ЛЕТНЕЕ ПИТАНИЕ СИВУЧА В ВОДАХ ДАЛЬНЕГО ВОСТОКА РОССИИ В 2004–2008 ГОДАХ

The diet of Steller sea lion Eumetopias jubatus was studied based on undigested food parts found in feces collected in the summer season on 20 rookeries in the Russian Far East. A total of 915 samples were analyzed between 2004 and 2008, in which 65 food items were identified. The frequency of occurrence of 11 diet items was greater than 5%, including Atka mackerel Pleurogrammus monopterygius (64.8%), Pollock Theragra chalcogramma (44.3%), Pacific salmon Salmonidae (20.5%), Irish lord Hemilepidotus sp. (20.4%), Pacific sand lance Ammodytes hexapterus (15.8%), Pacific herring Clupea pallasi (9.5%), Squid and Octopus Cephalopoda (8.4%), Pacific cod Gadus macrocephalus (5, 9%), Pacific sandfish Trichodon trichodon (5.9%), Flatfishes Pleuronectidae (5.8%), Threespine stickleback Gasterosteus aculaeatus (4.9%). Three regions with different diets were identified – the Sea of Okhotsk, the Kuril Islands, and Kamchatka with the Commander Islands. In the Sea of Okhotsk, Pollock and Herring (83.6% by frequency of occurrence) dominated among undigested food remains in feces. The diet at the Kuril Islands rookeries was variable within the region. The general pattern was a low diversity of diet at each Kuril Island sites and predominance of 1-3 food items, probably the most accessible near the sites (Pollock, Squid and Octopus, Atka mackerel, Pacific salmon). The diet pattern in Kamchatka and the Commander Islands in the summer season was characterized by a high diet diversity. In contrast to other regions, the diet includes in high proportion small non-commercial species – Sand lance, Irish lord, Pacific sandfish, Flatfishes, Threespine stickleback and others. The regional patterns of sea lion diets show the spatial distribution and areas of abundant biomass of the main food items. The diet patterns of sea lions from rookeries differed from haulouts in having a higher content of abundant food items. Long-term changes in diet structure were not statistically significant.

Cases of capture of Atka mackerel, Pleurogrammus monopterygius, transplanted to the Barents Sea from south-eastern Kamchatka

Atka mackerel, Pleurogrammus monopterygius was proposed for acclimatization to the Barents Sea long ago (Russ, 1958) and has been thoroughly studied in this regard. However, the number of experimental works by the transplantation of Atka mackerel from Kamchatka to the Barents Sea was small and their scale is insignificant. A total of 2 attempts were made in the 70s and 80s. The last time in 1982-1984, 6.5 millions of Atka mackerel caviar was transported from Kamchatka to Murmansk. Unfortunately, the systematic works by introduction was stopped. Meanwhile, the experience of acclimatization of Atka mackerel is very valuable not only for its practical orientation, which has in the future the additional production of fish in the Barents Sea, but also for a certain contribution to the development of the theory of acclimatization. The article provides information on the two repeated capture of Atka mackerel in the Barents Sea and six repeated in the White Sea. It is advisable to purposefully check the information on the White Sea; it is possible that the short time of the stay of adults Atka mackerel in the reservoir during the breeding period does not allow them to be identified during the annual ichthyological survey of the White Sea. It would be useful to catch of the Teribersky Cape of the Barents Sea, where adult Atka mackerel can be found during the breeding season. If the facts will not be confirmed, then our supposition remains true that the scale of work on the transplantation of Atka mackerel caviar was insignificant and the amount of imported caviar is small

The first evidence of intersexuality in Atka mackerel Pleurogrammus monopterygius (Hexagrammidae)

Summary Histological examination of Atka mackerel ovotestes reveals the possibility of intersexuality. Individuals with bisexual gonads have been caught in the North Pacific near the south-east coast of the Kamchatka peninsula. While intersex appeared to be normal females with developing ovaries, histological analysis showed the presence of both female and male tissue in the same gonad. Specifically, primary growth, cortical alveolar and primary vitellogenic oocytes were located among spermatogonia cysts. The prevalence of intersexuality in the population was less than 0.1%.

About the forced and later spawn of Atka mackerel Pleurogrammus monopterygius Pallas, 1810 (Scorpaeniformes: Hexagrammidae) in the waters of the North Kuril Islands

Results of the research indicate that the eggs of Atka mackerel are a part of forage for this speciesis from May to December. Captures of the Atka mackerel individuals spawning and feeding on the own eggs far from the coast indicate that a certain part of the stock spawns at the depths considerably lower than normal spawning grounds. Spawning individuals of Atka mackerel is were observed in research from June to December. Emergence of larvae from the eggs laid in November–December is expected in spring.

STATE OF STOCKS AND MODERN FISHERY OF ATKA MACKEREL PLEUROGRAMMUS MONOPTERYGIUS (PALLAS, 1810) IN THE OLYUTORSKY-NAVARINSKY AREA OF THE BERING SEA

Atka mackerel Pleurogrammus monopterygius is one of the mass species of fam. Hexagrammidae that inhabits the boreal and subarctic waters of the North Pacific and forms two large populations in its western and eastern parts. Reproductive range of the eastern, Aleutian population extends from the Gulf of Alaska, along Aleutian Islands to Commander Islands, with the main spawning grounds at the Aleutians and in the southeastern Bering Sea. From these areas, the fish at early stages of ontogenesis spread widely in system of the Bering Sea currents to the western-southwestern Bering Sea, where the atka mackerel aggregations are formed on the external shelf at prominent capes, as Cape Olyutorsky. Dynamics of the atka mackerel stock in the Olyutorsky-Navarinsky area in 1994–2019 is presented on the base of bottom trawl surveys, fishery statistics, and open NOAA data. After the period of low stock in the middle 1990s, the atka mackerel abundance increased sharply to the maximum in 2006–2008, when the spawning stock in this area was about 9.5 . 103 t and the commercial stock about 14.0 . 103 t. Since that time, trend to decreasing is observed, with the spawning stock 3.6 . 103 t and the commercial stock 5.6 . 103 t in 2013, and recent stabilization at the low level with slight decline continuing. A possible reason of the sharp increase in 2000s could be the intensive transport of the atka mackerel juveniles from the main spawning grounds at Aleutian Islands to the area at Cape Olyutorsky. The catches of atka mackerel in the Olyutorsky-Navarinsky area in 1994–2018 corresponded well with its stock dynamics.