Center for Biological Diversity

Protecting endangered species and wild places of western North America
and the Pacific through science, policy, education, and environmental law.

August 8, 2001
CONTACT: Dr. Karl Flessa, University of Arizona, 520 621-7336
David Hogan, Center for Biological Diversity, 760 809-9244
Kara Gillon, Defenders of Wildlife, 202 682-9400 x. 119
More Information: 2001 Report



A scientific report released today by the Center for Biological Diversity and Defenders of Wildlife concludes that a clam found at the mouth of the Colorado River in Mexico occurs nowhere else in the world. A related 1999 report concluded that drastically reduced Colorado River flows from the U.S. is the likely cause of near extinction of the species. Both reports’ conclusions will likely result in Endangered Species Act protection for the clam.

The latest report was authored by Dr. Karl Flessa, Professor of Geosciences and Ecology and Evolutionary Biology at the University of Arizona, and Miguel Agustin Tellez-Duarte, Professor of Marine Sciences at the Autonomous University of Baja California at Ensenada.

The new report, Taxonomic status and distribution of the bivalve mollusk Mulinia coloradoensis in the Gulf of California, answers a longstanding question of whether the clam found in the Colorado River delta is a distinct species, or whether it is the same as other clams found throughout much of the remainder of the Gulf of California. “Our research shows that the Colorado River delta clam is found no where else in the world,” said Dr. Flessa.

The related 1999 report found that the delta clam was once the most abundant mollusk inhabiting the estuary of the Colorado River Delta, where historically abundant fresh river water mixed with the salty Gulf of California. “Colorado River delta beaches and islands are made-up of the shells of this nearly extinct species,” said Dr. Flessa.

Today, only one tiny population is known to remain. “The delta clam is an indicator of ecosystem health, and its sharp decline illustrates the crash of what was once one of the worlds richest desert estuaries, “ said David Hogan, Rivers Program Coordinator for the Center for Biological Diversity.

Findings in both today’s and the 1999 report carry significant implications for U.S. management of the Colorado River. According to Hogan, “The reports’ conclusions mean this species will be listed under the Endangered Species Act, and that in turn means U.S. water agencies will finally have to learn to share water with the Colorado River delta environment.”

A U.S.-based Lower Colorado River MultiSpecies Conservation Program has repeatedly rejected calls from conservationists to consider the effects of U.S. dams and diversions on the river’s delta ecosystem in Mexico. Possible delta conservation measures under last year’s U.S. / Mexico Colorado River water treaty Minute 306 will come long after, and likely be precluded by, contracts under the Multi-Species program. Conservation organizations, including the Center and Defenders do not support the program as a result.


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