Effects of the age-composition of spawning sockeye salmon on future returns of sockeye salmon to Bristol, Bay, Alaska

Abstract

The age structure of sockeye salmon on spawning grounds is highly variable, yet little is known about the influence of spawner age composition on subsequent abundance and age composition of recruits. Management of Bristol Bay sockeye salmon relies on estimated spawner abundance to determine escapement goals, without regard to age or size composition. This may not accurately reflect reproductive potential as a basis for setting escapement goals. Parental age structure and environmental conditions were included as independent variables in statistical models to evaluate their effects on the age structure of their progeny. In addition, relationships between spawner age composition and recruit abundance were examined. I found a significant relationship between the age composition of spawners and that of their progeny, as well as environmental effects on age composition. A higher proportion of spawners that spent three years in the ocean were associated with a higher proportion of recruits with this life history pattern, suggesting direct genetic and/or environmental influences. However, redefining spawner-recruit models based on spawner age composition did not significantly improve predictions of the overall number of recruits originating in a given brood year. Nevertheless, the ability to predict the age and hence size composition of returns (with uncertainty), implies that improved predictions of the total biomass of returns in a given year is possible.