读文小说网

手机浏览器扫描二维码访问

绪论 虎鲸类型和种群（第4页）

英文原文：

OrcasorkillerwhaleshaveacosmopolitandistributionandseveraldistinctpopulationsortypeshavebeendocumentedorsuggestedThreetofivetypesoforcasmaybedistinctenoughtobeconsidereddifferentraces，subspecies，orpossiblyevenspeciesseeSpeciesproblemTheIUCNreportedin2008，“Thetaxonomyofthisgenusisclearlyinneedofreview，anditislikelythatOorcawillbesplitintoanumberofdifferentspeciesoratleastsubspeciesoverthenextfewyears“AlthoughlargevariationintheecologicaldistinctivenessofdifferentorcagroupscomplicatesimpledifferentiationintotypesMammaleatingorcasindifferentregionswerelongthoughtlikelytobecloselyrelated，butgenetictestinghasrefutedthishypothesis

Northernwaters

NorthPacific

ResearchoffthewestcoastofCanadaandtheUnitedStatesinthe1970sand1980sidentifiedthefollowingthreetypes

ResidentfisheatingorcasThecurveddorsalfinsaretypicalofresidentfemales

ResidentThesearethemostcommonlysightedofthethreepopulationsinthecoastalwatersofthenortheastPacificResidentsdietsconsistprimarilyoffishandsometimessquid，andtheyliveincomplexandcohesivefamilygroupscalledpodsFemaleresidentscharacteristicallyhaveroundeddorsalfintipsthatterminateinasharpcornerTheyvisitthesameareasconsistentlyBritishColumbiaandWashingtonresidentpopulationsareamongstthemostintensivelystudiedmarinemammalsanywhereintheworldResidentorcascanbedividedintoatleastthreedistinctcommunitiesnorthern，southernandsouthernAlaskanSouthernAlaskanresidentorcasaredistributedfromsoutheasternAlaskatotheKodiakArchipelagoandnumberover700individualsThesewhalesconsistoftwointerbreedingclansdistinguishedbyacousticcallsandwhoserangesoverlapThenorthernresidentcommunitylivesincoastalandinlandwatersfromsoutheasternAlaskatoVancouverIslandItconsistsofthreeclansand16podsandnumberover300orcastotalThesouthernresidentcommunitygenerallyinhabitstheinlandwatersofsouthernBritishColumbiaandWashington，butcanbefoundintheouterwatersoffVancouverIsland，Washington，OregonandCaliforniaTheyconsistofoneclanandthreepods，andnumberlessthan80individualsandarelistedasendangered

TransientorBiggsThedietsoftheseorcasconsistalmostexclusivelyofmarinemammalsTheyliveinthesameareasasresidents，butthetwoavoideachotherTransientsgenerallytravelinsmallgroups，usuallyoftwotosixanimals，andhavelesspersistentfamilybondsthanresidentsTransientsvocalizeinlessvariableandlesscomplexdialectsFemaletransientsarecharacterizedbymoretriangularandpointeddorsalfinsthanthoseofresidentsThegreyorwhiteareaaroundthedorsalfin，knownasthe“saddlepatch“，oftencontainssomeblackcolouringinresidentsHowever，thesaddlepatchesoftransientsaresolidanduniformlygreyTransientsroamwidelyalongthecoastsomeindividualshavebeensightedinbothsouthernAlaskaandCaliforniaTransientsarealsoreferredtoasBiggsorcainhonourofcetologistMichaelBiggThetermhasbecomeincreasinglycommonandmayeventuallyreplacethetransientlabelThetransientecotypeisestimatedtohavediverged700，000yearsagoThereareatleastthreedifferent“stocks“oftransientsoffNorthAmerica，theAT1stockwhichoccursfromPrinceWilliamSoundtoKenaiFjords，theGulfofAlaskaAleutianIslandsBeringSeaGOAAIBSstockandthewestcoaststockwhichrangesfromsoutheastAlaskatoCaliforniaAT1isconsideredadepletedstockitwasaffectedbytheExxonValdezoilspillanddeclinedfrom22individualstoeightbetween1989and2004TheGOAAIBSstockmaynumberaround500whaleswhilethewestcoasttransientsnumberover320orcaswithover200alongsoutheastAlaska，BritishColumbiaandWashingtonandover100orcasoffCaliforniaCaliforniatransientsdonotappeartointerminglemuchwiththosefurthernorthandwestcoasttransientsmaybedividedintosubcommunities

OffshoreAthirdpopulationoforcasinthenortheastPacificwasdiscoveredin1988，whenahumpbackwhaleresearcherobservedtheminopenwaterAstheirnamesuggests，theytravelfarfromshoreandfeedprimarilyonschoolingfishHowever，becausetheyhavelarge，scarredandnickeddorsalfinsresemblingthoseofmammalhuntingtransients，itmaybethattheyalsoeatmammalsandsharksTheyhavemostlybeenencounteredoffthewestcoastofVancouverIslandandnearHaidaGwaiiOffshorestypicallycongregateingroupsof20–75，withoccasionalsightingsoflargergroupsofupto200Littleisknownabouttheirhabits，buttheyaregeneticallydistinctfromresidentsandtransientsOffshoresappeartobesmallerthantheothers，andfemalesarecharacterizedbydorsalfintipsthatarecontinuouslyrounded

SeparatefisheatingandmammaleatingorcacommunitiesalsoexistoffthecoastoftheRussianFarEastandHokkaido，JapanRussianorcasarecommonlyseenaroundtheKamchatkaPeninsulaandCommanderIslandsOver2，000individualresidentlikeorcasand130transientlikeorcashavebeenidentifiedoffRussiaAtleast195individualorcashavebeencatalogedintheeasterntropicalPacific，rangingfromBajaCaliforniaandtheGulfofCaliforniainthenorthtothenorthwestcoastofSouthAmericainthesouthandwesttowardsHawaiiOrcasappeartoregularlyoccurofftheGalápagosIslandsOrcassightedinHawaiianwatersmaybelongtoagreaterpopulationinthecentralPacific

NorthAtlanticandadjacent

OrcatailslappinginVestfjorden，Norway

Atleast15，000whalesareestimatedtoinhabittheNorthAtlanticIntheNortheastAtlantic，twoorcaecotypeshavebeenproposedType1orcasconsistofsevenhaplotypesandincludeherringeatingorcasofNorwayandIcelandandmackereleatingorcasoftheNorthSea，aswellassealeatingorcasoffNorwayType2orcasconsistoftwohaplotypes，andmainlyfeedonbaleenwhales

IntheMediterraneanSea，orcasareconsidered“visitors“，likelyfromtheNorthAtlantic，andsightingsbecomelessfrequentfurthereastHowever，asmallyearroundpopulationexistsintheStraitofGibraltar，whichnumberedaround39in2011DistinctpopulationsmayalsoexistoffthewestcoastoftropicalAfrica，whichhavegeneralizeddiets

ThenorthwestAtlanticpopulationisfoundyearroundaroundLabradorandNewfoundland，whilesomeindividualsseasonallytraveltothewatersoftheeasternCanadianArcticwhentheicehasmeltedSightingsofthesewhaleshavebeendocumentedasfarsouthasCapeCodandLongIslandThispopulationispossiblycontinuouswithorcassightedoffGreenlandOrcasaresightedyearroundintheCaribbeanSea，andanestimated267asof2020isdocumentedinthenorthernGulfofMexico

NorthIndianOcean

Over50individualwhaleshavebeencatalogedinthenorthernIndianOcean，includingtwoindividualsthatweresightedinthePersianGulfin2008andoffSriLankain2015

Southernwaters

OrcabeachingtocapturesealionatValdesPeninsula

AsmallpopulationoforcasseasonallyvisitsthenorthernpointoftheValdesPeninsulaontheeastcoastofArgentinaandhuntforsealionsandelephantsealsontheshore，temporarystrandingthemselvesOffSouthAfrica，adistinctive“flattooth“morphotypeexistsandpreysonsharksApairofmaleorcas，PortandStarboard，havebecomewellknownforhuntinggreatwhitesandothersharksofftheSouthAfricancoast

OrcasoccurthroughoutthewatersofAustralia，NewZealandandPapuaNewGuineaTheyaresightedyearroundinNewZealandwaters，whileoffAustralia，theyareseasonallyconcentratedoffthenorthwest，intheinshorewatersofNingalooReef，andthesouthwest，attheBremerregionGeneticevidenceshowsthattheorcasofNewZealand，andnorthwestandsouthwestAustraliaformthreedistinctpopulationsNewZealandorcasmainlypreyonsharksandrays

Antarctic

Around25，000orcasareestimatedaroundtheAntarctic，andfourtypeshavebeendocumentedTwodwarfspecies，namedOrcinusnanusandOrcinusglacialis，weredescribedduringthe1980sbySovietresearchers，butmostcetaceanresearchersareskepticalabouttheirstatus，andlinkingthesedirectlytothetypesdescribedbelowisdifficult

Someexamplesofvariationsinorcas

TypeAorAntarcticorcaslooklikea“typical“orca，alarge，blackandwhiteformwithamediumsizedwhiteeyepatch，livinginopenwaterandfeedingmostlyonminkewhales

TypeB1orpackiceorcasaresmallerthantypeAIthasalargewhiteeyepatchMostofthedarkpartsofitsbodyaremediumgreyinsteadofblack，althoughithasadarkgreypatchcalleda“dorsalcape“stretchingbackfromitsforeheadtojustbehinditsdorsalfinThewhiteareasarestainedslightlyyellowItfeedsmostlyonsealsTypeB1orcaareabundantbetweenAdelaideIslandandthemainlandAntarcticpeninsula

TypeB2orGerlacheorcasaremorphologicallysimilartoTypeB1，butsmallerThisecotypehasbeenrecordedfeedingonpenguinsandseals，andisoftenfoundintheGerlacheStrait

TypeCorRossSeaorcasarethesmallestecotypeandliveinlargergroupsthantheothersItseyepatchisdistinctivelyslantedforwards，ratherthanparalleltothebodyaxisLiketypeB，itisprimarilywhiteandmediumgrey，withadarkgreydorsalcapeandyellowtingedpatchesItsonlyobservedpreyistheAntarcticcod

TypeDorSubAntarcticorcaswerefirstidentifiedbasedonphotographsofa1955massstrandinginNewZealandandsixatseasightingssince2004Thefirstvideorecordofthistypewasmadein2014betweentheKerguelenandCrozetIslands，andagainin2017offthecoastofCapeHorn，ChileItisrecognizablebyitssmallwhiteeyepatch，narrowerandshorterthanusualdorsalfin，bulbousheadsimilartoapilotwhale，andsmallerteethItsgeographicrangeappearstobecircumglobalinsubAntarcticwatersbetweenlatitudes40°Sand60°SAlthoughitsdietisnotdetermined，itlikelyincludesfish，asdeterminedbyphotographsaroundlonglinevessels，whereTypeDorcasappearedtobepreyingonPatagoniantoothfishDissostichuseleginoides

TypesBandCliveclosetotheice，anddiatomsinthesewatersmayberesponsiblefortheyellowishcolouringofbothtypesMitochondrialDNAsequencessupportthetheorythatthesearerecentlydivergedseparatespeciesMorerecently，completemitochondrialsequencingindicatesthetypesBandCberecognizedasdistinctspecies，asshouldtheNorthPacifictransients，leavingtheothersassubspeciespendingadditionaldataAdvancedmethodsthatsequencedtheentiremitochondrialgenomerevealedsystematicdifferencesinDNAbetweendifferentpopulationsA2019studyofTypeDorcasalsofoundthemtobedistinctfromotherpopulationsandpossiblyevenauniquespecies