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. Our study revealed that a distinct humpback dolphin habitat occurred at a specific off-shore distance, water depth and water transparency. Results of this study improves the better understanding of the humpback dolphin’s ecology and offers informed baselines essential for meaningful marine-mammal protection and management policies in the Gulf of Thailand. Keywords: population size, Indo-Pacific humpback dolphin, Donsak-Surat Thani, habitat patterns 1. INTRODUCTION The richness of complex marine and activities that consists of Donsak estuary, coastal ecosystems attracts human activities small islands, sea grasses beds, muddy beaches, which have caused marine and coastal mangroves, rocky shores, sandy beaches, habitat degradation and loss of natural rocky cliffs, headlands, coastal communities, resources [1]. The Donsak, Surat Thani, artisanal fishery, commercial fisheries, ferry Thailand is a complicated ecosystem with transportation piers, resorts and hotels, plentiful natural resources and anthropogenic manufacturing industries and famous Chiang Mai J. Sci. 2015; 42(1) 137 dolphin-watching tourism. Dolphin-watching dolphins (Unpublished data). In consequence, tourism industry exclusively targeting to the the humpback dolphin research in Thailand Indo-Pacific humpback dolphin, Sousa chinenis, is a critical need. Moreover, information was promoted to motivate tourism activities about stranded dolphins was collected along the coastlines of the Donsak district, along the coastline of the Gulf of Thailand Surat Thani province and Khanom, Nakhon (Unpublished data). However, dolphins are district, Si Thammarat province [2]. frequently found in the boundary areas Although many efforts were made for between Donsak, Surat Thani and Khanom, marine and coastal conservation policies, Nakhon Si Thammarat. Although there are anthropogenic overexploitation is still no tourism activities in the Donsak area, increasing. More information is needed to Indo-Pacific humpback dolphins inhabiting improve the effectiveness and scientific this shoreline may also form part of the basis of current conservation policies. dolphin population of the Khanom area. Data on the baseline dolphin population, A previous study identified 33 adults, including distribution, abundance and eight juveniles and eight calves with a habitat characteristics, are still very rare estimated population estimate of 49 dolphins across South-East Asia, a region considered (with no confidence interval) in the Khanom to be one of the important habitat for Sea, Nakhon Si Thammarat [2]. The current humpback dolphins. Scientific research is an study was conducted at Donsak, Surat Thani, important measure to provide essential north of the adjacent area, Khanom, baselines and must be included in the marine Nakhon Si Thamarat during a longer period conservation issues [3, 4]. The International and include distribution and habitat Union for Conservation of Nature (IUCN) characteristics of humpback dolphins. It is categorized the Indo-Pacific humpback hoped that the data generated by this study dolphin as a near-threatened species [5]. would lead to improved decision-making Not only are humpback dolphin population on humpback dolphin conservation by size information mentioned in the IUCN stakeholders in Donsak District, Surat Thani, report is needed, but also supportable habitat Thailand. quality information [6]. Although the humpback dolphins are currently known due 2. MATERIALS AND METHODS to dolphin shows (Oasis Sea World, 2.1 Study Site Chanthaburi, Thailand) and dolphin watching 2.1.1 Coastal area (CA) tourism in Khanom, Nakhon Si Thammarat, The study was conducted in the coastal Thailand, there is still a lack of understanding zone of Donsak district, Surat Thani province about population, habitat or general and Khanom district, Nakhon Si Thammarat information of humpback dolphin in the province, the east coast of Southern Thailand Thailand region. Marine and Coastal Resources (Taled Bay-TB, Thong Nian Bay-TNB, Research Center (MCRC), Central and Lower Lak Sor Mountain-LSM). The area is Gulf of Thailand have recorded an increase characterised by rocky shores, sandy beaches, in the mortality rate of humpback dolphins rocky cliffs, mud flats, mangroves and sea during the period 2006-2012 (Unpublished grass beds (Tarai island, TRI) (Figure 1). data). In the gulf of Thailand, the bycatch Human activities such as the Somserm Ferry, mortality rate of humpback dolphins was Sea Tran Ferry, Raja Ferry Transportation piers recorded as 24% of 62 stranded humpback (to the famous tourism islands, Samui 138 Chiang Mai J. Sci. 2015; 42(1) Island, Pha-ngan island), coastal fishery, Marine National Park. The protected marine dolphin watching tour activities, industrial navy base, the Gulf of Thailand, was factories are also found within this area. converted into a marine national park on 12th November 1980 due to the abundant 2.1.2 Offshore area (OA) species and natural marine resources [7]. The small islands of Ri Gun Island (RGI), This Ang Thong Marine National Park Nok Ta Pao (NTPI), Som (SI), Chuek (CI), consists of 42 small islands with dry evergreen Pa-luai (PLI) Pi Island (PI) and Jae Island (JI) forests, beaches, and lime stone and mangrove are located at the north of Donsak coastline. forests [7] (Figure 1). A part of Pa Luai Island is the Ang Thong Figure 1. Study area, Donsak, Surat Thani, Thailand. %: Som Serm Ferry, Seatran Ferry and Raja Ferry respectively. 2.2 Data Collection (WD), water transparency (SD), pH, sea 2.2.1 Boat surveys surface temperature (SST) salinity (SN) and Boat-based surveys were conducted Beaufort Sea State category were recorded at from between December 2011 - April 2013 the dolphin encounters. Further environmental during 08:00-14:00 with Beaufort Sea State conditions were recorded, noting tide (TD, category category between 0 and 2 off the 0 being low tidal and 1 being high tidal), coast of the Ang Thong islands of Donsak, cloud cover (CC, 0 being clear sky with <20% Surat Thani Province. A long-tailed fishing cloud cover, 1 between 20%-50% cloud boat with an outboard 175 hp engine was cover and 2 being > 50% cloud cover), used with speeds not exceeding 15 km/h. wind power (WP, 0 being no wind blow, 1 as Route tracking was recorded by GPS little wind blow and 2 being strong wind), (Garmin eTrex30) and the positions were rainy (RN, 0 being no rain and 1 being rain) marked when dolphin were sighted. The and sun light (SL, 0 being no sun shine and boat speed was slowed when dolphins were 1 being sun shine) conditions. A variable, encountered. We measured water depth “Seasonal change” was noted with May 16 Chiang Mai J. Sci. 2015; 42(1) 139 to January 31 was categorized as the Rainy during the study, or, alternatively, as the Season and February 1 to May 15 as the total number of animals ever sighted in the Summer Season. Habitat characteristics of sampled area between the first and last dolphin encounter sites were recorded as periods of the study [9]. The parameter Φ rocky shore (RS), man-made structure (MM), denotes apparent survival rate, P denotes mud flats (MF), sandy beach (SB) and sea grass the probability of capture, and b denotes beds (SG), and were abbreviated by RS, the probability that an animal from the super- MM, MF, SB and SG, respectively. Finally, population will enter the subpopulation distance off the shore (DS) was measured (subpopulation referring to the animals (meter) with the perpendicular straight line occurring in the study area). from nearest coastline to the encoutered position by GIS software. Variance of N was estimated using the delta method and the following equation: 2.2.2 Photo-identification Researchers attempted to photograph all the individual dorsal fins in a group that where n is the total number of dorsal were the most perpendicular to the dolphin’s fins from which θ was calculated. Confidence body axis with DSLR D80 D90 and D7000 intervals for N assumed the same error Nikon digital cameras with 70-300 mm total distribution as the mark-recapture estimates lenses. The processing of utilised 45,000 [10]. The population size was computed pictures that were selected based on the most by Parm-Specific as a Link function, Sin clearest dorsal fins. Though a systematic were Φ and P, mlogit (1) was b and logit process individuals were indentified and was N on POPAN parameterization model added to the catalogue by recording the option in MARK software.