Spawning grounds and distribution pattern of the Alaska pollack in the eastern Bering Sea

The authors sampled the Alaska Pollack, Theragra chalcogramma (PALLAS), eggs by a vertical haul of the plankton net from the sea botton to the sea surface and measured the specimens of the Alaska Pollack caught by the bottom trawl from mid-April to the end of May during the spawning season of 1972 and 1973 in the eastern Bering Sea. Also examined were the spawning grounds of the Alaska Pollack, by a study of the distribution of the larvae sampled by a larva net of the “Oshoro Maru”, from Jnne to August of 1966-1968. From these studies the distribution pattern of the fish shoals from the maturity stage of the gonads and the sex ratio in the spawning season were investigated. In 1972 and 1973, the spawning grounds of the Alaska Pollack were divided into two parts by the shallow part of the Pribilof Islands and the sea valley of the south-eastern part of the islands. The center part of the spawning grounds was formed in the north-western area of the Unimak Island and the south-western area of the Pribilof Islands. In addition to these, the authors wish to infer that other spawning grounds were formed in the near continental slope of the north western area of the Pribilof Islands as observed from the distribution of the spawning fish and the larvae. The sex ratio of the fish varied at each station. The male fish predominated in comparison with the female fish at the center part of the spawning grounds in the shallow part, but the male fish showed a slight decrease with the distance from the center part, and the female fish at the wintering grounds in the deep sea areas were more numerous than the male fish.