P. A. Dulenina’s research while affiliated with Pacific Research Fisheries Center and other places

The purpose of the work is to describe the changes of resources of commercial invertebrates in Russia and to analyze its use over the mentioned period. The research methods consisted in summarizing information on the state of the resources of commercial invertebrates in the seas of Russia and analyzing of the data of fishing statistics for 2000–2020. Results of the study are a description of the changes that have occurred with the main stocks of commercial invertebrates in the seas of Russia and the features of fishery, with an assessment of the current state of stocks. Discussion. The number of stocks for fishery prediction increased during the first two decades of the XXI century due to finding of new commercial fishery subjects. At the same time, a number of invertebrate stock units have lost their commercial significance over the past two decades of the XXI century. Сhanges in the structure of the resources and fishery of commercial invertebrates happened. The structure of invertebrates resources of the Far Eastern Fisheries basin proved to be the most conservative, while the importance of new fishing subjects significantly increased in the Northern and Azov-Black Sea fisheries basins. The novelty of the work lies in the analysis of the state invertebrates resources in the seas of Russia and their fishery in 2000–2020. Conclusion . In general, the fishery resources of invertebrates in the Russian Seas were fairly stable during 2000 to 2020, and ensured an increase in catch due to more full use.

The data of trap surveys and observations aboard fishing vessels conducted in the northwestern Tatar Strait (northward from Cape Zolotoy) in 2009–2022 are analyzed. Horsehair crabs dwell along the entire continental coast from Cape Zolotoy in the south to Cape Nakatov in the north, but commercial aggregations with the density on average 232 ind./km ² are concentrated in the southern part of this area (south of 49 о N). Seasonal bathymetric migrations of the crab include the fall moving of commercial males from the depths of 10–40 m to the depths of 40–60 m for wintering and their return to shallows in spring. Two dense wintering aggregations are formed usually between Cape Peschany – Cape Mapatsa and southward from 48 о 00′ N, whereas sparse summer aggregations are widely distributed along the coast. Regardless the season, the aggregations density decreases from south to north. The males are generally larger in the southern aggregations than in the northern ones (on average, 100.3 and 89.8 mm of carapace width, respectively), the difference is statistically significant (p < 0.0001). The stock of horsehair crab in the northwestern Tatar Strait has increased in the last 20 years from136 tons in 2003 to 1580 tons in 2022. Over the past 10 years, the optimal allowable catch in the Primorye subzone north of Cape Zolotoy was utilized less than 50 %. There is no specialized fishery of horsehair crab; the species is caught mainly as bycatch for other shelf crab species. High current level of the stock gives a good background for commercial removal of at least 158 t of horsehair crab without damage to the local population of this species.

The main part of the spawning grounds of herring in the northwestern Okhotsk Sea, from the Ayan Bay to the Eirineiskaya Bay, was surveyed on June 3–21, 2022 using standard methods of the roe diving survey. In order to rationalize the survey methodology, the herring population fertility (PF) was evaluated using two different approaches. The first is a standard method (described by Farkhutdinov, 2005) with calculation of the spawning ground areas and the roe density (RD) for each of them. The second method is based on the relationship between the total area of spawning grounds and PF detected previously by Dulenin and Didenko (2021). The spawning conditions for Okhotsk herring were abnormal in 2022. Just before the mass spawning, a strong storm had destroyed many spawning substrates and redistributed the spawning shoals of herring in the coastal zone. As the result, mean RD was extremely low – 1075318 eggs/m ² (long-term average value was 4170320 eggs/m ² ), but herring spawned in new areas, additionally to usual spawning grounds, so the total area of surveyed spawning grounds was rather large, as 38.68 km ² . The population fertility calculated for this total area using the relationship between these indices was 182 . 10 ¹² eggs that corresponded to the spawning stock number (SSN) of 6.513 . 10 ⁹ ind. and the spawning stock biomass (SSB) of 1.823 . 10 ⁶ t. These estimates match well with results of the stock assessment by other methods. On the contrary, unrealistic low assessments were provided using the routine method with calculation of RD on the annually surveyed spawning grounds (PF 51 . 10 ¹² eggs, SSN 1.936 . 10 ⁹ ind., SSB 0.542 . 10 ⁶ t), because the spawning on destructed substrate could not represent adequately the state of the herring population during 2–3 years, until restoration of the algae belt. Besides, the standard method for data processing of the roe diving surveys is based on a number of non-formalized subjective assessments and assumptions that cannot ensure verification of the survey results. In opposite to this disadvantage, the calculation of PF by the area of spawning grounds is methodologically simple and allows to use remotely operated underwater vehicles, unmanned aerial vehicles and geographic information systems, with complete hardware and software documentation of survey materials. Thus, the PF evaluation using its relationship with the total area of spawning grounds is recommended for introduction as the main method of the Okhotsk herring stock assessment.

Settlements of yesso scallop Mizuhopecten yessoensis in the northwestern Tatar Strait (within the waters of Khabarovsk Region) are considered on the data of scuba (< 20 m depth) and dredge (> 20 m depth) surveys conducted in 2001–2018. To 2018, only two settlements remain in this area from 9–12 ones in 2010–2014; both remained settlements have no commercial value. Trend to decreasing of the settlements density is shown: the mean density was 3.0 ind./m ² in 2001, 0.20 ind./m ² in 2010, and 0.0005 ind./m ² in 2018. Commercially valuable scallops with the shell height > 120 mm prevailed in the settlements (86–100 %), whereas juveniles were rare or absent (1.6 %, on average) in all years of surveys. CPUE decreased from 200 kg/diver/hour in 2001–2003 to 10 kg/diver/hour in 2018. These changes are obviously reasoned by overexploitation of the population using dredging and scuba gathering. Total commercial stock of yesso scallop dropped to the minimal value in 2018: 200 t, that was in 4.5 times lower than the established limit. Thus, 5 years ban is established for M. yessoensis landing in the area.

Data on commercial catches of japanese flying squid Todarodes pacificus in the northwestern Tatar Strait in 2003–2019 are analyzed. To assess the resours status in the study area, the relative number (individuals per jigger winch per hour) and biomass (kilograms per vessel per day) marks recognized to be the most applicable winch per hour or the catch in kg per vessel per day. The average CPUE value was 35.6 ± 3.6 ind./winch/hour; increasing trend of CPUE is observed (α = 1.5 ± 0.6, r ² = 0.3, p < 0.03). The squid abundance decreased slightly in the last 2 years, with CPUE decreasing to 28 ind./winch/hour in 2019, though the squid biomass was relatively stable (average CPUE 582.0 ± 45.8 kg/vessel/day) — decreased number of caught individuals was compensated by individual body weight increasing. Long-term tendency to the body weight increasing was noted: the average body weight was 205.0 ± 4.0 g in 2004, 256.0 ± 3.5 g in 2012, and 297.0 ± 6.3 g in 2019. Possible climate change influence on the squid population was discussed. Because of warming in the reproductive area of T. pacificus in the southern Japan Sea, SST in the spawning period reached 20–25 о C and exceeded the value optimal for reproduction and larvae development (15–23 о C), so the squid abundance decreased. On the contrary, in the northern Japan Sea (in the Tatar Strait) the warming caused better conditions for the squid feeding: the higher zooplankton biomass in this area was observed under SST 13–18 о C that is reached every year recently. On the other hand, the Tsushima Current intensifying promoted active migrations of T. pacificus to the northwestern Tatar Strait. These factors of climate warming ensure favorable environments for northward migrations of T. pacificus and forming of dense feeding aggregations in the northwestern Tatar Strait that allows to expect good conditions for the squid fishery in this area in the nearest future.

Dredgе survey (177 stations) was conducted in the northwestern Tatar Strait (northward from 48° N) at the depths 14–82 m in summer 2018 (from July 21 to August 7). In the dredge catches, 76 species and taxa of benthic invertebrates are recorded, including 42 epibenthic species, mainly Ophiura sarsi, Evasterias echinosoma, Strongylocentrotus pallidus, Paralithodes brevipes, Cucumaria japonica, P. camtschaticus, Mizuhopecten yessoensis, and S. intermedius. The areas of their aggregations are determined. The largest area was occupied by the settlements of polyphagous S. pallidus (5100 km ² 2 at the depths 30–60 m). Specific biomass of epibenthos is calculated, its average value within the surveyed area was 21.5 ± 2.0 g/m ² . Depth ranges of the species domination are defined. The dominant species changed with latitude: in the southern part of the survey, Paralithodes camtschaticus dominated with the biomass of 5.1 ± 4.4 g/m ² in the upper 20 m layer (48–49° N), replaced at the depth of 20–30 m by P. brevipes (22.2 ± 14.2 g/m ² between 48–49° N) or C. japonica (28.2 ± 3.0 g/m2 between 49–50° N), both species changed deeper to S. pallidus (4.3 ± 1.1 g/m ² ); in the northern part of the survey (50–51° N), S. intermedius dominated in the upper 30 m layer with the biomass of 14.7 ± 9.5 g/m ² , Mizuhopecten yessoensis (9.7 ± 6.2 g/m2 ) and Evasterias echinosoma (5.1 ± 1,0 g/m2 ) prevailed in the depth range of 30–40 m and were replaced by S. pallidus (18.0 ± 9.5 g/m ² ) below 50 m; in the northernmost shallow tip of the Strait, Ophiura sarsi dominated absolutely with the biomass of 13.0 ± 1.1 g/m ² ) in the whole depth range down to 30 m. The greatest species richness and abundance of epibenthos were observed at the depths not exceeding 40 m. Statistically significant decreasing of quantitative parameters of the epibenthos with the depth is observed because of the bottom temperature and topical diversity declination with depth. However, environmental conditions have no significant impact on latitudinal distribution of abundance, wealth and species diversity of the epifauna in the surveyed area. The grouping of epibenthos with specific species structure that could be classified as the circumlittoral one is defined in the upper shelf zone in the northernmost area with the depth < 30 m (somewhere < 40 m).

The distribution patterns, size, age structure, and growth of the scallop Mizuhopecten yessoensis were studied in the northwest of the Tatar Strait, Sea of Japan. We determined that the northern boundary of the species range occurred in the region of Tabo Bay, at 51°37′ N. The distribution of the mollusk, depending on latitude, depth, substrate, and age, was determined. The maximum depth of M. yessoensis habitat is 138 meters, the maximum shell height is 200 mm, and the maximum age is 14 years. The differences in the growth rate of the Japanese scallop in different areas are discussed in relation to the conditions of its habitat in the northern part of its range.

The study of materials that were collected by trawling and diving in the Tatar Strait (Sea of Japan) in 2010 showed that the commercial bivalve Crenomytilus grayanus is distributed northward along the continental coast of the Khabarovsk region to Mosolov Bay (51°14.308′ N, 140°42.358′ E). Mussel druses and single mussels were found at depths of 3–32 m in bays, along the open sea coast on rocks, boulders, and in other biotopes characteristic of this species. The growth rate of C. grayanus in the Tatar Strait varied depending on the habitat conditions and was markedly lower than in the warmer waters of Peter the Great Bay, where at similar depths this species reaches its legal size 5–8 years earlier. The lifespan of C. grayanus in the Tatar Strait is 126 years, a value comparable with the lifespan of this species in more southern areas.

The population of the Japanese (Yeso) scallop Mizuhopecten yessoensis (Jay, 1857) was found and studied near its north distributional limit, at Vanina Bay in Tatarsky Strait, Sea of Japan. The population is represented by 5–12-year-old individuals with shell height of 114–151 mm and total wet weight of 176–498 g. The 6- and 7-years old individuals constituted a bulk of the population. Environmental condi- tions in the bay are not quite favourable for growth of the scallops. Mollusks in the bay grow slowly, their lifetime is low (about 8 years), and the scallops usually reach the commercial size, 120 mm in the shell height, only at five-years old age.