噴火湾周辺海域におけるスケトウダラの漁場学的研究. II, 産卵期

• Published in: NIPPON SUISAN GAKKAISHI
• Main Authors: 前田, 辰昭, 高橋, 豊美, 伊地知, 誠, 平川, 英人, 上野, 元一
• Format: Article in Journal/Newspaper
• Language: Japanese
• Published: 日本水産学会
• Subjects: 664; Oyashio; Theragra chalcogramma; Alaska
• Online Access: http://hdl.handle.net/2115/38567; https://doi.org/10.2331/suisan.42.1213

In a previous paper, the authors reported on the distribution pattern of the Alaska pollack, Theragra chalcogramma (PALLAS), which have been found in fairly large numbers during the feeding season in the adjacent waters of the Funka Bay, Hokkaido. In this paper, the distribution, migration, and spawning grounds of the adult Alaska pollack in the spawning season during August 1973 through July 1974 have been examined and is reported. The spawning season marked by the maturation stage of the gonad in the Alaska pollack lasted during January to March in 1974. The shoal migrated toward the shallow parts with the progress of maturation of their gonads; they stayed at the front of the cold water mass near the 100 meter depth. The cold water mass in the shallow parts was caused by the cooling in winter and by the upper layer water mass of the Oyashio current, 1974. The spawning grounds of the Alaska pollack varied with the intensity of cooling in winter and with the upper layer cold water mass of the Oyashio current. In 1954, the main spawning grounds were reported to be inside the Funka Bay, when the sea water temperature of the shallow parts in this region was high, but in 1974 when the sea water temperature of the shallow parts is low, its grounds were at the entrance of the Bay near the 100-120 meter depth. The sex ratio of the fish in the spawning season varied at each station. The male fish remained for a long time in the spawning grounds, but the female fish migrated to the deep sea areas once spawning was over. Because there were more male fish than female fish at the spawning grounds, the female fish predominated at the feeding groounds in the deep sea areas. 1. 1973年8月から1974年7月に噴火湾周辺海域において底刺網による漁獲試験，魚探の利用，スケトウダラ卵の採集，海洋観測等を行い，産卵期を中心としたスケトウダラの分布回遊を明らかにした。2. 生殖巣の成熟Stageからみた1974年の産卵期は1月から3月であつた。3. 魚群は生殖巣の成熟に連れて，索餌期に棲息していた水深300m付近の餌生物が多い親潮系底層水域から浅海域に産卵のため回遊し，表層からの冬期冷却と寒冷な親潮系表層水の影響によつて100m付近に発生した冷水前線に停滞した。4. 産卵場は冬期間の冷却と親潮系表層冷水塊の強さによって変化する。中心部は浅海域の水温が高かつた1954年には噴火湾の内部にみられたが，水温が低かつた1974年には湾ロ部の水深100～120m付近に形成された。5. ...