Main Spawning Research Articles

Vertical distribution of Pacific oyster Crassostrea gigas larvae and modeling larval transport in Hiroshima Bay, Japan

Understanding vertical distribution of planktonic larvae is essential for elucidating larval dispersal and recruitment processes. We investigated the vertical distribution and horizontal transport of Pacific oyster Crassostrea gigas larvae by field observations and numerical simulations during their main spawning season in Hiroshima Bay, Japan. In field observations, despite horizontal differences and slight diurnal/semi-diurnal changes depending on larval sizes, most larvae were distributed in the upper 3 m layer. The relationship between C. gigas larvae and environmental conditions revealed that larval density increased with increasing temperature and chlorophyll a concentration, and the density peaked at salinity of approximately 20 for all larval sizes. The observed results suggest that the distribution characteristics of C. gigas larvae are suitable for survival in an estuarine area, where environmental conditions are potentially favorable but hydrodynamic conditions can drastically change over the short term due to variations in river discharge. To examine the effect of high river discharge on larval transport, numerical simulations were conducted using a particle-tracking model incorporating the vertical motion of C. gigas larvae. The simulation results reproduced the spatio-temporal dynamics of planktonic and settled larvae after the high river discharge. Although most particles simulating larvae outflowed from the main spawning area, an area of high particle density at the end of simulation corresponded with the offshore area for seedling collection. The present study suggests the role of vertical distribution of C. gigas larvae for recruitment, and the prospect of sustainability in oyster aquaculture with respect to seedling collection despite the frequent heavy rainfall associated with climate change.

Influence of temperature on hatching success of skipjack tuna (Katsuwonus pelamis): Implications for spawning availability of warm habitats.

Exploring the effects of water temperature on egg development in skipjack tuna (Katsuwonus pelamis) has substantial implications for evaluations of wild spawning habitats. In the present study, we examined the hatching success and duration as a function of temperature from 21 to 33°C under captive environments. A high hatching rate of over 50% between 23 and 31°C was observed, with the shortest hatching duration at 31°C. Because the egg period is vulnerable to predators, a shortened hatching duration with warming water would be ecologically advantageous for K. pelamis, as its main spawning grounds are located in tropical areas.

Effect of river discharge on spawning grounds around the Yellow River Estuary

The Yellow River discharge is unevenly distributed on a time scale, and the river discharge into the sea reached its peak in the past 20 years in 2021. River discharge has a great impact on the temperature and salinity distribution and fish spawning grounds around the Yellow River estuary and Laizhou Bay. This paper analyzes the variation trend of the Yellow River discharge in the past 20 years, and simulates the temperature and salinity distribution around the Yellow River estuary from 2020 to 2022 through a numerical model. The effects of river discharge on the distribution of ocean temperature, salinity and spawning grounds were studied. According to the temperature and salinity of the sampling location, the temperature of main spawning grounds is about 16 ℃, and the salinity range is 30 to 30.5 psu (practical salinity scale). Key spawning grounds are more distributed in the peripheral areas where the Yellow River water is mixed and has less impact. Meanwhile, the key spawning grounds are far away from the main axis of the freshwater diffusion. The key spawning grounds will change with the Yellow River discharge diffusion structure, and moved westward in 2022.

Generation abundance dynamics of peled at the lower reaches of the Ob’ River in 1981–2021

The generation abundance of peled has been assessed at the lower reaches of the Ob’ River. Based on data on the number of larvae migrated downstream from spawning grounds, obtained in 1981–2021 on the main spawning rivers, current population structure of peled at the lower reaches of the Ob’ River is described, the influence of anthropogenic factors and of the water content of the Ob’ River floodplain on peled reproduction is analyzed. The Severnaya Sos’va River definitely plays a decisive role in the reproduction of peled. In recent years, there has been an increase in the contribution of the Voikar and Sob’ rivers. Seven-year cycles have been identified (between the peaks in the larvae number); their maximums coincide with the peaks of water content at the lower reaches of the Ob’ River with a 1-year lag, which supports the world’s largest river peled population abundance. The presence of such cycles makes it possible to predict phases of high fish abundance. An equation describing the dependence of the generation size of peled at the lower reaches of the Ob’ River on the average water level of Ob’ River in June–August at the Salekhard gauging level in the previous year is proposed.

Will most suitable spawning grounds for coastal fishes be impacted by climate change? A larval drift modelling approach

For many fishes, their early life stages are transported (passively) by currents between spawning areas and coastal nurseries, but also potential dispersal towards new habitats. Therefore, species have developed strategies to enhance the recruitment success, including the selection of appropriate spawning grounds. However, increased temperature due to climate change may lead to changes in hydrodynamics, shorter larval drifts, and earlier spawning, and consequently the location of the most suitable spawning grounds may change. We investigated whether the location of the most favourable spawning areas (allowing higher rates of larvae reaching coastal nurseries) was stable over time, and if differences could be found between environmentally contrasted years. We used a larval drift model taking into account hydrodynamics, larval characteristics and behaviour for three commercially exploited fish species (sole Solea solea, flounder Platichthys flesus and seabass Dicentrarchus labrax) in the Western Europe (encompassing the Bay of Biscay, the Celtic Sea and the English Channel). According to our model, we conclude that despite contrasting environmental conditions, the location of spawning grounds allowing the best chance of recruitment to nurseries for the offspring was fairly similar. However, even if the location of the main spawning grounds is stable over time, their relative effectiveness varies greatly between years. This would suggest that natural selection may favour the emergence of homing behaviour. This stability in this fish essential habitat location could facilitate protection measures. Going further, it could be interesting to study the variations occurring in spawning grounds (in terms of recruitment success, and retention/dispersion) during the course of a spawning season.

Revisiting the spawning fraction of Pacific bluefin tuna (Thunnus orientalis) caught in the Sea of Japan based on diurnal changes in spawning markers

The spawning fraction (SF) is an important reproductive trait used to assess the reproductive potential of indeterminate spawning fishes. To estimate the SF more accurately, the durations of spawning markers in ovaries need to be determined. The SF of the Pacific bluefin tuna Thunnus orientalis (PBF) in the Sea of Japan (SOJ) is higher than the SFs in its other main spawning grounds. The present study aimed to revisit the SF of the PBF in the SOJ by focusing on diurnal changes in spawning markers and estimating the duration of spawning markers in PBF ovaries. According to diurnal changes in the postovulatory follicle (POF) degeneration process and final maturation process of oocytes, POFs were observed in ovaries up to 38.5 h after ovulation. The revisited total SF throughout the spawning season was 0.34–0.43 in Area 1 and 0.50–0.64 in Area 2; these values are smaller than the SF previously estimated in the SOJ. The estimated SF of the PBF in the present study was equal to or slightly higher than that in the water between the Nansei Islands, Japan, and the northeast of the Philippines and higher than that in the Kuroshio-Oyashio transition area.

New Record of Geoduck Clam Collected from the East Coast of South Korea and Its Reproductive Characteristics

Geoduck clams are important commercial marine resources in Southeast Asia. However, the complete mitochondrial genome of the native geoduck clam in South Korea has not been reported yet. This study reports a geoduck clam collected from the east coast of South Korea. Based on its morphological characteristics and molecular data, the geoduck clam was identified as Panopea sp. belonging to the bivalve family Hiatellidae. We determined the complete mitochondrial genome of this species and investigated the seasonal reproductive pattern for monthly changes in sex ratio, gametogenesis, and reproductive cycle from September 2019 to August 2020. The total length of the complete mitochondrial genome sequence is 16,006 bp, containing 13 protein-coding, 22 transfer RNA, 2 ribosomal RNA, and a control region (D-loop). A molecular phylogenetic comparison with 10 bivalve species showed that the geoduck clam specimen belongs to the family Hiatellidae, clustering with Panopea abrupta Chinese strain, P. generosa, and P. globosa. The gametogenesis of the geoduck clam was identified in six stages by histological analysis. The sex ratio was biased towards males from May 2019 to July 2019, the main spawning activity from the frequency of the gonads with ripe and spent stages occurred from October 2018 to April 2019, and there was no clear pattern of spawning peaks from May to August 2019 with gonads developed asynchronously between both sexes. This is the first study to report new records of the genus Panopea based on the complete mitochondrial genome and to examine the seasonal reproductive pattern of the native geoduck clam Panopea sp. in South Korea, providing valuable information for its sustainable management in South Korea.

Influence of the Volga-Kama cascade of reservoirs on the hydrological regime during the flood and the quality of the spawning cycle of fish in the Lower Volga

The Volga-Caspian fishing subarea is the most important inland fishery reservoir in Russia. For centuries, this region has been distinguished by the high productivity of mass commercial fish species. The main spawning of semi-anadromous (bream, roach, carp, zander, etc.) and river fish of the indicated subregion takes place in the lower zone of the Volga-Akhtuba floodplain, as well as in the central delta. The creation of the Volga-Kama cascade of hydroelectric power stations in the Volga basin has reduced the annual Volga runoff and a profound deformation of all its hydrological characteristics, which is especially evident during the flood period. The paper presents a detailed analysis of the influence of the Volga-Kama cascade of reservoirs on the hydrological regime during the flooding period and the quality of the spawning cycle of fish in the Lower Volga.

Modern assessment of the state of the fish fauna in the northern part of Agrakhanskaya bay, river Dagestan

The northern part of the Agrakhan Bay is of great fishery importance for the Tersko-Caspian region of the Dagestan, there are the main spawning grounds foralmost all types of fish, including valuable passing and semi-passing (roach, bream, carp, pike perch) as well as freshwater (perch, pike, catfish, rudd, silver crucian, gustera and perch). Studies were conducted to assess the qualitative structure of populations of commercial fish species in 2021, age and morpho-biological indicators were studied, as well as the sex ratio of semi-migratory fish species (for example, roach and walleye) and freshwater (perch and rudd). The results obtained indicate that all aquatic fish were in satisfactory condition, and semi-aquatic (roach, bream, carp and pike perch) — to a lesser extent met the required qualities. Younger age groups (3–5 years old) dominated in the structure of semi-passable fish — roach and walleye, which accounted for over 50%, males dominated in younger age groups, unlike older (6–8 years old), the proportion of females was over 80%. According to morpho-biological parameters, the roach and pike perch were superior to the Volga fish of the same species, and in terms of fatness by almost 2.5 times. Freshwater fish (perch, rudd) were represented by five age categories, of which 3–4-year-olds accounted for over 60%. In the qualitative structure of the perch of 2021, the indicators of length, weight and fatness were worse than the individuals caught in 2020. Morphometric indicators of the rudd had no significant discrepancies with the data of the previous year, which once again confirms the absence of the influence of the hydrological regime on the number and biological indicators of this little whimsical fish species.

Антропогенное воздействие на популяции атлантического лосося (Salmo salar) в Арктическом бассейне Российской Федерации

The global problems of anthropogenic impact on the planet Earth and marine ecosystems, pollution in the 21st century of the World Ocean, including the Arctic seas, negatively affecting the reproduction of marine biological resources are considered. For more than half a century, the intensively developing exploitation of the bioresources of the World Ocean shelf has led to a de-crease in the number of mammals, fish, mollusks, crustaceans, algae and other valuable aquatic organisms. In many developed countries, due to economic activity and industrial pollution of coastal territories, there is a depression in the number and a de-crease in intraspecific diversity, due to the loss of populations of passing marine "wild" Atlantic salmon and other aquatic organ-isms. Since the late 1980s, natural Atlantic salmon stocks have declined significantly. In the main spawning rivers of the Mur-mansk region, the content of pollutants in the spring is marked on the scale as high and extremely high levels of pollution. The oxygen content and water quality in rivers decrease, the number of saprophytic bacteria increases, the species diversity of zoo-plankton and phytoplankton decreases. Diseases and death of populations of spawning Atlantic salmon occur. A program has been developed to comprehensively investigate the causes of mass disease and death of Atlantic salmon populations, and to de-velop measures to restore a genetically healthy salmon population in the Arctic region of Russia.

Straightforward upriver migration to spawning sites by chum salmon Oncorhynchus keta homing to coastal short rivers in the Sanriku region.

In chum salmon (Oncorhynchus keta) homed to the Sanriku region, Japan, most of the fish are matured in bays and spawn near river mouths in coastal short rivers; therefore, their upriver migration is extremely short, but their behavioural characteristics have remained unknown. Upriver migration in the Otsuchi River, a typical coastal river, was evaluated from behavioural and physiological aspects. Homing salmon tracked in Otsuchi Bay held in the inner bay for less than 1 day to more than 10 days before river entry. The varied holding duration was negatively correlated with plasma 17α, 20β-dihydroxy-4-pregnen-3-one (DHP) concentration, an indicator of maturation. After river entry, however, most fish were captured in weirs near the river mouths within 2 days regardless of the DHP concentration. Of the 34 fish released in the river, on the contrary, eighteen and five fish were seen next day in the main spawning sites located at c. 1.5 km upstream and in the branch creek, respectively, and 85% of the fish held position there until their death. The mean survival time of released fish was 5.8 days. Plasma DHP level suggested that preparations for spawning were already completed at the timing of the release. Taken together, homing salmon completed spawning preparation in the bay, and then they moved to their spawning sites immediately after river entry and spawned there during their short remaining life. This upriver migration contrasts with those of other populations, such as early migrants and long river migrants, whose maturation is completed during upriver migration.

Effects of age composition of Pacific bluefin tuna on their spatiotemporal distribution of active breeding in the south-western North Pacific and on its recruitment strength

Context The south-western North Pacific is one of the main spawning grounds of the Pacific bluefin tuna (Thunnus orientalis) and is targeted by Japanese longline fisheries. Aims This study evaluated the influence of age composition of spawning groups in this area on the strength of recruitment through the spatiotemporal distribution of active breeding. Methods The variation in the recent year-class strength in the area was estimated on the basis of the otolith age estimation and catch data from 2007 to 2016. Key results In the age–frequency distribution, 9 years was the most frequent age class. The instantaneous total mortality after 9 years of age was 0.32. Conclusions On the basis of catch locations and age estimation results, the bias toward young individuals influenced the spatiotemporal pattern of active breeding to shifts to higher latitudes and earlier breeding. In this area, the abundance of the main spawning group (9- and 10-year-old fish) may affect the recruitment of 0-year-old fish, and the older fish are considered to serve as a ‘seed bank’. Implications These results are expected to contribute to the development of appropriate management strategies for spawning stocks in the area and demonstrate the magnitude of the influence of age composition on population fluctuations.

Northeast Arctic Cod and Prey Match-Mismatch in a High-Latitude Spring-Bloom System

By combining an ocean model, a nutrient-phytoplankton-zooplankton-detritus-model and an individual-based model for early life stages of Northeast Arctic cod we systematically investigate food limitations and growth performance for individual cod larvae drifting along the Norwegian coast from spawning grounds toward nursery areas in the Barents Sea. We hypothesize that there is food shortage for larvae spawned early and late in the 2-monthlong spawning period, and to a larger degree to the north and south of the main spawning grounds in the Lofoten. Model results for three contrasting years (1995, 2001, and 2002) show that spawning early in the season at spawning grounds in the Lofoten and farther north is favorable for larval growth close to their size- and temperature-dependent potential. Still, both early and late spawned larvae experience slower growth than individuals originating closer to the time of peak spawning late March/early April. The reasons are low temperatures and shortage in suitable prey, respectively, and this occurs more frequent in areas of strong currents about 1–2 months post hatching. In particular, late spawned larvae grow relatively slow despite higher temperatures later in the season because they are outgrown by their preferred prey.

Diet and feeding behaviour of albacore Thunnus alalunga in the western Mediterranean Sea during the spawning period.

Mature albacore tuna (Thunnus alalunga) are expected to have high energy requirements at the time of breeding. However, there are no descriptions of the diet of albacore in the Mediterranean Sea that can help us to understand if such requirements can be obtained from feeding during reproduction. In this study, we analysed the stomach contents of reproductively active albacore captured from 2010 to 2015 in the oligotrophic waters of the western Mediterranean Sea, one of their main spawning grounds. Estimates of stomach fullness revealed intense feeding activity, and prey composition indicated important consumption of mesopelagic fish, including barracudinas, myctophids and small pelagic crustaceans. Plastic debris occurred in 25%-53% of the stomachs sampled across all years. Prey composition was not different between males and females. However, females fed at higher rates and had higher hepatosomatic index values than males, suggesting that increased feeding could contribute to meet their higher energy demand associated with offspring production. We observed a diet shift from small crustaceans to fish prey along fish size. During the spawning period, albacore showed a specialist feeding behaviour by preying on aggregations of vertically migrating myctophids and small crustaceans, probably when they were near the surface. This study provides information and biological data to support ecosystem modelling and to increase the understanding of albacore ecology.

Distribution, Feeding Habits, and Growth of Chub Mackerel, Scomber japonicus, Larvae During a High-Stock Period in the Northern Satsunan Area, Southern Japan

To evaluate the importance of the northern Satsunan area in southern Japan as a spawning and nursery ground for chub mackerel (Scomber japonicus), we investigated the early life history characteristics (e.g., larval distribution, feeding habits, and growth) ofS. japonicusover five successive years. This area is considered the main habitat and spawning ground of the congeneric species,S. australasicus. Using polymerase chain reaction-restriction fragment length polymorphism analysis, we first confirmed thatS. japonicuslarvae were abundant in the northern Satsunan area, potentially representing a major spawning and nursery ground in the Japanese Pacific coastal area. The number of recorded larvae started to increase in 2016, corresponding to the population dynamics of the Pacific stock of the species, which has shown increasing trends in recent years. Morphological and DNA metabarcoding analyses of gut contents and stable isotope analysis showed that, in addition to copepods, the larvae fed substantially on appendicularians. The trophic pathway involving appendicularians might support the feeding habits ofS. japonicus, promoting its coexistence with other dominant species. Both the instantaneous growth rate and daily specific growth rate were comparable to those in the southern East China Sea, which is the main spawning and nursery ground of the species. Our data strongly suggest that the northern Satsunan area has favorable conditions for sustaining high larval population densities, even during phases with high population numbers. Our results provide insights for the fisheries management forS. japonicusin the Japanese Pacific coastal area, especially during high-stock periods.

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.

Oyster farms are the main spawning grounds of the black sea bream Acanthopagrus schlegelii in Hiroshima Bay, Japan.

Understanding the anthropogenic impact of oyster farms is essential for the management and conservation of marine fishes. In Japan, Hiroshima Bay is the region with the most intense oyster farming and thus suitable to study the impact of these farms. Here, we surveyed spherical planktonic eggs of the black sea bream Acanthopagrus schlegelii, one of the most abundant fish in the Bay. Our survey was performed at fourteen stations which included places with oyster farms and historical spawning grounds. We found the highest egg densities in four stations, one with historical spawning aggregations and three with major oyster farms. Besides, surveys at the innermost part of Hiroshima Bay, where two major rivers discharge, showed a low density of eggs indicating that black sea bream avoids spawning in low salinity areas. Our study suggests that oyster farms benefit spawners of black sea bream by providing more food sources than historical spawning grounds for efficient spawning. Yet, whether oyster farms represent a full advantage for the species remains unclear, particularly because they are known to host jellyfishes that prey on eggs and limit water flow that can influence the survival of fish eggs.

Estimation of the spawning ground of some fish species in the Nha Trang bay

The paper presents the results of determining the spawning grounds of some fish species in Nha Trang bay MPA, which were sampled in 9/2018, 11/2018, 5/2019 and 7/2019. The analysis results are based on the distribution of the general density and the developmental stages, analysis of decision trees from egg density, location of stations and months by CHAID (Chi-square Automatic Interaction Detector), allowing a relatively accurate estimate of the spawning ground of the red anchovy (Encrasicholina punctifer Fowler, 1938) and the species of the genus Scarus. As a result, the main spawning grounds for red anchovy were the east of Hon Rua and the northeast of Hon Tam and that of Scarus is the southwest of Hon Mun island.

Spatiotemporal Changes of the Environmental DNA Concentrations of Amphidromous Fish Plecoglossus altivelis altivelis in the Spawning Grounds in the Takatsu River, Western Japan

The Ayu Plecoglossus altivelis altivelis is an amphidromous fish that is not only the most important commercial fishery species in Japanese rivers but also has a high economic value in recreational fishing. However, the degradation of its spawning grounds has caused a decrease in its abundance. In this study, we used environmental DNA (eDNA) to monitor the Ayu in the Takatsu River in Japan to (1) identify the spawning season in three known spawning grounds, (2) clarify changes in the main spawning grounds during the spawning season, and (3) discover unknown spawning grounds. We collected 1 L of the surface river water at three known spawning grounds nine times in 2018 and seven times in 2019 in the lower reaches of the Takatsu River. We also collected samples from seven unknown sites in 2018. The water samples were filtered through glass fiber filters. Total eDNA was extracted from each filtered sample and a Real-time quantitative PCR was performed with the specific primers and probe for Ayu. The results of the eDNA analyses showed that (1) the spawning season was in November in 2018 and in September in 2019. (2) One site was used as a spawning ground in both the early and the late spawning season, depending on the year. At the second site, the frequency of use changed year by year. The third site was the main spawning ground in the middle to late spawning season every year. From these results, we elucidated that some spawning grounds are used regularly every year, while the use of others varies year by year. (3) In five of the seven unknown sites, the nighttime eDNA concentrations were high at least once during the four surveys, suggesting that these sites may have functioned as spawning grounds. In particular, one site could be an important new spawning ground.

The Status of the Stock and the Current Fishery for the Atka Mackerel, Pleurogrammus monopterygius (Pallas, 1810), in the Olyutorsky–Navarin Area, Bering Sea

The dynamics of the Atka mackerel stock in the Olyutorsky–Navarin area in 1994–2019 is inferred from bottom-trawl surveys, fishery statistics, open-access NOAA data, and the results of simulation by the method of virtual population analysis. After the period of low stock in the mid-1990s, the abundance of the Atka mackerel group in the area increased sharply to a maximum in 2006–2008, when the spawning biomass was estimated at approximately 9500 t and the fishery biomass at 14 000 t. In 2008, the stock showed a tendency to decrease; by 2013, the spawning stock decreased to 3600 t and the fishery stock to 5600 t; subsequently, there was a period of stabilization at a low level with a slight tendency to further reduction. One of the possible causes of the sharp increase in the Atka mackerel stock in the 2000s could be the increased transport of juveniles of strong year-classes from the main spawning grounds off the Aleutian Islands with their subsequent settlement on available parts of the shelf off Cape Olyutorsky. The development of the Atka mackerel fishery in the Olyutorsky–Navarin area in 1994–2019 had a pattern similar in general to the stock dynamics. Until 1995, no more than an average of 100 t were caught per year; in 2006–2010, the average annual catch increased to 790 t; in 2011–2015, it increased to 1150 t; and in 2016–2019, the catch again decreased to 950 t. Due to the emerging trend of a general reduction in the stock of the Aleutian population, this low level of catches in the Olyutorsky–Navarin area is expected to continue in the coming years.