Abstract
The structure of demersal fish assemblages was investigated based on a total of 134 trawl samples collected in the northern Bering Sea (NBS) and Chukchi Sea (CS) during 12 summers between 1990 and 2013. In recent years, the timing of sea ice retreat has become earlier in the NBS. The present study was performed to clarify the environmental factors that contribute to the structure of demersal fish assemblages. Walleye pollock Gadus chalcogrammus were numerically dominant, followed by Bering flounder Hippoglossoides robustus and Arctic cod Boreogadus saida. Stations were classified into four major faunal assemblages by cluster analysis based on species density: I) boreal assemblages occurring southeast of St. Lawrence Island; II) stations dominated by Arctic species in the CS; III) stations with mixed Arctic and boreal species southwest of St. Lawrence Island; and IV) a less abundant assemblage limited to the north of Point Hope, comprising Arctic species. A permutation test revealed that, of the four physical parameters considered (i.e., bottom temperature, bottom depth, timing of sea ice retreat (TSR) and timing of sampling), TSR was the most prominent variable; it constituted 19.4% of the overall variance in species density and 57.7% of the variance explained by environmental factors. Multiple regression was applied to further analyze the factors that affected interannual changes in the densities of three zoogeographic types in the NBS. While TSR was the major factor that affected the density of Arctic species, variables that included bottom temperature were important for boreal species. These results suggest that mechanisms associated with sea ice conditions (i.e., annual-scale factors), rather than summer bottom temperature (i.e., short-term factors), influence the distribution of demersal fish assemblages in the NBS and CS.
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More From: Deep Sea Research Part II: Topical Studies in Oceanography
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