoot.
    For the central Texas mussels we are listing as endangered species 
(Guadalupe fatmucket, Texas fatmucket, Guadalupe orb, Texas pimpleback, 
Balcones spike, and false spike), as discussed above, certain 
activities that are prohibited under section 9 may be permitted under 
section 10 of the Act. Additional activities that will not be 
considered likely to result in violation of section 9 of the Act may be 
identified during coordination with the local field office, and in some 
instances (e.g., with new information), the Service may conclude that 
one or more activities identified here will be considered likely to 
result in violation of section 9.
    For the central Texas mussels we are listing as endangered species, 
to the extent currently known, the following is a list of examples of 
activities that will be considered likely to result in violation of 
section 9 of the Act in addition to what is already clear from the 
descriptions of the prohibitions found at 50 CFR 17.21:
    (1) Unauthorized handling or collecting of the species;
    (2) Modification of the channel or water flow of any stream in 
which the central Texas mussels are known to occur;
    (3) Livestock grazing that results in direct or indirect 
destruction of stream habitat; and
    (4) Discharge of chemicals or fill material into any waters in 
which the central Texas mussels are known to occur.
    This list is intended to be illustrative and not exhaustive; 
additional activities that will be considered likely to result in 
violation of section 9 of the Act may be identified during coordination 
with the local field office, and in some instances (e.g., with new or 
site-specific information), the Service may conclude that one or more 
activities identified here will not be considered likely to result in 
violation of section 9. Questions regarding whether specific activities 
would constitute violation of section 9 of the Act should be directed 
to the Austin Ecological Services Field Office (see FOR FURTHER 
INFORMATION CONTACT, above).

II. Final Rule Issued Under Section 4(d) of the Act

Background

    Section 4(d) of the Act contains two sentences. The first sentence 
states that the Secretary shall issue such regulations as she deems 
necessary and advisable to provide for the conservation of species 
listed as threatened species. The U.S. Supreme Court has noted that 
statutory language similar to the language in section 4(d) of the Act 
authorizing the Secretary to take action that she ``deems necessary and 
advisable'' affords a large degree of deference to the agency (see 
Webster v. Doe, 486 U.S. 592 (1988)). Conservation is defined in the 
Act to mean the use of all methods and procedures which are necessary 
to bring any endangered species or threatened species to the point at 
which the measures provided pursuant to the Act are no longer 
necessary. Additionally, the second sentence of section 4(d) of the Act 
states that the Secretary may by regulation prohibit with respect to 
any threatened species any act prohibited under section 9(a)(1), in the 
case of fish or wildlife, or section 9(a)(2), in the case of plants. 
Thus, the combination of the two sentences of section 4(d) provides the 
Secretary with wide latitude of discretion to select and promulgate 
appropriate regulations tailored to the specific conservation needs of 
the threatened species. The second sentence grants particularly broad 
discretion to the Service when adopting one or more of the prohibitions 
under section 9.
    The courts have recognized the extent of the Secretary's discretion 
under this standard to develop rules that are appropriate for the 
conservation of a species. For example, courts have upheld, as a valid 
exercise of agency authority, rules developed under section 4(d) that 
included limited prohibitions against takings (see Alsea Valley 
Alliance v. Lautenbacher, 2007 WL

[[Page 48065]]

2344927 (D. Or. 2007); Washington Environmental Council v. National 
Marine Fisheries Service, 2002 WL 511479 (W.D. Wash. 2002)). Courts 
have also upheld 4(d) rules that do not address all of the threats a 
species faces (see State of Louisiana v. Verity, 853 F.2d 322 (5th Cir. 
1988)). As noted in the legislative history when the Act was initially 
enacted, ``once an animal is on the threatened list, the Secretary has 
an almost infinite number of options available to [her] with regard to 
the permitted activities for those species. [She] may, for example, 
permit taking, but not importation of such species, or [s]he may choose 
to forbid both taking and importation but allow the transportation of 
such species'' (H.R. Rep. No. 412, 93rd Cong., 1st Sess. 1973).
    The provisions of this 4(d) rule will promote conservation of the 
Texas fawnsfoot by encouraging management of the landscape in ways that 
meet both land management considerations and the conservation needs of 
the Texas fawnsfoot. The provisions of this rule are one of many tools 
that we will use to promote the conservation of the Texas fawnsfoot.
    As mentioned previously in Available Conservation Measures, section 
7(a)(2) of the Act requires Federal agencies, including the Service, to 
ensure that any action they authorize, fund, or carry out is not likely 
to jeopardize the continued existence of any endangered species or 
threatened species or result in the destruction or adverse modification 
of designated critical habitat of such species.
    These requirements are the same for a threatened species with a 
species-specific 4(d) rule. For example, as with an endangered species, 
a Federal agency's determination that an action is ``not likely to 
adversely affect'' a threatened species will require the Service's 
written concurrence (see 50 CFR 402.13(c)). Similarly, if a Federal 
agency determines that an action is ``likely to adversely affect'' a 
threatened species, the action will require formal consultation and the 
formulation of a biological opinion (see 50 CFR 402.14(a)).

Provisions of the 4(d) Rule

    Exercising the Secretary's authority under section 4(d) of the Act, 
we have developed a rule that is designed to address the Texas 
fawnsfoot's specific threats and conservation needs. As discussed above 
under Summary of Biological Status and Threats, we have concluded that 
the Texas fawnsfoot is likely to become in danger of extinction within 
the foreseeable future primarily due to habitat degradation or loss 
stemming from hydrologic alterations by impoundments, including dams 
and other barriers to fish movement, and diminished water quality from 
point and nonpoint source pollution and siltation. These threats 
contribute to the negative effects associated with the species' reduced 
range and the potential effects of climate change. Section 4(d) of the 
Act requires the Secretary to issue such regulations as she deems 
necessary and advisable to provide for the conservation of each 
threatened species and authorizes the Secretary to include among those 
protective regulations any of the prohibitions that section 9(a)(1) of 
the Act prescribes for endangered species. We find that the 
protections, prohibitions, and exceptions in this rule as a whole 
satisfy the requirement in section 4(d) of the Act to issue regulations 
deemed necessary and advisable to provide for the conservation of the 
Texas fawnsfoot.
    The protective regulations for the Texas fawnsfoot incorporate 
prohibitions from section 9(a)(1) to address the threats to the 
species. Section 9(a)(1) prohibits the following activities for 
endangered wildlife: importing or exporting; take; possession and other 
acts with unlawfully taken specimens; delivering, receiving, carrying, 
transporting, or shipping in interstate or foreign commerce in the 
course of commercial activity; and selling or offering for sale in 
interstate or foreign commerce. This protective regulation includes all 
of these prohibitions because the Texas fawnsfoot is at risk of 
extinction in the foreseeable future and putting these prohibitions in 
place will help to prevent further declines, preserve the species' 
remaining populations, slow its rate of decline, and decrease 
synergistic, negative effects from other ongoing or future threats.
    In particular, this 4(d) rule will provide for the conservation of 
the Texas fawnsfoot by prohibiting the following activities, except as 
otherwise authorized or permitted: import/export, take, possession of 
unlawfully taken specimens, interstate or foreign commerce, and sale or 
offer for sale. As discussed above under Summary of Biological Status 
and Threats, loss and fragmentation of habitat from siltation, water 
quality degradation, and impoundments are affecting the status of the 
Texas fawnsfoot. A range of activities have the potential to affect the 
Texas fawnsfoot, including instream construction, channel modification, 
water withdrawals, flow releases from upstream dams, riparian 
vegetation removal, improper handling, farming and grazing practices, 
and wastewater treatment facility outflows. Regulating take associated 
with these activities will help preserve the Texas fawnsfoot's 
remaining populations, slow the rate of population decline, and 
decrease synergistic, negative effects from other stressors. Therefore, 
regulating take associated with activities that increase siltation, 
diminish water quality, alter stream flow, or reduce fish passage will 
help preserve and potentially provide for expansion of remaining 
populations and decrease synergistic, negative effects from other 
threats.
    Under the Act, ``take'' means to harass, harm, pursue, hunt, shoot, 
wound, kill, trap, capture, or collect, or to attempt to engage in any 
such conduct. Some of these provisions have been further defined in 
regulations at 50 CFR 17.3. Take can result knowingly or otherwise, by 
direct and indirect impacts, intentionally or incidentally. Regulating 
take will help prevent further declines, preserve the species' 
remaining populations, slow its rate of decline, and decrease 
synergistic, negative effects from other ongoing or future threats. 
Therefore, we are prohibiting take of the Texas fawnsfoot, except for 
take resulting from those actions and activities specifically excepted 
by the 4(d) rule.
    Exceptions to the prohibition on take include most of the general 
exceptions to the prohibition on take of endangered wildlife, as set 
forth in 50 CFR 17.21 and certain other specific activities that we 
propose for exception, as described below.
    The 4(d) rule will also provide for the conservation of the species 
by allowing exceptions that incentivize conservation actions or that, 
while they may have some minimal impact on the Texas fawnsfoot, are not 
expected to rise to the level that would have a negative impact (i.e., 
would have only de minimis impacts) on the species' conservation. The 
exceptions to these prohibitions include incidental and intentional 
take (described below) that are expected to have negligible impacts to 
the Texas fawnsfoot and its habitat.
    Those exceptions include the following activities:
    (1) Channel restoration projects that create natural, physically 
stable (streambanks and substrate remaining relatively unchanging over 
time), ecologically functioning streams or stream and wetland systems 
(containing an assemblage of fish, mussels, other invertebrates, and 
plants) that are reconnected with their groundwater aquifers. These 
projects can be accomplished using a variety of methods, but the 
desired outcome is a

[[Page 48066]]

natural channel with low shear stress (force of water moving against 
the channel); bank heights that enable reconnection to the floodplain; 
a reconnection of surface and groundwater systems, resulting in 
perennial flows in the channel; riffles and pools composed of existing 
soil, rock, and wood instead of large imported materials; low 
compaction of soils within adjacent riparian areas; and inclusion of 
riparian wetlands and woodland buffers. To qualify for this exception, 
a channel restoration project must satisfy all applicable Federal, 
State, and local permitting requirements. In addition, at least 30 days 
prior to commencing actual construction within an area designated as 
critical habitat for Texas fawnsfoot, notice must be provided to the 
Service, through the Austin Ecological Services Field Office, of the 
location and nature of the proposed work to allow the Service to make 
arrangements for surveys and potential relocation of any mussels that 
might be adversely affected. This exception to the 4(d) rule for 
incidental take would promote conservation of Texas fawnsfoot by 
creating stable stream channels that are less likely to scour during 
high flow events, thereby increasing population resiliency.
    (2) Bioengineering methods such as streambank stabilization using 
native live stakes (live, vegetative cuttings inserted or tamped into 
the ground in a manner that allows the stake to take root and grow), 
native live fascines (live branch cuttings, usually willows, bound 
together into long, cigar-shaped bundles), or native brush layering 
(cuttings or branches of easily rooted tree species layered between 
successive lifts of soil fill). Methods that include the use of 
quarried rock (riprap) for more than 25 percent of the area within the 
streambanks or include the use of rock baskets or gabion structures do 
not qualify for this exception. In addition, to reduce streambank 
erosion and sedimentation into the stream, work using these 
bioengineering methods would be performed at base flow or low water 
conditions and when significant rainfall likely to result in 
significant runoff is not predicted at or upstream of the area where 
work is proposed for a period of at least 3 days after the work is 
scheduled to be undertaken. Further, streambank stabilization projects 
that involve the placement or use of equipment in the stream channels 
or water do not qualify for this exception. To qualify for this 
exception, a project using bioengineering methods must satisfy all 
applicable Federal, State, and local permitting requirements. Similar 
to channel restoration projects, this exception to the 4(d) rule for 
incidental take would promote conservation of Texas fawnsfoot by 
creating stable stream channels that are less likely to scour during 
high flow events, thereby increasing population resiliency.
    (3) Soil and water conservation practices and riparian and adjacent 
upland habitat management activities that restore instream habitats for 
the species, restore adjacent riparian habitats that enhance stream 
habitats for the species, stabilize degraded and eroding stream banks 
to limit sedimentation and scour of the species' habitats, restore or 
enhance nearby upland habitats to limit sedimentation of the species' 
habitats, and comply with conservation practice standards and 
specifications and technical guidelines developed by the NRCS and 
available from the Service. In addition, at least 30 days prior to 
commencing soil and water conservation practices within an area 
designated as critical habitat for the Texas fawnsfoot, notice must be 
provided to the Service, through the Austin Ecological Services Field 
Office, of the location and nature of the proposed work to allow the 
Service to make arrangements for surveys and potential relocation of 
any mussels that might be adversely affected. Soil and water 
conservation practices and aquatic species habitat restoration projects 
associated with NRCS conservation plans are designed to improve water 
quality and enhance fish and aquatic species habitats. This exception 
to the 4(d) rule for incidental take would promote conservation of 
Texas fawnsfoot by creating stable stream channels and reducing 
sediment inputs to the stream, thereby increasing population 
resiliency.
    (4) Presence or abundance surveys for Texas fawnsfoot conducted by 
individuals who successfully complete and show proficiency by passing 
the end-of-course test with a score equal to or greater than 90 
percent, and with 100 percent accuracy in identification of mussel 
species listed under the Act in an approved freshwater mussel 
identification and sampling course (specific to the species and basins 
in which the Texas fawnsfoot is known to occur), such as that 
administered by the Service, State wildlife agency, or qualified 
university experts. To qualify for this exception, those reports must 
be provided to the Service annually on the number, specific location 
(e.g., GPS coordinates), and date of the encounter. This exception does 
not apply if lethal take or collection is anticipated. This exception 
only applies for 5 years from the date of successful completion of the 
course. This provision of the 4(d) rule for intentional take would 
promote conservation of Texas fawnsfoot by ensuring surveyors are 
proficient at identification of freshwater mussels and would add to the 
knowledge and understanding of the distribution of Texas fawnsfoot 
populations.
    Despite these prohibitions regarding threatened species, we may 
under certain circumstances issue permits to carry out one or more 
otherwise prohibited activities, including those described above. The 
regulations that govern permits for threatened wildlife state that the 
Director may issue a permit authorizing any activity otherwise 
prohibited with regard to threatened species. These include permits 
issued for the following purposes: for scientific purposes, to enhance 
propagation or survival, for economic hardship, for zoological 
exhibition, for educational purposes, for incidental taking, or for 
special purposes consistent with the purposes of the Act (50 CFR 
17.32). The statute also contains certain exemptions from the 
prohibitions, which are found in sections 9 and 10 of the Act.
    We recognize the special and unique relationship with our State 
natural resource agency partners in contributing to conservation of 
listed species. State agencies often possess scientific data and 
valuable expertise on the status and distribution of endangered, 
threatened, and candidate species of wildlife and plants. State 
agencies, because of their authorities and their close working 
relationships with local governments and landowners, are in a unique 
position to assist us in implementing all aspects of the Act. In this 
regard, section 6 of the Act provides that we shall cooperate to the 
maximum extent practicable with the States in carrying out programs 
authorized by the Act. Therefore, any qualified employee or agent of a 
State conservation agency that is a party to a cooperative agreement 
with the Service in accordance with section 6(c) of the Act, who is 
designated by his or her agency for such purposes, will be able to 
conduct activities designed to conserve the Texas fawnsfoot that may 
result in otherwise prohibited take without additional authorization.
    Nothing in this 4(d) rule will change in any way the recovery 
planning provisions of section 4(f) of the Act, the consultation 
requirements under section 7 of the Act, or the ability of the Service 
to enter into partnerships for the management and protection of the 
Texas fawnsfoot. However, interagency cooperation may be further 
streamlined

[[Page 48067]]

through planned programmatic consultations for the species between 
Federal agencies and the Service.

III. Critical Habitat

Background

    Section 4(a)(3) of the Act requires that, to the maximum extent 
prudent and determinable, we designate a species' critical habitat 
concurrently with listing the species. Critical habitat is defined in 
section 3 of the Act as:
    (1) The specific areas within the geographical area occupied by the 
species, at the time it is listed in accordance with the Act, on which 
are found those physical or biological features
    (a) Essential to the conservation of the species, and
    (b) Which may require special management considerations or 
protection; and
    (2) Specific areas outside the geographical area occupied by the 
species at the time it is listed, upon a determination that such areas 
are essential for the conservation of the species.
    Our regulations at 50 CFR 424.02 define the geographical area 
occupied by the species as an area that may generally be delineated 
around species' occurrences, as determined by the Secretary (i.e., 
range). Such areas may include those areas used throughout all or part 
of the species' life cycle, even if not used on a regular basis (e.g., 
migratory corridors, seasonal habitats, and habitats used periodically, 
but not solely by vagrant individuals).
    This critical habitat designation was proposed when the regulations 
defining ``habitat'' (85 FR 81411; December 16, 2020) and governing the 
section 4(b)(2) exclusion process for the Service (85 FR 82376; 
December 18, 2020) were in place and in effect. However, those two 
regulations have been rescinded (87 FR 37757, June 24, 2022, and 87 FR 
43433; July 21, 2022) and no longer apply to any designations of 
critical habitat. Therefore, for this final rule designating critical 
habitat for the central Texas mussels, we apply the regulations at 50 
CFR 424.19 and the Policy Regarding Implementation of Section 4(b)(2) 
of the Endangered Species Act (hereafter, the ``2016 Policy''; 81 FR 
7226, February 11, 2016).
    Conservation, as defined under section 3 of the Act, means to use 
and the use of all methods and procedures that are necessary to bring 
an endangered or threatened species to the point at which the measures 
provided pursuant to the Act are no longer necessary. Such methods and 
procedures include, but are not limited to, all activities associated 
with scientific resources management such as research, census, law 
enforcement, habitat acquisition and maintenance, propagation, live 
trapping, and transplantation, and, in the extraordinary case where 
population pressures within a given ecosystem cannot be otherwise 
relieved, may include regulated taking.
    Critical habitat receives protection under section 7 of the Act 
through the requirement that each Federal action agency ensure, in 
consultation with the Service, that any action they authorize, fund, or 
carry out is not likely to result in the destruction or adverse 
modification of designated critical habitat. The designation of 
critical habitat does not affect land ownership or establish a refuge, 
wilderness, reserve, preserve, or other conservation area. Such 
designation also does not allow the government or public to access 
private lands. Such designation does not require implementation of 
restoration, recovery, or enhancement measures by non-Federal 
landowners. Rather, designation requires that, where a landowner 
requests Federal agency funding or authorization for an action that may 
affect an area designated as critical habitat, the Federal agency 
consult with the Service under section 7(a)(2) of the Act. If the 
action may affect the listed species itself (such as for occupied 
critical habitat), the Federal action agency would have already been 
required to consult with the Service even absent the critical habitat 
designation because of the requirement to ensure that the action is not 
likely to jeopardize the continued existence of the species. Even if 
the Service were to conclude after consultation that the proposed 
activity is likely to result in destruction or adverse modification of 
the critical habitat, the Federal action agency and the landowner are 
not required to abandon the proposed activity, or to restore or recover 
the species; instead, they must implement ``reasonable and prudent 
alternatives'' to avoid destruction or adverse modification of critical 
habitat.
    Under the first prong of the Act's definition of critical habitat, 
areas within the geographical area occupied by the species at the time 
it was listed are included in a critical habitat designation if they 
contain physical or biological features (1) which are essential to the 
conservation of the species and (2) which may require special 
management considerations or protection. For these areas, critical 
habitat designations identify, to the extent known using the best 
scientific data available, those physical or biological features that 
are essential to the conservation of the species (such as space, food, 
cover, and protected habitat).
    Under the second prong of the Act's definition of critical habitat, 
we can designate critical habitat in areas outside the geographical 
area occupied by the species at the time it is listed, upon a 
determination that such areas are essential for the conservation of the 
species.
    Section 4 of the Act requires that we designate critical habitat on 
the basis of the best scientific data available. Further, our Policy on 
Information Standards Under the Endangered Species Act (published in 
the Federal Register on July 1, 1994 (59 FR 34271)), the Information 
Quality Act (section 515 of the Treasury and General Government 
Appropriations Act for Fiscal Year 2001 (Pub. L. 106-554; H.R. 5658)), 
and our associated Information Quality Guidelines provide criteria, 
establish procedures, and provide guidance to ensure that our decisions 
are based on the best scientific data available. They require our 
biologists, to the extent consistent with the Act and with the use of 
the best scientific data available, to use primary and original sources 
of information as the basis for recommendations to designate critical 
habitat.
    When we are determining which areas should be designated as 
critical habitat, our primary source of information is generally the 
information from the SSA report and information developed during the 
listing process for the species. Additional information sources may 
include any generalized conservation strategy, criteria, or outline 
that may have been developed for the species; the recovery plan for the 
species; articles in peer-reviewed journals; conservation plans 
developed by States and counties; scientific status surveys and 
studies; biological assessments; other unpublished materials; or 
experts' opinions or personal knowledge.
    Habitat is dynamic, and species may move from one area to another 
over time. We recognize that critical habitat designated at a 
particular point in time may not include all of the habitat areas that 
we may later determine are necessary for the recovery of the species. 
For these reasons, a critical habitat designation does not signal that 
habitat outside the designated area is unimportant or may not be needed 
for recovery of the species. Areas that are important to the 
conservation of the species, both inside and outside the

[[Page 48068]]

critical habitat designation, will continue to be subject to: (1) 
Conservation actions implemented under section 7(a)(1) of the Act; (2) 
regulatory protections afforded by the requirement in section 7(a)(2) 
of the Act for Federal agencies to ensure their actions are not likely 
to jeopardize the continued existence of any endangered or threatened 
species; and (3) the prohibitions found in section 9 (for endangered 
species), and the 4(d) rule (for threatened species). Federally funded 
or permitted projects affecting listed species outside their designated 
critical habitat areas may still result in jeopardy findings in some 
cases. These protections and conservation tools will continue to 
contribute to recovery of this species. Similarly, critical habitat 
designations made on the basis of the best available information at the 
time of designation will not control the direction and substance of 
future recovery plans, habitat conservation plans (HCPs), or other 
species conservation planning efforts if new information available at 
the time of these planning efforts calls for a different outcome.

Physical or Biological Features Essential to the Conservation of the 
Species

    In accordance with section 3(5)(A)(i) of the Act and regulations at 
50 CFR 424.12(b), in determining which areas we will designate as 
critical habitat from within the geographical area occupied by the 
species at the time of listing, we consider the physical or biological 
features that are essential to the conservation of the species, and 
which may require special management considerations or protection. The 
regulations at 50 CFR 424.02 define ``physical or biological features 
essential to the conservation of the species'' as the features that 
occur in specific areas and that are essential to support the life-
history needs of the species, including, but not limited to, water 
characteristics, soil type, geological features, sites, prey, 
vegetation, symbiotic species, or other features. A feature may be a 
single habitat characteristic or a more complex combination of habitat 
characteristics. Features may include habitat characteristics that 
support ephemeral or dynamic habitat conditions. Features may also be 
expressed in terms relating to principles of conservation biology, such 
as patch size, distribution distances, and connectivity. For example, 
physical features essential to the conservation of the species might 
include gravel of a particular size required for spawning, alkaline 
soil for seed germination, protective cover for migration, or 
susceptibility to flooding or fire that maintains necessary early-
successional habitat characteristics. Biological features might include 
prey species, forage grasses, specific kinds or ages of trees for 
roosting or nesting, symbiotic fungi, or absence of a particular level 
of nonnative species consistent with conservation needs of the listed 
species. The features may also be combinations of habitat 
characteristics and may encompass the relationship between 
characteristics or the necessary amount of a characteristic essential 
to support the life history of the species.
    In considering whether features are essential to the conservation 
of the species, we may consider an appropriate quality, quantity, and 
spatial and temporal arrangement of habitat characteristics in the 
context of the life-history needs, condition, and status of the 
species. These characteristics include, but are not limited to, space 
for individual and population growth and for normal behavior; food, 
water, air, light, minerals, or other nutritional or physiological 
requirements; cover or shelter; sites for breeding, reproduction, or 
rearing (or development) of offspring; and habitats that are protected 
from disturbance.

Summary of Essential Physical or Biological Features

    We derive the specific physical or biological features essential to 
the conservation of the central Texas mussels from studies of the 
species' habitat, ecology, and life history as described below. 
Additional information can be found in the SSA report (Service 2022, 
entire; available on https://www.regulations.gov under Docket No. FWS-
R2-ES-2019-0061). The life histories of the seven central Texas mussel 
species are very similar--mussels need flowing water, suitable 
substrate, suitable water quality, flow refuges, and appropriate host 
fish--and so we will discuss their common habitat needs and then 
describe any species-specific needs thereafter.
Space for Individual and Population Growth and for Normal Behavior
    Most freshwater mussels, including the central Texas mussels, are 
found in aggregations, called mussel beds, that vary in size from about 
50 to greater than 5,000 square meters (m\2\), separated by stream 
reaches in which mussels are absent or rare (Vaughn 2012, p. 983). 
Freshwater mussel larvae (called glochidia) are parasites that must 
attach to a host fish. A population incorporates more than one mussel 
bed; it is the collection of mussel beds within a stream reach between 
which infested host fish may travel, allowing for ebbs and flows in 
mussel bed density and abundance over time throughout the population's 
occupied reach. Therefore, sufficiently resilient mussel populations 
must occupy stream reaches long enough so that stochastic events that 
affect individual mussel beds do not eliminate the entire population. 
Repopulation by infested host fish from other mussel beds within the 
reach can allow the population to recover from these events. Longer 
stream reaches are more likely to support populations of the central 
Texas mussels into the future than shorter stream reaches. Therefore, 
we determine that long stream reaches, of more than 50 miles (80 km) in 
length, are an important component of a riverine system with habitat to 
support all life stages of the central Texas mussels.
    All seven species of central Texas mussels need flowing water for 
survival. They are not found in lakes, reservoirs, or in pools without 
flow, or in areas that are regularly dewatered. River reaches with 
continuous flow support all life stages of the central Texas mussels, 
while those with little or no flow do not. Flow rates needed by each 
species will vary depending on the species and the river size, 
location, and substrate type.
    Additionally, each species of central Texas mussel has specific 
substrate needs, including gravel/cobble (Guadalupe orb, Texas 
pimpleback, false spike, and Balcones spike), gravel/sand/silt (Texas 
fawnsfoot), and bedrock crevices/vegetated runs (Guadalupe fatmucket 
and Texas fatmucket). Except for habitats for Texas fawnsfoot, these 
locations must be relatively free of fine sediments such that the 
mussels are not smothered.
Physiological Requirements: Water Quality Requirements
    Freshwater mussels, as a group, are sensitive to changes in water 
quality parameters such as dissolved oxygen, salinity, ammonia, and 
pollutants. Habitats with appropriate levels of these parameters are 
considered suitable, while those habitats with levels outside of the 
appropriate ranges are considered less suitable. We have used 
information for these seven central Texas mussel species, where 
available, and data from other species when species-specific 
information is not available. Juvenile freshwater mussels are 
particularly susceptible to low dissolved oxygen levels. Juveniles will 
reduce feeding behavior when dissolved oxygen is between 2-4 milligrams 
per liter (mg/L), and mortality has been shown to occur at dissolved 
oxygen levels below 1.3

[[Page 48069]]

mg/L. Increased salinity levels may also be stressful to freshwater 
mussels, and the central Texas mussels show signs of stress at salinity 
levels of 2 ppt or higher (Bonner et al. 2018, pp. 155-156).
    The release of pollutants into streams from point and nonpoint 
sources have immediate impacts on water quality conditions and may make 
environments unsuitable for habitation by mussels. Early life stages of 
freshwater mussels are some of the most sensitive organisms of all 
species to ammonia and copper (Naimo 1995, pp. 351-352; Augspurger et 
al. 2007, p. 2025). Additionally, sublethal effects of contaminants 
over time can result in reduced feeding efficiency, reduced growth, 
decreased reproduction, changes in enzyme activity, and behavioral 
changes to all mussel life stages. Even wastewater discharges with low 
ammonia levels have been shown to negatively affect mussel populations.
    Finally, water temperature plays a critical role in the life 
history of freshwater mussels. High water temperatures can cause valve 
closure, reduced reproductive output, and death. The central Texas 
mussels differ in their optimal temperature ranges, with some species 
much more tolerant of high temperatures than others. Laboratory studies 
investigating the effects of thermal stress on glochidia and adults has 
indicated thermal stress may occur at 29 [deg]C (84.2 [deg]F) (Bonner 
et al. 2018, pp. 123-146; Khan et al. 2019, entire).
    Based on the above information, we determine that stream reaches 
with the following water quality parameters are suitable for the 
Guadalupe fatmucket, Texas fatmucket, Texas fawnsfoot, Guadalupe orb, 
Texas pimpleback, false spike, and Balcones spike:
     Low salinity (less than 2 ppt);
     Low total ammonia (less than 0.77 mg/L total ammonia 
nitrogen);
     Low levels of contaminants;
     Dissolved oxygen levels greater than 2 mg/L;
     Water temperatures below 29 [deg]C (84.2 [deg]F).
Sites for Development of Offspring
    As discussed above, freshwater mussel larvae are parasites that 
must attach to a host fish to develop into juvenile mussels. The 
central Texas mussels use a variety of host fish, many of which are 
widely distributed throughout their ranges. The presence of these fish 
species, either singly or in combination, supports the life-history 
needs of the central Texas mussels:
     Balcones spike and false spike: blacktail shiner 
(Cyprinella venusta) and red shiner (C. lutrensis);
     Texas fawnsfoot: freshwater drum (Aplodinotus grunniens);
     Texas pimpleback and Guadalupe orb: channel catfish 
(Ictalurus punctatus), flathead catfish (Pylodictis olivaris), and 
tadpole madtom (Noturus gyrinus);
     Texas fatmucket and Guadalupe fatmucket: green sunfish 
(Lepomis cyanellus), bluegill (L. macrochirus), largemouth bass 
(Micropterus salmoides), and Guadalupe bass (M. treculii).
    While the specific PBFs for each species may differ slightly (as 
specified in the regulatory text at the end of this rule), in summary, 
we have determined that the following PBFs are essential to the 
conservation of the central Texas mussels:
    (1) Suitable substrates and connected instream habitats, 
characterized by geomorphically stable stream channels and banks (i.e., 
channels that maintain lateral dimensions, longitudinal profiles, and 
sinuosity patterns over time without an aggrading or degrading bed 
elevation) with habitats that support a diversity of freshwater mussel 
and native fish (such as stable riffle-run-pool habitats that provide 
flow refuges consisting of silt-free gravel and coarse sand 
substrates).
    (2) Adequate flows, or a hydrologic flow regime (which includes the 
severity, frequency, duration, and seasonality of discharge over time), 
necessary to maintain benthic habitats where the species are found and 
to maintain connectivity of streams with the floodplain, allowing the 
exchange of nutrients and sediment for maintenance of the mussels' and 
fish hosts' habitat, food availability, spawning habitat for native 
fishes, and the ability for newly transformed juveniles to settle and 
become established in their habitats.
    (3) Water and sediment quality (including, but not limited to, 
dissolved oxygen levels greater than 2 mg/L, conductivity, hardness, 
turbidity, temperatures below 29 [deg]C (84.2 [deg]F), pH (low 
salinity, less than 2 ppt), low total ammonia (less than 0.77 mg/L 
total ammonia nitrogen), heavy metals, and chemical constituents) 
necessary to sustain natural physiological processes for normal 
behavior, growth, and viability of all life stages.
    (4) The presence and abundance of fish hosts necessary for 
recruitment of the central Texas mussels.

Special Management Considerations or Protection

    When designating critical habitat, we assess whether the specific 
areas within the geographical area occupied by the species at the time 
of listing contain features which are essential to the conservation of 
the species and which may require special management considerations or 
protection. The features essential to the conservation of the central 
Texas mussels may require special management considerations or 
protections to reduce the following threats: increased fine sediment, 
changes in water quality, altered hydrology from both inundation and 
flow loss/scour, predation and collection, and barriers to fish 
movement.
    Management activities that could ameliorate these threats include, 
but are not limited to: Use of best management practices (BMPs) 
designed to reduce sedimentation, erosion, and bank side destruction; 
protection of riparian corridors and retention of sufficient canopy 
cover along banks; exclusion of livestock and nuisance wildlife (feral 
hogs, exotic ungulates); moderation of surface and groundwater 
withdrawals to maintain natural flow regimes; increased use of 
stormwater management and reduction of stormwater flows into the 
systems; use of highest water quality standards for wastewater and 
other return flows; and reduction of other watershed and floodplain 
disturbances that release sediments, pollutants, or nutrients into the 
water.
    In summary, we find that the occupied areas we are designating as 
critical habitat contain the PBFs that are essential to the 
conservation of the species and that may require special management 
considerations or protection. Special management considerations or 
protection may be required of the Federal action agency to eliminate, 
or to reduce to negligible levels, the threats affecting the PBFs of 
each unit.

Criteria Used To Identify Critical Habitat

    As required by section 4(b)(2) of the Act, we use the best 
scientific data available to designate critical habitat. In accordance 
with the Act and our implementing regulations at 50 CFR 424.12(b), we 
review available information pertaining to the habitat requirements of 
the species and identify specific areas within the geographical area 
occupied by the species at the time of listing and any specific areas 
outside the geographical area occupied by the species to be considered 
for designation as critical habitat.
    We are designating critical habitat in areas within the 
geographical area occupied by the central Texas mussels at the time of 
listing. We also are designating specific areas outside the

[[Page 48070]]

geographical area occupied by the Texas fatmucket, Texas pimpleback, 
and Texas fawnsfoot at the time of listing because we have determined 
that those areas are essential for the conservation of these three 
species. The designated unoccupied subunits provide for the growth and 
expansion of the current species' ranges within portions of their 
historical ranges. Each of the unoccupied subunits constitute habitat 
for the species because they support life history requirements from the 
species, have the host fish, and expand the occupied reach length of a 
smaller population to a length that will be more resilient to 
stochastic events. For the Guadalupe fatmucket, Guadalupe orb, Balcones 
spike, and false spike, we are not designating any areas outside the 
geographical area occupied by the species because we have not 
identified any unoccupied areas that meet the definition of critical 
habitat.
    The current distributions of all seven of the central Texas mussels 
are much reduced from their historical distributions. We anticipate 
that recovery will require continued protection of existing populations 
and habitat, as well as ensuring that there are adequate numbers of 
mussels in stable populations that occur over a wide geographic area. 
This strategy will help to ensure that catastrophic events, such as the 
effects of hurricanes (which can lead to flooding that causes excessive 
sedimentation, nutrients, and debris to disrupt stream ecology, etc.) 
and drought, cannot simultaneously affect all known populations. 
Rangewide recovery considerations, such as maintaining existing genetic 
diversity and striving for representation of all major portions of the 
species' current ranges, were considered in formulating this critical 
habitat designation.
    Sources of data for this critical habitat designation include 
multiple databases maintained by universities and State agencies, 
scientific and agency reports, and numerous survey reports on streams 
throughout the species' ranges (see Service 2022, pp. 31-44, and 75-
127).
    In summary, for areas within the geographic area occupied by the 
species at the time of listing, we delineated critical habitat unit 
boundaries by evaluating habitat suitability of stream segments within 
the geographical area occupied at the time of listing and retaining 
those segments that contain some or all of the PBFs to support life-
history functions essential for conservation of the species.
    As a final step, we evaluated those occupied stream segments 
retained through the above analysis and refined the starting and ending 
points by evaluating the presence or absence of appropriate PBFs. We 
selected upstream and downstream cutoff points to reference existing 
easily recognizable geopolitical features including confluences, 
highway crossings, and county lines. Using these features as end points 
allows the public to clearly understand the boundaries of critical 
habitat. Unless otherwise specified, any stream beds located directly 
beneath bridge crossings or other landmark features used to describe 
critical habitat spatially, such as stream confluences, are considered 
to be wholly included within the critical habitat unit. Critical 
habitat stream segments were then mapped using ArcMap version 10 (ESRI, 
Inc.), a Geographic Information Systems program.
    We consider the following streams to be occupied by the Guadalupe 
fatmucket at the time of listing: Guadalupe River, North Fork Guadalupe 
River, and Johnson Creek (see Final Critical Habitat Designation, 
below).
    We consider the following streams to be occupied by the Texas 
fatmucket at the time of listing: Bluff Creek, Lower Elm Creek, San 
Saba River, Cherokee Creek, North Llano River, South Llano River, Llano 
River, James River, Threadgill Creek, Beaver Creek, Pedernales River, 
Live Oak Creek, and Onion Creek (see Final Critical Habitat 
Designation, below).
    We consider the following streams to be occupied by the Texas 
fawnsfoot at the time of listing: Upper Clear Fork of the Brazos River, 
Upper Brazos River, Lower San Saba River, and Upper Colorado River (see 
Final Critical Habitat Designation, below).
    We consider the following streams to be occupied by the Guadalupe 
orb at the time of listing: Upper Guadalupe River, South Fork Guadalupe 
River, Lower Guadalupe River, and San Marcos River (see Final Critical 
Habitat Designation, below).
    We consider the following streams to be occupied by the Texas 
pimpleback at the time of listing: Bluff Creek, Lower Elm Creek, Lower 
Concho River, Upper Colorado River, Lower San Saba River, Upper San 
Saba River, and Upper Llano River (see Final Critical Habitat 
Designation, below).
    We consider the following streams to be occupied by false spike at 
the time of listing: San Marcos River and Guadalupe River (see Final 
Critical Habitat Designation, below).
    We consider the following streams to be occupied by Balcones spike 
at the time of listing: San Saba River and Llano River (see Final 
Critical Habitat Designation, below).
    For areas outside the geographic area occupied by the species at 
the time of listing, we delineated critical habitat unit boundaries by 
evaluating habitat suitability of stream segments and retaining those 
segments that contain some or all of the PBFs to support life-history 
functions essential for the conservation of the species.
    The unoccupied reaches we are designating for critical habitat 
designation are Upper Elm Creek for the Texas fatmucket (TXFM-1c); the 
Lower Clear Fork Brazos River for the Texas fawnsfoot (TXFF-1b); and 
the Upper Concho River and Lower Llano River for the Texas pimpleback 
(TXPB-2b and TXPB-5b, respectively) (see table 8, below). The longer 
the reach occupied by a species, the more likely it is that the 
population can withstand stochastic events such as extreme flooding, 
dewatering, or water contamination. These designated areas are located 
immediately adjacent to currently occupied stream reaches that are 
relatively short, ranging from 8.9 river mi (14.4 river km) to 27.9 
river mi (45.0 river km), include one or more of the essential PBFs, 
and allow for expansion of existing populations as necessary to improve 
population resiliency, extend physiographic representation, and reduce 
the risk of extinction for the species. The establishment of additional 
moderately healthy to healthy populations across the range of these 
species would sufficiently reduce their risk of extinction. Improving 
the resiliency of populations in the currently occupied streams, and 
into identified unoccupied areas, will improve species viability; 
therefore, these unoccupied subunits are each essential for the 
conservation of the species.

[[Page 48071]]

    When determining critical habitat boundaries, we made every effort 
to avoid including developed areas such as lands covered by buildings, 
pavement, and other structures because such lands lack physical or 
biological features necessary for the central Texas mussels. The scale 
of the maps we prepared under the parameters for publication within the 
Code of Federal Regulations may not reflect the exclusion of such 
developed lands. Any such lands inadvertently left inside critical 
habitat boundaries shown on the maps of this rule have been excluded by 
text in the rule and are not designated as critical habitat. Therefore, 
a Federal action involving these lands will not trigger section 7 
consultation with respect to critical habitat and the requirement of no 
adverse modification unless the specific action will affect the PBFs in 
the adjacent critical habitat.
    The critical habitat designation is defined by the map or maps, as 
modified by any accompanying regulatory text, presented at the end of 
this document under Regulation Promulgation. We include more detailed 
information on the boundaries of the critical habitat designation in 
the preamble of this document. We will make the coordinates or plot 
points or both on which each map is based available to the public on 
https://www.regulations.gov at Docket No. FWS-R2-ES-2019-0061, and on 
our internet site at https://www.fws.gov/office/austin-ecological-services.

Final Critical Habitat Designation

    We are designating approximately 1,577.5 river mi (2,538.7 river 
km) in total, accounting for overlapping units, in 20 units (with a 
total of 32 subunits; see table 8 and map, below) as critical habitat 
for the central Texas mussel species: the Guadalupe fatmucket, Texas 
fatmucket, Texas fawnsfoot, Texas pimpleback, Guadalupe orb, Balcones 
spike, and false spike. All but four of the subunits are currently 
occupied by one or more of the species, and each of the 20 units 
contains the physical and biological features essential to the 
conservation of each species. Each species historically occurred in a 
different subset of watersheds in central Texas; therefore, there are 
large differences in the amount of critical habitat designated for each 
species. Texas surface water is owned by the State, as are the beds of 
navigable streams; thus, the actual critical habitat units (occupied 
waters and streambeds up to the ordinary high-water mark) are owned by 
the State of Texas (Texas Water Code, sections 11.021 and 11.0235). 
Adjacent riparian areas are in most cases, privately owned, and are 
what is reported in the discussion that follows, although these 
adjacent riparian areas are not included in the critical habitat 
designation. The critical habitat areas we describe below constitute 
our current best assessment of areas that meet the definition of 
critical habitat for the seven central Texas mussel species. Table 8 
shows the critical habitat units and the approximate area of each unit.

                    Table 8--Final Designated Critical Habitat for the Central Texas Mussels
----------------------------------------------------------------------------------------------------------------
                                                                                 Designated critical habitat rmi
             Species                   Basin/unit name           Occupied                     (km)
----------------------------------------------------------------------------------------------------------------
Guadalupe fatmucket.............  Guadalupe River:........  Yes...............  Total: 52.2 (84.0).
                                  GUFM-1a: North Fork       ..................  6.9 (11.0).
                                   Guadalupe River.
                                  GUFM-1b: Johnson Creek..  ..................  10.1 (16.3).
                                  GUFM-1c: Guadalupe River  ..................  35.2 (56.7).
Texas fatmucket.................  Colorado River:.........  Yes...............  Total: 419.5 (675.2).
                                  TXFM-1a: Bluff Creek....  ..................  11.6 (18.7).
                                  TXFM-1b: Lower Elm Creek  ..................  12.3 (19.8).
                                  TXFM-2: San Saba River..  ..................  90.8 (146.1).
                                  TXFM-3: Cherokee Creek..  ..................  17.8 (28.6).
                                  TXFM-4a: North Llano      ..................  30.2 (48.7).
                                   River.
                                  TXFM-4b: South Llano      ..................  22.5 (36.2).
                                   River.
                                  TXFM-4c: Llano River....  ..................  90.9 (146.4).
                                  TXFM-4d: James River....  ..................  18.3 (29.4).
                                  TXFM-4e: Threadgill       ..................  8.1 (13.1).
                                   Creek.
                                  TXFM-4f: Beaver Creek...  ..................  12.7 (20.5).
                                  TXFM-5a: Pedernales       ..................  78.2 (125.8).
                                   River.
                                  TXFM-5b: Live Oak Creek.  ..................  2.6 (4.2).
                                  TXFM-6: Onion Creek.....  ..................  23.5 (37.8).
                                  Colorado River:.........  No................  Total: 8.9 (14.4).
                                  TXFM-1c: Upper Elm Creek  ..................  8.9 (14.4).
Texas fawnsfoot.................  Brazos River:...........  Yes...............  Total: 105.3 (169.5).
                                  TXFF-1a: Upper Clear      ..................  27.3 (44.0).
                                   Fork Brazos River.
                                  TXFF-2: Upper Brazos      ..................  78.0 (125.5).
                                   River.
                                  Brazos River:...........  No................  Total: 27.9 (45.0).
                                  TXFF-1b: Lower Clear      ..................  27.9 (45.0).
                                   Fork Brazos River.
                                  Colorado River:.........  Yes...............  Total: 59.5 (95.7).
                                  TXFF-5a: Lower San Saba   ..................  49.2 (79.1).
                                   River.
                                  TXFF-5b: Upper Colorado   ..................  10.3 (16.6).
                                   River.
Guadalupe orb...................  Guadalupe River:........  Yes...............  Total: 288.5 (464.3).
                                  GORB-1a: South Fork       ..................  5.1 (8.2).
                                   Guadalupe River.
                                  GORB-1b: Upper Guadalupe  ..................  97.1 (156.3).
                                   River.
                                  GORB-2a: San Marcos       ..................  63.9 (102.8).
                                   River.
                                  GORB-2b: Lower Guadalupe  ..................  122.4 (197.0).
                                   River.
Texas pimpleback................  Colorado River:.........  Yes...............  Total: 346.7 (558.0).
                                  TXPB-1a: Bluff Creek....  ..................  11.6 (18.7).
                                  TXPB-1b: Lower Elm Creek  ..................  12.3 (19.8).
                                  TXPB-2a: Lower Concho     ..................  34.6 (55.7).
                                   River.
                                  TXPB-3a: Upper Colorado   ..................  150.4 (242.1).
                                   River.
                                  TXPB-3b: Lower San Saba   ..................  49.2 (79.1).
                                   River.

[[Page 48072]]

 
                                  TXPB-4: Upper San Saba    ..................  51.4 (82.7).
                                   River.
                                  TXPB-5a: Upper Llano      ..................  37.2 (59.9).
                                   River.
                                  Colorado River:.........  No................  Total: 27.3 (44.0).
                                  TXPB-2b: Upper Concho     ..................  15.5 (25.0).
                                   River.
                                  TXPB-5b: Lower Llano      ..................  11.8 (19.1).
                                   River.
False spike.....................  Guadalupe River:........  Yes...............  Total: 143.6 (231.0).
                                  FASP-1a: San Marcos       ..................  21.2 (34.0).
                                   River.
                                  FASP-1b: Guadalupe River  ..................  122.4 (197.0).
Balcones spike..................  Colorado River:.........  Yes...............  Total: 98.1 (157.9).
                                  BASP-2: San Saba River..  ..................  49.1 (79.0).
                                  BASP-3: Llano River.....  ..................  49.0 (78.9).
----------------------------------------------------------------------------------------------------------------
Note: Stream lengths will not sum due to overlapping units, and due to rounding, kilometers (km) may not sum to
  total.

BILLING CODE 4333-15-P

[[Page 48073]]

Map of Final Designated Critical Habitat for the Central Texas Mussels
[GRAPHIC] [TIFF OMITTED] TR04JN24.000

BILLING CODE 4333-15-C
    We present brief descriptions of all units, and reasons why they 
meet the definition of critical habitat for each of the listed species, 
below.

Guadalupe Fatmucket

    We are designating approximately 52.2 river mi (84.0 river km) in a 
single unit, consisting of three subunits, as critical habitat for the 
Guadalupe fatmucket. The critical habitat areas we describe below 
constitute our current best assessment of areas that meet the 
definition of critical habitat for the Guadalupe fatmucket. The unit we 
have designated as critical habitat is GUFM-1: Guadalupe River Unit. 
Table 9 shows the occupancy of the unit, the ownership of adjacent 
riparian lands, and approximate length of the

[[Page 48074]]

designated areas for the Guadalupe fatmucket.

                     Table 9--Designated Critical Habitat Units for the Guadalupe Fatmucket
----------------------------------------------------------------------------------------------------------------
                                                         Adjacent riparian                          River miles
               Unit                      Subunit             ownership            Occupancy        (kilometers)
----------------------------------------------------------------------------------------------------------------
GUFM-1: Guadalupe River..........  GUFM-1a: North Fork  Private............  Occupied...........      6.9 (11.0)
                                    Guadalupe River.
                                   GUFM-1b: Johnson     Private............  Occupied...........     10.1 (16.3)
                                    Creek.
                                   GUFM-1c: Guadalupe   Private............  Occupied...........     32.9 (53.0)
                                    River.              State/Local........  Occupied...........       2.3 (3.7)
                                                                                                 ---------------
    Total........................  ...................  ...................  ...................     52.2 (84.0)
----------------------------------------------------------------------------------------------------------------
Note: Lengths may not sum due to rounding.

    We present a brief description of the unit, and reasons why it 
meets the definition of critical habitat for Guadalupe fatmucket, 
below.
Unit GUFM-1: Guadalupe River
    Subunit GUFM-1a: North Fork Guadalupe River. The North Fork 
Guadalupe River subunit consists of 6.9 river mi (11.0 river km) in 
Kerr County, Texas. The adjacent riparian areas of the subunit are 
privately owned. The entire subunit is currently occupied by the 
species. The North Fork Guadalupe River subunit extends from the Farm-
to-Market (FM) 1340 bridge crossing (just upstream of the Bear Creek 
Boy Scout camp) downstream to the confluence with the Guadalupe River. 
This subunit contains all of the PBFs essential to the conservation of 
the Guadalupe fatmucket. The North Fork Guadalupe River subunit is in a 
mostly rural setting; is influenced by drought, low flows, and flooding 
(leading to scour); and is being affected by ongoing agricultural 
activities and development resulting in excessive sedimentation, water 
quality degradation, and groundwater withdrawals and surface water 
diversions. Therefore, special management may be necessary to reduce 
sedimentation, improve water quality, maintain adequate flows, and 
improve habitat connectivity. Special management considerations may be 
necessary to ensure adequate instream flow and water quality.
    Subunit GUFM-1b: Johnson Creek. The Johnson Creek subunit consists 
of 10.1 river mi (16.3 river km) within Kerr County, Texas. The Johnson 
Creek subunit begins at the Byas Springs Road crossing downstream to 
the confluence with the Guadalupe River. The adjacent riparian area is 
privately owned. The subunit is occupied by the Guadalupe fatmucket. 
This site contains all of the PBFs essential to the conservation of the 
species, although certain PBFs, such as sufficient water flow and water 
quality (e.g., dissolved oxygen levels and water temperature) may be 
degraded during times of drought. The Johnson Creek subunit is in a 
mostly rural but urbanizing setting; is influenced by drought, low 
flows, and flooding (leading to scour); and is being affected by 
ongoing agricultural activities and development resulting in excessive 
sedimentation, water quality degradation, and groundwater withdrawals 
and surface water diversions. Therefore, special management 
considerations may be necessary to reduce sedimentation, improve water 
quality, maintain adequate flows, and improve habitat connectivity.
    Subunit GUFM-1c: Guadalupe River. This unit consists of 
approximately 35.2 river mi (56.7 river km) in Kendall and Kerr 
Counties, Texas. The Guadalupe River subunit extends from the 
confluence of the North and South Fork Guadalupe Rivers downstream to 
the Interstate Highway 10 bridge crossing near Comfort, Texas. 
Ownership of adjacent riparian areas is approximately 93 percent 
private and 7 percent State/local government. The subunit is occupied 
by the Guadalupe fatmucket. This portion of the Guadalupe River Basin 
is largely agricultural with several municipalities and multiple low-
head dams originally built for a variety of purposes and is now largely 
used for recreation (kayaking, fishing, camping, swimming, etc.). This 
subunit contains all of the PBFs essential to the conservation of the 
species. The Guadalupe River subunit is experiencing some urbanization; 
is influenced by drought, low flows, and flooding (leading to scour); 
and is being affected by ongoing agricultural activities and 
development resulting in excessive sedimentation, water quality 
degradation, groundwater withdrawals and surface water diversions, and 
wastewater inputs. Therefore, special management considerations may be 
necessary to reduce sedimentation, improve water quality, maintain 
adequate flows, and improve habitat connectivity. This subunit is also 
occupied by Guadalupe orb.

Texas Fatmucket

    We are designating approximately 419.5 river mi (675.2 km) in 6 
units, including 11 subunits, as critical habitat for Texas fatmucket. 
The critical habitat areas we describe below constitute our current 
best assessment of areas that meet the definition of critical habitat 
for the Texas fatmucket. The six areas we are designating as critical 
habitat are: TXFM-1: Elm Creek Unit; TXFM-2: San Saba River Unit; TXFM-
3: Cherokee Creek Unit; TXFM-4: Llano River Unit; TXFM-5: Pedernales 
River Unit; and TXFM-6: Onion Creek Unit. Table 10 shows the occupancy 
of the units, the ownership of adjacent riparian lands, and approximate 
length of the designated areas for the Texas fatmucket.

                         Table 10--Designated Critical Habitat Units for Texas Fatmucket
----------------------------------------------------------------------------------------------------------------
                                                         Adjacent riparian                          River miles
               Unit                      Subunit             ownership            Occupancy        (kilometers)
----------------------------------------------------------------------------------------------------------------
TXFM-1: Elm Creek................  TXFM-1a: Bluff       Private............  Occupied...........     11.6 (18.7)
                                    Creek.
                                   TXFM-1b: Lower Elm   Private............  Occupied...........     11.9 (19.2)
                                    Creek.              State/Local........                            0.4 (0.6)
                                   TXFM-1c: Upper Elm   Private............  Unoccupied.........      8.9 (14.4)
                                    Creek.

[[Page 48075]]

 
TXFM-2: San Saba River...........  ...................  Private............  Occupied...........    90.8 (146.1)
TXFM-3: Cherokee Creek...........  ...................  Private............  Occupied...........     17.8 (28.6)
TXFM-4: Llano River..............  TXFM-4a: North       Private............  Occupied...........     30.2 (48.7)
                                    Llano River.
                                   TXFM-4b: South       Private............  Occupied...........     20.2 (32.5)
                                    Llano River.        State..............                            2.3 (3.7)
                                   TXFM-4c: Llano       Private............  Occupied...........    90.4 (145.6)
                                    River.              State/Local........                            0.5 (0.8)
                                   TXFM-4d: James       Private............  Occupied...........     18.3 (29.4)
                                    River.
                                   TXFM-4e: Threadgill  Private............  Occupied...........      8.1 (13.1)
                                    Creek.
                                   TXFM-4f: Beaver      Private............  Occupied...........     12.7 (20.5)
                                    Creek.
TXFM-5: Pedernales River.........  TXFM-5a: Pedernales  Private............  Occupied...........    68.9 (110.9)
                                    River.              State/Local........                           6.8 (10.9)
                                                        Federal............                            2.5 (4.0)
                                   TXFM-5b: Live Oak    Private............  Occupied...........       1.2 (2.0)
                                    Creek.              State/Local........                            1.4 (2.2)
TXFM-6: Onion Creek..............  ...................  Private............  Occupied...........     10.3 (16.6)
                                                        State/Local........                          13.2 (21.2)
                                                                                                 ---------------
    Total........................  ...................  ...................  ...................   428.4 (689.4)
----------------------------------------------------------------------------------------------------------------
Note: Lengths may not sum due to rounding.

    We present brief descriptions of all units, and reasons why they 
meet the definition of critical habitat for Texas fatmucket, below.
Unit TXFM-1: Elm Creek
    Subunit TXFM-1a: Bluff Creek. This occupied critical habitat 
subunit consists of 11.6 river mi (18.7 km) of Bluff Creek, a tributary 
to Elm Creek, in Runnels County, Texas. The subunit extends from the 
County Road 153 bridge crossing, near the town of Winters, Texas, 
downstream to the confluence of Bluff and Elm creeks. The adjacent 
riparian area of this subunit is privately owned. This subunit is 
currently occupied by the Texas fatmucket. This subunit contains all of 
the PBFs, although suitable substrate, stream flow, and water quality 
are degraded. The Bluff Creek subunit is in a rural setting; is 
influenced by drought, low flows, and elevated chlorides; and is being 
affected by ongoing agricultural activities and development resulting 
in excessive sedimentation, water quality degradation, and groundwater 
withdrawals and surface water diversions. Therefore, special management 
considerations may be necessary to reduce sedimentation, improve water 
quality, maintain adequate flows, and improve habitat connectivity. 
This subunit is also occupied by the Texas pimpleback.
    Subunit TXFM-1b: Lower Elm Creek. This subunit consists of 12.3 
river mi (19.8 km) of Elm Creek beginning at the confluence of Bluff 
Creek and continuing downstream to Elm Creek's confluence with the 
Colorado River in Runnels County, Texas. Ownership of adjacent riparian 
areas is approximately 97 percent private and 3 percent State/local 
government. The Elm Creek watershed is relatively small and remains 
largely rural and dominated by agricultural practices. This stream 
regularly has extremely low or no flow during times of drought. 
Moreover, this stream has degraded quality, in the form of elevated 
chloride concentrations and sedimentation, resulting in reduced habitat 
quality and availability. Lower Elm Creek is occupied by the Texas 
fatmucket and contains at least one of the PBFs essential to the 
conservation of the species: the presence of host fish. Other PBFs are 
present in the subunit but are in degraded condition and would benefit 
from management actions such as improving water quality and substrate. 
The Lower Elm Creek subunit is influenced by drought, low flows, and 
elevated chlorides, and is being affected by ongoing agricultural 
activities and development resulting in excessive sedimentation, water 
quality degradation, and groundwater withdrawals and surface water 
diversions. Therefore, special management considerations may be 
necessary to reduce sedimentation, improve water quality, maintain 
adequate flows, and improve habitat connectivity. This subunit is also 
occupied by the Texas pimpleback.
    Subunit TXFM-1c: Upper Elm Creek. Upper Elm Creek is not currently 
occupied by the Texas fatmucket, but is essential for the conservation 
of the species. This subunit consists of 8.9 river mi (14.4 km) from 
the County Road 153 crossing, south of Lake Winters, downstream to the 
confluence of Bluff and Elm creeks. Adjacent riparian area is privately 
owned. The entire Elm Creek watershed is dominated by agriculture and 
remains rural. Upper Elm Creek is essential for the conservation of the 
species because it provides for the growth and expansion of the Texas 
fatmucket within a portion of its historical range on Elm Creek; the 
occupied Lower Elm Creek Subunit is too small to ensure conservation of 
the Texas fatmucket over the long term. This subunit is important to 
the conservation of the Texas fatmucket because it is the farthest 
upstream population, and its loss would shrink the overall range of the 
Texas fatmucket to the lower, larger tributaries of the Colorado River. 
Additionally, this population of Texas fatmucket is substantially far 
from the other population of the species, such that if a catastrophic 
event such as drought or extreme flooding were to occur, it is likely 
that this population would be affected differently, increasing the 
chance of the species surviving such an event.
    The Upper Elm Creek subunit is in a rural setting; is influenced by 
drought, low flows, and elevated chlorides; and is being affected by 
ongoing agricultural activities. Although it is considered unoccupied, 
portions of this subunit contain some or all of the PBFs essential for 
the conservation of the species. As previously mentioned, flow rates in 
this subunit are typically not within the range required by the Texas 
fatmucket. This subunit is often characterized by small, isolated pools 
separated by short riffles over bedrock during low flow and when dam 
releases are minimal.

[[Page 48076]]

    Suitable stream habitat and hydrological connectivity are 
unsupported throughout the entirety of this subunit but do occur in 
portions of the delineated unit. Specifically, low flows during times 
of drought punctuated by high flows are either scouring the stream 
habitat, or depositing stream sediments downstream. Because mussels are 
sedentary organisms, transportation of individuals during flooding 
events is often lethal.
    The Texas fatmucket uses predatory fish (e.g., bass and sunfishes) 
for its host infestation period of its lifecycle. These host fishes are 
estimated to be common throughout the State of Texas and within the 
Upper Elm Creek subunit.
    This subunit is not included in TCEQ classified stream segments; 
therefore, we have no specific water quality information for this area. 
During times of normal flow, this subunit likely supports healthy water 
quality parameters for the Texas fatmucket, but water quality is likely 
compromised during low flows, when water temperatures rise and 
dissolved oxygen drops. The Upper Elm Creek subunit will require 
additional management practices to ensure sufficient water quality 
standards are being met and maintained for the Texas fatmucket. Because 
this reach of Elm Creek periodically contains the flowing water 
conditions and host fish species used by the Texas fatmucket, it is 
habitat for Texas fatmucket.
    If the Texas fatmucket can be reestablished in this reach, it will 
expand the occupied reach in Elm Creek to a length that will be more 
resilient to the stressors that the species is facing. The longer the 
reach occupied by a species, the more likely it is that the population 
can withstand stochastic events such as extreme flooding, dewatering, 
or water contamination. In the SSA report, we identified 50 miles (80 
km) as a reach long enough for a population to be able to withstand 
stochastic events, and the addition of this 8.9-mile reach, as well as 
the adjacent tributary of Bluff Creek, will extend to closer to 50 
miles the existing Texas fatmucket population downstream in Lower Elm 
Creek and in Bluff Creek. The addition of multiple tributaries 
increases the value of the overall critical habitat unit, providing 
protection for the population should a stochastic event occur in one 
tributary. If Texas fatmucket were to become reestablished throughout 
this unit, it would likely be a moderately to highly resilient 
population due to longer stream length and would increase the species' 
future viability. This unoccupied unit is essential for the 
conservation of the species because it provides habitat for range 
expansion in portions of known historical habitat and is necessary to 
increase viability of the species by increasing population resiliency.
Unit TXFM-2: San Saba River
    This unit consists of 90.8 river mi (146.1 km) of the San Saba 
River in Mason, McCulloch, Menard, and San Saba Counties, Texas. This 
unit of the San Saba River extends from the Schleicher and Menard 
County line, near Fort McKavett, Texas, downstream to the San Saba 
River confluence with the Colorado River. The adjacent riparian areas 
are privately owned. This basin is largely rural and is dominated by 
mostly agricultural activities including cattle grazing, hay farming, 
and pecan farming. During the summer, this unit is affected by very low 
flows, which are exacerbated by pumping, and drought. This unit 
contains all of the PBFs essential to the conservation of the Texas 
fatmucket and is currently occupied by the species. The San Saba River 
unit is influenced by drought; low flows; underlying geology resulting 
in a losing reach; and ongoing agricultural activities and development 
resulting in excessive sedimentation, water quality degradation, 
groundwater withdrawals and surface water diversions, and collection. 
Therefore, special management considerations may be necessary to reduce 
sedimentation, improve water quality, maintain adequate flows, improve 
habitat connectivity, and manage collection. Special management may be 
necessary to ensure adequate flow and prevent water quality 
degradation. This unit is also occupied by the Texas fawnsfoot, Texas 
pimpleback, and Balcones spike.
Unit TXFM-3: Cherokee Creek
    This unit consists of 17.8 river mi (28.6 km) of Cherokee Creek in 
San Saba County, Texas. The adjacent riparian areas are privately 
owned. The Cherokee Creek unit extends from the County Road 409 bridge 
crossing downstream to the confluence with the Colorado River. This 
unit is occupied by the Texas fatmucket and contains all of the PBFs 
essential to the conservation of the species. Even though this unit is 
smaller than 50 miles, which we had determined was the reach length 
long enough to withstand stochastic events, this population increases 
the species' redundancy, making it more likely to withstand 
catastrophic events that may eliminate one or more of the other 
populations. The Cherokee Creek unit is in a rural setting; is 
influenced by drought and low flows; and is being affected by ongoing 
agricultural activities and development resulting in excessive 
sedimentation, water quality degradation, and groundwater withdrawals 
and surface water diversions. Therefore, special management 
considerations may be necessary to reduce sedimentation, improve water 
quality, maintain adequate flows, and improve habitat connectivity. 
Special management may be necessary to limit the effect of low flow and 
drought conditions.
Unit TXFM-4: Llano River
    Subunit TXFM-4a: North Llano River. This subunit consists of 30.2 
river mi (48.7 km) in Sutton and Kimble Counties, Texas. The North 
Llano River subunit extends from the most upstream County Road 307 
bridge crossing in Sutton County downstream for 30.2 river mi (48.7 
river km) into Kimble County at the confluence with the South Llano 
River near the city of Junction, Texas. The North Llano River is 
occupied by the Texas fatmucket and contains all of the PBFs essential 
to the conservation of the species. Riparian areas adjacent to this 
subunit are privately owned and largely dominated by rural agricultural 
operations. This subunit is not heavily influenced by spring inputs 
like some other tributaries to the Llano River, such as the South Llano 
River. During summertime low flows and extended periods of drought, 
this subunit often becomes a series of isolated pools separated by 
shallow flowing riffles over bedrock. These reduced flows can leave 
mussels stranded and desiccated in dry beds or isolated in shallow 
pools. Decreased flows can also result in decreased water quality, 
specifically in the form of reduced dissolved oxygen and increased 
temperature. Special management considerations may be necessary to 
address ongoing concerns of low flows and subsequent water quality 
degradation.
    Subunit TXFM-4b: South Llano River. The South Llano River subunit 
extends from the Edwards and Kimble County line downstream 22.5 river 
mi (36.2 river km) to the confluence with the North Llano River in 
Kimble County, Texas. Ownership of adjacent riparian areas is 90 
percent private and 10 percent State. Major activities in this basin 
are farming, ranching, and other agricultural uses, as the watershed 
remains largely rural. The South Llano River subunit is occupied by the 
Texas fatmucket and contains all of the PBFs essential to the 
conservation of the species. The South Llano River subunit is 
influenced by flooding (leading to

[[Page 48077]]

scour), drought, and low flows, and this subunit is being affected by 
ongoing agricultural activities and development resulting in excessive 
sedimentation, water quality degradation, and groundwater withdrawals 
and surface water diversions. Therefore, special management 
considerations may be necessary to reduce sedimentation, improve water 
quality, maintain adequate flows, and improve habitat connectivity. 
Special management may be required to address episodic low flows during 
summer drought and associated with reduced spring flow.
    Subunit TXFM-4c: Llano River. This subunit consists of 90.9 river 
mi (146.4 river km) in Kimble, Mason, and Llano Counties, Texas. The 
Llano River subunit begins at the confluence of the North and South 
Fork Llano River and continues downstream to the State Highway 16 
bridge crossing in Llano County. Ownership of adjacent riparian areas 
is 99.5 percent private and 0.5 percent State/local government, and the 
watershed remains largely rural. The Llano River subunit is occupied by 
the Texas fatmucket and contains all of the PBFs essential to the 
conservation of the species. The Llano River subunit is in a rural 
setting; is influenced by flooding (leading to scour), drought, and low 
flows; and is being affected by ongoing agricultural activities and 
development resulting in excessive sedimentation, water quality 
degradation, and groundwater withdrawals and surface water diversions. 
Therefore, special management considerations may be necessary to reduce 
sedimentation, improve water quality, maintain adequate flows, and 
improve habitat connectivity. This subunit is also occupied by the 
Texas pimpleback and Balcones spike.
    Subunit TXFM-4d: James River. The James River subunit consists of 
18.3 river mi (29.4 river km) of the James River in Kimble and Mason 
Counties, Texas. The subunit begins at the Kimble and Mason County line 
and continues downstream to the Llano River confluence. Adjacent 
riparian areas are privately owned. The James River subunit is occupied 
by the Texas fatmucket and contains all of the PBFs essential to the 
conservation of the species. The James River subunit is in a rural 
setting; is influenced by flooding (leading to scour), drought, and low 
flows; and is being affected by ongoing agricultural activities and 
development resulting in excessive sedimentation, water quality 
degradation, and groundwater withdrawals. Therefore, special management 
considerations may be necessary to reduce sedimentation, improve water 
quality, maintain adequate flows, and improve habitat connectivity.
    Subunit TXFM-4e: Threadgill Creek. The Threadgill Creek subunit 
consists of 8.1 river mi (13.1 river km) extending from the Ranch Road 
783 bridge crossing downstream to the confluence with Beaver Creek in 
Gillespie and Mason Counties, Texas. Riparian lands adjacent to this 
subunit are privately owned. Threadgill Creek is occupied by the Texas 
fatmucket and contains all of the PBFs essential to the conservation of 
the species. The Threadgill Creek subunit is in a rural setting; is 
influenced by flooding (leading to scour), drought, and low flows; and 
is being affected by ongoing agricultural activities and development 
resulting in excessive sedimentation, water quality degradation, and 
groundwater withdrawals. Therefore, special management considerations 
may be necessary to reduce sedimentation, improve water quality, 
maintain adequate flows, and improve habitat connectivity.
    Subunit TXFM-4f: Beaver Creek. The Beaver Creek Subunit consists of 
12.7 river mi (20.5 river km) and begins at the confluence with 
Threadgill Creek and continues downstream to the confluence with the 
Llano River in Mason County, Texas. Adjacent riparian habitats are 
privately owned. This subunit contains all of the PBFs essential to the 
conservation of the Texas fatmucket. The Beaver Creek subunit is in a 
rural setting; is influenced by flooding (leading to scour), drought, 
and low flows; and is being affected by ongoing agricultural activities 
and development resulting in excessive sedimentation, water quality 
degradation, and groundwater withdrawals. Therefore, special management 
considerations may be necessary to reduce sedimentation, improve water 
quality, maintain adequate flows, and improve habitat connectivity.
    This subunit is connected to known populations of the Texas 
fatmucket in subunits TXFM-4c and TXFM-4e, but there are no recent 
surveys of Beaver Creek itself. There are no instream structures in 
subunits TXFM-4c and TXFM-4e that would impede water flow; the flow 
regime is the same as in those subunits; and the host fish may move 
between the subunits freely. Based on this information, it is 
reasonable to conclude that the populations in subunits TXFM-4c and 
TXFM-4e are unlikely to stop at the most upstream or downstream survey 
location; therefore, we conclude that this subunit is occupied.
    However, due to the lack of recent surveys, we are analyzing this 
subunit against the second prong of the definition of critical habitat 
for unoccupied habitat out of an abundance of caution. If subunit TXFM-
4f is not, in fact, occupied, it is essential for the conservation of 
the species because it provides for needed growth and expansion of the 
species in this portion of its historical range and connectivity 
between documented occupied reaches. Connecting occupied reaches 
increases the resiliency of the occupied reaches by allowing for gene 
flow and repopulation after stochastic events. The longer the occupied 
reach, the more likely it is that the Texas fatmucket population can 
rebound after stochastic events such as extreme flooding, dewatering, 
or water contamination. This unoccupied unit is essential for the 
conservation of the species because it contains all of the PBFs, 
provides habitat for range expansion in portions of known historical 
habitat, and is necessary to increase viability of the species by 
increasing population resiliency.
Unit TXFM-5: Pedernales River
    Subunit TXFM-5a: Pedernales River. The Pedernales River subunit 
consists of 78.2 river mi (125.8 river km) in Blanco, Gillespie, Hays, 
and Travis Counties, Texas. The Pedernales River subunit extends from 
the origination of the Pedernales River at the confluence of Bear and 
Wolf creeks in Gillespie County downstream to the FM 3238 (Hamilton 
Pool Road) bridge crossing in Travis County. Ownership of adjacent 
riparian areas is 87 percent private, 10 percent State/local 
government, and 3 percent Federal; 2.5 river mi (4.0 river km) are 
within Lyndon B. Johnson National Historical Park, which is owned and 
managed by the National Park Service (NPS) in Gillespie County, Texas. 
The subunit is currently occupied by the Texas fatmucket and supports 
all of the PBFs essential to the conservation of the species. The 
watershed of the Pedernales River is characterized by agricultural 
uses, including irrigated orchards and vineyards. Excess nutrients, 
sediment, and pollutants enter the Pedernales River from wastewater, 
agricultural runoff, and urban stormwater runoff, all of which reduces 
instream water quality. The Pedernales River geology, like many central 
Texas rivers, is predominately limestone outcroppings; therefore, this 
system is subject to flashy, episodic flooding during rain events that 
mobilize large amounts of sediment and wood materials. Special 
management considerations may be

[[Page 48078]]

necessary in this subunit to address low water levels as a result of 
water withdrawals and drought. Additionally, implementation of the 
highest levels of treatment of wastewater practicable would improve 
water quality in this subunit, and maintenance of riparian habitat and 
upland buffers would maintain or improve substrate quality.
    Subunit TXFM-5b: Live Oak Creek. The Live Oak Creek subunit 
consists of 2.6 river mi (4.2 river km) in Gillespie County, Texas. 
Ownership of adjacent riparian areas is approximately 46 percent 
private and 54 percent State/local government. The Live Oak Creek 
subunit originates at the FM 2093 bridge crossing downstream to its 
confluence with the Pedernales River. This subunit is currently 
occupied by the Texas fatmucket and contains all of the PBFs essential 
to the conservation of the species. The Live Oak Creek subunit is in a 
mostly rural setting with some urbanization; is influenced by drought, 
low flows, and flooding (leading to scour); and is being affected by 
ongoing development and agricultural activities resulting in excessive 
sedimentation, water quality degradation, and groundwater withdrawals 
and surface water diversions. Therefore, special management 
considerations may be necessary to reduce sedimentation, improve water 
quality, maintain adequate flows, and improve habitat connectivity.
Unit TXFM-6: Onion Creek (Previously TXFM-6a: Lower Onion Creek)
    The Onion Creek unit consists of 23.5 river mi (37.8 river km) in 
Travis County, Texas. This unit combines the proposed Lower Onion Creek 
(TXFM-6a) subunit and the proposed Upper Onion Creek (TXFM-6b) subunit. 
We consolidated these proposed subunits into one unit (TXFM-6) due to 
recent survey data confirming that Texas fatmucket inhabit Upper Onion 
Creek, which had been thought to be unoccupied.
    Unit TXFM-6 begins at the Interstate Highway 35 bridge crossing 
downstream to the confluence with the Colorado River. The upper portion 
of this unit is in a rural but urbanizing setting and is influenced by 
drought, low flows, and flooding (leading to scour). Ownership of 
adjacent riparian areas is approximately 44 percent private and 56 
percent State/local government. The lower portion of this unit is in 
close proximity to the rapidly urbanizing city of Austin, Texas, and 
contains substantial municipal developments. The effects of such rapid 
and widespread urbanization have contributed to significantly altered 
flows in Onion Creek that have led to bank destabilization, increased 
sedimentation and streambed mobilization, and loss of stable substrate. 
Further, urban runoff pollutants are responsible for degraded water 
quality conditions. Even though this unit is smaller than 50 miles, 
which we had determined was the reach length long enough to withstand 
stochastic events, the population increases the species' redundancy, 
making it more likely to withstand catastrophic events that may 
eliminate one or more of the other populations. Further, it is the 
easternmost population of the Texas fatmucket, which expands the 
species' overall distribution. The Onion Creek unit is occupied by the 
Texas fatmucket and contains most of the PBFs essential to the 
conservation of Texas fatmucket. Several PBFs, such as water quality, 
sufficient flow rates, and suitable substrate, are present in the lower 
portions of the unit and at times of low flow may be either missing or 
minimally acceptable for the species in the upper portions of the unit. 
Suitable host fishes are believed to occur throughout the unit. Special 
management considerations may be necessary to reduce sedimentation, 
improve water quality, maintain adequate flows, and improve habitat 
connectivity.

Texas Fawnsfoot

    We are designating approximately 192.7 river mi (310.2 river km) in 
three units (including four subunits) as critical habitat for the Texas 
fawnsfoot. The critical habitat areas we describe below constitute our 
current best assessment of areas that meet the definition of critical 
habitat for the Texas fawnsfoot. The three areas we designate as 
critical habitat are: TXFF-1: Clear Fork Brazos River Unit; TXFF-2: 
Upper Brazos River Unit; and TXFF-5: Lower San Saba and Upper Colorado 
River Unit. We are excluding units TXFF-3: Lower Brazos River; TXFF-4: 
Little River; TSFF-6: Lower Colorado River; TXFF-7: East Fork of the 
Trinity River; and TXFF-8: Trinity River (see Summary of Exclusion, 
below). Table 11 shows the occupancy of the units, the ownership of 
adjacent riparian lands, and approximate length of the designated areas 
for the Texas fawnsfoot.

                       Table 11--Designated Critical Habitat Units for the Texas Fawnsfoot
                                              (Truncilla macrodon)
----------------------------------------------------------------------------------------------------------------
                                                         Adjacent riparian                          River miles
               Unit                      Subunit             ownership            Occupancy        (kilometers)
----------------------------------------------------------------------------------------------------------------
TXFF-1: Clear Fork Brazos River..  TXFF-1a: Upper       Private............  Occupied...........     27.3 (44.0)
                                    Clear Fork Brazos
                                    River.
                                   TXFF-1b: Lower       Private............  Unoccupied.........     27.5 (44.3)
                                    Clear Fork Brazos   State/Local........                            0.4 (0.7)
                                    River.
TXFF-2: Upper Brazos River.......  ...................  Private............  Occupied...........    78.0 (125.5)
TXFF-5: Lower San Saba and Upper   TXFF-5a. Lower San   Private............  Occupied...........     48.6 (78.1)
 Colorado River.                    Saba River.         State/Local........                            0.6 (1.0)
                                   TXFF-5b. Upper       Private............  Occupied...........     10.3 (16.6)
                                    Colorado River.
                                                                                                 ---------------
    Total........................  ...................  ...................  ...................   192.7 (310.2)
----------------------------------------------------------------------------------------------------------------
Note: Lengths may not sum due to rounding.

    We present brief descriptions of all units, and reasons why they 
meet the definition of critical habitat for Texas fawnsfoot, below.
Unit TXFF-1: Clear Fork of the Brazos River
    Subunit TXFF-1a: Upper Clear Fork of the Brazos River. The Upper 
Clear Fork of the Brazos River subunit consists of approximately 27.3 
river mi (44.0 river km) in Shackelford and Throckmorton Counties, 
Texas. The subunit begins at the confluence of Paint Creek and extends 
downstream to the U.S. Highway 283 bridge, near Fort Griffin, Texas. 
Adjacent riparian lands are privately owned. This subunit is occupied 
by the Texas fawnsfoot and

[[Page 48079]]

contains several of the PBFs essential to the conservation of the 
species, such as appropriate fish hosts and appropriate flows during 
portions of the year. Largely due to ongoing low-flow conditions from 
summertime drought and continued pressure on already strained water 
resources for municipal and agricultural uses, the Upper Clear Fork of 
the Brazos River does not consistently have sufficient flow and water 
quality is often inadequate for the Texas fawnsfoot in this subunit. 
Special management considerations may be necessary to address the 
threats in this unit by maintaining adequate flows and improving 
habitat connectivity.
    Subunit TXFF-1b: Lower Clear Fork of the Brazos River. Lower Clear 
Fork is not currently occupied by the Texas fawnsfoot, but is essential 
for the conservation of the species. The Lower Clear Fork of the Brazos 
River subunit consists of 27.9 river mi (45.0 river km) in Shackelford 
and Stephens Counties, Texas. This subunit begins at the U.S. Highway 
283 bridge and continues downstream to the U.S. Highway 183 bridge in 
Stephens County, Texas. Ownership of adjacent riparian areas is 
approximately 99 percent private and 1 percent State/local government.
    This unit is essential to the conservation of the Texas fawnsfoot 
because it would expand the most northern population and increase the 
distribution of Texas fawnsfoot outside of mainstem, higher order 
streams. Additionally, this population of Texas fawnsfoot is 
geographically distant from the other populations of the species, such 
that if a catastrophic event were to occur within the range of the 
Texas fawnsfoot, such as extreme flooding or drought, it is likely that 
this population would not be affected in the same way, increasing the 
chance of the species surviving such an event. The Lower Clear Fork 
Brazos River subunit is in a rural setting; is influenced by drought, 
low flows, and chlorides; and is being affected by ongoing agricultural 
activities and development, resulting in excessive sedimentation, water 
quality degradation, groundwater withdrawals and surface water 
diversions, and wastewater inputs.
    Although it is considered unoccupied, portions of this subunit 
contain some or all of the PBFs essential for the conservation of the 
species. Flowing water at rates needed by the Texas fawnsfoot are 
present in the subunit but may not be adequate in this subunit 
throughout portions of the year due to low precipitation, surface 
diversions, and groundwater withdrawals. In the SSA report, we noted 
that the Lower Clear Fork of the Brazos River experienced both the 
lowest flow rate (0 cfs) during the 2011 drought and the highest flow 
rate (approaching 4,000 cfs) during the 2015 floods (Service 2022, p. 
59). This altered hydrological regime also degrades stream habitat by 
either scouring out available substrate or depositing large amounts of 
sediment on top of otherwise suitable areas. Appropriate substrates are 
found only in isolated reaches. Management actions that allow for 
improvement of degraded habitat areas within this subunit would allow 
Texas fawnsfoot populations to expand and increase the subunit's 
resiliency.
    The freshwater drum, the Texas fawnsfoot's host fish, is expected 
to be present in the Lower Clear Fork of the Brazos River. Thus, 
management actions may be necessary to ensure appropriate populations 
of host fish are co-occurring with Texas fawnsfoot.
    Water quality may not be sufficient in the Lower Clear Fork of the 
Brazos River. Elevated chloride levels from naturally occurring 
underground salt formations are exacerbated by reduced water flow. In 
order for Texas fawnsfoot populations to expand and occupy the Lower 
Clear Fork of the Brazos River subunit, management actions may be 
necessary to reduce chloride levels. Because this reach of the Clear 
Fork Brazos River periodically contains the flowing water conditions 
and host fish species used by Texas fawnsfoot, it is habitat for the 
Texas fawnsfoot.
    If the Texas fawnsfoot can be reestablished in this reach, it will 
expand the occupied reach length in the Clear Fork Brazos River to a 
length that will be more resilient to the stressors that the species is 
experiencing. The longer the reach occupied by a species, the more 
likely it is that the population can withstand stochastic events such 
as extreme flooding, dewatering, or water contamination. In the SSA 
report, we identified 50 miles (80 km) as a reach long enough for a 
population to be able to withstand stochastic events, and the addition 
of this 27.9-mile reach to the 27.3-mile occupied section of the Clear 
Fork Brazos River (subunit TXFF-1a) expands the existing Texas 
fawnsfoot population in the Clear Fork Brazos River to 55.2 miles, 
achieving a length that allows for a highly resilient population to be 
reestablished, increasing the species' future viability. This unit is 
essential for the conservation of the species because it provides 
habitat for range expansion in portions of known historical habitat, 
which is necessary to increase viability of the species.
Unit TXFF-2: Upper Brazos River
    The Upper Brazos River Unit consists of approximately 78.0 river mi 
(125.5 river km) of the Brazos River in Palo Pinto and Parker Counties, 
Texas. The Upper Brazos River Unit extends from the FM 4 bridge 
crossing in Palo Pinto County, Texas, downstream to the FM 1189 bridge 
in Parker County, Texas. The unit is currently occupied by the species, 
and adjacent riparian lands are privately owned. This unit currently 
supports some of the PBFs essential to the conservation of Texas 
fawnsfoot, such as presence of appropriate fish hosts and suitable flow 
conditions during portions of the year (but flow conditions become 
unsuitable during times of drought). The PBFs of water quality and 
sufficient flow are present but degraded in this unit, as excessive 
chloride concentrations and persistent low flows diminish habitat 
quality in this unit. Elevated chloride concentrations in this portion 
of central Texas are often a result of natural causes, such as saline 
water inputs from spring releases flowing through subterranean salt 
deposits. However, while the Texas fawnsfoot may be able to tolerate 
some minor increases in salinity, low flow rates in this unit 
exacerbate the concentrations of chlorides.
    The Upper Brazos River Unit is in a rural setting with some 
urbanization; is influenced by drought, low flows, chlorides, and 
reservoir operations; and is being affected by mining (rock, sand, and 
gravel), ongoing agricultural activities, and development, which result 
in excessive sedimentation, water quality degradation, groundwater 
withdrawals and surface water diversions, and wastewater inputs. 
Therefore, special management considerations may be necessary to reduce 
sedimentation, improve water quality, maintain adequate flows, and 
improve habitat connectivity.
Unit TXFF-5: Lower San Saba River and Upper Colorado River
    Subunit TXFF-5a: Lower San Saba River. The Lower San Saba River 
subunit consists of approximately 49.2 river mi (79.1 river km) in San 
Saba County, Texas. This subunit begins at the Brady Creek confluence 
and extends to the Colorado River confluence. Ownership of adjacent 
riparian areas is approximately 99 percent private and 1 percent State/
local government, and these areas are primarily in agricultural use. 
The river experiences periods of low flow due to drought and water 
withdrawals, and water withdrawals are expected to increase in the 
future. The

[[Page 48080]]

subunit is occupied by the Texas fawnsfoot and contains all of the PBFs 
essential to the conservation of the species. The Lower San Saba River 
subunit is experiencing some urbanization and is influenced by drought, 
low flows, and wastewater discharges. The watershed is being affected 
by ongoing agricultural activities and development, resulting in 
excessive sedimentation, water quality degradation, groundwater 
withdrawals and surface water diversions, and wastewater inputs. 
Therefore, special management considerations may be necessary to reduce 
sedimentation, improve water quality, maintain adequate flows, and 
improve habitat connectivity. This subunit is also occupied by the 
Texas pimpleback and Balcones spike.
    Subunit TXFF-5b: Upper Colorado River. The Upper Colorado River 
subunit consists of 10.3 river mi (16.6 river km) of the Colorado River 
near its confluence with the San Saba River in Lampasas, Mills, and San 
Saba Counties, Texas. This subunit extends from the County Road 124 
bridge and continues downstream to the U.S. Highway 190 bridge. 
Activities in the watershed are mostly agricultural. The river 
experiences periodic low flows from drought and upstream water 
withdrawals. The average daily flow rate of the upper Colorado River in 
this segment has been declining since the early 1920s. This subunit is 
currently occupied, and adjacent riparian lands are privately owned. 
All of the PBFs essential to the conservation of Texas fawnsfoot are 
present in this subunit, with the exception of appropriate flows 
throughout the year.
    The Upper Colorado River subunit is influenced by reservoir 
operations and chlorides and is being affected by ongoing agricultural 
activities and development, resulting in excessive sedimentation, water 
quality degradation, groundwater withdrawals and surface water 
diversions, and wastewater inputs. Therefore, special management 
considerations may be necessary to reduce sedimentation, improve water 
quality, maintain adequate flows, and improve habitat connectivity. 
This subunit is also occupied by the Texas pimpleback.

Guadalupe Orb

    We are designating approximately 288.5 river mi (464.3 river km) in 
two units, consisting of four subunits, as critical habitat for the 
Guadalupe orb. The critical habitat areas we describe below constitute 
our current best assessment of areas that meet the definition of 
critical habitat for Guadalupe orb. The two areas we are designating as 
critical habitat are: GORB-1: Upper Guadalupe River Unit and GORB-2: 
Lower Guadalupe River Unit. Table 12 shows the occupancy of the units, 
the ownership of adjacent riparian lands, and approximate length of the 
designated areas for the Guadalupe orb.

                        Table 12--Designated Critical Habitat Units for the Guadalupe Orb
----------------------------------------------------------------------------------------------------------------
                                                         Adjacent riparian                          River miles
               Unit                      Subunit             ownership            Occupancy        (Kilometers)
----------------------------------------------------------------------------------------------------------------
GORB-1: Upper Guadalupe River....  GORB-1a: South Fork  Private............  Occupied...........       5.1 (8.2)
                                    Guadalupe River.
                                   GORB-1b: Upper       Private............  Occupied...........    91.3 (147.0)
                                    Guadalupe River.    State/Local........                            5.8 (9.3)
GORB-2: Lower Guadalupe River....  GORB-2a: San Marcos  Private............  Occupied...........     60.2 (96.9)
                                    River.              State/Local........                            3.7 (5.9)
                                   GORB-2b: Lower       Private............  Occupied...........   116.7 (187.8)
                                    Guadalupe River.    State/Local........                            5.7 (9.2)
                                                                                                 ---------------
    Total........................  ...................  ...................  ...................   288.5 (464.3)
----------------------------------------------------------------------------------------------------------------
Note: Lengths may not sum due to rounding.

    We present brief descriptions of all units, and reasons why they 
meet the definition of critical habitat for Guadalupe orb, below.
Unit GORB-1: Upper Guadalupe River
    Subunit GORB-1a: South Fork Guadalupe River. The South Fork 
Guadalupe River subunit consists of 5.1 river mi (8.2 river km) of the 
South Fork Guadalupe River in Kerr County, Texas. This subunit extends 
from Griffin Road crossing just downstream of the Texas Highway 39 
crossing in Kerr County, to its confluence with the North Fork 
Guadalupe River. This subunit is occupied by the Guadalupe orb, and the 
adjacent riparian area is privately owned. This subunit is mostly rural 
and agricultural, with organized recreational camps. These camps often 
operate very low dams that form small impoundments along the subunit. 
The South Fork Guadalupe River subunit contains all of the PBFs 
essential to the conservation of the species. This subunit, combined 
with the Upper Guadalupe River subunit (GORB-1b), results in a highly 
resilient population with presence in several tributaries, protecting 
the population from a single stochastic event eliminating the entire 
population.
    The South Fork Guadalupe River subunit is in a mostly rural 
setting; is influenced by drought, low flows, and flooding (leading to 
scour); and is being affected by ongoing agricultural activities and 
development, resulting in excessive sedimentation, water quality 
degradation, and groundwater withdrawals and surface water diversions. 
Therefore, special management considerations may be necessary to reduce 
sedimentation, improve water quality, maintain adequate flows, and 
improve habitat connectivity.
    Subunit GORB-1b: Upper Guadalupe River. The Upper Guadalupe River 
subunit consists of 97.1 river mi (156.3 river km) of the Guadalupe 
River in Comal, Kendall, and Kerr Counties, Texas. This subunit extends 
from the confluence of the North and South Forks of the Guadalupe River 
downstream to the U.S. Highway 311 bridge in Comal County, Texas. The 
Upper Guadalupe River subunit is occupied by the Guadalupe orb, and 
ownership of adjacent riparian areas is approximately 95 percent 
private and 5 percent State/local government. At times, the subunit 
contains all the PBFs essential to the conservation of the Guadalupe 
orb. In recent years, Guadalupe orb individuals in this reach have 
experienced some of the highest and lowest flows on record, as well as 
water quality degradation (high temperature and low dissolved oxygen). 
Extreme high flows removed needed gravel and cobble in some locations, 
while extended low flow periods have caused suspended sediment to 
settle out in areas, reducing substrate quality for the Guadalupe orb.

[[Page 48081]]

    The Upper Guadalupe River subunit is in a mostly rural setting with 
some urbanization; is influenced by drought, low flows, and flooding 
(leading to scour); and is being affected by ongoing agricultural 
activities and development, resulting in excessive sedimentation, water 
quality degradation, groundwater withdrawals and surface water 
diversions, and wastewater inputs. Therefore, special management 
considerations may be necessary to reduce sedimentation, improve water 
quality, maintain adequate flows, and improve habitat connectivity. 
This subunit is also occupied by the Guadalupe fatmucket.
Unit GORB-2: Lower Guadalupe River
    Subunit GORB-2a: San Marcos River. The San Marcos River subunit 
consists of approximately 63.9 river mi (102.8 river km) in Caldwell, 
Gonzales, and Guadalupe Counties, Texas. The subunit extends from the 
FM 1977 bridge crossing in Caldwell County to the Guadalupe River 
confluence. The subunit is currently occupied by the Guadalupe orb, and 
ownership of adjacent riparian areas is approximately 94 percent 
private and 6 percent State/local government. The San Marcos River 
drains the City of San Marcos, including the campus of Texas State 
University, leading to impacts of urban runoff, wastewater inputs, and 
altered hydrology. The large San Marcos springs complex, the second 
largest in Texas, contributes significantly to the flows in this river 
and the lower Guadalupe River. This subunit contains all of the PBFs 
essential to the conservation of the species.
    The San Marcos River subunit is in a mostly rural setting with some 
urbanization; is downstream from an urban area; is influenced by 
drought, low flows, flooding (leading to scour), and wastewater 
discharges; and is being affected by ongoing agricultural activities 
and development, resulting in excessive sedimentation, water quality 
degradation, groundwater withdrawals and surface water diversions, and 
wastewater inputs. Therefore, special management considerations may be 
necessary to reduce sedimentation, improve water quality, maintain 
adequate flows, and improve habitat connectivity. This subunit is also 
occupied by the false spike.
    Subunit GORB-2b: Lower Guadalupe River. The Lower Guadalupe River 
subunit consists of approximately 122.4 river mi (197 river km) in 
DeWitt, Gonzales, and Victoria Counties, Texas. This subunit extends 
from the San Marcos River confluence downstream to the U.S. Highway 59 
bridge crossing near Victoria, Texas. The Lower Guadalupe River subunit 
is currently occupied by the Guadalupe orb, and ownership of adjacent 
riparian areas is approximately 95 private and 5 percent State/local 
government. This subunit contains all of the PBFs necessary for the 
Guadalupe orb and is the most resilient population known. Existing 
protections for the San Marcos and Comal Springs from the Edwards 
Aquifer Authority Habitat Conservation Plan provide some protection to 
spring flows. It is believed that these protected spring flows help 
ensure that flow rates and water quality are suitable for downstream 
mussel beds during times of drought and low flows.
    The Lower Guadalupe River subunit is in a mostly rural setting with 
some urbanization downstream from some urban areas; is influenced by 
reservoir operations, drought, low flows, flooding (leading to scour), 
and wastewater discharges; and is being affected by ongoing 
agricultural activities and development, resulting in excessive 
sedimentation, water quality degradation, groundwater withdrawals and 
surface water diversions, and wastewater inputs. Therefore, special 
management considerations may be necessary to reduce sedimentation, 
improve water quality, maintain adequate flows, and improve habitat 
connectivity. This subunit is also occupied by the false spike.

Texas Pimpleback

    We are designating approximately 374 river mi (602.1 river km) in 
five units, including eight subunits, as critical habitat for the Texas 
pimpleback. The critical habitat areas we describe below constitute our 
current best assessment of areas that meet the definition of critical 
habitat for the Texas pimpleback. The five areas we are designating as 
critical habitat are: TXPB-1: Elm Creek Unit; TXPB-2: Concho River 
Unit; TXPB-3: Upper Colorado River/Lower San Saba River Unit; TXPB-4: 
Upper San Saba River Unit; and TXPB-5: Llano River Unit. We are 
excluding Unit TXPB-6: Lower Colorado River (see Summary of Exclusions, 
below). Table 13 shows the occupancy of the units, the ownership of 
riparian lands, and approximate length of the designated areas for the 
Texas pimpleback.

                      Table 13--Designated Critical Habitat Units for the Texas Pimpleback
----------------------------------------------------------------------------------------------------------------
                                                         Adjacent riparian                          River miles
               Unit                      Subunit             ownership            Occupancy        (kilometers)
----------------------------------------------------------------------------------------------------------------
TXPB-1: Elm Creek................  TXPB-1a: Bluff       Private............  Occupied...........     11.6 (18.7)
                                    Creek.
                                   TXPB-1b: Lower.....  Private............  Occupied...........       0.4 (0.6)
                                   Elm Creek..........  State/Local........  ...................     11.9 (19.2)
TXPB-2: Concho River.............  TXPB-2a: Lower       Private............  Occupied...........     34.6 (55.7)
                                    Concho River.
                                   TXPB-2b: Upper.....  Private............  Unoccupied.........     15.2 (24.5)
                                   Concho River.......  State/Local........  ...................       0.3 (0.5)
TXPB-3. Upper Colorado River/      TXPB-3a: Upper       Private............  Occupied...........   150.4 (242.1)
 Lower San Saba River.              Colorado River.
                                   TXPB-3b: Lower.....  Private............  Occupied...........     48.6 (78.1)
                                   San Saba River.....  State/Local........  ...................
                                                                             0.6 (1.0)..........
TXPB-4: Upper San Saba River.....  ...................  Private............  Occupied...........     51.4 (82.7)
TXPB-5: Llano River..............  TXPB-5a: Upper       Private............  Occupied...........     37.2 (59.9)
                                    Llano River.
                                   TXPB-5b: Lower       Private............  Unoccupied.........     11.8 (19.1)
                                    Llano River.
                                                                                                 ---------------
    Total........................  ...................  ...................  ...................   374.0 (602.0)
----------------------------------------------------------------------------------------------------------------
Note: Lengths may not sum due to rounding.


[[Page 48082]]

    We present brief descriptions of all units, and reasons why they 
meet the definition of critical habitat for Texas pimpleback, below.
Unit TXPB-1: Elm Creek
    Subunit TXPB-1a: Bluff Creek. This occupied critical habitat 
subunit consists of 11.6 river mi (18.7 river km) of Bluff Creek, a 
tributary to Elm Creek, in Runnels County, Texas. The subunit extends 
from the County Road 153 bridge crossing, near the town of Winters, 
Texas, downstream to the confluences of Bluff and Elm creeks. The 
adjacent riparian area of this subunit is privately owned. This subunit 
is currently occupied by Texas pimpleback. This subunit contains all of 
the PBFs, although suitable substrate, flow, and water quality are 
degraded. The Bluff Creek subunit is in a rural setting; is influenced 
by drought, low flows, and elevated chlorides; and is being affected by 
ongoing agricultural activities and development resulting in excessive 
sedimentation, water quality degradation, and groundwater withdrawals 
and surface water diversions. Therefore, special management 
considerations may be necessary to reduce sedimentation, improve water 
quality, maintain adequate flows, and improve habitat connectivity. 
This subunit is also occupied by the Texas fatmucket.
    Subunit TXPB-1b: Lower Elm Creek. This subunit consists of 12.3 
river mi (19.8 river km) of Elm Creek beginning at the County Road 344 
crossing downstream to Elm Creek's confluence with the Colorado River 
in Runnels County, Texas. Ownership of the adjacent riparian areas is 
approximately 97 percent private and 3 percent State/local government. 
The Elm Creek watershed is relatively small and remains largely rural 
and dominated by agricultural practices. This stream regularly has 
extremely low or no flow during times of drought. Moreover, this stream 
has elevated chloride concentrations and sedimentation, resulting in 
reduced habitat quality and availability, as well as decreased water 
quality. Lower Elm Creek is occupied by the Texas pimpleback and 
contains some of the PBFs essential to the conservation of the species 
such as presence of host fish. Other PBFS are present but are in 
degraded condition and would benefit from management actions such as 
improving water quality and substrate quality. The Lower Elm Creek 
subunit is influenced by drought, low flows, and elevated chlorides, 
and is being affected by ongoing agricultural activities and 
development resulting in excessive sedimentation, water quality 
degradation, and groundwater withdrawals and surface water diversions. 
Therefore, special management considerations may be necessary to reduce 
sedimentation, improve water quality, maintain adequate flows, and 
improve habitat connectivity. This unit is also occupied by the Texas 
fatmucket.
    Even though the Elm Creek unit is smaller than 50 miles, which had 
been determined as the reach length long enough to withstand stochastic 
events, the populations in the Bluff Creek and Lower Elm Creek subunits 
(TXPB-1a and TXPB-1b) increase the species' redundancy, making it more 
likely to withstand catastrophic events that may eliminate one or more 
of the other populations.
Unit TXPB-2: Concho River
    Subunit TXPB-2a: Lower Concho River. The Lower Concho River subunit 
consists of approximately 34.6 river mi (55.7 river km) in Concho and 
Tom Green Counties, Texas. The Lower Concho River subunit extends from 
the FM 1692 bridge crossing downstream to the FM 1929 crossing. This 
subunit is occupied, and its adjacent riparian area is privately owned. 
The Lower Concho River subunit contains some of the PBFs essential to 
the conservation of the Texas pimpleback, such as some suitable 
substrate and the presence of host fish. However, the unit does not 
currently have sufficient water quality (e.g., water temperature is 
high and dissolved oxygen is low), and instream flow is too low at 
certain times of the year. Upstream reservoirs, built for flood control 
and municipal water storage, have contributed to a downward trend in 
normal river base-flows in recent years. The Lower Concho River subunit 
is in a mostly rural setting downstream from an urban area, is 
influenced by reservoir operations and chlorides, and is being affected 
by ongoing agricultural activities and development resulting in 
excessive sedimentation, water quality degradation, groundwater 
withdrawals and surface water diversions, and wastewater inputs. 
Therefore, special management considerations may be necessary to reduce 
sedimentation, improve water quality, maintain adequate flows, and 
improve habitat connectivity.
    Subunit TXPB-2b: Upper Concho River. Upper Concho River is not 
currently occupied by the Texas pimpleback, but is essential for the 
conservation of the species B. The Upper Concho River subunit consists 
of 15.5 river mi (25.0 river km) of the Concho River in Tom Green 
County, Texas, from the FM 380 bridge crossing, downstream of San 
Angelo, Texas, to the FM 1692 bridge where it adjoins subunit TXPB-2a. 
Ownership of the adjacent riparian areas is approximately 98 percent 
private and 2 percent State/local government.
    This subunit is essential to the conservation of the Texas 
pimpleback because it expands one of the smaller populations to a 
length that will be highly resilient to stochastic events; its loss 
would shrink the distribution of the Texas pimpleback and reduce 
redundancy of the species, limiting its viability. The Upper Concho 
River subunit is in a mostly rural setting with some urbanization 
downstream from an urban area; is influenced by reservoir operations, 
wastewater discharges, and chlorides; and is being affected by ongoing 
agricultural activities and development resulting in excessive 
sedimentation, water quality degradation, groundwater withdrawals and 
surface water diversions, and wastewater inputs.
    Although it is considered unoccupied, portions of this subunit 
contain some of the PBFs essential for the conservation of the species. 
Flowing water is not consistently at levels appropriate for Texas 
pimpleback in this subunit. Several upstream reservoirs divert the 
already limited flows, and reduced precipitation has resulted in an 
overall decrease in river flow rates. Management actions to increase 
stream flows in this subunit may be necessary for the Texas pimpleback 
population to be reestablished.
    Currently, appropriate substrates exist in isolated areas 
throughout this subunit. These isolated pockets of suitable habitat 
could allow for expansion and recolonization of the Texas pimpleback. 
However, future management actions that focus on habitat restoration in 
this reach to improve connectivity between habitat patches would 
improve the resiliency of this population, once restored.
    Currently, we believe appropriate host fishes occur throughout the 
subunit and will allow for reproduction of Texas pimpleback when the 
species is reestablished. Management actions could address any deficit 
in the abundance and distribution of fish hosts in this area, which 
would allow for expansion and future reestablishment of this subunit 
from the adjacent occupied subunit TXPB-2a.
    Water quality is degraded in this subunit. The Upper Concho River 
subunit, due in part to low flows and elevated water temperatures, 
experiences decreased levels of dissolved oxygen at such a level that 
could preclude mussel occupancy. We

[[Page 48083]]

believe these periods of low dissolved oxygen primarily occur during 
hot summer months when droughts are common. Therefore, management 
actions that increase flow rates would also improve water quality in 
this reach.
    Because this reach of the Concho River periodically contains the 
appropriate substrate conditions and host fish species used by the 
Texas pimpleback, it is habitat for the Texas pimpleback.
    If the Texas pimpleback can be reestablished in this reach, it will 
expand the occupied reach length in the Concho River to a length that 
will be more resilient to the stressors that the species is facing. The 
longer the reach occupied by a species, the more likely it is that the 
population can withstand stochastic events such as extreme flooding, 
dewatering, or water contamination. In the SSA report, we identified 50 
miles (80 km) as a reach long enough for a population to be able to 
withstand stochastic events, and the addition of this 15.5-mile reach 
to the 34.6-mile occupied section of the Concho River expands the 
existing Texas fawnsfoot population in the Concho River to 50.1 miles, 
achieving a length that allows for a highly resilient population to be 
reestablished, increasing the species' future redundancy. This subunit 
is essential for the conservation of the species because it provides 
habitat for range expansion in portions of known historical habitat, 
and thus will increase viability of the species by increasing its 
resiliency, redundancy, and representation.
Unit TXPB-3: Upper Colorado River and Lower San Saba River
    Subunit TXPB-3a: Upper Colorado River. The Upper Colorado River 
subunit consists of approximately 150.4 river mi (242.1 river km) in 
Brown, Coleman, Lampasas, McCulloch, Mills, and San Saba Counties, 
Texas. The subunit extends from the Coleman and McCulloch county line 
downstream to the confluence of the Colorado River and Cherokee Creek. 
The adjacent riparian area of this subunit is privately owned. The 
Upper Colorado River subunit is occupied by the Texas pimpleback and 
contains some of the PBFs essential to the conservation of the species, 
including host fishes in appropriate abundance and portions of suitable 
substrate. The subunit does not always provide sufficient flow rate or 
sufficient water quality (e.g., dissolved oxygen is often low, and 
temperature reaches unsuitably high levels during summer drought) to 
support the Texas pimpleback. The Upper Colorado River subunit is in a 
mostly rural setting; is influenced by reservoir operations and 
chlorides; and is being affected by ongoing agricultural activities and 
development resulting in excessive sedimentation, water quality 
degradation, groundwater withdrawals and surface water diversions, and 
wastewater inputs. Therefore, special management considerations may be 
necessary to reduce sedimentation, improve water quality, maintain 
adequate flows, and improve habitat connectivity. This subunit is also 
occupied by the Texas fawnsfoot.
    Subunit TXPB-3b: Lower San Saba River. The Lower San Saba River 
subunit consists of 49.2 river mi (79.1 river km) of the San Saba River 
in San Saba County, Texas. This subunit is currently occupied by the 
species, and the ownership of adjacent riparian areas is approximately 
99 percent private and 1 percent State/local government. The Lower San 
Saba River subunit extends from the Brady Creek confluence in San Saba 
County, Texas, downstream to the Colorado River confluence where it 
adjoins the Upper Colorado River subunit (TXPB-3a). This subunit 
contains all the PBFs essential to the conservation of the Texas 
pimpleback most of the year. This population contains evidence of 
recent Texas pimpleback reproduction, which is largely absent from the 
rest of the species' range.
    This subunit is primarily rural, with cattle grazing and irrigated 
orchards. Summer drought and water withdrawals cause occasional periods 
of low flow, which result in water quality degradation as water 
temperatures are high and dissolved oxygen is low. Additionally, high-
flow events during flooding can result in habitat scour and 
sedimentation. The Lower San Saba River subunit is experiencing some 
urbanization; is influenced by drought, low flows, and wastewater 
discharges; and is being affected by ongoing agricultural activities 
and development, resulting in excessive sedimentation, water quality 
degradation, groundwater withdrawals and surface water diversions, and 
wastewater inputs. Therefore, special management considerations may be 
necessary to reduce sedimentation, improve water quality, maintain 
adequate flows, and improve habitat connectivity. This subunit is also 
occupied by the Texas fawnsfoot and false spike.
Unit TXPB-4: Upper San Saba River
    The Upper San Saba River Unit consists of approximately 51.4 river 
mi (82.7 river km) of the San Saba River in Menard County, Texas. 
Adjacent riparian areas are privately owned. The Upper San Saba River 
Unit extends from the Schleicher County line near Fort McKavett, Texas, 
downstream to the FM 1311 bridge crossing in Menard, County, Texas. 
Texas pimpleback occupies the Upper San Saba River Unit in low 
densities. The Upper San Saba River Unit contains the PBFs essential to 
the conservation of the Texas pimpleback most of the year, although 
flows decline to low levels during summer drought. During these low 
flow periods, the PBFs of sufficient water flow and water quality may 
not be present, as low-flow conditions can lead to high water 
temperature and low dissolved oxygen. The Upper San Saba River Unit is 
in a rural setting; is influenced by drought, low flows, and underlying 
geology resulting in a losing reach; and is being affected by ongoing 
agricultural activities and development resulting in excessive 
sedimentation, water quality degradation, groundwater withdrawals and 
surface water diversions, and collection. Therefore, special management 
considerations may be necessary to reduce sedimentation, improve water 
quality, maintain adequate flows, and improve habitat connectivity. 
This subunit is also occupied by the Texas fatmucket.
Unit TXPB-5: Llano River
    Subunit TXPB-5a: Upper Llano River. The Upper Llano River subunit 
consists of approximately 37.2 river mi (59.9 river km) in Kimble and 
Mason Counties, Texas. Adjacent riparian areas are privately owned. 
This subunit extends from the Ranch Road RR 385 bridge crossing 
downstream to the U.S. Highway 87 bridge. This reach of the Llano River 
is largely rural, with much of the land in agricultural use. The Upper 
Llano River subunit is occupied by the Texas pimpleback and contains 
all the necessary PBFs essential to the conservation of the species 
most of the year. However, drought conditions and flooding in the Llano 
River can be extreme, causing the species to experience either extreme 
low-flow conditions with related reduced water quality or extreme high 
flows that mobilize substrate, eroding habitat or depositing sediment 
on Texas pimpleback populations. The Upper Llano River subunit is in a 
rural setting; is influenced by drought, low flows, and flooding 
(leading to scour); and is being affected by ongoing agricultural 
activities and development resulting in excessive sedimentation, water 
quality degradation, groundwater withdrawals and surface water 
diversions, and collection. Therefore, special management 
considerations may be

[[Page 48084]]

necessary to reduce sedimentation, improve water quality, maintain 
adequate flows, improve habitat connectivity, and manage collection. 
This subunit is also occupied by the Texas fatmucket.
    Subunit TXPB-5b: Lower Llano River. Lower Llano River is not 
currently occupied by the Texas pimpleback, but is essential for the 
conservation of the species . The Lower Llano River subunit consists of 
11.8 river mi (19.1 river km) of the Llano River in Mason County, 
Texas. This subunit extends from the U.S. Highway 87 bridge in Mason 
County downstream to the Mason and Llano county line. Adjacent riparian 
lands are privately owned.
    This subunit is essential to the conservation of the Texas 
pimpleback because it expands one of the smaller populations to a 
length that will be highly resilient to stochastic events in a separate 
tributary; this subunit increases the distribution of Texas pimpleback 
and increases redundancy of the species, improving its viability. The 
Lower Llano River subunit is in a rural setting; is influenced by 
drought, low flows, and flooding (leading to scour); and is being 
affected by ongoing agricultural activities and development, resulting 
in excessive sedimentation, water quality degradation, and groundwater 
withdrawals and surface water diversions.
    Although it is considered unoccupied, portions of this subunit 
contain some or all of the PBFs essential for the conservation of the 
species. Flowing water is generally sufficient in this subunit during 
portions of the year. However, in the past decade the Llano River has 
seen both the highest and lowest flow rates ever recorded, with 
extremely low water levels and stranding of mussels during low flow 
conditions and scour and entrainment of mussels with subsequent 
deposition over suitable habitat during floods. Spring inputs from the 
South Llano River help mitigate the effects of drought in the lower 
portions of the Llano River, although water withdrawals for 
agricultural operations contribute to decreased flows during drought. 
Ongoing management actions by resource management agencies and 
nonprofit organizations are contributing to restoring a natural flow 
regime.
    In the Llano River, suitable substrates exist as isolated riffles 
between larger pools. Given the hydrology of the Llano River Basin, 
suitable substrates have been degraded in portions of this subunit and 
will need restoration.
    The Texas pimpleback uses similar host fishes as the closely 
related Guadalupe orb, including channel catfish, flathead catfish, and 
tadpole madtom. Sufficiently abundant host fishes are present in the 
Lower Llano River subunit to support a population of Texas pimpleback.
    Water quality in the Lower Llano River subunit is generally 
sufficient for the species during portions of the year. However, 
dissolved oxygen declines and water temperature increases during 
periods of low flow. Management to ensure sufficient flow rates in this 
reach would improve water quality as well.
    Because this reach of the Llano River frequently contains the 
flowing water conditions, suitable substrates, and host fish species 
used by the Texas pimpleback, it is adequate habitat for the Texas 
pimpleback.
    If the Texas pimpleback can be reestablished in this reach, it will 
expand the occupied reach in the Llano River to a length that would be 
more resilient. The longer the reach occupied by a species, the more 
likely it is that the population can withstand stochastic events such 
as extreme flooding, dewatering, or water contamination. In the SSA 
report, we identified 50 miles (80 km) as a reach long enough for a 
population to be able to withstand stochastic events, and the addition 
of this 11.8-mile reach to the 37.2-mile occupied section of the Llano 
River expands the existing Texas pimpleback population in the Llano 
River to 49.0 miles, achieving a length that allows for a highly 
resilient population to be reestablished, thereby increasing the 
species' future redundancy. This unit is essential for the conservation 
of the species because it provides habitat for range expansion in 
portions of known historical habitat, and thus will increase viability 
of the species by increasing its resiliency, redundancy, and 
representation.
    This subunit is also occupied by the Texas fatmucket and Balcones 
spike.

Balcones Spike

    We are designating approximately 98.1 river mi (157.9 river km) in 
two units as critical habitat for Balcones spike. Each of the units is 
currently occupied by the species and contains all of the PBFs 
essential to the conservation of the species. The critical habitat 
areas we describe below constitute our current best assessment of areas 
that meet the definition of critical habitat for Balcones spike. The 
two areas we designate as critical habitat are: BASP-2: San Saba River 
Unit; and BASP-3: Llano River Unit. We are excluding Unit BASP-1: 
Little River (see Summary of Exclusions, below). Table 14 shows the 
occupancy of the units, the ownership of adjacent riparian lands, and 
approximate length of the designated areas for the Balcones spike. We 
present brief descriptions of all nits, and reasons why they meet the 
definition of critical habitat for Balcones spike, below.

                         Table 14--Designated Critical Habitat Units for Balcones Spike
----------------------------------------------------------------------------------------------------------------
                                                         Adjacent riparian                          River miles
               Unit                      Subunit             ownership            Occupancy        (kilometers)
----------------------------------------------------------------------------------------------------------------
BASP-2: San Saba River...........  ...................  Private............  Occupied...........     48.5 (78.0)
                                   ...................  State/Local........  ...................       0.6 (1.0)
BASP-3: Llano River..............  ...................  Private............  Occupied...........     49.0 (78.9)
                                                                                                 ---------------
    Total........................  ...................  ...................  ...................    98.1 (157.9)
----------------------------------------------------------------------------------------------------------------
Note: Lengths may not sum due to rounding.

    We present brief descriptions of all units, and reasons why they 
meet the definition of critical habitat for Balcones spike, below.
Unit BASP-2: San Saba River
    The San Saba River Unit consists of 49.1 river mi (79.0 river km) 
of the San Saba River in San Saba County, Texas. The unit extends from 
the San Saba River and Brady Creek confluence and continues downstream 
to the confluence of the San Saba and Colorado Rivers. Ownership of 
adjacent riparian area is approximately 99 percent private and 1 
percent State/local government. The unit is currently occupied by the 
species and contains all of the PBFs essential to the conservation of 
the Balcones spike.

[[Page 48085]]

Even though this unit is smaller than 50 miles, which we had determined 
was the reach length long enough to withstand stochastic events, this 
population increases the species' redundancy, making it more likely to 
withstand catastrophic events that may eliminate one or more of the 
other populations. The San Saba River subunit is in a rural setting; is 
influenced by drought, low flows, and wastewater discharges; and is 
being affected by ongoing agricultural activities and development 
resulting in excessive sedimentation, water quality degradation, 
groundwater withdrawals and surface water diversions, and wastewater 
inputs. Therefore, special management considerations may be necessary 
to reduce sedimentation, improve water quality, maintain adequate 
flows, and improve habitat connectivity. Much of the land use in the 
watershed is agricultural, and special management considerations or 
protection may be necessary to address excess nutrients, sediment, and 
pollutants that enter the San Saba River and reduce instream water 
quality. Sources of these types of pollution are wastewater, 
agricultural runoff, and urban stormwater runoff. Additional special 
management considerations or protection may be necessary in this unit 
to address low water levels that result from water withdrawals and 
drought, as well as excessive erosion. This subunit is also occupied by 
the Texas pimpleback.
Unit BASP-3: Llano River
    The Llano River Unit consists of 49 river mi (78.9 river km) of the 
Llano River in Kimble and Mason Counties, Texas. The Llano River Unit 
begins at the Ranch Road 385 bridge crossing in Kimble County and 
continues downstream to the Mason and Llano County line. The unit is 
occupied by the species, and surrounding riparian areas are privately 
owned. Even though this unit is smaller than 50 miles, which we had 
determined was the reach length long enough to withstand stochastic 
events, this population increases the species' redundancy, making it 
more likely to withstand catastrophic events that may eliminate one or 
more of the other populations. The majority of the Llano River Basin is 
rural and composed of agricultural operations that were historically 
used for sheep and goat ranching. During 2018, the Llano River 
experienced some of the largest floods and most severe drought within 
the same year. Extreme floods and drought conditions result in both 
stream bed mobilization, sedimentation, and dewatering. The Llano River 
Unit contains all the PBFs essential to the conservation of the 
Balcones spike. The Llano River unit is in a rural setting; is 
influenced by drought, low flows, and flooding (leading to scour); and 
is being affected by ongoing agricultural activities and development 
resulting in excessive sedimentation, water quality degradation, 
groundwater withdrawals and surface water diversions, and collection. 
Therefore, special management considerations may be necessary to reduce 
sedimentation, improve water quality, maintain adequate flows, improve 
habitat connectivity, and manage collection. This subunit is also 
occupied by the Texas fatmucket, Texas fawnsfoot, and Texas pimpleback.

False Spike

    We are designating approximately 143.6 river mi (231 river km) in 
one unit, consisting of two subunits, as critical habitat for the false 
spike. Each of the two subunits is currently occupied by the species 
and contains all of the PBFs essential to the conservation of the 
species. The critical habitat areas we describe below constitute our 
current best assessment of areas that meet the definition of critical 
habitat for false spike. The one area we designate as critical habitat 
is FASP-1: Guadalupe River Unit. Table 15 shows the occupancy of the 
units, the ownership of adjacent riparian lands, and approximate length 
of the designated areas for the false spike.

                           Table 15--Designated Critical Habitat Unit for False Spike
----------------------------------------------------------------------------------------------------------------
                                                         Adjacent riparian                          River miles
               Unit                      Subunit             ownership            Occupancy        (kilometers)
----------------------------------------------------------------------------------------------------------------
FASP-1: Guadalupe River..........  FASP-1a: San Marcos  Private............  Occupied...........     19.4 (31.1)
                                    River.
                                                        State/Local........  ...................       1.8 (2.9)
                                   FASP-1b: Guadalupe   Private............  Occupied...........   116.6 (187.7)
                                    River.
                                                        State/Local........  ...................       5.8 (9.3)
                                                                                                 ---------------
    Total........................  ...................  ...................  ...................   143.6 (231.0)
----------------------------------------------------------------------------------------------------------------
Note: Lengths may not sum due to rounding.

    We present a brief description of the unit, and reasons why it 
meets the definition of critical habitat for false spike, below.
Unit FASP-1: Guadalupe River
    Subunit FASP-1a: San Marcos River. This subunit consists of 21.2 
river mi (34 river km) of the San Marcos River in Gonzales County, 
Texas. The San Marcos River subunit begins at the FM 2091 bridge 
crossing within Palmetto State Park (Park Road 11) and continues for 
21.2 river mi downstream to the San Marcos River confluence with the 
Guadalupe River. Ownership of the adjacent riparian area is 
approximately 92 percent private and 8 percent State/local government; 
TPWD's Palmetto State Park occurs in the upstream reaches. The San 
Marcos River drains the City of San Marcos, including the campus of 
Texas State University, which causes the river to be impacted by urban 
runoff, wastewater inputs, and altered hydrology. The San Marcos 
springs complex, the second largest in Texas, contributes significantly 
to the flows in this river and the lower Guadalupe River. The lower San 
Marcos River watershed is characterized by agricultural land in the 
lower portion of the San Marcos River. The subunit is occupied by the 
false spike and contains all of the PBFs essential to the conservation 
of the species. Because the San Marcos River subunit is downstream from 
an urban area in a rural but urbanizing setting, it is influenced by 
wastewater discharges and ongoing development in the upper reaches 
associated with the Austin-Round Rock metropolitan area. It is also 
being affected by ongoing development and agricultural activities 
resulting in excessive sedimentation, water quality degradation, 
groundwater withdrawals and surface water diversions, and wastewater 
inputs. Therefore, special management may be necessary to reduce 
sedimentation, improve water quality, maintain adequate flows, and 
improve habitat connectivity. Special management considerations may be

[[Page 48086]]

necessary to address riparian bank sloughing, increased sedimentation, 
and pollutants from upstream urbanization and agricultural practices. 
This subunit is also occupied by the Guadalupe orb.
    Subunit FASP-1b: Guadalupe River. This subunit consists of 122.4 
river mi (197 river km) of the Guadalupe River in DeWitt, Gonzales, and 
Victoria Counties, Texas. The Guadalupe River subunit begins at the 
confluence of the Guadalupe and San Marcos Rivers and continues 
downstream for 122.4 river mi to the U.S. Highway 59 bridge near 
Victoria, Texas. Ownership of adjacent riparian areas is approximately 
98 percent private and 2 percent State/local. This subunit is occupied 
by the false spike and contains all of the PBFs essential to the 
conservation of the species. The Guadalupe River subunit is in a mostly 
rural but urbanizing setting; is influenced by reservoir releases (from 
Canyon and Guadalupe Valley) and flooding (leading to scour); and is 
being affected by ongoing development and agricultural activities 
resulting in excessive sedimentation, water quality degradation, 
groundwater withdrawals and surface water diversions, and wastewater 
inputs. Therefore, special management considerations may be necessary 
to reduce sedimentation, improve water quality, maintain adequate 
flows, and improve habitat connectivity. This subunit contains the most 
resilient known population of false spike. During times of drought, 
spring water influence from the Comal and San Marcos Rivers can 
contribute as much as 50 percent of the flows to the lower Guadalupe 
River. Continued protections for these spring systems are imperative 
for protecting mussel beds in the lower Guadalupe River. Special 
management considerations may be necessary to ensure low flows, 
sedimentation, and degraded water quality parameters do not worsen and 
contribute to future population decline. This subunit is also occupied 
by the Guadalupe orb.

Effects of Critical Habitat Designation

Section 7 Consultation

    Section 7(a)(2) of the Act requires Federal agencies, including the 
Service, to ensure that any action they authorize, fund, or carry out 
is not likely to jeopardize the continued existence of any endangered 
species or threatened species or result in the destruction or adverse 
modification of designated critical habitat of such species.
    We published a final rule revising the definition of destruction or 
adverse modification on August 27, 2019 (84 FR 44976). Destruction or 
adverse modification means a direct or indirect alteration that 
appreciably diminishes the value of critical habitat as a whole for the 
conservation of a listed species.
    Compliance with the requirements of section 7(a)(2) of the Act is 
documented through our issuance of:
    (1) A concurrence letter for Federal actions that may affect, but 
are not likely to adversely affect, listed species or critical habitat; 
or
    (2) A biological opinion for Federal actions that may affect, and 
are likely to adversely affect, listed species or critical habitat.
    When we issue a biological opinion concluding that a project is 
likely to jeopardize the continued existence of a listed species and/or 
destroy or adversely modify critical habitat, we provide reasonable and 
prudent alternatives to the project, if any are identifiable, that 
would avoid the likelihood of jeopardy and/or destruction or adverse 
modification of critical habitat. We define ``reasonable and prudent 
alternatives'' (at 50 CFR 402.02) as alternative actions identified 
during consultation that:
    (1) Can be implemented in a manner consistent with the intended 
purpose of the action,
    (2) Can be implemented consistent with the scope of the Federal 
agency's legal authority and jurisdiction,
    (3) Are economically and technologically feasible, and
    (4) Would, in the Service Director's opinion, avoid the likelihood 
of jeopardizing the continued existence of the listed species and/or 
avoid the likelihood of destroying or adversely modifying critical 
habitat.
    Reasonable and prudent alternatives can vary from slight project 
modifications to extensive redesign or relocation of the project. Costs 
associated with implementing a reasonable and prudent alternative are 
similarly variable.
    Regulations at 50 CFR 402.16 set forth requirements for Federal 
agencies to reinitiate consultation. Reinitiation of consultation is 
required and shall be requested by the Federal agency, where 
discretionary Federal involvement or control over the action has been 
retained or is authorized by law and: (1) if the amount or extent of 
taking specified in the incidental take statement is exceeded; (2) if 
new information reveals effects of the action that may affect listed 
species or critical habitat in a manner or to an extent not previously 
considered; (3) if the identified action is subsequently modified in a 
manner that causes an effect to the listed species or critical habitat 
that was not considered in the biological opinion or written 
concurrence; or (4) if a new species is listed or critical habitat 
designated that may be affected by the identified action. As provided 
in 50 CFR 402.16, the requirement to reinitiate consultations for new 
species listings or critical habitat designation does not apply to 
certain agency actions (e.g., land management plans issued by the 
Bureau of Land Management in certain circumstances).

Destruction or Adverse Modification of Critical Habitat

    The key factor related to the destruction or adverse modification 
determination is whether implementation of the proposed Federal action 
directly or indirectly alters the designated critical habitat in a way 
that appreciably diminishes the value of the critical habitat as a 
whole for the conservation of the listed species. As discussed above, 
the role of critical habitat is to support physical or biological 
features essential to the conservation of a listed species and provide 
for the conservation of the species.
    Section 4(b)(8) of the Act requires that our Federal Register 
notices ``shall, to the maximum extent practicable also include a brief 
description and evaluation of those activities (whether public or 
private) which, in the opinion of the Secretary, if undertaken may 
adversely modify [critical] habitat, or may be affected by such 
designation. ''Activities that may be affected by designation of 
critical habitat for the Guadalupe fatmucket, Texas fatmucket, Texas 
fawnsfoot, Guadalupe orb, Texas pimpleback, Balcones spike, and false 
spike include those that may affect the physical or biological features 
of these seven central Texas mussels' critical habitat (see Physical or 
Biological Features Essential to the Conservation of the Species).

Exemptions

Application of Section 4(a)(3) of the Act

    Section 4(a)(3)(B)(i) of the Act (16 U.S.C. 1533(a)(3)(B)(i)) 
provides that the Secretary shall not designate as critical habitat any 
lands or other geographical areas owned or controlled by the Department 
of Defense (DoD), or designated for its use, that are subject to an 
integrated natural resources management plan (INRMP) prepared under 
section 101 of the Sikes Act Improvement Act of 1997 (16 U.S.C. 670a), 
if the Secretary determines in writing that such plan provides a 
benefit to the species for which critical habitat is proposed for 
designation. There are no DoD lands with a completed INRMP

[[Page 48087]]

within the final critical habitat designation.

Consideration of Impacts Under Section 4(b)(2) of the Act

    Section 4(b)(2) of the Act states that the Secretary shall 
designate and make revisions to critical habitat on the basis of the 
best available scientific data after taking into consideration the 
economic impact, national security impact, and any other relevant 
impact of specifying any particular area as critical habitat. The 
Secretary may exclude an area from critical habitat based on economic 
impacts, impacts on national security, or any other relevant impacts. 
Exclusion decisions are governed by the regulations at 50 CFR 424.19 
and the Policy Regarding Implementation of Section 4(b)(2) of the 
Endangered Species Act (hereafter, the ``2016 Policy''; 81 FR 7226, 
February 11, 2016)--both of which were developed jointly with the 
National Marine Fisheries Service (NMFS). We also refer to a 2008 
Department of the Interior Solicitor's opinion entitled, ``The 
Secretary's Authority to Exclude Areas from a Critical Habitat 
Designation under Section 4(b)(2) of the Endangered Species Act'' (M-
37016). We explain each decision to exclude areas, as well as decisions 
not to exclude, to demonstrate that the decision is reasonable.
    The Secretary may exclude any particular area if she determines 
that the benefits of such exclusion outweigh the benefits of including 
such area as part of the critical habitat, unless she determines, based 
on the best scientific data available, that the failure to designate 
such area as critical habitat will result in the extinction of the 
species. In making the determination to exclude a particular area, the 
statute on its face, as well as the legislative history, are clear that 
the Secretary has broad discretion regarding which factor(s) to use and 
how much weight to give to any factor.
    We describe below the process that we undertook for deciding 
whether to exclude any areas--taking into consideration each category 
of impacts and our analysis of the relevant impacts.

Exclusions Based on Economic Impacts

    Section 4(b)(2) of the Act and its implementing regulations require 
that we consider the economic impact that may result from a designation 
of critical habitat. In order to consider economic impacts, we prepared 
an incremental effects memorandum (IEM) and screening analysis which, 
together with our narrative and interpretation of effects, we consider 
our economic analysis of the critical habitat designation and related 
factors (IEc 2019, entire). The analysis, dated December 4, 2019, was 
made available for public review from August 26, 2021, through October 
25, 2021 (see 86 FR 47916). The economic analysis addressed probable 
economic impacts of critical habitat designation for the central Texas 
mussels. Following the close of the comment period, we reviewed and 
evaluated all information submitted during the comment period that may 
pertain to our consideration of the probable incremental economic 
impacts of this critical habitat designation. Additional information 
relevant to the probable incremental economic impacts of critical 
habitat designation for the seven central Texas mussels is summarized 
below and available in the screening analysis (IEc 2019, entire), 
available at https://www.regulations.gov.
    Executive Orders (E.O.s) 12866 and 13563 direct Federal agencies to 
assess the costs and benefits of available regulatory alternatives in 
quantitative (to the extent feasible) and qualitative terms. Executive 
Order 14094 reaffirms the principles of E.O. 12866 and E.O. 13563 and 
states that regulatory analysis should facilitate agency efforts to 
develop regulations that serve the public interest, advance statutory 
objectives, and are consistent with E.O. 12866, E.O. 13563, and the 
Presidential Memorandum of January 20, 2021 (Modernizing Regulatory 
Review). Consistent with the E.O. regulatory analysis requirements, our 
effects analysis under the Act may take into consideration impacts to 
both directly and indirectly affected entities, where practicable and 
reasonable. If sufficient data are available, we assess to the extent 
practicable the probable impacts to both directly and indirectly 
affected entities. As part of our screening analysis, we considered the 
types of economic activities that are likely to occur within the areas 
affected by the critical habitat designations. In our December 4, 2019, 
IEM describing probable incremental economic impacts that may result 
from the designations, we first identified probable incremental 
economic impacts associated with each of the following categories of 
activities: (1) Federal lands management (National Park Service, U.S. 
Forest Service, Department of Defense); (2) agriculture; (3) forest 
management/silviculture/timber; (4) development; (5) recreation; (6) 
restoration activities; and (7) transportation. We considered each 
industry or category individually. Additionally, we considered whether 
the activities have any Federal involvement. Critical habitat 
designation generally will not affect activities that do not have any 
Federal involvement; under the Act, designation of critical habitat 
only affects activities conducted, funded, permitted, or authorized by 
Federal agencies. When this rule is effective (see DATES, above), in 
areas where the central Texas mussels are present, under section 7 of 
the Act, Federal agencies will be required to consult with the Service 
on activities they fund, permit, or implement that may affect the 
species. Consultations to avoid the destruction or adverse modification 
of critical habitat will be incorporated into the existing consultation 
process.
    In our IEM, we attempted to clarify the distinction between the 
effects that result from the species being listed and those 
attributable to the critical habitat designations (i.e., difference 
between the jeopardy and adverse modification standards) for the 
central Texas mussels. Because the designation of critical habitat is 
being promulgated concurrently with the listing, it has been our 
experience that it is more difficult to discern which conservation 
efforts are attributable to the species being listed and those which 
will result solely from the designation of critical habitat. However, 
the following specific circumstances in this case help to inform our 
evaluation: (1) The essential physical or biological features 
identified for critical habitat are the same features essential for the 
life requisites of the species, and (2) any actions that would result 
in sufficient harm or harassment to constitute jeopardy to the central 
Texas mussels would also likely adversely affect the essential physical 
or biological features of critical habitat. The IEM outlines our 
rationale concerning this limited distinction between baseline 
conservation efforts and incremental impacts of the designations of 
critical habitat for these species. This evaluation of the incremental 
effects has been used as the basis to evaluate the probable incremental 
economic impacts of these designations of critical habitat.
    The critical habitat designations for the central Texas mussels 
total approximately 1,577.5 river mi (2,538.7 river km) in 20 units 
with a combination of occupied and unoccupied areas. In occupied areas, 
any actions that may affect the species or their habitat would likely 
also affect critical habitat, and it is unlikely that any additional 
conservation efforts would be required to address the adverse 
modification standard over and above those recommended as necessary to 
avoid

[[Page 48088]]

jeopardizing the continued existence of the species. Therefore, the 
only additional costs that are expected in the occupied critical 
habitat designations are administrative costs, due to the fact that 
this additional analysis will require time and resources by both the 
Federal action agency and the Service. However, it is believed that, in 
most circumstances, these costs will not reach the threshold of 
``significant'' under E.O. 12866. We anticipate incremental costs of 
section 7 consultations in occupied critical habitat to total less than 
$75,000 per year.
    In unoccupied critical habitat, any costs of section 7 
consultations will not be incurred due to the listing of the species, 
but instead due to the critical habitat designation. We are designating 
four subunits that are currently unoccupied by the central Texas 
mussels. We anticipate approximately five new formal section 7 
consultations to occur in the next 10 years in these subunits. 
Considering the costs of formal consultation as well as project 
modifications that arise from consultation, we project consultations in 
unoccupied critical habitat to cost approximately $15,000 per 
consultation.
    In total, in both occupied and unoccupied critical habitat, we 
expect the total cost of critical habitat designations not to exceed 
$82,500 per year.
    We considered the economic impacts of the critical habitat 
designation. The Secretary is not exercising her discretion to exclude 
any areas from this designation of critical habitat for the seven 
central Texas mussels based on economic impacts.

Exclusions Based on Impacts on National Security and Homeland Security

    In preparing this rule, we determined that there are no lands 
within the designated critical habitat for the central Texas mussels 
that are owned or managed by the DoD or Department of Homeland 
Security, and, therefore, we anticipate no impact on national security 
or homeland security. We did not receive any additional information 
during the public comment period for the proposed designation regarding 
impacts of the designation on national security or homeland security 
that would support excluding any specific areas from the final critical 
habitat designation under authority of section 4(b)(2) and our 
implementing regulations at 50 CFR 424.19, as well as the 2016 Policy.

Exclusions Based on Other Relevant Impacts

    Under section 4(b)(2) of the Act, we consider any other relevant 
impacts, in addition to economic impacts and impacts on national 
security discussed above. To identify other relevant impacts that may 
affect the exclusion analysis, we consider a number of factors, 
including whether there are permitted conservation plans covering the 
species in the area such as HCPs, safe harbor agreements, or CCAAs, or 
whether there are non-permitted conservation agreements and 
partnerships that would be encouraged by designation of, or exclusion 
from, critical habitat. In addition, we look at whether Tribal 
conservation plans or partnerships, Tribal resources, or government-to-
government relationships of the United States with Tribal entities may 
be affected by the designation. We also consider any State, local, 
social, or other impacts that might occur because of the designation.
    When identifying the benefits of inclusion for an area, we consider 
the additional regulatory benefits that area would receive due to the 
protection from destruction or adverse modification as a result of 
actions with a Federal nexus, the educational benefits of mapping 
essential habitat for recovery of the listed species, and any benefits 
that may result from a designation due to State or Federal laws that 
may apply to critical habitat.
    In the case of Texas fawnsfoot, Texas pimpleback, and Balcones 
spike, the benefits of critical habitat include public awareness of the 
presence of these species and the importance of habitat protection, 
and, where a Federal nexus exists, increased habitat protection for 
Texas fawnsfoot, Texas pimpleback, and Balcones spike due to protection 
from destruction or adverse modification of critical habitat.
    When identifying the benefits of exclusion, we consider, among 
other things, whether exclusion of a specific area is likely to result 
in conservation, or in the continuation, strengthening, or 
encouragement of partnerships. Additionally, continued implementation 
of an ongoing management plan that provides conservation equal to or 
more than the protections that result from a critical habitat 
designation would reduce those benefits of including that specific area 
in the critical habitat designation.
    We evaluate the existence of a conservation plan when considering 
the benefits of inclusion. We consider a variety of factors, including, 
but not limited to, whether the plan is finalized; how it provides for 
the conservation of the essential physical or biological features; 
whether there is a reasonable expectation that the conservation 
management strategies and actions contained in a management plan will 
be implemented into the future; whether the conservation strategies in 
the plan are likely to be effective; and whether the plan contains a 
monitoring program or adaptive management to ensure that the 
conservation measures are effective and can be adapted in the future in 
response to new information.
    After identifying the benefits of inclusion and the benefits of 
exclusion, we carefully weigh the two sides to evaluate whether the 
benefits of exclusion outweigh those of inclusion. If our analysis 
indicates that the benefits of exclusion outweigh the benefits of 
inclusion, we then determine whether exclusion would result in 
extinction of the species. If exclusion of an area from critical 
habitat will result in extinction, we will not exclude it from the 
designation.
    Based on the information provided by entities seeking exclusion, as 
well as additional public comments we received, and the best scientific 
data available, we evaluated whether certain river mi in units TXFF-3, 
TXFF-4,TXFF-6, TXFF-7, TXFF-8, TXPB-6, and BASP-1 (see table 16, below) 
are appropriate for exclusion from this final designation under section 
4(b)(2) of the Act. This analysis indicates that the benefits of 
excluding areas from the final designation outweigh the benefits of 
designating those areas as critical habitat; thus, the Secretary is 
exercising her discretion to exclude the areas from the final 
designation. In the paragraphs below, we provide a detailed balancing 
analysis of the areas being excluded under section 4(b)(2) of the Act.

Private or Other Non-Federal Conservation Plans Related to Permits 
Under Section 10 of the Act

    Habitat conservation plans (HCPs) for incidental take permits under 
section 10(a)(1)(B) of the Act provide for partnerships with non-
Federal entities to minimize and mitigate impacts to listed species and 
their habitats. In some cases, HCP permittees agree to do more for the 
conservation of the species and their habitats on private lands than 
designation of critical habitat would provide alone. We place great 
value on the partnerships that are developed during the preparation and 
implementation of HCPs.
    Candidate conservation agreements with assurances (CCAAs) and safe 
harbor agreements (SHAs) are voluntary agreements designed to conserve

[[Page 48089]]

candidate and listed species, respectively, on non-Federal lands. In 
exchange for actions that contribute to the conservation of species on 
non-Federal lands, participating property owners are covered by an 
``enhancement of survival'' permit under section 10(a)(1)(A) of the 
Act, which authorizes incidental take of the covered species that may 
result from implementation of conservation actions, specific land uses, 
and, in the case of SHAs, the option to return to a baseline condition 
under the agreements. We also provide enrollees assurances that we will 
not impose further land-, water-, or resource-use restrictions, or 
require additional commitments of land, water, or finances, beyond 
those agreed to in the agreements.
    When we undertake a discretionary section 4(b)(2) exclusion 
analysis based on permitted conservation plans such as CCAAs, SHAs, and 
HCPs, we anticipate consistently excluding such areas if incidental 
take caused by the activities in those areas is covered by the permit 
under section 10 of the Act and the CCAA/SHA/HCP meets all of the 
following three factors (see the 2016 Policy for additional details):
    a. The permittee is properly implementing the CCAA/SHA/HCP and is 
expected to continue to do so for the term of the agreement. A CCAA/
SHA/HCP is properly implemented if the permittee is, and has been, 
fully implementing the commitments and provisions in the CCAA/SHA/HCP, 
implementing agreement, and permit.
    b. The species for which critical habitat is being designated is a 
covered species in the CCAA/SHA/HCP, or very similar in its habitat 
requirements to a covered species. The recognition that we extend to 
such an agreement depends on the degree to which the conservation 
measures undertaken in the CCAA/SHA/HCP would also protect the habitat 
features of the similar species.
    c. The CCAA/SHA/HCP specifically addresses that species' habitat 
and meets the conservation needs of the species in the planning area.
    We conducted exclusion analyses on the BRA Agreement, LCRA 
Agreement, and TRA Agreement, which are presented below.
The Brazos River Authority Candidate Conservation Agreement With 
Assurances for the Balcones Spike and Texas Fawnsfoot in the Brazos 
River Basin
    We have determined that the BRA Agreement fulfills the above 
criteria, through the following actions:
    (i) The permittee (BRA) has implemented or is in the process of 
implementing conservation measures agreed upon as part of the CCAA, 
including, but not limited to, conducting knowledge gap surveys, 
providing public comment on projects in the basin that may affect the 
covered species or their habitats, and preparing appropriate drought 
contingency and long-term monitoring plans.
    (ii) The finalized CCAA includes the Balcones spike and Texas 
fawnsfoot as covered species.
    (iii) The CCAA specifically identifies conservation measures to be 
implemented within habitats included within proposed critical habitat 
stream reaches. This includes the implementation of avoidance and 
minimization measures as well as applied research to inform future 
stream and habitat management efforts.
    Therefore, we are excluding certain non-Federal lands covered by 
this plan that provide for the conservation of the Texas fawnsfoot and 
Balcones spike, as further explained below.
    In 2021, the Brazos River Authority submitted the BRA Agreement as 
part of an application for an enhancement-of-survival permit under 
section 10(a)(1)(A) of the Act. The BRA Agreement benefits freshwater 
mussels and concurrently other native aquatic species in the Brazos 
River Basin through facilitating studies, minimizing impacts, and 
conserving populations and habitat. The BRA Agreement is between the 
Brazos River Authority and the Service (collectively, ``the Parties''). 
The BRA Agreement covers eligible, non-Federal lands within the Brazos 
River Authority management area in the Brazos River Basin. Non-Federal 
lands are those lands owned by non-Federal landowners, which include, 
but are not limited to, State, Tribal, regional, or local governments; 
private or nonprofit organizations; or private citizens.
    The conservation goals of the BRA Agreement are to improve the 
health of existing populations of the Texas fawnsfoot and Balcones 
spike in the Brazos River Basin. Under the BRA Agreement, cooperators 
will avoid construction or other development impacts to instream 
habitat used by the Texas fawnsfoot and Balcones spike, will complete 
applied research and advocate for increased water quality and water 
quantity protections for these covered species, and will assist with 
habitat conservation for the remainder of the term of the BRA 
Agreement.
    Expected outcomes of implementing the BRA Agreement include the 
protection and study of instream habitat; completion of modeling that 
will guide future efforts to improve water quality and quantity; 
reduction of erosion and sedimentation; and research and monitoring to 
gain further understanding of existing Texas fawnsfoot and Balcones 
spike populations and the threats to them throughout the term of the 
BRA Agreement. The propagation activities included in the BRA Agreement 
will also increase probability that the Texas fawnsfoot, Balcones 
spike, and other covered species will expand their ranges and survive 
and recruit new cohorts in reintroduced areas. The BRA Agreement in its 
entirety can be found at: https://www.fws.gov/library/collections/candidate-conservation-agreement-assurances-balcones-spike-and-texas-fawnsfoot.
    Benefits of Inclusion--BRA Agreement Proposed Units TXFF-3, TXFF-4, 
and BASP-1: The principal benefit of including an area in critical 
habitat designation is the requirement of Federal agencies to ensure 
that actions that they fund, authorize, or carry out are not likely to 
result in the destruction or adverse modification of any designated 
critical habitat, which is the regulatory standard of section 7(a)(2) 
of the Act under which consultation is completed. In areas where a 
listed species occurs, Federal agencies must consult with the Service 
on actions that may affect a listed species, and refrain from actions 
that are likely to jeopardize the continued existence of such species. 
The analysis of effects to critical habitat is a separate and different 
analysis from that of the effects to the species. Therefore, the 
difference in outcomes of these two analyses represents the regulatory 
benefit of critical habitat. For some cases, the outcome of these 
analyses will be similar, because effects to habitat will often result 
in effects to the species. This situation applies to proposed Units 
TXFF-3 and TXFF-4 for the Texas fawnsfoot and Unit BASP-1 for the 
Balcones spike because the species currently occupy the units 
considered for exclusion. Additionally, the areas that we considered 
for exclusion do not contain any land where such a nexus would exist. 
Therefore, the benefit of including these areas in the critical habitat 
designation to further protect the species and their habitats via 
consultation is minimal.
    In section 9.4 of the CCAA, BRA agrees to conservation measures 
that implement avoidance and minimization measures in streams reaches 
included in the proposed critical habitat segments. These measures 
include: (1) The agreement to not construct additional dams in the 
mainstem Brazos River or Little River; (2) the agreement to not

[[Page 48090]]

sponsor any infrastructure or diversion projects in Zone A (includes 
portions of the Little River, San Gabriel River, or Brushy Creek); and 
(3) the agreement to conduct the necessary mussel surveys in Zones B 
and C to guide placement of infrastructure to minimize disturbance to 
populations of covered species and their habitats. The CCAA also notes 
that if new populations of covered species are discovered in the basin, 
conservation zones and the associated avoidance and minimization 
measures will be reevaluated. Due to the implementation of these 
avoidance and minimization measures for the covered species and their 
habitats, the benefit of including these proposed units in the final 
critical habitat designation to further protect the species and its 
habitat via consultation is minimal.
    Another possible benefit of designating lands as critical habitat 
is public education regarding the potential conservation value of an 
area that may help focus conservation efforts on areas of high 
conservation value for certain species. We consider any information 
about the Texas fawnsfoot, Balcones spike, and their habitats that 
reaches a wide audience, including parties engaged in conservation 
activities, to be valuable. Designation of critical habitat would 
provide educational benefits by informing Federal agencies and the 
public about the presence of listed species for all units.
    In summary, we find that the benefits of inclusion of approximately 
413.8 river mi (666.0 river km) in proposed Units TXFF-3 and TXFF-4 of 
waterways within the Brazos River Basin for the Texas fawnsfoot and 
approximately 79.2 river mi (127.5 river km) in proposed Unit BASP-1 of 
waterways within the Brazos River Basin for the Balcones spike are 
educational benefits for the Texas fawnsfoot, Balcones spike, and their 
habitats.
    Benefits of Exclusion--BRA Agreement Proposed Units TXFF-3, TXFF-4, 
and BASP-1: The benefits of excluding 413.8 river mi (666.0 river km) 
in the Brazos River Basin for the Texas fawnsfoot and 79.2 river mi 
(127.5 river km) in the Brazos River Basin for the Balcones spike under 
the BRA Agreement from the designation of critical habitat are 
substantial and include: (1) Continuance and strengthening of our 
effective working relationship with partners to promote voluntary, 
proactive conservation of the Texas fawnsfoot, Balcones spike, and 
their habitats; (2) allowance for continued meaningful collaboration 
and cooperation in working toward species recovery, including 
conservation benefits that might not otherwise occur; and (3) 
encouragement of developing additional conservation and management 
plans in the future for other federally listed and sensitive species.
    Partnerships with non-Federal landowners are vital to the 
conservation of at-risk species, especially on non-Federal lands; 
therefore, the Service is committed to supporting and encouraging such 
partnerships through the recognition of positive conservation 
contributions. TPWD reviewed the BRA Agreement while it was in 
development and has ensured the identified conservation activities are 
necessary and advisable. In the case considered here, excluding these 
areas from critical habitat will help foster the partnerships the 
landowners and land managers in question have developed with Federal 
and State agencies and local conservation organizations; will encourage 
the continued implementation of voluntary conservation actions for the 
benefit of the Texas fawnsfoot, Balcones spike, and their habitats on 
these lands; and may also serve as a model and aid in fostering future 
cooperative relationships with other parties here and in other 
locations for the benefit of other endangered or threatened species. 
Therefore, we consider the positive effect of excluding from critical 
habitat areas managed by active conservation partners to be a 
significant benefit of exclusion.
    Benefits of Exclusion Outweigh the Benefits of Inclusion--BRA 
Agreement Proposed Units TXFF-3, TXFF-4, and BASP-1: We evaluated the 
exclusion of 413.8 river mi (666.0 river km) of waterways adjacent to 
private land for the Texas fawnsfoot and 79.2 river mi (127.5 river km) 
of waterways adjacent to private land for the Balcones spike within the 
areas covered by the BRA Agreement from our designation of critical 
habitat, and we determined the benefits of excluding these lands 
outweigh the benefits of including them as critical habitat for the 
Texas fawnsfoot and Balcones spike.
    The BRA CCAA includes a variety of management, communication and 
education, and applied research conservation measures targeting these 
excluded critical habitat units. Some of these measures include, but 
are not limited to, the completion of additional hydrologic modeling on 
a repeating 5-year basis in the basin to identify the areas of the 
basin that are at highest risk of drought-associated low flow 
conditions and associated water management scenarios. As part of the 
CCAA, the BRA also implemented an extensive public outreach campaign to 
inform and educate private landowners of their covered species, the 
threats that they are experiencing in the basin, and ways in which they 
can promote the conservation of these species and their habitats. Most 
importantly, the BRA will maintain environmental flows included in 
their Water Management Plan and incorporate data from proposed applied 
research into the thermal tolerances of their covered species into an 
adaptive management process to provide conservation benefits to the 
species. The agreement also states that as new data become available 
regarding the flow needs of the covered species, they will work with 
the TCEQ to integrate these data into future updates of the Texas 
Environmental Flow Standards for Surface Water.
    We conclude that the additional regulatory and educational benefits 
of including these lands in the critical habitat designation are 
relatively small, because of the low likelihood of a Federal nexus 
occurring on private lands. These benefits are further reduced by the 
existence of the BRA Agreement and the conservation measures described 
above, which address many of the threats the species face in this area. 
We anticipate that there would be little additional Federal regulatory 
benefit to designating critical habitat for the species on private land 
because there is a low likelihood that these areas will have Federal 
activities requiring section 7 consultation. Additionally ongoing 
management activities as a result of the BRA Agreement obviate any 
additional requirements pursuant to a consultation that addresses 
critical habitat. Because any conservation actions that do result from 
consultations would already be required due to the presence of the 
species, there would be few or no additional actions required from the 
presence of critical habitat. Furthermore, the potential educational 
and informational benefits of critical habitat designation on areas 
containing the PBFs essential to the conservation of the Texas 
fawnsfoot and Balcones spike would be minimal, because the Brazos River 
Authority has demonstrated their knowledge of the species and its 
habitat needs in the process of developing their partnership with the 
Service.
    In contrast, the benefits derived from excluding the areas managed 
by these owners and enhancing our partnership with the Brazos River 
Authority are significant. Because voluntary conservation efforts for 
the benefit of the species on non-Federal lands are so valuable, the 
Service considers the maintenance and encouragement of

[[Page 48091]]

conservation partnerships to be a significant benefit of exclusion. The 
development and maintenance of effective working partnerships with non-
Federal partners for the conservation of at-risk species is 
particularly important in areas such as Texas, a State with relatively 
little Federal landownership but many species of conservation concern. 
Excluding these areas from critical habitat will help foster the 
partnerships in question that have been have developed with Federal and 
State agencies and local conservation organizations and will encourage 
the continued implementation of voluntary conservation actions for the 
benefit of the Texas fawnsfoot, Balcones spike, and their habitats in 
the Brazos River Basin. The current active conservation efforts on some 
of these areas contribute to our knowledge of the species through 
monitoring and scientific research. In addition, these partnerships not 
only provide a benefit for the conservation of these species but may 
also serve as a model and aid in fostering future cooperative 
relationships with other parties in Texas and in other locations for 
the benefit of other endangered or threatened species.
    We find that excluding areas from critical habitat that are 
receiving both long-term conservation and management for the purpose of 
protecting the habitat that supports the Texas fawnsfoot and Balcones 
spike will preserve our external partnerships in Texas and will 
encourage future collaboration towards conservation and recovery of 
listed species. The partnership benefits are significant and outweigh 
the small potential regulatory, educational, and ancillary benefits of 
including the land in the final critical habitat designation for the 
Texas fawnsfoot or Balcones spike. Therefore, the BRA Agreement 
provides greater protection of habitat for the Texas fawnsfoot and 
Balcones spike than could be gained through the project-by-project 
analysis of a critical habitat designation.
    Exclusion Will Not Result in Extinction of the Species--BRA 
Agreement Proposed Units TXFF-3, TXFF-4, and BASP-1: We determined that 
the exclusion of 413.8 river mi (666.0 river km) of waterways adjacent 
to private land for the Texas fawnsfoot and 79.2 river mi (127.5 river 
km) of waterways adjacent to private land for the Balcones spike within 
the boundaries of the Brazos River Basin covered by the BRA Agreement 
will not result in extinction of the taxa. Protections afforded to the 
species and their habitat by the BRA Agreement provide assurances that 
the species will not go extinct as a result of excluding these lands 
from the critical habitat designation.
    An important consideration as we evaluate these exclusions and 
their potential effect on the species in question is that critical 
habitat does not carry with it a regulatory requirement to restore or 
actively manage habitat for the benefit of listed species; the 
regulatory effect of critical habitat is only the avoidance of 
destruction or adverse modification of critical habitat should an 
action with a Federal nexus occur. It is, therefore, advantageous for 
the conservation of the species to support the proactive efforts of 
non-Federal landowners who are contributing to the enhancement of 
essential habitat features for listed species through exclusion. The 
jeopardy standard of section 7 of the Act will also provide protection 
in these occupied areas when there is a Federal nexus. Therefore, based 
on the above discussion, the Secretary is exercising her discretion to 
exclude approximately 413.8 river mi (666.0 river km) of waterways from 
the designation of critical habitat for the Texas fawnsfoot and 
approximately 79.2 river mi (127.5 river km) of waterways from the 
designation of critical habitat for the Balcones spike.
Candidate Conservation Agreement With Assurances for the Texas 
Pimpleback, Texas Fawnsfoot, Texas Fatmucket, and Balcones Spike in the 
Lower Colorado River Basin Below O.H. Ivie Reservoir
    We have determined that the LCRA Agreement fulfills the above 
criteria, through the following actions:
    (i) The permittees (LCRA and LCRA Transmission Services Corporation 
(TSC)) have implemented or are in the process of implementing 
conservation measures agreed upon as part of the CCAA, including, but 
not limited to, the continuation of water-quality monitoring in key 
reaches of the basin, providing adequate water for environmental flows 
protection, and funding of applied mussel restoration assessment 
research for the Texas pimpleback.
    (ii) The finalized CCAA includes the Texas pimpleback and Texas 
fawnsfoot, as well as the Texas fatmucket and Balcones spike, as 
covered species.
    (iii) The CCAA specifically identifies conservation measures to be 
implemented within habitats included within proposed critical habitat 
stream reaches. This includes the implementation of avoidance and 
minimization measures, maintenance of flows ensuring environmental 
flows protection, and applied research to inform future population 
restoration and stream and habitat management efforts.
    Therefore, we are excluding certain non-Federal lands covered by 
this plan that provide for the conservation of the Texas pimpleback and 
Texas fawnsfoot.
    In 2023, the Lower Colorado River Authority (LCRA) and Lower 
Colorado River Authority Transmission Services Corporation (LCRA TSC) 
submitted the LCRA Agreement as part of an application for an 
enhancement-of-survival permit under section 10(a)(1)(A) of the Act. 
The LCRA Agreement benefits freshwater mussels and concurrently other 
native aquatic species in the lower Colorado River Basin through 
facilitating studies, minimizing impacts, and conserving populations 
and habitat. The LCRA Agreement is between the Lower Colorado River 
Authority, the Lower Colorado River Authority Transmission Services 
Corporation, and the Service (collectively, ``the Parties''). The LCRA 
Agreement covers eligible non-Federal lands within the Lower Colorado 
River Authority management area in the lower Colorado River Basin. Non-
Federal lands are those lands owned by non-Federal landowners which 
include, but are not limited to, State, Tribal, regional, or local 
governments; private or nonprofit organizations; or private citizens.
    The conservation goals of the LCRA Agreement are to improve the 
health of existing populations of the Texas pimpleback, Texas 
fawnsfoot, Texas fatmucket, and Balcones spike populations in the lower 
Colorado River Basin and to reestablish one population of each of the 
covered species in the lower Colorado River Basin. Under the LCRA 
Agreement, cooperators will avoid construction or other development 
impacts to instream habitat available to the Texas pimpleback, Texas 
fawnsfoot, Texas fatmucket, and Balcones spike; will complete applied 
research and advocate for increased water quality and water quantity 
protections for the Texas pimpleback, Texas fawnsfoot, Texas fatmucket, 
and Balcones spike; and will assist with habitat conservation for the 
remainder of the term of the LCRA Agreement.
    Expected outcomes of implementing the LCRA Agreement include 
protection and study of instream habitat, completion of studies to 
guide future efforts to improve water quality and quantity, reduction 
of erosion and sedimentation, and research and monitoring to gain 
further

[[Page 48092]]

understanding of existing Texas pimpleback, Texas fawnsfoot, Texas 
fatmucket, and Balcones spike populations and the threats to them 
throughout the term of the LCRA Agreement. The conservation activities 
included in the LCRA Agreement increase the probability that the Texas 
pimpleback, Texas fawnsfoot, Texas fatmucket, and Balcones spike will 
expand their ranges, survive, and recruit new cohorts. The Agreement in 
its entirety can be found at: https://www.fws.gov/media/signed-ccaa-six-species-trinity-river-basin.
    Benefits of Inclusion--LCRA Agreement Proposed Units TXPB-6 and 
TXFF-6: The principal benefit of including an area in a critical 
habitat designation is the requirement of Federal agencies to ensure 
that actions that they fund, authorize, or carry out are not likely to 
result in the destruction or adverse modification of any designated 
critical habitat, which is the regulatory standard of section 7(a)(2) 
of the Act under which consultation is completed. In areas where a 
listed species occurs, Federal agencies must consult with the Service 
on actions that may affect a listed species, and refrain from actions 
that are likely to jeopardize the continued existence of such species. 
The analysis of effects to critical habitat is a separate and different 
analysis from that of the effects to the species. Therefore, the 
difference in outcomes of these two analyses represents the regulatory 
benefit of critical habitat. For some cases, the outcome of these 
analyses will be similar, because effects to habitat will often result 
in effects to the species. This situation applies to Unit TXPB-6 for 
the Texas pimpleback and Unit TXFF-6 for the Texas fawnsfoot because 
the species currently occupy the units considered for exclusion. 
Critical habitat designation may provide a regulatory benefit for the 
Texas pimpleback or the Texas fawnsfoot on lands covered under the LCRA 
Agreement when there is a Federal nexus present for a project that 
might adversely modify critical habitat. However, the areas that are 
considered for exclusion do not contain any land where such a Federal 
nexus would exist.
    In section 7.2 of the CCAA, LCRA and LCRA TSC agree to implement 
avoidance and minimization measures in designated management zones that 
include reaches of the proposed critical habitat segments. These 
measures include (1) completing appropriate mussel surveys and 
relocations in intermittent or perennial Zone A or Zone B stream 
reaches prior to initiating any disturbances associated with covered 
activities; (2) avoiding the placement of any new infrastructure in 
areas that are occupied by mussel beds unless agreed upon by the 
Service that the placement is necessary for the implementation of other 
conservation measures; and (3) implementing appropriate erosion and 
sediment control measures, minimizing vegetation clearing in riparian 
zones, and restoring streambanks, streambeds, and vegetation following 
site-level disturbances. Due to the implementation of these avoidance 
and minimization measures for the covered species and their habitats as 
well as the agreement to complete appropriate mussel survey and 
relocation efforts, the benefit of including these proposed units in 
the critical habitat designation to further protect the species and its 
habitat via consultation is minimal.
    Another possible benefit of designating lands as critical habitat 
is public education regarding the potential conservation value of an 
area that may help focus conservation efforts on areas of high 
conservation value for certain species. We consider any information 
about the Texas pimpleback, the Texas fawnsfoot, and their habitats 
that reaches a wide audience, including parties engaged in conservation 
activities, to be valuable. Designation of critical habitat would 
provide educational benefits by informing Federal agencies and the 
public about the presence of listed species for all units.
    In summary, we find that the benefits of inclusion of approximately 
108.9 river mi (175.2 river km) in proposed Unit TXPB-6 of waterways 
within the lower Colorado River Basin for the Texas pimpleback and 
approximately 121.8 river mi (196.0 river km) in proposed Unit TXFF-6 
of waterways within the lower Colorado River Basin for the Texas 
fawnsfoot are: (1) A regulatory benefit when there is a Federal nexus 
present for a project that might adversely modify critical habitat; and 
(2) educational benefits for the Texas pimpleback, Texas fawnsfoot, and 
their habitats.
    Benefits of Exclusion--LCRA Agreement Proposed Units TXPB-6 and 
TXFF-6: The benefits of excluding 108.9 river mi (175.2 river km) in 
the lower Colorado River Basin for the Texas pimpleback and 121.8 river 
mi (196.0 river km) in the lower Colorado River Basin for the Texas 
fawnsfoot under the LCRA Agreement from the designation of critical 
habitat are substantial and include: (1) Continuance and strengthening 
of our effective working relationship with partners to promote 
voluntary, proactive conservation of the Texas pimpleback, Texas 
fawnsfoot, and their habitats as opposed to reactive regulation; (2) 
allowance for continued meaningful collaboration and cooperation in 
working toward species recovery, including conservation benefits that 
might not otherwise occur; and (3) encouragement of developing 
additional conservation and management plans in the future for other 
federally listed and sensitive species. Additionally, partnerships with 
non-Federal landowners are vital to the conservation of at-risk 
species, especially on non-Federal lands; therefore, the Service is 
committed to supporting and encouraging such partnerships through the 
recognition of positive conservation contributions. In the case 
considered here, excluding these areas from critical habitat will help 
foster the partnerships the landowners and land managers in question 
have developed with Federal and State agencies and local conservation 
organizations; will encourage the continued implementation of voluntary 
conservation actions for the benefit of the Texas pimpleback, the Texas 
fawnsfoot, and their habitats on these lands; and may also serve as a 
model and aid in fostering future cooperative relationships with other 
parties here and in other locations for the benefit of other endangered 
or threatened species. Therefore, we consider the positive effect of 
excluding from critical habitat areas managed by active conservation 
partners to be a significant benefit of exclusion.
    Benefits of Exclusion Outweigh the Benefits of Inclusion--LCRA 
Agreement Proposed Units TXPB-6 and TXFF-6: We evaluated the exclusion 
of 108.9 river mi (175.2 river km) of waterways adjacent to private 
land for the Texas pimpleback and 121.8 river mi (196.0 river km) of 
waterways adjacent to private land for the Texas fawnsfoot within the 
areas covered by the LCRA Agreement from our designation of critical 
habitat, and we determined the benefits of excluding these areas 
outweigh the benefits of including them as critical habitat for the 
Texas pimpleback and the Texas fawnsfoot.
    The LCRA CCAA includes a variety of management, communication and 
education, and applied research conservation measures targeting these 
excluded critical habitat units. Some of these measures include, but 
are not limited to, the preparation of a drought management plan and 
facilitation of a water quality monitoring program in the basin to 
identify potential areas of stress or stranding of covered mussel 
species during low flow conditions. As part of

[[Page 48093]]

the CCAA, the LCRA and LCRA TSC also committed to providing comments to 
notifications of proposed construction projects occurring in 
Conservation Zones A and B where covered mussel species may be present. 
In these comments, the LCRA and LCRA TSC will include language 
notifying the responsible parties of the likelihood of presence of the 
covered species and encourage avoidance of disturbance of the covered 
species and their habitats. Most importantly, the LCRA and LCRA TSC 
will maintain environmental flows included in their Water Management 
Plan and incorporate data from proposed applied research into the 
thermal tolerances of the covered species into an adaptive management 
process to provide conservation benefits to the species. The agreement 
also states that as new data become available regarding the flow needs 
of the covered species, the LCRA and LCRA TSC will integrate new 
scientific information in future amendments of their Water Management 
Plan.
    We conclude that the additional regulatory and educational benefits 
of including these lands in the critical habitat designation are few, 
because the Act's requirements under section 7 will already apply on 
these private lands due to the known presence of the species. These 
benefits are further reduced by the existence of the LCRA Agreement. We 
anticipate that there would be little additional Federal regulatory 
benefit to the taxa on private land because there is a low likelihood 
that those parcels will be negatively affected to any significant 
degree by Federal activities requiring section 7 consultation, and 
ongoing management activities indicate there would be no additional 
requirements pursuant to a consultation that addresses critical habitat 
that would not already be in place due to the species' presence.
    Furthermore, the potential educational and informational benefits 
of critical habitat designation on areas containing the PBFs essential 
to the conservation of the Texas pimpleback and the Texas fawnsfoot 
would be minimal, because the Lower Colorado River Authority has 
demonstrated their knowledge of the species and their habitat needs in 
the process of developing their partnerships with the Service.
    In contrast, the benefits derived from excluding the areas managed 
by these owners and enhancing our partnership with the Lower Colorado 
River Authority is significant. Because voluntary conservation efforts 
for the benefit of species on non-Federal lands are so valuable, the 
Service considers the maintenance and encouragement of conservation 
partnerships to be a significant benefit of exclusion. The development 
and maintenance of effective working partnerships with non-Federal 
partners for the conservation of at-risk species is particularly 
important in areas such as Texas, a State with relatively little 
Federal landownership and many species of conservation concern. 
Excluding these areas from critical habitat will help foster the 
partnerships in question that have been developed with Federal and 
State agencies and local conservation organizations and will encourage 
the continued implementation of voluntary conservation actions for the 
benefit of the Texas pimpleback, Texas fawnsfoot, and their habitats in 
the lower Colorado River Basin. The current active conservation efforts 
on some of these areas contribute to our knowledge of the species 
through monitoring and scientific research. In addition, these 
partnerships not only provide a benefit for the conservation of these 
species but may also serve as a model and aid in fostering future 
cooperative relationships with other parties in Texas and in other 
locations for the benefit of other endangered or threatened species.
    We find that excluding areas from this critical habitat designation 
that are receiving both long-term conservation and management for the 
purpose of protecting the habitat that supports the Texas pimpleback 
and Texas fawnsfoot will preserve our external partnerships in Texas 
and will encourage future collaboration towards conservation and 
recovery of listed species. The partnership benefits are significant 
and outweigh the small potential regulatory, educational, and ancillary 
benefits of including the land in the final critical habitat 
designation for the Texas pimpleback or Texas fawnsfoot. Therefore, the 
LCRA Agreement provides greater protection of habitat for the Texas 
pimpleback and the Texas fawnsfoot than could be gained through the 
project-by-project analysis under a critical habitat designation.
    Exclusion Will Not Result in Extinction of the Species--LCRA 
Agreement Proposed Units TXPB-6 and TXFF-6: We determined that the 
exclusion of 108.9 river mi (175.2 river km) of waterways adjacent to 
private land for the Texas pimpleback and 121.8 river mi (196.0 river 
km) of waterways adjacent to private land for the Texas fawnsfoot 
within the boundaries of the lower Colorado River Basin covered by the 
LCRA Agreement will not result in extinction of the taxa. Protections 
afforded to the species and its habitat by the LCRA Agreement provide 
assurances that the species will not go extinct as a result of 
excluding these lands from the critical habitat designation.
    An important consideration as we evaluate these exclusions and 
their potential effect on the species in question is that critical 
habitat does not carry with it a regulatory requirement to restore or 
actively manage habitat for the benefit of listed species; the 
regulatory effect of critical habitat is only the avoidance of 
destruction or adverse modification of critical habitat should an 
action with a Federal nexus occur. It is, therefore, advantageous for 
the conservation of the species to support the proactive efforts of 
non-Federal landowners who are contributing to the enhancement of 
essential habitat features for listed species through exclusion. The 
jeopardy standard of section 7 of the Act will also provide protection 
in these occupied areas when there is a Federal nexus. Therefore, based 
on the above discussion, the Secretary is exercising her discretion to 
exclude approximately 108.9 river mi (175.2 river km) of waterways from 
the designation of critical habitat for the Texas pimpleback and 
approximately 121.8 river mi (196.0 river km) of waterways from the 
designation of critical habitat for the Texas fawnsfoot.
Candidate Conservation Agreement With Assurances for Six Species in the 
Trinity River Basin
    We have determined that the TRA Agreement fulfills the above 
criteria, through the following actions:
    (i) The permittees (TRA, North Texas Municipal Water District, City 
of Dallas, City of Fort Worth) have implemented or are in the process 
of implementing conservation measures agreed upon as part of the CCAA, 
including, but not limited to, the continued implementation of large-
scale watershed protection plans, participation in the U.S. Army Corps 
of Engineers Sustainable Rivers Project, and making proactive efforts 
to protect the aquatic environment. An example of this effort is the 
implementation of capital improvement programs that include watershed 
and sewer system modeling to ensure existing infrastructure meets 
future wastewater needs and reduces the risk of instream habitat 
degradation.
    (ii) The finalized CCAA includes the Texas fawnsfoot as a covered 
species.
    (iii) The CCAA specifically identifies conservation measures to be 
implemented within habitats included within proposed critical habitat 
stream reaches. This includes the

[[Page 48094]]

implementation of avoidance and minimization measures, maintenance of 
flows ensuring environmental flows protection, and applied research to 
inform future population restoration and stream and habitat management 
efforts.
    Therefore, we have determined that the TRA Agreement fulfills the 
above criteria, and we are excluding certain Federal and non-Federal 
lands impacted or covered by this plan that provide for the 
conservation of the Texas fawnsfoot, as further explained below.
    In 2023, the Trinity River Authority (TRA) and other permit 
applicants submitted the TRA Agreement as part of an application for an 
enhancement-of-survival permit under section 10(a)(1)(A) of the Act. 
The TRA Agreement benefits freshwater mussels and concurrently other 
native aquatic species in the Trinity River Basin through research and 
monitoring, minimization and avoidance of impacts, and conservation of 
Texas fawnsfoot populations and habitat. The Agreement is between the 
Trinity River Authority and the Service (collectively ``the Parties''). 
The TRA Agreement covers eligible, non-Federal lands within the Trinity 
River Basin that are under the control of the Trinity River Authority, 
or their partners enrolled through certificates of inclusion (covered 
parties). Non-Federal lands are those lands owned by non-Federal 
landowners which include, but are not limited to, State, Tribal, 
regional, or local governments; private or nonprofit organizations; or 
private citizens. There are 3.4 river mi (5.5 river km) within the 
larger covered area of the TRA Agreement that are enrolled in the 
Wetland Reserve Enhancement Partnership (WREP) through the U.S. 
Department of Agriculture Natural Resources Conservation Service (USDA 
NRCS) While these river miles are outside of TRA's authority and are 
not directly covered under the TRA Agreement, we anticipate that the 
TRA Agreement's conservation benefits, in addition to the on-site 
conservation management activities implemented through the WREP will 
remain throughout those areas. This is because conservation actions 
implemented under the TRA Agreement are occurring directly upstream and 
downstream of those enrolled areas. These stream segments are 2 percent 
of the total area excluded from critical habitat designation.
    The conservation goals of the TRA Agreement include reducing 
threats to freshwater mussels and improving the viability of Texas 
fawnsfoot. Under the TRA Agreement, covered parties will avoid or 
minimize impacts to instream habitat used by the Texas fawnsfoot, will 
complete applied research and monitoring, will advocate for increased 
water quality and water quantity protections for the Texas fawnsfoot, 
and will assist with habitat conservation and restoration for the 10-
year term of the TRA Agreement.
    Expected outcomes of implementing the TRA Agreement include the 
conservation, restoration, and study of instream habitat; completion of 
studies that will guide future efforts to improve water quality and 
quantity and to reduce erosion and sedimentation; and research and 
monitoring to gain further understanding of existing Texas fawnsfoot 
populations and the threats to them throughout the term of the TRA 
Agreement. The conservation activities included in the TRA Agreement 
will increase the viability of Texas fawnsfoot by increasing the 
resiliency of Texas fawnsfoot populations in the Trinity River Basin. 
The TRA Agreement in its entirety can be found at: https://www.fws.gov/media/20231026usfws-final-lcra-ccaard-signedlcra-signedpdf.
    Benefits of Inclusion--TRA Agreement Proposed Units TXFF-7 and 
TXFF-8: The principal benefit of including an area in a critical 
habitat designation is the requirement of Federal agencies to ensure 
that actions that they fund, authorize, or carry out are not likely to 
result in the destruction or adverse modification of any designated 
critical habitat, which is the regulatory standard of section 7(a)(2) 
of the Act under which consultation is completed. In areas where a 
listed species occurs, Federal agencies must consult with the Service 
on actions that may affect a listed species, and refrain from actions 
that are likely to jeopardize the continued existence of such species. 
The analysis of effects to critical habitat is a separate and different 
analysis from that of the effects to the species. Therefore, the 
difference in outcomes of these two analyses represents the regulatory 
benefit of critical habitat. For some cases, the outcome of these 
analyses will be similar, because effects to habitat will often result 
in effects to the species. This situation applies to Units TXFF-7 and 
TXFF-8 for the Texas fawnsfoot because the species currently occupies 
the units considered for exclusion. Critical habitat designation may 
provide a regulatory benefit for the Texas fawnsfoot on areas covered 
under the TRA Agreement when there is a Federal nexus present for a 
project that might adversely modify critical habitat. The WREP program 
conservation activities focus on wetland restoration in areas that 
occur adjacent to the river and do not include instream components. 
While there may be a Federal nexus for consultation on restoration 
activities, these activities will not occur within the Ordinary High 
Water Mark of the river, and therefore will not overlap the areas 
considered for exclusion.
    In section 8.10 of the CCAA, TRA and the other applicants agree to 
implement avoidance and minimization measures for areas that include 
the covered species, which include reaches of the proposed critical 
habitat segments. These measures include (1) the avoidance of mussel 
beds within defined Conservation Priority Areas when the implementation 
of covered activities requires Clean Water Act (33 U.S.C. 1251 et seq.) 
section 404 permitting and consultation between the USACE and Service; 
(2) the completion of appropriate mussel surveys and relocations 
consistent with the latest Service and TPWD sampling protocols prior to 
initiating any site-level disturbances; and (3) implementation of 
appropriate erosion and sediment control measures, minimization of 
vegetation clearing in riparian zones and streambed disturbances (as 
feasible), and implementation of natural channel design into stream 
construction projects. Due to the implementation of these avoidance and 
minimization measures for the covered species and their habitats, as 
well as the agreement to complete appropriate mussel survey and 
relocation efforts, the benefit of including the proposed units in the 
critical habitat designation to further protect the species and its 
habitat via consultation is minimal.
    Another possible benefit of designating lands as critical habitat 
is public education regarding the potential conservation value of an 
area that may help focus conservation efforts on areas of high 
conservation value. We consider any information about the Texas 
fawnsfoot and its habitats that reaches a wide audience, including 
parties engaged in conservation activities, to be valuable. Designation 
of critical habitat would provide educational benefits by informing 
Federal agencies and the public about the presence of Texas fawnsfoot 
in each unit. In summary, we find that the benefits of inclusion of 
approximately 169.3 river mi (272.5 river km) in proposed Units TXFF-7 
and Unit TXFF-8 of waterways within the Trinity River Basin for the 
Texas fawnsfoot are: (1) A regulatory benefit when there is a Federal 
nexus present for a project that might adversely modify critical 
habitat; and (2) educational benefits for the Texas fawnsfoot and its 
habitat.

[[Page 48095]]

    Benefits of Exclusion--TRA Agreement Proposed Units TXFF-7 and 
TXFF-8: The benefits of excluding 169.3 river mi (272.5 river km) in 
the Trinity River Basin for the Texas fawnsfoot under the TRA Agreement 
from the designation of critical habitat are substantial and include: 
(1) Continuance and strengthening of our effective working relationship 
with partners to promote voluntary, proactive conservation of the Texas 
fawnsfoot and its habitats as opposed to reactive regulation; (2) 
allowance for continued meaningful collaboration and cooperation in 
working toward species recovery, including conservation benefits that 
might not otherwise occur; and (3) encouragement of developing 
additional conservation and management plans in the future for other 
federally listed and sensitive species.
    According to some, the designation of critical habitat on (or 
adjacent to) private lands may reduce the likelihood that landowners 
will support and carry out conservation actions (Main et al. 1999, pp. 
1,263-1265; Bean 2002, p. 412). The magnitude of this negative outcome 
is greatly amplified in situations where active management measures 
(such as reintroduction, fire management, and control of invasive 
species) are necessary for species conservation (Bean 2002, pp. 412-
414). We find that the exclusion of these specific areas from the 
critical habitat designation for the Texas fawnsfoot can contribute to 
the species' recovery and provide a superior level of conservation than 
critical habitat can provide alone. We find that, where consistent with 
the discretion provided by the Act, it is necessary to implement 
policies that provide positive incentives to private landowners to 
voluntarily conserve natural resources and remove or reduce 
disincentives to conservation (Wilcove et al. 1996, pp. 1-15; Bean 
2002, entire).
    Additionally, partnerships with non-Federal landowners are vital to 
the conservation of at-risk species, especially on non-Federal lands; 
therefore, the Service is committed to supporting and encouraging such 
partnerships through the recognition of positive conservation 
contributions. In the case considered here, excluding these areas from 
critical habitat will help foster the partnerships that landowners and 
land managers have developed with Federal and State agencies and local 
conservation organizations; will encourage the continued implementation 
of voluntary conservation actions for the benefit of the Texas 
fawnsfoot and its habitat on these lands; and may also serve as a model 
and aid in fostering future cooperative relationships with other 
parties here and in other locations for the benefit of other endangered 
or threatened species. Therefore, we consider the positive effect of 
excluding from critical habitat designation those areas managed by 
active conservation partners to be a significant benefit of exclusion.
    Benefits of Exclusion Outweigh the Benefits of Inclusion--TRA 
Agreement Proposed Units TXFF-7 and TXFF-8: We evaluated the exclusion 
of 169.3 river mi (272.5 river km) of waterways for the Texas fawnsfoot 
within the areas covered by the TRA Agreement from our designation of 
critical habitat, and we determined the benefits of excluding these 
areas outweigh the benefits of including them as critical habitat for 
the Texas fawnsfoot.
    The TRA CCAA includes a variety of management, communication and 
education, and applied research conservation measures targeting these 
excluded critical habitat units. Some of these measures include, but 
are not limited to, the guaranteed continuation of an instream water 
quality sampling program that can aid in identifying potential external 
threats to the covered species or opportunities to implement 
operational changes that would improve water quality conditions for the 
covered species. As part of the CCAA, the TRA and other permit 
applicants also committed to increasing public awareness of the covered 
species and the threats they face through the development and 
dissemination of a conservation message, materials, and curricula. 
These will include language notifying the responsible parties of the 
likelihood of the presence of the covered species and will encourage 
avoidance of disturbance of the covered species and their habitats. 
Most importantly, the TRA Agreement commits to maintaining 
environmental flows within the basin and includes the implementation of 
instream flow protections between Lake Livingston and the Coastal Water 
Authority canal. This targeted effort will ensure there are adequate 
flows for an 86.5-mile stretch of the Trinity River during times of 
drought conditions. The TRA Agreement also states that as new data 
become available regarding the flow needs of the covered species, they 
will integrate new scientific information in future amendments of their 
Water Management Plan.
    We conclude that the additional regulatory and educational benefits 
of including these lands in the critical habitat designation are few, 
because the Act's requirements under section 7 will already apply on 
these private lands due to the known presence of the species. These 
benefits are further reduced by the existence of the TRA Agreement. We 
anticipate that there would be little additional Federal regulatory 
benefit to the species on private land because there is a low 
likelihood that those parcels will be negatively affected to any 
significant degree by Federal activities requiring section 7 
consultation, and ongoing management activities indicate there would be 
no additional requirements pursuant to a consultation that addresses 
critical habitat that would not already be in place due to the species' 
presence.
    Furthermore, the potential educational and informational benefits 
of critical habitat designation on areas containing the PBFs essential 
to the conservation of the Texas fawnsfoot would be minimal, because 
the Trinity River Authority has demonstrated its knowledge of the 
species and the species' habitat needs in the process of developing its 
partnership with the Service.
    In contrast, the benefits derived from excluding the areas managed 
by TRA and enhancing our partnership with TRA is significant. Because 
voluntary conservation efforts for the benefit of species on non-
Federal lands are so valuable, the Service considers the maintenance 
and encouragement of conservation partnerships to be a significant 
benefit of exclusion. The development and maintenance of effective 
working partnerships with non-Federal partners for the conservation of 
at-risk species is particularly important in areas such as Texas, a 
State with relatively little Federal land ownership and many species of 
conservation concern. Excluding these areas from critical habitat will 
help foster the partnerships that have been developed with Federal and 
State agencies and local conservation organizations and will encourage 
the continued implementation of voluntary conservation actions for the 
benefit of the Texas fawnsfoot and its habitats in the Trinity River 
Basin. The current active conservation efforts on these areas 
contribute to our knowledge of the species through monitoring and 
scientific research. In addition, these partnerships not only provide a 
benefit for the conservation of the Texas fawnsfoot but may also serve 
as a model and aid in fostering future cooperative relationships with 
other parties in Texas and in other locations for the benefit of other 
endangered or threatened species.
    We find that excluding areas from critical habitat designation that 
are

[[Page 48096]]

receiving both long-term conservation and management for the purpose of 
protecting the habitat that supports the Texas fawnsfoot will preserve 
our external partnerships in Texas and will encourage future 
collaboration towards conservation and recovery of listed species. The 
partnership benefits are significant and outweigh the small potential 
regulatory, educational, and ancillary benefits of including the areas 
in the final critical habitat designation for the Texas fawnsfoot. 
Therefore, the TRA Agreement provides greater protection of habitat for 
the Texas fawnsfoot than could be gained through the project-by-project 
analysis under a critical habitat designation.
    Exclusion Will Not Result in Extinction of the Species--TRA 
Agreement Proposed Units TXFF-7 and TXFF-8: We determined that the 
exclusion of 169.3 river mi (272.5 river km) of waterways for the Texas 
fawnsfoot within the boundaries of the Trinity River Basin covered by 
the TRA Agreement will not result in extinction of the species. 
Protections afforded to the species and its habitat by the TRA 
Agreement provide assurances that the species will not go extinct as a 
result of excluding these lands from the critical habitat designation.
    An important consideration as we evaluate these exclusions and 
their potential effect on the species in question is that critical 
habitat does not carry with it a regulatory requirement to restore or 
actively manage habitat for the benefit of listed species; the 
regulatory effect of critical habitat is only the avoidance of 
destruction or adverse modification of critical habitat should an 
action with a Federal nexus occur. It is, therefore, advantageous for 
the conservation of the species to support the proactive efforts of 
non-Federal landowners who are contributing to the enhancement of 
essential habitat features for listed species through exclusion. The 
jeopardy standard of section 7 of the Act will also provide protection 
in these occupied areas when there is a Federal nexus. Therefore, based 
on the above discussion, the Secretary is exercising her discretion to 
exclude approximately 169.3 river mi (272.5 river km) of waterways from 
the designation of critical habitat for the Texas fawnsfoot.

Summary of Exclusions

    As discussed above, based on the information provided by entities 
seeking exclusion, existence of private or non-Federal conservation 
plans, as well as any additional public comments we received, we 
evaluated whether certain lands in the proposed critical habitat were 
appropriate for exclusion from this final designation pursuant to 
section 4(b)(2) of the Act. We are excluding certain areas from 
critical habitat designation for the Texas fawnsfoot, Texas pimpleback, 
and Balcones spike; table 16, below, provides the approximate areas 
(mi, km) that meet the definition of critical habitat but which we are 
excluding under section 4(b)(2) of the Act from the final critical 
habitat designation.

   Table 16--Areas Excluded by Critical Habitat Unit for Texas Fawnsfoot, Texas Pimpleback, and Balcones Spike
----------------------------------------------------------------------------------------------------------------
                                                                     Proposed
                                                                     critical      Area excluded  Final critical
           Species                   Unit            Subunit        habitat (mi      (mi (km))      habitat (mi
                                                                       (km))                           (km))
----------------------------------------------------------------------------------------------------------------
Texas fawnsfoot..............  TXFF-3: Lower     TXFF-3a: Lower    340.5 (548.0)  340.5 (548.0)s               0
                                Brazos River.     Brazos River.
                                                 TXFF-3b:            38.5 (62.0)     38.5 (62.0)               0
                                                  Navasota River.
                               TXFF-4: Little    ...............     34.8 (56.0)     34.8 (56.0)               0
                                River.
                               TXFF-6: Lower     ...............   121.8 (196.0)   121.8 (196.0)               0
                                Colorado River.
                               TXFF-7: East      ...............     15.4 (24.8)     15.4 (24.8)               0
                                Fork Trinity
                                River.
                               TXFF-8: Trinity   ...............   153.9 (247.7)   153.9 (247.7)               0
                                River.
Texas pimpleback.............  TXPB-6: Lower     ...............   108.9 (175.2)   108.9 (175.2)               0
                                Colorado River.
Balcones spike...............  BASP-1: Little    BASP-1a: Little     34.8 (56.0)     34.8 (56.0)               0
                                River.            River.
                                                 BASP-1b: San        30.7 (49.4)     30.7 (49.4)               0
                                                  Gabriel River.
                                                 BASP-1c: Brushy     13.7 (22.1)     13.7 (22.1)               0
                                                  Creek.
----------------------------------------------------------------------------------------------------------------

Required Determinations

Regulatory Planning and Review (Executive Orders 12866, 13563, and 
14094)

    Executive Order (E.O.) 12866, as reaffirmed by E.O. 13563 and E.O. 
14094, provides that the Office of Information and Regulatory Affairs 
(OIRA) in the Office of Management and Budget (OMB) will review all 
significant rules. OIRA has determined that this rule is not 
significant.
    Executive Order 14094 reaffirms the principles of E.O. 12866 and 
E.O. 13563 and states that regulatory analysis should facilitate agency 
efforts to develop regulations that serve the public interest, advance 
statutory objectives, and are consistent with E.O. 12866, E.O. 13563, 
and the Presidential Memorandum of January 20, 2021 (Modernizing 
Regulatory Review). Regulatory analysis, as practicable and 
appropriate, shall recognize distributive impacts and equity, to the 
extent permitted by law. E.O. 13563 emphasizes further that regulations 
must be based on the best available science and that the rulemaking 
process must allow for public participation and an open exchange of 
ideas. We have developed this rule in a manner consistent with these 
requirements.

Regulatory Flexibility Act (5 U.S.C. 601 et seq.)

    Under the Regulatory Flexibility Act (RFA; 5 U.S.C. 601 et seq.), 
as amended by the Small Business Regulatory Enforcement Fairness Act of 
1996 (SBREFA; 5 U.S.C. 801 et seq.), whenever an agency is required to 
publish a notice of rulemaking for any proposed or final rule, it must 
prepare and make available for public comment a regulatory flexibility 
analysis that describes the effects of the rule on small entities 
(i.e., small businesses, small organizations, and small government 
jurisdictions). However, no regulatory flexibility analysis is required 
if the head of the agency certifies the rule will not have a 
significant economic impact on a substantial number of small entities. 
The SBREFA amended the RFA to require Federal agencies to provide the 
factual basis for certifying that the rule will not have a significant 
economic impact on a substantial number of small entities.
    According to the Small Business Administration, small entities 
include small organizations such as independent nonprofit 
organizations; small governmental jurisdictions, including school 
boards and city and town governments that serve fewer than 50,000 
residents; and small businesses (13 CFR 121.201). Small businesses 
include manufacturing and mining concerns with fewer than 500

[[Page 48097]]

employees, wholesale trade entities with fewer than 100 employees, 
retail and service businesses with less than $5 million in annual 
sales, general and heavy construction businesses with less than $27.5 
million in annual business, special trade contractors doing less than 
$11.5 million in annual business, and agricultural businesses with 
annual sales less than $750,000. To determine if potential economic 
impacts to these small entities are significant, we considered the 
types of activities that might trigger regulatory impacts under this 
designation as well as types of project modifications that may result. 
In general, the term ``significant economic impact'' is meant to apply 
to a typical small business firm's business operations.
    Under the RFA, as amended, as understood in light of recent court 
decisions, Federal agencies are required to evaluate the potential 
incremental impacts of rulemaking on those entities directly regulated 
by the rulemaking itself; in other words, the RFA does not require 
agencies to evaluate the potential impacts to indirectly regulated 
entities. The regulatory mechanism through which critical habitat 
protections are realized is section 7 of the Act, which requires 
Federal agencies, in consultation with the Service, to ensure that any 
action authorized, funded, or carried out by the agency is not likely 
to destroy or adversely modify critical habitat. Therefore, under 
section 7, only Federal action agencies are directly subject to the 
specific regulatory requirement (avoiding destruction and adverse 
modification) imposed by critical habitat designation. Consequently, it 
is our position that only Federal action agencies will be directly 
regulated by this designation. The RFA does not require evaluation of 
the potential impacts to entities not directly regulated. Moreover, 
Federal agencies are not small entities. Therefore, because no small 
entities will be directly regulated by this rulemaking, we certify that 
this critical habitat designation will not have a significant economic 
impact on a substantial number of small entities.
    During the development of this final rule, we reviewed and 
evaluated all information submitted during the comment period on the 
proposed rule (86 FR 47916; August 26, 2021) that may pertain to our 
consideration of the probable incremental economic impacts of this 
critical habitat designation. Based on this information, we affirm our 
certification that this critical habitat designation will not have a 
significant economic impact on a substantial number of small entities, 
and a regulatory flexibility analysis is not required.

Energy Supply, Distribution, or Use--Executive Order 13211

    Executive Order 13211 (Actions Concerning Regulations That 
Significantly Affect Energy Supply, Distribution, or Use) requires 
agencies to prepare Statements of Energy Effects ``to the extent 
permitted by law'' when undertaking actions identified as significant 
energy actions (66 FR 28355; May 22, 2001). E.O. 13211 defines a 
``significant energy action'' as an action that (i) is a significant 
regulatory action under E.O. 12866 (or any successor order, including 
most recently E.O. 14094 (88 FR 21879; Apr. 11, 2023)); and (ii) is 
likely to have a significant adverse effect on the supply, 
distribution, or use of energy. This rule is not a significant 
regulatory action under E.O. 12866 or 14094. Therefore, this action is 
not a significant energy action, and no Statement of Energy Effects is 
required.

Unfunded Mandates Reform Act (2 U.S.C. 1501 et seq.)

    In accordance with the Unfunded Mandates Reform Act (2 U.S.C. 1501 
et seq.), we make the following finding:
    (1) This rule will not produce a Federal mandate. In general, a 
Federal mandate is a provision in legislation, statute, or regulation 
that would impose an enforceable duty upon State, local, or Tribal 
governments, or the private sector, and includes both ``Federal 
intergovernmental mandates'' and ``Federal private sector mandates.'' 
These terms are defined in 2 U.S.C. 658(5)-(7). ``Federal 
intergovernmental mandate'' includes a regulation that ``would impose 
an enforceable duty upon State, local, or Tribal governments'' with two 
exceptions. It excludes ``a condition of Federal assistance.'' It also 
excludes ``a duty arising from participation in a voluntary Federal 
program,'' unless the regulation ``relates to a then-existing Federal 
program under which $500,000,000 or more is provided annually to State, 
local, and Tribal governments under entitlement authority,'' if the 
provision would ``increase the stringency of conditions of assistance'' 
or ``place caps upon, or otherwise decrease, the Federal Government's 
responsibility to provide funding,'' and the State, local, or Tribal 
governments ``lack authority'' to adjust accordingly. At the time of 
enactment, these entitlement programs were: Medicaid; Aid to Families 
with Dependent Children work programs; Child Nutrition; Food Stamps; 
Social Services Block Grants; Vocational Rehabilitation State Grants; 
Foster Care, Adoption Assistance, and Independent Living; Family 
Support Welfare Services; and Child Support Enforcement. ``Federal 
private sector mandate'' includes a regulation that ``would impose an 
enforceable duty upon the private sector, except (i) a condition of 
Federal assistance or (ii) a duty arising from participation in a 
voluntary Federal program.''
    The designation of critical habitat does not impose a legally 
binding duty on non-Federal Government entities or private parties. 
Under the Act, the only regulatory effect is that Federal agencies must 
ensure that their actions are not likely to destroy or adversely modify 
critical habitat under section 7. While non-Federal entities that 
receive Federal funding, assistance, or permits, or that otherwise 
require approval or authorization from a Federal agency for an action, 
may be indirectly impacted by the designation of critical habitat, the 
legally binding duty to avoid destruction or adverse modification of 
critical habitat rests squarely on the Federal agency. Furthermore, to 
the extent that non-Federal entities are indirectly impacted because 
they receive Federal assistance or participate in a voluntary Federal 
aid program, the Unfunded Mandates Reform Act would not apply, nor 
would critical habitat shift the costs of the large entitlement 
programs listed above onto State governments.
    (2) We do not believe that this rule will significantly or uniquely 
affect small governments because many of the public lands being 
designated as critical habitat are owned by the State of Texas. This 
government entity does not fit the definition of ``small governmental 
jurisdiction.'' Therefore, a Small Government Agency Plan is not 
required. Additionally, the public areas not owned by the State of 
Texas that are being designated as critical habitat are not likely to 
have a Federal nexus requiring section 7 consultation on designated 
critical habitat.

Takings--Executive Order 12630

    In accordance with E.O. 12630 (Government Actions and Interference 
with Constitutionally Protected Private Property Rights), we have 
analyzed the potential takings implications of designating critical 
habitat for the central Texas mussels in a takings implications 
assessment. The Act does not authorize us to regulate private actions 
on private lands or confiscate private property as a result of critical 
habitat designation. Designation of critical habitat does not affect 
land

[[Page 48098]]

ownership, or establish any closures, or restrictions on use of or 
access to the designated areas. Furthermore, the designation of 
critical habitat does not affect landowner actions that do not require 
Federal funding or permits, nor does it preclude development of habitat 
conservation programs or issuance of incidental take permits to permit 
actions that do require Federal funding or permits to go forward. 
However, Federal agencies are prohibited from carrying out, funding, or 
authorizing actions that would destroy or adversely modify critical 
habitat. A takings implications assessment has been completed and 
concludes that this designation of critical habitat for the central 
Texas mussels does not pose significant takings implications for lands 
within or affected by the designation.

Federalism--Executive Order 13132

    In accordance with E.O. 13132 (Federalism), this rule does not have 
significant federalism effects. A federalism summary impact statement 
is not required. In keeping with Department of the Interior and 
Department of Commerce policy, we requested information from, and 
coordinated development of this critical habitat designation with, 
appropriate State resource agencies. From a federalism perspective, the 
designation of critical habitat directly affects only the 
responsibilities of Federal agencies. The Act imposes no other duties 
with respect to critical habitat, either for States and local 
governments, or for anyone else. As a result, this final rule does not 
have substantial direct effects either on the States, or on the 
relationship between the national government and the States, or on the 
distribution of powers and responsibilities among the various levels of 
government. The designation may have some benefit to these governments 
because the areas that contain the features essential to the 
conservation of the species are more clearly defined, and the physical 
or biological features of the habitat necessary for the conservation of 
the species are specifically identified. This information does not 
alter where and what federally sponsored activities may occur. However, 
it may assist State and local governments in long-range planning 
because they no longer have to wait for case-by-case section 7 
consultations to occur.
    Where State and local governments require approval or authorization 
from a Federal agency for actions that may affect critical habitat, 
consultation under section 7(a)(2) of the Act will be required. While 
non-Federal entities that receive Federal funding, assistance, or 
permits, or that otherwise require approval or authorization from a 
Federal agency for an action, may be indirectly impacted by the 
designation of critical habitat, the legally binding duty to avoid 
destruction or adverse modification of critical habitat rests squarely 
on the Federal agency.

Civil Justice Reform--Executive Order 12988

    In accordance with Executive Order 12988 (Civil Justice Reform), 
the Office of the Solicitor has determined that this rule will not 
unduly burden the judicial system and that it meets the requirements of 
sections 3(a) and 3(b)(2) of the Order. We are designating critical 
habitat in accordance with the provisions of the Act. To assist the 
public in understanding the habitat needs of the species, this final 
rule identifies the physical or biological features essential to the 
conservation of the species. The designated areas of critical habitat 
are presented on maps, and the rule provides several options for the 
interested public to obtain more detailed location information, if 
desired.

Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.)

    This rule does not contain information collection requirements, and 
a submission to the Office of Management and Budget (OMB) under the 
Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.) is not 
required. We may not conduct or sponsor and you are not required to 
respond to a collection of information unless it displays a currently 
valid OMB control number.

National Environmental Policy Act (42 U.S.C. 4321 et seq.)

    Regulations adopted pursuant to section 4(a) of the Act are exempt 
from the National Environmental Policy Act (NEPA; 42 U.S.C. 4321 et 
seq.) and do not require an environmental analysis under NEPA. We 
published a notice outlining our reasons for this determination in the 
Federal Register on October 25, 1983 (48 FR 49244). This includes 
listing, delisting, and reclassification rules, as well as critical 
habitat designations and species-specific protective regulations 
promulgated concurrently with a decision to list or reclassify a 
species as threatened. The courts have upheld this position (e.g., 
Douglas County v. Babbitt, 48 F.3d 1495 (9th Cir. 1995) (critical 
habitat); Center for Biological Diversity v. U.S. Fish and Wildlife 
Service, 2005 WL 2000928 (N.D. Cal. Aug. 19, 2005) (concurrent 4(d) 
rule)).

Government-to-Government Relationship With Tribes

    In accordance with the President's memorandum of April 29, 1994 
(Government-to-Government Relations with Native American Tribal 
Governments; 59 FR 22951), Executive Order 13175 (Consultation and 
Coordination with Indian Tribal Governments), and the Department of the 
Interior's manual at 512 DM 2, we readily acknowledge our 
responsibility to communicate meaningfully with federally recognized 
Tribes on a government-to-government basis. In accordance with 
Secretaries' Order 3206 of June 5, 1997 (American Indian Tribal Rights, 
Federal-Tribal Trust Responsibilities, and the Endangered Species Act), 
we readily acknowledge our responsibilities to work directly with 
Tribes in developing programs for healthy ecosystems, to acknowledge 
that Tribal lands are not subject to the same controls as Federal 
public lands, to remain sensitive to Indian culture, and to make 
information available to Tribes. We have determined that no Tribal 
lands fall within the boundaries of the critical habitat designation 
for the central Texas mussels, so no Tribal lands will be affected by 
this designation.

References Cited

    A complete list of references cited in this rulemaking is available 
on the internet at https://www.regulations.gov and upon request from 
the Austin Ecological Services Field Office (see FOR FURTHER 
INFORMATION CONTACT).

Authors

    The primary authors of this final rule are the staff members of the 
Fish and Wildlife Service's Species Assessment Team and the Austin 
Ecological Services Field Office.

List of Subjects in 50 CFR Part 17

    Endangered and threatened species, Exports, Imports, Plants, 
Reporting and recordkeeping requirements, Transportation, Wildlife.

Regulation Promulgation

    Accordingly, we amend part 17, subchapter B of chapter I, title 50 
of the Code of Federal Regulations, as set forth below:

PART 17--ENDANGERED AND THREATENED WILDLIFE AND PLANTS

0
1. The authority citation for part 17 continues to read as follows:

    Authority: 16 U.S.C. 1361-1407; 1531-1544; and 4201-4245, unless 
otherwise noted.

[[Page 48099]]


0
2. In Sec.  17.11, in paragraph (h), amend the List of Endangered and 
Threatened Wildlife by adding entries for ``Fatmucket, Guadalupe''; 
``Fatmucket, Texas''; ``Fawnsfoot, Texas''; ``Orb, Guadalupe''; 
``Pimpleback, Texas''; ``Spike, Balcones''; and ``Spike, False'' in 
alphabetical order under CLAMS to read as follows:


Sec.  17.11  Endangered and threatened wildlife.

* * * * *
    (h) * * *

----------------------------------------------------------------------------------------------------------------
                                                                                              Listing citations
           Common name               Scientific name        Where listed         Status        and  applicable
                                                                                                    rules
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------
                                                      CLAMS
----------------------------------------------------------------------------------------------------------------
 
                                                  * * * * * * *
Fatmucket, Guadalupe.............  Lampsilis bergmanni  Wherever found.....  E               89 FR [INSERT
                                                                                              Federal Register
                                                                                              PAGE WHERE THE
                                                                                              DOCUMENT BEGINS],
                                                                                              June 4, 2024;
                                                                                             50 CFR
                                                                                              17.95(f).\CH\
Fatmucket, Texas.................  Lampsilis bracteata  Wherever found.....  E               89 FR [INSERT
                                                                                              Federal Register
                                                                                              PAGE WHERE THE
                                                                                              DOCUMENT BEGINS],
                                                                                              June 4, 2024;
                                                                                             50 CFR
                                                                                              17.95(f).\CH\
Fawnsfoot, Texas.................  Truncilla macrodon.  Wherever found.....  T               89 FR [INSERT
                                                                                              Federal Register
                                                                                              PAGE WHERE THE
                                                                                              DOCUMENT BEGINS],
                                                                                              June 4, 2024;
                                                                                             50 CFR
                                                                                              17.45(c);\4d\
                                                                                             50 CFR
                                                                                              17.95(f).\CH\
 
                                                  * * * * * * *
Orb, Guadalupe...................  Cyclonaias necki...  Wherever found.....  E               89 FR [INSERT
                                                                                              Federal Register
                                                                                              PAGE WHERE THE
                                                                                              DOCUMENT BEGINS],
                                                                                              June 4, 2024;
                                                                                             50 CFR
                                                                                              17.95(f).\CH\
 
                                                  * * * * * * *
Pimpleback, Texas................  Cyclonaias petrina.  Wherever found.....  E               89 FR [INSERT
                                                                                              Federal Register
                                                                                              PAGE WHERE THE
                                                                                              DOCUMENT BEGINS],
                                                                                              June 4, 2024;
                                                                                             50 CFR
                                                                                              17.95(f).\CH\
 
                                                  * * * * * * *
Spike, Balcones..................  Fusconaia iheringi.  Wherever found.....  E               89 FR [INSERT
                                                                                              Federal Register
                                                                                              PAGE WHERE THE
                                                                                              DOCUMENT BEGINS],
                                                                                              June 4, 2024;
                                                                                             50 CFR
                                                                                              17.95(f).\CH\
Spike, false.....................  Fusconaia mitchelli  Wherever found.....  E               89 FR [INSERT
                                                                                              Federal Register
                                                                                              PAGE WHERE THE
                                                                                              DOCUMENT BEGINS],
                                                                                              June 4, 2024;
                                                                                             50 CFR
                                                                                              17.95(f).\CH\
 
                                                  * * * * * * *
----------------------------------------------------------------------------------------------------------------


0
3. Amend Sec.  [thinsp]17.45 by adding a paragraph (c) to read as 
follows:


Sec.  [thinsp]17.45  Species-specific rules--snails and clams.

* * * * *
    (c) Texas fawnsfoot (Truncilla macrodon).
    (1) Prohibitions. The following prohibitions that apply to 
endangered wildlife also apply to Texas fawnsfoot. Except as provided 
under paragraph (c)(2) of this section and Sec. Sec.  17.4 and 17.5, it 
is unlawful for any person subject to the jurisdiction of the United 
States to commit, to attempt to commit, to solicit another to commit, 
or cause to be committed, any of the following acts in regard to the 
Texas fawnsfoot:
    (i) Import or export, as set forth at Sec.  17.21(b) for endangered 
wildlife.
    (ii) Take, as set forth at Sec.  17.21(c)(1) for endangered 
wildlife.
    (iii) Possession and other acts with unlawfully taken specimens, as 
set forth at Sec.  17.21(d)(1) for endangered wildlife.
    (iv) Interstate or foreign commerce in the course of commercial 
activity, as set forth at Sec.  17.21(e) for endangered wildlife.
    (v) Sale or offer for sale, as set forth at Sec.  17.21(f) for 
endangered wildlife.
    (2) Exceptions from prohibitions. In regard to this species, you 
may:
    (i) Conduct activities as authorized by a permit under Sec.  17.32.
    (ii) Take, as set forth at Sec.  17.21(c)(2) through (c)(4) for 
endangered wildlife.
    (iii) Take as set forth at Sec.  17.31(b).
    (iv) Possess and engage in other acts with unlawfully taken Texas 
fawnsfoot, as set forth at Sec.  17.21(d)(2) for endangered wildlife.
    (v) Take incidental to an otherwise lawful activity caused by:
    (A) Channel restoration projects that create natural, physically 
stable, ecologically functioning streams (or stream and wetland 
systems) that are reconnected with their groundwater aquifers. To 
qualify for the exception in this paragraph (c)(2)(v)(A), a channel

[[Page 48100]]

restoration project must satisfy all applicable Federal, State, and 
local permitting requirements. In addition, at least 30 days prior to 
commencing actual construction within an area designated as critical 
habitat for the Texas fawnsfoot (see 50 CFR 17.95(f)), notice must be 
provided to the Service, through the Austin Ecological Services Field 
Office, of the location and nature of the proposed work to allow the 
Service to make arrangements for surveys and potential relocation of 
any mussels that might be adversely affected. You may obtain field 
office contact information by contacting one of the Service regional 
offices, the addresses of which are listed at 50 CFR 2.2.
    (B) Bioengineering methods for streambank stabilization using 
native live stakes (live, vegetative cuttings inserted or tamped into 
the ground in a manner that allows the stake to take root and grow), 
native live fascines (live branch cuttings, usually willows, bound 
together into long, cigar-shaped bundles), or native brush layering 
(cuttings or branches of easily rooted tree species layered between 
successive lifts of soil fill). Methods that include the use of 
quarried rock (riprap) for more than 25 percent of the area within the 
streambanks or include the use of rock baskets or gabion structures do 
not qualify for the exception in this paragraph (c)(2)(v)(B). In 
addition, to reduce streambank erosion and sedimentation into the 
stream, work using these bioengineering methods qualifies for the 
exception in this paragraph (c)(2)(v)(B) only if it is performed during 
base-flow or low-water conditions and when significant rainfall likely 
to result in significant runoff is not predicted at or upstream of the 
area where work is proposed for a period of at least 3 days after the 
work is scheduled to be undertaken. Further, streambank stabilization 
projects that involve the placement or use of equipment in the stream 
channels or water do not qualify for the exception in this paragraph 
(c)(2)(v)(B). To qualify for the exception in this paragraph 
(c)(2)(v)(B), a project using bioengineering methods must satisfy all 
applicable Federal, State, and local permitting requirements.
    (C) Soil and water conservation practices and riparian and adjacent 
upland habitat management activities that restore in-stream habitats 
for the species, restore adjacent riparian habitats that enhance stream 
habitats for the species, stabilize degraded and eroding stream banks 
to limit sedimentation and scour of the species' habitats, restore or 
enhance nearby upland habitats to limit sedimentation of the species' 
habitats, and comply with conservation practice standards and 
specifications and with technical guidelines developed by the Natural 
Resources Conservation Service for application of the affected habitat 
types. In addition, at least 30 days prior to commencing soil and water 
conservation practices within an area designated as critical habitat 
for the Texas fawnsfoot (see 50 CFR 17.95(f)), notice must be provided 
to the Service, through the Austin Ecological Services Field Office, of 
the location and nature of the proposed work to allow the Service to 
make arrangements for surveys and potential relocation of any mussels 
that might be adversely affected. You may obtain field office contact 
information by contacting one of the Service regional offices, the 
addresses of which are listed at 50 CFR 2.2.
    (D) Presence or abundance surveys for Texas fawnsfoot conducted by 
individuals who successfully complete and show proficiency by passing 
the end-of-course test with a score equal to or greater than 90 
percent, with 100 percent accuracy in identification of mussel species 
listed under the Endangered Species Act, in an approved freshwater 
mussel identification and sampling course (specific to the species and 
basins in which the Texas fawnsfoot is known to occur), such as that 
administered by the Service, a State wildlife agency, or qualified 
university experts. Those individuals exercising the exemption in this 
paragraph (c)(2)(v)(D) should provide reports to the Service annually 
on number, location, and date of collection. The exemption in this 
paragraph (c)(2)(v)(D) does not apply if lethal take or collection is 
anticipated. The exemption in this paragraph (c)(2)(v)(D) only applies 
for 5 years from the date of successful course completion.
* * * * *

0
4. In Sec.  17.95, amend paragraph (f) by:
0
a. Adding entries for ``Guadalupe Fatmucket (Lampsilis bergmanni)'', 
``Texas Fatmucket (Lampsilis bracteata)'', and ``Texas Fawnsfoot 
(Truncilla macrodon)'' immediately following the entry for 
``Appalachian Elktoe (Alasmidonta raveneliana)'';
0
b. Adding an entry for ``Guadalupe Orb (Cyclonaias necki)'' immediately 
following the entry for ``Carolina Heelsplitter (Lasmigona decorata)''; 
and
0
c. Adding entries for ``Texas Pimpleback (Cyclonaias petrina)'', 
``Balcones Spike (Fusconaia iheringi)'', and ``False Spike (Fusconaia 
mitchelli)'' immediately following the entry for ``Georgia Pigtoe 
(Pleurobema hanleyianum)''.
    The additions read as follows:


Sec.  17.95  Critical habitat--fish and wildlife.

* * * * *
    (f) Clams and Snails.
* * * * *
    Guadalupe Fatmucket (Lampsilis bergmanni)
    (1) A critical habitat unit is depicted for Kendall and Kerr 
Counties, Texas, on the map in this entry.
    (2) Within this area, the physical or biological features essential 
to the conservation of Guadalupe fatmucket consist of the following 
components within waters and streambeds up to the ordinary high-water 
mark:
    (i) Flowing water at moderate to high rates with sufficient depth 
to remain sufficiently cool and oxygenated during low-flow periods;
    (ii) Substrate including bedrock and boulder crevices, point bars, 
and vegetated run habitat comprising sand, gravel, and larger cobbles;
    (iii) Green sunfish (Lepomis cyanellus), bluegill (L. macrochirus), 
largemouth bass (Micropterus salmoides), and Guadalupe bass (M. 
treculii) present; and
    (iv) Water quality parameters within the following ranges:
    (A) Dissolved oxygen greater than 2 milligrams per liter (mg/L);
    (B) Salinity less than 2 parts per thousand;
    (C) Total ammonia less than 0.77 mg/L total ammonia nitrogen;
    (D) Water temperature below 29 [deg]C (84.2 [deg]F); and
    (E) Low levels of contaminants.
    (3) Critical habitat does not include manmade structures (such as 
buildings, aqueducts, runways, roads, and other paved areas) and the 
land on which they are located existing within the legal boundaries on 
July 5, 2024.
    (4) Data layers defining the map unit were created on a base of 
U.S. Geological Survey digital ortho-photo quarter-quadrangles, and the 
critical habitat unit was then mapped using Universal Transverse 
Mercator (UTM) Zone 14N coordinates. The map in this entry, as modified 
by any accompanying regulatory text, establishes the boundaries of the 
critical habitat designation. The coordinates or plot points or both on 
which the map is based are available to the public at the Service's 
internet site at https://www.fws.gov/office/austin-ecological-services, 
at https://www.regulations.gov at Docket No. FWS-R2-ES-2019-0061, and 
at the field office responsible for this designation. You may obtain 
field office location information by

[[Page 48101]]

contacting one of the Service regional offices, the addresses of which 
are listed at 50 CFR 2.2.
    (5) Unit GUFM-1: Guadalupe River Unit; Kendall and Kerr Counties, 
Texas.
    (i) Unit GUFM-1 consists of three subunits:
    (A) Subunit GUFM-1a (North Fork Guadalupe River) consists of 6.9 
river miles (mi) (11.0 kilometers (km)) in Kerr County, Texas. All of 
the riparian lands that border this subunit are in private ownership.
    (B) Subunit GUFM-1b (Johnson Creek) consists of 10.1 river mi (16.3 
km) in Kerr County, Texas. All of the riparian lands that border this 
subunit are in private ownership.
    (C) Subunit GUFM-1c (Guadalupe River) consists of 35.2 river mi 
(56.7 km) in Kendall and Kerr Counties, Texas. This subunit is composed 
of lands in State/local government (7 percent) and private (93 percent) 
ownership.
    (ii) Unit GUFM-1 includes stream channel up to bankfull height.
    (iii) Map of Unit GUFM-1 follows:

Figure 1 to Guadalupe Fatmucket (Lampsilis bergmanni) paragraph 
(5)(iii)
BILLING CODE 4333-15-P
[GRAPHIC] [TIFF OMITTED] TR04JN24.001


[[Page 48102]]


BILLING CODE 4333-15-C
Texas Fatmucket (Lampsilis bracteata)
    (1) Critical habitat units are depicted for Blanco, Gillespie, 
Hays, Kimble, Llano, Mason, McCulloch, Menard, Runnels, San Saba, 
Sutton, and Travis Counties, Texas, on the maps in this entry.
    (2) Within these areas, the physical or biological features 
essential to the conservation of Texas fatmucket consist of the 
following components within waters and streambeds up to the ordinary 
high-water mark:
    (i) Flowing water at moderate to high rates with sufficient depth 
to remain sufficiently cool and oxygenated during low-flow periods;
    (ii) Substrate including bedrock and boulder crevices, point bars, 
and vegetated run habitat comprising sand, gravel, and larger cobbles;
    (iii) Green sunfish (Lepomis cyanellus), bluegill (L. macrochirus), 
largemouth bass (Micropterus salmoides), and Guadalupe bass (M. 
treculii) present; and
    (iv) Water quality parameters within the following ranges:
    (A) Dissolved oxygen greater than 2 milligrams per liter (mg/L);
    (B) Salinity less than 2 parts per thousand;
    (C) Total ammonia less than 0.77 mg/L total ammonia nitrogen;
    (D) Water temperature below 29 [deg]C (84.2 [deg]F); and
    (E) Low levels of contaminants.
    (3) Critical habitat does not include manmade structures (such as 
buildings, aqueducts, runways, roads, and other paved areas) and the 
land on which they are located existing within the legal boundaries on 
July 5, 2024.
    (4) Data layers defining the map units were created on a base of 
U.S. Geological Survey digital ortho-photo quarter-quadrangles, and the 
critical habitat units were then mapped using Universal Transverse 
Mercator (UTM) Zone 14N coordinates. The maps in this entry, as 
modified by any accompanying regulatory text, establish the boundaries 
of the critical habitat designation. The coordinates or plot points or 
both on which the maps are based are available to the public at the 
Service's internet site at https://www.fws.gov/office/austin-ecological-services, at https://www.regulations.gov at Docket No. FWS-
R2-ES-2019-0061, and at the field office responsible for this 
designation. You may obtain field office location information by 
contacting one of the Service regional offices, the addresses of which 
are listed at 50 CFR 2.2.
    (5) Index map of critical habitat units for the Texas fatmucket 
follows:

Figure 1 to Texas Fatmucket (Lampsilis bracteata) paragraph (5)
BILLING CODE 4333-15-P

[[Page 48103]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.002

    (6) Unit TXFM-1: Elm Creek Unit; Runnels County, Texas.
    (i) Unit TXFM-1 consists of three subunits:
    (A) Subunit TXFM-1a (Bluff Creek) consists of 11.6 river miles (mi) 
(18.7 river kilometers (km)) in Runnels County, Texas. All of the 
riparian lands that border this subunit are in private ownership.
    (B) Subunit TXFM-1b (Lower Elm Creek) consists of 12.3 river mi 
(19.8 km) in Runnels County, Texas. This subunit is composed of lands 
in State/local government (3 percent) and private (97 percent) 
ownership.
    (C) Subunit TXFM-1c (Upper Elm Creek) consists of 8.9 river mi 
(14.4 km) in Runnels County, Texas. All of the riparian lands that 
border this subunit are in private ownership.
    (ii) Unit TXFM-1 includes stream channel up to bankfull height.
    (iii) Map of Unit TXFM-1 follows:

Figure 2 to Texas Fatmucket (Lampsilis bracteata) paragraph (6)(iii)

[[Page 48104]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.003

    (7) Unit TXFM-2: San Saba River Unit; Mason, McCulloch, Menard, and 
San Saba Counties, Texas.
    (i) Unit TXFM-2 consists of 90.8 river mi (146.1 km) in Mason, 
McCulloch, Menard, and San Saba Counties, Texas. All of the riparian 
lands that border this unit are in private ownership.
    (ii) Unit TXFM-2 includes stream channel up to bankfull height.
    (iii) Map of TXFM-2 follows:

Figure 3 to Texas Fatmucket (Lampsilis bracteata) paragraph (7)(iii)

[[Page 48105]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.004

    (8) Unit TXFM-3: Cherokee Creek Unit; San Saba County, Texas.
    (i) Unit TXFM-3 consists of 17.8 river mi (28.6 km) in San Saba 
County, Texas. All of the riparian lands that border this unit are in 
private ownership.
    (ii) Unit TXFM-3 includes stream channel up to bankfull height.
    (iii) Map of Unit TXFM-3 follows:

Figure 4 to Texas Fatmucket (Lampsilis bracteata) paragraph (8)(iii)

[[Page 48106]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.005

    (9) Unit TXFM-4: Llano River Unit; Gillespie, Kimble, Llano, Mason, 
and Sutton Counites, Texas.
    (i) Unit TXFM-4 consists of six subunits:
    (A) Subunit TXFM-4a (North Llano River) consists of 30.2 river mi 
(48.7 km) in Sutton and Kimble Counties, Texas. All of the riparian 
lands that border this subunit are in private ownership.
    (B) Subunit TXFM-4b (South Llano River) consists of 22.5 river mi 
(36.2 km) in Kimble County, Texas. This subunit is composed of lands in 
State/local government (10 percent) and private (90 percent) ownership.
    (C) Subunit TXFM-4c (Llano River) consists of 90.9 river mi (146.4 
km) in Kimble, Llano, and Mason Counties, Texas. This subunit is 
composed of lands in State/local government (0.5 percent) and private 
(99.5 percent) ownership.
    (D) Subunit TXFM-4d (James River) consists of 18.3 river mi (29.4 
km) in Kimble and Mason Counties, Texas. All of the riparian lands that 
border this subunit are in private ownership.
    (E) Subunit TXFM-4e (Threadgill Creek) consists of 8.1 river mi 
(13.1 km) in Gillespie and Mason Counties, Texas. All of the riparian 
lands that border this subunit are in private ownership.
    (F) Subunit TXFM-4f (Beaver Creek) consists of 12.7 river mi (20.5 
km) in

[[Page 48107]]

Mason County, Texas. All of the riparian lands that border this subunit 
are in private ownership.
    (ii) Unit TXFM-4 includes stream channel up to bankfull height.
    (iii) Map of Unit TXFM-4 follows:

Figure 5 to Texas Fatmucket (Lampsilis bracteata) paragraph (9)(iii)
[GRAPHIC] [TIFF OMITTED] TR04JN24.006

    (10) Unit TXFM-5: Pedernales River Unit: Blanco, Gillespie, Hays, 
and Travis Counties, Texas.
    (i) Unit TXFM-5 consists of two subunits:
    (A) Subunit TXFM-5a (Pedernales River) consists of 78.2 river mi 
(125.8 km) in Blanco, Gillespie, Hays, and Travis Counties, Texas. This 
subunit is composed of lands in State/local government (10 percent), 
Federal Government (3 percent), and private (87 percent) ownership.
    (B) Subunit TXFM-5b (Live Oak Creek) consists of 2.6 river mi (4.2 
km) in Gillespie County, Texas. This subunit is composed of lands in 
State/local government (54 percent) and private (46 percent) ownership.

[[Page 48108]]

    (ii) Unit TXFM-5 includes stream channel up to bankfull height.
    (iii) Map of Unit TXFM-5 follows:

Figure 6 to Texas Fatmucket (Lampsilis bracteata) paragraph (10)(iii)
[GRAPHIC] [TIFF OMITTED] TR04JN24.007

    (11) Unit TXFM-6: Onion Creek Unit; Travis County, Texas.
    (i) Unit TXFM-6 consists of 23.5 river mi (37.8 km) in Travis 
County, Texas. This subunit is composed of lands in State/local 
government (56 percent) and private (44 percent) ownership.
    (ii) Unit TXFM-6 includes stream channel up to bankfull height.
    (iii) Map of Unit TXFM-6 follows:

Figure 7 to Texas Fatmucket (Lampsilis bracteata) paragraph (11)(iii)

[[Page 48109]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.008

Texas Fawnsfoot (Truncilla macrodon)
    (1) Critical habitat units are depicted for Lampasas, Mills, Palo 
Pinto, Parker, San Saba, Shackelford, Stephens, and Throckmorton 
Counties, Texas, on the maps in this entry.
    (2) Within these areas, the physical or biological features 
essential to the conservation of Texas fawnsfoot consist of the 
following components within waters and streambeds up to the ordinary 
high-water mark:
    (i) Flowing water at rates suitable to prevent excess sedimentation 
but not so high as to dislodge individuals or sediment;
    (ii) Stable bank and riffle habitats with gravel, sand, silt, and 
mud substrates that are clean swept by flushing flows;
    (iii) Freshwater drum (Aplodinotus grunniens) present; and
    (iv) Water quality parameters within the following ranges:
    (A) Dissolved oxygen greater than 2 milligrams per liter (mg/L);
    (B) Salinity less than 2 parts per thousand;
    (C) Total ammonia less than 0.77 mg/L total ammonia nitrogen;
    (D) Water temperature below 29 [deg]C (84.2 [deg]F); and
    (E) Low levels of contaminants.

[[Page 48110]]

    (3) Critical habitat does not include manmade structures (such as 
buildings, aqueducts, runways, roads, and other paved areas) and the 
land on which they are located existing within the legal boundaries on 
July 5, 2024.
    (4) Data layers defining the map units were created on a base of 
U.S. Geological Survey digital ortho-photo quarter-quadrangles, and the 
critical habitat units were then mapped using Universal Transverse 
Mercator (UTM) Zone 14N coordinates. The maps in this entry, as 
modified by any accompanying regulatory text, establish the boundaries 
of the critical habitat designation. The coordinates or plot points or 
both on which the maps are based are available to the public at the 
Service's internet site at https://www.fws.gov/office/austin-ecological-services, at https://www.regulations.gov at Docket No. FWS-
R2-ES-2019-0061, and at the field office responsible for this 
designation. You may obtain field office location information by 
contacting one of the Service regional offices, the addresses of which 
are listed at 50 CFR 2.2.
    (5) Index map of critical habitat units for the Texas fawnsfoot 
follows:

Figure 1 to Texas Fawnsfoot (Truncilla macrodon) paragraph (5)
[GRAPHIC] [TIFF OMITTED] TR04JN24.009


[[Page 48111]]


    (6) Unit TXFF-1: Clear Fork of the Brazos River Unit; Shackelford, 
Stephens, and Throckmorton Counties, Texas.
    (i) Unit TXFF-1 consists of two subunits:
    (A) Subunit TXFF-1a (Upper Clear Fork Brazos River) consists of 
27.3 river miles (mi) (44.0 kilometers (km)) in Shackelford and 
Throckmorton Counties, Texas. All of the riparian lands that border 
this subunit are in private ownership.
    (B) Subunit TXFF-1b (Lower Clear Fork Brazos River) consists of 
27.9 river mi (45.0 km) in Shackelford and Stephens Counties, Texas. 
This subunit is composed of lands in State/local government (1 percent) 
and private (99 percent) ownership.
    (ii) Unit TXFF-1 includes stream channel up to bankfull height.
    (iii) Map of Unit TXFF-1 follows:

Figure 2 to Texas Fawnsfoot (Truncilla macrodon) paragraph (6)(iii)
[GRAPHIC] [TIFF OMITTED] TR04JN24.010


[[Page 48112]]


    (7) Unit TXFF-2: Upper Brazos River Unit; Palo Pinto and Parker 
Counties, Texas.
    (i) Unit TXFF-2 consists of 78.0 river mi (125.5 km) in Palo Pinto 
and Parker Counties, Texas. All of the riparian lands that border this 
unit are in private ownership.
    (ii) Unit TXFF-2 includes stream channel up to bankfull height.
    (iii) Map of Unit TXFF-2 follows:

Figure 3 to Texas Fawnsfoot (Truncilla macrodon) paragraph (7)(iii)
[GRAPHIC] [TIFF OMITTED] TR04JN24.011

    (8) Units TXFF-3 and TXFF-4 are excluded from the designation 
pursuant to section 4(b)(2) of the Act.
    (9) Unit TXFF-5: Lower San Saba River and Upper Colorado River 
Unit; Lampasas, Mills, and San Saba Counties, Texas.
    (i) Unit TXFF-5 consists of two subunits:
    (A) Subunit TXFF-5a (Lower San Saba River) consists of 49.2 river 
mi (79.1 km) in San Saba County, Texas. The riparian lands that border 
this subunit are in State/local government (1

[[Page 48113]]

percent) and private (99 percent) ownership.
    (B) Subunit TXFF-5b (Upper Colorado River) consists of 10.3 river 
mi (16.6 km) in Lampasas, Mills, and San Saba Counties, Texas. All of 
the riparian lands that border this unit are in private ownership.
    (ii) Unit TXFF-5 includes stream channel up to bankfull height.
    (iii) Map of Unit TXFF-5 follows:

Figure 4 to Texas Fawnsfoot (Truncilla macrodon) paragraph (9)(iii)
[GRAPHIC] [TIFF OMITTED] TR04JN24.012

BILLING CODE 4333-15-C
    (10) Units TXFF-6, TXFF-7, and TXFF-8 are excluded from the 
designation pursuant to section 4(b)(2) of the Act.
* * * * *
Guadalupe Orb (Cyclonaias necki)
    (1) Critical habitat units are depicted for Caldwell, Comal, 
DeWitt, Gonzales, Guadalupe, Kendall, Kerr, and Victoria

[[Page 48114]]

Counties, Texas, on the maps in this entry.
    (2) Within these areas, the physical or biological features 
essential to the conservation of Guadalupe orb consist of the following 
components within waters and streambeds up to the ordinary high-water 
mark:
    (i) Flowing water at rates suitable to keep riffle habitats wetted 
and well-oxygenated and to prevent excess sedimentation or scour during 
high-flow events but not so high as to dislodge individuals;
    (ii) Stable riffles and runs with substrate composed of cobble, 
gravel, and fine sediments;
    (iii) Channel catfish (Ictalurus punctatus), flathead catfish 
(Pylodictis olivaris), and tadpole madtom (Noturus gyrinus) present; 
and
    (iv) Water quality parameters within the following ranges:
    (A) Dissolved oxygen greater than 2 milligrams per liter (mg/L);
    (B) Salinity less than 2 parts per thousand;
    (C) Total ammonia less than 0.77 mg/L total ammonia nitrogen;
    (D) Water temperature below 29 [deg]C (84.2 [deg]F); and
    (E) Low levels of contaminants.
    (3) Critical habitat does not include manmade structures (such as 
buildings, aqueducts, runways, roads, and other paved areas) and the 
land on which they are located existing within the legal boundaries on 
July 5, 2024.
    (4) Data layers defining the map units were created on a base of 
U.S. Geological Survey digital ortho-photo quarter-quadrangles, and the 
critical habitat units were then mapped using Universal Transverse 
Mercator (UTM) Zone 14N coordinates. The maps in this entry, as 
modified by any accompanying regulatory text, establish the boundaries 
of the critical habitat designation. The coordinates or plot points or 
both on which the maps are based are available to the public at the 
Service's internet site at https://www.fws.gov/office/austin-ecological-services, at https://www.regulations.gov at Docket No. FWS-
R2-ES-2019-0061, and at the field office responsible for this 
designation. You may obtain field office location information by 
contacting one of the Service regional offices, the addresses of which 
are listed at 50 CFR 2.2.
    (5) Index map of critical habitat units for the Guadalupe orb 
follows:

Figure 1 to Guadalupe Orb (Cyclonaias necki) paragraph (5)
BILLING CODE 4333-15-P

[[Page 48115]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.013

    (6) Unit GORB-1: Upper Guadalupe River; Comal, Kendall, and Kerr 
Counties, Texas.
    (i) Unit GORB-1 consists of two subunits:
    (A) Subunit GORB-1a (South Fork Guadalupe River) consists of 5.1 
river miles (mi) (8.2 kilometers (km)) in Kerr County, Texas. All of 
the riparian lands that border this unit are in private ownership.
    (B) Subunit GORB-1b (Upper Guadalupe River) consists of 97.1 river 
mi (156.3 km) of the Guadalupe River in Comal, Kendall, and Kerr 
Counties, Texas. The riparian lands that border this subunit are in 
State/local government (5 percent) and private (95 percent) ownership.
    (ii) Unit GORB-1 includes stream channel up to bankfull height.
    (iii) Map of Unit GORB-1 follows:

Figure 2 to Guadalupe Orb (Cyclonaias necki) paragraph (6)(iii)

[[Page 48116]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.014

    (7) Unit GORB-2: Lower Guadalupe River; Caldwell, DeWitt, Gonzales, 
Guadalupe, and Victoria Counties, Texas.
    (i) Unit GORB-2 consists of two subunits:
    (A) Subunit GORB-2a (San Marcos River) consists of 63.9 river mi 
(102.8 km) in Caldwell, Gonzales, and Guadalupe Counties, Texas. The 
riparian lands that border this subunit are in State/local government 
(6 percent) and private (94 percent) ownership.
    (B) Subunit GORB-2b (Lower Guadalupe River) consists of 122.4 river 
mi (197.0 km) in DeWitt, Gonzales, and Victoria Counties, Texas. The 
riparian lands that border this subunit are in State/local government 
(5 percent) and private (95 percent) ownership.
    (ii) Unit GORB-2 includes stream channel up to bankfull height.
    (iii) Map of Unit GORB-2 follows:

Figure 3 to Guadalupe Orb (Cyclonaias necki) paragraph (7)(iii)

[[Page 48117]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.015

* * * * *
Texas Pimpleback (Cyclonaias petrina)
    (1) Critical habitat units are depicted for Brown, Coleman, Concho, 
Kimble, Lampasas, Mason, McCulloch, Menard, Mills, Runnels, San Saba, 
and Tom Green Counties, Texas, on the maps in this entry.
    (2) Within these areas, the physical or biological features 
essential to the conservation of Texas pimpleback consist of the 
following components within waters and streambeds up to the ordinary 
high-water mark:
    (i) Flowing water at rates suitable to keep riffle habitats wetted 
and well-oxygenated and to prevent excess sedimentation or scour during 
high-flow events but not so high as to dislodge individuals;
    (ii) Stable riffles and runs with substrate composed of cobble, 
gravel, and fine sediments;
    (iii) Channel catfish (Ictalurus punctatus), flathead catfish 
(Pylodictis olivaris), and tadpole madtom (Noturus gyrinus) present; 
and
    (iv) Water quality parameters within the following ranges:
    (A) Dissolved oxygen greater than 2 milligrams per liter (mg/L);
    (B) Salinity less than 2 parts per thousand;
    (C) Total ammonia less than 0.77 mg/L total ammonia nitrogen;

[[Page 48118]]

    (D) Water temperature below 29 [deg]C (84.2 [deg]F); and
    (E) Low levels of contaminants.
    (3) Critical habitat does not include manmade structures (such as 
buildings, aqueducts, runways, roads, and other paved areas) and the 
land on which they are located existing within the legal boundaries on 
July 5, 2024.
    (4) Data layers defining the map units were created on a base of 
U.S. Geological Survey digital ortho-photo quarter-quadrangles, and the 
critical habitat units were then mapped using Universal Transverse 
Mercator (UTM) Zone 14N coordinates. The maps in this entry, as 
modified by any accompanying regulatory text, establish the boundaries 
of the critical habitat designation. The coordinates or plot points or 
both on which the maps are based are available to the public at the 
Service's internet site at https://www.fws.gov/office/austin-ecological-services, at https://www.regulations.gov at Docket No. FWS-
R2-ES-2019-0061, and at the field office responsible for this 
designation. You may obtain field office location information by 
contacting one of the Service regional offices, the addresses of which 
are listed at 50 CFR 2.2.
    (5) Index map of critical habitat units for the Texas pimpleback 
follows:

Figure 1 to Texas Pimpleback (Cyclonaias petrina) paragraph (5)

[[Page 48119]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.016

    (6) Unit TXPB-1: Elm Creek; Runnels County, Texas.
    (i) Unit TXPB-1 consists of two subunits:
    (A) Subunit TXPB-1a (Bluff Creek) consists of 11.6 river miles (mi) 
(18.7 kilometers (km)) in Runnels County, Texas. All of the riparian 
lands that border this unit are in private ownership.
    (B) Subunit TXPB-1b (Lower Elm Creek) consists of 12.3 river mi 
(19.8 km) in Runnels County, Texas. The riparian lands that border this 
subunit are in State/local government (3 percent) and private (97 
percent) ownership.
    (ii) Unit TXPB-1 includes stream channel up to bankfull height.
    (iii) Map of Unit TXPB-1 follows:

Figure 2 to Texas Pimpleback (Cyclonaias petrina) paragraph (6)(iii)

[[Page 48120]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.017

    (7) Unit TXPB-2: Concho River; Concho and Tom Green Counties, 
Texas.
    (i) Unit TXPB-2 consists of two subunits:
    (A) Subunit TXPB-2a (Lower Concho River) consists of 34.6 river mi 
(55.7 km) in Concho and Tom Green Counties, Texas. All of the riparian 
lands that border this subunit are in private ownership.
    (B) Subunit TXPB-2b (Upper Concho River) consists of 15.5 river mi 
(25.0 km) of the Concho River in Tom Green County, Texas. The riparian 
lands that border this subunit are in State/local government (2 
percent) and private (98 percent) ownership.
    (ii) Unit TXPB-2 includes stream channel up to bankfull height.
    (iii) Map of Unit TXPB-2 follows:

Figure 3 to Texas Pimpleback (Cyclonaias petrina) paragraph (7)(iii)

[[Page 48121]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.018

    (8) Unit TXPB-3: Upper Colorado River and Lower San Saba River; 
Brown, Coleman, Lampasas, McCulloch, Mills, and San Saba Counties, 
Texas.
    (i) Unit TXPB-3 consists of two subunits:
    (A) Subunit TXPB-3a (Upper Colorado River) consists of 150.4 river 
mi (242.1 km) in Brown, Coleman, Lampasas, McCulloch, Mills, and San 
Saba Counties, Texas. All of the riparian lands that border this 
subunit are in private ownership.
    (B) Subunit TXPB-3b (Lower San Saba River) consists of 49.2 river 
mi (79.1 km) in San Saba County, Texas. The riparian lands that border 
this subunit are in State/local government (1 percent) and private (99 
percent) ownership.
    (ii) Unit TXPB-3 includes stream channel up to bankfull height.
    (iii) Map of Unit TXPB-3 follows:

Figure 4 to Texas Pimpleback (Cyclonaias petrina) paragraph (8)(iii)

[[Page 48122]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.019

    (9) Unit TXPB-4: Upper San Saba River; Menard County, Texas.
    (i) Unit TXPB-4 consists of approximately 51.4 river mi (82.7 km) 
in Menard County, Texas. All of the riparian lands that border this 
subunit are in private ownership.
    (ii) Unit TXPB-4 includes stream channel up to bankfull height.
    (iii) Map of Unit TXPB-4: Upper San Saba River follows:

Figure 5 to Texas Pimpleback (Cyclonaias petrina) paragraph (9)(iii)

[[Page 48123]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.020

    (10) Unit TXPB-5: Llano River; Kimble and Mason Counties, Texas.
    (i) Unit TXPB-5 consists of two subunits.
    (A) Subunit TXPB-5a (Upper Llano River) consists of 37.2 river mi 
(59.9 km) in Kimble and Mason Counties, Texas. All of the riparian 
lands that border this subunit are in private ownership.
    (B) Subunit TXPB-5b (Lower Llano River) consists of 11.8 river mi 
(19.1 km) in Mason County, Texas. All of the riparian lands that border 
this subunit are in private ownership.
    (ii) Unit TXPB-5 includes stream channel up to bankfull height.
    (iii) Map of Unit TXPB-5 follows:

Figure 6 to Texas Pimpleback (Cyclonaias petrina) paragraph (10)(iii)

[[Page 48124]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.021

BILLING CODE 4333-15-C
    (11) Unit TXPB-6 is excluded from the designation pursuant to 
section 4(b)(2) of the Act.
Balcones Spike (Fusconaia iheringi)
    (1) Critical habitat units are depicted for Kimble, Mason, and San 
Saba Counties, Texas, on the maps in this entry.
    (2) Within these areas, the physical or biological features 
essential to the conservation of Balcones spike consist of the 
following components within waters and streambeds up to the ordinary 
high-water mark:
    (i) Flowing water at rates suitable to keep riffle habitats wetted 
and well-oxygenated and to prevent excess sedimentation but not so high 
as to dislodge individuals;
    (ii) Stable riffles and runs with cobble, gravel, and fine 
sediments;
    (iii) Blacktail shiner (Cyprinella venusta) and red shiner (C. 
lutrensis) present; and
    (iv) Water quality parameters within the following ranges:
    (A) Dissolved oxygen greater than 2 milligrams per liter (mg/L);
    (B) Salinity less than 2 parts per thousand;
    (C) Total ammonia less than 0.77 mg/L total ammonia nitrogen;

[[Page 48125]]

    (D) Water temperature below 29 [deg]C (84.2 [deg]F); and
    (E) Low levels of contaminants.
    (3) Critical habitat does not include manmade structures (such as 
buildings, aqueducts, runways, roads, and other paved areas) and the 
land on which they are located existing within the legal boundaries on 
July 5, 2024.
    (4) Data layers defining the map units were created on a base of 
U.S. Geological Survey digital ortho-photo quarter-quadrangles, and the 
critical habitat units were then mapped using Universal Transverse 
Mercator (UTM) Zone 14N coordinates. The maps in this entry, as 
modified by any accompanying regulatory text, establish the boundaries 
of the critical habitat designation. The coordinates or plot points or 
both on which the maps are based are available to the public at the 
Service's internet site at https://www.fws.gov/office/austin-ecological-services, at https://www.regulations.gov at Docket No. FWS-
R2-ES-2019-0061, and at the field office responsible for this 
designation. You may obtain field office location information by 
contacting one of the Service regional offices, the addresses of which 
are listed at 50 CFR 2.2.
    (5) Index map of critical habitat units for the Balcones spike 
follows:

Figure 1 to Balcones Spike (Fusconaia iheringi) paragraph (5)
BILLING CODE 4333-15-P

[[Page 48126]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.022

    (6) Unit BASP-1 is excluded from the designation pursuant to 
section 4(b)(2) of the Act.
    (7) Unit BASP-2: San Saba River; San Saba County, Texas.
    (i) Unit BASP-2 consists of 49.1 river miles (mi) (79.0 milometers 
(km)) in San Saba County, Texas. The riparian lands that border this 
subunit are in State/local government (1 percent) and private (99 
percent) ownership.
    (ii) Unit BASP-2 includes stream channel up to bankfull height.
    (iii) Map of Unit BASP-2 follows:
Figure 2 to Balcones Spike (Fusconaia iheringi) paragraph (7)(iii)

[[Page 48127]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.023

    (8) Unit BASP-3: Llano River; Kimble and Mason Counties, Texas.
    (i) Unit BASP-3 consists of 49 river mi (78.9 km) in Kimble and 
Mason Counties, Texas.
    (ii) Unit BASP-3 includes stream channel up to bankfull height.
    (iii) Map of Unit BASP-3 follows:

Figure 3 to Balcones Spike (Fusconaia iheringi) paragraph (8)(iii)

[[Page 48128]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.024

BILLING CODE 4333-15-C
False Spike (Fusconaia mitchelli)
    (1) The critical habitat unit is depicted for DeWitt, Gonzales, and 
Victoria Counties, Texas, on the map in this entry.
    (2) Within this area, the physical or biological features essential 
to the conservation of false spike consist of the following components 
within waters and streambeds up to the ordinary high-water mark:
    (i) Flowing water at rates suitable to keep riffle habitats wetted 
and well-oxygenated and to prevent excess sedimentation but not so high 
as to dislodge individuals;
    (ii) Stable riffles and runs with cobble, gravel, and fine 
sediments;
    (iii) Blacktail shiner (Cyprinella venusta) and red shiner (C. 
lutrensis) present; and
    (iv) Water quality parameters within the following ranges:
    (A) Dissolved oxygen greater than 2 milligrams per liter (mg/L);
    (B) Salinity less than 2 parts per thousand;
    (C) Total ammonia less than 0.77 mg/L total ammonia nitrogen;
    (D) Water temperature below 29 [deg]C (84.2 [deg]F); and
    (E) Low levels of contaminants.

[[Page 48129]]

    (3) Critical habitat does not include manmade structures (such as 
buildings, aqueducts, runways, roads, and other paved areas) and the 
land on which they are located existing within the legal boundaries on 
July 5, 2024.
    (4) Data layers defining the map unit were created on a base of 
U.S. Geological Survey digital ortho-photo quarter-quadrangles, and the 
critical habitat unit was then mapped using Universal Transverse 
Mercator (UTM) Zone 14N coordinates. The map in this entry, as modified 
by any accompanying regulatory text, establishes the boundaries of the 
critical habitat designation. The coordinates or plot points or both on 
which the map is based are available to the public at the Service's 
internet site at https://www.fws.gov/office/austin-ecological-services, 
at https://www.regulations.gov at Docket No. FWS-R2-ES-2019-0061, and 
at the field office responsible for this designation. You may obtain 
field office location information by contacting one of the Service 
regional offices, the addresses of which are listed at 50 CFR 2.2.
    (5) Unit FASP-1: Guadalupe River; DeWitt, Gonzales, and Victoria 
Counties, Texas.
    (i) Unit FASP-1 consists of two subunits:
    (A) Subunit FASP-1a (San Marcos River) consists of 21.2 river miles 
(mi) (34 kilometers (km)) of the in Gonzales County, Texas. The 
riparian lands that border this subunit are in State (8 percent) and 
private (92 percent) ownership.
    (B) Subunit FASP-1b (Guadalupe River) consists of 122.4 river mi 
(197 km) of the Guadalupe River in DeWitt, Gonzales, and Victoria 
Counties, Texas. The riparian lands that border this subunit are in 
State (2 percent) and private (98 percent) ownership.
    (ii) Unit FASP-1 includes stream channel up to bankfull height.
    (iii) Map of Unit FASP-1 follows:

Figure 1 to False Spike (Fusconaia mitchelli) paragraph (5)(iii)
BILLING CODE 4333-15-P

[[Page 48130]]

[GRAPHIC] [TIFF OMITTED] TR04JN24.025

* * * * *

Martha Williams,
Director, U.S. Fish and Wildlife Service.
[FR Doc. 2024-11645 Filed 6-3-24; 8:45 am]
 BILLING CODE 4333-15-C