Spatial distributions of groundfish in the northern Bering Sea in relation to environmental variation

Two bottom trawl surveys of fish were undertaken during the seasonal sea ice retreat in 2006 and 2007 in the northern Bering Sea. For each trawl, we calculated catch per unit area (CPUA) for all fish taxa. Arctic cod Boreogadus saida, Bering flounder Hippoglossoides robustus and snailfish (Liparidae) were the dominant species south of St. Lawrence Island (SLI), whereas Arctic alligatorfish Ulcina olrikli, Arctic staghorn sculpin Gymnocanthus tricuspis and shorthorn sculpin Myoxocephalus scorpius were the dominant fishes north of SLI. Cluster analysis and multidimensional scaling were used to investigate relationships between environmental conditions and fish community structure in the northern Bering Sea. One goal of the study was to assess the importance of environmental variables on groundfish assemblages. The results showed that sediment grain size (an indicator of current speed) was the most important environmental factor explaining fish community structure in both years of the study. Bottom water nutrients (nitrate + nitrite), bottom water chlorophyll a (ch1 a) (with similar results for total ch1 a in the water column), sediment grain size, and sediment C/N ratios had stronger relationships with fish distribution in 2006 (cold, pre-bloom conditions), whereas bottom water temperature and sediment grain size were more important in 2007 (warm, bloom conditions) among a total of 14 environmental variables that were analyzed. These findings indicate strong linkages between physical conditions (e.g. water temperature and hydrography as it affects sediment grain size) and biological conditions (e.g. bloom status) in structuring fish communities in the northern Bering Sea.