However, this correction is a problem which cannot be solved until future research has shown the 

 effect which branch line length has on the catch rates for each species at different seasons and in 

 different areas. Here we must, perforce, ignore the differences in construction of the fishing 

 gear, and assume that it all has equal catching power, just as we earlier assumed that the catch 

 rate is proportional to the density of occurrence of the fish, and on the basis of these two as- 

 sumptions, we will examine the distribution of each species. 



A. Black Tuna 



Stated very roughly, the distribution of the black tuna extends all over the 



northwestern Pacific Ocean and the northeastern part of the South China Sea between 15 and 41 



o 

 N. latitude and east of 120 E. longitude. Thus its range, if we except the South China Sea and 



the waters around the Ogasawaras, is definitely restricted to the Kuroshio and the North Pacific 



Current. 



The waters with a high density of occurrence, that is to say waters with high catch 

 rates, are extraordinarily linnited. Citing them from south to north, they are the coastal waters 

 east and west of Luzon, the waters off the Miyako chaun jind Okinawa, the waters around 

 Tanegashinna, and the northern part of the Northeastern Sea Area. They occur very widely be- 

 tween 30 and 35 N. latitude, and to the east of the meridian of 140 E. longitude, but the catch 

 rates in this area are very low jind fish are taken only sporadically. 



The season on the fishing grounds off the east and west coasts of Luzon and near 

 Formosa, although it may be slightly earlier or later from year to year, begins in March and 

 ends in early June. In some years the first catches are made in the latter part of February, but 

 fishing gradually becomes better from the latter part of March on. There are few data on the 

 catch rates and the seasonal changes are not clear. The following table presents data for the 

 period from March to May. 



Table 113. --Black tuna fishing conditions in Luzon waters 



Note: Data from vessels reporting to the Fornnosa Government-General. 

 As this table shows, the catch rates were surprisingly high, indicating 

 great density of occurrence. 



The season in the Miyako Islands and Okinawa is chiefly in May and June, somewhat 

 later thaui in the Luzon area; however, catches have been reported in April. Catch rates range 

 from a low of 0. 23 to a high of 9. 37, with remarkably high catch rates being recorded from time 

 to time. The catch rates of 9. 37 and 3. 76 were each recorded for only one trial and therefore 



139 



