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Accession Number 5004297

Title The Role of Pesticides in Declining Amphibian Populations in the Sierra Nevadas

Project Description The Role of Pesticides in Declining Amphibian Populations in the Sierra Nevadas Status: Active

Starting Date: 000630 Ending Date: 031230 Several species of amphibians are declining in the

Sierra Nevada Mountains of California. These include the red-legged frog (Rana aurora), mountain

yellow-legged frog (R. muscosa), Cascade frog, foothills yellow-legged frog(R. boylii), Yosemite

toad (Bufo canorus) and others. The populations most severely affected are those living at high

elevation in presumably pristine National Parks and federal lands (Yosemite, Sequoia, Lake Tahoe

Mgmt Basin). The red-legged frog is listed by the Fish and Wildlife Service as threatened and the

mountain yellow-legged frog is proposed for listing. Several factors such as habitat loss,

introduced predators and increased ultraviolet radiation have been proposed as contributors to

these declines. However, a growing body of information clearly suggests that pesticides are a

principal factor. According to this data, westerly winds from the coast sweep past the intensely

agricultural Central Valley of California and carry insecticides into the pristine higher elevations.

Pesticides have been found repeatedly in rainfall and snow of the National Parks. Recently,

depressed cholinesterase and body residues of pesticides in Pacific treefrogs (Hyla regilla), a

sentinel species for the rarer frogs, has been found to match the declines very closely. Up to 86%

of some populations had measurable levels of endosulfans and 30%+ of other populations had

detectable levels of chlorpyrifos or diazinon. This research is of considerable interest to the U.S.

Fish and Wildlife Service because of its mission of dealing with endangered species and to the

National Park Service on whose lands the problems are most expressed. The current study has

three main objectives: a) determine the extent of reduced cholinesterase activity and pesticide

residues in Hyla regilla and ponds as they relate to declines in Bufo and Rana species; b) conduct

translocation experiments to compare the survivorship of tadpoles in waters suspected of being

contaminated by pesticides; and c) quantify the sensitivities of Hyla regilla and Rana aurora or

Rana muscosa to pesticides suspected of affecting anuran populations in the Sierras through

standard toxicity tests.

Keywords amphibians, california, chlorpyrifos, declining populations, diazinon, endosulfan, hyla, pesticides,

population effects, rana, sierra nevada mountains,

Principal Donald W Sparling, USGS Patuxent Wildlife Research Center: don_sparling@usgs.gov; G.

Investigators Fellers, Western Ecology Research Center: gary_fellers@usgs.gov; Deborah Cowman,

Department of Fisheries and Wildlife, Texas A&M University: d-cowman@tamu.edu;

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