Migratory routes of different sized swordtip squid (Uroteuthis edulis) caught in the Tsushima Strait

Abstract Swordtip squid( Uroteuthisedulis ) of various sizes are caught on an almost daily basis from early spring to late autumn in the eastern Tsushima Strait and southern Sea of Japan. In this study, we estimated the migratory routes of different sized squidjigged in the Tsushima Strait using statolith analyses, information on seawater temperature distributions and currents, and tracer experiments. Estimates of age and historic water temperatures suggested that both small and large squidhatch in the southern East China Sea and are then transported northeastward with the currents to the northern Kuroshio region. Following this, the small squidare transported north-northwestward to offshore waters, from where many of the squidenter the southern Sea of Japan and some move into coastal waters in the eastern strait, whereas large squidslowly move northward from the northernmost part of the Kuroshio region. Based on these distributions, it is likely that the small squidremain immature due to insufficient water temperatures over shorter durations, whereas the large squidmature in the Kuroshio region. Since migratory routes affect fishing ground formation, this information is important for both efficient fishing operations and stockmanagement of this species.