appearing in the months between the maximum and the minimum, and with a tendency for the 

 catch rates to increase gradually in the period extending from the minimum to the maximum. All 

 of these areas, however, share the characteristic of two peaks and two lows in the catch rates 

 in the course of a year. 



UJ 



H 

 < 



X 



o 



I- 

 < 

 o 



erf - 



~ MONTH 

 STATIONS 



HOOKS 



Figure 23. — Bigeye tuna fishing conditions 



by months (24° to 30° N. , 120° 

 to 130° E.) 



The significance of 

 these two types of catch rate 

 curves is not clear at present. 

 Furthermore, the problem of 

 whether these two types indicate 

 conditions prevailing at all times 

 within the respective sea areas or 

 whether they simply reflect an 

 error due to the abundjince or scar- 

 city of the data can only be answer- 

 ed when future investigations have 

 amplified the data and when not only 

 comparisons of the fish catch rates 

 hut comparisons of the body di- 

 mensions of the fish have been thor- 

 oughly made. Thus at present it 

 is difficult to come to a decision 

 concerning this question, but prob- 

 lems of this sort C£in be thought to 

 have an extremely important signi- 

 ficance in the study of bigeye tuna 

 resources, distribution, amd migra- 

 tion. 



D. Yellowfin 



Appendix chart IV shows the distribution of catch rates throughout the year for 

 yellowfin tuna. As is clear from the chart, the distribution of yellowfin is also extremely broad, 

 extending from the Ecjuator to the vicinity of 40 N. latitude. The species also occurs widely 

 in the South China Sea, the Sulu Sea, the Celebes Sea, the Flores Sea, and similar enclosed 

 waters. Areas with a high density of occurrence axe, however, almost entirely limited to the 

 waters of low latitudes, the distribution of this species in the high latitudes being almost vestigial. 

 Consequently, the longline fishing grounds for yellowfin tuna are almost confined to the low lat- 

 itudes. 



Areas with a high density of occurrence, where catch rates are 5. or above, can be 

 very broadly said to be south of 3 N. in the Pacific Ocean. Off the east ajid west coasts of the 

 Philippine Islands, however, such areas extend farther north, waters with catch rates of 5.0 or 

 more appearing as far north as 10 N. off the east coast. In such enclosed waters as the Celebes, 

 Sulu, and South China seas the density of distribution is generally high and waters with catch 

 rates above 5.0 can be found as far north as 20 N. In any case, in the western North Pacific 

 the productively significant ramge of occurrence of yellowfin tvina can be considered to be south 

 of 10° N. latitude. 



The situation in the Southwest Pacific and Indian Ocean regions is not well known 

 because of the paucity of data from these areas, but in the Solomon Islands area it appears that, 

 as nnight be expected, the density of occurrence is greater in tlje low latitudes (sic) than it is 

 south of 5 S. The data from the Banda Sea, the Flores Sea, cind the waters of the Greater and 

 Lesser Sunda archipelagoes represent chiefly the season of northwesterly winds (the southern 

 summer), but in this region areas with catch rates of 5.0 or more extend southward to 12 S. 



149 



