Population Size and Habitat Patterns of Indo-Pacific Humpback Dolphins (Sousa chinensis) off Donsak, Surat Thani, Thailand

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1 136 Chiang Mai J. Sci. 2015; 42(1) Chiang Mai J. Sci. 2015; 42(1) : 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; suwat.j@psu.ac.th Presented at the International Graduate Research Conference 2013 (IGRC2013), 20 th 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 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 coastal ecosystems attracts human activities which have caused marine and coastal habitat degradation and loss of natural resources [1]. The Donsak, Surat Thani, Thailand is a complicated ecosystem with plentiful natural resources and anthropogenic activities that consists of Donsak estuary, small islands, sea grasses beds, muddy beaches, mangroves, rocky shores, sandy beaches, rocky cliffs, headlands, coastal communities, artisanal fishery, commercial fisheries, ferry transportation piers, resorts and hotels, manufacturing industries and famous

2 Chiang Mai J. Sci. 2015; 42(1) 137 dolphin-watching tourism. Dolphin-watching tourism industry exclusively targeting to the Indo-Pacific humpback dolphin, Sousa chinenis, was promoted to motivate tourism activities along the coastlines of the Donsak district, Surat Thani province and Khanom, Nakhon district, Si Thammarat province [2]. Although many efforts were made for marine and coastal conservation policies, anthropogenic overexploitation is still increasing. More information is needed to improve the effectiveness and scientific basis of current conservation policies. Data on the baseline dolphin population, including distribution, abundance and habitat characteristics, are still very rare across South-East Asia, a region considered to be one of the important habitat for humpback dolphins. Scientific research is an important measure to provide essential baselines and must be included in the marine conservation issues [3, 4]. The International Union for Conservation of Nature (IUCN) categorized the Indo-Pacific humpback dolphin as a near-threatened species [5]. Not only are humpback dolphin population size information mentioned in the IUCN report is needed, but also supportable habitat quality information [6]. Although the humpback dolphins are currently known due to dolphin shows (Oasis Sea World, Chanthaburi, Thailand) and dolphin watching tourism in Khanom, Nakhon Si Thammarat, Thailand, there is still a lack of understanding about population, habitat or general information of humpback dolphin in the Thailand region. Marine and Coastal Resources Research Center (MCRC), Central and Lower Gulf of Thailand have recorded an increase in the mortality rate of humpback dolphins during the period (Unpublished data). In the gulf of Thailand, the bycatch mortality rate of humpback dolphins was recorded as 24% of 62 stranded humpback dolphins (Unpublished data). In consequence, the humpback dolphin research in Thailand is a critical need. Moreover, information about stranded dolphins was collected along the coastline of the Gulf of Thailand (Unpublished data). However, dolphins are frequently found in the boundary areas between Donsak, Surat Thani and Khanom, Nakhon Si Thammarat. Although there are no tourism activities in the Donsak area, Indo-Pacific humpback dolphins inhabiting this shoreline may also form part of the dolphin population of the Khanom area. A previous study identified 33 adults, eight juveniles and eight calves with a estimated population estimate of 49 dolphins (with no confidence interval) in the Khanom Sea, Nakhon Si Thammarat [2]. The current study was conducted at Donsak, Surat Thani, north of the adjacent area, Khanom, Nakhon Si Thamarat during a longer period and include distribution and habitat characteristics of humpback dolphins. It is hoped that the data generated by this study would lead to improved decision-making on humpback dolphin conservation by stakeholders in Donsak District, Surat Thani, Thailand. 2. MATERIALS AND METHODS 2.1 Study Site Coastal area (CA) The study was conducted in the coastal zone of Donsak district, Surat Thani province and Khanom district, Nakhon Si Thammarat province, the east coast of Southern Thailand (Taled Bay-TB, Thong Nian Bay-TNB, Lak Sor Mountain-LSM). The area is characterised by rocky shores, sandy beaches, rocky cliffs, mud flats, mangroves and sea grass beds (Tarai island, TRI) (Figure 1). Human activities such as the Somserm Ferry, Sea Tran Ferry, Raja Ferry Transportation piers (to the famous tourism islands, Samui

3 138 Chiang Mai J. Sci. 2015; 42(1) Island, Pha-ngan island), coastal fishery, dolphin watching tour activities, industrial factories are also found within this area Offshore area (OA) The small islands of Ri Gun Island (RGI), Nok Ta Pao (NTPI), Som (SI), Chuek (CI), Pa-luai (PLI) Pi Island (PI) and Jae Island (JI) are located at the north of Donsak coastline. A part of Pa Luai Island is the Ang Thong Marine National Park. The protected marine navy base, the Gulf of Thailand, was converted into a marine national park on 12 th November 1980 due to the abundant species and natural marine resources [7]. This Ang Thong Marine National Park consists of 42 small islands with dry evergreen forests, beaches, and lime stone and mangrove forests [7] (Figure 1). Figure 1. Study area, Donsak, Surat Thani, Thailand. %: Som Serm Ferry, Seatran Ferry and Raja Ferry respectively. 2.2 Data Collection Boat surveys Boat-based surveys were conducted from between December April 2013 during 08:00-14:00 with Beaufort Sea State category category between 0 and 2 off the coast of the Ang Thong islands of Donsak, Surat Thani Province. A long-tailed fishing boat with an outboard 175 hp engine was used with speeds not exceeding 15 km/h. Route tracking was recorded by GPS (Garmin etrex30) and the positions were marked when dolphin were sighted. The boat speed was slowed when dolphins were encountered. We measured water depth (WD), water transparency (SD), ph, sea surface temperature (SST) salinity (SN) and Beaufort Sea State category were recorded at the dolphin encounters. Further environmental conditions were recorded, noting tide (TD, 0 being low tidal and 1 being high tidal), cloud cover (CC, 0 being clear sky with <20% cloud cover, 1 between 20%-50% cloud cover and 2 being > 50% cloud cover), wind power (WP, 0 being no wind blow, 1 as little wind blow and 2 being strong wind), rainy (RN, 0 being no rain and 1 being rain) and sun light (SL, 0 being no sun shine and 1 being sun shine) conditions. A variable, Seasonal change was noted with May 16

4 Chiang Mai J. Sci. 2015; 42(1) 139 to January 31 was categorized as the Rainy Season and February 1 to May 15 as the Summer Season. Habitat characteristics of dolphin encounter sites were recorded as rocky shore (RS), man-made structure (MM), mud flats (MF), sandy beach (SB) and sea grass beds (SG), and were abbreviated by RS, MM, MF, SB and SG, respectively. Finally, distance off the shore (DS) was measured (meter) with the perpendicular straight line from nearest coastline to the encoutered position by GIS software Photo-identification Researchers attempted to photograph all the individual dorsal fins in a group that were the most perpendicular to the dolphin s body axis with DSLR D80 D90 and D7000 Nikon digital cameras with mm lenses. The processing of utilised 45,000 pictures that were selected based on the most clearest dorsal fins. Though a systematic process individuals were indentified and added to the catalogue by recording the presence of nicks, notches, pigmentation patterns, color, dorsal fin edge figure, scar or wound. The datasheet was replaced with 0 and 1 to indicate either absence or presence of each individual per sighting. 2.3 Data Analysis Abundance The researchers recorded 89 sightings events from all surveys conducted over 17 months of. A dolphin sighting matrix data set was constructed with the occurrence of each individual per site and the population size was estimated by live recapture of open population model parameterization on POPAN in MARK Software [8] which includes the parameter N - the size of a superpopulation. N can be thought of as either the total number of animals available for capture at any time during the study, or, alternatively, as the total number of animals ever sighted in the sampled area between the first and last periods of the study [9]. The parameter Φ denotes apparent survival rate, P denotes the probability of capture, and b denotes the probability that an animal from the superpopulation will enter the subpopulation (subpopulation referring to the animals occurring in the study area). Variance of N was estimated using the delta method and the following equation: where n is the total number of dorsal fins from which θ was calculated. Confidence intervals for N total assumed the same error distribution as the mark-recapture estimates [10]. The population size was computed by Parm-Specific as a Link function, Sin were Φ and P, mlogit (1) was b and logit was N on POPAN parameterization model option in MARK software. 2.4 Habitat Characteristic Habitat characteristics were tested statistically by using Principal Component Analysis (PCA) and Canonical Correlation Analysis (CCA) analysis using R software and ade4 [11] and vegan library packages [12]. We categorized each sighting with environmental factor, season, habitat characteristics, inshore and offshore area, and the encountered area names. 3. RESULTS AND DISCUSSION 3.1 Survey Effort Forty-seven boat survey-days (205 h) were undertaken, covering a total distance of 2,618.4 km. The surveys resulted in 89 dolphin sightings within the 17 months. The cumulative sightings of humpback

5 140 Chiang Mai J. Sci. 2015; 42(1) dolphins in the study area are indicated in Figure 3. Solitary individuals comprised 14.6% of all sightings. The highest frequency of occurrence was found in the first five areas, Som Serm Ferry, Raja Ferry, Som Island, Nok Ta Pao Island and Ta Led Bay (Figure 3). The dolphins were encountered off-shore in 22.5% of all sightings. 3.2 Population Size Total 142 humpback dolphins were identified. These individuals were separated by age class from all 47 observation days from the 17-month survey (Figure 2). At least 15 individuals were identified as the same individuals from a previous study [2]. The average group size of humpback dolphins sighted in this study ranged between from two to eighteen dolphin with the average group size 4.72 ±.35 based on 455 individuals recorded for the full study. Solitary individual were observed in 10.34% of all sightings. A total of 160 individuals was observed with a range of at 95% CI from POPAN paramiterization on MARK software. Figure 2. Survey of Indo-Pacific humpback dolphin in the Donsak area. AD = adult; SA = sub-adult; JN = juvenile; CV = calf. Figure 3. The frequency of encountered positions of humpback dolphin in the study area, SSF - Som Serm Ferry, RF - Raja Ferry, SI - Som Island, NTPI - Nok Ta Pao Island, TLB - Taled Bay, RGI-Ri Gun Island, STF - Sea Tran Ferry, TRI - Ta Rai Island, PLI - Pa Luai Island, CPI - between Chuek and Palui Island, PI - Pee Island, JI - Jae Island.

6 Chiang Mai J. Sci. 2015; 42(1) Habitat Characteristics In 83 of the 89 sightings the environmental parameters were measured because five of all sighting were bad weather conditions. The PCA analysis showed the groups of habitat characteristic. The ellipses surround the group of environmental parameters that were categorized with encountered position, coastline and offshore, habitat characteristics and season. The offshore islands, Jae Island (JI), Pa Luai Island (PLI), the area between Chuek and Paluai Island (CPI), Som Island (SI) and Nok Ta Pao Island (NTPI) were seperalately grouped from encoutered position on coastline, Sea Tran Ferry (STF), Som Serm Ferry (SSF), Raja Ferry (RF), Ta Rai Island (TRI), Ta Led Bay (TLB) and Pi Island (PI) (Figure 4, 5). The rocky shore (RS) and sandy beach (SB) were surrounded with two ellipses that were not overlapped on mud flat (MF), mam-made structure (MM) and sea grass beds (SG) (Figure 6). The partial overlapped of two ellipses between rainy and summer seasons were shown on Figure 8. The PCA of dolphin encountered position on Figure 4 are Environmental parameters of dolphins encounter were analyzed in the groups of data by using CCA analysis with R software (Figure 8). The DS, WD and SD were significantly different from the habitat characteristics of humpback dolphin population in study area (Table 1). Figure 4. Principle component anlaysis of encounter positions of dolphins. Som Serm Ferry (SSF), Raja Ferry (RF), Som Island (SI), Nok Ta Pao Island (NTPI), Taled Bay (TLB), Ri Gun Island (RGI), Sea Tran Ferry (STF), Ta Rai Island (TRI), Pa Luai Island (PLI), between Chuek and Palui Island (CPI), Pee Island (PI) and Jae Island (JI).

7 142 Chiang Mai J. Sci. 2015; 42(1) Figure 5. PCA anlaysis of coastline and offshore data from the dolphin study areas. Figure 6. Principle component analysis of habitat characteristics of dolphins (RS: Rocky shore, SB: Sand beach, MF: Mud flat, MM: Man-made structures and SG: Seagrass area).

8 Chiang Mai J. Sci. 2015; 42(1) 143 Figure 7. Principle component analysis of seasonal data of dolphins. Figure 8. Canonical correlation analysis from R software, Distance of the shore (DS), Water depth (WD), Water transparency (SD), Sea surface temperature (SST), Salinity (SN), Tidal (TD), Cloud cover (CC), Wind power (WP), Sun light (SL), Rain (RN), Beaufort sea state category (BF).

9 144 Chiang Mai J. Sci. 2015; 42(1) Table 1. Range, Mean (± SD) and canonical correlation analysis of environmental parameters of humpback dolphins. Factors Range Mean ± SD CCA r 2 DS (m) WD (m) SD (m) SST (c) ph SN (ppm) TD CC WP SL RN BF ± ± ± ± ± ± ± ± ± ± ± ±0.50 Axis Axis *** *** *** Significance codes: 0 *** ** 0.01 * , Distance of the shore (DS), Water depth (WD), Water transparency (SD), Sea surface temperature (SST), Salinity (SN), Tidal (TD), Cloud cover (CC), Wind power (WP), Sun light (SL), Rain (RN), Beaufort sea state category (BF) 3.4 Population Size Our results of 160 ( ) Donsak humpback dolphin population estimation is a small population based on the 89 sightings. The recommended sighting numbers to estimate population on capture-markrecapture model is 60 sightings [12]. Our study gives a larger humpback dolphin population size estimate than that previously obtained at the east coast of Gulf of Thailand [2]. Moreover, 15 of the humpback dolphins were previously detected [2] in the overlap area, from Raja Ferry piers to Thong Nian Bay in this study were previously detected. This does provide evidence of larger scale movement between research areas and further supports a larger dolphin population in the study area due to further ranging individuals [13, 14]. Comparing sub-populations estimates from known population sizes throughout Sousa range, the humpback dolphin population size in Thailand might be similar to the Moreton Bay, Australia and Great Sandy Strait, Australia population estimates (see Table 2). 3.5 Habitat Patterns Our study showed that Indo-Pacific humpback dolphins in the Donsak area have some unique habitat characteristics. We found that the Donsak dolphins inhabit the coastline within km off shore, at an average depth of 4.9 m and water transparency < 3.0 m which supports the previous findings of humpback dolphin habitat characteristics [16, 17, 18, 19 and 20]. From the present study, an analysis of environmental factors (Figures 4-7) indicates that high densities of dolphins occur in inshore areas (mud flats, seagrass areas close to man-made structures) as opposed to off shore island groups. Humpback dolphins may be found all year round without seasonal differences in numbers. However, different groups of dolphins occur during the summer and rainy seasons. (Figure 7). Nevertheless, our results show significant differences of habitat characters in humpback dolphins (Distance of the shore, water transparency and water depth).

10 Chiang Mai J. Sci. 2015; 42(1) 145 Table 2. Population size and abundance estimates for Indo-Pacific humpback dolphins 1 [1, 15]. Rank Populations Pearl River Estuary Hong Kong + adjacent area Goa Bay Algoa Bay Leizhou Bay Gulf of Kachch Richards Bay Moreton Bay Great Sandy Strait Moreton Bay Dafengjiang River Maputo Bay Eastern Taiwan Strait Xiamen Xiamen Zanzibar (south coast) Cleveland Bay Khanom Hepu Areas India South Africa India South Africa Australia Australia Australia Mozambique Taiwan East Africa Australia Thailand No Implications for Conservation It is hoped that current and future marine conservation policies will help the populations of the Indo-Pacific humpback dolphin to increase. Adjacent areas to the study site include the Ang Thong Marine national park, Moo koh Tha Lae Tai Marine Protected area, Corporate Social Responsibility (CSR), mangroves area, seagrass area and dolphin watching tourism which promote dolphins conservation and awareness in coastal communities [23]. However, at present, there are no specific data suggesting that protected areas can improve dolphin reproduction. Unfortunately, humpback dolphin populations all around the world has been shown to be decline [5] due to many threats such as overfishing, accidental take during fishing for other species, pollution, vessel traffic and wildlife tourism [6]. The present study suggests that humpback dolphins are also facing these threats in the Donsak area. Som Serm Ferry is adjacent to the Donsak estuary where humpback dolphins are predominantly encountered and there is evidences showing that dolphins forage times overlap with coastal fishermen work leading to a high risk of entanglement. This study provides us with a better understanding and insight about humpback dolphin ecology which can directly guide marine and coastal resources management for the dolphin conservation in Thailand. At the same time, longer-term studies on population trends and impact of marine anthropogenic threats to dolphins are required to reach a science-based dolphin abundance assessment. 4. CONCLUSION The population size and habitat pattern of Indo-Pacific Humpback Dolphin are of

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