The Chinook salmon that swim upstream to spawn in the fall, the most robust run in the Sacramento River, have disappeared. The almost complete collapse of the richest and most dependable source of Chinook salmon south of Alaska left gloomy fisheries experts struggling for reliable explanations - and coming up dry.

Whatever the cause, there was widespread agreement among those attending a five-day meeting of the Pacific Fisheries Management Council here last week that the regional $150 million fishery, which usually opens for the four-month season on May 1, is almost certain to remain closed this year from northern Oregon to the Mexican border.
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So what happened? As Dave Bitts, a fisherman based in Eureka in Northern California, sees it, the variables are simple. “To survive, there are two things a salmon needs,” he said. “To eat. And not to be eaten.”

Fragmentary evidence about salmon mortality in the Sacramento River in recent years, as well as more robust but still inconclusive data about ocean conditions in 2005, indicates that the fall Chinook smolts, or baby fish, of 2005 may have lost out on both counts. But biologists, fishermen and fishery managers all emphasize that no one yet knows anything for sure.