PORTLAND, Ore. – Usually by now, the Columbia River's spring chinook salmon are heading upstream over fish ladders in the tens of thousands to spawn. Not this year.
Fish biologists had predicted a spring run of about 229,000 chinooks at the Bonneville Dam (search), about 140 miles from the Pacific Ocean (search). As of Tuesday, near the customary midpoint of the spring run, only about 200 had been counted there.
"It's a never-before-seen scarcity," said Charles Hudson (search) of the Columbia River Inter-Tribal Fish Commission.
It's so bad that the Indian tribes on the river had to get salmon somewhere else for their ceremonial celebration marking the return of the fish.
The chinooks enter the Columbia River from the Pacific at this time of year to return to the streams where they were hatched two or three years before. There, they spawn and die.
Scientists say they don't have an explanation for the scarcity.
"Nobody knows why," said Brian Gorman of the Pacific Marine Fisheries Service (search) in Seattle. "It's a mystery."
Gorman also described the run as "mysteriously late."
Most of this year's spring run went to sea in 2002 or 2003, said Norman, adding there were no conditions in those years that would readily explain the dearth of fish this spring.
Some fish managers wonder whether low water levels as a result of a dry winter — combined with murky water caused by recent rains — are keeping chinook from swimming up the Columbia.
"Spring chinook are pretty finicky when conditions are abnormal," said Guy Norman of the Washington state Department of Fish and Wildlife. "April and early May are the most significant times for spring chinook movement over the (Bonneville) dam. We're hoping for good things to come."
Fish swimming upstream on the Columbia are tallied at the Bonneville Dam, where they go up fish ladders — which resemble stairs — and swim past a large window. Their numbers are a factor in setting fishing seasons for sport, tribal and commercial fishermen.
Hudson, the tribal spokesman, said he's optimistic "there are fish out there gathering at the mouth of the river waiting for some biological trigger to send them up."
The economic impact of the small chinook return is not clear.
Fish managers hold weekly meetings to look at the size of the run and the size of the catch, and regulators aren't ready yet to recommend trimming the fishing season, said Curtis Melcher, marine salmon fisheries manager for the Oregon Department of Fish and Wildlife.
Melcher said sport fishermen are catching some chinooks but not as many as usual. He said many of those caught were bound for the Willamette River and other tributaries below the dam.
Hudson said the fish are back in near their usual numbers in the Willamette River, which joins the Columbia well below the Bonneville Dam, the first dam the returning fish encounter on their return.
Bonneville is required to release a certain amount of water past dams to help fish if the water flow is low to keep young salmon out of hydroelectric turbines. The turbines kill about 10 percent of the fish that go through them.
"With an impact of this kind you're usually talking about hydroelectric operations as a likely cause," Hudson said.