Dynamics of downstream migration is considered for juvenile pink salmon at West Kamchatka in 1975–2023. Lengthening of the migration period is noted for recent years with high parental stocks. These changes happened on the background of four-decade increasing of the sea surface temperature in waters at the western coast of Kamchatka (till 2016), on average from 3.0 to 6.5 ºC, and its further decreasing back to 3–4 ºC from 2017 to 2023. So, the warming trend in coastal waters at western Kamchatka is significantly weaker than that at eastern Kamchatka, that does not confirm a hypothesis on formation of super-strong year-classes of West Kamchatka pink salmon in recent years due to warmer environments for early marine feeding of the juveniles in the coastal zone. Presumably, these extreme year-classes were formed as a result of prolonged downstream migration of fry produced by rather numerous spawners in conditions of increased abundance of small-sized plankton transported to the coast of western Kamchatka from the deep-water areas of the Okhotsk Sea and the North-West Pacific.

Features of ecology are considered for euryhaline bivalve mollusk Potamocorbula amurensis dwelling in Peter the Great Bay. Spatial distribution of the species is not uniform, the mollusks settle mainly in the areas affected to the river discharge influence with water salinity from 5 to 30 ‰, in the uppermost layer of silty, silt-sandy, sandy, sandy-gravely, or sandy-gravel-pebbly soils at the depths from 0.3 to 7.0 m. The densest aggregations of P.amurensis are found in the top of Amur Bay, with the biomass up to 2.3 kg/m² and abundance > 31.10³ ind./m² at the depths shallower 2.0 m. They are able to form a byssus thread up to 30 mm long. This sestonophag species occupies usually a dominant or subdominant position in benthic communities, and itself is a prey for asian paddle crab Charybdis japonica and seabirds. Larvae of P. amurensis could be transported by estuarine streams to estuaries and lagoons where the species forms temporary aggregations dependent on the parental stocks, but in the vast Razdolnaya River estuary, especially in the relatively deep Tavrichansky Liman, there are stable mixed-age settlements where the specimens of age 5+ can be found that is the maximum life span of P. amurensis for Peter the Great Bay.

Behavior of baikal seal Pusa sibirica Gm. at the depth of 200 m under permanent artificial illumination was filmed for the first time using stationary videocameras. Several seals found dense aggregations of prey concentrated in the illuminated sector presented mainly by adult females of pelagic crustacean Macrohectopus branickii Dyb. For many days, the seals actively hunted on M. branickii, rarely on fish, as juvenile pelagic golomyanka Comephorus sp. and coastal-pelagic Cottoidei. Their feeding behavior is described, as hunting techniques, methods of prey capturing, feeding activity of seals and behavior of the prey. The constant illumination disrupted natural vertical daily migrations of the crustacean and so changed the strategy of food diving for baikal seal. Based on the new obtained data, the hypothesis of Japanese scientists on decisive role of M. branickii in diet of baikal seal and high importance of this food resource for prosperity of the population is criticized. Such hypothesis supposes stable dense aggregations of the crustacean with abundant adult females of late generation (comparable with those under artificial light) in the pelagic layer of Lake Baikal at the depths accessible to seals, easy found by seals, but these conditions are never observed in nature.

Modern data on dynamics of structure and abundance of zooplankton communities in the epipelagial layer of Pacific waters at the Kuril Islands and Kamchatka are presented on the data collected in summer of 2004–2023. On the background of changing environmental conditions, the portion of small- and medium-sized zooplankton is increased recently, mainly due to increasing abundance of moderately cold-water copepod Oithona similis and hyperiid Themisto pacifica. Among the large-sized zooplankton, increasing abundance of warm-water copepod Eucalanus bungii and decreasing number of cold-water Neocalanus copepods (especially N. cristatus) is observed. Inter-annual fluctuations of the total zooplankton stock did not exceed 3 times, while the biomass of some taxonomic groups varied in 4–9 times. The total biomass of zooplankton, which forms the basis of food base for fish and squids, is assessed as (96 ± 6).10⁶ t in the 0–50 m layer and (90 ± 6).10⁶ t in the 50–200 m layer. In summer, nekton consumes a small part of zooplankton production in this season (¹/₂₇). The studies of fish and squids consumption of zooplankton in the North-West Pacific did not reveal its significant dependence on the changes in structure and abundance of zooplankton communities, possibly related with oceanographic regime changes.

All available data on water temperature and salinity for the shelf of West Kamchatka are analyzed and all scientific publications and the most important unpublished thesises concerning this area are summarized. Current ideas about the water masses distribution and seasonal and long-term variability of water temperature and salinity on the shelf are discussed. There is noted that the existing estimates of seasonal and long-term variability of water temperature require significant additions for recent times (last 20 years) and certain spatial areas. Insufficient understanding is revealed for spatial-temporal dynamics of salinity in the mixing zone between the river and sea waters that requires special research.

Based on satellite images and standard sections obtained in 2000–2024, spatial structure of the Primorye Current as a band of cold waters along the coast of Primorye is considered. The archive of sea surface temperature reconstructed from the measurements of AVHRR radiometer (NOAA satellites) and MODIS spectroradiometer (AQUA, TERRA satellites) is used. The data were received and processed at the Center for collective use of regional satellite monitoring on environments in the Far-Eastern branch of Russian Ac. Sci. The main features of the Primorye Current structure are determined that allows to conclude that this cold-water area in the surface layer from the Tatar Strait to Peter the Great Bay is formed by a complex of coastal-shelf processes, including upwelling, vertical mixing, and desalination by terrestrial runoff. This cold, low-saline water mass spreads beyond the formation areas in general southwestward direction, along the coast, either as a continuous flow or as a chain of mesoscale eddies, spots, stripes, jets, etc., sometimes interrupted. The main provisions of this concept correspond with ideas established even before the satellite oceanography development, but some details concerning nature of the cold water of Primorye Current, its spreading along the coast of Primorye and interaction with surrounding waters were previously unknown.

Water quality is assessed in some coastal areas of Peter the Great Bay, Japan Sea, by means of microbial indication. In the areas polluted with heavy metals, the number of metal-resistant forms of bacteria in heterotrophic microbial communities varies in accordance with the type and degree of environmental pollution. The heightened numbers of metal-resistant microorganisms in the Amur, Ussuri, and Nakhodka Bays indicate a high degree of anthropogenic load. The heavy industrial pressure is recorded there more than 20 years in such sites as Cape Lagerny and Cape Firsov (at the mouths of Pervaya Rechka and Vtoraya Rechka Rivers in the Amur Bay) and Lazurnaya Bay (in the Ussuri Bay) and extends recently in the coastal area at Bolshoy Kamen (Ussuri Bay), at Cape Tokarevsky (Amur Bay) and Cape Petrovsky (Nakhodka Bay). The waters in the Far Eastern Marine Reserve in the southwestern Peter the Great Bay are quite clean, with the least industrial impact caused mainly by transboundary transfer of pollutants.

Species composition, abundance, ecological structure and spatial distribution of macrobenthos are considered in landscape and ecological conditions of the Astafiev and Srednyaya Bights in the eastern part of the Far Eastern Marine Biosphere State Nature Reserve. The main types of landscapes are identified on the data of landscape profiling. Granulometric composition of soils and organic matter content in the bottom sediments are analyzed. A total of 77 species are found in the macrobenthos of both bights. There are 28 species of epibenthos (similarity between bights by Jaccard index is 93 %) and 53 species of infauna (similarity 23 %), including 4 species common for both biotopes. Different ecological processes in the bottom-macrobenthos system occur in these nearby bights that affects biological diversity, abundance and structure of soft-soil benthos. Despite geomorphological similarity of the bights, the bottom environment in the Astafiev Bight is more enriched in organic matter, but taxonomic composition and abundance of infauna is poorer there. Bulk release of terrigenous matter from the eroded shore of Gamov Peninsula to this bight after rains destabilizes and jeopardizes its bottom environments and prevents formation of biologically stable, diverse and abundant benthos. In the neighbor Srednyaya Bight with a less erosive coastline, the bottom sediments are formed by marine processes mostly, so the macrobenthos on soft soils is distinguished there by great biodiversity. The epibenthos in both bights has no such differences and is represented by the most common species for Peter the Great Bay.

Basic properties of bottom sediments, including organic carbon content, are determined to understand biogeochemical cycles in the marine environment. The samples were collected using a geological column sampler from the upper 10-centimeter layer of the sediments at the depth of 12.2–99.0 m in Kievka Bay in the 83^rd cruise of RV Academician M.A. Lavrentiev. The bottom sediments in Kievka Bay are distinguished by significant content of organic carbon, in the medium to high categories, and high levels of major nutrients in the organic fraction, such as nitrogen, phosphorus and potassium. Their particle-size composition corresponds mainly to sandy loams, with prevalence of silicon, aluminum and iron in the mineral skeleton that is similar to coastal soils. The content of organic carbon and total nitrogen in the bottom sediments of Kievka Bay correlates positively with the portion of physical clay fraction. The same analytical techniques used for both bottom sediments and coastal soils allow to consider the continental-ocean transition zone as a single system.

Results of a quantitative diving survey of macrobenthos in the Avachinsky Bay at southeastern Kamchatka in October 2021 are presented. The survey was conducted in a year after the harmful algal bloom (HAB) with mass death of marine organisms in certain areas of the coastal zone. The depth range of 4–14 m was surveyed. In total, 92 species of macrobenthos were identified, the average biomass of macrobenthos was assessed in 2768.7 ± 2115.4 g/m², and the average abundance — in 2449.9 ± 1502.1 ind./m². The species structure of macrobenthos was similar to the results of survey conducted by Kamchatka researchers in the spring of 2021. Significant reduction in the number of species and biomass was detected then for sponges, anemones, gastropods, echinoderms and ascidia and confirmed again by our data. In October 2021, the portion of these taxonomic groups in the total biomass of macrobenthos on solid soils did not exceed 1–2 % that is evident consequence of significant changes in structure of the bottom community caused by mass death of benthic organisms during HAB in the fall of 2020. A year after the HAB, bivalves and polychaetes, as well as red and brown algae occupied the dominant positions in the community in terms of the species number and abundance, whereas pacific mussel Mytilus trossulus dominated by biomass (this species was dominant before the natural disaster and preserved this position) and subdominants were Hedophyllum bongardianum, Thalassiophyllum clathrus (Ochrophyta), Schisobranchia insignis (Polychaeta) and Ptilota asplenioides (Rhodophyta). Increasing in abundance of Amphipoda and Decapoda crustaceans was noted in 2021 relative to 2020.

Artificial reproduction of pacific salmon has been repeatedly criticized due to negative impact on natural populations. One of its aspects is replacement of wild spawners by spawners originated from hatchery on natural spawning grounds. This problem is relevant to Iturup Island, where the chum salmon stock is formed by both natural reproduction and artificial breeding. To evaluate their ratio, otolith marking of juveniles has been massively implemented at Iturup salmon hatcheries since 2009. The otoliths of chum salmon were collected for analysis from the spawning grounds in 6 rivers and lake-river systems of the Okhotsk Sea coast in the northern part of Iturup Island and at the slaughter point of salmon hatcheries from 2012 to 2022. Microstructure of otoliths from 8229 fish individuals, including 2709 specimens of сhum salmon, was examined to identify the tagged fish. The chum salmon of artificial origin were presented on all examined spawning grounds. Their number was calculated taking into account the percentage of tagged juveniles released from the hatcheries. Low level of straying was concluded for chum salmon on Iturup Island. Long-term dynamics of the ratio between wild and artificial spawners on spawning grounds was determined by changes in volume of juveniles release. Until 2014, the Reidovy and Kurilsky hatcheries released 50.10⁶ chum juveniles annually, and the spawners of artificial origin were found sporadically on the spawning grounds in “wild” rivers. New fish hatcheries constructed after 2010 provided increase of their portion in 2014–2022 to 9.6–13.6 % on the spawning grounds unaffected to artificial reproduction and up to 93.3 % on the spawning grounds in the rivers with hatcheries. These high returns were supported by release of 74.4–191.8.10⁶ juvenile fish annually. In the Reidovaya and Kurilka Rivers with a branched network of tributaries, the highest occurrence of artificial spawners was observed on the spawning grounds neighbored with hatcheries, whereas their portion decreased to 20 % on the spawning grounds in large tributaries of lower reaches; possibly, spawning grounds where the spawners of artificial origin are absent still exist in the basins of these rivers. Some increase of straying should be probably expected in future years because of huge amount of juvenile chum salmon released into the rivers of Prostor and Kurilsky Bays after 2020, at least 175.10⁶ ind.

State of the fishing industry in Russia is reviewed and preconditions are considered for transition from the historical principle of sharing quotas for catch to the principle of investment quotas. Such transition effects for fishermen and the Russian fish industry as a whole are discussed.

Basic principles of fishery forecasts developing and their performance evaluation are considered for the modern forecasting of pacific salmon stocks dynamics in Kamchatka in 2018–2024. The forecasts validity is critically analyzed for the main units of the stocks, with attention to correct interpretation of the results and possible reasons of discrepancy between predicted and actual stock dynamics. Methodological aspects of forecasting are described taking into account the species specifics for pacific salmon. Certain stock units whose abundance forecasting is available using mathematical modeling are outlined. In the modern period of high abundance of salmon, a trend approach to forecasting is rational, because of possibility of prompt adjustment of the catch values in dependence on actual volume of the salmon runs. Climate and oceanographic conditions at Kamchatka are described for the modern period. Ecosystem nature of the discrepancy between predicted and actual rates of runs and catches for pacific salmon in 2020 and 2024 is shown. Density factor in the ecosystem due to significant increase of the salmon abundance in 2010–2020s is determined as the most likely reason of unexpectedly weak runs, presumably because of heightened mortality of fish with the length and weight decreasing under environmental changes negative for their food base. Special attention in forecasting should be paid to vast areas of positive or negative SST anomalies on the feeding grounds of Kamchatka herds of pacific salmon in the southwestern Bering Sea and North-West Pacific during their early pre-spawning migrations.

New method for constructing size-and-age keys is proposed and tested on the data on size composition of yellowfin sole in commercial catches in the Patience Bay in 1950–2024, with the age of fish determined using the inverse growth calculations techniques. The method makes it possible to get a correct size-and-age key sufficient for estimating the age composition in catch on results of mass measurements when collection of age-recording samples is not available, and at the same time allows to neutralize an effect of fishing gear selectivity. The method was practically used in cases of pacific cod in the South Kuril fishing area and in the Japan Sea, yellowfin sole in Sakhalin waters, rock sole of genus Lepidopsetta in waters at the Kuril Islands and in the western Bering Sea, and pacific herring in the South Kuril area. The method may be useful for solving practical tasks of calculation the age composition in catches and subsequent assessments of stock and allowable catch volume for marine fish species.

Impact of environmental conditions on spatial distribution of size-sex groups is described statistically for snow crab Chionoecetes opilio. Based on the relationships identified, absolute values of catches are calculated for each such group. Machine learning approach is implemented for the feature engineering and statistical relationships evaluation. The approach can be adopted for other benthic stocks.