ill 



I 

 o 



I- 

 < 

 u 



Figure 23 ahows the 

 changes in fishing conditions by 

 months for the waters of the 

 Okinawa Islands, where the oceano- 

 graphical environment differs more 

 or less from that of other sea areas. 

 The form of the curve sonnewhat 

 resembles that for the waters south 

 of the Ogasawaras. In the latter 

 area, however, a second peak ap- 

 pears in July and no such peak ap- 

 pears in this area. There seems to 

 be a blunt peak appearing around 

 April and May, but it is extremely 

 unclear. 



As the foregoing figures 

 show, the monthly changes in fish- 

 ing conditions for bigeye tuna differ 

 rather strikingly between areas, 

 just as they did in the case of the 

 albacore. Not only do they differ 

 with respect to the months having 

 the highest and lowest catch rates, 

 but the values of the catch rates 

 themselves differ markedly. How- 

 ever, in spite of the fact that the 

 positions of the peaks and low 

 points on the curves of monthly 

 catch rates differ and despite the 

 differences in the catch rates them- 

 selves, it seems possible to detect a common character more or less clearly shared by all of the 

 carves for the various areas. For example, the catch rates begin to drop off sharply in the 

 month after the highest catch rates aire attained, and they reach their lowest point about half a 

 year later with no catch or almost none. One or two months after the month in which the lowest 



point is reached, a secondary peak 

 appears, and thereafter the catch 

 rates gradually decline until one or 

 two months before the month in 

 which the catch rates reach their 

 highest point. During this latter 

 period there is no month without 

 some catch. In other words, there 

 are two peaks ajid two low points 

 in the year, the period between the 

 maximum and minimum catch rates 

 being about half a year, and a 

 second peak and the second low 

 make their appearance during the 

 half year between the nninimum and 

 the maximum. 



Figure 21. --Bigeye tuna fishing conditions by 

 months (20° to 25 N. , 140° to 

 155° E.) 



UJ 



< 



I 

 o 



< 

 o 



12 3 4 



8 9 10 



NOTE •• 

 AS 



5 6 7 



MONTH 



NUMBERS OF STATIONS AND HOOKS SAME 

 IN FIG. 15 



Figure 22. --Bigeye tuna fishing conditions by 

 months (30° to 35 N., 140° to 

 150° E.) 



In the vicinity of 

 o o , 



the Equator from to 5 N. , and 



from 150 to 160 E. , and in the 



o o 



Nankal sea area from 25 to 30 N., 



130° to 140° E. , this relationship 



is reversed, with the secondary 



pecik and the secondary low 



148 



