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

Abstract For several species of salmonids, Oncorhynchus and Salvelinus spp., inhabiting Pacific coastal temperate streams, juvenile fish have been recorded moving between main‐stem and tributary habitats during the transition from the summer dry season to the winter wet season. Movement connecting summer and winter habitats may be particularly important for Coho Salmon O. kisutch because availability of overwintering habitat can limit freshwater survival for this species. Here, we describe basin‐scale variability in movement between main‐stem and tributary habitat for juvenile Coho Salmon tagged in the summer with PIT tags and detected in the fall at four stationary detection sites at tributary–main‐stem confluences of the West Fork Smith River, Oregon. We used odds ratios to evaluate spatial patterns in tributary–main‐stem movement across tributary junctions at upper‐river, midriver, and lower‐river locations. Three types of movement were assessed: (1) emigration out of tributaries into the main stem, (2) immigration into a tributary from the main stem downstream from the tributary junction, and (3) immigration from the main stem upstream from the tributary junction. The likelihood of emigration had a distinct spatial pattern. Only at the two upper‐river detection sites were juvenile Coho Salmon more likely to emigrate than immigrate. Fish immigrating into a midriver tributary were more likely to originate from the main stem downstream from the confluence, whereas fish immigrating into two lower‐river tributaries were more likely to originate from the main stem upstream from the confluence. This basin‐scale variation in patterns of immigration and emigration demonstrates complexity in the connectivity of juvenile Coho Salmon seasonal habitats within a stream network. We conclude that effective restoration planning and watershed management should account for the spatial pattern of connectivity of summer‐rearing and overwintering habitat throughout a stream network and consider the full diversity of movement patterns that may be required for fish to access seasonal habitats. Received December 30, 2015; accepted May 4, 2016 Published online August 5, 2016