Linkages Between Freshwater Temperature and Productivity of Afognak Lake Sockeye Salmon: A 30-Year Synthesis

The Afognak Lake sockeye salmon run has historically supported the largest subsistence salmon fishery on Afognak Island, Alaska, and the second largest in the Kodiak Archipelago. In the 2000s, the number of sockeye salmon returning to Afognak River diminished substantially, resulting in fishery closures and a renewed focus on understanding drivers of productivity across multiple life stages. The central goal of this study was to characterize changes in the Afognak Lake ecosystem and evaluate patterns in habitat quality for lake-rearing juvenile sockeye salmon from 1987 to 2013. We synthesized long-term data collected by the Alaska Department of Fish and Game to evaluate the hypothesis that thermal conditions and prey supply in Afognak Lake are important factors influencing productivity of lake-rearing juvenile sockeye. We evaluated the relative importance of lake temperature and zooplankton quality and quantity in explaining interannual variation in juvenile sockeye density, size-at-age, and nutritional condition. These analyses will provide a foundation for developing scenarios of Afognak Lake sockeye salmon responses to long-term changes in lake habitat.