Cooperative Fish and Wildlife Research Units Program: all
Education, Research and Technical Assistance for Managing Our Natural Resources

In Pacific salmon, downward trends in size and abundance have been reported for species and stocks for over 40 years, but the patterns are inconsistent among regions and species. Interpretation of these trends is complicated by the many possible contributing factors, including short time series, data comprising a mix of stocks, and varying gear types. Here, we present data on the mass of individual Chinook salmon, Oncorhynchus tshawytscha, caught in the winter from 1946 to 2019 in central Puget Sound, Washington by participants in what may be the longest running salmon derby in North America, the Tengu Derby. In this annual recreational fishing competition, established by Japanese-Americans immediately after release from internment camps at the end of World War II, participants follow strict gear, area, and methods regulations, and catch almost exclusively salmon originating from and remaining in Puget Sound. Records revealed an overall decline in fish mass over the decades with a high degree of variability throughout the time series. Specifically, resident Chinook salmon exhibited several shifts, including an increase in size from a high in the 1950s to a low around 1980, followed by an increase to another high around 1990, and then a decline over the most recent 30 years. These salmon, displaying a form of differential migration by remaining in Puget Sound rather than migrating to the ocean coast, showed dissimilar trajectories compared with size trends of Puget Sound Chinook salmon as a whole reported previously. These distinct patterns in size for Chinook salmon from common origins associated with different migration patterns exemplify yet another important factor to be considered in the analysis and interpretation of such trends.