Fish Resources in Near-Bottom Biotopes of the Shelf and the Upper Edge of the Continental Slope in the Northwestern Bering Sea

Abstract

The stocks of demersal, pelagic, and anadromous fish, as well as fish-like species, in near-bottom biotopes within a depth range of 20–386 m are considered based on the data of bottom trawl surveys conducted in the northwestern Bering Sea in the summer of 2017. The total recorded biomass of demersal fish was 1 756 870 t, including 1 578 430 t in the Western Bering Sea zone and 178 440 t in the Chukchi zone. The density of their concentrations was similar in both zones: 11 331.8 and 10 748.0 kg/km2, respectively. In the surveyed water area, Pacific cod constituted a major portion of the demersal fish biomass, 1 227 300 t. The total biomass of pelagic and anadromous fish species in near-bottom biotopes was 3 884 150 t, including 3 555 930 t in the Western Bering Sea zone and only 328 220 t in the Chukchi zone. They had a higher concentration density in the near-bottom layer of the Western Bering Sea zone than in the Chukchi zone, 25 527.9 kg/km2 and 19 769.9 kg/km2, respectively. Walleye pollock dominated the pelagic and anadromous species with its total biomass of 3 884 150 t (taking the catchability coefficient k = 0.4 into account), of which yearlings accounted for 36 080 t (k = 0.1). In 2017, the stocks of Alaska skate, Pacific herring, rock sole, and Alaska plaice decreased compared to the data of the analogous survey in 2015; however, the stocks of Arctic cod, saffron cod, Pacific cod, walleye pollock (both adults and yearlings), flathead soles, and yellowfin sole increased. The trend of variations in stocks of certain commercial species for future years can be predicted based on the pattern of distribution of positive and negative anomalies on Sunde’s curves for the size structure.