Abstract
Acoustic observation is well-known to be an effective method to detect calls of marine mam
mals. We applied this method to observe calls of dugong, Dugong dugon, which has become
highly endangered in the world. In this study, we described the technique to detect the arrival
direction and the acoustical characteristics of dugong calls. These aspects are needed in design
ing the observational equipments. In addition, specifications for an innovative observational de
vice were described. A number of dugong calls were recorded around Libong Island, Trang
province in Thailand, using two sets of dual channel stereo hydrophones on two research ves
sels. The center frequency of dugong calls ranged between about 3 and 8 kHz, and the duration
of the calls was classified roughly in two: 100-500ms and over 1000ms. Vocalization interval
was classified in two patterns: 0-5s and 20- s between each call. We applied the phase differ
ence analysis to dugong calls in order to calculate the arrival direction at the research vessels.
These preliminary results suggested that the acoustical analyses on the dugong calls are a pow
erful method to locate the vocalizing dugongs without any impact on them at all.
