There are no reports at all yet from the central Pacific, 

 particularly from the Ogasawara area. If it is as_sum8ds, for 

 example^ that the schools which are in the Ho^ikaido area during 

 the summer and autumn move south and appear in che Bashi Strait 

 region, it may be thought that there is a possibility that 

 their route touches the region of the Ogasai'-araso The need for 

 a thorough survey of this area is keenly felto 



This species is also known from Hawaiian waters o An 

 extremely similar species is also known from the Pacific coast 

 of Americai, and there is another similar species in the southern 

 hemisphereo It is thought by some scholars that these species 

 and the one in the Atlantic are all the same species,, In any 

 cases, there is a necessity for a thorough study of the question 

 of whether or not these are after all the same identical 

 specieso Assviming that they are all the same — » which may well 

 be believed to be the case -- unless their inter-relationships 

 are thoroughly studied it will be impossible to give a theoreti- 

 cal explanation of the decline of the stock in the waters 

 adjacent to Japano 



The big-eyed tuna has much stronger pelagic characteristics 

 than the black tuna, and no proof has been given of its being 

 distributed in the Japan Sea,, The northern limit of its dis- 

 tribution is 43*^ No It is broadly and generally distributed in 

 the waters to the souths but its density is roughly uniform with 

 no great diff erenceso 



The other tunas differ in their distribution mainly with 

 regard to latitude^ however j, it is an interesting fact that not 

 much change with latitude in the distribution of the big -eyed 

 tuna can be perceived | there appears to be a tendency for their 

 occurrence to be mainly related to the longitude (figure 4)o 



In figure 4 the range from 120° - 180° Eo has been cut 

 into sections of 5° of latitude and the longitude has been 

 marked off at every 2°o Then the catch rate for each division 

 of 5° of latitude by 2° of longitude has been calculated from 

 the records of investigations carried on theroc There is no 

 great difference in the curve with regard to the latitude^ but 

 there is clearly a slope from east to westo In other words p 

 the catch rate gradually increases toward the heart of the 

 Pacifico 



The yellowfin is the representative tuna of the tropical 

 sea areas, It also occurs in enclosed sea areas and is known 

 from the Japan Sea, although it is rare thereo The northern 

 limit of its distribution in the western Pacific is around 

 35° No, rarely reaching to 40° N„ , however j, it is rather excep- 

 tional for it to reach this far norths and it is almost without 

 significance as an object of the longline fisheryo Its possession 

 of a certain amount of significance in the longline catch varies 

 with the season, but at the farthest it extends to the vicinity 

 of 30° No 



18 



