Growth and habitat use of two anguillid eels, Anguilla marmorata and A. japonica, on Yakushima Island, Japan

Abstract

Tropical eels, Anguilla marmorata, and temperate eels, Anguilla japonica, coexist in rivers on Yakushima Island, southern Japan. Differences in growth rates and habitat use of these species were examined by conducting surveys at 14 stations in seven river systems of the island. Anguilla marmorata (n = 93) were collected from all seven river systems surveyed, four along the eastern coast and three along the western coast, while A. japonica (n = 52) were collected only from the three river systems on the western coast. Only one of the two species was captured at any given sampling station, but both species were collected from a concrete-paved channel of a small river. Anguilla marmorata occurred in fast-flowing river mainstems and tributaries, where the substratum comprised large rocks, while A. japonica frequented irrigation channels and stagnant reservoirs, where the substratum comprised smaller rocks, sand, or mud. Comparison of von Bertalanffy growth curves suggested that A. marmorata in Yakushima Island grows slower than A. japonica and its conspecifics in tropical regions. The mean gonadosomatic indices of female A. marmorata from Yakushima Island were also lower than those of its tropical conspecifics. The slow growth of A. marmorata in Yakushima Island might be a result of the cool and oligotrophic environment near the northern limit of their geographic distribution and environmental tolerance.