Stock-Specific Size and Migration of Juvenile Coho Salmon in British Columbia and Southeast Alaska Waters

The variation at 17 microsatellites was analyzed for 5,270 juvenile Coho Salmon Oncorhynchus kisutch obtained from coastal British Columbia and Gulf of Alaska surveys during 1998–2012. A 270-population baseline was used to determine the individual identifications of the fish sampled, with individuals being identified to 22 stocks of origin. Columbia River and Washington juveniles were consistently larger than those from British Columbia and Alaska. During June, the larger individuals within a stock were observed in more northerly locations. There was a relationship between the timing of northward migration and juvenile body size, with larger individuals migrating earlier than smaller individuals from the same stocks. Stock composition was more diverse in the northern sampling regions than in those in southern British Columbia. There was only a modest change in stock composition between fall and winter samples in both the Strait of Georgia and west coast of Vancouver Island sampling regions, indicating that juvenile migration had largely been completed by the fall. There was a wide divergence among stocks in juvenile size and dispersion among sampling locations.