The purpose of the work. To establish the relative index of the commercial stock (I%Z) of the red king crab Paralithodes camtschaticus and to qualitatively assess the dynamics of the stock status in the northwestern part of the Sea of Okhotsk for 1995-2023.

Material and methods. The annual estimates of the commercial stock of P. camtschaticus crab, obtained from direct accounting data, were converted into relative stock indices (I%Z) expressed as a percentage of the year with the maximum stock estimate in retrospect. Using a similar method of uniform scaling, relative indexes were set for: the total crab catch, the average daily catch of the vessel, the number of days spent on the total catch, and other parameters of fishing statistics.

Results. In the period 1995-2023, all relative indices of fishing statistics had fluctuations in values from 7-10 to 90-100% with varying inertia over time. The maximum values of the indices were: the index of commercial stocks (I%Z) in 2018; the index of average daily catch for the year (I%dV) in 2023; the index of annual total catch (I%V) and other commercial statistical indices in 2003. The minimum values of the indices were recorded in 2003-2004 and 2012-2015.

New data. The values of the crab fishing stock index (scale 0-100%) were divided into four zones (quartiles), each is given an estimated characteristic of the stock condition – good, satisfactory, uncertain and depressive. At the present stage, the red king crab stock index I%Z has a high level – 80% of the maximum value in 2018 and it is interconnected with other indices of fishing statistics.

Practical significance. The dynamics of the I%Z red king crab fishing stock index, being an operational indicator, visually demonstrates its significant variability in the studied historical period. At the present time, the I%Z index indicates that now in the northwestern part of the Sea of Okhotsk, the commercial stock of the red king crab is in a stable condition.

The purpose of the study was to reveal differences in age and growth patterns in two closely related species: Berryteuthis septemdentatus from the Japan Sea and schoolmaster gonate squid B. magister from the Bering Sea based on the analysis of age determining structures such as statoliths.

Methods included preparation and processing of statoliths (extraction, gluing and grinding) and counting increments (growth lines) followed by further statistical analysis of daily increments and obtaining characteristics of squids’ age and growth.

Results suggested that there were species-specific patterns in growth rates of these two squid species. It appeared that, at earlier ontogenetic stages, growth rates in B. septemdentatus are higher than in B. magister; however, at later ontogenetic stages, individuals of B. magister grow faster than B. septemdentatus.

Discussion on the revealed differences in growth patterns between these two morphologically and phylogenetically close species suggested that higher growth rates in B. septemdentatus at earlier ontogenetic stages might be related to larger size of ripe eggs and, henceforward, to larger size of newly hatched paralarvae. However, as the squid grow, growth rates in B. septemdentatus become slower than in B. magister presumably due to colder deepwater habitat in the Japan Sea for the former species compared to deep-sea areas occupied by the latter species.

Scientific novelty includes new information on growth rates and age in B. septemdentatus and its comparison with those in the schoolmaster gonate squid B. magister as revealed by the analysis of age-recording structures (statoliths), and the use of relatively large size range of B. septemdentatus with mantle length from 141 to 203 mm.

The aim of the work is to develop methodological approaches to GIS mapping of Pacific salmon spawning grounds based on the results of aerial visual surveys of their abundance and distribution in river systems.

Methods used: digitization of archive materials, compilation of spatial databases, GIS mapping.

Novelty: The mapping of the distribution of spawning grounds, abundance and occurrence of five Pacific salmon species in two model river systems was carried out based on the developed approaches.

The results obtained: GIS-database including a set of electronic maps on a single geo-referenced digital basis at a scale of 1:200 000. The input, search and use of cartographic information is carried out according to the generally accepted procedure provided by GIS technologies. All maps have an identical database structure and are grouped into 4 thematic sections: a list of watercourses of the Kol and Kekhta (Kuntovo) river basins; spatial distribution of spawning grounds in the river system – separately for each of the species (pink salmon, chum salmon, chinook salmon, sockeye salmon, coho salmon) and a map which summarized data for all species; species diversity of Pacific salmon, including a map of the distribution of the anadromous mykiss Parasalmo mykiss; contribution of watercourses regarding in the reproduction of subject species. A density index of spawning grounds is proposed to be calculated as the ratio of the area of spawning grounds to the length of a watercourse or its section.

Practical significance: The research results is of methodological significance for mapping of the spawning stock of Pacific salmon in the Russian Far East.

Objective: the aim of this study was to develop a method for evaluating fish sperm quality based on the mitochondrial status of spermatozoa, which is linked to their functional motility.

Methods: to assess sperm quality of sexually mature Black Sea turbot males of different ages from a spawning population, flow cytometric analysis with preliminary staining of live sperm samples using the fluorescent dye rhodamine 123, which characterizes the membrane potential of spermatozoa mitochondria, was applied for the first time.

Results: individual variability in concentration, size composition, and fluorescence of rhodamine-stained spermatozoa was determined in the sperm of 27 sexually mature turbot males of different ages from the same spawning population. The concentration of spermatozoa (with a head size of 2.2 μm) in turbot seminal fluid averaged 2.8 ± 1.3 × 109 cells ml-1, and individually varied from 0.56 to 4.98 × 109 cells ml-1. The proportion of fluorescent spermatozoa (i. e., with functional mitochondria stained by rhodamine 123) was 86.3 ± 13.9% of all spermatozoa in the sperm samples. Within the large group of rhodamine 123-stained spermatozoa, a subgroup of larger cells (approximately 2.4 μm) with the most intense fluorescence and, apparently, the highest metabolic activity was clearly distinguished, comprising 16.2 ± 3.8%.

Novelty and Practical significance: the developed cytometric protocol provides a more accurate assessment of spermatozoa functionality in the sperm of Black Sea turbot and other fish species. It can be applied for investigating reproductive characteristics of fish from natural populations, selecting the best breeders when creating broodstock for aquaculture, and evaluating fish sperm quality before and after cryopreservation.

The aim of the research to assess the pup production in the harp seal population in the White Sea in 2023 and 2024.

Methods. An aerial survey of marine mammals to assess the abundance of pups and adults of the White Sea harp seal population using unmanned aerial vehicles/drones (UAVs) was conducted over the areas of drifting ice in the White Sea. A multispectral technique was applied which consisted in simultaneous photographing of the sea surface done with a high-resolution photo-camera and an infrared (IR) camera. Aerial survey data (synchronized pairs of photo- and IR-images) were processed using the «Python» neural network with the «Yolo v4» module. An assessment of harp seal pup production was carried out using the method of discrete extrapolation. The harp seal population was calculated using cohort analysis takin into account of mortality by years.

Novelty. Full-scale multispectral aerial survey using several UAVs simultaneously. Automatic processing of huge amounts of digital photographs in optical and infrared ranges using computer vision technologies to find and recognize animals in photographs.

Result. The 2024 data provided a total number of the White Sea harp seal population of 141692 + 8696 newborn pups and a total harp seal population estimate of 1548840 individuals. The 2023 assessment pup production was lower and was estimated at 124645 + 20774 individuals. The distribution of harp seal pups on the drifting ice of the White Sea in the winter-spring period is determined mainly by the ice conditions and wind conditions. Interannual fluctuations in the number of harp seal pups are determined by the number of mature females participating in reproduction.

Practical significance: the data obtained will be used to assess the size of the White Sea population of harp seals and to develop recommendations for its conservation and rational use.

The purpose of the work: to assess the current state of reserves and fishery of aquatic biological resources in the Russian waters of the Bering and Chukchi seas and to develop recommendations to ensure their rational use. Methods used: to achieve this goal, data on commercial biomass, catch and development of marine fish and invertebrates for the period from 1997 to 2022 were analyzed. Recommendations for increasing the efficiency of using the raw material base of aquatic organisms are formed on the basis of our own and other studies, as well as an analysis of existing fisheries and measures to regulate them. Novelty: elements are modern materials on biomass, catch and development of marine fish and invertebrate resources in the Bering and Chukchi seas within the areas of Russian jurisdiction. Commercial stocks of aquatic biological resources in the western part of the Bering Sea averaged 5087 thousand tons, of which 4933 thousand tons (97%) were fish. In the Chukchi Sea, the biomass of hydrobionts is 26 times less than in the Bering Sea: on average 197 thousand tons (189 thousand tons of fish). In the Bering Sea, fishing has been carried out for more than 100 years and at the present stage is based on 14 species or groups of fish species and 10 invertebrate objects. In the Chukchi Sea, fishing, the basis of which is exclusively walleye pollock, is carried out only in 2021-2024. Practical significance: the results of the study can be used in forecasting the dynamics of aquatic biological resources and conducting their fishery. The priority directions for increasing the efficiency of using the raw material base of aquatic organisms are also highlighted: clarification of reserves, increasing the efficiency of existing fisheries, improving the regulatory framework for fishing. Within the framework of these areas, specific measures are recommended to maintain catches of fish and invertebrates at the highest possible level for a long period of time during the exploitation of their stocks without the risk of causing irreparable damage to them.

The aim: assessment of the current state and long-term dynamics of the populations of anadromous and semi-anadromous fish of the Sea of Azov, the efficiency of their reproduction and forecast of the formation of their commercial stocks in the medium term in changing hydrological conditions.

Methods: the work is based on the results of complex and accounting expeditions of the Azov-Black Sea branch of the State Scientific Center of the Russian Federation FGBNU «VNIRO» («AzNIIRKH»), stock data for the period from 1923 to 2023, fishing statistics materials. When considering possible scenarios for the formation of commercial stocks of anadromous and semi-anadromous fish species in the Sea of Azov for the period up to 2030, data on the actual dynamics and trends of changes in their populations in analogous periods were used. Data on the ecological valence of various species fish at different stages of ontogenesis in relation to salinity were also analyzed.

Novelty: the article presents long-term materials on the state of stocks and catches of anadromous and semi-anadromous fish species of the Sea of Azov in changing environmental conditions. Three possible scenarios for the formation of commercial stocks of anadromous and semi-anadromous fish species in the Sea of Azov in the medium term under conditions of a changing hydrological regime are presented.

Results: an analysis of the long-term dynamics of populations, stocks and catches of anadromous and semi-anadromous fish species of the Azov Sea in changing environmental conditions was performed. Possible scenarios for the development of the hydrological regime of the Azov Sea and the formation of commercial stocks of anadromous and semi-anadromous fish species for the period up to 2030 are shown.

Practical significance: the forecast of the formation of stocks and possible catches of anadromous and semi-anadromous fish species in the Sea of Azov at different salinity levels in the medium term is presented.

The purpose of the review is to summarize current information about viral, bacterial and parasitic fish diseases, for which molecular markers are currently being investigated for resistance. The advantages of conducting experimental studies on individuals included in genome-wide associative studies in combination with a comparative analysis of immune genes expression in affected fish, affected asymptomatic and control fish that do not exposed to the pathogen.

Methods used: comparative analysis of modern literature data, deconstruction method: careful selecting studies that reflect the main points of the data on the immune response of fish studied to date. The review results in structured data on studies of the immune response of fish to various pathogens.

Importance: aquaculture is facing an increasing number of pathogenic microorganisms affecting cultivated fish from year to year. The fishing industry needs more efficient and faster breeding methods. Traditional breeding approaches aimed at increasing the natural resistance of fish to diseases require decades, which is associated with a long time to reach sexual maturity of fish. The use of genome-wide association studies (GWAS), as well as the registration of markers such as microsatellites and single nucleotide polymorphisms (SNPs), allows for selection using marker methods. Research shows that these technical approaches can identify quantitative trait loci (QTL) and identify individuals with high natural resistance to diseases. Comparative analysis of SNPs in surviving and dead fish makes it possible to detect specific genetic markers associated with resistance and accurately determine their location in the genome. The data obtained are the basis for the selection of parental genotyped individuals for breeding generations of fish with increased resistance in a relatively short time.

Aim of this work is to investigate the variability of the hydrometeorological conditions in Kerch Bay in 2007- 2024.

Methods used: the methodology of this study involves plotting and analyzing the graphs for the long-term variability of the average monthly values of the hydrometeorological parameters for 2007-2024 based on the data collected over the course of weekly monitoring conducted from April 2017 to April 2024.

Novelty: for the first time, the variability of the environmental conditions in this region has been investigated for 17-year time range, including the most recent years.

Results: the analysis of the long-term (2007-2024) variability of the average monthly near-ground air and water surface temperature, upper water layer salinity, near-ground wind speed and direction, wave action, and water transparency in Kerch Bay has been conducted. The prevalence of positive anomalies of air and water temperature involving the increased number of hot summer days and reduction in the number of winter sub-zero cold days as compared to the preceding 50-year time range has been identified. Considerable increase in the salinity is recorded for 2007-2014, which is followed by the lowering rates of its increase and stabilization of its values after 2017, mainly due to the water advection via the Kerch Strait and the wind regime in this area. The long-term variability of the average monthly wave heights has been categorized into three time ranges: 2017-2019 characterized by medium values, 2020-2022 characterized by decreased values, and 2023-2024 characterized by increased values. It is shown that the lowest water transparency in the bay (≤1.0 m) is recorded mainly in February–March under variable winds; the highest one (>3.0 m) is observed from April to December (since July 2021) in the context of the northerly winds and the lowest average wind speed. Practical significance: results obtained and discussed in this article can be vital for the assessment of the ecosystem variability in Kerch Bay as a region heavily involved into industrial and fishing activity.

This study aims to obtain new data on the content of total mercury (Hg) and organic matter (OM) in bottom sediments (BS) of the Barents and Kara Seas, as well as an assessment of the relationship of these parameters.

The material for this study: The research material was samples of BS selected during the expedition of the scientific research vessel Akademik Nikolay Strakhov from June 25 to July 28, 2019 in the Barents and Kara Seas when performing the tasks of studying BS and assessing the anthropogenic impact on ecosystems.

Novelty: The paper presents new original materials on the study of the content of total Hg and OM in BS of the Barents and Kara Seas, as well as an assessment of the relationship of these parameters for marine soils of these Arctic waters.

Methods used: the total mercury content in the samples was estimated by the method of flame-free atomic absorption on the mercury analyzer RA-915M (Russia). The determination of the relative content of organic matter was performed in accordance with Russian standard (GOST 23740-2016) by the gravimetric calcination method to a constant mass (“Loss on Ignition”). Statistical data processing and charting were carried out in the MS Excel 2016 environment and the Statistica 13.

Results: The results of a study of the content of total Hg and OM in the BS of the Barents and the Kara Seas are presented. In the BS of the Barents Sea, the Hg content varied from 13.95 to 50,15 μg/kg with an average value of 29.5 μg/kg of dry sediment, and in the BS of the Kara Sea – from 17.25 to 52.79 μg/kg with an average value of 37.5 μg/kg. The OM in the BS of both seas turned out to be approximately the same and amounted 2.4-2.6%. For the Barents Sea, a correlation has been established between the content of Hg and OM. The increased total Hg content in the BS of the Kara Sea probably reflects the contribution of the regional component.

Practical relevance: The results obtained will make it possible to better understand the processes associated with global mercury pollution of ecosystems in the Arctic.

The aim of the work is to prove the possibility of using software for calculating the hydrodynamic characteristics of trawl doors. The methods used: computer and physical modeling of the hydrodynamic characteristics of trawl doors makes it possible to set the correct angle of attack of the trawl for more successful catch. The search for optimal settings of trawl doors is possible using the computer program “Hydrodynamics of trawl doors”, which was developed on the basis of many studies of dynamic characteristics. Such characteristics include: current speed, depth, angle of attack, angle of heel and trim, maximum value of the spreading force coefficient cy, minimum value of the trawl door resistance coefficient cx, maximum value of the hydrodynamic quality k. Novelty: based on the results of physical and mathematical experiments, an analysis was carried out and a technique was developed that allows calculating the setting of trawl doors on a vessel without resorting to physical experiments on the water. Result: the developed methodology can allow harvesting technicians to correctly adjust the angle of attack of the trawl door on the vessel for the correct horizontal opening of the trawl, without resorting to testing on the water. Practical significance: based on the developed calculation methodology, mining technology specialists can adjust the angle of attack of trawl doors to achieve high fishing efficiency directly on the vessel, avoiding the need to conduct experiments on the water. Using specialized software, they can simulate various parameters such as the angle of inclination and dimensions of the trawl door, as well as environmental conditions. This will allow them to accurately predict the behavior of the board and optimize its settings, which ultimately contributes to an increase in catch and minimizes costs and work.

The purpose of the work is to evaluate the biological status of the main commercial crab species in the northwestern part of the Sea of Okhotsk based on the results of direct accounting. Materials and methods. From 13.08 to 10.10. 2024, data was collected in the range of 11-104 m. Lithodidae crabs (the red king crab Paralithodes camtschaticus, the blue king crab P. platypus and the brown king crab P. brevipes) and crabs Majoidea (the snow crab Chionoecetes opilio) were studied. Sampler – cone traps. The database was created and processed using standard methods of fisheries research. The parameters describing their biological state in the summer and autumn period are given for crabs. Commercial and statistical information on functional groups is given to mass species. Results. In the North Okhotsk subzone, there is an increase in the commercial biomass of P. camtschaticus due to an increase in the number of older size and age groups of postrecruits and the spatial expansion of this group northward from the Ayano-Shantarsky district. In the population P. platypus currently has a significant increase in the number of all functional groups in areas located west of 147°Е. The crab P. brevipes was not common during the research period and only west of 147°Е. The crab C. opilio is in satisfactory condition in the research area, which is typical for this water area, the crab was represented by a stunted group west of 147°Е. and the usual group to the east. Practical significance. The results of the trap survey will be taken into account in the prognostic materials for establishing the total allowable catches for P. camtschaticus, P. platypus, P. brevipes and C. opilio in the Northern part of the Sea of Okhotsk.

The aim: assessment of the current biological status and distribution of Siberian sturgeon in the Vilyui River.

Material: data from a survey using bottom drift and fixed nets in June 2024.

Results: on the 470-kilometer section of the lower reaches of the Vilyui River, sturgeon were distributed unevenly: the average density was 197 specimens/km2, the highest density of 1307 specimens/km2 was reached in the middle part of the section, significantly thinning out to 7-28 specimens/km2 upstream and to 116 specimens/km2 downstream. In the area adjacent to the river mouth, sturgeon was not recorded in the catches due to a sharp rise in the flood level. In the sample series from the catch of drift bottom gillnets, the value of the commercial length of sturgeon (ac) varied from 36.0 to 60.0 cm, with an average of 47.6 cm. In the sample series of set gillnets, these values were 40.0-65.0 and 52.3 cm, respectively. The modal size class for Siberian sturgeon in the catch of 2024 was 41-50 cm (59% of the total catch). The average weight of an individual was 0.6 kg. There was not any individuals that had reached the size at which fishing is permitted (> 62 cm) in drift bottom gillnets; while the proportion of commercial individuals was 7% in set gillnets. Sexually mature individuals were not noted.

Practical value: results will be used to assess the size and weight composition of part of the Siberian sturgeon population feeding in the middle reaches of the Lena River.

The purpose of the work: to monitor aquatic bioresources, obtain biostatic data, determine the age composition of catches, determine the parasitic infestation of fish and hematological parameters.

Methods used: During longline fishing, fishing information was collected, ichthyological and ichthyopathological work (hematological and partial helminthological analysis of fish) was carried out using generally accepted methods.

Novelty: commercial, biological, and ichthyopathological data were obtained on the state of the commercial population of Pacific cod in the western Bering Sea in the autumn of 2024.

Results: Average daily catches varied from 1161 kg to 10255 kg (average 3998 kg). The size of cod catches in one order varied from 99 kg to 4600 kg (average 822 kg). The size composition of Pacific cod in the West Bering Sea zone was within 39-102 cm (average 54.3 cm). The share of non-commercial size fish (less than 40 cm) was 0.6%. The age range is represented by individuals from 2 to 7 years. The modal group consisted of individuals 3 and 4 years old with a length of 40 to 70 cm. As a result of parasitological research, a low degree of invasion of the muscles and liver of cod by larvae of nematodes Anisakis sp. and Pseudoterranova decipiens was established. Hematological parameters were determined; in isolated cases, erythrocyte pathologies were noted (less than 1%).

Practical significance: the results of the work can be used in the development and adjustment of materials for forecasting the total allowable and recommended catch and recommendations for effective fishing.

The aim: quantitative account and collect material on the qualitative characteristics of commercial fish species and monitor the habitat of aquatic biological resources of the Sea of Azov in the autumn period of 2024.

Methods: during the execution of trawl survey, the collection and primary processing of materials were carried out in accordance with generally accepted methods.

Innovations: materials on the biological state of fish, qualitative and quantitative composition of aggregations have been collected, identified patterns in the spatial and seasonal distribution of the main commercial fish species of the Sea of Azov.

Results: the average water temperature in the Sea of Azov was 10,8 °C, in the Taganrog Bay – 6,5 °C. The average weighting salt’s concentration of the Sea of Azov was 15,22‰, and that of the Taganrog Bay was 11,67‰. The first place in catches was occupied by the Black and Caspian Sea sprat (26,3%), the second by the European anchovy (25,4%), and the third by the Danube sturgeon (20,3%). Black and Caspian Sea sprat and European anchovy were concentrated mainly in the central part of the Sea of Azov and the Taganrog Bay, with the largest catches amounting to 100 and 55 kg/hour of trawling. Concentration of Danube sturgeon was observed in the western part of the sea off the coast of Crimea and in the northern part of the sea in the area of Byriuchyi Island. The largest catch was 102 kg/hour of trawling. Concentration of Black Sea turbot were mainly recorded in the northwestern and central parts of the Sea of Azov, with the largest catch being 16 kg/ hour of trawling. The Pontic shad was mainly found in the northwestern, southwestern, and central parts of the Sea of Azov and in the pre-strait, with a maximum catch of 6 kg/hour of trawling.

The practical significance: the results of the work will be used to refine and develop forecasts of the recommended volume of extraction (catch) of aquatic biological resources and recommendations for effective fishing.