Effects of hydroelectric development and fisheries enhancement on spring and summer Chinook salmon and steelhead in the Columbia River basin
hydroelectric, chinook, salmon, steelhead, Columbia River, Snake River, adult, smolt, mortality, juvenile, dams, impoundments, ocean, migration, hatchery, spillway, deflectors, bypass, transportation, reservoirs, turbine mortality
Journal or Book Title
North American Journal of Fisheries Management
Trends in abundance of spring and summer Chinook salmon (Oncorhynchustshawytscha) and steelhead (Salmo gairdneri) returning to the Snake River and mid-ColumbiaRiver above Priest Rapids Dam were determined by analyzing the percentage of adults returningfrom the smolt out-migrations of 1962-1984. Runs declined as a result of hydroelectricdevelopment of the river; the main cause for the decline was the mortality of juveniles migratingdownstream though as many as nine dams and impoundments en route to the ocean. Mid-Columbia River summer Chinook salmon runs experienced the greatest decline because of thehigher mortalities incurred during their migration to sea as subyearlings in July and August.Mortality was lower for remaining races of fish that migrate to sea as yearlings in the springduring higher river flows, more spill at dams, and cooler water temperatures. Enhancementmeasures to offset dam-related mortality of smolts began in 1970 on the Snake River and in 1975on the mid-Columbia River. These measures included increased numbers of smolts releasedfrom hatcheries, spillway deflectors to reduce dissolved gas saturation, fingerling bypasses atdams, transportation of smolts around dams, supplemental river flows to minimize delay forsmolts passing through reservoirs, and supplemental spill at dams to minimize turbine mortality ofsmolts at dams without fingerling bypasses. These actions have reversed the decline of steelhead but not of salmon. Enhancement has improved the rate of return of wild spring Chinooksalmon, but wild fish contribution is minimal at this time because stocks were reduced by earlierhydroelectric development. Presently, runs are mostly of hatchery origin and have not respondedwell to enhancement. Mortality of hatchery fish may be due to activation of bacterial kidneydisease by stresses encountered during downriver migrations, transportation, or subsequenttransition into seawater.