Evaluation of Deschutes River Fall Chinook Salmon
Fall chinook (Oncorhynchus tshawytscha) runs in the Deschutes R., particularly the component that spawns above Sherars Falls, have been low, declining, and highly variable in recent years. Estimates of overall summer/fall chinook run size between 1977 and 1992 can be described as generally declining and variable on a cycle of approximately five years. Redd counts indicate that most, if not all, of the total decline has occurred above Sherars Falls, which suggests that smaller-scale factors may differentially and adversely affect the survival and/or distribution of the above-falls component of the summer/fall run.
Because present estimation methods use fish trapped and tagged during upstream passage at Sherars Falls, the resulting estimates are less accurate and precise when the relative and absolute sizes of the above-falls component are low. Gravel conditions for spawning and incubation below Pelton Reregulating Dam have declined. Subyearling summer/fall chinook, particularly those migrating later in summer, are killed by mainstem dams (Bonneville and The Dalles) and predators. Ocean conditions seem to have a large impact on survival of Deschutes R. summer/fall chinook, as reflected in widespread synchrony in run size among salmonid stocks, high correlation between recruits-per-spawner of Deschutes R. stock and indices of upwelling and the Aleutian low pressure system, and associations between physical ocean conditions and biological conditions important for salmon production. Using ocean harvest rate estimates for Lewis R. wild fall chinook as a surrogate, it appears that ocean fisheries continue to take a relatively constant 20-25% of the Deschutes R. summer/fall chinook that would otherwise return to spawn. I believe that the summer component, the above-falls component, and the fisheries at Sherars Falls are integrally related: the fisheries depend on a healthy run above the falls and the above-falls run is probably dependent on restoration of the summer run native to upstream reaches. My first recommendation is to establish management goals for the stock that explicitly address the summer and above-falls components and the Sherars Falls fisheries. Subsequent recommendations are organized according to two alternative potential management goals: 1) restore the summer run, the above-falls component, and meaningful Sherars Falls fisheries, or 2) modify the status quo.
Beaty, R.E. 1996. Evaluation of Deschutes River Fall Chinook Salmon. Columbia River Inter-Tribal Fish Commission Report reference #96-06, Portland, Oregon.