Some aspects of spawning schools of ribbon fish Trichurus lepturus derived from catch records of experimental longline fishing

Abstract

This paper describes some appearances of the spawning schools of ribbon fish Trichiurus lepturus by the catch records of experimental longline fishing in the western Wakasa Bay, Jpan Sea, From June to July, 1981.
Before the spawning season (until late June), sex rato of the fish obtained by the experimental fishings was nearly equal to 1:1 and femnales were mainly composed of immature fish. Both sexes were hooked impartially on the positions of the longline. The size of fish became smaller with time in this period.
During spawning season (after early June), females, mainly composed of mature and spent fish, outnumbered males in the catch and the sex ratio was not 1:1. Males were hooked partially at the offshore side of the longline. Large size fish were caught during this period.
According to the changes of sex ratio and size composition in the catch and position of hooked fish on the longline during the experimental period, it is suggested that the distributions and movements of the sexes were different to each other concerning their spawining habits