Migrational Behavior and Seaward Movement of Wild Subyearling Fall Chinook Salmon in the Snake River

Abstract

Abstract Flow augmentation increases flow and decreases temperature in reservoirs in the lower Snake River during the seaward migration of wild subyearling fall chinook salmon Oncorhynchus tshawytscha. A study of the migrational behavior and seaward movement of wild subyearling fall chinook salmon in the Snake River was necessary to help understand the efficacy of flow augmentation. We studied fall chinook salmon in the Snake River during 1992–2001. After analyzing mark–recapture data, we deduced that fall chinook salmon passed through at least four migrational phases, including (1) discontinuous downstream dispersal along the shorelines of the free-flowing river, (2) abrupt and mostly continuous downstream dispersal offshore in the free-flowing river, (3) passive, discontinuous downstream dispersal offshore in the first reservoir encountered en route to the sea, and (4) active and mostly continuous seaward migration. We used ordinary-least-squares multiple regression to test the effects of flow (m3/s), t...