136 Chiang Mai J. Sci. 2015; 42(1)

Chiang Mai J. Sci. 2015; 42(1) : 136-147http://epg.science.cmu.ac.th/ejournal/Contributed Paper

Population Size and Habitat Patterns of Indo-PacificHumpback 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: suwat.j@psu.ac.th

Presented at the International Graduate Research Conference 2013 (IGRC2013), 20th December 2013, Chiang Mai, Thailand.

Received: 24 December 2013Accepted: 5 May 2014

ABSTRACTThis study investigated the population size and distribution pattern of the

Indo-Pacific humpback dolphin (Soasa chinesis) off Donsak, Surat Thani, Thailand. The fieldsurveys were conducted along the coastline of the mainland and the offshore area of theAngthong Marine National Park. The population size was estimated by applying amark-recapture model to the individual photo-identification records collected from fieldsurveys. 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 ata 95% CI. Spatial (GPS data) and environmental information were recorded for distributionand habitat analysis. The most frequent encounters with humpback dolphins occurred,in decreasing order of magnitude, at Somserm Ferry, Raja Ferry, Som Island, Nok Ta PaoIsland and Taled Bay. The present study showed that the humpback dolphins off Donsakwere frequently found near the coast in close proximity to man-made structures, sea grassareas and mudflat habitats. Our study revealed that a distinct humpback dolphin habitat occurredat a specific off-shore distance, water depth and water transparency. Results of this studyimproves the better understanding of the humpback dolphin’s ecology and offers informedbaselines essential for meaningful marine-mammal protection and management policies in theGulf of Thailand.

Keywords: population size, Indo-Pacific humpback dolphin, Donsak-Surat Thani, habitat patterns

1. INTRODUCTIONThe richness of complex marine and

coastal ecosystems attracts human activitieswhich have caused marine and coastalhabitat degradation and loss of naturalresources [1]. The Donsak, Surat Thani,Thailand is a complicated ecosystem withplentiful 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, ferrytransportation piers, resorts and hotels,manufacturing industries and famous

Chiang Mai J. Sci. 2015; 42(1) 137

dolphin-watching tourism. Dolphin-watchingtourism industry exclusively targeting to theIndo-Pacific humpback dolphin, Sousa chinenis,was promoted to motivate tourism activitiesalong the coastlines of the Donsak district,Surat Thani province and Khanom, Nakhondistrict, Si Thammarat province [2].

Although many efforts were made formarine and coastal conservation policies,anthropogenic overexploitation is stillincreasing. More information is needed toimprove the effectiveness and scientificbasis of current conservation policies.Data on the baseline dolphin population,including distribution, abundance andhabitat characteristics, are still very rareacross South-East Asia, a region consideredto be one of the important habitat forhumpback dolphins. Scientific research is animportant measure to provide essentialbaselines and must be included in the marineconservation issues [3, 4]. The InternationalUnion for Conservation of Nature (IUCN)categorized the Indo-Pacific humpbackdolphin as a near-threatened species [5].Not only are humpback dolphin populationsize information mentioned in the IUCNreport is needed, but also supportable habitatquality information [6]. Although thehumpback dolphins are currently known dueto dolphin shows (Oasis Sea World,Chanthaburi, Thailand) and dolphin watchingtourism in Khanom, Nakhon Si Thammarat,Thailand, there is still a lack of understandingabout population, habitat or generalinformation of humpback dolphin in theThailand region. Marine and Coastal ResourcesResearch Center (MCRC), Central and LowerGulf of Thailand have recorded an increasein the mortality rate of humpback dolphinsduring the period 2006-2012 (Unpublisheddata). In the gulf of Thailand, the bycatchmortality rate of humpback dolphins wasrecorded as 24% of 62 stranded humpback

dolphins (Unpublished data). In consequence,the humpback dolphin research in Thailandis a critical need. Moreover, informationabout stranded dolphins was collectedalong the coastline of the Gulf of Thailand(Unpublished data). However, dolphins arefrequently found in the boundary areasbetween Donsak, Surat Thani and Khanom,Nakhon Si Thammarat. Although there areno tourism activities in the Donsak area,Indo-Pacific humpback dolphins inhabitingthis shoreline may also form part of thedolphin population of the Khanom area.

A previous study identified 33 adults,eight juveniles and eight calves with aestimated population estimate of 49 dolphins(with no confidence interval) in the KhanomSea, Nakhon Si Thammarat [2]. The currentstudy was conducted at Donsak, Surat Thani,north of the adjacent area, Khanom,Nakhon Si Thamarat during a longer periodand include distribution and habitatcharacteristics of humpback dolphins. It ishoped that the data generated by this studywould lead to improved decision-makingon humpback dolphin conservation bystakeholders in Donsak District, Surat Thani,Thailand.

2. MATERIALS AND METHODS2.1 Study Site2.1.1 Coastal area (CA)

The study was conducted in the coastalzone of Donsak district, Surat Thani provinceand Khanom district, Nakhon Si Thammaratprovince, the east coast of Southern Thailand(Taled Bay-TB, Thong Nian Bay-TNB,Lak Sor Mountain-LSM). The area ischaracterised by rocky shores, sandy beaches,rocky cliffs, mud flats, mangroves and seagrass 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

138 Chiang Mai J. Sci. 2015; 42(1)

Island, Pha-ngan island), coastal fishery,dolphin watching tour activities, industrialfactories are also found within this area.

2.1.2 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 marinenavy base, the Gulf of Thailand, wasconverted into a marine national park on12th November 1980 due to the abundantspecies and natural marine resources [7].This Ang Thong Marine National Parkconsists of 42 small islands with dry evergreenforests, beaches, and lime stone and mangroveforests [7] (Figure 1).

Figure 1. Study area, Donsak, Surat Thani, Thailand. %: Som Serm Ferry, Seatran Ferry andRaja Ferry respectively.

2.2 Data Collection2.2.1 Boat surveys

Boat-based surveys were conductedfrom between December 2011 - April 2013during 08:00-14:00 with Beaufort Sea Statecategory category between 0 and 2 off thecoast of the Ang Thong islands of Donsak,Surat Thani Province. A long-tailed fishingboat with an outboard 175 hp engine wasused with speeds not exceeding 15 km/h.Route tracking was recorded by GPS(Garmin eTrex30) and the positions weremarked when dolphin were sighted. Theboat speed was slowed when dolphins wereencountered. We measured water depth

(WD), water transparency (SD), pH, seasurface temperature (SST) salinity (SN) andBeaufort Sea State category were recorded atthe dolphin encounters. Further environmentalconditions 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% cloudcover and 2 being > 50% cloud cover),wind power (WP, 0 being no wind blow, 1 aslittle 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 and1 being sun shine) conditions. A variable,“Seasonal change” was noted with May 16

Chiang Mai J. Sci. 2015; 42(1) 139

to January 31 was categorized as the RainySeason and February 1 to May 15 as theSummer Season. Habitat characteristics ofdolphin encounter sites were recorded asrocky shore (RS), man-made structure (MM),mud flats (MF), sandy beach (SB) and sea grassbeds (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 linefrom nearest coastline to the encouteredposition by GIS software.

2.2.2 Photo-identificationResearchers attempted to photograph

all the individual dorsal fins in a group thatwere the most perpendicular to the dolphin’sbody axis with DSLR D80 D90 and D7000Nikon digital cameras with 70-300 mmlenses. The processing of utilised 45,000pictures that were selected based on the mostclearest dorsal fins. Though a systematicprocess individuals were indentified andadded to the catalogue by recording thepresence of nicks, notches, pigmentationpatterns, color, dorsal fin edge figure, scaror wound. The datasheet was replaced with0 and 1 to indicate either absence or presenceof each individual per sighting.

2.3 Data Analysis2.3.1 Abundance

The researchers recorded 89 sightingsevents from all surveys conducted over17 months of. A dolphin sighting matrixdata set was constructed with the occurrenceof each individual per site and thepopulation size was estimated by liverecapture of open population modelparameterization on POPAN in MARKSoftware [8] which includes the parameterN - the size of a superpopulation. N can bethought of as either the total number ofanimals available for capture at any time

during the study, or, alternatively, as thetotal number of animals ever sighted in thesampled area between the first and lastperiods of the study [9]. The parameter Φdenotes apparent survival rate, P denotesthe probability of capture, and b denotesthe probability that an animal from the super-population will enter the subpopulation(subpopulation referring to the animalsoccurring in the study area).

Variance of N was estimated using thedelta method and the following equation:

where n is the total number of dorsalfins from which θ was calculated. Confidenceintervals for Ntotal assumed the same errordistribution as the mark-recapture estimates[10]. The population size was computedby Parm-Specific as a Link function, Sinwere Φ and P, mlogit (1) was b and logitwas N on POPAN parameterization modeloption in MARK software.

2.4 Habitat CharacteristicHabitat characteristics were tested

statistically by using Principal ComponentAnalysis (PCA) and Canonical CorrelationAnalysis (CCA) analysis using R softwareand ade4 [11] and vegan library packages[12]. We categorized each sighting withenvironmental factor, season, habitatcharacteristics, inshore and offshore area,and the encountered area names.

3. RESULTS AND DISCUSSION3.1 Survey Effort

Forty-seven boat survey-days (205 h)were undertaken, covering a total distanceof 2,618.4 km. The surveys resulted in89 dolphin sightings within the 17 months.The cumulative sightings of humpback

140 Chiang Mai J. Sci. 2015; 42(1)

dolphins in the study area are indicated inFigure 3. Solitary individuals comprised14.6% of all sightings. The highest frequencyof occurrence was found in the firstfive areas, Som Serm Ferry, Raja Ferry,Som Island, Nok Ta Pao Island and Ta LedBay (Figure 3). The dolphins were encounteredoff-shore in 22.5% of all sightings.

3.2 Population SizeTotal 142 humpback dolphins were

identified. These individuals were separatedby age class from all 47 observation days

from the 17-month survey (Figure 2). Atleast 15 individuals were identified as thesame individuals from a previous study [2].The average group size of humpbackdolphins sighted in this study rangedbetween from two to eighteen dolphin withthe average group size 4.72 ± .35 based on455 individuals recorded for the full study.Solitary individual were observed in 10.34%of all sightings. A total of 160 individualswas observed with a range of 152 - 178 at95% CI from POPAN paramiterization onMARK 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.

Chiang Mai J. Sci. 2015; 42(1) 141

3.3 Habitat CharacteristicsIn 83 of the 89 sightings the

environmental parameters were measuredbecause five of all sighting were bad weatherconditions. The PCA analysis showed thegroups of habitat characteristic. The ellipsessurround the group of environmentalparameters that were categorized withencountered position, coastline and offshore,habitat characteristics and season. The offshoreislands, 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 fromencoutered position on coastline, Sea TranFerry (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 surroundedwith two ellipses that were not overlappedon mud flat (MF), mam-made structure(MM) and sea grass beds (SG) (Figure 6).The partial overlapped of two ellipsesbetween rainy and summer seasons wereshown on Figure 8. The PCA of dolphinencountered position on Figure 4 areEnvironmental parameters of dolphinsencounter were analyzed in the groups ofdata by using CCA analysis with R software(Figure 8).

The DS, WD and SD were significantlydifferent from the habitat characteristics ofhumpback dolphin population in studyarea (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 GunIsland (RGI), Sea Tran Ferry (STF), Ta Rai Island (TRI), Pa Luai Island (PLI), between Chuekand Palui Island (CPI), Pee Island (PI) and Jae Island (JI).

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: Rockyshore, SB: Sand beach, MF: Mud flat, MM: Man-made structures and SG: Seagrass area).

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), Waterdepth (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 statecategory (BF).

144 Chiang Mai J. Sci. 2015; 42(1)

Table 1. Range, Mean (± SD) and canonical correlation analysis of environmental parametersof humpback dolphins.

Significance codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1, Distance of the shore (DS), Water depth (WD), Watertransparency (SD), Sea surface temperature (SST), Salinity (SN), Tidal (TD), Cloud cover (CC), Wind power (WP), Sunlight (SL), Rain (RN), Beaufort sea state category (BF)

Factors

DS (m)WD (m)SD (m)SST (�c)

pHSN (ppm)

TDCCWPSLRNBF

Range

17-2976.731.70-16.40

0.5-326.60-32.607.15-9.07

25-350-10-10-10-20-10-2

Mean ± SD

468.21±603.064.92±2.731.27±0.6129.95±1.388.22±0.3130.22±2.280.67±0.470.08±0.280.35±0.481.65±0.570.02±0.110.33±0.50

CCAAxis1-0.633-0.999-0.999-0.9200.2570.987-0.5230.5490.727-0.9270.3680.999

Axis2-0.7740.0370.0190.3920.9670.1630.8520.8360.6860.3750.9300.051

r2

0.2692***0.4884***0.4243***

0.01260.01010.03660.05090.01870.01500.06620.01870.0063

3.4 Population SizeOur results of 160 (152 - 178) Donsak

humpback dolphin population estimation isa small population based on the 89 sightings.The recommended sighting numbers toestimate population on capture-mark-recapture model is 60 sightings [12]. Ourstudy gives a larger humpback dolphinpopulation size estimate than that previouslyobtained at the east coast of Gulf ofThailand [2]. Moreover, 15 of the humpbackdolphins were previously detected [2] in theoverlap area, from Raja Ferry piers to ThongNian Bay in this study were previouslydetected. This does provide evidence oflarger scale movement between researchareas and further supports a larger dolphinpopulation in the study area due to furtherranging individuals [13, 14]. Comparingsub-populations estimates from knownpopulation sizes throughout Sousa range,the humpback dolphin population size inThailand might be similar to the Moreton Bay,Australia and Great Sandy Strait, Australiapopulation estimates (see Table 2).

3.5 Habitat PatternsOur study showed that Indo-Pacific

humpback dolphins in the Donsak areahave some unique habitat characteristics.We found that the Donsak dolphins inhabitthe coastline within 0.47 - 2.9 km off shore,at an average depth of 4.9 m and watertransparency < 3.0 m which supports theprevious findings of humpback dolphinhabitat characteristics [16, 17, 18, 19 and 20].From the present study, an analysis ofenvironmental factors (Figures 4-7) indicatesthat high densities of dolphins occur ininshore areas (mud flats, seagrass areas closeto man-made structures) as opposed to offshore island groups. Humpback dolphinsmay be found all year round without seasonaldifferences in numbers. However, differentgroups of dolphins occur during the summerand rainy seasons. (Figure 7). Nevertheless,our results show significant differences ofhabitat characters in humpback dolphins(Distance of the shore, water transparencyand water depth).

Chiang Mai J. Sci. 2015; 42(1) 145

Table 2. Population size and abundance estimates for Indo-Pacific humpback dolphins1

[1, 15].

Rank1.2.3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.

PopulationsPearl River EstuaryHong Kong + adjacent areaGoa BayAlgoa BayLeizhou BayGulf of KachchRichards BayMoreton BayGreat Sandy StraitMoreton BayDafengjiang RiverMaputo BayEastern Taiwan StraitXiamenXiamenZanzibar (south coast)Cleveland BayKhanomHepu

AreasChinaChinaIndia

South AfricaChinaIndia

South AfricaAustraliaAustraliaAustralia

ChinaMozambique

TaiwanChinaChina

East AfricaAustraliaThailand

China

No.25521028842466237174

1661701631501191141059985867663544939

3.6 Implications for ConservationIt is hoped that current and future marine

conservation policies will help the populationsof the Indo-Pacific humpback dolphin toincrease. Adjacent areas to the study siteinclude the Ang Thong Marine national park,Moo koh Tha Lae Tai Marine Protectedarea, Corporate Social Responsibility (CSR),mangroves area, seagrass area and dolphinwatching tourism which promote dolphinsconservation and awareness in coastalcommunities [23]. However, at present, thereare no specific data suggesting that protectedareas can improve dolphin reproduction.Unfortunately, humpback dolphin populationsall around the world has been shown to bedecline [5] due to many threats such asoverfishing, accidental take during fishingfor other species, pollution, vessel trafficand wildlife tourism [6]. The present studysuggests that humpback dolphins are also

facing these threats in the Donsak area.Som Serm Ferry is adjacent to the Donsakestuary where humpback dolphins arepredominantly encountered and there isevidences showing that dolphins foragetimes overlap with coastal fishermen workleading to a high risk of entanglement.

This study provides us with a betterunderstanding and insight about humpbackdolphin ecology which can directly guidemarine and coastal resources managementfor the dolphin conservation in Thailand.At the same time, longer-term studies onpopulation trends and impact of marineanthropogenic threats to dolphins arerequired to reach a science-based dolphinabundance assessment.

4. CONCLUSIONThe population size and habitat pattern

of Indo-Pacific Humpback Dolphin are of

146 Chiang Mai J. Sci. 2015; 42(1)

fundamental importance for cetaceanconservation policies which can assessthe cetacean abundance and define themarine protected area. At the very least,this information can be used for conservationof the marine eco-system and habitatincluding the marine food chain resourcesthat relate to these dolphins.

ACKNOWLEDGEMENTSThis research received financial support

from the Graduate School of the Prince ofSongkla University. We would like to thankthe Marine and Coastal Resources ResearchCenter for providing observation recordsfrom the Central and Lower Gulf ofThailand.

REFFERENCES

[1] Bulleri F. and Chapman M.G., Theintroduction of coastal infrastructureas a driver of change in marineenvironments, J. Appl. Ecol., 2010; 47:26-35. DOI: 10.1111/j.1365-2664.2009.01751.x.

[2] Jaroensutasinee M., Jutapruet S. andJaroensutasinee K., Population size ofIndo–Pacific humpback dolphins (Sousachinensis) at Khanom, Thailand, WalailakJ. Sci. Technol., 2010; 7: 115-126.

[3] Agardy T., Di Sciara G.N. and ChristieP., Mind the gap: Addressing theshortcomings of marine protected areasthrough large scale marine spatialplanning, Mar. Policy, 2011; 35: 226-232.DOI: 10.1016/j.marpol.2010.10.006.

[4] Lundquist C.J. and Granek E.F., Strategiesfor successful marine conservation:Integrating socioeconomic, political,and scientific factors, Conserv. Biol.,2005; 19: 1771-1778. DOI: 10.1111/j.1523-1739. 2005.00279.x.

[5] IUCN, IUCN Red List Categories andCriteria version 3.1, 2001. InternationalUnion for Conservation of Natureand Natural Resources; Available at:http://www.iucnredlist.org/technical-documents/categories-and-criteria/2001-categories-criteria. Accessed 20October 2013.

[6] Parra G.J., Corkeron P.J. and Marsh H.,The Indo–Pacific humpback dolphin,Sousa chinensis (Osbeck, 1765), inAustralian waters: A summary of currentknowledge, Aquat. Mammals, 2004;30: 197-206. DOI: 10.1578/AM.30.1.2004. 197.

[7] National Park Thailand, Moo Ko AngThong; Available at: http://park.dnp.go.th/visitor/nationparkshow.php?PTA_CODE=1021. Accessed 2 April 2014

[8] White G.C. and Burham K.P., ProgramMARK: Survival estimation frompopulations of marked animals, BirdStudy 1999; 46(suppl.): S120-S138.

[9] Nichols J.D., Modern Open-PopulationCapture-Recapture Models; in AmstrupS.C., McDonald T.L. and Manly B.F.J.,eds., Handbook of Capture-RecaptureAnalysis, Princeton University Press,Princeton, New Jersey, 2005: 88-123.

[10] Wilson B., Hammond P.S. andThompson P.M., Estimating size andassessing trends in a coastal bottlenosedolphin population, Ecol. Appl., 1999; 9:288-300. DOI: 10.1890/1051-0761(1999)009[0288:ESAATI]2.0.CO;2.

[11] Dray S. and Dufour A.B., The ade4package: Implementing the dualitydiagram for ecologists, J. Stat. Softw.,2007; 22(4): 1-20.

[12] Oksanen J., Kindt R., Legendre P.,O’Hara B., Stevens M.H.H., Oksanen M.J.and Suggests M.A.S.S., The Vegan

Chiang Mai J. Sci. 2015; 42(1) 147

package. Community ecology package;Available at: http://www. R-project.org. Accessed 10 October 2013.

[13] Atkins S. and Atkins B.L., Abundanceand site fidelity of Indo-Pacifichumpbacked dolphins (Sousa chinensis) atRichards Bay, South Africa, Working paperSC/54/SM25 of the 54th Meeting of theInternational Whaling Commission,Shimonoseki, Japan, April 2002.

[14] Parra G.J., Corkeron P.J., and Marsh H.,The Indo-Pacific humpback dolphin,Sousa chinensis (Osbeck, 1765), inAustralian waters: A summary of currentknowledge, Aquat. Mammals, 2004; 30(1):197-206.

[15] Huang S.L. and Karczmarski L., Indo-Pacific Humpback Dolphins: ADemographic Perspective of aThreatened Species; in Yamagiwa J. andKarczmarski L., eds., Primates andCetaceans, Springer Japan, 2014: 249-272.

[16] Stensland E., Carlen I., Sarnblad A.,Bignert A. and Berggren P., Populationsize, distribution, and behavior ofIndo-Pacific bottlenose (Tursiops aduncus)and humpback (Sousa chinensis)dolphins off the south coast ofZanzibar, Mar. Mammal Sci., 2006; 22:667-682. DOI: OI: 10.1111/j.1748-7692.2006. 00051.x.

[17] Jefferson T.A., Hung S.K., RobertsonK.M. and Archer F.I., Life history of theIndo-Pacific humpback dolphin in thePearl river estuary, southern China,Mar. Mammal Sci., 2012; 28: 84-104. DOI:10.1111/j.1748-7692.2010.00462. x.

[18] Hung S.K. and Jefferson T.A.,Ranging patterns of Indo-Pacifichumpback dolphins (Sousa chinensis) in

the Pearl river estuary, People’sRepublic of China, Aquat. Mammals,2004; 30: 159-174. DOI: 10.1578/AM.30.1.2004.149.

[19] Karczmarski L., Victor G.C. andMcLachlan A., Group size and seasonalpattern of occurence of humpbackdolphins Sousa chinensis in Algoa Bay,Afr. J. Mar. Sci., 1999; 21: 89-97.DOI: 10.2989/025776199784126024.

[20] Ross G.J.B., Heinsohn G.E. andCockcroft V.G., Humpback DolphinsSousa chinensis (Osbeck 1765), Sousa plumbea(G. Cuvier 1829) and Sousa teuszii(Kukenthal 1892); in Ridgway S.H. andHarrison R., eds., Handbook of MarineMammals 5: The First Book of Dolphins,Academic Press, San Diego, 1994:23-42.

[21] Wang J.T., Hung S.K. and Yang S.C.,Records of Indo-Pacific humpbackdolphins, Sousa chinensis (Osbeck 1765),from the waters of western Taiwan,Aquat. Mammals, 2004; 30: 187-194.

[22] Wang J.T., Yang S.C., Hung S.K. andJefferson T.A., Distribution, abundanceand conservation status of the easternTaiwan strait population of Indo-Pacifichumpback dolphins, Sousa chinensis,Mammalia, 2007; 157-165. DOI: 10.1515/MAMM.2007.032.

[23] Ratana P., Khanom district administrationorganization promoted Khanom districtas dolphin watching ecotourism forconservation; Available at http://www.coastalaqua.com/webboard/index.php?topic=2508.0. Accessed 2April 2014.