Using Plasma Insulin-like Growth Factor 1 Levels to Assess Trophic Status of Juvenile Salmon in Marine Pelagic Ecosystems

The growth of juvenile salmon is dependent on food available within pelagic marine food webs: the number of organisms present, their size and their nutritional quality.  The organisms salmon actually consume results in a given growth rate, this growth rate represents an integration of consumption and food quality and encompasses many aspects of a fishes ability to find and capture prey.  Thus growth rate represents an index of trophic success and differences in growth rate reflect variation in trophic status.  Herein we present data on the hormone insulin-like growth factor 1 (IGF1), an index of short-term growth rate.  In the northern California Current juvenile coho and Chinook salmon IGF1 varies significantly between years and is correlated to indices of zooplankton abundance.  In the northern Bering Sea IGF1 level is correlated with other measures of pelagic ecosystem productivity.  Finally, in the Salish Sea, IGF1 levels varied spatially as juvenile salmon migrated from the Strait of Georgia through Johnstone Strait and into Queen Charlotte Sound.  These examples demonstrate the efficacy of using IGF1 levels to evaluate the trophic status of juvenile salmon, IGF1 levels varying on both inter-annual and spatial scales that match variation in food availability and oceanographic structure.