Movement Patterns of Sub-Adult Coho Salmon In Puget Sound

Migration is a central mechanism affecting the distribution of mobile populations, and intra-specific variation in migration patterns can affect many aspects of their ecology and conservation. Most sub-adult Chinook and coho salmon rear over the continental shelf or offshore waters of the North Pacific Ocean, but some Puget Sound salmon exhibit an alternative migratory pattern, spending all or part of their marine lives within Puget Sound. This “resident” behavior has been linked to decreased growth and increased contaminant accumulation. However, little is known about the movements of individual salmon and duration of their residency in Puget Sound. Accordingly, we tagged 45 sub-adult coho salmon in central Puget Sound with acoustic transmitters and tracked their movements using the array of moored receivers throughout the Salish Sea. Our initial results indicated that most individuals remained in Puget Sound, though several individuals were detected leaving through the Strait of Juan de Fuca and the San Juan Islands. Additionally, between basin movement was minimal; no individuals were detected entering Hood Canal or southern Puget Sound, but there was some movement into the Whidbey Basin. Overall, these results indicate that coho salmon found within Puget Sound in winter-spring are largely separated from those rearing off the coast. Thus resident and migratory individuals seem to be distinct categories, though the factors determining these two pathways are unclear.