value of the fishing grounds of the southern part of this sea area are in many ways not clearly 

 known. 



Table 49. --Oceanographic conditions by months in the 

 waters of the Ogasawara Islands 



Note: From report of Ogasawara Fisheries Enterprises for 1931, 



Considering this sea area as a whole as a tuna longlining ground, it is by no means 



unifornn everywhere, but presents fishing grounds of different character in different localities 



such as the black tuna grounds south of Tanegashima, the yellowfin and spearfish grounds from 



Daito Island to the Koho ShoaJ area, the albacore grounds of the Kinansho area, the spearfish 



grounds in the coastal waters of the Ogasawara and Volcano islands, and the bigeye tuna and 



albacore grounds to the eastward. And as will be explained, fishing conditions are quite different 



o o 



to the north and south of a boundary in the vicinity of 24 to 25 N, 



In the following discussion this sea cirea is divided into three regions from west to 

 east and the characteristics of the fishing grounds in each of these regions are discussed separate- 



ly. 



(a) 130° to 140° E. longitude 



The northwestern part of this sea area forms part of the so-called Tanegashima 

 black tuna grounds. In recent years the black tuna have completely disappeared and only a 

 certain number of bigeye are taken during the season. In the vicinity of 30 N. , 137 E. there are 

 the famous Kinansho fishing grounds and here albacore are abundant in the winter. The vicinity 

 of 24 to 26 N. , 131 E. is fannous as the so-called Daito Island fishing ground, and the principal 

 catch here is spearfishes and yellowfin. The KohS Shoal, discovered by and named for the K5chi 

 Prefecture fishery research vessel Koho Maru, is at 26 N. , 136 E. At certain seasons yellow- 

 fin and spearfishes are abundant on this ground. 



Table 50 summarizes data from surveys carried out in this sea area. 



The overall average catch rate is 2,4, with a slightly higher rate of 2,84 to the south 

 of 25 N, as compared with 2, 24 to the north. The composition of the catch is quite different 

 north and south of 25 N. In the south yellowfin make up more than half the catch while albacore 

 are nnost abundant in the north. Black tuna are taken only in the north, there being no record of 

 their capture in the southern part of the area, and their average catch rate throughout the year 

 is 0.22. There is almost no difference between the catch rates for the spearfishes, but the 

 catch rate for bigeye tuna is somewhat higher in the south. 



86 



