Seasonal Distribution of Threaded Sculpin Gymnocanthus pistilliger (Cottidae) in Russian Waters of the Sea of Japan

— In Russian waters of the Sea of Japan, the threaded sculpin Gymnocanthus pistilliger occurs at depths of 5 to 217 m and water temperature in the near bottom layer from –1.4 to +18.7°С in the spring–autumn season. In spring, it migrates from the outer border of the shelf towards its heated middle and upper parts where it forms feeding aggregations in summer and prespawning aggregations in autumn. The largest concentrations are observed in Peter the Great Bay, while the smallest ones in the northern part of Tatar Strait. In summer, juveniles stay in a heated shallow zone that is avoided by adults. As the water temperature starts to get cooler in autumn, small-sized fishes move to deeper layers and spawners penetrate into shallow areas. Only adult fishes live at the maximum depths during all seasons. G. pistilliger reaches a larger size (33 cm) in waters of the Sea of Japan than in the northern part of its range. Females reaching larger sizes than males prevail in the population. In summer, the sex ratio is even at relatively small depths; the proportion of females gradually increases with depth.