Age-specific effects of sockeye abundance on adult body size of selected British Columbia sockeye stocks

Abstract

Annual mean body lengths of adult sockeye salmon (Oncorhynchus nerka) covary systematically from year to year in major northern and central British Columbia stocks (Nass River, Skeena River, and Rivers Inlet). These positive correlations are greatest between sexes within rivers, followed by age-classes among rivers. A common factor or factors affecting sockeye length in the North Pacific Ocean is suggested. The mean length of age 1.3 sockeye salmon but not age 1.2 sockeye caught annually in these B.C. fisheries was negatively correlated with the magnitude of Bristol Bay (western Alaska) sockeye catches. During the spring of maturation, age 1.3 sockeye from these B.C. stocks were further from their natal streams, and likely subject to more intense competition with Bristol Bay sockeye than age 1.2 sockeye. The pattern of annual marine growth measured from Skeena River sockeye scales collected during the 1960s provides additional evidence that the length of age 1.3 sockeye was related to Bristol Bay sockeye abundance in the year of maturation. No such correlation was evident in scales collected from age 1.2 sockeye. These results suggest that sockeye populations have more systematic distributions in the North Pacific Ocean than has been previously reported.