Distribution, quantitative composition, and feeding of jellyfish in the Western Bering Sea in summer and fall

Materials from six complex trawl surveys conducted by the TINRO-Center in the upper epipelagic zone of the Western Bering Sea during the summer-fall seasons from 2002 through 2006 were used as the basis of this paper. The overall biomass (and abundance) of jellyfish increased from 0.6–0.8 million t (1.1–1.8 billion individuals) in the summer up to 0.9–1.7 million t (4.4–4.8 billion individuals) in fall. Scyphomedusa Chrysaora melanaster and the Hydromedusa Aequorea forskalea made up the major part of the jellyfish biomass (67–97%). Their distribution varied significantly. A. forskalea aggregated mainly in the deepwater part of the Bering Sea. Ch. melanaster was widely dispersed across the entire area of the investigations and formed the most considerable aggregations in the Anadyr-Navarin area. In the fall of 2006 the diet of jellyfish generally consisted of plankton organisms (copepods, euphausiids, amphipods, pteropods, chaetognaths, ostracods, and larval decapods). However, Ch. melanaster had a greater portion of fish and larval squid in its diet.