In both areas the size of the fish has become markedly smaller 



with the passage of time, and it will be noted that the fish taken at the 



o o 



close of the season in the area of 170 E. to 180 , where the fish are on 



the average largest, are smaller than those taken at the beginning of the 

 season at 140 E, to 150 E. , where the fish average smallest. Table 4 

 shows the relationship between the sizes of the fish taken in December 

 at 140°E. to 150°E. , and those taken in March at 170°E. to 180 . This 

 indicates that we must take into consideration as one cause for the larger 

 size of the fish far off to the eastward the possibility that the small alba- 

 core put in their appearance later in this area, and in view of the point 

 that the formation of the North Pacific fishing ground begins in the areas 

 east of 160 E. , it may be wondered whether this does not mean that the 

 albacore in the western sea areas begin their southward movement earlier. 

 At the close of the season between 170 E. and 180 there are rather con- 

 centrated catches of small albacore of less than 3 kan /25 lbs. /in the 

 northern part of the fishing ground; an example of this may be shown in 

 the results of an investigation carried on from the middle to the latter 

 part of March 1950. 



According to table 6, at stations 1, 9, and 10 concentrated catches 

 of small albacore were made. Their size was very small, the average 

 weights being 2. 6 kan / 21. 5 lbs. / at station 1 and 2. kan /1 6. 5 lbs. / 

 at stations 9 and 10. At all other stations, the catch was mainly large 

 albacore, with the average body weight in all cases above 4 kan / 33 lbs. /. 

 It is noted that the water temperatures were lower where the small alba- 

 core were taken than where the big albacore were caught, and this is 

 thought to represent a difference in the environments inhabited by the 

 large and small fish. 



There is also a difference in the size of the fish from east to west, 

 «md as reasons for the greater size of the fish to the eastward we may cite: 



(1) Off to the eastward the quantity of large albacore is greater 

 than it is in the sea areas nearer to the Japanese coast. 



(2) Small albacore also occur in the waters far off to the eastward, 

 but their appearance is late. 



It is also thought that we cannot overlook the factor of "economic 

 selection. " On the far offshore grounds, because of financial considera- 

 tions, large-size albacore are the main objective of the fishing, and when 

 the size of the fish in the catch declines the vessels immediately move 

 south and look again for schools of larger fish, which results in an increase 

 in the average size of fish in their catches. Nevertheless, the question of 



105 



