Movement Patterns and Diel Activity of Anguilla japonica in the Middle Part of a Large River in South Korea

To investigate movement patterns and diel activities of in the freshwater ecosystem, we applied acoustic telemetry on in the Geum River, a large river in South Korea. The acoustic tags were attached on 19 individuals of (12 with a depth sensor) in May and October 2015 and tracked at approximately 100-km sections from an estuary barrage by 20 automatic listening stations. Only four individuals showed longitudinal movement (mean, 5.2 km), and others were detected by the receivers at release sites; therefore, showed high site fidelity. We did not identify seaward migration during the study period (May to November). Conversely, showed active diel movement. The number of detections ( = 0.002) and movement distance ( = 0.004) were higher at night-time (18:00-06:00). As most individuals were actively moving at nighttime, we confirmed that is nocturnal, although few individuals also showed daytime movement. Although the population and habitats of have been decreasing simultaneously, the East-Asian countries are still severely exploiting rivers and streams to use water resources, and result in habitat simplification generated. Therefore, these results contribute to effective management regarding habitat and population conservation and restoration.