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The Effect of Melting Arctic Sea Ice on Arctic Whales · The Effect of Melting Arctic Sea Ice on Arctic Whales Amélie Paulin, Undergraduate Student, Dalhousie University Abstract

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Page 1: The Effect of Melting Arctic Sea Ice on Arctic Whales · The Effect of Melting Arctic Sea Ice on Arctic Whales Amélie Paulin, Undergraduate Student, Dalhousie University Abstract

TheEffectofMeltingArcticSeaIceonArcticWhales

AméliePaulin,UndergraduateStudent,DalhousieUniversity

AbstractInthepastfewdecades,Arcticseaicehasbeenexperiencingsomedramaticchangesdueinlargeparttoclimatechange.Arcticseaiceismeltinganddecreasinginbothsurfaceareaandthickness. Annual ice melt and freeze timings are being altered. These changes affect theprecarious balance of the Arctic ecosystem from themicroscopic organisms to its largestinhabitants, the Arctic whales. The factors influencing Arctic cetaceans include ultravioletradiationexposure, invasivespecies,andkillerwhalepredation.Thereducedsea icecoverdecreasesthenetreflectivityoftheArctic,increasingabsorptionofUVraysinArcticwaterswhich cause skin lesions inwhales and reduce primary production.With reduced sea icecover, invasive species – including predatory killer whales – have been extending theirranges northward, creating a possible competition for food with endemic Arctic species.Arcticwhalesareverysusceptibletochangesintheirhabitatandmaynotbeabletosurvivethepresentrateofchangeintheirenvironment.ThisreviewsynthesizesdatagatheredfrompreviousstudiesontheimpactsofdecreasingseaiceextentonArcticcetaceansinanefforttobetterassesstheconservationstatusofthethreespecies.

1.IntroductionClimate change is one of the most important environmental issues of the century,predominantlycausedbyanthropogenicforcing.Theeffectsofthisglobalphenomenonaremost pronounced in the Arctic. Rising ocean temperatures in the region are causing asubstantial increase in sea ice melt, leading to loss of sea ice volume and area. For allmonthsoftheyear,Arcticseaiceextentandthicknesshasbeenshowingasteepeningrateofdecline(Kwoketal.,2009;Stroeveetal.,2012).Septembericecoverhasdecreasedbyover30%sincethelate1970s(Stroeveetal.,2012).Multi-yeariceisbeingreplacedbythinfirst-yearice(Kwoketal.,2009).AlengtheningofthemeltseasonisapparentinalmostallregionsoftheArcticOcean(Stroeveetal.,2014)andischaracterizedbyearliermeltonsetand laterautumn freeze-up.Thesedramatic changes jeopardize thebalanceof theArcticecosystem,duetotheice'sinfluenceonalmostallbiologicalprocessesnecessaryforlifetothriveintheArctic(Laidreetal.,2008). Thedecreasingiceextentcouldalsohaveglobalrepercussionsbypotentiallyaffectingothermarineecosystems.

ThechangestheseaiceisundergoingwillinevitablyimpactcetaceansresidingintheArcticandpossiblythreatentheirsurvival.Amajorlossinbiodiversityandtheimperilmentoftheentire Arctic ecosystem could be the outcomes in failing to determine those impacts. Incontrast,determininghow thechanges in the ice coveraffectArcticwhales1may lead tobetterconservationpoliciesforthosespeciesandtheprotectionoftheArcticenvironment.

1Forthepurposesofthispaper,ArcticwhalesreferonlytothethreespeciesofcetaceansendemictotheArctic:bowheadwhales(Balaenamysticetus),narwhals(Monodonmonoceros)andbelugas(Delphinapterusleucas).

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AlthoughArcticwhalesarecloselyaffiliatedwithsea ice, thedirectrelationshipbetweenthetwohasnotyetbeenclearlydefined(MooreandHuntington,2008).Thismissingkeyconcept limits understanding and creates contrasting theories as to how themelting icewillaffectArcticwhales.Somestudiesdisagreeonwhetheradecreaseinseaiceextentwillresult inan increase in feedingopportunities(Laidreetal.,2008;MooreandHuntington,2008).Otherstudiesdifferontheoverallcapacityoftheicetoserveasphysicalprotectionforice-associatedwhales.Overall,thereisalackofresearchinascertainingtheneteffectchanges in sea ice coverwill have on cetaceans. This information is crucial in assessingtheirconservationstatus.

In order to provide a better understanding of the possible threats to Arcticwhales, thisreview summarizes key information on the melt of the Arctic sea ice and the differentspeciesofArcticwhales.TherelationshipbetweenthesecetaceansandseaiceisstudiedinordertodeterminetheimpactsoficemeltonArcticwhales.Thisreviewfocusesonthreecategoriesofpossibleimpacts:(1)ultravioletradiationexposure,(2)invasivespecies,and(3)killerwhalepredation.

2.Ultravioletradiationexposure

Arcticmulti-year sea ice (MYI) is known for its high albedo, reflecting up to 90%of thetransmitted solar energy (National Snow and Ice Data Center, 2015). This energy iscomprisedofultraviolet(UV)radiation,visible lightandinfraredradiation. IncontrasttoMYI reflectivity, the ocean-surface reflectsmuch less effectively solar radiation than ice.First-year ice(FYI)alsoabsorbs50%moresolarenergythanMYI(Nicolausetal.,2012).Figure 1 illustrates these facts by comparing the respective absorption and reflectivityfractions of FYI andMYI. Due to the decreasing Arctic sea ice extent and loss ofMYI, alargerportionoftheArcticOceansurfaceisconstitutedofopenwaterandFYI.Theeffectofdecreased ice cover is coupled with high ozone layer depletion over the Arctic region,whichwillallowmoreUVradiationtobetransmittedtowardsthesurface.

AstudybyBaisetal.(2014)analyzestheeffectofthedecreaseofArcticreflectivityonUV-Birradiance.TheycompiledinformationsurveyedfromavailablestudiesonthedecreasingArctic ice cover and UV-B transmittance data for existing Arctic snow-covered ice. Theyfound that themeltingof the sea ice in theArcticwould lead to theocean surfacebeingexposedto10timesthenormallevelsofUV-Bradiation.Overall,theArctic’stotalcapacitytoreflectUVrayswouldbereducedby10%,therebyincreasingUVradiationabsorptionbytheArcticecosystemasawhole.

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Figure1:Short-wavereflectivityandabsorbanceof first-year icevsmulti-year ice fractions.Darkarrowsrefertomeltpondswhilewhitearrowsrefertoseaice.Dashedlinesindicatesealevel. “Total” arrows indicate averages of absorbance and reflectivity. Photographs showrepresentativefirst-yeariceandmulti-yearsummerseaiceconditions(Nicolausetal.,2012).

IncreasedUV radiation absorption has serious implications for the Arcticwhale species.WhaleshavebeendocumentedsufferingfromskinlesionsduetocontinuousUVradiationexposure(Martinez-Levasseuretal.,2013).Moreresearchisstillneededtofullyassessthelong-term effects of UV exposure on whales. Nonetheless, the greatest consequence ofincreasedUVabsorptionforArcticwhalesispossiblythatofreducedprimaryproduction.Helblingetal.(1996)studiedtheimpactsofUVradiationexposureonnorthernpost-bloomphytoplankton.Theyobtainedsamplesofphytoplanktonduringthesummerandexposedsome toUVradiation.Theydiscovered that ratesofphotosynthesiswere150% larger insamples not exposed to additional UV radiation than those that were exposed.Photosynthesis being phytoplankton’s primary mechanism for energy aquisition,photosynthetic inhibition leaves phytoplankton populations susceptible to increasingUVexposure.Arcticwhalesdonotdirectlyfeedonphytoplankton.Thebowheadwhalefeedsonvastquantitiesofzooplankton,whilebelugasandnarwhalsfeedonamultitudeofArcticfish and marine invertebrate species. However, since phytoplankton forms the base ofmarine food chains, zooplankton andwhaleswill be facedwith a reduced food supply ifphytoplanktonpopulationscollapseduetohigherUVexposure.

3.Invasivespecies

Retreating Arctic ice cover is allowing seasonally migrant species to extend their rangenorthward(MooreandHuntington,2008;SimmondsandEliott,2009).AstudybyMooreand Huntington (2008) focuses on assessing the impacts of climate change on Arcticmarinemammals.Theirreviewaddressesthemigrationofsubarcticspeciesasathreattothe specializedmarine Arctic species. To this end, they surveyedmultiple sources fromother peer-reviewed studies to personal communications with northern researchers.Helblinget al. (1996) gathered their data first-handby collecting samples and subjected

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them to different conditions. Moore and Huntington found that species like the fin(Balaenoptera physalus), minke (Balaenoptera acutorostrata), humpback (Megapteranovaeangliae), and gray (Eschrichtius robustus) whales were ranging further north inrecentyearsinareasofsubstantialdecreaseinseaiceextent.Duetoincreasingmeltperiodlength, thesemigrant speciesmay be able to remain at higher latitudes for an extendedperiodof time, thus increasing the impactof food competition. Laidreet al. (2008) statefurtherthat, inadditiontothespecieslistedabove,theblue(Balaenopteramusculus)andpilot(Globicephalamelas)whalesarealsousingtheArcticasfeedinggrounds.Theypredictthesespecieswill range furthernorthatearlier timesof theyeardue to theearliermeltperiods.

Cetaceansarenottheonlyspeciestoextendtheirrangenorthward.SeveralhundredfishspeciesarealsomigratingtowardstheArctic.AstudybyJonesandCheung(2015)appliedspecies distributionsmodels in order to predict future population shifts of 802 fish andinvertebrate speciesunderclimatechangescenarios.Thesemethodsdiffer from those inMooreandHuntington(2008)andHelblingetal.(1996)astheyusepredictionmodelstodrawtheirconclusions,withoutrelyingonfirst-handsamplingorpersonalcommuniqués.Theyfoundthatareasathigherlatitudes,suchastheArcticOcean,weremoresusceptibleto larger-scale fish immigration than other regions. Figure 2 demonstrates the averageinvasion and extinction intensities of fish species between the years 2000 to 2050 atvarying latitudes according to two prediction models. In this case, “invasion” refers toimmigrationand“extinction”referstoemigrationoffishspecies.Bothmodelsanticipateasignificant increase in fish invasion in northern latitudes and in fish extinction near theequator. These trends suggest that temperate fish species aremigrating northward andenteringtheformerlyisolatedArcticecosystem.

This “invasion” could be considered a benefit to the Arctic ecosystem by increasingbiodiversity,butinvadingfishspeciescouldposeastruggleforresourceswithexistingice-associated species and alter predator-prey relationships (Simmonds and Eliott, 2009;McLeish, 2013).Moreover,manyof the fish species selected for the study are sought bycommercial fisheries.Therefore,ashiftof fishpopulations to theArcticwould lead toanequal northward shift in commercial fishing fleets (Simmonds and Eliott, 2009). Anorthward fishing fleet shift increases the susceptibility of Arctic cetaceans toanthropogenic threats,suchasacousticpollution,bycatch, fishinggearentanglementandshipstrikes(SimmondsandEliott,2009;McLeish,2013).

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Figure2:Averagelatitudinalinvasionandextinctionintensityforevery0.5°latitudebetween2000 and 2050 under (a) low-emissions and (b) high-emissions climate change scenarios.Bluelinesindicatetheaverageinvasionintensityandredlinesindicatetheaverageextinctionintensity.Theshadedareas indicateconfidence intervalsat1standarddeviation(JonesandCheung,2015).

4.Killerwhalepredation

Seaicefunctionsasanaturalphysicalbarrieragainstkillerwhale(Orcinusorca)predationonArcticcetaceans.Killerwhales,althoughconsideredan invasivespecies,arediscussedseparately due to the direct impacts of their presence in the Arctic on Arctic endemiccetaceans.Overthepastcentury,killerwhaleshavebeenobservedmorefrequentlyintheeastern Canadian Arctic (ECA) as sea ice cover decreases (Higdon and Ferguson, 2009).Killer whales are renowned top predators, capable of creating trophic cascades andalteringentiremarineecosystemsviatop-downcontrol(HigdonandFerguson,2009).Anecosystem isdesignatedunder top-downcontrolwhena toppredatordirectly influencestheabundanceoflowertrophiclevels.Theresultofstrongtop-downcontrolcanbetrophiccascades, which are a reduction in abundance of lower trophic organisms due to heavypredation.

Higdon and Ferguson’s study (2009) examined the relationship between ice cover andkillerwhalesightings.Theyconsultedwithnorthernresearchersandlocalsandsurveyedavailable literature on killer whale sightings over the last century in the ECA. Thesemethods resemble those used in Moore and Huntington (2008) as they review otherstudies’ findings in order to draw new conclusions. However, they additionally usetraditional Inuit knowledge to gather information on killer whale sightings. The studyfoundaclearnegativecorrelationbetweeniceconcentrationandkillerwhalesightingsinthe ECA. As seen in Figures 3 and 4, killerwhale sightings increase exponentially as iceconcentration decreases over the decades. Consequently, as ice extent continues to

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decrease over the coming years, killer whales will undoubtedly continue a northwardprogression. Thismigration poses a direct threat to Arctic-endemic cetacean species, askillerwhaleshavebeenknowntopreyonbelugas,bowheads,andnarwhalsalike(Higdonand Ferguson, 2009; Darnis et al., 2012). The results from the previous studymay alsoexplain the increase in proportion of bowhead whales with killer whale-inflicted rakemarks(Reinhartetal.,2013).DeadlyattackshavealsobeenreportedonArcticwhales.Inone case in Admiralty Inlet, a killer whale attack caused the death of approximately 4narwhals in 6 hours (Laidreet al., 2006).Another attack atKakiakPoint resulted in thedeathofayoungbowheadwhale(Laidreetal.,2006).Theseoccurrencesdemonstratetheimpact killer whales are already having on the Arctic whale species. More deadlyencounterswillundoubtedlyfollowifkillerwhalescontinueanorthwardprogression.

As for other invasive species, it can be argued that the introduction of killerwhales canincrease biodiversity in the Arctic ecosystem. However, killer whales are recognizedthreats to Arctic endemic whales due to their renowned hunting abilities. As discussedabove, killerwhaleshave alreadybeenknown to attack andkill all three kindsofArcticwhalesalike.Additionally,theirabilityastop-downcontrollerstoinfluenceabundancesinlowertrophiclevelsalsoposesalong-termthreattotheviabilityoftheentireecosystem.Anyshort-termgainsinbiodiversitythatmayariseafterkillerwhales’introductionwouldbeoffsetbylossesinthebiodiversityofArcticendemicspecies.

Figure3:Numberofkillerwhale sightingsperdecadeduring the20thcentury for the fourregions in the ECA. The black trendline represents an exponential curve (Higdon andFerguson,2009).

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Figure4:Median ice concentrationaverages (%) for the regionsofwestern (WHS), central(CHS)andeastern(EHS)HudsonStraitfrom1902to2004(HigdonandFerguson,2009).

5.Conclusion

ThepurposeofthisreviewwastosummarizeimportantinformationonArcticseaiceandArctic whales in order to determinewhat effects changes in sea ice will have on Arcticendemiccetaceans.Arcticseaiceextentisdeterminedtoberapidlydecreasing.Near-freesummerseaiceconditionshavebeenpredictedfor2040(Hollandetal.,2006).TheiceisthefoundationforlifeintheharshArcticenvironment(Laidreetal.,2008),andchangesinthisfoundationwillsignificantlyalterthebalanceoftheentireecosystem.

ThisreviewdemonstratedthatendemicArcticwhaleswillfacenumerousthreatstotheirsurvivalasaresultofthedecreaseinseaiceextent.Increasesinkillerwhalesightingsinareas of decreased ice density in Arctic waters have been observed by Higdon andFerguson(2009).Throughtop-downcontrol, theyhave theability tobecometheArctic’snext apex predator (Darnis et al., 2012) and thus endanger the populations of all threespecies of Arcticwhales, such as belugas, bowheadwhales, andnarwhals. IncreasingUVabsorption as a result of decreasing Arctic albedo (Bais et al., 2015) impacts cetaceansthroughskinlesions(Martinez-Levasseuretal.,2013)andareducedfoodsupply(Helblinget al., 1996). Decreasing ice extent also allows for northward migrations of subarcticcetacean species (Laidre et al., 2008; Moore and Huntington, 2008) and multiplecommercially important fish species (Jones and Cheung, 2015). These species invasionsmay create a competition over food with endemic Arctic cetaceans (Laidre et al., 2008;Moore and Huntington, 2008) as well as attract commercial fishing fleets to the Arctic,therebyincreasinganthropogenicthreats.

Theseimpactswillonlybecomeaccentuatedastheseaicemeltsfurther,nearingthezero-ice extentmark. Althoughmarinemammal species have previously adapted to dramaticenvironmentalchanges,theincreasedrateofchangecastsdoubtonthefutureviabilityof

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thethreeArcticspecies(SimmondsandEliott,2009).Moreresearchisneededtoascertainthecombinedimpactofindividualfactorsofincreasedicemeltonice-associatedcetaceanstodeterminethewhales’viabilityinafutureoflowiceextent.Tothisend,therelationshipbetweenthewhalesandtheicemustbeclearlydefinedsoastoknowhowdependentthecetaceansareonthiskeyphysicalhabitatfeature(Laidreetal.,2008).Futurestudiescoulduse acousticmonitoring devices to detectwhales over long periods of timewithout theneed for costly expeditions. The studies could also use traditional knowledge to gatherinformationonwhalesightingsandsea iceconditionsover time.Thesestudiesmayhelpcreate better conservation policies for Arctic whales and the Arctic environment as awhole.

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