30- 



Figure 3. --Length frequency of 

 males and females caught in 

 the North Equatorial Current 

 area. 



North Equatorial Current area. The length 

 distribution of the males very closely re- 

 sembles that for the North Equatorial Current, 

 and that for the females just as closely re- 

 sembles the size composition for the Equator- 

 ial Countercurrent. Since we have no data 

 with sex determinations for the albacore of the 

 Countercurrent area, we cannot immediately 

 conclude that the discrepancy between the 

 sizes in c and d is due to a difference in sex 

 ratios, but at any rate it is certain that there 

 is an extraordinarily high proportion of males 

 in the North Equatorial Current area (table 2). 

 On the other hand, we cannot rule out the 

 possible influence of the albacore of the 

 Southern Hemisphere, so there is a need for 

 further investigation in this field. 



(2) Size Differences Within Currents and Size 

 Differences Between Different Currents 



The internal differences in size compo- 

 sition seen within a current area are, as has 

 already been pointed out, regional and seasonal. 

 Within the North Pacific Current area there is 



a marked tendency for the size of albacore 

 taken along the same latitude to increase grad- 

 ually from west to east {Suda 1954b). This 

 change in the size composition in an east-west 

 direction is not uniform, being extremely 

 gradual in some cases and rather abrupt in 

 others. For example, the change seen in the 

 vicinity of 150 E. is conspicuous. Such regional 

 variations can be regarded as corresponding 

 to internal changes in the character of the North 

 Pacific Current?* It has already been remarked 

 that the seasonal variations*** are thought to 

 rest largely on ecological causes. 



Table 3 has been compiled in order to 

 compare the degree of difference between size 

 compositions within currents with that between 

 currents. This table shows the discrepancies 

 between the size group composition for each 

 area (the length frequencies analyzed by normal 

 distributions into 5 groups (Suda 1954a)) and the 

 average size group composition for the North 

 Pacific Current. The reason for using the 

 average values for this area as the base for 

 comparison is that this is the area for which 



**For example, east of 150°E. the North 

 Pacific Current flows almost regularly east- 

 ward, but west of that longitude is the place 

 where the Kuroshio turns the direction of its 

 flow from northeast to east, and there are many 

 irregular currents. 



***Since it is the prevailing rule all over the 

 area of the North Pacific Current that the size 

 of the fish gradually increases from west to 

 east, there is thought to be little possibility of 

 the existence of different stocks (Uda and 

 Tokunaga 1937). 



Table 2. --Sex ratio of albacore* in the North Equatorial Current area 



♦Includes the individuals whose body length was not measured. 



46 



