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NBERWORKINGPAPERSERIES
INTERNATIONALTRADE,NOISEPOLLUTION,ANDKILLERWHALES
M.ScottTaylor
FruzsinaMayer
WorkingPaper31390
/papers/w31390
NATIONALBUREAUOFECONOMICRESEARCH
1050MassachusettsAvenue
Cambridge,MA02138
June2023
FundingprovidedbytheSSHRCofCanada.TheviewsexpressedhereinarethoseoftheauthorsanddonotnecessarilyreflecttheviewsoftheNationalBureauofEconomicResearch.
NBERworkingpapersarecirculatedfordiscussionandcommentpurposes.Theyhavenotbeenpeer-reviewedorbeensubjecttothereviewbytheNBERBoardofDirectorsthataccompaniesofficialNBERpublications.
©2023byM.ScottTaylorandFruzsinaMayer.Allrightsreserved.Shortsectionsoftext,nottoexceedtwoparagraphs,maybequotedwithoutexplicitpermissionprovidedthatfullcredit,including©notice,isgiventothesource.
InternationalTrade,NoisePollution,andKillerWhales
M.ScottTaylorandFruzsinaMayerNBERWorkingPaperNo.31390June2023
JELNo.F1,Q01,Q20,Q53
ABSTRACT
OrcinusOrcaistheworld’slargestpredator,andsimultaneouslyasignificanttouristassetandculturaliconformuchofthePacificNorthwest.Inthepasttwodecades,theSouthernResidentKillerwhale(SRKW)populationhasdeclinedbymorethan25percent,puttingthematriskofextinction.Thecauseofthisdeclineishotlydebated.Thispaperemploysnoveldata,aninnovativenoisepollutionmodel,andquasi-experimentalmethodsborrowedfromenvironmentaleconomicstosolvethispuzzle.WefindconsistentevidencethatvesselnoisepollutionfrominternationalshippinghasloweredfertilityandraisedthemortalityoftheSRKWsignificantly.Hadnoisepollutionremainedatitspre-1998levels,theSRKWpopulationwouldbe30%larger.Noisepollutionisagrowingthreattomarinemammalsworldwide.
M.ScottTaylor
ProfessorofEconomics
DepartmentofEconomics
TheUniversityofCalgary
2500UniversityDrive,N.W.
Calgary,ABT2N1N4
andNBER
m.scott.taylor1@
FruzsinaMayer
2500UniversitydriveNWDepartmentofEconomicsCalgary,ABT2N1N4Canada
fruzsina.mayer@ucalgary.ca
Adataappendixisavailableat/data-appendix/w31390Additionaldetailsareavailableat/work#/whats-new/
1
IIntroduction
OrcinusOrcaistheworld’slargestpredator,andsimultaneouslyasignificanttouristassetandculturaliconformuchofthePacificNorthwest.Inthepasttwenty-fiveyearstheSouth-ernResidentKillerwhales(SRKW)havedeclinedbymorethan25%andnowappearonaslow-motionpathtowardextinction.Despiteextensivescientificinquiry,severalgovernmenttaskforces,andmillionsofdollarsofresearchmoneybeingspent,thereisasyetnocon-sensusastothekeydrivingforcesbehindtheirdecline.Limitationsinprey,disturbancebywhalewatchingvessels,andcontaminationbyPCBsallfeatureprominentlyinthecurrentdiscussion,butitisunclearwhichoftheseisthemostsignificantdriver.Surprisingly,otherOrcapopulationshavenotfaredaspoorly.Forexample,theNorthernResidentKillerwhales(NRKW),whoserangeoverlapswiththeSouth,hasgrownoverthisperiod.
ThispaperexploitsseveraltoolsfromeconomicstoprovideananswertowhatailstheSRKW.Weemploynoveldata,developaninnovativemodelofnoisepollutiondispersion,andemployquasi-experimentalmethodsborrowedfromenvironmentaleconomicstoprovidewhatwethinkisaconvincinganswer.VesselnoisefromincreasedinternationaltradewithAsiaisthekeyfactordrivingtheSRKWdecline.Ifnoisepollutionhadremainedatitspre-1998average,ratherthangrownbyover50%intheinterveningyears,ourestimatessuggesttheSRKWpopulationwouldbe30%higherthanotherwise.Thischangewouldlargelyundothelasttwenty-fiveyearsofpopulationdecline.
Thepapermakesseveralcontributions.Whilenoisepollutionhaslongbeenknowntonegativelyaffectmarinemammals,thisstudyisthefirsttodocumentadirectlinkbetweenexposuretonoisepollutionandapopulation-levelevent-thebirthanddeathratesoftheSRKW.Wefindconsistentevidencethatnoisepollutioncomingfromcommercialshipping,tiedtogrowinginternationaltradeflows,hasdegradedtheircriticalhabitat,loweredtheirbirthrates,andraisedtheirdeathrates.
Previousworkhasfoundvesselsdisturbforaging,socializing,andrestingbehaviorsimply-inganenergeticcosttowhales.Ithashoweverbeenverydifficultforresearcherstomovefromtheseindividual-specificobservationstotheircumulativepopulation-levelimpacts.Absentthislink,policymakershavebeenreluctanttoregulateorconstraininanywayinternationalcommercialshipping,despitealegislativerequirementtodosoiftheircriticalhabitatisdegradedbyeconomicactivity.
Ourabilitytoestimatethelinkbetweennoisepollutionandpopulationsizecomesfromaluckyhappenstance:theSRKWhappenstobetheworld’smostintensivelystudiedwhale
2
population;theircriticalhabitathappenstocoincidewithseveraloftheworld’sbusiestports;andtheseportshappentohaveexperiencedarapidchangeinthecompositionandscaleoftheirvesseltrafficoverthelast40yearsastheUnitedStatesandCanadiantradeturnedincreasinglytoAsia.Together,theyprovideuswithasettingwherekillerwhalesareexposedtoquasi-experimentalvariationinnoisepollution.
Weexploitthisluckyhappenstancebycollectingover40yearsofveryrichdemographicdataonKWbirths,deaths,andfamilyhistorytoestablishabaselineunderstandingofwhatdrivesbirthsanddeaths.Wecombinethiswithalargedatabaseweconstructedofmorethan5millioncommercialvessellandingsacross121portsalongtheWestcoastofNorthAmerica.UsingthemethodsdevelopedinTaylor(2021a)weusethislandingsdatatoestimatethekmtraveledbylargecommercialshipsintheSRKWcriticalhabitat.1Thechangeinvesseltrafficoveroursampleperiodisverylarge:theannualvesselkmtraveled,bylargecommercialvesselswithinthecriticalhabitat,rosefromapproximately1.5millionkmin1977toover3.5millionin2019.Sincecommercialvesselsdiffergreatlyinthenoisetheyradiate,wethenmatchthesemanyvesseltripswiththeirassociatednoisedisturbance.
Wethenexploitquasi-experimentalvariationinournoisedisturbancemeasure-drivenbychangesineconomicactivityintheU.S.,Canada,anditsAsiantradingpartners-toestimatethecausalimpactofvesselnoisepollutiononKWbirthsanddeaths.Inessence,wecomparebirthanddeathoutcomesforKWinnoisyversusquietyears.ThekeyempiricalchallengewefaceisensuringthatourexogenousvariationinnoisepollutiongeneratesasgoodasrandomvariationinKWexposuretonoisepollution.
Todosoweexploitmethodsoftenusedbyenvironmentaleconomiststoidentifytheimpactofairpollutiononhumanhealthoutcomesandfollowthisliteraturebytakingseveralstepstoensurethatassignmenttotreatment(exposure)isasgoodasrandom.
Whaleswithpoor(orverygood)fitnessmayaltertravelpatternsandsortacrosslocationstoavoidtheimpactsofvesseldisturbancemakingtheintensityofexposureendogenoustoKWhealth.Toaddressthisrisk,weemployshockstoournoisedisturbancemeasureratherthanitslevel.Thelogicfordoingsoissimple-ifmitigationactionstaketimetolearn,arehabitdriven,orcomeaboutfromslow-movingvariationinoverallfitness,thennoisedisturbance
1ThemethodsdescribedinTaylor(2021a)allowresearcherstoestimatethedistancetraveledbycommer-cialvesselsinaparticularhabitatfromthelate1970sonwards.Althoughsatellitedatathattracksvesselsthroughtheirautomatedidentificationsystem(AIS)couldbeusedtocalculatesimilarestimates,thisdataisonlyavailable,atbest,from2009andhaslimitedgeographiccoverage.SincethedeclineoftheSRKWpopulationbeganinthe1990sourretrospective40-yearstudyperiodiscriticaltoidentifyingthecauseoftheirdecline.
3
shocksshouldgenerateshort-runvariationinexposureindependentofhealthstatus.Thisshockmethodologyis,ofcourse,commonlyemployedinstudieslinkingindustrialpollutiontohumanhealth.
Evenifwhalesdonotsortacrosslocations,theymaychoosetoavoidnoisecontempora-neouslytolessenitsimpact.Avoidancebyitselfimpliesourestimatesofcausaleffectsmaybeunderestimatedsinceexposureislessenedbydefensiveactions.However,iftheabilitytoavoidistiedtofitness,thenexposureisagainendogenoustohealth.FeaturesofKWsocialstructuremakethisthreatunlikely.Individualkillerwhalestravelcloselywiththoseintheirmatriline,andmatrilinesinturntendtotracktheirspecificpod.Thismeansthatindividual-levelvariationinfitnessisunlikelytoaffectpod-leveltravelpatternsandhenceexposure.
Inaddition,wepresentdatashowingkillerwhaleshaveverylimitedabilitytoavoidvesselnoise.Thisisbecausetheverysamedeepchannelsusedbyinternationalshipping,andtheverysamerivermouthsleadingtomajorports,arealsolocationsfavoredbytheirpreyreturningfromtheoceantospawn.Therefore,avoidanceormitigationcomesataverysteepcost,andasaresult,conflictisinevitable(thisispresentedasfact#8insectionIII).
Ourdataisanunbalancedpanelcapturingoutcomesfromachangingpopulation;andwestudywhale-specificresponsestovariationinnoisepollutioninagivenyear,withthesewhalesdrawnfromthethen-currentpopulation.Thecharacteristicsofthispopulationchangeovertime,andthereforeitisimportanttoensurethatthedistributionofnoisyandquietyearsisindependentofchangesinpopulationcharacteristicsthatmaybetiedtofitness.Forexample,ifallthenoisyyearsoccurredwhenthepopulationwasalreadyunderstressbecauseofalackofprey(orotherreasons),ourtreatmentandcontrolgroupsarenotcomparable.
Toaddressthisconcernweshowthatthedistributionofnoiseshocksisindependentofotherimportantcovariatesdeterminingfitness.Preyabundance,sexratios,competitivepressuresfromotherwhales,andthepopulation’saverageageareverysimilaracrossnoisyvs.quietyears.Thiscomparisonsuggestsweareindeedmakinglike-to-likecomparisonsinnoisyversusquietyears.Thiscomparisonishoweverbasedonobservables.
Toensurethatotherpotentiallyimportant-butunobservable-determinantsoffitnessbethey-genetic,environmental,relatedtospecifictravelpatterns,orforagingsuccess-arealsocomparableacrossyears,weemploymatrilinefixedeffects.Matrilinesarecomprisedofverycloselyrelatedwhaleswhosharegenetics,buttheyalsotravelinverycloseproximity,sharesuccessfulkills,andhavecommonlearnedbehaviorsandlanguage.Someofthesefeaturescouldaffectbothfitnessandexposure;fortunately,mostarealsofixedandovertime.Asa
4
result,matrilinefixedeffectsshouldsweepawaytheirinfluence.
Thispaperusestoolsdrawnfromseveralfieldsofeconomicstoprovide,whatwehope,isaconvincingsolutiontoanimportantpuzzle-whatisresponsiblefortheprecipitousdeclineoftheSouthernresidentkillerwhales?Ourmethodsarecloselyrelatedtothoseexploitedbyquasi-experimentalworkinenvironmentaleconomicslinkingpollutionexposuretohealthoutcomes.TwoveryusefulreviewsofthisworkareGraffZivinandNeidell(2013)andGreenstoneandGayer(2009).Prominentsimilarwork,suchasChayandGreenstone(2003),Currieetal.(2009),andHannaandOliva(2015),allemployasimilarpollutionshockresearchdesign.SchlenkerandWalker(2016)alsoreliesonpollutionshocksbutinadditioncontainsanexplicitmodelofpollutiondispersionandexposure,whichissimilarinspiritandpurposetothesoundexposuremodelwedevelop.Thisliteraturehasbeenveryinfluentialandthesubstantialhealthcostsofpollutionarenowwelldocumented(Fulleretal.,2022).
ThepaperalsobearsafamilyresemblancetoearlierworkonMalthusianpopulationdynamics.Anincreaseinvesselnoisedegradestheacousticenvironmentmakinghunting,socializing,andforaginglessproductive.Toaneconomist,thisistechnologicalregress.Notsurprisinglyithasshorttomedium-runconsequencesforbirthsanddeathsforanypopulationwhosefitnessdrivesreproduction.Inthissense,cropfailuresandweathershocksinfluencedearlymodernEuropeanpopulationsmuchlikevesselnoiseshocksinfluencethepopulationofkillerwhalestoday.2
Whileeconomicscanbeapowerfullever,thispaperowesitsexistencetothehundredsofresearchers,academicandotherwise,whocollectedandcollatedthemanysourcesofdataneeded.Thedatacomesfromfoursources.First,weacquiredacompleteinventoryofallSouthernandNorthernresidentwhalesstartingfromtheveryfirstexploratorywhalecensusinthe1970s,throughtothelatestfiguresupto2020.Itrepresentsacompleteaccountingofallkillerwhalebirthsanddeathsforeitherpopulation,foreveryyear.Thisdataistheworkofalargescientificcommunityspanningprofessionalgovernmentscientists,whaleenthusiasts,andalargecommunity-drivenwhalespottingnetwork.
Second,weobtainedaseriesofsalmonabundancemeasuresfromthePacificSalmonCommission.TheCommission’sChinookTechnicalCommitteecollectsdatafromthirtyindicatorstocks,eachdistinguishedbytheirspawninglocationandinsomecasesbytheageoffishconsidered.Thesestockmeasuresarethenaggregatedtoproduceabundancemeasuresthatweemploy.3
2InfluentialworkinthisveinincludesAshrafandGalor(2011)andLagerl¨of(2015).
3SeeSectionA.Xintheappendixfordetailsontheabundancemeasuresandouruseofthem.
5
Third,weobtainedover40yearsofcommercialvessellandingsdataatover120portsontheWestCoastofNorthAmerica.Therichnessofthisdata(over5millionlandings)allowsforthecalculationofyearlyvesselkmtraveled,byvariouslargevesseltypes,withintheSRKWcriticalhabitat.Combiningthiswithestimatesoftriplengthprovidedbyacommerciallogisticsprovider(SeaRoutes),generatesestimatesforthekmtraveledinthecriticalhabitat(fordetailsseeTaylor(2021a)).ThisdataprovidesuswithinformationonpotentialvesseldisturbancedecadesbeforetheAutomatedIdentificationSystem(AIS)andsatellitetrackingofvesselsmadesimilarcalculationspossible.
Fourth,thereareonlyahandfulofstudiesthatdocumentrecordednoisefromcommercialvessels.MostofourdatacomesfromVeirs,VeirsandWood(2016),whichweaugmentwithdatapublishedinMcKennaetal.(2012).Bothstudiescollectshipsoundswiththehelpofaseafloor-mountedhydrophone.Theycombinethesereadingswithinformationabouttheship’spassagefromAIStocalculatethenoiseradiatedatthesourcelevel,SL,indecibels.4Theresultisadatasetconsistingof2,828observationsoncommercialvesselsthatcoverabroadrangeofvesselclasses.Importantly,Veirs,VeirsandWood(2016)recordshipspassingintheHaroStraitwhichislocatedinsidethecriticalhabitatoftheSRKW;and,inbothcases,vesselsweretrackedopportunistically,andthereforeselectionintothesampleswasrandomlydetermined.
Whilethereareliterallyhundredsofarticlesdiscussingtheconservation,reproduction,andprotectionofkillerwhales,therehavebeenrelativelyfewstudiesexaminingpopulation-leveleventsempirically.Oneearlyapproachwasthroughtheconstructionanduseoflifetables(Olesiuk,BiggandEllis,1990;Olesiuk,EllisandFord,2005a,b).Morerecently,ahandfulofresearchershavetriedtoexplainKWpopulationgrowthviaregressionmethods.Forexample,Ward,HolmesandBalcomb(2009)employsdatafrom1981to2007onboththeNRKWandSRKWtoevaluatehowsalmonabundanceandclimaticfactorsmayaffectKW.Theirmostimportantfindingisthatsalmonabundancehasalargepositiveeffectonfertility,whereasmatrilineandpod-relatedvariablesdonot.SalmonabundancehasalsobeenfoundtobeimportantbyFordetal.(2010)andFord,EllisandOlesiuk(2005).RelatedworkhasexaminedthestresshormoneresponsesofKWtosummertrafficpulsesintheSalishSea(Ayresetal.,2012),whilemanyothershavedocumentedbehavioralchangesarisingfromvesseltrafficandassociatednoise(e.g.Williamsetal.(2014)).
Ourworkissimilartotheextentthatweconditiononsalmonabundanceandadoptthe
4Bothpapersmeasuredsourcelevelnoiseindecibels(dB)relativetothestandardpressureanddistanceof1µPaatadistanceof1mfromthevessel.
6
samediscretechoiceframeworkfavoredbynaturalscientists.Itisuniqueineveryotherway-intermsofourresearchdesignwhichfocusesontheidentificationofacausalimpact,ourconstructionanduseofanewnoisedisturbancemeasure,ouruseofaMalthusianframe-worktoguideestimationandprovidecounterfactuals,ourtreatmentofwithinandacrosspopulationcompetitionforprey,andbythesheerlengthofoursampleperiod.
Ourworkisalsoacontributiontothelargeandgrowingliteratureexaminingtheenviron-mentalconsequencesofinternationaltrade(SeeCopeland,ShapiroandTaylor(2022)).Theclosestconnectionistothesmallsetofstudieslinkingtheinternationaltransportofgoodstocarbonemissions.Cristeaetal.(2013)wasthefirsttodocumenttradeandtransportemissions,withvaluablesubsequentworkbyShapiro(2016).Thispaperisrelatedtotheseearliercontributionsinthesensethatvesselnoise,justlikecarbonemissions,areanunin-tendedconsequenceofcommercialshipping.Vesselnoiseisnowthoughttobeamajorformofunderwaterpollutionthatcanaffectalltypesofmarinelife,especiallymarinemammals.
Finally,thispaperisrelatedtoearlierworkbyoneofus.Taylor(2021a)developsthemethodforcalculatingkmtraveledinthecriticalhabitatfromlandingsdata.ItpresentssummarystatisticsandconjecturesthatvesseldisturbanceisdrivingtheSRKWtoextinction.PartsofTaylor(2021b)werecannibalizedtoproduceTaylor(2021a);otherelementswererefinedandsignificantlyextended(afterinputfromseminaraudiences)tobeincludedhere.Theresearchdesign,soundexposuremodel,econometricresultsandMalthusianresourcemodel,etc.areallnoveltothispaper.Inacompanionpaperinprocess,weusetheestimatesdevelopedheretocreateamarketforpricingoceannoisedisturbances.Wearguethismarket-basedsolutionisrelativelyeasytoimplementgiventoday’ssatellitetrackingofvesselsviatheAutomatedIdentificationSystem(AIS).Asaresult,themethodswedevelopherecouldbeemployedtomeasureandtheninformpoliciestolowernoisedisturbanceelsewhere.5
Therestofthepaperproceedsasfollows.SectionIIpresentsashorthistoryandrelevantbiologyofKWwithafocusontheSRKW.InsectionIII,weturntoeightfactsdrawnfromourdata.Thesefactsallowustoframeourargumentwhileintroducingdatasources.WedevelopourresearchdesigninsectionIV.Ourempiricalimplementationthenfollows.Ashortconclusionendsthepaper.Alllengthycalculations,plusconsiderabledetailonourmethodsanddataiscontainedinourAppendixAwhichisavailableonline.
5IntheUnitedStatesalone,thereare30marinemammalsintheCetacean(whaleanddolphinfamily)listedundereithertheEndangeredSpeciesAct(ESA)asendangeredorthreatened,ordepletedundertheMarineMammalProtectionAct(MMPA).Worldwidethisnumbergrowsto124cetaceanpopulationsunderthreat.See/status-of-the-worlds-cetaceans/.Noisedisturbanceisapotentialcauseinmanyofthesecases.
7
IIAnIntroductiontoKillerWhales(OrcinusOrca)
Killerwhalesaretheworld’slargestpredator;theworld’smostcosmopolitanwhalespecieswithpopulationsinallsevenseas;andprobablytheworld’smosteasilyrecognizablewhalegiventheirstrikingblackandwhitecoloration.Whiletodayalmosteveryoneknowssome-thingaboutkillerwhales,beforetheearly1960s,verylittlewasknown.Duringthistime,killerwhaleswereviewedasapesttocommercialfishingandadangertohumans.6Notsurprisingly,KWwereoftenshotbyfishermen,boaters,andsometimesbytheUSairforce.7Followingtheinitial(andinadvertent)captureofalivekillerwhaleofftheBCcoastintheearly1960s,thedisplayandlivecaptureindustrywasbornwiththeVancouverAquariumtakingaleadingrole.Theindustryisstillinexistencetoday.8
Inresponsetoboomingdemandfordisplayspecimens,andthelackofregulationoncapture,bothUSandCanadianauthoritiesstartedtofundresearchstudyingkillerwhales.Initially,thegoalwastocalculatewhatmightbea“sustainable”harvestforthedisplayindustrybutsoongrewintoamuchbroaderresearchagendastudyingmarinemammals.Almostallofourcurrentscientificknowledgecomesfromresearchpost-1970.
Akillerwhalecensusbeganintheearly1970sandcontinuestothisday.ItcoverswhalesfromboththeNorthernResidentpopulation,thoseKWmostlyresidentinCanada,andwhalesfromtheSouthernResidentpopulation,thoseKWmostlyresidentintheU.S..UsingnoveltechniquesdevelopedbyCanadianfisheriesscientistMichaelBigg,researcherscouldidentifyindividualwhales,andsoondiscoveredkillerwhaleshavelifelongattachmentstotheirmatrilinealgroupwhichinturnistied,againforlife,tolargergroupingstheynamedpods.FarlooserassociationsofpodsconstitutewhatwenowcalltheNRKWandSRKWpopulations.Aftermorethanfiftyyearsofresearch,theSRKWisarguablythemoststudiedwhalepopulationintheworld.TheNRKWwouldnotbefarbehind.AmapofthehabitatsforUSandCanadianwhalestogetherwithafrequencyofsightingmapisinAppendixA.I.
Ourdetailedknowledgeofthekillerwhalesocietyiskeytoourresearchdesign.Forexample,ourstudyisbasedononlyoneeco-type,butthereareinfactthreedifferenteco-
6Aquotebywell-knownUSnaturalistWilliamTempleHornaday(Hornaday,1914,p.148)fromtheturnofthecenturywasstillcommonlyheldwisdomsixtyyearslater:“TheKillerWhale,orOrca,isthedemonoftheseas.Thiscreaturehastheappetiteofahog,thecrueltyofawolf,thecourageofabulldog,andthemostterriblejawsafloat.Itsteetharesurpassedinsizeonlybythoseofthespermwhale.Itattackswhalesofthelargestsize,anddevourssea-lions,seals,andsmallporpoisesasahungrylongshoremandestroyssaddle-rockoysters.”
7See“AirForceGunstoShootWhales”,SeattleTimes,October16,1955.
8Forthefullstory,seethevideoofthecaptive,MobyDoll,availableathttps://youtu.be/U39Dc87G2yo
8
typesofkillerwhalesdefinedbytheirecologicalniche.Thesethreedifferintheirsocialstructure,theirsizeandbodystructure,andtheirmovementandcommunicationpatterns,butitissimplesttodefinethembytheirprey.Residentkillerwhaleseatfish;Transientkillerwhaleseatmarinemammals(seals,sealions,whales);andOffshorekillerwhaleseatsharks,squidsandrays.BoththeSRKWandtheNRKWareResidentKWpopulations,althoughallthreeeco-typeshavebeenspottedinbothCanadianandUSwaters.
Mostimportanttous,isthatresidencymeansthat,almosteveryyear,everylivingwhaleintheresidentpopulationisspotted,counted,andrecordedinourdata.Ifawhaleiscontinuouslyabsent,itisdead.Theonlypopulationeventsmissingfromthedatacouldbeunsuccessfulbirthsorneonataldeathsofveryyoungwhalesyettoberecorded.Ourdataisthereforeapopulationcensusandnotasampleofthesewhales.
Second,theNRKWandSRKWdonotbreedwitheachothernorinteract.LanguageorcallsdiffersignificantlyacrossmembersoftheNRKWandSRKW.Theonlypointofcontactbetweenthesepopulationsisovertheircommonprey-salmon.Accordingly,wewillallowforbothwithinandacross-populationcompetitionforpreytoaffectwhalefitnessandhenceoutcomes.ThecriticalhabitatfortheSRKWisprimarily,butnotexclusivelyusedbysouthernresidents.ThecriticalhabitatfortheNRKWisrarelyusedbysouthernresidents.9CommercialvesseltrafficintheNRKWcriticalhabitatisalsoordersofmagnitudelowerthanthetrafficintheSalishsinceitneithercontainsnoristheentrychannelforanydeepwaterport.Asaresult,wefocusonnoisedisturbanceintheSalishSeabecausethereisverylittleifanyvesseldisturbanceintheNRKWcriticalhabitat.10
Third,thesocietalstructureofafamilygrouping(pod),consistsofseveralmatrilines,eachledbyaseniorfemale.Matrilinescontainalllivingoffspring(bothmalesandfemales)andtheirdescendants.Nowhalehaseverswitchedmatrilines,andonlyoneorphanedwhalehaseverchangedpods.Calvestendtobeborninautumnandwintermonths,andgestationis16to18months.Theselifelongfamilyconnectionscarryovertotheirtravelpatternsandhenceexposuretonoise,andweexploitthesefactsinouridentificationstrategy.Ourknowledgeof
9TheNRKWcriticalhabitatliesbetweenthecontinentalmainlandofB.C.andVancouverIslandstartingjustnorthofEastThurlowIslandandcoveringtheentirewidthofJohnstonStraittoavertexatNumasIslandjustnorthofPortMcNeil.
10Oneofus(Taylor)hasvisitedtheNRKWcriticalhabitatfourtimesinthelastsixyearsbyeitherkayak,fishingboat,orcruiseship.Partofthereasonforvisitingwastogaugetheextentofvesseltrafficnotcapturedinourdata.Interactionswithguidesandcaptainsconfirmwhatourdata,andcommonsense,toldus-withnomajorportinornearthehabitat,andgiventhedifficultpassageforlargevesselsthroughSeymourNarrowsattheendofGeorgiaStrait,thereisverylittlecommercialvesseltrafficthroughtheinsidepassageviaJohnsonStrait.
9
birthdatesandlengthofgestation,alsoimpliesconceptionoccursintheimportantspringandsummermonthsoftheprecedingyearwhenthewhalesareoftenresidentintheSalishSea.Accordingly,weinvestigatebothcontemporaneousandone-periodlaggedvaluesfornoisedisturbanceshocksandsalmonabundance.
Fourth,killerwhalesareveryspecializedpredators.Thetworesidentpopulationsnotonlyspecializeineatingalmostexclusivelymembersofthesalmonfamily,buttheyarealsohighlydependentonChinooksalmon.Estimatesofthisreliancevaryacrossstudies,butsalmonmakeupperhaps70-80%
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