Spatial distribution of dugongs by acoustic and visual observation in Thailand

Abstract

Dugong calls were collected using a towed stereo hydrophone system around Talibong Island and Muk Island in Thailand in January 2008. Standard visual observation was conducted simultaneously to record the dugong distribution. A total of 223 dugong calls and 80 dugongs were detected. Spatial distributions of both of the acoustical and visual detections were analyzed using Iδ-index. The spatial distribution of the visual detections showed almost uniform distribution and that of the acoustical observations showed concentrated distribution (Iδ=0.85 and 3.18, respectively). The number of snapping noises per minute was less in the areas where dugong calls were observed (P < 0.001). It was suggested that dugongs vocalized selectively in less noisy areas.