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USM. DAT. In this study, detection of arrival direction and acoustic characteristics of dugong call are described. These aspects are necessary in designing a new ...
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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

暮.

即椚“肌





〟〃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・



ダfg・j・∫0〝αrgrα椚げ血go′−gC刷Ⅳ/−∫c力∫∫∫克ow乃

. ム

.r・■・・

、ノ..



difEererlCe.Thearrivaldirectionofacallateachvesselis

1■−

⋮川

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●

川15 Z0 25 30 ヨ5 4015 50 55 60 6S T0 75 80 85 90 9 100



・・し・・、l′、‘‥‥∫・■・・・r・



ぞ 5□

一丁▼・こ︰

川 28 30

Vm1=a伽nht8Ⅳd【s) ダ7g.∂.♪f∫′r肋J血刀一オVOCαJ∠z瓜如〃f〝ferv‘才J.

68 78

署竺ど碧≡E眉§三雲⊃∈弓ギ

¢口



・∴、・∴ ‥

銅 川

′ .g庁

Jノ

イダ





Ffg.タ.CJ!α〃gef〃∫んe∫0〟〝dクre∫∫〟rgJピソeり叩p叫β柁d 班eαrrfvβJdわ一eCJio〃rわweり.





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・■

、、− 官﹀ず‘巴邑冒■一︵廣



,▼ノJrJ十

/i

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・



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.