Comparative analyses of changes in the ice cover of the Tatar Strait in relation to 1961-1990 and 1991-2020 climate normals

Current warming in the Northern Hemisphere has encompassed not only the surface atmosphere, but also manifested itself in a change in the state of the sea ice cover, as an integral part of the climate system. One of the indicators of the warming was a reduction in ice cover observed in the water area of the Far Eastern seas since the late 1980s. The prospective areas of hydrocarbon deposits discovered in the Tatar Strait, as well as the existing needs for the transportation of hydrocarbons along the shipping routes in the strait, led to the emerging interest in researching the ice regime of the Sea of Japan in the modern climatic era. The proposed paper analyses the changes in ice cover of the Tatar Strait in relation to 1961–1990 and 1991–2020 climate normals. The regularities of the long-term variability of ice cover within non-overlapping 30-year periods were revealed. The analysis of the dynamics of ice cover anomalies, calculated for each normal separately, was carried out. An assessment of the distribution of winter types in the periods under study was carried out. The characteristic features of variations in the intra-seasonal course of ice cover and the dates of the onset of ice phases in different types of winters were identified.

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.

Fishery and traditional fishing problems of Pacific salmon on Tatar strait coast (Khabarovsk region)

The peculiarities of the fishing of Pacific salmon, especially pink salmon, on the coast of the Tatar Strait (Khabarovsk region) are considered. After the 2016 harvest generation, there has been a significant decline in approaches in 2018 and 2020. The problems of traditional fishing by aboriginal peoples have been analyzed. During observations of the fishery in 2016, factors influencing the efficiency of reproduction of pink salmon were noted, with significant restrictions on traditional fishing. Solutions related to the development of aquaculture, improving the organization of fisheries and granting preferences, and the development of public-private partnerships have been proposed.

Global earthquakes in the 2020 second half according to the GS RAS

The data on the seismicity of the Earth in the second half of 2020 at the level of strong earthquakes with magnitudes mb≥6.0 are given according to the data of the Alert Service of the Geophysical Survey RAS. The review also includes information on 54 tangible earthquakes in Russia and five earthquakes in adjacent territories that were felt in the settlements of the Russian Federation. Two of 67 strong earthquakes of the Earth with mb≥6.0 for the period under consideration were registered in the territory of Russia. For 15 strong earthquakes, the Alert Service published Information Messages within one or two days after their occurrence, for 14 earthquakes the information on focal mechanisms is provided. The strongest earthquake of the Earth with MS=7.9 occurred on July, 22 in the region of the Alaska Peninsula. The maximum human casualties and material damage during the study period were the result of the catastrophic intraplate earthquake with MS=6.8, which occurred on October, 30 in the Aegean Sea, near the Samos Island. As a result of the earthquake, 117 people died, 1054 were injured. The strongest earthquake on the territory of Russia was the deep-focus one with mb=6.4, which took place on November, 30 in the Tatar Strait, separating Sakhalin Island from continental Eurasia. The crustal Bystrinsk earthquake on September, 21 with MS=5.2, which occurred in the area of Lake Baikal, was felt with a maximum intensity I=6–7 on the territory of Russia. Comparative analysis of the rate of seismic energy released in the Globe in 2010-2020 showed that its value in the second half of 2020, as well as for 2019-2020 on average, is one of the lowest for the eleven-year period and indicates a seismic calm, which should be replaced by a period of intensification of global seismic and deformation processes

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).