The acoustical characteristics of dugong calls and the behavioral correlates observed in Toba aquarium

Abstract

Dugongs, Dugong dugon, are listed as Vulnerable to extinction in IUCN Red List. Previous reports suggested that there were some correlation between the behavior and the acoustical characteristics of dugongs. However, there was no continuous observation of an identified individual. We analyzed the acoustical characteristics of a captive dugong and the behavioral correlation in Toba aquarium, Japan. The purpose of this study was to predict its behavior based on the acoustical characteristics of dugong calls. In December in 2003 and 2004, we observed the male dugong (Junichi) in Toba aquarium. We used a digital video camera and a hydrophone to record the behavior and the vocalization of the dugong. Video-recording was taken in the daylight for 18 hours each (total 36 hours). The underwater sound recording was performed all through the survey for 31 hours each (total 62 hours). We recorded active movements (exposing its penis, rubbing its penis or body against objects, jumping out of the water, beating a water pillow with its flipper and running hard into wall). Through the observation, 616 calls were recorded. Call duration ranged 34-5039ms. These calls could be categorized by two types : short calls (chirp) that are under 300ms (380 samples) and long calls (trill) that are 300ms and above (236 samples). Call frequency ranged from 1.0 kHz to 8.6 kHz. All of the trains of calls with more than four calls were observed within 10 minutes from the active movements. The dugong made 38 very long calls (over 3000 ms). Almost all (94.7%) of the long calls were observed within 10 minutes from the active movements.