(2) Albacore West of the Izu and Ogasawara Archipelagoes 

 (Albacore of Waters Around Okinotorishima) 



In the waters around Okinotorishima there continues to be in April 

 a considerable occurrence of albacore, just as in March, However, the 

 catch rates axe lower than in March, and compared with the peak fishing 

 season on this ground the area of the grounds is much reduced and is 

 limited to the immediate vicinity of the island of Okinotorishima. The 

 catch rates are about 1 . in the immediate vicinity of the island and drop 

 off as one goes toward the periphery. The albacore in this sea area con- 

 tinue to be present even in May and June, although they gradually decline 

 in abundance. Seasonally, the rise cind decline of this fishing ground is 

 similar to that of the North Pacific fishing ground, but it remains in exist- 

 ence for about 2 months longer before it fades out, making one of its charac- 

 teristics this extremely long fishing season. Furthermore, the fishing 

 ground itself does not move much, but expands to the southwest in the fall 

 and winter (the center of the ground appears to move somewhat), and in 

 the spring it shrinks into the very close proximity of Okinotorishima, this 

 pattern of movement being repeated from year to year. Taking such points 

 into consideration, it is thought that this area offers some conditions which 

 make albacore likely to stop there, auid that this probably naturally increases 

 the density of occurrence. As was noted in the March section, just like the 

 sea areas east of the Izu and Ogasawara archipelagoes, this area is entered 

 by large albacore moving south from the Kinaji fishing ground around March 

 and April, but judging by the size composition of fish taken on the Kinan 

 ground, the quantity of such fish is extremely small, and since the fishing 

 ground shows a decline fronn January onward, it is imagined that there is 

 no important direct connection between it and the fishing grounds north of 

 the Subtropical Convergence. 



In the size composition, 85- to 95-cm. fish are about 10 percent, 

 95- to 105-cm. fish about 60 percent, and fish abov£ 105 cm. about 30 per- 

 cent, with the average weight around 6 kan /50 lbs. /, These values are 

 based on measurements of only 16 fish, and although it appears that the 

 weight is somewhat greater than in March, when we consider the changes 

 in the average weight for the whole period of November to April, we may 

 wonder whether the average size is not gradually getting smaller. 



The oceanographic conditions show almost no change from December 

 to March, and it is thought that this may be one reason why the close of 

 the fishing season is so much later than in other fishing grounds. 



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