Efforts to restock Lake Tahoe with its original top predator, the Lahontan cutthroat trout, would be better directed toward lakes with fewer human impacts, says a new UC Davis analysis.

The study was conducted by the UC Davis Tahoe Research Group, a pioneer in Tahoe ecological studies for more than 40 years.

When white settlers arrived in the Tahoe Basin in the mid-1800s, Lake Tahoe teemed with native Lahontan cutthroat trout (Oncorhynchus clarkii henshawi). Named for the distinctive red streak under its chin, the Lahontan trout topped the lake food chain and reached weights of 40 pounds. Due to overfishing, dam-building and habitat destruction, Lahontan trout currently are among the most endangered western salmonids and have been extinct in Lake Tahoe for 70 years. Some related but genetically distinct strains still live in lakes and streams outside of the Tahoe Basin.

At the 1997 Lake Tahoe Presidential Forum, then-President Bill Clinton and Interior Secretary Bruce Babbitt called for the Lahontan cutthroat trout to be restored to the lake. The U.S. Fish and Wildlife Service is working to restore Lahontan trout in streams and lakes throughout their historic range, including the Tahoe Basin.

"We undertook this study to show how resource managers could use historical food-web analyses to assess the prospects for restoring fish to their original ranges," said UC Davis staff researcher Brant Allen. "In the particular case of Lake Tahoe, we found that the food web has changed so dramatically, efforts to reestablish the Lahontan trout could be better directed to surrounding, less-impacted lakes and streams."

An unexpected discovery was made in the course of the study: Lahontan trout are alive and well in nearby Cascade Lake.

In the new study, Allen and colleagues reconstructed the diets of Lake Tahoe and Cascade Lake fish since 1872 through analyzing museum specimens and comparing them to fresh catches. They identified two major obstacles to restoring Lahontan trout to Lake Tahoe: Introduced lake trout (Salvelinus namaycush) are so large and abundant that they would eat the Lahontans, and introduced freshwater shrimp (Mysis relicta) have eaten all the water fleas (Daphnia) that were a primary food source for the Lahontan trout.

The study was published recently by the peer-reviewed journal Ecosystems. Lead authors are M. Jake Vander Zanden and Sudeep Chandra. When the study was conducted, Vander Zanden was a postdoctoral researcher in the lab of Tahoe Research Group director Charles Goldman; Chandra was a doctoral candidate there. Vander Zanden and Chandra are now researchers at the University of Wisconsin, Madison.

The research was funded by the David H. Smith Conservation Research Program, the U.S. EPA's Center for Ecological Health Research at UC Davis, the Tahoe-Baikal Institute and the University of California Toxic Substances Research and Teaching Program.

The University of California is one of the world's foremost research and teaching institutions, and UC Davis is the University of California's flagship campus for environmental studies. UC Davis is a global leader in environmental studies relating to air and water pollution; water and land use; agricultural practices; endangered species management; invasive plants and animals; climate change; resource economics; information technology; and human society and culture. One in six of UC Davis' 1,500 faculty members specializes in an environment-related subject.