Variation in age and size at maturity among Lake Clark, Alaska sockeye salmon spawning locations

Age and size at maturity are key life history traits in sockeye salmon closely linked to fecundity, growth, and survival, and vary within and among populations.  Consistent patterns of variation in age and size at maturity among salmon spawning in river and beach habitats are considered to be evidence of local adaptations to spawning environment.  Age composition and size at maturity were compared among nine Lake Clark, Alaska sockeye salmon spawning locations from brood years 1998 and 1999 to test the hypothesis that age and size at maturity would be greater for river spawning sockeye salmon compared to beach spawning sockeye salmon.  Lake Clark sockeye salmon displayed significant variation in age composition and length at maturity among spawning locations by location and brood year, but no consistent patterns were observed among habitat types.  These differences may be related to differences in migration distance, growing conditions, or genetic factors.  While spawning habitat did not influence age and size at maturity, a relationship between habitat type and other life history traits has been documented in Lake Clark.  These findings indicate that trends in age and size at maturity across beach and tributary habitats are not necessarily consistent among systems or years.