Increasing Growth and Younger Age-at-Migration of Sockeye Salmon in a Southwest Alaska Watershed: A 50-Year Retrospective

Lake ecosystems throughout the world are changing rapidly due to climate warming and these changes include increased water temperature, longer growing seasons, decreased ice cover, and increased runoff and turbidity in glacially influenced systems.  Despite many studies on the implications of climate warming in lakes, how fish populations will respond to these changes remains uncertain. We examined long-term trends in climate, fish abundance, and freshwater growth and age-at-migration of Sockeye Salmon from Lake Clark, a glacially influenced lake within the Kvichak River watershed in southwest Alaska. To reconstruct freshwater growth and determine age-at-migration we used otoliths collected from adult salmon between 1961 and 2012. During this time period, we found that freshwater growth increased and age at migration had shifted from mostly age-2 smolts in the 1960s and 1970s to mostly age-1 smolts in the 2000s. We explore relations of fish growth to environmental controls and discuss future projections of growth based on a range of potential climate change scenarios.