Morphological description of deepwater skate Bathyraja trachura from the North-West Pacific

Morphological description is given for deepwater skates Bathyraja trachura caught in the North-West Pacific in 1980–1989, both juveniles and adults. Counts for vertebras, pectoral fin, teeth rows, and intestinal valves are presented.

Helminth fauna of spawning pacific herring Clupea pallasii from the Taui population (Tauiskaya Guba Bay, Okhotsk Sea)

Parasites of spawning pacific herring (Clupea pallasii Valenciennes in Cuvier et Valenciennes, 1947) from the Taui population are explored on the samples caught on two spawning grounds located in the Ola lagoon and Amakhton Bay (Tauiskaya Guba Bay, Okhotsk Sea), and 17 species of helminthes are found, including 6 trematodes, 5 cestodes, 4 nematodes, and 2 acanthocephalans. Some differences in species composition of helminthes and their infestation were found between these estuarine and marine spawning grounds. In the Ola lagoon, 16 species of helminthes were identified, including 5 species of cestodes, whereas only 13 species of helminthes, including 3 species of cestodes, were found in the Amakhton Bay. The Taui population of herring is distinguished from the Okhotsk and Gizhiga-Kamchatka populations by presence of nematodes Hysterothylacium aduncum, l, and Ascorophis pacificus with rather high rates of invasion (occurence = 52.9 %; mean abundance = 4.16) and trematode Bucephaloides spp. On the other hand, the herring from the Taui population has common dangerous parasites with other populations in the Okhotsk Sea, as trematode Brachyphallus crenatus and nematode Anisakis spp. (larvae), with high degree of infestation.

Growth and survival of the hatchery juveniles of pacific oyster Crassostrea gigas (Thunberg, 1793) in Peter the Great Bay

Growth and survival rates of juveniles of pacific oyster Crassostrea gigas are estimated for the first time in conditions of Peter the Great Bay (Japan Sea). The data were collected at artificial hatchery in the Aquaculture Center located on Popov Island in 2019. The juveniles were settled and reared on two types of substrate: 1) perforated plastic plates with the diameter of 30 cm (area 7.1 dm2), and 2) scallop shells with the height about 10 cm (average area 0.8 dm2) mounted in the western Peter the Great Bay (Voevoda Bay) in September 2019. Before placing in this site, the average height of the juveniles’ shells did not exceed 7 mm. In July 2020, after the 9-month exposure of the collectors with spat in the Voevoda Bay, the height increased in 12–18 times and reached 55–90 mm on the substrate 1 and 25–65 mm on the substrate 2. Then the oysters reared on the substrate 1 were replaced from the plastic plates to the cage shelves and the cages were moved to the Stark Strait. Difference in the growth rate became more apparent in September 2020, when the height of shells settled on the plastic plates reached 67 mm, on average (73 % in the range 50–85 mm) and for the shells settled on the scallops — 32 mm, on average (72 % in the range 20–45 mm). The shell height increased to 76.6 and 52.4 mm, respectively, to the end of October 2020. Finally, about 59 % of the oysters reared on the substrate 1 and cage shelves and 9 % of the oysters reared on the substrate 2 reached the commercial size (80–100 mm). Their survival in the period from mid-October 2019 to July 2020 is estimated as 46.9 % (28.8–98.2 %) for the substrate 1 and 33.5 % (4.0–78.3 %) for the substrate 2. On the substrate 1, survival of the mollusks attached to lower surface of the plates was twice higher. The survival had a tendency to decrease with increasing of the juveniles density. The experiment showed good viability for artificially hatched juveniles of pacific oyster in conditions of Peter the Great Bay. Their growth in the Voevoda Bay and the Stark Strait, with necessary technological measures, as replacing, thinning, and substrate cleaning from fouling, allows to produce oysters with the commercial size.

Seasonal changes of biological condition and reproductive cycle of hampback shrimp Pandalus hypsinotus (Caridea, Pandalidae) in the Tatar Strait

Research and commercial trawl catches of humpback shrimp Pandalus hypsinotus from the Tatar Strait (Japan Sea) in 2004–2020 were investigated, with bioanalysis of about 45 thousand specimens. Average timing of group molting, spawning, and eggs laying are determined, terms of gonads and eggs development are estimated. Prespawning and molting of the females occur between January-April, with the peaks in early February and middle February, respectively. All oviparous females have 30–40 days to lay eggs, and molt during 50–55 days; the peak of the eggs laying occurs in late June. The males molt in July-August, afterwards the largest individuals change gender and new intersexes are formed. The males have the second molting in October-December, with the peak in late November. In January, after finish of the males molting, a new annual reproduction cycle starts from the prespawning molting of females. Both vitellogenesis and embryogenesis are observed through the year, though females with developing gonads prevail from August to January (because of a long time span between winter and summer moltings while the egg carrying continued 15 months) but oviparous females — from February to July. The individual reproductive cycle of Pandalus hypsinotus in the Tatar Strait lasts 24 months, with 9 months of vitellogenesis (quick growth of gonads) and 15 months of embryogenesis. During the 2-year reproductive cycle, most of females pass through the following stages: i) gonads development (just after eggs laying) when almost all oviparous females (up to 95 % in May) have green gonads under carapace that corresponds to the stage of development «eggs laid — gonads weakly developed»; ii) summer molting from August when females lose hairs on pleopods and the gonads growth accelerates; iii) respawning in January-March (together with the firstly spawning intersexes, with slight delay of the latter); iv) initial developing of eggs during summer; v) stage of «eyed eggs» from December to March; and vi) eggs laying and molting from late March to late May; then the 2-year reproductive cycle repeats.

Dynamics of stock for yesso scallop Mizuhopecten yessoensis (Jay, 1856) in the northwestern Tatar Strait from the beginning of its fishery to nowadays

Settlements of yesso scallop Mizuhopecten yessoensis in the northwestern Tatar Strait (within the waters of Khabarovsk Region) are considered on the data of scuba (< 20 m depth) and dredge (> 20 m depth) surveys conducted in 2001–2018. To 2018, only two settlements remain in this area from 9–12 ones in 2010–2014; both remained settlements have no commercial value. Trend to decreasing of the settlements density is shown: the mean density was 3.0 ind./m2 in 2001, 0.20 ind./m2 in 2010, and 0.0005 ind./m2 in 2018. Commercially valuable scallops with the shell height > 120 mm prevailed in the settlements (86–100 %), whereas juveniles were rare or absent (1.6 %, on average) in all years of surveys. CPUE decreased from 200 kg/diver/hour in 2001–2003 to 10 kg/diver/hour in 2018. These changes are obviously reasoned by overexploitation of the population using dredging and scuba gathering. Total commercial stock of yesso scallop dropped to the minimal value in 2018: 200 t, that was in 4.5 times lower than the established limit. Thus, 5 years ban is established for M. yessoensis landing in the area.

Stock-recruitment models, principles of management and rules for regulating the fishery on the main Chukotka stocks of sockeye and chum salmon

Fishery pressure on populations of pacific salmons has increased in the Rusian Far East in the last decade because of growing fishing and processing capacity, so measures for the fishery regulation are necessary, as the regime of pass days in rivers and marine coastal areas. Chukotka is now almost the only region where such restrictions are still absent. However, if the interest of fishery industry to the stocks of pacific salmon in Chukotka will grow, a successful scientifically based strategy of fishery should be developed to maintain exploitation of the stocks without exceeding the limits of excessive use. Year-to-year time series on spawning stock and recruitment of chum salmon in the Anadyr area and sockeye salmon in the Meynypilgyn area were analysed for development of recruitment models and establishment of general principles for adaptive fishery management. Nonlinear adaptive fishery management based on principles of buffer managing is proposed and tested under various regimes of landing using the stock simulation models accounting deviations from the standard stock-recruitment model. There is concluded that the level of exploitation is much lower than optimal for the Anadyr chum salmon, whereas escapement for spawning of the Meynypilgyn sockeye salmon should be increased in cases of low spawning stock of this species.

Сurrent state of artificial reproduction of chum salmon in Primorye Region

Results of 4 salmon hatcheries operation in Primorye Region are overviewed. Dynamics of chum salmon producers return to the rivers is presented for 4 last years. Recent tendency of shifting the peak of return from middle October to late September — early October is noted both for the rivers flowing into Peter the Great Bay (Barabashevka) and for the rivers of central Primorye (Verbnaya and Milogradovka). High percentage of producers aged 2+ was observed in the hatchery rivers in some years (32.9 % in the Barabashevka in 2019, 31.0 % in the Verbnaya in 2020, 37.8 % in the Bezymyanny in 2020). Interannual fluctuations in the number of producers return are possibly caused by malfunctions of hatcheries. A problem of water supply to the hatcheries is considered. Expediency of temperature control at hatcheries is shown. Data on release of chum salmon juveniles in the last decade are presented for each hatchery: the number of juveniles released, the average weight of juveniles, and the timing of release. Total release to the Barabashevka River was 119.29 . 106 juveniles, to the Ryazanovka — 114.24 . 106 juveniles, to the Poyma — 49.43 . 106 juveniles, to the Narva — 6.02 . 106 juveniles, to the Brusya — 3.11 . 106 juveniles, to the Verbnaya — 69.66 . 106 juveniles, to the Milogradovka — 1.00 . 106 juveniles, to the Lidovka — 1.71 . 106 juveniles, to the Bezymyanny — 69.45 . 106 juveniles, and 2.00 . 106 juveniles each to the Kievka and Margaritovka Rivers.

Hematological analysis of hatchery-reared and wild juveniles of pink salmon Oncorhynchus gorbuscha and chum salmon Oncorhynchus keta in Sakhalin Region

State of blood cells is examined for juveniles of pink and chum salmon sampled from Lesnoy Pugachevsky, Taranaisky and Okhotsky hatcheries in Sakhalin in May-June of 2018 and 2019 and caught in the Ochepukha, Pugachevka and Taranay Rivers during their catadromous migration to the sea. Both hatchery and wild juveniles of both species were characterized by high adaptive capabilities evidenced with high content of young forms of erythrocytes in the blood (17.0–31.0 %), significant portion of lymphocytes (60.8–92.0 %), and small number of neutrophils. The high adaptive capabilities were confirmed in the experiment, when juveniles of pink salmon were placed in the seawater without preliminary acclimation, but noticeable changes in the state of blood cells were not revealed both for wild and hatchery-reared specimens. Proportion of different blood cells was highly variable for juveniles of both artificial and natural origin but was more similar between the fry hatched at the same hatcheries or in the same rivers. A case of increased number of neutrophils was noted in 2019 for certain groups of juveniles, with total increasing of platelets in the blood that was explained by an external influence on the juveniles.

Hypoxia in Peter the Great Bay

Studies on hypoxia in Peter the Great Bay (Japan Sea) are reviewed. Seasonal hypoxia is observed in warm season at the bottom of three areas: Amur Bay, Ussuri Bay, and the southwestern part of Peter the Great Bay occupied by the Far-Eastern Marine Biosphere Reserve (FEMBR). Processes of the hypoxia forming are similar in all these areas. The main reason is the dissolved oxygen consumption by microbial degradation of organic matter within topographic depressions in conditions of limited ventilation because of strong summer stratification. The bottom depressions prevent horizontal water exchange and provide accumulation of organic and inorganic suspension, that is another factor important for development of hypoxia. The Amur Bay is the most subjected to hypoxia, being a semiclosed estuarine basin eutrophed by nutrients input from the Razdolnaya River and waste waters of Vladivostok city. The Ussuri Bay has better water exchange and less eutrophication, therefore there are scarce data about hypoxia in this area. FEMBR area has good water exchange and is only episodically influenced by nutrients discharge from the Tumen River, so hypoxia is observed there occasionally. Another consequence of microbial degradation of organic matter in these areas is acidification: pH decreased in 0.5 unit in the bottom water of the Amur Bay in eight decades from 1932 to 2013. Synchronism between regional and global processes of eutrophication, deoxygenation, and acidification of bottom waters is discussed.

Analysis of Sr and Ba profiles measured by ultra-high-resolution mass spectrometry LA-ICP-MS in otoliths of juvenile anadromous sockeye salmon Oncorhynchus nerka in the early marine life-history stage as a proxy for fresh to marine water transition

The strontium (Sr) and barium (Ba) profiles in otoliths of juvenile sockeye salmon Oncorhynchus nerka from British Columbia are measured using a Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) system and analyzed. The highest possible measurement resolution (near-daily) was used to assess variability and repeatability of the breakpoint (marine entry) estimates inferred from Sr:Ca and Ba:Ca ratios. Such resolution for the otolith chemical composition (to an accuracy of 2 μm) was reached using the rotating slit, which width was close to the daily circulus width of the otoliths. So, daily or 2-day changes in the elemental composition were recorded during the period of transition to the marine environment. Sr profiles were generally similar among the fish, starting with low values of Sr:Ca in the fresh water and increasing sharply after the marine entry. The Ba:Ca signal was more complex, showing in most cases a dramatic increase immediately before the breakpoint. Besides, multiple peaks in the Ba profiles were recorded prior to the marine transition with a significant difference of their number between fish from different populations. A breakpoint was detectable in the Ba profiles 3–11 µm prior to its appearance in the Sr profiles. The complexity of Ba profiles may cause erroneous estimates of the marine entry date; thus, the Sr signal is a more reliable marker of marine transition for juvenile sockeye.