< May 2005 Issue

Spring Chinook return remains far below normal; focus turns to accuracy of run-size forecasting

Link: Pete Hassemer's PowerPoint presentation (380k PDF)

Through May 9, just over 52,000 spring Chinook salmon had crossed Bonneville Dam on their way to spawn in upriver tributaries of the Columbia and Snake Rivers. The total is less than half the 10-year average for the date.

Pete Hassemer of the Idaho Department of Fish and Game told the Council at its May 10-11 meeting in Walla Walla that the run appeared in the river about two weeks later than normal this year, and that after a daily peak of just over 6,000 fish on May 5, the run dropped off dramatically to fewer than 400 fish by May 10. Typically, the run would continue after that peak at 1,000-2000 fish per day into early June.

The "missing fish" most likely are 4-year-olds, which would have resulted from fish that spawned in 2001, Hassemer said. They would have spent a year rearing and then gone to the ocean in 2003. It isn't clear why this component of the run is so low or why the overall run was delayed, Hassemer, said, but fish and wildlife agencies and Indian tribes that predict annual salmon run sizes plan to take a careful look at the data and assumptions in their computer models.

The 2005 run had been forecast at more than 250,000 fish, but it now appears the run will be between 74,000 and 89,000 fish. Biologists also plan to carefully monitor spring Chinook returns to lower-Columbia tributaries to determine whether the low runs are systemwide or more prevalent among upper-river runs. This could help clarify whether the low run resulted from problems in the spawning and rearing habitat, the river during smolt migration, in the ocean or in all three areas, he said.