Population-Specific Variation in Growth of Yearling Columbia River Chinook Salmon During Early Ocean Residence as Indicated by Levels of the Hormone Insulin-Like Growth Factor-1 (IGF-1)

Growth of juvenile salmon during early ocean residence is a determining factor in their long-term survival to adulthood.  Assessing growth rates of juvenile salmon along the coast of Washington and Oregon is of great interest in order to better predict smolt-to-adult return (SAR) rate, especially for imperiled Columbia River Chinook salmon.  The development of a robust biomarker of growth, the hormone insulin-like growth factor-1 (IGF-1), has allowed for the ability to assess growth in juvenile salmon captured at sea.  The IGF-1 hormone is a protein released by the liver to directly stimulate cell division and growth in somatic tissues in fishes.  The level of IGF-1 measured in the blood plasma is positively correlated with instantaneous growth such that IGF-1 level is an informative and robust index of growth in juveniles caught in their first 2-3 months at sea.  In this study, IGF-1 levels in juvenile Chinook caught along the Washington and Oregon coast in May and June from 2000 to 2009 were assessed.  Variation in IGF-1 level is examined in relation to population, year, fish size, catch location, and month. Significant inter-annual differences were found, similar to earlier results presented on coho salmon.  In addition, population-specific differences in IGF-1 levels were apparent, requiring us to examine population-specific IGF-1 levels in regard to fish size, catch location, month.  Finally, the mean June IGF-1 levels of yearling upper Snake/Columbia River spring Chinook salmon were found to be correlated with adult returns of spring Chinook salmon to Bonneville Dam.  These results suggest that the early marine growth of these important populations of Chinook salmon is related to adult survival and that IGF-1 levels of these fish may be used to predict adult returns.