小说园

绪论 虎鲸类型和种群（第2页）

orcasorkillerwhaleshaveacosmopolitandistributionandseveraldistinctpopulationsortypeshavebeendocumentedorsuggested。threetofivetypesoforcasmaybedistinctenoughtobeconsidereddifferentraces，subspecies，orpossiblyevenspecies（seeSpeciesproblem）。theIUcNreportedin2008，“thetaxonomyofthisgenusisclearlyinneedofreview，anditislikelythato。orcawillbesplitintoanumberofdifferentspeciesoratleastsubspeciesoverthenextfewyears。“Althoughlargevariationintheecologicaldistinctivenessofdifferentorcagroupsplicatesimpledifferentiationintotypes。mammal-eatingorcasindifferentregionswerelongthoughtlikelytobecloselyrelated，butgenetictestinghasrefutedthishypothesis。

Northernwaters

Northpacific

ResearchoffthewestcoastofcanadaandtheUnitedStatesinthe1970sand1980sidentifiedthefollowingthreetypes:

Resident（fish-eating）orcas:thecurveddorsalfinsaretypicalofresidentfemales。

Resident:thesearethemostmonlysightedofthethreepopulationsinthecoastalwatersofthenortheastpacific。Residentsdietsconsistprimarilyoffishandsometimessquid，andtheyliveinplexandcohesivefamilygroupscalledpods。Femaleresidentscharacteristicallyhaveroundeddorsalfintipsthatterminateinasharpcorner。theyvisitthesameareasconsistently。britishcolumbiaandwashingtonresidentpopulationsareamongstthemostintensivelystudiedmarinemammalsanywhereintheworld。Residentorcascanbedividedintoatleastthreedistinctmunities;northern，southernandsouthernAlaskan。SouthernAlaskanresidentorcasaredistributedfromsoutheasternAlaskatotheKodiakArchipelagoandnumberover700individuals。thesewhalesconsistoftwointerbreedingclansdistinguishedbyacousticcallsandwhoserangesoverlap。thenorthernresidentmunitylivesincoastalandinlandwatersfromsoutheasternAlaskatoVancouverIsland。Itconsistsofthreeclansand16podsandnumberover300orcastotal。thesouthernresidentmunitygenerallyinhabitstheinlandwatersofsouthernbritishcolumbiaandwashington，butcanbefoundintheouterwatersoffVancouverIsland，washington，oregonandcalifornia。theyconsistofoneclanandthreepods，andnumberlessthan80individualsandarelistedasendangered。

transientorbiggs:thedietsoftheseorcasconsistalmostexclusivelyofmarinemammals。theyliveinthesameareasasresidents，butthetwoavoideachother。transientsgenerallytravelinsmallgroups，usuallyoftwotosixanimals，andhavelesspersistentfamilybondsthanresidents。transientsvocalizeinlessvariableandlessplexdialects。Femaletransientsarecharacterizedbymoretriangularandpointeddorsalfinsthanthoseofresidents。thegreyorwhiteareaaroundthedorsalfin，knownasthe“saddlepatch“，oftencontainssomeblackcolouringinresidents。however，thesaddlepatchesoftransientsaresolidanduniformlygrey。transientsroamwidelyalongthecoast;someindividualshavebeensightedinbothsouthernAlaskaandcalifornia。transientsarealsoreferredtoasbiggsorcainhonourofcetologistmichaelbigg。thetermhasbeeincreasinglymonandmayeventuallyreplacethetransientlabel。thetransientecotypeisestimatedtohavediverged700，000yearsago。thereareatleastthreedifferent“stocks“oftransientsoffNorthAmerica，theAt1stockwhichoccursfromprincewilliamSoundtoKenaiFjords，theGulfofAlaskaAleutianIslandsberingSea（GoAAIbS）stockandthewestcoaststockwhichrangesfromsoutheastAlaskatocalifornia。At1isconsideredadepletedstock;itwasaffectedbytheExxonValdezoilspillanddeclinedfrom22individualstoeightbetween1989and2004。theGoAAIbSstockmaynumberaround500whaleswhilethewestcoasttransientsnumberover320orcaswithover200alongsoutheastAlaska，britishcolumbiaandwashingtonandover100orcasoffcalifornia。californiatransientsdonotappeartointerminglemuchwiththosefurthernorthandwestcoasttransientsmaybedividedintosub-munities。

offshore:Athirdpopulationoforcasinthenortheastpacificwasdiscoveredin1988，whenahumpbackwhaleresearcherobservedtheminopenwater。Astheirnamesuggests，theytravelfarfromshoreandfeedprimarilyonschoolingfish。however，becausetheyhavelarge，scarredandnickeddorsalfinsresemblingthoseofmammal-huntingtransients，itmaybethattheyalsoeatmammalsandsharks。theyhavemostlybeenencounteredoffthewestcoastofVancouverIslandandnearhaidaGwaii。offshorestypicallycongregateingroupsof20–75，withoccasionalsightingsoflargergroupsofupto200。Littleisknownabouttheirhabits，buttheyaregeneticallydistinctfromresidentsandtransients。offshoresappeartobesmallerthantheothers，andfemalesarecharacterizedbydorsalfintipsthatarecontinuouslyrounded。

Separatefish-eatingandmammal-eatingorcamunitiesalsoexistoffthecoastoftheRussianFarEastandhokkaido，Japan。RussianorcasaremonlyseenaroundtheKamchatkapeninsulaandmanderIslands。over2，000individualresident-likeorcasand130transient-likeorcashavebeenidentifiedoffRussia。Atleast195individualorcashavebeencatalogedintheeasterntropicalpacific，rangingfrombajacaliforniaandtheGulfofcaliforniainthenorthtothenorthwestcoastofSouthAmericainthesouthandwesttowardshawaii。orcasappeartoregularlyoccurofftheGalápagosIslands。orcassightedinhawaiianwatersmaybelongtoagreaterpopulationinthecentralpacific。

NorthAtlanticandadjacent

orcatail-slappinginVestfjorden，Norway

Atleast15，000whalesareestimatedtoinhabittheNorthAtlantic。IntheNortheastAtlantic，twoorcaecotypeshavebeenproposed。type1orcasconsistofsevenhaplotypesandincludeherring-eatingorcasofNorwayandIcelandandmackerel-eatingorcasoftheNorthSea，aswellasseal-eatingorcasoffNorway。type2orcasconsistoftwohaplotypes，andmainlyfeedonbaleenwhales。

InthemediterraneanSea，orcasareconsidered“visitors“，likelyfromtheNorthAtlantic，andsightingsbeelessfrequentfurthereast。however，asmallyear-roundpopulationexistsintheStraitofGibraltar，whichnumberedaround39in2011。distinctpopulationsmayalsoexistoffthewestcoastoftropicalAfrica，whichhavegeneralizeddiets。

thenorthwestAtlanticpopulationisfoundyear-roundaroundLabradorandNewfoundland，whilesomeindividualsseasonallytraveltothewatersoftheeasterncanadianArcticwhentheicehasmelted。SightingsofthesewhaleshavebeendocumentedasfarsouthascapecodandLongIsland。thispopulationispossiblycontinuouswithorcassightedoffGreenland。orcasaresightedyear-roundinthecaribbeanSea，andanestimated267（asof2020）isdocumentedinthenorthernGulfofmexico。

NorthIndianocean

over50individualwhaleshavebeencatalogedinthenorthernIndianocean，includingtwoindividualsthatweresightedinthepersianGulfin2008andoffSriLankain2015。

Southernwaters

orcabeachingtocapturesealionatValdespeninsula

AsmallpopulationoforcasseasonallyvisitsthenorthernpointoftheValdespeninsulaontheeastcoastofArgentinaandhuntforsealionsandelephantsealsontheshore，temporarystrandingthemselves。offSouthAfrica，adistinctive“flat-tooth“morphotypeexistsandpreysonsharks。Apairofmaleorcas，portandStarboard，havebeewellknownforhuntinggreatwhitesandothersharksofftheSouthAfricancoast。

orcasoccurthroughoutthewatersofAustralia，NewZealandandpapuaNewGuinea。theyaresightedyearroundinNewZealandwaters，whileoffAustralia，theyareseasonallyconcentratedoffthenorthwest，intheinshorewatersofNingalooReef，andthesouthwest，atthebremerregion。GeneticevidenceshowsthattheorcasofNewZealand，andnorthwestandsouthwestAustraliaformthreedistinctpopulations。NewZealandorcasmainlypreyonsharksandrays。

Antarctic

Around25，000orcasareestimatedaroundtheAntarctic，andfourtypeshavebeendocumented。twodwarfspecies，namedorcinusnanusandorcinusglacialis，weredescribedduringthe1980sbySovietresearchers，butmostcetaceanresearchersareskepticalabouttheirstatus，andlinkingthesedirectlytothetypesdescribedbelowisdifficult。

Someexamplesofvariationsinorcas

typeAorAntarcticorcaslooklikea“typical“orca，alarge，black-and-whiteformwithamedium-sizedwhiteeyepatch，livinginopenwaterandfeedingmostlyonminkewhales。

typeb1orpackiceorcasaresmallerthantypeA。Ithasalargewhiteeyepatch。mostofthedarkpartsofitsbodyaremediumgreyinsteadofblack，althoughithasadarkgreypatchcalleda“dorsalcape“stretchingbackfromitsforeheadtojustbehinditsdorsalfin。thewhiteareasarestainedslightlyyellow。Itfeedsmostlyonseals。typeb1orcaareabundantbetweenAdelaideIslandandthemainlandAntarcticpeninsula。

typeb2orGerlacheorcasaremorphologicallysimilartotypeb1，butsmaller。thisecotypehasbeenrecordedfeedingonpenguinsandseals，andisoftenfoundintheGerlacheStrait。

typecorRossSeaorcasarethesmallestecotypeandliveinlargergroupsthantheothers。Itseyepatchisdistinctivelyslantedforwards，ratherthanparalleltothebodyaxis。Liketypeb，itisprimarilywhiteandmediumgrey，withadarkgreydorsalcapeandyellow-tingedpatches。ItsonlyobservedpreyistheAntarcticcod。

typedorSub-Antarcticorcaswerefirstidentifiedbasedonphotographsofa1955massstrandinginNewZealandandsixat-seasightingssince2004。thefirstvideorecordofthistypewasmadein2014betweentheKerguelenandcrozetIslands，andagainin2017offthecoastofcapehorn，chile。Itisrecognizablebyitssmallwhiteeyepatch，narrowerandshorterthanusualdorsalfin，bulboushead（similartoapilotwhale），andsmallerteeth。Itsgeographicrangeappearstobecircumglobalinsub-Antarcticwatersbetweenlatitudes40°Sand60°S。Althoughitsdietisnotdetermined，itlikelyincludesfish，asdeterminedbyphotographsaroundlonglinevessels，wheretypedorcasappearedtobepreyingonpatagoniantoothfish（dissostichuseleginoides）。

typesbandcliveclosetotheice，anddiatomsinthesewatersmayberesponsiblefortheyellowishcolouringofbothtypes。mitochondrialdNAsequencessupportthetheorythatthesearerecentlydivergedseparatespecies。morerecently，pletemitochondrialsequencingindicatesthetypesbandcberecognizedasdistinctspecies，asshouldtheNorthpacifictransients，leavingtheothersassubspeciespendingadditionaldata。AdvancedmethodsthatsequencedtheentiremitochondrialgenomerevealedsystematicdifferencesindNAbetweendifferentpopulations。A2019studyoftypedorcasalsofoundthemtobedistinctfromotherpopulationsandpossiblyevenauniquespecies。