ハタハタ日本海西部系群の資源変動を説明するために2つの数理モデルを開発した．モデル1：年tの本系群の漁獲量C_tは親魚量指数により決定される．モデル2：Ct_tは親魚量指数と環境要因（Ct_tと有意な相関関係を示したt―1とt―2における朝鮮半島東岸沖の水温）により決定される．Ct_tの変動の再現性を検討した結果，モデル2は，モデル1に比べて精度良くCt_tの変動を説明した．また，1980–1999年までを予測（外挿）する場合についてシミュレーションを行った結果，モデル2により精度のよい予測が可能であった．モデル2において有意な環境要因として採用した水深150m以深の冬季水温は，冬季混合層の厚さの推定値(MLD) と有意な正の相関関係を示した．また，MLDとCt_tの長期変動は類似していた．以上の結果から，本系群の資源変動は親魚量とMLDの年変動に関連した環境要因に強く影響を受けていることが示唆された．

We described spatial distribution, length frequency compositions and hatching date distributions of juvenile jack mackerel and young Japanese common squid collected from the Kuroshio-Oyashio Transition Zone (KOTZ) in May 2003. Numerical model experiments incorporating geostrophic and wind-driven currents confirmed transport routes of larvae and juveniles of jack mackerel and common squid from their reported major spawning grounds in the East China Sea (and from southern Japan for jack mackerel) to KOTZ. Spatial distribution and length frequency data and numerical transport model results of common squid suggested their northward migration during spring. Jack mackerel distributed in the KOTZ may not recruit to fishing grounds in the central and northern Japan, since their northward migration was not evident and jack mackerel catch in the northern Japan was much smaller than that of common squid.

To reveal the accurate biomass and detailed vertical distribution of Cnidaria and Ctenophora, new Video Plankton Recorder (VPRII) and plankton net were towed while obtaining environmental (CTD) data from 25 to 500 m depth during July 2003 and June to July 2004 at 5 stations in the Oyashio and Transition zone off the Joban, Sanriku and Eastern Hokkaido coast, Japan. The vertical distributions of Hydromedusa and Ctenophora biomass in every 10 m depth obtained from the VPRII images were intermittent. The biomass peaks of Hydromedusa in the vertical distribution were found in the North Pacific Intermediate Water (NPIW). While the peaks of Ctenophora were both in the surface layer and NPIW, and the surface peak seems to have been associated with their food source because it was located directly below the surface fluorescence peak. To supplement the underestimation of larger size organisms by VPRII measurement, we used the <10 mm sized Hydromedusa and Ctenophora from VPRII, whereas the >10 mm Hydromedusa and Ctenophora and whole size Siphonophora was used from the plankton net data. Cnidaria and Ctenophora biomass estimated from VPRII images and plankton net samples averaged over 25 to 500m were from 0.021 to 0.063mgCm^-3 in the Oyashio and Transition zone, and these biomasses were 14 times higher (0.3 to 260, SD-=44, n=40) than only using the plankton net samples. The ratio of Cnidaria and Ctenophora to Copepoda biomass was only from 0.2 to 0.7%. However, it seems that the biomass of Cnidaria and Ctenophora was higher than in our estimation by either depth or location due to the intermittent distribution and underestimation of larger Ctenophora biomass in our methods.