PORTLAND - Spring chinook salmon are finally moving up the Columbia River at Bonneville Dam, making their latest run on record.

The three-week delay is a mystery to wildlife managers. And lower-than-expected numbers in the run have some fishermen thinking the fishing season will not reopen.

A spring Chinook run typically peaks at mid-April, but it wasn't until last week that sustained numbers of salmon were counted as they went through the ladder at Bonneville Dam, according to the Oregon and Washington fish and wildlife departments.

The fish count for the year is 35,796 so far, almost 14,000 fewer than at the same time last year.

Fish and wildlife officials said the count is unlikely to reach the preseason forecast of 88,000. An advisory board of scientists and others met Monday to work on an official estimate for the season, which will be the primary factor in determining if the fishing season will resume.

The fishing season closed in mid-April because of low counts. If the count is too low, the season might not reopen because regulations limit the percentage of the total population that can be fished.

“There is a sense of relief that we are finally seeing the fish coming back, but opportunities for fishing are pretty much over,” said Bruce Buckmaster, a board member of fishing industry group Salmon For All.

Fishing industry groups said while they've written off the season, they are still concerned about the early trends in low and late salmon runs. This is the second consecutive year the run has been late.

“We watch (the fish count) daily - minute to minute,” said Liz Hamilton, executive director of the Northwest Sportfishing Industry Association. “We're really concerned about the fish.”

Fish and wildlife officials said they don't know why the run is so late or if the pattern will repeat next year. Salmon change their migration for a number of reasons, ranging from temperature to clarity of water, said Bill Tweit, of the Washington Department of Fish and Wildlife.

Based on early-season fishing, wildlife officials said they know the spring chinook were entering the Columbia from the Pacific Ocean at their usual time. But the fish seemed to hang around the 40 miles between the Interstate 5 bridge at Portland and the Bonneville Dam. The area is heavy with predatory animals such as sea lions, but fish officials don't know what impact that has on the count.

The first place they are counted is at the Bonneville Dam.

“It has us scratching our heads,” Tweit said. “We don't know why the fish were doing that.”