Bull. Jpn. Soc. Fish. Oceanogr. 80(3), Page 222-230, 2016   Relationship between the distribution of skipjack (Katsuwonus pelamis) fishing grounds and the formation of cold water masses in the region to the south of the Kuroshio Current Mitsuhiro Ishii1†, Yutaka Kobayashi1, Takashi Setou2 and Osamu Honda3 1 Chiba Prefectural Fisheries Research Center, 2492 Chikura-cho, Hiraiso, Minamiboso, Chiba 295-0024, Japan 2 National Research Institute of Fisheries Science, Fisheries Research Agency, Japan, 2-12-4 Fukuura, Kanazawa-ku, Yokohama, Kanagawa 236-0004, Japan 3 Japan Fisheries Information Service Center, Toyomi-shinko Bldg. 6F, 4-5 Toyomi-cho, Chuo-ku, Tokyo 104-0055, Japan † E-mail: m.ishi26@pref.chiba.lg.jp The distribution and occurrence of cold water masses on the south side of the Kuroshio Current was examined in relation to the formation of fishing grounds for migrating skipjack. Fishing range of skipjack inshore pole fishery is formed in areas with sea surface temperatures lower than 19°C. To the south of the Kuroshio Current in spring, cold water mass with a sea surface temperature lower than 19°C sometimes stretches from the area north of 28°N, the Boso offing, to around 133°E of the Shikoku offing. Therefore, in years when a cold water mass occurred it was observed that the northward migration of skipjack was either blocked or bypassed the cold water mass. The northward migration course of skipjack and the time remaining in areas during its northward migration can be predicted from the water temperature on the south side of the Kuroshio Current during spring. Key words: skipjack, cold water mass, northward migration