Beckman, B.R.*; Fairgrieve, W.; Cooper, K.A.; Mahnken, C.V.W.; Dickhoff, W.W.: Endocrine Correlates of Growth in Ocean Dwelling Coho Salmon

Pacific Salmon typically spend 1-3 years foraging and growing in the ocean prior to returning to freshwater spawning sites. Inter-annual differences in ocean temperatures and productivity may have profound effects on the growth of these animals. Growth variation may influence age of maturation, size at maturation, and overall year-class survival. Thus, understanding variation in oceanic growth rates is important to understanding variation in the fitness of Pacific salmon. However, it is very difficult to measure oceanic growth rates. Growth is mediated by the endocrine system; consequently, endocrine correlates of growth may provide a valuable tool for assessing relative growth rate and related fitness values, based on a single blood sample. We conducted an experiment relating growth rate to plasma hormone levels in order to test this idea. Specifically, we individually tagged approximately 1200 yearling coho salmon, placed them in seawater tanks and assessed growth at two month intervals. Plasma was obtained in September and November and we found a significant, highly correlated (r2>0.5) relation between IGF-I and growth rate. We found little relation between insulin and growth. Subsequently, we obtained samples from coho salmon in the Strait of Georgia and Puget Sound (West Coast of North America). IGF-I data obtained from these samples shows both geographic and interannual variability. These preliminary data suggest that a more extensive sampling regime (geographically and temporally) for IGF-I levels of Pacific salmon may give us insight into environmental factors regulating growth and fitness.