Dugong vocalization in relation to ambient noise

Abstract

Ocean noise has a possibility to interfere with acoustic communication of marine mammals by masking biological signals. Some species of marine mammals change their vocalization (e.g., increasing amplitude, duration, repetition and shifting frequency) with elevated ambient noise level to avoid acoustic interference. We studied the dial pattern of ambient noise and dugong calls. We used the underwater sound data recorded off the south coast of Talibong Island, Trang, Thailand, by Automatic Underwater SOund Monitoring System for Dugong (AUSOMS-D). We used the data recorded from 10:00h on November 16 to 9:00h November 23, 2006. To quantify the dial pattern of the ambient noise, hourly ambient noise levels were analyzed. Then, we counted the number of dugong calls and analyzed their acoustic characteristics. Finally, we tested the relationship between the peak frequency of calls and the ambient noise level to investigate whether and how dugongs change their vocalizations. We found high ambient noise levels in the morning through noon (6:00-12:00h) and evening (18:00-21:00h). Dugongs calls were frequently observed at night as described in previous studies. Dugongs call showed the high frequency (6-9 kHz) with elevated level of the ambient noise, while they usually use 3-6 kHz call. Dugongs may adapt their vocalization in relation to the continuous ambient noise.