On the Hooked Rates of the Tuna and Shark in Tuna Long Line Fishing with Underwater Lamps, with Luminous Baits and with Ordinary Hooks

1. To study the baiting conditions of the tuna and shark based on their phototaxis, the authors performed a test fishing in the Indian Ocean on board "Nagasaki-maru" of Nagasaki University for 7 days from 3 to 9 August 1966, using the tuna long line with underwater lamps and with luminous baits. 2. The fishing, methods with underwater lamps and with luminous baits were compared with the fishing method with ordinary hooks only, and the significance in the difference between them was studied. 3. For the hooked rates, the method with underwater lamps gave 3.91%, the method with luminous baits 3.18%, and the method with ordinary hooks 1.70%. 4. The means for the three methods were compared with eachother, but it cannot be mentioned that the means of their respective population are necessarily different from each other. Accordingly, it is impossible to judge which method is the most effective without further accumulation of experiment.1) マグロ延縄に水中ランプおよび自発光物を用いたものと普通の釣針のみを使用したものと比較検討して,それらの有意性の考察を試みた. 2) 釣獲率からみると,水中ランプを用いた釣針3.91%,自発光物質を用いた釣針3.18%,普通の釣針のみの場合1.70%であった. 3) 二組の平均値を相互に比較した結果,それぞれの母平均が異なっているとは言えなかった.したがって,いずれの方法が有効であるかは多くの実験例によらなければ判別することができない