The Irrawaddy dolphin is patchily distributed in shallow, near-shore tropical and subtropical marine waters of the Indo-Pacific, from northeastern Australia in the south, north to the Philippines (Dolar et al. 2002) and west to northeastern India (Stacey and Leatherwood 1997, Stacey and Arnold 1999). Its marine distribution is concentrated in estuaries and semi-enclosed water bodies (i.e., bays and sounds), generally adjacent to mangrove forests. Freshwater populations occur in three river systems ? the Mahakam of Indonesia, the Ayeyarwady (formerly Irrawaddy) of Myanmar (formerly Burma) and the Mekong of Lao PDR, Cambodia and Viet Nam. Irrawaddy dolphins also occur in completely or partially isolated brackish or freshwater bodies, including Chilka Lake in India and Songkhla Lake in Thailand. Irrawaddy dolphins were first documented as occurring in Malampaya Sound, Palawan, Philippines, during an investigation of dugongs (Dugong dugon) in 1986 (Kataoka et al. 1995). This is the only known subpopulation of the species in the Philippines and the nearest other known subpopulation is in northern Borneo, some 550 km to the south. The species occurs only in the inner portion of the sound, an area of about 134 km².
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