Can an invader support commercial fishing? A case study of walleye pollock Gadus chalcogrammus in the western Chukchi Sea

Based on research of bottom and mid-water trawl surveys conducted onboard Russian research vessels in 2003–2020, data on the spatial and vertical distributions of walleye pollock Gadus chalcogrammus in the western Chukchi Sea are presented. The response of walleye pollock distribution related to water temperature, as well as the features of its distribution are also presented. In the water column, schools were mainly comprised of juveniles, while medium-sized and large individuals were scarce. Approximately 98% of the total number of juveniles and 100% of the large pollock caught by bottom trawls were observed in the southern part of the study area, while most of medium-sized fish were found in the northern part. In the water column, walleye pollock was found within the upper 65 m layer. Near the bottom, the majority of small-sized fish and all large individuals were observed at depths shallower 100 m, while over 70% of medium-sized walleye pollock were found at depths than 100 m. In the water column, juveniles were observed at temperatures from −0.4 to 3.3 °C with largest concentrations within a temperature ranges of 0.9–1.8 °C) and 3.0 °C. Near the bottom, walleye pollock were recorded at a temperature from −1.2 to 4.3 °C with maximum number within the ranges 2–3 °C, > 3 °C, and 1–2 °C. A few individuals were found at bottom temperatures below 0 °C. In the water column, the abundance was low during the entire study period. Acoustic estimates were notably higher compared to those based on the results of bottom trawl surveys. The recent dramatic increase of walleye pollock abundance in the western Chukchi Sea appears to reflect a complex of factors, including warming of bottom temperatures, decreasing of ice cover, increasing of northward currents, better foraging conditions, and increasing abundance and biomass in the Bering Sea. An attempt is made to determine the prospects for commercial fishing of walleye pollock in the western Chukchi Sea. Bottom trawl surveys in 2019–2020 indicated an estimate of total allowable catch of 37,200 t for the 2021 and 2022 fishing seasons; in 2021 over 4000 t were caught. However, this kind of fishing cannot be considered sustainable due to several reasons, including the inability to forecast the number of fish migrating from the Bering Sea, the limited fishing season due to harsh climatic conditions, the remoteness of main ports, and the uncertain population status of its stocks.