136 Chiang Mai J. Sci. 2015; 42(1) Chiang Mai J. Sci. 2015; 42(1) : 136-147 http://epg.science.cmu.ac.th/ejournal/ Contributed Paper Population Size and Habitat Patterns of Indo-Pacific Humpback Dolphins (Sousa chinensis) off Donsak, Surat Thani, Thailand Suwat Jutapruet*[a], Kongkiat Kittiwattanawong [b] and Siriporn Pradit [a] [a] Marine and Coastal Resources Institute, Prince of Songkla University, Hat Yai, Songkhla, 90110, Thailand. [b] Phuket Marine Biological Research Center, Phuket, 83000,Thailand. *Author for correspondence; e-mail:
[email protected] Presented at the International Graduate Research Conference 2013 (IGRC2013), 20th December 2013, Chiang Mai, Thailand. Received: 24 December 2013 Accepted: 5 May 2014 ABSTRACT This study investigated the population size and distribution pattern of the Indo-Pacific humpback dolphin (Soasa chinesis) off Donsak, Surat Thani, Thailand. The field surveys were conducted along the coastline of the mainland and the offshore area of the Angthong Marine National Park. The population size was estimated by applying a mark-recapture model to the individual photo-identification records collected from field surveys. In total, 142 individuals were photo-identified using dorsal fin characteristics. The population size was estimated to consist of 160 individuals with a range of 152 - 178 at a 95% CI. Spatial (GPS data) and environmental information were recorded for distribution and habitat analysis. The most frequent encounters with humpback dolphins occurred, in decreasing order of magnitude, at Somserm Ferry, Raja Ferry, Som Island, Nok Ta Pao Island and Taled Bay. The present study showed that the humpback dolphins off Donsak were frequently found near the coast in close proximity to man-made structures, sea grass areas and mudflat habitats.