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Assignment of nesting loggerhead turtles to their foraging areas in the Northwest Atlantic using stable isotopes
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Title: Assignment of nesting loggerhead turtles to their foraging areas in the Northwest Atlantic using stable isotopes
Series Title: Pajuelo, M., K. A. Bjorndal, K. J. Reich, H. B. Vander Zanden, L. A. Hawkes, and A. B. Bolten. 2012. Assignment of nesting loggerhead turtles to their foraging areas in the Northwest Atlantic using stable isotopes. Ecosphere 3(10):89. http://dx.doi.org/10.1890/ES12-00220.1
Physical Description: Journal Article
Creator: Pajuelo, Mariela
Publisher: Ecological Society of America
Place of Publication: Ecosphere
Publication Date: 19 October 2012
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Abstract: Differential foraging area use can affect population demographics of highly migratory fauna because of differential environmental changes and anthropogenic threats among those areas. Thus, identification of foraging areas is vital for the development of effective management strategies for endangered migratory species. In this study, we assigned 375 loggerhead turtles (Caretta caretta) nesting at six locations along the east coast of the United States to their foraging areas in the Northwest Atlantic (NWA) using carbon and nitrogen stable isotope values (δ13C and δ15N). We first evaluated the epidermis δ13C and δ15N values from 60 adult loggerheads with known foraging grounds. Twenty-two females from 6 nesting beaches and 23 males from one breeding area were tracked with satellite transmitters to identify their foraging locations following breeding, and 15 adult turtles were sampled at one foraging ground. Significant trends were observed between both δ13C and δ15N values of satellite-tracked loggerheads and the latitude of the foraging grounds to which the turtles migrated, reflecting a geographic pattern in the stable isotope values. Both δ13C and δ15N values characterized three geographic areas—with distinct abiotic and biotic features—used by adult loggerheads in the NWA. Discriminant analysis assigned all 375 female loggerheads to one of the three foraging areas; 91% were assigned with probabilities of ≥ 80%. The proportion of nesting turtles using each foraging ground varied geographically; most turtles nesting in northern beaches (72-80%) tend to forage at higher latitudes while most turtles nesting in southern beaches (46-81%) tend to forage at lower latitudes. Stable isotopes can reveal the foraging location of loggerhead turtles in the NWA, which will allow robust analyses of foraging ground effects on demography and improve the design of management strategies for the conservation of loggerhead populations. The conclusions and methods developed in this study are also relevant for other populations of sea turtles and for other highly migratory species.
Acquisition: Collected for University of Florida's Institutional Repository by the UFIR Self-Submittal tool. Submitted by Mariela Pajuelo.
Publication Status: Published
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Source Institution: University of Florida Institutional Repository
Holding Location: University of Florida
Rights Management: Applicable rights reserved.
System ID: IR00001331:00001

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Assignmentofnestingloggerheadturtlestotheirforagingareas intheNorthwestAtlanticusingstableisotopes M ARIELA P AJUELO 1, K AREN A.B JORNDAL 1 K IMBERLY J.R EICH 1 H ANNAH B.V ANDER Z ANDEN 1 L UCY A.H AWKES 2,3 AND A LAN B.B OLTEN 1 1 ArchieCarrCenterforSeaTurtleResearchandDepartmentofBiology,UniversityofFlorida,Gainesville,Florida32611USA 2 BangorUniversity,SchoolofBiologicalSciences,BrambellLaboratories,Bangor,GwyneddLL572UWUnitedKingdom 3 UniversityofExeter,CollegeofLifeandEnvironmentalSciences,TremoughCampus, Penryn,CornwallTR109EZUnitedKingdom Citation: Pajuelo,M.,K.A.Bjorndal,K.J.Reich,H.B.VanderZanden,L.A.Hawkes,andA.B.Bolten.2012.Assignment ofnestingloggerheadturtlestotheirforagingareasintheNorthwestAtlanticusingstableisotopes.Ecosphere3(10):89. http://dx.doi.org/10.1890/ES12-00220.1 Abstract. Differentialforagingareausecanaffectpopulationdemographicsofhighlymigratoryfauna becauseofdifferentialenvironmentalchangesandanthropogenicthreatsamongthoseareas.Thus, identificationofforagingareasisvitalforthedevelopmentofeffectivemanagementstrategiesfor endangeredmigratoryspecies.Inthisstudy,weassigned375loggerheadturtles( Carettacaretta )nestingatsix locationsalongtheeastcoastoftheUnitedStatestotheirforagingareasintheNorthwestAtlantic(NWA) usingcarbonandnitrogenstableisotopevalues( d 13 Cand d 15 N).Wefirstevaluatedtheepidermis d 13 Cand d 15 Nvaluesfrom60adultloggerheadswithknownforaginggrounds.Twenty-twofemalesfrom6nesting beachesand23malesfromonebreedingareaweretrackedwithsatellitetransmitterstoidentifytheir foraginglocationsfollowingbreeding,and15adultturtlesweresampledatoneforagingground.Significant trendswereobservedbetweenboth d 13 Cand d 15 Nvaluesofsatellite-trackedloggerheadsandthelatitudeof theforaginggroundstowhichtheturtlesmigrated,reflectingageographicpatterninthestableisotope values.Both d 13 Cand d 15 Nvaluescharacterizedthreegeographicareaswithdistinctabioticandbiotic featuresusedbyadultloggerheadsintheNWA.Discriminantanalysisassignedall375femaleloggerheads tooneofthethreeforagingareas;91 % wereassignedwithprobabilitiesof 80 % .Theproportionofnesting turtlesusingeachforaginggroundvariedgeographically;mostturtlesnestinginnorthernbeaches(7280 % ) tendtoforageathigherlatitudeswhilemostturtlesnestinginsouthernbeaches(4681 % )tendtoforageat lowerlatitudes.StableisotopescanrevealtheforaginglocationofloggerheadturtlesintheNWA,whichwill allowrobustanalysesofforaginggroundeffectsondemographyandimprovethedesignofmanagement strategiesfortheconservationofloggerheadpopulations.Theconclusionsandmethodsdevelopedinthis studyarealsorelevantforotherpopulationsofseaturtlesandforotherhighlymigratoryspecies. Keywords: Carettacaretta ; d 15 N; d 13 C;foragingarea;loggerheadturtles,Mid-AtlanticBight;NorthwestAtlantic; satellitetelemetry;SouthAtlanticBight;stableisotopes. Received 18July2012;revised25September2012;accepted27September2012; published 19October2012. CorrespondingEditor:D.P.C.Peters. Copyright: 2012Pajueloetal.Thisisanopen-accessarticledistributedunderthetermsoftheCreativeCommons AttributionLicense,whichpermitsrestricteduse,distribution,andreproductioninanymedium,providedtheoriginal authorandsourcesarecredited. E-mail: mpajuelo@ufl.edu I NTRODUCTION Forendangeredmigratoryfauna,knowledge ofdemographicparametersiskeytoaccurately assessthestatusandtrendsofpopulations(Esler 2000,NationalResearchCouncil2010,Wallaceet al.2010).Becausevaluesofdemographicparameterscanvarywithenvironmentalconditionsat v www.esajournals.org 1 October2012 v Volume3(10) v Article89

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theforaginghabitats(Coochetal.2001,Chaloupkaetal.2008,Sabaetal.2008),information onmovementpatternsandforaginglocationsof populationsareofcrucialimportance. Populationsoftheloggerheadseaturtle( Carettacaretta )nestingintheNorthwestAtlantic (NWA)representoneofthemajornesting aggregationsforthespeciesintheworld(Ehrhart etal.2003).NWAloggerheadnestingaggregationsarecomposedofgeneticallyanddemographicallydistinctpopulations(Encaladaetal. 1998;Shamblinetal., inpress ).Loggerheads swimhundredsofkilometersfromawiderange offoraginggroundstotheirnestingbeaches. Concernwasraisedwhennestingactivityinone oftheseNWApopulationsdeclinedmarkedly from1998to2007(Witheringtonetal.2009); however,anincreaseinnestingnumbershas beenreportedinrecentyears(VanHoutanand Halley2011).Anthropogenicthreats(Jacksonet al.2001,Witheringtonetal.2009,Finkbeineret al.2011)andchangingoceanographicconditions (Chaloupkaetal.2008,Sabaetal.2008,Van HoutanandHalley2011)havebeenproposedas themaindriversoffluctuationsinseaturtle abundance.Becausethesefactorsmaychange dependingongeographiclocation(Kotetal. 2010andreferencestherein),effortstoidentify foraginggroundsofseaturtlesarevitalto understandspatialandtemporalfluctuationsin nestingnumbers. Tobetterunderstandhowenvironmental changesandhumanthreatsatdifferentforaging groundsaffectthevariousnestingpopulationsin theNWA,itisimportanttoevaluatenotonlythe demographicparametersofeachbreedingpopulationbutalsotheproportionsoffemalesin eachbreedingpopulationlocatedindifferent foragingareas.Initialeffortshavebeenundertakentounderstandhowdifferentialforaging locationsandoceanographicconditionsaffect demographicparameterssuchasclutchsize, numberofclutchespernestingseason,clutch sexratio,andfemalebodysizeinloggerhead populations(Hataseetal.2002,Hawkesetal. 2007 a b ,Zbindenetal.2011,Baileyetal.2012). Satellitetelemetrystudieshaverevealedthat NWAadultfemaleloggerheadshaveatleasttwo differentmigrationpatterns(seasonalshuttling migrationandyear-roundresidency)whenthey leavethenestingbeachesandreturntotheir foragingareas.Femalesmaytravelupto hundredsofkilometersandforageincoastal areasalongtheU.S.Atlanticcoast,Gulfof Mexico,Cuba,andtheBahamas(Plotkinand Spotila2002,DoddandByles2003,Foleyetal. 2008,Hawkesetal.2007 a ,2011).Theyalsoshow sitefidelitytotheirforagingareas,characterized bydifferentenvironmentalfeatures(Hawkeset al.2007 a ,2011),thusrevealingpatternsof migratoryconnectivitybetweennestingsites, foragingareas,andwinteringareas. Stableisotopeanalysis,atechniquethatuses ratiosofstableisotopesofnaturallyoccurring elements(e.g.,carbon,nitrogen),cancomplement informationfromsatellitetelemetryonpopulation connectivity(Websteretal.2002).Becausestable isotopesintheenvironmentareincorporatedinto primaryproducersandthentransferredupthe foodchain(DeNiroandEpstein1978,Minagawa andWada1984),theisotopicvaluesoftissuesof highertrophiclevelorganismsreflectdifferences inthestableisotopevaluesofprimaryproducers oftheenvironmentinwhichtheseorganisms foraged(Schelletal.1989,MinamiandOgi1997, BurtonandKoch1999,KurleandWorthy2002, CherelandHobson2007,Pajueloetal.2010). Thesespatialisotopicdifferencesinprimary producerscreateisotopicallydistinctregionsthat canbeusedtoinferresidencyandmovement patternsoforganismsmigratingamongthem (RubensteinandHobson2004,Grahametal. 2010).Withinanor ganism,differenttissues incorporateandturnoverstableisotopesat differentrates.Inseaturtles,epidermis,keratin, andredbloodcellsreflectalonger-termforaging history(Reichetal.2008).Therefore,suchtissues collectedforturtlesatbreedingareasreflecttheir dietaryhistoryatforaginggroundspriorto migrationtothebreedingarea(Wallaceetal. 2006,Cautetal.2008,Reichetal.2010,Vander Zandenetal.2010,Zbindenetal.2011,Pajueloet al.2012,Seminoffetal.2012). Stableisotopevaluesofanimalscanbeusedto identifytheirforagingareasif(1)different foragingareasareisotopicallydistinctand(2) sampledtissuesreflecttheisotopicsignaturesof theforaginggrounds(RubensteinandHobson 2004).Theserequirementsaremetforadult loggerheadsintheNWAandhavebeendemonstratedforadultmales(Pajueloetal.2012).Male loggerheadsshowdifferencesintheirstable v www.esajournals.org 2 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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isotopevaluesreflectingtheuseofthreegeographicareas:theMid-AtlanticBight(MAB),the SouthAtlanticBight(SAB),andthesubtropical NWA(SNWA)(Pajueloetal.2012;Fig.1),which representwell-establishedbiogeographicregions withdistinctivebioticandabioticfeatures (Hutchins1947,Wilkinsonetal.2009).Moreover, basedonsatellitetelemetry,adultmalesappear touseforaginggroundssimilartothoseofadult femalesintheNWA(Arendtetal.2012).The largevariationin d 13 Cand d 15 Nvaluesfrom nestingloggerheadsinFlorida,USA(Reichetal. 2010)issimilartothatobservedinthesatellitetrackedmaleloggerheads(Fig.1),andprobably representsagradientofnorthtosouthforaging locationsusedbyadultfemaleloggerheadsinthe NWA. Themainobjectiveofourstudywastoassign loggerheadseaturtlesnestingalongtheU.S. Atlanticcoasttotheirforaginglocationsinthe NWAusingstableisotopeanalysis.First,we evaluatedwhethersatellite-trackedadultfemale loggerheadshavethesamerelationshipbetween geographicareasandstableisotopevaluesas adultmales.Second,wecharacterizedthegeographicareasusedbyadultloggerheadswith isotopicvaluesofsatellite-trackedadultloggerheadsandadditionalturtleswithknownforaginglocations.Then,wecomparedtheisotopic valuesofnestingturtlesnotfittedwithsatellite transmitterswiththoseofadultloggerheadswith knownforaginglocationtodeterminetheir foragingareasbasedonassignmentsfrom discriminantanalysis.Finally,weestimatedthe proportionofeachnestingpopulationforaging ineachgeographicarea.Bycombiningstable isotopeanalysisandsatellitetelemetrytoidentify foraginglocationsofbreedingpopulations,we canthenrelyonstableisotopeanalysisaloneto assignlargenumbersoffemaleloggerheadsto theirforaginggroundsrapidlyandatlowcost. Thisknowledgewillallowustoassesswith robustsamplesizeshowdifferentenvironmental factorsandthreatsatthedifferentforaging Fig.1.Distributionofstableisotoperatios( d 13 Cand d 15 N)ofadultmale( n 25)andfemale( n 310) loggerheadsintheNorthwestAtlantic(NWA).Maleloggerheads(blacksymbols)arecodedbytheforagingarea usedbasedonsatellitetelemetry:Mid-AtlanticBight(MAB),SouthAtlanticBight(SAB),SubtropicalNorthwest Atlantic(SNWA).TwomaleturtlesthatusedcoastalwatersoftheGulfofMexico(GoM)arealsoshown.Female data(opencircles)arefromReichetal.(2010)andweresampledatvariousnestingbeachesinFlorida;maledata arefromPajueloetal.(2012).Therightpaneldepictsthemaingeographicareasusedbyadultmaleloggerheads intheNWAandtheGulfofMexico. v www.esajournals.org 3 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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groundsaffectthedemographyofadultloggerheadsintheNWAandfocusmanagementand conservationeffortsappropriately. M ATERIALAND M ETHODS Dataandsamplecollection Epidermissampleswerecollectedfrom87 adultfemaleloggerheadturtlesduringthe2004 and2005nestingseasons(MayJul)atsixnesting areas(Table1;Fig.2):BaldHeadIslandinNorth Carolina(BHI;33.86 8 N,77.99 8 W),andWassaw (WAS;31.84 8 N,80.98 8 W),Blackbeard(BLA; 31.61 8 N,81.14 8 W),Sapelo(SAP;31.40 8 N,81.28 8 W),Jekyll(JEK;31.07 8 N,81.42 8 W),and Cumberland(CUM;30.85 8 N,81.45 8 W)Islands inGeorgia.Additionally,15adult-sizeturtles (curvedcarapacelength,CCL 84cm)were sampledatoneforagingareainFloridaBay, Florida(24.08 8 N,81.03 8 W)inMarchandJune 2011(Table1;Fig.2).Previouslypublished isotopicdatafromepidermissamplesofadult femaleloggerheadscollectedatfournesting areasinFlorida( n 310;Reichetal.2010)and adultmaleloggerheadscollectedatonebreeding areainFlorida( n 23;Pajueloetal.2012)were alsoincludedinthisstudy(Table1;Fig.2). Allepidermissampleswerecollectedusinga6 mmbiopsypunchandstoredin70 % ethanolat roomtemperatureuntildriedat60 8 Cpriorto samplepreparationandanalysis.Epidermis samplesreflecttheturtle sdietaryhistoryovera longperiodoftime(i.e.,upto4months)based onstudiesconductedonjuvenileloggerheads (Reichetal.2008).Anevenlongerforaging historyisprobableinadultloggerheadsbecause ratesofisotopicincorporationslowwithreduced growthrates(Reichetal.2008)andincreasing bodymass(CarletonandMart nezdelRio2005). Twenty-twofemaleturtleswerefittedwith satellitetransmittersafterclutchdepositionin Georgia( n 18)andNorthCarolina( n 4) beaches(Table1).Hawkesetal.(2007 a ,2011) characterizedthedistinctmovementpatternsof theseadultfemaleloggerheadsandclassified themintotwogroups,(1)turtleswithseasonal migrationbetweensummerandwintercoastal areasand(2)turtleswithmigrationtoyearroundforagingareas.Wegroupedturtlesinto threegroupsaccordingtothecoastalregionto wheretheymigrated:thefirstgroupistheMAB turtles,withseasonalmigrationbetweensummer foragingareasintheMABandwinteringareasin theSAB;thesecondandthirdgroupsaretheSAB Table1.Location(state,breeding/foragingarea,andlatitude),yearofcollection,andsamplesizeofepidermis samplesfromadultloggerheadturtleswithknownandunknownforaginggroundsusedinthisstudy. AreaLatitude( 8 N)Year n Foragingarea Isotopedatasource Known Unknown Breedingarea NorthCarolina BaldHeadIsland33.920041046Thisstudy Georgia20051212Thisstudy WassawIsland31.820054747Thisstudy BlackbeardIsland31.6200544Thisstudy SapeloIsland31.4200422Thisstudy 200588Thisstudy JekyllIsland31.1200433Thisstudy CumberlandIsland30.9200411Thisstudy Florida CanaveralNationalSeashore28.820034444Reichetal.2010 20043131Reichetal.2010 MelbourneBeach28.120036060Reichetal.2010 20044646Reichetal.2010 JunoBeach26.920034141Reichetal.2010 20044141Reichetal.2010 BrowardCounty26.220034747Reichetal.2010 PortCanaveral28.42006072323Pajueloetal.2012 Foragingarea Florida FloridaBay25.020111515Thisstudy Total43560375 TurtlesfittedwithsatellitetransmittersexceptforturtlessampledatFloridaBay. v www.esajournals.org 4 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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andSNWAturtles,withmigrationtoyear-round foragingareasinwatersoftheSABandSNWA, respectively.Turtlesweretrackedfor344.2 6 148.4days(mean 6 SD)(individuals58,4043, 4952,and5463;Hawkesetal.2011:TableS1). Mostoftheturtles( n 19)weretrackedforthe entireforagingperiodforturtlesusingMAB waters,andfor6monthsormoreattheforaging groundforturtlesusingSABandSNWAwaters. Theremainingturtlesweretrackedforaperiod of80daysormoreafterreachingtheforaging ground.Telemetrydatawerefilteredfollowing Hawkesetal.(2011)toretainlocationclasses3,2, 1andA,andturninganglesgreaterthan25 8 ,and thelatitudeofthecentroidoftheforaging ground(arithmeticmeanofallthefiltered locationpointsfromtheforagingground)was usedtoevaluatetherelationshipbetweenstable isotopevaluesandgeographiclocation. Stableisotopevaluesofepidermissamples fromsatellite-trackedfemaleturtles( n 22)were usedtocharacterizethethreegeographicareas usedbyadultloggerheads,assumingthatisotopicvaluesfromforagingareasusedpriorto nestingreflectedthoseusedpost-nesting(identifiedbysatellitetelemetry),asadultfemale loggerheadsareknowntoexhibitsitefidelityto foragingareas(Hawkesetal.2007 a ,2011,Vander Zandenetal.2010).Also,becausetheisotopic valuesofsatellite-trackedmaleloggerheadshave shownageographicpatternconsistentwiththe useofthethreegeographicareasmentioned above(Pajueloetal.2012),maledata( n 23) wereincorporatedintheisotopiccharacterizationofthethreegeographicareasusedbyadult loggerheads.FewsatellitetrackedturtlesmigratedtotheSNWA,soweincludedadditional epidermissamplesfromadult-sizeloggerheads collectedatoneforaginggroundintheSNWA (FloridaBay; n 15). Finally,weusedtheisotopicvaluesfrom epidermissamplesofnestingturtlesnotfitted Fig.2.Mapshowingthelocationsofthesixnestingareasandsingleforagingground(filledsymbols)sampled inthisstudy:BaldHeadIsland(BHI),WassawIsland(WAS),SapeloIsland(SAP),BlackbeardIsland(BLA), JekyllIsland(JEK),CumberlandIsland(CUM),andFloridaBay(FLBay).NestingareassampledintheReichet al.(2010)study(opensymbols)arealsoshown:CanaveralNationalSeashore(CNS),MelbourneBeach(MEL), JunoBeach(JUN),andBrowardCounty(BRO). v www.esajournals.org 5 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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withsatellitetransmittersfromBHIinNorth Carolina( n 18)andWASinGeorgia( n 47),in combinationwithpublishedisotopicdatafrom nestingturtlesatfournestingareasinFlorida( n 310;Reichetal.2010)(Table1),tocompareto thoseofturtleswithknownforaginggroundto assignthemtooneofthethreegeographicareas usedbyadultloggerheadsintheNWA. Samplepreparationandanalysis Epidermissampleswerewashedwithdeionizedwaterandwipedwithisopropylalcoholto removeepibiontsandextraneousparticles.The outermostlayeroftheturtleepidermiswas separatedfromtheunderlyingtissue,finely dicedwithascalpelblade,anddriedat60 8 C for24h.Lipidswereextractedfromsamples withpetroleumetherusinganASE300acceleratedsolventextractor(Dionex). Forstableisotopeanalysis,0.50.6mgofeach samplewasweighedandsealedinatincapsule. Sampleswereanalyzedfor d 13 Cand d 15 Nratios bycombustioninaCOSTECHECS4010elementalanalyzerinterfacedviaaConFloIIIdevicetoa DeltaPlusXLisotoperatiomassspectrometer (ThermoFisherScientific)intheStableIsotope GeochemistryLabattheUniversityofFlorida, Gainesville.Resultsarepresentedasstable isotoperatiosofasamplerelativetoaninternationalstandardandreportedintheconventional d notation: d X [( R sample / R standard ) # 1] 3 1000, where d X istherelativeabundanceof 13 Cor 15 N inthesampleexpressedinpartsperthousand ( % ); R sample and R standard aretheratiosofheavy tolightisotope( 13 C/ 12 Cand 15 N/ 14 N)inthe sampleandinternationalstandard,respectively. Thestandardusedfor 13 CwasViennaPeeDee Belemniteandfor 15 NwasatmosphericN 2 .The referencematerialUSGS40(L-glutamicacid)( n 22)wasusedtonormalizeallresults,SD 0.05 % and0.13 % for d 13 Cand d 15 N,respectively. Statisticalanalyses Theeffectofgeographiclocationon d 13 Cand d 15 NvalueswasevaluatedwithaSpearmanrank correlationtestbetweenisotopevaluesandthe latitudesoftheforaginggroundsoftheadult femaleturtles. Todeterminethesimilarityoftheisotopic valuesofsamplesfromturtlesofunknown foragingground(hereafterreferredtoasunknownturtles)tothoseofsamplesfromturtlesof knownforaginglocation(hereafterreferredtoas knownturtles),weclassifiedtheisotopicvalues ofknownturtlesintothreegroups:MAB,SAB, andSNWA.Multivariateanalysisofvariance (MANOVA)wasusedtotestforvariationin d 13 C and d 15 Nvaluesamonggroupstotestifthey werequantitativelydiscrete.Then,thesethree isotopicallydefinedgroupswerecombinedwith theunknownturtlesinaquadraticdiscriminant analysis,duetounequalvarianceamonggroups. Thediscriminantanalysisassignedeachunknownturtletothegeographicareaforwhich ithadthehighestprobabilityofmembership.To testtheaccuracyofassignment,weappliedthe leave-one-outcrossvalidationmethodtothe referencegroups,whereasingleturtleis removedfromthetotalandclassifiedtoa foragingregionbythefunctionsderivedfrom allturtlesotherthantheexcludedturtle,withthe processbeingrepeatedforeachremainingturtle. Followingthedeterminationofgeographic areaforunknownturtles,weevaluatedthe populationstructureofallbreedingpopulations usingonlyturtlesassignedtooneofthethree groupswith 80 % probabilityofgroupmembership(Rocqueetal.2006,Seminoffetal.2012) (340outof375turtles).Finally,achi-squaretest wasperformedtotestforinter-annualvariation intheproportionofturtlesusingdifferent foraginggroundsfornestingbeachesthatwere sampledintwoconsecutiveyears,whenever samplesizeallowed(i.e.,CNS,MEL,andJUN beaches;Table1).Alldatawereanalyzedusing programR(RDevelopmentCoreTeam2011) withan a levelof0.05. R ESULTS Epidermisisotopicvaluesofadultfemalesin theNWArangedfrom3.5to18.7 % and # 6.9to # 17.6 % for d 15 Nand d 13 C,respectively(Fig.3). Theepidermalisotopevaluesfromsatellitetrackedfemaleloggerheads(trackedlongenough toidentifytheirforagingareas)revealeda geographicpattern:femalesthatmigratednorth toseasonalforaginggroundsintheMAB(e.g., NewJersey,Virginia,andDelaware)afterthe nestingseasonhadhigh d 15 Nvaluesandlow d 13 Cvalues(Fig.3).Thelowest d 15 Nvalueand highest d 13 Cvaluewerefoundinafemalethat v www.esajournals.org 6 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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migratedsouthtoayear-roundforagingground intheSNWA(TheBahamas)(Fig.3).Intermediate d 15 Nand d 13 Cvalueswerefoundinturtles migratingtocoastalwatersoftheSAB(e.g., GeorgiaandnorthernFlorida)(Fig.3).A significantnegativecorrelationwasfoundbetween d 13 Cvaluesandthelatitudetowhich femalesmigratedafterthenestingseason(Spearman srankcorrelation r s "# 0.64, n 22, P 0.001;Fig.4A),whileasignificantpositive correlationwasfoundbetween d 15 Nvaluesand latitude(Spearman srankcorrelation r s 0.46, n 22, P 0.029;Fig.4B). Stableisotopevaluesofepidermisfromadult loggerheadmalesandfemalesusingthesame geographicareasweresimilar.Eventhoughthree satellite-trackedturtleshadisotopicvaluesthat werenotconsistentwiththegeographicareato whichtheymigrated(turtles1,2,and3;Fig.5A), wefoundsignificantdifferencesincombined d 13 Cand d 15 Nvaluesamonggeographicareas usedbyadultloggerheadsintheNWA(MANOVA, F 29.32, P 0.001).Theisotopic signaturesofthesethreegroupswereusedasa referencefromwhichtocomparetheisotopic valuesofunknownturtles.Discriminantanalysis assignedallunknownturtlestooneofthethree geographicareaswith91 % (340out375)ofthose turtlesassignedtoauniquegeographicareawith aprobability 80 % ofgroupmembership(Table 2;Fig.5B).Thepercentagesofturtlesassignedat higherprobabilitieswerelowerbutremained substantial:85and79 % withaprobability 90 and95 % ,respectively.Leave-one-outcrossvalidationrevealeda6 % ( n 4)misclassification rate,whichcorrespondedtothemisclassification ofturtles1,2,3,andanadditionalturtle. Unknownturtlesassignedwith 80 % probabilitytoageographicareawereusedtoevaluatethe foragingstructureofbreedingpopulations.A latitudinaltrendintheforagingareauseby nestingloggerheadswasrevealed;theproportion ofturtlesusingtheMABincreasedfromsouthto northandtheproportionusingtheSNWA increasedfromnorthtosouth(Fig.6).The majorityofturtles(7280 % )nestingathigher Fig.3.Stableisotoperatios( d 13 Cand d 15 N)ofadultfemaleloggerheadsintheNorthwestAtlantic.Females trackedwithsatellitetelemetry( n 22;blackfilledsymbols)weresampledduringnestingseasonsin2004and 2005atBaldHeadIsland,SapeloIsland,BlackbeardIsland,JekyllIsland,andCumberlandIsland,andare groupedbasedonthegeographicareatowhichtheymigratedafterthenestingseason:Mid-AtlanticBight (MAB),SouthAtlanticBight(SAB),orSubtropicalNorthwestAtlantic(SNWA).Additionalfemalessampled (greyfilledcircles)inthisstudyandfemalessampledintheReichetal.(2010)study(opencircles)ofunknown foraginglocationarealsoshown. v www.esajournals.org 7 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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latitudes(i.e.,BHIandWI)usedforagingareasin theMABandfewturtles(6 % )usedtheSNWA (Fig.6).Mostturtles(4681 % )nestingatlower latitudes(i.e.,JunoBeachandBrowardCounty) usedtheSNWAandfew(221 % )usedtheMAB (Fig.6).Alargenumber(3659 % )ofnesting turtlesfromCNSusedtheSAB.Theuseofthe SABdeclinednorthandsouthofCNS(Fig.6). Theproportionofturtlesusingthedifferent foragingareasvariedbetweenyearsinCNS (Pearson schi-squaretest,df 2, v 2 11.51, P 0.003),MEL(Pearson schi-squaretest,df 2, v 2 11.39, P 0.003),andJUN(Pearson schi-square test,df 2, v 2 22.70, P 0.001)beaches(Fig.6). Amarkedpatterninthereductioninthe proportionofturtlesusingMABwatersandthe increaseofturtlesusingSNWAwaterswas observedinMELandJUNin2004(Fig.6). D ISCUSSION Isotopiccharacterizationofthegeographic areasusedbyadultloggerheadsintheNWA Inthisstudy,acombinationofstableisotope Fig.4.Relationshipbetween(A)carbon( d 13 C)and(B)nitrogen( d 15 N)stableisotopevaluesofadultfemale loggerheads( n 22)andthelatitude( 8 N)towhichtheymigratedafterthenestingseason.Spearmanrank correlationissignificantforboth d 13 C( r s "# 0.64, P 0.002)and d 15 Nvalues( r s 0.46, P 0.029).Geographic regionsintheNorthwestAtlantic:Mid-AtlanticBight(MAB),SouthAtlanticBight(SAB),andSubtropical NorthwestAtlantic(SNWA)areshownunderthex-axisseparatedbydottedlines.Dashedlinesdenotetrend lines. v www.esajournals.org 8 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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andsatellite-telemetrydataallowedustocharacterizethreemaingeographicregionsusedby adultloggerheadsintheNWA(Fig.5A).Recent studieshaveintegratedtelemetrydatatovalidate marinegeographicpatternsin d 13 Cor d 15 N valuesofhighlymigratoryanimalssuchas seabirds(Jaegeretal.2010)andseaturtles (Seminoffetal.2012)overbroadspatialscales (e.g.,withinoceanbasins).Here,wepresentthe combined d 13 Cand d 15 Nspatialcharacterization forahighlymigratoryanimalataregionalscale intheNWA. Isotopicturnoverinepidermissamplesof adultloggerheadturtlesisestimatedtobeat least4months(see Introduction ),longerthanthe expectedmigrationperiodbetweentheforaging Fig.5.(A)Stableisotoperatiosofcarbon( d 13 C)andnitrogen( d 15 N)ofadultloggerheadturtleswithknown foraginglocation( n 60)showingthreegroupsrepresentingthethreegeographicareasusedbyadult loggerheadsintheNorthwestAtlantic:Mid-AtlanticBight(MAB)SouthAtlanticBight(SAB),andSubtropical NorthwestAtlantic(SNWA).Theisotopicvaluesofturtles1,2,and3fellwithinagroupthatdidnotcorrespond totheforaginglocationasobservedthroughsatellitetelemetry.Combined d 13 Cand d 15 Nvalueswere significantlydifferentamonggroups(MANOVA, F 29.62, P 0.001).(B)Stableisotoperatiosofcarbon( d 13 C) andnitrogen( d 15 N)of375adultfemaleloggerheadturtlesofunknownforagingground.Symbols(sameas above)indicatethegeographicareatowhicheachindividualunknownfemaleturtlewasassignedbythe discriminantanalysis.Turtlesassignedwithaprobability 80 % ofgroupmembershipareshownasfilled symbols( n 340).Opensymbolsrepresentadditionalturtlesassignedwithaprobability 80 % ofgroup membership( n 35). v www.esajournals.org 9 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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Table2.Assignmentofadultfemaleloggerheadsofunknownforaginglocationtoageographicareawith 80 % probabilityofgroupmembership.Valuesinparenthesesareadditionalturtlesassignedwithaprobability 80 % ofgroupmembership. NestingareaLatitude( 8 N) n Geographicarea MABSABSNWA NorthCarolina BaldHeadIsland,BHI33.91810(2)3(2)1 Georgia WassawIsland,WAS31.84731(3)6(5)2 Florida CanaveralNationalSeashore,CNS28.8751034(5)25(1) MelbourneBeach,MEL28.110613(2)37(2)50(2) JunoBeach,JUN26.982916(6)50(1) BrowardCounty,BRO26.247114(3)28(1) Total37574(7)110(23)156(5) Note: Abbreviationsare:MAB:Mid-AtlanticBight,SAB:SouthAtlanticBight,SNWA:SubtropicalNorthwestAtlantic. Fig.6.BreedingpopulationstructureaccordingtoforagingareausedbyloggerheadsnestingalongtheU.S. Atlanticcoastasdeterminedthroughdiscriminantanalysisusingcarbonandnitrogenstableisotopevaluesof adultloggerheadturtleswithknownforaginggroundsasreferencedata.ForagingareasareMid-AtlanticBight (MAB;whitefill),SouthAtlanticBight(SAB;greyfill),andtheSubtropicalNorthwestAtlantic(SNWA;blackfill). NestingturtlesfromBaldHeadIsland(BHI)andWassawIsland(WAS)weresampledin20042005and2005 nestingseasons,respectively.Floridanestingturtlesweresampledin2003and2004nestingseasons;resultsfrom nestingseason2003areshowninthemainmap.Insetshowsresultsfrom2004forCanaveralNationalSeashore (CNS),Melbourne(MEL),andJuno(JUN)beaches.BROisBrowardCountybeaches.Theproportionofturtles usingthedifferentgeographicareasvariedbetweenyearsforCNS,MELandJUNbeaches(seetextforstatistics). Theboundariesofthethreegeographicareas:MAB,SAB,andSNWAaredepictedbydottedlines. v www.esajournals.org 10 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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areaandbreedinggroundforasatellite-tracked turtleusedinthisstudy( ; 1month,basedon meantraveldurationbetweennestingareaand foraginggroundsandbetweenforagingand winteringgrounds;Hawkesetal.2011;L. Hawkes, unpublisheddata ).Thus,isotopicvalues ofepidermistissuesfromnestingloggerheads shouldreflectthatoftheforaginggroundsused priortomigratingtothenestingbeaches. Satellite-trackednestingloggerheadsdemonstratedageographicpatterninthestableisotope values(Fig.3)similartotheonepreviously observedinsatellite-trackedmaleloggerhead turtles(Fig.1;Pajueloetal.2012).Althoughthe MABturtlesusewatersofboththeMAB (summer)andSAB(winter),theymaintain distinctstableisotopevaluesfromthoseofturtles thatusewatersintheSAByear-round.The differencecouldresultfromveryslowturnover ratesinepidermisofadultturtles.Also,Hawkes etal.(2007 a )suggestedthatseasonalturtles(i.e., MABturtles)thatmigratesouthintoSABareas duringwintermightundergofastingduringpart ofthewinter.Ithasbeenproposedthat d 15 N valuesmightincreasewithfastingduration (Mart nezdelRioetal.2009).Becausetheextent oftheenrichmentin d 15 Nappearstobetissuedependent,thishypothesishasreceivedmixed support(Mart nezdelRioetal.2009)and remainstobetestedinseaturtles. Nestingloggerheadturtlescanbeassignedto theircoastalforagingareasintheNWAusing stableisotopevaluesbecauseNWAadultfemale turtlesshowfidelitytotheirforaginggrounds bothwithinandbetweenyears(Hawkesetal. 2007 a ,2011),ashasbeenobservedinother loggerheadpopulations(Brodericketal.2007, Schofieldetal.2010,Thomsonetal.2012). However,someNWAturtleshavebeenfound tooccasionallyuseoceanicwaters(Hawkesetal. 2007 a ,2011),whichmayresultinunusualstable isotopevalues.Theisotopicvaluesofthree turtles(1,2,and3;Fig.5A)didnotcorrespond tothegeographicareatowhichtheymigrated afterthebreedingseason.Themostlikely explanationisthattheseturtlesdidnotreturn tothesamegeographicareafromwhichthey originallycame.Forexample,ifaturtleused watersoftheSABpriortoitscaptureinthe nestingbeachandlatermigratedtowatersinthe MAB,itsisotopicvalueswouldshowlower d 15 N andhigher d 13 Cvaluesthanwouldbeexpected foraturtleusingMABwaters(e.g.,turtle2;Fig. 5A).Althoughadultturtlesaregenerallysitefixedtotheirforaginggrounds,occasionalshifts canbeexpected. Thedistinctbioticandabioticcharacteristicsof thethreegeographicareasusedbyloggerheadsMAB,SAB,andSNWAlikelyinfluence isotopicvaluesofturtlesusingthoseareas.High anthropogenicinputappearstoraisethe d 15 N valuesofprimaryproducersintheMAB (McKinneyetal.2010).Also,highratesof denitrification,whichalsoraisebaseline d 15 N values,havebeenreportedintheMAB(Fennelet al.2006)althoughitseffectonthe d 15 Ncoastal biotahasnotbeenassessedyet(McKinneyetal. 2010).Inaddition,therateofnitrogenfixation, whichlowersthe d 15 Nvaluesofprimary producers,ishighestintheSNWA(Montoyaet al.2002).Available d 15 Nvaluesofparticulate organicmatter(aproxyforprimaryproducers) alongthelatitudinalgradientusedbyloggerheadsrevealthispattern:nitrogenstableisotope ratiosrangefrom7.2to7.7 % innear-shore watersoffofVirginiaandDelawareinthe MAB(McKinneyetal.2010),from4.0to6.4 % innear-shorewatersoffofSouthCarolinaand GeorgiaintheSAB(M.PajueloandM.Arendt, unpublisheddata ),andfrom # 0.9to3.6 % in FloridaBayintheSNWA(Mackoetal.1984, BehringerandButler2006,LambandSwart 2008). Watertemperaturecanalsoaffect d 13 Cvalues atthebaseofthefoodwebbyaffectingcell growthrateanddissolvedcarbonateconcentration,whichhaveadirecteffectonthe d 13 Cvalues ofprimaryproducers(MacKenzieetal.2011). SeasurfacetemperaturesintheMABduring summertheseasonwhenadultloggerheads mainlyuseMABwatersrangefrom1527 8 C, whilewatertemperaturesintheSNWArange from22.528 8 Cyearround(Wilkinsonetal. 2009).WatersintheSNWAarealsocharacterized bythepresenceofextensiveseagrasscommunities(Wilkinsonetal.2009),whosecontributionto benthicfoodwebsmaybeevidencedbyrelativelylow d 13 Cvaluesinfoodweborganisms (Fryetal.1982).Ultimately,variationinbaseline isotopicvalueswillbereflectedinhighertrophic levelorganismssuchasNWAadultloggerheads, whichpreymainlyonbenthicinvertebratesin v www.esajournals.org 11 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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coastalwaters(Hopkins-Murphyetal.2003). StableisotopevaluesofotherfoodweborganismsintheNWAexhibitapatternsimilartothat ofadultloggerheadturtles(Pajueloetal.2012) andindicatethatbaselinedifferencesratherthan trophicleveldifferencesaredrivingthelarge isotopicvariationinadultloggerheadturtles. WhileturtlesusingtheMABandSNWAhave distinctstableisotopevalues(Fig.5A),Pajueloet al.(2012)foundthatisotopicvaluesfrommale turtlesusingtheSABweresimilartothoseof turtlesusingcoastalwatersintheGulfofMexico (whichwerenotincludedinouranalysis)(Fig. 1).Becauseweareinterestedindeterminingthe foraginglocationsofloggerheadsnestingalong theU.S.Atlanticcoast,weneedtoconsiderthat adultfemaleturtlesuseforagingareasinregions otherthantheNWA.Telemetrystudieshave revealedthatadultfemaleloggerheadsnestingin Floridabeachesusecoastalwatersinboththe NWAandtheGulfofMexico(Foleyetal.2008). Therefore,theisotopicvaluesreflectingtheuseof watersintheSABforturtlesfromsouthern nestingbeachesmaybeconfoundedwiththose ofturtlesusingwatersintheGulfofMexico. Othermarkers,suchastraceelementsandlead stableisotopes,mayhelpdifferentiatethesetwo foragingareaswithsimilar d 13 Cand d 15 N signatures(M.Lo pez-Castro, personalcommunication ). Inthisstudy,wechosetodefinethethree loggerheadgeographicforaginggroundsinthe NWAbasedontheknowledgethatthese representwell-establishedbiogeographicregions,eachofwhichshowsdistinctoceanographicconditionsand faunalcommunities (Hutchins1947,Wilkinsonetal.2009).Because stableisotopesmaybeinfluencedbyfactors(see above)thatvaryamongthebiogeographicareas, wewereabletofindsignificantdifferencesinthe stableisotopevaluesofturtlesamongthesethree areas.However,withinaparticularforaging ground,stableisotopevaluesofloggerheads canvaryduetodifferencesinhabitattypeand/ ordiet(RubensteinandHobson2004).Thus,to identifyfeedingareasatafinerscalethantheone presentedherewilllikelyrequiretheuseof additionalbiomarkers(e.g.,traceelements). Foraginglocationsofadultfemale loggerheadsintheNWA Formanyyears,muchofwhatwasknown abouttheforaginglocationsofadultfemale loggerheadsintheNWAreliedoninformation fromflippertagreturns(BellandRichardson 1978,Meylanetal.1983,WilliamsandFrick 2008).Whileinformative,tagreturndatacanbe biasedbecausethesedatamainlyrelyonthe captureofflippertaggedturtlesbyfisheries.In recentyears,satellitetransmittershavebeen deployedonnestingloggerheads,whichhave providedmoreaccurateinformationonthepostnestingmigratoryroutes,locationofforaging grounds,andfeedingbehaviorofadultfemale loggerheadsintheNWA(Godleyetal.2008). However,theexpenseofsatellitetags,which limitsthenumberofindividualsthatcanbe tracked,haspreventedmorewidespreaduse. Thus,stableisotopeanalysis,whichislowcost andcanyieldresultsrapidly,canbeusefulin identifyingforagingareasofalargenumberof individuals. Carbonandnitrogenstableisotopesallowed ustoassignmostnestingloggerheadstoa distinctgeographicareaintheNWAata probabilityof 80 % .Theremainingturtles assignedtoanareawithaprobabilityof 80 % donotsuggestthattheyuseunidentified foraginglocations.Becausewefoundalatitudinaltrendinboth d 13 Cand d 15 NalongtheNWA (Fig.4),webelievethatthoseforaginglocations arefoundwithinoneofthethreegeographic areasintheNWA.Wecouldnotassignallturtles withaprobability 80 % probablyasaresultof isotopicvariationwithineachofthethree geographicareasthatwasnotcapturedbythe satellite-trackedturtles,orbecausetheytravelled totheGulfofMexico. Wefoundthatnestingloggerheadsshowed geographicsegregationofforaginggrounds; northernnestingturtlespreferredhigherlatitude foragingareaswhiletheoppositewasseenin southernnestingturtles.Thus,ourinitialobservationsrevealedthatfemaleloggerheadsinthe NWAgenerallyuseforagingareasinthevicinity oftheirnatalnestingbeaches.Theseresultsare consistentwithsatellitetelemetrydatafrom nestingloggerheadsintheNWA.Forturtles nestinginNorthCarolina,SouthCarolina,and Georgia,Hawkesetal.(2011)revealedthatmost v www.esajournals.org 12 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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females( n 48)migratednorthtoseasonal foraginggroundsintheMAB,whilefew( n 18) movetoyear-roundwatersoftheSABand SNWAafterthenestingseason.Similarly,based onsmallersamplesizes,DoddandByles(2003) andFoleyetal.(2008)revealedthatnesting turtlesfromsouthernbeachesinFloridamigratedtowatersintheSNWAandrarelymigratedto northernwatersintheMAB. Theuseofforaginggroundsadjacenttonatal nestingareashasbeensuggestedpreviouslyfor largejuvenileloggerheadsintheNWAbymixed stockanalysisofmitochondrialDNAhaplotypes foraggregationsofjuvenilesalongtheU.S.east coast(Bowenetal.2004).Thestableisotope approachusedinourstudyallowedustosample adultfemaleloggerheadsatvariousnesting areaswheretheyaremoreeasilyaccessible withouthavingtosampleturtlesatthedifferent foragingareastorevealasimilarpatternof foraginggroundsegregation.MixedstockanalysisofmitochondrialDNAhaplotypeshasbeen widelyusedtoassessthecontributionofvarious nestingareastofeedinggrounds(Bolkeretal. 2007).Becausethistechniquereliesondifferentialhaplotypefrequenciesatthevariousnesting areas,eachnestingindividualcannotbeassigned toitsforagingground.Theexistenceofhabitatspecificstableisotopesignaturesallowsstable isotopeanalysistoassigneachindividualtoits foragingarea(RubensteinandHobson2004). Thus,geographicassignmentmodelsinsea turtlesmaybeimprovedbyincorporating traditionaltoolssuchasgeneticanalyses,markrecapturedata,andsatellitetelemetryalongwith stableisotopeanalysestounderstandtheconnectionbetweennestingareasandforaging grounds. Thetemporalvariationintheproportionof turtlesusingdifferentgeographicareaswithin threeFloridanestingbeaches,CNS,MELand JUN,suggestsdifferentialremigrationintervals mayexist(i.e.,theperiodoftimebetween reproductiveseasons)amongforagingsubpopulations.Giventhegreaterdistancethatturtles foraginginMABwaterstraveltoreachsouthern beaches,theremaybedifferentialremigration intervalsfortheseturtleswithinasouthern nestingpopulation.Adultfemaleturtlesthat forageinhighlyproductivewatersoftheMAB duringsummerareknowntomigratetotheSAB duringwintermonths(Hawkesetal.2007 a ). AnotherpossibilityisthatturtlesusingMAB watersseasonallymayspendmoreenergy undergoingseasonalmigration(Hawkesetal. 2007 a ),whichmaybereflectedinlongerremigrationintervals.Hawkesetal.(2007 a ),basedon asmallsamplesizeoffemalesfromanorthern nestingbeachinNorthCarolina,didnotfind differencesinremigrationintervals(andother fecunditymeasures)betweenfemalesusing seasonalforagingareasintheMAB( n 9) versusyearroundareasintheSABandSNWA( n 3),suggestingthatneitherdifferentialforaging/ migratorystrategieswithinthisnorthernbreedingpopulationwasmoreadvantageous(Hawkes etal.2007 a ).However,femalesusingMAB watersintheHawkesetal.(2007 a )studywere closertotheirnorthernnestingbeach.Recently, variationsinreproductiveoutputanddemographyduetointer-basindifferencesinfeedingand movementbehaviorhavebeenreportedin leatherbackturtles(Baileyetal.2012).Further researchisneededtoassesswhetherthepattern observedinnorthernnestingloggerheadsis consistentwithalargersamplesizeandin differentnestingpopulations. Ourstudyincorporatedpreviouslypublished stableisotopevaluesofepidermisfromadult femaleloggerheadsnestinginFloridabeaches fromReichetal.(2010).Additionally,Vander Zandenetal.(2010)collectedscute(carapace keratin)fromasubsampleoftheseloggerheads toinvestigatethelong-termconsistencyin resourceusethroughstableisotopeanalysisof scutelayers.Bothstudiessuggestedthatlarge differencesin d 13 Cand d 15 Nobservedcouldbe accountedforbyforaginglocation(Reichetal. 2010,VanderZandenetal.2010).Inthisstudy, weconfirmedthatstableisotopevaluesoffemale loggerheadsintheNWAreflecttheirforaging locationsbyground-truthingstableisotopevalueswithinformationobtainedthroughsatellite telemetry.Themuchgreaternumberoffemales thatcanbeassignedtoforaginggroundsbased onstableisotopeanalysisthanonsatellite telemetrywillallowrobustanalysesofforaging groundeffectsondemographicparameterssuch asnumberofeggsperclutch,numberofclutches depositedduringanestingseason,andremigrationintervals,whicharecriticaltounderstand trendsinseaturtlenestingpopulations(National v www.esajournals.org 13 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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ResearchCouncil2010). Conservationimplications Inordertoeffectivelymanagepopulationsof highlymigratoryendangeredspecies,anunderstandingofspatio-temporaldistributionisessential.Intheparticularcaseofadultloggerhead populationsintheNWAthatusewatersovera widegeographicrange,knowingwhichfeeding areasamajornestingpopulationprimarilyuses isimportant,becauseitallowsmanagerstofocus conservationeffortswhereappropriate. Adultfemaleloggerheadpopulationssegregateamongforaginggrounds,whichispromisingforrefiningmanagementstrategies.Wecan identify,atalargescale,whatareasaremoreor lessimportantforaparticularnestingpopulation intheNWA.Forexample,inthisstudywe identifiedthatforagingareasintheSNWAare highlyimportantforturtlesnestinginFlorida beaches,followedbyareasintheSAB;while areasintheMABareusedtoalesserdegree. Fisheriesbycatchisoneofthemajorthreatsfor loggerheadturtlesintheNWA(Boltenetal. 2010).ResearchonseaturtlebycatchhasrevealedspatialandtemporalvariationsinloggerheadbycatchinU.S.fisheries(Kotetal.2010, Finkbeineretal.2011 ),withshrimptrawl fisheriesintheSAB,SNWAandGulfofMexico accountingforthemostinteractionswithloggerheadturtlesintheU.S.(Finkbeineretal.2011). Thus,effortscanbefocusedintheSABand SNWAtoassesshowfisheriesinteraction,aswell asotherenvironmentalfactorssuchaschanging oceanographicconditionsandpreydistribution, impactfecunditymeasuresofFloridanesting populations.Additionally,wecanfurtherour understandingofhowthesethreatsandfactors drivethetemporalfluctuationsintheproportion ofindividualswithineachnestingpopulation thatusethedifferentforagingareas.However, morenortherlyandlesserusedforagingareas maycurrentlybeimportant,regardingconservationefforts,becausetheyareusedbysmalleror moreat-risknestingpopulations.Theseforaging areasmaybecomeevenmoreimportantinthe future,ifsouthernturtlepopulationswereto shiftnorthward,assuggestedunderfuture climatescenarios(i.e.,ifsouthernbeachesbecometoohot;Hawkesetal.2007 b ). Organicpollutantsareanotheranthropogenic threattowhichturtlesareexposedintheNWA (Alavaetal.2011andreferencestherein).Recent researchrevealedthatadultloggerheadsusing northernforaginggroundsintheMABhave higherconcentrationsoforganicpollutantsthan turtlesthatusewatersoffcentralFlorida,andour resultssupportthehypothesisthatthismaybe duetospatialstructuringofforaginggroundsby population(Raglandetal.2011).Similarly,a recentstudyfoundthatloggerheadeggslaidina northernnestingbeachinNorthCarolinahad higherorganicconcentrationofpollutantsthan eggslaidinsouthernnestingbeachesinFlorida (Alavaetal.2011).Thesedifferentialthreatscan alsoaffectdemographicparametersandhealthof theforagingsubpopulationsandshouldalsobe consideredinmanagementplans. Conclusions Ourstudydemonstratesthatstableisotope analysiscanbeusedparsimoniouslytoidentify foragingareasofadultloggerheadsintheNWA ataregionalscale.Futureresearchisneededto assessifstableisotopeanalyses,perhapsintegratedwithotherbiomarkerssuchastrace elements,couldidentifyforagingareasatafiner scale.Additionally,wefoundthatadultfemale loggerheadsnestingalongtheU.S.Atlanticcoast tendtouseforagingareasclosertotheirnatal nestingbeaches;asmallerproportionofindividualsundertakemigrationstodistantforaging grounds.Theseresultsareusefulforthedesign ofmanagementstrategiesfortheconservationof loggerheadturtlepopulationsintheNWA. Assignmentoflargenumbersofnestingfemales toforaginggroundswithstableisotopeanalysis willallowfutureresearchtoexploretheeffectsof foraginggroundlocationondemographicparameters.Theconclusionsandmethodsdevelopedinthisstudyarealsorelevantforother populationsofseaturtlesandforotherhighly migratoryspecies. A CKNOWLEDGMENTS Wethankallthepeoplewhocollectedsamplesfor uswithoutwhomthisstudywouldnothavebeen possible:M.GodfreyforsamplecollectionatBald HeadIsland,NorthCarolina;M.Dodd,M.Frick,and K.WilliamsforsamplecollectioninGeorgia;andB. Schroeder,A.Foley,andB.Witheringtonforsample collectionatFloridaBay,Florida.TheNationalFish v www.esajournals.org 14 October2012 v Volume3(10) v Article89 PAJUELOETAL.

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