Exploring the Biological Basis of Production (Return) Variability of Sockeye Salmon ( <scp> <i>Oncorhynchus nerka</i> </scp> ) Populations in the Fraser River, Canada Watershed

ABSTRACT The persistently complicated age structure of sockeye salmon ( Oncorhynchus nerka ) populations is intriguing. There is a variety of ages, and each age describes the number of winters spent as a free‐living fish in freshwater and then the number of winters spent at sea. I used multiple linear regression analysis to test the influences of total female and age‐specific female spawner abundances and prey, predator and competitor abundance/biomass on return for each of the 18 natural populations of sockeye salmon in the Fraser River, Canada watershed. I found that return variability was best explained age‐specifically and that age‐specific female spawner abundance had the dominant effect on return in all cases. Prey, predator and competitor biomass contributed to explaining return variability. Pink salmon ( Oncorhynchus gorbuscha ) biomass in the Gulf of Alaska exerted the dominant secondary effect. Explanations were unique within and between populations.