Longitudinal distribution and microhabitat use of young Japanese eel Anguilla japonica in a small river flowing through paddy areas

Although the Japanese eel Anguilla japonica is a commercially important species, its habitat use is not well understood during its life stages in the river. In this study, we investigated the longitudinal distribution and microhabitat use of young Japanese eels (<200 mm in total length [TL], which correspond to elver and early yellow stages) using 180 quadrates (1 m x 1 m) in six stations in a small river (approximately 11.5 km long, 3.0-25.0 m wide) that flows through paddy areas in Fukushima Prefecture, Japan. No differences were observed in the TL of eels among the sampling stations. The analysis using generalized linear models showed that eel density increased as number of weirs decreased. The analysis using generalized additive models showed that water depth, current velocity, and substrate complexity were important factors determining microhabitat use. Eels used shallow habitats (<35 cm) with slow currents (5-40 cm/s) and high complex riverbeds (>0.35 in index of substrate complexity). These findings provide useful information to conserve and manage wild eels inhabiting small rivers flowing through paddy areas.