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

摘要

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.