Fluctuations in Chinook Salmon (Oncorhynchus tshawytscha) Counts at three lower Columbia River spawning sites

Several hypotheses were developed to explore the pronounced increase in Chinook salmon (Oncorhynchus tshawytscha) returning to spawning grounds at the Cowlitz, Kalama, and Lewis Rivers, three tributaries of the lower Columbia River. The study was conducted using data compiled over a ten-year span from 1991-2001. Preliminary indications are that trends in climate are linked to these increases, with the absence of El Niño events and fluctuations in winter precipitation as likely explanations of these phenomena. The unique nature of Chinook life cycles causes them to utilize a variety of habitats that require ideal conditions for maximum survival rates. Correlations between ideal environmental conditions and the decision by hatcheries to release greater stocks were also analyzed. Overall, considerations were made that each of these hypotheses are inter-connected in explaining the fluctuations. Status report data from the Washington Department of Fish and Wildlife served as the baseline for this study. The data provided a means to graph population trends over time, along with climate patterns over the same time period in an attempt to explain why some years experience higher Chinook counts at spawning grounds than others. The importance of Pacific salmon abundance as an indicator of ecosystem health stresses the need to improve our understanding of the mechanisms regulating their dynamic fluctuations.