worth while discussing their significance in the catch. Bigeye tuna have their highest catch rate 

 in JaJiuary, are still fairly abundant in February, and thereafter gradually decrease. Albacore 

 suddenly become abundjint in January and continue to show rather high catch rates in February 

 and March, but they appear to be taken hardly at all in the sunnmer. The spearfishes show their 

 highest catch rate of the year in December. From January to March they continue to be taken 

 with no great changes in their catch rates. It appears that their catch rate again tends to in- 

 crease in the summer, but as there aie very few data it is difficult to describe the situation ac- 

 curately. 



If we compare the foregoing with conditions in the southern part of the sea area, the 

 trends of increase and decrease are in agreement, although there are differences in the catch 

 rate values for yellowfin, bigeye, albacore, and spearfishes. However, in the case of the spear- 

 fishes there is a difference in the month in which the pezik catch rate appears in the winter, this 

 being earlier (December) in the north and later (February) in the south. 



Comparing table 62 with table 57 (northern part of the Ogasawara Islands area), the 

 trends of seasonal fluctuations in the catch rates axe very similar, but the peaks in the catch 

 rate in the Ogasawara ajrea appear to be generally about one nnonth earlier. 



The following table shows changes in fishing conditions with longitude. 



Table 63. --Fishing conditions by sections (20 - 25 N. , 

 150° - 180° E.) 



The catch rates are highest in the section between 154 E. and 156 E. In the 

 sections farther to the west they are about 1. 7, while to the eastward the rates are very low. 

 Both yellowfin and bigeye are most abundant between 154 and 156 E. , while spearfishes are 

 most abundant in the extreme western part, with rather high catch rates centering around 155 E. 

 This fact is thought to indicate that the vicinity of Marcus Isljind is a fairly good fishing ground 

 for this species. 



If changes in the fishing conditions resulting from the uneven seasonal distribution of 



the data are ignored, the highest catch rates are shown for the sections centered on 155 E. , 



, o o 



165 E. , and 175 E. Taking up the species individually, yellowfin are taken rarely throughout 



the whole area auid it is difficult to recognize any local variations in the catch pattern. Bigeye 



show a tendency to be somewhat more abundant in the vicinity of 160 E. , 165 E. , and 175 E. 



Albacore are the moat important element in the catch throughout the whole area, and the local 



variations in their catch rates agree perfectly with those of the total catch rate. Their pattern is 



also in rough agreement with that for the bigeye tuna. Spearfish catch rates are somewhat higher 



in the extreme western portion, that is, near to Japanese waters, Jind they appear to present 



roughly equal catch rates from the vicinity of 160 on eastward. South of 25 N. the data are 



scarce and are completely lacking for many sections, so it is almost impossible to make any 



comparison between the northern and southern parts of the area. 



96 



