Local Delta smelt populations have crashed more than 95 percent since the fish was listed in 1993 as threatened by federal and state governments, prompting environmental groups to push the government to list the fish as endangered.

The smelt was once one of the most common fish in the Sacramento-San Joaquin Delta, which includes Old River and San Joaquin River near Tracy, until four-fifths of its population disappeared during the 1980s, according to information provided by The Bay Institute, Center for Biological Diversity and Natural Resources Defense Council.

The three groups filed a joint emergency petition Wednesday with the California Fish and Wildlife Service to list the Delta smelt as endangered.

Bay Institute senior scientist Tina Swanson said pumping plants in Tracy and Byron have contributed to the smelt’s population drain.

Paul Fujitani, who heads the U.S. Bureau of Reclamation’s Central Valley operations, said the intake channels at the Tracy plant are protected with fish screens that divert the animals into holding tanks. Fish found in the tanks are transferred to water away from the pumps.

Delta smelt migrate in winter and early spring to spawn in inland rivers. The smelt’s eggs stick to vegetation and rocks, according to Swanson, but the adults and larvae are often killed when they are sucked into the mesh around Tracy’s pumps.

“They try to screen these fish out,” Swanson said, “but even if they’re successfully diverted, they’re such a small and delicate fish that they usually doesn’t survive.”

Delta smelt grow to about 2.5 inches, and their slender bodies are nearly transparent. Most females die after laying as many as 2,000 eggs, and the males usually survive for just one year.

They are found only in upper San Francisco Bay and in the estuarine Sacramento-San Joaquin Delta, which branches from the bay throughout the Central Valley.

California Sportfishing Protection Alliance executive director Bill Jennings likened the smelt to a canary in a mine — “it’s the indicator species that symbolizes the health of the estuary,” he said.

Jennings said fish species such as Delta smelt, striped bass, salmon and steelhead trout in the Delta are in the midst of a “catastrophic collapse,” in part because water is increasingly being diverted to farms and homes in Southern California.

“There are a number of potential culprits, from toxicity in the water to invasive species,” Jennings said of the dwindling numbers. “But I think most people agree that the increase in pumping in recent years during crucial winter months has contributed to this recent collapse.”

Center for Biological Diversity spokesman Jeff Miller said listing the fish as endangered would free government funding to save the species and force government agencies to better scrutinize the impact of proposed projects on population numbers.

Kate Poole, senior attorney with Natural Resources Defense Council, called for urgent action to protect the smelt and to protect clean water supplies for 20 million Californians.

“We think that getting the listing changed from threatened to endangered very quickly will help lend some urgency to the actual actions (reduced pumping) that should be taken in the Delta,” Poole said.

The three environmental groups last March asked the federal government to change the smelt’s listing from threatened to endangered, which would give it more protection.

The species has a 50 percent chance of being wiped out during the next 20 years, according to 2005 research published by Bill Bennett, a researcher at the University of California, Davis.

To reach reporter John Upton, call 830-4274 or e-mail jupton@tracypress.com.