延繩の浸漬時間とマグロ類の漁獲との関係

Abstract

The soaking time increases in the direction of hauling. There is no signification variation of yellowfin catch, with increasing hours of soaking. Probably a fair amount of yellowfin tuna are hooked when the gear is sinking to the settling depth or when being hauled to the surface. The yellowfin catch has a position of maximum catch, on the longline. Probably albacore and marlins also do so. But big eye tuna does not show such a phenomenon very clearly like yellowfin. Schooling or aggregating habit of yellowfin is capable of nullifying the effect of soaking time on the longline catch. Probably there is some variation in the tuna catch with the time of the day. Behaviour of tuna has a major effect on the longline catch. Probably this factor exhibits greater effect on the big eye tuna catch than on the yellowfin catch by longline.