Fishery managers have shut down salmon fishing off Oregon’s coast through April to protect collapsing fish stocks, presaging what could become the largest West Coast closure in history.

The biggest factor is the plummeting returns of normally robust chinook salmon to the Sacramento River in California, although salmon numbers in many other rivers are down sharply, too.

Sacramento River fish typically range northward and account for 60 percent to 80 percent of the ocean catch off Oregon.

“It’s getting uglier by the day,” said Frank Warrens, a member of the Pacific Fishery Management Council, meeting this week in Sacramento to discuss fishing seasons.

While past years have seen poor salmon numbers in certain regions, this year the decline seems to extend along almost the entire West Coast, Warrens said.

“I’m personally terming it the perfect storm of salmon declines,” he said. “It’s worse now coastwide than anything I’ve seen.”

Part of the reason may be shifts in ocean conditions when salmon that should be returning this year first entered the ocean. Unusually warm conditions shut down a pipeline of nutrients from deep waters, leaving the marine food chain with little to eat.

That would have hit salmon at a crucial time, when they are small and vulnerable to predators also desperate for food.

Next month, federal fishery managers may close ocean salmon fishing from May through its typical end-date in mid-November from northern Oregon to the Mexican border. At a minimum, the key fishery will be severely restricted, Oregon officials said.

That would be an unprecedented blow to commercial and sport fishermen and coastal communities. It would also eliminate much of the Pacific Northwest salmon from store shelves and likely drive up salmon prices.

“In some communities, it would be absolutely devastating,” said Wayne Butler, who serves on the Pacific Fishery Management Council’s groundfish advisory committee. A salmon ban would likely push fishermen to harvest more rockfish, which could hurt those stocks, he said.

Some fishermen will turn to other species such as tuna, said Rod Moore, a management council member and head of the West Coast Seafood Processors Association. Owners of large boats might try Washington’s waters, though more boats fishing there will shorten the season.

“For a lot of the smaller vessels and a lot of communities, it’s going to be a major economic problem, and that will trickle down to the gear suppliers, the marinas, the gas stations,” Moore said.

The likely shutdown comes only two years after low salmon returns to the Klamath River forced a broad but less severe closure. Fishing resumed last summer but there were few salmon caught, said Eric Schindler, a biologist with the Oregon Department of Fish and Wildlife.

“The third year in a row of really disastrous catch levels is really what we can expect,” he said.

Biologists are stunned by the failing returns to the Sacramento River, typically one of the healthiest and most abundant stocks on the West Coast. The Pacific Fishery Management Council predicts that numbers of Sacramento River fall chinook will fall to an all-time low this year, about 22 percent of the long-term average.

From 2001 to 2005, commercial and recreational salmon fishing brought in $61 million for coastal communities in California and Oregon, the council says.

Because the declines this year affect so many rivers, many biologists believe a main factor behind them are ocean conditions rather than problems on individual river systems. National Oceanic and Atmospheric Administration scientists think poor ocean food production, a product of unusual ocean currents, contributed to lower salmon returns in 2007 in rivers all along the West Coast.

“This is a dramatic downturn in ocean productivity,” Schindler said.

NOAA hasn’t ruled out other reasons for the decline. At a meeting in Sacramento this week, the fishery council is reviewing a list of 46 possible factors, ranging from increased sea-lion consumption to pesticide pollution to water diversions from dams.

“We don’t frankly have all the answers as to why,” said Steve Williams, assistant administrator of the Oregon Department of Fish and Wildlife’s fish division. “That’s very frustrating to fishermen, and I understand that.”

The council is setting options for managing salmon. Public hearings will be held on those options. The council will make a final decision at its April meeting in Seattle.