Annual life period of the Adult Alaska pollack in the Adjacent Waters of the Funka Bay, Hokkaido

Abstract

Once a month from February 1974 to February 1975, adult Alaska pollack Theragra chalcogramma (Pallas) were caught by bottom gill nets at four definite stations in the adjacent waters of the Funka Bay, Hokkaido. The authors examined several biological factors of the Alaska pollack, density of the fish shoal, and distribution of the eggs. As a result, the annual life cycle of the adult Alaska pollack from February 1974 to February 1975 was divided into four periods as follows. 1) Spawning period, judging from the value of gonad index and the maturation stage of the adult Alaska pollack, was from December to March, and the peak in the period was from December to February. 2) Feeding period, judging from the value of feeding index, percentage of empty stomach and the value of liver index, was from May to October, and the peak was during July and August. 3) As the transitional periods, the terms from the end of spawning period to the beginning Of feeding period and from the end of feeding period to the beginning of spawning period were assigned. The former was from the last of March to the last of April, and the latter was from the last of October to the last of November. © 1981, The Japanese Society of Fisheries Science. All rights reserved.