Harvests of Yukon and Kuskokwim Chinook salmon declined significantly during 1998- 2002 in response to fewer returning salmon. Factors affecting the decline in Chinook salmon abundance are largely unknown. Growth of salmon in freshwater and the ocean is generally thought to influence salmon survival, therefore we examined historical Chinook salmon catch trends and developed growth indices of age-1.3 and age-1.4 Yukon and Kuskokwim Chinook salmon during each year and life stage in freshwater and the ocean, 1964-2004, using measurements of salmon scale growth. Availability of Yukon scales was greater than that of Kuskokwim scales during 1964-2004.
Harvests of Yukon and Kuskokwim Chinook salmon rapidly increased in the mid-1970s, then rapidly declined in the late 1990s, apparently in response to the 1976/77 ocean regime shift and the 1997/98 El Nino event. Runs of Nushagak District Chinook salmon (Bristol Bay) also appeared to have been affected by these events in addition to the 1989 regime shift. The rapid responses of Chinook salmon abundance to climate change suggest late life stages were primarily affected, at least initially. Therefore, we searched for Chinook salmon growth patterns that might be related to changes in climate.
