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

Abstract

To investigate movement patterns and diel activities of Anguilla japonica in the freshwater ecosystem, we applied acoustic telemetry on A. japonica in the Geum River, a large river in South Korea. The acoustic tags were attached on 19 individuals of A. japonica (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, A. japonica showed high site fidelity. We did not identify seaward migration during the study period (May to November). Conversely, A. japonica showed active diel movement. The number of detections (p = 0.002) and movement distance (p = 0.004) were higher at night-time (18:00-06:00). As most individuals were actively moving at nighttime, we confirmed that A. japonica is nocturnal, although few individuals also showed daytime movement. Although the population and habitats of A. japonica 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 A. japonica management regarding habitat and population conservation and restoration.

Keywords: acoustic telemetry; diel movement; nocturnal species; vertical movement.

Figure 1

A map showing the study sites. Black circles are sites with installed VR2W acoustic receivers.

Figure 2

Migration pattern and distance of four A. japonica individuals that showed longitudinal movement. The plus value on the y-axis means movement toward an upstream direction, and the minus value means movement toward a downstream direction.

Figure 3

The number of diel detection patterns of tagged A. japonica in the Geum River.

Figure 4

The proportion of detections during the nighttime (18:00–06:00) and daytime (06:00–18:00).

Figure 5

Average diel movement of 11 A. japonica fitted with a depth sensor; the diagonal line and white backgrounds represent nighttime and daytime based on average 12-h periods during 24 h, respectively. (a) AJ4, AJ5, AJ6, (b) AJ7, AJ8, AJ9, (c) AJ10, AJ11, AJ12, (d) AJ18, AJ19.

Figure 6

Daily movement patterns of 11 A. japonica fitted with a depth sensor: black and white circles indicate nighttime and daytime detection, respectively. AJ15 was excluded because there was no vertical movement.