MARINE MAMMAL SCIENCE, 21(3):536-549 (July 2005) zyxw 0 2005 by the Society for Marine Mammalogy DUGONG zyxwv (DUGONG DUGON) ABUNDANCE ALONG THE ANDAMAN COAST OF THAILAND ELLEN M. HINES Department of Geography and Human Environmental Studies, San Francisco State University, 1600 Holloway Avenue, San Francisco, California 941 32, U.S.A. E-mail: ehines@sfsu.edu KANJANA ADULYANUKOSOL Phuket Marine Biological Center, P. 0. Box 60, Phuket 83000 Thailand DAVID A. DUFFUS Whale Research Lab, Department of Geography, University of Victoria, Victoria, British Columbia V8W 3P5, Canada zyxw ABSTRACT In 2000 and 2001, dugong abundance was estimated using aerial surveys in three provinces along the Andaman coast of Thailand. A microlite aircraft was used to fly aerial transects over seagrass areas. All surveys were done during rising tides as the dugongs came to the seagrass beds to feed. The largest population was found in Trang province. In Trang, the total number of sightings during 22 surveys was 264, out of which 31.5% were single dugongs. The largest group seen in 2000 was 30, and in 2001, 53. The maximum number of calves seen in one day was 13. The best minimum estimate ofpopulation abundance is 123 animals (CV= 60.8%) in Trang province. Higher numbers of dugong sightings and group sizes corresponded with higher tides until water turbidity impeded sightings after the highest spring tide. In other areas the number of animals seen was too small for population estimates. Key words: dugong, Dugong dugon, population assessment, Thailand, Andaman Sea. The dugong (Dugong zyxwvut dugon) is critically endangered. Outside of Australia, the country with the largest estimated dugong population, dugongs only survive in fragmented populations in the Eastern hemisphere. Neither the number of dugongs remaining in these populations nor its range is known beyond incidental sightings and the reports of fishermen (Marsh et al. 1999, 2002). In Thailand the dugong has been under Federal protection since 1947 (Humphrey and Bain 1990). Our study along the Andaman coast is the first systematic dugong population survey in Thailand (also see Hines 20024 b). There are five population centers along the Andaman coast: Ranong, Phuket, Krabi, Trang, and Satun (Fig. 1). Aerial surveys were flown near Phuket, Krabi, and Trang. Many of the seagrass beds surrounding the island of Phuket have been 536