West coast sardine fishermen for a second straight season will have to keep their boats moored or find something else to catch.

The Pacific Fishery Management Council on Sunday closed the sardine fishery off Oregon, California and Washington following the second straight year of sardine population estimates that fall below the minimum abundance required to allow fishing.

The closure is likely to continue for years as the small, schooling fish species struggles to rebound from a host of factors that might have contributed to its collapse.

Despite fishery managers' decision last summer to close the fishery mid-season after realizing their stock estimates for the year had been overoptimistic, the sardine population continues to shrink.

There are fewer than 65,000 metric tons adult sardines in the ocean this year, federal scientists estimated. West coast fishery rules require sardine fishing to cease once the adult stock drops below 150,000 metric tons.

It's unclear what's causing the fish to struggle. Theories range from climatic factors to overfishing to an unavoidable boom-and-bust population trend typical of sardines.

Others wonder whether the "warm blob," a mass of unusually warm water that's been hovering off the Pacific coast, has anything to do with the collapse. Sardines aren't the only species struggling off the West Coast, and some scientists suspect the blob is to blame.

Research shows adding fishing pressures to cyclical population downturns intensifies their impact. Ocean conservationists who argue fishery managers waited too long to ban fishing say they'll spend the coming years lobbying for policy changes that would trigger a shutdown earlier.

The sardine order is one of two high-profile decisions the council will make this week during a meeting in Vancouver. On Tuesday, councilmembers will consider closing coastal salmon fishing off Northwest Oregon and Washington to protect struggling coho runs.

--Kelly House

khouse@oregonian.com

503-221-8178