SACRAMENTO  Where did they go?

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. A final decision on salmon fishing in the area is expected next month.

As a result, Chinook, or king salmon, the most prized species of Pacific wild salmon, will be hard to come by until the Alaskan season opens in July. Even then, wild Chinook are likely to be very expensive in markets and restaurants nationwide.

“It’s unprecedented that this fishery is in this kind of shape,” said Donald McIsaac, executive director of the council, which is organized under the auspices of the Commerce Department.