Climate and intraspecific competition control the growth and life history of juvenile sockeye salmon (Oncorhynchus nerka) in Iliamna Lake, Alaska

Recent climate changes have had marked effects on the ice-free season and thermal conditions in many high-latitude lakes, but their ecological effects combine with density-dependent processes to affect fish growth and life history. To better understand the relative roles of climate and intraspecific density, we applied Gaussian state–space models to long-term data (1962–2006) on growth of juvenile sockeye salmon ( Oncorhynchus nerka ) in Iliamna Lake, Alaska, USA. Both temperature and density influenced fry size at the end of their first growing season, but the positive effect of temperature exceeded the negative effects of density. Fry growth was affected by the magnitude of their own cohort more strongly than by the previous brood (i.e., yearlings). In contrast, density was more important than temperature in Lake Aleknagik, also in Bristol Bay, over the same period of record, probably because Iliamna Lake is cooler and has generally lower densities of juvenile sockeye salmon than Lake Aleknagik. In both lakes, the size of the fish at the end of the first growing season affects smolt size and age at seaward migration, hence survival at sea and age at maturity, so the relative effects of climate and density depend on the ecological context.