Long-term dynamics of stocks of greenland halibut Reinhardtius hippoglossoides matsuurae in the Bering Sea and Pacifc waters at Kamchatka and Kuril Islands

Abstract

Despite the long history of studies, some aspects of the greenland halibut biology in the North Pacifc are still poorly known. In particular, scientifc publications on its groupings in the Bering Sea and at the continental slope of the North Pacifc and their dynamics are rather few, with exception of the western Bering Sea area from Cape Olyutorsky to the Anadyr Bay where its dynamics is well traced by surveys of Pacifc Fish. Res. Center (TINRO). All data on long-term dynamics of the greenland halibut abundance and distribution in the Bering Sea and Pacifc waters at Kamchatka and Kuril Islands are overviewed and comparatively analyzed, including materials of bottom trawl surveys conducted in 1950–2015 and published research reports, in total the data of 66 surveys (4,350 bottom trawls) in the Karaginsky and Olyutorsky Bays, 43 surveys (4,900 trawls) on the Pacifc shelf and continental slope of Kamchatka and northern Kuril Islands, and 24 surveys (2,048 trawls) at southern Kuril Islands. Biomass of greenland halibut is assessed for the western Bering Sea and the Pacifc waters at Kamchatka and the Kuriles using the data of TINRO and for the eastern Bering Sea using the published data of NOAA and NPFMC. Gradual decreasing of commercial value of the halibut groups is shown with increase of the distance from its main spawning grounds in the southeastern Bering Sea. Self-reproduction of the halibut groups supposedly decreases in the same direction. This assumption is confrmed by the data on its larvae and juveniles density in the epipelagic layer of the western Bering Sea and North-West Pacifc that decreases from the maximum values in the Anadyr Bay to the Olyutorsko-Navarinsky district and further southward to the minimum value at southern Kuril Islands. The average portions of certain groups of greenland halibut in its total biomass in the North Pacifc (without the Okhotsk Sea) are estimated as follows: almost 85 % (146.0 . 103 t) is contributed by the southeastern Bering Sea, about 14 % (23.2 . 103 t) — by Olyutorsko-Navarinsky district and the Anadyr Bay, and 1% (about 1.5 . 103 t) — by the waters at northeastern and eastern Kamchatka and at Kuril Islands. Stock dynamics is similar for all groups: the stocks increased until the early 1970s with the peak in 1976–1980, when the species biomass was estimated as 280 . 103 t in the southwestern Bering Sea, 40 . 103 t in the Anadyr Bay and Olyutorsko-Navarinsky district, and 5 . 103 t in the bays of eastern Kamchatka and at northern Kuril Islands, then declined to the minimum in 1990–2000s, and recently the peripheral groups show a gradual growth. The dynamics similarity is possibly reasoned by passive transfer of the halibut eggs and larvae from the Bering Sea toward eastern Kamchatka and Kuril Islands by the system of oceanic currents.