Northwest Fisheries Science Center

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Document Type: Report
Center: NWFSC
Document ID: 7718
Title: Blueback salmon, Oncorhynchus nerka, age and length at seaward migration past Bonneville Dam
Author/Editor: Raymond E. Anas, Joseph R. Gauley
Year: 1956
Institution: U. S. Fish and Wildlife Service Special Scientific Report--Fisheries No. 185

Some downstream-migrant blueback salmon Oncorhynchus nerka pass Bonneville Dam in each month of the year, but trap catches indicate that the bulk of migration occurs during April and May.  Of the bluebacks in this study, 93 percent were yearlings or in their second year.  Ages ranged from 1 to 5 years.  Length-frequency graphs show no consistent separation of the races of Columbia River bluebacks.  More marked bluebacks were caught from spring than from fall releases from Leavenworth and Winthrop Hatcheries; the reverse was true of releases from Little White Hatchery.  Spring releases tend to migrate immediately, but not as a single school.  Bluebacks released in the fall tend to migrate the following spring.