Influence of environmental parameters on habitat use by sympatric freshwater eels Anguilla marmorata and Anguilla japonica on Yakushima Island, Japan

It is known that environmental parameters, such as water depth, size of substrate material, and current velocity, influence the organization of stream fish communities. However, few studies have investigated the effects of these parameters on the sympatric freshwater eels. Here, the habitat use of two anguillid eels, the Indo-Pacific eel (Anguilla marmorata Quoy and Gaimard, 1824) and the Japanese eel (Anguilla japonica Temminck and Schlegel, 1846), coexisting in the same river systems in Japan, was investigated. It was found that the tropical species A. marmorata exclusively used habitats with larger substrate materials, fewer fallen leaves and less leaf detritus, higher current velocity, and lower turbidity than the temperate species A. japonica, and the distributions of the two anguillid eels were clearly segregated. Thus, when both species cooccur in the same river systems, clear flowing mainstems and tributaries are preferred habitats for A. marmorata, whereas stagnant muddy estuaries, backwater areas, irrigation channels, and reservoirs are preferred habitats for A. japonica. These habitat segregations were consistent as body size increased and life-stage developments from elver to yellow eel and did not show ontogenetic shifts. The findings indicated that both species had strong habitat preferences, and these environmental parameters must be considered in the conservation of anguillid eels in sympatric zones.

Automated summary

This study investigated the habitat use of two anguillid eels, the Indo-Pacific eel and the Japanese eel, coexisting in the same river systems in Japan. It found that the two eels had clearly segregated distributions and strong habitat preferences, with the tropical species preferring clear flowing mainstems and tributaries, while the temperate species favored stagnant muddy estuaries and backwater areas. These habitat segregations remained consistent as body size increased and life-stage developments progressed, highlighting the importance of considering environmental parameters in the conservation of sympatric anguillid eels.