TWILIGHT MIGRATIONS OF THE TEMPERATE JAPANESE SURFPERCH NEODITREMA-RANSONNETI (EMBIOTOCIDAE)

Daily twilight migrations of the Japanese surfperch, Neoditrema ranson neti, a temperate rocky reef inhabitant, are described on the basis of studies around Fukudomari Harbor, Saiki Bay, Kyushu. Migrations occur red from late August through January, being the time of year of high N . ransonneti abundance in nearshore waters. At dusk, fish moved from c oastal rocky reefs, where they had been diurnally active, to the harbo r, either solitarily or in schools. Movement into the harbor began on average, 30.4 min. before sunset, the last arrival taking place 10.2 m in. after sunset. During nighttime, the fish remained in the harbor, s ubsequently. The beginning their migration to open waters some 27.6 mi n. before sunrise. Migration routes were established up to at least 10 0 to 150 m from the harbor. The sequence of migratory behavior at the entrance of the harbor was categorized according to certain behavioral events, such as migration in schools and migration in procession (a l ong dense school). Each behavioral event began and ceased with precise timing relative to sunset or sunrise, the effect of variations in und erwater illumination on each event being small. Practically all of the individuals (approximately 48,000) observed around the harbor were co nsidered to migrate.