Salmon numbers fall, but possible explanations grow

Tom Stienstra

March 23, 2008

(03-22) 19:27 PDT -- A Chronicle story in 2006 warned of a deteriorating marine food chain off the California coast that has since led to the collapse of salmon stocks.

Environmental Jane Kay wrote, "By now, the offshore waters should be roiling with plankton and the shrimp-like krill, the foundation of the ocean's food chain. Instead, the researchers say, the organisms appear to be in short supply." ("Sea life counts dive for 2nd year - Decrease in essential plankton and krill disrupt food chain," June 23, 2006 .)

To explain the lack of marine food production, National Oceanic and Atmospheric Administration oceanographer Frank Schwing said, "The upwelling that we normally expect in the springtime hasn't kicked in. We think there might be real consequences for the seabirds, fish and mammals."

This year's salmon season for the Bay Area coast was supposed to open on April 5, but the opener has been postponed and the season is in jeopardy because of a collapse of stocks. Salmon that spawn or are released from hatcheries in the Central Valley are down from 804,401 fish in 2002 to 90,414 in 2007.

"It is pretty clear that poor ocean conditions in 2006 and 2007 are the major factor in the decline in salmon abundance this year (and projected for next year)," said John Carlos Garza of the federal Southwest Fisheries Science Center out of Pacific Grove.

Since coho salmon on coastal streams have also declined, that also indicates that the problem is largely focused with ocean conditions. "The only thing that they all share in common is their residence in the coastal ocean," he said.

He said that high water exports out of the Delta and direct fish losses at water pumps could explain why salmon from the Central Valley have had "an inordinately large decline relative to other stocks."

With low rain and snow last year, and yet high water exports to points south, fall-run salmon were down 80 percent in the San Joaquin River Basin, with only 1,158 fish, according to the San Joaquin Basin Newsletter.

"Concurrent declines," Garza said, in other Delta species, such as the endangered Delta smelt, makes it "seem likely" that Delta conditions are a contributing factor.

"As with most things, it appears that there are multiple causes to the salmon decline," Garza said. Based on his group's studies, he predicted dramatic fluctuations in the future.

Chronicle readers have suggested additional reasons why the salmon have disappeared:

Wiped out by netters: Foreign trawlers, the giant mother ships that drag huge scoop nets, have the capabilities to wipe out thousands of salmon with one swipe of the net, and they do so without United States oversight.

Humboldt squid: Voracious swarms of 50-pound Humboldt squid, which seem to devour everything in their path, are now wintering off the Bay Area coast and have located and annihilated schools of salmon (and rockfish).

Predators galore: High numbers of predators, including sea lions, elephant seals and killer whales, are eating the fish into a decline, similar to how mountain lions killing both deer and Sierra bighorns have put those species on the brink in the Sierra Nevada .

Using smolts as striper feed: By releasing salmon smolts from the hatcheries on a routine schedule in the Lower Delta, they have trained striped bass into a feeding program, where the smolts get wiped out every time they're plunked in the water.

Delta fish grinders: The suction force of the Delta pumps, which reverses tide flows near Clifton Court at the intake, is simply grinding up all the juvenile fish that try to swim past the area.

Carrying capacity: The basic "carrying capacity" of the rivers/delta/bay system, that is, the amount of food and freshwater available as habitat, has declined because of water diversion and industrial pollution, and in turn, the habitat can support far fewer fish than in the past.

"The Great Outdoors With Tom Stienstra" airs Sundays at 10 a.m. on KMAX television in Sacramento . E-mail Stienstra at tstienstra@sfchronicle.com.

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Source:  http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/03/23/SPCAVNC8F.DTL