< 

 a: 



X 



o 



< 

 O 



3 4 5 6 7 8 

 MONTH 



10 II 12 



Figure 20.--Bigeye fishing con- 

 ditions by months 



As we have almost no data for 

 o o 



the area from 10 to 20 N. , it is im- 

 possible to make any comparison with 

 changes in fishing conditions throughout 

 the year there. 



o o 



For the area fronn 20 to 25 



N. , 140° to 150° E. , that is, from the 

 southern Ogasawara Islands to the north- 

 ern Marianas and eastward the data are 

 summarized in figure 21, 



As the figure shows, in this 

 sea area catch rates for May and June 

 are 0. 0, but a rather conspicuous peak 

 is seen in July. From July through 

 September the catch rates continue to 

 drop, and although there are no data for 

 October, the catch rate continues to 

 climb from the Septennber low until it 

 reaches the highest point of the year in 

 January with a figure of slightly over 1. 0. 

 From February to May the catch rate 

 falls off sharply. 



The pattern shown by this 

 curve differs rather markedly from that 

 for equatorial waters, with a lag of 1 to 

 2 months, and it appears to show a trend 

 which rather approximates the curve for 

 the South China Sea. 



Continuing to the northward, the fishing conditions by months for bigeye tuna in the 

 area 30 to 35 N. , 140 to 150 E. , to the east of the Izu Islands, is shown in the following 

 figure. The situation shown here differs conspicuously from that previously shown for the curea 

 south of the Ogasawara Islands. In this area the highest catch rates for the year appear as a 

 sharp peak in April. From April to June the catch rates drop off sharply, but a low pe£ik appears 

 in July. However, our data for May and June are so few that it is not possible to decide whether 

 or not the curve reaches a low point in June. From January on the catch rate graduailly in- 

 creases, with a blunt peak appearing again from December to Januciry. 



If this curve is compared with that for the area south of the Ogasawara grouo. there 

 is agreement in the appearance in peaks in January. However, in the area south of the 

 Ogasawaras this peak is extremely conspicuous, while in this airea it is blunt and inconspicuous. 

 The most outstanding peak in this krea appears in April, and in this month the catch rate south 

 of the Ogasawara Islajids shows extremely small values. Small, peaks appear in both areas in 

 July, but as was said earlier, it is doubtful whether or not that which occurs in the curve for 

 this area is really a peak at all. 



Feirther to the north the data are almost entirely confined to the winter and therefore 

 the monthly changes in the fishing conditions throughout the year are not clear. As was already 

 stated in the section on fishing grounds, the pattern of bigeye tuna fishing in this region varies 

 from area to area, but in general the catch rates reach their highest point in November or 

 December. 



147 



