NBER-国际贸易、噪音污染和虎鲸

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/

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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

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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.

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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

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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.

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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.

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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.

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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

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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.

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birthdatesandlengthofgestation,alsoimpliesconceptionoccursintheimportantspringandsummermonthsoftheprecedingyearwhenthewhalesareoftenresidentintheSalishSea.Accordingly,weinvestigatebothcontemporaneousandone-periodlaggedvaluesfornoisedisturbanceshocksandsalmonabundance.

Fourth,killerwhalesareveryspecializedpredators.Thetworesidentpopulationsnotonlyspecializeineatingalmostexclusivelymembersofthesalmonfamily,buttheyarealsohighlydependentonChinooksalmon.Estimatesofthisreliancevaryacrossstudies,butsalmonmakeupperhaps70-80%