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Survival and Breeding Response of a Sea-ice Obligate Seabird Following the Unprecedented Low Extent of Winter Ice in the Bering Sea
  • George Divoky,
  • David Douglas,
  • Christophe Barbraud
George Divoky
Cooper Island Arctic Research

Corresponding Author:divoky@cooperisland.org

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David Douglas
USGS Alaska Science Center
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Christophe Barbraud
Centre d’Etudes Biologiques de Chizé (CEBC), UMR 7372 Université de la Rochelle-CNRS
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Sea ice extent in the Bering Sea during the winter of 2017–2018 was the lowest on record with ice cover attaining less than half the long-term average. Mandt’s Black Guillemot (Cepphus grylle mandtii), one of the few Arctic ice-obligate seabirds, typically winters in the Marginal Ice Zone over the Bering Sea shelf, occurring as far south as the shelf break. Adult survival and breeding biology of the species has been studied since 1975 at a breeding colony near Point Barrow, Alaska in the western Beaufort Sea, with nonbreeding distribution and movements monitored since 2011 with light-sensitive geolocators. Preliminary analysis of geolocators retrieved at the start of the 2018 breeding season indicates guillemots wintered further north than in any previous year with most birds remaining near the Bering Strait or in the southern Chukchi Sea. It appears the lack of sea ice in the traditional wintering area and resulting anomalous winter distribution had a major effect on the survival and condition of Mandt’s Black Guillemot in the Western Arctic, although direct causative factors have yet to be determined. Adult overwinter apparent mortality was the highest on record with 32 percent of the birds breeding in 2017 failing to return to the colony, compared to 11 percent apparent overwinter mortality for the period 1976–2013. Of the 70 pairs occupying nest sites in 2018, only 50 pairs produced eggs. Of those 50 nests, nearly one-half had no incubation occur after egg laying. Nonbreeding by established breeders occupying nest sites and abandonment of nests immediately after egg laying were extremely rare in earlier years. The number of breeding birds in 2018 was the lowest in four decades and punctuates a long-term decrease in the population since 1989. Analysis of geolocation and behavioral data from the 2017–2018 nonbreeding period will lend insights into how the anomalous winter sea ice conditions might have contributed to the observed high mortality and poor condition of surviving birds. Decreased prey availability in the Arctic Basin and Bering Strait regions, compared to the southern Bering Sea shelf, could be a factor, as could atypical oceanographic and sea ice conditions in the winter Marginal Ice Zone.