Stock specific relative abundance of Columbia River juvenile Chinook salmon off the Southeast Alaska coast

Abstract

Migration patterns of juvenile Columbia River Chinook salmon (Oncorhynchus tshawytscha) differ among stocks and life history types, creating diverse marine distributions of these fish. This results in different stocks being subject to different ocean conditions during their first summer of marine residence, a time that is critical for their survival. Understanding their early marine distributions, and the conditions that affect their survival, may enhance conservation efforts for these stocks, many of which are protected under the Endangered Species Act. We analyzed juvenile Chinook salmon samples collected in trawls made from 2011 to 2015 off the southeastern (SE) Alaskan panhandle, and off the coasts of Washington and Oregon. We used genetic stock identification techniques to estimate stock proportions of juvenile Chinook salmon in each of these areas. Results indicated that most juvenile Chinook salmon in our SE Alaska coast study area in July originate from Columbia River spring-run stocks. We found a significant relationship in catch per unit effort (CPUE) over all stocks between the SE Alaska and the Washington and Oregon coast samples. In 2011, CPUE for Columbia River spring-run stocks for the SE Alaska coast was lower than for the Washington and Oregon coast, suggesting a differing level of marine mortality that year. We also found a significant relationship between juvenile CPUE of interior Columbia River spring-run stocks off the SE Alaska coast and adult counts at Bonneville Dam two years later. Our results provide marine life history, performance and survival information that supports management and recovery efforts for Columbia River Chinook salmon.