改良II型たて繩による太平洋熱帯海域におけるメバチの釣獲層

抄録

In January to February 1974, a total of 12 daytime sets of the further improved vertical long-line gear was made in the North Equatorial Current areas. Compared with the improved vertical long-line gear that had been used previously, there appeared to be no difference in the frequency of branch line fouling, and the time required to retrieve the gear was reduced by 11% per unit (one basket). Compared with the commercial long-line gear fished at the same time, there was no significant difference in the catch rates, but a highly significant difference was detected in the species composition of the catch. According to the 95% confidence intervals for ratio of occurrence of the species, this vertical long-line catch was significantly higher than the commercial long-line catch, in bigeye tuna, Tunnus obesus, only. It is indi-cated that this gear is effective in catching fish. The depth layer in which bigeye tuna were captured was below or near the vicinity of the bottom of the thermocline, where the tempera-ture ranged from 11°C to 15°C.