Russian Federal Research Institute of Fisheries and Oceanography

Buccinum osagawai is a valuable commercially exploited gastropod species inhabiting the northern Pacific. An accurate and reliable method for estimation the mollusk’s individual age is needed to understand the population dynamics and size-age structure of B. osagawai stock. The most commonly used method of estimation of the individual age of mollusks of the genus Buccinum is counting the increments on the operculum. However, this method has disadvantages, for example, since the operculum is an external recording structure, its readability is relatively low. To develop a more accurate method for determining individual age, the microstructure of statoliths of the gastropod B. osagawai and its features were studied and the possibility of using B. osagawai statoliths to determine the individual age of an animal by counting increments on thin sections of statoliths was tested. The relationship between the number of statolith increments and the number of marks on the operculum surface was studied. A comparative analysis of these two methods of age determination is provided.

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and salinity for the shelf of West Kamchatka are analyzed and all scientific publications and the most important unpublished thesises concerning this area are summarized.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.

In the long-term aspect (from 2000 to 2020 years), there is a decrease in the growth rate of individuals of the muksun of the Ob River. These changes occur against the background of population decline, are unnatural and associated with long-term highly selective fishing and climate warming. As a result of climate warming, the feeding conditions of the muksun have worsened, as well as competition from other more thermophilic species has increased. Prolonged intensive and highly selective fishing is the main negative factor that has led to a change in the population size/age structure. In general, the changes are in the direction of stunting, and a further decrease in reproductive capacities of muksun specimens and productivity indicators of its population.

Based on the materials collected in August–September 2019 during the Transarctic expedition onboard R/V “Professor Levanidov”, new data on the spatial and vertical distributions, bottom temperatures of habitat and biological features (size-age and size-sex structures, maturation, fecundity, diet composition) of the poorly studied slender eelblenny Lumpenus fabricii in the Chukchi and Kara seas are presented. In the Chukchi Sea, its main catches were recorded in the southwestern part of the sea (northeast of the Bering Strait) at shallower depths (100 m) and bottom temperatures 3.0 to 5.0 °C. In the Kara Sea, this species was found in catches mainly on the southwestern shelf of the sea (the western coast of the Yamal Peninsula and outer Baidaratskaya Bay) at depths shallower 25 m and bottom temperatures around 1.5 °C. Its individuals aged 4–9 years with a total length of 102–268 mm and a body weight of 3.1–28.3 g were recorded in trawl catches. However, 5–6-year–old fish 111–130 mm long weighing 4–6 g dominated in the Chukchi Sea, while individuals aged 6–7 years with a total length of 141–200 mm and a body weight of 8–16 g were most abundant in the Kara Sea. This species is characterized by sexual dimorphism in sizes, i.e. males are larger than females, whose fecundity varies from 115 to 436 eggs. Among individuals longer than 180 mm, the proportion of females decreases sharply, reaching zero in fish longer than 220 mm. As a result, the largest individuals of this species are represented exclusively by males. Slender eelblenny is a consumer of small- and medium-sized benthos, the main prey of which in the Chukchi and Kara seas are small benthic invertebrates (mostly polychaete worms and amphipods). Comparison with other common ground fishes in the study area showed that slender eelblenny in the Siberian Arctic seas occupies specific ecological niche with different depths and bottom temperatures. The diet of this species was similar to that of the Arctic staghorn sculpin Gymnocanthus tricuspis and the Arctic alligatorfish Aspidophoroides olrikii but differed from that of the ribbed sculpin Triglops pingelii and the bigeye sculpin T. nybelini.

The qualitative and quantitative composition of phytoplankton of the unregulated section of the Ural River and different types of channelized shoulders of the Iriklinsky Reservoir in spring 2016–2022 was analyzed. It is shown that the decrease in the amount of precipitation, the volume of inflow to the reservoir and its level, the volume of discharge and water exchange in 2019–2022 has a significant impact on phytoplankton communities: species richness, number of species in the sample, abundance and biomass, average individual cell mass, and Shannon index decrease. On average for the reservoir during this period, the share of golden algae in the total phytoplankton abundance and biomass increases significantly. The most striking changes in communities occur in the upper section of the reservoir, characterized by shallower depths and proximity to the main river. No increase in the number and proportion of indicator species of α-mesosaprobic and polysaprobic conditions was observed in the composition of the dominant complex of organisms. In case of significant increase in air and water temperature during the low-water period, changes in phytoplankton indicators characteristic of later stages of eutrophication are observed in the upper section, while in the lower section – for earlier stages. During the low-water period, a statistically significant decrease in the saprobic index values was detected. The trophic status of the river waters and different types of the Iriklinskoye Reservoir, determined by phytoplankton biomass, decreases in the lowwater period. The revealed features of oligotrophization cannot be attributed to positive consequences of water availability reduction. Firstly, the reduction of quantitative and qualitative characteristics of phytoplankton indicates the impoverishment of the food base of planktonic consuls and, indirectly, the food base of fish population, and the reduction of biological self-purification potential. Secondly, the scenario of phytoplankton changes in summer and fall seasons of the low-water period can be quite different and demonstrate negative consequences of water availability reduction.

Estimates of methane emissions in the warm season from the Zeya reservoir, one of the biggest hydropower facilities that affects Russia’s carbon balance, were obtained for the first time based on the field measurements of methane concentrations in water and methane fluxes from the water surface. During expeditionary investigations conducted in September 2021 and July 2022, field data were collected. It was feasible to create the aquatory zoning and learn more about the water body’s thermal, oxygen, and chemical structure based on hydrological and chemical investigations. In conjunction with zoning, a digital elevation model of the Zeya reservoir’s bed was created, allowing calculating the reservoir’s total methane emission. It has been determined that marshy tributaries and shallow aquatories, where organic matter flows from the banks, are the primary sources of organic matter and methane. During the summer, when shallow waters are heated, there is a significantly larger overall methane flux from the reservoir’s surface. Methane emission coefficients from the Zeya Reservoir (8.6–17.2 kg CH4/ha) are consistent with those from surface-based boreal reservoirs that are provided in the supplements to the 2019 IPCC Guidelines.

Data of bottom trawl surveys conducted in the shelf zone of Kronotsky and Avachinsky Bays and off the southeastern coast of the Kamchatka Peninsula at depths of 65-210 m in 2018 and 2022, before and after the harmful microalgal bloom that occurred off the Kamchatka coast in the fall of 2020, were compared. The results indicate a significant decrease in the species diversity, population density, and biomass of benthic organisms in the lower sublittoral zone in 2022 compared to 2018. The least affected area was the northern-most region (Kronotsky Bay), while the most severely affected area was the southernmost region off the southeastern Kamchatka coast south of Cape Povorotny, where the biomass and species diversity dramatically decreased. This is consistent with the satellite monitoring data on chlorophyll a concentration off the Kamchatka coast in September 2020. According to these data, the area of the highest chlorophyll a concentration was the greatest in Avachinsky Bay and off the southeastern Kamchatka coast, where the strongest reduction in biodiversity of marine invertebrates was recorded.

The article presents new information about the distribution of two alien Asian fish species in the Ural River. The topmouth gudgeon Pseudorasbora parva observed for the first time in the river basin was recorded only at several locations along a 300-km section between the mouths of the Kolpachka and Urtaburtya rivers, which apparently is due to its relatively recent invasion. The species could have entered the river from fish farms, in which its appearance was the result of an accidental introduction together with phy-tophagous fishes. Further, it has been established that the Amur sleeper Perccottus glenii previously known to occur only in the upper reaches is now widely distributed in the rivers of the Ural basin located in Russia. For both fish species, the variation in values of their meristic features falls within their spectrum of variability. A comparative description of nutrition is also presented. The spectrum of objects consumed by Amur sleeper is wider and their sizes are larger than for topmouth gudgeon. Among the common species of Chironomidae, benthic organisms (Chironomus plumosus, Glyptotendipes gripekoveni) predominate in the diet of Amur sleeper, while for topmouth gudgeon the diet includes organisms localized on aquatic macrophytes (Cricoto-pus algarum, C. sylvestris, and Tanytarsus gregarius) as well as swimming larvae (Cloeon dipterum) and crawling larvae (Caenis macrura) from the order of Ephemeroptera. The nutritional similarity of Amur sleeper and top-mouth gudgeon, as species with similar biotopes, is characterized as relatively low in the Ural River.

This study presents new data on population-genetic polymorphism, phylogeny and phylogeography of two vicariant species belonging to the Daphnia longispina s.lat. complex (Crustacea: Cladocera) in northern Eurasia, D. longispina s.str. and D. dentifera. Based on the variability of the fragments of non-coding 12S rRNA and the protein coding ND2 genes of mitochondrial DNA, the demographic processes that took place in populations of this vast region have been reconstructed. The previously suggested hypothesis about the different demographic history of the “Siberian” and “European” D. longispina s.str. clades has not been confirmed, since we first revealed a deep mitochondrial divergence within the “Siberian” clade. Moreover, a new divergent lineage of D. longispina s.str. in Siberia has been identified. Nevertheless, the phylogeographic patterns of D. longispina s.str. and D. dentifera in northern Eurasia confirm the earlier conclusion that repeated, combined effects on their populations of dispersion and vicariate events occurred in different phases of the Pleistocene.

The purpose of the research is determination of the species belonging to the Dibothriocephalus spp. plerocercoids from the autumn chum salmon Oncorhynchus keta of the Amur River basin based on the analysis of a gene fragment of the first cytochrome c oxidase (COX1) subunit of mitochondrial DNA. Materials and methods . A total number of 61 salmon specimens (Oncorhynchus keta) caught in the Amur River and its tributaries were examined with helminthological analysis. DNA of Dibothriocephalus spp. was isolated from plerocercoids and afterwards amplified to detect mitochondrial COX1 partial gene of the D. nihonkaiensis. Products of amplification were sequenced via Sanger sequencing. Obtained nucleotide sequences were analyzed in BLAST. Results and discussion . Type F plerocercoids were detected in nine specimens of O. keta. The sequenced fragments showed 99.31–100 % similarity with GenBank reference sequences of D. nihonkaiensis. The conducted research confirmed infestation with Dibothriocephalus nihonkaiensis (dyphyllobotriosis pathogen) of O. keta species caught in the Amur River in the territory of the Khabarovsk krai.

Data on the first reliable record of Branchinecta orientalis G.O. Sars, 1901 in Western Siberia are presented. This species was found in July 2022 in a small brackish lake Bolshoi Sor, Kulunda District, on the plain part of Altai krai. Data on the species morphology and size of adult individuals are given; the geographical location of the water body and its ecological characteristics are provided.

Scientific monitoring of pelagic fish stocks in 2004–2005 and 2014–2017 provided information on characteristics of sexual maturation of Atlantic chub mackerel Scomber colias in the coastal waters of the Central-Eastern Atlantic. Based on these results we describe ecological and geographical variability of some biological characteristics of the species. Features of sexual maturation of females and males of the mackerel can be described by a logistic equation obtained in the R programming environment. Fork length, at which 50% of individuals aged 1+ are mature, is 18.4 cm for females and 20.0 cm for males; 100% of individuals are mature at age 3+ with a fork length of 32.3 and 30.8 cm for females and males, respectively. A high proportion of spawning chub mackerel individuals in the Central-Eastern Atlantic have been recorded from February to March and from June to July. Chub mackerel in the coastal waters of this region are similar in life cycle characteristics to the populations of the waters off the Canary Islands and the Madeira Archipelago, but differ from the populations of the waters off mainland Portugal, the Azores, South Africa, and the Bay of Biscay in faster sexual maturation and growth rates.

The first recorded case of leucism is reported in the Greenland halibut Reinhardtius hippoglossoides from the waters off the northeastern tip of Sakhalin Island. The caught individual, a sexually mature female with a fork length of 83 cm, had depigmentation over almost entire body. The only pigmented parts on the eyed side of the body were pupils, a small spot on the caudal fin, a spot around the pectoral fin, and a border of the gill slit.

The results of studying the bathymetric and spatial distribution of the barred snailfish Crystallias matsushimae are presented according to bottom trawl surveys in the Russian waters of the Sea of Japan. The species does not form dense aggregations, although it is not as rare as was previously thought: in bottom trawl catches on the continental slope, the frequency of its occurrence is about 30%. The main areas of the species aggregations are the western part of the Peter the Great Gulf and the deep-water section of the Tatar Strait between the mainland and Sakhalin Island. Despite the relatively wide range of water temperature and depths at which the snailfish was found in catches, the species prefers rather narrow thermal and bathymetric ranges: 0.6–1.5°C and 200–500 m. Mysids, amphipods and decapods dominate in the diet.