The relation between sexes and migration of black marlin in the area of 10°-24°N was formerly reported by Ueyanagi1).
The author's results are as follows.
The hooked-rate changes seasonally. The rate in the division A is high in summer and low in winter. In D division it is in contrast with this. In B and C it is high in spring and autumn and low in summer and winter. The seasonal variation of hooked-rate agrees accordingly with the theory4) on the migration.
The mean fork length changes seasonally, too. When the hooked-rate is high the mean fork length is small, and when the rate is low the mean value is large in the divisions of A and D. When the rate is high the mean is large and when the former is low the latter is small in B and C divisions.
The ratio of female to male changes also seasonally attaining the female to a fairly rich amount in spring and autumn.
The value of its ratio is small during the whole year in the division of B (Fig. 4).
The shoal of migrated marlin consists of nearly male.
A large number of female appears in B and C divisions in spring and autumn. These females seem to spawn distributing extensively in the northern equatorial region in summer and swimming scatteringly in the southern equatorial area in winter.