Spatial distribution, size composition, and dynamics of catches of the Okhotsk skate Bathyraja violacea in the North Pacific Ocean

Abstract

The results of the long-term (1963–2015) studies of spatial and vertical distributions, dynamics of abundance and size composition of the Okhotsk skate Bathyraja violacea in the North Pacific Ocean are presented. This species is the most abundant at depths of 100–400 m; in the cold season, it migrates to the larger depths for wintering, while it migrates to shallower depths in the warm season. Specimens of the length 12 to 132 cm with prevalence of skates of 50 to 80 cm long were recorded in catches. The difference between males and females in body weight and length was not considerable. Condition factor of specimens decreases from January to August and begins to increase in September. Males dominate among the skates up to 30 cm long, females dominate in the size groups of 30–60 cm and >70 cm, while an almost equal sex ratio is observed in the size group of 60–70 cm. The dynamics of the catches of the Okhotsk skate vary in different regions: in the western Bering Sea and in the Sea of Okhotsk, the catches consistently increased during the study period, the catches increased to the mid-1980s–early 1990s in the Kuril and Kamchatka waters of the Pacific Ocean, and then a decrease has been observed; in the eastern Bering Sea, the peak of catches occurred in the mid-1970s, and then they decreased subsequently.