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The studies carried out in this work made it possible to characterize the dynamics of the raw material base of aquatic biological resources of the Russian waters of the Chukchi Sea in 1997–2020 and evaluate its value at the present stage. The raw material base of marine fish and invertebrates varied from 5,4 to 450,1 thousand tons (with an average value of 196,7 thousand tons). It was based on marine fish – an average of 189,0 thousand tons (96,1% of all resources), stocks of invertebrates – 7,7 thousand tons (3,9%). Estimates of the commercial WBR biomass in the Chukchi Sea are approximately 24 times lower than the estimates of the resource base of the western part of the Bering Sea: 4,1 and 5,1% of the biomass of marine fish and invertebrates, respectively. Stocks of hydrobionts showed a gradual downward trend from 1997 to 2007, a low level in 2008–2017 and a sharp rise in 2018–2020. Significant growth in resources in the late 2010s led to mass walleye pollock migration to the Chukchi shelf from the Bering Sea, which led to an increase in the raw material base of WBR by 431 thousand tons and a concomitant increase in its cost by 23,7 billion rubles. The cost of the raw material base of the Russian waters of the Chukchi Sea in 2019–2020 amounted to 34–51 billion rubles, in absolute terms yielding to the Bering and Okhotsk seas by 14,0 and 31,3 times. The most valuable species of bioresources in terms of value were cod fish (walleye pollock Gadus chalcogrammus) and crabs (snow crab Chionoecetes opilio), the total contribution of which exceeds 90% of the total value of the estimated commercial stocks of the sea. With a high probability, it can be assumed that it is these types of WBR that will form the economic basis of the Russian fishery in the Chukchi Sea in the future.

Purpose of the work: revealing the relationship between the emergence of high-yielding generations of mass commercial fish and the temperature regime of surface waters and the ice cover of the Far Eastern seas and adjacent areas of the open part of the Pacific Ocean.Methods used: to achieve the set goal from 1921 to 2020, data on the yield of generations of 27 groups of marine fish were analyzed. As part of the discovery of the initial factors that have a potential impact on the biomass of aquatic organisms, long-term data on water temperature and ice cover are involved.Novelty: elements of novelty are the relationship of fish productivity with certain environmental factors, which can be used for forecasting purposes. The results of the study showed that the largest number of productive generations in fish as a whole falls on temperate years, followed by warm types of years, and to a lesser extent such generations are born in cold years. This is true for most of the analyzed species, with the exception of Pacific cod, which was dominated by generations that appeared in years warm in terms of water temperature, and flounders, with their maximum occurrence of overproductive generations (after moderate years) in years with cold ice cover.Practical significance: the results of this study in the form of regularities found in the impact of abiotic environmental factors on the productivity of fish will improve the efficiency of the use of their raw material base.

The purpose: to identification of the features of the distribution and biology of walleye pollock Gadus chalcogrammus, as well as the presentation of information on the stocks of the species and the initial stage of development of its resources in the western part of the Chukchi Sea.Methods used: to achieve this goal, we used materials from nine integrated trawl surveys carried out in 1995– 2020 on research vessels, as well as coastal studies on the Arctic coast of the Chukotka Autonomous Okrug, which analyzed data on the distribution, biology, biomass and fishery of walleye pollock.Novelty: elements of novelty are generalized modern materials on the distribution, biology and for the first time organized pollock fishery.Practical significance: the Chukchi Sea can be attributed to the most favorable areas for studying the variability of the organization of Arctic ecosystems, due to the instability of climatic conditions on Earth during the period of warming. The obtained results of studies on the distribution, biology, stocks and fishery of such a mass indicator species as walleye pollock will increase the efficiency of using the raw material base of marine fish in this reservoir.

The purpose of the work: to identify the features of the distribution and biology of walleye pollock Gadus chalcogrammus, as well as to provide information on the reserves and development of its resources in the Bering Sea.Methods used: to achieve the goal, data on distribution, biology, biomass and fishery of walleye pollock were analyzed.Novelty: elements of novelty are generalized modern materials on the distribution, biology, stocks and fishery of walleye pollock.Practical significance: at the present stage, the East Bering Sea and northwestern pollock populations are at the average long-term level of biomass, their annual changes largely depend on the background conditions of the natural environment and the development of the food supply, which determine the scale of fish migration from the southeastern part of the Bering Sea to the northwestern and back. In the West Bering Sea walleye pollock, there is a trend towards a gradual recovery of stocks after a period of minimum values in the late 1990s — e arly 2000s. In general, the current state of walleye pollock stocks in the Bering Sea is characterized as stable, which maintains the fishery at a relatively high level. The results obtained in this work on the characteristics of the distribution and biology of walleye pollock, the state of its stocks and fishing will improve the efficiency of using the raw material base of marine fish in the Bering Sea.

Information on the distribution and main features of the biology of the largest groups of herring in the Bering Sea: Korfo-Karaginsky and the East Beringovomorskaya is presented. Data on the features of their reproduction are given. Showing the state of stocks and fishing.

Based on the materials of investigations conducted for 20 years (1995−2015), the features of biology of the common fish species of the family Cottidae from the northwestern Bering Sea are studied. These species are found during summer and fall in the waters of the Olyutorsky-Navarin region. The size–age parameters of the fishes collected with different fishing gears, as well as the features of their body length and body weight dynamics, spawning time, and spawning conditions, are described. The largest exemplars of shorthorn sculpin Myoxocephalus verrucosus and staghorn sculpins, armorhead sculpin Gymnocanthus galeatus and G. detrisus, are recorded in the catches of snurrevads, while the fishes caught in trawls are characterized by smaller size. Interannual variability of the size composition of the fish is related to the abundance of certain generations or to the fishery directed to different associations of sculpins. In the coastal waters, comparatively low average body size is usual for the majority of common sculpin species (with the exception of lords, yellow Irish lord H. jordani and Gilbert’s Irish lord H. gilberti) because of the dominance of juveniles.

Biological features of the seven abundant commercial species—the Pacific halibut Hippoglossus stenolepis, the Greenland halibut Reinhardtius hippoglossoides, the Alaska plaice Pleuronectes quadrituberculatus, the northern rock sole Lepidopsetta polyxystra, the yellowfin sole Limanda aspera, the flathead sole Hippoglossoides elassodon, and the Bering flounder H. robustus (Pleuronectidae)—have been studied for a 20-year period (1995−2015). These species are present in the northwestern Bering Sea in the summer–autumn season; they form the gatherings in Olyutorsky-Navarin region. The size-weight spectra of the fish caught by different fishing gear has been analyzed, the peculiarities of the linear growth and the weight gain, as well as the spawning period and scale and the spawning conditions, have been described. The largest halibut specimens have been registered in the bottom setlines and gill nets, while flounders were in snurrevad catches; the smallest specimens have been observed in trawl catches. The abundant year-class in most of the studied species is seen well on the long-term plots of the fish size spectra and is tracked by the decrease of their biological parameters. The species that demand vast growing grounds (Pacific halibut, Alaska plaice, northern rock sole, and yellowfin sole) are characterized by a smaller average body size of the fish sampled in the coastal waters due to the prevalence of the young specimens in this area.

Biological features of the four common fish species, giant grenadier Albatrossia pectoralis (Macrouridae), Pacific herring Clupea pallasii (Clupeidae), Pacific rainbow smelt Osmerus mordax dentex, and Pacific capelin Mallotus villosus catervarius (Osmeridae), were studied under the 20-year dataset (1995−2015). These species inhabit the northwestern Bering Sea in the summer–autumn period and form the schoolings in the Olyutorsky-Navarin region. The size–age parameters of the fish caught by different sampling gear, as well as the peculiarities of the body length and body weight dynamics, spawning periods, spawning range, and conditions, were analyzed. The largest specimens of giant grenadier, Pacific herring, and Pacific rainbow smelt were observed in the catches performed by the bottom setline and the gill nets; the smallest fish were found in the trawl catches. The body length and body weight of Pacific herring were larger in the pelagic trawls compared to the bottom trawls; an opposite pattern was observed for the Pacific capelin. The abundant year-class in the species with short life cycle (capelin and herring) is well tracked on the longterm plots of the fish body size; this is accompanied by the decrease of their biological parameters. Herring stock covers large growing grounds; smaller body size was observed for the herring grazing in the coastal waters; young specimens dominate here.

Biological features of the three common fish species, pollock Theragra chalcogramma, Pacific cod Gadus macrocephalus, and saffron cod Eleginus gracilis (Gadidae), have been studied using a 20-year dataset (1995−2015). These species inhabit the northwestern Bering Sea in the summer–autumn period and form the schoolings in Olyutorsky-Navarin region. The size–age parameters, as well as the peculiarities of the body length and body weight dynamics, spawning periods, spawning range, and conditions, of the fish caught by different sampling gear have been analyzed. Due to the construction peculiarities and catch efficiency of the different catching gear, the largest specimens are found in the setlines and snurrevads; the fish caught by the trawls are characterized by the smallest size. The body length and body weight of pollock is greater in the pelagic trawl catches compared to the bottom trawl catches. The abundant brood of Gadidae may well be tracked on the multiyear dynamics graphs reflecting the size distribution, as well as by the decrease of biological parameters of the fish. The studied species inhabit the vast growth areas, so smaller body size of them in the coastal waters may be a result of a high ratio of the young specimens there.

The commercial value of the ichthyofauna of the Bering Sea within Russian waters (Exclusive Economic Zone) is discussed. The ichthyofauna of this region comprises 344 species of fish and fish-like. Most of the species (283 species, or 82.3%) have no commercial value. The rest have commercial value (47 species, or 13.7%) or have the potential commercial value (14 species, 4.1%). Active and large-scale fishery is performed for 27 commercial species both in the open sea and in the coastal areas (mostly by ships); another twenty species are harvested irregularly by local coastal or nearshore fishery.

The ecological and zoogeographical characteristics of 344 species of Pisces and fish-like species comprising the ichthyofauna of the Bering Sea (Russian Exclusive Economic Zone) are presented for the study period of 1995−2012 (original studies) and those for previous findings in this area. The benthic species (elittoral, mesobenthic, and sublittoral; 216 species, or 62.8%) dominate if one takes into account the biotopic characteristics of the species; the majority belongs to the wide-boreal Pacific, wide-boreal Asiatic, and arcticboreal species (255 species, or 74.1%) by the zoogeographic characteristics. The comparative analysis of the fish communities of the western Bering Sea evidences to the significant changes of the ichthyofauna within the depth southwards Navarin Cape. Arctic-boreal species can be considered as a specific faunistic “margin” between the northern and the southern ichthyofauna of the western Bering Sea due to their eurybiont characteristics.

The species list of ichthyofauna of the Russian exclusive economic zone of the Bering Sea has been developed using the original data obtained in 1995–2012 and the data published since the very beginning of the studies in this region. The species list includes 344 species belonging to 188 genera, 65 families, and 23 orders. The diversity of the ichthyofauna of the western Bering Sea, calculated under the ratio of species, genera, and families, is significantly higher than that observed for the Arctic seas, the seas of the European part of Russia (except the Caspian Sea), and the Sea of Japan. It is similar to the diversity of the ichthyofauna of coastal waters of the northern Kuril Islands and the northern Sea of Okhotsk. The maximal diversity has been found for scorpion fishes and sculpins (Scorpaeniformes), perch-like fishes (Perciformes), salmons (Salmoniformes), flatfishes (Pleuronectiformes), and cods and hakes (Gadiformes). These orders comprise 33 families (50.8% of total number of families), 139 genera (73.9% of total number of genera), and 279 species (81.1% of total number of species) in total. The maximal diversity belongs to the scorpion fishes and sculpins and the perch-like fishes; they dominate absolutely by the number of the lower-order taxa (families, genera, and species). Such families as sculpins (Cottidae), eelpouts (Zoarcidae), snailfishes (Liparidae), righteye flounders (Pleuronectidae), pricklebacks (Stichaeidae), and poachers (Agonidae) are presented by 175 species, or comprise 50.9% of the total diversity of ichthyofauna.

Based on studies of 1995–2010 and other registered captures of fishes and fish-like over the entire history of the study of the Chukchi Sea, a list of its fish fauna species is compiled, including 110 species belonging to 68 genera, 26 families, and 11 orders. Taxonomic diversity of the fish fauna is considered and its characteristics for belonging to a geographical area and biotopical groups of fish are given. For the ratio of species, genera, and families, the fish fauna of the Chukchi Sea is significantly more diverse than that of the other Arctic seas, including the Barents Sea, and demonstrates a certain similarity for these indicators with the fish fauna of the western Bering Sea. Fish communities of the Chukchi Sea are dominated by Cottidae, Zoarcidae, Pleuronectidae, Stichaeidae, Agonidae, and Salmonidae, constituting a total of 73 species, or 66.4% of the species diversity. Benthic fishes of elittoral and sublittoral complexes dominate in terms of the biotopic belonging (74 species, 67.2%); arctic, arctic-boreal, and Pacific and Asiatic boreal species (89 species, 80.9%) dominate in terms of the zoogeographic belonging. Information availability for the bioresource potential of the Chukchi Sea is insufficient: fishing is not carried out or there are no accessible data on it. Most of the fish fauna of the Chukchi Sea (68 species or 61.8% of species diversity) consists of rare species. Out of the 42 species regularly registered in the fishing gear, 11 species are recommended for commercial use.

According to results of integrated record summer-autumn trawl surveys performed in 2004, 2005, and 2008 in the shelf-continental region of the northwestern Bering Sea from Cape Olyutorsky to Bering Strait in the range of depths 14–563 m, eight bottom communities of fish and fish-like were distinguished and their structure was described. In the composition of communities, 142 species from 29 families were recorded, among which Cottidae, Pleuronectidae, Zoarcidae, Agonidae, Stichaeidae, and Liparidae dominate by the number of species. According to biotopic belonging, bottom fish of elittoral, mesobenthal, and sublittoral complexes dominate in catches; according to zoogeographic belonging, wide boreal, arctic-boreal, and high boreal species dominate. Spatial change in the species structure of fish communities proceeds in correspondence with main regularities of life distribution in the ocean—principles of vertical and latitudinal zonality. The strongest relation of spatial variation of bottom fish communities was established with depth. Using multivariate nonmetrical scaling, five fish communities corresponding to different bathymetric ranges (sublittoral, elittoral, transitory shelf-bathyal, α-bathyal, and β-bathyal) were distinguished. Within sublittoral, elittoral, and shelf-bathyal communities, latitude zonal groups of Olyutorsky-Navarin and Anadyr regions having a lower hierarchic status were distinguished. In an interannual aspect, stability of the number of separated bottom fish communities and similarity of their spatial distribution in the examined sea areas is traced.

Data of trawling censuses (1996–2005) are used to analyze the specifics of the distribution of commercial fishes present in the northwestern Bering Sea in summer and autumn and forming accumulations in the waters of the Olyutorsky-Navarin region. Areas with maximum fish density usually have a temperature range of 2.4–4.0°C in near-bottom water layers; they are observed in the same localities, with some interannual variation: in the middle shelf, with depths of 50–160 m southwest of Cape Navarin to Cape Khaiidin and between the Dezhneva Bay and Expeditsii Bay, and in waters of the continental slope adjacent to the first area, with depths over 270 m. The accumulations on the shelf mainly consist of such commercial species as the Alaska pollock Theragra chalcogramma, Pacific cod Gadus macrocephalus, saffron cod Eleginus gracilis, northern rock sole Lepidopsetta polyxystra, Alaska plaice Pleuronectes quadrituberculatus, and righteye flounders of the genus Hippoglossoides (H. robustus and H. elassodon); on the continental slope, they consist mainly of the Greenland halibut Reinhardtius hippoglossoides and Pacific halibut Hippoglossus stenolepis. The recorded density of fish in the Olyutorsky-Navarin region was the highest in 2004–2005 and the lowest in 1999, 2001, and 2002. This variation was determined mainly by the interannual variation in the fishing for cods (Gadidae), which reflected the emergence of abundant generations and migration activity in fishes of this family, as well as from differences in the efficiency of fishing gear. Fishing for many species can and should be performed simultaneously; special attention should be paid to the coastal areas of the Olyutorsky-Navarin region, where considerable fish resources (such as the saffron cod, Pacific halibut, and other righteye flounders) are present.

Based on the trawl surveys of 1996–2012, regularities and biological features have been studied in the arrow-toothed halibuts (Atheresthes evermanni and A. stomias) from Olyutorsky-Navarin region and adjacent waters of the Bering Sea. The abundance of the species has increased since 2004. Their remunerative concentrations have been found on the continental slope and shelf. The majority of fish captured during our survey were mature specimens with a length of 37–54 cm and a weight of 0.8–1.4 kg; in the course of our investigation, there was a trend towards a decrease in the average sizes. According to the data obtained in the recent years, if one considers the biomass parameters, arrow-toothed halibuts are among ten dominant species (0.1–0.5% of the total biomass of fish registered in Olyutorsky-Navarin region) and prevail among flatfish (Pleuronectidae). Currently, arrow-toothed flounders are undesirable bycatch in the fishery of Reinhardtius hippoglossoides and Hippoglossus stenolepis.

Purpose: The unintentional and unrecognized cannulation of an extradural vein is a potentially serious complication of an epidural anesthetic. The present study was undertaken to assess the incidence of blood vessel puncture related to epidural catheterization performed in three different body positions. — Methods: The study was conducted in 900 (three groups of 300) obstetric patients undergoing continuous epidural analgesia during their labour and who were randomly allocated to three groups. Epidural catheterization was performed with patients in the sitting, lateral recumbent horizontal, or lateral recumbent head-down position. Results: There was a lower incidence of vessel cannulation when this procedure was performed in the lateral recumbent head-down position (2%) than in the lateral recumbent horizontal (6%) and in the sitting position (10.7%). Conclusion: Adoption of the lateral recumbent head-down position for the performance of lumbar epidural blockade, in labour at term, reduces the incidence of lumbar epidural venous puncture.