Distribution and abundance of walleye pollock Theragra chalcogramma in the northwestern Bering Sea in the summer-fall period of 2020 and their interannual variability

Spatial distribution and abundance of walleye pollock are considered for the northwestern Bering Sea in the summer-fall of 2020 on the data of echo-integration trawl-acoustic survey. The pollock aggregated mostly in the shelf areas with positive or close to zero water temperature, with the higher concentration in the high-gradient zones. The densest aggregations (> 300 . 103  pcs./nmi²) were found in the eastern part of the Gulf of Anadyr and at the line between the economic zones of Russia and USA. Characteristic acoustic images and daily distribution of walleye pollock on the survey transects are presented. Spatial and bathymetric differentiation of certain size groups of pollock are revealed. More than 83 % of the fish were counted in the areas with bottom depth of 50–150 m. Immature walleye pollock with the size of 21–37 cm accumulated mainly in the areas with bottom depth of 75–125 m. Interannual dynamics of the size composition and abundance of walleye pollock in the northwestern Bering Sea is considered on the data of trawl-acoustic surveys in 2013–2020. The fluctuations of abundance and distribution are compared with changes of thermal conditions. Significant dependence of the pollock abundance on the mean anomaly of bottom temperature is confirmed (correlation coefficient +0.69): the species biomass was noticeably higher and its distribution was wider in the years with favorable (relatively warm) thermal regime than in cold periods.

1. Borets, L.A., Stepanenko, M.A., Nikolaev A.V., and Gritsai, E.V., The state of pollock stocks in the Navarin region of the Bering Sea and the reasons that determine the effectiveness of its fishing, Izv. Tikhookean. Nauchno-Issled. Inst. Rybn. Khoz. Okeanogr., 2002, vol. 130, pp. 1001–1014.

2. Glubokov, A.I., Features of pollock distribution in the northern part of the Bering Sea (1997–2001), Vopr. Rybolov., 2003, vol. 4, no. 1(13). pp. 74–92.

3. Glubokov, A.I. and Norvillo, G.V., Reproduction of walleye pollock in the northwestern part of the Bering Sea, Vopr. Rybolov., 2002, vol. 3, no. 3(11), pp. 474–485.

4. Gritsay, E.V., Variance of walleye pollock length-age structure on the eastern and northern shelves of Bering Sea, Izv. Tikhookean. Nauchno-Issled. Inst. Rybn. Khoz. Okeanog., 2006, vol. 147, pp. 84–102.

5. Kuznetsov, M.Yu., Hydroacoustic methods and tools for fish stock assessment and fishery maintenance. Part 1. Hydroacoustic tools and technologies of their use in bioresource researches of TINRO-center, Izv. Tikhookean. Nauchno-Issled. Inst. Rybn. Khoz. Okeanog., 2013, vol. 172, pp. 20–51.

6. Kuznetsov, M.Yu., Basyuk, E.O., Chulchekov. D.N., and Syrovatkin, E.V., Distribution and oceanographic conditions of habitat for walleye pollock in the northwestern Bering Sea in summer-fall season, Izv. Tikhookean. Nauchno-Issled. Inst. Rybn. Khoz. Okeanogr., 2013, vol. 174, pp. 104–124.

7. Kuznetsov, M.Yu., Efimkin, A.Ya., and Basyuk, E.O., Distribution and habitat conditions of walleye pollock in the navarin-anadyr region of Bering Sea in summer-autumn, 2002–2003, Izv. Tikhookean. Nauchno-Issled. Inst. Rybn. Khoz. Okeanog, 2006, vol. 144, pp. 247–264.

8. Kuznetsov, M.Yu., Nikolaev, A.V., Borets, L.A., and Gavrilov, G.M., Features of walleye pollock distribution in the northwestern part of the Bering Sea in autumn 2000 and their interannual variability based on the results of survey surveys in 1997–2000, Vopr. Rybolov., 2002, vol. 3, no. 2(10), pp. 288–303.

9. Kuznetsov, M.Yu., Nikolaev, A.V., and Gavrilov, G.M., Distribution, size–age composition, abundance, and biomass of walleye pollock in the northwestern part of the Bering Sea in summer 2002, Vopr. Rybolov., 2004, vol. 5, no. 2(18), pp. 226–240.

10. Kuznetsov, M.Yu., Nikolaev, A.V., Borets, L.A., Autumnal distribution and vertical migrations of age-0 walleye pollock in the northwestern bering sea by results of trawl-acoustic surveys in 1997–2001, Izv. Tikhookean. Nauchno-Issled. Inst. Rybn. Khoz. Okeanog., 2004, vol. 139, pp. 91–101.

11. Kuznetsov, M.Yu., Ubarchuk, I.A., Polyanichko, V.I., and Syrovatkin, E.V., The software complex for visualization, multiple-view processing and data storage of hydroacoustic resource surveys, Tr. Vses. Nauchno-Issled. Inst. Rybn. Khoz. Okeanogr., 2021, vol. 183, pp. 174−190. doi:10.36038/2307-3497-2021-183-174-190

12. Stepanenko, M.A., Relationship between age and spatial distribution of walleye pollock Theragra Chalcogramma in the eastern and northwestern Bering Sea, Izv. Tikhookean. Nauchno-Issled. Inst. Rybn. Khoz. Okeanog., 2001, vol. 128, pp. 125–135.

13. Stepanenko, M.A., Interannual variability of spatial differentiation of pollock Theragra chalcogramma and cod Gadus macrocephalus of the Bering Sea, Vopr. ichthyol., 1997, vol. 37, no. 1, pp. 19–26.

14. Stepanenko, M.A. and Nikolaev, A.V., Some features of Pollock reproduction in the Bering Sea, Izv. Tikhookean. Nauchno-Issled. Inst. Rybn. Khoz. Okeanog., 2004, vol. 139, pp. 102–122.

15. Shuntov, V.P., Volkov, A.F., Temnykh, O.S., and Dulepova, E.P., Mintay v ekosistemakh dal’nevostochnykh morey (Walleye pollock in the ecosystems of the Far Eastern seas), Vladivostok: TINRO, 1993.

16. Traynor, J.J., Target-strength measurement of walley pollock (Theragra chalcogramma) and Pacific whiting (Merluccius productus), ICES J. Mar. Sci., 1996, volo. 53, no. 2, pp. 253–258.

17. Operator manual for Simrad ER60 Scientific Echo Sounder application, Horten, Norway, 2004. doi:10.1006/jmsc.1996.0031

18. Sheybak, A.Yu., Gritsay, Ye.V., Bomko, S.P., Ksenofontov, M.M., Bel’dy, M.V., Borilko, O.Yu., Gostrenko, L.M., Chul’chekov, D.N., Polyanichko, V.I., and Lysenko, A.V., O rezul’tatakh nauchno-issledovatel’skikh rabot po otsenke biologicheskikh resursov v Beringovom i Chukotskom moryakh na NIS «TINRO» s 7 avgusta po 31 oktyabrya 2020 g. (On the results of research work on the assessment of biological resources in the Bering and Chukchi Seas on the R/V TINRO from August 7 to October 31, 2020), Reysovyy otchet, Vladivostok: TINRO, 2020, № 28402.