Arctic | Ecosystem Perspectives
An apparent multi-decadal decline in Arctic cod, a keystone species in the Western Arctic marine ecosystem Presenter: George Divoky , divoky@cooperisland.org, Cooper Island Arctic Research Christophe Barbraud , christophe.barbraud@cebc.cnrs.fr, CNRS Arctic cod ( Boreogadus saida ) is the primary fish species of the Arctic’s cryopelagic ecosystem and primary prey of Arctic piscivorous marine predators. Adult Arctic cod were the principal prey of the large seabird and marine mammal populations in the Chukchi and Beaufort seas in the 1970s and 1980s. The cryopelagic ecosystem has undergone major decreases since 1979, with the Western Arctic losing 1.9 million km² of summer sea ice. The effect of this habitat loss on Arctic cod has gone largely unnoticed as lack of a commercial fishery justified only minor survey efforts. Seabirds, as highly visible marine predators, can be valuable monitors of change in marine trophic webs. Our 47- year study of an Arctic cod specialist, Mandt’s Black Guillemot, provides insights into temporal variation in Arctic cod availability in the region in the last half century. The Beaufort Sea study colony grew rapidly in the 1970s and 1980s, from 10 to >200 pairs, with high immigration indicating a productive metapopulation and high Arctic cod availability at the Chukchi source colonies, which supported tens of thousands of guillemots in the 1980s. Study colony growth ended in the early 1990s as an extreme shift in the Arctic Oscillation in 1989/90 modified atmospheric and oceanic circulation, decreasing sea ice and increasing SST. The ensuing three decades saw the study colony decrease to <30 pairs in 2022, due primarily to decreased immigration, evidence of a region-wide decrease in guillemot numbers and productivity, but also decreased adult survival and breeding productivity at the study colony. Fledging success is sensitive to Arctic cod availability, with decreases in the nestling diet at SST of >2°C and absence at >3.5 °C. Recent trawl surveys in the Chukchi, two decades after regional warming began, found few adult Arctic cod in waters that once supported large seabird populations. Adult overwinter survival of guillemots recently decreased from a long-term mean of near 90% to <80% from 2018-2022, associated with a decrease in Bering Sea ice extent. Groundfish surveys have found major decreases of Arctic cod in the region. Our study of Mandt’s Black Guillemot indicates a major reduction in Arctic cod in the Western Arctic in the 21st Century.
Alaska Marine Science Symposium 2023 85
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