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Genetic Research Provides Insight Into The Production And Behavior Of Western Alaska Chum Salmon

July 01, 2014

Alaska Fisheries Science Center Quarterly Report.


The six large regional groupings of spawning chum salmon stocks throughout the Pacific Rim: Southeast (SE) Asia; Northeast (NE) Asia; Coastal Western Alaska (W AK); Upper/Middle Yukon River (Up/Mid Yukon); Southwest Alaska (SW AK); and the Gulf of Alaska/Pacific Northwest (GOA/PNW)

In Western Alaska, Chum Salmon (Oncorhynchus keta) is critical for subsistence, commercial, and cultural reasons. Over the last few decades, declines in chum salmon returns in some western Alaskan drainages prompted various disaster declarations by the State of  Alaska and federal agencies. In addition, chum salmon fisheries on the Yukon and Kuskokwim Rivers, two of the largest chum salmon production drainages in western Alaska, have been complicated in recent years by various restrictions designed to limit the take of Chinook salmon, which are currently at very low abundance. 

The two distinct Yukon River chum salmon life-history types, an earlier and typically more abundant summer run and a later fall run, are managed by the Alaska Department of Fish and Game (ADF&G) to provide escapement and maximize harvest opportunity. Summer-run chum salmon generally spawn in the lower to middle reaches of the Yukon drainage, whereas fall-run chum salmon are typically larger and generally spawn in spring-fed regions of the middle to upper reaches in Alaska and Canada. The summer run of chum salmon has averaged 1.8 million fish between 2000 and 2012, and the fall run has averaged 864,000 fish over the same time period, although there is variation in the two run strengths between years. Concern about low fall-run chum salmon abundance in some years has resulted in reduced subsistence fishing opportunities and has created challenges in fulfilling treaty obligations with Canada that specify escapement objectives.

Little is known about the survival of juvenile Yukon River chum salmon in their freshwater or saltwater environments. Juvenile chum salmon out-migrate from the Yukon River in the spring and are found in the pelagic waters on the eastern Bering Sea shelf during summer and fall months. Juvenile chum salmon have been collected as part of annual U.S. Bering-Aleutian Salmon International Surveys (BASIS) in the eastern Bering Sea since 2002. A previous genetic analysis of the 2002 juvenile chum salmon based on allozyme markers determined that a substantial proportion of juvenile chum salmon samples collected in this area were from the Yukon River; however, samples from other years remained unanalyzed. 

With support from the Arctic-Yukon-Kuskokwim Sustainable Salmon Initiative and the Alaska Sustainable Salmon Fund, scientists with Auke Bay Laboratories Genetics Program genetically analyzed juvenile chum salmon samples collected on the 2003–07 BASIS cruises. Their study had three objectives. First, with genetic mixed-stock analyses, determine the extent of stock contributions of juvenile chum salmon on the eastern Bering Sea shelf off the mouth of the Yukon River and compare the distribution across years. Second, develop a relative abundance index of summer- and fall-run Yukon River juvenile chum salmon on the eastern Bering Sea shelf. Third, examine the potential to correlate juvenile relative abundances with adult returns for summer and fall Yukon River chum salmon runs.

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