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Delta Smelt's Fate Worries Scientists

The once-populous tiny fish is vanishing from the Sacramento-San Joaquin estuary. That may signal big trouble.

April 17, 2006|Bettina Boxall | Times Staff Writer

DAVIS, Calif. — Last summer, state fish and game workers dragged a net dozens of times through the milk-chocolate waters of the Sacramento-San Joaquin Delta, looking for a tiny, steely blue fish found nowhere else in the world. The catch, 17 delta smelt, was shockingly small.

Never in the nearly five decades that the state has monitored smelt in the sprawling delta, where two of the state's biggest rivers converge just east of San Francisco Bay, have their numbers been as dismal. So abundant a generation ago that fishermen used the translucent, finger-length fish for bait, the delta smelt population has plummeted from the millions to an estimated 100,000 or less -- bringing it, some warn, to the brink of extinction.

The smelt's recent collapse, coupled with the decline of three other fish species that swim in the delta, has launched a multimillion-dollar scientific detective hunt for the reason.

There is a sense of urgency because the smelt's only home is one of California's most important, if troubled, ecosystems. The hub of the state's giant water system and a Bay Area playground, the delta is a vital link in the estuary chain that supports most of California's commercial fish species.

If the smelt is lost, it will be one more sign that the delta is too taxed to give Californians everything they demand of it.

"The only way we'll be able to save this estuary and the valuable resources it provides ... is by figuring out what's going wrong for this little fish," said Tina Swanson, a senior scientist with the Bay Institute, which last month petitioned the federal government to upgrade the smelt's protected status to endangered.

Environmental safeguards in place for more than a decade have altered the operation of the big government water projects, sometimes even shutting down the enormous delta pumps that supply two out of three Californians. But that hasn't been enough.

"I think for delta smelt it's looking pretty gloomy," said UC Davis research ecologist Bill Bennett, who has spent much of the last decade studying the fish's decline. The delta "is really not a good place for them to live anymore. It's a very different aquarium these fish are in than it was 30 years ago."

The delta's degradation started with the Gold Rush, when settlers drained its vast, rich tidal marshes for cropland and walled its meandering waterways with earthen levees. More recently, the estuary's natural rhythms of flow and saltiness have been broken by upstream dams and delta water exports that rocketed after completion of the State Water Project in the late 1960s. Farm and urban runoff has brought a stew of pesticides and other contaminants, and an ever-expanding array of nonnative species competes for food and habitat.

Yet scientists aren't sure exactly what in that grim summary is pushing the smelt to the edge of survival.

"Is it one more straw on the camel's back or did something new creep in?" asked Bruce Herbold, a U.S. Environmental Protection Agency fish biologist who is helping coordinate the scientific sleuthing by a consortium of federal and state agencies.

The smelt's numbers began to plunge in the early 1980s. In 1993, the fish was listed as threatened under the Endangered Species Act. The Bay Institute and two other groups say the listing should now be changed to endangered.

"Many of us watching the situation fully expected, because last year was a good water year, the numbers would be better," said David Harlow, an assistant field supervisor with the U.S. Fish and Wildlife Service. "They aren't."

Moreover, three other delta fish have also taken a dive since 2002: the native longfin smelt, young striped bass and -- most surprising to biologists -- the threadfin shad.

"That blew everyone away because they had been doing wonderfully for years," said Ted Sommer, a state Department of Water Resources environmental specialist.

After a year of data-crunching, the science team suspects there is not one culprit, but many.

Inevitably, any look at the delta turns to the mammoth government pumping operations in the south delta that fill the aqueducts carrying water to the vegetable fields of the San Joaquin Valley and the subdivisions of Southern California. The pumps are so powerful that they can reverse the natural flow in delta channels.

In 2003, enough fresh water was sucked out of the delta to fill a lake the size of Los Angeles to a depth of nearly 22 feet. Delta water exports in the last five years have been among the highest on record, according to state figures, and the timing of exports has also changed. Less water is being pumped in the spring and more at other times of the year, particularly during winter, a shift that was intended to protect spawning female fish.

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