2010 Arctic Yukon Kuskokwim (AYK) Sustainable Salmon Initiative Project Final Product: Climate-Ocean Effects on AYK Chinook Salmon
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Date
2010-11Author
Myers, Katherine W.
Walker, Robert V.
Davis, Nancy D.
Armstrong, Janet L.
Fournier, Wyatt J.
Mantua, Nathan J.
Raymond-Yakoubian, Julie
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Show full item recordAbstract
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.
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