Tracking of Japanese eel Anguilla japonica by ultrasonic transmitter in the southwestern waters of Taiwan

Abstract

Artificially induced maturing Japanese eels, Anguilla japonica, were released in southwestern waters of Taiwan on 26-28 January 1994, and tracked with ultrasonic transmitter to collect informations on the spawning migration of this species. Among five eels tagged with identical transmitters, different type of signals, pulse length and frequency, two specimens moved southeastward (137.2 ° ), while the other two swam northwestward (328.4 ° and 347.0 ° ). The direction of movement, except No. 5 specimen, coincided with the tidal currents of release time and location. The last eel (No. 5) was lost 5 minutes after release because of a rapid movement. Northwestward movement of the eel might be explained as a preference for deeper waters, just as observed in European eel. The distance between the release point and the end of tracking ranged from 490m to 750m. Mean swimming speed during tracking ranged from 0.5 to 40.1 cm/sec. The changes in strength and direction of the signals indicated that the eels seemed to swim downward to the sea bottom just after the release and might be moving in and out of a "shelter" or "hole" at the bottom. Once the eel dived and reached the bottom, they might move little either horizontally or vertically.