Species Composition and Migration Timing of Juvenile Fishes in the Upper Yukon River

Migration and distribution patterns of juvenile fish in the upper Yukon River in Alaska are poorly understood.  To characterize the juvenile fish community as part of a broader study assessing the impacts of a hydrokinetic turbine on down-migrating juvenile fishes, we used fyke nets to capture fishes in five shoreline locations of the Yukon River at Eagle, AK from June to September 2010.  All captured fish were identified to the lowest taxonomic level, measured for fork length and released alive.  In addition to capturing fishes, multiple environmental variables were recorded at each location for each set.  Longnose suckers (Catostomus catostomus), Arctic grayling (Thymallus arcticus), whitefishes (Prosopium spp. and Coregonus spp.) and chum salmon (Oncorhynchus keta) were our most commonly captured species and showed distinct temporal patterns in catches.  Catch of longnose suckers was directly correlated to river discharge while Arctic grayling, whitefishes and chum salmon appeared to show species-specific timing in downstream migration that was independent of environmental factors.  Chinook salmon (Oncorhynchus tshawytscha), inconnu (Stenodus leucichthys), lake chub (Couesius plumbeus), burbot (Lota lota), lamprey (Lamptera spp.) and slimy sculpin (Cottus cognatus) were infrequently captured and did not show any temporal trends in catches.  Species-specific variation in catch among sampling locations suggests that juvenile fishes exhibit preference for distinct habitats within the river channel during their downstream migrations.  This knowledge advances our baseline understanding of migration and distribution patterns of juvenile fishes in the upper Yukon River, which is valuable for assessing impacts of human development, such as hydrokinetic turbines.