San Francisco ? The number of chinook salmon returning to California’s Central Valley has reached a near-record low, pointing to an “unprecedented collapse” that could lead to severe restrictions on West Coast salmon fishing this year, according to federal fishery regulators.

The sharp drop in chinook, or “king,” salmon returning from the Pacific Ocean to spawn in the Sacramento River and its tributaries this past fall is part of broader decline in wild salmon runs in rivers across the West.

The population dropped more than 88 percent from its all-time high five years ago, according to an internal memo sent to members of the Pacific Fishery Management Council and obtained by The Associated Press.

Regulators are still trying to understand the reasons for the shrinking number of spawners; some scientists believe it could be related to changes in the ocean linked to global warming.

Only about 90,000 returning adult salmon were counted in the Central Valley in 2007, the second lowest number on record, the memo said. The population was at 277,000 in 2006 and 804,000 five years ago.

It’s only the second time in 35 years that the Central Valley has not met the management council’s conservation goal of 122,000 to 180,000 returning fish.

More worrisome is that only about 2,000 2-year-old juvenile chinooks – used to predict returns of adult spawners in the coming season – returned to the Central Valley last year, by far the lowest number ever counted. On average, about 40,000 juveniles, or “jacks,” return each year.