(3) Zunan area 



Schools of small skipjack increase in numbers progressively from 

 April on and reach their peak around July after which time they gradually 

 decrease o In this area schools of small fish make up 35^ of the total,, 

 Medium fish appear in these waters at the same time as the small fish and 

 for a tim.e comprise 305^ of all schools. They increase until about July 

 and thereafter decrease to 55%^ Schools of large skipjack come in from 

 May to July and form about 10^ of all schools. Note; It is thought that 

 actually the ratio of schools of large fish should be increased somevihat 

 because few fishermen fish these schoolSo 



(a) Northeastern area 



The schools of small skipjack appear in this area in May and remain 

 until around September, but their number gradually diminshes„ They make 

 up 5% of the schools in the area. It is thought that during this period 

 quite a number of them grow large enough to enter the medium skipjack 

 category. Medium skipjack along 'with small skipjack make up the bulk of 

 the fish in this area, and they gradually increase until they reach their 

 peak in June and July after vjhich they decreaseo In these waters they 

 comprise 75'^ of all schools^ Schools of large fish are still very scarce 

 in May and gradually increase from July to September, but these are thought 

 to include fish which grew into the large category in these waters as well 

 as fish which were large when they entered the area. 



To summarize the facts which have been given above for each of the 

 several areas, the skipjack schools which enter Japanese waters are 

 principally medium fishj these occupying 60% of the total „ In the North- 

 eastern and Zunan areas they are remarkably abundant, while in the Kinan 

 and Satsunan areas the schools of small fish predominate, forming 30$ of 

 all schools. Large fish are comparatively abundant in the Satsunan area, 

 but they form only about 10% of the total population. Table 2 shows the 

 distribution of ohe total skipjack population by areas. 



2, fiJigration routes of the skipjack schools 



The migrations of the skipjack are controlled by the instincts peculiar 

 to the fish and by tho condition of the ocean currents. There is one great 

 migration, as described abovej, but it takes place along the following 

 routes, 



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