Poor Survival of Acoustically-Tagged Juvenile Chinook Salmon in the Strait of Georgia, British Columbia, Canada

Abstract

The collapse of the commercial fishery and the major decline in catches in the recreational fishery for Chinook Salmon Oncorhynchus tshawytscha in the Strait of Georgia since the mid-1990s represents a major economic loss to British Columbia. Early marine residence is critical for survival of Chinook Salmon, but measuring the amount of mortality has been difficult. Acoustic tags can be used to measure marine mortality and study migratory behavior. We surgically implanted 278 juvenile Chinook Salmon with acoustic tags to monitor when and how many tagged fish moved out of the Strait of Georgia. Only eight tagged fish were detected leaving the Strait of Georgia, indicating that there could have been substantial mortality of the tagged juvenile Chinook Salmon within the strait. Tagging mortality was minimal, and the detection of tags was shown not to be a major source of error in this study. A major change in population structure between the spring and fall tagging periods meant that it was unlikely that most of the fish tagged in June and July remained within the Strait of Georgia. The decline in abundance of juvenile Chinook Salmon in November 2008 also indicates that the lack of detections of all tagged fish is unlikely a consequence of fish remaining in the Strait of Georgia. This information and the low catches in winter surveys indicated that most juvenile Chinook salmon were no longer in the strait in the late fall and winter. If the tagged fish were representative of the untagged fish, the current brood-year strength probably is largely determined within the Strait of Georgia.

Received January 31, 2014; accepted July 31, 2014

ACKNOWLEDGMENTS

Funding for this study was provided by the Pacific Salmon Foundation and the Department of Fisheries and Oceans Canada. Additional funding by the Department of Fisheries and Oceans Canada Ecosystem Research Initiative permitted us to replicate the tag effects study in 2010. We thank the managers and staff of the Cowichan River and Quinsam River hatcheries for their assistance in obtaining, transferring, and maintaining juvenile salmon in net pen systems. We thank the managers of the Hidden Harbour Marina in Campbell River for providing space in their marina for the net pen. Lana Fitzpatrick provided assistance with editing the manuscript.