SNFPA Draft Supplemental Environmental Impact Statement

June 2003

Chapter 3: Affected Environment

3.2.2.7. Mountain Yellow-Legged Frog (Rana muscosa)

The information below was compiled and summarized from the following reference: USDA Forest Service. unpublished. Draft Conservation Assessment and Strategy for the Mountain Yellow-Legged Frog (Rana muscosa). USDA Forest Service, Pacific Southwest Region, Vallejo, CA. This section updates and supplements the information found in FEIS Volume 3, Chapter 3, Part 4.4, pp. 213-214. Detailed references can be found in that document.

Biology

In the 12-Month Finding for a Petition to list (USDI FWS 2003) the mountain yellow-legged frog, the U.S. Fish and Wildlife Service concluded that the Sierra Nevada population of the mountain yellow-legged frog is discrete from the southern California population, on the basis of their geographic separation, differences in vocalization, differences between their habitats, and apparent genetic differences. They also concluded that the Sierra Nevada population of the mountain yellow-legged frog is significant because the loss of the species from the Sierra Nevada would result in a significant reduction in the species' range and its population numbers, and would constitute the loss of a genetically discrete population that differs markedly from the southern California population of mountain yellow-legged frogs. The US Fish and Wildlife Service consider the Sierra Nevada mountain yellow-legged frog to be a distinct population segment.

Habitat Requirements

Mountain yellow-legged frogs in the Sierra Nevada live in high mountain lakes, ponds, tarns, and streams - largely in areas that were glaciated as recently as 10,000 years ago. This species is usually associated with montane riparian habitats in lodgepole pine, yellow pine, sugar pine, white fir, whitebark pine, and wet meadow vegetation types.

Alpine lakes used by mountain yellow-legged frogs usually have margins that are grassy or muddy, but they are not limited to this habitat. Mountain yellow-legged frogs extensively utilize deep water ponds (greater than 2.5 meters [greater than 8.2 feet]) that have open shorelines and lack introduced fishes. Adults are typically found sitting on rocks along the shoreline, usually where there is little or no vegetation. Both larvae and adults prefer open shorelines that gently slope up to shallow waters of 5 to 8 centimeters (2 to 3 inches) deep. Shallow water likely provides a refuge from predation if fishes occur in adjacent deeper water. Mountain yellow-legged frogs also use stream habitats, especially in the northern part of their range.

Some of the highest observed densities of frogs have been found both at creek junctions with irregular banks and a variety of water depths, and in open areas on the edges of glaciated lakes. Mountain yellow-legged frog populations seem to be most successful where predatory fishes are absent.

In the Sierra Nevada, adult frogs apparently hibernate during the coldest winter months probably because they can tolerate only limited dehydration. Larvae and adults generally overwinter under ice. Both adults and larvae have been found to overwinter (up to 9 months) in the bottoms of lakes (at least 1.7 meters (5.6 feet) deep, and preferably at least 2.5 meters (8.2 feet) deep), or in rocky streams. In some instances, frogs have been found to overwinter in bedrock crevices which allows them to survive in shallower water bodies that freeze to the bottom in winter. This activity may also be in response to the presence of introduced fishes that cannot survive in ponds that completely freeze.

Mountain yellow-legged frogs emerge from overwintering sites immediately following snowmelt. Adults sometimes travel over snow to reach preferred breeding sites early in the season. Breeding activity begins early in the spring and can range from April at lower elevations to June and July in higher elevations. The timing of the onset of breeding depends on the amount of snowfall and subsequent ice-out dates of ponds, lakes, and streams. In years with particularly cold winters, high elevation frog populations may only be active for approximately 90 days during the warmest part of the summer.

Life history characteristics, such as overwintering under frozen lakes and multi-year larval development, make the mountain yellow-legged frog susceptible to large-scale die-offs. In lakes less than 4 meters (less than 13 feet) deep, overwintering frogs may die apparently due to oxygen depletion, while larvae are able to survive. Conversely, in dry years larvae are lost to desiccation in the late summer or fall.

Because many of the remaining populations of Sierra Nevada mountain yellow-legged frog are small isolated remnants, they are vulnerable to random natural events that could quickly extirpate them. It is widely recognized that, in general, small populations are more vulnerable to extinction than large ones identified four major factors that predispose small populations to extinction: (1) environmental variation and natural catastrophes, such as unusually harsh weather, fires, or other unpredictable environmental phenomena; (2) chance variation in age and sex ratios or other population parameters (demographic stochastisity); (3) genetic deterioration resulting in inbreeding depression and genetic drift (random changes in gene frequencies); and (4) disruption of metapopulation dynamics (the extinction-colonization balance among interconnected populations is disrupted).

Historic and Current Range and Distribution

The mountain yellow-legged frog was once extremely abundant in aquatic ecosystems of the Sierra Nevada. It was distributed nearly continuously in high elevation water bodies in the Sierra Nevada Mountains of California and Nevada, from southern Plumas County to southern Tulare County at elevations mostly above 1,820 meters (6,000 feet). The historic range of the Sierra Nevada mountain yellow-legged frog encompasses 10 National Forests (Lassen, Plumas, Tahoe, Lake Tahoe Basin Management Unit, Eldorado, Stanislaus, Toiyabe, Inyo, Sierra and Sequoia) and 3 National Parks (Yosemite, Sequoia and Kings Canyon).

Since about 1970, mountain yellow-legged frog numbers and populations have undergone a precipitous decline throughout the Sierra Nevada. Further declines continue to be documented. Mountain yellow-legged frogs have disappeared from between 70 and 90 percent of their historic localities. Remaining populations are widely scattered and consist of few breeding adults.

Numerous factors, separately and in combination, have contributed to the species' decline. Introduction of non-native fishes, pesticides, ultraviolet radiation, pathogens, acidification from atmospheric deposition, nitrate deposition, livestock grazing, recreational activities, and drought have all been identified as potential factors impacting this species and its habitat. Because many of the remaining populations of Sierra Nevada mountain yellow-legged frog are small isolated remnants, they are vulnerable to random natural events that could quickly extirpate them. It is widely recognized that, in general, small populations are more vulnerable to extinction than large ones.

The distribution of the Sierra Nevada mountain yellow-legged frog is restricted primarily to publicly managed lands at high elevations, including streams, lakes, ponds, and meadow wetlands located on national forests, including wilderness and non-wilderness on the forests, and national parks. Approximately 210 known mountain yellow-legged frog populations (or populations within metapopulations) exist on the national forests within the Sierra Nevada, though not all of these populations may be reproducing successfully.

Overall, U.S. Fish and Wildlife Service estimates that 22 percent of the remaining mountain yellow-legged frog sites within the Sierra Nevada are found within the national forests (including those with and those without evidence of successful reproduction), while 78 percent are found within the national parks (including those with and those without evidence of successful reproduction). These percentages represent the number of sites within the national forests and the national parks of the Sierra Nevada; they do not represent the number of individuals present at each site. The methods for measuring the numbers of populations and metapopulations in the national forests and the national parks have not been standardized and, therefore caution should be used when comparing national forests numbers to national park numbers.

In 1999, a team of agency managers and researchers agreed that a mountain yellow-legged frog conservation assessment and strategy was needed to provide for the protection and conservation of this species. The Forest Service Pacific Southwest Region Ecosystem Conservation Director and the State Director of the California Department of Fish and Game approved preparation of a mountain yellow-legged frog conservation assessment and strategy. In 2000, a working group of biologists from the Forest Service, National Park Service, USDI Fish and Wildlife Service, and California Department of Fish and Game and research scientists was established to complete this effort.

Status

On February 8, 2000, the Center for Biological Diversity and the Pacific Rivers Council petitioned the Fish and Wildlife Service to list the Sierra Nevada population segment of mountain yellow-legged frog as an endangered species. The Fish and Wildlife Service (FWS) published a 90-Day Finding warranting the listing under the Endangered Species Act, ESA. On October 12, 2000, the FWS announced a 90-day finding on the petition to list the mountain yellow-legged frog as endangered (Federal Register, Vol. 65, No. 198). FWS found that the petition presents substantial information indicating that listing the species may be warranted. The FWS twelve-month petition finding was completed on January 16, 2003, it concluded that the petitioned action is warranted, but precluded by higher priority actions to amend the Lists of Endangered and Threatened Wildlife and Plants. Upon publication of this 12-month petition finding, this species will be added to the FWS candidate species list. A 2081 permit is required to handle or possess the mountain yellow-legged frog at any time.

The mountain yellow-legged frog is listed as Sensitive on the Region Five Regional Forester's Sensitive Species List (USDA Forest Service 1998). It is a State Species of Special Concern.

Risk Factors

A summary of risk factors can be found in SNFPA Chapter 3, Part 4.4, pp. 213 -215.

USDA Forest Service · Pacific Southwest Region