Diurnal vertical migration of a ribbon fish [Trichiurus lepturus] in the western Wakasa Bay [Japan]

To clarify diurnal movements of a ribbon fish Trichiurus lepturus, exploratory fishing expedi-tions utilizing handline, longline and observations through fish finder were made at the mouth of Maixuru Bay, the western Wakasa Bay, on 5 and 8 June, 1985. Hourly angling and observations of echo traces of T. lepturus indicated that the fish signicantly showed diurnal vertical migration.T. lepturus mainly distributed from middle tosurface layers and made scattering school in nighttime. T. lepturus descended to bottom layer until just before sunrise, and made dense school at bottom layer in daytime. T. lepturus ascended and scattered from middle to surface layers in twilight. Feeding activity of T. lepturus was increased in twilights. Diurnal movements of T. lepturus synchronized with that of anchovy Engraulis japonicus which was thelr main food in this area. This sychronizing might brought T. lepturus to increase chances of encounter wih the food. Bottom longliners at this area also synchronized their managements with diurnal movomots of the fish to effeciently catch them.