[Federal Register Volume 78, Number 80 (Thursday, April 25, 2013)]
[Proposed Rules]
[Pages 24472-24514]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2013-09600]



[[Page 24471]]

Vol. 78

Thursday,

No. 80

April 25, 2013

Part II





Department of the Interior





-----------------------------------------------------------------------





Fish and Wildlife Service





-----------------------------------------------------------------------





50 CFR Part 17





Endangered and Threatened Wildlife and Plants; Endangered Status for 
the Sierra Nevada Yellow-Legged Frog and the Northern Distinct 
Population Segment of the Mountain Yellow-Legged Frog, and Threatened 
Status for the Yosemite Toad; Proposed Rule

  Federal Register / Vol. 78 , No. 80 / Thursday, April 25, 2013 / 
Proposed Rules  

[[Page 24472]]


-----------------------------------------------------------------------

DEPARTMENT OF THE INTERIOR

Fish and Wildlife Service

50 CFR Part 17

[Docket No. FWS-R8-ES-2012-0100; 4500030113]
RIN 1018-AZ21


Endangered and Threatened Wildlife and Plants; Endangered Status 
for the Sierra Nevada Yellow-Legged Frog and the Northern Distinct 
Population Segment of the Mountain Yellow-Legged Frog, and Threatened 
Status for the Yosemite Toad

AGENCY: Fish and Wildlife Service, Interior.

ACTION: Proposed rule.

-----------------------------------------------------------------------

SUMMARY: We, the U.S. Fish and Wildlife Service, propose to list the 
Sierra Nevada yellow-legged frog and the northern distinct population 
segment (DPS) (populations that occur north of the Tehachapi Mountains) 
of the mountain yellow-legged frog as endangered species, and the 
Yosemite toad as a threatened species under the Endangered Species Act 
of 1973, as amended (Act). The effect of this regulation would be to 
add the species to the List of Endangered and Threatened Wildlife under 
the Act.

DATES: We will accept comments received or postmarked on or before June 
24, 2013. Comments submitted electronically using the Federal 
eRulemaking Portal (see ADDRESSES below) must be received by 11:59 p.m. 
Eastern Time on the closing date. We must receive requests for public 
hearings, in writing, at the address shown in the FOR FURTHER 
INFORMATION CONTACT section by June 10, 2013.

ADDRESSES: You may submit comments by one of the following methods:
    (1) Electronically: Go to the Federal eRulemaking Portal: http://www.regulations.gov. In the Search box, enter Docket No. FWS-R8-ES-
2012-0100, which is the docket number for this rulemaking. Then, in the 
Search panel on the left side of the screen, under the Document Type 
heading, click on the Proposed Rules link to locate this document. You 
may submit a comment by clicking on ``Comment Now!''
    (2) By hard copy: Submit by U.S. mail or hand-delivery to: Public 
Comments Processing, Attn: FWS-R8-ES-2012-0100; Division of Policy and 
Directives Management; U.S. Fish and Wildlife Service; 4401 N. Fairfax 
Drive, MS 2042-PDM; Arlington, VA 22203.
    We request that you send comments only by the methods described 
above. We will post all comments on http://www.regulations.gov. This 
generally means that we will post any personal information you provide 
us (see Information Requested below for more information).

FOR FURTHER INFORMATION CONTACT: Jan Knight, Acting Field Supervisor, 
U.S. Fish and Wildlife Service, Sacramento Fish and Wildlife Office, 
2800 Cottage Way Room W-2605, Sacramento CA 95825; by telephone 916-
414-6600; or by facsimile 916-414-6712. Persons who use a 
telecommunications device for the deaf (TDD) may call the Federal 
Information Relay Service (FIRS) at 800-877-8339.

SUPPLEMENTARY INFORMATION: 
    This document consists of: a proposed rule to list the Sierra 
Nevada yellow-legged frog and the northern DPS of the mountain yellow-
legged frog as endangered, and to list the Yosemite toad as threatened.

Executive Summary

    Why we need to publish a rule. Under the Act, if a species is 
determined to be an endangered or threatened species throughout all or 
a significant portion of its range, we are required to promptly publish 
a proposal in the Federal Register and make a determination on our 
proposal within one year. Listing a species as an endangered or 
threatened species can only be completed by issuing a rule.
    This rule proposes the listing of the Sierra Nevada yellow-legged 
frog and the northern DPS of the mountain yellow-legged frog as 
endangered, and to list the Yosemite toad as threatened.
     We are proposing to list the Sierra Nevada yellow-legged 
frog as endangered under the Endangered Species Act.
     We are proposing to list the northern DPS of the mountain 
yellow-legged frog as endangered under the Endangered Species Act.
     We are proposing to list the Yosemite toad as threatened 
under the Endangered Species Act.
    The basis for our action. Under the Act, we can determine that a 
species is an endangered or threatened species based on any of five 
factors: (A) The present or threatened destruction, modification, or 
curtailment of its habitat or range; (B) overutilization for 
commercial, recreational, scientific, or educational purposes; (C) 
disease or predation; (D) the inadequacy of existing regulatory 
mechanisms; or (E) other natural or manmade factors affecting its 
continued existence. We reviewed all available scientific and 
commercial information pertaining to the five threat factors in our 
evaluation of each species.
    We have made the following findings related to these criteria:

Sierra Nevada Yellow-Legged Frog (Rana Sierrae)

    The Sierra Nevada yellow-legged frog is presently in danger of 
extinction throughout its entire range, based on the immediacy, 
severity, and scope of the threats to its continued existence. These 
include habitat degradation and fragmentation, predation and disease, 
climate change, inadequate regulatory protections, and the interaction 
of these various stressors impacting small remnant populations. There 
has been a rangewide reduction in abundance and geographic extent of 
surviving populations of frogs following decades of fish stocking, 
habitat fragmentation, and most recently a disease epidemic. Surviving 
populations are smaller and more isolated, and recruitment in disease-
infested populations is much reduced relative to historic norms. This 
combination of population stressors makes persistence of the species 
precarious throughout the currently occupied range in the Sierra 
Nevada.

Northern Distinct Population Segment of the Mountain Yellow-Legged Frog 
(Rana Muscosa)

    Populations within the southern DPS of the mountain yellow-legged 
frog inhabiting the Transverse Ranges of Southern California are 
currently listed as an endangered species. The northern DPS of the 
mountain yellow-legged frog is presently in danger of extinction 
throughout its range within the Sierra Nevada, based on the immediacy, 
severity, and scope of the threats to its continued existence. These 
include habitat degradation and fragmentation, predation and disease, 
climate change, inadequate regulatory protections, and the interaction 
of these various stressors impacting small remnant populations. There 
has been a rangewide reduction in abundance and geographic extent of 
surviving populations of frogs following decades of fish stocking, 
habitat fragmentation, and most recently a disease epidemic. Surviving 
populations are smaller and more isolated, and recruitment in disease-
infested populations is much reduced relative to historic norms. This 
combination of population stressors makes persistence of the species 
precarious throughout the Sierra Nevada range of the mountain yellow-
legged frog.
    The northern DPS of the mountain yellow-legged frog has different 
habitat, requires different management, and has

[[Page 24473]]

different primary constituent elements than the already listed southern 
DPS . For these reasons, we have proposed a separate DPS for the 
northern population in this rule. However, if we finalize this rule, 
the entire range of the mountain yellow-legged frog may be listed as 
endangered. We request public input on whether we should retain the 
northern and southern DPS's or combine the two into one listed species 
in the final rule. Thus, we are giving notice that we may combine the 
two DPS's into one listed species if we finalize this proposed rule.

Yosemite Toad (Anaxyrus Canorus)

    The Yosemite toad is likely to become endangered throughout its 
range within the foreseeable future, based on the immediacy, severity, 
and scope of the threats to its continued existence. These include 
habitat loss associated with degradation of meadow hydrology following 
stream incision consequent to the cumulative effects of historic land 
management activities, notably livestock grazing, and also the 
anticipated hydrologic effects upon habitat from climate change. We 
also find that the Yosemite toad is likely to become endangered through 
the direct effects of climate change impacting small remnant 
populations, likely compounded with the cumulative effect of other 
threat factors (such as disease).
    We will seek peer review. We are seeking comments from 
knowledgeable individuals with scientific expertise to review our 
analysis of the best available science and application of that science 
and to provide any additional scientific information to improve this 
proposed rule. Because we will consider all comments and information 
received during the comment period, our final determination may differ 
from this proposal.

Information Requested

    We intend that any final action resulting from this proposed rule 
will be based on the best scientific and commercial data available and 
be as accurate and as effective as possible. Therefore, we request 
comments or information from other concerned governmental agencies, 
Native American tribes, the scientific community, industry, or any 
other interested parties concerning this proposed rule. We particularly 
seek comments concerning:
    (1) Biological, commercial trade, or other relevant data concerning 
any threats (or lack thereof) to these species, and regulations that 
may be addressing those threats.
    (2) Additional information concerning the historical and current 
status, range, distribution, and population size of these species, 
including the locations of any additional populations of these species.
    (3) Any information on the biological or ecological requirements of 
these species, and ongoing conservation measures for these species and 
their habitats.
    (4) The factors that are the basis for making a listing 
determination for a species under section 4(a) of the Act 16 U.S.C. 
1531 et seq.), which are:
    (a) The present or threatened destruction, modification, or 
curtailment of its habitat or range;
    (b) Overutilization for commercial, recreational, scientific, or 
educational purposes;
    (c) Disease or predation;
    (d) The inadequacy of existing regulatory mechanisms; or
    (e) Other natural or manmade factors affecting its continued 
existence.
    (5) Land use designations and current or planned activities in the 
areas occupied by the species, and possible impacts of these activities 
on these species.
    (6) Information on the projected and reasonably likely impacts of 
climate change on the Sierra Nevada yellow-legged frog, the northern 
DPS of the mountain yellow-legged frog, and the Yosemite toad.
    (7) Input on whether we should retain the northern and southern 
DPS's of the mountain yellow-legged frog in the final rule or should we 
combine the two DPS's into one listed entity for the species.
    Please include sufficient information with your submission (such as 
scientific journal articles or other publications) to allow us to 
verify any scientific or commercial information you include.
    Please note that submissions merely stating support for or 
opposition to the action under consideration without providing 
supporting information, although noted, will not be considered in 
making a determination, as section 4(b)(1)(A) of the Act directs that 
determinations as to whether any species is an endangered or threatened 
species must be made ``solely on the basis of the best scientific and 
commercial data available.''
    You may submit your comments and materials concerning this proposed 
rule by one of the methods listed in the ADDRESSES section. We request 
that you send comments only by the methods described in the ADDRESSES 
section.
    If you submit information via http://www.regulations.gov, your 
entire submission--including any personal identifying information--will 
be posted on the Web site. If your submission is made via a hardcopy 
that includes personal identifying information, you may request at the 
top of your document that we withhold this information from public 
review. However, we cannot guarantee that we will be able to do so. We 
will post all hardcopy submissions on http://www.regulations.gov. 
Please include sufficient information with your comments to allow us to 
verify any scientific or commercial information you include.
    Comments and materials we receive, as well as supporting 
documentation we used in preparing this proposed rule, will be 
available for public inspection on http://www.regulations.gov, or by 
appointment, during normal business hours, at the U.S. Fish and 
Wildlife Service, Sacramento Fish and Wildlife Office (see FOR FURTHER 
INFORMATION CONTACT).

Previous Federal Actions

Mountain Yellow-Legged Frog

    In February 2000, we received a petition from the Center for 
Biological Diversity and Pacific Rivers Council to list the Sierra 
Nevada population of the mountain yellow-legged frog (Rana muscosa). 
The petition stated that this population met the criteria in our DPS 
Policy and that it should be listed as endangered. On October 12, 2000, 
we published a 90-day finding on that petition in the Federal Register 
(65 FR 60603), concluding that the petition presented substantial 
scientific or commercial information to indicate that the listing of 
the Sierra Nevada population of the mountain yellow-legged frog may be 
warranted, and we concurrently requested information and data regarding 
the species. On January 16, 2003, we published a 12-month petition 
finding in the Federal Register that listing was warranted but 
precluded (68 FR 2283). This finding was in accordance with a court 
order requiring us to complete a finding by January 10, 2003 (Center 
for Biological Diversity v. Norton, No. 01-2106 (N. D. Cal. Dec. 12, 
2001)). Upon publication of the finding, we added the Sierra Nevada DPS 
of the mountain yellow-legged frog to our list of species that are 
candidates for listing.
    The Center for Biological Diversity and Pacific Rivers Council 
challenged our finding that listing was warranted but precluded, and 
sought to compel the Service to proceed with listing. On June 21, 2004, 
the U.S. District Court for the Eastern District of California granted 
summary judgment in favor of the United States (Center for Biological 
Diversity v. Norton, No. 03-01758 (E.D.

[[Page 24474]]

Cal. June 21, 2004)). In response to an appeal of the District Court 
decision, on October 18, 2006, the 9th Circuit Court of Appeals 
reversed and remanded the lower Court's judgment, concluding that the 
12-month finding we published on January 16, 2003, did not meet the 
requirements of section 4(b)(3)(B) of the Act.
    We addressed the 9th Circuit Court's remand by amending our January 
16, 2003, warranted-but-precluded finding to include a description of 
our underlying rationale and an evaluation of the data demonstrating 
why listing the Sierra Nevada DPS of the mountain yellow-legged frog 
was precluded from listing. We further described the expeditious 
progress we had made toward adding qualified species to the Federal 
Lists of Endangered and Threatened Wildlife and Plants at the time. The 
revised 12-month finding was published on June 25, 2007 (72 FR 34657), 
reiterating a warranted-but-precluded finding, and maintaining the 
Sierra Nevada DPS of the mountain yellow-legged frog as a candidate for 
listing under the Act. In the intervening time, this entity has been 
taxonomically split (See Background section in Endangered Status For 
Sierra Nevada Yellow-legged Frog and the Northern DPS of the Mountain 
Yellow-legged Frog).
    Candidate assessments for the Sierra Nevada DPS of the mountain 
yellow-legged frog have been prepared annually since the 2007 12-month 
finding (2008, 73 FR 75176; 2009, 74 FR 57804, corrected 75 FR 8293; 
2010, 75 FR 69222; 2011, 76 FR 66370). The taxonomic split was 
officially recognized in the 2011 Candidate Assessment (76 FR 66370), 
where we noted that we would include the change in the upcoming 
proposed rule. Accordingly, in this proposed rule, we address two 
separate species within the mountain yellow-legged frog ``species 
complex'': Rana muscosa and Rana sierrae.

Yosemite Toad

    In April 2000, we received a petition from the Center for 
Biological Diversity and Pacific Rivers Council to list the Yosemite 
toad as endangered under the Act, and to designate critical habitat 
concurrent with listing. On October 12, 2000, the Service published a 
90-day finding (65 FR 60607) concluding that the petition presented 
substantial scientific or commercial information to indicate that the 
listing of the Yosemite toad may be warranted, and we concurrently 
requested information and data regarding the species. On December 10, 
2002, we published a 12-month finding (67 FR 75834), concluding that 
the Yosemite toad warranted protection under the Act; however, 
budgetary constraints precluded the Service from listing the Yosemite 
toad as endangered or threatened at the time. This finding was in 
accordance with a court order requiring us to complete a finding by 
November 30, 2002 (Center for Biological Diversity v. Norton, No. 01-
2106 (N. D. Cal. Dec. 12, 2001)).
    Candidate assessments for the Yosemite toad have been prepared 
annually since the 2002 12-month finding (2004, 69 FR 24876; 2005, 70 
FR 24870; 2006, 71 FR 53756; 2007, 72 FR 69034; 2008, 73 FR 75176; 
2009, 74 FR 57804; 2010, 75 FR 69222; 2011, 76 FR 66370).

Status for Sierra Nevada Yellow-Legged Frog and the Northern DPS of the 
Mountain Yellow-Legged Frog

Background

    In this section of the proposed rule, it is our intent to discuss 
only those topics directly relevant to the proposed listing of the 
Sierra Nevada yellow-legged frog as endangered and the proposed listing 
of the northern DPS of the mountain yellow-legged frog as endangered.

Taxonomy

    Mountain yellow-legged frogs were once thought to be a subspecies 
of the foothill yellow-legged frog, Rana boylii (Camp 1917, pp. 118-
123), and were therefore designated as R. b. sierrae in the Sierra 
Nevada and R. b. muscosa in southern California. At that time, it was 
presumed that yellow-legged frog populations from southern California 
through northern California were a single species. Additional 
morphological data supported the classification of the two subspecies 
separate from R. boylii as the species R. muscosa (Zweifel 1955, pp. 
210-240). Macey et al. (2001, p. 141) conducted a phylogenetic analysis 
of mitochondrial deoxyribonucleic acid (DNA) sequences of the mountain 
yellow-legged frog and concluded that there were two major genetic 
lineages (and four groups), with populations in the Sierra Nevada 
falling into three distinct groups, the fourth being the southern 
California population.
    Based on mitochondrial DNA, morphological information, and acoustic 
studies, Vredenburg et al. (2007, p. 371) recently recognized two 
distinct species of mountain yellow-legged frog in the Sierra Nevada, 
Rana muscosa and R. sierrae. This taxonomic distinction was 
subsequently adopted by the American Society of Ichthyologists and 
Herpetologists, the Herpetologists' League, and the Society for the 
Study of Amphibians and Reptiles (Crother et al. 2008, p. 11). The 
Vredenburg study determined that R. sierrae occurs in the Sierra Nevada 
north of the Kern River watershed and over the eastern crest of the 
Sierra Nevada into Inyo County at its most southern extent, and that R. 
muscosa occurs in the southern portion of the Sierra Nevada within the 
Kern River watershed to the west of the Sierra Nevada crest (along with 
those populations inhabiting southern California) (Vredenburg et al. 
2007, p. 361).
    Macey et al. (2001, p. 140) suggested that the initial divergence 
between the Sierra Nevada yellow-legged frog and the mountain yellow-
legged frog occurred 2.2 million years before present (mybp). The 
biogeographic pattern of genetic divergence as detected in the mountain 
yellow-legged frog complex of the Sierra Nevada has also been observed 
in four other reptiles and amphibians in this area, suggesting that a 
common event fragmented their ranges (Macey et al. 2001, p. 140).
    We identify Rana sierrae in this proposed rule as the Sierra Nevada 
yellow-legged frog, and refer to the Sierra Nevada populations of R. 
muscosa as the northern range of the mountain yellow-legged frog. 
Together, these species may be termed the ``mountain yellow-legged frog 
complex.'' Figure 1 shows the newly recognized species split within 
their historical ranges as determined by Knapp (unpubl. data).
BILLING CODE 4310-55-P

[[Page 24475]]

[GRAPHIC] [TIFF OMITTED] TP25AP13.028

BILLING CODE 4310-55-C
    For purposes of this proposed rule, we recognize the species 
designation as presented in Vredenburg et al. (2007, p. 371) and 
adopted by the official societies mentioned above (Crother et al. 2008, 
p. 11). Specifically, Sierra Nevada yellow-legged frogs occupy the 
western Sierra Nevada north of the Monarch Divide (in Fresno County) 
and the eastern Sierra Nevada (east of the crest) in Inyo and Mono 
Counties. The southern DPS of the mountain yellow-legged frog occupies 
the canyons of the Transverse Ranges in southern California, and is 
already listed as an endangered species (67 FR 44382, July 2, 2002). 
The northern portion of the range of mountain yellow-legged frog 
(extending in the western Sierra Nevada from south of the Monarch 
Divide in Fresno County through portions of the Kern River drainage) is 
referred to in this proposed rule as the northern DPS of the mountain 
yellow-legged frog.
    Many studies cited in this document include articles and reports 
that were published prior to the official species reclassification, 
where the researchers may reference either one or both species. Where 
possible and appropriate, information will be referenced specifically 
(either as Sierra Nevada yellow-legged frog or the northern DPS of the 
mountain yellow-legged frog) to reflect the split of the species. Where 
information applies to both species, the two species will be referred 
to collectively as mountain yellow-legged frogs (or frog complex), 
consistent with the designation in each particular source document.

Species Description

    The body length (snout to vent) of the mountain yellow-legged frog 
ranges from 40 to 80 millimeters (mm) (1.5 to 3.25 inches (in)) 
(Jennings and Hayes 1994, p. 74). Females average slightly larger than 
males, and males have a swollen, darkened thumb base (Wright and Wright 
1949, pp. 424-430; Stebbins

[[Page 24476]]

1951, pp. 330-335; Zweifel 1955, p. 235; Zweifel 1968, p. 65.1). Dorsal 
(upper) coloration in adults is variable, exhibiting a mix of brown and 
yellow, but also can be grey, red, or green-brown, and is usually 
patterned with dark spots (Jennings and Hayes 1994, p. 74; Stebbins 
2003, p. 233). These spots may be large (6 mm (0.25 in)) and few, 
smaller and more numerous, or a mixture of both (Zweifel 1955, p. 230). 
Irregular lichen- or moss-like patches (to which the name muscosa 
refers) may also be present on the dorsal surface (Zweifel 1955, pp. 
230, 235; Stebbins 2003, p. 233).
    The belly and undersurfaces of the hind limbs are yellow or orange, 
and this pigmentation may extend forward from the abdomen to the 
forelimbs (Wright and Wright 1949, pp. 424-429; Stebbins 2003, p. 233). 
Mountain yellow-legged frogs may produce a distinctive mink or garlic-
like odor when disturbed (Wright and Wright 1949, p. 432; Stebbins 
2003, p. 233). Although these species lack vocal sacs, they can 
vocalize in or out of water, producing what has been described as a 
flat clicking sound (Zweifel 1955, p. 234; Ziesmer 1997, pp. 46-47; 
Stebbins 2003, p. 233). Mountain yellow-legged frogs have smoother 
skin, generally with heavier spotting and mottling dorsally, darker toe 
tips (Zweifel 1955, p. 234), and more opaque ventral coloration 
(Stebbins 2003, pp. 233) than the foothill yellow-legged frog.
    The Sierra Nevada yellow-legged frog and the northern DPS of the 
mountain yellow-legged frog are similar morphologically and 
behaviorally (hence their shared taxonomic designation until recently). 
However, these two species can be distinguished from each other 
physically by the ratio of the lower leg (fibulotibia) length to snout 
vent length. The northern DPS of the mountain yellow-legged frog has 
longer limbs (Vredenburg et al. 2007, p. 368). Typically, this ratio is 
greater than or equal to 0.55 in the northern DPS of the mountain 
yellow-legged frog and less than 0.55 in the Sierra Nevada yellow-
legged frog.
    Mountain yellow-legged frogs deposit their eggs in globular clumps, 
which are often somewhat flattened and roughly 2.5 to 5 centimeters 
(cm) (1 to 2 in) in diameter (Stebbins 2003, p. 444). When eggs are 
close to hatching, egg mass volume averages 198 cubic cm (78 cubic in) 
(Pope 1999a, p. 30). Eggs have three firm, jelly-like, transparent 
envelopes surrounding a grey-tan or black vitelline (egg yolk) capsule 
(Wright and Wright 1949, pp. 431-433). Clutch size varies from 15 to 
350 eggs per egg mass (Livezey and Wright 1945, p. 703; Vredenburg et 
al. 2005, p. 565). Egg development is temperature dependent. In 
laboratory breeding experiments, egg hatching time ranged from 18 to 21 
days at temperatures of 5 to 13.5 degrees Celsius ([deg]C) (41 to 56 
degrees Fahrenheit ([deg]F)) (Zweifel 1955, pp. 262-264). Field 
observations show similar results (Pope 1999a, p. 31).
    The tadpoles of mountain yellow-legged frogs generally are mottled 
brown on the dorsal side with a faintly yellow venter (underside) 
(Zweifel 1955, p. 231; Stebbins 2003, p. 460). Total tadpole length 
reaches 72 mm (2.8 in), the body is flattened, and the tail musculature 
is wide (about 2.5 cm (1 in) or more) before tapering into a rounded 
tip (Wright and Wright 1949, p. 431). The mouth has a maximum of eight 
labial (lip) tooth rows (two to four upper and four lower) (Stebbins 
2003, p. 460). Tadpoles may take more than 1 year (Wright and Wright 
1949, p. 431), and often require 2 to 4 years, to reach metamorphosis 
(transformation from tadpoles to frogs) (Cory 1962b, p. 515; Bradford 
1983, pp. 1171, 1182; Bradford et al. 1993, p. 883; Knapp and Matthews 
2000, p. 435), depending on local climate conditions and site-specific 
variables.
    The time required to reach reproductive maturity in mountain 
yellow-legged frogs is thought to vary between 3 and 4 years post 
metamorphosis (Zweifel 1955, p. 254). This information, in combination 
with the extended amount of time as a tadpole before metamorphosis, 
means that it may take 5 to 8 years for mountain yellow-legged frogs to 
begin reproducing. Longevity of adults is unknown, but under normal 
circumstances, adult survivorship from year to year is very high, so 
mountain yellow-legged frogs are presumed to be long-lived amphibians 
(Pope 1999a, p. 46).

Habitat and Life History

    Mountain yellow-legged frogs currently exist in montane regions of 
the Sierra Nevada of California. Throughout their range, these species 
historically inhabited lakes, ponds, marshes, meadows, and streams at 
elevations ranging from 1,370 to 3,660 meters (m) (4,500 to 12,000 feet 
(ft)) (California Department of Fish and Game (CDFG) 2011b, pp. A-1-A-
5). Mountain yellow-legged frogs are highly aquatic; they are generally 
not found more than 1 m (3.3 ft) from water (Stebbins 1951, p. 340; 
Mullally and Cunningham 1956a, p. 191; Bradford et al. 1993, p. 886). 
Adults typically are found sitting on rocks along the shoreline, 
usually where there is little or no vegetation (Mullally and Cunningham 
1956a, p. 191). Although mountain yellow-legged frogs may use a variety 
of shoreline habitats, both tadpoles and adults are less common at 
shorelines that drop abruptly to a depth of 60 cm (2 ft) than at open 
shorelines that gently slope up to shallow waters of only 5 to 8 cm (2 
to 3 in) in depth (Mullally and Cunningham 1956a, p. 191; Jennings and 
Hayes 1994, p. 77).
    At lower elevations within their historical range, these species 
are known to be associated with rocky streambeds and wet meadows 
surrounded by coniferous forest (Zweifel 1955, p. 237; Zeiner et al. 
1988, p. 88). Streams utilized by adults vary from streams having high 
gradients and numerous pools, rapids, and small waterfalls, to streams 
with low gradients and slow flows, marshy edges, and sod banks (Zweifel 
1955, p. 237). Aquatic substrates vary from bedrock to fine sand, 
rubble (rock fragments), and boulders (Zweifel 1955, p. 237). Mountain 
yellow-legged frogs appear absent from the smallest creeks, probably 
because these creeks have insufficient depth for adequate refuge and 
overwintering habitat (Jennings and Hayes 1994, p. 77). Sierra Nevada 
yellow-legged frogs do use stream habitats, especially the remnant 
populations in the northern part of their range.
    At higher elevations, these species occupy lakes, ponds, tarns 
(small steep-banked mountain lake or pool), and streams (Zweifel 1955, 
p. 237; Mullally and Cunningham 1956a, p. 191). Mountain yellow-legged 
frogs in the Sierra Nevada are most abundant in high-elevation lakes 
and slow-moving portions of streams (Zweifel 1955, p. 237; Mullally and 
Cunningham 1956a, p. 191). The borders of alpine (above the tree line) 
lakes and mountain meadow streams used by mountain yellow-legged frogs 
are frequently grassy or muddy. This differs from the sandy or rocky 
shores inhabited by mountain yellow-legged frogs in lower elevation 
streams (Zweifel 1955, pp. 237-238).
    Adult mountain yellow-legged frogs breed in the shallows of ponds 
or in inlet streams (Vredenburg et al. 2005, p. 565). Adults emerge 
from overwintering sites immediately following snowmelt, and will even 
move over ice to reach breeding sites (Pope 1999a, pp. 46-47; 
Vredenburg et al. 2005, p. 565). Mountain yellow-legged frogs deposit 
their eggs underwater in clusters, which they attach to rocks, gravel, 
or vegetation, or which they deposit under banks (Wright and Wright 
1949, p. 431; Stebbins 1951,

[[Page 24477]]

p. 341; Zweifel 1955, p. 243; Pope 1999a, p. 30).
    Lake depth is an important attribute defining habitat suitability 
for mountain yellow-legged frogs. As tadpoles must overwinter multiple 
years before metamorphosis, successful breeding sites are located in 
(or connected to) lakes and ponds that do not dry out in the summer, 
and also are deep enough that they do not completely freeze or become 
oxygen depleted (anoxic) in winter. Both adults and tadpole mountain 
yellow-legged frogs overwinter for up to 9 months in the bottoms of 
lakes that are at least 1.7 m (5.6 ft) deep; however, overwinter 
survival may be greater in lakes that are at least 2.5 m (8.2 ft) deep 
(Bradford 1983, p. 1179; Vredenburg et al. 2005, p. 565).
    Bradford (1983, p. 1173) found that mountain yellow-legged frog 
die-offs sometimes result from oxygen depletion during winter in lakes 
less than 4 m (13 ft) in depth. However, tadpoles may survive for 
months in nearly anoxic conditions when shallow lakes are frozen to the 
bottom. More recent work reported populations of mountain yellow-legged 
frogs overwintering in lakes less than 1.5 m (5 ft) deep that were 
assumed to have frozen to the bottom, and yet healthy frogs emerged the 
following July (Matthews and Pope 1999, pp. 622-623; Pope 1999a, pp. 
42-43). Radio telemetry indicated that the frogs were utilizing rock 
crevices, holes, and ledges near shore, where water depths ranged from 
0.2 m (0.7 ft) to 1.5 m (5 ft) (Matthews and Pope 1999, p. 619). The 
granite surrounding these overwintering habitats probably insulates 
mountain yellow-legged frogs from extreme winter temperatures, provided 
there is an adequate supply of oxygen (Matthews and Pope 1999, p. 622). 
In lakes and ponds that do not freeze to the bottom in winter, mountain 
yellow-legged frogs may overwinter in the shelter of bedrock crevices 
as a behavioral response to the presence of introduced fishes 
(Vredenburg et al. 2005, p. 565).
    Mountain yellow-legged frog tadpoles maintain a relatively high 
body temperature by selecting warmer microhabitats (Bradford 1984, p. 
973). During winter, tadpoles remain in warmer water below the 
thermocline (the transition layer between thermally stratified water). 
After spring overturn (thaw and thermal mixing of the water), they 
behaviorally modulate their body temperature by moving to shallow, near 
shore water when warmer days raise surface water temperatures. During 
the late afternoon and evening, mountain yellow-legged frogs retreat to 
offshore waters that are less subject to night cooling (Bradford 1984, 
p. 974).
    Available evidence suggests that mountain yellow-legged frogs 
display strong site fidelity and return to the same overwintering and 
summer habitats from year to year (Pope 1999a, p. 45). In aquatic 
habitats of high mountain lakes, mountain yellow-legged frog adults 
typically move only a few hundred meters (few hundred yards) (Matthews 
and Pope 1999, p. 623; Pope 1999a, p. 45), but single-season distances 
of up to 3.3 kilometers (km) (2.05 miles (mi)) have been recorded along 
streams (Wengert 2008, p. 18). Adults tend to move between selected 
breeding, feeding, and overwintering habitats during the course of the 
year. Though typically found near water, overland movements by adults 
of over 66 m (217 ft) have been routinely recorded (Pope 1999a, p. 45); 
the farthest reported distance of a mountain yellow-legged frog from 
water is 400 m (1,300 ft) (Vredenburg 2002, p. 4). Along stream 
habitats, adults have been observed greater than 22 m (71 ft) from the 
water during the overwintering period (Wengert 2008, p. 20).
    Almost no data exist on the dispersal of juvenile mountain yellow-
legged frogs away from breeding sites; however, juveniles that may be 
dispersing to permanent water have been observed in small intermittent 
streams (Bradford 1991, p. 176). Regionally, mountain yellow-legged 
frogs are thought to exhibit a metapopulation structure (Bradford et 
al. 1993, p. 886; Drost and Fellers 1996, p. 424). Metapopulations are 
spatially separated population subunits within migratory distance of 
one another such that individuals may interbreed among subunits and 
populations may become reestablished if they are extirpated (Hanski and 
Simberloff 1997, p. 6).

Historical Range and Distribution

    Mountain yellow-legged frogs were historically abundant and 
ubiquitous across much of the higher elevations within the Sierra 
Nevada. Grinnell and Storer (1924, p. 664) reported the Sierra Nevada 
yellow-legged frog to be the most common amphibian surveyed in the 
Yosemite area. It is difficult to know the precise historical ranges of 
the Sierra Nevada yellow-legged frog and the mountain yellow-legged 
frog, because projections must be inferred from museum collections that 
do not reflect systematic surveys, and survey information predating 
significant rangewide reduction is very limited. However, projections 
of historical ranges are available using predictive habitat modeling 
based on recent research (Knapp, unpubl. data).
    The Sierra Nevada yellow-legged frog historically occurred in 
Nevada on the slopes of Mount Rose in Washoe County and likely in the 
vicinity of Lake Tahoe in Douglas County (Linsdale 1940, pp. 208-210; 
Zweifel 1955, p. 231; Jennings 1984, p. 52). The historical range of 
the Sierra Nevada yellow-legged frog extends in California from north 
of the Feather River, in Butte and Plumas Counties, to the south at the 
Monarch Divide, in Fresno County, west of the Sierra Nevada crest. East 
of the Sierra Nevada crest, the historical range of the Sierra Nevada 
yellow-legged frog extends from the Glass Mountains of Mono County, 
through Inyo County, to areas north of Lake Tahoe.
    The northern DPS of the mountain yellow-legged frog ranges from the 
Monarch Divide in Fresno County southward through the headwaters of the 
Kern River Watershed. The ranges of the two frog species within the 
mountain yellow-legged complex therefore meet each other roughly along 
the Monarch Divide to the north, and along the crest of the Sierra 
Nevada to the east.

Current Range and Distribution

    Since the time of the mountain yellow-legged frog observations of 
Grinnell and Storer (1924, pp. 664-665), a number of researchers have 
reported disappearances of these species from a large fraction of their 
historical ranges in the Sierra Nevada (Hayes and Jennings 1986, p. 
490; Bradford 1989, p. 775; Bradford et al. 1994a, pp. 323-327; 
Jennings and Hayes 1994, p. 78; Jennings 1995, p. 133; Stebbins and 
Cohen 1995, pp. 225-226; Drost and Fellers 1996, p. 414; Jennings 1996, 
pp. 934-935; Knapp and Matthews 2000, p. 428; Vredenburg et al. 2005, 
p. 564).
    The current distributions of the Sierra Nevada yellow-legged frog 
and the northern DPS of the mountain yellow-legged frog are restricted 
primarily to publicly managed lands at high elevations, including 
streams, lakes, ponds, and meadow wetlands located within National 
Forests and National Parks. National Forests with extant (surviving) 
populations of mountain yellow-legged frogs include the Plumas National 
Forest, Tahoe National Forest, Humboldt-Toiyabe National Forest, Lake 
Tahoe Basin Management Unit, Eldorado National Forest, Stanislaus 
National Forest, Sierra National Forest, Sequoia National Forest, and 
Inyo National Forest. National Parks with extant populations of 
mountain yellow-legged frogs include Yosemite National

[[Page 24478]]

Park, Kings Canyon National Park, and Sequoia National Park.
    The most pronounced declines within the mountain yellow-legged frog 
complex have occurred north of Lake Tahoe in the northernmost 125-km 
(78-mi) portion of the range (Sierra Nevada yellow-legged frog) and 
south of Sequoia and Kings Canyon National Parks in Tulare County, in 
the southernmost 50-km (31-mi) portion, where only a few populations of 
the northern DPS of the mountain yellow-legged frog remain (Fellers 
1994, p. 5; Jennings and Hayes 1994, pp. 74-78). Mountain yellow-legged 
frog populations have persisted in greater density in the National 
Parks of the Sierra Nevada as compared to the surrounding U.S. Forest 
Service (USFS) lands, and the populations that do occur in the National 
Parks generally exhibit higher abundances than those on USFS lands 
(Bradford et al. 1994a, p. 323; Knapp and Matthews 2000, p. 430).

Population Estimates and Status

    Monitoring efforts and research studies have documented substantial 
declines of mountain yellow-legged frog populations in the Sierra 
Nevada. The number of extant populations has declined greatly over the 
last few decades. Remaining populations are patchily scattered 
throughout the historical range (Jennings and Hayes 1994, pp. 74-78; 
Jennings 1995, p. 133; Jennings 1996, p. 936). In the northernmost 
portion of the range (Butte and Plumas Counties), only a few Sierra 
Nevada yellow-legged frog populations have been documented since 1970 
(Jennings and Hayes 1994, pp. 74-78; CDFG et al., unpubl. data). 
Declines have also been noted in the central and southern Sierra Nevada 
(Drost and Fellers 1996, p. 420). In the south (Sierra, Sequoia, and 
Inyo National Forests; and Sequoia, Kings Canyon, and Yosemite National 
Parks), modest to relatively large populations (for example, breeding 
populations of approximately 40 to more than 200 adults) of mountain 
yellow-legged frogs do remain; however, in recent years some of the 
largest of these populations have been extirpated (Bradford 1991, p. 
176; Bradford et al. 1994a, pp. 325-326; Knapp 2002a, p. 10).
    Davidson et al. (2002, p. 1591) reviewed 255 previously documented 
mountain yellow-legged frog locations (based on Jennings and Hayes 
1994, pp. 74-78) throughout the historical range and concluded that 83 
percent of these sites no longer support frog populations. Vredenburg 
et al. (2007, pp. 369-371) compared recent survey records (1995-2004) 
with museum records from 1899-1994 and reported that 92.5 percent of 
historical Sierra Nevada yellow-legged frog populations and 92.3 
percent of populations of the northern DPS of mountain yellow-legged 
frog are now extirpated.
    CDFG (2011b, pp. 17-20) used historical localities from museum 
records covering the same time interval (1899-1994), but updated recent 
locality information with additional survey data (1995-2010) to 
significantly increase proportional coverage from the Vredenburg et al. 
(2007) study. These more recent surveys failed to detect any extant 
frog population (within 1 km (0.63 mi), a metric used to capture 
interbreeding individuals within metapopulations) at 220 of 318 
historical Sierra Nevada yellow-legged frog localities and 94 of 109 
historical mountain yellow-legged frog localities (in the Sierran 
portion of their range). This calculates to an estimated loss of 69 
percent of Sierra Nevada yellow-legged frog metapopulations and 86 
percent of northern DPS of the mountain yellow-legged frog 
metapopulations from historical occurrences.
    In addition to comparisons based on individual localities, CDFG 
(2011b, pp. 20-25) compared historical and recent population status at 
the watershed scale. This is a rough index of the geographic extent of 
the species through their respective ranges. Within the Sierra Nevada, 
44 percent of watersheds historically utilized by Sierra Nevada yellow-
legged frogs, and 59 percent of watersheds historically utilized by 
northern DPS mountain yellow-legged frogs, no longer support extant 
populations. However, as recent survey efforts generally are more 
thorough than historical ones (they target all aquatic habitats in each 
surveyed watershed), this watershed-level comparison likely 
underestimates rangewide declines in total populations because several 
individual populations may be lost even though a watershed is counted 
as recently occupied if a single individual (at any life stage) is 
observed within the entire watershed (CDFG 2011b, p. 20). Furthermore, 
remaining populations are generally very small. Many watersheds support 
only a single extant metapopulation, which occupies one to several 
adjacent water bodies (CDFG 2011b, p. 20).
    Rangewide, declines of mountain yellow-legged frog populations were 
estimated at around one-half of historical populations by the end of 
the 1980s (Bradford et al. 1994a, p. 323). Between 1988 and 1991, 
Bradford et al. (1994a, pp. 323-327) resurveyed sites known 
historically (1955 through 1979 surveys) to support mountain yellow-
legged frogs. They did not detect frogs at 27 historical sites on the 
Kaweah River, and they detected frogs at 52 percent of historical sites 
within Sequoia and Kings Canyon National Parks and 12.5 percent of 
historical sites outside of Sequoia and Kings Canyon National Parks. 
When both species are combined, this resurvey effort detected mountain 
yellow-legged frogs at 19.4 percent of historical sites (Bradford et 
al. 1994a, pp. 324-325).
    Available information discussed below indicates that the rates of 
population decline have not abated, and they have likely accelerated 
during the 1990s into the 2000s. Drost and Fellers (1996, p. 417) 
repeated Grinnell and Storer's early 20th century surveys, and reported 
frog presence at 2 of 14 historical sites. The two positive sightings 
consisted of a single tadpole at one site and a single adult female at 
another. They identified 17 additional sites with suitable mountain 
yellow-legged frog habitat, and in those surveys, they detected three 
additional populations. In 2002, Knapp (2002a, p. 10) resurveyed 302 
water bodies known to be occupied by mountain yellow-legged frogs 
between 1995 and 1997, and 744 sites where frogs were not previously 
detected. Knapp found frogs at 59 percent of the previously occupied 
sites, whereas 8 percent of previously unoccupied sites were 
recolonized. These data suggest an extirpation rate five to six times 
higher than the colonization rate within this study area. The 
documented extirpations appeared to occur non-randomly across the 
landscape, were typically spatially clumped, and involved the 
disappearance of all or nearly all of the mountain yellow-legged frog 
populations in a watershed (Knapp 2002a, p. 9). CDFG (2011b, p. 20) 
assessed data from sites where multiple surveys were completed since 
1995 (at least 5 years apart). They found that the Sierra Nevada 
yellow-legged frog was not detected at 45 percent of sites where they 
previously had been confirmed, while the mountain yellow-legged frog 
(rangewide, including southern California) was no longer detectable at 
81 percent of historically occupied sites.
    The USFS conducts a rangewide, long-term monitoring program for the 
Sierra Nevada yellow-legged frog and the northern DPS of the mountain 
yellow-legged frog known as the Sierra Nevada Amphibian Monitoring 
Program (SNAMPH). This monitoring effort provides unbiased estimates by 
using an integrated unequal probability design, and it provides numbers 
for robust statistical comparisons across 5-year

[[Page 24479]]

monitoring cycles spanning 208 watersheds (Brown et al. 2011, pp. 3-4). 
The results of this assessment indicate that breeding activity for the 
frogs is limited to 4 percent of watersheds rangewide, and the species 
have declined in both distribution and abundance from historical 
records. For the recent historical record (positive surveys during 
1990-2002 versus 2006-2009), breeding was found in about half (48 
percent) of the survey sites. When compared to data prior to 1990, 
recent frog occurrence is limited to 3 percent of watersheds for which 
data exist. Moreover, relative abundances were low; an estimated 9 
percent of populations were large (numbering more than 100 frogs or 500 
tadpoles); about 90 percent of the watersheds had fewer than 10 adults, 
while 80 percent had fewer than 10 subadults and 100 tadpoles (Brown et 
al. 2011, p. 24).
    To summarize population trends over the available historical 
record, estimates range from losses between 69 to 93 percent of Sierra 
Nevada yellow-legged frog populations and 86 to 92 percent of northern 
DPS of the mountain yellow-legged frog. Rangewide reduction has 
diminished the number of watersheds that support mountain yellow-legged 
frogs somewhere between the conservative estimates of 44 percent in the 
case of Sierra Nevada yellow-legged frogs and at least 59 percent in 
the case of northern DPS of the mountain yellow-legged frogs, to as 
high as 97 percent of watersheds for the mountain yellow-legged frog 
complex across the Sierra Nevada. Remaining populations are much 
smaller relative to historical norms, and the density of populations 
per watershed has declined greatly; as a result, many watersheds 
currently support single metapopulations at low abundances.

Distinct Population Segment (DPS) Analysis

    Under the Act, we must consider for listing any species, 
subspecies, or, for vertebrates, any DPS of these taxa if there is 
sufficient information to indicate that such action may be warranted. 
To implement the measures prescribed by the Act, we, along with the 
National Marine Fisheries Service (National Oceanic and Atmospheric 
Administration--Fisheries), developed a joint policy that addresses the 
recognition of DPSes for potential listing actions (61 FR 4722). The 
policy allows for a more refined application of the Act that better 
reflects the biological needs of the taxon being considered and avoids 
the inclusion of entities that do not require the Act's protective 
measures.
    Under our DPS Policy, we use two elements to assess whether a 
population segment under consideration for listing may be recognized as 
a DPS: (1) The population segment's discreteness from the remainder of 
the species to which it belongs and (2) the significance of the 
population segment to the species to which it belongs. If we determine 
that a population segment being considered for listing is a DPS, then 
the level of threat to the population is evaluated based on the five 
listing factors established by the Act to determine if listing it as 
either endangered or threatened is warranted.
    The newly recognized species, the Sierra Nevada yellow-legged frog 
(Rana sierrae), is confirmed by genetic analysis as distinct from 
populations of mountain yellow-legged frogs (R. muscosa) extant in the 
southern Sierra Nevada (Vredenburg et al. 2007, p. 367). Other 
distinguishing features have already been mentioned (see ``Taxonomy'' 
above). We are not conducting a DPS assessment in this proposed rule 
for the Sierra Nevada yellow-legged frog because we have determined the 
species is warranted for listing across its entire range. It is our 
intent to discuss below only those topics directly relevant to the 
identification and determination of the northern DPS of the mountain 
yellow-legged frog.

Discreteness

    Under our DPS Policy, a population segment of a vertebrate species 
may be considered discrete if it satisfies either one of the following 
two conditions: (1) It is markedly separated from other populations of 
the same taxon as a consequence of physical, physiological, ecological, 
or behavioral factors (quantitative measures of genetic or 
morphological discontinuity may provide evidence of this separation); 
or (2) it is delimited by international governmental boundaries within 
which significant differences in control of exploitation, management of 
habitat, conservation, status, or regulatory mechanisms exist.
    The proposed DPS, the northern DPS of the mountain yellow-legged 
frog (northern DPS of Rana muscosa), satisfies the first condition for 
discreteness, the marked separation from other populations. The range 
of these mountain yellow-legged frogs is divided by a natural 
geographic barrier, the Tehachapi Mountains, which physically isolates 
populations in the southern Sierra Nevada from those in the mountains 
of southern California. The distance of the geographic separation is 
about 225 km (140 mi). Between the two population segments, there 
remains no connectivity through the presence of contiguous habitat 
sufficient for the migration, growth, rearing, or reproduction of 
dispersing frogs. Genetic discreteness is also well-supported in the 
scientific literature (see ``Taxonomy'' above). Therefore, we find 
these two population segments are discrete.

Significance

    Under our DPS Policy, once we have determined that a population 
segment is discrete, we consider its biological and ecological 
significance to the larger taxon to which it belongs. This 
consideration may include, but is not limited to: (1) Evidence of the 
persistence of the discrete population segment in an ecological setting 
that is unusual or unique for the taxon, (2) evidence that loss of the 
population segment would result in a significant gap in the range of 
the taxon, (3) evidence that the population segment represents the only 
surviving natural occurrence of a taxon that may be more abundant 
elsewhere as an introduced population outside its historical range, or 
(4) evidence that the discrete population segment differs markedly from 
other populations of the species in its genetic characteristics.
    We have found substantial evidence that three of four significance 
criteria are met by the northern DPS of the mountain yellow-legged frog 
in the Sierra Nevada. These include ecological uniqueness, its loss 
would result in a significant gap in the range of the taxon, and 
genetic uniqueness (reflecting significant reproductive isolation over 
time). There are no introduced populations of mountain yellow-legged 
frogs outside of the species' historical range.
    One of the most striking differences between northern DPS mountain 
yellow-legged frogs and southern California mountain yellow-legged 
frogs is the ecological settings they occupy. Zweifel (1955, pp. 237-
241) observed that the frogs in southern California are typically found 
in steep gradient streams in the chaparral belt, even though they may 
range into small meadow streams at higher elevations. In contrast, 
northern DPS frogs are most abundant in high-elevation lakes and slow-
moving portions of streams in the Sierra Nevada. The rugged canyons of 
the arid mountain ranges of southern California bear little resemblance 
to the alpine lakes and streams of the Sierra Nevada. The significantly 
different ecological settings between mountain yellow-legged frogs in 
southern California and those in the Sierra

[[Page 24480]]

Nevada distinguish these populations from each other.
    Furthermore, the northern DPS populations of the mountain yellow-
legged frog are significant because a catastrophic reduction in 
abundance of the species as a whole would occur if the populations 
constituting the northern range of the species were extirpated. The 
northern DPS mountain yellow-legged frogs comprise the main 
distribution of the species at the northern limits of the species' 
range. Loss of the northern DPS would be significant, as it would 
eliminate the species from a large portion of its range and would 
reduce the species to 9 small, isolated sites in southern California 
(USFWS, Jul 2012, pp. 11-12).
    Finally, the northern DPS populations of mountain yellow-legged 
frog are biologically and ecologically significant based on genetic 
criteria. Vredenburg et al. (2007, p. 361) identified that two of three 
distinct genetic clades (groups of distinct lineage) constitute the 
northern range of the mountain yellow-legged frog found in the Sierra 
Nevada, with the remaining single clade represented by the endangered 
southern California DPS of the mountain yellow-legged frog.
    Based on the differences between the ecological settings for the 
mountain yellow-legged frogs found in southern California (steep 
gradient streams) and the frogs found in the Sierra Nevada (high-
elevation lakes and slow-moving portions of streams), the importance of 
the northern population found in the Sierra Nevada to the entire range 
of this species, and the genetic composition of northern clades 
reflecting isolation over a substantial period of time (more than 1 
mybp), mountain yellow-legged frogs found in the Sierra Nevada 
mountains meet the significance criteria under our Policy Regarding the 
Recognition of Distinct Vertebrate Population Segments (61 FR 4722).

Summary of Factors Affecting the Species

    Section 4 of the Act (16 U.S.C. 1533), and its implementing 
regulations at 50 CFR part 424, set forth the procedures for adding 
species to the Federal Lists of Endangered and Threatened Wildlife and 
Plants. Under section 4(a)(1) of the Act, we may list a species based 
on any of the following five factors: (A) The present or threatened 
destruction, modification, or curtailment of its habitat or range; (B) 
overutilization for commercial, recreational, scientific, or 
educational purposes; (C) disease or predation; (D) the inadequacy of 
existing regulatory mechanisms; and (E) other natural or manmade 
factors affecting its continued existence. Listing actions may be 
warranted based on any of the above threat factors, singly or in 
combination. Each of these factors is discussed below. The following 
analysis is applicable to both the Sierra Nevada yellow-legged frog 
(Rana sierrae) and the Northern Distinct Population Segment of the 
mountain yellow-legged frog (Rana muscosa).

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

Habitat Destruction
    A number of hypotheses, including habitat loss, have been proposed 
for recent global amphibian declines (Bradford et al. 1993, p. 883; 
Corn 1994, p. 62; Alford and Richards 1999, p. 4). However, physical 
habitat destruction does not appear to be the primary factor associated 
with the decline of mountain yellow-legged frogs. Mountain yellow-
legged frogs occur at high elevations in the Sierra Nevada, which have 
not had the types or extent of large-scale habitat conversion and 
physical disturbance that have occurred at lower elevations (Knapp and 
Matthews 2000, p. 429). Thus, direct habitat destruction or 
modification associated with intensive human activities has not been 
implicated in the decline of this species (Davidson et al. 2002, p. 
1597).
    However, other human activities have played a role in the 
modification of mountain yellow-legged frog habitats and the 
curtailment of their range. The aggregation of these threats has 
degraded and fragmented habitats rangewide to a significant extent. 
These threats include: Recreational activities, fish introductions (see 
also Factor C below), dams and water diversions, livestock grazing, 
timber management, road construction and maintenance, and fire 
management activities. Such activities have degraded habitat in ways 
that have reduced their capacity to sustain viable populations and have 
fragmented and isolated mountain yellow-legged frog populations from 
each other.
Recreation
    Recreational activities take place throughout the Sierra Nevada and 
have significant negative impacts on many plant and animal species and 
their habitats (U.S. Department of Agriculture (USDA) 2001a, pp. 483-
493). High-elevation wilderness areas, where much of the increased 
recreational activity occurs, are naturally stressed ecosystems because 
of intense solar exposure; extremes in temperatures, precipitation 
levels, and wind; short growing seasons; and shallow, nutrient-poor 
soil. Such habitats are typically not resilient to disturbance 
(Schoenherr 1992, p. 167; Cole and Landres 1996, p. 170).
    Recreational foot traffic in riparian areas tramples the 
vegetation, compacts the soils, and can physically damage the 
streambanks (Kondolf et al. 1996, pp. 1018-1020). Hiking, horse, 
bicycle, or off-highway motor vehicle trails compact soils within 
riparian habitat (Kondolf et al. 1996, p. 1019), and can lower the 
water table and cause increased erosion. The recreational activity of 
anglers at high mountain lakes can be locally intense in the Sierra 
Nevada, with most regions reporting a level of use greater than the 
fragile lakeshore environments can withstand (Bahls 1992, p. 190). 
However, studies have not been conducted to determine the extent to 
which recreational activities are directly contributing to the decline 
of the mountain yellow-legged frog complex, and direct effects from 
recreation have not been implicated as a major cause of the decline of 
these species. Nevertheless, recreational activities are the fastest 
growing use of National Forests. As such, their impacts on the mountain 
yellow-legged frog complex are likely to continue and to increase (USDA 
2001b, p. 213). Currently, recreational activities are considered a 
threat of low significance to the species' habitat overall.
Habitat Modification Due to Introduction of Trout to Historically 
Fishless Areas
    One habitat feature that is documented to have a significant 
detrimental impact to mountain yellow-legged frog populations is the 
presence of trout from current and historical stocking for the 
maintenance of a sport fishery. To further angling success and 
opportunity, trout stocking programs in the Sierra Nevada started in 
the late 19th century (Bahls 1992, p. 185; Pister 2001, p. 280). This 
anthropogenic activity has community-level effects and constitutes the 
primary detrimental impact to mountain yellow-legged frog habitat and 
species viability.
    Prior to extensive trout planting programs, almost all streams and 
lakes in the Sierra Nevada at elevations above 1,800 m (6,000 ft) were 
fishless. Several native fish species occur naturally in aquatic 
habitats below this elevation in the Sierra Nevada (Knapp 1996, pp. 12-
14; Moyle et al. 1996, p. 354; Moyle 2002, p. 25). Natural barriers 
prevented fish from colonizing the higher elevation headwaters of the 
Sierra Nevada watershed (Moyle et al. 1996, p. 354). The upper reaches 
of the Kern

[[Page 24481]]

River, where native fish such as the Little Kern golden trout 
(Oncorhynchus mykiss whitei) and California golden trout (O. m. 
aguabonita) evolved, represent the only major exception to the 1,800-m 
(6,000-ft) elevation limit for fishes within the range of the mountain 
yellow-legged frog in the Sierra Nevada (Moyle 2002, p. 25). 
Additionally, prior to extensive planting, native Paiute cutthroat (O. 
clarki seleneris) and Lahontan cutthroat (O. c. henshawi) also occurred 
within the range of the mountain yellow-legged frog in the Sierra 
Nevada, but were limited in their distribution (Moyle 2002, pp. 288-
289).
    Some of the first practitioners of trout stocking in the Sierra 
Nevada were the Sierra Club, local sportsmen's clubs, private citizens, 
and the U.S. military (Knapp 1996, p. 8; Pister 2001, p. 280). As more 
hatcheries were built, and the management of the trout fishery became 
better organized, fish planting continued for the purpose of increased 
angler opportunities and success (Pister 2001, p. 281). After World War 
II, the method of transporting trout to high-elevation areas changed 
from packstock to aircraft, which allowed stocking in more remote lakes 
and in greater numbers. With the advent of aerial stocking, trout 
planting expanded to new areas, with higher efficiency.
    Brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), 
rainbow trout (Oncorhynchus mykiss), and other trout species 
assemblages have been planted in most streams and lakes of the Sierra 
Nevada (Knapp 1996, p. 8; Moyle 2002, p. 25). National Forests in the 
Sierra Nevada have a higher proportion of lakes with fish occupancy 
than do National Parks (Knapp 1996, p. 3). This is primarily because 
the National Park Service (NPS) adopted a policy that greatly reduced 
fish stocking within their jurisdictional boundaries in the late 1970s. 
Fish stocking was terminated altogether in Sierra Nevada National Parks 
in 1991 (Knapp 1996, p. 9). CDFG continues to stock trout in National 
Forest water bodies, but has recently reduced the number of stocked 
water bodies to reduce impacts to native amphibians (ICF Jones & Stokes 
2010, pp. ES-1-ES-16). Stocking decisions are based on criteria 
outlined in the Environmental Impact Report for the Hatchery and 
Stocking Program (ICF Jones & Stokes 2010, Appendix K).
    Fish stocking as a practice has been widespread throughout the 
range of both species of mountain yellow-legged frogs. Knapp and 
Matthews (2000, p. 428) indicated that 65 percent of the water bodies 
that were 1 ha (2.5 ac) or larger in National Forests they studied were 
stocked with fish on a regular basis. Over 90 percent of the total 
water body surface area in the John Muir Wilderness was occupied by 
nonnative trout (Knapp and Matthews 2000, p. 434).
    Another detrimental feature of fish stocking is that fish often 
persist in water bodies even after stocking ceases. Lakes larger than 1 
ha (2.5 ac) within Sierra Nevada National Parks were estimated to have 
from 35 to 50 percent nonnative fish occupancy, only a 29 to 44 percent 
decrease since fish stocking was terminated around 2 decades before the 
study (Knapp 1996, p. 1). Though data on fish occupancy in streams are 
lacking throughout the Sierra Nevada, Knapp (1996, p. 11) estimated 
that 60 percent of the streams in Yosemite National Park were still 
occupied by introduced trout.
    Trout both compete for limited resources and directly prey on 
mountain yellow-legged frog tadpoles and adults (see Factor C below). 
The presence of these fish decimates frog populations through 
competition and predation (see below). The impact of introduced trout 
was greatest in the past, as it eliminated frogs across a large expanse 
of their historical range. Fundamentally, this has removed deeper lakes 
from being mountain yellow-legged frog habitat at a landscape scale, 
because fish now populate these areas instead of frogs. Moreover, 
introduced trout continue to limit species viability because remaining 
populations are now isolated, and functional dispersal barriers make 
emigration difficult. Finally, the few frogs that do successfully 
emigrate will move to inhospitable, fish-occupied habitat where they 
are often outcompeted or preyed upon by trout. These factors make 
recolonization of extirpated sites unlikely.
    The body of scientific research has demonstrated that introduced 
trout have negatively impacted mountain yellow-legged frogs over much 
of the Sierra Nevada (Grinnell and Storer 1924, p. 664; Bradford 1989, 
pp. 775-778; Bradford et al. 1993, pp. 882-888; Knapp 1994, p. 3; Drost 
and Fellers 1996, p. 422; Knapp 1996, pp. 13-15; Knapp and Matthews 
2000, p. 428; Knapp et al. 2001, p. 401). Fish stocking programs have 
negative ecological implications because fish eat aquatic flora and 
fauna, including amphibians and invertebrates (Bahls 1992, p. 191; 
Erman 1996, p. 992; Matthews et al. 2001, pp. 1135-1136; Pilliod and 
Peterson 2001, p. 329; Schindler et al. 2001, p. 309; Moyle 2002, p. 
58; Epanchin et al. 2010, p. 2406). Finlay and Vredenburg (2007, p. 
2187) documented that the same benthic (bottom-dwelling) invertebrate 
resource base sustains the growth of both frogs and trout, suggesting 
that competition with trout for prey is an important factor that may 
contribute to the decline of the mountain yellow-legged frog.
    Knapp and Matthews (2000, p. 428) surveyed more than 1,700 water 
bodies, and concluded that a strong negative correlation exists between 
introduced trout and mountain yellow-legged frogs (Knapp and Matthews 
2000, p. 435). Consistent with this finding are the results of an 
analysis of the distribution of mountain yellow-legged frog tadpoles, 
which indicate that the presence and abundance of this life stage are 
reduced dramatically in fish-stocked lakes (Knapp et al. 2001, p. 408). 
Knapp (2005a, pp. 265-279) also compared the distribution of nonnative 
trout with the distributions of several amphibian and reptile species 
in 2,239 lakes and ponds in Yosemite National Park, and found that 
mountain yellow-legged frogs were five times less likely to be detected 
in waters where trout were present. Even though stocking within the 
National Park ceased in 1991, more than 50 percent of water bodies 
deeper than 4 m (13 ft) and 75 percent deeper than 16 m (52 ft) still 
contained trout populations in 2000-2002 (Knapp 2005a, p. 270). Both 
trout and mountain yellow-legged frogs utilize deeper water bodies. 
Based on the results from Knapp (2005a), the reduced detection of frogs 
in trout-occupied waters indicates that trout are excluding mountain 
yellow-legged frogs from some of the best aquatic habitat.
    Several aspects of the mountain yellow-legged frog's life history 
may exacerbate its vulnerability to extirpation by trout (Bradford 
1989, pp. 777-778; Bradford et al. 1993, pp. 886-888; Knapp 1996, p. 
14; Knapp and Matthews 2000, p. 435). Mountain yellow-legged frogs are 
aquatic and found mainly in lakes. This increases the probability that 
they will encounter introduced fishes whose distribution has been 
greatly expanded throughout the Sierra Nevada. The multiple-year 
tadpole stage of the mountain yellow-legged frog necessitates their use 
of permanent water bodies deep enough to not freeze solid during 
multiple winters (unless there is some other refuge from freezing and 
oxygen depletion, such as submerged crevices). Also, overwintering 
adults must avoid oxygen depletion when the water is covered by ice 
(Mullally and Cunningham 1956a, p. 194; Bradford 1983, p. 1179; Knapp 
and Matthews 2000, pp. 435-436). This functionally restricts tadpoles 
to the same water bodies most suitable for fishes (Knapp 1996, p. 14), 
and the consequences of predation and

[[Page 24482]]

competition thereby isolate mountain yellow-legged frogs to fishless, 
marginal habitats (Bradford et al. 1993, pp. 886-887; Knapp and 
Matthews 2000, p. 435).
    Mountain yellow-legged frogs and trout (native and nonnative) do 
co-occur at some sites, but these co-occurrences are probably mountain 
yellow-legged frog population sinks (areas with negative population 
growth rates in the absence of immigration) (Bradford et al. 1998, p. 
2489; Knapp and Matthews 2000, p. 436). Mountain yellow-legged frogs 
have also been extirpated at some fishless bodies of water (Bradford 
1991, p. 176; Drost and Fellers 1996, p. 422). A possible explanation 
is the isolation and fragmentation of remaining populations due to 
introduced fishes in the streams that once provided mountain yellow-
legged frogs with dispersal and recolonization routes; these remote 
populations are now non-functional as metapopulations (Bradford 1991, 
p. 176; Bradford et al. 1993, p. 887). Based on a survey of 95 basins 
within Sequoia and Kings Canyon National Parks, Bradford et al. (1993, 
pp. 885-886) estimated that the introduction of fishes into the study 
area resulted in an approximately 10-fold increase in habitat 
fragmentation between populations of mountain yellow-legged frogs. 
Knapp and Matthews (2000, p. 436) believe that this fragmentation has 
further isolated mountain yellow-legged frogs within the already 
marginal habitat left unused by fishes.
    Fragmentation of mountain yellow-legged frog habitat renders 
metapopulations more vulnerable to extirpation from random events (such 
as disease) (Wilcox 1980, pp. 114-115; Bradford et al. 1993, p. 887; 
Hanski and Simberloff 1997, p. 21; Knapp and Matthews 2000, p. 436). 
Isolated population locations may have higher extinction rates because 
trout prevent successful recolonization and dispersal to and from these 
sites (Bradford et al. 1993, p. 887; Blaustein et al. 1994a, p. 7; 
Knapp and Matthews 2000, p. 436). Amphibians may be unable to 
recolonize unoccupied sites following local extinctions because of 
physiological constraints, the tendency to move only short distances, 
and high site fidelity (Blaustein et al. 1994a, p. 8). Finally, frogs 
that do attempt recolonization may emigrate into fish-occupied habitat 
and perish, rendering sites with such metapopulation dynamics less able 
to sustain frog populations.
    Although fish stocking has been curtailed within many occupied 
basins, the impacts to frog populations persist due to the presence of 
self-sustaining fish populations in some of the best habitat that 
normally would have sustained mountain yellow-legged frogs. The 
fragmentation that persists across the range of these frog species 
renders them more vulnerable to other population stressors, and 
recovery is slow, if not impossible, without costly and physically 
difficult direct human intervention (such as physical and chemical 
trout removal). While most of the impacts occurred historically, the 
impact upon the biogeographic (population/metapopulation) integrity of 
the species will be long-lasting. Currently, habitat degradation and 
fragmentation by fish is considered a highly significant and prevalent 
threat to persistence and recovery of the species.
Dams and Water Diversions
    Numerous reservoirs have been constructed within the ranges of the 
mountain yellow-legged frog complex. These include Huntington Lake, 
Florence Lake, Lake Thomas A. Edison, Saddlebag Lake, Convict Lake, 
Cherry Lake, and other reservoirs associated with Hetch Hetchy, Upper 
and Lower Blue Lakes, Lake Aloha, Silver Lake, Hell Hole Reservoir, 
French Meadow Reservoir, Lake Spaulding, Alpine Lake, Loon Lake, Ice 
House Reservoir, and others. Dams and water diversions have altered 
aquatic habitats in the Sierra Nevada (Kondolf et al. 1996, p. 1014). 
The combination of these two features has reduced habitat suitability 
within the range of the species by creating migration barriers and 
altering local hydrology. This stressor causes considerable habitat 
fragmentation and direct habitat loss in those areas where water 
projects were constructed and are operating.
    The extent of the impact to mountain yellow-legged frog populations 
from habitat loss or modification due to these projects has not been 
quantified. However, the construction of dams has affected populations 
in the Sierra Nevada by altering the distribution of predators 
(reservoirs are often stocked with fish species that prey on mountain 
yellow-legged frogs) and affecting the effective dispersal of migrating 
frogs. Mountain yellow-legged frogs cannot live in or disperse 
effectively through the exposed shorelines created by reservoirs, nor 
can they successfully reproduce in these environments unless there are 
shallow side channels or disjunct pools free of predatory fishes 
(Jennings 1996, p. 939). In this fashion, reservoirs represent 
considerable dispersal barriers that further fragment the range of the 
mountain yellow-legged frogs.
    Dams alter the temperature and sediment load of the rivers they 
impound (Cole and Landres 1996, p. 175). Dams, water diversions, and 
their associated structures also alter the natural flow regime with 
unseasonal and fluctuating releases of water. These features may create 
habitat conditions unsuitable for native amphibians both upstream and 
downstream of dams, and they may act as barriers to movement by 
dispersing juvenile and migrating adult amphibians (Jennings 1996, p. 
939). Where dams act as barriers to mountain yellow-legged frog 
movement, they effectively prevent genetic exchange between populations 
and the recolonization of vacant sites.
    Water diversions may remove water from mountain yellow-legged frog 
habitat and adversely impact breeding success and adult survivorship. 
This results in physical reduction in habitat area and potentially 
lowers water levels to the extent that the entire water column freezes 
in the winter, thereby removing aquatic habitat altogether. Given the 
amount of water development within the historical ranges of mountain 
yellow-legged frogs, these factors likely have contributed to 
population declines, and ongoing management and habitat fragmentation 
will continue to pose a risk to the species. The magnitude of such 
impacts would increase if long droughts become more frequent in the 
future (see Factor E below) or if increasing diversions and storage 
facilities are constructed and implemented to meet growing needs for 
water and power. Currently, dams and water diversions are considered a 
moderate, prevalent threat to persistence and recovery of the species.
Livestock Use (Grazing)
    As discussed below, grazing reduces the suitability of habitat for 
mountain yellow-legged frogs by reducing its capability to sustain 
frogs and facilitate dispersal and migration, especially in stream 
areas. The impact of this stressor to mountain yellow-legged frogs is 
ongoing, but of relatively low importance as a limiting factor on 
extant populations. While this stressor may have played a greater role 
historically, leading in part to rangewide reduction of the species 
(see below), the geographic extent of livestock grazing activity within 
current mountain yellow-legged frog habitat does not encompass the 
entire range of the species.
    Grazing of livestock in riparian areas impacts vegetation in 
multiple ways, including soil compaction, which increases runoff and 
decreases water availability to plants; vegetation

[[Page 24483]]

removal, which promotes increased soil temperatures and evaporation 
rates at the soil surface; and direct physical damage to the vegetation 
(Kauffman and Krueger 1984, pp. 433-434; Cole and Landres 1996, pp. 
171-172; Knapp and Matthews 1996, pp. 816-817). Streamside vegetation 
protects and stabilizes streambanks by binding soils to resist erosion 
and trap sediment (Kauffman et al. 1983, p. 683; Chaney et al. 1990, p. 
2). Removal of vegetative cover within mountain yellow-legged frog 
habitat decreases available habitat, exposes frogs to predation (Knapp 
1993b, p.1), and increases the threat of desiccation (Jennings 1996, p. 
539).
    Aquatic habitat can also be degraded by grazing. Mass erosion from 
trampling and hoof slide causes streambank collapse and an accelerated 
rate of soil transport to streams (Meehan and Platts 1978, p. 274). 
Accelerated rates of erosion lead to elevated instream sediment loads 
and depositions, and changes in stream-channel morphology (Meehan and 
Platts 1978, pp. 275-276; Kauffman and Krueger 1984, p. 432). Livestock 
grazing may lead to diminished perennial streamflows (Armour et al. 
1994, p. 10). Livestock can increase nutrient-loading in water bodies 
due to urination and defecation in or near the water, and can cause 
elevated bacteria levels in areas where cattle are concentrated (Meehan 
and Platts 1978, p. 276; Stephenson and Street 1978, p. 156; Kauffman 
and Krueger 1984, p. 432). With increased grazing intensity, these 
adverse effects to the aquatic ecosystem increase proportionately 
(Meehan and Platts 1978, p. 275; Clary and Kinney 2000, p. 294).
    Observational data indicate that livestock negatively impact 
mountain yellow-legged frogs by altering riparian habitat and trampling 
individuals (Knapp 1993a, p. 1; 1993b, p. 1; 1994, p. 3; Jennings 1996, 
p. 938; Carlson 2002, pers. comm.; Knapp 2002a, p. 29). Livestock tend 
to concentrate along streams and wet areas where there is water and 
herbaceous vegetation; grazing impacts are therefore most pronounced in 
these habitats (Meehan and Platts 1978, p. 274; U.S. Government 
Accounting Office (GAO) 1988, pp. 10-11; Fleischner 1994, p. 635; Menke 
et al. 1996, p. 17). This concentration of livestock contributes to the 
destabilization of streambanks, causing undercuts and bank failures 
(Kauffman et al. 1983, p. 684; Marlow and Pogacnik 1985, pp. 282-283; 
Knapp and Matthews 1996, p. 816; Moyle 2002, p. 55). Grazing activity 
contributes to the downcutting of streambeds and lowers the water table 
(Meehan and Platts 1978, pp. 275-276; Kauffman et al. 1983, p. 685; 
Kauffman and Krueger 1984, p. 432; Bohn and Buckhouse 1985, p. 378; GAO 
1988, p. 11; Armour et al. 1994, pp. 9-11; Moyle 2002, p. 55).
    Livestock grazing may impact other wetland systems, including ponds 
that can serve as mountain yellow-legged frog habitat. Grazing modifies 
shoreline habitats by removing overhanging banks that provide shelter, 
and grazing contributes to the siltation of breeding ponds. Pond 
siltation has been demonstrated to reduce the depth of breeding ponds 
and to cover underwater crevices, thereby making the ponds less 
suitable, or unsuitable, as overwintering habitat for tadpoles and 
adult mountain yellow-legged frogs (Bradford 1983, p. 1179; Pope 1999a, 
pp. 43-44).
    In general, historical livestock grazing within the range of the 
mountain yellow-legged frog was at a high (although undocumented) level 
until the establishment of National Parks (beginning in 1890) and 
National Forests (beginning in 1905) (UC 1996a, p. 114; Menke et al. 
1996, p. 14). Within the newly established National Parks, grazing by 
cattle and sheep was replaced by that of packstock, such as horses and 
burros. Within the National Forests, the amount of livestock grazing 
was gradually reduced, and the types of animals shifted away from sheep 
and toward cattle and packstock.
    For mountain yellow-legged frogs, livestock grazing activity is 
likely a minor prevalent threat to currently extant populations, 
although in certain areas it may exacerbate habitat fragmentation 
already facilitated by the introduction of trout. There are currently 
161 active Rangeland Management Unit Allotments for grazing in USFS-
administered lands. Twenty-seven of these allotments have extant 
mountain yellow-legged frog populations (based on surveys performed 
after 2005). Currently, other allotments have been closed in certain 
sensitive areas, and standards have been implemented in remaining 
allotments to protect aquatic habitats. This threat is likely more one 
of historical significance. While it may be a factor in certain 
allotments with active grazing and extant populations, rangewide it is 
likely not a significant risk factor as many populations persist 
outside of actively grazed areas.
Packstock Use
    Packstock grazing is the only grazing currently permitted in the 
National Parks of the Sierra Nevada. Use of packstock in the Sierra 
Nevada has increased since World War II as a result of improved road 
access and increases in leisure time and disposable income (Menke et 
al. 1996, p. 14). In the Sixty-Lakes Basin of Kings Canyon National 
Park, packstock use is regulated in wet meadows to protect mountain 
yellow-legged frog breeding habitat in bogs and lake shores from 
trampling and associated degradation (Vredenburg 2002, p. 11; Werner 
2002, p. 2). Packstock use is also permitted in National Forests within 
the Sierra Nevada. However, there has been very little monitoring of 
the impacts of such activity in this region (Menke et al. 1996, p. 14), 
so its contribution to the decline of frog populations is impossible to 
quantify.
    Packstock use is likely a threat of low significance to mountain 
yellow-legged frogs at the current time, except on a limited, site-
specific basis. As California's human population increases, the impact 
of recreational activities, including packstock use and riding in the 
Sierra Nevada, are projected to increase (USDA 2001a, pp. 473-474). 
This activity may pose a risk to some remnant populations of frogs and, 
in certain circumstances, a hindrance to recovery of populations in 
heavily used lakes.
Roads and Timber Harvest
    Activities that alter the terrestrial environment (such as road 
construction and timber harvest) may impact amphibian populations in 
the Sierra Nevada (Jennings 1996, p. 938). These impacts are 
understandably in proportion to the magnitude of the alteration to the 
environment, and are more pronounced in areas with less stringent 
mitigation measures (that is, outside National Parks or wilderness 
areas). Road construction and timber harvest were likely of greater 
significance historically, and may have acted to reduce the species' 
range prior to the more recent detailed studies and systematic 
monitoring that have quantified and documented these losses.
    Timber harvest activities remove vegetation and cause ground 
disturbance and compaction, making the ground more susceptible to 
erosion (Helms and Tappeiner 1996, p. 446). This erosion increases 
siltation downstream that could potentially damage mountain yellow-
legged frog breeding habitat. Timber harvest may alter the annual 
hydrograph (timing and volume of surface flows), possibly lowering the 
water table, which could dewater riparian habitats used by mountain 
yellow-legged frogs. The majority of erosion caused by timber harvests 
is from logging roads (Helms and Tappeiner 1996, p. 447). Prior to the 
formation of National Parks in 1890 and

[[Page 24484]]

National Forests in 1905, timber harvest was widespread and 
unregulated, but primarily took place at elevations on the western 
slope of the Sierra Nevada below the range of the mountain yellow-
legged frog (University of California (UC) 1996b, pp. 24-25). Between 
1900 and 1950, the majority of timber harvest occurred in old-growth 
forests on private land (UC 1996b, p. 25). Between 1950 and the early 
1990s, there were increases in timber harvest on National Forests, and 
the majority of timber harvest-associated impacts on mountain yellow-
legged frogs may therefore have taken place during this period.
    Roads, including those associated with timber harvests, can 
contribute to habitat fragmentation and limit amphibian movement, thus 
having a negative effect on amphibian species richness (Lehtinen et al. 
1999, pp. 8-9; deMaynadier and Hunter 2000, p. 56). This effect could 
fragment mountain yellow-legged frog habitat if the road bisected 
habitat consisting of water bodies in close proximity.
    Currently, most of the mountain yellow-legged frog populations 
occur in National Parks or designated wilderness areas where timber is 
not harvested (Bradford et al. 1994a, p. 323; Drost and Fellers 1996, 
p. 421; Knapp and Matthews 2000, p. 430). Other mountain yellow-legged 
frog populations outside of these areas are located above the 
timberline, so timber harvest activity is not expected to affect the 
majority of extant mountain yellow-legged frog populations. There 
remain some mountain yellow-legged frog populations in areas where 
timber harvests occur or may occur in the future. Roads also exist 
within the range of the mountain yellow-legged frog, and more may be 
constructed. However, neither of these factors has been implicated as 
an important contributor to the decline of this species (Jennings 1996, 
pp. 921-941). It is likely a minor prevalent threat to mountain yellow-
legged frogs factored across the range of the species.
Fire and Fire Management Activities
    Mountain yellow-legged frogs are generally found at high elevations 
in wilderness areas and National Parks where vegetation is sparse and 
fire suppression activities are infrequently implemented. Where such 
activities may occur, potential impacts to the species resulting from 
fire management activities include: Habitat degradation through water 
drafting (taking of water) from occupied ponds and lakes, erosion and 
siltation of habitat from construction of fuel breaks, and 
contamination by fire retardants from chemical fire suppression.
    In some areas within the current range of the mountain yellow-
legged frog, long-term fire suppression has changed the forest 
structure and created conditions that increase fire severity and 
intensity (McKelvey et al. 1996, pp. 1934-1935). Excessive erosion and 
siltation of habitats following wildfire is a concern in shallow, lower 
elevation areas below forested stands. However, prescribed fire has 
been used by land managers to achieve various silvicultural objectives, 
including fuel load reduction. In some systems, fire is thought to be 
important in maintaining open aquatic and riparian habitats for 
amphibians (Russell ASLO 1999, p. 378), although severe and intense 
wildfires may reduce amphibian survival, as the moist and permeable 
skin of amphibians increases their susceptibility to heat and 
desiccation (Russell et al. 1999, p. 374). Amphibians may avoid direct 
mortality from fire by retreating to wet habitats or sheltering in 
subterranean burrows.
    It is not known what impacts fire and fire management activities 
have had on historical populations of mountain yellow-legged frogs. 
Neither the direct nor indirect effects of prescribed fire or wildfire 
on the mountain yellow-legged frog have been studied. Where fire has 
occurred in southern California, the character of the habitat has been 
significantly altered, leading to erosive scouring and flooding after 
surface vegetation is denuded (North 2012, pers. comm.). When a large 
fire does occur in occupied habitat, mountain yellow-legged frogs are 
susceptible to direct mortality (leading to significantly reduced 
population sizes) and indirect effects (habitat alteration and reduced 
breeding habitat). It is suspected that at least one population in the 
southern DPS was nearly extirpated by fire on the East Fork City Creek 
(San Bernadino Mountains) in 2003 (North 2012, pers. comm.). It is 
possible that fire has caused localized extirpations in the past. 
However, because the species generally occupies high-elevation habitat, 
fire is likely not a significant risk to this species over much of its 
current range.
    In summary, based on the best available scientific and commercial 
information, we consider the threats of modification and curtailment of 
the species' habitat and range to be significant, ongoing threats to 
the Sierra Nevada yellow-legged frog and northern DPS of the mountain 
yellow-legged frog. Threats from recreational foot traffic, camping, 
and timber harvest and related activities are not quantified, but they 
are not thought to be major drivers of frog population dynamics. 
Threats of low prevalence (important limiting factors in some areas, 
but not across a large part of the mountain yellow-legged frog 
complex's range) include grazing and fire management activities. Dams 
and water diversions likely present a moderate prevalent threat. 
Habitat fragmentation and degradation (loss of habitat through 
competitive exclusion) by stocked and persistent introduced trout 
across the majority of the species' range are a threat of high 
prevalence. This threat is a significant limiting factor to persistence 
and recovery of the species rangewide.

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

    There is no known commercial market for mountain yellow-legged 
frogs, nor are there documented recreational or educational uses for 
these species. Mountain yellow-legged frogs do not appear to be 
particularly popular among amphibian and reptile collectors; however, 
Federal listing could raise the value of the animals within wildlife 
trade markets and increase the threat of unauthorized collection above 
current levels (McCloud 2002, pers. comm.).
    Scientific collection for museum specimens has resulted in the 
death of numerous individuals (Zweifel 1955, p. 207; Jennings and Hayes 
1994, pp. 74-78). However, this occurred at times when the populations 
were at greater abundances and geographic distribution and in numbers 
that likely had little influence on the overall population from which 
individuals were sampled. Scientific research may cause stress to 
mountain yellow-legged frogs through disturbance, including disruption 
of the species' behavior, handling of individual frogs, and injuries 
associated with marking and tracking individuals. However, this is a 
relatively minor nuisance and not likely a negative impact to the 
survival and reproduction of individuals or the viability of the 
population.
    Based on the best available scientific and commercial information, 
we do not consider the overutilization for commercial, recreational, 
scientific, or educational purposes to be a threat to the mountain 
yellow-legged frog complex now or in the future.

Factor C. Disease or Predation

Predation
    Researchers have observed predation of mountain yellow-legged frogs 
by the mountain garter snake (Thamnophis

[[Page 24485]]

elegans elegans), Brewer's blackbird (Euphagus cyanocephalus), Clark's 
nutcracker (Nucifraga columbiana), coyote (Canis latrans), and black 
bear (Ursus americanus) (Mullally and Cunningham 1956a, p. 193; 
Bradford 1991, pp. 176-177; Jennings et al. 1992, p. 505; Feldman and 
Wilkinson 2000, p. 102; Vredenburg et al. 2005, p. 565). However, none 
of these has been implicated as a driver of population dynamics, so it 
is presumed that such predation occurrences are incidental and do not 
significantly impact frog populations (except perhaps in circumstances 
where so few individuals remain that the loss of low numbers of 
individuals would be of significant concern).
    The most prominent predator of mountain yellow-legged frogs is 
introduced trout, whose significance is well-established because it has 
been repeatedly observed that nonnative fishes and frogs rarely 
coexist, and it is known that introduced trout can and do prey on all 
frog life stages (Grinnell and Storer 1924, p. 664; Mullally and 
Cunningham 1956a, p. 190; Cory 1962a, p. 401; 1963, p. 172; Bradford 
1989, pp. 775-778; Bradford and Gordon 1992, p. 65; Bradford et al. 
1993, pp. 882-888; 1994a, p. 326; Drost and Fellers 1996, p. 422; 
Jennings 1996, p. 940; Knapp 1996, p. 14; Knapp and Matthews 2000, p. 
428; Knapp et al. 2001, p. 401; Vredenburg 2004, p. 7649). It is 
estimated that 63 percent of lakes larger than 1 ha (2.5 ac) in the 
Sierra Nevada contain one or more nonnative trout species, and greater 
than 60 percent of streams contain nonnative trout (Knapp, 1996, pp. 1-
44), in some areas comprising greater than 90 percent of total water 
body surface area (Knapp and Matthews 2000, p. 434).
    The multiple-year tadpole stage of the mountain yellow-legged frog 
requires submersion in the aquatic habitat year-round until 
metamorphosis. Moreover, all life stages are highly aquatic, increasing 
the frog's susceptibility to predation by trout (where they co-occur) 
throughout its lifespan. Overwinter mortality due to predation is 
especially significant because, when water bodies ice over in winter, 
tadpoles are forced from shallow margins of lakes and ponds into deeper 
unfrozen water where they are more vulnerable to predation; fish 
encounters in such areas increase, while refuge is less available.
    The predation of mountain yellow-legged frogs by fishes observed in 
the early 20th century by Grinnell and Storer and the documented 
declines of the 1970s (Bradford 1991, pp. 174-177; Bradford et al. 
1994a, pp. 323-327; Stebbins and Cohen 1995, pp. 226-227) were not the 
beginning of the mountain yellow-legged frog's decline, but rather the 
end of a long decline that started soon after fish introductions to the 
Sierra Nevada began in the mid-1800s (Knapp and Matthews 2000, p. 436). 
Metapopulation theory (Hanski 1997, pp. 85-86) predicts this type of 
time lag from habitat modification to population extinction (Knapp and 
Matthews 2000, p. 436). In 2004, Vredenburg (2004, p. 7647) concluded 
that introduced trout are effective predators on mountain yellow-legged 
frog tadpoles and suggested that the introduction of trout is the most 
likely reason for the decline of the mountain yellow-legged frog 
complex. This threat is a significant, prevalent risk to mountain 
yellow-legged frogs rangewide, and it will persist into the future.
Disease
    Over roughly the last 2 decades, pathogens have been associated 
with amphibian population declines, mass die-offs, and even extinctions 
worldwide (Bradford 1991, pp. 174-177; Blaustein et al. 1994b, pp. 251-
254; Alford and Richards 1999, pp. 506; Muths et al. 2003, p. 357; 
Weldon et al. 2004, p. 2100; Rachowicz et al. 2005, p. 1446; Fisher et 
al. 2009, p. 292). One pathogen strongly associated with dramatic 
declines on all five continents is the chytrid fungus, Batrachochytrium 
dendrobatidis (Bd) (Rachowicz et al. 2005, p. 1442). This chytrid 
fungus has now been reported in amphibian species worldwide (Fellers et 
al. 2001, p. 945; Rachowicz et al. 2005, p. 1442). Early doubt that 
this particular pathogen was responsible for worldwide die-offs has 
largely been overcome by the weight of evidence documenting the 
appearance, spread, and detrimental effects to affected populations 
(Vredenburg et al. 2010a, p. 9689). The correlation of notable 
amphibian declines with reports of outbreaks of fatal chytridiomycosis 
(the disease caused by Bd) in montane areas has led to a general 
association between high altitude, cooler climates, and population 
extirpations associated with Bd (Fisher et al. 2009, p. 298).
    Bd affects the mouth parts and epidermal (skin) tissue of tadpoles 
and metamorphosed frogs (Fellers et al. 2001, pp. 950-951). The fungus 
can reproduce asexually, and can generally withstand adverse conditions 
such as freezing or drought (Briggs et al. 2002, p. 38). It also may 
reproduce sexually, leading to thick-walled sporangia that would be 
capable of long-term survival (for distant transport and persistence in 
sites even after all susceptible host animal populations are 
extirpated) (Morgan et al. 2007, p. 13849). Adult frogs can acquire 
this fungus from tadpoles, and it can also be transmitted between 
tadpoles (Rachowicz and Vredenburg 2004, p. 80).
    In California, chytridiomycosis has been detected in many amphibian 
species, including mountain yellow-legged frogs (Briggs et al. 2002, p. 
38; Knapp 2002b, p. 1). The earliest documented case in the mountain 
yellow-legged frog complex was in 1998, at Yosemite National Park 
(Fellers et al. 2001, p. 945). It is unclear how Bd was originally 
transmitted to the frogs (Briggs et al. 2002, p. 39). Visual 
examination of 43 tadpole specimens collected between 1955 and 1976 
revealed no evidence of Bd infection; however 14 of 36 specimens 
preserved between 1993 and 1999 did have abnormalities attributable to 
Bd (Fellers et al. 2001, p. 947). Since at least 1976, Bd has affected 
adult Yosemite toads (Green and Kagarise Sherman 2001, p. 92), whose 
range overlaps with the mountain yellow-legged frogs. Therefore, it is 
possible that this pathogen has affected all three amphibian species 
covered in this proposed rule since at least the mid-1970s. Mountain 
yellow-legged frogs may be especially vulnerable to Bd infections 
because all life stages share the same aquatic habitat nearly year 
round, facilitating the transmission of this fungus among individuals 
at different life stages (Fellers et al. 2001, p. 951).
    During the epidemic phase of chytrid infection into unexposed 
populations, rapid die-offs are observed within short order for adult 
and subadult lifestages (Vredenburg et al. 2010a, p. 9691), while 
tadpoles are less affected at first (Vredenburg et al. 2010a, p. 9689). 
In mountain yellow-legged frogs, Bd causes overwinter mortality and 
mortality during metamorphosis (Briggs et al. 2002, p. 39; Rachowicz 
2005, pp. 2-3); metamorphs are the most sensitive life stage to Bd 
infection (Kilpatrick et al. 2009, p. 113; Vredenburg et al. 2010b, p. 
3). Field and laboratory experiments indicate that Bd infection is 
generally lethal to mountain yellow-legged frogs, and is likely 
responsible for recent declines (Knapp 2005b; Rachowicz 2005, pers. 
comm.). Rachowicz et al. (2006, p. 1671) monitored several infected and 
uninfected populations in Sequoia and Kings Canyon National Parks over 
multiple years, documenting dramatic declines and extirpations in only 
the infected populations. Rapid die-offs of mountain yellow-legged 
frogs from chytridiomycosis have been observed in more than 50 water 
bodies in the southern Sierra Nevada (Briggs et al.

[[Page 24486]]

2005, p. 3151). Studies of the microscopic structure of tissue and 
other evidence suggests Bd caused many of the recent extinctions in the 
Sierra National Forest's John Muir Wilderness Area and in Kings Canyon 
National Park, where 41 percent of the populations went extinct between 
1995 and 2002 (Knapp 2002a, p. 10).
    In several areas where detailed studies of the effects of Bd on the 
mountain yellow-legged frog are ongoing, substantial declines have been 
observed following the course of the disease infection and spread. 
Survey results from 2000 in Yosemite and Sequoia-Kings Canyon National 
Parks indicate that 24 percent of the mountain yellow-legged frog 
populations showed signs of Bd infection (Briggs et al. 2002, p. 40). 
In both 2003 and 2004, 19 percent of assayed populations in Sequoia and 
Kings Canyon National Parks were infected with Bd (Rachowicz 2005, pp. 
2-3). By 2005, 91 percent of assayed populations in Yosemite National 
Park showed evidence of Bd infection (Knapp 2005b, pp. 1-2). Currently, 
it is believed that all populations in Yosemite Park are infected with 
Bd (Briggs et al. 2010, p. 9695).
    The effects of Bd on host populations of the mountain yellow-legged 
frog are variable, ranging from extinction, to persistence with a high 
level of infection, to persistence with a low level of infection 
(Briggs et al. 2002, pp. 40-41). In populations where Bd infection 
first occurs, the most common outcome is epidemic spread of the disease 
and population extirpation (Briggs et al. 2010, p. 9699). Die-offs are 
characterized by rapid onset of high level Bd infections, followed by 
death due to chytridiomycosis. Adults in persistent populations 
frequently recover and are subsequently re-infected by Bd at low levels 
(Briggs et al. 2010, pp. 9695-9696). However, it is apparent that even 
at sites exhibiting population persistence with Bd, high mortality of 
metamorphosing frogs persists, and this phenomenon may explain the 
lower abundances observed in such populations (Briggs et al. 2010, p. 
9699).
    Vredenburg et al. (2010a, pp. 2-4) studied frog populations before, 
during, and after the infection and spread of Bd in three study basins 
constituting 13, 33, and 42 frog populations, then comprising the most 
intact metapopulations remaining for these species throughout their 
range. The spread of Bd averaged 688 m/year (yr) (2,257 ft/yr), 
reaching all areas of the smaller basin in 1 year, and taking 3 to 5 
years to completely infect the larger basins, progressing like a wave 
across the landscape. The researchers documented die-offs following the 
spread of Bd, with decreased population growth rates evident within the 
first year of infection. Basinwide, metapopulations crashed from 1,680 
to 22 individuals (northern DPS of the mountain yellow-legged frog) in 
Milestone Basin, with 9 of 13 populations extirpated; from 2,193 to 47 
individuals (northern DPS of the mountain yellow-legged frog) in Sixty 
Lakes Basin, with 27 of 33 populations extirpated; and from 5,588 to 
436 individuals (Sierra Nevada yellow-legged frog) in Barrett Lakes 
Basin, with 33 of 42 populations extirpated. It is clear from the 
evidence that Bd can and does decimate newly infected frog populations. 
Moreover, this rangewide population threat is acting upon a landscape 
already impacted by habitat modification and degradation by introduced 
fishes (see Factor A discussion, above). As a result, remnant 
populations in fishless lakes are now impacted by Bd.
    Vredenburg et al. (2010a, p. 3) projected that at current 
extinction rates, and given the disease dynamics of Bd (infected 
tadpoles succumb to chytridiomycosis at metamorphosis), most if not all 
extant populations within the recently infected basins they studied 
will go extinct within the next 3 years. Available data (CDFG, unpubl. 
data; Knapp 2005b; Rachowicz 2005, pers. comm.; Rachowicz et al. 2006, 
p. 1671) indicate that Bd is now widespread throughout the Sierra 
Nevada, and, although it has not infected all populations at this time, 
it is effectively a serious and substantial threat rangewide to the 
mountain yellow-legged frog complex.
    Other diseases have also been reported as adversely affecting 
amphibian species, and these may be present within the range of the 
mountain yellow-legged frog. Bradford (1991, p. 174-177) reported an 
outbreak of red-leg disease in Kings Canyon National Park, and 
suggested this was a result of overcrowding within a mountain yellow-
legged frog population. Red-leg disease is caused by the bacterial 
pathogen Aeromonas hydrophila, along with other pathogens. Though red-
leg disease is opportunistic and successfully attacks immune-suppressed 
individuals, this pathogen appears to be highly contagious, affecting 
the epidermis and digestive tract of otherwise healthy amphibians 
(Shotts 1984, pp. 51-52; Carey 1993, p. 358; Carey and Bryant 1995, pp. 
14-15). Although it has been observed in at least one instance 
correlated to frog population decline, red-leg disease is likely not a 
significant contributor to observed frog population declines rangewide, 
based on the available literature.
    Saprolegnia is a globally distributed fungus that commonly attacks 
all life stages of fishes (especially hatchery-reared fishes), and has 
recently been documented to attack and kill egg masses of western toads 
(Bufo boreas) (Blaustein et al. 1994b, p. 252). This pathogen may be 
introduced through fish stocking, or it may already be established in 
the aquatic ecosystem. Fishes and migrating or dispersing amphibians 
may be a vector for this fungus (Blaustein et al. 1994b, p. 253; 
Kiesecker et al. 2001, p. 1068). Saprolegnia has been reported in the 
southern DPS of the mountain yellow-legged frog (North 2012, pers. 
comm.); however, its prevalence within the Sierran range of the 
mountain yellow-legged frog complex and associated influence on 
population dynamics (if any) are unknown.
    Other pathogens of concern for amphibian species include 
ranaviruses (Family Iridoviridae). Mao et al. (1999, pp. 49-50) 
isolated identical iridoviruses from co-occurring populations of the 
threespine stickleback (Gasterosteus aculeatus) and the red-legged frog 
(Rana aurora), indicating that infection by a given virus is not 
limited to a single species, and that iridoviruses can infect animals 
of different taxonomic classes. This suggests that virus-hosting trout 
introduced into mountain yellow-legged frog habitat may be a vector for 
amphibian viruses. Recreationists also may contribute to the spread of 
pathogens between water bodies and populations via clothing and fishing 
equipment. However, definitive mechanisms for disease transmission to 
the mountain yellow-legged frog remain unknown. No viruses were 
detected in the mountain yellow-legged frogs that Fellers et al. (2001, 
p. 950) analyzed for Bd. In Kings Canyon National Park, Knapp (2002a, 
p. 20) found mountain yellow-legged frogs showing symptoms 
preliminarily attributed to a ranavirus. To date, ranaviruses remain a 
concern for the mountain yellow-legged frog complex, but there is 
insufficient evidence to indicate they are negatively affecting 
populations.
    It is unknown whether amphibian pathogens in the high Sierra Nevada 
have always coexisted with amphibian populations or if the presence of 
such pathogens is a recent phenomenon. However, it has been suggested 
that the susceptibility of amphibians to pathogens may have recently 
increased in response to anthropogenic

[[Page 24487]]

environmental disruption (Carey 1993, pp. 355-360; Blaustein et al. 
1994b, p. 253; Carey et al. 1999, p. 7). This hypothesis suggests that 
environmental changes may be indirectly responsible for certain 
amphibian die-offs due to immune system suppression of tadpoles or 
post-metamorphic amphibians (Carey 1993, p. 358; Blaustein et al. 
1994b, p. 253; Carey et al. 1999, p. 7-8). Pathogens such as Aeromonas 
hydrophila, which are present in fresh water and in healthy organisms, 
may become more of a threat, potentially causing localized amphibian 
population die-offs when the immune systems of individuals within the 
host population are suppressed (Carey 1993, p. 358; Carey and Bryant 
1995, p. 14).
    The contribution of Bd as an environmental stressor and limiting 
factor on mountain yellow-legged frog population dynamics is currently 
extremely high, and it poses a significant future threat to remnant 
uninfected populations in the southern Sierra Nevada. Its effects are 
most dramatic following the epidemic stage as it spreads across newly 
infected habitats; massive die-off events follow the spread of the 
fungus, and it is likely that survival through metamorphosis is 
substantially reduced even years after the initial epidemic (Rachowicz 
et al. 2006, pp. 1679-1680). The relative impact from other diseases 
and the interaction of other stressors and disease on the immune 
systems of mountain yellow-legged frogs remains poorly documented to 
date.
    In summary, based on the best available scientific and commercial 
information, we consider the threats of predation and disease to be 
significant, ongoing threats to the Sierra Nevada yellow-legged frog 
and the northern DPS of the mountain yellow-legged frog. These threats 
include amphibian pathogens (most specifically, the chytrid fungus) and 
predation by introduced fishes, two primary driving forces leading to 
population declines in the mountain yellow-legged frog complex. These 
are highly prevalent threats, and they are predominant limiting factors 
hindering population viability and precluding recovery across the 
ranges of the mountain yellow-legged frog complex.

Factor D. The Inadequacy of Existing Regulatory Mechanisms

    In determining whether the inadequacy of regulatory mechanisms 
constitutes a threat to the mountain yellow-legged frog complex, we 
analyzed the existing Federal and State laws and regulations that may 
address the threats to these species or contain relevant protective 
measures. Regulatory mechanisms are typically nondiscretionary and 
enforceable, and may preclude the need for listing if such mechanisms 
are judged to adequately address the threat(s) to the species such that 
listing is not warranted. Conversely, threats on the landscape are not 
addressed where existing regulatory mechanisms are not adequate (or 
when existing mechanisms are not adequately implemented or enforced).
Federal
Wilderness Act
    The Wilderness Act of 1964 (16 U.S.C. 1131 et seq.) established a 
National Wilderness Preservation System made up of federally owned 
areas designated by Congress as ``wilderness'' for the purpose of 
preserving and protecting designated areas in their natural condition. 
Within these areas, the Wilderness Act states, with limited exception 
to administer the area as wilderness, the following: (1) New or 
temporary roads cannot be built; (2) there can be no use of motor 
vehicles, motorized equipment, or motorboats; (3) there can be no 
landing of aircrafts; (4) there can be no form of mechanical transport; 
and (5) no structure or installation may be built. A large number of 
mountain yellow-legged frog locations occur within wilderness areas 
managed by the USFS and NPS and, therefore, are afforded protection 
from direct loss or degradation of habitat by some human activities 
(such as, development, commercial timber harvest, road construction, 
some fire management actions). Livestock grazing and fish stocking are 
both permitted within designated wilderness areas.
National Forest Management Act of 1976
    Under the National Forest Management Act of 1976, as amended (NFMA) 
(16 U.S.C. 1600 et seq.), the USFS is tasked to manage National Forest 
lands based on multiple-use, sustained-yield principles, and implement 
land and resource management plans (LRMP) on each National Forest to 
provide for a diversity of plant and animal communities. The purpose of 
an LRMP is to guide and set standards for all natural resource 
management activities for the life of the plan (10 to 15 years). NFMA 
requires the USFS to incorporate standards and guidelines into LRMPs. 
The 1982 planning regulations for implementing NFMA (47 FR 43026; 
September 30, 1982), under which all existing forest plans in the 
Sierra Nevada were prepared until recently, guided management of 
National Forests and required that fish and wildlife habitat on 
National Forest system lands be managed to maintain viable populations 
of existing native and desired nonnative vertebrate species in the 
planning area. A viable population is defined as a population of a 
species that continues to persist over the long term with sufficient 
distribution to be resilient and adaptable to stressors and likely 
future environments. In order to insure that viable populations will be 
maintained, habitat must be provided to support, at least, a minimum 
number of reproductive individuals and that habitat must be well 
distributed so that those individuals can interact with others in the 
planning area.
    On April 9, 2012, the USFS published a final rule (77 FR 21162) 
amending 36 CFR 219 to adopt new National Forest System land management 
regulations to guide the development, amendment, and revision of LRMPs 
for all Forest System lands. These revised regulations, which became 
effective on May 9, 2012, replace the 1982 planning rule. The 2012 
planning rule requires that the USFS maintain viable populations of 
species of conservation concern at the discretion of regional 
foresters. This rule could thereby result in removal of the limited 
protections that are currently in place for mountain yellow-legged 
frogs under the Sierra Nevada Forest Plan Amendment (SNFPA), as 
described below.
Sierra Nevada Forest Plan Amendment
    In 2001, a record of decision was signed by the USFS for the Sierra 
Nevada Forest Plan Amendment (SNFPA), based on the final environmental 
impact statement for the SNFPA effort and prepared under the 1982 NFMA 
planning regulations. The Record of Decision amends the USFS Pacific 
Southwest Regional Guide, the Intermountain Regional Guide, and the 
LRMPs for National Forests in the Sierra Nevada and Modoc Plateau. This 
document affects land management on all National Forests throughout the 
range of the mountain yellow-legged frog complex. The SNFPA addresses 
and gives management direction on issues pertaining to old forest 
ecosystems; aquatic, riparian, and meadow ecosystems; fire and fuels; 
noxious weeds; and lower west-side hardwood ecosystems of the Sierra 
Nevada. In January 2004, the USFS amended the SNFPA, based on the final 
supplemental environmental impact statement, following a review of fire 
and fuels treatments, compatibility with the National Fire Plan, 
compatibility with the Herger-Feinstein Quincy Library

[[Page 24488]]

Group Forest Recovery Pilot Project, and effects of the SNFPA on 
grazing, recreation, and local communities (USDA 2004, pp. 26-30).
    Relevant to the mountain yellow-legged frog complex, the Record of 
Decision for SNFPA aims to protect and restore aquatic, riparian, and 
meadow ecosystems, and to provide for the viability of associated 
native species through implementation of an aquatic management 
strategy. The aquatic management strategy is a general framework with 
broad policy direction. Implementation of this strategy is intended to 
take place at the landscape and project levels. There are nine goals 
associated with the aquatic management strategy:
    (1) The maintenance and restoration of water quality to comply with 
the Clean Water Act (CWA) and the Safe Drinking Water Act;
    (2) The maintenance and restoration of habitat to support viable 
populations of native and desired nonnative riparian-dependent species, 
and to reduce negative impacts of nonnative species on native 
populations;
    (3) The maintenance and restoration of species diversity in 
riparian areas, wetlands, and meadows to provide desired habitats and 
ecological functions;
    (4) The maintenance and restoration of the distribution and 
function of biotic communities and biological diversity in special 
aquatic habitats (such as springs, seeps, vernal pools, fens, bogs, and 
marshes);
    (5) The maintenance and restoration of spatial and temporal 
connectivity for aquatic and riparian species within and between 
watersheds to provide physically, chemically, and biologically 
unobstructed movement for their survival, migration, and reproduction;
    (6) The maintenance and restoration of hydrologic connectivity 
between floodplains, channels, and water tables to distribute flood 
flows and to sustain diverse habitats;
    (7) The maintenance and restoration of watershed conditions as 
measured by favorable infiltration characteristics of soils and diverse 
vegetation cover to absorb and filter precipitation, and to sustain 
favorable conditions of streamflows;
    (8) The maintenance and restoration of instream flows sufficient to 
sustain desired conditions of riparian, aquatic, wetland, and meadow 
habitats, and to keep sediment regimes within the natural range of 
variability; and
    (9) The maintenance and restoration of the physical structure and 
condition of streambanks and shorelines to minimize erosion and sustain 
desired habitat diversity.
    If these goals of the aquatic management strategy are pursued and 
met, threats to the mountain yellow-legged frog complex resulting from 
habitat alterations could be reduced. However, the aquatic management 
strategy is a generalized approach that does not contain specific 
implementation timeframes or objectives, and it does not provide direct 
protections for the mountain yellow-legged frog. Additionally, as 
described above, the April 9, 2012, final rule (77 FR 21162) that 
amended 36 CFR 219 to adopt new National Forest System land management 
planning regulations could result in removal of the limited protections 
that are currently in place for mountain yellow-legged frogs under the 
SNFPA.
Federal Power Act
    The Federal Power Act of 1920, as amended (FPA) (16 U.S.C. 791 et 
seq.) was enacted to regulate non-federal hydroelectric projects to 
support the development of rivers for energy generation and other 
beneficial uses. The FPA provides for cooperation between the Federal 
Energy Regulatory Commission (Commission) and other Federal agencies in 
licensing and relicensing power projects. The FPA mandates that each 
license includes conditions to protect, mitigate, and enhance fish and 
wildlife and their habitat affected by the project. However, the FPA 
also requires that the Commission give equal consideration to competing 
priorities, such as power and development, energy conservation, 
protection of recreational opportunities, and preservation of other 
aspects of environmental quality. Further, the FPA does not mandate 
protections of habitat or enhancements for fish and wildlife species, 
but provides a mechanism for resource agency recommendations that are 
incorporated into a license at the discretion of the Commission. 
Additionally, the FPA provides for the issuance of a license for the 
duration of up to 50 years, and the FPA contains no provision for 
modification of the project for the benefit of species, such as 
mountain yellow-legged frogs, before a current license expires.
    Numerous mountain yellow-legged frog populations occur within 
developed and managed aquatic systems (such as reservoirs and water 
diversions) operated for the purpose of power generation and regulated 
by the FPA.
State
California Endangered Species Act
    The California Endangered Species Act (CESA) (California Fish and 
Game Code, section 2080 et seq.) prohibits the unauthorized take of 
State-listed endangered or threatened species. CESA requires State 
agencies to consult with CDFG on activities that may affect a State-
listed species, and mitigate for any adverse impacts to the species or 
its habitat. Pursuant to CESA, it is unlawful to import or export, 
take, possess, purchase, or sell any species or part or product of any 
species listed as endangered or threatened. The State may authorize 
permits for scientific, educational, or management purposes, and allow 
take that is incidental to otherwise lawful activities.
    Recently, the California Fish and Game Commission approved the 
listing of the Sierra Nevada yellow-legged frog as a threatened species 
and the mountain yellow-legged frog (Statewide) as an endangered 
species under CESA (CDFG 2012, pp. 1-10). However, CDFG has not yet 
officially listed these species under CESA, and therefore both species 
remain candidate species under State law.
    As a candidate species under CESA, the mountain yellow-legged frog 
complex receives the same protections as a listed species, with 
specified exceptions. However, CESA is not expected to provide adequate 
protection for the mountain yellow-legged frog complex given that the 
CDFG has currently approved take authorization for the Statewide 
stocking program under CESA for fish hatchery and stocking activities 
consistent with the joint Environmental Impact Statement/Environmental 
Impact Report (ICF Jones & Stokes 2010, App. K), wildland fire response 
and related vegetation management, water storage and conveyance 
activities, and forest practices and timber harvest (CDFG 2011a, pp. 2-
3).
    In 2001, CDFG revised fish stocking practices and implemented an 
informal policy on fish stocking in the range of the Sierra Nevada 
yellow-legged frog and northern DPS of the mountain yellow-legged frog. 
This policy directs that: (1) Fish will not be stocked in lakes with 
known populations of mountain yellow-legged frogs, nor in lakes that 
have not yet been surveyed for mountain yellow-legged frog presence; 
(2) waters will be stocked only with a fisheries management 
justification; and (3) the number of stocked lakes will be reduced over 
time. In 2001, the number of lakes stocked with fish within the range 
of the mountain yellow-legged

[[Page 24489]]

frog in the Sierra Nevada was reduced by 75 percent (Milliron 2002, pp. 
6-7; Pert et al. 2002, pers. comm.). Water bodies within the same basin 
and 2 km (1.25 mi) from a known mountain yellow-legged frog population 
will not be stocked with fish unless stocking is justified through a 
management plan that considers all the aquatic resources in the basin, 
or unless there is heavy angler use and no opportunity to improve the 
mountain yellow-legged frog habitat (Milliron 2002a, p. 5). The 
Hatchery and Stocking Program Environmental Impact Report/Environmental 
Impact Statement, finalized in 2010 (ICF Jones & Stokes 2010, Appendix 
K), outlines a decision approach to mitigate fish stocking effects on 
Sierra amphibians that prohibits fish stocking in lakes with confirmed 
presence of frogs using recognized survey protocols.
    CDFG is in the process of developing management plans for basins 
within the range of the Sierra Nevada yellow-legged frog and the 
northern DPS of mountain yellow-legged frog (CDFG 2001, p. 1; Lockhart 
2011, pers. comm.). The objectives of the basin plans specific to the 
mountain yellow-legged frog include management in a manner that 
maintains or restores native biodiversity and habitat quality, supports 
viable populations of native species, and provides for recreational 
opportunities that consider historical use patterns (CDFG 2001, p. 3). 
Under this approach, some lakes are managed primarily for the mountain 
yellow-legged frogs and other amphibian resources, with few or no 
angling opportunities, while lakes with high demand for recreational 
angling are managed primarily for angling purposes (CDFG 2001, p. 3).
    Existing Federal and State laws and regulatory mechanisms currently 
offer some level of protection for the mountain yellow-legged frog 
complex.

Factor E. Other Natural or Manmade Factors Affecting Its Continued 
Existence

    The mountain yellow-legged frog is sensitive to environmental 
change or degradation because it has an aquatic and terrestrial life 
history and highly permeable skin that increases exposure of 
individuals to substances in the water, air, and terrestrial substrates 
(Blaustein and Wake 1990, p. 203; Bradford and Gordon 1992. p. 9; 
Blaustein and Wake 1995, p. 52; Stebbins and Cohen 1995, pp. 227-228). 
Several natural or anthropogenically influenced factors, including 
contaminants, acid precipitation, ambient ultraviolet radiation, and 
climate change, have been implicated as contributing to amphibian 
declines (Corn 1994, pp. 62-63; Alford and Richards 1999, pp. 2-7). 
These factors have been studied to varying degrees specific to the 
mountain yellow-legged frog and are discussed below. There are also 
documented incidences of direct mortality of, or the potential for 
direct disturbance to, individuals from some activities already 
discussed; in severe instances, these actions may have population-level 
consequences.
Contaminants
    Environmental contaminants have been suggested, and in some cases 
documented, to negatively affect amphibians by causing direct mortality 
(Hall and Henry 1992, pp. 66-67; Berrill et al. 1994, p. 663; 1995, pp. 
1016-1018; Carey and Bryant 1995, p. 16; Relyea and Mills 2001, p. 
2493); immune system suppression, which makes amphibians more 
vulnerable to disease (Carey 1993, pp. 358-360; Carey and Bryant 1995, 
p. 15; Carey et al. 1999, p. 9; Daszak et al. 1999, p. 741; Taylor et 
al. 1999, p. 540); disruption of breeding behavior and physiology 
(Berrill et al. 1994, p. 663; Carey and Bryant 1995, p. 16; Hayes et 
al. 2002, p. 5479); disruption of growth or development (Hall and Henry 
1992, p. 66; Berrill et al. 1993, p. 537; 1994, p. 663; Berrill et al. 
1995, pp. 1016-1018; Carey and Bryant 1995, p. 8; Berrill et al. 1998, 
pp. 1741-1744; Sparling et al. 2001, p. 1595; Brunelli et al. 2009, p. 
135); and disruption of predator avoidance behavior (Hall and Henry 
1992, p. 66; Berrill et al. 1993, p. 537; 1994, p. 663; Berrill et al. 
1995, p. 1017; Carey and Bryant 1995, pp. 8-9; Berrill et al. 1998, p. 
1744; Relyea and Mills 2001, p. 2493; Sparling et al. 2001, p. 1595).
    Wind-borne pesticides that are deposited in the Sierra Nevada from 
upwind agricultural sources have been suggested as a cause of sublethal 
effects to amphibians (Cory et al. 1971, p. 3; Davidson et al. 2001, 
pp. 474-475; Sparling et al. 2001, p. 1591; Davidson 2004, p. 1892; 
Fellers et al. 2004, p. 2176). In 1998, more than 97 million kilograms 
(215 million pounds) of pesticides were reportedly used in California 
(California Department of Pesticide Regulation (CDPR) 1998, p. ix). 
Originating from the agriculture in California's Central Valley, and 
mainly from the San Joaquin Valley, where upwind agricultural activity 
is greatest, pesticides are passively transported eastward to the high 
Sierra Nevada where they have been detected in precipitation (rain and 
snow), air, dry deposition, surface water, plants, fish, and amphibians 
(including Pacific tree frogs (Pseudacris regilla) and mountain yellow-
legged frogs) (Cory et al. 1970, p. 204; Zabik and Seiber 1993, p. 80; 
Aston and Seiber 1997, p. 1488; Datta et al. 1998, p. 829; McConnell et 
al. 1998, pp. 1910-1911; LeNoir et al. 1999, p. 2721; Sparling et al. 
2001, p. 1591; Angermann et al. 2002, p. 2213; Fellers et al. 2004, pp. 
2173-2174).
    Spatial analysis of mountain yellow-legged frog population trends 
in the Sierra Nevada showed a strong positive association between 
population decline and areas with greater amounts of upwind agriculture 
(Davidson et al. 2002, pp. 1597-1598). Analysis of upwind pesticide use 
determined that pesticides may play a role in the decline of the 
mountain yellow-legged frog in pristine regions of the Sierra Nevada 
(Davidson and Knapp 2007, pp. 593-594). Although pesticide detections 
decrease with altitudinal gain, they have been detected at elevations 
in excess of 3,200 m (10,500 ft) (Zabik and Seiber 1993, p. 88; 
McConnell et al. 1998, p. 1908; LeNoir et al. 1999, p. 2721; Angermann 
et al. 2002, pp. 2210-2211).
    Snow core samples from the Sierra Nevada contain a variety of 
contaminants from industrial and automotive sources, including excess 
hydrogen ions that are indicative of acidic precipitation, nitrogen and 
sulfur compounds (ammonium, nitrate, sulfite, and sulfate), and heavy 
metals (lead, iron, manganese, copper, and cadmium) (Laird et al. 1986, 
p. 275).
    The pattern of recent frog extirpations in the southern Sierra 
Nevada corresponds with the pattern of highest concentration of air 
pollutants from automotive exhaust, and it has been suggested that this 
may be due to increases in nitrification (or other changes) caused by 
those pollutants (Jennings 1996, p. 940). Shinn et al. (2008, p. 186) 
suggested that mountain amphibians may be more sensitive to nitrite 
toxicity based on acute toxicity observed at low concentrations (less 
than 0.5 milligrams/liter in Iberian water frogs (Pelophylax perezi)). 
Macias and Blaustein (2007, p. 55) observed a synergistic effect (when 
the net effect of two things acting together exceeds the sum of both 
alone) in the common toad (Bufo bufo) where nitrite in combination with 
ultraviolet radiation (UV-B; 280 to 320 nanometers (11-12.6 
microinches)) was up to seven times more lethal than mortality from 
either stressor alone (the synergy was four times the summed effect 
from both treatments alone in the Iberian water frog).
    The correlative evidence between areas of pesticide (and other) 
contamination in the Sierra Nevada and areas of amphibian decline 
support

[[Page 24490]]

hypotheses that contaminants may present a risk to the mountain yellow-
legged frog and could have contributed to the species' decline 
(Jennings 1996, p. 940; Sparling et al. 2001, p. 1591; Davidson et al. 
2002. p. 1599; Davidson and Knapp 2007, p. 587). However, studies 
confirming exposure in remote locations to ecotoxicologically relevant 
concentrations of contaminants are not available to support this 
hypothesis.
    To the contrary, efforts to date have found fairly low 
concentrations of many of the primary suspect constituents commonly 
indicating agricultural and industrial pollution (organochlorines, 
organophosphates/carbamates, polycyclic hydrocarbons). Bradford et al. 
(2010, p. 1064) observed a rapid decline in concentrations of 
endosulfan, chlorpyrifos, and DDE (among others) going out to 42 km (26 
mi) linear distance from the valley floor in air, water, and tadpole 
tissues. These researchers also found relatively minute variation in 
concentrations among high-elevation study sites relative to the 
differences observed between the San Joaquin Valley and the nearest 
high-elevation sites. Essentially, sites beyond 42 km (26 mi) exhibited 
very low concentrations of measured compounds, which did not 
appreciably decrease with distance (Bradford et al. 2010, p. 1064). 
These observations make the contaminant decline hypotheses less 
tenable, and so windborne organic contaminants are currently considered 
minor contributors (if at all) to observed frog declines.
    Acidic deposition has been suggested to contribute to amphibian 
declines in the western United States (Blaustein and Wake 1990, p. 204; 
Carey 1993, p. 357; Alford and Richards 1999, pp. 4-5). Acid 
precipitation has also been postulated as a cause of amphibian declines 
at high elevations in the Sierra Nevada (Bradford et al. 1994b, p. 156) 
because waters there are low in acid neutralizing capacity and, 
therefore, are susceptible to changes in water chemistry caused by acid 
deposition (Byron et al. 1991, p. 271). Extreme pH in surface waters of 
the Sierra Nevada is estimated at 5.0, with most high-elevation lakes 
having a pH of greater than 6 (Bradford et al. 1992, p. 374). Near Lake 
Tahoe, at an elevation of approximately 2,100 m (6,900 ft), 
precipitation acidity has increased significantly (Byron et al. 1991, 
p. 272). In surface waters of the Sierra Nevada, acidity increases and 
acid neutralizing capacity decreases during snow melt and summer 
storms, though rarely does pH drop below 5.4 (Nikolaidis et al. 1991, 
p. 339; Bradford and Gordon 1992, p. 73; Bradford et al. 1998, p. 
2489). The mountain yellow-legged frog breeds shortly after snow melt; 
therefore, its most sensitive early life stages are exposed to 
acidification (Bradford and Gordon 1992, p. 9). Bradford et al. (1998, 
p. 2482) found that mountain yellow-legged frog tadpoles were sensitive 
to naturally acidic conditions, and that their distribution was 
significantly related to lake acidity (they were not found in lakes 
with a pH lower than 6).
    Laboratory studies have documented sublethal effects (reduced 
growth) on mountain yellow-legged frog embryos at pH 5.25 (Bradford et 
al. 1992, p. 369). Survivorship of mountain yellow-legged frog embryos 
and tadpoles was negatively affected as acidity increased (at 
approximately pH 4.5 or lower); embryos were more sensitive to 
increased acidity than tadpoles (Bradford and Gordon 1992, p. 3; 
Bradford et al. 1992, pp. 374-375). Potential indirect effects via 
impacts to the larger pond community were suggested by the observation 
that mountain yellow-legged frogs, common microcrustaceans, and 
caddisfly larvae were rare or absent at lakes with lower pH, and 
community richness declined with decreasing pH (Bradford et al. 1998, 
p. 2478).
    However, other studies do not support this hypothesis of acid 
deposition as a contributing factor to amphibian population declines in 
this area (Bradford and Gordon 1992, pp. 74-77; Bradford et al. 1992, 
p. 375; Corn and Vertucci 1992, p. 366; Bradford et al. 1994a, p. 326; 
1994b, p. 160; Corn 1994, p. 61). The hypothesis of acidic deposition 
as a cause of mountain yellow-legged frog declines has been rejected by 
field experiments that failed to show differences in water chemistry 
parameters between occupied and unoccupied mountain yellow-legged frog 
sites (Bradford et al. 1994b, p. 160). Though acidity may have an 
influence on mountain yellow-legged frog abundance or distribution, it 
is unlikely to have contributed significantly to the species' decline, 
given the rarity of lakes acidified either by natural or anthropogenic 
sources (Bradford et al. 1998, pp. 2488-2489).
    Collectively, contaminant risks to mountain yellow-legged frogs are 
likely a minor risk factor across the range of the species that does 
not represent a threat to the species at a population level. Frogs are 
sensitive to contaminants, although exposure to contaminants from 
upwind sources has not been substantiated. Localized exposure to 
upgradient or directly applied compounds is of theoretical concern. 
However, the overlap of extant populations and such land uses, and 
contribution of these management activities to aquatic pollution, is 
undocumented.
Ultraviolet Radiation
    Melanic pigment on the upper surfaces of amphibian eggs and 
tadpoles protects these sensitive life stages against UV-B damage, an 
important protection for normal development of amphibians exposed to 
sunlight, especially at high elevations in clear and shallow waters 
(Perotti and Di[eacute]guez 2006, p. 2064). Blaustein et al. (1994c, p. 
1793) observed decreased hatching success in several species of 
amphibian embryos (the mountain yellow-legged frog was not tested) 
exposed to increased UV-B radiation, and proposed that this may be a 
cause of amphibian declines.
    Ambient UV-B radiation has increased at north temperate latitudes 
over the past 2 decades (Adams et al. 2001, p. 521). If UV-B is 
contributing to amphibian population declines, the declines would 
likely be greater at higher elevations and more southerly latitudes 
where the thinner atmosphere allows greater penetration (Davidson et 
al. 2001, p. 474; Davidson et al. 2002, p. 1589). In California, where 
there is a north-to-south gradient of increasing UV-B exposure, 
amphibian declines would also likely be more prevalent at southerly 
latitudes (Davidson et al. 2001, p. 474; Davidson et al. 2002, p. 
1589). In a spatial test of the hypothesis that UV-B has contributed to 
the decline of the mountain yellow-legged frog in the Sierra Nevada, 
Davidson et al. (2002, p. 1598) concluded that patterns of this 
species' decline are inconsistent with the predictions of where UV-B-
related population declines would occur. Greater numbers of extant 
populations of this species were present at higher elevations than at 
lower elevations, and population decline was greater in the northern 
portion of the species' range than it was in the southern portion.
    Adams et al. (2005, p. 497) also found no evidence that the 
distribution of mountain yellow-legged frogs in lakes in Sequoia and 
Kings Canyon National Parks was determined by UV-B. Pahkala et al. 
(2003, p. 197) even observed enhanced tadpole growth rates in two of 
three amphibian species exposed to moderate amounts of UV-B. Vredenburg 
et al. (2010b, p. 509) studied the effects of field level exposures of 
UV-B on hatching success in mountain the yellow-legged frog, Yosemite 
toad, and Pacific tree frog and found only a small increase in time to 
hatching in one of three lakes for the mountain yellow-

[[Page 24491]]

legged frog. The authors suggested that amphibians occupying habitats 
with high UV-B exposure may have evolved mechanisms for coping with or 
avoiding the damaging UV rays. This is plausible, given that such a 
field level experiment was testing a persistent population, one that 
would logically be a survivor from past exposure (made up of tolerant 
individuals), and this level of experimental bias is inherent to 
experiments with such designs.
    The UV-B hypothesis is controversial and has been the topic of much 
scientific debate. Support is undermined by lack of evidence linking 
experimental results to observed changes in abundance and distribution 
in the wild, and also the inability of proponents to document increased 
exposure in amphibian populations (Corn 2005, p. 60). In weighing the 
available evidence, UV-B does not appear to be a contributing factor to 
mountain yellow-legged frog population declines in the Sierra Nevada.
Climate Change
    Our analyses under the Act include consideration of ongoing and 
projected changes in climate. The terms ``climate'' and ``climate 
change'' are defined by the Intergovernmental Panel on Climate Change 
(IPCC). The term ``climate'' refers to the mean and variability of 
different types of weather conditions over time, with 30 years being a 
typical period for such measurements, although shorter or longer 
periods also may be used (IPCC 2007a, p. 78). The term ``climate 
change'' thus refers to a change in the mean or variability of one or 
more measures of climate (for example, temperature or precipitation) 
that persists for an extended period, typically decades or longer, 
whether the change is due to natural variability, human activity, or 
both (IPCC 2007a, p. 78).
    Scientific measurements spanning several decades demonstrate that 
changes in climate are occurring, and that the rate of change has 
increased since the 1950s. Examples include warming of the global 
climate system, and substantial increases in precipitation in some 
regions of the world and decreases in other regions (for these and 
other examples, see IPCC 2007a, p. 30 and Solomon et al. 2007, pp. 35-
54, 82-85). Results of scientific analyses presented by the IPCC show 
that most of the observed increase in global average temperature since 
the mid-20th century cannot be explained by natural variability in 
climate, and is ``very likely'' (defined by the IPCC as 90 percent or 
higher probability) due to the observed increase in greenhouse gas 
(GHG) concentrations in the atmosphere as a result of human activities, 
particularly carbon dioxide emissions from use of fossil fuels (IPCC 
2007a, pp. 5-6 and figures SPM.3 and SPM.4; Solomon et al. 2007, pp. 
21-35). Further confirmation of the role of GHGs comes from analyses by 
Huber and Knutti (2011, p. 4), who concluded it is extremely likely 
that approximately 75 percent of global warming since 1950 has been 
caused by human activities.
    Scientists use a variety of climate models, which include 
consideration of natural processes and variability, as well as various 
scenarios of potential levels and timing of GHG emissions, to evaluate 
the causes of changes already observed and to project future changes in 
temperature and other climate conditions (for example, Meehl et al. 
2007, entire; Ganguly et al. 2009, pp. 11555, 15558; Prinn et al. 2011, 
pp. 527, 529). All combinations of models and emissions scenarios yield 
very similar projections of increases in the most common measure of 
climate change, average global surface temperature (commonly known as 
global warming), until about 2030. Although projections of the 
magnitude and rate of warming differ after about 2030, the overall 
trajectory of all the projections is one of increased global warming 
through the end of this century, even for the projections based on 
scenarios that assume that GHG emissions will stabilize or decline. 
Thus, there is strong scientific support for projections that warming 
will continue through the 21st century, and that the magnitude and rate 
of change will be influenced substantially by the extent of GHG 
emissions (IPCC 2007a, pp. 44-45; Meehl et al. 2007, pp. 760-764, 797-
811; Ganguly et al. 2009, pp. 15555-15558; Prinn et al. 2011, pp. 527, 
529). (See IPCC 2007b, p. 8, for a summary of other global projections 
of climate-related changes, such as frequency of heat waves and changes 
in precipitation. Also see IPCC 2011 (entire) for a summary of 
observations and projections of extreme climate events.)
    Various changes in climate may have direct or indirect effects on 
species. These effects may be positive, neutral, or negative, and they 
may change over time, depending on the species and other relevant 
considerations, such as interactions of climate with other variables 
(for example, habitat fragmentation) (IPCC 2007a, pp. 8-14, 18-19). 
Identifying likely effects often involves aspects of climate change 
vulnerability analysis. Vulnerability refers to the degree to which a 
species (or system) is susceptible to, and unable to cope with, adverse 
effects of climate change, including climate variability and extremes. 
Vulnerability is a function of the type, magnitude, and rate of climate 
change and variation to which a species is exposed, its sensitivity, 
and its adaptive capacity (IPCC 2007a, p. 89; see also Glick et al. 
2011, pp. 19-22). There is no single method for conducting such 
analyses that applies to all situations (Glick et al. 2011, p. 3). We 
use our expert judgment and appropriate analytical approaches to weigh 
relevant information, including uncertainty, in our consideration of 
various aspects of climate change.
    Global climate projections are informative and, in some cases, the 
only or the best scientific information available for us to use. 
However, projected changes in climate and related impacts can vary 
substantially across and within different regions of the world (for 
example, IPCC 2007a, pp. 8-12). Therefore, we use downscaled 
projections when they are available and have been developed through 
appropriate scientific procedures, because such projections provide 
higher resolution information that is more relevant to the spatial 
scales used for analyses of a given species (see Glick et al. 2011, pp. 
58-61, for a discussion of downscaling). With regard to our analysis 
for the Sierra Nevada of California (and western United States), 
downscaled projections are available.
    Variability exists in outputs from different climate models, and 
uncertainty regarding future GHG emissions is also a factor in modeling 
(PRBO 2011, p. 3). A general pattern that holds for many predictive 
models indicates northern areas of the United States will become 
wetter, and southern areas (particularly the Southwest) will become 
drier. These models also predict that extreme events, such as heavier 
storms, heat waves, and regional droughts, may become more frequent 
(Glick et al. 2011, p. 7). Moreover, it is generally expected that the 
duration and intensity of droughts will increase in the future (Glick 
et al. 2011, p. 45; PRBO 2011, p. 21).
    The last century has included some of the most variable climate 
reversals documented, at both the annual and near-decadal scales, 
including a high frequency of El Ni[ntilde]o (associated with more 
severe winters) and La Ni[ntilde]a (associated with milder winters) 
events (reflecting drought periods of 5 to 8 years alternating with wet 
periods) (USDA 2001b, p. 33). Scientists have confirmed a longer 
duration climate cycle termed the Pacific Decadal Oscillation (PDO), 
which operates on cycles between 2 to 3 decades, and

[[Page 24492]]

generally is characterized by warm and dry (PDO positive) followed by 
cool and wet cycles (PDO negative) (Mantua et al. 1997, pp. 1069-1079; 
Zhang et al. 1997, pp. 1004-1018). Snowpack is seen to follow this 
pattern--heavier in the PDO negative phase in California, and lighter 
in the positive phase (Mantua et al. 1997, p. 14; Cayan et al. 1998, p. 
3148; McCabe and Dettinger 2002, p. 24).
    Mantua et al. (1997, pp. 15-19) observed a relationship in 
population trends in Pacific salmon that mirror the PDO. The last turn 
of this cycle was in 1977, towards a warm and dry phase for the western 
United States. If this interdecadal trend holds, indications are that 
we are currently trending back into a cooler and wetter phase in 
California. Given the impacts to climate (snowpack, and therefore, 
hydrology in the alpine system), and the extended duration of these 
cycles relative to generation time for these species, it is logical to 
presume that amphibian population trends (other things being equal) 
would also tend to track these cycles. Drost and Fellers (1996, p. 423) 
indicated that drought probably has an exacerbating or compounding 
effect in mountain yellow-legged frog complex population declines.
    For the Sierra Nevada ecoregion, climate models predict that mean 
annual temperatures will increase by 1.8 to 2.4 [deg]C (3.2 to 4.3 
[deg]F) by 2070, including warmer winters with earlier spring snowmelt 
and higher summer temperatures. However, it is expected that 
temperature and climate variability will vary based on topographic 
diversity (for example, wind intensity will determine east versus west 
slope variability) (PRBO 2011, p. 18). Mean annual rainfall is 
projected to decrease from 9.2-33.9 cm (3.6-13.3 in) by 2070; however, 
projections have high uncertainty and one study predicts the opposite 
effect (PRBO 2011, p. 18). Given the varied outputs from differing 
modeling assumptions, and the influence of complex topography on 
microclimate patterns, it is difficult to draw general conclusions 
about the effects of climate change on precipitation patterns in the 
Sierra Nevada (PRBO, 2011, p. 18). Snowpack is, by all projections, 
going to decrease dramatically (following the temperature rise and more 
precipitation falling as rain). Higher winter streamflows, earlier 
runoff, and reduced spring and summer streamflows are projected, with 
increasing severity in the southern Sierra Nevada (PRBO 2011, pp. 20-
22).
    Snow-dominated elevations from 2,000-2,800 m (6,560-9,190 ft) will 
be the most sensitive to temperature increases, and a warming of 5 
[deg]C (9 [deg]F) is projected to shift center timing (the measure when 
half a stream's annual flow has passed a given point in time) to more 
than 45 days earlier in the year as compared to the 1961-1990 baseline 
(PRBO 2011, p. 23). Lakes, ponds, and other standing waters fed by 
snowmelt or streams may dry out or be more ephemeral during the non-
winter months (PRBO 2011, p. 24). This pattern could influence ground 
water transport, and springs may be similarly depleted, leading to 
lower lake levels.
    Vulnerability of species to climate change is a function of three 
factors: Sensitivity of a species or its habitat to climate change, 
exposure of individuals to such physical changes in the environment, 
and their capacity to adapt to those changes (Glick et al. 2011, pp. 
19-22). Critical sensitivity elements broadly applicable across 
organizational levels (from species through habitats to ecosystems) are 
associated with physical variables, such as hydrology (timing, 
magnitude, and volume of waterflows), fire regime (frequency, extent, 
and severity of fires), and wind (Glick et al. 2011, pp. 39-40). 
Species-level sensitivities generally include physiological factors, 
such as changes in temperature, moisture, or pH as they influence 
individuals; these also include dependence on sensitive habitats, 
ecological linkages to other species, and changes in phenology (timing 
of key life-history events) (Glick et al. 2011, pp. 40-41).
    Exposure to environmental stressors renders species vulnerable to 
climate change impacts, either through direct mechanisms (for example, 
physical temperature extremes or changes in solar radiation), or 
indirectly through impacts upon habitat (hydrology; fire regime; or 
abundance and distribution of prey, competitors, or predator species). 
A species' capacity to adapt to climate change is increased by 
behavioral plasticity (the ability to modify behavior to mitigate the 
impacts of the stressor), dispersal ability (the ability to relocate to 
meet shifting conditions), and evolutionary potential (for example, 
shorter-lived species with multiple generations have more capacity to 
adapt through evolution) (Glick et al. 2011, pp. 48-49).
    The International Union for Conservation of Nature describes five 
categories of life-history traits that render species more vulnerable 
to climate change (Foden et al. 2008 in Glick et al. 2011, p. 33): (1) 
Specialized habitat or microhabitat requirements, (2) narrow 
environmental tolerances or thresholds that are likely to be exceeded 
under climate change, (3) dependence on specific triggers or cues that 
are likely to be disrupted (for example, rainfall or temperature cues 
for breeding, migration, or hibernation), (4) dependence on 
interactions between species that are likely to be disrupted, and (5) 
inability or poor ability to disperse quickly or to colonize more 
suitable range. We apply these criteria in this proposed rule to assess 
the vulnerability of mountain yellow-legged frogs to climate change.
    The mountain yellow-legged frog is not necessarily a habitat 
specialist, although it does depend on fishless high mountain lakes 
with particular properties necessary to sustain a multi-year life 
cycle. As a species that inhabits areas with relative climate extremes, 
some conditions may directly push mountain yellow-legged frogs past 
physiological or ecological tolerance thresholds, and therefore enhance 
risk from the effects of climate change. For example, the increased 
severity of some winter storms may freeze lakes to greater depths than 
is historically typical. Severe winters (typical of El Ni[ntilde]o 
Southern Oscillation years and PDO negative decades) would force longer 
hibernation times and could stress mountain yellow-legged frogs by 
reducing the time available for them to feed and breed. The deeper 
lakes that once supported frog populations (but now harbor introduced 
trout) are no longer available as refuge for frogs in a drier climate 
with possible severe cold winters. It is important to note that these 
episodic stressors may be infrequent, but they are important to long-
lived species with small populations.
    In summer, reduced snowpack and enhanced evapotranspiration 
following higher temperatures may dry out ponds that otherwise would 
have sustained rearing tadpoles (Lacan et al. 2008, p. 220), and may 
also reduce fecundity (egg production) (Lacan et al. 2008, p. 222). 
Lacan et al. (2008, p. 211) observed most frog breeding in the smaller, 
fishless lakes of Kings Canyon National Park, lakes that are shallow 
and prone to summer drying. Thus, climate change will likely reduce 
available breeding habitat for mountain yellow-legged frogs and lead to 
greater frequency of stranding and death of tadpoles (Corn 2005, p. 64; 
Lacan et al. 2008, p. 222).
    Earlier snowmelt is expected to cue breeding earlier in the year. 
The advance of this primary signal for breeding phenology in montane 
and boreal habitats (Corn 2005, p. 61) may have both positive and 
negative effects. Additional time for growth and development may render 
larger individuals more fit to overwinter;

[[Page 24493]]

however, earlier breeding may also expose young tadpoles (or eggs) to 
killing frosts in more variable conditions of early spring (Corn 2005, 
p. 60).
    It is unclear if there are dependencies upon other species with 
which mountain yellow-legged frogs interact that may be affected either 
positively or negatively by climate change. Climate change may alter 
invertebrate communities (PRBO 2011 p. 24). In one study, an 
experimental increase in stream temperature was shown to decrease 
density and biomass of invertebrates (Hogg and Williams 1996, p. 401). 
Thus, climate change might have a negative impact on the mountain 
yellow-legged frog prey base.
    Indirect effects from climate change may lead to greater risk to 
mountain yellow-legged frog population persistence. For example, fire 
intensity and magnitude are projected to increase (PRBO 2011, pp. 24-
25), and therefore the contribution and influence of this stressor upon 
frog habitat and populations will increase. Climate change may alter 
lake productivity through changes in water chemistry, the extent and 
timing of mixing, and nutrient inputs from increased fires, all of 
which may influence community dynamics and composition (Melack et al. 
1997, p. 971; Parker et al. 2008, p. 12927). These changes may not all 
be negative; for example, water chemistry and nutrient inputs, along 
with warmer summer temperatures, could increase net primary 
productivity in high mountain lakes to enhance frog food sources.
    Changes in temperature may also affect virulence of pathogens 
(Carey 1993, p. 359), which could make mountain yellow-legged frogs 
more susceptible to disease. Climate change could also affect the 
distribution of pathogens and their vectors, exposing mountain yellow-
legged frogs (potentially with weakened immune systems as a result of 
other environmental stressors) to new pathogens (Blaustein et al. 2001, 
p. 1808). Climate change (warming) has been hypothesized as a driver 
for the range shift of Bd (Pounds et al. 2006, p. 161; Bosch et al. 
2007, p. 253). However, other work has indicated that survival and 
transmission of Bd is more likely facilitated by cooler and wetter 
conditions (Corn 2005, p. 63). Fisher et al. (2009, p. 299) present a 
review of information available to date, and evaluate the competing 
hypotheses regarding Bd dynamics and present some cases that suggest a 
changing climate can change the host-pathogen dynamic to a more 
virulent state.
    The key risk factor for climate change impacts on mountain yellow-
legged frogs is likely the combined effect of reduced water levels in 
high mountain lakes and ponds and the relative inability of individuals 
to disperse and colonize across longer distances in order to occupy 
more favorable habitat conditions (if they exist). Although such 
adaptive range shifts have been observed in some plant and animal 
species, they have not been reported in amphibians. The changes 
observed in amphibians to date have been more associated with changes 
in timing of breeding (phenology) (Corn 2005, p. 60). This reduced 
adaptive capacity for mountain yellow-legged frogs is a function of 
high site fidelity and the extensive habitat fragmentation due to the 
introduction of fishes in many of the more productive and persistent 
high mountain lake habitats and streams that constitute critical 
dispersal corridors throughout much of the frog's range (see Factor C 
discussion above).
    An increase in the frequency, intensity, and duration of droughts 
caused by climate change may have compounding effects on populations of 
mountain yellow-legged frogs already in decline. In situations where 
other stressors have resulted in the isolation of mountain yellow-
legged frogs in marginal habitats factors (such as introduced fish), 
localized mountain yellow-legged frog population crashes or 
extirpations resulting from drought may exacerbate their isolation and 
preclude natural recolonization (Bradford et al. 1993, p. 887; Drost 
and Fellers 1996, p. 424; Lacan et al. 2008, p. 222). Climate change 
represents a substantial future threat to the persistence of mountain 
yellow-legged frog populations.
Direct and Indirect Mortality
    Other risk factors include direct and indirect mortality as an 
unintentional consequence of activities within mountain yellow-legged 
frog habitat. Recreation may threaten all life stages of the mountain 
yellow-legged frog through trampling by humans, packstock, or vehicles, 
including off-highway vehicles; harassment by pets; and habitat 
degradation associated with these various land uses (Cole and Landres 
1996, p. 170; USDA 2001b, pp. 213-214). Fire management activities 
probably lead to some direct mortality and have the potential to 
disrupt behavior. Fire retardant chemicals contain nitrogen compounds 
and surfactants (chemical additive used to facilitate application). 
Laboratory tests have shown that surfactants or ammonia byproducts can 
cause mortality in fishes and aquatic invertebrates (Hamilton et al. 
1996, pp. 132-144); similar effects are possible in amphibians. Calfee 
and Little (2003, pp. 1529-1530) report that southern leopard frogs 
(Rana sphenocephala) and boreal toads (Bufo boreas) are more tolerant 
than rainbow trout (Oncorhynchus mykiss) to fire retardant chemicals; 
however the acute toxicity of some compounds is enhanced by ultraviolet 
light, which may harm amphibians at environmentally relevant 
concentrations. Therefore, if fire retardant chemicals are dropped in 
or near mountain yellow-legged frog habitat, they could have negative 
effects on individuals. The prevalence of this impact is undetermined, 
but this threat may be sporadically significant. Roads create the 
potential for direct mortality of amphibians by vehicle strikes 
(deMaynadier and Hunter 2000, p. 56) and the possible introduction of 
contaminants into new areas; however, most extant populations are not 
located near roads. Collectively, direct mortality risks to mountain 
yellow-legged frogs are likely of sporadic significance. They may be 
important incidentally on a site-specific basis, but are likely of low 
prevalence across the range of the species.
Small Population Size
    Remaining populations for both the Sierra Nevada yellow-legged frog 
and the mountain yellow-legged frog are small in many localities (CDFG, 
unpubl. data). Brown et al. (2011, p. 24) reported that about 90 
percent of watersheds have fewer than 10 adults and 80 percent have 
fewer than 10 subadults and 100 tadpoles. Remnant populations in the 
far northern extent of the range for the Sierra Nevada yellow-legged 
frog (from Lake Tahoe north) and the southern extent of the Sierran 
populations of the mountain yellow-legged frog (south of Kings Canyon 
National Park) currently also exhibit very low abundances (CDFG, 
unpubl. data).
    Compared to large populations, small populations are more 
vulnerable to extirpation from environmental, demographic, and genetic 
stochasticity (random natural occurrences), and unforeseen (natural or 
unnatural) catastrophes (Shaffer 1981, p. 131). Environmental 
stochasticity refers to annual variation in birth and death rates in 
response to weather, disease, competition, predation, or other factors 
external to the population (Shaffer 1981, p. 131). Small populations 
may be less able to respond to natural environmental changes 
(K[eacute]ry et al. 2000, p. 28), such as a prolonged drought or even a 
significant natural

[[Page 24494]]

predation event. Periods of prolonged drought are more likely to have a 
significant effect on mountain yellow-legged frogs because drought 
conditions occur on a landscape scale and all life stages are dependent 
on habitat with a perennial water source. Demographic stochasticity is 
random variability in survival or reproduction among individuals within 
a population (Shaffer 1981, p. 131) and could increase the risk of 
extirpation of the remaining populations. Genetic stochasticity results 
from changes in gene frequencies due to the founder effect (loss of 
genetic variation that occurs when a new population is established by a 
small number of individuals) (Reiger 1968, p. 163); random fixation 
(the complete loss of one of two alleles in a population, the other 
allele reaching a frequency of 100 percent) (Reiger 1968, p. 371); or 
inbreeding depression (loss of fitness or vigor due to mating among 
relatives) (Soul[eacute] 1980, p. 96). Additionally, small populations 
generally have an increased chance of genetic drift (random changes in 
gene frequencies from generation to generation that can lead to a loss 
of variation) and inbreeding (Ellstrand and Elam 1993, p. 225).
    Allee effects (Dennis 1989, pp. 481-538) occur when a population 
loses its positive stock-recruitment relationship (when population is 
in decline). In a declining population, an extinction threshold or 
``Allee threshold'' (Berec et al. 2006, pp. 185-191) may be crossed, 
where adults in the population either cease to breed or the population 
becomes so compromised that breeding does not contribute to population 
growth. Allee effects typically fall into three broad categories 
(Courchamp et al. 1999, pp. 405-410): Lack of facilitation (including 
low mate detection and loss of breeding cues), demographic 
stochasticity, and loss of heterozygosity (a measure of genetic 
variability). Environmental stochasticity amplifies Allee effects 
(Dennis 1989, pp. 481-538; Dennis 2002, pp, 389-401). The Allee effects 
of demographic stochasticity and loss of heterozygosity are likely as 
mountain yellow-legged frog populations continue to diminish. Lack of 
facilitation is a possible threat, though less probable as frogs can 
vocalize to advertise presence.
    The extinction risk of a species represented by few small 
populations is magnified when those populations are isolated from one 
another. This is especially true for species whose populations normally 
function in a metapopulation structure, whereby dispersal or migration 
of individuals to new or formerly occupied areas is necessary. 
Connectivity between these populations is essential to increase the 
number of reproductively active individuals in a population; mitigate 
the genetic, demographic, and environmental effects of small population 
size; and recolonize extirpated areas. Additionally, fewer populations 
increase the risk of extinction.
    The combination of low numbers with the other extant stressors of 
disease, fish persistence, and potential for climate extremes could 
have adverse consequences for the mountain yellow-legged frog complex 
as populations approach the Allee threshold. Small population size is 
currently a significant threat to most populations of mountain yellow-
legged frogs across the range of the species.
Cumulative Impacts of Extant Threats
    Stressors may act additively or synergistically. An additive effect 
would mean that an accumulation of otherwise low threat factors acting 
in combination may collectively result in individual losses that are 
meaningful at the population level. A synergistic effect is one where 
the interaction of one or more stressors together leads to effects 
greater than the sum of those individual factors combined. Further, the 
cumulative effect of multiple added stressors can erode population 
viability over successive generations and act as a chronic strain on 
the viability of a species, resulting in a progressive loss of 
populations over time. Such interactive effects from compounded 
stressors thereby act synergistically to curtail the viability of frog 
metapopulations and increase the risks of extinction.
    It is difficult to predict the precise impact of the cumulative 
threat represented by the relatively novel Bd epidemic across a 
landscape already fragmented by fish stocking. The singular threat of 
the Bd epidemic wave in the uninfected populations of the mountain 
yellow-legged frog complex in the southern Sierra Nevada could 
extirpate those populations as the lethal pathogen spreads. A 
compounding effect of disease-caused extirpation is that recolonization 
may never occur because streams connecting extirpated sites to extant 
populations now contain introduced fishes, which act as barriers to 
frog movement within metapopulations. This isolates the remaining 
populations of mountain yellow-legged frogs from one another (Bradford 
1991, p. 176; Bradford et al. 1993, p. 887). It is logical to presume 
that the small, fragmented populations left in the recent wake of Bd 
spread through the majority of the range of the Sierra Nevada yellow-
legged frog may experience further extirpations as surviving adults 
eventually die, and recruitment into the breeding pool from the Bd-
positive subadult class is significantly reduced. These may be 
exacerbated by the present and growing threat of climate change, 
although this effect may take years to materialize.
    In summary, based on the best available scientific and commercial 
information, we consider other natural and manmade factors to be 
substantial ongoing threats to the Sierra Nevada yellow-legged frog and 
the northern DPS of the mountain yellow-legged frog. These include 
high, prevalent risk associated with climate change and small 
population sizes, and the associated risk from the additive or 
synergistic effects of these two stressors interacting with other 
acknowledged threats, including habitat fragmentation and degradation 
(see Factor A), disease (see Factor C), or other threats currently 
present but with low relative contribution in isolation.

Proposed Determination for the Sierra Nevada Yellow-legged Frog

    We have carefully assessed the best scientific information 
available regarding the past, present, and future threats to the Sierra 
Nevada yellow-legged frog.
    There has been a rangewide decline in the geographic extent of 
populations, and losses of populations have continued in recent 
decades. There are now fewer, increasingly isolated populations 
maintaining viable recruitment (entry of post-metamorphic frogs into 
the breeding population). Coupled with the observation that remnant 
populations are also numerically smaller (in some cases consisting of 
few individuals), this reduction in occupancy and population density 
across the landscape suggests significant losses in metapopulation 
viability and high attendant risk to the overall population. The 
impacts of the declines on population resilience are two-fold: (1) The 
geographic extent and number of populations are reduced across the 
landscape, resulting in fewer and more isolated populations (the 
species is less able to withstand population stressors and unfavorable 
conditions exist for genetic exchange or dispersal to unoccupied areas 
(habitat fragmentation)); and (2) species abundance (in any given 
population) is reduced, making local extirpations much more likely 
(decreased population viability). Knapp et al. (2007b, pp. 1-2) 
estimated a 10 percent decline per year in the number of remaining 
mountain yellow-legged frog populations, and argued for the listing of 
the species as

[[Page 24495]]

endangered based on this observed rate of population loss.
    The best available science indicates the cause of the decline of 
the Sierra Nevada yellow-legged frog is the introduction of fishes to 
its habitat (Factor A, C) to support recreational angling. Water bodies 
throughout this range have been intensively stocked with introduced 
fish (principally trout). It is a threat of significant influence, and 
although it more directly impacted populations historically, it remains 
prevalent today because fish persist in many high-elevation habitats 
even where stocking has ceased. Competitive exclusion and predation by 
fish have reduced frog populations in stocked habitats, and left 
remnant populations isolated. It is important to recognize that 
throughout the vast majority of its range, Sierra Nevada yellow-legged 
frogs did not co-evolve with any species of fish, as they predominantly 
occur in water bodies above natural fish barriers. Further, the 
introduction of fish has generally restricted remaining Sierra Nevada 
yellow-legged frog populations to more marginal habitats, thereby 
increasing the likelihood of localized extinctions. Recolonization in 
these situations is difficult for a highly aquatic species with high 
site fidelity and unfavorable dispersal conditions. Climate change is 
likely to exacerbate these other threats and further threaten 
population resilience.
    Historical grazing activities may have modified the habitat of the 
Sierra Nevada yellow-legged frog throughout much of its range (Factor 
A). Grazing pressure has been significantly reduced from historical 
levels, although grazing may continue to contribute to some localized 
degradation and loss of suitable habitat. The effects of recreation, 
dams and water diversions, roads, timber harvests, and fire management 
activities on the Sierra Nevada yellow-legged frog are not well-
studied, and although they may negatively affect frog populations and 
their habitat, these effects have not been implicated as primary 
factors in the decline of this species. However, these activities may 
be factors of secondary importance in the decline of the Sierra Nevada 
yellow-legged frog and the modification of its habitat. Although these 
threat factors are of relatively lower current magnitude and imminence, 
part of their lesser studied, more uncertain contribution to population 
dynamics may be a function of timing. Historical losses may already be 
realized in areas where impacts are greater, and these would not be 
documented in studies that have mostly been conducted over the last 2 
to 3 decades amongst surviving populations. During this same time 
interval, management practices by Federal agencies with jurisdiction 
within the current range of the Sierra Nevada yellow-legged frog have 
generally improved.
    Sierra Nevada yellow-legged frogs are vulnerable to multiple 
pathogens, whose effects range from low levels of infection within 
persistent populations to disease-induced extirpation of entire 
populations. The Bd epidemic has caused localized extirpations of 
Sierra Nevada yellow-legged frog populations and associated significant 
declines in numbers of individuals. Though Bd was only recently 
discovered to affect the Sierra Nevada yellow-legged frog, it appears 
to infect populations at much higher rates than other diseases. The 
imminence of this risk to currently uninfected habitats is immediate, 
and the potential effects severe. The already-realized effects to the 
survival of sensitive amphibian life stages in Bd-positive areas are 
well-documented. Although some populations survive the initial Bd wave, 
survival rates of metamorphs and population viability are markedly 
reduced relative to historical (pre-Bd) norms.
    The main and interactive effects of these various risk factors have 
acted to reduce Sierra Nevada yellow-legged frog populations to a small 
fraction of its historical range and reduce population abundances 
significantly throughout most of its range. Remaining areas in the 
southern Sierra Nevada that have yet to be impacted by Bd are at 
immediate and severe risk.
    Given the life history of this species, dispersal, recolonization, 
and genetic exchange are largely precluded by the fragmentation of 
habitat common throughout its current range as a result of fish 
introductions. Frogs that may disperse are susceptible to hostile 
conditions in many circumstances. In essence, Sierra Nevada yellow-
legged frogs have been marginalized by historical fish introductions 
and, likely, other land management activities. Populations have 
recently been decimated by Bd, and the accumulation of other stressors 
(such as anticipated reduction of required aquatic breeding habitats 
with climate change and more extreme weather) upon a fragmented 
landscape make adaptation and recovery a highly improbable scenario 
without active intervention. The cumulative risk from these stressors 
to the persistence of the Sierra Nevada yellow-legged frog throughout 
its range is significant.
    The Act defines an endangered species as any species that is ``in 
danger of extinction throughout all or a significant portion of its 
range'' and a threatened species as any species ``that is likely to 
become endangered throughout all or a significant portion of its range 
within the foreseeable future.'' We find that the Sierra Nevada yellow-
legged frog is presently in danger of extinction throughout its entire 
range, based on the immediacy, severity, and scope of the threats 
described above. Specifically, these include habitat degradation and 
fragmentation under Factor A, predation and disease under Factor C, and 
climate change and the interaction of these various stressors 
cumulatively impacting small remnant populations under Factor E. There 
has been a rangewide reduction in abundance and geographic extent of 
surviving populations of the Sierra Nevada yellow-legged frog following 
decades of fish stocking, habitat fragmentation, and, most recently, a 
disease epidemic. Surviving populations are smaller and more isolated, 
and recruitment in Bd-positive populations is much reduced relative to 
historical norms. This combination of population stressors makes 
species persistence precarious throughout the currently occupied range 
in the Sierra Nevada.
    We have carefully assessed the best scientific and commercial 
information available regarding the past, present, and future threats 
to the species, and have determined that the Sierra Nevada yellow-
legged frog meets the definition of endangered under the Act, rather 
than threatened. This is because significant threats are occurring now 
and will occur in the future, at a high magnitude and across the 
species' entire range, making the species in danger of extinction at 
the present time. The rate of population decline remains high in the 
wake of chytrid epidemics, and core areas are at high, imminent risk. 
Population declines are expected to continue as maturing tadpoles 
succumb to Bd infection, and fragmented populations at very low 
abundances will face significant obstacles to recovery.
    Under the Act and our implementing regulations, a species may 
warrant listing if it is endangered or threatened throughout all or a 
significant portion of its range. The Sierra Nevada yellow-legged frog 
proposed for listing in this rule is restricted in its range, and the 
threats occur throughout the remaining occupied habitat. Therefore, we 
assessed the status of this species throughout its entire range. The 
threats to the survival of the species occur throughout the species' 
range and are not restricted to any particular

[[Page 24496]]

significant portion of that range. Accordingly, our assessment and 
proposed determination applies to the species throughout its entire 
range.

Proposed Determination for the Northern DPS of the Mountain Yellow-
legged Frog

    We have carefully assessed the best scientific information 
available regarding the past, present, and future threats to the 
northern DPS of the mountain yellow-legged frog.
    There has been a rangewide decline in the geographic extent of 
populations, and losses of populations have continued in recent 
decades. There are now fewer, increasingly isolated populations 
maintaining viable recruitment (entry of post-metamorphic frogs into 
the breeding population). Coupled with the observation that remnant 
populations are also numerically smaller (in some cases consisting of 
few individuals), this reduction in occupancy and population density 
across the landscape suggests significant losses in metapopulation 
viability and high attendant risk to the overall population. The 
impacts of the declines on population resilience are two-fold: (1) The 
geographic extent and number of populations are reduced across the 
landscape, resulting in fewer and more isolated populations (the 
species is less able to withstand population stressors and unfavorable 
conditions exist for genetic exchange or dispersal to unoccupied areas 
(habitat fragmentation)); and (2) species abundance (in any given 
population) is reduced, making local extirpations much more likely 
(decreased population viability). Knapp et al. (2007b, pp. 1-2) 
estimated a 10 percent decline per year in the number of remaining 
mountain yellow-legged frog populations, and argued for the listing of 
the species as endangered based on this observed rate of population 
loss.
    The best available science indicates the cause of the decline of 
the northern DPS of the mountain yellow-legged frog is the introduction 
of fishes to its habitat (Factor A, C) to support recreational angling. 
Water bodies throughout this range have been intensively stocked with 
introduced fish (principally trout). It is a threat of significant 
influence, and although it more directly impacted populations 
historically, it remains prevalent today because fish persist in many 
high-elevation habitats even where stocking has ceased. Competitive 
exclusion and predation by fish have reduced frog populations in 
stocked habitats, and left remnant populations isolated. It is 
important to recognize that throughout the vast majority of their 
range, mountain yellow-legged frogs did not co-evolve with any species 
of fish, as they predominantly occur in water bodies above natural fish 
barriers. Further, the introduction of fish has generally restricted 
remaining mountain yellow-legged frog populations to more marginal 
habitats, thereby increasing the likelihood of localized extinctions. 
Recolonization in these situations is difficult for a highly aquatic 
species with high site fidelity and unfavorable dispersal conditions. 
Climate change is likely to exacerbate these other threats and further 
threaten population resilience.
    Historical grazing activities may have modified the habitat of the 
mountain yellow-legged frog throughout much of its range (Factor A). 
Grazing pressure has been significantly reduced from historical levels, 
although grazing may continue to contribute to some localized 
degradation and loss of suitable habitat. The effects of recreation, 
dams and water diversions, roads, timber harvests, and fire management 
activities on the mountain yellow-legged frog are not well-studied, and 
although they may negatively affect frog populations and their habitat, 
these effects have not been implicated as primary factors in the 
decline of this species. However, these activities may be factors of 
secondary importance in the decline of the mountain yellow-legged frog 
and the modification of its habitat. Although these threat factors are 
of relatively lower current magnitude and imminence, part of their 
lesser studied, more uncertain contribution to population dynamics may 
be a function of timing. Historical losses may already be realized in 
areas where impacts are greater, and these would not be documented in 
studies that have mostly been conducted over the last 2 to 3 decades 
amongst surviving populations. During this same time interval, 
management practices by Federal agencies with jurisdiction within the 
current range of the mountain yellow-legged frog have generally 
improved.
    Mountain yellow-legged frogs are vulnerable to multiple pathogens, 
whose effects range from low levels of infection within persistent 
populations to disease-induced extirpation of entire populations. The 
Bd epidemic has caused localized extirpations of mountain yellow-legged 
frog populations and associated significant declines in numbers of 
individuals. Though Bd was only recently discovered to affect the 
mountain yellow-legged frog, it appears to infect populations at much 
higher rates than other diseases. The imminence of this risk to 
currently uninfected habitats is immediate, and the potential effects 
severe. The already-realized effects to the survival of sensitive 
amphibian life stages in Bd-positive areas are well-documented. 
Although some populations survive the initial Bd wave, survival rates 
of metamorphs and population viability are markedly reduced relative to 
historical (pre-Bd) norms.
    The main and interactive effects of these various risk factors have 
acted to reduce the northern DPS of the mountain yellow-legged frog 
populations to a small fraction of its historical range and reduce 
population abundances significantly throughout most of its range. 
Remaining areas in the southern Sierra Nevada that have yet to be 
impacted by Bd are at immediate and severe risk.
    Given the life history of this species, dispersal, recolonization, 
and genetic exchange are largely precluded by the fragmentation of 
habitat common throughout its current range as a result of fish 
introductions. Frogs that may disperse are susceptible to hostile 
conditions in many circumstances. In essence, mountain yellow-legged 
frogs have been marginalized by historical fish introductions and, 
likely, other land management activities. Populations have recently 
been decimated by Bd, and the accumulation of other stressors (such as 
anticipated reduction of required aquatic breeding habitats with 
climate change and more extreme weather) upon a fragmented landscape 
make adaptation and recovery a highly improbable scenario without 
active intervention. The cumulative risk from these stressors to the 
persistence of the mountain yellow-legged frog throughout its range is 
significant.
    The Act defines an endangered species as any species that is ``in 
danger of extinction throughout all or a significant portion of its 
range'' and a threatened species as any species ``that is likely to 
become endangered throughout all or a significant portion of its range 
within the foreseeable future.'' We find that the northern DPS of the 
mountain yellow-legged frog is presently in danger of extinction 
throughout its entire range, based on the immediacy, severity, and 
scope of the threats described above. Specifically, these include 
habitat degradation and fragmentation under Factor A, predation and 
disease under Factor C, and climate change and the interaction of these 
various stressors cumulatively impacting small remnant populations 
under Factor E. There has been a rangewide reduction in abundance and 
geographic extent of surviving populations of the northern DPS of the

[[Page 24497]]

mountain yellow-legged frog following decades of fish stocking, habitat 
fragmentation, and, most recently, a disease epidemic. Surviving 
populations are smaller and more isolated, and recruitment in Bd-
positive populations is much reduced relative to historical norms. This 
combination of population stressors makes species persistence 
precarious throughout the currently occupied range in the Sierra 
Nevada.
    We have carefully assessed the best scientific and commercial 
information available regarding the past, present, and future threats 
to the species, and have determined that the northern DPS of the 
mountain yellow-legged frog, already endangered in the southern part of 
its range, meets the definition of endangered under the Act, rather 
than threatened. This is because significant threats are occurring now 
and will occur in the future, at a high magnitude and across the 
species' entire range, making the species in danger of extinction at 
the present time. The rate of population decline remains high in the 
wake of chytrid epidemics, and core areas are at high, imminent risk. 
The recent rates of decline for these populations are even higher than 
declines in the Sierra Nevada yellow-legged frog, and as Bd infects 
remaining core areas, population viability will be significantly 
reduced, and extirpations or significant population declines are 
expected. Population declines are further expected to continue as 
maturing tadpoles succumb to Bd infection, and fragmented populations 
at very low abundances will face significant obstacles to recovery. 
Therefore, on the basis of the best available scientific and commercial 
information, and the threats posed to these species under the listing 
factors above, we propose listing the northern DPS of the mountain 
yellow-legged frog as endangered in accordance with sections 3(6) and 
4(a)(1) of the Act.
    Under the Act and our implementing regulations, a species may 
warrant listing if it is endangered or threatened throughout all or a 
significant portion of its range. The northern DPS of the mountain 
yellow-legged frog proposed for listing in this rule is restricted in 
its range, and the threats occur throughout the remaining occupied 
habitat. Therefore, we assessed the status of this DPS throughout its 
entire range in the Sierra Nevada of California. The threats to the 
survival of this DPS occur throughout its range in the southern Sierra 
Nevada and are not restricted to any particular significant portion of 
that range. Accordingly, our assessment and proposed determination 
applies to the DPS throughout its entire range.

Status for Yosemite Toad

Background

    In this section of the proposed rule, it is our intent to discuss 
only those topics directly relevant to the listing of the Yosemite toad 
(Anaxyrus canorus) as threatened.

Taxonomy

    The Yosemite toad (Anaxyrus canorus; formerly Bufo canorus) was 
originally described by Camp (1916, pp. 59-62), and given the common 
name Yosemite Park toad. The word ``canorus'' means ``tuneful'' in 
Latin, referring to the male's sustained melodious trill, which 
attracts mates during the early spring breeding season. Later, Grinnell 
and Storer (1924, pp. 657-660) referred to this species as the Yosemite 
toad when the species' range was found to extend beyond the boundaries 
of Yosemite National Park.
    When he described the species, Camp noted similarities in 
appearance of the Yosemite toad and the western toad (Camp 1916, pp. 
59-62). Based on general appearance, structure, and distribution, it 
appeared that the western toad and the Yosemite toad were closely 
related (Myers 1942, p. 10; Stebbins 1951, pp. 245-248; Mullally 1956b, 
pp. 133-135; Savage 1958, pp. 251-253). The close relationship between 
the western toad and the Yosemite toad is also supported by studies of 
bone structure (Tihen 1962, pp. 1-50) and by the survivorship of hybrid 
toads produced by artificially crossing the two species (Blair 1959, 
pp. 427-453; 1963, pp. 1-16; 1964, pp. 181-192).
    Camp (1916, pp. 59-62), using characteristics of the skull, 
concluded that Bufo boreas, B. canorus, and B. nestor (extinct) were 
more closely related to one another than to other North American toads 
(Family Bufonidae), and that these species comprised the most primitive 
group of Bufo in North America. Blair (1972, pp. 93-95) grouped B. 
boreas, B. canorus, black toads (B. exsul), and Amargosa toads (B. 
nelsoni) together taxonomically as the ``boreas group.'' Subsequently, 
Frost et al. (2006, p. 297) divided the paraphyletic genus ``Bufo'' 
into three separate genera, assigning the North American toads to the 
genus Anaxyrus. This taxonomic distinction has been recently adopted by 
the American Society of Ichthyologists and Herpetologists, the 
Herpetologists' League, and the Society for the Study of Amphibians and 
Reptiles (Crother et al. 2008. p. 3).
    Feder (1977, pp. 43-55) found Yosemite toads to be the most 
genetically distinct member of the boreas group based on samples from a 
limited geographic range. However, Yosemite toads hybridize with 
western toads in the northern part of their range (Karlstrom 1962, p. 
84; Morton and Sokolski 1978, pp. 52-55). A genetic analysis of a 
segment of mitochondrial DNA from Yosemite toads was performed by 
Shaffer et al. (2000, pp. 245-257) using 372 toads from Yosemite and 
Kings Canyon National Parks. These data showed significant genetic 
differences in Yosemite toads between the two National Parks. They 
observed that genetic divergence among regionally proximate populations 
of Yosemite toads was high, implying low rates of genetic exchange. 
Their data also suggest that black toads are a nested subgroup within 
Yosemite toads, rather than a separate species, and that a group of 
western toad populations in the Oregon Cascades appears more closely 
related to Yosemite toads than their current classification would 
indicate. However, sufficient molecular evidence to change the 
taxonomic classification of these three species is not yet available.
    Stephens (2001, pp. 1-62) examined mitochondrial DNA from 8 
Yosemite toads (selected to represent the range of variability found in 
the Shaffer et al. (2000, pp. 245-257) study) and 173 western toads. 
This study indicated that Bufo in the Sierra Nevada occurs in northern 
and southern evolutionary groups, each of which includes both Yosemite 
toads and western toads (that is, toads of both species are more 
closely related to each other within an evolutionary group than they 
are to members of their own species in the other evolutionary group). 
Goebel et al. (2008, p. 223) also concluded that the Yosemite toad is 
paraphyletic, split between a northwest and southwest haplotype group.
    Further genetic analysis of Yosemite toads is needed to fully 
understand the evolutionary history and appropriate taxonomic status of 
the Yosemite toad (Stephens 2001, pp. 1-62). Current information 
indicates that the range is segregated between northern and southern 
evolutionary groups. This information also indicates that genetic 
introgression (movement of genes into the native gene pool to create 
hybrid populations) is occurring from a closely related counterpart 
(likely over an extended period), possibly associated with range 
expansion and overlap with the western toad following reproductive 
isolation that occurred during the Pleistocene glaciation (Feder 1977, 
p. 43). It therefore appears that natural hybridization has occurred 
where

[[Page 24498]]

Yosemite toad and western toad ranges overlap. We have assessed the 
available information, and have determined that the Yosemite toad is a 
valid species, following its current classification by the American 
Society of Ichthyologists and Herpetologists, the Herpetologists' 
League, and the Society for the Study of Amphibians and Reptiles 
(Crother et al. 2008, p. 3).

Species Description

    The Yosemite toad is moderately sized, with a snout-urostyle length 
(measured from the tip of the snout to the posterior edge of the 
urostyle, a bony structure at the posterior end of the spinal column) 
of 30-71 mm (1.2-2.8 in) with rounded to slightly oval paratoid glands 
(a pair of glands, one on each side of the head, that produce toxins) 
(Karlstrom 1962, pp. 21-23). The paratoid glands are less than the 
width of a gland apart (Stebbins 1985, pp. 71-72). A thin mid-dorsal 
stripe (on the middle of the back) is present in juveniles of both 
sexes. The stripe disappears or is reduced with age; this process takes 
place more quickly in males (Jennings and Hayes 1994, pp. 50-53). The 
iris of the eye is dark brown with gold iridophores (reflective pigment 
cells) (Jennings and Hayes 1994, pp. 50-53).
    Male Yosemite toads are smaller than female Yosemite toads, with 
less conspicuous warts (Stebbins 1951, p. 246). Differences in 
coloration between males and females are more pronounced in the 
Yosemite toad than in any other North American frog or toad (Stebbins 
1951, p. 246). Females have black spots or blotches edged with white or 
cream set against a grey, tan, or brown background color (Jennings and 
Hayes 1994, pp. 50-53). Males have a nearly uniform dorsal coloration 
of yellow-green to olive drab to darker greenish brown (Jennings and 
Hayes 1994, pp. 50-53). Karlstrom (1962, pp. 80-81) suggested that 
differences in coloration between the sexes evolved because they 
provide the Yosemite toad with protective coloration (camouflage). The 
uniform coloration of the adult males matches and blends with the silt 
and grasses that they frequent during the breeding season, whereas the 
young and females with disruptive coloration tend to use a wider range 
of habitats with broken backgrounds; thus, coloration may help conceal 
individual toads from predators.

Habitat and Life History

    Yosemite toads are found in wet meadow habitats and lake shores 
surrounded by lodgepole (Pinus contorta) or whitebark (P. albicaulis) 
pines (Camp 1916, pp. 59-62). They are most often found in areas with 
thick meadow vegetation or patches of low willows (Salix spp.) 
(Mullally 1953, pp. 182-183). Liang (2010, p. 81) observed Yosemite 
toads most frequently associated with (in order of preference): wet 
meadows, alpine-dwarf scrub, red fir (Abies magnifica), water, 
lodgepole pine, and subalpine conifer habitats.
    Yosemite toads were found as often at large as at small sites 
(Liang 2010, p. 19), suggesting that this species is capable of 
successfully utilizing small habitat patches. Liang also found that 
population persistence was greater at higher elevations, with an 
affinity for relatively flat sites with a southwesterly aspect (Liang 
2010, p. 20). These areas receive higher solar radiation and are 
capable of sustaining hydric (wet), seasonally ponded, and mesic 
(moist) breeding and rearing habitat. The Yosemite toad is more common 
in areas with less variation in mean annual temperature, or more 
temperate sites with less climate variation (Liang 2010, pp. 21-22).
    Adults are thought to be long-lived, and this factor allows for 
persistence in variable conditions and more marginal habitats where 
only periodic good years allow high reproductive success (USFS et al. 
2009, p. 27). Females have been documented to reach 15 years of age, 
and males as many as 12 years (Kagarise Sherman and Morton 1993, p. 
195); however the average longevity of the Yosemite toad in the wild is 
not known. Jennings and Hayes (1994, p. 52) indicated that females 
begin breeding at ages four to six, while males begin breeding at ages 
three to five.
    Adults tend to breed at a single site and appear to have high site-
fidelity (Liang 2010, p. 99), although individuals will move between 
breeding areas (Liang 2010, p. 52). Breeding habitat includes the edges 
of wet meadows and slow-flowing streams (Jennings and Hayes 1994, pp. 
50-53). Tadpoles have also been observed in shallow ponds and shallow 
areas of lakes (Mullally 1953, pp. 182-183).
    Males exit burrows first, and spend more time in breeding pools 
than females, who do not breed every year (Kagarise Sherman and Morton, 
1993, p. 196). It is suggested that higher lipid storage in females, 
which enhances overwinter survival, also precludes the energetic 
expense of breeding every year (Morton 1981, p. 237). The Yosemite toad 
is a prolific breeder, laying many eggs immediately at snowmelt. This 
is accomplished in a short period of time, coinciding with water levels 
in meadow habitats and ephemeral pools they use for breeding. Female 
toads lay approximately 700-2,000 eggs in two strings (one from each 
ovary) (USFS et al. 2009, p. 21). Females may split their egg clutches 
within the same pool, or even between different pools, and may lay eggs 
communally with other toads (USFS et al. 2009, p.22).
    Eggs hatch within 3-15 days, depending on ambient water 
temperatures (Kagarise Sherman 1980, pp. 46-47; Jennings and Hayes 
1994, p. 52). Tadpoles typically metamorphose around 40-50 days after 
fertilization, and are not known to overwinter (Jennings and Hayes 
1994. p. 52). Tadpoles are black in color, tend to congregate together 
(Brattstrom 1962, pp. 38-46) in warm shallow waters during the day 
(Cunningham 1963, pp. 60-61), and then retreat to deeper waters at 
night (Mullaly 1953, p. 182). Rearing through metamorphosis takes 
approximately 5-7 weeks after eggs are laid (USFS et al. 2009, p. 25).
    Reproductive success is dependent on the persistence of tadpole 
rearing sites and conditions for breeding, egg deposition, hatching, 
and rearing to metamorphosis (USFS et al. 2009, p. 23). Given their 
association with shallow, ephemeral habitats, Yosemite toads are 
susceptible to droughts and weather extremes. Abiotic factors leading 
to mortality (such as freezing or desiccation) appear to be more 
significant during the early life stages of toads, while biotic factors 
(such as predation) are probably more prominent factors during later 
life stages (USFS et al. 2009, p. 30). However, since adult toads lead 
a much more inconspicuous lifestyle, direct observation of adult 
mortality is difficult and it is usually not possible to determine 
causes of adult mortality.
    Adult Yosemite toads are most often observed near water, but only 
occasionally in water (Mullally and Cunningham 1956b, pp. 57-67). Moist 
upland areas such as seeps and springheads are important summer non-
breeding habitats for adult toads (Martin 2002, pp. 1-3). The majority 
of their life is spent in the upland habitats proximate to their 
breeding meadows. They use rodent burrows for overwintering and 
probably for temporary refuge during the summer (Jennings and Hayes 
1994, pp. 50-53), and they spend most of their time in burrows (Liang 
2010, p. 95). They also use spaces under surface objects, including 
logs and rocks, for temporary refuge (Stebbins 1951, pp. 245-248; 
Karlstrom 1962, pp. 9-10). Males and females also likely inhabit 
different areas and habitats when not breeding, and females tend to 
move farther from

[[Page 24499]]

breeding ponds than males (USFS et al. 2009, p. 28).
    Yosemite toads can move farther than 1 km (0.63 mi) from their 
breeding meadows (average movement is 275 m (902 ft)), and they utilize 
terrestrial environments extensively (Liang 2010, p. 85). The average 
distance traveled by females is twice as far as males, and home ranges 
for females are 1.5 times greater than those for males (Liang 2010, p. 
94). Movement into the upland terrestrial environment following 
breeding does not follow a predictable path, and toads tend to traverse 
longer distances at night, perhaps to minimize evaporative water loss 
(Liang 2010, p. 98). Martin (2008, p. 123) radio-tracked adult toads 
during the active season and found that on average toads traveled a 
total linear distance of of 494 m (1,620 ft) within the season, with 
minimum travel distance of 78 m (256 ft) and maximum of 1.76 km (1.09 
mi).

Historical Range and Distribution

    The historical range of the Yosemite toad in the Sierra Nevada 
extended from the Blue Lakes region north of Ebbetts Pass (Alpine 
County) to just south of Kaiser Pass in the Evolution Lake/Darwin 
Canyon area (Fresno County) (Jennings and Hayes 1994, pp. 50-53). 
Yosemite toad habitat historically spanned elevations from 1,460 to 
3,630 m (4,790 to 11,910 ft) (Stebbins 1985, pp. 72; Stephens 2001, p. 
12).

Current Range and Distribution

    The current range of the Yosemite toad, at least in terms of 
overall geographic extent, remains largely similar to the historical 
range defined above (USFS et al. 2009, p. 41). However, within that 
range, toad habitats have been degraded and may be decreasing in area 
as a result of conifer encroachment and livestock grazing (see Factor A 
below). The vast majority of the Yosemite toad's range is within 
Federal land. Figure 2, Estimated Range of Yosemite Toad, displays a 
range map for the species.
BILLING CODE 4310-55-P

[[Page 24500]]

[GRAPHIC] [TIFF OMITTED] TP25AP13.029

BILLING CODE 4310-55-C

Population Estimates and Status

    Baseline data on the number and size of historical Yosemite toad 
populations are limited, and historic records are largely based on 
accounts from field notes, or pieced together through museum 
collections. Systematic survey information across the range of the 
species largely follows the designation of the Yosemite toad as a 
candidate species under the Act. From these recent inventories, 
Yosemite toads have been found at 469 localities collectively on six 
National Forests (more sites than previously known), indicating that 
the species is still widespread throughout its range (USFS et al. 2009, 
p. 40). These inventories were conducted to determine toad presence or 
absence (they were not censuses), and the referenced figure does not 
explicitly compare historic sites to recent surveys. Moreover, single-
visit surveys of toads are unreliable as indices of abundance because 
timing is so critical to the presence of detectable life stages (USFS 
et al. 2009, p. 41; Liang 2010, p. 10). Given these considerations, 
conclusions about population trends, abundance, or extirpation rates 
are not possible relative to this specific dataset.
    One pair of studies allows us to compare current distribution with 
historic distributions and indicates that large reductions have 
occurred. In 1915 and 1919, Grinnell and Storer (1924, pp. 657-660) 
surveyed for vertebrates at 40 sites along a 143-km (89-mi) west-to-
east transect across the Sierra Nevada, through Yosemite National Park, 
and found Yosemite toads at 13 of those sites. Drost and Fellers (1996, 
pp. 414-425) conducted more thorough surveys, specifically for 
amphibians, at 38 of the Grinnell and Storer sites plus additional 
nearby sites in 1992. Drost and Fellers found that Yosemite toads were 
absent from 6 of 13 sites where they had been

[[Page 24501]]

found in the original Grinnell and Storer survey. Moreover, at the 
sites where they were present, Yosemite toads occurred in very low 
numbers relative to general abundance reported in the historical record 
(Grinnell and Storer 1924, pp. 657-660). Specifically, by the early 
1990s, the species was either undetectable or had declined in numbers 
at 9 of 13 (69 percent) of the Grinnell and Storer (1924, pp. 657-660) 
sites.
    Another study comparing historic and current occurrences also found 
a large decline in Yosemite toad distribution. In 1990, David Martin 
surveyed 75 sites throughout the range of the Yosemite toad for which 
there were historical records of the species' presence. This study 
found that 47 percent of historically occupied sites showed no evidence 
of any life stage of the species (Stebbins and Cohen 1995, pp. 213-
215). This result suggests a rangewide decline to about one half of 
historical sites, based on occupancy alone.
    A third study comparing historic and recent surveys indicates 
declines in Yosemite toad distribution. Jennings and Hayes (1994, pp. 
50-53) reviewed the current status of Yosemite toads using museum 
records of historic and recent sightings, published data, and 
unpublished data and field notes from biologists working with the 
species. They estimated a loss of over 50 percent of former Yosemite 
toad locations throughout the range of the species (based on 144 
specific sites).
    The only long-term, site-specific population study for Yosemite 
toads documented a dramatic decline over 2 decades of monitoring. 
Kagarise Sherman and Morton (1993, pp. 186-198) studied Yosemite toads 
at Tioga Pass Meadow (Mono County, California) from 1971 through 1991 
(with the most intensive monitoring through 1982). They documented a 
decline in the average number of males entering the breeding pools from 
258 to 28 during the mid-1970s through 1982. During the same time 
period, the number of females varied between 45 and 100, but there was 
no apparent trend in number observed. During the 1980s, it appeared 
that both males and females continued to decline, and breeding activity 
became sporadic. By 1991, they found only one male and two egg masses. 
The researchers also found similar population declines in local 
nonbreeding habitat.
    Kagarise Sherman and Morton (1993, pp. 186-198) also conducted 
occasional surveys of six other populations in the eastern Sierra 
Nevada. Five of these populations showed long-term declines that were 
evident beginning between 1978 through 1981, while the sixth population 
held relatively steady until the final survey in 1990, at which time it 
dropped. In 1991, E.L. Karlstrom revisited the site where he had 
studied a breeding population of Yosemite toads from 1954 to 1958 (just 
south of Tioga Pass Meadow within Yosemite National Park), and found no 
evidence of toads or signs of breeding (Kagarise Sherman and Morton 
1993, pp. 190).
    The most reliable information about Yosemite toad population status 
and trends is the USFS SNAMPH. This study is designed to provide 
statistical comparisons across 5-year monitoring cycles with at 134 
watersheds (Brown et al. 2011, pp. 3-4). This approach allows 
researchers to assess trends for the entire range of the toad, rather 
than make year-to-year comparisons at limited survey sites (C. Brown 
2012, pers. comm.). The results of this assessment indicate the species 
has declined from historical levels, with Yosemite toads occurring in 
only 12 percent of watersheds where they existed prior to 1990. This 
study also found that breeding currently occurs in an estimated 22 
percent of watersheds within their current estimated range. 
Additionally, the study found that breeding was occurring in 81 percent 
of the watersheds that were occupied from 1990-2001, suggesting that 
the number of locations where breeding occurs has continued to decline 
(Brown et al. 2011, p. 4).
    Moreover, overall abundances in the intensively monitored 
watersheds were very low (fewer than 20 males per meadow per year) 
relative to other historically reported abundances of the species 
(Brown et al. 2011, p. 4). Brown et al. (2011, p. 35) suggest that 
populations are now very small across the range of the species. They 
found only 18 percent of occupied survey watersheds rangewide had 
``large'' populations during their monitoring over the past decade 
(more than 1,000 tadpoles or 100 of any other lifestage detected at the 
time of survey). The researchers interpret this data, in combination 
with documented local population declines from other studies (see 
above), to support the hypothesis that population declines have 
occurred rangewide (Brown et al. 2012, p. 11).

Summary of Factors Affecting the Species

    Section 4 of the Act (16 U.S.C. 1533), and its implementing 
regulations at 50 CFR part 424, set forth the procedures for adding 
species to the Federal Lists of Endangered and Threatened Wildlife and 
Plants. Under section 4(a)(1) of the Act, we may list a species based 
on any of the following five factors: (A) The present or threatened 
destruction, modification, or curtailment of its habitat or range; (B) 
overutilization for commercial, recreational, scientific, or 
educational purposes; (C) disease or predation; (D) the inadequacy of 
existing regulatory mechanisms; and (E) other natural or manmade 
factors affecting its continued existence. Listing actions may be 
warranted based on any of the above threat factors, singly or in 
combination. Each of these factors is discussed below.

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

    The habitat comprising the current range of the Yosemite toad is 
generally characterized by low levels of physical disturbance (there is 
little to no current development pressure). However, these areas are 
also generally more sensitive to perturbation and take longer to 
recover from disturbances due to reduced growing seasons and harsher 
environmental conditions. Past management and development activity has 
played a role in the degradation of certain habitat features within the 
Sierra Nevada. Anthropogenic activities within these habitats include 
grazing, timber harvest, fuels management, recreation, and water 
development. Collectively, these factors continue to degrade habitat 
conditions for the toad, although the contribution of this factor to 
population dynamics has probably lessened over time, perhaps because 
toad populations disappear from impacted areas first, but also through 
improved management practices implemented in recent decades.
Meadow Habitat Loss and Degradation
    Some of the threat factors associated with grazing activities for 
the mountain yellow-legged frogs (see their Summary of Factors 
Affecting the Species section, above) also apply to Yosemite toads. 
However, there are differences based on the Yosemite toad's affinity 
for meadow and pool habitats versus the lakes and streams frequented by 
mountain yellow-legged frogs. Meadow habitat quality in the Western 
United States, and specifically the Sierra Nevada, has been degraded by 
various stressors over the last century (Stillwater Sciences 2008, pp. 
1-53; Halpern et al. 2010, pp. 717-732; Vale 1987, pp. 1-18; Ratliff 
1985, pp. i-48). These various stressors have contributed to erosion 
and stream incision, leading to meadow dewatering and encroachment by 
invasive vegetation (Menke et al. 1996, pp. 25-28; Linquist 2000, p. 
2). The legacy of these impacts remains extant to this day

[[Page 24502]]

in the ecosystems of the high Sierra Nevada (Vankat and Major 1978, pp. 
386-397).
    Given the reliance of the Yosemite toad on these meadow and pool 
habitats for breeding, rearing, and adult survival, it is logical to 
conclude that the various stressors have had an indirect effect on the 
viability of Yosemite toad populations via degradation of their 
habitat. Loss of connectivity of habitats leads to further isolation 
and population fragmentation. Due to constraints of their physiology, 
low mobility, and higher site fidelity, many amphibian populations may 
be unable to recolonize after local extirpations (Blaustein et al. 
1994a, p. 60).
    Since the existence of meadows is largely dependent on their 
hydrologic setting, most meadow degradation is due fundamentally to 
hydrologic alterations (Stillwater Sciences 2008, p. 13). There are 
many drivers of hydrologic alterations in meadow ecosystems. Historic 
water development and ongoing management has physically changed the 
underlying hydrologic landscape. Diversion and irrigation ditches 
formed a vast network that altered local and regional stream hydrology. 
Timber harvest and associated road construction further affected 
erosion and sediment delivery patterns in rivers and meadow streams. 
Changes in the pre-settlement fire regime, fire suppression, and an 
increase in the frequency of large wildfires due to excessive fuel 
buildup, introduced additional disturbance pressure to the meadows of 
the Sierra Nevada (Stillwater Sciences 2008, p. 13). Many meadows now 
have downcut stream courses, compacted soils, altered plant community 
compositions, and diminished wildlife and aquatic habitats (SNEP 1996, 
pp. 120-121). Meadow dewatering by these changes within the watershed 
has facilitated these shifts in the vegetative community. Finally, 
climate variability has also played a role in the conifer encroachment.
    Land uses causing channel erosion threaten Sierra Nevada meadows. 
These threats include erosive activities within the watershed upslope 
of the meadow, along with impacts from land use directly in the meadows 
themselves. Compaction of meadow soils by roads and/or intensive 
trampling (for example, overgrazing) can reduce infiltration, 
accelerate surface run-off, and thereby lead to channel incision (Menke 
et al. 1996, pp. 25-28). Mining, overgrazing, timber harvesting, and 
railroad and road construction and maintenance have contributed to 
watershed degradation, resulting in accelerated erosion, sedimentation 
in streams and reservoirs, meadow dewatering, and degraded terrestrial 
and aquatic habitats (Linquist 2000, p. 2). Deep incision has been 
documented in several meadows in the Sierra Nevada. One example is 
Halstead Meadow in Sequoia National Park, where headcutting exceeds 10 
feet in many areas and is resulting in widening channels, erosion in 
additional meadows, and a lowered water table (Cooper 2006, p. 1).
    The hydrologic effects of stream incision on the groundwater system 
may significantly impact groundwater storage, affecting late summer 
soil moisture and facilitating vegetation change (Bergmann 2004, pp. 
24-31). For example, in the Last Chance Watershed in the northern 
Sierra Nevada, logging, overgrazing, and road/railroad construction 
have caused stream incision, resulting in dewatering of riparian meadow 
sediments and a succession from native wet meadow vegetation to 
sagebrush and dryland grasses (Loehide and Gorelick 2007, p. 2). A 
woody shrub (Artemisia rothrockii) is invading meadows as channel 
incision causes shallow-water-dependent herbs to die back, allowing 
shrub seedlings to establish in disturbed areas during wet years 
(Darrouzet-Nardi et al. 2006, p. 31).
    Mountain meadows in the western United States and Sierra Nevada 
have also been progressively colonized by trees (Thompson 2007, p. 3; 
Vale 1987, p. 6), with an apparent pattern of encroachment during two 
distinct periods in the late 1800s and mid 1900s (Halpern et al. 2010, 
p. 717). This trend has been attributed to a number of factors, 
including climate, changes in fire regime, and cessation of sheep 
grazing (Halpern et al. 2010, pp. 717-718; Vale 1987, pp. 10-13), but 
analyses are limited to correlational comparisons and research results 
are mixed, so the fundamental contribution of each potential driver 
remains uncertain. We discuss the contribution of these factors to 
habitat loss and degradation for the Yosemite toad below.
Livestock Use (Grazing) Effects to Meadow Habitat
    Grazing of livestock in Sierra Nevada meadows and riparian areas 
(rivers, streams, and adjacent upland areas that directly affect them) 
began in the mid-1700s with the European settlement of California 
(Menke et al. 1996, p. 7). Following the gold rush of the mid-1800s, 
grazing increased to a level exceeding the carrying capacity of the 
available range, causing significant impacts to meadow and riparian 
ecosystems (Meehan and Platts 1978, p. 275; Menke et al. 1996, p. 7). 
By the turn of the 20th century, high Sierra Nevada meadows were 
converted to summer rangelands for grazing cattle, sheep, horses, 
goats, and pigs, although the alpine areas were mainly grazed by sheep 
(Beesley 1996, pp. 7-8; Menke et al. 1996, p. 14). Stocking rates of 
both cattle and sheep in Sierra meadows in the late 19th and early 20th 
centuries were very heavy (Kosco and Bartolome 1981, pp. 248-250), and 
grazing severely degraded many meadows (Ratliff 1985, pp. 26-31; Menke 
et al. 1996, p. 14). Grazing impacts occurred rangewide, as cattle and 
sheep were driven virtually everywhere in the Sierra Nevada where 
forage was available (Kinney 1996, pp. 37-42; Menke et al. 1996, p. 
14).
    Grazing within the National Forests has continued into modern 
times, with reduction in activity (motivated by resource concerns, 
conflicts with other uses, and deteriorating range conditions) 
beginning in the 1920s. A brief wartime increase in the 1940s followed, 
before activity continued to be scaled back beginning in the 1950s 
through the early 1970s. However, despite these reductions, grazing 
still exceeded sustainable capacity in many areas (Menke et al. 1996, 
p. 9; UC 1996a, p. 115). Currently, approximately 33 percent of the 
estimated range of the Yosemite toad is within active USFS grazing 
allotments (USFS 2008, geospatial data). While stocking rates have been 
reduced or eliminated in most areas, many meadows remain disturbed from 
the historical period of heavy grazing, with legacy effects including 
eroded channels, non-vegetated patches from heavy trampling and 
grazing, altered plant composition, and reduced plant production 
(Vankat and Major 1978, pp. 386-397; Ratliff 1985, pp. ii-iii).
    Livestock grazing in the Sierra Nevada has been widespread for so 
long that, in most places, no ungrazed areas are available to 
illustrate the natural condition of the habitat (Kattelmann and Embury 
1996, pp. 16-18). Dull (1999, p. 899) conducted stratigraphic pollen 
analysis (identification of pollen in sedimentary layers) in mountain 
meadows of the Kern Plateau, and found significant vegetation changes 
attributable to sheep and cattle grazing by 1900 (though fire regime 
change was also implicated; see below). This degradation is widespread 
across the Sierra Nevada. Cooper 2006 (p. 1) reports that 50 to 80 
percent of grazed meadows now dominated by dry meadow plants were 
formerly wet meadows (Cooper 2006, p. 1).
    Overgrazing has been associated with accelerated erosion and 
gullying of

[[Page 24503]]

meadows (Kattelmann 1996, p. 13), which leads to siltation and more 
rapid succession of meadows. Grazing can cause erosion by disturbing 
the ground, damaging and reducing vegetative cover, and destroying peat 
layers in meadows, which lowers the groundwater table and summer flows 
(Armour et al. 1994, pp. 9-12; Martin 2002, pp. 1-3; Kauffman and 
Krueger 1984, pp. 431-434). Downcut channels, no longer connected to 
the historic, wide floodplains of the meadow, instead are confined 
within narrow, incised channels. Downstream, formerly perennial (year-
round) streams often become intermittent or dry due to loss of water 
storage capacity in the meadow aquifers that formerly sustained them 
(Lindquist et al. 1997, pp. 7-8). Many examples exist like the one at 
Cottonwood Creek (in the Feather River watershed) where overgrazing of 
meadow vegetation and soil erosion of streambanks led to meadow channel 
incision (Linquist 2000, pp. 1-7; Odion et al. 1988, pp. 277-292, 
Schoenherr 1992, pp. 167-227).
    Heavy grazing can alter vegetative species composition and 
contribute to lodgepole pine (Pinus contorta) invasion (Ratliff 1985, 
pp. 33-36). Lowering of the water table facilitates encroachment of 
conifers into meadows. Gully formation and lowering of water tables, 
changes in the composition of herbaceous vegetation, increases in the 
density of forested stands, and the expansion of trees into areas that 
formerly were treeless have been documented in California Wilderness 
areas and National Parks (Cole and Landres 1996, p. 171). This invasion 
has been attributed to sheep grazing, though the phenomenon has been 
observed on both ungrazed meadows and on meadows grazed continually 
since about 1900 (Ratliff 1985, p. 35), suggesting an interaction with 
other drivers (see ``Fire Management Regime Effects to Meadow 
Habitats'' and ``Climate Effects to Meadow Habitat'' below).
    Due to the long history (Menke et al. 1996, Ch. 22 pp. 1-52) of 
livestock and packstock grazing in the Sierra Nevada and the lack of 
historical Yosemite toad population size estimates, it is impossible to 
establish a reliable quantitative estimate for the historical 
significance and contribution of grazing on Yosemite toad populations. 
However, because of the documented negative effects of livestock on 
Yosemite toad habitat, and the documented direct mortality caused by 
livestock, the decline of some populations of Yosemite toad has been 
attributed to the effects of livestock grazing (Jennings and Hayes 
1994, pp. 50-53; Jennings 1996, pp. 921-944). Because Yosemite toad 
breeding habitat is in shallow waters at high elevation, the habitat is 
believed to be more vulnerable to changes in hydrology caused by 
grazing (Knapp 2002c, p. 1; Martin 2002, pp. 1-3; USFS et al. 2009, p. 
62).
    The influence of grazing on toad populations in recent history is 
uncertain, despite more available data on land use and Yosemite toad 
occurrence. In 2005, the USFS began a long-term study to assess the 
effects of grazing on Yosemite toads (Allen Diaz et al. 2010, pp. 1-
45). The researchers assessed: (1) Whether livestock grazing under 
SNFPA Riparian Standards and Guidelines has a measurable effect on 
Yosemite toad populations and (2) effects of livestock grazing 
intensity on key habitat components that affect survival and 
recruitment of Yosemite toad populations. SNFPA standards and 
guidelines limit livestock utilization of grass and grass-like plants 
to a maximum of 40 percent (or a minimum 4-inch stubble height) (USDA 
2004, p. 56). This study did not detect an effect from grazing activity 
on young-of-year toad density or breeding pool occupancy, water 
quality, or cover (when grazing under SNFPA Riparian Standards and 
Guidelines) (Allen Diaz et al. 2010, p. 1).
    However, the design of these studies did not include direct 
measurements of toad survival (for example, mark-recapture analysis of 
population trends), and the design was limited in numbers of years and 
treatment replicates. It is plausible that for longer-lived species 
with irregular female breeding activity over the time course of this 
particular study, statistical power was not sufficient to discern a 
treatment effect. Further, there may be a time lag between effect and 
discernible impacts, and significant confounding variability in known 
drivers such as interannual variation in climate.
    Additionally, the experimental design in the Allen Diaz study 
tested the hypothesis that forest management guidelines (at 40 percent 
use threshold) were impacting toad populations, and this limited some 
analyses and experimental design to sites with lower treatment 
intensities. Researchers reported annual utilization by cattle ranging 
from 10-48 percent, while individual meadow use ranged from 0-76 
percent (the SNFPA allowable use is capped at 40 percent) (Allen Diaz 
et al. 2010, p. 5). As a result of the study design, the Allen Diaz 
study does not provide sufficient information on the impacts of grazing 
on Yosemite toads above the prescribed management guidelines. It is 
also not clear to what extent brief episodes of intense use (such as in 
cattle gathering areas) have as negative impacts on toads, or over what 
percentage of the grazed meadow landscape such heavier usage may occur.
    The researchers observed significant variation in young-of-year 
occupancy in pools between meadows and years, and within meadows over 
years (Allen Diaz et al. 2010, p. 7). This variability would likely 
mask treatment effects, unless the grazing variable was a dominant 
factor driving site occupancy, and the magnitude of the effect was 
quite severe. Further, Lind et al. (2011, pp. 12-14) report 
statistically significant negative (inverse) relationships for tadpole 
density and grazing intensity (tadpole densities decreased when percent 
use exceeded between 30 and 40 percent). This result supports the 
hypothesis that grazing at intensities approaching and above the 40 
percent threshold can negatively affect Yosemite toad populations.
    Allen Diaz et al. (2010, p. 2) found that toad occupancy is 
strongly driven by meadow wetness (hydrology) and suggested attention 
should focus on contemporary factors directly impacting meadow wetness, 
such as climate, fire regime changes, and conifer encroachment (see 
Factor A above). Lind et al. (2011, pp. 12-14) noted a positive 
relationship between meadow dryness and livestock use (cattle prefer 
drier meadows), and also found that the proportion of Yosemite toad-
occupied pools and tadpole and young-of-year densities declined in 
drier sites (toads prefer wetter meadows). The researchers suggest that 
this provides for some segregation of toad and livestock use in meadow 
habitats, so that at least direct mortality threats may be mitigated by 
behavioral isolation.
    The available grazing studies focus on breeding habitat (wet 
meadows) and do not consider impacts to upland habitats. The USFS 
grazing guidelines for protection of meadow habitats of the Yosemite 
toad include fencing breeding meadows, but they do not necessarily 
protect upland habitat. Grazing removes vegetative cover, and surveys 
have shown reductions in the number of Yosemite toads in an area after 
the herbaceous cover was grazed (Martin 2008, p. 298). Grazing can also 
degrade or destroy moist upland areas used as nonbreeding habitat by 
Yosemite toads (Martin 2008, pp. 159), especially when nearby meadow 
and riparian areas have been fenced to exclude livestock. Livestock may 
also collapse rodent burrows used by Yosemite toads as cover and 
hibernation sites (Martin 2008, p. 159) or disturb toads and

[[Page 24504]]

disrupt their behavior. Martin (2008, pp. 305-306) observed that 
grazing significantly reduced vegetation height, and since these areas 
are not protected by current grazing guidelines, deduced that cattle 
grazing is having a negative effect on terrestrial life stage 
survivorship in Yosemite toads. This problem was exacerbated as fenced 
areas effectively shifted grazing activity to upland areas actively 
used by terrestrial life stages of the Yosemite toad (Martin 2008, p. 
306). Based on the limitations of the study as described above, we find 
the initial results from Allen Diaz et al. (2010, pp. 1-45) to be 
inconclusive to discern the impacts of grazing on Yosemite toad 
populations rangewide.
    Although we lack definitive data to assess the link between 
Yosemite toad population dynamics and habitat degradation by livestock 
grazing activity (see Factor E below), in light of the documented 
impacts to meadow habitats (including effects on local hydrology) from 
grazing activity in general, we consider this threat prevalent with 
moderate impacts to the Yosemite toad and a potential limiting factor 
in population recovery rangewide. In addition, given the potential for 
negative impacts from heavy use, and the vulnerability of toad habitat 
should grazing management practices change with new management plans, 
we expect this threat to continue into the future.
Roads and Timber Harvest Effects to Meadow Habitat
    Road construction and use, along with timber harvest activity, may 
impact Yosemite toad habitat via fragmentation, ground disturbance, and 
soil compaction or erosion (Helms and Tappeiner 1996, pp. 439-476). 
These activities, similar to overgrazing, may lead to increased rates 
of siltation and succession of wet meadows, contributing to the loss of 
breeding habitats for the Yosemite toad.
    Prior to the formation of National Parks and National Forests, 
timber harvest was widespread and unregulated in the Sierra Nevada; 
however, most cutting occurred below the current elevation range of the 
Yosemite toad (University of California at Davis (UCD) UC 1996b, pp. 
17-45). Between 1900 and 1950, most timber harvest occurred in old 
growth forests on private land (UC 1996b, pp. 17-45). The majority of 
roads in National Forests of the Sierra Nevada were built between 1950 
and 1990, to support major increases in timber harvest on National 
Forests and also at higher elevations (USDA 2001a, p. 445).
    It is plausible to hypothesize that the majority of timber harvest, 
road development, and associated management impacts (see ``Fire 
Management Regime Effects to Meadow Habitats'' below) to Yosemite toads 
would have taken place during this expansion period in the latter half 
of the 20th century. However, the magnitude (and perhaps even whether 
it is positive or negative) of this effect would likely be a function 
of site-specific parameters, and the level of intensity of each 
particular land use. In contrast to overharvest, it is also possible 
that moderate harvest activity adjacent to meadow habitats could 
benefit meadows and upland habitat by discouraging encroachment and 
opening the forest canopy (Liang et al. 2010, p. 16). Despite this 
possibility, there is no evidence that the current level of timber 
harvest occurring within watersheds currently inhabited by the Yosemite 
toad is adversely affecting habitat. Therefore the best available 
scientific and commercial information does not indicate whether ongoing 
road construction and maintenance or timber harvest are significant 
threats to the Yosemite toad.
Fire Management Regime Effects to Meadow Habitats
    Fire management refers to activities over the past century to 
combat forest fires. Historically, it is known that American Indians 
regularly burned the mountains (Parsons and Botti 1996, p. 29), and in 
the latter 19th century, the active use of fire to eliminate tree 
canopy in favor of forage plants continued by sheepherders (Kilgore and 
Taylor 1979, p. 139). Beginning in the 20th century, land management in 
the Sierra Nevada shifted to focus on fire suppression as a guiding 
policy (UC 2007, p. 10).
    Long-term fire suppression has influenced forest structure and 
altered ecosystem dynamics in the Sierra Nevada. In general, the time 
between fires is now much longer than it was historically, and live and 
dead fuels are more abundant and continuous (USDA 2001a, p. 35). It is 
not clear how this has precisely affected Yosemite toad populations; 
however Liang et al. (2010, p. 16) observed that toads were less likely 
to occur in areas where the fire regime was significantly altered from 
historical conditions, and suggested that the toads are affected by 
some unknown or unmeasured factors related to fire management.
    Evidence indicates that fire plays a significant role in the 
evolution and maintenance of meadows of the Sierra Nevada. Under 
natural conditions, conifers are excluded from meadows by fire and 
saturated soils. Small fires thin and/or destroy encroaching conifers, 
while large fires are believed to determine the meadow-forest boundary 
(Vankat and Major 1978, p. 394; Parsons and DeBenedetti 1979, pp. 29-
31). Fire is thought to be important in maintaining open aquatic and 
riparian habitats for amphibians in some systems (Russel et al. 1999, 
pp. 374-384), and fire suppression may have thereby contributed to 
conifer encroachment on meadows (Chang 1996, pp. 1071-1099; NPS 2002, 
p. 1).
    While no definitive studies have confirmed a link between fire 
management and rangewide population decline of the Yosemite toad, 
circumstantial evidence to date suggests that historic fire suppression 
has been a factor underlying meadow encroachment that has reduced the 
suitability of these areas to sustain the life history of the Yosemite 
toad. Given this link and based on the best available information, we 
find it likely that habitat modification due to reduced fire frequency 
is an extant threat to Yosemite toad habitat, acting with moderate 
prevalence.
Recreation Effects to Meadow Habitat
    Recreational activities take place throughout the Sierra Nevada, 
and they can have significant negative impacts on wildlife and their 
habitats (USDA 2001a, pp. 221, 453-500). Recreation can cause 
considerable impact to western U.S. Wilderness Areas and National Parks 
even with light use, with recovery only occurring after considerable 
periods of non-use (USFS et al. 2009, p. 66). Heavy foot traffic in 
riparian areas tramples vegetation, compacts soils, and can physically 
damage streambanks. Trails (foot, horse, bicycle, or off-highway motor 
vehicle) compact the soil, displace vegetation, and increase erosion, 
thereby potentially lowering the water table (Kondolph et al. 1996, pp. 
1009-1026).
    Packstock use has similar effects to those discussed for livestock 
grazing, although this risk factor is potentially more problematic as 
this land use typically takes place in more remote and higher elevation 
areas occupied by Yosemite toads, and packstock tend to graze in many 
of the same locations that the toads prefer (USFS et al. 2009, p. 65). 
Currently, there are very few studies on the effects of packstock 
grazing on amphibians, especially in the Sierra Nevada. It is not clear 
how well studies on livestock grazing can be extrapolated to packstock, 
and even then, shorter-term experiments may not show effects if 
landscapes have already

[[Page 24505]]

been pushed beyond a threshold of effect (Brooks 2012, pers. comm.). 
However, current guidelines in the National Parks limit trips to 20-25 
animals, regulated under conditional use permits (Brooks 2012, pers. 
comm.). In general, National Parks and commercial users are reducing 
their usage, so packstock impacts, if they occur, are declining within 
the National Parks (Berlow 2012, pers. comm.).
    The effects of recreational activities on the Yosemite toad are not 
quantified, but they may have impacts in certain areas and under 
certain conditions. For example, where foot traffic or vehicle activity 
adjacent to occupied meadows is more prevalent, erosion and channel 
incision could result. The cumulative impact to the species from 
localized threats associated with recreational impacts is not possible 
to quantify, but we do know that recreation is the fastest growing use 
of National Forests (USDA 2001a, pp. 453-500). The relative sensitivity 
of high-elevation sites to recreational use makes them vulnerable to 
disturbance, and the significance of this impact is expected to 
increase into the future as recreational use continues to increase. 
Nevertheless, collectively at this time, we consider recreational 
activities to be a low prevalence threat across the range of the 
Yosemite toad.
Dams and Water Diversions Effects to Meadow Habitat
    Diversion and irrigation ditches form a vast network that altered 
local and regional stream hydrology in the Sierra Nevada (SNEP 1996, p. 
120). Several artificial lakes are located in or above Yosemite toad 
habitat, most notably Edison, Florence, Huntington, Courtright, and 
Wishon Reservoirs. By altering the timing and magnitude of water flows, 
these reservoirs have caused changes in hydrology that may have altered 
Yosemite toad habitat. Changes in water flows have increased water 
levels upstream of the reservoirs, which may have reduced the 
suitability of shallow water habitats necessary for egg laying and 
allowed fish competitors into those habitats. Moreover, water level 
declines caused by drawdown of reservoirs can lead to the mortality of 
eggs and tadpoles by stranding and desiccation.
    The artificial lakes (reservoirs) mentioned above were probably 
created within, and inundated, Yosemite toad habitat, and most native 
Sierra Nevada amphibians cannot live in or move through reservoirs 
(Jennings 1996, pp. 921-944). Therefore, reservoirs represent both a 
loss of habitat and a barrier to dispersal and gene flow. These factors 
have likely contributed to the decline of the Yosemite toad and 
continue to pose a risk to the species. Impacts due to increasing 
effects from climate change, or new water supply development in 
response to such effects, may exacerbate this risk in the future. The 
contribution of reservoir construction and operation to population 
losses was likely of high historical significance in these developed 
areas, but less so in the current extent of the Yosemite toad's 
(remnant) range. Therefore, currently, we consider this threat to be of 
low prevalence to the Yosemite toad across its range.
Climate Effects to Meadow Habitat
    Different studies indicate that multiple drivers are behind the 
phenomenon of conifer encroachment on meadows. The first factor 
affecting the rate of conifer encroachment on meadow habitats, fire 
suppression, was discussed above. Climate variability is another factor 
affecting the rate of conifer encroachment on meadow habitats. A study 
by Franklin et al. (1971, p. 215) concluded that fire had little 
influence on meadow maintenance of their study area, while another 
study concluded that climate change is a more likely explanation for 
encroachment of trees into the adjacent meadow at their site, rather 
than fire suppression or changes in grazing intensity (Dyer and 
Moffett, 1999, pp. 444).
    Climatic variability is strongly correlated with encroachment of 
dry subalpine meadows (Jakubos and Romme 1993, p. 382). In the Sierra 
Nevada, most lodgepole pine seedlings become established during years 
of low snowpack when soil meadow moisture is reduced (Wood 1975, p. 
129). The length of the snow-free period may be the most critical 
variable in tree invasion of subalpine meadows (Franklin et al. 1971, 
pp. 222), with the establishment of a good seed crop, followed by an 
early snowmelt, resulting in significant tree establishment. It is 
apparent that periods of low snowpack and early melt may in fact be 
necessary for seedling establishment (Ratliff, 1985, p. 35). Millar et 
al. (2004, p. 181) reported that increased temperature, coupled with 
reduced moisture availability in relation to large-scale temporal 
shifts in climate, facilitated the invasion of 10 subapline meadows 
studied in the Sierra Nevada.
    Our analyses under the Act include consideration of ongoing and 
projected changes in climate. The terms ``climate'' and ``climate 
change'' are defined by the Intergovernmental Panel on Climate Change 
(IPCC). ``Climate'' refers to the mean and variability of different 
types of weather conditions over time, with 30 years being a typical 
period for such measurements, although shorter or longer periods also 
may be used (IPCC 2007, p. 78). The term ``climate change'' thus refers 
to a change in the mean or variability of one or more measures of 
climate (for example, temperature or precipitation) that persists for 
an extended period, typically decades or longer, whether the change is 
due to natural variability, human activity, or both (IPCC 2007, p. 78). 
Various types of changes in climate can have direct or indirect effects 
on species. These effects may be positive, neutral, or negative, and 
they may change over time, depending on the species and other relevant 
considerations, such as the effects of interactions of climate with 
other variables (for example, habitat fragmentation) (IPCC 2007, pp. 8-
14, 18-19). In our analyses, we use our expert judgment to weigh 
relevant information, including uncertainty, in our consideration of 
various aspects of climate change.
    For the Sierra Nevada ecoregion, climate models predict that mean 
annual temperatures will increase by 1.8 to 2.4 [deg]C (3.2 to 4.3 
[deg]F) by 2070, including warmer winters with earlier spring snowmelt 
and higher summer temperatures (PRBO 2011, p. 18). Additionally, mean 
annual rainfall is projected to decrease from the current average by 
some 9.2-33.9 cm (3.6-13.3 in) by 2070 (PRBO 2011, p. 18). However, 
projections have high uncertainty and one study predicts the opposite 
effect (PRBO 2011, p. 18). Snowpack is, by all projections, going to 
decrease dramatically (following the temperature rise and increase in 
precipitation falling as rain) (PRBO 2011, p. 19). Higher winter 
streamflows, earlier runoff, and reduced spring and summer streamflows 
are projected, with increasing severity in the southern Sierra Nevada 
(PRBO 2011, pp. 20-22).
    Snow-dominated elevations from 2,000-2,800 m (6,560-9,190 ft) will 
be the most sensitive to temperature increases (PRBO 2011, p. 23). 
Meadows fed by snowmelt may dry out or be more ephemeral during the 
non-winter months (PRBO 2011, p. 24). This pattern could influence 
ground water transport, and springs may be similarly depleted, leading 
to lower water levels in available breeding habitat and decreased area 
of suitable habitat for rearing tadpoles of Yosemite toads.
    Historically, drought has contributed to the decline of the 
Yosemite toad (Kagarise Sherman and Morton 1993, p. 186; Jennings and 
Hayes 1994, pp. 50-53). Climate change itself may also have contributed 
to that decline if greenhouse

[[Page 24506]]

gas emissions have contributed to the intensity of droughts and 
severity of occasional extreme cold winters during the last several 
decades. Extended and more severe droughts pose an ongoing, rangewide 
risk to the species. Less water, specifically less water as snow, means 
less and lower quality habitat for Yosemite toads. However, it is 
difficult to discern the effects of climate change on Yosemite toad 
populations without focused, long-term study.
    Davidson et al. (2002, p. 1598) analyzed geographic decline 
patterns in Yosemite toad. They compared known areas of extirpation 
against a hypothesized model for climate change that would predict 
greater numbers of extirpations at lower altitudes, and in more 
southern latitudes. The researchers did not observe a pattern in the 
available historic data to support the climate change hypothesis as a 
driver of historic population losses, although they acknowledge that 
climate change may be a contributor in more complex or subtle ways. 
Additionally, this study was limited by small sample size, and it is 
possible that climate change effects on the Yosemite toad (a long-lived 
species) may not become evident for many years (USFS et al. 2009, p. 
48). Finally, Davidson et al. (2002, p. 1598) did find an increase in 
occupancy with elevation (greater densities of populations at 
altitude), and it is suggested that this observation is consistent with 
a pattern that would fit a response to climate change (USFS et al. 
2009, p. 48). However, this observation would also be consistent if the 
features of these particular habitats (such as at higher elevation) 
were more suited to the special ecological requirements of the toad, or 
if other stressors acting on populations at lower elevations were 
responsible for the declines. We therefore find these results 
inconclusive.
    The breeding ecology and life history of the Yosemite toad are that 
of a habitat specialist, as it utilizes pool and meadow habitats during 
the onset of snowmelt and carefully times its reproduction to fit 
available conditions within ephemeral breeding sites. The most striking 
documented declines in Yosemite toad populations in the historical 
record are correlated with extreme climate episodes (drought) (Kagarise 
Sherman and Morton 1993, pp. 186-198). Given these observations, it is 
likely that climate change (see also discussion in mountain yellow-
legged frog's Summary of Factors Affecting the Species, under Factor E) 
poses a significant risk to the Yosemite toad now and in the future. It 
is quite possible that these impacts are occurring currently, and have 
occurred over the last few decades. However, it is difficult in short 
time intervals to discern the degree of effect from climate change 
within the variability of natural climate cycles.
    In summary, based on the best available scientific and commercial 
information, we consider the threats of destruction, modification, and 
curtailment of the species' habitat and range to be significant ongoing 
threats to the Yosemite toad. The legacy effects of past land uses have 
altered meadow communities through the mechanism of stream incision by 
permanently reducing habitat quantity and quality unless active and 
costly restoration is implemented. Climate change is a current threat 
of high magnitude. Threats considered of moderate magnitude include 
livestock grazing and fire management regime. Threats considered 
currently low magnitude include roads and timber harvest, dams and 
water diversions, and recreational land uses.

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

    We do not have any scientific or commercial information to indicate 
that overutilization for commercial, recreational, or scientific 
purposes poses a threat to the Yosemite toad. There is no known 
commercial market for Yosemite toads, and there is also no documented 
recreational or educational use for Yosemite toads.
    Scientific research may cause some stress to Yosemite toads through 
disturbance and disruption of behavior, handling, and injuries 
associated with marking individuals. This activity has resulted in the 
known death of a few individuals through accidental trampling (Green 
and Kagarise Sherman 2001, pp. 92-103), irradiation from radioactive 
tags (Karlstrom 1957, pp. 187-195), and collection for museum specimens 
(Jennings and Hayes 1994, pp. 50-53). However, there is currently 
relatively little research effort on this species, and scientists as a 
general rule take actions to mitigate harm to their study species. 
Therefore, scientific research is not a threat to the Yosemite toad. It 
is anticipated that further research into the genetics and life history 
of the Yosemite toad and broader methodological censuses will provide a 
net conservation benefit to this under-studied species.
    Based on the best available scientific and commercial information, 
we do not consider the overutilization for commercial, recreational, 
scientific, or educational purposes to be a threat to the Yosemite 
toad.

Factor C. Disease or Predation

Predation
    Prior to the trout stocking of high Sierra Nevada lakes, which 
began over a century ago, fish were entirely absent from most of this 
region (Bradford 1989, pp. 775-778). Observations regarding the effects 
of introduced fishes on the Yosemite toad are mixed. However, re-
surveys of historical Yosemite toad sites have shown that the species 
has disappeared from several lakes where they formerly bred, and these 
areas are now occupied by fish (Stebbins and Cohen 1995, pp. 213-215; 
Martin 2002, p. 1).
    Drost and Fellers (1994, pp. 414-425) suggested that Yosemite toads 
are less vulnerable to fish predation than frogs because they breed 
primarily in ephemeral waters that do not support fish. Further, 
Jennings and Hayes (1994, pp. 50-53) stated that the palatability of 
Yosemite toad tadpoles to fish predators is unknown, but often assumed 
to be low based on the unpalatability of western toads (Drost and 
Fellers 1994, pp. 414-425; Kiesecker et al. 1996, pp. 1237-1245), to 
which Yosemite toads are closely related. Grasso (2005, p. 1) observed 
brook trout swimming near, but the trout ignored Yosemite toad 
tadpoles, suggesting that tadpoles are unpalatable. The study also 
found that subadult Yosemite toads were not consumed by brook trout 
(Grasso 2005, p. 1), although the sublethal effects of trout 
``sampling'' (mouthing and ejecting tadpoles) and the palatability of 
subadults to other trout species are unknown. Martin (2002, p. 1) 
observed brook trout preying on Yosemite toad tadpoles, and also saw 
them ``pick at'' Yosemite toad eggs (which later became infected with 
fungus). In addition, metamorph western toads have been observed in 
golden trout stomach contents (Knapp 2002c, p. 1). Nevertheless, Grasso 
et al. (2010, p. 457) concluded that early life stages of the Yosemite 
toad likely possess chemical defenses that provide sufficient 
protection from native trout predation.
    The observed predation of Yosemite toad tadpoles by trout (Martin 
1992, p.1) indicates that introduced fishes may pose a predation risk 
to the species in some situations, which may be accentuated during 
drought years. At a site where Yosemite toads normally breed in small 
meadow ponds, they have been observed to successfully switch breeding 
activities to stream habitat containing fish during years of low water 
(Strand 2002, p. 1). Thus,

[[Page 24507]]

drought conditions may increase the toads' exposure to predatory fish, 
and place them in habitats where they compete with fish for 
invertebrate prey. Additionally, although the number of lake breeding 
sites used by Yosemite toads is small relative to the number of 
ephemeral sites, lake sites may be especially important because they 
are more likely to be habitable during years with low water (Knapp 
2002c, p. 1).
    Overall, the data and available literature suggest that direct 
mortality from fish predation is likely not an important factor driving 
Yosemite toad population dynamics. This does not discount other 
indirect impacts, such as the possibility that fish may be effective 
disease vectors (see below). Yosemite toad use of more ephemeral 
breeding habitats (which are less habitable to fish species as they 
cannot tolerate drying or freezing) minimizes the interaction of fish 
and toad tadpoles. Further, where fish and toads co-occur, it is 
possible that food depletion (outcompetition) by fish negatively 
affects Yosemite toads (USFS et al. 2009, p. 58).
    Other predators may also have an effect on Yosemite toad 
populations. Kagarise Sherman and Morton (1993, p. 194) reported 
evidence of toad predation by common ravens (Corvus corax) and 
concluded this was the responsible factor in the elimination of toads 
from one site. These researchers also confirmed, as reported in other 
studies, predation on Yosemite toad by Clark's nutcrackers (Nucifraga 
columbiana). The significance of avian predation may increase if the 
abundance of common ravens within the current range of the Yosemite 
toad increases as it has in nearby regions (Camp et al. 1993, p. 138; 
Boarman et al. 1995, p. 1; Kelly et al. 2002, p. 202). However, the 
degree to which avian predation may be affecting Yosemite toad 
populations has not been quantified.
Disease
    Although not all vectors have been confirmed in the Sierra Nevada, 
introduced fishes, humans, pets, livestock, packstock, vehicles, and 
wild animals may all act to facilitate disease transmission between 
amphibian populations. Infection of both fish and amphibians by a 
common disease has been documented with viral (Mao et al. 1999, pp. 45-
52) and fungal pathogens in the western United States (Blaustein et al. 
1994b, pp. 251-254). Mass die-offs of amphibians in the western United 
States and around the world have been attributed to Bd fungal 
infections of metamorphs and adults (Carey et al. 1999, pp. 1-14), 
Saprolegnia fungal infections of eggs (Blaustein et al. 1994b, pp. 251-
254), ranavirus infections, and bacterial infections (Carey et al. 
1999, pp. 1-14).
    Various diseases are confirmed to be lethal to Yosemite toads 
(Green and Kagarise Sherman 2001, pp. 92-103), and recent research has 
elucidated the potential role of Bd infection as a threat to Yosemite 
toad populations (Dodge and Vredenburg 2012, p.1). These various 
diseases and infections, in concert with other factors, have likely 
contributed to the decline of the Yosemite toad (Kagarise Sherman and 
Morton 1993, pp. 193-194), and may continue to pose a risk to the 
species (Dodge and Vredenburg 2012, p. 1).
    Die-offs in Yosemite toad populations have been documented in the 
literature, and an interaction with diseases in these events has been 
confirmed. However, no single cause has been validated by field 
studies. Tissue samples from dead or dying adult Yosemite toads and 
healthy tadpoles were collected during a die-off at Tioga Pass Meadow 
and Saddlebag Lake and analyzed for disease (Green and Kagarise Sherman 
2001, pp. 92-103). Six infections were found in the adults, including 
infection with Bd, bacillary bacterial septicemia (red-leg disease), 
Dermosporidium (a fungus), myxozoa spp. (parasitic cnidarians), 
Rhabdias spp. (parasitic roundworms), and several species of trematode 
(parasitic flatworms). Despite positive detections, no single 
infectious disease was found in more than 25 percent of individuals, 
and some dead toads showed no signs of infection to explain their 
death. Further, no evidence of infection was found in tadpoles. A meta-
analysis of red-leg disease also revealed that the disease is a 
secondary infection that may be associated with a suite of different 
pathogens, and so actual causes of decline in these instances were 
ambiguous (Kagarise Sherman and Morton 1993, p. 194). The authors 
concluded that the die-off was caused by suppression of the immune 
system caused by an undiagnosed viral infection or chemical 
contamination that made the toads susceptible to the variety of 
diagnosed infections.
    Saprolegnia ferax, a species of water mold that commonly infects 
fish in hatcheries, caused a massive lethal infection of eggs of 
western toads at a site in Oregon (Blaustein et al. 1994b, pp. 252). It 
is unclear whether this event was caused by the introduction of the 
fungal pathogen via fish stocking, or if the fungus was already present 
and the eggs' ability to resist infection was inhibited by some unknown 
environmental factor (Blaustein et al. 1994b, pp. 253). Subsequent 
laboratory experiments have shown that the fungus could be passed from 
hatchery fish to western toads (Kiesecker et al. 2001, pp. 1064-1070). 
Fungal growth on Yosemite toad eggs has been observed in the field, but 
the fungus was not identified and it was unclear whether the fungus was 
the source of the egg mortality (Kagarise Sherman 1980, p. 46). Field 
studies conducted in Yosemite National Park found that an undetermined 
species of water mold infected only the egg masses that contained dead 
embryos of Yosemite toads (Sadinski 2004, pp. 33-34). The researchers 
also observed that the water mold became established on egg masses only 
after embryo death, and subsequently spread, causing the mortality of 
additional embryos of Yosemite toads.
    Sadinski (2004, p. 35) discovered that mortality of Yosemite toad 
embryos may be attributed to an unidentified species of a free-living 
flatworm (Turbellaria spp.). In Yosemite National Park, these worms 
were observed to penetrate Yosemite toad egg masses and feed directly 
on the embryos. In some locations, Turbellaria spp. reached such large 
densities that they consumed all the embryos within a Yosemite toad egg 
mass. Predation also facilitated the colonization and spread of water 
mold on egg masses, leading to further embryo mortality. Further 
studies would be needed to determine which species of Turbellaria feeds 
on Yosemite toad eggs, and the extent of this impact on Yosemite toad 
populations.
    Until recently, the contribution of Bd infection to Yosemite toad 
population declines was relatively unknown. Although the toad is 
hypothetically susceptible due to co-occurrence with the mountain 
yellow-legged frog, it is suspected that the spread and growth of Bd in 
the warmer pool habitats, occupied for a much shorter time relative to 
the frog, renders individuals less prone to epidemic outbreaks (USFS et 
al. 2009, p. 50). Fellers et al. (2011, p. 391) documented the 
occurrence of Bd infection in Yosemite National Park toads over at 
least a couple of decades, and they note population persistence in 
spite of the continued presence of the pathogen. In a survey of 196 
museum specimens, Dodge and Vredenburg (2012, p. 1) report the first 
presence of Bd infection in Yosemite toads beginning in 1961, with the 
pathogen becoming highly prevalent during the recorded declines of the 
late 1970s, before it peaked in the 1990s at 85 percent positive 
incidence. In live specimen sampling, Dodge and Vredenburg (2012, p. 1) 
collected 1,266 swabs of Yosemite toads between 2006 and 2011, and 
found Bd infection

[[Page 24508]]

intensities at 17-26 percent (with juvenile toads most affected). The 
results from these studies support the hypothesis that Bd infection and 
chytridiomycosis have played an important role in Yosemite toad 
population dynamics over the period of their recent recorded decline.
    Carey (1993, pp. 355-361) developed a model to explain the 
disappearance of boreal toads (Bufo boreas boreas) in the Rocky 
Mountains, suggesting immune system suppression from extreme winter 
stress (``winter stress syndrome'') could have contributed to the 
decline in that species. This model may also fit Yosemite toad die-offs 
observed by Kagarise Sherman and Morton (1993, pp. 186-198), given the 
close relationship between the two toads, and their occupation of 
similar habitats. However, an analysis of immune system suppression and 
the potential role of winter stress relative to Yosemite toad 
population trends is not available at this time. Yet, the decline 
pattern observed in the Carey study is mirrored by the pattern in the 
Yosemite toad (heavy mortality exhibited in males first) (Knapp 2012, 
pers. comm.). This observation, in concert with the recent results from 
museum swabs (Dodge and Vredenburg 2012, p. 1), provides a correlative 
link to the timing of the recorded Yosemite toad declines and Bd 
infection intensities.
    Although disease as a threat factor to the Yosemite toad is 
relatively less documented, there is evidence for Bd infection related 
to historical die-offs in Yosemite toads. Much of the historic research 
documenting Yosemite toad declines predated our awareness of Bd as a 
major amphibian pathogen. Additionally, the life history of the 
Yosemite toad, as a rapid breeder during early snowmelt, limits the 
opportunities to observe population crashes in the context of varied 
environmental stressors. Currently available evidence indicates that Bd 
was likely a significant factor contributing to the recent historical 
declines observed in Yosemite toad populations (Dodge and Vredenburg 
2012, p. 1). Although infection intensities are currently lower than 
some peak historic measurements, this threat remains a potential factor 
to date that may continue to reduce survival through metamorphosis, and 
therefore recruitment to the breeding population (Knapp 2012, pers. 
comm.). Additionally, the interaction of disease and other stressors, 
such as climate extremes, is not well understood in the Yosemite toad. 
Research does suggest that the combination of these threats represents 
a factor in the historical decline of the species (Kagarise Sherman and 
Morton 1993, p. 186).
    In summary, based on the best available scientific and commercial 
information, we consider disease to be a threat to the Yosemite toad 
that has a moderate, ongoing effect on populations of the species 
rangewide. The threat most specifically includes the amphibian 
pathogen, Bd. Based on the best available scientific and commercial 
information, we are uncertain about the impacts of avian predation on 
Yosemite toads at this time, and therefore do not consider it to be a 
listing factor. Although definitive empirical data quantifying the 
contribution of disease to Yosemite toad population declines are not 
currently available, the concurrence of population declines with the 
prevalence and spread of Bd across the Sierra Nevada support the 
assertion that disease has played a role in the observed trend. 
Further, Bd infection, even at lower intensities, may interact with 
climate extremes and continue to depress recruitment of yearling and 
subadult Yosemite toads to breeding Yosemite toad populations. We 
suspect this threat was historically significant, that it is currently 
having a moderate influence on toad populations, and we expect it to be 
a future concern.

Factor D. The Inadequacy of Existing Regulatory Mechanisms

    In determining whether the inadequacy of regulatory mechanisms 
constitutes a threat to the Yosemite toad, we analyzed the existing 
Federal and State laws and regulations that may address the threats to 
the species or contain relevant protective measures. Regulatory 
mechanisms are typically nondiscretionary and enforceable, and may 
preclude the need for listing if such mechanisms are judged to 
adequately address the threat(s) to the species such that listing is 
not warranted. Conversely, threats on the landscape are not addressed 
by existing regulatory mechanisms where the existing mechanisms are not 
adequate (or not adequately implemented or enforced).
    We discussed the applicable State and Federal laws and regulations, 
including the Wilderness Act, NFMA above (see Factor D discussion for 
mountain yellow-legged frog complex). In general, the same 
administrative policies and statutes are in effect for the Yosemite 
toad. This section additionally addresses regulatory mechanisms with a 
specific emphasis on the Yosemite toad.
Taylor Grazing Act of 1934
    In response to overgrazing of available rangelands by livestock 
from the 1800s to the 1930s, Congress passed the Taylor Grazing Act in 
1934 (43 U.S.C. 315 et seq.). This action was an effort to stop the 
damage to the remaining public lands as a result of overgrazing and 
soil depletion, to provide coordination for grazing on public lands, 
and to attempt to stabilize the livestock industry (Meehan and Platts 
1978, p. 275; Public Lands Council et al. v. Babbitt Secretary of the 
Interior et al. (167 F. 3d 1287)). Although passage of the Taylor 
Grazing Act resulted in reduced grazing in some areas, it did not 
reduce grazing severity, and localized use remained high, precluding 
regeneration of many meadow areas (Beesley 1996, p. 14; Menke et al. 
1996, p. 14; Public Lands Council et al. v. Babbitt Secretary of the 
Interior et al. (167 F. 3d 1287)).
    Existing Federal and State laws and regulatory mechanisms currently 
offer some level of protection for the Yosemite toad. Specifically, 
these include the Wilderness Act, the NFMA, the SNFPA, and the FPA (see 
Factor D discussion for mountain yellow-legged frog complex). Based on 
the best available scientific and commercial information, we do not 
consider the inadequacy of existing regulatory mechanisms to be a 
threat to the Yosemite toad.

Factor E. Other Natural or Manmade Factors Affecting Its Continued 
Existence

    The Yosemite toad is sensitive to environmental change or 
degradation due to its life history, biology, and existence in 
ephemeral habitats characterized by climate extremes and low 
productivity. It is also sensitive to anthropogenically influenced 
factors. For example, contaminants, acid precipitation, ambient 
ultraviolet radiation, and climate change have been implicated as 
contributing to amphibian declines (Corn 1994, pp. 62-63; Alford and 
Richards 1999, pp. 2-7). These factors are discussed in the context of 
the mountain yellow-legged frog above (see Factor E discussion for 
mountain yellow-legged frog complex), and are largely applicable to the 
Yosemite toad. The following discussion will focus on potential threat 
factors specifically studied in the Yosemite toad, or areas where the 
prevalence of the threat may differ based on the unique life history, 
population status, demographics, or biological factors specific to 
Yosemite toad populations.
Contaminants
    The Yosemite toad is likely exposed to a variety of pesticides and 
other chemicals throughout its range. This includes those imported via 
aerial drift and precipitation (see ``Contaminants''

[[Page 24509]]

discussion for mountain yellow-legged frog complex). But, given their 
life history that includes significant time in upland habitats, there 
are also locally applied pesticides that may have more of an impact on 
the terrestrial life stages of Yosemite toads. In order of their 
application rate, the most commonly used locally applied pesticides for 
forest resource management are: glyphosate, triclopyr, clopyralid, 
hexazinone, aminopyralid, chlorsulfuron, imazapyr, and aluminum 
phosphide (applied to rodent burrows) (USFS et al. 2009, p. 63).
    Large amounts of ammonia-based fire retardants and surfactant-based 
fire-suppressant foams, including ammonium phosphate, ammonium sulfate, 
and sodium ferrocyanide, are applied to areas managed by the USFS 
(National Forests and Wilderness Areas) that may be inhabited by 
Yosemite toads when wildfires occur within their range (USFS et al. 
2009, p. 54). Fire retardant chemicals contain nitrogen compounds and 
surfactants. Applied surfactants and dyes include: R-11, Hasten, 
Syltac, highlight blue, bas-oil red, and colorfast purple (USFS et al. 
2009, p. 63). Laboratory tests of these chemicals have shown that they 
cause mortality in fish and aquatic invertebrates (Hamilton et al. 
1996, pp. 132-144); similar effects are possible in amphibians. Calfee 
and Little (2003, pp. 1529-1530) report that southern leopard frogs 
(Rana sphenocephala) and boreal toads (Bufo boreas) are more tolerant 
than rainbow trout (Oncorhynchus mykiss) to fire retardant chemicals. 
However, the acute toxicity of some compounds is enhanced by 
ultraviolet light, which may harm amphibians at environmentally 
relevant concentrations. Therefore, if fire retardant chemicals are 
dropped in or near Yosemite toad habitat, they may have negative 
effects on individual toads. Yosemite toad populations span wilderness 
areas and sparsely vegetated, high-elevation habitats. As fire is 
infrequent in these areas, fire retardant chemicals are likely not a 
threat through much of the species' range (USFS et al. 2009, p. 55).
    The risk to Yosemite toad from locally applied pesticides, 
surfactants, and dyes is not known. However, most of the use of these 
chemicals also largely occurs below the current elevational range of 
the toad, so this risk factor is likewise limited in scale.
    The effect of contamination from other environmental pollutants is 
not well-studied. Preliminary research indicates that Yosemite toad 
tadpoles in grazed areas take longer to metamorphose and produce 
smaller metamorphs than those in areas being rested from grazing, 
potentially due to high bacterial and nutrient levels in the grazed 
areas (Martin 2002, pp. 1-3; Martin 2008, p. 157). Finally, water 
quality may be affected by the introduction of chemicals and wastes 
from camp use (USFS et al. 2009, p. 68), which would logically have 
greater influence on the more aquatic life stages. However, given the 
early season breeding for this species, the coincidence of recreational 
use wastes and tadpoles is likely relatively minor.
    Acid precipitation has been hypothesized as a cause of amphibian 
declines (including toads) in the Sierra Nevada because waters there 
are extremely low in acid-neutralizing capacity, and therefore 
susceptible to changes in water chemistry due to acidic deposition 
(Bradford et al. 1994b, pp. 155-161). In addition to raising the 
acidity of water bodies, acid deposition may also cause increases in 
dissolved aluminum (from soils), which may be toxic to amphibians 
(Bradford et al. 1992, 271-275). In laboratory experiments (Bradford et 
al. 1992, pp. 369-377; Bradford and Gordon 1992, pp. 75-76), high 
acidity and high aluminum concentrations did not have significant 
effects on survival of Yosemite toad embryos or newly hatched tadpoles. 
However, at pH 5.0 and at high aluminum concentrations, Yosemite toad 
embryos hatched earlier and the tadpoles showed a reduction in body 
size.
    In a complementary field study of 235 amphibian breeding sites, 
Bradford et al. (1994, pp. 155-161) concluded that acid precipitation 
is an unlikely cause of decline in Yosemite toad populations. However, 
researchers suggest this risk factor should still be considered in 
conservation efforts because of the possibility of sublethal effects, 
of its interaction with other factors, and of the potential for more 
severe acid deposition in the future (Bradford et al. 1992, p. 375; 
USFS et al. 2009, p. 44). Overall, we consider acid deposition a low 
risk to the species at this time, and likely not a significant threat 
into the future (see discussion under Factor E for mountain yellow-
legged frogs above).
    In summary, a number of studies have investigated the potential 
threats of a number of contaminants, such as pesticides, fire 
retardants, and acid precipitation. Based on the best available 
commercial and scientific information, we do not believe that 
contaminants pose a significant threat to populations of the Yosemite 
toad.
Ultraviolet Radiation
    Ambient UV-B radiation has increased at north temperate latitudes 
in the past 2 decades (Adams et al. 2001, pp. 519-525). Ambient levels 
of UV-B were demonstrated to cause significant decreases in survival of 
western toad eggs in field experiments (Blaustein 1994, pp. 32-39). In 
a laboratory experiment (Kats et al. 2000, pp. 921-931), western toad 
metamorphs exposed to levels of UV-B below those found in ambient 
sunlight showed a lower alarm response to chemical cues of injured 
toads than metamorphs that were completely shielded from UV-B. This 
indicates that ambient levels of UV-B may cause sublethal effects on 
toad behavior that could increase their vulnerability to predation. In 
a field experiment (Kiesecker and Blaustein 1995, pp. 11049-11052), the 
combined effects of exposure to ambient levels of UV-B radiation and 
exposure to a pathogenic fungus (Saprolegnia) were shown to cause 
significantly higher mortality of western toad embryos than either 
factor alone.
    Sadinski et al. (1997, pp. 1-8) observed a high percentage of 
embryo mortality in Yosemite toads at six breeding sites in Yosemite 
National Park, but in a subsequent field experiment this mortality did 
not appear to be related to UV-B (Sadinski 2004, p. 37). In spatial 
analyses of extant and extinct populations, higher elevation was 
positively correlated with extant Yosemite toad populations. This is 
counter to what would be expected if UV-B were the primary cause of 
decline (Davidson 2002, p. 15), as sites at higher elevations would be 
expected to receive more solar radiation due to the thinner atmosphere. 
UV-B at high elevations in the Sierra Nevada has increased less than 5 
percent in the past several decades (Jennings 1996, pp. 921-944). These 
data further indicate that UV-B has likely not contributed 
significantly to the decline of Yosemite toads. Based on the best 
available commercial and scientific information, this threat factor is 
currently considered a low risk to the species.
Climate Change Effects on Individuals
    As discussed above in Factor A, climate change can result in 
detrimental impacts to Yosemite toad habitat. Climate variability could 
also negatively impact populations through alteration of the frequency, 
duration, and magnitude of either droughts or severe winters (USFS et 
al. 2009, p. 47). Yosemite toads breed and their tadpoles develop in 
shallow meadow and ephemeral habitats, where mortality from

[[Page 24510]]

desiccation and freezing can be very high, often causing complete loss 
of an annual cohort (USFS et al. 2009, p. 10). Kagarise Sherman and 
Morton (1993, pp. 192-193) documented in a long-term population study 
that Yosemite toad hatching success and survival were subject to a 
balance between the snowpack water contribution to breeding pools and 
the periodicity and character of breeding season storms and post-
breeding climate (whether it is cold or warm). When it is too cold, 
eggs and tadpoles are lost to freezing. This poses a risk as earlier 
snowmelt is expected to cue breeding earlier in the year, exposing 
young tadpoles (or eggs) to killing frosts in more variable conditions 
of early spring (Corn 2005, p. 60). When it is too warm, tadpoles are 
lost to pool desiccation. Alterations in the annual and seasonal 
hydrologic cycles that influence water volume and persistence in 
Yosemite toad breeding areas can thereby impact breeding success. The 
threat of climate change on individuals is significant, and is of high 
prevalence now and into the future.
Other Sources of Direct and Indirect Mortality
    Direct and indirect mortality of Yosemite toads has occurred as a 
result of livestock grazing. Recently metamorphosed (juvenile) toads 
congregate in large numbers in mesic meadow habitats, and are at 
highest risk for trampling because their presence coincides with 
grazing activity (USFS et al. 2009, p. 61). Cattle have been observed 
to trample Yosemite toad eggs, and new metamorphs and subadult toads 
can fall into deep hoof prints and die (Martin 2008, p. 158). Martin 
(2008, p. 158) also witnessed some 60 subadult and metamorph toad 
deaths during the movement of 25 cattle across a stream channel 
bordered by willows within a meadow complex. Adult Yosemite toads 
trampled to death by cattle have also been observed (Martin 2002, pp. 
1-3). This risk factor is likely of sporadic significance, and is of 
greatest concern where active grazing allotments coincide with breeding 
meadows. However, it is difficult to determine the degree of this 
impact without quantitative data.
    Trampling and collapse of rodent burrows by recreationists, pets, 
and vehicles could lead to direct mortality of terrestrial life stages 
of the Yosemite toad. Recreational activity may also disturb toads and 
disrupt their behavior (Karlstrom 1962, pp. 3-34). Recreational anglers 
may be a source of introduced pathogens and parasites, and they have 
been observed using toads and tadpoles as bait (USFS et al. 2009, p. 
66). However, Kagarise Sherman and Morton (1993, p. 196) did not find a 
relationship between the distance from the nearest road and the 
declines in their study populations, suggesting that human activity was 
not the cause of decline in that situation. Recreational activity may 
be of conservation concern, and this may increase with greater activity 
in mountain meadows. However, current available information does not 
indicate that recreational activity is a significant stressor for 
Yosemite toads.
    Fire management practices over the last century have created the 
potential for severe fires in the Sierra Nevada. Wildfires do pose a 
potential direct mortality threat to Yosemite toads, although 
amphibians in general are thought to retreat to moist or subterranean 
refuges and thereby suffer low mortality during natural fires (Russel 
et al. 1999, pp. 374-384). However, data on the direct and indirect 
effects of fire on Yosemite toads are lacking.
    USFS et al. (2009, p. 74) suggested that the negative effects of 
roads that have been documented in other amphibians, in concert with 
the substantial road network across a portion of the Yosemite toad's 
range, indicate this risk factor may be potentially significant to the 
species. Roads may facilitate direct mortality of amphibians through 
vehicle strikes (DeMaynadier and Hunter 2000, pp. 56-65). Levels of 
timber harvest and road construction have declined substantially since 
implementation of the California Spotted Owl Sierran Province Interim 
Guidelines in 1993, and some existing roads have been decommissioned or 
are scheduled to be decommissioned (USDA 2001a, p. 445). Therefore, the 
risks posed by new roads and timber harvests have declined, but those 
already existing still may pose risks to the species and its habitat. 
Collectively, direct mortality from land uses within the Yosemite toad 
range may have a population-level impact. However, we are aware of no 
studies that have quantified or estimated the prevalence of this 
particular threat to be able to assess its impact to frog populations. 
At the current time, direct and indirect mortality from roads are not 
considered to be a significant factor affecting the Yosemite toad.
Small Population Size
    Although it is believed that the range of the Yosemite toad has not 
significantly contracted, the majority of populations across this area 
have been extirpated, and this loss has been significant relative to 
the historical condition (reflecting multitudes of populations within 
many watersheds across their geographic range) (see ``Population 
Estimates and Status'' above). Further, the populations that remain are 
small, numbering less than 20 males in most cases (Brown et al. 2011, 
p. 4). This situation renders these remnant populations susceptible to 
risks inherent to small populations (see Factor E discussion, ``Small 
Population Size,'' for mountain yellow-legged frogs, above) including 
inbreeding depression and genetic drift, along with a higher 
probability of extirpation from unpredictable events such as severe 
storms or extended droughts.
    Traill et al. (2009, p. 32) argued for a benchmark viable 
population size of 5,000 adult individuals (and 500 to prevent 
inbreeding) for a broad range of taxa, although this type of blanket 
figure has been disputed as an approach to conservation (Flather et al. 
2011, pp. 307-308). Another estimate, specific to amphibians, is that 
populations of at least 100 individuals are less susceptible to 
demographic stochasticity (Schad 2007, p. 10). Amphibian species with 
highly fluctuating population size, high frequencies of local 
extinctions, and living in changeable environments may be especially 
susceptible to curtailment of dispersal and restriction of habitat 
(Green 2003, p. 331). These conditions are all likely applicable to the 
Yosemite toad.
    Therefore, based on the best available commercial and scientific 
information, we conclude that small population size is a prevalent and 
significant threat to the species viability of the Yosemite toad across 
its range, especially in concert with other extant stressors (such as 
climate change).
Cumulative Impacts of Extant Threats
    Interactive effects or cumulative impacts from multiple additive 
stressors acting upon Yosemite toad populations over time are evident 
by the documented declines in populations and abundance across the 
range of the species. Although no single causative factor linked to 
population declines in Yosemite toads has been confirmed in the 
literature (excepting perhaps extreme climate conditions such as 
droughts) (Kagarise Sherman and Morton 1993, p. 186; Jennings and Hayes 
1994, pp. 50-53), there has been a decline in population abundance and 
numbers of extant populations inhabiting the landscape (Brown et al. 
2012, pp. 115-131; Kagarise Sherman and Morton 1993, pp. 186-198). This 
pattern of decline suggests a factor or combination of factors common 
throughout the range of the toad. The available literature (Kagarise 
Sherman

[[Page 24511]]

and Morton 1993, pp. 186-198; Jennings and Hayes 1994, pp. 50-53; USFS 
et al. 2009, pp. 1-133; Martin 2008, pp. i-393) supports the contention 
that a combination of factors has interacted and is responsible for the 
decline observed in Yosemite toad populations over the past few 
decades.
    Disease has been documented in Yosemite toad populations, and 
recent data documenting historic trends in Bd infection intensity are 
compelling (Dodge and Vredenburg 2012, p. 1), but disease has not been 
definitively tied to the observed rangewide decline. There is 
considerable evidence that various stressors, mediated via impacts to 
meadow hydrology following upslope land management practices over the 
last century, have detrimentally affected the quantity and quality of 
breeding meadows. Many of these stressors, such as grazing, have likely 
been more significant in the past than under current management 
standards. However, legacy effects remain and meadows tend not to 
recover without active intervention once excessive stream incision in 
their watershed is set in motion (Vankat and Major 1978, pp. 386-397). 
Certain stressors may be of concern, such as increasing recreational 
impacts and avian predation upon terrestrial life stages of toads, 
although we do not have sufficient data to document the magnitude of 
these particular stressors.
    Given the evidence supporting the role of climate in reducing 
populations and potentially leading to the extirpation of many of the 
populations studied through the 1970s and into the early 1990s 
(Kagarise Sherman and Morton 1993, pp. 186-198), it is likely that this 
factor is either a primary driver, or at least a significant 
contributing factor in the declines that have been observed. Climate 
models predict increasing drought intensity and changes to the 
hydroperiod based on reduced snowpack, along with greater climate 
variability in the future (PRBO 2011, pp. 18-25). It is likely that 
these changes will exacerbate stress to the habitat specialist Yosemite 
toad through a pronounced impact on its ephemeral aquatic habitat, and 
also through an increase in the frequency of freezing and drying events 
that kill exposed Yosemite toad eggs and tadpoles. These changes and 
the resultant impacts will effectively reduce breeding success of 
remnant populations already at low abundance and still in decline. If 
an interaction such as winter stress and disease (Carey 1993, pp. 355-
362) is the underlying mechanism for Yosemite toad declines, then the 
enhanced influence of climate change as a stressor may tip the balance 
further towards higher incidence and increased disease virulence, which 
would also lead to greater population declines and extirpations.

Proposed Determination

    We have carefully assessed the best scientific and commercial 
information available regarding the past, present, and future threats 
to the Yosemite toad. The Yosemite toad is the most narrowly 
distributed, Sierra Nevada endemic, pond-breeding amphibian (Shaffer et 
al. 2000, p. 246). Although it apparently still persists throughout a 
large portion of its historical range, it has been reduced to an 
estimated 12 percent of historical watersheds. In addition, remnant 
populations are predominantly small.
    Yosemite toad populations are subject to threats from habitat 
degradation associated with land uses that negatively influence meadow 
hydrology, fostering meadow dewatering, and conifer and other invasive 
plant encroachment. These activities include grazing, the fire 
management regime of the past century, historic timber management 
activities, and associated road construction. The impacts from these 
threats are cumulatively of moderate magnitude, and their legacy 
impacts on meadow habitats act as a constraint upon extant populations 
now and are expected to hinder persistence and recovery into the 
future. Disease are threats of conservation concern that have likely 
also had an effect on populations leading to historical population 
decline, and these threats are operating currently and will continue to 
do so into the future, likely with impacts of moderate magnitude 
effects on Yosemite toad populations.
    The direct, interactive, and cumulative effects of these various 
risk factors have acted to reduce the geographic extent and abundance 
of this species throughout its habitat in the Sierra Nevada. The 
combined effect of these stressors acting upon small remnant 
populations of Yosemite toads is of significant conservation concern. 
The Yosemite toad has a life history and ecology that make it sensitive 
to drought and anticipated weather extremes associated with climate 
change. Climate change is expected to become increasingly significant 
to the Yosemite toad and its habitat in the future throughout its 
range. Therefore, climate change represents a threat that has a high 
magnitude of impact as an indirect stressor via habitat loss and 
degradation, and as a direct stressor via enhanced risk of climate 
extremes to all life stages of toads.
    The Act defines an endangered species as any species that is ``in 
danger of extinction throughout all or a significant portion of its 
range'' and a threatened species as any species ``that is likely to 
become endangered throughout all or a significant portion of its range 
within the foreseeable future.'' We find that the Yosemite toad is 
likely to become endangered throughout all or a significant portion of 
its range within the foreseeable future, based on the immediacy, 
severity, and scope of the threats described above. These include 
habitat loss associated with degradation of meadow hydrology following 
stream incision consequent to the cumulative effects of historic land 
management activities, notably livestock grazing, and also the 
anticipated hydrologic effects upon habitat from climate change under 
listing Factor A. Additionally, we find that disease under listing 
Factor C was likely a contributor to the recent historic decline of the 
Yosemite toad, and may remain an important factor limiting recruitment 
in remnant populations. We also find that the Yosemite toad is likely 
to become endangered through the direct effects of climate change 
impacting small remnant populations under Factor E, likely compounded 
with the cumulative effect of other threat factors (such as disease).
    We have carefully assessed the best scientific and commercial 
information available regarding the past, present, and future threats 
to the species, and have determined that the Yosemite toad meets the 
definition of threatened under the Act, rather than endangered. This is 
because the impacts from the threats are occurring now at moderate 
magnitude, but are likely to become of high magnitude in the 
foreseeable future across the species' entire range, making the species 
likely to become in danger of extinction. While population decline has 
been widespread, the rate of decline is not so severe to indicate 
extinction is imminent, but this rate could increase as stressors such 
as climate change impact small remnant populations. Further, the 
geographic extent of the species remains rather widespread throughout 
its historic range, conferring some measure of ecological and 
geographic redundancy. Therefore, on the basis of the best available 
scientific and commercial information, we propose listing the Yosemite 
toad as threatened in accordance with sections 3(20) and 4(a)(1) of the 
Act.
    The term ``threatened species'' means any species (or subspecies 
or, for vertebrates, distinct population segments) that is likely to 
become an

[[Page 24512]]

endangered species within the foreseeable future throughout all or a 
significant portion of its range. The Act does not define the term 
``foreseeable future'' but it likely describes the extent to which the 
Service could reasonably rely on predictions about the future in making 
determinations about the future conservation status of the species. In 
considering the foreseeable future as it relates to the status of the 
Yosemite Toad, we considered the historical data to identify any 
relevant existing trends that might allow for reliable prediction of 
the future (in the form of extrapolating the trends). We also 
considered how current stressors are affecting the species and whether 
we could reliably predict any future trends in those stressors that 
might affect the species recognizing that our ability to make reliable 
predictions for the future is limited by the quantity and quality of 
available data. Thus the foreseeable future includes the species 
response to these stressors and any trends.
    Under the Act and our implementing regulations, a species may 
warrant listing if it is endangered or threatened throughout all or a 
significant portion of its range. The Yosemite toad proposed for 
listing in this rule is highly restricted in its range and the threats 
occur throughout its range. Therefore, we assessed the status of the 
species throughout its entire range. The threats to the survival of the 
species occur throughout the species' range and are not restricted to 
any particular significant portion of that range. Accordingly, our 
assessment and proposed determination applies to the species throughout 
its entire range.

Available Conservation Measures

    Conservation measures provided to species listed as endangered or 
threatened under the Act include recognition, recovery actions, 
requirements for Federal protection, and prohibitions against certain 
practices. Recognition through listing results in public awareness and 
conservation by Federal, State, tribal, and local agencies, private 
organizations, and individuals. The Act encourages cooperation with the 
States and requires that recovery actions be carried out for all listed 
species. The protection required by Federal agencies and the 
prohibitions against certain activities are discussed, in part, above.
    The primary purpose of the Act is the conservation of endangered 
and threatened species and the ecosystems upon which they depend. The 
ultimate goal of such conservation efforts is the recovery of these 
listed species, so that they no longer need the protective measures of 
the Act. Subsection 4(f) of the Act requires the Service to develop and 
implement recovery plans for the conservation of endangered and 
threatened species. The recovery planning process involves the 
identification of actions that are necessary to halt or reverse the 
species' decline by addressing the threats to its survival and 
recovery. The goal of this process is to restore listed species to a 
point where they are secure, self-sustaining, and functioning 
components of their ecosystems.
    Recovery planning includes the development of a recovery outline 
shortly after a species is listed, preparation of a draft and final 
recovery plan, and revisions to the plan as significant new information 
becomes available. The recovery outline guides the immediate 
implementation of urgent recovery actions and describes the process to 
be used to develop a recovery plan. The recovery plan identifies site-
specific management actions that will achieve recovery of the species, 
measurable criteria that determine when a species may be downlisted or 
delisted, and methods for monitoring recovery progress. Recovery plans 
also establish a framework for agencies to coordinate their recovery 
efforts and provide estimates of the cost of implementing recovery 
tasks. Recovery teams (comprised of species experts, Federal and State 
agencies, nongovernmental organizations, and stakeholders) are often 
established to develop recovery plans. When completed, the recovery 
outline, draft recovery plan, and final recovery plan will be available 
on our Web site (http://www.fws.gov/endangered), or from our Sacramento 
Fish and Wildlife Office (see FOR FURTHER INFORMATION CONTACT).
    Implementation of recovery actions generally requires the 
participation of a broad range of partners, including other Federal 
agencies, States, tribal, nongovernmental organizations, businesses, 
and private landowners. Examples of recovery actions include habitat 
restoration (for example, restoration of native vegetation), research, 
captive propagation and reintroduction, and outreach and education. The 
recovery of many listed species cannot be accomplished solely on 
Federal lands because their range may occur primarily or solely on non-
Federal lands. To achieve recovery of these species requires 
cooperative conservation efforts on private, State, and tribal lands.
    If these species are listed, funding for recovery actions will be 
available from a variety of sources, including Federal budgets, State 
programs, and cost-share grants for non-Federal landowners, the 
academic community, and nongovernmental organizations. In addition, 
pursuant to section 6 of the Act, the State of California would be 
eligible for Federal funds to implement management actions that promote 
the protection and recovery of the Sierra Nevada yellow-legged frog, 
the northern DPS of the mountain yellow-legged frog, and the Yosemite 
toad. Information on our grant programs that are available to aid 
species recovery can be found at: http://www.fws.gov/grants.
    Although the Sierra Nevada mountain yellow-legged frog, the 
northern DPS of the mountain yellow-legged frog, and the Yosemite toad 
are only proposed for listing under the Act at this time, please let us 
know if you are interested in participating in recovery efforts for 
this species. Additionally, we invite you to submit any new information 
on these species whenever it becomes available and any information you 
may have for recovery planning purposes (see FOR FURTHER INFORMATION 
CONTACT).
    The Act and its implementing regulations set forth a series of 
general prohibitions and exceptions that apply to all endangered 
wildlife. The prohibitions of section 9(a)(2) of the Act, codified at 
50 CFR 17.21 for endangered wildlife, in part, make it illegal for any 
person subject to the jurisdiction of the United States to take 
(includes harass, harm, pursue, hunt, shoot, wound, kill, trap, 
capture, or collect; or to attempt any of these), import, export, ship 
in interstate commerce in the course of commercial activity, or sell or 
offer for sale in interstate or foreign commerce any listed species. 
Under the Lacey Act (18 U.S.C. 42-43; 16 U.S.C. 3371-3378), it is also 
illegal to possess, sell, deliver, carry, transport, or ship any such 
wildlife that has been taken illegally. Certain exceptions apply to 
agents of the Service and State conservation agencies.
    We may issue permits to carry out otherwise prohibited activities 
involving endangered and threatened wildlife species under certain 
circumstances. Regulations governing permits are codified at 50 CFR 
17.22 for endangered species, and at 17.32 for threatened species. With 
regard to endangered wildlife, a permit must be issued for the 
following purposes: for scientific purposes, to enhance the propagation 
or survival of the species, and for incidental take in connection with 
otherwise lawful activities.
    It is our policy, as published in the Federal Register on July 1, 
1994 (59 FR 34272), to identify to the maximum extent practicable at 
the time a species is listed, those activities that would or would not 
constitute a violation of

[[Page 24513]]

section 9 of the Act. The intent of this policy is to increase public 
awareness of the effect of a proposed listing on proposed and ongoing 
activities within the range of species proposed for listing. The 
following activities could potentially result in a violation of section 
9 of the Act; this list is not comprehensive:
    (1) Unauthorized collecting, handling, possessing, selling, 
delivering, carrying, or transporting of the species, including import 
or export across State lines and international boundaries, except for 
properly documented antique specimens of these taxa at least 100 years 
old, as defined by section 10(h)(1) of the Act;
    (2) Introduction of species that compete with or prey upon the 
Sierra Nevada yellow-legged frog, the northern DPS of the mountain 
yellow-legged frog, or the Yosemite toad;
    (3) The unauthorized release of biological control agents that 
attack any life stage of these species;
    (4) Unauthorized modification of the mountain meadow habitats or 
associated upland areas important for the breeding, rearing, and 
survival of these species; and
    (5) Unauthorized discharge of chemicals or fill material into any 
waters in which the Sierra Nevada yellow-legged frog, the northern DPS 
of the mountain yellow-legged frog, or the Yosemite toad are known to 
occur.
    Questions regarding whether specific activities would constitute a 
violation of section 9 of the Act should be directed to the Sacramento 
Fish and Wildlife Office (see FOR FURTHER INFORMATION CONTACT). 
Requests for copies of the regulations concerning listed animals and 
general inquiries regarding prohibitions and permits may be addressed 
to the U.S. Fish and Wildlife Service, Endangered Species Permits, 2800 
Cottage Way, Suite W-2606, Sacramento, CA 95825-1846 (telephone 916-
414-6464; facsimile 916-414-6486).

Peer Review

    In accordance with our joint policy on peer review published in the 
Federal Register on July 1, 1994 (59 FR 34270), we will seek the expert 
opinions of at least three appropriate and independent specialists 
regarding this proposed rule. The purpose of such review is to ensure 
that our proposed actions are based on scientifically sound data, 
assumptions, and analyses. We have invited these peer reviewers to 
comment, during the public comment period, on the specific assumptions 
and conclusions in this proposed listing.
    We will consider all comments and information we receive during the 
comment period on this proposed rule during preparation of a final 
determination. Accordingly, the final decision may differ from this 
proposal.

Public Hearings

    Section 4(b)(5) of the Act provides for one or more public hearings 
on this proposal, if requested. Requests must be received within 45 
days after the date of publication of this proposed rule in the Federal 
Register. Such requests must be sent to the address shown in the FOR 
FURTHER INFORMATION CONTACT. We will schedule public hearings on this 
proposal, if any are requested, and announce the dates, times, and 
places of those hearings, as well as how to obtain reasonable 
accommodations, in the Federal Register and local newspapers at least 
15 days before the hearing.

Required Determinations

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

    This rule does not contain any new collections of information that 
require approval by OMB under the Paperwork Reduction Act of 1995 (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 (42 U.S.C. 4321 et seq.)

    We have determined that environmental assessments and environmental 
impact statements, as defined under the authority of the National 
Environmental Policy Act (NEPA; 42 U.S.C. 4321 et seq.), need not be 
prepared in connection with listing a species as endangered or 
threatened under the Endangered Species Act. We published a notice 
outlining our reasons for this determination in the Federal Register on 
October 25, 1983 (48 FR 49244).

Clarity of the Rule

    We are required by Executive Orders 12866 and 12988 and by the 
Presidential Memorandum of June 1, 1998, to write all rules in plain 
language. This means that each rule we publish must:
    (1) Be logically organized;
    (2) Use the active voice to address readers directly;
    (3) Use clear language rather than jargon;
    (4) Be divided into short sections and sentences; and
    (5) Use lists and tables wherever possible.
    If you feel that we have not met these requirements, send us 
comments by one of the methods listed in the ADDRESSES section. To 
better help us revise the rule, your comments should be as specific as 
possible. For example, you should tell us the numbers of the sections 
or paragraphs that are unclearly written, which sections or sentences 
are too long, the sections where you feel lists or tables would be 
useful, etc.

References Cited

    A complete list of references cited in this rulemaking is available 
on the Internet at http://www.regulations.gov and upon request from the 
Sacramento Fish and Wildlife Office (see FOR FURTHER INFORMATION 
CONTACT).

Authors

    The primary authors of this package are the staff members of the 
Sacramento Fish and Wildlife Office.

List of Subjects in 50 CFR Part 17

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

Proposed Regulation Promulgation

    Accordingly, we propose to 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; 1531-1544; and 4201-4245, unless 
otherwise noted.

0
2. Amend Sec.  17.11(h) by adding entries for ``Frog, mountain yellow-
legged (northern California DPS)'', ``Frog, Sierra Nevada yellow-
legged'', and ``Toad, Yosemite'' to the List of Endangered and 
Threatened Wildlife in alphabetical order under AMPHIBIANS to read as 
follows:


Sec.  17.11  Endangered and threatened wildlife.

* * * * *
    (h) * * *

[[Page 24514]]



--------------------------------------------------------------------------------------------------------------------------------------------------------
                        Species                                                    Vertebrate
--------------------------------------------------------                        population where                                  Critical     Special
                                                           Historical range      endangered or         Status      When listed    habitat       rules
           Common name                Scientific name                              threatened
--------------------------------------------------------------------------------------------------------------------------------------------------------
 
                                                                      * * * * * * *
            AMPHIBIANS
 
                                                                      * * * * * * *
Frog, mountain yellow-legged       Rana muscosa........  U.S.A. (CA)........  Entire.............  E               ...........           NA           NA
 (northern California DPS).
 
                                                                      * * * * * * *
Frog, Sierra Nevada yellow-legged  Rana sierrae........  U.S.A. (CA, NV)....  Entire.............  E               ...........           NA           NA
 
                                                                      * * * * * * *
Toad, Yosemite...................  Anaxyrus canorus....  U.S.A. (CA)........  Entire.............  T               ...........           NA           NA
 
                                                                      * * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------


    Dated: March 15, 2013.
Rowan Gould,
Director, U.S. Fish and Wildlife Service.
[FR Doc. 2013-09600 Filed 4-24-13; 8:45 am]
BILLING CODE 4310-55-P