SACRAMENTO, California — A dramatic plunge in the populations of several fish species in the California Delta has experts worried that the entire ecosystem may be collapsing.
Surveys for juvenile striped bass and the threatened Delta smelt indicated the lowest populations ever recorded for both species in decades of counting. Even populations of more resilient animals farther down the food chain are declining, including threadfin shad, a normally abundant non-native baitfish, and copepods, a variety of zooplankton that's a key food source for juvenile fish.
"It's pretty serious, partly because (the decline) was not expected to be so severe," says Peter Moyle, a professor of fish biology at the University of California at Davis, and a leading authority on Delta fish. "The fact that it's among multiple species suggests it's some problem with the ecosystem, with the whole food web."
Once among the planet's most vibrant wetlands, the Delta — formed by the confluence of the Sacramento and San Joaquin rivers — is now one of its most heavily altered water systems, and a flash point for the state's epic water battles. The Delta used to funnel two-thirds of all the rain and snow that fell on California into the ocean. Now, state and federal water projects deliver its water to 20 million people and millions of acres of farmland.
The fish decline comes at a crucial time for California water agencies. A coalition of state and federal officials, known as the CalFed Bay-Delta Authority, has spent $3 billion over the last 10 years trying to meet water demand while restoring the Delta's ecology (HCN, 9/30/02: Delta Blues). But critics contend that thirsty farms, as well as the cities of Los Angeles and San Diego — which depend on pumps in the Delta that "export" water hundreds of miles to the south — now dominate CalFed and have pushed environmental concerns to the background. Water exports in three of the last five years have been the biggest in history, and pressure is mounting to increase them further.
A bevy of suspects
The CalFed program was developed in 1994 to coordinate the Delta's water systems and allow agencies to continue sending water south without breaking environmental laws. The program has funded numerous habitat improvements, including the "Environmental Water Account," which sets aside at least 190,000 acre-feet of water annually so that flows can be altered to benefit fish.
But suddenly the key question is: Will there by any fish left to save?
No one is sure what's putting Delta fish in peril. One suspect is water project pumps, which are powerful enough to reverse normal currents in the Delta. CalFed and other water managers have been experimenting with the timing of water exports to reduce impacts on fish. Most of the exports previously occurred in spring, when the finger-sized Delta smelt were upstream in the estuary and would often get ground up in the pumps. Water managers tried moving the exports into summer, after the smelt moved downstream.
"(But) instead of exporting smelt, you may be exporting (their) food," including the copepods that are also in decline, says Moyle. "There are experiments going on trying to figure out the best time to export water. What everything seems to point to is that there really is no optimal time."
Invasive species have also been a problem in the Delta for years. A foreign clam species consumes vast quantities of phytoplankton, and numerous invasive aquarium plants grow so thickly that they alter water flow in some channels. A new variety of blue-green algae blooms in masses, choking off aquatic oxygen and possibly releasing toxins into the food chain.
Another factor is toxic agricultural runoff. One class of pesticides, organophosphates, is being phased out by the 1996 Food Quality Protection Act because it is toxic to people and other mammals. Instead, farmers are turning to another class of pesticides, called pyrethroids — which, it turns out, are toxic to fish.
A search for answers
Whatever the cause of the decline, it is sure to wreak havoc on a renewed campaign for more water from the Delta. In 2003, in a closed-door meeting with CalFed officials in Napa, Calif., the largest exporters developed what has come to be known as "the Napa agreement." It will increase the capacity of state water pumps and could lead to at least 200,000 additional acre-feet of water exports each year.
In February, conservation groups, led by Earthjustice, sued the U.S. Fish and Wildlife Service in federal court after the agency ruled the new pumping capacity would not harm the threatened Delta smelt.
Tim Quinn, vice president of the Metropolitan Water District of Southern California, which supplies Los Angeles and San Diego, says, "There's no evidence the pumping has had all that much effect. There's no doubt there is something going on out there in the Delta, and we need to figure it out.
"It probably has something to do with the food chain, but nobody's sure," he says, noting that smelt numbers have plunged repeatedly in the past and have always rebounded.
But the simultaneous decline of these fish species, together with their key food source, may be unprecedented. "It's a really tough case to make that we should increase exports in the face of some of these fish declines," says Ted Sommer, a senior scientist with the state Department of Water Resources.
On May 12, 16 members of Congress, led by Rep. George Miller, D-Calif., wrote to Interior Secretary Gale Norton and California Resources Secretary Michael Chrisman, suggesting that they "rethink" policies that may have led to the fish declines. Meanwhile, experts plan a large-scale research effort this summer in hopes of learning what's killing the fish.
"We think there's a pretty obvious connection there when you have the highest rate of water diversions in history and the lowest level of Delta smelt and these other fish," says Barry Nelson, Natural Resources Defense Council spokesman. "The (water users) are falling all over themselves to avoid that connection because they want to increase Delta pumping further."
Matt Weiser is a freelance writer in Sacramento, California.