Potential Causes of Size Trends in Yukon River Chinook Salmon Populations
Dates
Year
2006
Citation
JTC (Joint Technical Committee of the Yukon River US/Canada Panel),, 2006, Potential Causes of Size Trends in Yukon River Chinook Salmon Populations: Yukon River Joint Technical Committee: Anchorage, AK, v. Regional Information Report No. 3A06-07.
Summary
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 [...]
Summary
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. Overall, evidence that the morphology of Yukon River Chinook salmon has been altered over time is limited, but suggestive. Existing analyses document a decrease in the mean weight of commercial harvests, a reduction in the prevalence of the largest fish, and the apparent near disappearance of age-8 fish. However, other important metrics, such as mean length-at-age, do not appear to have changed substantially. Whether the changes observed within Yukon River Chinook salmon have resulted from environmental or fishery-induced selective pressures, or a combination of both, is difficult to determine with certainty. In any case, the morphology of Yukon River Chinook salmon may be slowly changing. Expanded monitoring of age, sex, and size is warranted, as is directed research to identify causes and consequences. Key words: Oncorhynchus tshawytscha, age, sex, length, morphology, commercial, subsistence, fishery, harvest, escapement, net selectivity, selective harvest, heritability, competition, survival, growth, adaptation, Bering Sea, Pacific Ocean.
