of areas of high catch rates extending from the east side of the fishing 

 grounds to their southern edge. The variation in the catch rates in this 

 sea area gives a coefficient of variance of about 50 percent, so that we 

 can consider this a fairly stabilized fishing ground. 



Table 9. --Frequency of coefficients of variation of catch rates in 



o o 



unit areas on the KinaJi ground at 130 -140 E. 



The majority of the albacore taken in this sea area are naedium- 

 sized (2 to 4 kan /TS to 33 VobTJ), and the proportion of admixture of large 

 (over 5 kaui fA\~\ha.l ) and small (under 2 kan ) fish is less than in the North 

 Pacific fishing ground at the sanne longitudes. The outstanding peculiarity 

 of the size composition of the albacore in this sea area is the extraordinary 

 uniformity of size, as shown clearly in figure 10, where it can be seen that 

 there is not a number of modes but one single predominant mode. With 

 regard to the question of whether or not greater variability in fish size 

 appears as one goes farther to the north and south, we have only data for 

 the year 1952, but according to this the fish are somewhat larger to the 

 south. It is difficult, however, to affirm that this difference represents 

 a difference in age groups. 



Grounds South of the Subtropical Convergence 

 (1) Okinotorishima Ground 



The distribution of the, fishing grounds in January is considerably 

 different from what it was in December. That is, the fishing grounds 

 have extended markedly to the southward and their center has moved to 

 the vicinity of 14 N. to 20 N. North of 20 N. latitude signs of a falling 

 off of the fishery can already be seen. As the fishing grounds move south, 

 they simultaneously extend gradually to the westward and reach the waters 

 west of 130 E. longitude, indicating that their position has moved consi- 

 derably to the southeast as compared with the first part of the fishing 

 season in October. In general, the central part of the fishing ground 

 has catch rates of 1. to 2. 0, but there are not a few areas with high 

 catch rates of 2.0 to 4.0, The fishing grounds reach their maximum 

 extent at this season. 



74 



