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Author(s)

Acoustical analyses on the calls of dugong

Ichikawa, Kotaro; Arai, Nobuaki; Akamatsu, Tomonori; Shinke, Tomio; Hara, Takeshi; Adulyanukosol, Kanjana

Citation

Issue Date

URL

2003

http://hdl.handle.net/2433/44136

Right

Type

Textversion

Conference Paper

publisher

Kyoto University

72

Acousticalanalysesonthecallsofdugong KoTAROIcHIKAWÅ1，NoBUAKIARAl1，ToMONARIAKAMArSU2，ToMIOSHINKE3， TAKESHTHARA4，andKANJANA ADUlヱANUKOSOL5 JGrd血αfe5cJ王00Jザ坤mα庇ち埠′0わ助言verぶ坤麒リ0わ∂0∂−∂50J，J呼α〃 且間扇たた魚油馴化＠ムrg・∫OC・よ・勧加−〟・dC・加

納〟0〝〟用e∫e〟rCゐ血5血よrgげダfざんerね∫g〝g∫乃eer東方∂g血g乃2（）−ろ月〟ぶ弼乃〟r弼j上州イ2JJ呼α〃

斌＆かCe〃叫即5∫e川舟fecみCoリ上房． 舟0〃ガerre5e〟Ⅳゐce〃叫7ゎたαfU乃ゴve相和2（フーム鎚血加−Orgdロブ，∫ゐ≠z〃0れ424堵6JOJ呼〟〝 り呼α〃ダf∫ゐer如月eざ0〟rCeC（7那eⅣd才わ〝A∫∫〃Cgd如〝

月ej∽ef∫砂月可irerェ‘1俺∫β0ゴーろ2−Jβ−J，励cゐgゐんちCJ王〟0一血工払わ旦J仇−0の4∫呼d〃 、川∫山■J・lhr山・イh−ん−ゞ血／し、川Jl・「ハ）、抽）．い巾．／ソ＝▲【て・ヾ、て什畑打J山／．州J AβS乃‡ACr

Dugong，Dugongdugon，hasbecomeoneofhighIyendangeredspeciesintheworld，rtissaidthatthe

decreaseinthe numberofdugong populationis mainlydueto accidentalcatches byfishnets．A

breakthroughtoavoidtheaccidentalcatches，by−CatChes，isinurgentneed．Inthisstudy，Wedescribed

thetechniquetodetectthedirectionofvocalizngdugongandtheacousticaIcharacteristicsofdugong

Ca”s・ThisstudycanIeadtoanewobservationmethodofwiIdanimals．Anumberofdugongca”swere recordedaroundLibonglsland，Trang，Thailand，uSingtwosetsofduaFchannelstereohydrophon OntWOreSearChvessels・Thecenterfrequencyofdugongcarlsrangedfrom3−8kHz，andtheduration OfthecallswasclassifiedroughIyintwo：100−500msandoveraroundlOOOms．Vocalizationintervals WereClassifiedintwopatterns：0−5sandaboutover20sbetweeneachcal【．Weappliedthephase difFerenceanarysistodugongca”srecordedbyastereohydrophone．ThepreriminaryresuEtssuggested thattheacoustica［analysesonthedugongcalIswi”beapowerfulmethodtolocatethevocarizing

dugongswithoutanylmPaCtOnthematall．

KEWORDS： Pa＄SiveacousticaIobseTVation，aCOuSticaIcharacteristic＄，VOCalization interval，directionanaly＄lS，arrivaldirection，arrivaIphasedifference，

SOundpressurelevel

mTRODtJCTION

Dugong，Dugongdugon，isoneoftheendangeredspecies． theusageofseagrassbedsintheproposedarea．Tneecology Theyliveinwarmand畠hallowseawatersdistributing Ofdugong，however，1SnOtWell−known，yet・Recently，

throughouttheworld．Thenorthernlimitoftheirhabitat PaSSivebiotelemetrytechnlqueSuSingunderwateracoustics

isaroundthemalnislandofOkinawa，Japan・ThepopulatlOnbl（境ー［eortoobseⅣep陀SenCeOfv∝肋Ilgmamemmds OfdugonginOkinawa，however，issaidtobelessthan50 havebeendevelopedrapidly．Passi∇eaCOuSticobservation CrhemammalogicalsocietyofJapan），Whichisverysrna11hasbeenappliedextensivelyfornon−Observableanimals COmparedtootherdugonghabitatsinmanypar（SOfthe SuChasmanatees（Phillipsetal．，2004），Inthemarlatee WOrld・Thedecreaseinthenumberofdugongpopulation CaSe，COllisionwithboatshasbeenama】OrCauSeOfits

ismain1yduetoaccidentalcatchesbyfish−netSanda deaths・TbavoidthecolllSions，manateeCan；areautOmatlCally deathofanindividualcancauseaslgnificantdamageto detectedoutofthebackgroundnoiseinordertowam

thepopulation・Itisalsoofgreatinteresttothe煮shermenboatersofpresenceofmanatee・Weappliedthistechnique

inOkinawa，theareawherethemostsightingsofdugong tostudythebehavioralecologyofdugongLThepassive havebeenreportedoverlapsthemain鮎hingarea，Which

acousticobseIVationuLSeSamValtimedi飴renceatsepamted

hydrophonestocalculateamvaldirectionofacall．ItsT D11gOngprOteCtionandfishingrestrictionarethetwo mainadvantageisthatithasnoeffectonbehaviorofthe COnflictingmatterstobesoIved・Apowerfu1breakthroughanimalofstudyanditcmbeusedtomonltOrVOCalbehavior topreventduBOngfromtheseby−CatChesisinurgent Ofseveralindividualsatonce・TbperformanefEective isoffthenorth−eaStCOaSt｛）fthemainislandofOkiTlaWa．

need．

rnonltOrlng，theaIlimalofstudymustvocalize仕equently

Tbprotectthedugongpopulation，Weneedto arldtheircal1smustbeeasilyseparatedfromthebackground knowtheirbehavioralecologysuchasmovlngPathsand noise．

73

Inthisstudy，detectionofarrivaldirectionand aco11Sticcharacteristicsofdugongcallaredescribed．These aspectsarenecessaryindesignlnganeWmOnltOringdevice toidentifyeachindivldualandtowamfIShermenofpresence Ofdugong・ThlSShdywi111eadtoanirmovativemonitorlng metllOdfordugong・ MArERIALSANDMETIIODS ∫f〟め′∫f絶

ForotlrSurvey，behavioralrecordsandvocalizatlOndata areindispensable・Becausethepopulationofdugongln Okinawaistoosmalltoperformasuccessives11rVey，We SetOurStudysitearo11ndLibongIsland，Trang，Thailand ★USM：Uれd訂Wa血幻11m‖知柁1met訂 （longitudeNO7012158・4’’1atitudeE99024121，9”），Where

∫gg・2・βわcたdよ〟gr〟mげ班grecor‘ブ和平∫ge刑．

manysightingsofd11gOnBWererePOrtedbeforehand，We Set5studyareas（柵一削）aroumdtheLibongIsland（Fig．1）．

TbesurveyWaSCOnd11Ctedfrom3rdofMarchto6（hof．LlrrMJ∫〃ハ・り・ Ma托hOn仇e五指t血y（3d，Ma血），r∝0撼11gWaS匹血med aroumd＃0，＃1，and＃2・Butthebackgroundnoiseincl11dlng

Anaerlalsurveywasperformedsimultaneouslytosupport thevisualobservationfromtheresearchvessels．Itisone pulsesoundswasverylolldandneithersightlngSOfdugong Ofthemosteffectivemethodstoobservethepresenceof marinemammals・MicroLiteflewatrightanglestothe northed11gOngVOCalizatlOnWaSObserved．Onthesecond Shorerepeatedlytoperformanaerialsurveyatthesame day（4Lh），WemOVedtothesouthernpartoftheIsland 伊3and＃4），Wheremanysightingsofdugongwerereported timeastherecordingoftheunderwatersound・Thepilot OfMicroLitesatirlfrontandthepassengerintheback duringtheproceedingsurveythatwasconductedfrom Sincethepilothadagoodlooko11taheadandsideways， 23［dto29LhofJanuary，2003・Thebackgroundnoiseat thepilotwatchedthefrontandthesides，andthepa5Senger Station＃3wasalsotooloudtorecordd11gOngCall．Stationwatchedthebothsides．WhentheobserversontheMicro ＃4bestsuitedthesurveycondltlOninthematterofrecording Litefo11nddugongs，then11mberofd11gOngSandtheir andthenumberofdugongssighted．So，fortherestofthe behaviorwerereportedtotherecordingvesselsuslng Survey（5thand6（h），therecordingswereconductedin mobilephones・MicroLitenewtwiceaday，inthemornlng statioll＃4． andtheafternoon．Theflightd11rationvarieddepending Onthemlmberoftheanimalstheyfotlnd． Libongrsl8咄T「8ng．Th日‖and

鳳相即叔喝 りぅ

Recordingsofunderwatersoundwerestartedsoonaf（er thevesselsreachedthestudysite，uSlngtheDArrecorder， TCD−D8，withsamPllngrateOf44・1kHz・Thehydrophones WereSetatlmdeep・Therecordingrangewas120dB， andlkI七highpassfilterwasapplied．Thevesselswere anchoredtokeepthedistancebetweeneachvesselin lOO−300m．The distance between the research vessels was measuredwitha distancemeter．The directlOn from

ダよg．了．動画＝祓．

VeSSelLAtovessel−Bwasmeasuredwithacompass・ Whentheobserversinthevesselsfounddugongs，the dlStanCeandthedirectiontod11gOngSWeremeaSured．At thesametme，theheadmgdirectlOnSOftheresearchvessels WerereCOrdedusingacompass．

風脚頑仰劇痛 Eachofthetworesearchvessels（vessel−A，B）were equlPpedwithasetoftwod11alchannelstereo−hydro− 11dl・り旭爪，rlI（川叫・∫I，、† Phones（OKISTlO20），anamPlifier（OKISWlO20），a WavepatternanalysesweredoneusingCooIEditPro2 digitalaudiotaperecorder（SONYTCD−D8），GPS（CEP2forshort）andIshmaell■0（ISHforshort）・CEP2 （GarminGPS工1Ⅰ），aneChosounder（HONDEXHE−5620），

Showsthesonargramsofdugongca11，inwhlChthehonzontal

acompassandadistancemeter・Thearraydistancesofthe axisistimeandtheverticalaxisisfrequency（Fig・3）・ hydrophoneswere5．2m（vesselrA）and7，Om（vessel−B）．

（SeeFigL2fortheblockdiagramofthedevices・）

Centerfrequency，d11ration，andsoundpressurelevelofa CallwerecalculatedusingCEP2．

74

︵畳む貞当■訂−h 爪V nV O l

RESULTS Tbtalofl175audiblecallswererecordedthroughthe survey．ThereTsariskthatCEP2andISHfailtodistingush betweendugongcal1sandshortpulsesoundsfromthe backgro11ndnoise・Tbavoidthisconfusion，Onlythecalls WithfrequencyofoverlkHzanddurationofover50ms wereselected氏〉rtheanalyses．Thereasonforthethreshold isthatalkHzhighpassfilterwasappliedtotheoriginal recordingsandthedurationoftypicalp111sesoundswas around40ms．Thenumberofthecallsbecame774after

the selection．No availabledatawas obtainedfromthe recordingson3rdofMarch・

爪V 2

いりハ′J川＝…・…ff‥りJ・J−…′ヾ川JJ Figtlre5andThblelshowtheacoustlCalcharacteristics Ofdugongcall■Thecallsofdugongwerecategorized rough1yintwointhematterofduratiom．Onewasashort Ca11withd11rationoflOO−500msandtheotherwasalong CallwithoveraroundlOOOms．Thecenterfrequencyof dugongcallsrangedfrom3to6kHz・Onlyintheshort Calls，8kHzcallswereobserved．

1 爪U

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〟〃削肋d血“血＝細れ恒w抑IC）′叩〝rO∬よmβJe秒‘げJ．9∫ α乃dま∂たfたre甲eCかeJy r仰eり〟〃dわ〃g血rαffβ〃C〟JJ W油呼PrOズimdfeけ￠r4．∂∫α〃dエβた〃z仲〝叫・

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ダfg・j・∫0〝αrgrα椚げ血go′−gC刷Ⅳ／−∫c力∫∫∫克ow乃

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⋮

difEererlCe．Thearrivaldirectionofacallateachvesselis

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Then，Phase differencebetweenthe two hydrophonesineachvesselwascalculatedbycross− COrrelationuslngISHtohavethecorrespondingtime

Ffg，5，β〟r（‡f∽柁V∫舟eq〟e柁Cγqr血g（）〃gC（‡JJ，

Calculatedusingtrigonometricfunctionasfollows，Where thetwohydrophonesarehlandh2，andd■isdistance rIbblel．Acousticalcharacteristicsofdugongca11 betweenthehydrophonesarld△1isthearrivaltime difEerenceandCistheunderwatersoundspeed（1500m／s）L Thecalculationisdoneunderassumptionthatthecallis COmlngfromSandtheso11rCeOfthesoundisfarenough totreatthesoundwaveasaplanewave（Fig・4）．Thereis Oneambig11ityinthiscalculation．Itsho111dbenotedthat theScanbeontheothersideofthehydrophonearray， forthearrivaldirection8wouldbeexactlythesamevalue inthecase． Figure6showsthedistrib11tionofvocalization intervals，Horizontalaxisis time between each callin

〆／／ぶ

sin♂＝ d− △d＝△7×C

JJ ダ7g▲〃・Geo刑erけqrC‘コJc〟Jβ血g（m・よvdJdgrecrわ〝β．

SeCOnds・Verticalaxisisnumberofcall．Dugongswere mostlikelytovocalizeonceinO−5seconds， Figure7showsthevocalizationintervalson 4thand5thofMarch・Horizontalaxisiselapsedtime fromthestartofrecording．Verticalaxisisaccumulated numberofvocalization・Thesteeppartsoftheslope mearlthatd11gOngSWereVOCaliziTlgfrequently・Thesteep PartSOnthe4th（2・Osbetweeneachcall）andthe5th （1・69s，1・74s，1・93s，1・71schronologically）ofMarch hadverysimilars10Pe．Ontheotherhand，thevalueof themoderatepartsraTlgedwidelyfrom7to180seconds betweeneachcallLDugonghadstartedvocalizevery frequentlyatsomepoints．Ithasbeenmadeclearthat dugonghadtwopattemsinvocalizationiIlterVal

75 apparentlyonlyoneindividualnearbyourresearchvesse］s accordlngtOthevISualdbseⅣador．sa刀dnooverlappingca11sT Figure9showsthechangeinthearrivaldiredlOn 卿d仇esoundp口実好u∫elevelatves駈1Amnzontalax巧is elapsed也mefromthestartoftherecordlngLl毎鵬calaxISis SOtmdpressurelevel（dB）andarrivaldirecdon（degree），WhlCh areshcFwnintheupperandlowergraphs，reSpeCtively二The amvdd胱donofthed11gOngdlisdan由Igm∝1e血elyas 6megcNSby・Thesoundpressurelevelincreasedaccordlnglyto 血ed姐鮮血仇eadval血陀doll． I■●■．Ⅶ叫●

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Ela阿】um8（9〉

ダ≠g，7．1心cdJ∼zαJわ乃よ乃ferv‘JJo乃イオんα〃d∫rゐ，〟drC九○，◆

corre乎0ね血わ〟ほ血J瓜reCOrded舟0椚了仇−∫00〃4れ Jj．■ヰ00柁5fゐre5pgCかgウ▲

Adu姐弟a∝OrdingtotⅣ血血い永朋k触eⅣ鵬0Ⅰ鳩 fromMicroLiteandfromourresearchvessels andto OVerlapplngCallsinthesonargram，therehadbeenmore thanonedugongneartheshipson4thand5thofMarch

FigurelOshowsthevocallZationinterval匝ppeT） andtheOundpressurelevel（lower）LThefrequencyof VOCalizatlOnislowat丘rst，andishighforthenext2000s andislowagalnatlast・ThisalternationinthevocalizatlOn rateisduetothedetectabilityoftherecordingdevices・The fartherthedistancebetweendugongandthevessel，the lessalldiblevocalizatlOnSarereCOrded．Thesepreliminary res111tssuggestthatad11gOngWaSCOmlngCloseratasteady angletotheresearchvessel・

（Fig．8）． ←でJ「

l・■

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，▼ノJrJ十

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Ffg．J仇物cαJよzαJわ〃f〝rerV腐り叩p叫α〃d′カe∫0〟〝d クre∫∫〃rβJevg川∂ルビり・

り

Ti】TIC（rl】S）

3758

Fよg▲g・OvビrんⅥ）ヱ〃gC〟JJ∫・A血断血・〟f∫∂乃CβJJ∫∂VerJ叩∫ 才加♪r∫rCαJJf〃rわe椚fddJe▲′〃〟ほJα∫r′”0椚e叫α∫烏orf 血rβ′∽〝CαJJoverJ岬∫J加わ几gCαJJ∫．

DISCUSSION Theaco11Sticalcharacteristicsofdugongcallswere described． 1iI川Jた‘汀l川，J〟什n・dJ

Theval11eSOfshortintervalsshowedverysimilarrange＝ 0−5sbetweeneachcal1．Periodsoflonginterval，Oralmost Forthedirectionanalyses，VOCalizationdatarecordedfrom 12：250nthe6爪ofMardlWere11Sed．On6（h，therehadbeennon−VOCalizmgwerealsoobserved・Thereweresudden

刀カⅤ（血〉〝〟Jゆ併

76 Changesinthevocalizationfreq11enCyOn4thand5thof tanq＝ プ。 March，Whenan11mberofdugongswereobservednearthe researchvessels・Itwassuggestedthatdugonghadstar（ed 血色＝J tovocalizefreq11entlyonacertainoccasionLSub）eCtlVely ThesesimultaneOuSequationsaresoIvedand SPeaking，theoccasioTlmighthavebeenanenCOllnterWith anotherindividual．Thesepreliminaryres111tsmadethe thentanOisconvertedtoresultirlEq．（2，a）and（2．b）． authorstothinkthatdugongappeartobeexchanglng （1・a）

（1・b）

l

ズ＝

theircallswitheachother．

（2▲a）

γ＝；…：d ShortcallslastedforlOO−500msandlongcal1swereover aroundlOOOmsLFreq11enCybandwasverynarrow，ranglng Oncethepositionsofvocalizlngdugongsare 3to6krrz，andabout8kHzjustintheshortcalls・High Obtained，byp】ottingthelocatedposit10nSinchronologlCal Order，theswimmlngpathofdugongwo111dbedescribed■ frequencymodulatedcallcaneasilybemaskedinthe IfthemovlngPathisdescribed，WeWOuldbeableto backgroundnoise・Thelengthofthecallsmaybedecided accordingtothedistancebetweenthevocalizingindividualStudythebehaviorofdugongthatisdirectlyrelatedto theirvocalactivity・ThisinnovatlVetraCklngteChniq11eis andtheothers．Ifthedistancebetweenindlvidualsisfar，Short COmPletelynewinmonitoringdugonganddoesnotaffect andsuccessivecallsareeasierforthereceiverindividllalto recognlZethecalls．Inclosedistancetoeachother，the thebehaviorofdugongatall．Itis，then，pOSSibletowarll theflShermenofthepresenceofdugongbeforetheanimal longcallsmaybevocalized． isaccidentallycaughtinthefishingnet，andtoresc11ethe dugongbeforedrowning．Thea11thorsbelievethatthe 凱Ⅵ血勘助ゆ椚 proposedtechniquecontributesgreatlyasaflrStStePtO Movementofadugongwasdescrlbedwiththechangein achievepeacefu1coexistenceofdugongprotectionand thearTivaldistance atvessel−A．Withtheres111tsofthe COaStalfishing． directionanalysesfrommorethanoneresearchpolntS， SOmeintersectionpointsofthedirectionsforeachca11 ACKNOWLEDGEM「ENTS Canbeobtained，Whichcanbes11pPOSedasapositionof ThisstudywaspartlysupportedbyaGrantLin−Aidfor adugong・Usinganumberofhydrophoneseliminatesthe ScientlficResearch（13375005，12556032and14560149） ambiguitythathasbeenmentionedbefore． andInformationResearchCenterforDevelopmentof 1もeb戚coonceptofthepsidonmgofav∝dinng KlOWledgeS∝ietyh丘astruCture，theMhistryofEducation， dugongisshowninflgurell，Wherethedugongca11sare Culture，Sports，ScienceatldTもChnologyL Theauthors toberecordedbythesetsofdual−Channelhydrophones thaJlkMs・KaTt］anaAdl11yanukosolforal1hercoordination ateachofA（0，d）andB（0，0），anddisadistancebetween inTllailand． AandB・01andO2arethearrivaldirectionsofacallatsite AandB，andthepositionofthesoundsourceisS（Ⅹ，y）． REFERENCI己S AkamatsuTletal．，2001．Comparisonbetweenvisual andpassiveacousticdetectionoffinlessporpoISeSinthe lねngbeRiver，China，エAc‘フM乙∫oc．A軋，10，，1723−1727．

nlJ和正…＝川lり毎wJ〃HT可◆l、〟仙

（2・b）

Phil】jpsR．etal．，2004．I）eterminationofl穐stIndian manateeVOCalizationlevelsaTldrate，］．AcoustlSoc．Am． 115（1）422−428．

Janik，VM・2000・WhisdeMatchinginWildBottlenose Dolphins，∫cfe〃Cち28，，1355−1357． Milne，P・lI・（1983）UnderwaterAcousticPositioning Systems，Gulfpublishingcompany，284pp・ 叩・0）

x＿鉱is

ダfg▲JJ・馳胱呵ガ如押印血血如Ⅶ如呵叩抑呵

UricちRJ・（1，83）PrlnCiplesofUnderwaterSound3rd edition，McGraw−Hill，423pp・

TheunknownpositionSisestimatedusing lehikawa，KetaL，2003・Detectlngthevocalizingdugong trigonometrlCfunctionasshowninEq・（1・a），（1，b），（2．a） and（2．b）．

−a】1eWaPprOaChtobehavioralobservationthe22nd COnferenceofJapanEthologlCalSociety，Abstracts74．