The aggregation of polar cod (Boreogadus saida) in the deep Atlantic layer of ice-covered Amundsen Gulf (Beaufort Sea) in winter |
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Authors: | Maxime Geoffroy Dominique Robert G??rald Darnis Louis Fortier |
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Institution: | (1) Qu?bec-Oc?an, D?partement de biologie, Universit? Laval, Qu?bec, QC, G1V 0A6, Canada |
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Abstract: | During the Circumpolar Flaw Lead System Study (CFL, 2007–2008), large aggregations of polar cod were detected in winter in
the Amundsen Gulf (Western Canadian Arctic) using the EK60 echosounder of the CCGS Amundsen research icebreaker. Biomass estimated over 10 months reached a maximum of 0.732 kg m−2 in February. Aggregations were encountered only in the presence of an ice cover from December to April. The vertical extent
of the aggregations was dictated by temperature and zooplankton prey distribution. In winter, polar cod generally occupied
the relatively warm deep Atlantic Layer (>0°C), but a fraction of the densest aggregations occasionally followed zooplankton
prey up into the cold Pacific Halocline (−1.6 to 0°C). The diel vertical migration of polar cod was precisely synchronized
with the seasonally increasing photoperiod. Throughout winter, polar cod aggregations migrated to progressively deeper regions
(from 220 to 550 m bottom depths) in response to increasing light intensity, presumably to avoid predation by visual predators
such as the ringed seal. Comparing Amundsen Gulf and Franklin Bay indicates that the entrapment of polar cod in embayments
during winter is an important mechanism to provide marine mammal predators with dense concentrations of their main prey within
their diving range. |
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