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Title: PESTICIDES AND AMPHIBIAN POPULATION DECLINES IN CALIFORNIA, USA

Author
item SPARLING, DONALD - USGS
item FELLERS, GARY - USGS
item McConnell, Laura

Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/4/2000
Publication Date: 7/1/2001
Citation: Sparling, D.W., Fellers, G.M., McConnell, L.L. 2001. Pesticides and amphibian population declines in California, USA. Environmental Toxicology and Chemistry. 20:1591-1595.

Interpretive Summary: There is a rapidly growing concern about worldwide declines in amphibian populations. In California, red-legged frogs (Rana aurora), foothills yellow-legged frogs (R. boylii), mountain yellow-legged frogs (R. muscosa), and Yosemite toads (B. canorus) have undergone drastic population declines over the last 10-15 years. Rana aurora is listed as threatened under the U.S. Endangered Species Act, and both R. muscosa and B. canorus have been proposed for listing. Pacific treefrogs (Hyla regilla) and Western toads (Bufo boreas) have undergone less severe declines. The most drastic declines are found in the Sierra Nevada Mountains lying east of the San Joaquin Valley agricultural region. Currently, no single cause for these declines has been positively identified but previous work has shown that pesticide residues are transported and deposited into the Mountain ecosystem. Here we present the first clear demonstration that pesticides are implicated in declines of California amphibians. In areas of greatest decline, we found depressed cholinesterase activity in Hyla regilla and elevated pesticide residues in their tissues.

Technical Abstract: There is a rapidly growing concern about worldwide declines in amphibian populations. In California, red-legged frogs (Rana aurora), foothills yellow-legged frogs (R. boylii), mountain yellow-legged frogs (R. muscosa), and Yosemite toads (B. canorus) have undergone drastic population declines over the last 10-15 years. Rana aurora is listed as threatened under the U.S. Endangered Species Act, and both R. muscosa and B. canorus have been proposed for listing. Pacific treefrogs (Hyla regilla) and Western toads (Bufo boreas) have undergone less severe declines. The most drastic declines are found in the Sierra Nevada Mountains lying east of the San Joaquin Valley agricultural region. Currently, no single cause for these declines has been positively identified but previous work has shown that pesticide residues are transported and deposited into the Mountain ecosystem. Here we present the first clear demonstration that pesticides are implicated in declines of California amphibians. In areas of greatest decline, we found depressed cholinesterase activity in Hyla regilla and elevated pesticide residues in their tissues.