little danger of overfishing. The same is true of fishes which have an extremely broad range 

 of occurrence. However, where the fishing is extremely efficient and effective, it may naturally 

 be thought that there is danger of its outweighing such considerations as the reproductive 

 potential. 



Except in some special cases, net fishing has not become established in the tuna 

 fisheries. The longline fishery is the nucleus of the fishery. The great majority of the fish 

 taken by longlines axe already mature. The fishing implement is a hook, and the meuiner of its 

 use traces across the open sea a broken rather than a solid line. Consequently, there is almost 

 no danger of cleaning up a school of fish with one set, as happens in net fisheries. It is nnore 

 reasonable rather, at least under present conditions, to think of it as a kind of thinning out. As 

 yet no one has expressed a definite opinion as to whether or not the resources of the tuna longline 

 fishery are being overfished. This can be thought to mean that there are no data with which to 

 arrive at a definite opinion. 



To sum up the foregoing, it is considered that the resources of the tuna longline 

 fishery are of such character that there is little danger of their being overfished, judging both 

 from the conditions under which they are propagated and maintained and from the type of gear 

 and the fishing method used. In short, the effect of man's effort on the resource is really very 

 slight when connpared with the effect of natural conditions. This mejins, on the other hand, that 

 this fishery is lacking in planability and stability and this is the reason why it is one of the nnost 

 primitive in character of all fisheries. 



III. General Outline of Fishing Grounds and Fishing Seasons 



The longline fishery for tuna has developed in very close association with the pole 

 and line live-bait fishery for skipjack. The majority of the boats in this fishery fish for skip- 

 jack approximately half of the year, including the sunnnner season, and engage in the longline 

 fishery during approximately half the year, including the winter season. This manner of opera- 

 tion, in general, is connected with the prospects for profit to the operators. As was stated 

 earlier, the vessels which engage only in this fishery, taking no part in skipjack fishing at any 

 tinne of the year, now junount to 25 percent of sill skipjack and tuna vessels. Furthermore, in 

 areas where the geographical distribution of the fishes makes longline fishing profitable, the 

 boats engage in longlining even during the sumnner season. The longline fishery for spearfishes 

 on the grounds west of Kyushu is an example, although in recent years the catch has dropped to 

 nothing and the fishery has been abandoned, and the fishery for black tuna off northeastern Honshu 

 and Hokkaido is a good example as the fishing season is chiefly during the summer. 



The tunas and spearfishes are basically warm-water fishes. A short account of their 

 species will be given in the next chapter, but the number of species is rather large and they differ 

 among themselves as regards the areas around which their distributions center, and they differ 

 too in the seasons and routes by which they migrate into Japanese waters. 



The black tuna is the most resistant to low temperature of all the tunas, migrating as 

 far as Hokkaido and the coast of Sakhalin, where it is found in waters as cold as 5 C. This is, 



however, rather exceptional, and in Japcinese waters this species is taken in the greatest numbers 



o o o 



in water having temperatures of 14 - 15 C. to 20 C. As far as is known at present the warm- 

 est waters in which this species occurs are off the Philippines, where teinperatures reach 26 

 to 29 C. This is the southern limit of their distribution in the North Pacific Ocean. This 

 species has the characteristic of penetrating into coastal waters and occurs in the Japan Sea. 

 There are records of their having been taken by fixed gear from Kyushu to southern Hokkaido 

 ajid on the Japan Sea coast of Sakhalin. 



o , o 



The albacore is said to occur in areas having water temperatures of 17 to 26 or 



27 C. The northern and southern limits of its distribution extend from the Equator to past 40 



N. latitude. In Japanese waters they are most abundant in areas where the water teinperature 



is around 20 C. and generally occur only in offshore waters, seldom appearing in the coastal 



areas. 



26 



