SNFPA Draft Supplemental Environmental Impact Statement

June 2003

Chapter 3: Affected Environment

3.2.2.10. Cascades Frog (Rana cascadae)

The information below was extracted and compiled from the following reference: USDA Forest Service. unpublished. Draft Conservation Assessment for the Cascades Frog (Rana cascadae). USDA Forest Service, Pacific Southwest Region, Vallejo, CA. Detailed references can be found in that document. This section updates and supplements the information found in FEIS Volume 3, Chapter 3, part 4.4, pp. 223.

Habitat Requirements

Cascades frogs are highly aquatic and are found in or around ephemeral and permanent water sources including wet meadows, marshes, ponds, creeks, and lakes. Breeding sites are found in vegetated ponds, potholes, flooded areas in meadows, and shallow alcoves of lakes that generally contain protected gently sloping shallow areas close to shore.

Breeding habitat is less well-known in California than in Oregon and Washington where more research has been conducted. A recent study conducted in the Klamath Mountains of California found that Cascades frogs primarily breed in lakes, ponds and wet meadows that are fish-free and contain a high percentage of silt in the near-shore habitats. The three known remaining reproductive sites on the Lassen National Forest are in springs or wet meadows adjacent to mainstem streams, or in upper headwater shallow ponds. Because these are the only remaining breeding populations of a historically common frog in the Lassen area, interpretations about general habitat associations in this region should be made with caution.

Adults and juveniles use a wider variety of habitats than those used for breeding. Brown and Welsh (unpublished data) found adults in all types of aquatic habitats including ponds, meadows, deep lakes, and creeks. In a study in Olympia National Park in Washington, Cascade frog adults were found in a high proportion of lakes, ponds, meadows and streams. Cascade frogs in Mt. St. Helens National Park, Washington also showed similar habitat utilization (C. Crisafulli pers. comm.). Microhabitat of adults has not been well-studied, but adults seem to prefer sites with open, sunny areas along the shoreline for basking. Brown often found adults and subadults along small side channels of creeks that had muddy substrate for cover.

Little is known about overwintering habitat for the Cascades frog. Frogs are believed to over-winter in the sediment on the bottom of lakes and ponds under the ice or in spring-water saturated ground.

Cascades frogs are relatively long-lived and late maturing. In one study in Oregon, six- and seven-year old males and females were found at one site. Ages at maturity are estimated to be at least 3 years for males and 4 years for females. The frog has a high degree of site fidelity. Adults are diurnally active and bask and feed along the shoreline of lakes, ponds, streams and wet meadows.

The Cascades frog may undergo severe population fluctuations caused by natural stochastic events such as drought and prolonged winters. Because populations tend to be small they are vulnerable to random natural events that could quickly extirpate them.

Natural Mortality: Known natural predators of the Cascades frog include rough-skinned newt, garter snakes, black bear, raccoon, mink, and coyote. Tadpoles are also prey to aquatic insect larvae, several species of birds, and salamander larvae. In addition, introduced trout are known to prey on Cascades frogs.

Frogs are also susceptible to mortality from diseases. Mass mortality of developing R. cascadae eggs in Oregon has been documented and linked to the pathogenic fungus, Saprolegnia ferax. Because the frogs lay eggs in communal egg masses, they are extremely susceptible to mortality from Saprolegnia. Saprolegnia is a common fish pathogen and may be introduced by fish into lakes and ponds during fish stocking. Saprolegnia has not been found in California.

Life history characteristics such as over-wintering under frozen lakes and ponds, larval development in ephemeral ponds that may dry up before metamorphosis, and multi-year larval development in high elevation sites make the Cascades frog susceptible to die-offs due to extreme winter or drought conditions.

Because many of the remaining populations of Cascades frogs in the Mount Lassen area, Russian Wilderness and Marble Mountains are small isolated remnants, they are vulnerable to random natural events that could quickly extirpate them.

Historic and Current Range and Distribution

The Cascades frog is distributed along the Cascade Range from northern California to northern Washington, with a disjunct population on the Olympic Peninsula in Washington. In California, Cascades frog populations were historically distributed from the Shasta-Trinity area to the Modoc plateau. The southward extent was to the Lassen region and the upper Feather River. The known elevational range in California was from around 230 meters (750 feet) at Anderson Fork, Butte County, to 2500 meters (8000 feet) at Emerald Lake in Lassen Volcanic National Park. The frog's range has traditionally been depicted as two disjunct populations centered around the Lassen area and the Klamath area. However, this may be an artifact of historic knowledge of their distribution. The frog's distribution in California is poorly understood.

In northern California, north of the McCloud River, the Cascades frog seems to be doing well. At historic localities in the upper McCloud River system to the Trinity Alps, the frog was found to be moderately to extremely abundant in areas with no fish. In the southern-most part of its range, however, roughly south of the McCloud River, recent research has shown that this frog is extremely rare.

Although no significant changes in distribution have been documented over the last two decades, major changes in population densities were thought to have occurred. Localities with heavy grazing pressure showed dramatic declines in the frequency of Cascades frog occurrence during habitat walk-throughs, while localities that had not experienced grazing for a two-three year period showed dramatic increases in frequency of occurrence. No localized extirpations were recorded.

Status

The Cascades frog is listed as a sensitive species on the Region 5 Regional Forester's Sensitive Species List. It is also a California State Species of Special Concern.

Risk Factors =

For a summary of risk factors see SNFPA Chapter 3, Part 4.4, page 223.

USDA Forest Service · Pacific Southwest Region