| Summary: | Groundfish distributions were examined in spring 2006 and 2007 in the northern Bering Sea around St. Lawrence Island (SLI). Arctic cod (Boreogadus saida), Bering flounder (Hippoglossoides robustus), and snailfish (Liparidae) were the dominant species south of SLI, whereas Arctic alligatorfish (Ulcina olrikii) and Arctic staghorn sculpin (Gymnocanthus tricuspis), or shorthorn sculpin (Myoxocephalus scorpius) were dominant north of SLI. The results indicate that bottom water (or water column) chlorophyll a and sediment parameters had greater influence on 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 suggest 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.
The diet and feeding relationship of six dominant groundfish, specifically Arctic cod, Bering flounder, snailfish, Arctic staghorn sculpin, Arctic alligatorfish, and shorthorn sculpin in the northern Bering Sea were studied using stomach content data in spring 2006 and 2007. All of Bering flounder had empty stomachs. Amphipods were the primary prey in five fish species characterized by feeding narrow niches except snailfish, which consumed a diverse diet. Arctic cod was the only occasional pelagic feeder; all the other fish studied were benthic feeders. High diet overlap was found among some fish species; however, competition was likely reduced by differences in feeding strategies and available food resources.
Stable carbon and nitrogen isotopes of groundfish and their potential prey items were measured for trophic relationships and energy flow in the northern Bering Sea in 2006 and 2007. Lipid content impacts on stable isotope analyses were reduced using a mathematical normalization technique using C/N ratios. Values of del13C in fish species showed significantly different between seasons. Trophic levels (TL) were estimated by del15N values of fish and prey species with primary consumer as a baseline indicator. Bivalves and amphipods had the lowest TL values, 2.4 – 3.4, followed by polychaetes (TL = 3.6 – 4.1), and fish (TL = 3.5 – 4.6).
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