Migration of juvenile pink salmon Oncorhynсhus gorbuscha in the Malaya Khuzi River (northeastern Sakhalin Island) was studied in May-July of 2022, 2023 and 2024. In these three years, they migrated downstream in different timing and in different number. In 2022, only 468 ind./min. on average migrated in the period of mass migration on June 12–18 with a peak on June 15. In 2023, the average number of counted fry was significantly higher — 3545 ind./min., and the mass migration occurred earlier — on June 6–10 with a peak on June 8. In 2024, on average 9467 ind./min. were counted in the extended period of mass migration from May 26 to June 7 with a peak on June 1. In 2023 and 2024, dense sea ice was observed near the seashore and water temperature in the coastal area was about 0 °C during the mass migration of juveniles. Spatial distribution of commercial pink salmon catches along the southern part of the northeastern Sakhalin coast is analyzed and it is concluded that their downstream migration in the Malaya Khuzi River is not representative for the entire area, at least for the year-class of 2022 migrated in 2023.

Based on the allometric equation of J. Huxley and S. Brody model of body weight, sexual dimorphism and allometric variability between males and females is determined for the first time in postembryonic development of three fish species, using factor and cluster analyses for a set of morphometric parameters. The sexual differences for such parameters as eye diameter, greatest body depth, antedorsal and anteanal distances apper very early and are already evident in juveniles. Females in almost all size-age groups of saffron cod and walleye pollock are ahead of males in the head size, forehead width, antedorsal distance, eye diameter, and body depth. Growth of these species is characterized by alternation of isometry, positive and negative allometry. On the contrary, sexual dimorphism is not revealed for pacific cod that is distinguished by linear growth of all studied plastic features, except the body weight increasing relative to the body length. According to the results of factor analysis, the greatest specific weight in total morphometric variability within age groups and between them was contributed for the studied species by four indices: body length without caudal fin, greatest body depth, eye diameter and forehead width. The cluster analysis allows us to identify general trends in morphophysiological variability of saffron cod and walleye pollock.

Spatial distribution of fish species, in particular japanese huchen Parahucho perryi, was examined by fry seine (length 20.0 m, height 1.5 m, mesh size 4 mm in the belly) in Lake Lebedinoye in the period from May to December 2024. In total, 10 fish species were identified in the lake, the most common of which were amur stickleback Pungitius sinensis and juvenile chum salmon Oncorhynchus keta, always presented in the catches. The third numerous species was japanese dace Tribolodon hakonensis, which number in 2024 was almost four times less than in the year before. The salmon species competing with japanese huchen, as whitespotted char Salvelinus leucomaenis and juveniles and dwarf males of masu salmon Oncorhynchus masou, were caught occasionally. In summer, the lake were significantly overgrown with higher aquatic vegetation, both at the bottom and alongshore, though filamentous algae were not abundant and the phytoplankton blooming was not detected. The ichthyocenosis composition changed noticeably between May and August — juvenile chum salmon had gone, japanese smelt Hypomesus nipponensis became presented in each catch of seine net in the number > 10 ind. (up to 50–100 ind. per catch), and the number of japanese dace underyearlings increased many times. Japanese huchen were presented in noticeable quantity at least in the western and southern parts of lake where this species was captured in each towing. So, 20 ind. of huchen were caught in 18 catches obtained in May 20–27, of which 6 fish weighed 1.5–2.5 kg. Short-time migration of young chum salmon across the lake enhanced prominently the food supply for japanese huchen.

Common dolphinfish Coryphaena hippurus, 104 cm long and weighing 6.0 kg, was caught in the Razdolnaya River estuary (Peter the Great Bay, Japan Sea) at a distance of more than 2.5 km upstream from the mouth bar. This species is an active epipelagic predator and has not been previously recorded anywhere in the internal estuaries of Russia.

Feeding of bearded seal is investigated in the Ulban Bay (Okhotsk Sea), strongly desalinated by terrestrial freshwater discharge. The river runoff and high daily tides create a unique ecosystem there. Such oceanographic conditions cause poor species diversity of benthic community in the bay, that is formed mainly by some eurytopic and eurytherm representatives of infauna and epifauna tolerant to contrast changes in environments. However, massive aggregations of bearded seals in the top of Ulban Bay in the feeding season indicate food supply favorable for the mammals. The seals feed there on several species of crustaceans, bivalves and gastropods, typical for shallow brackish waters, where these species form dense clusters with high biomass.

Spatial variability of temperature and salinity in the cold intermediate layer and water circulation in the Okhotsk Sea are considered for typical cold and warm conditions of the spring season (May-June) determined by separate averaging of all available data of oceanographic observations and diagnostic modeling. The «cold» and «warm» years were separated following to the typization proposed by V.A. Luchin and V.I. Matveev [2016]. The total area with water temperature below 0 ^oC is evaluated for both types. The difference of water temperature between the types reaches 1 ^oС on the depths of 30 and 90 m in certain parts of the sea, but decreases to 0.5 ^oС at the lower boundary of the cold layer. The northward (West Kamchatka Current) and northwestward (Middle Okhotsk Sea flow) transport of the warm and salty transformed North Pacific Intermediate water prevails for the «warm» type, as could be seen from spatial distribution of temperature and salinity in the above cold subsurface layer and the isolines patterns. Water density in the cold layer generally increases toward the northern and northwestern coasts of the sea where it is significantly higher in springs of «cold» years than in «warm» years. The density increases in the southern part of the sea, too, but without such difference between the types because of advective nature of this pattern. The major water gyres vary in size and intensity between the types, in particular, the anticyclonic gyre over the deep-water Kuril Basin is more intense in cold springs. The North Okhotsk Current, flowing westward along the northern shore, turns to the south at 144^o E in springs of the cold type. Besides, another alongshore current appears under cold conditions that flows from the Shantar Islands to northern Sakhalin Island and blocks the Amur River outflow to the Okhotsk Sea. On the contrary, in springs of the warm type, the outflow of freshened water from the Amur to the north reaches the latitude of 56.5^o N, then turns to the south and replenishes the East Sakhalin Current.

The data on parameters of biological productivity measured in the Academy Bay in September 2020, as chlorophyll a concentration in the euphotic layer, primary production, phytoplankton and zooplankton biomass, and results of echo sounding at 200 kHz are presented. The primary production estimated by Zvalinsky model varied from 300 to 6050 mgC per m² per day. Diatoms with the biomass of 660–1220 mg/m³ dominated in phytoplankton, whereas Copepoda with the biomass ranged from 18 to 478 mg/m³ was the dominant zooplankton group. A discrepancy is noted between the measured net zooplankton biomass and thickness of the sound diffusion layer. The more productive area with the highest biomass of zooplankton was found in the northern Academy Bay enriched by nutrients transferred there from the Okhotsk Sea due to patterns of the estuarine circulation, but the thickest sound-diffusing layer was observed in the southern and central parts of the bay where it was presumably formed by shoals of juvenile fish rather than copepod aggregations. The feeding grounds of bowhead whales were located in the southern Academy Bay, too. This spatial misalignment of the feeding grounds with the highly productive area is explained by the hypothesis that juvenile fish may be important prey for whales, in addition to zooplankton.

Species composition and abundance of megazoobenthos is considered on results of SCUBA survey in the Alekseev Bay conducted in 2017. Six groupings of megabenthos are determined within the bay. The stock of megabenthos and general patterns of its biomass spatial distribution did not change much over the past 50 years, but some changes are detected for the boundaries of biotic groupings and their quantitative species composition. Filtering sestonophages, as mussel Crenomytilus grayanus and horsemussel Modiolus kurilensis, still dominated, but the latter became more abundant and wider distributed. Sea urchins Mesocentrotus nudus and Strongylocentrotus intermedius, yesso scallop Mizuhopecten yessoensis and japanese spiky sea cucumber Apostichopus japonicus became less abundant; sea peach Halocynthia aurantium, rather common previously, became rare in the benthic fauna and did not longer form a separate grouping. On the contrary, a new grouping appeared formed by oyster Crassostrea gigas and mussel Crenomytilus grayanus. Possible causes of the occurred changes are discussed.

Lake Kronotskoe is the largest freshwater body in Kamchatka. It is a unique natural laboratory of evolution: the largest in the world sympatric flock of salmonids has been described here. Complex ecosystem researches, including hydrological surveys, are conducted on the lake since 2010. Thermodynamic and oxygen regime of this dimictic water body are described, preceded by history of researches and review of scientific literature. Data on morphometry of the lake, its water level fluctuations, ice phenomena, spatio-temporal variability of water temperature and dissolved oxygen content, wind and convective mixing are provided. Specific features of the lake, important for salmonids, as a large cold water mass, high oxygen saturation, and spatial heterogeneity of the surface temperature are discussed.

Juveniles of chum salmon Oncorhynchus keta and pink salmon O. gorbuscha reared at Pfusung fish hatchery in the Margaritovka River basin (central Primorye) are investigated. The chum salmon eggs were incubated from the breeders of local stock between September 30 and November 7, fed in cages installed in the riverbed between February 26 and April 15, and were released into the wild in amount of 7.665.10⁶ ind. between April 11 and May 15 with the body weight of 895–1100 mg. Over the entire rearing period from start of incubation to release, the juvenile chum salmon had accumulated 1103.7 degree-days of heat, on average. The pink salmon embryos were transported to the hatchery from southeastern Sakhalin immediately before hatching, with the heat accumulation of 501.8 degree-days. Their feeding began on February 26. These fish were released on April 11, after the total accumulation of 1335.9 degree-days of heat. Histological control of cardiac and pyloric sections of stomach, mid-gut and spiral valve, liver and gonads development was conducted for both species during the period from hatching to release. Consistent changes in functional activity of the gastric glands and digestive epithelial cells were detected, with increasing the number of mucus cells in the intestines of fry. Differences in fat content in the liver were noted between age groups. 

Results of experimental growing of Australian red-clawed crayfish with immobilized dactylopodites (movable fingers) of claws are considered. Effects of planting density on body size and weight gains, duration of intermolting intervals, number of completed moults, and survival of crayfish were evaluated in three sections of aquarium with the same bottom area but different density, as 150, 255 and 350 ind./m². At the end of the experiment (120 days), 75 ind./m² had survived in the first section (50.0 %), 102 ind./m² (40.0 %) in the second section, and 114 ind./m² (37.5 %) in the third section. Crayfish in the first section were less aggressive towards their neighbors, less stressed, and their mortality during molting was lower than in the other sections (35 %). In the intermolting period, the crayfish mortality was approximately equal in all sections (15.0–17.5 %). Effect of the dactylopodites immobilization for reducing aggression and cannibalism of redclaws during their growing in artificial conditions is discussed.

Recommendations for measuring underwater noise from vessels intended for fisheries researches and monitoring of bioresources are compiled based on current technical regulations and standards. Key terms and tools for the measurement are described, requirements for conditions of the measuring are determined, potential uncertainties of the data and procedures of the data recording and postprocessing are explained. The principles of placement, operation, and interaction are established for the main components of the hydroacoustic measurement system and the object of measurement. The sound pressure levels of noise emitted by vessel in the frequency range of 10–25,000 Hz in narrow and 1/3-octave frequency bands is measured. Parameters of the vessel movement along the track and distance to the registration point are monitored during the testing; the noise level is measured in the far acoustic field of the vessel and then normalized to a distance of 1 m. The sound pressure levels of noise are presented in dB relative to the reference sound pressure of 1 μPa. The measured noise levels are compared with the thresholds recommended by the International Council for the Exploration of the Sea (ICES). These thresholds represent the levels below which the effect of fish avoiding the vessel can be ignored. Frequency ranges and levels of the noise exceeding these limits are identified. These recommendations will be used as a component of the acceptance testing program for new research fishing vessels of Project 17050, as well as for acoustic certification of other vessels engaged in researches conducted by the Russian Research Institute of Fisheries and Oceanography (VNIRO) and its branches.