# 78 FR 24472: 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

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URL: https://www.frixlaw.com/law-library/statutes/FR_PRORULE_2013-09600

## Section

- **Citation:** 78 FR 24472
- **Heading:** 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
- **Jurisdiction:** Federal
- **Kind:** Regulations
- **Status:** In force
- **Text as of:** August 14, 2026
- **Source:** Compiled text
- **Location:** Federal Register / Vol. 78 / 78 FR 24472

## Text

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!”
s:
(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
ary
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
ommercial 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
e 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
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
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
al 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
ted 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.
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
er 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
ndicate 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
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)
uthern 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 EP25AP13.028
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)
pecifically, 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 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)
have a swollen, darkened thumb base (Wright and Wright 1949, pp. 424-430; Stebbins 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)
hern 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 (°C) (41 to 56 degrees Fahrenheit (°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)
tamorphosis (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)
ation (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)
evation 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,
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
ay 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)
yer 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)
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
opes 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
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
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
; 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
cluded 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
torical 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
quoia 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
(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 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
les); 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
ies 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
ready 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
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
e 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
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
ange. 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
a 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
ellow-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
bitats 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
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 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
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)
hout 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
rogs. 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
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)
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 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
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)
aining 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
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
ange 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 et al. 1983, p. 683; Chaney et al. 1990, p. 2)
es (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 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
act 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
cal 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)
d 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)
mber 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
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
tions 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
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
ted 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.)
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 ), 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)
ion of mountain yellow-legged frogs by the mountain garter snake ( Thamnophis ), 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
as 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
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)
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
emic 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.
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)
02, 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
hese 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 fro

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Source: Frix Law Library, https://www.frixlaw.com/law-library/statutes/FR_PRORULE_2013-09600. Check the current official text before relying on it. Not legal advice.