Dugong Aerial Surveys 2011-2012: Declining Trend of the Dugong Population in Muk-Talibong Island, Thaland

Abstract

The Muk-Talibong Islands in Trang Province is a habitat for the largest group of dugongs on Thailand's Andaman coast. Since 1994, the Phuket Marine Biological Center has regularly conducted aerial surveys over the area with various kinds of aircrafts. In 2011 and 2012, the small aircraft model Tecnum P92J was used in line transect aerial surveys. Survey efforts were four flights (15.01 hours) and seven flights (17.14 hours) respectively. In 2011, the dugong detection rate was 51±50 animals per day, with a maximum count of 122 animals. In 2012, however, the dugong detection rate was 26±14 animals per day, with a maximum count of 54 animals. As a result of comparing the dugong detection rates for both years, we found that the number of dugongs is decreasing, even though the aerial survey periods in each year were the same month and tidal time. Windspeed is likely to be a physical factor that might lead to these results. Ranges of wind speed were 0-6 knot in 2011 and 5-17 knot in 2012. The wind speed affects waves and turbidity, and this may negatively affect visual detection of dugongs. Therefore, further aerial surveys in different weather conditions and dugong stranding reports may help to better understand the declining trends of dugongs in the area.