ABSTRACT 



Some downstream-migrant blueback salmon 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 follow- 

 ing spring. 



