延繩によるマグロの釣獲時刻について

抄録

In order to clarify the time of capture of tunas by the long-line gear, the catch data and the records of capture that was measured by an automatic depth meter were examined. The experiments were carried out in the tropical Pacific for bigeye and yellowfin from January to March, 1974, and in the western South Pacific for albacore in November, 1969.
Assuming that tuna catch is in proportion to the soaking time of the long-line gear, the CPUE/hour (soaking time) was estimated from the CPUE by soaking time. The lethal time (lapse time from capture to death) was calculated from the CPUE of dead fish by soaking time. The lethal times of bigeye, yellowfin and albacore were 4.82, 2.90 and 2.57 hours (soaking time), respectively. The CPUE/hour of live fish could be estimated by the lethal time. Then, comparisons of the variances and means of these CPUE/hour were made between daytime and nighttime.
The bigeye showed greater values than the yellowfin not only in the lethal time but also in the variance of CPUE of dead fish. Accordingly, from pooled CPUE/hour of live and dead fishes in the bigeye and from the CPUE/hour of live fish in the yellowfin, it was considered that the feeding in the daytime is more active than that in the nighttime. In the albacore, the catch data in the nighttime was insufficient, but it was presumed that the feeding is of a similar tendency to the former species.