Potential causes of size trends in Yukon River chinook salmon populations

Concerns regarding the size and sex composition of Yukon River Chinook salmon, Oncorhynchus tshawytscha, have been expressed in public meetings for over a decade. However, reports of small size and low numbers of females have become increasingly common in recent years, and apprehension over the long-term health of the stock has grown within the drainage. In response to these reports, the Salmon Size Subcommittee of the US/Canada Yukon River Joint Technical Committee was formed and charged with advising the Committee, and thereby the US/Canada Yukon River Panel, with respect to changes in chinook salmon age, sex, and size composition. This report, which summarizes the findings of prior investigations and the scientific literature on factors that influence salmon morphology, represents the first product of the subcommittee.