The dynamics of demersal fish biomass is considered based on the results of trawl surveys conducted in 1977–2015. An analysis of the status of fish stocks has shown that fishing pressure did not have a significant impact on the dynamics of their biomass and abundance. This applies not only to the fluctuating species (walleye pollock, arabesque greenling, and Pacific herring) but also to the species with weakly pronounced dynamics. Low estimates were obtained for the bay during the period of low intensity of fishing, when its pressure was at its minimum. Not only did a decrease in biomass estimates occur at that time, there was also a change in the proportions of species in catches: the biomass of cottids substantially increased, which apparently greatly influenced the variation in the biomass of commercial species, since their young made up a significant portion in the diets of cottid fishes. With a decrease in the intensity of fishery activity, the roles of abiotic and biotic factors, including predation, which have effects on variations in the biomass and abundance of fish, increases. The fishing pressure in the bay is significantly lower than recommended; for this reason, the fish biomass and abundance dynamics are influenced to a greater extent by the climatic, oceanological, and ecological conditions of reproduction and trophic relationships. Due to the low number of such consumers as marine mammals in Peter the Great Bay, the group of predatory fish, with cottids constituting its major part, is ranked first. Based on the ecosystem approach to resource management, sizes of landings should be distributed proportionally, taking the status of populations of not only traditional target species of fisheries, but also predators feeding on them and competitors into account. This requires continuous monitoring of the communities.

Dynamics of demersal fish biomass is considered on results of trawl surveys conducted in Peter the Great Bay (Japan Sea) in 1977-2015. Fishery did not have a significant impact on this complex of fish species, including both fluctuating species (walleye pollock, arabesque greenling, pacific herring) and species with stable stock, because of low intensity. Annual landings in the bay were much lower than recommended volumes (TAC). However, a tendency to the total biomass decreasing was observed, accompanied with growth of the sculpins (Cottidae) portion in the ratio of species biomass. The sculpins prey on juveniles of many other species, so maybe their higher abundance was one of reasons for general depletion of the benthic fish community. Other predators, as marine mammals, were not abundant in Peter the Great Bay. For rational resource management, the fishery impact should be distributed proportionally between populations, taking into account their state, so both traditional commercial objects and predators with growing abundance should be landed. This ecosystem approach requires permanent monitoring to all groups of fish species.

The specificity of the species composition of the ichthyofauna in the Russian and Korean waters in the Sea of Japan/East Sea (northwards from 35°17′N) is considered. The population and the proportion of species from the order of the perch-like fishes (Perciformes) steadily decline from the south towards the north; the proportion of the species from the order of the ray-finned fish (Scorpaeniformes) tends to rise. The northward latitudinal gradient in the family composition variability results in a decrease of their numbers along with a significant increase in the sculpins (Cottidae) and the picklebacks (Stichaeidae) in the species composition. In the southernmost region of the studied water area, the sublittoral species tend to prevail; in all of the others, the elittoral species are predominant. The four northern areas are characterized by a high similarity in the species composition (81.8%); this value is significantly lower (63.1%) in case of their comparison with the more southern areas. The similarity in the ichthyofauna composition between the southernmost area and the other studied water area comprises 44.1%.

The population structure of Pacific cod Gadus macrocephalus in the southern part of the range and adjacent regions is studied on the basis of the results of microsatellite analyses. Collected data indicate heterogeneity of this species population within the studied area. According to the obtained F-ST values, Pacific cod from the waters of the Republic of Korea (Yellow Sea side) and northwestern part of the Sea of Okhotsk significantly differ from all other studied regions (Table 4). Significant differentiation was also revealed between samples from the waters of the Tatar Strait and all other regions except for South Kurils Pacific cod (both Sea of Okhotsk and Pacific Ocean sides). These two latter sample collections were similar to each other as well. A low level of differentiation was also shown for the Peter the Great Bay and the East Sea/Sea of Japan waters of the Republic of Korea.

The spatial and depth-related distribution, the size spectra, and the feeding peculiarities have been studied for the bottom skate Bathyraja bergi in the Russian waters of the Sea of Japan for the trawl catches performed in 1986−2015. The species is found at the depths of 38−577 m at the water temperature of 0.3−3.8°C; during the warm season, the fish keep mainly at the shelf, while they keep at the continental slope in the cold period of the year. This species is found nearly everywhere at the preferred depth range, except a part of the Strait of Tartary. The highest population density has been registered in the southwestern Peter the Great Gulf, along the border with the Korean waters. The schools of the bottom skate of the continental slope and the island shallows do not interact with each other. The specimens reach a body length of 129 cm and a body weight of 13.84 kg. The feeding habits indicate that this species is a predator; decapods (59.9%), cephalopods (23.0%), and fish (15.3%) dominate in the food. In spring, average daily ration constitutes 0.9% of the body weight. In the Russian waters of the Sea of Japan, the bottom skate is a common species, however, it is not abundant; the biomass of the population in this area is approximately 1500 tons.

A bottom trawl survey was conducted over all of the shelf and continental slope in the Russian waters of the Sea of Japan, from Peter the Great Bay to the La Perouse Strait, from March 31 to July 8, 2015. The species composition and biomass of demersal fish were determined for Peter the Great Bay, waters of southern and northern Primorye, and the West Sakhalin subzone. The bulk of the biomass (over 90% of the estimated biomass in the study areas) was formed by four families: Gadidae, Pleuronectidae, Cottidae, and Clupeidae. The highest biomass, 218000 t, was recorded from the West Sakhalin subzone; the lowest, 77400 t, was found from Peter the Great Bay. The proportions of biomasses of the considered species varied substantially between areas: walleye pollock and plain sculpin dominated by biomass in Peter the Great Bay; walleye pollock and scale-eye plaice dominated off southern Primorye; herring dominated off northern Primorye; and scale-eye plaice and speckled founder were dominant in the West Sakhalin subzone. The density of the fish concentration was determined for several bathymetric ranges in the considered areas. In the period of studies, the pattern of distribution of fish in Peter the Great Bay was still of the winter type, which is characterized by high concentrations over the continental slope. There was some shift towards shallower depths in Primorye waters; however, taking the great latitudinal span of the area of the research and the early spring into account, these migrations were not so clearly pronounced, as would be observed in later periods. The most distinct differences in the bathymetric distribution were found in the West Sakhalin subzone, where the distribution pattern corresponded mostly to the summer type with its high concentrations in shallow waters and low ones over the continental slope. According to the estimates in 2015, the biomass of demersal fish slightly increased as compared to the values of the 1980s–1990s.

New data on the maximum sizes and habitation depths for 83 species belonging to 15 families of demersal fish in the Russian zone of the Sea of Japan are provided on the basis of the results of the long-term studies conducted at the TINRO center.

Three specimens (56.7~92.4 mm in standard length) of the small psychrolutid Psychrolutes pustulosus (Schmidt, 1937) were collected by bottom trawl in the coastal waters off Pohang, the southern East Sea, Korea. This species is characterized by large cephalic pores, no markings on the body or fins, no spines on the head, and no notch between the spiny and soft-rayed dorsal fin. We describe specimens the southernmost distribution in the world, and compare them with two congeneric species from Russia. We thus present the first record of Psychrolutes pustulosus (Schmidt, 1937) within the Korean fish fauna and propose the new Korean name “Min-mu-nui-mul-subae-gi” for this species.

In the Peter the Great Bay, there are 16 species of sea poachers (Agonidae), 13 of which occur in catches regularly. According to results of summer bottom trawl surveys, spatial and bathymetric distribution of six of the most mass species are considered and data on their size composition and biomass are presented. As the main factor determining distribution of most species, hydrological conditions of the bay and aquatic environmental inhomogeneity are considered.

По материалам донных траловых съёмок приводятся данные о поимках редких видов рыб в зал. Петра Великого. Зарегистрировано несколько видов, ранее здесь не отмеченных. Видовой состав ихтиофауны зал. Петра Великого в последние годы меняется вследствие двух разнонаправленных гидрологических процессов. Повышение температуры поверхностных вод приводит к увеличению числа видов южных мигрантов, а уменьшение теплосодержания придонных шельфовых вод – к проникновению в залив рыб бореального происхождения.

The information on the catches of rare fish species in Peter the Great Bay is presented based on trawl surveys. Several species that have not been observed previously are registered. The species composition of Peter the Great Bay has changed in recent years because of two multidirectional hydrological processes. The rise of surface water temperature leads to the increasing number of southern migrants, and the decrease of heat content of near-bottom waters in the shelf is favorable for the invasion of fishes of boreal origin into the bay.

Main features of spatial distribution and thermal regime of habitation of Lycodes nakamurae and L. yamatoi in Russian waters of the Sea of Japan are discussed. Comparative analysis of specific features of distribution of eelpouts of the mesobenthal group (L. nakamurae, L. yamatoi, L. tanakae) in some areas of the Sea of Japan with different hydrological conditions is provided. No horizontal migrations directed along isobaths were revealed in these species. In Russian waters of the Sea of Japan, L. nakamurae inhabits depths 130–760 m, preferring the range of depths 200–700 m (it was found in catches of 95.7% of trawlings); L. yamatai inhabits depths 140–800 m, but most frequently is found in the range of depths 200–500 m (86.1% of trawlings). L. nakamurae occurs at a temperature of 0.4–1.2°C and L. yamatoi is found at 0.3–1.9°C. Seasonal migrational activity in the former species is more pronounced than in the latter. Spring-summer migration towards the shelf for feeding and reproduction and autumn-winter wintering migration towards the continental slope taking place with the cooling of the shelf are noticeable. Maximum range of vertical migrations is typical of medium-size fish and minimal is typical of juveniles of the studied species that inhabit the upper section of the bathyal (200–400 m). It is suggested that the lower limit of distribution of eelpouts of the mesobenthal group in the southern and northern sectors of the Sea of Japan coincide. The upper boundary of habitation of the species in different seasons of the year is totally determined by the thermal regime of water masses in different areas of the sea.

Обсуждаются основные черты пространственного распределения и термического режима обитания Lycodes nakamurae и L. yamatoi в российских водах Японского моря. Приводится сравнительный анализ особенностей распределения ликодов мезобентальной группировки (L. nakamurae, L. yamatoi, L. tanakae) в некоторых районах Японского моря с разными гидрологическими условиями. Горизонтальные миграции, направленные вдоль изобат, у данных видов не выявлены. В российских водах Японского моря L. nakamurae обитает на глубинах 130–760 м, предпочитая диапазон глубин 200–700 м (обнаружен в уловах 95.7% тралений); L. yamatoi обитает на глубинах 140–800 м, но наиболее часто встречается в диапазоне глубин 200–500 м (86.1% тралений). L. nakamurae встречается при температуре 0.4–1.2°С, L. yamatoi – при 0.3–1.9°С. Сезонная миграционная активность у первого вида более выражена, чем у второго. Заметны весенне-летнее перемещение рыб в сторону шельфа для нагула и размножения и осенне-зимняя зимовальная миграция в сторону материкового склона, происходящая по мере выхолаживания шельфа. Наибольший диапазон вертикальных миграций свойствен среднеразмерным рыбам, наименьший – молоди исследованных видов, которая обитает в верхнем отделе батиали (200–400 м). Предполагается, что нижний предел распространения ликодов мезобентальной группировки в южном и северном секторах Японского моря совпадает. Верхняя граница обитания видов в разные сезоны года целиком определяется термическим режимом водных масс в разных районах моря.

On the basis of standard trawl survey made at the shores of the Republic of Korea in the Sea of Japan, species composition, ratio of species in catches, and size composition of eelpouts (fam. Zoarcidae) at depths 123–330 m is analyzed. Five species of eelpouts are found in the investigated region: Bothocara hollandi, Lycodes nakamurae, L. sadoensis, L. tanakae , and Petroschmidtia toyamensis . For the first time for the south-western part of the Sea of Japan, quantitative characteristics of distribution, size composition, and bottom temperature of capture are reported for each eelpout species. L. sadoensis is a common species in this region.