Nutrient Status of 16 Sockeye Salmon Lakes in the Kodiak Archipelago: Implications for Potential Rehabilitation and Enhancement

Limnological investigations have been ongoing for 30 years on 16 lakes with native or introduced sockeye salmon populations on the Kodiak Archipelago in Alaska with some systems having limnological data from over 90 years ago.  In some of these lakes, nutrient enrichment has been used as a restoration tool to increase returns of sockeye salmon. This series of data from multiple lakes coupled with sockeye salmon production information provides an unprecedented opportunity to relate the nutrient status of lakes to historical changes in sockeye salmon production.  We analysed temporal trends in nutrient status as well as other environmental variables and assessed how the trends relate to primary productivity, secondary productivity, and abundance of sockeye salmon. Trends in nutrient status of lakes almost always corresponded with changes in primary productivity, and usually corresponded with changes in secondary productivity, although these relationships can be affected by cropping of invertebrates by juvenile sockeye salmon and the resulting trophic cascades.  The response of sockeye salmon populations to changes in nutrient levels, whether natural or enriched, was highly variable, likely due to the strong influence of other factors such as marine survival of salmon or competitor/predator interactions in lakes.   We evaluated the role of past and potential future nutrient enrichment programs in maintaining salmon production and discuss potential risks associated with such programs.