Turtle hearing classification for turtle excluder devices design

Abstract

The process of reducing the accidental capture and subsequent mortalities of sea turtles in regional captured fisheries through the use of Turtle Excluder Device (TED) has been extremely important. The objectives of this study is to determine the hearing ability for Green Turtle (Chelonia Midas), identify the green turtle and fish behavior on various sound exposures, and determine the specification of TED using underwater sound technique. Auditory Brainstem Response system is used to identify the hearing threshold of the turtle. The measurements were performed at Turtle and Marine Ecosystem Center (TUMEC) Terengganu, Perak, and Melaka Malaysia. It was conducted at a turtle tank by employing click and tone stimulus. Turtle ages of 2 years, 5 years, 9 years, and 30 years were deployed. The measured data were analyzed in time and frequency domains. It is found that the green turtle has a hearing ability in the range of 50 Hz to 1200 Hz. The results showed that turtle hearing sensitivity is about 300 Hz to 500 Hz. Also, the measurement of ambient noise in the life habitat has been conducted. The measurements were divided into 3 different distances from the sea shore: 200 m, 400 m, and 800 m and within 3 different sea depth: 2 m, 5 m, and 10 m for each point, respectively. The frequency and maximum magnitude of ambient noise are found to increase as the depth increased. Finally, the behavior of the turtle and fish towards the emitted sound has been observed. A group of signals that dispel turtles have been determined. The types of signals are Low and High Frequency Modulation, white noise, and sinusoidal signal. These signals do not give any respond to the fish. Therefore, this information is very useful in the development of TED using sound.