Transportation of Chinook salmon and steelhead smolts 1968-80 and its impact on adult returns to the Snake River
transportation, chinook, salmon, steelhead, smolt, adult, Snake River, dams, mortality, fingerlings, turbines, gas bubble disease, spillway, predation, reservoirs, migration, juvenile, Bonneville Dam, Ice Harbor Dam, Little Goose Dam, Lower Granite Dam, McNary Dam, Columbia River
National Marine Fisheries Service, Northwest and Alaska Fisheries Centre
Chinook salmon and steelhead runs in the Snake River have been in a seriousdownward trend since the late 1960' s (Figure 1). The major factor contributing to low fish runswas the completion of four new dams (John Day 1968, Lower M:mumental 1969, Little Goose1970, and Lower Granite 1975) on the Columbia and Snake Rivers. The new dams greatlyincreased mortality to seaward migrating fingerlings in a variety of ways: passage throughturbines, gas bubble disease (caused by river water entrained with atmospheric gases passingover spillways), predation in reservoirs, and delays in migration.In 1965, National Marine Fisheries Service (NMFS) scientists began preliminary work on a plan tocollect seaward bound smolts at upper dams and transport the juveniles to safe release sitesbelow Bonneville Dam, thereby bypassing. as many as eight dams and their associated problemareas. The concept was first studied on the Snake River at Ice Harbor Dam in 1968-70, then atLittle Goose Dam 1971-73 and 1976-78, and Lower Granite Dam in 1975-78. It was expanded toinclude 'McNary Dam on the Columbia River in 1978.