Walleye pollock (Gadus chalcogrammus, Pallas, 1814) fishery, size and age composition, state of stocks and catch prospects in the waters adjacent to Kamchatka peninsula and Northern Kuril Islands

The article provides data on the catch of the Northern Okhotsk, Eastern Kamchatka and Western Bering Sea walleye pollock stocks, fishery structure by the fishing gears in 2016–2019, size and age composition of the fish in the commercial trawl and Danish seine catches in 2010–2019. Data on the generation abundance and stock condition indices used in the stock assessment models are also demonstrated. Interannual dynamics of the total and spawning stock biomass, determinants of the dynamics and prospects of fishing are analyzed.

Intermediate- and Deep-Water Oxygenation History in the Subarctic North Pacific During the Last Deglacial Period

Deglacial dissolved oxygen concentrations were semiquantitatively estimated for intermediate and deep waters in the western Bering Sea using the benthic foraminiferal-based transfer function developed by Tetard et al. (2017), Tetard et al. (2021a). Benthic foraminiferal assemblages were analyzed from two sediment cores, SO201-2-85KL (963 m below sea level (mbsl), the intermediate-water core) and SO201-2-77KL (2,163 mbsl, the deep-water core), collected from the Shirshov Ridge in the western Bering Sea. Intermediate waters were characterized by an oxygen content of ∼2.0 ml L−1 or more during the Last Glacial Maximum (LGM)–Heinrich 1 (H1), around 0.15 ml L−1 during the middle Bølling/Allerød (B/A)–Early Holocene (EH), and a slight increase in [O2] (∼0.20 ml L−1) at the beginning of the Younger Dryas (YD) mbsl. Deep-water oxygen concentrations ranged from 0.9 to 2.5 ml L−1 during the LGM–H1, hovered around 0.08 ml L−1 at the onset of B/A, and were within the 0.30–0.85 ml L−1 range from the middle B/A to the first half of YD and the 1.0–1.7 ml L−1 range from the middle to late Holocene. The [O2] variations remind the δ18O NGRIP record thereby providing evidence for a link between the Bering Sea oxygenation at intermediate depths and the deglacial North Atlantic climate. Changes in the deep-water oxygen concentrations mostly resemble the deglacial dynamics of the Southern Ocean upwelling intensity which is supposed to be closely coupled with the Antarctic climate variability. This coherence suggests that deglacial deep-water [O2] variations were primarily controlled by changes in the circulation of southern-sourced waters. Nevertheless, the signal from the south at the deeper site might be amplified by the Northern Hemisphere climate warming via an increase in sea-surface bioproductivity during the B/A and EH. A semi-enclosed position of the Bering Sea and sea-level oscillations might significantly contribute to the magnitude of oxygenation changes in the study area during the last deglaciation. Interregional correlation of different proxy data from a wide range of water depths indicates that deglacial oxygenation changes were more pronounced in the Bering and Okhotsk marginal seas than along the open-ocean continental margin and abyssal settings of the North Pacific.

Monitoring on the output of pollock roe during fishing season in 2021

The output of roe from pre-spawning pollock was analyzed in the Western Bering Sea, Eastern Kamchatka fishing zones and the Sea of Okhotsk fishing zone during legal specialized fishing for pollock from 01.01.2021 to 10.04.2021 in order to preserve and rational exploitation the pollock population. It was concluded that the output of pollock roe (raw fish eggs) calculated as a percentage of the total weight of raw fish, which were subjected to processing irrespective of sex (females and males treated together) during the 2021 fishing season, when legal specialized fishing for pollock was conducted in the Western Bering Sea fishing zone, Karaginsky subzones, Petropavlovsk-Commander subzones and the Sea of Okhotsk fishing zone, did not exceed the values determined in the Order №267 issued on 23 May 2019 by the Ministry of Agriculture of the Russian Federation.

Long-term dynamics for stocks of sablefish Anoplopoma fimbria in the western Bering Sea and prospects for their fishery

Sablefish is an endemic species of the North Pacific. Its range extends from California Peninsula, along the Pacific coast of the US and Canada to Aleutian Islands and further, along the Pacific coast of Kamchatka and the Kuriles to the central part of Honshu Island. They dwell also in the Bering Sea and southeastern Okhotsk Sea. Sablefish are the most abundant in the southeastern Bering Sea and in the Gulf of Alaska, that is conditioned by favorable conditions for their larvae and juveniles. In the Asian part of the range, the environments are generally more severe, and reproduction of sablefish is rather risky. Following to the results of modern genetic studies, the sablefish stocks are distinguished by high genetic homogeneity that suggests a common population with the main spawning grounds in the southeastern Bering Sea, at the Pacific coasts of Aleutian Islands, in the Gulf of Alaska, and at the coasts of British Columbia, Washington, Oregon and California. Dynamics of the sablefish biomass is considered on the data of bottom and midwater trawl surveys conducted by TINRO in 2003–2020, fishery statistics, and accessible data of NOAA (USA). Sharp increasing of the biomass and annual catches is noted both in the eastern and western Bering Sea in the last few years because of appearance of several strong year-classes. Western Bering Sea stock depends on migration of recruits from the common spawning grounds in the southeastern Bering Sea. For the western Bering Sea, two main ways of such migration are possible: i) active migration of juveniles with benthic habitat; and ii) passive transfer of pelagic larvae and early juveniles across the Bering Sea through the system of surface currents. The latter mechanism supports the sablefish recruitment in the bays of the western Bering Sea and, to a lesser extent, at the eastern coast of Kamchatka. Sablefish in the West Bering Sea fishery zone were caught in 2010–2020 mostly as by-catch for trawling and longline fishery (93 %), other 7 % were landed by specialized longline fishery. The basic points for managing the sablefish fishery in the West Bering Sea zone are defined. About 400 t of sablefish is permissible to catch annually in the West Bering Sea fishery zone in conditions of modern high stock of this species. This value includes 100–120 t that will inevitably be caught as by-catch and the rest of 280–300 t is a foreseeable resource for organization of specialized fishery.

Role of arrowworm Sagitta elegans (Chaetognatha) in plankton communities of the western Bering Sea

Arrowworm Saggita elegans is one of the important and abundant species in zooplankton communities of the western Bering Sea. Interannual variability of their biomass is considered on the data of long-term surveys conducted in 1986–2018, the species production is determined for the Anadyr-Navarin region and deep-water basin in 2008–2018, and the total production of zooplankton communities is calculated for 2008, 2015, and 2018. In the modern period, the biomass of S. elegans has significantly decreased compared to 1990–2000s, with exception of the shallow areas where it is relatively stable. The last decade included two periods with different oceanographic regime: the cold years (2007–2013) and the warm ones (2014–2018), but S. elegans did not demonstrate rapid response to such change of abiotic factors. However, the water circulation patterns in the upper layer were important for them and determined their transport and accumulation. For example, the high abundance and production of arrowworms in the deep-water area in 2008 and in the Anadyr-Navarin region in 2011 were conditioned by their transport and accumulation in these areas. S. elegans are predators, preying mainly upon copepods, so their impact on structure and production of zooplankton community is determined by significant grazing estimated at 50–100 % of Copepoda production or even more. The total production of zooplankton communities was higher in «warm» 2015 and 2018 than in «cold» 2008. The arrowworm production decreased in these warm years but production of non-predatory species (basically small- and medium-sized copepods) increased sharply because of their rapid response to temperature changes realized in high growth rate under higher temperature. Thus, the role of S. elegans in formation of the community production becomes lower in conditions favorable for high growth rate of non-predatory species.

Modern specialized fishery of sea fish in the western Bering Sea

The shelf and continental slope of the western Bering Sea, being among the most productive areas of the Far-Eastern Seas of Russia, became exploited by commercial fishery half a century ago, after introduction of 200-mile exclusive economic zones in 1977 and relocation of the Russian fishing fleet from the eastern Bering Sea to its western part. In 2010-2019, about 20 % of the total catch of sea fish in the Far-Eastern basin (excluding pacific salmons) were caught in the West Bering Sea fishery zone. Among the fishery districts of the Russian Far East, this area is currently the 1st one by annual catch of pacific cod, grenadiers, sculpins and sablefish, 2nd — by catch of walleye pollock, halibuts and skates, 3rd — by catch of rockfishes, and 4th — by catch of pacific herring and flounders. Features of specialized fishery in the West Bering Sea fishery zone in 2010-2019 are clarified. Now 48 types of the specialized fishery can be distinguished here, while 96.3 % of the average annual landing is provided by the following 8 most important types: walleye pollock midwater trawl fishery (77.8 % of mean annual catch); pacific herring midwater trawl fishery (6.1 %); pacific cod bottom longline fishery (4.7 %); walleye pollock Danish seine fishery (2.7 %); grenadiers bottom longline fishery (2.4 %), pacific cod Danish seine fishery (0.9 %); squids bottom trawl fishery (0.9 %); and pacific cod bottom trawl fishery (0.8 %). All these types of fishery are highly specialized and portion of the target objects in the catches ranges from 76 to 96 % (according to official statistics), while the by-catch accounted as 4-24 %. The is no specialized fishery on such objects as rockfishes, arrowtooth and kamchatka flounders, and sablefish in the West Bering Sea fishery zone, but they are landed as by-catch. The fishery statistics with the data sorting to specialized fishery and by-catch can be used quite effectively for the stocks assessment and determining acceptable level of their exploitation, with recommendations for fishery regulation, including evaluation the possible level of non-specialized by-catch.