Scientists have confirmed that agricultural contaminants may be an important factor in amphibian declines in California. According to an article recently accepted by the journal Environmental Toxicology and Chemistry, a study by scientists of the U.S. Geological Survey and U.S. Department of Agriculture indicates that organophosphorus pesticides from agricultural areas, which are transported to the Sierra Nevada on prevailing summer winds, may be affecting populations of amphibians that breed in mountain ponds and streams.
Dramatic population declines in red-legged frogs, foothills yellow-legged frogs, mountain yellow-legged frogs and Yosemite toads have occurred in California over the last 10-15 years, but no single cause for these declines has been positively identified. Scientists and managers have been especially concerned because many of these declines occurred in some of the state's most seemingly pristine areas. Declines have been particularly drastic in the Sierra Nevada, which lie east of the intensely agricultural San Joaquin Valley. The red-legged frog is listed as threatened under the U.S. Endangered Species Act, and the mountain yellow-legged frog and Yosemite toad have been proposed for listing.
"While crucial to the agriculture industry, pesticides by their very nature can result in serious harm to wildlife both by directly killing animals and through more subtle effects on reproduction, development and behavior," said Dr. Donald Sparling, a research biologist and contaminants specialist at the USGS Patuxent Wildlife Research Center in Maryland. "Unfortunately, now there appears to be a close correlation between declining populations of amphibians in the Sierra Nevada and exposure to agricultural pesticides."
The scientists found proof that pesticides are being absorbed by frogs in both aquatic and terrestrial systems and are suppressing an enzyme called cholinesterase, which is essential for the proper functioning of the nervous sys
Contact: Catherine Haecker
United States Geological Survey