Comparing tables 53 asid 54, fluctuations in yellowfin fishing conditions show 

 approximately the Bame trend, as do those for the bigeye. The trend for the albacore also ap- 

 pears to agree, but a very great difference in catch rates can be detected. The apearfishes ap- 

 pear to differ somewhat, but it is difficult to detect any clear-cut tendency. 



Ample note should be tjiken of this complete change in the composition of the catch 

 north and south of 25 N. latitude. 



(b) Ogasawara, Volcano, and Mariana islands (20 to 30 N. , 140° to 150° E.) 



The northern part of this sea area has been exploited as a fishing ground since very 

 old tinnes. The southern portion, too, has quite a history as a fishing ground and has been fished 

 by many vessels. The principal components of the catch are albacore and spearfishes in the 

 north and yellowfin and spearfishes in the south. Among the spearfishes of the north quite a 

 few broadbill are included, these being taken together with albacore during the winter. The 

 spearfishes in the southern part of the area are mainly striped nnarlin and black marlin, and 

 their season is in the summer. 



Table 55 summarizes the data from investigations carried on in this area. 



Table 55. --Fishing conditions in the waters of the Ogasawara, 

 Volcano, and Mariana islands (140 to 150 E. ) 



Throughout this sea area as a whole the catch rate is slightly more than 3. 0, a bit 



higher than that of the area of 130 to 140 E, adjoining on the west. The principjil catch is 



albacore and spearfishes. There eire vestigial catches of black tuna in the northern part, but 



they ajre not taken at all in the south. Yellowfin are abundcint in the southern part, where their 



catch rate is twice that of the northern section. No local differences in the fishing situation for 



o 

 bigeye tuna north and south of 25 N, can be detected, Albacore are extremely scarce in the 



south but have a fairly high catch rate in the north, Spearfishes are somewhat more abundant in 



the north, but the difference is slight. Many sharks, of which the most important is the great 



blue shark, are taken in this area, their numbers rivaling the combined total for tunas and 



spearfishes sind in many cases surpassing them. 



If tables 55 and 50 are compared, rather conspicuous differences in the values of the 

 catch rates can be seen, but the trends of changes in fishing conditions north and south of 25 N. 

 are shown to be in good agreement. This fact is believed to show the similarity of the pattern of 

 distribution of these fishes in both areas. 



Tables 56 and 57 present the fishing conditions by months in order to show seasonal 

 change*. The data are unfortunately not evenly distributed, but there are data for almost the 

 whole year so that it is possible to ascertain the fluctuations in fishing conditions during the year. 



90 



