Despite a historic shutdown of coastal salmon fishing, the number of salmon returning to the Sacramento River is collapsing, according to preliminary data released by the Pacific Fishery Management Council.

Returning fall Chinook salmon numbers have dropped to their lowest level since monitoring began in the 1970s, the report said.

The finding means it is unlikely that fishing will resume this year, disappointing fishermen who have eked out the last two years on disaster aid, waiting for salmon fishing bans to be lifted.

“Almost certainly this will be another year of total closure,” said Glen Spain, Northwest regional director of the Pacific Coast Federation of Fishermen’s Assns.

As recently as eight years ago, the fall Chinook salmon run into the Sacramento River, the backbone of the state’s ocean salmon stocks, numbered nearly 800,000.

But as return numbers dropped more than tenfold, fisheries managers took the unprecedented step of canceling two salmon seasons along the California coast.

They hoped this would help the fish recover. Instead, the new counts indicate that last fall’s return dropped nearly 40% from the previous fall’s. Only 39,500 salmon were counted returning to the Sacramento, a “severe crisis” level, said Dan Wolford, vice chairman of the council, which will make its decision on the fishing season in April.

Scientists had predicted that three times as many salmon would return.

“Oh, my God!” said Jim Hie, a member of the council’s salmon advisory panel. “It’s the worst in history. We have just seen the whole thing tumble.”

The cumulative impact of factors such as less resilient fish, drought, freshwater habitat loss in the ailing Sacramento Delta and more variable ocean conditions is putting salmon populations at risk, said Steve Lindley, research ecologist for the National Marine Fisheries Service.

Wolford said that three years ago, low salmon numbers had been blamed on poor ocean conditions but that those conditions had since improved. So this year’s poor salmon numbers are likely to renew concerns about water draws from the delta, he said.

The issue of such draws has pitted fisheries advocates against agricultural interests and has bloomed in recent years into what Wolford called a “classic water war.”

The salmon report noted a few bright spots in the otherwise grim news: The number of younger adult salmon, called “jacks,” increased somewhat, though it remained far below historic averages.

Also, the report noted a greater number of salmon returning to spawn in the Klamath-Trinity river system. There were 44,500 in the fall, exceeding objectives, the report said.

Still, the crashing Sacramento River salmon population is suggesting to some observers that what once was the state’s biggest salmon run has reached a turning point.

“These are at extinction levels,” Spain said. “These are not even enough fish coming back to replace this generation.”

jill.leovy@latimes.com