Movement and spawner distribution of hatchery fall Chinook salmon adults acclimated and released as yearlings at three locations in the Snake River basin

As part of the supplementation program for fall Chinook salmon Oncorhynchus tshawytscha in the Snake River basin, yearlings from Lyons Ferry Hatchery were released at acclimation facilities stationed along the lower Clearwater River and the lower and upper reaches of the Snake River. The distance required for migration out of the release reach was greatest for juveniles released in the lower Clearwater River. The distance required for migration out of the release river was greatest for juveniles released in the upper Snake River. We captured and radio-tagged returning adults at Lower Granite Dam (the last dam encountered prior to entering the release reaches), monitored adult movements, and assessed the performance of acclimation facilities in terms of their ability to distribute adults to their corresponding release reaches. Adults from the lower Clearwater River acclimation group had the lowest frequency of movement, the most restricted spatial movement, and the highest observed rate of spawning in the intended reach. The upper Snake River acclimation facility distributed spawners to the intended river at the highest rate observed. Though differences in water flow and temperature during immigration were possible explanations for these findings, acclimation facility location provided the most plausible explanation. We conclude that acclimation facility location can affect prespawning movement and the spawning distribution of hatchery fall Chinook salmon in the Snake River basin