Acoustic detection of dugong using automatic underwater sound monitoring systems : AUSOMS-D

Abstract

Dugongs are the only marine mammals that feed on benthic seagrass. They are found in warm shallow waters of tropical to sub-tropical areas. Many of the dugong populations are close to extinction. Effective protection measures are needed for this species, but the dugongs are one of the most difficult animals to observe in the wild. We have attempted to establish a new methodology to record the presence of dugongs by a passive acoustic monitoring technique. In March, 2004, ten sets of automatic underwater sound monitoring systems for dugong - AUSOMS-D - were deployed on the seafloor in the southern part of the Talibong Island, Trang, Thailand. The underwater sound was recorded in stereo for 5 consecutive days. An acoustical filter was developed to detect the dugong calls automatically out of the background noise. The receiver operating characteristics has been evaluated. False alarm and correct detection rates of the system were 2.9% and 39.1%, respectively. The false detection rate was low enough to perform a scientific study on the dugong but the correct detection rate should be improved. The reason for the low correct detection rate appeared to be due to the low signal-to-noise ratio. For calibration purpose, artificially composed dugong calls were transmitted in the water from a research vessel. The GPS position and the acoustically calculated position were compared. The average error of the positioning of the sound source by AUSOMS-D was less than 20 m.