Understanding Energy Expenditure of Upstream Migration, Sexual Maturation, and Kelt Emigration of Snake River Steelhead Trout with Bioenergetic Models and Empirical Data from Tissues

After re-entering freshwater, adult steelhead trout (Oncorhynchus mykiss) rely on stored energy to complete migration to their natal spawning streams, gonad maturation, successful reproduction and post spawning migrations.  Very little is known about energy use and allocation in adult steelhead trout, especially in how somatic energy stores contribute to successful iteroparity.  In 2009 and 2010, we lethally sampled 402 steelhead trout from the Columbia/Snake River at three stages: pre-spawning, sexually mature, and post spawning (kelts) to model changes in stored energy. We determined lipid content and calculated total energy in the liver and white muscle using proximate analysis and bomb calorimetry. We found the proportion of lipids in livers of mature steelhead trout in 2009 was significantly higher than kelts, but this trend was not observed in 2010.  The proportion of lipids in white muscle and whole body analyses showed a significant depletion from highest levels in the early pre-spawning steelhead trout to nearly complete depletion (< 0.5%) in kelts. Protein was gradually depleted in both the liver and white muscle over migration and spawning.  We used a deterministic bioenergetic model to examine the energetic costs (kcal/g) of upstream migration based on existing model parameters determined for adult steelhead trout in the Great Lakes, but since steelhead trout cease feeding during sexual maturation in freshwater, consumption was set to zero.  We simulated the relative costs for migration in two sizes of steelhead, and determined that the smaller (one ocean) fish expended approximately 10% more energy in a similar migration history to larger (two and three ocean) fish due to the differences associated with fish size.  Our model simulations are limited in that stochasticity in run-timing and environmental conditions were not accounted for.  We plan to provide and present further analysis and insight into bioenergetic potential of these important steelhead trout stocks with other relevant variables and scenarios to improve our evaluation of energy expenditure of migration and spawning in Snake River steelhead trout.