[Federal Register Volume 76, Number 208 (Thursday, October 27, 2011)]
[Rules and Regulations]
[Pages 66780-66804]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2011-27375]



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Vol. 76

Thursday,

No. 208

October 27, 2011

Part II





Department of Interior





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Fish and Wildlife Service





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50 CFR Part 17





Endangered and Threatened Wildlife and Plants; Removal of the Concho 
Water Snake From the Federal List of Endangered and Threatened Wildlife 
and Removal of Designated Critical Habitat; Final Rule

  Federal Register / Vol. 76 , No. 208 / Thursday, October 27, 2011 / 
Rules and Regulations  

[[Page 66780]]


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DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[FWS-R2-ES-2008-0080; 92220-1113-0000-C6]
RIN 1018--AU97


Endangered and Threatened Wildlife and Plants; Removal of the 
Concho Water Snake From the Federal List of Endangered and Threatened 
Wildlife and Removal of Designated Critical Habitat

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Final rule.

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SUMMARY: The best available scientific and commercial data indicate 
that the Concho water snake (Nerodia paucimaculata), a reptile endemic 
to central Texas, is recovered. Therefore, under the authority of the 
Endangered Species Act of 1973, as amended (Act), we, the U.S. Fish and 
Wildlife Service (Service) remove (delist) the Concho water snake from 
the Federal List of Endangered and Threatened Wildlife, and 
accordingly, also remove its federally designated critical habitat. 
This determination is based on a thorough review of all available 
information, including new information, which indicates that the 
threats to this species have been eliminated or reduced to the point 
that the species has recovered and no longer meets the definition of 
threatened or endangered under the Act. We are also providing notice 
that the final post-delisting monitoring for the Concho water snake has 
been completed.

DATES: This final rule becomes effective on November 28, 2011.

ADDRESSES: The proposed rule, all comments received, the post-delisting 
monitoring plan, and this final rule are all available on the Internet 
at http://www.regulations.gov and http://www.fws.gov/southwest/es/AustinTexas/. Supporting documentation we used in preparing this final 
rule will be available for public inspection, by appointment, during 
normal business hours, at the U.S. Fish and Wildlife Service, Austin 
Ecological Services Field Office, 10711 Burnet Road, Suite 200, Austin, 
TX 78758; telephone 512-490-0057; facsimile 512-490-0974.

FOR FURTHER INFORMATION CONTACT: Adam Zerrenner, Field Supervisor, U.S. 
Fish and Wildlife Service, Austin Ecological Services Field Office (see 
ADDRESSES). If you use a telecommunications device for the deaf (TDD), 
call the Federal Information Relay Service (FIRS) at 800/877-8339.

SUPPLEMENTARY INFORMATION:

Background

    It is our intent to discuss in this final rule only those topics 
directly relevant to the removal of the Concho water snake from the 
Federal list of threatened species under the Endangered Species Act of 
1973, as amended (Act; 16 U.S.C. 1531 et seq.). The Concho water snake 
is endemic to the Colorado and Concho Rivers in central Texas (Tennant 
1984, p. 344; Scott et al. 1989, p. 373). It occurs on the Colorado 
River from E.V. Spence Reservoir to Colorado Bend State Park, including 
Ballinger Municipal Lake and O.H. Ivie Reservoir, and on the Concho 
River from the City of San Angelo, Texas, to its confluence with the 
Colorado River at O.H. Ivie Reservoir. At the time the species was 
listed as threatened in 1986 (51 FR 31412), there were considered to be 
two subspecies of Nerodia harteri, the Concho water snake (N.h. 
paucimaculata) and the Brazos water snake (N.h. harteri). Densmore et 
al. (1992, p. 66) determined the Concho water snake was a distinct 
species, and in 1996 we changed our reference to the species to 
recognize the scientific name N. paucimaculata (50 CFR 17.11). Some 
authors use the common name of Concho watersnake, based on Crother 
(2000, p. 67). However, this has not been universally adopted, so we 
continue to use Concho water snake in this rule. For more background 
information on the Concho water snake, refer to the proposed delisting 
rule published in the Federal Register on July 8, 2008 (73 FR 38956), 
the final listing rule published in the Federal Register on September 
3, 1986 (51 FR 31412), Campbell (2003, pp. 1-4), the 2004 revised 
biological opinion (BO) on water operations on the Concho and Colorado 
Rivers (Service 2004, pp. 1-76), and the 1993 Concho Water Snake 
Recovery Plan available online at http://ecos.fws.gov/docs/recovery_plan/930927b.pdf. We note that research conducted since the recovery 
plan was completed in 1993 has provided new information on the species.

Previous Federal Actions

    In June 1998, we received a petition from the Colorado River 
Municipal Water District (District) to delist the Concho water snake 
because our original data (regarding snake distribution and abundance 
and threats) for listing the snake were in error. On August 2, 1999, we 
published a 90-day petition finding (1999 petition finding) that the 
petitioner did not present substantial information indicating that 
delisting the species may be warranted (64 FR 41903). The petition did 
not contain any information addressing the threats to the species nor 
did it include a discussion of the three recovery criteria. As a result 
of the negative 90-day finding, we did not conduct a full status review 
at that time. However, in the process of revising the biological 
opinion under section 7 of the Act for the operations of the upper 
Colorado River dams in 2004 (Service 2004a), the Service determined 
there was sufficient new information available to warrant a status 
review of the species. This final rule constitutes the conclusion of a 
full status review of the Concho water snake and analyzes all of the 
outstanding concerns from the 1999 petition finding.
    On July 8, 2008, we published a proposed rule to remove the Concho 
water snake from the list of threatened species (73 FR 38956). A draft 
of the post-delisting monitoring plan was made available for public 
review and comment on September 23, 2009 (74 FR 48595).
    Additional background information regarding other previous Federal 
actions for the Concho water snake can be obtained by consulting the 
species' regulatory profile found at: http://ecos.fws.gov/speciesProfile/SpeciesReport.do?spcode=C04E.

Recovery

    Section 4(f) of the Act directs us to develop and implement 
recovery plans for listed species unless the Director determines that 
such a plan will not benefit the conservation of the species. The 
Service completed the Concho Water Snake Recovery Plan in 1993 (Service 
1993). The Concho Water Snake Recovery Plan outlines recovery criteria 
to assist in determining when the snake has recovered to the point that 
the protections afforded by the Act are no longer needed (Service 1993, 
p. 33). These criteria are: (1) Adequate instream flows are assured 
even when the species is delisted. (2) Viable populations are present 
in each of the three major reaches (the Colorado River above Freese Dam 
(forms O.H. Ivie Reservoir), Colorado River below Freese Dam, and the 
Concho River). Here, population is defined as all Concho water snakes 
in a given area, in this case, each major river reach. (3) Movement of 
an adequate number of Concho water snakes is assured to counteract the 
adverse impacts of population fragmentation. These movements should 
occur as long as Freese Dam is in place or until such time that the 
Service determines that Concho water snake populations in the

[[Page 66781]]

three reaches are viable and ``artificial movement'' among them is not 
needed.
    We used the recovery plan to provide guidance to the Service, State 
of Texas, and other partners on methods to minimize and reduce the 
threats to the Concho water snake and to provide criteria that could be 
used to help determine when the threats to the Concho water snake had 
been reduced so that it could be removed from the Federal List of 
Endangered and Threatened Wildlife.
    Provisions in recovery plans are recommendations that are not 
binding and can be superseded by more current scientific information. 
There are many paths to accomplishing recovery of a species in all or a 
significant portion of its range. The main goal is to remove the 
threats to a species, which sometimes may occur without meeting all 
recovery criteria contained in a recovery plan. For example, one or 
more criteria may have been exceeded while other criteria may not have 
been accomplished. In that instance, the Service may judge that, 
overall, the threats have been reduced sufficiently, and the species is 
robust enough, to reclassify the species from endangered to threatened 
or perhaps to delist the species. In other cases, recovery 
opportunities may be recognized that were not known at the time the 
recovery plan was finalized. Achievement of these opportunities may 
result in progress toward recovery in lieu of methods identified in the 
recovery plan. Likewise, we may learn information about the species 
that was not known at the time the recovery plan was finalized. The new 
information may change the extent that criteria need to be met for 
recognizing recovery of the species. Overall, recovery of a species is 
a dynamic process requiring adaptive management. Judging the degree of 
recovery of a species is also an adaptive management process that may, 
or may not, fully follow the guidance provided in a recovery plan.
    A review of the best scientific and commercial data currently 
available (see Summary of Factors Affecting the Species section below) 
indicates that all three criteria in the Concho water snake recovery 
plan (adequate instream flows even after delisting, viable populations 
in each of the three major river reaches, and movement of snakes to 
assure adequate genetic mixing) have been met. Further, recovery of the 
Concho water snake has been a dynamic process, which has been fostered 
by the significant amount of new data collected on the biology and 
ecology of the species by numerous species experts. Since the time of 
listing and preparation of the recovery plan, biologists have 
discovered that the snakes are able to persist and reproduce along the 
shorelines of reservoirs and that the snakes have managed to persist in 
all three population segments, surviving many years of drought. 
Including this new information, the analysis below considers the best 
available data in determining that the Concho water snake no longer 
meets the definition of a threatened or endangered species.

Summary of Comments and Recommendations

    In our proposed rule (71 FR 38956), we requested comments from the 
public on the proposed removal of the Concho water snake from the list 
of threatened species during a 60-day comment period that ended on 
September 8, 2008. We also contacted Federal agencies, State agencies, 
local officials, and congressional representatives to invite comment on 
the proposed rule.
    During the public comment period, we received no requests for a 
public hearing and none was held. Overall we received 23 written 
comments from the public. Twenty of these were similar letters that 
supported removal of the species from the protected list and stated 
that our decision to delist the Concho water snake was based on sound 
science. Two of these letters of support came from the Texas Department 
of Transportation (TxDOT) and Texas Parks and Wildlife Department 
(TPWD). Six of these letters were from city officials, ten were from 
river authorities or water districts, including the Colorado River 
Municipal Water District (District), and two were from private 
businesses. We also received one nonsubstantive comment and two 
substantive critical comments from professional biologists (one 
specifically expressed opposition to the proposal). Our responses are 
provided below to a summary of each substantive comment received.

Peer Review

    In accordance with our policy published on July 1, 1994 (59 FR 
34270), we solicited independent expert opinions from knowledgeable 
individuals with scientific expertise that included ecology of water 
snakes, conservation biology principles, and river hydrology. Out of 
seven individuals that agreed to provide peer review, we received six 
peer review comments. One peer reviewer stated support for the 
proposal. Three peer reviewers were noncommittal on their support, but 
provided many substantive comments and questions. Two peer reviewers 
stated opposition to the proposal and provided substantive criticism. 
Our responses are provided below to a summary of each substantive 
comment received from the peer reviewers.

Comments From Peer Reviewers

    (1) Comment: It is premature to delist the Concho water snake 
because essential data are lacking. For example, no data are presented 
on population structure, demographics, trends, or genetics.
    Our Response: The Act requires us to consider the best available 
information when making decisions on what species should be protected. 
Population demographic estimates have been reported for the Concho 
water snake (Whiting et al. 2008, pp. 441-442). While more quantitative 
analysis of population structure, trends, and genetics would be 
informative and useful to us in formulating this rule, we believe the 
data used in this final rule support our decision because it is derived 
from many years of monitoring collections (Thornton 1996, pp. 26-50, 
Forstner et al. 2006, p. 18) and consistent with the opinion of most 
experts on the Concho water snake. Reference the following sections 
below for descriptions of the best available information related to 
population structure, demographics, and genetics: A. The Present or 
Threatened Destruction, Modification, or Curtailment of Its Habitat or 
Range, Habitat Modification from Fragmentation; and Application of the 
Recovery Plan's Criteria, Population Viability. We find that the best 
available information supports the decision that the Concho water snake 
has recovered and no longer qualify as threatened.
    Past studies of the Concho water snake were intended to monitor the 
populations over time using mark-recapture techniques (that is, 
inserting a tag in captured snakes so that individuals can be 
identified when they are recaptured). Although these studies by the 
District (summarized in District 1998) resulted in a large number of 
snakes collected over 10 years (9,069 unique snakes), the study did not 
quantify the amount of effort expended during each survey, so that 
reliable population estimates or trends over time could not be 
calculated. Whiting et al. (2008) utilized these data to attempt to 
model population trends. However, the results proved too unreliable to 
effectively model population trends because the dispersal rates of 
snakes out of the study areas were not quantified. This resulted in a 
potential overestimate of the death rate of snakes that were not 
recaptured, when they could have, in fact, simply moved out of the 
study area

[[Page 66782]]

(Whiting et al. 2008, p. 443). The original study was not designed to 
accommodate a population viability analysis and attempts to do so 
provided results with an unacceptable degree of uncertainty and with 
imprecise conclusions. As a result, the best available information on 
snake populations supports that the snakes have persisted over a long 
time period throughout the majority of their historic range and have 
continued to persist following habitat alterations from reservoir 
inundation and drought.
    (2) Comment: The Concho water snake occupies an extremely small 
area of Texas, and one small mistake could easily cause the extinction 
in a significant portion (i.e., all) of its range. It is better to err 
on the side of caution than face the consequences of early protection 
removal.
    Our Response: The current range of the snake is estimated to total 
about 280 miles (mi) (451 kilometers (km)) of river and about 40 mi (64 
km) of reservoir shoreline. The best available information, including 
the reports of species experts (in particular Dr. James Dixon and Dr. 
Michael Forstner), does not indicate that the species is vulnerable to 
extinction. The recent studies available to us report that the species 
is capable of withstanding significant environmental perturbations 
(Dixon 2004, pp. 10-11; Forstner et al. 2006, pp. 16-18; Whiting et al. 
2008, p. 343). Under our post-delisting monitoring plan, we will be 
monitoring the status of the species and can emergency list it if 
necessary (see the Post-Delisting Monitoring Plan section below).
    (3) Comment: My strong conclusion is that viable populations of the 
Concho water snake have not been demonstrated. Documentation of 
persistence and reproduction is not adequate to determine population 
viability.
    Our Response: Please see our response below to Comment (28). We 
have updated the discussion of viable population in the final rule to 
be more consistent with the description used in the recovery plan for 
the species (see Application of the Recovery Plan's Criteria section 
below).
    (4) Comment: Survey results from Dixon (2004) and Forstner et al. 
(2006) failed to find snakes at some sample sites, indicating possible 
local extinctions and suggesting that recovery criterion 2 for viable 
populations has not been met and site occupancy may have decreased by 
23 to 27 percent.
    Our Response: Dixon made only one sampling visit to 13 sites and 
found Concho water snakes at all but 3 sites (Dixon 2004, pp. 4-5). 
Forstner et al. (2006, pp. 6-7, 12) surveyed several sites up to three 
times in 2005. They found snakes at all sites except for three sites on 
the Concho River, which were only sampled one time following a 
rainstorm event making detection difficult (Forstner et al. 2006, p. 
12). In contrast, earlier studies (District 1998, p. 13) resulted in 
consistent captures of snakes at nearly all sites surveyed, however, 
those sites were sampled three times or more annually. Both Dixon 
(2004, pp. 9, 14-15) and Forstner et al. (2006, p. 13) explain that 
there are a variety of field conditions that influence the ability to 
capture snakes at a given time and location. Variability of sampling 
success is common in field investigations, and both of these reports 
consisted of sampling efforts too small to interpret negative capture 
data as local extinctions or a decline in site occupancy.
    (5) Comment: I agree with the proposed rule to delist the Concho 
water snake, although I don't know if I believe that the Concho water 
snake has ``recovered'' as much as it continues to persist despite 
marked modifications to its habitat along the Colorado and Concho 
rivers. The snake is more of a habitat generalist than originally 
thought, and successful reproduction takes place under lower stream 
flows than previously indicated. The 2008 Memorandum of Understanding 
(MOU) between the Service and the Colorado Municipal Water District 
ensures adequate stream flows, although it may be strained by drought 
conditions. Twenty years of field studies demonstrate continued 
reproductive success in both the Concho and Colorado Rivers, including 
reservoirs. Dixon (2004) reports finding that dense vegetation and 
beavers failed to impede reproduction at the Freese Dam site, and he 
found the Elm Creek site, devoid of water for three years, still 
contained a reproducing population.
    Our Response: We agree that the best available information supports 
the decision to remove the Concho water snake from the list of 
threatened species under the Act. We recognize that our understanding 
of the snake's ecology has benefitted from new information that has 
been collected since the listing and since the recovery plan was 
completed. The removal of the snake from the list of threatened species 
is due both to recovery actions, such as the 2008 MOU with the 
District, and new biological information on the species' ability to 
persist in habitats such as reservoirs and no change (or slight 
increase) in the species' known range (about 80 river miles more than 
known at the time of listing).
    (6) Comment: The proposed rule uses an inappropriate timeframe for 
analysis of factors that could affect the species in the future. 
Factors that are not considered threats on a 20-year timeframe may 
threaten the species on a more meaningful timeframe of 50-100 years, 
which is consistent with the recovery plan.
    Our Response: We agree the 20-year foreseeable future was not a 
sufficiently long timeframe for our analysis. We have updated the rule 
to evaluate the threats to the species considering longer timeframes, 
as available information allows. In considering the foreseeable future 
in the threats analysis, we generally regarded 50 to 100 years as a 
time frame where some reasonable predictions could be made. This range 
of time originated from the analysis of forecasting for water 
management, which is looking ahead to expected conditions in the year 
2060 (TWDB 2007, p. 2), and consideration of climate change models, 
which typically forecast 50 to 100 years into the future (Bernstein et 
al. 2007, pp. 8-9; Jackson 2008, p. 8; Mace and Wade 2008, p. 656).
    (7) Comment: Lake populations are not as robust as the river 
populations (low densities via low recruitment), and their mere 
presence is not an indicator of population health. Lake populations 
appear to be isolated sinks and there may not be riverine recruitment 
from these populations. Due to the relatively recent appearance of the 
lakes, the data are only isolated snapshots and more monitoring is 
necessary before we know the true effects of river modification on 
Concho water snake populations.
    Our Response: Recruitment is the successful influx of new members 
into a population by reproduction or immigration (Lincoln et al. 1998, 
p. 257). Sinks are populations or breeding groups that do not produce 
enough offspring to maintain themselves without immigrants from other 
populations. Please see our responses to Comments (1) and (28) for 
related information. Dixon (2004, p. 14) states that both reservoirs 
(Ivie and Spence) provide prime habitat for Concho water snakes along 
the rocky shorelines. Whiting et al. (1997, p. 331) found over 300 
individual snakes in Lake Spence 20 years after the reservoir was 
filled. Also, analysis by Whiting et al. (2008, pp. 439, 443) found no 
evidence of a difference in survival among the five subpopulations 
(including three riverine reaches and two reservoirs). This suggests 
there may be no difference in survival rates between reservoir and

[[Page 66783]]

riverine snake populations, although the authors recognize that the 
data from reservoirs were not sufficient for reliable estimates of 
snake survival and population growth (Whiting et al. 2008, p. 443).
    Successful use of the reservoirs by Concho water snakes is one 
factor we considered in this decision and provides some added assurance 
that the snakes are not likely to become endangered in the foreseeable 
future. It is not unexpected that populations of the snakes in the 
artificial habitat of the reservoirs may not be as robust by some 
measures compared with populations in the natural riverine habitat. 
However, we have no information that indicates the snakes in reservoirs 
are population sinks. We know that the snakes have been shown to 
persist and reproduce in Spence Reservoir for at least 35 years after 
construction (1969 to 2005) and in Ivie Reservoir for at least over 15 
years after construction (1989 to 2005) (Forstner et al. 2006, p. 12). 
The Service finds that this is a sufficient amount of time to determine 
that snakes are likely to continue to persist in reservoirs in the 
foreseeable future.
    (8) Comment: Evidence of successful reproduction from Forstner et 
al. (2006) is based on flawed analysis of mass-length relationships for 
female snakes. This relationship is curvilinear (represented by a 
curved, rather than straight, line) and, therefore, the data should 
have been log transformed or fit using a power function rather than a 
simple linear analysis. Based on this, at most only one of the four 
females found by Forstner et al. (2006) appears to have low mass 
suggesting a post-partum state that indicates reproduction. Also, since 
evidence of reproduction was found at only a single site below Freese 
Dam (Ivie Reservoir) by Forstner et al. (2006), it is premature to 
conclude that a viable population exists in this reach.
    Our Response: We agree that the use of a curvilinear function 
analysis would have been more statistically robust in the Forstner et 
al. (2006, p. 11) report to evaluate reproductive status of females. 
However, this analysis was not intended to make a strong statistical 
argument, but simply to substantiate the field observations of females 
appearing to be post-partum. These adult female snakes had lower body 
tone in the rear third of the body indicating (in the authors' 
experience with this taxon and with snakes in general) that recent 
offspring had been released. Although access to the river reach 
downstream of Freese Dam (Ivie Reservoir) was limited due to private 
property, Forstner et al. (2006, p. 18) conclude that, even with 
limited samples, snakes were found at the two sites available in this 
reach documenting that the species was persisting and reproducing in 
this reach. This information serves to confirm the results of the 
earlier 10 years of monitoring studies that found large numbers of 
snakes in this reach, and throughout the species' current range.
    (9) Comment: The simple interpretation of lambda ([lambda], a 
calculation of the finite rate of population increase) from Whiting et 
al. (2008) using the preferred stage-based model ([lambda] = 0.67 to 
0.78) is that the species is declining 22 to 33 percent per generation. 
This, in addition to low survivorship of neonates, is strong evidence 
that Concho water snake populations are not viable.
    Our Response: Whiting et al. (2008, p. 443) explains that the 
modeling results of the finite rate of increase from the mark-recapture 
study were biased low due to the effect of dispersal of snakes out of 
the study areas, and this is what produced the low estimate of 
[lambda]. Since dispersal rates were not measured in the study, the 
analysis resulted in a large standard error and imprecise conclusions 
with high uncertainty. Whiting et al. (2008, p. 443) go on to conclude 
that the Concho water snakes have evolved through stochastic 
environmental fluctuation (such as droughts, floods, and fires) and 
occur in high densities in riverine habitats, with low extinction risk. 
This finding is consistent with the conclusion by Forstner et al. 
(2006, p. 19) that the populations of the snake appear to be viable. 
Whiting et al. (2008, p. 442) suggested that low survivorship values 
(for both juveniles and adults--rates for neonates were not calculated) 
compared to other similar snakes are being offset by increased 
reproductive effort with higher clutch sizes (number of young produced) 
in Concho water snakes than other similar snakes (Greene et al. 1999, 
pp. 706-707). Also see our response to (1) Comment above.
    (10) Comment: The documented persistence of Concho water snakes 
during long-term droughts, coupled with the 2008 MOU, which will 
maintain minimum flow releases, provide a reasonable amount of 
confidence that the recovery criterion for maintaining adequate flows 
has been met. Loss of flows no longer poses a significant threat to the 
Concho water snake.
    Our Response: We agree. The minimum flow releases provided by the 
2008 MOU, other reservoir releases for water delivery and water quality 
management, and natural inputs to the rivers from springs and tributary 
streams, combined with the snakes' ability to withstand stochastic 
events like droughts, make this threat no longer of sufficient 
magnitude to warrant the species' listing as threatened.
    (11) Comment: The 2008 MOU states that the District can further 
reduce or even terminate flows during times of extremely low inflow. 
Given the fairly well documented climate change that is now occurring, 
which may influence the lengths of drought in the region (and hence the 
amount of inflow), coupled with the thought that these animals rarely 
live longer than 5 years, I question whether it is reasonable to leave 
the MOU so loosely written. Perhaps the Service might choose to be 
notified after some length of time has passed with no flow occurring so 
that an assessment can be made as to its effects on the snake 
populations?
    Our Response: The 2008 MOU between the Service and the District 
does provide the District the ability to forego the minimum flow 
releases in the event of ``extended hydrological drought and to provide 
water for health and human safety needs.'' The drought measure is based 
on reservoir elevation (1,843.5 feet (ft) (561.9 meters (m)) above mean 
sea level at Spence Reservoir, and 1,504.5 ft (458.5 m) at Ivie 
Reservoir). These elevations represent the stage when the reservoirs 
are at about 12 percent of reservoir capacity. These criteria for 
foregoing minimum flow releases are consistent with the operations 
included in the 2004 Biological Opinion (Service 2004a, pp. 11-12). 
Since Spence Reservoir was initially filled in 1971, the water level 
elevation has only been below this mark during 2002 to 2004, at the end 
of a prolonged drought extending from 1992 to 2003 (District 2005, pp. 
39-43). This reach of the Colorado River below Spence Reservoir makes 
up about 36 percent of all estimated available habitat within the 
current range of the Concho water snake (Service 2004a, p. 72). Ivie 
Reservoir has not been below this mark since it initially filled in 
1991. Discharge in the river is well-monitored with gauges maintained 
by the U.S. Geological Survey (USGS), and flow data (historical and 
real time) are available on-line. Reservoir stage data are also 
available on-line on the District's webpage. Therefore, these data can 
be easily accessed making a notification process unnecessary. Under our 
post-delisting monitoring plan, we will be using existing stream gauges 
to monitor instream flows throughout the range of the snake. This 
information will be used in combination with biological monitoring data 
to assess the status of the species in the future (see

[[Page 66784]]

the Post-Delisting Monitoring Plan section below).
    We have revised our discussion of the effects of drought on the 
Concho water snake and included in the discussion a consideration of 
future climate change (see section A. The Present or Threatened 
Destruction, Modification, or Curtailment of Its Habitat or Range, 
Habitat Modification from Reduced Instream Flows, below). Also, see our 
response to Comment 12 below.
    (12) Comment: Drought continues to be a threat because, despite the 
species' persistence through historic droughts, it now occurs in 
combination with other stressors, such as reduced availability of 
riffles, vegetation encroachment, and changing prey base that may 
compromise survival and population recovery following a drought.
    Our Response: We have substantially increased our analysis in this 
final rule of the potential effects of declining flows due to drought, 
as well as other threats (see Summary of Factors Affecting the 
Species). We found none of these potential threats, either acting alone 
or in combination, have resulted in negative responses by the snake 
sufficient to justify the species' continued listing as threatened. 
Forecasting the impacts from future climatic events, such as drought, 
is difficult to quantify because of the large amount of uncertainty 
associated with climate modeling, particularly related to precipitation 
forecasting. However, we revised our discussion of threats related to 
drought and climate change in this final rule (see section A. The 
Present or Threatened Destruction, Modification, or Curtailment of Its 
Habitat or Range, Habitat Modification from Reduced Instream Flows 
below).
    We do not foresee future habitat conditions deteriorating to a 
point where the species is likely to become endangered. Forstner et al. 
(2006, pp. 15-17) and Whiting et al. (2008, p. 343) explain that the 
snake is well adapted to extreme drought conditions. This is 
demonstrated in the Concho River where the snake continues to persist 
despite extremely low flow conditions (Dixon 2004, pp. 8-9, Forstner et 
al. 2006, p. 8). The snake has been shown to be more abundant and 
widespread than originally thought and capable of surviving in 
reservoirs (District 1998, pp. 18-29). Reservoir operations have 
provided continual stream flows that have sustained the habitat for the 
species, even during the prolonged drought extending from 1992 to 2003 
(District 2005, pp. 39-43), and we expect minimum reservoir releases to 
continue. In addition, the snake is equipped to handle stochastic 
environmental fluctuations, such as low stream flow conditions 
resulting from drought, and has demonstrated the ability to persist in 
these less-than-favorable habitat conditions (Forstner et al. 2006, p. 
17; Whiting et al. 2008, p. 443). Also, the threat of vegetation 
encroachment is no longer considered a significant threat because the 
snake has shown the ability to maintain populations in river reaches 
with substantial vegetation encroachment (Dixon 2004, p. 9). 
Additionally, habitat restoration efforts such as the removal of salt 
cedar and other brushy species and the creation of artificial instream 
riffle structures are aimed at improving habitat for the Concho water 
snake to increase their likelihood of survival during droughts and 
other stressors. We expect some salt cedar control efforts to continue 
into the foreseeable future.
    (13) Comment: The importance of groundwater-surface water 
interactions to maintain adequate flows is stressed in the proposed 
rule. However, there does not appear to be a clear understanding of 
where groundwater pumpage for consumptive use has influenced base 
flows. Existing groundwater-surface water interaction models, and even 
simple gain and loss studies, could provide critical information 
regarding where the influence of groundwater pumping may influence 
critical flows and available habitat.
    Our Response: We agree this could be important information to 
consider. We assume there is some influence of local and regional 
groundwater withdrawals on the availability of water for instream 
flows. However, we are not aware that such information is currently 
available or that to quantify this relationship within the range of the 
Concho water snake is possible at this time.
    (14) Comment: Has the occurrence and status of riffle habitat been 
quantified using GIS or remote imagery in the reaches where the species 
is known to occur?
    Our Response: We are not aware of the availability of this type of 
information, and the publicly available imagery is not of sufficient 
resolution to reliably quantify snake habitat in the river. The Service 
did estimate the quantity and quality of snake habitat by reach in the 
2004 Biological Opinion (Service 2004a, Appendix B, pp. 70-72), and we 
consider it to still be reasonably accurate and the best information 
available . The information has been added to this final rule (see A. 
The Present or Threatened Destruction, Modification, or Curtailment of 
Its Habitat or Range, Habitat Quality and Quantity section below). The 
river reaches in question remain largely undeveloped.
    (15) Comment: The suggestion that pool habitats, created by the 
backwater behind low-head dams, provide refuges for snakes during 
drought is unsubstantiated. These habitats may represent population 
sinks, where mortality exceeds recruitment.
    Our Response: The suggestion that pools behind low-head dams act as 
refuge habitats comes from the expert opinion of Dr. James Dixon (Dixon 
2004, p. 16). Dr. Dixon is considered a reliable source, as he has 
studied this species since 1991 (see Werler and Dixon 2000, pp. 209-
216).
    (16) Comment: The proposed rule indicates that `an excellent first 
step' in reversing vegetation encroachment has been accomplished (73 FR 
38962). While laudable, a `first step' should not be construed as 
success in eliminating vegetation encroachment as a threat.
    Our Response: Recent efforts by the District to control salt cedar 
are conservation actions that we expect will benefit the Concho water 
snake through maintaining native riparian vegetation and possibly 
providing additional instream flows. These actions do not completely 
eliminate vegetation encroachment. However, vegetation encroachment, 
such as has occurred on the Concho River, is not considered a 
significant threat since the snake has shown the ability to maintain 
populations in river reaches with substantial vegetation encroachment 
(Dixon 2004, p. 9). We have revised the discussion of vegetation 
encroachment within this final rule (see A. The Present or Threatened 
Destruction, Modification, or Curtailment of Its Habitat or Range, 
Habitat Modification from Reduced Channel Maintenance Flows section 
below).
    (17) Comment: It seems reasonable to assume that there is likely 
movement between snake populations with the discovery that the snakes 
are living in the reservoirs, and, therefore, likely little threat from 
population fragmentation. Have there been studies of possible gene flow 
between the populations?
    Our Response: We agree that fragmentation has been reduced with the 
new information on the persistence of the snake in reservoirs. We 
presume that over time, this allows snakes from the upper Colorado 
River reach (below Spence Reservoir) to interact with snakes from the 
Concho River reach by moving through Ivie Reservoir. Previous studies 
conducted on gene flow suggested that populations of snakes above and 
below Freese Dam should be more than large enough to maintain

[[Page 66785]]

existing genetic variation based on mitochondrial DNA analysis (Sites 
and Densmore 1991, p. 10). We presume that is still the case. Densmore 
(1991, pp. 10-11) went on to say that periodic transfer of snakes 
should probably be implemented to mimic gene flow. More recent analysis 
has been initiated using modern molecular techniques to evaluate 
possible gene flow between populations, but data or results from these 
studies by Dr. Michael Forstner (2008) have not yet been reported. 
Forstner (2008, p. 14) does suggest that there is no evidence that 
Freese Dam (Ivie Reservoir) is a barrier to gene flow for either water 
snake in the Colorado River. However, the report notes that it may have 
been too short a time to detect such a change (Forstner 2008, pp. 14-
15), and we do not know whether there are adequate sample sizes from 
this study to reliably describe gene flow levels between populations or 
river reaches; however, the 2008 MOU calls for the movement of snakes 
to provide some gene flow between river reaches.
    (18) Comment: Have any mark and recapture studies been done to 
demonstrate the movement of snakes between fragmented habitat, e.g., 
from reservoir to below reservoir and to quantify dispersal of 
individuals within reservoirs?
    Our Response: Some mark-recapture and radio telemetry studies have 
documented movements in Concho water snakes (Werler and Dixon 2000, p. 
212). Although most snakes showed strong site fidelity, some snakes 
moved as far as 12 mi (19 km). No studies have documented long-range 
movements between populations or around a large dam. However, the 2008 
MOU calls for periodic movement of snakes around the large dams. In 
addition, the 2008 MOU was amended in 2011 to also include the movement 
of five snakes from above both dams to below both dams. The 2008 MOU 
calls for the movement of five snakes from below Spence and Freese dams 
to above these dams every 3 years. This amount of transfer of snakes 
should be more than sufficient to maintain gene flow, as studies have 
shown that as few as one individual exchanged with each generation may 
be sufficient to maintain adequate gene flow between animal populations 
(Mills and Allendorf 1996, p. 1,557). Also see the discussion below 
under Habitat Modification from Fragmentation.
    (19) Comment: What is the evidence that fish populations are viable 
and that cyprinids (minnows) and their habitat (e.g., riffles) are of 
sufficient quality and quantity in all three reaches? Is the opinion of 
one or more scientists adequate, or is there sufficient data on the 
status or trends of fishes in the three reaches to support the 
assumption that the fish prey base for the Concho water snake is 
sufficient? Are there data, such as the Texas Commission on 
Environmental Quality's (TCEQ) Clean Rivers Program data on fishes, 
which could be analyzed to determine if there are any trends in fish 
populations worth noting? How are the fish populations that the snakes 
depend on for food going to fare in situations like prolonged drought?
    Our Response: We have revised the discussion of forage fish 
availability under the section A. The Present or Threatened 
Destruction, Modification, or Curtailment of Its Habitat or Range, 
Habitat Modification from Reduced Instream Flows below to better 
explain why we do not find that lack of forage fish is a significant 
threat to the snake. We are not aware of additional fish data that 
could inform our decision on the Concho water snake. However, a review 
of the 10 years of fish surveys by the District from 1987 to 1996 
showed that the snakes were opportunistic predators on a variety of 
fish species (Service 2004a, Appendix A, pp. 68-69). The most abundant 
fish available and in the snakes' diet are fish species that are 
adapted to harsh stream conditions (intermittent flow and poor water 
quality), such as red shiners (Cyprinella lutrensis) (Burkhead and Huge 
2002, p. 1) and fathead minnows (Pimephales vigilax) (Sublette et al. 
1990, pp. 162-166). Together these two fishes made up two-thirds of the 
diet of the Concho water snakes. We expect populations of these fish 
species to persist in harsh environments with intermittent water 
available (Burkhead and Huge 2002, p. 1; Sublette et al. 1990, pp. 162-
166). We also expect them to quickly recolonize stream reaches from 
reservoirs or other refuge habitats after dewatered conditions due to 
drought have ended. This is based on observations of the snakes being 
found at sites where they were absent due to lack of water and being 
found again when the water returns. This occurred in 2004 at Ballinger 
Lake and Elm Creek (Dixon 2004, pp. 4, 11-12; Forstner et al. 2006, p. 
15).
    (20) Comment: Were nutrient concentrations in water actually 
evaluated in relation to algal productivity? Is the fish assemblage 
changing in species composition or relative abundance in response to 
changing nutrient conditions?
    Our Response: The reference to nutrient concentrations and algal 
productivity was related to past concerns as a possible threat to the 
Concho water snake during the 1986 listing. We are not aware of data 
connecting increases in nutrient concentrations to algal productivity 
or changes in fish species composition or relative abundance within the 
range of the Concho water snake. There has been no subsequent 
indication that these threats are actually occurring or are affecting 
fish communities or snake populations.
    (21) Comment: References in reports indicate decreased cooperation 
by private landowners, indicating stakeholder buy-in is inadequate, 
raising the possibility that harassment and persecution of snakes now 
and following delisting is a threat.
    Our Response: We have no information that intentional harassment 
and persecution by landowners or recreationists are likely to affect 
the species on a rangewide or local population level. The reference 
(Forstner et al. 2006, p. 18) did not indicate decreased cooperation by 
private landowners, but that new landowners were not easily contacted 
due to changing ownership. We have revised the discussion to further 
explain this threat under Factor B. Overutilization for Commercial, 
Recreational, Scientific, or Educational Purposes.

Comments From State Agencies

    (22) Comment: The TPWD accepted the District's 1998 arguments to 
delist the Concho water snake and did so on November 16, 2000. TPWD 
believes the continuing conservation efforts of the District and other 
interested parties will ensure the snake's place as a member of the 
native fauna of Texas for the foreseeable future.
    Our Response: We agree with the comment by the TPWD that the Concho 
water snake no longer qualifies as a threatened species.
    (23) Comment: Removing the Concho water snake from protection under 
the Act will reduce the costs and time associated with section 7 
consultations with the U.S. Fish and Wildlife Service. As a result, 
TxDOT may now delay the letting of some projects until after the final 
delisting occurs.
    Our Response: We understand that removing the species from the 
Federal list of threatened species will benefit some planned actions by 
eliminating the requirement for section 7 consultations for actions 
with a Federal nexus that may affect the Concho water snake.

Comments From the Public

    (24) Comment: A comment from the District explained that they 
conducted field studies on the Concho water snake

[[Page 66786]]

from 1987 to 1996 that demonstrated the snake population was much more 
stable than previously thought. Later field studies in 2003 to 2007 
determined the snake was in a recovered state. Additionally, the 
District agreed to provide stream flow discharge from two of its 
Colorado River reservoirs (E.V. Spence and O.H. Ivie Reservoirs), which 
further supports the long-term existence of the snake.
    Our Response: The Service recognizes the many years of field 
studies that the District conducted, and the benefits of the District's 
partnership with the Service in signing the 2008 MOU to provide 
reservoir releases for the Concho water snake. The recovery of the 
Concho water snake and its removal from the list of threatened species 
are largely due to the efforts of the District to provide reservoir 
releases to maintain snake habitats over the past 20 years and into the 
future, and to collect new information documenting the biology, 
distribution, and abundance of the snake.
    (25) Comment: The proposed delisting fails to make a convincing 
case that recovery of the Concho water snake is sufficient to justify 
its removal from threatened species protections. The proposal's 
arguments are vague, circular, repetitive, and sometimes contradictory. 
There is little supporting data or science provided. The delisting is 
premature and unsupported.
    Our Response: We disagree with the commenter's conclusions. We have 
updated and clarified the text in this final rule in response to this 
and other comments received to better explain our analysis and 
conclusions. Specifically, we revised the discussion and analysis under 
section A. The Present or Threatened Destruction, Modification, or 
Curtailment of Its Habitat or Range. The Service believes the removal 
of the snake is warranted based on the best available scientific 
information.
    (26) Comment: The proposed rule fails to adequately address 
availability of, and threats to, the important riffle habitats of the 
Concho water snake. For example, reservoir habitats used by the snake 
must be equal to or greater than the amount of riverine riffle habitats 
lost due to effects of the reservoir construction at O.H. Ivie 
Reservoir. The range extension for the snake does not include 
information on the amount and quality of habitat and its use by snakes. 
There is no estimate provided of past or future loss of riffle habitat, 
or an assessment of the long-term success of the artificial riffles, to 
support that riffle habitat loss is not still a threat to the Concho 
water snake.
    Our Response: We recognize that there has been, and will continue 
to be, changes in the characteristics of the riverine habitat within 
the range of the Concho water snake as a result of past and ongoing 
human activities. While there have not been any recent studies to 
quantify these changes, the best available data indicate that any 
possible loss of riffle habitat is not resulting in impacts that would 
likely cause the snake to become endangered. The best example is 
observed in the Concho River where the long-term substantial decline in 
minimum stream flows and the loss of flushing flood flows have reduced 
natural riffle habitats available (Dixon 2004, pp. 8-9). However, 
Concho water snakes continue to persist in relatively high numbers in 
this reach. For example, 20 of the 45 Concho water snakes observed or 
captured by Forstner et al. (2006, p. 8) were from the Concho River. In 
addition, the snake's use of other habitats, including reservoir 
shorelines, lessens the overall effect of decreased riffle habitat 
availability. We have revised our discussion in this final rule and 
provided a quantified estimate of habitat availability by reach 
throughout the range of the species (see section A. The Present or 
Threatened Destruction, Modification, or Curtailment of Its Habitat or 
Range, Habitat Quality and Quantity below).
    (27) Comment: The proposed rule fails to address the size and 
health of reservoir populations. Whiting et al. (2008) notes that the 
species occurs in relatively low densities in reservoirs, and they 
believe the snake may be more vulnerable to extinction in reservoirs. 
It appears unlikely that the use of reservoir habitats by Concho water 
snakes provides sufficient improvement in species status to support 
removal of threatened protection.
    Our Response: The ability of Concho water snakes to survive and 
reproduce in reservoirs is one factor among many we considered in 
determining that the species is no longer threatened. There is some 
evidence that snake populations in the reservoirs are not as robust as 
those in their native riverine habitats. We would expect this given 
that the snake habitat in reservoirs is likely of a somewhat lower 
quality and in less abundance compared to natural riverine habitats. 
This is because the reservoirs may have less shallow flowing water over 
rocky substrates that support small fish that are the prey base for the 
snake. However, Whiting et al. (2008, p. 443) concluded that data are 
not sufficient for truly reliable estimates of snake survival and 
population growth in either of the two main reservoirs. Although the 
authors aimed to compare populations in reservoirs with those in 
rivers, data did not allow that analysis due to the inability to 
sufficiently quantify immigration rates (Whiting et al. 2008, p. 443). 
The statement by Whiting et al. (2008, p. 443) that Concho water snakes 
may be more vulnerable to local extinction in lakes was in the context 
that the extinction risk in natural river habitats is relatively low 
due to the snake's occurrence in high densities and their ability to 
grow fast and mature early. The ability of the species to utilize 
reservoirs is a positive discovery and supports the conclusion that the 
impacts of the reservoirs were not as great as initially predicted. 
Also, see our response to (1) Comment above.
    (28) Comment: The proposed rule indicated that confirming that a 
species has persisted over time and continues to demonstrate 
reproductive success is sufficient to assume that populations are 
viable. Persistence and reproduction are not adequate to demonstrate 
population viability. The statement that the populations are 
``seemingly viable'' is a tentative conclusion that is scientifically 
and legally unsupportable.
    Our Response: Our explanation of population viability may have 
oversimplified the explanation by Forstner et al. (2006, p. 20) 
describing the status of Concho water snake populations. We understand 
that documenting persistence and reproduction is not adequate to 
precisely determine viability in most quantitative ecological contexts. 
In response to this comment, we have updated our explanation to 
describe that there are not adequate data for quantitative modeling for 
population viability analysis of this species (see Application of the 
Recovery Plan's Criteria section below). We have revised this 
discussion in the final rule to instead refer to the definition of 
viable population given in the recovery plan. The recovery plan defines 
viable population as one that is self-sustaining, can persist for the 
long-term (typically hundreds of years), and can maintain its vigor and 
its potential for evolutionary adaptation (Service 1993, p. 33). We 
have also included a more detailed summary of the results of the 10 
years of snake monitoring, which concluded in 1996. These extensive 
data, in conjunction with updated limited survey data in 2004 and 2005, 
are the basis for determining that populations of Concho water snake 
are viable. In addition, it is important to recognize the standard 
under the Act is to determine if the species is likely to become 
endangered in the foreseeable future. Given the best available 
information, weighing the status of the species and

[[Page 66787]]

the current and future threats, we have concluded that the snake is no 
longer likely to become endangered in the foreseeable future throughout 
all or a significant portion of its range.
    (29) Comment: The discussion in the proposed rule regarding effects 
of drought is poorly articulated and circular. The stated belief that 
the Concho water snake and its fish prey base can and will survive any 
level and duration of drought is unsupported by data or analysis in the 
proposal.
    Our Response: We did not intend to imply that snakes can survive 
any level of drought, but we believe they can survive the expected 
drought conditions in the foreseeable future, based on historical 
records and considerations over the last thousand years based on tree-
ring analysis (summarized in Forstner et al. 2006, p. 16). We are 
relying on the expert opinion and field experience of long-term 
herpetologists, explained in Forstner et al. (2006, pp. 15-17) and 
Whiting et al. (2008, p. 443) that the Concho water snake has evolved 
in a drought-prone, hydrologically dynamic system and has demonstrated 
the ability to withstand stochastic environmental fluctuations. This 
characteristic of the snake to endure periods of drought and resulting 
poor habitat conditions was documented for the Concho River reach and 
at Lake Ballinger on Elm Creek, a Colorado River tributary (Dixon 2004, 
pp. 9, 11-12; Forstner et al. 2006, p. 17; Whiting et al. 2008, p. 
443). Due to water management and climate change, future droughts could 
be more severe than the historical record over the last 100 years. 
However, we cannot foresee that these conditions are likely to be so 
severe as to result in the extinction or endangerment of the snake. To 
make this explanation clearer, we have rewritten the discussion in this 
final rule (see section A. The Present or Threatened Destruction, 
Modification, or Curtailment of Its Habitat or Range, Habitat 
Modification from Reduced Instream Flows below).
    (30) Comment: The success in abatement of threats over the 22 years 
since the Concho water snake was listed appears to be overstated in the 
proposed rule. Long-term success of artificial riffle construction to 
increase riverine habitat is not yet determinable. The 15 or so years 
since artificial riffle installation are not long-term in a hydrologic 
sense. It is my understanding the artificial riffles have not been 
assessed for several years.
    Our Response: The artificial riffles constructed in 1989 produced 
immediate results as snakes were found there by 1991 (District 1998, 
pp. 13, 15). The six riffles were monitored from their creation in 1991 
through 1996, and snakes were consistently found at five of the six 
sites (Thornton 1996, pp. 44-49). The success of the snakes in the 
reservoirs and in the artificial riffles resulted in less attention 
being given to the need to mitigate further for the habitat loss from 
reservoir construction. We are not aware of any recent monitoring 
efforts focused on the artificial riffles, but we have no reason to 
believe the snakes are not continuing to persist there.
    (31) Comment: Other than species persistence, data and studies upon 
which the 2004 reduction of minimum instream flows was based are not 
discussed. There are also no studies documenting the results of the 
reductions in the required flow.
    Our Response: A full explanation and analysis of effects of the 
2004 reduction in required flows is documented in the Service's 
biological opinion provided to the U.S. Army Corps of Engineers as a 
conclusion to the formal section 7 interagency consultation for the 
change in reservoir operations (Service 2004a, pp. 1-76). The analysis 
included updated biological information that the snakes use more 
diverse riverine habitats (such as pools, in addition to riffles) and 
were found in the reservoirs and tributaries (Dixon 2004, pp. 9, 16; 
Service 2004, pp. 53-54). As a result of that consultation, we gave our 
biological opinion that the reduced reservoir releases described in the 
proposed agency action were not likely to jeopardize the continued 
existence of the Concho water snake and were not likely to destroy or 
adversely modify designated critical habitat. These same flow rates 
were used in the 2008 MOU. In making the delisting proposal and now the 
final rule, we relied heavily on the results of monitoring by Forstner 
et al. (2006, p. 1-22) in concluding that the reduced flow rates are 
sufficient for the snake.
    (32) Comment: The 2004 Biological Opinion substantially changed the 
1986 requirement for high discharge channel maintenance flows below 
O.H. Ivie Reservoir. That change is not discussed in the proposed rule, 
and would be of particular importance in understanding the basis for 
the habitat loss downstream of reservoirs.
    Our Response: We have added information to the final rule 
explaining the changes in requirements for channel maintenance flows 
(see section A. The Present or Threatened Destruction, Modification, or 
Curtailment of Its Habitat or Range, Habitat Modification from Reduced 
Channel Maintenance Flows below). The 2004 Biological Opinion and the 
2008 MOU both recognize the benefits of periodic high discharges from 
either reservoir releases or flood runoff events to function in river 
channel maintenance to maintain suitable rock substrates and abate 
vegetation invasion of riffle habitat. Our analysis concludes that some 
flushing flows are likely to naturally occur, slowing the degradation 
of aquatic habitats. In addition, the snakes appear capable of 
sustaining populations in areas where instream habitats have been 
altered due, in part, to reducing flushing flows. In some areas, such 
as on the Concho River, the dominant substrate is solid bedrock and not 
as subject to invasion of vegetation. Cracks and breaks in the bedrock 
provide foraging habitat similar to riffles. Therefore, we did not find 
that the threats of reduced flushing flows are significant.
    (33) Comment: Although the proposed rule says that the District has 
implemented every activity requested by the Service in previous 
biological opinions, the District's compliance was largely due to 
removal of requirements that they objected to prior to finalizing the 
opinion and removal of others by later amendments. The statement that 
the District has an excellent track record of carrying out conservation 
actions should be supported by information.
    Our Response: The 1986 Biological Opinion was amended many times up 
until the major revision in 2004 due to changing conditions based on 
new information being collected (Service 2004a, pp. 1-3). A discussion 
of the District's compliance efforts under the previous biological 
opinions is documented in the 2004 revised biological opinion (Service 
2004a, pp. 42-47). We have also added information throughout this final 
rule to document important areas where the District has fulfilled its 
requirements.
    (34) Comment: There is no evidence provided that the instream flow 
requirements from the 2004 Biological Opinion and 2008 MOU are 
sufficient to ensure long-term species survival.
    Our Response: We believe the flows provided in the 2008 MOU are 
sufficient to ensure long-term species survival. This is based on the 
information demonstrating that the species can survive under 
substantially lower flows compared to what was previously thought. 
These conclusions are based on the observations and reports of species 
experts (Dixon 2004, p. 16; Forstner et al. 2006, pp. 19-21; Whiting et 
al. 2008, p. 443). We have also revised the discussion of the threats 
from reduced instream flows in this final rule to include additional 
information and discussion on hydrology, climate

[[Page 66788]]

change, and the potential response by the snake (see section A. The 
Present or Threatened Destruction, Modification, or Curtailment of Its 
Habitat or Range, Habitat Modification from Reduced Instream Flows 
below).
    (35) Comment: The 2008 MOU was entered in good faith, but it is not 
legally enforceable. There is no consequence to the District for a 
lapse in conservation actions. The MOU is not an adequate substitute 
for legal protection under the Act.
    Our Response: We do not consider the 2008 MOU (including the 2011 
amendment) as a substitute for the legal protections under the Act. It 
does document the commitment that the District will continue to 
cooperate in maintaining instream flows downstream of the two Colorado 
River reservoirs. These flows are in addition to other reservoir 
releases for water delivery and water quality management, and natural 
inputs to the rivers from springs and tributary streams. Given the 
District's track record of compliance and completing conservation 
actions, we have no reason to doubt that the District will continue to 
carry out the actions agreed to in the 2008 MOU (including the 2011 
amendment). In addition, Section 5.2 of the MOU notes the Service's 
ability to list the snake again under protection of the Act. This 
provision includes use of emergency listing procedures if warranted.
    (36) Comment: Initiation of salt cedar control does nothing to 
guarantee threat abatement to Concho water snake habitat. Salt cedar 
control has a long history of variable and generally quite limited 
success. It will be many years before it can be determined if the 
recently initiated project will provide any benefit to the snake.
    Our Response: Salt cedar control is one conservation action that 
can provide benefits to the Concho water snake through restoration of 
native riparian vegetation to provide natural stream-side habitat 
conditions and potential water savings for instream flow increases. We 
agree with the comment that it will take time to document the actual 
benefits to the snake.
    (37) Comment: The proposal acknowledges that delisting recovery 
criteria from the recovery plan have not been met, but claims 
additional information has rendered those criteria partially invalid. 
This undermines the recovery planning process and is offensive to the 
many stakeholders who participate in recovery plan development. If the 
recovery plan is out-of-date or otherwise invalid, the Service should 
convene the recovery team and amend or rewrite the plan with 
appropriate public and stakeholder review. This will yield a firmer 
basis and greater support than the current process for delisting.
    Our Response: The Service believes that the Concho water snake has 
recovered and generally met the criteria from the 1993 recovery plan. 
Although meeting the recovery criteria is not necessarily required for 
delisting, we have discussed the criteria below in this final rule 
section Application of the Recovery Plan's Criteria. The Service does 
not believe it is necessary to revise the recovery plan for the Concho 
water snake. We have found the current information is sufficient to 
support that the species no longer qualifies as a threatened species. 
Therefore, additional time and resources would not be well spent to 
revise the recovery plan. Also we have sought the input of the public, 
stakeholders, and experts, including former recovery team members, 
during the comment period for the proposal to remove the snake from the 
threatened list.
    (38) Comment: While District water rights may ensure water 
deliveries to downstream users, they do not ensure that deliveries will 
occur through the natural streambed where Concho water snake exists. 
Such rights can be fulfilled through other means, like canals, water 
trades, storage, etc., that result in dewatered stream channels.
    Our Response: The primary water releases for downstream water users 
that provide benefits to the snake occur from the required minimum flow 
releases from Ivie Reservoir for the Lower Colorado River Authority 
(LCRA). These releases are required by the District's State water right 
permit for Ivie Reservoir. The deliveries are made using the natural 
channel. Other deliveries made for water quality improvement occur 
between Spence and Ivie Reservoirs and also use the natural channel. We 
have no reason to believe that these water deliveries would not use the 
natural stream channel in the future. The District already uses a 
sophisticated system of pipelines to deliver most of their water to its 
customers, the majority of whom are cities upstream of the two 
reservoirs (District 2005, pp. 2-5). Therefore, we do not foresee the 
District using any other methods than the natural channel to deliver 
water downstream.
    (39) Comment: The Service statement that the snakes may not need to 
be transferred between populations to prevent genetic isolation 
illustrates the prematurity of this proposed rule. A delisting decision 
should be based on something more reliable than that the species ``may 
not need'' this conservation action.
    Our Response: We have clarified this language in this final rule 
(see Application of the Recovery Plan's Criteria section below). 
Section 4.1 of the 2008 MOU, as amended in 2011, states that, ``In the 
springtime once every 3 years, the District, in coordination with the 
Service, should move five male snakes (each) from below Spence and 
below Freese [Ivie Reservoir] dams to above these dams, and move 5 
different male snakes from above both dams to below both dams. Moving 
snakes will be dependent upon availability of funding for the 
District.'' This requirement was included in the 2004 Biological 
Opinion (Service 2004a, p. 61). Should funding be unavailable in any 
particular snake-moving year, every effort will be made to move snakes 
in the succeeding year. Previously, movement of snakes was suggested 
with the Concho River population as well (Service 1986, p. 24). 
However, because the snakes exist in Ivie Reservoir they have access 
from the Colorado River to the Concho River so transferring snakes to 
the Concho River was determined not necessary.
    (40) Comment: The reference to the uncertainties in the results 
from Whiting et al. (2008) should be clarified that the uncertainties 
resulted from the data being insufficient to estimate survival and 
trend reliably due primarily to insufficient sampling at any single 
study site, along with a host of variables, especially environmental 
variability within a site and among sites, and also because dispersal 
rates were not measured among sites. Therefore, study results have not 
been robust enough to allow either population or trend estimates with 
satisfactory precision.
    Our Response: We have updated the text in the final rule to be 
consistent with this comment (see Application of the Recovery Plan's 
Criteria section below).
    (41) Comment: A reliable trend estimate for the Concho water snake 
over a span of years seems to be lacking for the species, and there are 
no reasons given for why this was so. A trend analysis would be better 
to ascertain if the species should be delisted.
    Our Response: We agree that a reliable trend analysis over time 
would be useful in confirming the status of the species. Despite many 
years of monitoring surveys over time, no reliable trend analysis has 
been completed due to variations in study efforts and methods and to 
environmental conditions (District 1998, p. 18; Service 2004a, p. 23; 
Forstner et

[[Page 66789]]

al. 2006, p. 12-13; Whiting et al. 2008, p. 343). However, the best 
available information on the population status of the snake from the 
large numbers of snakes captured during the 10 years of monitoring 
(District 1998, p. 21) and confirmed in 2005 (Forstner et al. 2005, pp. 
19-20) demonstrates that its status is sufficiently good to warrant 
removal from the list of threatened species. For more discussion on 
this issue, see Application of the Recovery Plan's Criteria, Viable 
Populatins section of this rule.

Summary of Factors Affecting the Species

    Section 4 of the Act and its implementing regulations (50 CFR part 
424) set forth the procedures for listing, reclassifying, or removing 
species from listed status. ``Species'' is defined by the Act as 
including any species or subspecies of fish or wildlife or plants, and 
any distinct vertebrate population segment of fish or wildlife that 
interbreeds when mature (16 U.S.C. 1532(16)). Once the ``species'' is 
determined, we then evaluate whether that species may be endangered or 
threatened because of one or more of the five factors described in 
section 4(a)(1) of the Act. We must consider these same five factors in 
delisting a species. We may delist a species according to 50 CFR 
424.11(d) if the best available scientific and commercial data indicate 
that the species is neither endangered nor threatened for one of the 
following reasons: (1) The species is extinct; (2) the species has 
recovered and is no longer endangered or threatened (as is the case 
with the Concho water snake); and/or (3) the original scientific data 
used at the time the species was classified were in error.
    A recovered species is one that no longer meets the Act's 
definition of threatened or endangered. The analysis for a delisting 
due to recovery must be based on the five factors outlined in section 
4(a)(1) of the Act. This analysis must include an evaluation of threats 
that existed at the time of listing, those that currently exist, and 
those that could potentially affect the species once the protections of 
the Act are removed.
    The Act defines ``endangered species'' as any species which is in 
danger of extinction throughout all or a significant portion of its 
range, and ``threatened species'' as any species that is likely to 
become an endangered species within the foreseeable future throughout 
all or a significant portion of its range. The word ``range'' in the 
phrase ``significant portion of its range'' refers to the range in 
which the species currently exists. For the purposes of this analysis, 
we will evaluate whether the currently listed species, the Concho water 
snake, should be considered threatened or endangered throughout all of 
its range. Then we will consider whether there are any significant 
portions of the Concho water snake's range in which it is in danger of 
extinction or likely to become endangered within the foreseeable future 
(see Significant Portion of the Range Analysis section below). For the 
purposes of this finding, the ``foreseeable future'' is the period of 
time over which events or effects reasonably can be anticipated, or 
trends reasonably extrapolated, such that reliable predictions can be 
made concerning the status of the species. We considered this temporal 
component in the analysis in each substantive discussion under the five 
factors below and provide a discussion of the foreseeable future in the 
Conclusion of the Five-Factor Analysis section below.
    Section 4(a)(1) of the Act requires that we determine whether a 
species is endangered or threatened based on one or more of the five 
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; and (E) other natural or manmade 
factors affecting its continued existence. Our evaluation of these five 
factors is presented below. Following this threats analysis, we 
evaluate whether the Concho water snake is threatened or endangered 
within any significant portion of its range.

A. The Present or Threatened Destruction, Modification, or Curtailment 
of Its Habitat or Range

Habitat Description
    Concho water snakes are known to occur in rivers, streams, and 
along the shoreline of reservoirs. These snakes are air-breathing; 
however, they feed almost exclusively on fish and are, therefore, found 
only near water sources capable of supporting at least a minimal fish 
population. Unlike many other species of Nerodia, Concho water snakes 
do not seem to move far from water (Werler and Dixon 2000, p. 208). 
During Greene's (1993, p. 96) visual and radio telemetry surveys, all 
snakes occurred within 33 ft (10 m) of water.
    Stream and river habitat used by the Concho water snake is 
primarily associated with riffles (Greene 1993, p. 96; Werler and Dixon 
2000, p. 210; Forstner et al. 2006, p. 13) where the water is usually 
shallow and the current is of greater velocity than in the connecting 
pools. Riffles begin when an upper pool overflows at a small change in 
gradient and forms rapids. The stream flows over rock rubble or solid 
to terraced bedrock substrate through a chute channel that is usually 
narrower than the streambed. The riffle can extend to over 300 feet 
(100 m) in some locations and ends when the rapids enter the next 
downstream pool. Riffles are believed to be the favored habitat for 
foraging, with young snakes using shallow parts of riffles and adult 
snakes using deeper parts of riffles (Williams 1969, p. 8; Scott et al. 
1989, pp. 380-381; Greene 1993, pp. 13, 96; Werler and Dixon 2000, p. 
215; Forstner et al. 2006, p. 13). Juvenile snakes are closely 
associated with gravel shallows or riffles (Scott and Fitzgerald 1985, 
p. 35; Rose 1989, pp. 121-122; Scott et al. 1989, p. 379). This habitat 
is likely the best for juvenile snakes to successfully prey on small 
fish because the rocky shallows concentrate prey and are inaccessible 
to large predatory fish. The exposed rocky shoals act as thermal sinks, 
which maintain heat and may help keep the juvenile snakes warm and 
maintain a high growth rate (Scott et al. 1989, pp. 380-381).
    Observations on the Concho and Colorado Rivers also indicated 
Concho water snakes were found in the shallow pools between riffles 
(Williams 1969, p. 8; Dixon 2004, p. 16). Dixon et al. (1989, p. 16) 
demonstrated that adult snakes used a variety of cover sites for 
resting, including exposed bedrock, thick herbaceous vegetation, debris 
piles, and crayfish burrows. Adult and maturing Concho water snakes use 
a wider range of habitats than do juveniles including pools with 
deeper, slower water (Williams 1969, p. 8; Scott et al. 1989, pp. 379-
381; Werler and Dixon 2000, p. 211).
Range
    Historically the Concho water snake was known to occur in spotty 
distribution in central Texas on the Colorado River below E.V. Spence 
Reservoir (constructed in 1969) near the City of Robert Lee, Texas, 
downstream to the F.M. 45 highway bridge crossing and then not again 
until further downstream near the City of Bend, Texas (Tinkle and 
Conant 1961, pp. 42-43; Williams 1969, p. 3). On the Concho River and 
its tributaries, Concho water snakes were historically known from 
Spring Creek, Dove Creek, and the South Concho River, all upstream of 
the Twin Buttes and O.C. Fisher Reservoirs near San Angelo, Texas, and 
in the Concho River downstream from San Angelo to the confluence with 
the

[[Page 66790]]

Colorado River (Marr 1944, pp. 486-487; Tinkle and Conant 1961, pp. 42-
43). Prior to the Federal listing of the Concho water snake in 1986, it 
had been extirpated from Concho River tributaries upstream of the City 
of San Angelo (Flury and Maxwell 1981, p. 31), and surveys had not 
located snakes in lakes or reservoirs (Scott and Fitzgerald 1985, pp. 
17, 34). At the time of listing, the range of the snake had been 
affected by O.C. Fisher, Twin Buttes, and Spence Reservoirs and one 
tributary creek reservoir, Ballinger Municipal Lake (on Elm Creek). A 
fifth reservoir, O.H. Ivie Reservoir (formerly known as Stacy), was 
planned for construction at the confluence of the Concho and Colorado 
Rivers and was expected to reduce the snake's range by more than 50 
percent (Scott and Fitzgerald 1985, pp. 31, 35).
    At the time of listing in 1986 the range was described as 
approximately 199 mi (320 km) (51 FR 31412). By 1993, Scott et al. 
(1989, pp. 382, 384), Thornton (1992, pp. 3-16), and Whiting (1993, pp. 
8, 28, 117-118, 121) had found additional locations of the snake 
upstream and downstream and determined the Concho water snake's 
distribution to be approximately 233 mi (375 km) of river (Service 
1993, p. 9). While the Concho water snake has been extirpated from some 
reaches of its historical distribution, mainly upstream of San Angelo 
(Flury and Maxwell 1981, p. 31), since the time of listing it has been 
confirmed farther downstream from Ivie Reservoir and farther upstream 
from Spence Reservoir (District 1998, pp. 10, 22, 26, Dixon et al. 
1988, p. 12; 1990, pp. 50, 62-65; 1991, pp. 60-67; 1992, pp. 84, 87, 
96-97; Scott et al. 1989, p. 384). Analysis for the 2004 revision to 
the 1986 Biological Opinion (BO; Service 2004a, p. 32) summarized the 
current known distribution of the Concho water snake as being the 
Colorado River from the confluence of Beals Creek (upstream of Spence 
Reservoir), depending on reservoir stage, to downstream of Ivie 
Reservoir (constructed in 1989) to Colorado Bend State Park, and on the 
Concho River downstream of the City of San Angelo to the confluence 
with the Colorado River. This is a total of about 280 mi (451 km) of 
river and about 40 mi (64 km) of reservoir shoreline.
    The information on the current range of the snake is based largely 
on the monitoring studies performed by the District between 1987 and 
1996 (District 1998, p.10). In addition to monitoring 3 times a year at 
15 riverine sites, the District also conducted searches throughout the 
upper Colorado River and Concho River basins. Additional surveys taught 
researches that late summer and early fall were the times when the 
snake was most active and that snakes can often be captured in minnow 
traps when they are not found with searches (District 1998, pp. 16, 
18). The results confirmed a larger distribution than was thought at 
the time of listing. For example, the snake was believed to be 
extirpated from the area downstream of Spence Reservoir in the Colorado 
River, but was found to occur there with more intensive sample efforts 
(District 1998, p. 22). The snake overall was found throughout its 
historic range, with the only exception being the small tributary 
streams upstream of San Angelo, where only a few snakes had been 
collected in the past.
    To confirm the distribution of the species, Concho water snake 
surveys were conducted across the species' range in 2004 and 2005 
(Dixon 2004; Forstner et al. 2006). One goal of Forstner et al. (2006, 
pp. 4-5) was to evaluate whether viable Concho water snake populations 
existed in all reaches of the Colorado and Concho Rivers. To do this, 
snake localities were surveyed ``for evidence of reproduction (one 
measure of sustainability).'' In all, 14 sites were sampled, and 45 
Concho water snakes were collected from 11 of those sites (Forstner et 
al. 2006, pp. 9-12). Sample efforts were limited to the extent 
necessary to document the presence of the species and evidence of 
reproduction in each reach, based on the capture of either neonate 
snakes or post-partum females. The collection efforts were brief, and 
more effort would have likely increased the total number of snakes 
collected (Forstner et al. 2006, p. 11).
    Persistence and reproduction were documented in the Concho River 
and upstream of Ivie Reservoir in the Colorado River, as well as in 
both Spence and Ivie Reservoirs (Forstner et al. 2006, pp. 12, 18). 
However, access downstream of Ivie Reservoir was limited by inability 
to contact private property owners, preventing a thorough assessment 
downstream of that impoundment (Dixon 2004, p. 2; Forstner et al. 2006, 
p. 18). Despite limited access downstream of Ivie Reservoir, four 
snakes were captured during the surveys at two sites and at least one 
female exhibited signs of recently giving birth. Forstner et al. (2006, 
p. 18) described these results as technically sufficient to demonstrate 
persistence and reproduction downstream of Ivie Reservoir 15 years 
after its construction. These authors conclude that, ``Even in the face 
of landscape scale or ecosystem wide stresses by severely reduced 
precipitation, increased human uses of instream flows, introduced 
species, and ever increasing human densities, the Concho water snake 
remains in the majority of the sites visited and continues to reproduce 
at those locations'' (Forstner et al. 2006, p. 18). Forstner et al. 
(2006, p. 20) state that ``self sustain[ing], seemingly viable 
populations in the Concho and Colorado rivers at the end of a decade of 
monitoring'' occur in the three reaches of the snake's range. We find 
that the range of the species has not declined since it was listed in 
1986 and has been found to be larger, about 80 more river-mi (129 
river-km), than at the time of listing. Therefore, because of its 
continued persistence throughout its range, the species is not 
threatened with endangerment due to range reduction.
Population Trends
    Following listing of the Concho water snake in 1986, a 10-year 
monitoring study began throughout the snake's range, including several 
reservoirs and tributaries (District 1998, pp. 10, 22, 26). The study 
included mark-recapture techniques by inserting a unique tag in each 
captured snake of sufficient size so that individuals could be 
identified when they were recaptured. Over the 10 years of study, 9,069 
unique Concho water snakes were captured (District 1998, p. 21). Of 
this total, 1,535 (17 percent) were captured in reservoirs, 1,517 (17 
percent) were captured in the Concho River reach, 5,586 (62 percent) 
were captured in the Colorado River reach, and another 415 (5 percent) 
were captured in tributary streams. All of the more than 20 study sites 
monitored had multiple captures of snakes every year, with a variety of 
age classes (Thornton 1996, pp. 26-50). Sampling effort at each survey 
site was not quantified, and was highly variable. Therefore, an 
increase or decrease in numbers of snakes at a site or cluster of sites 
in a river reach over the 10 years of the survey does not necessarily 
indicate an actual increase or decrease in snakes because the effort 
made to find them varied from survey to survey. The high variation in 
sample efforts and environmental conditions prevented a thorough 
analysis of population trends over time or calculation of total 
population estimates (District 1998, p. 18).
    Forstner et al. (2006, pp. 6-8, 18, 20) updated the past 
information by conducting brief field surveys in 2004 and 2005 to 
verify that snakes continued to be present and were reproducing in each 
river reach and reservoir where it had been documented in previous 
studies. This study, which incorporated

[[Page 66791]]

the results by Dixon (2004), confirmed reproducing populations of 
Concho water snakes in each river reach and in both Ivie and Spence 
Reservoirs (Forstner et al. 2006, p. 12). Based on the snakes' 
persistence and reproduction throughout its range over the past 20 
years, Forstner et al. (2006, pp. 18, 20) concluded that viable 
populations of Concho water snakes could be presumed to exist in all 
three reaches of the species' range.
    Only two sample locations (below Freese Dam and at River Bend 
Ranch, about 25 miles (40 km) downstream of the dam) were available for 
access by the updated study in the reach of the Colorado River 
downstream of Freese Dam (Ivie Reservoir) (Dixon 2004, pp. 8, 14). This 
was due to the difficulties in establishing contact with private 
landowners in this area. However, Dixon did collect three snakes from 
these two sites in 2004, and one was a juvenile female (Dixon 2004, pp. 
16-17). In 2005, Forstner et al. (2006, pp. 12, 18) collected one post-
partum female below Freese Dam indicating the snake had given birth to 
young and confirming reproduction. Although only four snakes were 
captured in limited sampling efforts in 2004 and 2005 in this reach, 
data from the District's earlier monitoring showed large numbers of 
snakes in this reach (District 1998, pp. 34-38, 50). We have no reason 
to conclude that the snake population downstream of Freese Dam is of 
additional concern.
    The 10 years of Concho water snake monitoring data (1987 to 1996) 
was reanalyzed in an attempt to evaluate population trends and quantify 
long-term viability (Whiting et al. 2008, pp. 438-439). The results, 
however, were inconclusive because the data were insufficient to 
reliably estimate survival and emigration. This was due primarily to 
insufficient sampling at any single study site to quantify dispersal 
rates, along with a host of other variables, especially different 
environmental conditions within a site and among sites (Whiting et al. 
2008, p. 443). This resulted in the survival rates from the capture-
recapture study being biased low and producing low estimates of annual 
survival with large standard errors (Whiting et al. 2008, p. 443). The 
study stated that snakes continued to persist even in drought-prone 
areas, some with almost total water loss, with hydrologically dynamic 
systems (Whiting et al. 2008, pp. 442-443).
    In conclusion, although recent data on population trends are 
sparse, data showing a stable range, long-term persistence, and 
continuing breeding success indicate that populations have persisted 
and remain distributed throughout the species' range over time and do 
not indicate population concerns.
Habitat Quality and Quantity
    At the time of listing, we believed the Concho water snakes did not 
exist in reservoir habitats. In fact, at the time of listing, the 
imminent construction of Ivie Reservoir was considered a primary threat 
because of the assumed habitat loss that would occur due to the 
reservoir. However, the magnitude of this threat did not materialize 
because subsequent research confirmed that Concho water snakes inhabit 
shallow water with minimal wave action and rocks along reservoir 
shorelines (Scott et al. 1989, pp. 379-380; Whiting 1993, p. 112). 
Juvenile Concho water snakes are generally found in low-gradient, 
loose-rock shoals adjacent to silt-free cobble. However, Concho water 
snakes have also been observed on steep shorelines (Whiting 1993, p. 
112) and around the foundations of boat houses (Scott et al. 1989, p. 
379).
    We quantified the amount and quality of potential Concho water 
snake habitat and compared it by river reach and reservoir (Service 
2004a, Appendix B, pp. 70-72). These data were habitat quality 
estimates provided by District biologist and species expert, Mr. Okla 
Thornton, and were digitized and summarized by the Service using a 
Geographic Information System. We categorized the habitat quality as 
high, medium, or low, and calculated the quantity of habitat based on 
linear meters of river bank or shoreline and summed the results by 
river reach and reservoir. The results were presented by five segments: 
(1) The Concho River segment (San Angelo to the inflow of Ivie 
Reservoir); (2) the Spence Reservoir segment (shoreline of the lake); 
(3) the upper Colorado River segment (outflow of Spence Reservoir 
downstream to the inflow of Ivie Reservoir) segment; (4) the Ivie 
Reservoir (shoreline of the lake); and (5) the lower Colorado River 
segment (outflow of Ivie Reservoir downstream to Colorado Bend State 
Park).
    In total, the analysis showed over 112 mi (180 km) of snake habitat 
is generally available along the rivers and in the reservoirs within 
the species' range. The results indicated that 82 percent of overall 
available habitat is found in the three river reaches and 18 percent of 
available snake habitat is in the two reservoirs. The largest percent 
of ``high quality'' habitat (total of 59 mi (96 km)) was found in the 
upper and lower Colorado River segments (42 percent and 27 percent, 
respectively) (Service 2004a, p. 71). The two reservoirs combined 
contain 15 percent of available ``high quality'' habitats and the 
Concho River segment contained 16 percent (Service 2004a, p. 71). These 
data demonstrate that Concho water snake habitat is distributed 
throughout its range in both the riverine and reservoir segments.
Habitat Destruction From Reservoir Inundation
    At the time we listed the Concho water snake in 1986, we believed 
the construction of Ivie Reservoir would result in the loss of Concho 
water snake habitat upstream of the dam by inundating the natural 
riverine rocky and riffle habitats. The site of the proposed reservoir 
on the Colorado River was believed to support the highest concentration 
of Concho water snakes (Flurry and Maxwell 1981, pp. 36, 48; 51 FR 
31419). Outside of this area, the snake had been found only in isolated 
occurrences, which indicated an already disjunct, fragmented 
distribution. The snake had not been found in reservoirs or in the 
silted-in riverine habitat below Spence Reservoir (Scott and Fitzgerald 
1985, pp. 13, 28). It also had not been found in perennial tributaries 
except Elm Creek near Ballinger (Scott and Fitzgerald 1985, pp. 15, 
34). Thus, in 1986 we believed the inundation by Ivie Reservoir would 
result in a substantial loss of habitat (as much as 50 percent) for the 
Concho water snake by eliminating them from a substantial portion of 
their range.
    As a result of a 1986 formal consultation conducted under section 7 
of the Act with the U.S. Army Corps of Engineers on construction of 
Freese Dam to form Ivie Reservoir (1986 BO), the District agreed to 
implement a number of conservation measures under required reasonable 
and prudent alternatives to avoid jeopardizing the snake. These 
measures included, but were not limited to: Long-term monitoring of the 
snakes, completing life-history studies, maintaining specific flow 
regimes from Spence and Ivie Reservoirs, creating six artificial 
riffles below Spence Reservoir, and transplanting snakes between 
populations above and below Ivie Reservoir (Service 1986, pp. 12-24). 
Ivie Reservoir was constructed in 1989 and the District carried out the 
required measures over the following 10 years (District 1998, p. 29; 
Service 2004a, pp. 42-47).
    As part of their long-term monitoring plan, District field 
biologists conducted extensive searches for the Concho water snake 
beginning in 1987. According to Dixon et al. (1988, p. 12; 1990, pp. 
50,

[[Page 66792]]

62-65; 1991, pp. 60-67; 1992, pp. 84, 87, 96-97), snakes were 
documented within and above Spence Reservoir, downstream of Spence 
Reservoir in the artificial riffles, at Ballinger Municipal Lake, the 
old Ballinger Lake, and the connecting channel between the two 
Ballinger lakes. The snake was also documented in multiple locations on 
Elm Creek and two of its tributaries, Bluff Creek and Coyote Creek 
(Scott and Fitzgerald 1985, pp.14-15, 30; and Scott et al. 1989, p. 
384). Snakes were regularly found in Spence, Ivie, and Lake Ballinger 
Reservoirs, a habitat type they were not known to occupy at the time of 
listing. Concho water snakes have continued to be found in reservoirs. 
Dixon's (2004, pp. 3-4) surveys in 2004 confirmed that snakes persist 
in Spence and Ivie Reservoirs. In 2004, Ballinger Lake had only a small 
pool of water remaining, and no snakes were found there at that time. 
However, after rains in 2005, Forstner et al. (2006, p. 12) confirmed 
snakes were again present and reproducing within Lake Ballinger. These 
observations confirm that Concho water snakes have adapted to using 
reservoirs as habitat.
    Studies have found that rocky shorelines were the single most 
important component of snake habitat in reservoirs, and that changes in 
water surface elevation of Spence Reservoir will affect the 
availability of that shoreline habitat (Whiting 1993, p. 13; Whiting et 
al. 1997, pp. 333-334). Although Forstner et al. (2006, p. 17) refer to 
the lakes overall as ``very poor Concho water snake habitat,'' while 
Dixon (2004, p. 14) calls them ``prime habitat,'' both reports conclude 
that there are rocky outcrops and boulder slopes in limited areas 
within the reservoirs that are occupied by the snake. The snakes have 
remained in Spence Reservoir for nearly 40 years following its 
construction and for at least 15 years following construction of Ivie 
Reservoir. Because Concho water snakes are now known to be reproducing 
and persisting over time in reservoirs and their current distribution 
is larger than reported historically and at the time of listing, 
habitat loss from reservoir inundation is no longer believed to be a 
threat to the long-term survival of the species.
Habitat Modification From Reduced Instream Flows
    a. Hydrology and Historic Instream Flows.
    Even prior to the Concho water snake listing in 1986, a primary 
concern for the conservation of the species has been the potential 
impacts of habitat modification that occurs with reductions in instream 
river flow rates throughout its range (Scott and Fitzgerald 1985, p. 
33). The source of these concerns originates from the storage and use 
of water for human consumption (primarily the damming and diversion of 
surface water for municipal uses) and the compounding effects of 
drought (natural rainfall levels below average). In the following 
discussions we analyze the sources, potential mechanisms, and possible 
effects arising from the threats related to the reduction of instream 
flows.
    Beginning in eastern New Mexico, the upper Colorado River 
watershed, including the Concho River drainage, is semi-arid with 
average annual rainfall ranging from 15 to 35 inches (in) (38 to 89 
centimeters (cm)) (TWDB 2007, p. 132). The area has a warm and windy 
climate that produces average annual gross lake surface evaporation of 
65 to 80 in (165 to 203 cm) (TWDB 2007, p. 133). The water that 
produces river flows where the Concho water snake occurs originates 
exclusively from rainfall precipitation. This occurs through either 
direct surface runoff or natural groundwater storage of rainfall and 
then later discharge to surface flows through spring flows or seepage 
out of stream banks. The Colorado River generally increases in flow 
rate downstream, depending on rainfall, aquifer conditions, and water 
releases from reservoirs.
    Since the early 1900s the upper Colorado River watershed (including 
the Concho River) has been modified to accommodate human water demands, 
primarily for agricultural irrigation (about 80 percent of all water 
used), municipal, and industrial uses. The construction of numerous 
reservoirs for surface water storage significantly affects the 
hydrology in every part of the river system and all of the snake's 
range. Most of the surface water storage in reservoirs is for municipal 
use, while groundwater pumping serves most agricultural irrigation 
needs. To assess the changes in stream flow conditions over time that 
have already occurred, we reviewed the flow data derived from stream 
flow gauges within the snake's range.
    The USGS operates many stream gauges that monitor stream flow 
conditions within the range of the Concho water snake. Asquith and 
Heitmuller (2008, pp. 1-10) analyzed streamflow data in Texas using 
statistical tools to evaluate trends over time in low-flow discharge 
rates. A review of seven mainstem stream gauges within the range of the 
Concho water snake found statistically significant declining trends in 
mean streamflow over the period of record at six of these seven stream 
gauges. They also found significant declining trends in harmonic mean 
streamflow for the period of record at four of the seven gauges 
(Asquith and Heitmuller 2008, pp. 810-813, 846-853). The period of 
record encompassed by analysis of these gauges ranged from 39 to 100 
years of data, ending in water year 2007. The ``harmonic mean 
streamflow'' is a statistic derived from daily mean streamflow and is 
commonly used as a design streamflow for contaminant load allocations 
by Texas Commission on Environmental Quality (TCEQ) to address the 
effects of dilution to protect human health and other aquatic life 
forms. It is a useful statistic for evaluation of low-flow conditions 
to explain hydrologic changes resulting from streamflow regulation, 
climate change, or land-use practices (Asquith and Heitmuller 2008, p. 
2). Other abbreviated analyses of stream flows have also indicated 
substantial historical declines (Service 2004a, pp. 35-38; Forstner et 
al. 2006, pp. 13-16). Although annual precipitation in this region 
varies substantially from year to year (TWDB 2007, p. 135), an 
assessment of statewide annual average trends of precipitation and 
temperature across Texas suggested no significant changes over more 
than the last 100 years (TWDB 2007, pp. 299-300). This suggests that 
human-induced changes in land and water uses over the past 50 to 100 
years have resulted in lesser overall flows in the rivers of the upper 
Colorado River watershed.
    Asquith and Heitmuller (2008, p. 8) also analyzed the percent of 
days where the stream gauges recorded zero flow in the river. These 
data are important as they would be indicative of extreme environmental 
conditions that could cause stress to the snake or its fish prey base. 
For the period of record at these gauges, the results ranged from 0.1 
percent of days with zero flow at the stream gauge near San Angelo on 
the Concho River to 9.3 percent at the stream gauge measuring outflow 
from Spence Reservoir. The outflow of Spence Reservoir had many no-flow 
days in the period of time prior to the listing of the snake when the 
District routinely did not release water from the reservoir. Over the 
10 years from 1998 to 2007, the percent of zero-flow days ranged from 
none at two gauges on the Colorado River to 25.8 percent at the gauge 
on the Concho River at Paint Rock (Asquith and Heitmuller 2008, pp. 
810-813, 846-853). These data demonstrate that there have been 
considerable periods of time in recent history where

[[Page 66793]]

there has been no flow in the river where the snakes occur. Asquith et 
al. (2007b, pp. 469-473, 493-494) also summarized the percentage of 
zero-stream-flow days by month at USGS gauges and found the highest 
proportion of zero-stream-flow days at the seven gauges on the Colorado 
River within the snake's range occur during the months of July and 
August. For example, the stream gauge near Ballinger (located on the 
Colorado River between Spence and Ivie Reservoirs) had 5.1 percent of 
zero mean daily flow for all days from 1908 through 2003. Of the zero-
flow days, over 15 percent occurred in each of the months of July and 
August, which was more than any other months (Asquith et al. 2007b, pp. 
473). This may be a critical period in the life history of the snake 
because it is generally this time of year when female snakes give birth 
to young snakes (Werler and Dixon 2000, p. 216).
    b. Future Instream Flows
    To consider the expected water availability conditions in the 
foreseeable future within the upper Colorado River watershed, we 
reviewed the 2007 Texas State Water Plan. This planning document was 
developed from information provided by local regional water planning 
groups and it was approved by the Texas Water Development Board. It 
represents the best available information to use in forecasting the 
likely future water availability and use in Texas in the year 2060 
(TWDB 2007, pp. 1-10). The range of the Concho water snake occurs in 
the Texas Water Planning Region F. Although this Region is somewhat 
larger than the upper Colorado River watershed, it is a reasonable area 
for us to consider for future water conditions in the range of the 
Concho water snake. The Region encompasses the entire upper Colorado 
River watershed and projections for the larger area would not be 
expected to differ greatly from the portion within the upper Colorado 
River watershed that comprises Concho watersnake habitat.
    The projections from this water plan indicate that the overall 
human water use in Region F is expected to increase only slightly in 
the next 50 years. The human population is predicted to grow about 17 
percent in the next 50 years, from 620,000 people in 2010 to 724,000 in 
2060 (TWDB 2007, p. 43). Over the same time, the total water use in the 
region is expected to increase by only about 2 percent, from 807,453 
acre-feet used in 2010 to 825,581 acre-feet in 2060 (TWDB 2007, p. 43). 
Agricultural irrigation demands are expected to decrease by 5 percent 
and make up 551,774 acre-feet in 2060, while municipal water demands 
are projected to increase 11 percent over the same period, to 135,597 
acre-feet in 2060 (TWDB 2007, p. 44). Based on these projections, we do 
not foresee the threat of losses of instream flow substantially 
increasing beyond their current level in the next 50 years. However, 
the forecasting of future water conditions within this area has high 
uncertainty, largely due to the unpredictable climatic conditions (TWDB 
2007, p. 297-299). The region is particularly susceptible to extreme 
drought, where precipitation is below average for extended periods of 
time (10 years or more), as the region experienced during the late 
1990s and early 2000s (TWDB 2006, 1-60, 1-67). Droughts will certainly 
continue to occur and produce additional challenges to the water system 
of the upper Colorado River watershed.
    An additional source of uncertainty for future instream flows is 
the potential effects of global climate change on water availability in 
this region. According to the Intergovernmental Panel on Climate 
Change, ``Warming of the climate system is unequivocal, as is now 
evident from observations of increases in global average air and ocean 
temperatures, widespread melting of snow and ice, and rising global 
average sea level'' (IPCC 2007, p. 1). Average Northern Hemisphere 
temperatures during the second half of the 20th century were very 
likely higher than during any other 50-year period in the last 500 
years and likely the highest in at least the past 1300 years (IPCC 
2007, p. 1). It is very likely that over the past 50 years cold days, 
cold nights and frosts have become less frequent over most land areas, 
and hot days and hot nights have become more frequent (IPCC 2007, p. 
1). Data suggest that heat waves are occurring more often over most 
land areas, and the frequency of heavy precipitation events has 
increased over most areas (IPCC 2007, p. 1).
    The IPCC (2007, p. 6) predicts that changes in the global climate 
system during the 21st century are very likely to be larger than those 
observed during the 20th century. For the next two decades a warming of 
about 0.2 [deg]C (0.4 [deg]F) per decade is projected (IPCC 2007, p. 
6). Afterwards, temperature projections increasingly depend on specific 
emission scenarios (IPCC 2007, p. 6). Various emissions scenarios 
suggest that, by the end of the 21st century, average global 
temperatures are expected to increase 0.6 [deg]C to 4.0 [deg]C (1.1 
[deg]F to 7.2 [deg]F) with the greatest warming expected over land 
(IPCC 2007, p. 6-8).
    Localized projections suggest the Southwest may experience the 
greatest temperature increase of any area in the lower 48 States (IPCC 
2007, p. 8), with warming in southwestern States greatest in the 
summer. The IPCC also predicts hot extremes, heat waves, and heavy 
precipitation will increase in frequency, resulting in high intensity 
and variability of precipitation that increases flooding events and 
long periods of drought (IPCC 2007, p. 8). Modeling efforts evaluating 
climate change in this region of Texas have only recently been 
initiated (CH2M HILL 2008; Jackson 2008; Mace and Wade 2008; TWDB 
2008). As with many areas of North America, this area (central and 
western Texas) is projected to experience an overall warming trend in 
the range of 2.5-3.9 [deg]C (4.5-6 [deg]F) over the next 50 to 200 
years (IPCC 2007, p. 9; CH2M HILL 2008, p. 6-3; Mace and Wade 2008, p. 
656). The IPCC (2007, p. 8) states there is high confidence that semi-
arid areas, like the western United States, will suffer a decrease in 
water resources by mid-century due to climate change. Although more 
local precipitation models vary substantially, with some even 
predicting increased annual precipitation, a consensus is emerging that 
evaporation rates in central and western Texas are likely to increase 
significantly (Jackson 2008, p. 21; CH2M HILL 2008, p. 7-30, 7-31). 
Many models are also predicting that seasonal variability in flow rates 
is likely to increase with more precipitation occurring in the wet 
seasons and more extended dry periods (CH2M HILL 2008, p. 7-30; Jackson 
2008, p. 19; Mace and Wade 2008, p. 656).
    An evaluation of the hydrological impacts of climate change on the 
annual runoff and its seasonality in the upper Colorado River watershed 
was conducted by CH2M HILL (2008). Four modeling scenarios (chosen to 
represent a range of possible future climatic conditions) were each run 
under a 2050 and 2080 time scenario producing annual runoff estimates 
at 6 sites in this watershed. For the 2050 scenarios, the results from 
all 4 scenarios predicted declines in annual runoff at all 6 gauges 
ranging from 11 to 44 percent. Annual runoff at the stream gauge on the 
Colorado River at Ballinger, for example, was predicted to decline by 
19 to 38 percent (CH2M HILL 2008, pp. A-1-A-4). For the 2080 scenarios, 
one model predicted increases in annual runoff ranging from 41 to 90 
percent. The other three 2080 scenarios predicted declines in annual 
runoff ranging from 9 to 65 percent at 6 gauges. Annual runoff at the 
stream gauge at Ballinger was predicted to decline by 25 to 40 percent 
(CH2M HILL 2008, pp. A-1-A-4). However, the modeling efforts

[[Page 66794]]

from this study focus on annual averages and do not account for the 
flooding events or long periods of drought. It is these specific 
extreme events that are important for maintaining habitat for the 
snake, and they cannot be reliably based on historic patterns upon 
which this study was predicated.
    In addition, all climate change modeling has inherently large 
uncertainties due to the incorporation of many variables that are 
difficult, if not impossible, to accurately predict (CH2M HILL 2008, p. 
ES-1; Jackson 2008, p. 20). As an example, the Texas State Water Plan 
considered future global climate change to be a challenge for water 
availability forecasting in 2060. However, the uncertainties associated 
with climate change were very large in comparison with other 
uncertainties, such as those associated with population growth and 
water demand. As a result, the State did not believe that climate 
change concerns warranted specific planning measures at the time (TWDB 
2007, p. 299). However, expected future warming from climate change 
could significantly increase potential evaporation rates in the region, 
in combination with expected reduced precipitation and extended 
droughts in western Texas.
c. Maintenance of Instream Flows
    Efforts to minimize the potential impacts of reduced instream flows 
by securing minimum flow releases from the Colorado River reservoirs 
began with the 1986 BO. It included measures for the District to 
maintain certain flow conditions downstream of both Spence and Ivie 
Reservoirs (Service 1986, pp. 14-19) for the benefit of the snake and 
its habitat. These two reaches represent an estimated 57 percent of all 
snake habitat available and 69 percent of available high-quality 
habitat (Service 2004a, p. 70). These minimum reservoir releases were 
maintained by the District until 2004 (Service 2004a, pp. 43, 45) when 
the Service revised the 1986 BO and reduced the required flow rates 
from both reservoirs (Service 2004a, pp. 11-13). The analysis in the 
2004 BO included updated biological information that the snakes use 
more diverse riverine habitats (such as pools, in addition to riffles) 
and were found in the reservoirs and tributaries (Dixon 2004, pp. 9, 
16; Service 2004a, pp. 53-54). As a result of that consultation we gave 
our biological opinion that the reduced reservoir releases described in 
the proposed agency action were not likely to jeopardize the continued 
existence of the Concho water snake and were not likely to destroy or 
adversely modify designated critical habitat.
    The Service determined that lower minimum flow rates were 
sufficient to maintain the habitat and populations of the Concho water 
snake (Service 2004a, pp. 53-54). The District will, to the extent 
there is inflow into Spence Reservoir, maintain a minimum flow in the 
Colorado River downstream of not less than 4.0 cubic feet per second 
(cfs) (0.11 cubic meters per second (cms)) during April through 
September and 1.5 cfs (0.04 cms) during October through March. To the 
extent there is inflow into Ivie Reservoir, the District will maintain 
a minimum flow in the Colorado River downstream of Ivie Reservoir of 
not less than 8.0 cfs (0.23 cms) during the months of April through 
September and 2.5 cfs (0.07 cms) during the months of October through 
March (Service 2004, pp. 11-12). The expectation for the District to 
implement the 2008 MOU and the expected extent of low-flow conditions 
are addressed in detail in discussions below.
    When the Concho water snake is delisted, the minimum flow 
requirements required by the 2004 BO will no longer apply. However, the 
purpose of the 2008 MOU is for the District to provide assurance that 
minimum reservoir releases will continue in perpetuity, consistent with 
the 2004 Biological Opinion (BO, Service 2004a, pp. 11-12). The 
releases are the same as those required in the 2004 BO, and the 
District has agreed to maintain these flows, to the extent there is 
inflow, when the Concho water snake is removed from the Federal list of 
threatened species. The 2008 MOU acknowledges the Service's ability to 
add the Concho water snake back to the list of protected wildlife, even 
under emergency listing provisions, if future conditions warrant.
    We have confidence that the District will implement the MOU in good 
faith after the Concho water snake is removed from the threatened list. 
The District has implemented every activity requested by the Service in 
previous biological opinions beginning in 1986 (Service 2004a, p. 42-
47). The minimum flows required in the 2004 BO have been implemented by 
the District, and those flow requirements were duplicated in the 2008 
MOU. The District has an excellent track record of carrying out 
conservation actions to benefit the Concho water snake (Freese and 
Nichols 2006, pp. 6.1-6.13). In addition, the post-delisting monitoring 
plan for the Concho water snake includes monitoring of instream flows 
to monitor stream conditions and verify that flows called for in the 
2008 MOU are being realized.
    The District has maintained flows from both Spence and Ivie 
Reservoirs. This is demonstrated by measures of the daily median flow 
at two gauges downstream of the reservoirs. Daily median flows (i.e., 
the number where half the recorded flows are higher and half are lower 
within a given day of records) provide a better assessment for this 
purpose than the daily mean flow, which would be skewed higher due to 
very short-term high-flow flood events. Daily median flows (calculated 
for each calendar day from the mean daily discharges for the time 
period referenced) in the reach of the Colorado River below Spence 
Reservoir (as measured at the USGS gauge near Ballinger since Spence 
Reservoir was constructed, 1969-2007) exceeded 4.0 cfs (0.11 cms) in 
the summer (April through September) all but 12 days out of a total of 
183 days. During the winter (October through March), daily median flows 
always exceeded 1.5 cfs (0.04 cms). Daily median flows in the reach of 
the Colorado River below Ivie Reservoir (as measured at the USGS gauge 
at Winchell since Ivie Reservoir was constructed, 1990-2007) exceeded 
8.0 cfs (0.23 cms) in the summer (April through September) all but 15 
days out of a total of 183 days. During the winter (October through 
March), daily median flows always exceeded 2.5 cfs (0.07 cms). Based on 
these past actions, we believe that the District will continue to 
maintain instream flows in the foreseeable future.
    The 2008 MOU allows the District to reduce or discontinue minimum 
flow releases below either reservoir based on inflow or when water 
storage in that reservoir falls below about 12 percent of capacity. 
Since Spence Reservoir was initially filled in 1971, the water level 
elevation has only been below this mark during the period from 2002 to 
2004, at the end of a prolonged drought from 1992 to 2003 (District 
2005, pp. 39-43). Ivie Reservoir has not been below this mark since it 
initially filled in 1991 (District 2008, pp. 1-2). Based on the 
historic record and the foreseeable future of about 50 years, we would 
expect these conditions to occur infrequently. Using data from Spence 
Reservoir where this storage level has occurred, it has happened less 
than 10 percent of the time since 1971 (3 years out of 37 years of 
operation).
    We also anticipate that small amounts of water and minimal stream 
flows will still be present at most times of the year in the gaining 
reaches of the Colorado River and below Spence and Ivie Reservoirs due 
to dam leakage and

[[Page 66795]]

seepage, contributing inflow from creeks and sub drainages, and 
discharges from springs where shallow groundwater interfaces with the 
stream (Dixon 2004, p. 9). The gaining nature of the river reach 
downstream of Spence Reservoir is particularly evident as both the 
annual mean flow and harmonic mean streamflow increased between the 
stream gauge measuring outflow of the reservoir and the gauge at 
Ballinger, some 50 mi (80 km) downstream (Asquith and Heitmuller 2008, 
pp. 810-813). This gaining stream trend is greatly controlled by 
ambient weather conditions. For example, during periods of long-term 
drought (more than 10 years), the tributaries and springs will cease 
flowing or have significantly lower flow. However, during average 
rainfall periods, these sources of water help to restore and maintain 
more stable instream flows in the main rivers (Service 2004a, p. 50). 
Additionally, even when releases from dams have ceased, normal seepage 
from a dam occurs and provides for the formation of pools (large and 
small) that can provide habitat for the Concho water snake and the fish 
it preys upon for varying periods of time. When dam releases are 
resumed, the pools (located upstream of low-head dams and up and 
downstream from spring areas) that may have served as refuge habitat 
are reconnected by flowing water (Dixon 2004, p. 16).
    Texas water law requirements also result in maintenance of some 
instream flow. Texas observes traditional appropriative water rights, 
which is also known as the ``first in time, first in right'' rule (see 
Texas Water Code Sec.  11.027). The State's water policy requires the 
TCEQ to set, to the extent practicable, minimum instream flows to 
protect the State's water quality when issuing water rights permits 
(see Texas Water Code Sec.  11.0235(c)). Furthermore, Texas water law 
prohibits the owner of stored water from interfering with water rights 
holders downstream or releasing water that will degrade the water 
flowing through the stream or stored downstream (Texas Water Code Sec.  
297.93). The District's 1985 water rights permit associated with Ivie 
Reservoir (TCEQ 1985, Permit 3676, p. 4) requires the District 
to maintain minimum flows below Ivie Reservoir of 8 cfs (0.23 cms) from 
April through September and 2.5 cfs (0.07 cms) from October through 
March (consistent with flows called for in the 2008 MOU). Flows are 
often also provided downstream of both Spence and Ivie Reservoirs to 
ensure water quality and provide for downstream water rights. Releases 
from Spence Reservoir are periodically made to improve the quality of 
water entering Ivie Reservoir. Spence Reservoir is known to be high in 
dissolved solids and chlorides (District 2005, pp. 24-27), so if flows 
into Spence Reservoir are low, water quality in the reservoir can 
become degraded unless high volumes of water are released. Therefore, 
long-term low-flow releases or no releases from Spence and Ivie 
Reservoirs are rare unless an emergency situation occurs.
d. Response of Species to Reduced Instream Flows
    We considered the potential impacts on the Concho water snake of 
reduction of instream flows from water management actions. We also 
considered the effects of short-term large-magnitude instream flow 
declines resulting from droughts that are expected to occur in some 
frequency over the next 50 years in the foreseeable future. In summary, 
we found that the best available information from numerous ecological 
studies by snake experts supports the conclusion that the species is 
well adapted to endure the occasional conditions of extreme low flows 
or periodic cessation of flows.
    There are no specific studies that have evaluated the effects of 
declining instream flows on the snake's habitat or populations. 
However, we can assume that the linear extent of dewatered riverine 
habitats during extended drought periods could be quite large and the 
length of time without flows could extend for several months or more 
(Service 2004a, p. 51). These habitat modifications could impact the 
snake by decreasing reproductive success during the summer months, 
reducing the snake's fish prey base, or reducing over-winter survival 
during their hibernation period.
    Recent monitoring studies have provided observations that suggest 
Concho water snakes have the ability to survive extreme low-flow 
periods. For example, Elm Creek had experienced a number of extended 
no-flow periods over several years prior to 2004 and then flooded in 
August 2004. A review of the flow data from the USGS stream gauge on 
Elm Creek near Ballinger found 44 percent of all days between January 
2000 and July 2004 recorded no discharge. In September 2004, Dixon 
(2004, p. 11) noted Concho water snakes inhabited the site. Dixon 
(2004, p. 12) surmised that snakes either moved from the mouth of Elm 
Creek at the Colorado River (a distance of 4.6 mi (7.4 km)), or existed 
in deep pools somewhere within a returnable distance to the site. 
Another example of snake persistence during dry times was the drying of 
Ballinger Lake in 2004 and confirmation of reproductive snakes in the 
lake in 2005 following rains (Dixon 2004, p. 4; Forstner et al. 2006, 
p. 15; Whiting et al. 2008, p. 443).
    The best demonstration of the Concho water snake's endurance of 
low-flow conditions is found in the Concho River. Two large dams on the 
Concho River just upstream of the City of San Angelo capture 
essentially the entire upper Concho River watershed. There have never 
been minimum flows purposely provided for the snake in the Concho 
River. This has resulted in extreme low flows in the downstream 
reaches. We presume the low flows are maintained from small gains from 
groundwater discharge or return flows (Dixon 2004, pp. 8-9). Since 
1916, the annual mean streamflow at the flow gauge at Paint Rock on the 
Concho River has declined from 136 cfs (3.85 cms) for the 92-year 
period of record down to 24.8 cfs (0.7 cms) for the recent 10 years 
from 1998 through 2007. The harmonic mean streamflow at this gauge has 
declined from 1.0 cfs (0.03 cms) for the period of record to 0.3 cfs 
(0.01 cms) for the recent 10 years (Asquith and Heitmuller 2008, pp. 
849-850). Over the same time periods the gauge has recorded zero flow 
for 8 percent of the days for the period of record and 25 percent of 
the days from the recent 10 years (Asquith and Heitmuller 2008, pp. 
849-850). These flow data represent extreme low-flow conditions 
resulting from long-term human water use and recent short-term drought 
and have been accompanied by degradation of habitat by silting in of 
the stream and encroachment of vegetation (Dixon 2004, pp. 8-9). 
Despite this apparent long-term habitat modification, the snake 
continues to persist in this reach, and Forstner et al. (2006, p. 8) 
found the highest numbers of Concho water snakes (20 of all 45 snakes 
captured or observed during their brief surveys) in this reach of the 
Concho River.
    The mechanism for persistence in these conditions of long periods 
of drought, according to Dixon (2004, p. 9), is the ability of the 
snakes to use pools of water that form upstream of low-head dams (small 
private dams, a few feet tall, that create pools upstream and riffle-
like areas downstream). Within both the Concho and Colorado Rivers, 
these pools can extend two-thirds of a mile (1 km) or more up river 
(depending on dam height). The riffles and pools that lie upstream of 
these low-head dams may not completely dry up because of small springs 
and creeks nearby. These pools act as refuges for juvenile and adult 
Concho water snakes when measurable flow ceases (Dixon

[[Page 66796]]

2004, p. 9). Concho water snakes have been located in pools behind low-
head dams along the Colorado River, and Dixon (2004, p. 9) states that 
it is reasonable to expect the small pools behind low-head dams on the 
Concho River to act in the same way. Also, even during drought, water 
continues to flow over bedrock in some areas, and snakes have been 
observed foraging for fish in the diminished flow. The extent of solid 
bedrock in some of the riffle systems tends to maintain the nature of 
the riffle and does not allow vegetation to root and collect debris and 
silt (Dixon 2004, p. 9).
    Another way the snakes may endure drying conditions is to use deep 
burrows for over-winter hibernacula (shelters for hibernating snakes). 
Greene (1993, pp. 89, 94) found Concho water snake hibernacula within 
19.7 ft (6 m) of water with a mean depth of 1.7 ft (0.52 m). 
Hibernacula types included crayfish burrows, rock ledges, debris piles, 
and cracks in concrete of low water crossings for adults and loose 
embankments of rock and soil for juveniles. Dixon (2006, p. 2) stated 
that during droughts the snakes were possibly in the crayfish burrows, 
since they may retain moisture longer.
    Lack of forage fishes available for prey by the snakes is another 
reason that drought and resulting decreasing flows could impact Concho 
water snakes. Fish are the principal food of the Concho water snake 
(Williams 1969, pp. 9-10; Dixon et al. 1988, p. 16; 1989, p. 8; 1990, 
p. 36; 1992, p. 6; Thornton 1990, p. 14; Greene et al. 1994, p. 167). 
At the time of listing, we believed that declining flows, inundation, 
pollution, and other habitat threats would have adverse impacts on 
riffle-dwelling fish (51 FR 31419). However, the snakes are not 
species-specific and have been shown to take advantage of whatever 
small-bodied species is most abundant. A review of the 10 years of fish 
surveys by the District from 1987 to 1996 showed that the snakes were 
opportunistic predators on a variety of fish species (Thorton 1992, pp. 
16-34; Service 2004a, pp. 68-69). The most abundant fish available and 
in the snake diet are fish species that are adapted to harsh stream 
conditions (intermittent flow and poor water quality), such as red 
shiners (Burkhead and Huge 2002, p. 1) and fathead minnows (Sublette et 
al. 1990, pp. 162-166). Together these two fishes made up two-thirds of 
the diet of the Concho water snakes. Because of their ability to 
withstand harsh stream conditions, we expect these fish species to 
persist in the harshest environments, and they can recolonize stream 
reaches after dewatered conditions end. In addition, information 
indicates the snake is able to survive in captivity for up to 12 months 
with a reduced food supply (Dixon 2006, p. 2). This suggests that the 
snakes can endure a short-term absence of food resources when forage 
fish are scarce. The periodic loss of stream flows due to drought will 
impact fish availability in the river, but the snakes are adaptable to 
prey upon whatever fish species survives the low flows or survive 
without food for short periods.
e. Summary of Habitat Modification From Reduced Instream Flows
    In conclusion, we expect extreme low-flow and drying river 
conditions to occur only rarely within most of the range of the snake. 
However, when extreme drought (10 years or more of below-average annual 
precipitation) does occur, the snake is adapted to withstand harsh 
conditions. Species experts are confident that the Concho water snake 
has evolved and adapted for thousands of years through many documented 
extreme droughts (Forstner et al. 2006, pp. 17-19). Forstner et al. 
(2006, pp. 16, 20) indicate that, despite the inevitable impacts and 
future stressors on this taxon by anthropogenic and natural cycles, the 
snake has persisted in an environment for the past several millennia 
that has seen ``frighteningly intense periods of drought.'' The Concho 
water snake has survived historically under extreme drought and low-
flow conditions (Forstner et al. 2006, p. 22). Climate change could 
alter the overall water availability and seasonality of flows in the 
range of the snake, but the uncertainties associated with forecasting 
the effects of climate change and where they will occur are so great, 
relative to the threats of population growth and water demand, that the 
State did not believe that it warranted planning efforts. Because of 
the high uncertainty on the effects of climate change, we cannot 
reliably predict if river conditions in the foreseeable future will be 
significantly worse than historical conditions. Thus, we find that the 
threat of habitat modification from the reduction of instream flows 
caused by reservoir operations and drought is not likely to endanger 
the Concho water snake in the foreseeable future.
Habitat Modification From Reduced Channel Maintenance Flows
    At the time of listing, we were concerned that the construction of 
Ivie Reservoir would prevent floodwater scouring by large flows that 
serve to maintain natural river conditions. Channel scouring occurs 
when flood waters transport silt and fine materials downstream and 
displace encroaching vegetation from the river channel. In other words, 
large flood events serve to physically displace vegetation growing in 
the silt and sand along the banks within the stream channel. These 
channel maintenance flows are important to remove the fine substrates 
and vegetation and maintain the riffles, gravel bars, and rocky stream 
bank habitats often used by the snakes as foraging habitat. Without 
such flooding, riffle habitat is modified as the rocky streambed 
becomes covered with silt and vegetation becomes established and armors 
the stream bank. Riffle habitat creates sites for reproduction and 
habitat for small fish that young snakes prey upon. Although in some 
reaches, such as some sites on the Concho River, the dominant substrate 
is solid bedrock, and the cracks and breaks in the rock serve the same 
purpose as riffles as a place for snakes to feed (Dixon 2004, p. 9).
    Asquith et al. (2007a, pp. 469-473, 491-494) analyzed trends over 
time for the annual maximum streamflow and found statistically 
significant declining trends in flow during the period of record at six 
of the seven gauges on the Concho and Colorado Rivers within the range 
of the Concho water snake. Also, review of the hydrograph of the daily 
stream flow data for the period of record at these seven stream gauges 
shows a decline in the frequency and duration of high-flow events 
(Asquith and Heitmuller 2008, pp. 810-813, 846-853).
    However, some high flows continue to occur naturally even during 
recent drought periods. For example, over the 10 years from 1999 to 
2008 the USGS stream gauge on the Colorado River near Ballinger, 
downstream of Spence Reservoir, recorded streamflow events of over 
1,000 cfs (28 cms) in 6 of the 10 years and had a peak flow of over 
9,500 cfs (270 cms) in June of 2000 (USGS 2008). For the same time 
period at the gauge at Winchell, downstream of Ivie Reservoir, 9 years 
had flow events exceeding 1,000 cfs (28 cms) with a peak flow of 16,500 
cfs (470 cms) in July 2002 (USGS 2008). The gauge at Paint Rock, on the 
Concho River, also had streamflow events exceeding 1,000 cfs (28 cms) 
for 9 of the 10 years with a peak flow of over 5,000 cfs (140 cms) in 
November 2004 (USGS 2008). In addition, the 2008 MOU with the District 
calls for periodic high rates of discharges to manage water quality in 
the reservoirs. These releases could be coupled with flood runoff 
events and may function as channel maintenance flows. We have no 
reliable means to

[[Page 66797]]

reasonably forecast the frequency and occurrence of future high flows 
in the river. However, some global climate change models are indicating 
a possible future trend of more precipitation occurring during wet 
seasons (Mace and Wade 2008, p. 656), although there is substantial 
uncertainty with future predictions. If this occurs over the next 50 
years, it could increase the number and magnitude of high discharge 
events that would serve as channel maintenance flows in the range of 
the Concho water snake.
    One consequence of reduced flushing flows is the increase in 
abundance of salt cedar (Tamarisk sp.), a nonnative species of tree 
that was introduced to the United States in the 1800s from southern 
Europe or the eastern Mediterranean region (DiTomaso 1998, p. 326). In 
the watersheds of Spence and Ivie Reservoirs, these plants are abundant 
and have been reported to have affected water quality and quantity 
because they consume large volumes of water and then transport salts 
from the water to the surfaces of their leaves. When the leaves are 
dropped in the fall, the salt is concentrated at the soil surface 
(DiTomaso 1998, p. 334; Freese and Nichols 2006, p. 5.5). The lack of 
flushing flows in the rivers allows these invasive plants to become 
established in the fine substrates along the banks and eventually 
reduce the amount of gravel and rocky stream substrates.
    In an effort to increase water yield and reduce salt concentrations 
in Spence and Ivie Reservoirs, the District, in cooperation with the 
Texas Cooperative Extension Service, the Texas Department of 
Agriculture, the U.S. Department of Agriculture-Agricultural Research 
Service, and the Texas State Soil and Water Conservation Board 
(TSSWCB), has initiated a salt cedar control project in the Upper 
Colorado River Basin. The program includes spraying an herbicide to 
eradicate mass concentrations of salt cedar and then using a leaf 
beetle for biological control of new plant growth (Freese and Nichols 
2006, p. 6.4). According to Freese and Nichols (2006, pp. 6.5-6.6), 
this project ``is an excellent first step in the recovery of the Upper 
Colorado River Basin back to many of its [pre-infestation] functions, 
including native riparian habitat for wildlife and improved habitat for 
fish and other aquatic organisms,'' and is ``one of the most crucial 
options for improving water quality and quantity.'' We have no 
information that the herbicide to be used (Arsenal) poses a direct 
poisoning threat to the Concho water snake and a previous section 7 
consultation found only beneficial effects to the species (Service 
2004b, p. 39).
    Additionally, control programs for invasive brush species, such as 
juniper (Juniperus sp.) and mesquite (Prosopis sp.), are also being 
implemented in the Concho and Upper Colorado River Basins to increase 
water quantity (TSSWCB 2004, pp. 2-3; Freese and Nichols 2006, p. 6.6). 
The TSSWCB is focusing above O.C. Fisher and Twin Buttes Reservoirs 
upstream of San Angelo on the Concho River and over 175,000 acres 
(70,820 hectares) of invasive brush have been treated in these 
watersheds (TSSWCB 2004, pp. 2-3). The removal and control of salt 
cedar and other invasive brush from the riparian reaches of the 
Colorado and Concho Rivers helps augment existing stream discharge and 
also reduces buildup of dissolved solids (salts) in the soils of the 
riparian zone (Service 2004a, p. 56). Additionally, this removal 
encourages reformation of riffle areas, increases stream flow, and 
reduces sediment deposition, which improves instream habitat for the 
Concho water snake and other aquatic species (Freese and Nichols 2006, 
p. 6.6).
    While both Dixon (2004, pp. 8-9) and Forstner et al. (2006, pp. 12, 
15) document degradation of riffles from siltation, there are still 
numerous riffles throughout the range continuing to support Concho 
water snakes (Dixon 2004, pp. 5-8). In their recent survey of the 
Concho water snake and its habitat, Forstner et al. (2006, pp. 14, 16) 
found that the lack of flushing flows has allowed silt to settle and 
cover many of the riffles at historically occupied sites and that 
several sites have changed from riffles to slow-flowing sandy sections 
of river. Sand and silt fill in graveled cobble substrate and provide 
areas for growth of salt cedar and other vegetation, which further 
eliminates the rocky-bottomed riffle areas required by Concho water 
snakes (51 FR 31419; Scott and Fitzgerald 1985, p. 13; Forstner et al. 
2006, p. 15). These changes are particularly evident at sites on the 
Concho River (Dixon 2004, p. 9). However, despite some riffle habitat 
loss and the presence of other system stressors, Forstner et al. (2006, 
p. 18) noted that the Concho water snake persisted and continued to 
reproduce at the majority of the sites they visited. In fact, the 
Concho River, where degradation has been most evident, contained the 
largest number of Concho water snakes captured by Forstner et al. 
(2006, p. 8).
    Dixon (2004, p. 9) indicated that changes in the Concho River where 
the lack of flushing flow has allowed the accumulation of vegetation 
and debris likely caused the adult and juvenile snakes to retreat to 
refuge habitats in nearby pools and to areas where water flows over 
bedrock. Although some changes have occurred in the riverine habitat as 
a result of the loss of channel maintenance flows over time, the snakes 
appear to be adaptable to using other habitats and maintaining 
populations despite these changes. Therefore, we find that the threats 
associated with habitat modification from the reduction of frequency 
and magnitude of high-discharge channel-maintenance flows are not 
likely to endanger the Concho water snake in the foreseeable future.
Habitat Modification From Fragmentation
    At the time of listing, we believed construction of Ivie Reservoir 
(Freese Dam) would likely segment Concho water snakes into three 
separate populations and thereby reduce genetic exchange (Scott and 
Fitzgerald 1985, p. 34). Prior to the snake's listing in 1986, no 
researchers had documented Concho water snakes traveling over land to 
circumvent the barriers caused by large dams, and snakes had not been 
located in reservoirs. Due to this separation, a reasonable and prudent 
measure in the 1986 BO was to transfer snakes annually between the 
river reaches separated by the dam. In 1995, four male snakes were 
moved from below Ivie Reservoir to river habitats above the Reservoir 
(District 199, p. 1). In 2006, five adult male snakes and one adult 
female snake were captured below Ivie Reservoir and released in the 
Concho River upstream of Ivie Reservoir (District 2006, pp. 1-2). Also 
in 2006, three male snakes and one female snake were transferred from 
the Concho River to Spence Reservoir (District 2006, pp. 3-4).
    Because we now know Ivie Reservoir, which receives flow from both 
the Concho and Colorado Rivers, is occupied by the snake, we believe it 
is reasonable to surmise that snakes are capable of genetic interchange 
between the Concho and Colorado Rivers via the reservoir's shoreline. 
The District (1998, p. 14) summarized Concho water snake habitat within 
Ivie Reservoir and found that although the habitat is not linearly 
consistent, it does occur throughout the reservoir. Concho water snakes 
have been documented in mark-recapture studies to move up to 12 mi (19 
km) (Werler and Dixon 2000, p. 212). Based on the occupancy of 
reservoirs by the snakes and the ability to move large distances, we 
have a high level of confidence that gene flow occurs between these 
river reaches.
    In 2005 surveys, Forstner et al. 2006 (pp. 10-13, 18) found that 
Concho water

[[Page 66798]]

snakes were reproducing in the Concho and Colorado Rivers above Ivie 
Reservoir and in the Colorado River below it; they concluded that the 
populations in those three river reaches were self sustaining and 
seemingly viable (Forstner et al. 2006, pp. 16-18, 20). The 2008 MOU, 
as amended in 2011 and described above, Article 4.1 also provides that, 
in the springtime at 3-year intervals, the District, in coordination 
with the Service, should move five male snakes from below Spence and 
Freese dams to above these dams and move five different male snakes 
from above to below both dams. Moving snakes will be dependent upon 
availability of funding for the District. If the District is unable to 
carry out the snake movements, the Service will work with TPWD or other 
partners to ensure it occurs. We believe this movement will benefit the 
snake by enhancing genetic exchange between the three river reaches. 
The periodic movement of five snakes is believed to be sufficient to 
mimic natural gene flow (Sites and Densmore 1991, pp. 10-11) and reduce 
potential effects of genetic isolation among separated populations. 
This level of exchange exceeds the rule-of-thumb minimum of one 
individual exchanged with each generation (Mills and Allendorf 1996, p. 
1,557). Should funding be unavailable in any particular snake-moving 
year, every effort will be made to move snakes in the succeeding year.
    Based on the available information, we do not believe the species 
is likely to become endangered in the foreseeable future due to genetic 
isolation or habitat fragmentation.
Habitat Modification From Pollution and Water Quality Degradation
    At the time of listing, we believed buildup of algae in riffle 
areas reduced oxygen and nutrients available to populations of fish, 
the Concho water snake's primary food (51 FR 31419). We were also 
concerned that the inflow of nutrients into the Concho River in the San 
Angelo area, along with reduced dilution capability associated with 
lower flows, created large concentrations of algae in portions of the 
river (51 FR 31419). A summary of the 1987-1996 fish surveys in the 
Colorado and Concho rivers, included in the Service's 2004 BO (Service 
2004a, Appendix A, pp. 68-69), suggested that fish populations have 
persisted despite the presence of algae. Also, no impacts to snakes 
have been observed or documented as a result of water quality 
conditions during the ongoing drought (Service 2004a, p. 52). We have 
no further indication that algae buildup has occurred or has impacted 
the snake or its prey base. Therefore, we no longer consider algal 
growth and nutrient enrichment to be significant threats to the snake's 
survival.
    The Texas State Legislature implemented the Texas Clean Rivers 
program in 1991. The District has actively participated in the program 
since that time and monitors surface water quality in the upper 
Colorado River basin, which includes the distribution of the Concho 
water snake above Freese Dam (District 2005, p. 28). The LCRA has the 
responsibility for water quality monitoring below Freese Dam. Both of 
these entities have participated in the Clean Rivers Program since 1991 
and have provided a proactive response for ensuring a high level of 
surface water quality in the Colorado River and its main stem 
reservoirs (LCRA et al. 2007, pp. 3-4). These programs (including 
routine chemical and biological monitoring, environmental education, 
oil field clean up, superfund site cleanup, and well plugging) are 
ongoing and designed to ensure water quality integrity for all aquatic 
resources, including the Concho water snake and fish, its primary food 
source, in the upper basin (LCRA et al. 2007, pp. 13-15, 22, 28, 33-
34). As water quality problems (biological or chemical) are detected, 
swift responses by the District and LCRA to affect corrective actions 
through State of Texas regulatory agencies (TCEQ and the Texas Railroad 
Commission) are completed (Service 2004a, pp. 52-53).
    Additional water quality protections for Concho water snakes in 
riverine and reservoir habitats will continue indirectly under the 
Clean Water Act (CWA). According to the U.S. Environmental Protection 
Agency (2006, p. 1), the CWA establishes basic structures for 
regulating discharges of pollutants into United States waters, 
protecting water quality for species dependent on rivers and streams 
for their survival. Discharges are controlled through permits issued by 
TCEQ; within the range of the Concho water snake, these permits are 
mainly to small towns. With human population growth in the region 
forecasted at relatively small rates (estimated 17 percent increase) 
over the next 50 years (TWDB 2007, p. 43), we do not predict any 
significant increase in this threat in the foreseeable future.
    Based on the lack of information documenting effects of pollution 
or water quality degradation on snake populations and the ongoing 
efforts of water agencies to monitor and maintain healthy water 
quality, we find that the pollution and water quality degradation is 
not a significant threat to the Concho water snake.
Summary of Factor A Threats
    The Concho water snake was listed in 1986 largely due to threats to 
its habitat from the potential for habitat modification resulting from 
the construction and operation of reservoirs within its range. Since 
the listing, the snake has been shown to be more abundant and 
widespread than originally thought and capable of surviving in 
reservoirs (District 1998, pp. 18-29). Reservoir operations have 
provided continual stream flows that have sustained the habitat for the 
species, even during an extreme drought, and we expect minimum 
reservoir releases to continue into the foreseeable future. In 
addition, the snake has been shown to be equipped to handle stochastic 
environmental fluctuations, such as low stream-flow conditions, and has 
demonstrated the ability to persist even when habitat conditions appear 
to be less than favorable (from reservoir inundation, low river flows, 
or silting in of riffles) (Forstner et al. 2006, pp. 13-18; Whiting et 
al. 2008, p. 443). Additionally, habitat restoration efforts such as 
the removal of salt cedar and other brushy species and the creation of 
artificial instream riffle structures are aimed at improving habitat 
for the Concho water snake and other aquatic species. Other potential 
threats to snake habitat from reduced flushing flows, fragmentation, 
and pollution and water quality degradation have not been found to 
occur at the level anticipated when the species was listed in 1986, and 
no impacts to the Concho water snakes have been documented.
    Therefore, we believe that destruction, modification, or 
curtailment of the Concho water snake habitat or range due to habitat 
loss, altered instream flows and floodwater scouring, drought, 
vegetation encroachment, fragmentation, and pollution no longer 
threaten the Concho water snake with becoming endangered in the 
foreseeable future of about 50 years.

B. Overutilization for Commercial, Recreational, Scientific, or 
Educational Purposes

    At the time of listing, Concho water snakes were known to sometimes 
be captured or killed by recreationists (51 FR 31420). The effect of 
this activity on Concho water snake populations was and still is 
believed to be minimal. However, instances of Concho and Brazos (a 
closely related species occurring in an adjacent drainage) water

[[Page 66799]]

snakes being killed have been reported in both populated and 
unpopulated areas (Werler and Dixon 2000, p. 215). For example, Brazos 
water snakes have been crushed under stones at the water's edge by 
people walking on the banks and snakes have been shot by small caliber 
firearms. Concho water snakes may be confused with poisonous species of 
snakes. Fishermen have commented on their success in removing the 
``water moccasins'' from the river (Forstner et al. 2006, pp. 18-19). 
At one of the historically most productive localities for Brazos water 
snakes, Forstner et al. (2006, p. 18) found no snakes in two years of 
searching. They noted dozens to hundreds of campers at the site each 
year. According to Dixon (2004, p. 2), there is not as much recreation 
occurring on the Concho and Colorado rivers, where the Concho water 
snake occurs, as there is on the Brazos River. The vast majority of the 
range of the Concho water snake occurs in remote, rural locations with 
very limited human access or use of the river. This fact suggests there 
is limited opportunity for direct mortality by humans. Even in areas 
with high recreational use, such as Paint Rock Park (a city park on the 
Concho River) the snake was still collected there in relatively large 
numbers in 2005 (Forstner et al. 2006, p. 8). We are unaware of any 
plans to increase recreational opportunities on the Colorado and Concho 
Rivers. Therefore, we believe that impacts from recreationists will 
continue to be minimal in the foreseeable future in the areas occupied 
by Concho water snakes.
    While some limited killing of snakes is likely still occurring, 
there is no indication that any possible mortalities are affecting the 
species population levels, either rangewide or locally. Werler and 
Dixon (2000, p. 215) stated that malicious destruction of Concho water 
snakes ``probably does not constitute a major cause of mortality.'' We 
also have no reason to believe that this threat is likely to increase 
in the future.
    Therefore, we find that mortality from this factor is not likely to 
cause the species to become threatened or endangered in the foreseeable 
future.

C. Disease or Predation

    At the time of listing, no problems of disease or predation on 
Concho water snakes were known to exist (51 FR 31420). While currently 
no disease problems are known, predators on Concho water snakes have 
been identified. As is true for most snakes, predation by other 
wildlife is considered a major natural source of mortality for Concho 
water snakes (Werler and Dixon 2000, p. 215). Predators documented to 
prey on Concho water snakes include kingsnakes (Lampropeltis getula), 
coachwhip snakes (Masticophis flagellum), racers (Coluber constrictor), 
raccoons (Procyon lotor), and great blue herons (Ardea herodias) 
(Williams 1969, p. 15; Dixon et al. 1988, p. 18; Greene 1993, p. 102). 
Raptors such as hawks (Buteo spp.) and falcons (Falco spp.) are also 
known to prey upon snakes (Steenhof and Kochert 1988, p. 42). Predatory 
fish include bass (Micropterus salmoides) and channel catfish 
(Ictaclurus punctatus) (McGrew 1963, pp. 178-179; Jordan and Arrington 
2001, p. 158). However, all of these predators are native to this 
region, Concho water snakes evolved tolerating predation by these 
species, and we have no information indicating that the natural levels 
of predation are likely to increase.
    Therefore, we find that impacts from predation by other wildlife 
are not likely to cause the Concho water snake to become threatened or 
endangered in the foreseeable future.

D. The Inadequacy of Existing Regulatory Mechanisms

    The Concho water snake was listed as endangered by the State of 
Texas in 1984. In 2000, it was removed from the State's list of 
threatened species (TPWD 2000, p.3) because TPWD no longer considered 
it likely to become endangered based on the information provided by the 
District (District 1998); therefore, it will not protect Concho water 
snakes if we delist the species. However, the lack of protection of the 
Concho water snake by the State is not considered a threat because TPWD 
regulations only prohibit the taking, possession, transportation, or 
sale of designated animal species without the issuance of a permit. 
There is no protection by State law for the habitat of state-listed 
species. Since the Concho water snake is not threatened due to taking, 
possession, or sale of individuals, the lack of State protections does 
not affect the status of the species.
    The Texas Clean Rivers program, the Clean Water Act, and other 
Texas water law requirements, all discussed earlier under Factor A, 
provide some benefits to protect the habitat of the Concho water snake. 
These programs, in conjunction, with natural stream inflows and minimum 
flows from dam operations, indirectly conserve riverine habitats for 
the species.
    As a result, inadequacy of existing regulatory mechanisms does not 
constitute a threat to the Concho water snake such that it is likely to 
become endangered in the foreseeable future.

E. Other Natural or Manmade Factors Affecting Its Continued Existence

    We are unaware of any other natural or manmade factors affecting 
the continued existence of the Concho water snake at this time.

Conclusion of the Five-Factor Analysis

Foreseeable Future

    In considering the foreseeable future in the threats analysis for 
the Concho water snake, we generally regarded about 50 years as a 
timeframe where some reasonable predictions could be made. This range 
of time originated from the analysis of forecasting for water 
management, which is looking ahead to expected conditions in the year 
2060 (TWDB 2007, p. 2), and consideration of climate change models, 
which typically forecast 50 to 100 years into the future; however, 
there was too much uncertainty with the 100-year timeframe to serve as 
a reasonable foreseeable future (Jackson 2008, p. 8; Mace and Wade 
2008, p. 656). Since habitat modification from changing stream flows as 
a result of water availability and management is the primary threat of 
concern, this timeframe is appropriate for our analysis. This is also a 
reasonable timeframe for analysis considering the biology of the Concho 
water snake. The snakes become sexually mature at 2 or 3 years old and 
reproduce annually (Werner and Dixon 2000, p. 216), with a likely 
lifespan rarely exceeding 5 years (Mueller 1999, p. iii; Greene et al. 
1999, p. 707). A 50-year timeframe would encompass about 10 lifespans 
and multiple generations for the species. Considering multiple 
generations is important for any possible changes over time in rates of 
reproductive success and recruitment (growth to adulthood). This 
timeframe also captures the future stochastic hydrologic conditions 
(particularly droughts of 10 years or more and floods) and the expected 
responses by a short-lived, fast-growing species such as the Concho 
water snake.

Application of the Recovery Plan's Criteria

    The recovery plan provides important guidance on the direction and 
strategy for recovery, and indicates when a rulemaking process may be 
initiated; the determination to remove a species from the Federal List 
of Endangered and Threatened Wildlife is ultimately based on an 
analysis of whether a species is no longer endangered or threatened. 
The following discussion provides a brief

[[Page 66800]]

review of the recovery criteria and goals as they relate to evaluating 
the status of the species.
Recovery Criterion 1: Adequate Instream Flows
    The 1993 Recovery Plan called for assurance of adequate instream 
flows to maintain both the quantity and quality of Concho water snake 
habitat so that occupied habitat would continue to support viable 
populations of the species (Service 1993, p. 33). At the time the 
recovery plan was completed, adequate instream flow rates were based on 
the constituent elements identified in the 1989 critical habitat 
designation (54 FR 27382) and the reasonable and prudent alternatives 
identified in the 1986 BO for the construction of Ivie Reservoir. 
However, as the following new information became available, our 
understanding of the instream flow requirements necessary to support 
viable population of the Concho water snake has changed substantially. 
The topics summarized here are discussed at length above in section A. 
The Present or Threatened Destruction, Modification, or Curtailment of 
Its Habitat or Range, Habitat Modification from Reduced Instream Flows.
    First, lower flow rates have supported reproductive snake 
populations despite extended droughts. The revised lower flow rates 
were found adequate to support riverine habitat for the snake (Service 
2004a, pp. 50-52). This was based on new information from numerous 
studies funded by the District in the 1990s that greatly added to our 
knowledge of the biology of the snake and its habitat (District 1998, 
pp. 18-29). Additional monitoring of the snake indicated that the 
population was sustained by the lower flows required in the 2004 BO 
(Forstner et al. 2006, pp. 13-18). While riverine habitat is important 
for the conservation of the snake, the need to maintain continuous 
flows at levels previously required were determined to no longer be 
necessary to provide adequate habitat for snakes. The flows described 
in the Recovery Plan and the specific flows included in the 1989 
critical habitat designation were based on the best scientific 
information at that time. However, subsequent information provided by 
species experts Forstner, Dixon, and Thornton indicates that the snake 
will survive, reproduce, and maintain population viability with less 
stream flow.
    Second, information on the snake's habitat indicates they are more 
of a generalist (Dixon 2004, pp. 8-9) occurring in reservoirs and pools 
in rivers and do not depend on the previously accepted narrow habitat 
requirements restricted to riffles in rivers (Dixon 2004, 14-16). In 
addition to riverine habitat, the snake is known to use areas above and 
below low-head dams, pools created by the dams, man-made lakes, 
naturally occurring pools in the river, and tributaries, as Concho 
water snake has been found in Elm Creek and two of its tributaries.
    Third, adequate flow to maintain the snake's habitat and the snake 
population is provided by a variety of sources in addition to the 
minimum flows agreed to in the 2004 BO (Service 2004a, p. 11-12), and 
subsequently agreed to in the 2008 MOU. We expect minimal stream flows 
will be present at most times of the year in the gaining reaches of the 
Colorado River from contributing inflow from creeks and subdrainages, 
and discharges from springs where shallow groundwater interfaces with 
the stream (Dixon 2004, p. 9). Low flows are also present below Spence 
and Ivie Reservoirs due to dam leakage and seepage even when no 
releases are being made (Dixon 2004, p. 9). In addition, Texas water 
law requirements also result in maintenance of some instream flow, 
particularly in the river reach below Ivie Reservoir where the 
District's water right permit requires minimum flows of 8 cfs (0.23 
cms) from April through September and 2.5 cfs (0.07 cms) from October 
through March. Finally, dam releases from Spence Reservoir are 
periodically made to improve the quality of water (by diluting the salt 
content) entering Ivie Reservoir. All of these sources help maintain 
instream flows that provided habitat to the Concho water snake.
Recovery Criterion 2: Viable Populations
    The Recovery Plan (Service 1993, p.33) also called for maintaining 
viable populations of the snake in each of the three major reaches. The 
Recovery Plan defines viable population as one that is self-sustaining, 
can persist for the long-term (typically hundreds of years), and can 
maintain its vigor and its potential for evolutionary adaptation 
(Service 1993, p. 33).
    As previously described (see A. The Present or Threatened 
Destruction, Modification, or Curtailment of Its Habitat or Range, 
Range and Population Trends), monitoring studies from 1987 through 1996 
confirmed a larger and more consistent distribution of the Concho water 
snake throughout its range, including several reservoirs and 
tributaries (District 1998, pp. 10, 22, 26). In addition, over the 10 
years of study, 9,069 Concho water snakes were captured (excluding 
recaptures) (District 1998, p. 21). Of this total, 1,535 (17 percent) 
were captured in reservoirs, 1,517 (17 percent) were captured in the 
Concho River reach, 5,586 (62 percent) were captured in the Colorado 
River reach, and another 415 (5 percent) were captured in tributary 
streams. Although the results varied by year and location, each of the 
more than 20 sites monitored throughout the study had multiple captures 
of snakes, usually with a variety of age classes (Thornton 1996, pp. 
26-50).
    Unfortunately, the high variation in sample efforts and 
environmental conditions prevented a thorough analysis of population 
trends over time or calculation of total population estimates (District 
1998, p. 18). In other words, in order to measure the changes in 
abundance over time the study would have had to include a 
quantification of the amount of effort expended during each survey. 
Such data would have allowed a standardization of results over time to 
evaluate potential trends in population abundance of the snake. The 
researchers decided there was too much variation in the environmental 
conditions and resulting catch rates to produce such estimates and did 
not report the amount of effort expended during the surveys, making a 
trend analysis inappropriate.
    Forstner et al. (2006, pp. 6-8, 18, 20) reviewed the past 
population data collected on the snake (District 1998, p. 18-26), as 
well as conducted field surveys in 2004 and 2005 to document that 
snakes continued to be present and were reproducing in each river reach 
and reservoir where they occurred in previous studies. The study, which 
incorporated the results by Dixon (2004), confirmed reproducing 
populations of Concho water snakes in each river reach and in both Ivie 
and Spence Reservoirs (Forstner et al. 2006, p. 12). Based on the 
snakes' persistence and continued reproduction throughout its range 
over the past 20 years, Forstner et al. (2006, pp. 18, 20) concluded 
that viable populations of Concho water snakes could be presumed to 
exist in all three reaches of the species' range.
    There was some concern by peer reviewers of the proposed rule 
regarding the population of the snake in the reach of the Colorado 
River downstream of Freese Dam (Ivie Reservoir) where only two sample 
locations (below Freese Dam and at River Bend Ranch, about 25 miles (40 
km) downstream of the dam) (Dixon 2004, pp. 8, 14) were sampled due to 
the difficulties in establishing contact with private landowners in 
this reach. Dixon collected three snakes from these two sites in 2004, 
and one was a juvenile female (Dixon 2004, pp. 16-17). In 2005, 
Forstner et al. (2006, pp. 12, 18)

[[Page 66801]]

reports collection of one post-partum female below Freese Dam 
indicating the snake had given birth to young, confirming reproduction. 
Although only four snakes were captured in limited sampling efforts in 
2004 and 2005 in this reach, data from the District's earlier 
monitoring showed healthy populations in this reach (District 1998, pp. 
34-38, 50). We have no reason to conclude that the snake population 
downstream of Freese Dam is of additional concern.
    A reanalysis of Concho water snake monitoring data collected from 
1987 to 1996 attempted to evaluate the population dynamics of the 
species and quantitatively assess the long-term viability (Whiting et 
al. 2008, pp. 438-439). The results, however, were inconclusive because 
the data were insufficient to reliably estimate survival and 
emigration. This was due primarily to insufficient sampling at any 
single study site, along with a host of variables, especially different 
environmental conditions within a site and among sites, and also 
because dispersal rates were not measured among sites (Whiting et al. 
2008, p. 443). This situation resulted in the survival rates from the 
capture-recapture study being biased low and producing low estimates of 
annual survival with large standard errors (Whiting et al. 2008, p. 
443). However, Whiting also stated that snakes continued to persist 
even in drought-prone areas, some with almost total water loss, with 
hydrologically dynamic systems (Whiting et al. 2008, pp. 442-443). 
Although we lack recent data on population size and viability, we have 
used data on current range, long-term persistence, and verification of 
recent breeding success as indicators that the current populations meet 
the definition of a viable population.
Recovery Criterion 3: Movement of Snakes
    The Recovery Plan also provided for the movement of Concho water 
snakes (Service 1993, p. 33) to counteract adverse impacts of 
population fragmentation and prescribed the movement of four snakes 
(two of each sex) every 5 years in a specific pattern above and below 
Ivie Reservoir and between the Concho River reach and the Colorado 
River reach downstream of Spence Reservoir. The 2004 BO discussed 
population fragmentation (Service 2004a, p. 52) and found that the 
specific requirement for snake movements would best be served by moving 
five male snakes from downstream to upstream of both the dams at Spence 
and Ivie Reservoirs once every 3 years. The 2008 MOU, as amended in 
2010, now calls for the same movements of snakes and also includes 
movement of snakes from above to below both dams by the District even 
after the species is delisted. Since snakes are now known to occur in 
Ivie Reservoir, there is no longer a need to move snakes between the 
Concho River reach and the Colorado River reach downstream of Spence 
Reservoir, as those reaches are naturally connected. We added the 
requirement to move snakes above Spence Reservoir so that the 
population in Spence Reservoir can maintain genetic mixing with the 
riverine snakes downstream. We determined that moving only male snakes 
was sufficient to accomplish the objective of genetic exchange because 
a male will fertilize multiple females, providing opportunities for 
maintaining genetic diversity. We increased the frequency of snake 
transfers from 5 years called for in the recovery plan to an interval 
of 3 years to decrease the likelihood of population fragmentation. The 
Service believes that these movements are more than sufficient to 
maintain genetic heterogeneity between the separated populations 
(Service 2004a, p. 52) because research has shown that as few as one 
individual exchanged with each generation is sufficient to maintain 
adequate gene flow between animal populations (Mills and Allendorf 
1996, p. 1,557). Also see the discussion above under Habitat 
Modification From Fragmentation.

Conclusion

    As required by the Act, we considered all potential threats under 
the 5 factors to assess whether the Concho water snake is threatened or 
endangered throughout its range. We found that the best available 
information indicates that the Concho water snake is no longer 
threatened with becoming endangered throughout all of its range due to 
recovery accomplishments and new information on the ecology of the 
species. Concho water snakes can survive lower flows than previously 
thought necessary for their survival. Natural inflows and downstream 
senior water rights, in concert with assurances from the 2008 MOU, will 
maintain adequate instream flows and reduce the impacts of 
uncontrollable extreme drought periods. Populations of reproducing 
Concho water snakes are persisting in all 3 reaches of the species' 
range. The snake is capable of living and reproducing in reservoirs and 
persisting during droughts and in apparently degraded habitats. 
Considering these findings, evaluated in the five-factor analysis 
above, and that the three Recovery Plan Criteria have either been met 
outright, determined here to no longer be appropriate, or conditions 
are insured to meet the intent of each of the criteria, we have 
determined that none of the existing or potential threats, either alone 
or in combination with others, are likely to cause the Concho water 
snake to become in danger of extinction throughout all of its range 
within the foreseeable future of about 50 years.
Significant Portion of the Range Analysis
    Having determined that the Concho water snake is not endangered or 
threatened throughout all its range, we must next consider whether 
there are any significant portions of the range where the Concho water 
snake is in danger of extinction or is likely to become endangered in 
the foreseeable future.
    The Act defines ``endangered species'' as any species which is ``in 
danger of extinction throughout all or a significant portion of its 
range,'' and ``threatened species'' as any species which is ``likely to 
become an endangered species within the foreseeable future throughout 
all or a significant portion of its range.'' The definition of 
``species'' is also relevant to this discussion. The Act defines the 
term ``species'' as follows: ``The term `species' includes any 
subspecies of fish or wildlife or plants, and any distinct population 
segment [DPS] of any species of vertebrate fish or wildlife which 
interbreeds when mature.'' The phrase ``significant portion of its 
range'' (SPR) is not defined by the statute, and we have never 
addressed in our regulations: (1) The consequences of a determination 
that a species is either endangered or likely to become so throughout a 
significant portion of its range, but not throughout all of its range; 
or (2) what qualifies a portion of a range as ``significant.''
    Two recent district court decisions have addressed whether the SPR 
language allows the Service to list or protect less than all members of 
a defined ``species'': Defenders of Wildlife v. Salazar, 729 F. Supp. 
2d 1207 (D. Mont. 2010), concerning the Service's delisting of the 
Northern Rocky Mountain gray wolf (74 FR 15123, Apr. 12, 2009); and 
WildEarth Guardians v. Salazar, 2010 U.S. Dist. LEXIS 105253 (D. Ariz. 
Sept. 30, 2010), concerning the Service's 2008 finding on a petition to 
list the Gunnison's prairie dog (73 FR 6660, Feb. 5, 2008). The Service 
had asserted in both of these determinations that it had authority, in 
effect, to protect only some members of a ``species,'' as

[[Page 66802]]

defined by the Act (i.e., species, subspecies, or DPS), under the Act. 
Both courts ruled that the determinations were arbitrary and capricious 
on the grounds that this approach violated the plain and unambiguous 
language of the Act. The courts concluded that reading the SPR language 
to allow protecting only a portion of a species' range is inconsistent 
with the Act's definition of ``species.'' The courts concluded that, 
once a determination is made that a species (i.e., species, subspecies, 
or DPS) meets the definition of ``endangered species'' or ``threatened 
species,'' it must be placed on the list in its entirety and the Act's 
protections applied consistently to all members of that species 
(subject to modification of protections through special rules under 
sections 4(d) and 10(j) of the Act).
    Consistent with that interpretation, and for the purposes of this 
finding, we interpret the phrase ``significant portion of its range'' 
in the Act's definitions of ``endangered species'' and ``threatened 
species'' to provide an independent basis for listing; thus there are 
two situations (or factual bases) under which a species would qualify 
for listing: a species may be endangered or threatened throughout all 
of its range; or a species may be endangered or threatened in only a 
significant portion of its range. If a species is in danger of 
extinction throughout an SPR, it, the species, is an ``endangered 
species.'' The same analysis applies to ``threatened species.'' 
Therefore, the consequence of finding that a species is endangered or 
threatened in only a significant portion of its range is that the 
entire species shall be listed as endangered or threatened, 
respectively, and the Act's protections shall be applied across the 
species' entire range.
    We conclude, for the purposes of this finding, that interpreting 
the SPR phrase as providing an independent basis for listing is the 
best interpretation of the Act because it is consistent with the 
purposes and the plain meaning of the key definitions of the Act; it 
does not conflict with established past agency practice (i.e., prior to 
the 2007 Solicitor's Opinion), as no consistent, long-term agency 
practice has been established; and it is consistent with the judicial 
opinions that have most closely examined this issue. Having concluded 
that the phrase ``significant portion of its range'' provides an 
independent basis for listing and protecting the entire species, we 
next turn to the meaning of ``significant'' to determine the threshold 
for when such an independent basis for listing exists.
    Although there are potentially many ways to determine whether a 
portion of a species' range is ``significant,'' we conclude, for the 
purposes of this finding, that the significance of the portion of the 
range should be determined based on its biological contribution to the 
conservation of the species. For this reason, we describe the threshold 
for ``significant'' in terms of an increase in the risk of extinction 
for the species. We conclude that a biologically based definition of 
``significant'' best conforms to the purposes of the Act, is consistent 
with judicial interpretations, and best ensures species' conservation. 
Thus, for the purposes of this finding, a portion of the range of a 
species is ``significant'' if its contribution to the viability of the 
species is so important that, without that portion, the species would 
be in danger of extinction.
    We evaluate biological significance based on the principles of 
conservation biology using the concepts of redundancy, resiliency, and 
representation. Resiliency describes the characteristics of a species 
that allow it to recover from periodic disturbance. Redundancy (having 
multiple populations distributed across the landscape) may be needed to 
provide a margin of safety for the species to withstand catastrophic 
events. Representation (the range of variation found in a species) 
ensures that the species' adaptive capabilities are conserved. 
Redundancy, resiliency, and representation are not independent of each 
other, and some characteristic of a species or area may contribute to 
all three. For example, distribution across a wide variety of habitats 
is an indicator of representation, but it may also indicate a broad 
geographic distribution contributing to redundancy (decreasing the 
chance that any one event affects the entire species), and the 
likelihood that some habitat types are less susceptible to certain 
threats, contributing to resiliency (the ability of the species to 
recover from disturbance). None of these concepts is intended to be 
mutually exclusive, and a portion of a species' range may be determined 
to be ``significant'' due to its contributions under any one of these 
concepts.
    For the purposes of this finding, we determine if a portion's 
biological contribution is so important that the portion qualifies as 
``significant'' by asking whether, without that portion, the 
representation, redundancy, or resiliency of the species would be so 
impaired that the species would have an increased vulnerability to 
threats to the point that the overall species would be in danger of 
extinction (i.e., would be ``endangered''). Conversely, we would not 
consider the portion of the range at issue to be ``significant'' if 
there is sufficient resiliency, redundancy, and representation 
elsewhere in the species' range that the species would not be in danger 
of extinction throughout its range if the population in that portion of 
the range in question became extirpated (extinct locally).
    We recognize that this definition of ``significant'' establishes a 
threshold that is relatively high. On the one hand, given that the 
consequences of finding a species to be endangered or threatened in an 
SPR would be listing the species throughout its entire range, it is 
important to use a threshold for ``significant'' that is robust. It 
would not be meaningful or appropriate to establish a very low 
threshold whereby a portion of the range can be considered 
``significant'' even if only a negligible increase in extinction risk 
would result from its loss. Because nearly any portion of a species' 
range can be said to contribute some increment to a species' viability, 
use of such a low threshold would require us to impose restrictions and 
expend conservation resources disproportionately to conservation 
benefit: listing would be rangewide, even if only a portion of the 
range of minor conservation importance to the species is imperiled. On 
the other hand, it would be inappropriate to establish a threshold for 
``significant'' that is too high. This would be the case if the 
standard were, for example, that a portion of the range can be 
considered ``significant'' only if threats in that portion result in 
the entire species' being currently endangered or threatened. Such a 
high bar would not give the SPR phrase independent meaning, as the 
Ninth Circuit held in Defenders of Wildlife v. Norton, 258 F.3d 1136 
(9th Cir. 2001).
    The definition of ``significant'' used in this finding carefully 
balances these concerns. By setting a relatively high threshold, we 
minimize the degree to which restrictions will be imposed or resources 
expended that do not contribute substantially to species conservation. 
But we have not set the threshold so high that the phrase ``in a 
significant portion of its range'' loses independent meaning. 
Specifically, we have not set the threshold as high as it was under the 
interpretation presented by the Service in the Defenders litigation. 
Under that interpretation, the portion of the range would have to be so 
important that current imperilment there would mean that the species 
would be currently imperiled everywhere. Under the definition of 
``significant'' used in this finding, the portion of the range need not 
rise to such an exceptionally high level of

[[Page 66803]]

biological significance. (We recognize that if the species is imperiled 
in a portion that rises to that level of biological significance, then 
we should conclude that the species is in fact imperiled throughout all 
of its range, and that we would not need to rely on the SPR language 
for such a listing). Rather, under this interpretation we ask whether 
the species would be endangered everywhere without that portion, i.e., 
if that portion were completely extirpated. In other words, the portion 
of the range need not be so important that even being in danger of 
extinction in that portion would be sufficient to cause the remainder 
of the range to be endangered; rather, the complete extirpation (in a 
hypothetical future) of the species in that portion would be required 
to cause the remainder of the range to be endangered.
    The range of a species can theoretically be divided into portions 
in an infinite number of ways. However, there is no purpose to 
analyzing portions of the range that have no reasonable potential to be 
significant and threatened or endangered. To identify only those 
portions that warrant further consideration, we determine whether there 
is substantial information indicating that: (1) The portions may be 
``significant,'' and (2) the species may be in danger of extinction 
there or likely to become so within the foreseeable future. Depending 
on the biology of the species, its range, and the threats it faces, it 
might be more efficient for us to address the significance question 
first or the status question first. Thus, if we determine that a 
portion of the range is not ``significant,'' we do not need to 
determine whether the species is endangered or threatened there; if we 
determine that the species is not endangered or threatened in a portion 
of its range, we do not need to determine if that portion is 
``significant.'' In practice, a key part of the portion status analysis 
is whether the threats are geographically concentrated in some way. If 
the threats to the species are essentially uniform throughout its 
range, no portion is likely to warrant further consideration. Moreover, 
if any concentration of threats applies only to portions of the 
species' range that clearly would not meet the biologically based 
definition of ``significant'', such portions will not warrant further 
consideration.
    Based on our review of the best available information concerning 
the distribution of the species and the potential threats, we have 
determined that the Concho water snake does not warrant further 
consideration to determine if there is a significant portion of the 
range that is threatened or endangered. Through the five-factor 
analysis we found no areas where one or more threats are geographically 
concentrated. The range of the snake can readily be divided into three 
portions, based on the presence of large dams: (1) The Concho River 
segment (San Angelo to the inflow of Ivie Reservoir); (2) the upper 
Colorado River segment (Spence Reservoir and the Colorado River outflow 
downstream to Ivie Reservoir); and (3) the lower Colorado River segment 
(outflow of Ivie Reservoir downstream to Colorado Bend State Park). 
Generally, all of the potential threats to the species that were 
evaluated in the Summary of Factors Affecting the Species section above 
occur at similarly low levels in each of the three segments. However, 
there are some differences in flow regimes that were described in the 
Habitat Modification from Reduced Instream Flows section above and are 
considered here.
    The Concho River segment has undergone the most dramatic flow 
reduction due to upstream dams and water diversion for human use. The 
result has been extended periods of very low discharges throughout much 
of the reach (Asquith and Heitmuller 2008, pp. 849-850). Despite the 
habitat alterations, the snake continues to persist in this reach and 
Forstner et al. (2006, p. 8) found the highest numbers of Concho water 
snakes (20 of all 45 snakes captured or observed during their brief 
surveys in 2004 and 2005) in this reach of the Concho River. Dixon 
(2004, p. 9) explains that the snakes endure these conditions by using 
low-flow areas over bedrock substrate for foraging and also using the 
pools that form behind low-head dams as habitat. Therefore, we find 
that the potential threats from low flows, or any other threats, in 
this portion of its range do not warrant continued listing of the 
snake.
    Both the upper and lower Colorado River segments have also 
undergone hydrologic changes and decreases in stream flows from 
reservoir construction and operation (Asquith et al. 2008, pp. 810-813; 
850-853). However, river flows have been maintained due to natural 
drainage inflows and minimum reservoir releases (Service 2004, pp. 35-
38). Water has been released from Spence Reservoir for the benefit of 
the Concho water snake under the requirements of biological opinions 
and as part of the 2008 MOU. In addition, releases from Ivie Reservoir 
are required to fulfill requirements for downstream users, consistent 
with the flows called for in the 2008 MOU, which will continue to be 
implemented even if the snake is delisted. As evaluated under Summary 
of Factors Affecting the Species section above, we find that these flow 
reductions, or any other threats, in either of these segments are not 
threatening the species. Because the low level of threats to the 
species is essentially uniform throughout its range, no portion 
warrants further consideration to determine if they are significant.
    Therefore, we find the Concho water snake is no longer threatened 
with becoming endangered throughout all or a significant portion of its 
range within the foreseeable future. We believe the Concho water snake 
no longer requires the protection of the Act, and, therefore, we are 
removing it from the Federal List of Endangered and Threatened 
Wildlife.

Effects of the Rule

    This final rule revises 50 CFR 17.11(h) to remove the Concho water 
snake from the Federal List of Endangered and Threatened Wildlife. 
Promulgation of this final rule will affect protection afforded the 
Concho water snake under the Act. Taking, interstate commerce, import, 
and export of Concho water snakes are no longer prohibited under the 
Act. Federal agencies are no longer required to consult with us under 
section 7 of the Act to ensure that any action they authorize, fund, or 
carry out is not likely to jeopardize the species' continued existence. 
This final rule also revises 50 CFR 17.95(c) to remove the critical 
habitat designation.

Post-Delisting Monitoring Plan

    Section 4(g)(1) of the Act requires us, in cooperation with the 
States, to implement a monitoring program for not less than 5 years for 
all species that have been recovered and delisted (50 CFR 17.11, 
17.12). The purpose of this post-delisting monitoring (PDM) is to 
verify that the species remains secure from risk of extinction after it 
has been removed from the protections of the Act. The PDM is designed 
to detect the failure of any delisted species to sustain itself without 
the protective measures provided by the Act. If, at any time during the 
monitoring period, data indicate that protective status under the Act 
should be reinstated, we can initiate listing procedures, including, if 
appropriate, emergency listing under section 4(b)(7) of the Act. 
Section 4(g) of the Act explicitly requires cooperation with the States 
in development and implementation of PDM programs, but we remain 
responsible for compliance with section 4(g) and, therefore, must 
remain actively engaged in all phases of

[[Page 66804]]

PDM. We also seek active participation of other entities that are 
expected to assume responsibilities for the species' conservation, 
post-delisting.
    The Service has developed a PDM plan in cooperation with the 
District and TPWD. We published a notice of availability of the draft 
plan in the Federal Register on September 23, 2009, (74 FR 48595) to 
solicit public comments and peer review on the plan. No public comments 
on the PDM plan were received. Comments from six peer reviewers were 
considered and incorporated into the final PDM plan as appropriate. The 
final PDM plan and any future revisions will be posted on our 
Endangered Species Program's national web page (http://endangered.fws.gov) and on the Austin Ecological Services Field Office 
web page (http://www.fws.gov/southwest/es/AustinTexas/).
    PDM for Concho water snakes will consist of two monitoring 
components: biological (to monitor the status of the snake) and 
hydrological (to monitor instream flow conditions). Over a 14-year 
period, surveys to measure the presence, reproduction, and abundance of 
snakes will be conducted annually in the fall for 13 consecutive years 
at 9 core biological sample sites across the snake's range. In 
addition, more intense biological surveys will be conducted during the 
spring and fall of 3 years spread over the monitoring period at 18 
sample sites. Evaluation of stream conditions will consist of analysis 
of hydrologic data collected at eight existing stream gauges from 
across the snake's range, which will verify that flows called for in 
the 2008 MOU are being realized. Quantitative and qualitative 
monitoring triggers for additional conservation actions are based on 
documented changes to the snake's range-wide distribution; observed 
presence and abundance at sample sites; and successful reproduction. 
Triggers are also established based on instream flow conditions within 
the snake's habitat. If monitoring results in concern regarding the 
snake's status or increasing threats, possible responses may include an 
extended or intensified monitoring effort, additional research (such as 
modeling metapopulation dynamics or assessing the status of the fish 
prey base), enhancement of riverine or shoreline habitats, or an 
increased effort to improve habitat connectivity by additional 
translocation of snakes between reaches. If future information 
collected from the PDM, or any other reliable source, indicates an 
increased likelihood that the species may become endangered with 
extinction, the Service will initiate a status review of the Concho 
water snake and determine if relisting the species is warranted.

Paperwork Reduction Act

    This rule does not contain any new collections of information that 
require approval by OMB under the Paperwork Reduction Act (44 U.S.C. 
3501 et seq.). This rule will not impose recordkeeping or reporting 
requirements on State or local governments, individuals, businesses, or 
organizations. An agency may not conduct or sponsor, and a person is 
not required to respond to, a collection of information unless it 
displays a currently valid OMB control number.

National Environmental Policy Act

    We have determined that an Environmental Assessment or an 
Environmental Impact Statement, as defined under the authority of the 
National Environmental Policy Act of 1969, need not be prepared in 
connection with regulations adopted pursuant to section 4 of the Act. 
We published a notice outlining our reasons for this determination in 
the Federal Register on October 25, 1983 (48 FR 49244).

References Cited

    A complete list of all references cited herein is available upon 
request from the U.S. Fish and Wildlife Service, Austin Ecological 
Services Field Office (see FOR FURTHER INFORMATION CONTACT above).

Authors

    The primary authors of this document are staff located at the 
Austin Ecological Services Field Office (see FOR FURTHER INFORMATION 
CONTACT above).

List of Subjects in 50 CFR Part 17

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

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--[AMENDED]

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

    Authority:  16 U.S.C. 1361-1407; 16 U.S.C. 1531-1544; 16 U.S.C. 
4201-4245; Pub. L. 99-625, 100 Stat. 3500; unless otherwise noted.


Sec.  17.11  [Amended]

0
2. Amend Sec.  17.11(h) by removing the entry ``Snake, Concho water'' 
under ``REPTILES'' from the List of Endangered and Threatened Wildlife.


Sec.  17.95  [Amended]

0
3. Amend Sec.  17. 95(c) by removing the critical habitat entry for 
``Concho Water Snake (Nerodia harteri paucimaculata).''

    Dated: October 7, 2011.
Gregory E. Siekaniec,
Acting Director, U.S. Fish and Wildlife Service.
[FR Doc. 2011-27375 Filed 10-26-11; 8:45 am]
BILLING CODE 4310-55-P