State of the pacific oyster Crassostrea gigas (Thunberg, 1793) population in the Losos Bight (Sakhalin Island) in 2013–2020

The state of the aggregation of Pacific oyster Crassostrea gigas (Thunberg, 1793) in the Losos Bight (Aniva Bay) in 2013–2020 was assessed. For now, this aggregation has been in depression as a result of intense fishing. The abundance of the aggregation of commercial individuals (shell height >120 mm) was poor two recent years. The total stock estimated is 31.5 t; the commercial stock – 4.7 t.

Characteristics of antioxidant activity for certain fractions of polyphenols from seagrass of genus Zostera

Some components of alcohol extracts from seagrass of genus Zostera were fractioned in the column filled with sorbent Sephadex LH-20 using the methods of size exclusion chromatography. Content of polyphenols in the fractions and their antioxidant activity were determined. The total content of polyphenols in the extracts from Zostera asiatica collected in the Rudnaya Bay (Japan Sea) and Zostera marina from the Aniva Bay (Okhotsk Sea) was 2.10 and 2.15 mg/mL, or 0.4 and 1.8 mg/g DW, respectively. The antioxidant activity varied by fractions in the range 19.1–118.0 μg of ascorbic acid per mL for Z. asiatica and 96.2–213.9 μg of ascorbic acid per mL for Z. marina, in dependence on qualitative and quantitative composition of the fractions. The alcohol extracts of Zostera were heterogeneous systems with different polyphenol components and included protein substances covalently bound with polysaccharides and/or polyphenols, that was confirmed by UV spectrometry and thin-layer chromatography. Phenolic acids, flavones and flavonols were presented in the extracts.

Spatial distribution and interannual variability of catches for pink salmon of artificial origin in the waters of eastern coast of Sakhalin Island in modern times

Mixed herds of pink salmon including the fish of both artificial and natural origin are exploited by fishery in many areas of Sakhalin Island. To separate the fish of different origin, large-scale tagging of the juveniles otoliths is conducted at salmon hatcheries since 2008. The hatcheries contribution to pink salmon catches in certain areas of East Sakhalin (from the Langeri River to Cape Crillon) is assessed for 2011–2017 on the base of previously published and new data on occurrence of the fish with marked otoliths. The specimens were sampled from commercial catches of 5–13 fixed nets and from research catches in 5–9 rivers throughout entire spawning season. In total, 40,992 otoliths of pink salmon were collected. The otoliths were prepared for microstructure analysis using standard methods of processing. All marked otoliths had the tags of hatcheries located on the eastern coast of Sakhalin. The fish of artificial origin were caught in all examined sites between Cape Soymonov and Cape Crillon every year, but in some years their distribution was wider, up to the northern limit of the investigated area (Langeri River). The fish of artificial origin migrated to all rivers within this area. The total annual landing of the pink salmon marked at artificial hatcheries in the East Sakhalin waters was estimated as 300–10600 t, by years. The rest of the fish of artificial origin (0.4–2.3 . 106 ind.) entered to the rivers and mostly reached the spawning grounds. Long-term dynamics of landing was compared for the pink salmon of artificial and natural origin and their independence was concluded. Distribution of pink salmon originated from certain artificial hatcheries by sites of catch was rather constant that allowed to extrapolate the results for marked fish to all released pink salmon. The highest contribution of pink salmon of artificial origin was noted for catches in the Aniva Bay (23.9 %, on average), it was lower for catches at the southeastern coast of Sakhalin (13.2 %), and more lower for catches in the Patience Bay (7.6 %). Total number of pink adults of artificial origin caught on a particular stretch of coast did not depend directly on the number of pink juveniles released from a local hatchery, but was determined mainly by number of fish migrated there from other hatcheries. The landing of pink salmon originated from artificial hatcheries directly in the rivers where these hatcheries were located and at their mouths was < 10 % of the total catch of pink salmon of artificial origin. Schemes of quantitative distribution of pink salmon with marked otoliths in the waters of East Sakhalin are presented.

Migrations of young spotted seals (Phoca largha) from Peter the Great Bay, Sea of Japan/East Sea, and the pattern of their use of seasonal habitats

We studied the migrations of young spotted seals during their annual cycle. In May 2017, we attached satellite tags (SPOT-293A) to three individuals (two underyearlings and one yearling) captured at their breeding ground in Peter the Great Bay, western Sea of Japan/East Sea. The operational time of the installed tags ranged from 207 to 333 days; a total of 27195 locations were uploaded. All three seals migrated east and further north along the coast of the mainland. The average daily migration speed of the seals ranged between 70 and 135 km/day. The yearling moved faster than the underyearlings. During early August, they arrived at their summer habitats, which were located in the northern part of the Tatar Strait (Sea of Japan/East Sea) for the underyearling seals and in Aniva Bay (Sea of Okhotsk) for the yearling seal. While moving from the place of tagging to the summer feeding grounds, the seals covered a distance of 2300 to 3100 km. From August to October, each seal permanently stayed within the same isolated area. The reverse migration of all three seals began in November. When the seals traveled south, they used the same routes by which they had moved north in the spring, but they moved at a faster speed. By December, two seals returned to their natal islands, where both stayed until their transmitters stopped sending signals (in March 2018).

Spreading of the Amur River Water in the Eastern Aniva Bay in Late Autumn

As a result of an analysis of the long-term average salinity distributions at four standard sections of the Aniva Bay, it was shown that in the late autumn (November-December) there was an inflow of modified Amur low-salinity water along its eastern shore. According to the results of two oceanographic surveys performed on October 29-31, 2013 and November 29-03, 2013, a large-scale desalination in the northeastern part of the bay occurred in conditions of extreme river flow, much earlier than usual, was revealed. A year earlier, instrumental measurements of temperature and salinity revealed the appearance of this water in the area (salinity decreased to 27.5 psu) at the beginning of December 2012 it retained its influence until mid-March 2013. The revealed feature makes it necessary to consider the ecological habitats of certain species of aquatic organisms in the area in a different way.

On the unusual distribution of modified Amur River water in the Aniva Bay (Sakhalin) in November 2001

In addition to the distribution of modified water of the Amur River runoff in the Aniva Bay, remote from its mouth, according to the data from 2012–2013 (Shevchenko G.V., Chastikov V.N. Distribution of the Amur waters in the eastern part of the Aniva Bay in late autumn. Meteorology and Hydrology, 2021, no. 1), the materials of the oceanological survey carried out in this basin in mid-November 2001 are presented. It is shown that desalinated water entered the bay in an unusually wide stream in the upper 30-meter layer and occupied a vast area, almost to the middle of the bay. At the same time, the differences in salinity with local waters were less than usual. The most probable reason for such specific features of oceanological conditions in 2001 was an increase (by about 30% in comparison with the usual values) of the wind of west-northwest rhumb of an offshore character. The obtained results show that the influence of this water can manifest itself not only near the eastern coast of the bay, as was demonstrated in the mentioned article, but also at a distance of more than 30 km from it. Accordingly, abrupt decreases in salinity can affect the marine biota not only of the coastal complex, but also inhabiting the central part of the bay.

Size-age structure of oyster Crassostrea gigas in the Losos Bight (Aniva Bay, Okhotsk Sea)

Data on age structure, shell size (height, length, thickness) and weight of oyster Crassostrea gigas in the Losos Bight (Aniva Bay, Okhotsk Sea) are presented on results of the surveys conducted in 2018 and 2019. The size-age key for the total weight is plotted. The size-age structure is compared with oysters from other habitats.

ESTIMATION OF ABUNDANCE FOR THE MIGRATING JUVENILE PINK SALMON IN THE RIVERS OF SAKHALIN AND ITURUP ISLANDS IN 2019

Number of the pink salmon fry migrating downstream from their spawning grounds in the control rivers in 2019 is assessed as 17546.2 . 103 and 14795.7 . 103 ind. for the Dagi and Bolshoi Khuzi Rivers (northeastern Sakhalin), as 89.1 . 103 and 2636.1 . 103 ind. for the Poronai River tributaries — the Kholodny and Orlovka, as 2759.8 . 103 and 21456.0 . 103 ind. for the Lazovaya and Pugachevka Rivers (western coast of the Patience/Terpeniya Bay), as 5803.8 . 103 and 19020.0 . 103 ind. for the Voznesenka and Ochepuha Rivers (southeastern Sakhalin), as 1822.4 . 103 and 2139.0 . 103 for the Taranai and Kura Rivers (Aniva Bay coast), and as 15834.1 . 103 and 7626.1 . 103 ind. for the Rybatskaya and Olya Rivers (Iturup Island), respectively. In all areas, the pink juveniles migrated from the spawning grounds earlier than usual, obviously because of accelerated development of the embryos in conditions of abnormally warm autumn. The number of juveniles migrated from all spawning grounds in the rivers of respective regions is estimated taking into account the escapement of pink salmon spawners and the downstream migration index determined for the control rivers (ratio of the spawners escapement and the number of subsequent downstream migrating juveniles): the total number for the natural spawning grounds is estimated as 1168.9 . 106 ind. for the rivers of the eastern coast of Sakhalin (including the Aniva Bay) and 471.1 . 106 ind. for the rivers of Iturup Island (Okhotsk Sea coast). Additional 141.3 . 106 ind. were released from artificial hatcheries of eastern Sakhalin and 122.0 . 106 ind. — from artificial hatcheries of Iturup Island. The downstream migration is considered as highly abundant for northeastern Sakhalin and Iturup Island, but is insufficiently abundant for the Patience/Terpeniya Bay and Aniva Bay where the landings of this generation should be limited. The pink salmon return to southeastern Sakhalin in 2020 is expected to be better than in 2018 due to satisfactory abundance of the juveniles from natural spawning grounds.

DISTRIBUTION AND RESOURCES OF YESSO SCALLOP MIZUHOPECTEN YESSOENSIS IN THE SAKHALINKURIL REGION ON RESULTS OF THEIR EXPLOITATION FROM 2000 TO 2011

Results of commercial exploitation of the yesso scallop resources in the Sakhalin-Kuril region in 2000–2011 are analyzed, taking into account the data of diving surveys at the depth of 2–30 m (on average 5 stations with sampling from 50 m2 per transect) in the 2009–2012. The results are compared with published and archived data for unexploited period. Range of the scallop spatial distribution did not changed. Size of the scallop increased, but its abundance and biomass decreased, in general, in particular in the Aniva Bay and on the shoal at southern Kuril Islands, though the scallop became more abundant in the Aleksandrovsky Bay and Patience Bay. The stocks reducing in the Aniva Bay was possibly caused by lack of feeding.