Climate, Growth and Population Dynamics of Yukon River Chinook Salmon

Harvests of Yukon Chinook salmon increased in the mid-1970s, then declined during 1998 to 2007 in response to fewer returning salmon. We examined annual growth of age-1.3 and age-1.4 Yukon Chinook salmon scales, 1965–2004, and tested the hypothesis that shifts in Chinook salmon abundance were related to annual growth at sea. Annual scale growth trends were not significantly correlated with salmon abundance indices, sea surface temperature, or climate indices, although growth during the first year at sea appeared to have been affected by the 1977 and 1989 ocean regime shifts. Chinook salmon scale growth was dependent on growth during the previous year, a factor that may have confounded detection of relationships among growth, environmental conditions, and abundance. Scale growth during the second year at sea was greater in oddnumbered years compared with even-numbered years, leading to greater adult length of age-1.3 salmon in oddnumbered years. The alternating-year pattern in Chinook salmon growth was opposite that observed in Bristol Bay sockeye salmon, and it may be related to the higher trophic level of Chinook salmon and indirect competition with pink salmon. This finding highlights the need to investigate alternating-year patterns in salmon growth, prey abundance, and factors that influence these patterns, such as pink salmon. All correspondence should be addressed to G. Ruggerone. e-mail: [email protected] Climate, Growth and Population Dynamics of Yukon River Chinook Salmon Gregory T. Ruggerone1, Jennifer L. Nielsen2, and Beverly A. Agler3 1Natural Resources Consultants Inc. 4039 21st Avenue West, Suite 404, Seattle, WA 98199, USA 2Alaska Science Center, U.S. Geological Survey, 4210 University Drive, Anchorage, AK 99508, USA 3Alaska Department of Fish and Game, Division of Commercial Fisheries, Mark, Tag, and Age Lab, 10107 Bentwood Place, Juneau, AK 99801, USA