Influence of Wood and Other Habitat Characteristics on the Distribution and Abundance of Coho Salmon in a Relatively Large River

The influences of wood and other habitat variables on juvenile coho salmon (Oncorhynchus kisutch) summer distribution and relative abundance, which has rarely been studied in relatively large river channels (>15 m wide), were assessed in a relatively large river channel in Washington State (summer wetted width 15-30 m). The influence of wood and habitat variables including water depth, velocity, and substrate on juvenile coho salmon summer relative abundance was assessed by snorkelling areas with introduced (generally 2-3 evergreen trees from the riparian zone), natural, and no wood. Juvenile coho salmon relative densities were compared at stations with introduced, natural, and no wood and their distribution (presence) assessed at natural wood stations using logistic regression. Relative densities of coho salmon were greatest at stations with introduced wood and were greater at introduced and natural wood stations than stations lacking wood, where juvenile coho salmon were generally absent. Wood cover complexity influenced juvenile coho salmon presence at natural wood stations, while wood type, wood surface area, and substrate influenced presence during one of two years. The results suggest that wood and aspects of wood cover (i.e., complexity and size) are important components of juvenile coho salmon summer rearing habitat in larger river channels, and managers should attempt to maintain and/or restore complex wood cover in relatively large river channels to provide summer habitat for juvenile coho salmon.