It it thought that this situation is controlled mainly by such geographical factors as the 

 arrangement of islands. 



The following figures show catch-rate curves for each month for the yellowfin tuna 

 in areas for which data are fairly abundant throughout the year, just as was done in the case of 

 the albacore and the bigeye tuna. 



Figrure 24 is a catch rate 



curve by months for the area ex- 



o o 



tending from to 10 N, latitude 



and from 150 to 160 E. longitude. 

 The peaks on the curve appear 

 quite clearly in March and Septem- 

 ber. We have no data at all for 

 June, but it appears that the high- 

 est catch rates for the year occur 

 in May and June. The minimunn 

 catch rate for the year appears in 

 February, with a fairly clearly de- 

 fined low in April and another less 

 clear in August. From October to 

 December the fishing is compara- 

 tively stabilized, with catch rates 

 of about 4. 0. As there are alnriost 

 no cases in which data for the whole 

 year are available for particular 

 areas, the monthly changes in the 

 fishing conditions in waters to the 

 east and west of this area are not 

 known, however, in some cases 

 rather high catch rates are indicated in February and April so that it seems difficult to believe 

 that these changes take place uniformly in the equatorial waters of the western Pacific. It is im- 

 possible to determine at present whether these changes indicate local differences in the fishing 

 season or whether they are completely fortuitous. 



Figure 24. 



-Yellowfin tuna fishing conditions b 

 months (0° to 10° N. , 150° to 1 60° E. ) 



?^. 



Figure 25 shows the yellowfin fishing conditions by months for the vicinity of Palau, 

 7 to 8 N. latitude, 133 to 135 E. longitude. The data cannot be said to be complete, however, 

 the figure shows the peaks on the curve to appear in May, October, and December. The May and 

 Decennber peaks are particularly conspicuous. The low points on the curve appear in March, 

 July, and November, that in March being extremely conspicuous. Comparing this figure with the 

 preceding graph, we find that the latter had peaks in March, May, June, and September with lows 

 in February, April, and August. Thus the conspicv.ous peaks of May generally coincide, but the 

 December peak did not appear in the former figure, and the other peaks and low points, with 

 Sonne lag, appear with about 1 month's difference. 



Figure 26 shows the fishing conditions by months in the South China Sea. Data are 

 completely lacking for April and May and therefore the year-round pattern is not known. There is 

 an extremely conspicuous peak in October, but no outstanding differences in the fishing conditions 

 can be detected from November to about March. There appears, however, to be a rather marked 

 low point in January. The catch rate is at its lowest in August, a month for which we have few 

 data. There eire no data at all for April and May, but if we assume that there is a pronounced 

 peak in May, the form of the curve would closely resemble that for Palau waters. If we further 

 assume that the catch rate gradually declined from March to August, the curve would have two 

 peaks and two low points and would show the same trend as the monthly catch rate curve for 

 bigeye tuna. 



150 



