Findings of tuna and billfish species in the Far Eastern waters of Russia are overviewed and current status of their stocks and fishery is described briefly. These species invasion to the Russian waters is caused mainly by increased warming of the sea surface layer and active migrations of sardine, mackerel, and anchovy. Most of these species are encountered sporadically and irregularly due to patterns of their distribution, but bluefin and skipjack tuna are rather abundant, with prospects for commercial fishing. Their migrations in search for food in the waters at southern Kuril Islands, southern Primorye and southern Sakhalin begin in June and last until November, the most favorable season for fishery is July-October.

Distribution patterns and size composition for underyearlings of Sakhalin-Hokkaido herring are analyzed and their abundance is determined on results of the bottom trawl surveys in the Aniva Bay, Patience Bay, and on the shelf of southern Kuril Islands in autumn of 2024 and 2025. In 2024, the highest density of underyearlings was observed in the northern and northwestern Aniva Bay at the depths up to 40 m, but with their abundance increasing in 2025 the feeding area expanded toward south-west and south-east and some juveniles were caught off the southwestern coast of Sakhalin. In the Patience Bay, the underyearlings concentrated mainly in its northern part, off Lake Nevskoye, at the depth of 20–30 m. The main accumulations on the shelf of southern Kuril Islands were observed in the South Kuril Strait between the islands of Shikotan and Kunashir at the depth ranged from 30 to 160 m, with the highest concentration at 60–90 m where about 70 % of the population were accounted; some herring juveniles were caught beyond the strait on the Pacific and Okhotsk Sea shelves of Kunashir Island. The number of herring underyearlings was assessed in the Aniva Bay as 125.7 ^. 10⁶ ind. in 2024 and 2420 ^. 10⁶ ind. in 2025, in the Patience Bay as 440 ^. 10⁶ ind. in 2025, and at the southern Kuril Islands as 5260 ^. 10⁶ ind. in 2025. The total number of herring underyearlings in these three areas reached 8.12 ^. 10⁹ ind. in 2025, over 67 % of them were counted on the shelf of southern Kuril Islands. Taking into account natural mortality, the year-class of this year contributes to the commercial stock of herring about 177 ^. 10³ t in 2029, when these fish will reach the commercial size (9.6 ^. 10³ t in the Patience Bay, 52.8 ^. 10³ t in the Aniva Bay, and 114.8 ^. 10³ t at the southern Kuril Islands). The trawl survey of underyearlings is a promising tool for assessing recruitment of Sakhalin-Hokkaido herring in the waters of Sakhalin Island and southern Kuril Islands.

Biology of triangle tanner crab Chionoecetes angulatus in the deep-water TINRO Basin (Okhotsk Sea) is studied in details on the data collected in comprehensive bottom trawl surveys in summer-autumn (2010, 2012) and spring (2018) seasons. Aggregations of the species were found at the depths of 540–980 m, under temperature 0–2 ^оC. Males dominated over females in catches (sex ratio ranged from 1.00 : 0.16 to 1.00 : 0.69, the ranges of biomass were 596–1002 kg/km² for males versus 55–189 kg/km² for females), possibly because of specific catchability of the trawl gear. The carapace width (CW) was 12–171 mm for males and 17–99 mm for females. The size levels of functional maturity were determined for males with the method of claw allometry as: CW_{50% maturity} 100.8 mm, CW_{75% maturity} 112.9 mm, and CW_{100% maturity} 151.7 mm. The CW₅₀ value in TINRO Basin exceeds this level for the population in eastern Bering Sea (91.4 mm) that indicates later maturation of the crabs in Okhotsk Sea. Growth parameters were estimated for first time: the maximum carapace width of 147.2 mm for males and 81.6 mm for females and the size of physiological sexual maturity of 67.5 mm and 49.4 mm, respectively. Clear seasonal patterns were identified, namely moulting of males with the peak in late spring or early summer and synchronous reproductive cycle in females with external eggs laid on pleopods in summer-autumn.

Dramatic change in patterns of the japanese sardine feeding migration in 2025 had a decisive impact on the Russian fishery in Far East and caused a sharp decrease of annual catch. It was reasoned by anomalous oceanographic conditions in spring of this year, with the strong Oyashio Current, poor advection of transformed subtropical water mass with the warm anticyclonic eddy into the South Kuril fishing zone, and accordingly delayed warming of the surface layer there in the southernmost corner of the exclusive economic zone of Russia. The conditions favorable for sardine migration to this area developed too late, that’s why their feeding schools either remained within the Japanese EEZ or migrated northeastward and eastward to the open ocean, too far from the Russian coasts.

Six ecological types of macrozoobenthic communities are revealed in Peter the Great Bay by a procedure based on fuzzy set theory, with statistically significant differences between them. There are the type BB for biologically balanced or nearly balanced communities, the type PC for physically controlled ones, the intermediate between them types MD, D and HD with the moderately disbalanced, disbalanced, and strongly disbalanced communities, respectively, and the type De that presents destroyed or recovering communities presumably formed after short-term extreme negative impact of natural or anthropogenic factors. In the order from BB to PC types, the portion of animals extremely sensitive, sensitive and moderately tolerant to pollution and eutrophication is decreased and the contribution of extremely tolerant and tolerant animals is increased, as well as the portion of eurybiontic species. Quantitative indices of communities change correspondingly in this order that reflects, in general, increasing degree of disturbance and decreasing status of the bottom population. This approach can be applied for development of a new method for the benthos monitoring, though more detailed analysis of the environments for all identified ecological types of communities is necessary.

The ice cover dynamics in the Okhotsk Sea since 1970s is analyzed and synoptic atmospheric conditions for ice-rich and low-ice periods are determined. These periods were distinguished by combination of certain synoptic patterns from October to March. The extremely vast ice cover was observed in 1977–1983 and 1998–2003 when the winter centers of atmospheric action were active, the Aleutian Low located in the extreme eastern position, the ridge of Siberian High extended far north, the air pressure gradient over the Okhotsk Sea was high, and cyclonic activity over the sea was weak. As the result, cold Arctic air invaded to the Okhotsk Sea and contributed to rapid forming the sea ice. Typical prerequisite of this process was a vast cold zone of high pressure at high latitudes promoted early transition of the barometric pressure field to winter patterns in early September. In the winters with moderate ice cover, the atmospheric centers were less active and the tracks of cyclones were directed mainly to the western Bering Sea that provided transfer of rather warm air masses from Bering Sea to the Okhotsk Sea. Under these conditions, winter monsoon began in late September. The periods of low-ice winters in 1989–1997 and 2004–2015 were distinguished by low activity of the Siberian High and Aleutian Low with westward shift of the latter and abnormally high frequency of cyclones passed over the Okhotsk Sea and induced warm air advection. In this case the winter monsoon formed in 10–20 days later, in October. Such conditions were proceeded by lowered atmospheric pressure in the polar zone.

Seasonal dynamics of phytoplankton biomass is analyzed on the base of phytoplankton samples collected within monitored 4 polygons located near the mouths of spawning rivers at southeastern Sakhalin in May-October of 2019–2022. During the surveys, the water temperature ranged from –1.55 to 22.50 оC and salinity – from 11.8 to 32.8 psu that reflected strong freshwater influence. The phytoplankton biomass at certain stations ranged from 4.7 to 26058.1 mg/m³ indicating high spatial heterogeneity driven by local hydrodynamics. Three distinct biomass pulses were observed in spring, summer, and autumn. In 2019 when the Dolinka mouth was surveyed, the peaks of biomass dynamics occurred in May-June (with domination of Alexandrium cf. tamarense and Kryptoperidinium triquetrum) and October. In 2020 at the Dudinka mouth, the peaks were recorded in May (Sundstroemia setigera), June (A. cf. tamarense  with the biomass up to 3.2 g/m³), and September. In 2021 at the Manuy mouth, two peaks were observed in May and September; the former bloom was formed under water temperature at the bottom of –0.9 оC by Thalassiosira nordenskioeldii with the biomass up to 25.1 g/m³ – the first record of such high biomass in shallow coastal waters of the Okhotsk Sea. In 2022 at the Gornaya mouth, the succeeding peaks appeared in June (K. triquetrum and Rhizosolenia hebetata), July (Leptocylindrus danicus and Noctiluca scintillans), August (Coscinodiscus asteromphalus), and October (Guinardia striata and Thalassionema frauenfeldii). Dominant species in spring changed with temperature: T. nordenskioeldii and R. hebetata dominated in the years with cold spring (below 4 оC) but S. setigera dominated in warmer years (above 5 оC). The autumn peaks of biomass were observed in all years. This phenomenon contradicts with typical succession of phytoplankton on the shelf of Okhotsk Sea where an autumn peak is not usual, that reflects local specificity of pre-estuarine areas where the river runoff, wind and tidal mixing, and upwelling provide additional abilities for diatoms development. Among dinoflagellates, A. cf. tamarense reached high biomass under stable thermal conditions (~8 оC), whereas K. triquetrum dominated under windy and colder conditions. However, both species were rare at the Manuy mouth (in 2021), possibly because of rocky substrates unfavorable for the dinoflagellate cysts accumulation.

The formulas are proposed for estimating the haline component of entropy flux generated by uneven spatial distribution of evaporation, precipitation, and salinity at the ocean–atmosphere boundary. The entropy flux is calculated with 4о discretion on GODAS (Global Ocean Data Assimilation System) data for the meridian transect in the Pacific along 180о in 1984–2024 and its decadal variability is analyzed. The transect is separated to blocks with prevalence of evaporation (the salt flux into the ocean) and precipitation (the salt flux from the ocean). The fluxes of temperature, salinity, and mass are determined for each block and the haline component of entropy flux is estimated as ~ –5.10–5 W/m2K. This value does not exceed 1 % of the entropy flux caused by heat exchange between the ocean and atmosphere. However, this parameter is important for monitoring of the water exchange stability in conditions of changing climate. Increasing difference of the sea surface temperature is observed between blocks with opposite balance of evaporation and precipitation, but the tendency for the total entropy flux (due to heat and mass transfer) to increase presumably stabilizes spatial gradients of temperature and salinity on climate scale.