Spatially Clustered Movement Patterns and Segregation of Subadult Chinook Salmon within the Salish Sea

Abstract

While Pacific salmon are known for their extensive marine migrations, some species display much more limited alternative patterns, including residence within interior marine waters. To more clearly define the scale of movement of these residents, we used acoustic telemetry to track subadult Chinook Salmon Oncorhynchus tshawytscha caught in and released from discrete areas of the Salish Sea. Their movements were determined from detections at fixed receivers in central Puget Sound, Admiralty Inlet, the San Juan Islands, and the Strait of Juan de Fuca. Cluster analysis of the detections indicated four groups, with much less commonality of movement than might be inferred from the proximity of the tagging locations, which were only tens of kilometers apart. For example, none of the salmon tagged in central Puget Sound were detected in the San Juan Islands and vice versa. Thus, Chinook Salmon occupying central Puget Sound and the San Juan Islands may exhibit different distributions, extents of movement, and degrees of basin fidelity. These results provide information relevant to the management and conservation of this species, which is listed as threatened under the U.S. Endangered Species Act, and whose movements cross the U.S.–Canadian boundary. These findings may also help explain the variation in organic contaminant levels among Puget Sound-origin Chinook Salmon.

Received June 24, 2016; accepted October 4, 2016

Acknowledgments

We thank the crews of the sportfishing charter vessels and especially Jay Field for capturing the fish for tagging, Jennifer Scheuerell for data management, Fred Goetz for his role in the formation of this project, Sandra O’Neill for input that helped shape the work and interpret the results, and Kinsey Frick, Todd Sandell, Jason Hall, Joshua Chamberlin, and many others for field assistance. We thank Scott Veirs, Tina Echeverria, and Beam Reach for their assistance with deploying and retrieving receivers, and the many agencies that deployed and retrieved receivers and shared data with us, especially the Pacific Ocean Shelf Tracking Project. We are also very grateful to the many landowners who gave us permission to deploy receivers from their docks or near their property. Funding for this project was provided by the State of Washington’s Salmon Recovery Funding Board through the Recreation and Conservation Office; National Oceanic and Atmospheric Administration (NOAA) Fisheries; the Clarence H. Campbell Endowed Lauren Donaldson Scholarship in Ocean and Fishery Sciences; the H. Mason Keeler Endowment and Richard and Lois Worthington Endowment at the School of Aquatic and Fishery Sciences, University of Washington; and the Achievement Rewards for College Scientists Foundation, Seattle Chapter, via the Barton family. Permits for the deployment of receivers were obtained from NOAA Fisheries, the Washington Department of Natural Resources, WDFW, and San Juan County. Permits for the capture and handling of fish were obtained from NOAA Fisheries, WDFW, and the University of Washington’s Institutional Animal Care and Use Committee.