As was stated earlier, at about the same time as the fishing season around 

 Tanegashima there are catches of black tuna all over the area around 30 N. latitude. However, 

 one can detect a difference in that the catches around Tanegashima are highly concentrated, 

 whereas those nnade in other sea areas are extremely scattered. Fairly considerable catches 

 are £l1so made from April to June between Luzon on the south and the Izu Islands, principally 

 within the Kuroshio. 



In view of the oceanographic character of this sea airea, it appears possible that most 

 of the fish from the various areas mentioned above may concentrate here. Furthermore, because 

 of the conspicuous variations in oceanographic conditions from year to year, a high degree of 

 variability in fishing conditions must also be taken into account. In other words, compared to 

 the schools which congregate around Tjinegashima, the fish which gather in this sea area are of 

 many different migratory systems cind age groups and the conditions change fronn year to year. 

 The obvious difference between the average body weight at Aburatsu and at Kushiro, it is 

 thought, can be explained from this point of view, but we do not yet have the data to prove it. 

 In any case, it is a fact that black tuna in Japanese waters showed a peak in the catch curve for 

 their representative fishing grounds in both the south and north in 1931 and thereafter, with 

 some difference in the length of the period, they gradually declined. The phenomenon of a mark- 

 ed increase in the body weight of the fish accompanying this gradual decline in fishing was com- 

 nnon to both grounds. 



There appear to be vajious theories with regard to the poor fishing for black tuna in 

 Japanese waters, but the writer thinks that it is probably a natural cyclical fluctuation due to 

 cyclical changes in oceanographic conditions. It is expected, therefore, that there will be a 

 natural recovery, but it is believed that the sort of phenomena described above will have an 

 important significance in establishing policies for this fishery in the future. 



Table 78 shows fishing conditions in this sea area based on data from experimental 

 fishing. More data should have been included, as it is thought that quite a large part of the 

 existing data were missed because of difficulty in obtaining them. 



The overall catch rate is slightly less than 3.2. First place in the catch is occupied 

 by eilbacore, which make up about 70 percent of the total. Next in importance are the spear- 

 fishes, followed by black tuna and bigeye, with yellowfin appearing only vestigially. 



Table 78, --Fishing conditions in the northeastern 

 sea area 



Table 79 provides a comparison of fishing conditions north and south of the line of 40 



N. latitude. 



113 



