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The Endangered Desert Pupfish and Selenium

Date Posted: September 14, 2001

Populations of the endangered desert pupfish (Cyprinodon macularius) inhabit the agricultural drains in the Imperial Valley of California. The Imperial Valley is a productive farming area. However, the long summers and hot, dry climate that make the Valley so attractive for farming also demand the extensive use of irrigation. Unfortunately, long-term irrigation flushes selenium out of the soil into the agricultural drains. Selenium is an essential trace element that occurs naturally in the environment. Although small amounts of selenium are important for both wildlife and people, too much is toxic. Water entering the Imperial Valley’s agricultural drains via subsurface tile drains has been shown to contain selenium concentrations of up to 360 ppb; the Federal selenium criteria for protection of aquatic life allows no more 5 ppb in surface water.

An ongoing investigation by the Carlsbad Field Office is evaluating selenium contamination in desert pupfish habitat on and around the Sonny Bono Salton Sea National Wildlife Refuge, located in the Imperial Valley, and determining the potential for impacts to pupfish reproduction. The desert pupfish is the only fish native to the Salton Sea area. Earlier investigation efforts looked at the amount of selenium desert pupfish were being exposed to. This season, the Carlsbad Environmental Contaminants office and the US Geological Survey Columbia Environmental Research Laboratory are conducting a study to determine the reproductive and developmental effects of selenium on desert pupfish.

Scott Sobiech or Carol Roberts, 760-431-9440

Last updated: June 12, 2015