north, the schools in the western areas are 

 thought to be forced by the configuration of the 

 Japanese coast to move gradually eastward 

 with a resultant intensification of their con- 

 tacts with the schools moving northward in the 

 more easterly areas that would greatly pro- 

 mote the mingling of the two. It is deduced 

 that the internal structure of the population in 

 June and July corresponds to just this stage. 

 Consequently, if the fact that within the same 

 group the proportion of small fish is greater 

 in the more westerly areas, with the proportion 

 of large fish increasing to the eastward, is 

 taken to originate from a difference in the 

 source of the migrations of the schools moving 

 north in the westerly areas and those moving 

 north in the easterly areas, then it is deduced 

 that even though both may be in a stage where 

 their mingling is being brought about, the 

 mingling is not yet complete. 



In the first report of this series the 

 authors studied the annual changes in the size 

 composition of the bigeye tuna taken on long- 

 lines in the North Pacific area, and in that re- 

 port too, as the result of a comparison of the 

 size compositions in different localities, it 

 was pointed out that the same sort of phenome- 

 non could be seen in the case of the longline- 

 caught fish. Whether this phenomenon common 

 to the fish in the catches of both fisheries 

 arises through exactly the same mechanism in 

 both cases can neither be affirmed or denied, 

 but the probable presence of a close relation- 

 ship is hypothesized. If the hypothesis set 

 forth above in regard to the relationship be- 

 tween the east-west gradient and the source of 

 migration were correct, it would be noteworthy 

 as an example of the migratory pattern and 

 mixing process of the bigeye tuna in the North 

 Pacific. 



Albacore Studies. III. Size Compositions 

 Seen in the Several Ocean Currents* 



Bv 



Akira Suda 

 Nankai Regional Fisheries Research Laboratory 



/English title and summary/ 



Studies on the Albacore - III. Size 

 Compositions Classified by Ocean Current 



The size compositions of albacore 

 distributing in various current areas of 

 the Pacific have been examined. The following 

 have been found with the fish caught in the 

 Western North Pacific areas. 



1) The albacore occurring in the North 

 Pacific Current area seem to b e remarkably 

 different from those in the North Equatorial 

 Current and in the Equatorial Countercurrent 

 areas in size composition. A greater majority 

 of the fish distributing in the North Pacific 

 Current area consisted of the ones less than 

 100 cm. in body length. They are supposed to 

 belong to a group of immature fish. However, 

 most of those caught in the areas of the North 

 Equatorial Current and the Equatorial Counter- 

 current measured more than 90 cm. in length 

 and likely belonged to a mature group (figs. 1 

 and 2). 



2) There is a discrepancy of about 10 cm. 

 between the modal length of albacore caught in 

 the North Equatorial Current and that of the 

 fish in the Equatorial Countercurrent. This 

 phenomenon may have a close relation with the 

 sex ratio of the fish (fig. 2 and table 2). 



3) Variance in the size compositions 

 between albacores in the North Pacific Current 

 area and in the other current areas is more 

 conspicuous then the regional difference and 

 seasonal one within the North Pacific Current 

 area (table 3). 



The above evidences are indicative of the 

 fact that each of the various ocean currents 

 would present an environment considerably 

 different from the others for tunas, as has 

 been pointed out by Nakamura (1954). 



/end of English summary/ 



♦Published in Bulletin of the Japanese Society 

 of Scientific Fisheries 21(12), 1956. Contr. No. 

 67, Nankai Regional Fisheries Research Lab. 



43 



