) Journal of the Bombay Natural History Society, 102 (2), May-Aug 2005 158-161 STATUS AND DISTRIBUTION OF A NEWLY DOCUMENTED RESIDENTIAL GANGETIC DOLPHIN (PLATANISTA GANGETICA ROXBURGH 1801) POPULATION IN EASTERN ASSAM1 A. Wakid2 'Accepted June, 2003 department of Life Sciences, Dibrugarh University, Dibrugarh 786 004, Assam, India. Email: [email protected] Amongthefourfreshwaterspeciesofdolphin,theGangeticDolphin(Platanistagangetica isfoundintheGangaand BrahmaputradrainagesystemsofIndia.Atpresent,P.gangeticaisconsideredahighlyendangeredmammalinIndiaand isstrictly protectedundertheWildlife (Protection)Act, 1972 as aSchedule I species.Thisspecies wasoncecommon in the Brahmaputrariversystem, butdue to various natural and anthropogenicpressures, itspopulation isdecreasing rapidly,resultinginthedisappearanceofmostoftheresidentialdolphinpopulations,especiallyfromeasternAssam. In this critical situation, a residential dolphin population has recently been identified downstream of Lohit river. An extensiveefforthasbeenmade toinvestigatethepopulation statusanddistributionpatternofthisdolphinpopulation. The present communication is a resultofthateffort. Key words: Platanistagangetica, status, distribution, population, Brahmaputra, conservation INTRODUCTION entersAssam(Sarma 1993)andbecomesanimportanttributary ofRiverBrahmaputra. RiverLohitstartedchangingchannels There are only four species offreshwater dolphins in due to frequent floods in the Dibang river, another major the world. Amongthem, Buoto(Iniageoffrensis) isfound in tributaryofRiverBrahmaputra,in 1985-1986;withintenyears, SouthAmerica. Baiji (Lipotesvexillifer)intheYangtzeriver by 1995-96,theLohitstartedflowingdownfromSaikhowaghat, system ofChina, Bhulan (Platanista minor) in Pakistan and through the southern boundary of the Dibru-Saikhowa Gangetic Dolphin (Platanista gangetica) in the Ganga- National Park, engulfing Dangori and Dibru rivers, finally Brahmaputra-Meghnaand Karnapuli riversystems ofIndia, joiningBrahmaputraatBalijan. Bangladesh and Nepal (Anderson 1878; Kasua and Haque The study was carried out downstream ofLohit river 1972;Jones 1982; Mohan 1989; Reevesand Brownell 1989; fromSaikhowaghat(27°47 N,95°40 E)toBalijan(27°34'N, Shrestha 1989; Reevesetal. 1993). 95° 10E),astretchof60km(Lig. 1). The distributional range and numbers ofthe Gangetic METHODOLOGY Dolphin have been declining in many areas (Reeves and Leatherwood 1995)andtheIUCNreviseditsthreatenedstatus fromVulnerable(Klinowska 1991)toEndangered(IUCN 1996). Atthebeginningofthis study, wecollectedsecondary Some studies have been undertaken to determine the informationonthedolphin’sexistence(throughouttheyear), status and distribution of Platanista gangetica in inthemajortributariesofRiverBrahmaputraineasternAssam. Brahmaputra river (Biswas et al. 1997; Mohan et al. 1997; We targeted the local fishermen and villagers for this BiswasandBaruah2000). Butinformationonitsconservation information. The information so collected revealed the status in the tributaries of Brahmaputra is very poor. No existenceofdolphinsdownstreamofLohitRiverthroughout intensive study has been undertaken in these tributaries the year. (whichonceprovidedgoodhabitatsfortheGangeticDolphin), Surveys wereconducted upstreamanddownstreamof exceptMohanetal.(1998)ontheKulsiriverofmiddleAssam. theRiveronacountryboat,withlocalboatmenasfieldguides. During our study, we investigated new dolphin habitats in a I covered 20 km of the river in a single day during the few tributaries in eastern Assam, and found that a dolphin downstreamjourneyand 15kmduringtheupstreamjourney, population exists downstream ofLohit river throughout the spendingmaximumtimeindolphinsurfacingareas.Thesurvey year. An effort has been made to determine the status and took three days for downstream and four days for upstream distribution ofthis population. observations. A direct-count method (Perrin and Brownell 1989) was followed during the survey.Afterconfirming the STUDY AREA existenceofdolphins,onecontinuoussurveywasmadefrom upstreamtodownstreamandviceversainamotorboatoflow Thestudywascarriedoutin2000-2002,downstreamof soundemission,atanoptimumspeed(8-9km/hr).Duringthis Lohitriver,whichoriginatesfromtheYokupeak(6,614mabove survey, three observers sat at the front ofthe boat. One was msl) ofChina(Sarma 1993).Afterflowing c. 350km, Lohit a secondary observer and the data collector, while the other GANGETIC DOLPHIN POPULATION IN EASTERN ASSAM 90°E 91°E 92°E 93°E 94°E 95°E 96°E Fig. 1: MapshowingthelocationofLohitRiver two, on either side of him, were primary observers. The indensityanddistributionwereobservedindifferentstretches maximum,minimumandbestcountmethodwasfollowedfor of the Lohit river. The encounter rate was higher (0.26 afairlyaccurateestimationofthepopulation. Maximum and individualperkm)between SaikhowaandGuijan (27° 34 N, minimum counts indicate the maximum and minimum 95° 19 E)thanbetweenGuijanandBalijan(0.16individualper possibilitiesofdolphinoccurrenceinaparticularriverstretch, km).Guijanwasfoundtobeademarcatinglinebetweenthese while the best counts indicate the optimum occurrence of tworiverstretches,astherewasfrequent motorboatcrossing dolphins.Astandarddatasheetwasusedtorecordthedolphin here (two motorboats perhour). While determining the rate sightings,habitatstatusandanthropogenicpressures.AGPS of anthropogenic disturbances, it was found that the Lohit instrumentwasusedatonekilometre intervalstocollectdata riverbetween Saikhowaand Guijan had less fishing activity on coordinates. Altogether five surveys (three by row boat (2.14gill netsperkm)thanbetweenGuijanand Balijan(5.22 andtwobymotorboat) weremadewithinthestudy periodin gillnetsperkm).Also,theintensityoftrafficbetweenSaikhowa theLohitriver. and Guijan (0.07 motorboat per km) was less than between GuijanandBalijan(0.55 motorboatsperkm). RESULTS Agegroup PopulationstatusanddistributionofdolphinsinLohitriver Duringthestudyperiod,onecalfeach wasobservedin During this two yearsurvey, altogether 14 (maximum DighaltarangandMemdubi.Threesubadultswereobserved, 16, minimum 13, best 14) dolphins (group size 1-3) were oneeachinHatighuli, MemdubiandBalijan.Altogethernine observed in the stretchofRiverLohitfrom Saikhowaghatto adults were observed in the entire stretch, one each in Balijan. Thesedolphins were observed atdifferent locations Hatighuli,LainaandMemdubi,andtwoeachinDoijan,Balijan asdifferentgroupsintheLohitriver(Table 1),identifiedonly and Dighaltarang (Table 1). The age class analysis of the inthewinter.Duringsummer,especiallyduringthehighflood dolphinsofLohitriverispresentedinFig. 2. season, the groups were hardly observed in these locations; mostofthemweretracedinthestreamsoftheDibru-Saikhowa Habitatuse NationalPark,whichjointheLohitriver. During the survey period, the dolphins were observed The encounter rate of dolphins in Lohit river was indifferenthabitats. Mostofthedolphins(43%)wereseen in estimatedtobe0.23individualsperkm.However,differences the river confluences (Memdubi and Balijan), followed by J. Bombay Nat. Hist. Soc., 102 (2), May-Aug 2005 159 E GANGETIC DOLPHIN POPULATION IN EASTERN ASSAM Adult Confluence (65%) Wide single channel (36%) Fig.2:AgeclassanalysisofdolphinsinLohitRiver Fig.3: HabitatusebythedolphinsinLohitRiver wide single channel (> 300m) in the Lohit river.The results river. Before 1995-96,they werecommonlyseeninthisarea are presented inFig. 3. during high flood season.At that time, they migratedduring floodseasonsfromtheBrahmaputrarivertotheDangoririver DISCUSSION which would have high levels ofwater owing to flood. But duetochangingofchannels,the Lohit Riverstartedflowing The distribution ofdolphins in Lohit riveris seasonal. throughtheAtlantanallahandDangoririver.Thisresultedin During the investigations, the above mentioned dolphin the widening of Dangori and Dibru rivers at least three groupsinLohitriverwereseenonlyduringwinter(November- times (pers. comm., local villagers). The seasonally sighted March).FromApril,monsoonprecipitationleadstoanincrease dolphins started to live in that stretch of Lohit river from inthe water level ofLohit river.As aresult, the dolphins are 1995-96 and in the last seven years they have become found scattered in the river. During July-August, the area residents. experienceshighfloodingduetoheavyrainfall.Atthattime, The dolphin population of Lohit river is now facing thedolphinsmigratelocallytotheperennialstreams(Kolomi, seriousproblems,themajorthreatbeingfishing.Aboutthirty Ajuka,Hamukjan,Laikajan,Dodhiajanetc.),seasonalstreams fringevillageswithapopulationof25,000-30,000liveonthe (Garamjan,Erasutietc.)andwetlands(Tarali, Sal,Burhibeel leftbankoftheLohitriver.Ofthese,about30%aredependent etc.)oftheDibru-SaikhowaNationalPark,aswellastoother on fishing, and for them this stretch of Lohit river is an partsofthe Lohitriver.Fromthe lastweekofSeptember,the importantfishingground.These fishermenemploydifferent water level in these water bodies starts shrinking, and by fishinggearintheriver,includingthemostdangerousgill-net OctobertheLohitriverandthelocationsmentionedonLohit fishing. During the study period, an average of2.9 gill-net river (Table 1), are the only deep water bodies in the area. fishing per km was observed. This heavy fishing leads to These become the ultimate shelter for the dolphins ofLohit accidental dolphin killing. In the last two years, there were river. fourdolphindeathsintheriver,ofwhichthreewereaccidental Aninterestingaspectofthisdolphin population isthat from gill-net fishing. On the other hand, round-the-clock they are comparatively newcomers to this stretch of Lohit fishing and fish poisoning (especially in the Taralimukh area) are also serious threats to the food sources of these dolphins. Table 1: Distribution of dolphins in Lohit river Though dolphin poaching is not so prominent in this Sighting area Sightinglocation No. of dolphins riverstretch,onedolphinwaskilledintheDighaltarangarea Max. Min. Best inNovember,2001. Hatighuli 27°45 N,95°33 E 2 2 2 CONCLUSION Laina 27°41 N,95°30E 1 1 1 Doijan 27°39 N,95°26 E 3 2 2 Dighaltarang 27°36 N.95°24' 3 3 3 At present, the status of freshwater dolphin in India Memdubi 27°34'N,95°20 E 4 3 3 has been considered critical due to a steep decrease in their Balijan 27°34N,95° 11 E 3 2 3 population; hence they are protected under the Wildlife (Protection)Act, 1972 as aSchedule I species. Protection of Total 16 13 14 the dolphin population ofLohit river shouldbe the topmost 160 J. Bombay Nat. Hist. Soc., 102 (2), May-Aug 2005 GANGETIC DOLPHIN POPULATION IN EASTERN ASSAM priority ofconcerned management bodies, as well as locals inLohit.Thiswilldefinitelyimprovethesocio-economic for ecological equilibrium of the region. For effective conditionsofthe fringe villagersandencouragethemto conservation, the following measures are suggested, based participate actively in dolphinconservation, onmyexperienceinthisregion. e. Awareness programme: A long-term and continuous a. Fishing control: Use ofsmall mesh cast nets, gill nets, awareness programme for dolphin conservation is the using ofpesticides and round-the-clock fishing should top-mostpriorityin all thefringevillagesofLohitriver, be strictly banned in theLohitriver. withoutwhichonecanonlyexpectableakfuture forthis b. Fishingfreezone:Hatighuli,Laina,Doijan,Dighaltarang, dolphin population. Memdubi and Balijan should be declared fishing free ACKNOWLEDGEMENTS zones,especially in the winter. c. Traditionalfishing:Thefishermenshouldbeencouraged tousetraditional fishingpractices, likeJhengfishingin IsincerelythankDr.S.P. BiswasofDibrugarhUniversity theriverstretchfromSaikhowato BalijanofLohitriver and Prof. R.K. Sinha of Patna University for their valuable forsustainabledevelopmentoffisheryresourcesforthe guidanceandencouragementforcompletingthiswork.Ialso localcommunities and the dolphins. thankMr.J.Abedin,Mr. S.DasandtheD.F.O.,RangeOfficers d. 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