2010 Arctic Yukon Kuskokwim (AYK) Sustainable Salmon Initiative Project Final Product: Climate-Ocean Effects on AYK Chinook Salmon

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2010 Arctic Yukon Kuskokwim (AYK) Sustainable Salmon Initiative Project Final Product: Climate-Ocean Effects on AYK Chinook Salmon

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Title: 2010 Arctic Yukon Kuskokwim (AYK) Sustainable Salmon Initiative Project Final Product: Climate-Ocean Effects on AYK Chinook Salmon
Author: Myers, Katherine W.; Walker, Robert V.; Davis, Nancy D.; Armstrong, Janet L.; Fournier, Wyatt J.; Mantua, Nathan J.; Raymond-Yakoubian, Julie
Abstract: A high-priority research issue identified by the Arctic-Yukon-Kuskokwim (AYK) Sustainable Salmon Initiative (SSI) is to determine whether the ocean environment is a more important cause of variation in the abundance of AYK Pacific salmon (Oncorhynchus spp.) populations than marine fishing mortality. At the outset of this project, however, data on ocean life history of AYK salmon were too limited to test hypotheses about the effects of environmental conditions versus fishing on marine survival. Our goal was to identify and evaluate life history patterns of use of marine resources (habitat and food) by Chinook salmon (O. tshawytscha) and to explore how these patterns are affected by climate-ocean conditions, including documentation of local traditional knowledge (LTK) of this high-priority issue. Synthesis of LTK from the Bering Straits region identified important changes in adult AYK Chinook salmon biological characteristics, climate, and fishing. Local experts observed later run timing, a decrease in body size and stomach contents, and an increase in diseases, parasites, and deformities in adult salmon; environmental changes, including strength and direction of wind, timing of freeze- and break-up, warming of ocean and river temperatures, accompanied by increases in algae, water grasses, jellyfish, and erosion events; an increase in marine subsistence harvests of salmon; and salmon bycatch in Bering Sea/Aleutian Islands (BSAI) trawl fisheries for walleye pollock. Multiple lines of scientific evidence indicated that Chinook salmon respond to variation in climate-ocean conditions and fishing by changes in distribution, diet, size and age at maturation, growth, and survival. Evidence from tagging and other stock identification methods suggested that AYK Chinook spend most of their ocean life in the Bering Sea. Distribution of immature AYK Chinook is farthest offshore in their second summer-fall at sea, extending into the Russian Exclusive Economic Zone in the northwestern Bering Sea. Unlike other species of AYK salmon, AYK Chinook overwinter in the BSAI fishery area. Limited data from electronic tags showed Chinook have a deeper vertical distribution than any other salmon species, with the known vertical range extending from the surface to a depth of 523 m (1,717 ft). These life-history traits make AYK Chinook more susceptible than other AYK salmon species to bycatch in winter BSAI trawl fisheries. Reconstructions of growth histories indicated growth of Yukon River Chinook salmon shifted to a positive phase in 1999-2000 that continued through 2009, but did not result in increased adult returns to the river. We completed the first study of winter diets of Chinook in the BSAI bycatch. The primary prey was squid, although many fish had empty stomachs. All age groups of Chinook in winter consumed fish offal, which is of low nutritional quality (identified by DNA analysis as walleye pollock, likely from fishery catch-processing activities). Bioenergetics models indicated that warm temperatures over Alaska and at sea and high quality diets are associated with increased growth of AYK Chinook. Climate-ocean variables most linked to increased AYK Chinook salmon growth – lower sea ice cover and warmer temperatures – are projected by climate models to change in the Bering Sea this century, with temperatures increasing at higher latitudes by 2°C (3.6°F) and ice cover diminishing and retreating earlier. We concluded that the low abundance of some populations of AYK Chinook makes them vulnerable to adverse changes in climate-ocean conditions and fisheries. Relationships among climate, fishery, and other factors affecting growth and survival of AYK Chinook in both marine and freshwater habitats are complex and point to critical needs for additional research, management, and restoration actions to ensure sustainability of this valuable natural resource.
URI: http://hdl.handle.net/1773/16308

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