抄録
底曳漁獲量からみたマダラの濃密な分布は, 太平洋では北海道の襟裳岬以東の海域, 北海道恵山沖および三陸沖の3つの海域にみられ, 日本海では, 青森・秋田県沖および山形県沖の2つの海域にみられた。月別1曳網当り漁獲量を用いて因子分析を行った結果, 襟裳岬以東海域, 北海道恵山沖および三陸沖の魚群はそれぞれ異なる変動傾向を示す魚群であった。また脊椎骨数の解析から, 襟裳以東海域は他海域より脊椎骨数が有意に多いことが分った。これらの結果と産卵場の知見を考慮すると, 太平洋側海域には襟裳岬以東群, 陸奥湾・恵山沖群および三陸沖群の3つの系群が存在すると結論された。
Density of the fish shoal and vertebral counts of Pacific cod at various locations in the Sea of Japan and in the Pacific Ocean off the Tohoku District, and in the Pacific Ocean off Hokkaido were studied. Off the Pacific coast, there were three high density areas of fish shoal, i. e., the waters off Sanriku in the Tohoku district, the waters off Cape Esan and the waters off Kushiro in Hokkaido. In the Sea of Japan, there were two high density areas of fish shoal, i. e., the waters off Aomori and Akita prefectures and the waters off Yamagata prefecture. In addition, factor analysis of the monthly catch per seine net showed that the fish in the eastern waters off Cape Erimo, those in the western waters off Cape Erimo, and those in the waters off Sanriku each have peculiar trends of change in the CPUE (catch/net) among monthly catches. Furthermore, the statistical analysis of the vertebral counts showed that the Pacific cod from the eastern waters off Cape Erimo had significantly higher vertebral counts than the Pacific cod in other areas. The results of the present research and the information on spawning grounds previously reported, suggest that there are three subpopulations of Pacific cod in the present research area in the Pacific Ocean, i. e., a subpopulation in the eastern waters off Cape Erimo, a subpopulation off Cape Esan and a subpopulation off Sanriku District. Further studies are needed to determine the locations of subpopulations of this species in the Sea of Japan.
