ビンナガの研究-III

海流別にみた体長組成

抄録

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 Pa-cific areas.
1) The albacore occurring in the North Pacific Current area seems to be remarkably different from those in the North Equatorial Current and in the Equatorial Counter Current areas in the size compositions. A greater majority of the fish distributing in the North Pacific Current area consisted of the ones less than 100cm in the body length. They are supposed to belong to a group of immature fish. However, most of those caught in the areas of the North Equa-trial Current and the Equatorial Counter Current measured more than 90cm in length and likely belonged to a mature group (Figs. 1 and 2).
2) There is discrepancy of about 10cm between the modal length of albacore caught in the North Equatorial Current and that of the fish in the Equatorial Counter Current. 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 than the regional difference and seasonal one within the North Pacific Current area (Table 3).
The above evidences are indicative of a fact that each of various ocean currents would present an environment considerably different from the other for tunas as has been pointed out by N_AKAMURA (1954).