Pollutants entering the Pacific Ocean from the U.S. West Coast may be killing hundreds of southern sea otters each year.
Although sea otters normally live for about 15 years, large numbers of dead breeding-age animals have been reported, National Geographic News reported.
Scientists believe the pollutants suppress the sea otters' immune systems, allowing them to become more susceptible to infectious diseases.
Conservationists told NGN the deaths could erase decades of conservation efforts that have helped restore the population to about 2,500.
Sea otters were hunted to the brink of extinction during the 18th and 19th centuries, but they have been protected by the U.S. Endangered Species Act since 1977.
Lillian Carswell, a Santa Cruz, Calif., biologist told NGN scientists have not yet determined the precise reasons for the deaths.
Copyright 2006 by United Press International
Explore further: Research finds numerous unknown jets from young stars and planetary nebulae