in nature and has not yet been taken in the Sea of Japan, furthermore, as 



will be detailed below, even in the south it is scarce in enclosed sea 



areas, while it is abundant in the area of the South Seas Government-^ 

 General o 



(d) kihada / yellowfin, N. macropterus 7 



This is the most common species in warm seas and is extremely 

 widely distributedo The northern limit of its range is about the same as 

 for the big-eyed tuna, but in late summer it is occasionally taken as far 

 north as the neighborhood of 4.0°N, It occurs in waters of 15° - 25°C, 

 and the optimum temperature is said to be 20'-'G, however, in the South the 

 yellowfin appears generally to occur in waters of higher temperature So 



In recent years the fishing grounds in the South Seas Government- 

 General have become famous and many boats have gone to fish there » As a 

 result it has become known that in general yellowfin are scarce in the 

 Equatorial Current and abundant in the Equatorial Countercurrento 



(e) spearfishes 



Because the species are difficult to distinguish, the distribution 

 by species has not yet been made very clear. Considered very summarily, 

 it appears that whereas the yellowfin is most abundant in the Equatorial 

 Countercurrent, the spearfishes are most abundant in the Equatorial Current 

 and in the Kuroshio. 



b„ Outline of the distribution in the various areas of the Southwest Pacific 



In the sea areas of the South the year is divided into two seasons 

 of northeast winds and southwest winds. The former prevail from about 

 October to March of the following year, while the latter last from April 

 to September, With this seasonal change the ocean currents also change, 

 and the distribution of fishes also necessarily changeSo 



Table 1 is made up of the combined results of past experimental 

 surveys. In the table "number of hooks used" is the total number of 

 hooks fished in past surveys added together without regard to year or 

 seasono The "catch rate" shows the number of fish taken per 100 hooks 

 fished. It represents only tunas and spearfishes and does not include 

 sharks or other miscellaneous fishes. The "rate of appearance" is the 

 proportion of each kind of fish in the total catch of tunas and spear- 

 fishes, or in other words, the composition of the catch. Table 2 shows 

 the catch with regard to seasons. 



18 



