The author has earlier pointed out that the 

 size composition of albacore in the area of the 

 North Pacific Current presents regional (Suda 

 1954b) and seasonal (Suda 1955) variations. It 

 has frequently been pointed out that different 

 ocean currents represent different environ- 

 ments for the tunas, and that if the current 

 differs, the ecological significance of the tunas 

 distributed there also comes to differ 

 (Nakamura 1949, 1954; Nakamura, Yabuta, and 

 Ueyanagi 1953). From this point of view, the 

 manner in which the size composition of the 

 albacore distributed in the North Pacific Cur- 

 rent differs from those of albacore in other 

 current area8--in this case the North Equa- 

 torial Current and the Equatorial Counter- 

 current--isa matter of extraordinary interest. 



(1) Sizes of Albacore Distributed in the North 



Pacific Current, the North Eqxiatorial 



Current, and the Equatorial Countercurrent 



The size compositions for these three 

 current areas are summarized in figure 1. 

 (The fishing method in all cases is the longline.) 

 The size compositions for the North Equatorial 

 Current and the Equatorial Countercurrent 

 differ conspicuously from that for the area of 

 the North Pacific Current (Suda 1954a, 1955). 

 Almost the whole is composed of fish of 90-120 

 cm., that is the largest sizes attained by 

 albacore. This is markedly different from the 

 albacore of the North Pacific Current area, 

 where the greater part is medixun and small 

 fish (under 90 cm.). 



Consequently the range of the size composition 

 is notably narrow as compared with that found 

 for the North Pacific Current. From the oppo- 

 site point of view, this can be regarded as an 

 outstanding point shared in common by the 

 albacore of the North Equatorial Current and 

 those of the Equatorial Countercurrent. 

 However, a difference can still be detected be- 

 tween the albacore of the North Equatorial Cur- 

 rent and those of the Equatorial Countercurrent, 

 and that is that there is a discrepancy of about 

 10 cm. in the modal length between thealbacore 

 of the two areas. For the albacore of the North 

 Equatorial Current, fish about 110 cm. long are 

 the principal group, while in the area of the 

 Equatorial Countercurrent the principal group 

 is at about 100 cm. , which means that the fish 

 in the North Equatorial Current are larger. 



Figure 2 shows the size compositions of 

 the albacore distributed in the three current 

 areas schematically using the average values 

 of data obtained in the years 1948-1952. The 

 symbol a represents the period of southward 

 movement in the North Pacific Current (long- 

 line fishery), b the period of northward move- 

 ment in the same area (pole-and-line fishery), 

 c the North Equatorial Current (longline), and 

 d the Equatorial Countercurrent (longline). The 

 size groups are numbered as in Suda (1954a), 

 and the shaded portion represents the size 

 group which the author has treated as the group 

 of fish of advanced age (Suda 1954a). The lower 

 root of the latter is in approximate coincidence 

 with what Ueyanagi (1954a) has hypothesized as 



so 60 70 80 90 100 



North Pacific 

 Currenf 



noon. 



90 100 noon. 



90 100 iiocm. 



North Eauatbiia^ Eauatoria^ Counter 

 CaTrent CurreTit 



Figure 1. --Size composition classified by the current. 



44 



