Fish and Frogs
JB: This is Earth and Sky, on mountain yellow-legged frogs. . .
DB: This species lives in snow-fed lakes and streams, in the mountains of California. These frogs – with bright yellow underbellies and legs- used to be seen in nearly every lake in the Sierra Nevada.
JB: But, despite many pristine lakes in the high Sierra, the mountain yellow-legged frog is in trouble – because of trout with a taste for tadpoles.
DB: Historically, mountain lakes had few or no fish. California settlers started stocking trout in mountain lakes more than a century ago. Today, the technology has changed – each summer, the State Department of Fish and Game drops millions of fingerling trout into mountain lakes from airplanes. Mountain yellow-legged frogs are more vulnerable to fish predation than most other frogs. They spend two or more years as tadpoles . . .
JB: And because they evolved in a fish-free world, yellow-legged frogs and tadpoles don’t have the usual frog defenses – no toxic slime or escape behaviors. Trout fishing is a popular pastime, so it’s not likely that stocking will stop in California’s mountain lakes. But certain lakes may be restored to a fish-free state – to give the frogs a jump-start to recovery. Special thanks to the National Fish and Wildlife Foundation- and to the U.S. Forest Service. We’re Block and Byrd for Earth and Sky.
The following individuals were interviewed for today’s show. Our thanks to:
Dr. Kathleen Matthews
Pacific Southwest Research Station
Berkeley, CA
The following articles were used in preparing this script:
Forstenzer, Martin. “The Frog and the Fish.” Los Angeles Times, April 17, 1997, Metro, Part B, page 2.
Hall, Carl. “Fighting for the frogs.” San Francisco Chronicle, December 4, 2000, News, page A10.
Web sites to visit:
U.S. Fish and Wildlife Service website with Federal Register entry with the petition to list the mountain yellow-legged frog as an endangered species:
An article by Dr. Kathleen Matthews about her research, posted on the website of the USDA Forest Service’s Pacific Southwest Research Station:
USDA Forest Service species account of the mountain yellow-legged frog, with lots of natural history facts:
Reference books:
Stebbins, Robert C. Western Reptiles and Amphibians Houghton Mifflin Company, July1998
Conant, Roger, Joseph T. Collins, Robert C. Stebbins. Reptiles and Amphibians: The Concise Field Guide to Nearly 200 Reptiles and Amphibians of North America. Houghton Mifflin Company, March1999
Author’s notes: Not all scientists are convinced that trout are the main cause of the yellow-legged frog’s decline. They point to lakes that have never contained fish, from which the frogs have also disappeared; and they suggest that airborne pesticides and herbicides, transported from the agricultural valleys below the mountains, may be a contributing factor. Meanwhile, avid anglers and businesses that rely on them are urging that stocking programs be continued.
Other scientists, however, point to the fact that almost all of the remaining mountain yellow-legged frogs survive in National Parks, where fish stocking stopped in the 1970s.
The evidence suggests that if fish-free zones are created, the frogs can recover. In spring of 1997, biologists netted out all the fish from a small lake located at 11,500 feet; at that point only 20 adult frogs and 20 tadpoles were found in the lake. That fall, the biologists counted 120 adult frogs and 1,300 tadpoles.
Frog fun fact: This frog smells like garlic.
Additional Teacher Resources
California Department of Fish & Game, California Wildlife Habitat Relationships System: Mountain Yellow-legged Frog-
A scientific overview of the species distribution, abundance, habitat requirements, and life history.
USDA Forest Service: Rana muscosa
The Mountain Yellow-legged Frog is 2 to 3 ? inches long and has black or brown spots or vermiculations on the back. The dorsolateral ridges are present but may not be distinct. The tips of the fully webbed toes are dark. The ventral surface of the legs and sometimes the entire belly is yellow or pale orange.
tchester.org: Proposed Endangered Status for the Southern California Mountain Yellow-Legged Frog
This report provides information concerning the natural history of the Yellow-legged frog as well as information on habitat, historic and current range, decline, mechanisms of decline, and restoration efforts currently underway.
U.S. Forest Service, Final Supplemental Environmental Impact Statement: Species of the Sierra Nevada, Mountain Yellow-Legged Frog
This report covers how environment of the Yellow-legged frog has been effected through life history, habitat, historical and current distribution, risk factors, and its currently given endangered status.
