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

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A2014-09488

## Record

- **Collection:** Federal Register
- **Document type:** Rule
- **Published:** April 29, 2014
- **Citation:** 79 FR 24256

## 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 Species Status for Sierra Nevada Yellow-Legged Frog and Northern Distinct Population Segment of the Mountain Yellow-Legged Frog, and Threatened Species Status for Yosemite Toad

AGENCY:

Fish and Wildlife Service, Interior.

ACTION:

Final rule.

SUMMARY:

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

DATES:

This rule becomes effective June 30, 2014.

ADDRESSES:

This final rule is available on the Internet at
http://www.regulations.gov
and at the Sacramento Fish and Wildlife Office. Comments and materials we received, as well as supporting documentation used in preparing this rule, are available for public inspection at
http://www.regulations.gov.
All of the comments, materials, and documentation that we considered in this rulemaking are available by appointment, during normal business hours at: U.S. Fish and Wildlife Service, Sacramento Fish and Wildlife Office, 2800 Cottage Way, Room W-2605, Sacramento, CA 95825; 916-414-6600 (telephone); 916-414-6712 (facsimile).

FOR FURTHER INFORMATION CONTACT:

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

SUPPLEMENTARY INFORMATION:

Executive Summary

Why we need to publish a rule.
Under the Endangered Species Act, a species may warrant protection through listing if it is endangered or threatened throughout all or a significant portion of its range. Listing a species as an endangered or threatened species can be only completed by issuing a rule.

This rule will
finalize the listing of the Sierra Nevada yellow-legged frog (
Rana sierrae
) as an endangered species, the northern DPS of the mountain yellow-legged frog (
Rana muscosa
) as an endangered species, and the Yosemite toad (
Anaxyrus canorus
) as a threatened species.

The basis for our action.
Under the Endangered Species 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 have determined that both the Sierra Nevada yellow-legged frog and the northern DPS of the mountain yellow-legged frog are presently in danger of extinction throughout their entire ranges, based on the immediacy, severity, and scope of the threats to their 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. A rangewide reduction in abundance and geographic extent of surviving populations of frogs has occurred following decades of fish stocking, habitat fragmentation, and most recently a disease epidemic. Surviving populations are smaller and more isolated, and recruitment in diseased populations is much reduced relative to historic norms. This combination of population stressors makes persistence of these species precarious throughout the currently occupied range in the Sierra Nevada.

We have also determined that 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 historical 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).

Peer review and public comment.
We sought comments from independent specialists to ensure that our designations are based on scientifically sound data, assumptions, and analyses. We invited these peer reviewers to comment on our listing proposal. We also considered all comments and information received during the comment period.

Previous Federal Actions

Please refer to the proposed listing rule for the Sierra Nevada yellow-legged frog, the northern DPS of the mountain yellow-legged frog, and the Yosemite toad (78 FR 24472, April 25, 2013) for a detailed description of previous Federal actions concerning these species.

We will also be finalizing critical habitat designations for the Sierra Nevada yellow-legged frog, the northern DPS of the mountain yellow-legged, and the Yosemite toad under the Act in the near future.

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

Background

Please refer to the proposed listing rule for the Sierra Nevada yellow-legged frog and the northern DPS of the mountain yellow-legged frog under the Act (16 U.S.C. 1531
et seq.
) for additional species information. In the proposed rule, we described two separate species of yellow-legged frogs,
Rana sierrae
and
Rana muscosa,
that resulted from the recent taxonomic split (see Taxonomy section below) of the previously known
Rana muscosa,
which we referred to in our proposed rule as the mountain yellow-legged frog “species complex.” For clarity and in order to maintain consistency with our previous treatment of the southern DPS of the mountain yellow legged frog in southern California (67 FR 44382, July 2, 2002) as well as with our proposed rule, and for the purposes of this document, we retain the common name of mountain yellow-legged frog for
Rana muscosa,
as opposed to the new common name, southern mountain yellow-legged frog, as published by

Crother
et al.
(2008, p. 11). We also note that the California Department of Fish and Game (CDFG) was recently renamed the California Department of Fish and Wildlife (CDFW). We refer to the California Department of Fish and Wildlife in all cases when discussing the agency in the text. Where citations are from CDFG documents, we include CDFW in parentheses for clarification.

Taxonomy

Please refer to the proposed listing rule for the Sierra Nevada yellow-legged frog and the northern DPS of the mountain yellow-legged frog under the Act (16 U.S.C. 1531
et seq.
) for detailed species information on taxonomy (78 FR 24472, April 25, 2013).

Vredenburg
et al.
(2007, p. 371) determined that
Rana sierrae
occurs in the Sierra Nevada north of the South Fork Kings River watershed, along the east slope of the Sierra Nevada south into Inyo County at the southern extent of its range, and in the Glass Mountains just south of Mono Lake; and that
R. muscosa
occurs in the southern portion of the Sierra Nevada within and south of the South Fork Kings River watershed to the west of the Sierra Nevada crest (along with those populations inhabiting southern California) (Vredenburg
et al.
2007, pp. 370-371). The Monarch Divide separates these species in the western Sierra Nevada, while they are separated by the Cirque Crest to the east (Knapp 2013, unpaginated).

For purposes of this rule, we recognize the species differentiation as presented in Vredenburg
et al.
(2007, p. 371) and adopted by the official societies mentioned above (Crother
et al.
2008, p. 11), and in this final rule we refer to
Rana sierrae
as the Sierra Nevada yellow-legged frog, and we refer to the Sierra Nevada populations of
R. muscosa
as the northern DPS of the mountain yellow-legged frog. In California and Nevada, the Sierra Nevada yellow-legged frogs occupy the western Sierra Nevada north of the Monarch Divide (in Fresno County) and the eastern slope of the Sierra Nevada (east of the crest) from Inyo County through Mono County (including the Glass Mountains), to areas north of Lake Tahoe. The northern DPS of the mountain yellow-legged frog occurs only in California in the western Sierra Nevada and extends from south of the Monarch Divide in Fresno County through portions of the Kern River drainage. Figure 1 shows the approximate species boundaries within their historical ranges as determined by Knapp (unpubl. data).

BILLING CODE 4310-55-P

ER29AP14.001

BILLING CODE 4310-55-C
Many studies cited in the rest of 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 frog or mountain yellow-legged frog species complex.

Species Description

Please refer to the proposed listing rule for the Sierra Nevada yellow-legged frog and the northern DPS of the mountain yellow-legged frog under the Act (16 U.S.C. 1531
et seq.
) for additional information about species descriptions (78 FR 24472, April 25, 2013). The body lengths (snout to vent) of the mountain yellow-legged frogs range 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 1951, pp. 330-335; Zweifel 1955, p. 235; Zweifel 1968, p. 65.1). Dorsal (upper) coloration in adults is variable, exhibiting a mix of brown and yellow, but also can be grey, red, or green-brown, and is usually patterned with dark spots (Jennings and Hayes 1994, p. 74; Stebbins 2003, p. 233). These spots may be large (6 mm (0.25 in)) and few, smaller and more numerous, or a mixture of both (Zweifel 1955, p. 230). Irregular lichen- or moss-like patches (to which the name
muscosa
refers) may also be present on the dorsal surface (Zweifel 1955, pp. 230, 235; Stebbins 2003, p. 233).

The belly and undersurfaces of the hind limbs are yellow or orange, and this pigmentation may extend forward from the abdomen to the forelimbs (Wright and Wright 1949, pp. 424-429; Stebbins 2003, p. 233). Mountain yellow-legged frogs may produce a distinctive mink or garlic-like odor when disturbed (Wright and Wright 1949, p. 432; Stebbins 2003, p. 233). Although these species lack vocal sacs, they can vocalize in or out of water, producing what has been described as a faint 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, p. 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 1999, 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 1999, p. 31).

The tadpoles of mountain yellow-legged frogs generally are mottled brown on the dorsal side with a faintly yellow venter (underside) (Zweifel 1955, p. 231; Stebbins 2003, p. 460). Total tadpole length reaches 72 mm (2.8 in), the body is flattened, and the tail musculature is wide (about 2.5 cm (1 in) or more) before tapering into a rounded tip (Wright and Wright 1949, p. 431). The mouth has a maximum of eight labial (lip) tooth rows (two to four upper and four lower) (Stebbins 2003, p. 460). Tadpoles may take more than 1 year (Wright and Wright 1949, p. 431), and often require 2 to 4 years, to reach metamorphosis (transformation from tadpoles to frogs) (Cory 1962b, p. 515; Bradford 1983, pp. 1171, 1182; Bradford
et al.
1993, p. 883; Knapp and Matthews 2000, p. 435), depending on local climate conditions and site-specific variables.

The time required to reach reproductive maturity in mountain yellow-legged frogs is thought to vary between 3 and 4 years post metamorphosis (Zweifel 1955, p. 254). This information, in combination with the extended amount of time as a tadpole before metamorphosis, means that it may take 5 to 8 years for mountain yellow-legged frogs to begin reproducing. While the typical lifespan of mountain yellow-legged frogs is largely unknown, Matthews and Miaud (2007, p. 991) estimated that the total lifespan (including tadpole and adult life stages) ranges up to 14 years, with other documented estimates of up to 16 years of age for the Sierra Nevada yellow-legged frog (Fellers
et al.
2013, p. 155), suggesting that mountain yellow-legged frogs are long-lived amphibians.

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 typically ranging from 1,370 to 3,660 meters (m) (4,500 to 12,000 feet (ft)) ((CDFG (CDFW)) 2011, pp. A-1-A-5), but can occur as low as 1,067 m (3,500 ft) in the northern portions of their range (USFS 2011, geospatial data; USFS 2013, p. 4). 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). Mullally and Cunningham (1956a, p. 191) found adults sitting on rocks along the shoreline, where there was little or no vegetation. Although mountain yellow-legged frogs may use a variety of shoreline habitats, both tadpoles and adults are observed less frequently 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 have been associated with rocky streambeds and wet meadows surrounded by coniferous forest (Zweifel 1955, p. 237; Zeiner
et al.
1988, p. 88), although, in general, little is known about the ecology of mountain yellow-legged frogs in Sierra Nevada stream habitats (Brown 2013, unpaginated). Zweifel (1955, p. 237) found that streams utilized by adults varied 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, while aquatic substrates varied from bedrock to fine sand, rubble (rock fragments), and boulders. Jennings and Hayes (1994, p. 77) have indicated that mountain yellow-legged frogs appear absent from the smallest creeks, and suggest that it is probably because these creeks have insufficient depth for adequate refuge and overwintering habitat. However, Brown (2013, unpaginated) reports that the frogs are found in small creeks, although she notes that the extent to which these are remnant populations now excluded from preferred habitat is not known. In the northern portion of the Sierra Nevada yellow-legged frog range, the remnant populations primarily occur in stream habitats.

At higher elevations, these species occupy lakes, ponds, tarns (small steep-banked mountain lakes or pools, generally of glacial origin), 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, although many are bordered by exposed glaciated bedrock. Zweifel (1955, pp. 237-238) suggested that alpine lakeshores differ from the sandy or rocky shores inhabited by mountain yellow-legged frogs in lower elevation streams.

Adult mountain yellow-legged frogs breed in a variety of habitats including the shallows of stillwater habitat (lakes or ponds) and flowing inlet streams (Zweifel 1955, p. 243; Pope 1999, p. 30). Adults emerge from overwintering sites immediately following snowmelt, and will even move over ice to reach breeding sites (Pope 1999, 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, p. 341; Zweifel 1955, p. 243; Pope 1999, p. 30).

Lake depth is an important attribute defining habitat suitability for mountain yellow-legged frogs. At high elevations, both frogs and tadpoles overwinter under ice in lakes and streams. 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, pp. 1173, 1178-1179) found that, in years with exceptional precipitation (61 percent above average) and greater than normal ice-depths, mountain yellow-legged frog die-offs sometimes result from oxygen depletion during winter in lakes less than 4 m (13 ft) in depth, finding that in ice-covered lakes, oxygen depletion occurs most rapidly in shallow lakes relative to deeper lakes. 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 1999, pp. 42-43). Matthews and Pope 1999, p. 619) used radio telemetry to find that, when lakes had begun to freeze over, 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). Vredenburg
et al.
(2005, p. 565) noted that such behavior may be a response to presence of introduced fish. Matthews and Pope (1999, p. 622) suggested that the granite surrounding these overwintering habitats probably insulates mountain yellow-legged frogs from extreme winter temperatures, and that they can survive, provided there is an adequate supply of oxygen.

Mountain yellow-legged frog tadpoles maintain a relatively high body temperature by selecting warmer microhabitats (Bradford 1984, p. 973). During winter, tadpoles remain in warmer water below the thermocline (the transition layer between thermally stratified water). After spring overturn (thaw and thermal mixing of the water), they behaviorally modulate their body temperature by moving to shallow, near-shore water when warmer days raise surface water temperatures. During the late afternoon and evening, mountain yellow-legged frogs retreat to offshore waters that are less subject to night cooling (Bradford 1984, p. 974).

Available evidence suggests that adult mountain yellow-legged frogs display strong site fidelity and return to the same overwintering and summer habitats from year to year (Pope 1999, p. 45; Matthews and Preisler 2010, p. 252). Matthews and Pope (1999, pp. 618-623) observed that the frogs' movement patterns and habitat associations shifted seasonally. Frogs were well-distributed in most lakes, ponds, and creeks during August, but moved to only a few lakes by October. Matthews and Pope (1999, pp. 618-623) established home-range areas for 10 frogs and found that frogs remained through August in the lake or creek where they'd been captured, with movement confined to areas ranging from 19.4 to 1,028 square meters (m
2
) (23.20 to 1,229 square yards (y
2
)). In September, movements increased, with home-ranges varying from 53 to 9,807 m
2
in size (63.4 to 11,729 y
2
); six of nine frogs tagged in September moved from that lake by the end of the month, suggesting a pattern in which adult mountain yellow-legged frogs move among overwintering, breeding, and feeding sites during the year, with narrow distributions in early spring and late fall due to restricted overwintering habitat (Pope and Matthews 2001, p. 791). Although terrestrial movements of more than two or three hops from water were previously undocumented, overland movements exceeding 66 m (217 ft) were observed in 17 percent of tagged frogs, demonstrating that mountain yellow-legged frogs move overland as well as along aquatic pathways (Pope and Matthews 2001, p. 791). Pope and Matthews (2001, p. 791) also recorded a movement distance of over 1 km (including a minimum of 420 m (0.26 miles) overland movement and movement through a stream course). The farthest reported distance of a mountain yellow-legged frog from water is 400 m (1,300 ft) (Vredenburg 2002, p. 4).

Within stream systems, Sierra Nevada yellow-legged frogs have been documented to move 1,032 m (3,385 ft) over a 29-day period (Fellers
et al.
2013, p. 159). Wengert (2008, p. 18) conducted a telemetry study that documented single-season movement distances for Sierra Nevada yellow-legged frog of up to 3.3 kilometers (km) (2.05 miles (mi)) along streams. Along stream habitats, adults have been observed greater than 22 m (71 ft) from the water during the overwintering period (Wengert 2008, p. 20). Additionally, during the duration of the study, Wengert (2008, p. 13) found that 14 percent of the documented frog locations occurred greater than 0.2 m (0.66 ft) from the stream edge. While recent information suggests that the frogs in the Wengert study may have actually been foothill yellow-legged frog
(Rana boylii
) (Poorten
et al.,
2013, p. 4), we expect that the movement distances recorded are applicable to the Sierra Nevada yellow-legged frog within a stream-based system, as the ecology is comparable between the two sister taxa in regard to stream systems.

Almost no data exist on the dispersal of juvenile mountain yellow-legged frogs away from breeding sites; however, juveniles that may be dispersing 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 many 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 northern DPS of 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).

Historically, the range of the Sierra Nevada yellow-legged frog extended in California from north of the Feather River, in Butte and Plumas Counties, south to the Monarch Divide on the west side of the Sierra Nevada crest in Fresno County. East of the Sierra Nevada crest in California, the historical

range of the Sierra Nevada yellow-legged frog extends from areas north of Lake Tahoe, through Mono County (including the Glass Mountains) to Inyo County. Historical records indicate that the Sierra Nevada yellow-legged frog also occurred at locations within the Carson Range of Nevada, including Mount Rose in Washoe County, and also occurred in the vicinity of Lake Tahoe in Douglas County, Nevada (Linsdale 1940, pp. 208-210; Zweifel 1955, p. 231; Jennings 1984, p. 52; Knapp 2013, unpaginated).

Historically, the northern DPS of the mountain yellow-legged frog ranged from the Monarch Divide in Fresno County as far southward as Breckenridge Mountain, in Kern County (Vredenburg
et al.
2007, p. 371). The historical 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. Because we have determined that the historic range of
R. muscosa
is entirely within the State of California, in this final rule we correct the listing for the southern DPS of the mountain yellow-legged frog to remove Nevada from its historic range.

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.
1994, pp. 323-327; Jennings and Hayes 1994, p. 78; Jennings 1995, p. 133; Stebbins and Cohen 1995, pp. 225-226; Drost and Fellers 1996, p. 414; Jennings 1996, pp. 934-935; Knapp and Matthews 2000, p. 428; Vredenburg
et al.
2005, p. 564).

The current distributions of the Sierra Nevada yellow-legged frog and the northern DPS of the mountain yellow-legged frog are restricted primarily to publicly managed lands at high elevations, including streams, lakes, ponds, and meadow wetlands located within National Forests and National Parks. National Forests with extant (surviving) populations of mountain yellow-legged frogs include the Plumas National Forest, Tahoe National Forest, Humboldt-Toiyabe National Forest, Lake Tahoe Basin Management Unit, Eldorado National Forest, Stanislaus National Forest, Sierra National Forest, Sequoia National Forest, and Inyo National Forest. National Parks with extant populations of mountain yellow-legged frogs include Yosemite National Park, Kings Canyon National Park, and Sequoia National Park.

The most pronounced declines within the mountain yellow-legged frog complex have occurred north of Lake Tahoe in the northernmost 125-km (78-mi) portion of the range (Sierra Nevada yellow-legged frog) and south of Kings Canyon National Park in Tulare County (the northern DPS of the mountain yellow-legged frog). In the southernmost 50-km (31-mi) portion of the range, 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); except for a few small populations in the Kern River drainage, the northern DPS of the mountain yellow-legged frog is entirely extirpated from all of Sequoia National Park (Knapp 2013, unpaginated). As of 2000, mountain yellow-legged frog populations were known to 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 did occur in the National Parks generally exhibited higher abundances than those on USFS lands (Bradford
et al.
1994, p. 323; Knapp and Matthews 2000, p. 430).

Population Estimates and Status

Monitoring efforts and research studies have documented substantial declines of mountain yellow-legged frog populations in the Sierra Nevada. The number of extant populations has declined greatly over the last few decades. Remaining populations are patchily scattered throughout the historical range (Jennings and Hayes 1994, pp. 74-78; Jennings 1995, p. 133; Jennings 1996, p. 936). In the northernmost portion of the range (Butte and Plumas Counties), only a few Sierra Nevada yellow-legged frog populations have been documented since 1970 (Jennings and Hayes 1994, pp. 74-78; CDFG (CDFW)
et al.,
unpubl. data). Declines of both species have also been noted in the central and southern Sierra Nevada (Drost and Fellers 1996, p. 420; Knapp and Matthews 2001, pp. 433-437; Knapp 2013, unpaginated). In the southern Sierra Nevada (Sierra, Sequoia, and Inyo National Forests; and 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 large populations have been extirpated in this area (Bradford 1991, p. 176; Bradford
et al.
1994, pp. 325-326; Knapp 2002a, p. 10, Wake and Vredenburg 2009, pp. 11467-11470).

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.

CDFW (CDFG (CDFW) 2011, 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 populations (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 northern DPS of the 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, CDFW (CDFG 2011, pp. 20-25) compared historical and recent population status at the watershed scale. This is a rough index of the geographic extent of the species through their respective ranges. Within the Sierra Nevada, 44 percent of watersheds historically utilized by Sierra Nevada yellow-legged frogs, and 59 percent of watersheds historically utilized by northern DPS mountain yellow-legged frogs, no longer support extant populations. However, this watershed-level survey methodology is not a good indicator of population changes because a watershed is counted as recently occupied if a single individual (at any life stage) is observed within the entire watershed even though several individual populations may have been lost (CDFG (CDFW) 2011b, p. 20). Therefore, these surveys likely underestimate population declines. Many watersheds support only a single extant metapopulation, which occupies one to several adjacent water bodies

(CDFG (CDFW) 2011, p. 20). Remaining populations are generally very small.

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.
1994, 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. Because this work was completed before the taxonomic division of mountain yellow-legged frogs, we have not differentiated between the two species here. When both species are combined, this resurvey effort detected mountain yellow-legged frogs at 19.4 percent of historical sites (Bradford
et al.
1994, 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 in Yosemite National Park, and reported frog presence at 2 of 14 historical sites where what is now known as Sierra Nevada yellow-legged frogs occurred. 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 3 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 colonized. 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). CDFW (CDFG 2011, p. 20) assessed data from sites where multiple surveys were completed after 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 has been conducting a rangewide, long-term monitoring program for the Sierra Nevada yellow-legged frog and the northern DPS of the mountain yellow-legged frog on National Forest lands in the Sierra Nevada, 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 monitoring cycles spanning 208 watersheds (Brown
et al.
2011, pp. 3-4). The results of this assessment indicate that the species have declined in both distribution and abundance. Based on surveys conducted from 2002 through 2009, breeding activity was found in about half (48 percent) of the watersheds where the species were found in the decade prior to SNAMPH monitoring (1990 and 2001) (Brown
et al.
2011, p. 4). Breeding was found in 3 percent of watersheds where species had been found prior to 1990. Rangewide, breeding was found in 4 percent of watersheds. 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 the 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 the 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 than historical norms, and the density of populations per watershed has declined substantially; as a result, many watersheds currently support single metapopulations at low abundances.

Distinct Vertebrate Population Segment 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 DPSs 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, three elements are considered in a decision regarding the status of a possible DPS as endangered or threatened under the Act. The elements are: (1) Discreteness of the population segment in relation to the remainder of the species to which it belongs; (2) the significance of the population segment to the species to which it belongs; and (3) the population segment's conservation status in relation to the Act's standards for listing. In other words, if we determine that a population segment of a vertebrate species being considered for listing is both discrete and significant, we would conclude that it represents a DPS, and thus a “species” under section 3(16) of the Act, whereupon we would evaluate the level of threat to the DPS based on the five listing factors established under section 4(a)(1) of the Act to determine whether listing the DPS as an “endangered species” or a “threatened species” is warranted.

Please refer to the proposed listing rule for detailed information about the distinct vertebrate population segment analysis for the northern DPS of the mountain yellow-legged frog (78 FR 24472, April 25, 2013). We previously confirmed the status of the southern California population of the mountain yellow-legged frog as a DPS at the time that it was listed as endangered under the Act (67 FR 44382, pp. 44384-44385). We summarize below the analysis for discreteness and significance for the northern California population of the mountain yellow-legged frog (in the Sierra Nevada); this summary includes changes from the proposed rule to address comments received from the public (78 FR 24472, April 25, 2013).

Discreteness

Under our DPS Policy, a population segment of a vertebrate species may be considered discrete if it satisfies either 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 analysis of the northern population segment of the mountain yellow-legged frog (
Rana muscosa
) (in the Sierra Nevada) is based on the marked separation from other populations. The range of the mountain yellow-legged frog is divided by a natural geographic barrier, the Tehachapi Mountains, which physically isolates the 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). The geographic separation of the Sierra Nevada and southern California frogs was recognized in the earliest description of the species by Camp (1917), who treated frogs from the two areas as separate subspecies within the
R. boylii
group (see more on classification of the mountain yellow-legged frogs in Taxonomy). There is no contiguous habitat that provides connectivity between the two populations that is sufficient for the migration, growth, rearing, or reproduction of dispersing frogs. Genetic differences well-supported in the scientific literature also provide evidence of this separation (see Taxonomy). Therefore, we find that the northern population segment of the mountain yellow-legged frog (
Rana muscosa
) (in the Sierra Nevada) is discrete from the remainder of the species.

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. Our DPS policy provides several potential considerations that may demonstrate the significance of a population segment to the remainder of its taxon, including: (1) Evidence of the persistence of the discrete population segment in an ecological setting unusual or unique for the taxon, (2) evidence that loss of the discrete 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 historic range, or (4) evidence that the discrete population segment differs markedly from the remainder of the species in its genetic characteristics.

We have found substantial evidence that three of the four significance criteria are met by the discrete northern population segment of the mountain yellow-legged frog that occurs in the Sierra Nevada. These include its persistence in an ecological setting that is unique for the taxon, evidence that its loss would result in a significant gap in the range of the taxon, and its genetic uniqueness (reflecting significant reproductive isolation over time). To establish the significance of the discrete northern population segment, we rely on the effect that the loss of this population segment would have on the range of the taxon, and supplement that with evidence that the population segment persists in an ecological setting unusual or unique for the taxon and also differs from other population segments in its genetic characteristics. There are no introduced populations of the northern DPS of the mountain yellow-legged frog outside of the species' historical range.

Evidence indicates that loss of the northern population segment of the mountain yellow-legged frog (in the Sierra Nevada) would result in a significant gap in the range of the taxon. The Sierran mountain yellow-legged frogs comprise the entire distribution of the species in approximately the northern half of the species' range, and loss of the distinct population segment in the northern portion of the range could have significant conservation implications for the species. Furthermore, loss of the northern population segment of the mountain yellow-legged frog (in the Sierra Nevada) would reduce the species to the remaining small, isolated sites in the streams of southern California (USFWS, Jul 2012, pp. 11-12). Loss of the northern population segment of the mountain yellow-legged frog would leave an area of the southern Sierra Nevada over 150 km (93 mi) in length without any ranid (frogs in the genus Ranidae) frogs, which were once abundant and widespread in the higher elevation Sierra Nevada (Cory 1962b, p. 515; Fellers 1994, p. 5). The potential loss of the northern population segment of the mountain yellow-legged frog would constitute a significant gap in the range of the species.

One of the most striking differences between the northern population segment and the southern population segment of the mountain yellow-legged frogs is the difference in the ecological setting in which they each persist. Zweifel (1955, pp. 237-241) observed that the frogs in southern California are typically found in steep-gradient streams in the chaparral belt at low elevations (370 m (1,220 ft)), even though they may range into small meadow streams at higher elevations up to 2,290 m (7,560 ft). In contrast, frogs from the northern population segment of mountain yellow-legged frogs are most abundant in high-elevation lakes and slow-moving portions of streams where winter conditions are extreme. David Bradford's (1989) southern Sierra Nevada study of mountain yellow-legged frogs, for example, was conducted in Sequoia and Kings Canyon National Parks at high elevations between 2,910 and 3,430 m (9,600 to 11,319 ft). The rugged canyons of the arid mountain ranges of southern California, where waters seldom freeze, bear little resemblance to the alpine lakes and streams of the Sierra Nevada where adult frogs and tadpoles must overwinter at the bottoms of ice and snow-covered lakes for up to 9 months of the year. The significantly different ecological settings between mountain yellow-legged frogs in southern California and those in the northern population segment (in the Sierra Nevada) distinguish these populations from each other.

Finally, the northern population segment of the mountain yellow-legged frog is biologically significant based on genetic differences. 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 clade represented by the endangered southern California DPS of the mountain yellow-legged frog. Macey
et al.
(2001, p. 141) estimated the genetic divergence between the northern population of mountain yellow-legged frogs (in the Sierra Nevada) and the southern population of mountain yellow-legged frogs (in southern California) to have occurred 1.4 million years before present (mybp), thereby indicating functional isolation.

The loss of the northern population of the mountain yellow-legged frog would result in a significant gap in the range of the mountain yellow-legged frog species. The differences between the ecological settings for the southern

population of mountain yellow-legged frogs (steep-gradient streams that seldom freeze) and the northern population of mountain yellow-legged frogs (high-elevation lakes and slow-moving portions of streams where frogs overwinter under ice and snow for up to 75 percent of the year) are significant. Additionally, the genetic distinction between these two populations reflects isolation for over a million years. Therefore based on the information discussed above, we find that northern population of the mountain yellow-legged frog (in the Sierra Nevada mountains) meets the significance criteria under our Policy Regarding the Recognition of Distinct Vertebrate Population Segments (61 FR 4722).

DPS Conclusion

Based on the best scientific and commercial data available on distribution as well as ecological setting and genetic characteristics of the species, we have determined that the northern population segment of the mountain yellow-legged frog (in the Sierra Nevada) is both discrete and significant per our DPS policy. Therefore, we conclude that the northern discrete population segment of the mountain yellow-legged frog is a DPS, and thus a “species” under section 3(16) of the Act. Our determination of biological and ecological significance is appropriate because the population segment has a geographical distribution that is biologically meaningful.

Summary of Changes From the Proposed Rule for the Sierra Nevada Yellow-Legged Frog and the Northern DPS of the Mountain Yellow-Legged Frog

Based on peer review, Federal and State, and public comments (see comments in the Summary of Comments and Recommendations section below), we have clarified information in the sections provided for the Sierra Nevada yellow-legged frog and the northern DPS of the mountain yellow-legged frog to better characterize our knowledge of the species' habitat requirements, correcting some information based on peer review (vocalizations (Species Description), species ranges (Taxonomy and Historic and Current Ranges and Distribution sections), current distribution in Sequoia National Park (Historic and Current Ranges and Distribution), and clarifying the basis for our determination of significance for the northern population of the mountain yellow-legged frog in response to public comments (Distinct Vertebrate Population Segment)), occasionally adding additional information where needed. In the Summary of Factors Affecting the Species section, we have re-ordered threats in Factor A so that the primary activity that has modified the habitat of the mountain yellow-legged frog complex is addressed first, while activities with potential only for localized effects are addressed later. Based on peer review, and Federal, State, county, and public comments, we have added information where needed and clarified our findings on the role of current activities, such as grazing, recreation, packstock use, etc., in species declines. We reviewed the analysis of dams and diversions that we presented in the proposed rule and determined that most large reservoir facilities are below the current range of the mountain yellow-legged frogs. We revised the dams and water diversions threat magnitude from moderate prevalent in the proposed rule to minor localized where such structures occur in this final rule.

In the proposed rule, we stated that grazing presented a minor prevalent threat. We reworded this final rule to more accurately reflect the contribution of legacy effects of past grazing levels to this threat assessment. We found that current livestock grazing that complies with forest standards and guidelines is not expected to negatively affect mountain yellow-legged frog populations in most cases, although limited exceptions could occur (where extant habitat is limited and legacy effects to meadows still require restoration, where habitat is limited such as in stream riparian zones or small meadows, or where grazing standards are exceeded). Rangewide, livestock grazing is not a substantial threat to the species.

In response to information provided during the public comment period, we added a discussion of mining activities in the Factor A discussion. In this final rule, we determine that, while most mining activities take place below the extant ranges of the species, where some types of mining activities occur, localized habitat-related effects may result.

We added new information available on packstock grazing, retaining our finding that packstock grazing is only likely to be a threat to mountain yellow-legged frogs in limited situations. We also added more information on roads and timber harvests, and we clarified that these activities primarily do not occur where there are extant populations (except where frogs occur in the northern or lower elevation portions of the range), and that USFS standards are generally designed to limit potential effects of such activities. We clarified the threat magnitude for roads and timber harvest from minor prevalence rangewide to not a threat to extant populations across much of the species' ranges (although they may pose important habitat-related effects to the species in localized areas). We reviewed information provided by the U.S. Forest Service (USFS), the National Park Service (NPS), CDFW, and others on recreation activities, and we changed our conclusion on the recreation threat magnitude from low significance to the species overall to not considered a threat to populations over much of their range. However, we recognize that there may be localized effects, especially outside of backcountry areas where use is high or where motorized and mechanical use occurs in extant frog habitat.

We added a brief discussion of bullfrogs (
Lithobates catesbeiana
) under Factor C for mountain yellow-legged frogs noting that bullfrog predation and competition is expected to have population-level effects to mountain yellow-legged frog populations in those low elevation areas, or in the Lake Tahoe Basin, where the two species may co-occur. We slightly revised our characterization of the recent population declines of the mountain yellow-legged frogs due to
Batrachochytrium dendrobatidis
(Bd), identifying the fungus as one of the primary drivers of recent declines, and adding information provided by peer reviewers and agencies. We also added information to our discussion under Factor D, including information about the National Park Service Organic Act, information on the provision in the Wilderness Act about withdrawing minerals, and information on the status of the Sierra Nevada yellow-legged frog and the mountain yellow-legged frog under the California Endangered Species Act (CESA). We also moved discussion of current CDFW fisheries management to the “Habitat Modification Due to Introduction of Trout to Historically Fishless Areas” section under Factor A.

We removed the discussion of contaminants under Factor E and refer readers to the proposed rule. Although we received additional information that clarified some text and provided additional references regarding contaminants, the clarifications supported our conclusions in the proposed rule that the best available information indicates that contaminants do not pose a current or continuing threat to the species. We also added additional information either available in our files, or provided by commenters,

to clarify and support our finding on the threat of climate change. We revised the explanation in the determinations for each species to reflect the above changes.

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, and changes from the proposed rule (78 FR 24472, April 25, 2013) are reflected in these discussions. 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

A number of hypotheses, including habitat modification (including loss of vegetation, loss of wetlands, habitat modification for urban development, and degradation of upland habitats) have been proposed for recent global amphibian declines (Bradford
et al.
1993, p. 883; Corn 1994, p. 62; Alford and Richards 1999, p. 134). However, physical habitat modification has not been associated with the rangewide decline of mountain yellow-legged frogs. Mountain yellow-legged frogs occur primarily 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 may have played a role in the modification of mountain yellow-legged frog habitat. We have identified the following habitat-related activities as potentially relevant to the conservation status of the mountain yellow-legged frog complex: Fish introductions (see also Factor C, below), dams and water diversions, livestock grazing, timber management, road construction and maintenance, packstock use, recreational activities, and fire management activities. Such activities may have degraded habitat in ways that have reduced its capacity to sustain viable populations and may have fragmented and isolated mountain yellow-legged frog populations from each other.

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 introduced trout resulting from stocking programs for the creation and maintenance of a recreational 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 is one of the primary threats 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), but natural barriers prevented fish from colonizing the higher-elevation waters of the Sierra Nevada watershed (Moyle
et al.
1996, p. 354). The upper reaches of the Kern River, where native fish such as the Little Kern golden trout (
Oncorhynchus mykiss whitei
) and California golden trout (
O. m. aguabonita
) evolved, represent the only major exception to the 1,800-m (6,000-ft) elevation limit for fishes within the range of the mountain yellow-legged frog in the Sierra Nevada (Moyle 2002, p. 25). Additionally, prior to extensive planting, native Paiute cutthroat (
O. clarki seleneris
) and Lahontan cutthroat (
O. c. henshawi
) were limited in their distribution to several rivers, streams, and limited large lakes in the eastern Sierra Nevada (Knapp 1996, p. 369; Moyle 1996
et al.,
pp. 954-958), indicating some overlap with the range of the Sierra Nevada yellow-legged frog.

Some of the first practitioners of trout stocking in the Sierra Nevada were the Sierra Club, local sportsmen's clubs, private citizens, and the U.S. military (Knapp 1996, p. 8; Pister 2001, p. 280). As more hatcheries were built and the management of the trout fishery became better organized, fish planting continued for the purpose of increased angler opportunities and success (Pister 2001, p. 281). After World War II, the method of transporting trout to high-elevation areas changed from packstock to aircraft, which allowed stocking in more remote lakes and in greater numbers. With the advent of aerial stocking, trout planting expanded to new areas, with higher efficiency.

Brook trout (
Salvelinus fontinalis
), brown trout (
Salmo trutta
), rainbow trout (
Oncorhynchus mykiss
), and other trout species assemblages have been planted in most streams and lakes of the Sierra Nevada (Knapp 1996, p. 8; Moyle 2002, p. 25). Since the advent of aerial stocking, backcountry areas not accessible by truck are stocked by air (Pert 2002, pers. comm.), which limits stocking to lakes. National Forests in the Sierra Nevada have a higher proportion of lakes with fish occupancy than do National Parks (Knapp 1996, p. 3), primarily because the National Park Service (NPS) began phasing out fish stocking within their jurisdictional boundaries in 1969, with limited stocking occurring until it was terminated altogether in Sierra Nevada National Parks in 1991 (Knapp 1996, p. 9). California Department of Fish and Wildlife (CDFW) continues to stock trout in National Forest water bodies, but in 2001 reduced the number of stocked water bodies to reduce impacts to native amphibians (ICF Jones & Stokes 2010, pp. ES-1-ES-16). Current stocking decisions are based on criteria outlined in the Environmental Impact Report for the Hatchery and Stocking Program (ICF Jones & Stokes 2010, Appendix K).

Fish stocking as a practice has been widespread throughout the range of both species of mountain yellow-legged frogs. Knapp and Matthews (2000, p. 428) indicated that 65 percent of the water bodies that were 1 ha (2.5 ac) or larger in National Forests they studied were stocked with fish on a regular basis. Over 90 percent of the total water body surface area in the John Muir Wilderness was occupied by nonnative trout (Knapp and Matthews 2000, p. 434).

Another detrimental feature of fish stocking is that, in the Sierra Nevada, fish often persist in water bodies even after stocking ceases. Thirty-five to 50 percent of lakes larger than 1 ha (2.5 ac) within Sierra Nevada National Parks are occupied by nonnative fish, which is

only a 29 to 44 percent decrease in fish occupancy since fish stocking was terminated around 2 decades before the estimate was made (Knapp 1996, p. 1). Though data on fish occupancy in streams are lacking throughout the Sierra Nevada, Knapp (1996, pp. 9-11) estimated that 60 percent of the streams in Yosemite National Park were still occupied by introduced trout because trout readily move out of lakes to colonize both inlet and outlet streams. The presence of trout in these once fishless waters has modified the habitat at a landscape scale.

Thus, the frog's habitat has been modified due to the introduction of a nonnative predator that both competes for limited food resources and directly preys on mountain yellow-legged frog tadpoles and adults (see Factor C below). Presence of nonnative trout in naturally fishless ecosystems has had profound effects on the structure and composition of faunal assemblages, severely reducing not only amphibians, but also zooplankton and large invertebrate species (see Knapp 1996, p. 6; Bradford
et al.
1998, p. 2489; Finlay and Vredenburg 2007, pp. 2194-2197). Within the frog's historical range, past trout introductions and the continuing presence of fish in most lakes resulted in the elimination of frogs from most waters that were suitable for fish. Across the range of these species in the Sierra Nevada, the presence of fish in most of the deeper lakes has altered the aquatic habitat that mountain yellow-legged frogs rely on for overwintering and breeding, and has also reduced connectivity among frog populations. Fish now populate the deeper lakes and connecting streams and largely separate and increase the distance between the current sites inhabited by the highly-aquatic frogs (the connectivity of occupied sites in present versus former fishless conditions differs by approximately 10-fold) (Bradford
et al.
1993, pp. 884-887; Knapp 1996, pp. 373-379). Where reservoirs harbor introduced fish, successful reproduction of mountain yellow-legged frogs may be reduced if there are no shallow side channels or separate pools (Jennings 1996, p. 939). Most reservoirs do not overlap significantly with the current extant range of the species (CDFW 2013, p. 3) (see Dams and Water Diversions below); however, a number of reservoirs were constructed in the mid-1900s at mid-elevations within lower edges of the species' historic range (for example, Sierra Nevada yellow-legged frogs were taken from Bear River Reservoir (Eldorado National Forest), Union Reservoir (Stanislaus National Forest), and several others). With the exception of one 1999 record from Faggs Reservoir on the Plumas National Forest, all of several dozen records of the species from reservoirs are pre-1975, and at least half pre-date the water development projects at those locations (Brown
et al.
2009, p. 78). All of these reservoirs now harbor introduced fish species, and at least two also harbor bullfrogs, suggesting that subsequent introductions may have played a role in past declines in those areas (see Brown
et al.
2009, p. 78).

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; Bradford
et al.
1998, pp. 2482, 2489; Knapp and Matthews 2000, p. 428; Knapp
et al.
2001, p. 401). Fish stocking programs have negative ecological implications because fish eat aquatic fauna, including amphibians and invertebrates (Bahls 1992, p. 191; Erman 1996, p. 992; Jennings 1996, p. 939; Knapp 1996, pp. 373-379; 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. Introductions of salmonids to fishless lakes have also been associated with alteration of nutrient cycles and primary productivity in mountain lakes, including those in the Sierra Nevada (Schindler
et al.
2001, pp. 308, 313-319).

Knapp and Matthews (2000, p. 428) surveyed more than 1,700 water bodies, and concluded that a strong negative correlation exists between introduced trout and mountain yellow-legged frogs (Knapp and Matthews 2000, p. 435). Consistent with this finding are the results of an analysis of the distribution of mountain yellow-legged frog tadpoles, which indicate that the presence and abundance of this life stage are reduced dramatically in fish-stocked lakes (Knapp
et al.
2001, p. 408). Knapp (2005a, pp. 265-279) also compared the distribution of nonnative trout with the distributions of several amphibian and reptile species in 2,239 lakes and ponds in Yosemite National Park, and found that mountain yellow-legged frogs were five times less likely to be detected in waters where trout were present. Even though stocking within the National Park ceased in 1991, more than 50 percent of water bodies deeper than 4 m (13 ft) and 75 percent deeper than 16 m (52 ft) still contained trout populations in 2000-2002 (Knapp 2005a, p. 270). Both trout and mountain yellow-legged frogs utilize deeper water bodies. Based on the results from Knapp (2005a), the reduced detection of frogs in trout-occupied waters indicates that trout are excluding mountain yellow-legged frogs from some of the best aquatic habitat.

Several aspects of the mountain yellow-legged frog's life history are thought to 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 highly aquatic and are found primarily in lakes, most of which now contain trout (Knapp 1996, p. 14). In comparison to other Sierran frogs, mountain yellow-legged frog tadpoles generally need at least 2 years to reach metamorphosis, which restricts breeding to waters that are deep enough to avoid depletion of oxygen when ice-covered (Knapp 1996, p.14). Overwintering adults must also avoid oxygen depletion when the water is covered by ice, generally limiting overwintering to deeper waters that do not become anoxic (Mullally and Cunningham 1956a, p. 194; Bradford 1983, p. 1179; Knapp and Matthews 2000, pp. 435-436). At high elevations, both tadpoles and adults overwinter under ice for up to 9 months (Bradford 1983, p. 1171). These habitat requirements appear to restrict successful breeding and overwintering to the deeper water bodies where the chances of summer drying and winter freezing are reduced, the same water bodies that are most suitable for fishes; fishes also need deeper water bodies where the chances of summer drying and winter freezing are reduced (Bradford 1983, pp. 1172-1179; Knapp 1996, p. 14; Knapp and Matthews 2000, pp. 429, 435-436). Past fish-stocking practices targeted the deeper lakes, so the percentage of water bodies containing fish has increased with water depth, resulting in elimination of mountain yellow-legged frogs from once suitable habitats in which they were historically most common, and thereby generally isolating populations to the shallower, marginal habitats that do not have fish (Bradford 1983, pp. 1172-1179; Bradford
et al.
1993, pp. 884, 886-

887; Knapp and Matthews 2000, pp. 435-436).

Mountain yellow-legged frogs and trout (native and nonnative) do co-occur at some sites, but these co-occurrences are generally thought to represent mountain yellow-legged frog “sink” populations (areas with negative population growth rates in the absence of immigration) (Bradford
et al.
1998, p. 2489; Knapp and Matthews 2000, p. 436). Mountain yellow-legged frogs have also been extirpated at some fishless bodies of water (Bradford 1991, p. 176; Drost and Fellers 1996, p. 422). A possible explanation is the isolation and fragmentation of remaining populations due to introduced fishes in the streams that once provided mountain yellow-legged frogs with dispersal and recolonization routes; these remote populations are now non-functional as metapopulations (Bradford 1991, p. 176; Bradford
et al.
1993, p. 887). Based on a survey of 95 basins within Sequoia and Kings Canyon National Parks, Bradford
et al.
(1993, pp. 885-886) estimated that the introduction of fishes into the study area resulted in an approximately 10-fold increase in habitat fragmentation between populations of mountain yellow-legged frogs. Knapp and Matthews (2000, p. 436) believe that this fragmentation has further isolated mountain yellow-legged frogs within the already marginal habitat left unused by fishes.

Fragmentation of mountain yellow-legged frog habitat renders populations 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). If the distance between sites is too great, amphibians may not readily recolonize unoccupied sites following local extinctions because of physiological constraints, the tendency to move only short distances, and high site fidelity. 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.

In 2001, CDFW revised fish stocking practices and implemented an informal policy on fish stocking in the range of the Sierra Nevada yellow-legged frog and northern DPS of the mountain yellow-legged frog. This policy directs that: (1) Fish will not be stocked in lakes with known populations of mountain yellow-legged frogs, nor in lakes that have not yet been surveyed for mountain yellow-legged frog presence; (2) waters will be stocked only with a fisheries management justification; and (3) the number of stocked lakes will be reduced over time. In 2001, the number of lakes stocked with fish within the range of the mountain yellow-legged frog in the Sierra Nevada was reduced by 75 percent (Milliron 2002, pp. 6-7; Pert
et al.
2002, pers. comm.). Current CDFW guidelines stipulate that water bodies within the same basin and 2 km (1.25 mi) from a known mountain yellow-legged frog population will not be stocked with fish unless stocking is justified through a management plan that considers all the aquatic resources in the basin, or unless there is heavy angler use and no opportunity to improve the mountain yellow-legged frog habitat (Milliron 2002a, p. 5). The Hatchery and Stocking Program Environmental Impact Report/Environmental Impact Statement, finalized in 2010 (ICF Jones & Stokes 2010, Appendix K), outlines a decision approach to mitigate fish stocking effects on Sierra amphibians that prohibits fish stocking in lakes with confirmed presence of a limited number of designated species, including the mountain yellow-legged frogs (see ICF Jones & Stokes 2010, Appendix E) using recognized survey protocols. Large reservoirs generally continue to be stocked to provide a put-and-take fishery for recreational angling.

As part of the High Mountain Lakes Project, CDFW is in the process of developing management plans for basins within the range of the Sierra Nevada yellow-legged frog and the northern DPS of mountain yellow-legged frog (CDFG (CDFW) 2001, p. 1; Lockhart 2011, pers. comm.). CDFW states that objectives of the basin plans specific to the mountain yellow-legged frog include management in a manner that maintains or restores native biodiversity and habitat quality, supports viable populations of native species, and provides for recreational opportunities that consider historical use patterns (CDFG (CDFW) 2001, p. 3). They state that, under this approach, lakes that support mountain yellow-legged populations in breeding, foraging, or dispersal, and/or present opportunities to restore or expand habitat, are managed for the conservation of the species. Lakes that do not support mountain yellow-legged frogs are not viable restoration opportunities, and lakes that support trout populations are managed primarily for recreational angling (CDFG (CDFW) 2001, p. 3). They further note that lakes managed for recreational angling may be stocked if CDFW determines that stocking the lake will achieve a desirable fisheries management objective and is not otherwise precluded by stocking decision guidelines and agreements (for stocking decision documents, see CDFW 2013, pp. 1, 2).

Since the mid-1990s, various parties, including researchers, CDFW, NPS, and the USFS, have implemented a variety of projects to actively restore habitat for the mountain yellow-legged frog via the removal of nonnative trout (USFS 2011, pp. 128-130; NPS 2013, pp. 3-5).

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) (see Knapp
et al.
2007a, pp. 11-19). 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

While a majority of dams and water diversions within the Sierra Nevada are located at lower elevations (USFS 2011, p. 83), some large reservoirs have been constructed within the historic range of the mountain yellow-legged frog complex. These large reservoirs include, but are not limited to Huntington Lake, Florence Lake, Lake Thomas A. Edison, Saddlebag Lake, Cherry Lake, Hetch Hetchy, Upper and Lower Blue Lakes, Lake Aloha, Silver Lake, Hell Hole Reservoir, French Meadow Reservoir, Lake Spaulding, Alpine Lake, Loon Lake, and Ice House Reservoir. A number of these occur at elevations below the current range of the species, indicating that the network of large water and power projects found at lower elevations does not overlap significantly with the current accepted distribution of the mountain yellow-legged frogs in the Sierra Nevada (CDFW 2013, p. 3).

Kondolf
et al.
(1996, p. 1014) report that dams can have direct effects to

riparian habitat through permanent removal of habitat to construct roads, penstocks, powerhouses, canals, and dams. Impacts of reservoirs include flooding of riparian vegetation and impediments to establishment of new shoreline vegetation by fluctuating water levels. Dams can alter the temperature and sediment load of the rivers they impound (Cole and Landres 1996, p. 175). Dams, water diversions, and their associated structures can also alter the natural flow regime with unseasonal and fluctuating releases of water (Kondolf
et al.
1996, p. 1014). We expect most such effects to occur in stream systems below the extant range of the mountain yellow-legged frogs, although it is possible that stream localities at the northern extent of the range or at low elevations may be affected (see also CDFW 2013, pp. 2-4).

The extent of past impacts to mountain yellow-legged frog populations from habitat loss or modification due to reservoir projects has not been quantified. CDFW (2013, p. 3) has noted that there are locations where the habitat inundated as the result of dam construction (for example, Lake Aloha in the Desolation Wilderness) may have been of higher quality for mountain yellow-legged frogs than the created impoundment. Reservoirs can provide habitat for introduced predators, including fish, bullfrogs, and crayfish, and in some cases, the past construction of reservoirs has facilitated the spread of nonnative fish (CDFW 2013, pp. 3, 4). In such cases, reservoirs may function as barriers to movement of mountain yellow-legged frogs. However, CDFW reported observing mountain yellow-legged frogs dispersing through fishless reservoirs (CDFW 2013, p. 4). (For a complete discussion of the impacts of fish stocking see Habitat Modification Due to Introduction of Trout to Historically Fishless Areas above and the discussion under Factor C.).

Most of the dams constructed within the historic range of the mountain yellow-legged frogs are small streamflow-maintenance dams (CDFW 2013, p. 13) at the outflows of high-elevation lakes. These small dams may create additional habitat for the species and can act as barriers to fish migration from downstream tributaries into fishless habitats, although they do not impede frog movement (CDFW 2013, p. 3). CDFW staff (2013, p. 13) have observed that extant frog populations may have persisted where such dams have helped to preserve a fishless environment behind the dam.

Based on comments from CDFW and others and the provision of additional information, we have reviewed the analysis of dams and diversions that we presented in the proposed rule. We find that most large facilities are below the current range of the mountain yellow-legged frogs and have revised our finding. In the proposed rule, we stated that dams and diversions presented a moderate, prevalent threat to persistence and recovery of the species. In this final rule, we find that dams and water diversions present a minor, localized threat to persistence and recovery of the species where structures occur.

Livestock Use (Grazing)

The combined effect of legacy conditions from historically excessive grazing use and current livestock grazing activities has the potential to impact habitat in the range of the mountain yellow-legged frog. The following subsections discuss the effects of excessive historical grazing, current extent of grazing, and current grazing management practices. As discussed below, grazing has the potential to reduce 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.

Grazing of livestock in riparian areas impacts the function of the aquatic system in multiple ways, including soil compaction, which increases runoff and decreases water availability to plants; vegetation removal, which promotes increased soil temperatures and evaporation rates at the soil surface; and direct physical damage to the vegetation (Kauffman and Krueger 1984, pp. 433-434; Cole and Landres 1996, pp. 171-172; Knapp and Matthews 1996, pp. 816-817). Streamside vegetation protects and stabilizes streambanks by binding soils to resist erosion and trap sediment (Kauffman
et al.
1983, p. 683; Chaney
et al.
1990, p. 2). Grazing within mountain yellow-legged frog habitat has been observed to remove vegetative cover, potentially exposing frogs to predation and increased desiccation (Knapp 1993b, p. 1; Jennings 1996, p. 539), and to lead to erosion which may silt in ponds and thereby reduce the water depth needed for overwinter survival (Knapp 1993b, p. 1). However, an appropriately managed grazing regime (including timing and intensity) can enhance primary riparian vegetation attributes that are strongly correlated to stream channel and riparian soil stability conditions necessary to maintain a functioning riparian system (George
et al.
2011, p. 227). Although, where highly degraded conditions such as downcut channels exist, grazing management alone may not be sufficient to restore former riparian conditions (George
et al.
2011, p. 227).

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 can negatively impact mountain yellow-legged frogs by altering riparian habitat (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 can contribute to the downcutting of streambeds and lower the water table. The degree of erosion caused by livestock grazing can vary with slope gradient, aspect, soil condition, vegetation density, and accessibility to livestock, with soil disturbance greater in areas overused by livestock (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 can modify shoreline habitats by removing overhanging banks that provide shelter, and grazing contributes to the siltation of breeding ponds. Bradford (1983, p. 1179) and Pope (1999, pp. 43-44) have documented the importance of deep lakes to overwinter survival of these species. We expect that pond siltation due to grazing may reduce the depth of breeding ponds and cover underwater crevices in some circumstances where grazing is heavy and where soils are highly erodable, thereby making the ponds less suitable, or unsuitable, as overwintering habitat for tadpoles and adult mountain yellow-legged frogs.

Effects of Excessive Historical Grazing

In general, historical livestock grazing within the range of the mountain yellow-legged frog was at a high (although undocumented), unregulated and unsustainable 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). Historical evidence indicates that heavy livestock use in the Sierra Nevada has resulted in widespread damage to rangelands and riparian systems due to sod destruction in meadows, vegetation destruction, and gully erosion (see review in Brown
et al.
2009, pp. 56-58). Within the newly established National Parks, grazing by cattle and sheep was eliminated, although grazing by packstock, such as horses and mules, continued. 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, with cattle becoming the dominant livestock. During World Wars I and II, increased livestock use occurred on National Forests in the west, causing overuse in the periods 1914-1920 and 1939-1946. Between 1950 and 1970 livestock numbers were permanently reduced due to allotment closures and uneconomical operations, with increased emphasis on resource protection and riparian enhancement. Further reductions in livestock use began again in the 1990s, due in part to USFS reductions in permitted livestock numbers, seasons of use, implementation of rest-rotation grazing systems, and to responses to drought (Menke
et al.
1996, pp. 7, 8). Between 1981 and 1998, livestock numbers on National Forests in the Sierra Nevada decreased from 163,000 to approximately 97,000 head, concurrent with Forest Service implementation of standards and guidelines for grazing and other resource management (USFS 2001, pp. 399-416).

Effects of Current Grazing

Yosemite, Sequoia, and Kings Canyon National Parks remain closed to livestock grazing. On USFS-administered lands that overlap the historical ranges of the mountain yellow-legged frog in the Sierra Nevada, there are currently 161 active Rangeland Management Unit Allotments for livestock grazing. However, based on frog surveys performed since 2005, only 27 of these allotments have extant mountain yellow-legged frog populations, while some allotments that were located in sensitive areas have been closed (USFS 2008, unpubl. data; CDFW (CDFG) unpubl. data). As of 2009, USFS data indicated that grazing occurs on about 65 percent of National Forest lands within the range of the mountain yellow-legged frog; that livestock numbers remain greatly reduced from historical levels; and that numerous watershed restoration projects have been implemented, although grazing may still impact many meadows above mid-elevation and restoration efforts are far from complete (Brown
et al.
2009, pp. 56, 57). However, Brown
et al.
(2009, p. 56) report that livestock grazing is more likely to occur in certain habitat types used by mountain yellow-legged frogs than others, indicating that populations found in meadows, stream riparian zones, and lakes in meadows are more likely to encounter habitat effects of grazing than populations found in the deeper alpine lakes that the species more likely inhabit (Brown
et al.
2009, p. 56).

USFS standards and guidelines in forest land and resource management plans have been implemented to protect water quality, sensitive species, vegetation, and stream morphology. Further, USFS standards have been implemented in remaining allotments to protect aquatic habitats (see discussion of the aquatic management strategy under Factor D for examples). USFS data from long-term meadow monitoring collected from 1999 to 2006 indicate that most meadows appear to be in an intermediate quality condition class, with seeming limited change in condition class over the first 6 years of monitoring. In addition, USFS grazing standards and guidelines are based on current science and are designed to improve or maintain range ecological conditions, and standards for managing habitat for threatened, endangered, and sensitive species have also been incorporated (Brown
et al.
2009, pp. 56-58). The seasonal turn-out dates (dates at which livestock are permitted to move onto USFS allotments) are set yearly based on factors such as elevation, annual precipitation, soil moisture, and forage plant phenology, and meadow readiness dates are also set for montane meadows. However, animals turned out to graze on low-elevation range (until higher elevation meadows are ready) may reach upper portions of allotments before the meadows have reached range readiness (Brown
et al.
2009, p. 58).

Menke
et al.
(1996) have reported that grazing livestock in numbers that are consistent with grazing capacity and use of sustainable methods led to better range management in the Sierra Nevada over the 20 years prior to development of the report. They also noted that moderate livestock grazing has the potential to increase native species diversity in wet and mesic meadows by allowing native plant cover to increase on site. Brown
et al.
(2009, p. 58) expect proper livestock management, such as proper timing, intensity, and duration, to result in a trend towards increased riparian species and a trend towards restored wet and mesic meadows on National Forests. To date, the scientific and commercial information available to us does not include descriptive or cause-effect research that establishes a causal link between habitat effects of livestock grazing and mountain yellow-legged frog populations; however, anecdotal information of specific habitat effects suggests that, in specific locations, the current grazing levels may have population-level effects (see Knapp 1993b, p. 1; Brown
et al.
2009, p. 56). In addition, where low-elevation populations occur in meadows, additional conservation measures may be required for recovery (USFS 2013, p. 5).

In summary, the legacy effects to habitat from historical grazing levels, such as increased erosion, stream downcutting and headcutting, lowered water tables, and increased siltation, are a threat to mountain yellow-legged frogs in those areas where such conditions still occur and may need active restoration. In the proposed rule, we stated that grazing presented a minor prevalent threat. Based on USFS and public comments, we have reevaluated our analysis of grazing to clarify effects of past versus current grazing. We have reworded the finding to more accurately reflect the contribution of legacy effects of past grazing levels to this threat assessment, as follows: Current livestock grazing activities may present an ongoing, localized threat to individual populations in locations where the populations occur in stream

riparian zones and in small waters within meadow systems, where active grazing co-occurs with extant frog populations. Livestock grazing that complies with forest standards and guidelines is not expected to negatively affect mountain yellow-legged frog populations in most cases, although limited exceptions could occur, especially where extant habitat is limited. In addition, mountain yellow-legged frogs may be negatively affected where grazing standards are exceeded. Rangewide, current livestock grazing is not a substantial threat to the species.

Mining

Several types of mining activities have occurred, or may currently occur, on National Forests, including aggregate mining (the extraction of materials from streams or stream terraces for use in construction), hardrock mining (the extraction of minerals by drilling or digging into solid rock), hydraulic mining (a historical practice using pressurized water to erode hillsides, outlawed in 1884), placer mining (mining in sand or gravel, or on the surface, without resorting to mechanically assisted means or explosives), and suction-dredge mining (the extraction of gold from riverine materials, in which water, sediment, and rocks are vacuumed from portions of streams and rivers, sorted to obtain gold, and the spoils redeposited in the stream (see review in Brown
et al.
2009, pp. 62-64).

Aggregate mining can alter sediment transport in streams, altering and incising stream channels, and can cause downstream deposition of sediment, altering or eliminating habitat. Aggregate mining typically occurs in large riverine channels that are downstream of much of the range of the mountain yellow-legged frog complex (see review in Brown
et al.
2009, pp. 62-64). However, Brown
et al.
(2009, pp. 62-64) note that effects of aggregate mining may occur in some portions of the Feather River system where such operations occur within the historic range of the Sierra Nevada yellow-legged frog, and potentially in localized areas within the range of both species, where the USFS maintains small quarries for road work. They note that, although effects of aggregate mining on mountain yellow-legged frogs are unstudied, impacts are probably slight.

Hardrock mining can be a source of pollution where potentially toxic metals are solubilized by waters that are slightly acidic. Past mining activities have resulted in the existence of many shaft or tunnel mines on the forest in the Sierra Nevada, although most are thought to occur below the range of the species. Most operations that are thought to have the potential to impact the mountain yellow-legged frogs occur in the lower elevation portions of the Sierra Nevada yellow-legged frog range on the Plumas National Forest and in the ranges of both species on the Inyo National Forest (see review in Brown
et al.
2009, pp. 62-64).

Hydraulic mining has exposed previously concealed rocks that can increase pollutants such as acid, cadmium, mercury, and asbestos, and its effect on water pollution may still be apparent on the Feather River. However, most of the area that was mined in this way is below the elevation where Sierra Nevada yellow-legged frogs are present, so effects are likely highly localized (see review in Brown
et al.
2009, pp. 63, 64). Although placer mining was dominant historically, today it's almost exclusively recreational and is not expected to have habitat-related effects.

Brown
et al.
(2009, p. 64) report that suction-dredge mining is also primarily recreational noting that, because nozzles are currently restricted to 6 inches or smaller, CDFW (CDFG, 1994) expects disturbed areas to recover quickly (although CDFW notes that such dredging may increase suspended sediments, change stream geomorphology, and bury or suffocate larvae). Suction dredge mining occurs primarily in the foothills of the Sierra Nevada, thus presenting a risk primarily to mountain yellow-legged frog populations at the lower elevations of the species' range. Suction dredging is highly regulated by the CDFW, and in the past, many streams have been seasonally or permanently closed (see review in Brown
et al.
2009, p. 64). Currently CDFW has imposed a moratorium on suction dredging.

The high-elevation areas where most Sierra Nevada yellow-legged frogs and mountain yellow-legged frogs occur are within designated wilderness, where mechanical uses are prohibited by the Wilderness Act. Designated wilderness was withdrawn for new mining claims on January 1, 1984, although a limited number of active mines that predated the withdrawal still occur within wilderness (see Wilderness Act under Factor D, below). Therefore, we expect that mining activities may pose local habitat-related impacts to the species at specific localities where mining occurs.

Packstock Use

Similar to cattle, horses and mules may significantly overgraze, trample, or pollute riparian and aquatic habitat if too many are concentrated in riparian areas too often or for too long. Commercial packstock trips are permitted in National Forests and National Parks within the Sierra Nevada, often providing transport services into wilderness areas through the use of horses or mules. Use of packstock in the Sierra Nevada increased after World War II as road access, leisure time, and disposable income increased (Menke
et al.
1996, p. 919). Packstock grazing is the only grazing currently permitted in the National Parks of the Sierra Nevada. Since the mid-1970s, National Forests and National Parks have generally implemented regulations to manage visitor use and group sizes, including measures to reduce packstock impacts to vegetation and soils in order to protect wilderness resources. For example, Sequoia and Kings Canyon National Parks have the backcountry area with the longest history of research and management of packstock impacts (Hendee
et al.
1990, p. 461). Hendee
et al.
(1990, p. 461) report that the extensive and long-term monitoring for Sequoia, Kings Canyon, and Yosemite National Parks makes it possible to quantify impacts of packstock use, showing that the vast majority of Sierra Nevada yellow-legged frog and mountain yellow-legged frog populations in the Parks show no to negligible impacts from packstock use (National Park Service 2013, p. 3). 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 along lake shores from trampling and associated degradation (Vredenburg 2002, p. 11; Werner 2002, p. 2; National Park Service 2013, p. 3). Packstock use is also regulated in designated wilderness in National Forests within the Sierra Nevada.

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 on the National Forests in the Sierra Nevada, are projected to increase (USDA 2001a, pp. 473-474). However, on the Inyo National Forest, current commercial packstock use is approximately 27 percent of the level of use in the 1980s reflecting a decline in the public's need and demand for packstock trips. From 2001 to 2005, commercial packstock outfitters within the Golden Trout and South Sierra Wilderness Areas averaged 28 percent of their current authorized use (USFS

2006, p. 3-18). Similarly, long-term permitting data for administrative, commercial, and recreational packstock use in the three National Parks indicates that packstock use is declining in the Parks, providing no evidence to suggest that packstock use will increase in the future in the Parks (National Park Service 2013, pp. 3, 4). Habitat changes due to packstock grazing may pose a risk to some remnant populations of frogs and, in certain circumstances, a hindrance to recovery of populations in heavily used areas.

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) at locations where these activities occur. Historically, road construction and timber harvest may have acted to reduce the species' range prior to the more recent detailed studies and systematic monitoring that have quantified and documented species losses. Prior to the formation of National Parks in 1890 and National Forests in 1905, timber harvest was widespread and unregulated, but primarily took place at elevations on the western slope of the Sierra Nevada below the range of the mountain yellow-legged frog (University of California (UC) 1996b, pp. 24-25). Between 1900 and 1950, the majority of timber harvest occurred in old-growth forests on private land (UC 1996b, p. 25). Between 1950 and the early 1990s, timber harvest on National Forests increased, and the majority of timber harvest-associated impacts on mountain yellow-legged frogs may therefore have taken place during this period in lower elevation locations where timber harvest and species occurrences overlapped. Currently, these activities are expected to occur outside National Parks or National Forest wilderness areas, with limited exceptions.

Timber harvest activities (including vegetation management and fuels management) remove vegetation and cause ground disturbance and compaction, making the ground more susceptible to erosion (Helms and Tappeiner 1996, p. 446). This erosion can increase siltation downstream and potentially damage mountain yellow-legged frog breeding habitat. Timber harvest may alter the annual hydrograph (timing and volume of surface flows) in areas where harvests occur. The majority of erosion caused by timber harvests is from logging roads (Helms and Tappeiner 1996, p. 447). A recent monitoring effort, which was conducted by the USFS in stream habitats in the northern part of the Sierra Nevada yellow-legged frog's range, attempted to assess the impact of vegetation management activities, which would include activities similar to timber harvest, on mountain yellow-legged frog populations (Foote
et al.
2013, p. 2). However, given the timing of project implementation, the results were limited to the impacts of these management activities on mountain yellow-legged frog habitat. The results of the monitoring suggest these activities did not significantly impact perennial stream habitat for the mountain yellow-legged frog, although there were instances of habitat degradation attributed to sedimentation resulting from road decommissioning and culvert replacement (Foote
et al.
2013, p. 32).

Roadways have the potential to affect riparian habitat by altering the physical and chemical environment, including alteration of surface-water run-off, with potential changes to hydrology in high-mountain lake and stream systems (Brown
et al.
2009, pp. 71-72). Roads, including those associated with timber harvests, have also been found to contribute to habitat fragmentation and limit amphibian movement, thus having a negative effect on amphibian species richness. Therefore, road construction could fragment mountain yellow-legged frog habitat if a road bisects habitat consisting of water bodies in close proximity. In the prairies and forests of Minnesota, Lehtinen
et al.
(1999, pp. 8-9) found that increased road density reduced amphibian species richness. DeMaynadier and Hunter (2000, p. 56) found similar results in a study of eight amphibian species in Maine, although results varied with road type and width. Results showed that anuran (true frogs, the group of frogs that includes the mountain yellow-legged frogs) habitat use and movement were not affected even by a wide, heavily used logging road (deMaynadier and Hunter 2000, p. 56); this finding suggests that forest roads may not fragment populations where such roads occur.

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.
1994, p. 323; Drost and Fellers 1996, p. 421; Knapp and Matthews 2000, p. 430) and where motorized access (and roads) does not occur. Mountain yellow-legged frog populations outside of these areas are most often located above the timberline, so timber harvest activity is not expected to affect the majority of extant mountain yellow-legged frog populations. There is a higher potential overlap of timber harvest activities with the species in the northern and lower elevation portions of the species' ranges where the frogs occur in streams and meadows in forested environments; in these areas, populations are very small and fragmented (Brown 2013, unpaginated). Likewise, at lower elevations of the Sierra Nevada, forest roads and logging roads are more common (Brown
et al.
2009, p. 71). Habitat effects associated with roads are most likely to occur where existing roadways occur (for example, see Knapp 1993b, unpaginated). Although additional roads may be constructed within the range of the mountain yellow-legged frogs, we are not aware of any proposals to build new roads at this time.

In riparian areas, the USFS generally maintains standards and guidelines for land management activities, such as timber harvests, that are designed to maintain the hydrologic, geomorphic, and ecologic processes that directly affect streams, stream processes, and aquatic habitats, and which can limit potential effects of such activities (Foote
et al.
2013, pp. 4, 32). In general, we expect the standards to be effective in preventing habitat-related effects to these species. Additionally, neither timber harvests nor roads have been implicated as important contributors to the decline of this species (Jennings 1996, pp. 921-941), although habitat alterations due to these activities may, in site-specific, localized cases, have population-level effects to mountain yellow-legged frogs. We expect that such cases would be more likely at lower elevations or in the more northern portion of the species' range where limited extant populations occur in close proximity to timber harvest, or where populations occur in drainages adjacent to roadways. In the proposed rule, we stated that roads and timber harvest likely present minor prevalent threats to the mountain yellow-legged frogs factored across the range of the species. We are clarifying that language, noting that they may pose important habitat-related effects to the species in localized areas, but are not likely threats across most of the species' ranges.

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 where fire may have historically played a limited role in the ecosystem. However, at lower elevations and in the northern portion of the range, mountain yellow-legged frogs occur in stream or lake environments within areas that are

forested to various extents. 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 mountain yellow-legged frog habitats following wildfire is a concern where shallow, lower elevation aquatic areas occur 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
et al.
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.

The effects of past fire and fire management activities on historical populations of mountain yellow-legged frogs are not known. Neither the direct nor indirect effects of prescribed fire or wildfire on the mountain yellow-legged frog have been studied. Hossack
et al.
(2012, pp. 221, 226), in a study of the effects of six stand-replacing fires on three amphibians that breed in temporary ponds in low-elevation dense coniferous forests or in high-elevation open, subalpine forests in Glacier National Park, found that effects of wildfire on amphibians may not be evident for several years post-fire with time-lagged declines. The decline in populations was presumably due to the proximity of high-severity fires to important breeding habitats, which resulted in low recruitment of juveniles into the breeding population. They cautioned, however, that amphibian responses to fire are context specific and cannot be generalized too broadly; they found no change in occupancy after wildfire at high elevations where wetlands were in sparse forest or open meadows where there was less change in canopy cover and insolation after wildfire. Where fire has occurred in the steep canyons of southern California where the southern DPS of the mountain yellow-legged frog occurs, the character of the habitat has been significantly altered, leading to erosive scouring and flooding of creeks after surface vegetation is denuded (North 2012, pers. comm.). North (2012, pers. comm.) reported that at least one population of the federally endangered southern DPS of the mountain yellow-legged frog, which occurs in streams, declined substantially after fire on the East Fork City Creek (San Bernardino Mountains) in 2003 and, by 2012, was approaching extirpation. Although most populations of mountain yellow-legged frogs are in alpine habitat that differs from the habitat in southern California, when they occur in lower-elevation stream habitats, they could be similarly affected by large wildfires. When a large fire does occur in occupied habitat, mountain yellow-legged frogs can be susceptible to both direct mortality (leading to significantly reduced population sizes) and indirect effects (habitat alteration and reduced breeding habitat). It is possible that fire has caused localized extirpations in the past. However, because these species generally occupy high-elevation habitat, we have determined that fire is not a significant threat to the mountain yellow-legged frog complex over much of its current range, although where the species occur at lower elevations or in the most northerly portion of their ranges, fire-related changes to habitat may have population-level effects to the species.

Recreation

Recreational activities that include hiking, camping, and backpacking take place throughout the Sierra Nevada, whereas off-road vehicle (ORV) use takes place in areas outside of designated wilderness. These activities can have significant negative impacts on many plant and animal species and their habitats (U.S. Department of Agriculture (USDA) 2001a, pp. 483-493). Extant populations of the mountain yellow-legged frog complex are primarily located at high elevations in sub-alpine and alpine habitat within designated wilderness. High-elevation wilderness areas are ecosystems that are subject to 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).

In easily accessible areas, heavy foot traffic in riparian areas can trample vegetation, compact soils, and physically damage stream banks (Kondolf
et al.
1996, pp. 1014, 1019). Human foot, horse, bicycle, or off-highway motor vehicle trails can replace riparian habitat with compacted soil (Kondolph
et al.
1996, pp. 1014, 1017, 1019), lower the water table, and cause increased erosion where such activities occur. Bahls (1992, p. 190) reported that the recreational activity of anglers at high mountain lakes can be locally intense in western wilderness areas, with most regions reporting a level of use greater than the fragile lakeshore environments can withstand. Heavy recreation use has been associated with changes in the basic ecology of lakes. In the 1970s, Silverman and Erman (1979) found that the most heavily used back-country lakes in their study had less nitrate and more iron and aquatic plants than other lakes. These researchers suggested that erosion at trails and campsites, improper waste disposal, destruction of vegetation, and campsites might cause an increase in elements that formerly limited plant growth (Hendee
et al.
1990, pp. 435, 436). The NPS considers hiking and backpacking to be a negligible risk for the mountain yellow-legged frogs within the Parks, noting that, while hiking and backpacking occur adjacent to many populations, evidence indicates that risk to habitat is slight to none. For example, monitoring of a high-use trail that allows thousands of hikers annually to come into close contact with several populations of mountain yellow-legged frogs, whose habitat is immediately adjacent to the trail, shows that the populations have grown substantially over the last decade (NPS 2013, p. 6). In one location where high hiking levels may be having an impact due to access via an adjacent road, Yosemite National Park personnel have restricted access (NPS 2013, p. 6). Although recreation was noted in 1998 as the fastest growing use of National Forests (USFS 2001a, p. 453), to our knowledge, no studies to date have identified a correlation between such recreation-related impacts to habitat and effects to populations of the mountain yellow-legged frog complex.

Because of demand for wilderness recreational experiences and concern about wilderness resource conditions, wilderness land management now includes standards for wilderness conditions, implementing permit systems and group-size limits for visitors and packstock, prohibitions on camping and packstock use close to water, and other visitor management techniques to reduce impacts to habitat, including riparian habitat (Cole 2001, pp. 4-5). These wilderness land management techniques are currently being used in National Forest Wilderness areas in the Sierra Nevada and in backcountry areas of Yosemite, Sequoia, and Kings Canyon National Parks. In the proposed rule, we stated that current recreation activities were considered a threat of low significance to the species' habitat overall. Based on

comments from the National Park Service, the USFS, CDFW, and the public, we have reevaluated the previous analysis and have revised our finding. Therefore, current habitat effects of recreational activities are not considered to have population-level effects to mountain yellow-legged frogs over much of their respective ranges, although there may be localized effects especially outside of backcountry areas where use levels are not limited, or where motorized use occurs in extant frog habitat.

In summary, based on the best available scientific and commercial information, we consider the modification of habitat and curtailment of the species' ranges to be a significant and ongoing threat to the Sierra Nevada yellow-legged frog and northern DPS of the mountain yellow-legged frog. Habitat fragmentation and degradation (loss of habitat through competitive exclusion) from stocking and the continued presence of introduced trout across the majority of the species' range is a threat of high prevalence. This threat is a significant limiting factor to persistence and recovery of the species rangewide. Threats of low prevalence (threats that may be important limiting factors in some areas, but not across a large part of the mountain yellow-legged frog complex's range) include dams and water diversions, grazing, packstock use, timber harvest and roads, recreation, and fire management activities.

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

No commercial market for mountain yellow-legged frogs exists, nor any documented recreational or educational uses for these species. 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 populations.

Based on the best available scientific and commercial information, we do not consider 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 elegans elegans
), Brewer's blackbird (
Euphagus cyanocephalus
), Clark's nutcracker (
Nucifraga columbiana
), coyote (
Canis latrans
), and black bear (
Ursus americanus
) (Mullally and Cunningham 1956a, p. 193; Bradford 1991, pp. 176-177; Jennings
et al.
1992, p. 505; Feldman and Wilkinson 2000, p. 102; Vredenburg
et al.
2005, p. 565). However, none of these has been implicated as a driver of population dynamics, and we expect that such predation events do not generally have population-level impacts except where so few individuals remain that such predation is associated with loss of a population (Bradford 1991, pp 174-177; Jennings 1996, p. 938).

The American bullfrog (
Lithobates catesbeiana
) is native to the United States east of the Rocky Mountains, but was introduced to California about a century ago. The American bullfrog has become common in California in most permanent lakes and ponds below 1,829 m (6,000 ft) and is implicated in the declines of a number of native frog species (Jennings 1996, p. 931). Mountain yellow-legged frogs are thought to be particularly vulnerable to bullfrogs and introduced crayfish, potentially because the frogs did not evolve with a predator (Jennings 1996, p. 939). In addition, research indicates that bullfrogs may outcompete other species of amphibians where fish are present because bullfrogs are both unpalatable to fish and are naturally vulnerable to invertebrate predators such as dragonfly (Anisoptera) nymphs, which fish pr

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2014-09488. Public record. Not legal advice.