Development of a sonar-responding acoustic tag for fish behavior observation

Ultrasonic telemetry system was one of the most useful methods to observe the underwater target. But this system had disadvantage to need exclusive receiving device. We developed the sonar responding acoustic tag (called SRAT) to resolve the disadvantage. SRAT was acoustic tag that signals are appeared on the sonar display. The prototype of SRAT is responded the sonar signal between 20 kHz to 90 kHz. The response frequency was 31.25 kHz or 62.50 kHz. SRAT size was Φ 25 × 150mm, 100 g in air and 70 g in water. The transducer of SRAT was made from multi layer PZT. The battery life was about one month. The basic experiment was carried out for the response distance measurement of the device. Depth of the experiment sea area was around 50 m. The sonar frequency was 68 kHz and source level was 210 dB re 1 μPa. In this experiment, we were able to observe the SRAT signal around 200 m distance on sonar display. The actual experiment was performed in purse seine for tuna fishing. The sonar frequency was 28 kHz and the source level was 220 dB re 1 μPa. SRAT was attached to the purse seine net. Result of this experiment, maximum response distance of SRAT was confirmed as 400 m. We have confirmed the effectiveness of sonar responding acoustic tag through the actual experiment. The research work and actual fishing would be advanced using the SRAT device. And the near future, suppose SRAT will be more small and light weight, It becomes functional methods to research migration of marine animals like a fish.