Distribution of leptocephali in the Kuroshio Current and East China Sea

A first-of-its-kind sampling survey using a large midwater plankton net appropriate for collecting leptocephali was carried out in transects across the shelf break at the edge of the Kuroshio Current and East China Sea and in the western North Pacific Ocean south of the Ryukyu Islands during late November and early December. Leptocephali of at least 45 species of 10 families of anguilliform eels were collected, Catch rates and the species richness of leptocephali were higher in the Kuroshio region than in the western Pacific Ocean. The most abundant leptocephali in the region were of the eel fan-Lilies Congridae, Synaphobranchidae, Ophichthidae, Muraenidae and Nettastomatidae. Several taxa of congrid eels, including Gnathophis nystromi nystromi and Ariosoma spp., were spawning along the edge of the Kuroshio Current, as were muraenids, ophichthids, nettastomatids and Dysomma anguillare (Synaphobranchidae). The 2 most abundant species, G. nystromi nystromi and D. anguillare, appeared to be spawning near the edge of the shelf break in the central Kuroshio region, but the spawning of Ariosoma spp, and several other species was centered farther south to the northeast of Taiwan. This is the first discovery of the spawning of eels along a shelf break adjacent to a major western boundary current, and spawning in this region would result in their leptocephali having the potential for being transported to a wide range of areas by the Kuroshio and Tsushima Warm Currents.