Larson, M.S., A. Choudhury, E.N. Gardner, P. Konstantinidis, C.A. Murphy, M.L. Kent, J.T. Peterson, and C.E. Couch. 2024. Diet and Philonema oncorhynchi infections in reservoir-rearing juvenile Chinook salmon (Oncorhynchus tshawytscha). Transactions of the American Fisheries Society153(3): 312-325.
Abstract
Dams and reservoirs can alter juvenile growth and survival of migratory salmonids through several physical and biological mechanisms. Juvenile Chinook salmon (Oncorhynchus tshawytscha) produced above large hydropower dams may have associated passage mortality, but reservoirs created by these dams can support rapid growth. Characterizing the biotic drivers of growth and mortality in reservoirs may aid in understanding the cumulative effects of river impoundments on migratory salmonid populations. The purpose of this study is to understand how reservoirs facilitate rapid growth in juvenile Chinook salmon by characterizing diet composition throughout the summer and fall. We found that juvenile Chinook salmon frequently consume young-of-year centrarchids, which likely contributes to rapid growth. Piscivory was highest from July through September and decreased with surface temperature beginning in late September and continuing through December. Correspondingly, zooplankton and arthropod consumption increased in November and December. We also recorded prevalence of the parasitic nematode Philonema oncorhynchi in the coelom. Prevalence of macroscopic P. oncorhynchi infections was high (35%) but decreased over time and was lower in the larger fish, indicating parasite-associated mortality.