Migratory behavior of yearling juvenile chinook salmon and steelhead in relation to water movement in the Yakima River, Washington
behavior, chinook, juvenile, salmon, steelhead, statistics, migration, juvenile salmon
Hypotheses are presented to explain the juvenile migratory behavior of yearling chinook salmon and steelhead in the Yakima River over a thirteen-year period with particular reference to water movement. Interactions of emigrations with water movements, measured as daily flow, and daily change in flow, are pervasive, however annual variations in the annual timing of emigrations are not explained by timing of water movement. Even though annual emigrations of yearling chinook and juvenile steelhead can be tightly synchronized with water movements, under time patterns of water movement associated with impoundment and regulation, emigrations and water movements are not necessarily synchronous. An approach to statistical analysis using fish-weighted statistics is recommended in order to best capture the ambient physical conditions experienced by the average fish. Timing of emigrations of juvenile steelhead and yearling chinook overlap, but yearling chinook usually emigrate earlier (grand mean April 25) than juvenile steelhead (grand mean April 29). Yearling chinook and juvenile steelhead emigrate under all observed water movement conditions, however individuals of both species are virtually certain to emigrate when sharp positive changes in daily water volume occur during the migration season. Both yearling chinook and juvenile steelhead emigrants are positively associated with water accelerations. Yearling chinook and juvenile steelhead emigrants are predominantly positively associated with flow, and they are only occasionally negatively associated with flow. When annual average instantaneous Yakima River flow is below the long term average (102.4 m3/s), the average Yakima River yearling chinook and juvenile steelhead emigrates within the highest water flows and accelerations available. These findings support theories of juvenile salmon migration advanced by Hoar, Groot, Thorpe, and Northcote.