Basin-Scale Variation in the Spatial Pattern of Fall Movement of Juvenile Coho Salmon in the West Fork Smith River, Oregon

For several species of salmonids (Oncorhynchus and Salvelinus spp.) inhabiting Pacific coastal streams, juvenile fish have been recorded moving between mainstem and tributary habitats during the fall. Fall movement that connects summer and winter habitats may be particularly important for coho salmon, O. kisutch, because availability of overwintering habitat can limit freshwater survival. Here, we describe basin-scale variability in spatial patterns of movement between mainstem and tributary habitat for juvenile coho salmon during the fall. Juvenile coho salmon were tagged with passive integrated transponders over a multi-kilometer spatial extent and could be detected at four stationary detection sites in tributaries near confluences with the mainstem, and one in the upper mainstem of the West Fork Smith River, Oregon. We demonstrate differences among detections sites in whether juvenile coho salmon were more likely to emigrate from or immigrate into tributary streams and whether immigrating fish were more likely to originate from the mainsteam upstream or downstream of the confluence. We conclude that assuming that fish do not move, or that the pattern of fish movement is generally the same throughout stream networks, will yield erroneous conclusions about how the spatial arrangement and quality of seasonal habitats impact life-cycle productivity and survival.