Finding Death: The Relationship Between Energy and Iteroparity in Steelhead Trout

Steelhead iteroparity is of interest to fisheries managers in the Pacific Northwest who recognize repeat-spawning as a potential conservation tool for endangered or threatened steelhead stocks. Using lethally sampled Snake/Columbia River steelhead as a model, we quantified the proximate and total energy content of white muscle tissue during five phases of the reproductive cycle: (1) summer migration, (2) fall migration, (3) overwintering, (4) sexual maturity, and (5) kelt emigration. White muscle tissues were also collected from natural kelt mortalities in the Potlatch River, ID and Situk River, AK to provide estimates of somatic energy at death. Proportionally 97% of lipid, 25% of protein, and 44% of total energy in the white muscle were depleted from summer migration to kelt emigration. The largest energetic costs occurred between summer migration and fall migration and between sexual maturity and kelt emigration. Little to no changes were observed in lipid, protein, and total energy content from winter to sexual maturity. Only 2.5% of the initial lipid content remained following spawning indicating that protein is the only somatic energy source available to kelts for emigration. The approximate lethal limits of white muscle lipid, protein, and total energy, were 0.15%, 17.5%, 3.95 kJ/g, respectively.