Bull. Jpn. Soc. Fish. Oceanogr. 84(2), Page 79-88, 2020   Fishery characteristics of large bigeye tuna Thunnus obesus caught by longline fishing ‘Kajiki-nawa’ along the Boso coast, Japan Mitsuhiro Ishii1†, Hiroaki Ishiguro2a, Toru Shinohara2b, Hidetaka Noguchi3, Masao Suzuki3, Nobuaki Horikawa3, Yutaka Takimoto3 and Kotaro Yokawa4 1 Chiba Prefectural Fisheries Research Center, 2492 Chikura-cho Hiraiso, Minamiboso, Chiba 295–0024, Japan 2 Katsuura Marine Industries Office, 815–12 Tona, Katsuura, Chiba 299–5225, Japan a Chiba Prefectural Marine Industries Promotion Division, 1–1 Ichiba-cho, Chuo-ku, Chiba, Chiba 260–8667, Japan b Chiba Prefectural Fishery Resources Division, 1–1 Ichiba-cho, Chuo-ku, Chiba, Chiba 260–8667, Japan 3 Chiba Coastal Small Fishing Boat Fishing Cooperative, 1963–2, Matsube Katsuura, Chiba 299–5241, Japan 4 National Research Institute of Far Seas Fisheries, Japan Fisheries Research and Education Agency, 5–7–1 Orido, Shimizu-ku, Shizuoka-shi, Shizuoka 424–8633, Japan † E-mail: m.ishi26@pref.chiba.lg.jp The catch characteristics of large bigeye tuna fish caught by near-shore longline boats, NL, ‘Kajiki-nawa’ along the Boso coast were analyzed. NL were operated around the Kuroshio channel of the Boso coast from November to June of previous year. The fishing line operated a shallow line with a reach of about 70 m deep during the daytime, and mainly caught fish with a fork length of 110 cm or more. Monthly mean surface water temperature for the bigeye tuna was 18.5–23.2°C, which is different from records for bigeye tuna so far, with fish caught in the high-water temperature area at shallow water depth during the day. Key words: bigeye tuna, fishing ground formation, fishing depth, fishing temperature, near shore longline boats