<Session 6: Wildlife Tracking II>Application of ultrasonic telemetry system for monitoring depth of trolling gear

Abstract

Cutlass fish (Trichiurus lepturus) is fished with trolling in the west of Japan. In that fishing, because the trolling depth affects the catch, the fishing gear has to be positioned at the depth of fish school accurately. Normally, fishermen estimate the gear depth from the length of reeling the sinker from the bottom by a spool. However, if the sea state gets worse and/or if the fishing is operated in a deeper fishing place, it becomes difficult to make the adjustment of the gear depth and fatiguing the fishermen. In order to reduce the workload and make it easy to adjust the gear depth, we applied ultrasonic telemetry system to the trolling gear as a system for monitoring depth in real-time. The system is consisted of a pinger and a receiving system with an omni-directional wired hydrophone and a display of the pinger's depth. The pinger's battery is easily-exchangeable to use it repetitively. The system was tested by experiments in actual fishing operations and could show the gear depth every few seconds. Therefore, without letting the sinker touch the bottom, it is possible to obtain the accurate gear depth. In addition, it was possible to easily handle the system by fishermen themselves. From this study, it is expected that our system can reduce the workload.