Biogeographic distribution of the eel Anguilla luzonensis: Dependence upon larval duration and oceanic currents

Anguilla luzonensis, a recently identified tropical Anguilla species, was categorized as 'Near Threatened' in the International Union for Conservation of Nature (IUCN) Red List in 2014. However, its biogeographic distribution and dispersal mechanism remain unconfirmed. This study aimed to clarify the biotic and abiotic factors that may shape the eel's dispersal range, which could help to establish suitable conservation strategies. Glass eel distribution was investigated in Taiwan, Luzon, Mindanao, and Sulawesi. A. marmorata was used as a reference eel species for comparison. Although both species were found year-round, A. marmorata was found in all locations and was abundant at most sites. However, A. luzonensis was concentrated only on Luzon Island, mainly between June and October. It was rarely observed in Taiwan and Mindanao, and was not found in Sulawesi. The spawning site of A. luzonensis is probably located more northward in the North Equatorial Current (NEC), whereby the eel larvae avoid entering the Mindanao Current (MC). In addition, A. luzonensis typically spawns between February and May, and is preferentially transported into the Kuroshio from May to August, when the NEC bifurcation latitude reaches its southernmost position and the Kuroshio transport volume peaks. Furthermore, A. luzonensis has a shorter/narrower range of larval duration than A. marmorata, and its dispersal distance is therefore restricted. The life history traits of A. luzonensis, together with the oceanic current regime, may act together to concentrate its biogeographic distribution on Luzon Island.