3. Grounds South of the Subtropical Convergence 

 (1) Okinotorishima Ground 



In February the number of vessels operating in this sea area 

 declines and the details of the fishing ground become unclear. The alba- 

 core catch rates still appear to be high, indicating that there is still a 

 considerable occurrence of albacore in the area. It is particularly noted 

 that the fishing grounds are thought to be still expanding in area, extending 

 on the south to the northern edge of the nnain current of the North Equatorial 

 Current and on the west to the eastern side of the area where the Kuroshio 

 originates east of the Philippines. It is not clear, however, whether the 

 density of distribution of the albacore has remained at the Scime level and 

 the fishing grounds have expanded over a greater area, or whether the fish 

 have already begun to diminish in numbers and the schools have begun to 

 disperse with a resultant expansion of the fishing grounds. The size conn- 

 position is shown by the following small table. 



The average weight is 5.45 kan /47. 5 lbs. /somewhat smaller 

 than in the period of November to January, 



Considerable numbers of large albacore also appear from time to 

 time in the waters of the Ryukyu archipelago. It is not clear whether this 

 group originates in the albacore on the Okinotorishinna ground or, as will 

 be explained later, whether they have come from north of the Subtropical 

 convergence to join the population on the south side of the Convergence. 



(2) Other Grounds Between 10°N. and 25°N. 



In the South China Sea, as in the preceding months, some occurrence 

 of albacore is noted, although it is sparse. From the areas south of the 

 Kinan fishing ground and the North Pacific fishing ground to the vicinity 

 of 10 N. we find no catch rates as high as 1.0, with the exception of the 

 Okinotorishima ground, but there is thought to be a broad occurrence here 

 of large albacore. On the grounds from the area northeast of the Marshall 

 Islands to Hawaii the albacore catch rates appear to be sonnewhat lower 

 than in January. 



The size composition is as shown in table 8 and reveals the highest 

 average weight of any sea area in the northwest Pacific. 



95 



