llJ 

 q: 



X 



o 



I- 

 < 



C TOTAL 

 ^s STRIPED 

 € BLACK 



I - 



10 II 12 



Shifting farther to the west- 

 wcird, fiahing conditions in the watera 

 ciround the Ry-ukyu Islands are shown in 

 figure 37. As the figure shows the 

 pattern of increase smd decrease in 

 black marlin catch rates more closely 

 resembles that of the sea area to the 

 east of the Izu and Ogasawara islands 

 than it does that of the Nankai sea area, 

 although there is a lag of about 1 month. 



The striped marlin catch 

 rate rises sharply from April on and 

 reaches its high of the year in July. 

 After August it drops off steeply and 

 fornna a low in October, aiter which a 

 fairly conspicuous peak is formed in 

 November. This pattern resembles 

 that for the sea area east of the Izu 

 and Ogctsawara islands. In Decennber 

 it again goes down emd the second peak 

 of the year is formed in Jsuiuary and 

 February. In the area east of the 

 Ogasawara lalands a peak appears for 

 the spearfishes aa a whole in February, 

 but it is formed by broadbill swordfish 

 and differs entirely in character from 

 the January-February peak in this sea 

 area. 



MONTH 



As was stated above, the 

 season of the highest catch rates in this 

 sea area is about Z nnonths later than 

 that in other areas in the same latitude. 

 Furthernnore, the period during which 

 the catch rate is over 1.0 extends about 

 half of the year from May to September, 

 a situation which differs markedly from other areas of the same latitude. 



Figure 35. --Spearfish fishing conditions by 

 months (25° to 30° N. , 140° to 

 150° E.) 



The form of the striped marlin catch rate curve described above very closely re- 

 sembles the increases and decreases in the number of black marlin taken each month in Formosa 

 (table 115). As was stated at the beginning of the chapter, until recent years the spearfishes 

 were not thoroughly classified and it is knowil that in some cases both the black marlin and the 

 white marlin were recorded as striped marlin, so there is a suspicion that this may be such a 

 case ajid that other spearfishes may have been recorded as striped maurlin. In recent years, 

 particularly, boats based at Kushikino in Kagoshima have been taking a rather Icirge number of 

 black marlin around July to September, and this makes the suspicion all the stronger. At any 

 rate, if we construct a curve of catch rates on the basis of data from past surveys we get the 

 results shown in the foregoing figure. 



According to what has been said, the season in which the highest catch rates appear 

 in the vicinity of 20 to 30 N. is everywhere about the same, although there are differences 

 between areas in the numerical values of the catch rates. This is believed to show that the 

 movements of the schools have no important relationship to longitude but that they move rapidly 

 and simultaneously, chiefly in a north-south direction. In other words, this indicates the diffi- 

 culty of postulating the existence of definite paiths of migration. It appears that only the waters 



162 



