FISHING MECHANISM ANYLYSIS OF SKIPJACK PURSE SEINE FISHERIES

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The research project deals with the Experimental and analytical study on the fishing mechanism of skipjack purse seine fisheries, from the view points of the comrehensive approach including both the practical and theoretical research fiels such as fish behavior, fishing gear, fishing boat, fisheries oceanography and the fisheries information sciences. The results for three years project are summarized as follows :The project research cruise was conducted in the western tropic Pacific region on December 1991, with two vessels of the resarch boat and the purse seiner. The Umitaka-Maru, R/T veseel of the Tokyo University of Fisheries, was engaged in the oceanographic observation with CTD and XBT in the fishing ground, where the Taishin-Maru No.18 operated 30 hauls during the same period to aquire the data such as meteological and ocenographic conditions, boat maneuvering strategies and corresponding catch data, as well as the detailed observation data on the dynamic geometies of the fishi … More ng gear. Another individual cruise by the Korean purse seiner in December 1993 also deliver the additional XBT observation data with the catch data for the surface migrating school, which can be available in good comparison to the drift-timber attarated school in 1991.According to the long-term operation records, the catch analysis was conducted in special attention with the ditribution of target school. The seasonal variation of catch in relation to the ecological characteristics of skipjack school was already published in the Jounal of the Tokyo Univerisy of Fisheries. The influence of E1 nino on the fishing ground for yellowfin tuna varied yeary, which can be attributed to the E1 nino phenomena. According to the statistical analysis on the catch distribution pattern, the intensive catch could be observed in the good fishing years.The flume tank experiments with the model gear could offer the informative results on the improvement of gear desining as well as the operation strategy, with the comparison to the static and dynamic values of gear geometry which were obtained from the reserach cruise data of Taishin-Maru No.18. The data on the vibration, pitching and rolling characteristics of purse seiners were obtaind in the practical operation starategy, and has been in processing for analysis.Concerning the behavioral physiology of target species, the experimental and theoretical approach was done with the special focusing on the fish capture process of skipjack purse seining. The cruising speed of skipjack tuna was measured as 2-3 BL/s, while the maximum speed 15-20 BL/s from the muscle activity check. In addition with the visual physiology experiment on skipjack tunas, the theoretical model on the surrounding and interrupting procedure was discussed for the future task on the strategy improvement of purse seine operation in catch failure and success aspects. Less