Acoustical analyses on the calls of dugong

Abstract

Dugong, Dugong dugon, has become one of highly endangered species in the world. It is said that the decrease in the number of dugong population is mainly due to accidental catches by fishnets. A breakthrough to avoid the accidental catches, by-catches, is in urgent need. In this study, we described the technique to detect the direction of vocalizing dugong and the acoustical characteristics of dugong calls. This study can lead to a new observation method of wild animals. A number of dugong calls were recorded around Libong Island, Trang, Thailand, using two sets of dual channel stereo hydrophones on two research vessels. The center frequency of dugong calls ranged from 3-8 kHz, and the duration of the calls was classified roughly in two : 100-500 ms and over around 1000 ms. Vocalization intervals were classified in two patterns : 0 - 5 s and about over 20 s between each call. We applied the phase difference analysis to dugong calls recorded by a stereo hydrophone. The preliminary results suggested that the acoustical analyses on the dugong calls will be a powerful method to locate the vocalizing dugongs without any impact on them at all.