OvervIew Of The ecOLOgy Of The Bras d’Or Lakes wITh

OvervIew Of The ecOLOgy Of The Bras d’Or LakeswITh eMphasIs On The fIsh

TIMOTHYC.LAMBERTMarine Fish Division

Fisheries and Oceans CanadaBedford Institute of Oceanography

Dartmouth, Nova Scotia

InthisreviewofbiologicalresearchintheBrasd’OrLakes,groundfishtrawlsurveysfrom1952,1967and1999/2000arecomparedandchangesinabundanceanddistributionofmajorgroundfishspeciesarenoted.Themostcommonspecieswerewinterflounder(Pseudopleronectes americanus)andcod(Gadus morhua).Thebiggestchangeoverthenearly50yearspanoftheseinvestigationswasintheabundanceofAmericanplaice(Hippoglossoides platessoides)whichusedtobeverycommonintheLakesbutwererareinrecentsurveys.TheLakescontainatleastone,andprobablytwo,residentpopulationsofcodandarehometoapopulationofspring-spawningherring.TheuniquenatureoftheBrasd’OrLakesisemphasizedinrelationtothediversityofspeciestheycontain.Glacialrelicts,survivorssincethelasticeage,canbefoundwithinafewkilometresofwarmtemperatespecies,persisting since the ‘climaticoptimum’.TheLakesare ideally suited for ecosystemstudies, for inadditiontotheiruniquebiology,theyarereadilyaccessibleandcanbeeasilysampledonadailybasis.

CedocumentpasseenrevuelesrecherchesbiologiqueseffectuéesparlepassédansleslacsBrasd’Oretprésentelesrésultatsd’étudesrécentesetencours.Nouscomparonslesrelevésdupoissondefondréalisésen1952,en1967eten1999/2000ennotantleschangementsdansl’abondanceetlarépartitiondesprincipalesespècesdepoissondefond.Danstouscesrelevés,lesespèceslespluscourantesétaientlaplierouge(Pseudopleronectes americanus)etlamorue(Gadus morhua).Leplusimportantchangementobservésurles50ansquecouvrentcesétudesatouchélapliecanadienne(Hippoglossoides platessoides),quel’ontrouvaittrèscourammentdansleslacsparlepassémaisquiétaitraredanslesrelevésrécents.Leslacscontiennentaumoinsuneetprobablementdeuxpopulationsrésidantesdemorueetunepopulationdeharengquifraieauprintemps.Ledocumentmetl’accentsurlarelationentrelanatureparticulièredeslacsBrasd’Oretladiversitédesespècesqu’ilsabritent.Desespècesreliquesdel’âgeglaciaireyviventàquelqueskilomètresd’espècescaractéristiquesd’unclimattempéréchaudquipersistentdepuislapériodederéchauffementmédiéval.Leslacsseprêtentparfaitementàdesétudesécosystémiques,car,enplusd’êtreuniquessurleplanbiologique,ilssontfacilesd’accès,etonpeutaisémentyeffectuerdeséchantillonnagesquotidiens.

Introduction

ManypeoplearesurprisedtolearnthattheBrasd’OrLakesarenotactuallylakesintheusualsenseoftheword,thatis,abodyoffreshwater.Atfirstencountertheyhaveeveryappearanceoflakes,beingborderedbylowmountainstothewestandrollinghillstotheeastand,unlikethenearbyocean,appeartohavenotide.However,atasteofthewaterandanexaminationofthefishcaughtbyyoungstersoffadockwillquicklydispelthisfirstimpression.Thewaterisdistinctlysaltyandthefishonthedockwillprobablybeacunner(seaperch),codorevenamackerel.Thisinlandsea,oneofCanada’sscenichighlights,sustainsanecosystemwhichisuniqueinmanyrespects.TheBrasd’OrLakesaresituatedinCapeBretonIslandatthenorthernendofNova

Scotia.Thisbodyofwaterofabout1,100km2isessentiallyanenclosedestuarywiththreeoutletstothesea.TheGreatBrasd’OrChannelandtheLittleBrasd’OrChannelconnectwithSydneyBighttothenorth,andSt.Peter’sCanalgivesaccesstoCheda-buctoBaytothesouth(Fig1).OnlytheGreatBrasd’OrChannelislargeenoughtopermitanysignificantexchangeofwater.TheBrasd’OrLakeswatershedisabout2500km2;thisareaaddedtothatoftheLakesthemselvesgivesatotalcatchmentareaof3600km2(Krauel,1976).

PROC.N.S.INST.SCI.(2002)Volume42,Part1,pp.65-99.

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Inputfromsixriversandrestrictedaccesstotheoceankeepssalinityintherangeof20to26,whereas,seawaterjustoutsidetheLakesinSydneyBightrangesfromabout28to32.TheLakesareusuallyicecoveredinthewinterandsurfacewatersoftenexceed20oCinthelatesummer,particularlyinsmaller,shallowbays(PetrieandBugden,2002).ThewatersoftheBrasd’OrLakesarecharacterisedbyatwo-layersystem;alow

salinitysurfacelayerwhichhasawideannualrangeintemperatureandalowerlayer

Fig 1 MapoftheBrasd’OrLakesindicatingplacesmentionedinthetext.

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ofhighersalinityinwhichtemperaturerangeismuchlesspronounced.Ingeneral,surfacewatermovestowardtheentranceoftheLakesandoutintoSydneyBightandisreplacedwithoutsideoceanicwaterwhichenterstheLakesnearthebottomandflowsunderneaththesurfacelayer(Krauel,1976;PetrieandBugden,2002).Withtheexceptionofrestrictedchannels,thereislittlemixingbetweentheselayersexceptforwintermonthswhenhigherwindsandwaveactiondisruptthestabilityofthissystem.Insomeareaswherecurrentsandexchangeratesareverylow,theamountofdissolvedoxygencanbecomequitedepressedandinWhycocomaghBay,anoxic(nooxygen)conditionsexist(PetrieandBugden,2002;StrainandYeats,2002).Awiderangeofhabitats,withbottomtypesrangingfromrockythroughgraveland

sandtomud,canbefound.Theseincludemarshyflats,“barachois”(small,shallowpond-likeembayments,moreorlesscutofffromthemainlakebyasandbar),bays,inletsofvariousdepths (somewell-flushedandothersanoxic),deepbasinsandatrenchabout280m,adepthmatchedonlybeyondtheedgeofthecontinentalshelf.GiventhediversityofhabitatsitisnotsurprisingtofindthattheBrasd’OrLakesarehometoawidevarietyofmarinelife.ThespecieswithintheLakesare,ingeneral,characteristicofthoseoccurringalongNovaScotia’sAtlanticcoast.However,theBrasd’Orisprobablyuniqueinthatitisalsohometobothwarmandcoldwaterspecieswhicharerareinthispartoftheworld.Ecologistsdividetheearthintoregions,whichhavecharacteristicfaunalassem-

blages,whichcanberelatedtoclimaticconditions.IntheNorthernHemisphere,thesezoogeographicalregions,rangingfromcoldwatertowarm,areArctic,boreal,temperateandtropical.Theboundariesbetweentheseregionsarenotdistinctandarc-tic-borealandboreal-temperatebordersinthewesternNorthAtlantictendtofluctuateaccordingtotheseason;transitionzonesbetweenzoogeographicalareasarebroad.NovaScotiaisintheborealregion,whichroughlyextendsfromsouth-eastLabradorinthenorthtoCapeCodinthesouth(Ekman,1953).Althoughadistinctassemblageofanimalsdominatesthiszone,ArcticspeciesareintermittentlycarriedsouthintotheborealzonebytheLabradorCurrent,andconversely,temperateandevensubtropicalspeciesareregularlycarriedfarnorthoftheirnormalrangesbytheGulfStream.Mostobviousofthesetransientvisitorsarepelagiccreaturessuchasthesunfishandseaturtle.Lessnoticedbecauseoftheirsmallersize,butmorecommon,areplanktonictransients.Insummary,thereisnosmooth,transitionofnorthernspeciestosouthernspeciesinthisareaoftheworld(BousfieldandThomas1975).ManyofthefishintheBrasd’OrLakesareresidentthereandmostaredemersalor

bottomliving.Migratorypelagic(livinginsurfaceandmid-waters)species,suchasmackerel,herringandsalmon,areseasonalvisitorstotheLakes.Speciesthatdo,ordid,supportcommercialfisheriesarewinterflounderandherring.Thewinterfloun-derfisheryendedin1992withthebarringofcommercialdraggersfromtheLakes(MacIsaac,2001),andthespringherringfisherywasstoppedin1999becauseoftheimminentcollapseofthestock,mostlikelyduetooverfishing.Cod,mackerel,smelt,andeelsupportlimitedrecreationalfishing.SomeinvertebratesfishedintheBrasd’OrLakesarelobsters,oysters,scallopsand

rockcrab.LobstersarefishedinmostrockyareasthroughouttheLakesbutpresentlandingsarepoor,whichmaybea resultofoverfishingorbecauseofpoor larvalsurvival resulting from reduced salinity (Tremblay, 2002). Scallop and rock crabfishingislimitedtoasmallareaatthenorthendoftheGreatBrasd’OrChannelim-mediatelyadjacenttoSydneyBight.Here,thehighersalinitybottomwaterenteringtheLakesfromtheBightissaltyenoughtosupportthese2species,butprobablynotfartherintotheLakes,sinceitbecomesprogressivelydilutedbylowsalinityLakes’

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water.Oysters,oncecommonthroughouttheBrasd’OrLakes,havebeenseriouslydepletedonpublicbedsduetooverharvesting(Dennis,2001)andarenowfoundinquantityonlyatleasesites,wheretheyformthebasisofanimportantandgrowingaquacultureindustry.Thepresenceofthegreencrab,arecentlyintroducednon-nativespecies,isofgreatconcernsinceitisknowntofeedvoraciouslyonjuvenilebivalvemolluscssuchasclamsandoysters(Tremblay,2002).RainbowtroutandsalmonarealsofarmedintheLakes.DespitetheculturalandeconomicimportanceoftheBrasd’OrLakestoCapeBreton

Island,andtheiraccessibility,wehavebutarudimentaryknowledgeoftheirbiology.However,thelimitedresearchthathasbeencarriedoutdoesseemtoindicatethattheLakesareunique,atleastbiologically.TheyhavemanysimilaritieswithadjacentSydneyBight,but alsohave intriguingdifferences.Thispaperwill reviewwhat isknownoftheLakes’biology,highlightinguniqueaspects,andaswellwillexaminethegroundfishcommunity,comparingrecentsurveyworktosurveyscarriedoutover30and50yearsago.

previous studies

MuchoftheresearchconductedwithintheBrasd’OrLakesinthepastwasmotivatedbyaninterestinaquaculture.Someoftheresultsoftheseearlystudieswerepresentedataconferencein1975(McKay,1976),whereinformationonwaterchemistry(Young,1976);physicaloceanography (Krauel,1976);primaryproduction (Wright,1976);andmarinebiology(Black,1976)weregiven.Forthoseinterestedinengineeringdesignofculturesystems,theremainderoftheproceedingsareausefulreference.AdescriptionoftheBrasd’OrregionandacomprehensivebibliographyofliteraturerelatingtotheBrasd’OrLakesisbeingpreparedbyKenchingtonandCarruthers1onbehalfoftheUnama’kiInstituteofNaturalResources.

Primary Production Phytoplankton(planktonicplants)areveryimportantinmarineecosystems,fortheyarethebasefoodsourceuponwhichvirtuallyallmarinelifedepends.Geen(1965),GeenandHargrave(1966),Wright(1976)andrecentlyStrainandYeats(2002)suggestthatthelevelofphytoplanktongrowth(primaryproduction)intheLakesislow,sincenutrientinputwassmall.StrainandYeats(2002)estimatethatthecontributionofsewageandotherman-madesourcesofnutrientsisminor;although,insomelocalisedareas,suchasbarachoisandthewesternendofWhy-cocomaghBaythereissufficientbuildup,togetherwithnaturalnutrients,tocauseeutrophication(explosivegrowthofplantlifewhichchokeswaterways).Theresultinganoxicconditionskillmarineorganismsandproducesulfidesduringdecomposition.

Plankton. Thebestwaytodeterminetherangeofspeciesthatliveintheoceanistotowaplanktonnetthroughit.Manyanimalsthatliveinthesea,whethertheyarefishesorinvertebrates,orwhethertheyliveonthebottomorswimfreelyinthewatercolumn,haveaplanktonicstagethatdriftswiththecurrent.Thismaybeanegg,alarva,orboth.Thusinaplanktonsampleitispossibletofindlarvalstagesofanimalsasdiverseasfish,clams,oysters,scallops,starfish,seaurchins,marineseaworms,barnacles,crabsandlobsters.Thesearemixedwithmicroscopicanimalse.g.copepods,whoseentirelifespanisplanktonic.TheNationalMuseumofCanadaundertookaseriesofinvestigationsofthebenthos

andplanktonintheLakesduringthesummerof1981.Shih et al.(1988)directedtheir1 Anunpublisheddocument“Unamapaqt:AdescriptionoftheBrasd’Ormarineenvironment”commissioned

bytheUnama’kiEnvironmentalCommitteeoftheUnionofNovaScotiaIndians

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attentiontothecopepodfauna,tinycrustaceansthatarethefoodsourceformanylarvalfishandevensomeadultfish,whichstrainthemfromthewaterwithspecialisedgillrakers.Fifteenspeciesofcopepods(Fig2)werefound,butthesespecieswerenotevenlydistributed.Pseudocalanus minutus, Oithona similis, Temora longicornis and Tortanus discaudatuswerethemostcommonandfoundthroughouttheLakes.Brasd’OrLakehadthelowestdiversitywithvirtuallyonlythese4speciespresent.St.Andrew’sChannelhad thehighestdiversity including theonlyoccurrencesofAnomalocera opalus, Calanus finmarchicus, Calanus hyperboreus and Microcalanus pusillus(acoldwaterspeciescommonintheArctic).PlanktonsampleswerecollectedintheLakesbythefederalDepartmentofFisheries

andOceans(DFO)duringthe1990s,generallyduringMayandearlyJune.Thefocus

Fig 2 SelectedinvertebratesandfishlarvaoccurringintheLakesandmentionedinthetext.

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ofthisworkwastodeterminetimeandlocationofspawningoffishspeciesthroughcollectionofeggsandlarvae.In1991,aspartofacodeggsurveyofSydneyBight,afewtowsweremadeintheBrasd’OrLakes.Later,adedicatedsurveywasmadeoftheLakesduringMayandJuneof1996.In2000,anannualplanktonsurveywasbegunaspartofacooperativeventurebetweentheDFOandtheEskasoniFishandWildlifeCommission(EFWC).ThesamplesarebeinganalysedatEFWCandresultswillbereportedelsewhere;however,afewhighlightsoftheirichthyoplankton(larvalfish)contentbearmentioning.Themostabundantfisheggsfoundwerethoseofthefour-beardrockling(Enchelyopus cimbrius),cunner(Tautogolabrus adspersus),win-dowpaneflounder(Scophthalmusaquosus)andmackerel(Scomber scombrus).Themostcommonfishlarvaewerefour-beardrockling,winterflounder(Pseudopleuronect-es americanus),cod(Gadus morhua)andsmelt(Osmerus mordax).SomespeciesknowntofrequenttheLakeswereabsentorpoorlyrepresentedinthesamplesduetothetimingofthesurveys.CodeggsinanearlystageofdevelopmentwerescarcebecausethesurveysweretoolatetocatchthepeakofcodspawningwhichapparentlyoccursinlateFebruaryandearlyMarch;however,codlarvae(Fig2)werecommon.Ontheotherhand,thesurveysoccurredjustasmackerelwerebeginningtospawn;hencetheireggswereplentifulbutlarvaewerenot,sincefeweggshadyethatched.

Benthic Invertebrates Duringgroundfishtrawlsurveysin1951-1952(Black,1976),1967(MacDonald,1968)and1999-2000(thispaper),thepresenceofthelargerbottomdwellinginvertebrateswasdocumented.Tremblay(2002)presentsdetailsonthesespeciesandabriefoverviewofspecieshedidnotincludewillbepresentedhere.

Mysid shrimps Mysidshrimps(Fig2)liveincloseassociationwiththeoceanfloorandareanimportantfoodsourceformanybottom-feedingfish.Black(1958)studiedthesesmallshrimpsfrom3locationsintheBrasd’Or(see‘Groundfishtrawlsurveys’below).Heidentified5species,themostcommonofwhichwere Neomysis amer-icanaandMysis stenolepis.ThesetwowerefoundinallpartsoftheLakesandareborealinshoreformsthathaveawidetemperatureandsalinitytolerance.Mysis mixtaandErythrops erythrophthalmaareArctic-borealformswhichavoidwarmwaterandwerefoundinthecoldwaterofdeepareas,althoughtheymovedtoshallowerdepthsinthewinterwhensurfacewaterscooled.Thefifthspecies,Mysis oculataisatrueArcticanimalandisgenerallyfoundinshallowpolarregions.Here,atconsiderabledistancefromitsnormalhomerange,itsurvivesinthecold,deepwatersoftheLakes.

Polychaete worms FournierandPocklington(1984)identifiedmorethan70speciesofpolychaetes(marineworms)frombenthicsamplestakenfromallpartsoftheLakes(Fig2).TheGreatBrasd’OrChannelhadthegreatestnumberofspecieswith43,19ofwhichoccurredonlyintheChannel,andnotinotherareasoftheLakes.TheyrecognisedarangeofzoogeographicalaffinitiesfromwarmwatertemperatespeciesthroughborealtoArctic.St.Patrick’sChannelandWhycocomaghBayhadthepoorestrepresentationofpolychaetewormswithonly15speciesrecorded.ProbablythemostcommonpolychaetefoundthroughouttheLakeswasEuchone papillosa.Thiswormconstructsaslenderclay-walledtubewithinwhichitlives.Thesetubesoftenformdensematstowhichasmallclam,Hiatella arctica,attaches(FournierandPocklington,1984.OneoftheArctic‘relicts’foundintheLakeswasClymenura polaris,whoseoccurrencehereisthefirstrecordsouthofDavisStraitintheArctic.

Foraminifera Vilks(1967)surveyedtheforaminiferaoftheBrasd’OrLakes(Fig2).Thetinyshellsofthesemarineprotozoaformacalcareousoozewhich,overtime,canfossilizeandbecomethemajorconstituentofchalkdeposits.Foraminiferaarecloselyassociatedwithsediments,soVilksclassifiedthesedimentsoftheLakesandmappedtheirdistribution.Fromcoarsetofine,theyrangedfromboulderstoclay,withfineclays

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beingpredominantinthedeepbasinsandcoarserelementsbeingmorecommoninshallowerlocationsandareasofstrongcurrents,suchastheGreatBrasd’OrChannelandtheBarraStrait.Heidentified39speciesofforaminifera,groupsofwhichheassociatedwithspecificsedimenttypes.TheBrasd’OrLakeassemblagewasquitedif-ferentfromthatofthenorthernextremityoftheGreatBrasd’OrChannelandadjacentSydneyBight.IntheLakes,themostcommonspecieswasEggerella advena followedbyTrochammina squamataandMilliamina fusca.Onthewhole,theLakes’protozoanfaunalassemblagewasfoundtobeverysimilartothatseeninSt.Margaret’sBayandMahoneBay,southwestofHalifax.However,E. advenaandalessabundantgroupofforaminifera(Reophacidae)foundintheLakesarecommoninArcticinshorewaters.

Herring TheBrasd’OrLakesisconsideredhometoat leastonepopulationofherring since spawning takesplace there in the spring. (Byconvention,biologistshaveagreedthattheareainwhichaspeciesspawnswillberegardedasitshome).OpinionsdifferastowhethertheseherringmoveintotheLakestospawnandthenmoveoutafterwards.LimitedreturnsfromataggingprogramconductedinSydneyBight(Sinclair et al.,1980)supportthisview;threefishtaggedinSydneyBightwerecaptured inWhycocomaghBayandnearMilitiaPointandaherring tagged inSt.Ann’sBay,outsidetheLakes,wascaughtoffPipersCoveinBrasd’OrLake(Crawford et al.,1982).However,someherringmayresideinlakesastheyhavebeencaughtthereduringthewinter.Tofurthercomplicatematters,autumnspawningherringhavebeenfound(Dennyetat1998);whetherthisgroupactuallyspawnsinthelakesisnotknown.Until1999therewasaspringfisherytargetingthespawningherring;thisbeganaftericebreak-upandlastedfor3-4weeks.ThemainspawningareaswerealongthewesternshoreofWestBay,DenysBasin,St.Peter’sInletandoffEskasoni.However,inthelastfewyearsofthefisheryitwasapparentthat,withtheexceptionofalimitedareanearMalagawatch,herringhadceasedtospawnsouthoftheBarraStraitandtheonlyeggdepositionofnoteoccurredinBaddeckBay(Denny et al.,1998).Inrecentyears,mackerel,usedtraditionallyaslobsterbait,hasbecomeex-pensive;thustheuseofcheaperherringasanalternativeledtoasubstantialincreaseinitsdemand.ThesuddenincreaseinfishingeffortonthedecliningBrasd’OrLakesstockrapidlybroughtthisherringpopulationtothepointofcollapseandthefisherywasorderedclosedin1999.Crawford et al.(1982)studiedtheBrasd’OrLakesspring-spawningherringin1980

and1981.TheylookedatadultcharacteristicsandcarriedouteggandlarvalsurveysataspawninggroundinRossCovewithinWestBay.TheyfoundthattheLakesher-ringdifferedfromotherherringinanumberofcharacteristics.TheyweresmalleratagivenagethanAtlanticcoastorNorthumberlandStraitspring-spawnersanddifferedinmeristiccounts(meristicsreferstonumbersofphysicalstructures,suchasfinrays,gillrakers,andvertebrae,whichareusefulindifferentiatingpopulations).Asixyear-oldBrasd’OrLakesfemaleherringproducedabout47,500eggsandanineyear-old,about165,250. This fecunditywasonaverageabout8%higher thanthatofNorthumber-landStrait spring-spawningherring.Crawfordandhis teamnoted spawning inRossCoveinearlyAprilatdepthsofonly1/4mto3/4m;thisisoneoftheshallowestonrecordfortheAtlanticcoast.Themajority(80%)ofeggsweredepositedontheeelgrass(Zosteramarina)andmostoftheremainderonsealettuce(Ulva lactuca).Alossof85%oftheeggswasestimatedandalthoughsomeeggswereseentohavedied,themajorityofthereductionwasthoughttobeduemainlytopredationbywinterflounderandtoalesserextentcodandperhapsevengulls,whichwereseentocongregateinthearea.HerringeggsatRossCovebegantohatchonApril27andatpeakhatchingthedensity

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oflarvaeoverthespawningbedwasover4,500percubicmetreofwater.Thelarvaewereabout7mmlongathatchingandgrewatarateofabout1/4mmaday.

Seaweed. Duringthesummerof1970,McLachlanandEdelstein(1971)established45samplingstationsalongtheshoresoftheBrasd’OrLakestoobserveandcollectseaweeds.Theyfoundthatthemarinealgaewererestrictedtoanarrowbandfromtheshorelinedownto3to4mdepth.Atotalof92speciesandvarietieswereidenti-fiedintheirsurvey;31redalgae,31brownalgae,23greenalgaeand7microscopicblue-greenalgae.Nowherewasthemarineplantcoververydenseandmuchofthebottomwasunsuitableforattachmentofseaweed,beingmuddyormadeupofotherloosematerial.Onespecieshowever,whichcanrootinthistypeofunconsolidatedbottom,istheeelgrass,(Zostera marina),whichisthemostcommonmarineplantintheLakesystem.Itoccurredatallstationsandalsotendedtogrowatgreaterdepthsthanotherspecies.ThreealgalspecieswerenewrecordsforNovaScotiaandoneother,foundinSt.Andrew’sChannel,hadbeenonlyreportedfromtheSaremaandKhiumaIslandsintheformerSovietUnion.McLachlan and Edelstein (1971) recognised two seaweed associations in the

Lakes;inone,thespecieswerethesameasthoseoftheopenAtlanticcoastofCapeBreton,andintheother,thespecieswereshallowwarm-waterplantscharacteristicofprotectedbaysalongtheNorthumberlandStrait.Thefirstgroup,mostlycommonbrownseaweeds,weredominantintheGreatBrasd’OrChannelandextendedintoSt.Andrew’sChannel,WestBayandthewesternpartofEastBay.Thesespeciesincludedthecommonrockweedorbladderwrack(Fucus vesiculosus),knotweed(Ascophyl-lum nodusum),kelp(Laminaria agardii),Irishmoss(Chondrus crispus)and,similartoIrishmoss,theleafweed(Phyllophora membranifolia).TheseoceanicspeciesdiedoutasonemovedfartherintoEastBay.InSt.Peter’sInlet,thealgalfloraweresparseandresembledthatoftheupperreachesofEastBay.Onlyeelgrassandthewhip-like,smoothcordweed,(Chorda filum)werefoundthere.ThewarmwatergroupofseaweedsweredominantinSt.Patrick’sChannel,DenysBasinandNorthBasin.Thisincludedsealettuce(Ulvalactuca),thefern-likeBryopsis hypnoides,twigweed(Ah-nfeltia plicata),thecoarselybushyredseaweeds,chenilleweed(Dasya pedicellata) andgracefulredweed(Gracillaria foliifera) andthefinelybushyredseaweeds,bandedweed(Ceramium fastigiatum), roughtangleweed(Stilophera rhizodes) andslipperytangleweed(Sphaerotrichia divaricata).Uncommonmorphologicalformsofsomecommonseaweedspecieswerefoundin

theLakes.Unusualbushiness,reductionorabsenceofflotationvesiclesandcolourvariationweresomeoftheanomaliesrecorded.McLachlanandEdelsteinthoughtthewiderangeofenvironmentalconditions(temperature,salinity,lackoftidesandperhapslownutrients)intheLakesmightberesponsiblefortheseaberrantforms.

groundfish Trawl surveys

Survey methodology 1951-1952. TheFisheriesResearchBoardofCanadainves-tigatedthebiologyofthesealworm(Pseudoterranova decipiensKrabbe)from1948to1953withintheBrasd’OrLakes.AspartofthesestudiesBlack(1976)conductedtrawlsurveysintheLakesin1951(MaytotheendofDecember)and1952(MaytoAugust).Heprovidednodetailsonthetypeoffishinggearusedotherthanreferringtoitasashrimptrawl.Thirtymintowsweremaderegularlyat3stations:BaddeckBay(15-20m),WhycocomaghBay(10-30m)andKemptHead(55-75m).Inaddi-tion,afewadditionalsetsweremadealongthelengthsoftheGreatBrasd’OrandSt.Patrick’sChannelsinJuneandJulyof1952,respectively(Appendix/1).

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Survey methodology 1967. In 1967, theNova ScotiaDepartment of Fisheriescontracteda40ftcommercialfishingboattoconductatrawlsurveyoftheBrasd’OrLakes(MacDonald,1968).A3/4number35Yankeetrawlwasused.Thenethadmeshof41/2in(11.4cm)andwasfittedwitha11/8in(2.8cm)meshlinertoretainsmallfish.Thetrawlheadlinelengthwas40ft(12.2m),footropelength54ft(16.5m)andheightatmouth7ft(2.13m)(Fig3).Towingspeedwasapproximately2.5knots(4.6kmperh).BetweenSeptember20andNovember16,117towsweremadethroughoutmostoftheLakes.Towingtimevariedinlength,rangingfrom25to120minwithanaverageof75min.Setposition,depth,typeofbottomandweightoffishbyspecieswererecorded;numberoffishonlywasgivenwhenaparticularspecieswasscarce.

Fig 3 Componentsofageneralisedbottomtrawlnet.

Survey methodology1999-2000. In1999,theEFWC,DFOandthe4VnSentinelFisheryAssociation(4VnSFA),beganacooperative5yearinvestigationofthegroundfishoftheBrasd’OrLakes.Includingtrawl,longlineandichthyoplanktonsurveys,thesestudiesfocussedonthebiologyofcod.Larval,juvenileandadultpopulationsweresampledwithavarietyofgears.TheDFO’s20mCCGCNaviculacarriedoutbottomtrawlingfor4weeksduringSeptemberandOctober,andplanktonsamplinginthelatespring.A4VnSFAlonglinersetgearintheLakesonceamonth,exceptwhenpreventedbyice.Inaddition,ataggingprogramwasstartedin2000toinvestigatemovementofcodwithintheLakesandalsotodeterminewhetherthereisexchangeoffishbetweentheLakesandSydneyBight.GroundfishweresampledwithasmallfloundertrawlFig3.Theheadropeofthe

netwas50.5ft(15.4m),thefootrope(wirecoredropereinforcedwithchain)was59.5ft(18.1m),theheightofthewingattheattachmentpointtothenetis6ft(1.83m)andtheheightofthemouthopeningofthenet,10ft(3.05m).Themainmeshofthetrawlwas5in(12.7cm)andthecod-endisequippedwitha1in(2.54cm)meshlinertoretainjuvenilefish.Thetrawlwastowed1nauticalmi(1.853km)ataspeedof2.5knot(4.6

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kmperh),thusthetowdurationwasapproximately25min.Totalweight,numberandlengthfrequencieswererecordedforallspeciesoffish.Inaddition,forcodonly,otoliths(earbonesusedforageingthefish)wereextracted,maturitydeterminedandstomachcontentsandfullnessassessed.Also,thebottominvertebratefaunacapturedbythetrawlwereidentified,countedandweighed(Tremblay,2002).Watertemperatureandsalinitydatawerecollectedwithaconductivity/temperature/depth(CTD)profiler.

Comparison of surveys. Whencomparingthethreesurveys,severalpointsshouldbekeptinmind.Althoughyear-specificdataareavailableforthe1999/2000surveys,theywerecombinedand,withoneexception,noattemptwasmadetolookatannualvariation.Thisisbecausethe1967surveyrepresents1yandalthoughBlack’s(1976)earliersurveyrepresents2yofsampling,hisdataarepresentedincombinedform.Black’ssurveyislimitedingeographicalextent,whereastheother2covermostoftheLakes.Ontheotherhand,Blacksampledthreeseasons,springtoautumn,whereasthelatertwosurveyssampledonlytheautumn.The1967survey(MacDonald,1968),whichextendedtomidNovember,waslongerthanthe1999/2000one,whichend-edinmidOctober.However,60%ofthe1967setscoincidedwiththetimeperiodsampledbythe1999/2000survey.Atrawlnetistowedbehindaboatbytwocables(warps)whicharespooledontwo

drumsofalargewinch.Thesewarpsareled,onetoeachsideoftheboat,throughaseriesofpulleysandthenconnectedtotrawl‘doors’(sometimescalledotterboards).Eachofthedoorsareattachedtobridles,whichinturnfastentothewingsofthenet(Fig3).Whenfishing,theheadropeofthenet,whichisfittedwithfloats,liftsthetopofthenettherebyopeningitsmouth.Thefootrope,beinglongerthantheheadrope,dragsalongthebottominanarcbeneathandbehindtheleadingedgeofthenet;thusthetopoverhangsthebottomofthenetandpreventsanyupwardescapeoffishwhichencounterthefootrope.Thetrawldoors,angledlikekites,spreadthemouthofthetrawlastheyaretowedthroughthewater.Thewidthofthemouthofthenetisconstrainedbythelengthoftheheadrope(shorterthanthefootrope),anditsheightisafunctionofthesidewayspullofthetrawldoorsandtheupwardliftofthefloatsontheheadrope.Basedonmeasurementsandmeshsize(MacDonald,1968),thetrawlnetusedduringthe1967surveywasverysimilartothenetusedintherecentEFWC/DFOsurveys.Fishencounteringthewingsofatrawlnetareherdedtowarditscentre.Thusthe

effectivesweptareaofthebottomisgenerallyconsideredtobethedistancebetweentheouterendsofthewingsmultipliedbythedistancetowed.Unfortunately,MacDonald(1968)doesnotindicatethelengthofthewingsofthetrawlnetsheused.Therefore,inthefollowingcalculationsIhaveassumedthatthewingsofthetrawlnetsusedinthetwosurveyswerethesameandhavebasedanydifferencesonthetrawlnetbodymeasurements.Iestimatedthemouthwidthofthenetsbyrepresentingtheareaofthemouthastwobacktobackrighttriangleswhoseangledtopsapproximatetheheadropeandwhosecoincidentapexescorrespondtotheheightofthenetmouth.Theircombinedbasesformthetopofanarrowrectanglebeneath,whosespanwillbeequivalenttothewidthofthenetmouth.ThisdistanceiseasilycalculatedandindicatedthattheMacDonald(1968)trawlnetmouthwidthwasnarrower,andsohertrawlwouldhavesweptasmallerareathanthatusedinthe1999/2000surveys.Accordingly,basedonnetconfiguration,Ihaveestimatedthat,overagivendistance,thenetusedinthe1999/2000surveyswouldcatchabout1.3timesmorefishthanthatusedinthe1967survey.

75FISH ECOLOGY

MacDonald’s(1968)dataareexpressedaslbperhour.Althoughthetowingspeedislistedas2.5knots,theactualspeed-over-ground(asopposedtoboatspeedthroughthewater)whentowinganetcanvaryconsiderably.Maintainingaconstanttowingspeedrequirescontinualmonitoringofspeed-over-ground(withpositioningdevicessuchasGPS)andcontinualadjustmentofboatenginespeedtocompensateforvaryingwind,currentandtrawlnetdrag(relatedtodegreeofbottomroughness).Toillustrate,theaveragetimeforaonenauticalmiletowwithCCGCNaviculawas27min(Std.Dev.4.3min).Thelongestdurationforthisdistancewas38min,andtheshortest,20min.The1967surveyboatcarriednoelectronicnavigationalequipmentotherthanadepthsounder,soanaccuratemeansofdeterminingdistanceoftowwasnotpossible.Tocomparewith1999/2000catchrates,thoseforthe1967surveywereconvertedtokgpertowusingtowdurationandatowingspeedof2.5knotsandthenadjustedbythe1.3conversionfactor.Theseestimateswouldbesubjecttotheerrorsdiscussedabove,andalthoughthecalculatedvalueforanyspecifictowmightbeinaccurate,theaveragevalueforalltowsshouldbereasonable.Wherecertainspecieswerescarce in1967,MacDonald (1968)expressed their

quantitybynumberratherthanbyweight.Forcomparison,averageindividualspe-ciesweightswerecalculatedusing1999/2000data: theconversionweightswere;windowpaneflounder-210g,whitehake-201.3g,andyellowtailflounder-191.6g.

Trawl survey results

1951-1952 Black(1976)lists22speciesfoundduringhisinvestigation(TableI).Mostcommonwerewinterflounder,whitehake,AtlanticcodandAmericanplaice;

Fig 4 Trawlcatch,1951-1952byarea.

LAMBERT76

someof thescarcestwereeels,haddock, four-beard rockling,dogfish,andoceanpout.DistributionofsomeofthemoreimportantspeciesinthecatchcanbefoundinFig4andTableAII.Ofthe3principalsites,WhycocomaghBayhadthelowestoverallcatchrateandKemptHeadthehighest.ThehighestcatchratewasofwinterflounderintheGreatBrasd’OrChannelinJuneof1952.Smeltwerequitecommoninthecatch,particularlyinshallowareasalongSt.Patrick’sChannelinJulyof1952.Althoughtheyarenotconsideredabottomfishandtendtobefoundswimmingnearerthesurface,smeltaresufficientlyabundantthattheyareoftencapturedasthenetpassesthroughsurfacelayersatthebeginningandendofatow.

Table ITotalcatchofgroundfishtakenintheBrasd’OrLakes,1951-52.Black(1976).

Species Totalcatch(number)

Winterflounder 7,010Whitehake 4,616Cod 2,448Plaice 2,247Smelt 517Yellowtailflounder 307Cunner 260Windowpaneflounder 113Herring 70Mailedsculpin 70Skates 60Pollock 59Longhornsculpin 22Alewife 19Eel 12Alligatorfish 7Spinydogfish 5Searaven 3Shorthornsculpin 3Fourbeardrockling 2Haddock 2Oceanpout 1

Blacknotedseasonalchangesinthedistributionoffishthathethoughtmightberelatedtotemperature.CodandplaicenumbersdiminishedwithincreasingbottomtemperatureinBaddeckBayduringthesummerandwhileabundantatthedeeperKemptHeadstationduringthesummer,diminishedthereduringthewinterandearlyspring.Blacksuggestedamovementfromthedeeperareatoashallowerone,perhapsBaddeckBay,wheretemperaturemightbemoresuitableforthesespecies.Healsonotedseasonalchangesinabundanceofwhitehake,cunnerandwinterflounder.Hakeapparentlymovedawayfromthedeeper,KemptHeadstationtotheshallower,BaddeckBaystationinthelatesummerandautumn.ThenumberofcunnerandwinterflounderincreasedrapidlyinBaddeckBaywithincreasingbottomwatertemperature.Inthecaseofwinterflounder,theincreasewasmainlyinsmallersize-classes.Blacknotedthatthelengthfrequencyofwhitehakealsochangedinfavourofsmallerfishduringautumn.

1967 MacDonald(1968)foundatotalof18speciesoffishwithAmericanplaice,winterflounderandAtlanticcodbeingthemostabundant(TableII,Fig5).AsBlackhad found,eels, four-beard rockling,andpoutwere rare.However,haddockand

77FISH ECOLOGY

dogfish thatwere scarce in 1951/52werenot caught at all. Pollock,whichhadappearedinmoderatelylownumbersonlyattheKemptHeadstation,wereabsent.

Table IITotalcatchofgroundfishtakenintheBrasd’OrLakes,1967.MacDonald(1968).

Species Totalcatch(kg)

Plaice 3,334Winterflounder 3,008Cod 2,756Skate 145Yellowtail 86Smelt 40Whitehake 15Windowpaneflounder *14(67)Sculpins *10(32)Perch(probablyCunner) 10Witchflounder *6(10)Herring 1Gaspareau 1Dollarfish <1Eel <1Eel-pout <1Four-beardrockling <1Silverside <1

*Estimatedweightbasedonnumberoffish(inbrackets)reported.

Fig 5 Trawlcatch,1967byarea.LegendforFig4alsoappliestothisFig.

LAMBERT78

1999/2000 Surveys Atotalof25speciesweretakeninthesesurveys,themostabundantbeingwinterflounderandAtlanticcod(TableIII,Fig6).ThemostnoticeabledifferencebetweenthissurveyandthoseofearlieryearswasthelargedecreaseinthenumberofAmericanplaice.Eels,pollock,haddock,dogfishandpout,presentinthetwoearliersurveyperiods,werenotcaught.Smelt,asinearliersurveys,continuedtobeacommonpartofthecatchandalso,aspreviously,werefoundinabundanceinSt.Patrick’sChannel.Smeltspawninfreshwater,therefore,itisnotsurprisingtofindtheminthisChannelasitreceivesmostofthefreshwaterenteringtheLakes.

Table III.TotalcatchofgroundfishtakenintheBrasd’OrLakes,1999/2000

Species Totalcatch(kg)

Winterflounder 1,509.1Cod 1,296.1Whitehake 195.1Winterskate 100.3Windowpaneflounder 85.6Plaice 49.9Whiteperch 34.9Longhornsculpin 19.1Yellowtailflounder 12.5Smelt 12.5Littleskate 8.8Thornyskate 6.9Cunner 6.4Shorthornsculpin 6.2Searaven 3.3Witchflounder 0.6Gaspareau 0.5Herring 0.2Dollarfish 0.1Silverhake <0.1Silverside <0.1Mailedsculpin <0.1Alligatorfish <0.1Flyinggurnard <0.1Atlanticmoonfish <0.1

Atotalof46speciesoffishhasbeenrecordedfortheBrasd’OrLakes(TableIV).Most,likecod,areresident,whileotherssuchasmackerel,areregularvisitorsmakingseasonaltripsintotheLakes.Stillothers,strayintotheLakesonanirregularbasis;these are considered vagrants, individuals that havewandered from their normalrangeandarepresentbecauseofusuallywarmconditionsintheAtlanticoutsidetheLakes.ThisoftenoccursinthelatesummerorearlyautumnwhenexoticvisitorsaretransportednorthwardsbytheGulfStream.Notonlydoforeignfishspecieslikethesunfish,Mola mola;flyinggurnard,Dactylopterus volitans;anddollarfish,Poronotus triacanthusreachNovaScotiashoresinthisway,butalsoothercreaturessuchasseaturtles.

Distribution. Thereappearstobelittledifferenceinthegeographicaldistributionofgroundfishasdocumentedbythe1967and1999/2000surveys.Therefore,thedistributionoffishinthemoredenselysampled1967surveyisprovidedforillustra-tion(Fig7a,b).

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Table IVSpecieslistandstatusoffishreportedfromtheBrasd’OrLakes.

CommonName ScientificName Status Reported Captured

Atlanticcod Gadus morhua C B,M,L T,PAtlanticmoonfish Vomer setapinnis R(v) L TAtlanticsalmon1 Salmo salar R B,L HAlligatorfish Aspidophoroides monopterygius R B,L TAmericanplaice Hippoglossoides platessoides L B,M,L TBluebackherring Alosa aestivalis L D TrBrooktrout Salvelinus fontinalis R B HCunner Tautogolabrus adspersus C B,M,L T,PDaubedshanny Lumpenus maculatus L L PDollarfish(butterfish) Poronotus triacanthus R(v) M,L TEel Anguilla rostrata L B,M TEelpout R M TFlyinggurnard Dactylopterus volitans R(v) L TFourbeardrockling Enchelyopus cimbrius C B,M,L T,PGaspareau(alewife) Alosa pseudoharengus C(m) B,M,L TGreenlandcod2 Gadus ogac R L HHaddock Melanogrammus aegelfinus R B THerring Clupea harengus L(m) B,M,L T,PLittleskate Raja erinacea R L TLonghornsculpin Myoxocephalus octodecemspinus M B,L T,PMackerel Scomber scombrus C(m) L P,HMailedsculpin Triglops murrayi R B,L TOceanpout Macrozoarces americanus R B TPipefish Sygnathus fuscus M D BPollock Pollachius virens R B TRainbowtrout3 Salmo gairdneri L B,L HRockgunnel Pholis gunnellis L L PSculpins L M TSearaven Hemitripterus americanus L B,L TShorthornsculpin Myoxocephalus scorpius L B,L TSilverhake Merluccius bilinearis R L TSilverside Menidia menidia M L,M TSkate M B,M TSmelt Osmerus mordax C B,M,L T,PSpinydogfish Squalus acanthius R(m) B TSnakeblenny Lumpenus lumpaetiformis L B,L PSunfish Mola mola R(v) B,L WThornyskate Raja radiata L L TThree-spinedstickleback Gasterosteus aculeatus C L T4Whitehake Urophycis tenuis M B,M,L T,PWhiteperch Roccus americanus M(m) L TWindowpaneflounder(brill) Scophthalmus aquosus L B,M,L T,PWinterflounder(blackback) Pseudopleuronectes americanus C B,M,L T,PWinterskate Raja ocellata M L TWitchflounder(greysole) Glyptocephalus cynoglossus R M,L TYellowtailflounder Limanda ferruginea M B,M,L T

1Wildsalmonveryrarebutfarmedsalmonoccasionallyfairlycommonafterescapesfrompens.2Takenbylongline(4VnSFA),recentlyinSept.2001bybottomtrawlandrecordedbyScott(1952)3StockedinthelakesbyNSDepartmentofFisheriesinthepast;alsofarmedandcommonafterescapes.4Ofteninstomachsofcod.Status:C-common;M-mediumabundance;L-lowabundance;R-rare;v-vagrant,m-migratory Reported:B-Black(1976);M-MacDonald(1967);L-Lambert(presentstudy);D-Denny(2001) Captured:T-trawl;P-planktonnet;B-beachseine;Tr-trap;H-hook&line;W-washedashore

LAMBERT80

Ofthe8speciesshown,themostcommon,winterflounder,wasfoundatalltrawllocations throughout the Lakes (Fig 4-6).Codwere caught atmost locations andwindowpaneflounder,whitehakeandwinterskate,althoughnotplentiful,werealsowidespread.Themostcommonskatefoundinthe1999/2000surveyswasthewinterskate.Whereas,skateswerenotspecifiedinearliersurveys,mostwerelikelywinterskate,sincetheywerecaughtinfairlyshallowwater,wheretheytendtodominate.Plaicewerefairlywidespreadin1967,butconfinedtodeepareasofSt.Andrew’sChannelandBrasd’OrLakein1999/2000.Inbothsurveysthedistributionofyel-lowtailflounderwaslimitedtoNorthBasinandasmallareaofBrasd’OrLakeoffPipersCove.ThedistributionofwitchflounderwasalsounchangedandrestrictedtothedeeptrenchofSt.Andrew’sChannel.Depthappearedtobeimportantindeterminingthedistributionofsomespecies,

butlesssowithothers(TableV).Duringthe1999/2000survey,whichfishedoverthegreatestdepthrange,mostwinterskate,yellowtailflounderandwinterflounderwerefoundinwater21morless.Themajorityofwhitehake,windowpaneflounderandcodwerecaughtbetween29and45mandmostplaiceandwitchflounderoccurredinwaterbelow150m.Witchflounder,yellowtailflounderandprobablywinterskatehadthenarrowestrangeofdepthdistribution,whereastheothermajorspeciesoc-curredovermanydepths.Althoughtheothertwosurveysfishedatshallowerdepths(1951/1952,10-75mand1967,5.5-106m),and theearliersurveyhadaseasonalcomponent,similartrendsareevident.

Fig 6 Trawlcatch,1999-2000byarea.LegendforFig4alsoappliestothisFig..

81FISH ECOLOGY

Fig 7 Distributionofmajorfishspeciesfrom1967survey.(a)cod,plaice,winterflounderandyellowtailflounder;(b)windowpaneflounder,whitehake,skateandwitchflounder.

LAMBERT82

Table VDistributionofselectedspeciesbydepth(m)bysurvey.Averagevalueisweightedbycatch.

MinimumMaximum WeightedAverage Species 99/00 1967 99/00 1967 99/00 1967 51/52

Winterskate* 7 5 27 73 18 25 25Winterflounder 7 5 260 82 19 26 32Yellowtailflounder 10 15 27 37 21 23 20Whitehake 9 5 134 40 29 22 38Windowpaneflounder 7 5 125 59 31 15 20Cod 7 5 260 92 45 32 32Plaice 20 18 263 92 169 53 62Witchflounder 260 40 260 55 260 51 -

*Assumedtobethepredominantspeciesforpre-1999surveysthatspecifiedonly“Skate”.

Abundance. Someinterestingdifferencesareevidentinthefindingsofthetrawlsurveysconductedduringthe3surveyperiods.Themostnoticeablearechangesintherelativeabundanceofspecieswithineachsurveyperiod(Fig8).Whereaslittlechangeisevidentforwinterflounderandcod,whichdominatethecatchinallsurveys,Americanplaice,whichinearlieryearswerecommon,nowformaminorfractionofthetotalcatch.Whitehakemadeupasubstantialproportionofthecatchin1951/1952,wereveryscarcein1967,butincreasedin1999/2000catches.However,thehighnumbersofhakein1951/1952couldbeduetoageographicalbias,sincetheywereseeninlatersurveystobemorecommoninthenorth-westoftheLakes,wheremostofBlack’s(1976)fishingsetswerelocated.In1999/2000catchesmade in theGreatBrasd’OrChannel andBaddeckBay

were noticeably lower than other locations (Fig 6). However, catches from theearliersurveysinthesesametworegionswerenotsubstantiallylowerthaninotherareasoftheLakes(Fig4,5).In1951/1952boththeseareasproducedagoodcatch,dominatedbywinterflounder. In fact, theGreatBrasd’OrChannel,withonly6tows,yieldedalmostasmanywinterflounderas36towsoffKemptHead.BaddeckBaywasnotsampledin1967,buttowsweremadeintheGreatBrasd’OrChannelandproducedanamountoffishslightlylessthantheaverageforallsites(Fig5).In1999/2000onlyonesetwasmadeineachofthetwoareasinquestionwithfewfishcaught.BottomtemperatureattheBaddeckBaysitewashigh,whichwouldbethereasonforthescarcityofcodandpossiblyotherspecies;whereas,Black’s1951/1952surveyfishedduringthespringandearlysummerwhenbottomtemperatureswouldbemoreacceptabletocod.TheonesetintheGreatBrasd’OrChannelin1999wasmadejustinsidetheentrancetotheLakes;whereas,in1951/1952,towsweremadealongtheentirelengthoftheChannel.In1967,mostofthefishingsetsweremadeatthesouthernendoftheChannelclosetoNorthBasin(Fig7).ThusthedifferencesinfishabundanceintheChannelbetweenthe1999andearliersurveysareprobablyrelatedtodifferencesintowlocation,moresothanindicativeofageneralchangeinabundancewithintheChannel.Whencatchratesarestandardisedtokgpernauticalmile,thedatashowthat,on

average,fishseemtobeaboutthreetimesmoreabundantin1999/2000thanin1967(Fig5,6;TablesAIII,AIV).CatchesinEastBayandWestBayinparticular,appeartohaveincreasedbyabout5-10times;mostofthisisappearstobeduetoanincreaseinthenumberofwinterflounder.Althoughthenetusedbythe1999/2000surveyprobablycatchesmore(approx.1/3moreoveragivendistance)thanthatusedin

83FISH ECOLOGY

the1967survey,itseemsimprobablethatsuchlargeincreasescanbeattributedtodifferencesintrawlgearalone.Amoreaccurateestimationofcatchratesofthemorecommonspecieswasattemptedbyaccountingfordifferencesingearefficiency(seeearliersectiononcomparisonofsurveys).Formostspecies,thedifferencesintherecalculatedcatchratesappearlargeenoughtobereal(TableVI).Cod,winterflounderandwhitehakeseemtohaveincreasedinabundanceandAmericanplaicedecreased.Littlechangewasindicatedinthecaseofyellowtailflounderandwinterskate.

Perc

ent

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Plaice

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floun

derCod Ska

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ent

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401999 - 2000

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1951 - 1952

Fig 8 RelativeabundanceoffishspeciesintheBrasd’OrLakesbetweensurveys.

LAMBERT84

Table VI Comparisonofcatchrate(kg/naut.mile)ofsomeBrasd’OrLakes'groundfishspeciesbetweentwosurveyperiods.The1967datahavebeenmultipliedby1.3tocompensateforgeardifferencesfromthe1999/2000surveys.

Species 1967 1999/2000

Winterflounder 11.9 39.8Cod 10.0 34.2Plaice 9.9 1.1Yellowtailflounder 0.4 0.2Skate 0.7 1.5Whitehake 0.1 3.5

Length frequency. In1999/2000,fishlengthsweremeasuredandlength-frequencyplotsconstructedfor6ofthemostabundantspecies(>95%oftotalbiomasscaught).Lengthdataweresegregatedbyyearwhenabundancewarrantedit,andcombinedwhennumbersweretoofew(Fig9a-e).DataforfishfromSydneyBighttotheGulfofMaine(TableVII)fromBigelowandShroeder(1953),Beacham(1982and1983a,b),LeimandScott(1966),andO’Brien et al.(1993)allowinterpretationoftheinforma-tionprovidedinFig9.AssumingthatBrasd’OrLakesfishdonotdiffersubstantiallyfromthosewithinthegeographicalrangeofTableVII,onlycod,winterflounderandwindowpaneflounderhadclearrepresentationasmatureadults,juvenilesandyoung-of-the-year(0-group).Veryfewofthewhitehakecouldbeconsideredmatureasonlyaboutsixofthe501collectedwere40cmorgreaterinlength.Mostofthehakewerejuvenileswithafew0-grouptakenin1999.Alloftheplaicewereprobablymatureadults.Yellowtailflounderwerescarceandmostlyadultswithafewjuveniles.

Table VII Thresholdlengthsatdifferentlifestagesforselectedspecies.

Species Lengthat1year(cm) Lengthatmaturity(cm)

Cod 10-15 30-40Winterflounder 10-15 25-30Whitehake 15-20 40-50Windowpaneflounder 10-12 22-25Yellowtailflounder 12-14 25-30Plaice 7-8 20-40

Cleargrowthpatternsarepresentinthecodlengthfrequencyplots,asyear-classmodescanbetracedfromoneyeartothenext.0-groupcod,about7monthsoldatthetimeofsurveyifspawnedinearlyMarch,appearasamodeat8cmin1999(Fig9a).Theyear2000plotshowsthisgroup(now1yearand7monthsold)asasecondmodeatabout18cm.Thenumberof0-groupfishwasaboutthreetimesgreaterin1999(1999year-class)thanin2000implyingthatmoreyoungcodwereborninthespringof1999(assumingjuvenilesurvivalwasthesameinbothyears).Incomparisonto2000,fewcodaround18cmwerecaughtin1999.Thissuggeststhatrelativelyfewcodwerehatchedin1998,unlessofcourse,therewashighmortalityofyearlingcodsometimeduringtheyearfollowingspawning.Thusitappearsthe1999year-classwasbetterthaneitheroftheyearbeforeortheyearafter.Duringtherecentsurveys,andinparticular1999,thenumberofsmallwhitehake

wasstrikingFig9d.Lengthfrequencydataindicateaninterestinggeographicaltrendinsize.Theaveragelengthofhakeincreasesfrom14.4cmintheGreatBrasd’OrChannel,to23.5cmwithinareasnorthoftheBarraStrait,to26.8cmsouthoftheStrait(TableVIII).

85FISH ECOLOGY

Fig

9aFi

g 9b

Fig 9 LengthfrequenciesofselectedBrasd’OrLakesgroundfishfromtrawlsamplestakenin1999and2000;(a)cod,(b)winterflounder,(c)windowpaneflounder,(d)whitehake,(e)Americanplaiceandyellowtailflounder[datacombinedfor1999and2000]

LAMBERT86

Fig

9cFi

g 9d

Fig 9cont'd

87FISH ECOLOGY

Table VIIIWeightedaveragelengthofwhitehakebyareaoftheBrasd’OrLakes,1999-2000.

Location Wt.Averagelength(cm)

GreatBrasd’OrChannel 14.4BaddeckBay 21.8St.Andrew’sChannel 23.5EntranceDenysBasin 23.7St.Patrick’sChannel 23.9NorthBasin 24.9St.Peter’sInlet 25.3EastBay 26.8Brasd’OrLake 28.9WestBay 29.3

Cod - The case for resident populations. ArethecodintheBrasd’OrLakespartoftheSydneyBightcodpopulationoraretheyaseparatestock?CertainlymanycodintheLakeslookdifferentfromSydneyBightcod,oftenhavingadifferentcolouration.However,colourisvariablewithinanycodpopulation.ManyBrasd’OrLakecodareheavilyinfestedbyaparasiticworm,oftentotheextenttheyappearemaciated.Unfortunately,aswithcolouration,thereistoomuchvariabilityinthischaracteristicforittobeareliableindicatorofpopulationaffinity.MoreconvincingareresultsfromplanktonsamplingwhichrevealthatcodspawnintheBrasd’OrLakes.Thisspawning,

Fig 9cont'd

Fig 9e

LAMBERT88

mostofwhichoccursinSt.Andrew’sChannelandEastBay,isatleastamonthearlierthaninadjacentSydneyBight,wherecodspawninlateAprilandMay,suggestingthatthecodintheLakesareadifferentstock.ThiswasconfirmedbystudiesthatshoweddistinctgeneticdifferencesbetweenBrasd’OrLakesandScotianShelfcod(Pogson et al.,2001).Inaddition,laboratorytestingrevealedphysiologicaldifferencesbetweenLakescodandtheirScotianShelfcounterparts(Nelsonetal,1994&1996).Inthesetests,codweremadetoswimagainstacurrentina‘swimtunnel’whiletheirbloodchemistrywasmonitored.Thetemperatureandsalinityofthewatercirculatinginthistunnelwerethenvariedandthelengthoftimeuntilthefishtiredwasmeasured.TheBrasd’OrLakescodwerefoundtobemoreadaptabletochangingconditionsthanweretheir‘open-ocean’cousins.Evidenceintheformofparasiteprevalencesuggestsstronglythatanotherdistinct

stockofcodresidesinWhycocomaghBay. ManycodintheBrasd’OrLakesareheavilyinfestedwiththesealworm(Pseudoterranova decipiensKrabbe).However,thecodinhabitingWhycocomaghBayharbourveryfewoftheseparasites.Black(1976)quantifiedtheincidenceofwormsincodat3locations(TableIX);thelowerratesofworminfestationinWhycocomaghareclear.Only10%to20%ofyoungcodcarriedwormsdespitethefactthatWhycocomaghBayisadjacenttoSt.Patrick’sChannelwhereover80%ofyoungcodwereinfested(ScottandBlack,1960).

Table IXAveragenumberofPseudoterranova decipienspercodatthreelocationsintheBrasd’OrLakes(Black,1976).

BaddeckBay KemptHead WhycocomaghBay

Age(y) 1950 1951 1950 1951 1950 1951

1 2.3 3.1 5.4 2.5 0.1 0.12 11.0 9.9 8.3 8.9 0.3 0.33 9.7 17.7 16.0 12.8 0.0 0.34 11.9 13.9 14.6 16.2 0.5 0.45 15.2 20.3 16.8 21.5 1.3 1.76 31.4 26.2 27.9 1.3 2.07 34.1 30.1 37.9 4.3 3.2

Thewormhasacomplexlifecyclewhichrequiresanumberofhosts.Theadultwormresidesintheintestinesofthesealanditseggsareshedalongwiththefaecesoftheseal.Greyseals(Halichoerus grypus)areheavilyinfested,harbourseals(Phoca vitulina)carrymuchlowerwormburdens,andharpseals (Phoca groenlandia)arerarelyinfested(BratteyandStobo,1990).Themicroscopiceggs(approx.0.04mmdiameter)settletothebottomandhatchintotinyworm-likelarvaeabout0.2mminlength(Bratty,1990).Thelarvaeattachthemselvesbytheirtailstothesubstratewheretheir‘wiggling’motionattractssmallbenthiccopepods(Fig2)whichconsumethelarvalparasite.Withinthebodycavityofthecopepod,theparasitegrowstoabout0.5mmatwhichsizeitistoosmalltobeabletoinfectafish.Furthergrowthoccursaftertransmissiontolargerinvertebrateswhichpreyonthecopepod.Thehostsatthisstageincludeamphipods,mysids,sandshrimps,nudibranchs(seaslugs)andpolychaeteworms(McLelland,1990).Thelarvalwormgrowsto2mmormorewithintheselargerhosts atwhichpoint it is capableof surviving thedigestiveprocessof afishandpenetrating thewallof its intestine (McLelland et al.,1983). Theparasitecanbetransmittedtoawiderangeoffish;somesuchassmelts,pouts,sculpinsandfloun-ders,whicheatinfectedinvertebratesandothers,suchascodandwhitehake,whichconsumebothinvertebratesandotherinfectedfish(McLelland et al.1990).Thusthe

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transmissionpathofP. decipiensthroughsuccessivehostsisnotsimpleanddirect;itisanetworkofinterconnectingpathsleadingtoamyriadofalternatehosts.Successivelylargerhostsallowthelarvalparasitetogrowuntilfinally,whenitsintermediatefishhostfallspreytoaseal,itislargeenoughtoestablishresidenceinthestomachanddigestivetractofthesealwhereitgrowstosexualmaturity.ItisuncertainwhetherthenumberofsealsintheBrasd’OrLakesrelativetonum-

bersintheAtlanticcoastalregionoutsidetheLakesishighorlow.ScottandBlack(1960)showedthatbothharboursealsandgreysealsintheBrasd’OrLakeswerecarriersofadultP. decipiens ( theaveragenumberintheirstomachswas250and1500,respectively).TheyreportthatsealsfrequenttheLakesinwinterbutarescarceinthesummer;highestreportedsitingswerebetweenBaddeckBayandGrandNar-rows.ItisclearthatsealsintheLakeshaveagreaterwormloadthanthoseoutside.Inasummarywhichcomparesanumberofseal investigations,BratteyandStobo(1990)indicatedthat3greysealsthatwereautopsiedbyScottandFisher(1958)hadanaveragewormload5timesgreaterthansealsfromeasternCapeBretonoutsidetheLakes.ThemeannumbersofadultandlarvalparasitesfoundinthesesealsintheLakewere169and2727,respectively.AdistinguishingfeatureofWhycocomaghBayisthelowlevelofoxygenindeep

basinsateachendoftheBay;thewesternonebeingcompletelyanoxic(PetrieandBugden,2002;StrainandYeats,2002).CodavoidtheseareasoflowoxygenandaggregateatintermediateandshallowdepthswithintheBay.Duetothislackofox-ygenoveralargeareaofthebottomoftheBay,benthicorganismsotherthansomemicroorganismscouldnotsurvive.Thusmanyoftheintermediateinvertebratehostsofthecodwormsuchasmarineworms,amphipodsandmysidshrimpswouldbescarceorabsent.ScottandBlack(1960)havereportedlowabundanceofmysidsinWhycocomaghBay.Intheabsenceofintermediateinvertebratehosts,theparasitewouldnotbeabletocompleteitslifecycle.Furthermore,ScottandBlack(1960)reportthatsealswererarelyseeninWhycocomaghBay.Therefore,thelowlevelofparasitesseeninthecodoftheBaymaybeduetoboththescarcityofprimary(seals)andintermediate(benthicinvertebrate)hosts.Itfollowsthattheremustbelittlemove-mentofcodoutofWhycocomaghBay,andconversely,fewfishcanbemovingintotheBayfromSt.Patrick’sChannelwhereinfestationsarehigh.PossiblythisisduetotherestrictedpassagewayatLittleNarrows,whichmaydiscouragethemovementofcodbetweentheBayandSt.Patrick’sChannel(Black,1976).CodinmanypartsofthenorthAtlanticareknowntoundergoextensivemigrations

relatedtofeeding,spawningandoverwintering.ThecodoftheGulfofStLawrencespendabouthalftheyearinsidetheGulfandtheremainderoutsideinSydneyBight.After spawning in theGulf during June, they feed throughout the summerbeforeforminglargeaggregationsinOctoberpriortomovingeasttodeepwaterinCabotStraitoffSydneyBighttoavoidsubzerowatertemperaturesthatareprevalentinmanyareasoftheGulfofSt.Lawrenceduringwinter.InlateAprilandMay,thecodreturntotheGulftospawnandbeginthecycleanew.OthercodstocksonthenortheastcoastofNovaScotia,includingtheresidentSydneyBightstock,alsoundergosim-ilarmigrations,buttoamuchlesserextent.Theyinhabitcoastalwatersduringthesummermonthsbutthenmovetodeeper,offshorewatersduringthewintertoavoidcoldwaterontheshallowcoastalbanks.WhatofthecodintheBrasd’OrLakes?Althoughmostevidenceseemstoindicate

thatmostcodintheLakesdonotventureintoSydneyBight,itislargelycircumstantialandqualitative. Asmentionedpreviously,differences inappearanceandparasiteloadssuggestexchangebetween theLakesand theBight is limited,but theseareunreliableindicators.Tagging,theonlysurewayofdeterminingmovementoffish,

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startedin2000whenabout1000codweretaggedatvariouslocationsthroughouttheLakes.Bytheautumnof2001,12tagshadbeenrecovered;notenoughtomakeanyfirmconclusions,butnevertheless,suggestive.TherecapturedcodweretaggedinSt.Patrick’sChannelbetweenBaddeckandNyanzaduringMayinwaterlessthan10mdeepandrecoveredduringthewinterbythe4VnSFAlonglinerinSt.Andrew’sChannelinwatergreaterthan100mdeep.ContrarytoBlack’s(1976)suggestion,thissuggeststhatthesecod,liketheircousinsinSydneyBight,movetodeeper,relativelywarmwatertooverwinterwithintheLakes(waterof2to4oC,asopposedto0oCandlowerintheshallows).NoLakestaggedcodhaveyetbeenrecapturedinSydneyBight.

discussion

Zoogeography. TheanimalsthatinhabitNovaScotia’sborealregioncanbebroadlydividedintotwogroups.Onegroup,byfarthelarger,isrestrictedtothetemperaturesnormallyexperiencedinthisregion;thesmallergroupcantolerateamuchwiderrangeoftemperaturesandcanbefoundfromtemperateregionstothesouthernboundaryof theArcticzone.Thefirstgroupcomprises trueborealanimalsaswellas sometransitionalzone(Arctic-boreal)animals.Theborealcomponentincludescod,whitehake,haddock,pollock,herring,longhornsculpin,searaven,cunner,rockgunnelandeelpout;Arctic-borealrepresentativesincludealligatorfishandradiatedshanny.Gaspareauandwinterflounderareexamplesof the secondgroupof temperaturetolerantfishspecies.AlloftheabovespecieshavebeenreportedfromtheLakes.Another twogroupsofanimalsdistinguish theBrasd’OrLakes from the restof

coastalNovaScotia.Theyareisolatedfromtheirmaincentresofdistributionandarerestrictedtonarrowrangesoftemperature.Surprisingly,onesetoftheseisolatedspeciesareArcticandtheotherarewarmwatertemperatecreaturesmorecommonlyfoundoffthecoastofVirginia(hencetheyaresometimesreferredtoas“Virginianenclave”species).BothgroupsareremnantsofpopulationsthatwerecommonatsomepointduringthepastgeologichistoryoftheBrasd’OrLakeswhenclimaterangedbetweendistinctlyArctictowarmerthanitistoday.TheArcticanimalscolonisedtheLakesasglaciersretreatedafterthelasticeageabout10,000yearsago.Thereafter,theearth’sclimatebegantowarmuntil,untilbetween4,000and7,000yearsago,globaltemperatureswere2.0oCwarmerthantoday.Duringthisperiod,calledtheclimaticoptimum,warmtemperatespeciesinvadedtheLakes.TheArcticspeciescontinuetoexistinthecolddepthsofSt.Andrew’sChannel,the

NorthBasinandsomeofthedeeperportionsoftheBrasd’OrLake,wheretemperaturesdonotvarymuchabove0oCthroughouttheyear(PetrieandBugden,2002).Severaltaxonomicgroupsarerepresented;thecopepod,Microcalanus pusillus (Shih et al, 1988);themysidshrimp,Mysis oculata(Black,1958);polychaeteworms,Clymenura polaris, Sabellides borealisandLysippe labiata(FournierandPocklington,1984);andforaminifera,Eggerella advenaandRheophax arctica(Vilks,1967).Relictpopulationsattheotherendoftheclimaticscalearespeciesthatareadaptedtowarmwaterorrequirehighertemperaturestoreproducesuccessfully.Theoyster,Crassostrea virgini-carequireswarmtemperaturesforitsgonadstodevelopproperlyandtemperaturesinexcessof20oCtotriggerspawning.Similarly,itisthoughtthatthewindowpaneflounder,Scophthalmus aquosusrequireswarmwatertobreedproperly(BigelowandShroeder,1953).Otherexamplesofisolatedwarm-waterenclavespeciesintheLakes,arethepolychaetewormsEuchone elegans,Polydora quadrilobata,andMyriochele heeri(FournierandPocklington,1984).

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Biodiversity ThewiderangeofhabitatsavailablewithintheBrasd’OrLakessystemallowsforacorrespondingdiversityofspecies.ThegreatestnumberofspecieswerecollectedinSt.Andrew’sChannel,theNorthBasinandtheGreatBrasd’OrChannel(TableX).Thefirsttwoareashavethegreatestrangeofdepth,temperatureandsalinityandtheGreatBrasd’OrChannelisatransitionzonebetweentheoutsideAtlanticpopulationsandthoseoftheLakes.NorthBasinhasthehighestoverallrankingforspeciesdiversity(TableXI)andSt.Andrew’sandGreatBrasd’OrChannelsweresec-ond.NyanzaBay,BaddeckBayandSt.Peter’sInletranklow,butnoneoftheseareasisfullyrepresentedintaxonomicgroupsduetoincompletesamplingoftheLakesbysomesurveys,sotheirrankingscannotbedirectlycomparedtothefullysampledareas.Certainlythough,forthosegroupsoforganismswheretheydohaverepresentation,theydonotrankparticularlyhigh,withtheexceptionofBaddeckBay,whereBlack(1976)recordedhissecondhighestnumberoffishspecies.Ofthe4areasthatarefullyrepresented,St.Patrick’sChannelhasthepoorestvarietyofspecies,althoughWhycocomaghBay,whichwasnotsampledforcopepods,isprobablylowerduetoprevalentlowoxygenatdepthandlowsalinitynearthesurface(PetrieandBugden,2002;StrainandYeats,2002).

Table X NumberofSpeciesbyArea.

Organisms GBC BB NyB StPC Why StAC NB BDL WB StPI DB EB

Foraminifera 19 9 8 11 9 14 16 16 11 - 11 15Algae 26 18 20 19 23 26 30 20 20 19 21 20Polychaetes 48 - - 16 16 40 27 38 - - - -Copepods 10 - - 7 - 14 10 10 - - - -Fish (1950-1) 10 16 - 10 11 16 19 - - - - -Fish (1967) 15 - - 13 6 16 17 16 12 - 15 9Fish (1999-0) 10 6 6 12 5 11 17 12 6 8 8 8Total 138 49 34 88 70 137 136 112 49 27 55 52

Average 19.7 12.3 11.3 12.6 11.6 19.6 19.4 18.7 12.2 13.5 13.8 13

GBC-GreatBrasd’OrChannel;BB-BaddeckBay;NyB-NyanzaBay;StPC-St.Patrick’sChannel;Why-WhycocomaghBay;StAC-St.Andrew’sChannel;NB-NorthBasin;BDL-Brasd’OrLake;WB-WestBay;StPI-St.Peter’sInlet;DB-DenysBasin;EB-EastBay.FournierandPocklington(1984)didnotdistinguishbetweenSt.Patrick’sChannelandWhycocomaghBaysothesamevaluesareassignedtoeachareainTablesXIandXII.

Table XI RankedSpeciesTotalsbyArea.

Organisms GBC BB NyB StPC Why StAC NB BDL WB StPI DB EB

Foraminifera 1 9 11 6 9 5 2 2 6 - 6 4Algae 2 12 5 10 4 2 1 5 5 10 9 5Polychaetes 1 - - 5 5 2 4 3 - - - -Copepods 2 - - 5 - 1 2 2 - - - -Fish(1950-1) 4 2 - 4 5 2 1 - - - - -Fish(1967) 4 - - 6 9 2 1 2 7 - 4 8Fish(1999-0) 5 9 9 2 12 4 1 2 9 6 6 6

Overall 2 10 12 5 9 2 1 4 8 10 7 6

ColumnheadingsasinTableX.

Abundance and distribution Thequantityofanimalsfoundinthecatchofatrawlnetmayreflectabundance,butmaynotbecauseofsamplingefficiency.Somebottomdwellingfish such as, eel-pout,which inhabit burrows in soft,muddybottoms are

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normallypassedoverby thenet; four-beardrockling,which,asplanktonsamplesshowarecommon,liveincavitiesunderrocks,wheretheyarealsonotvulnerabletothenet.Rockybottoms,whichtearthenet,areavoidedwhenfishing,soanyspeciespreferringthistypeofhabitatwillbeundersampled.Realchangesinabundanceoffishspecies,whicharereflectedintrawlcatches,couldbecausedbyanumberofdifferentfactorsrangingfromoceanclimatechangetofishingpressuresbothwithinandoutsidetheLakes.SomespeciesoffishdonotappeartospawnwithintheLakes,oratleastnottotheextentthatself-sustainingpopulationscanbeestablished;there-fore,theirpresenceintheBrasd’Orisdependentonexchangewiththeocean.Inthiscase,changesinabundancemaymerelyreflectchangesonalargerscaleinadjacentSydneyBight.Haddockandpollockforexample,werenotedinearliertrawlsurveysbutnotcaughtinthe1999/2000survey.InSydneyBight,from1994to1998,the4VnSentinelSurveycaught567kgofhaddockand134kgofpollock,comparedto400tonnesofcodand32tonnesofAmericanplaice.Fromthemiddle1980s,haddockandpollockabundancedecreasedoffnorth-eastNovaScotiaprobablybecauseoffishingpressure,butforhaddock,alsobecauseofawidespreaddecadelongdecreaseinbottomtemperaturesinthearea(Drinkwateret.al.,1999).Haddock,whichhadbeenrareinSydneyBightarebeginningtoreappearperhapsduetoarecentwarmingtrendinbottomtemperatures (Drinkwater et al.,1999).Possibly intime, theywillreappearintheLakesystemifstocksrebuildinSydneyBight.WinterskateareverycommonbothinsideandoutsidetheLakes,withnobreakintheirdistributionbetweenthetwoareas,probablyindicatingfreeexchangebetweenSydneyBightandtheLakes.Whereasthepresenceofsomespeciesappearstoberelatedtofactorsexternaltothe

Brasd’OrLakes,thesuccessofspeciessuchasherring,cod,winterflounder,plaice,yellowtailflounder,windowpaneflounderandwitchflounderseemsmorerelatedtolocaleventswithintheLakes.HerringhavebeenseriouslydepletedduetooverfishingintheLakeandthatfisheryisnowclosed.Cod,andparticularlywinterflounder,appeartohaveincreasedinabundancesince1967.Theclosureofthebottomtrawlfisheryhasprobablyallowedthesestockstorebuild.PlaiceandyellowtailflounderarecommonoutsidetheLakesinSydneyBight,therefore,thelownumbersintheBrasd’Orwouldappeartoindicatelittleornomovementbetweenthetwoareas.Eggsandlarvaeofthesetwoflatfishappearinplanktonsamples,butinverysmallnumbers.ThesecouldoriginatewiththefewmatureadultsintheLakesorpossiblytheymayhavebeentransportedintotheLakesfromSydneyBight.Fig9eindicatesthatjuvenileyellowtailarepresentintheLakesbuttherewasnoevidenceofyoungplaice,asnoindividualssmallerthan30cmwerecaught;thusitwouldappeartherehasbeen littleorno recruitment to theplaicepopulation in recentyears. In thecaseofwindowpaneflounder,however,therecanbenodoubtthatthisspeciesisaself-sustainingpopulationwithintheLakesforthisspeciesrequireswateraround20oCtoreproduce(BigelowandShroeder,1953)andthesetemperaturesarerarelyattainedinoutsidecoastalwaters.Witchflounder,ontheotherhand,arefoundonlyindeep,coldwateratthebottomofSt.Andrew’sChannel;inSydneyBighttheyarecommon,butwelloffshoreatdepthsover100m.Thisspecieswasarareoccurrenceinthe1967survey,andisprobablyevenscarcernowsinceonlyoneindividualwascaughtinthe1999/2000surveys.WhetherthisisolatedpocketofwitchflounderisaresultofoccasionallarvaedriftingintotheLakesandsettlingthere,orwhetherthereisaself-sustainingisdifficulttosay.Whitehakeappeartohavebeenplentifulintheearly1950s,tohavedecreased

substantiallyby1967,andhaveincreasedsincethen.Draggers(bottomtrawling)wereactiveuntil1992whentheywerebannedfromoperatingintheLakes.Itispossible

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thisfishingactivitymayhavereducedthenumbersofhakeduringtheperiodrepre-sentedbythe1967survey,andthattheyreboundedaftertheprohibitionontrawling.However,sincewhitehakelarvaeareextremelyrareinplanktonsamples,itisunlikelythathakespawnintheLakes;theirabundanceisprobablymoredependentonthefortunesofthestockoutsidetheBrasd’OrLakes.However,thereappearstobemoretothewhitehakestory.RecallthatmostofthecatchofhakeintheLakesconsistedofjuvenilefish(Fig9d),withatrendofincreasingsizefromtheentranceinward(TableVIII).Thiscanbeinterpretedasa“seeding”fromSydneyBightofyounghake,whichmoveintotheLakesforthedurationoftheirjuvenilestagebeforemovingbackoutintotheBightasnear-matureadults.Possibly,theBrasd’OrLakesisanurseryareaforatleastsomeportionofawhitehakestockexternaltotheLakes.Similarly,innearbySt.Ann’sHarbour,highnumbersofsmallwhitehake,butnoadults,havealsobeentakeninanongoingDFOinshoresurveybegunin1991.OfthefishspecieswithintheBrasd’OrLakes,herring,cod,winterflounder,win-

dowpaneflounder,plaice,yellowtailflounderandprobablywitchflounderappeartoberesident;whereas,whitehake,winterskateand,inthepast,haddockandpollockaremorelikelypartofacontinuousdistributionwiththelarger,adjacentcoastalarea.Are theBrasd’OrLakesunique? Atfirstglance theBrasd’OrLakes,albeit far

smaller,mayappearsimilartootherlarge,moreorlessenclosedseas,suchastheBalticandBlack.Allthreehavebeentermedbrackish,buttheBrasd’OrLakesbyfarthemostsalty,wouldnotqualifyasbrackishaccordingtoEkman’s(1953)clas-sificationsystem.Apartfromestuarineconditionswhereriversenter,thesalinityoftheBrasd’OrLakesrangesfromabout20atthesurfacetoabout26atdepth(Krauel,1976;PetrieandBugden,2002).InEkman’sscheme,thethresholdsalinitybetweenbrackishandsaltwateris17to20.ThustheBaltic,whichismostlybelow10,andwiththehighestvaluesneartheentranceonly15,isbrackish.Withtheexceptionofdeepwaters,theBlackSeaismostlybelow20soitisaborderlinecase.MostoftheglacialrelictsdescribedarefromtheBalticandthusfoundinclearlybrackishwater.Arcticrelictsfromwatermoresaltythan20areveryrare;onlyoneortwohavebeenreported(Ekman1953).Therefore,theBrasd’OrLakeswithanumberofrelictspecies(andnotconfinedtoonetaxonomicgroup)isararity.IfweacceptEkman’sdefinitionofbrackish,theBrasd’OrLakesmaybetheonlytrulymarinebodyofwaterthatishometosomanyglacialrelicts.Furthermore,notonlyarethereglacialrelicts,butparadoxicallyalsowarmwaterenclaverelicts.ThismustmaketheLakesunique.Abetterplacetoundertakemarineecosystemresearchwouldbehardtofind.In

additiontotheiruniqueassemblageoforganismsanddiversehabitats,theBrasd’OrLakeshaveanumberofotherattributeswhichideallysuitthemtomarineresearch.WhereasthelowflushingratesoftheLakescouldbeconsideredaliability,renderingthemhighlyvulnerabletospillsofpollutants,thissamecharacteristicisaboontobiologistsinterestedinthestudyoflifehistoriesofmarineorganisms.Usuallyitisverydifficulttomeasurethesurvivalrateofanimalsinthesea,particularlyeggandlarvalstages,becauseonecannevertellwhetherdecreasesinnumbersareduetodriftoutofthestudyareaortoon-sitemortality.Planktonpatchesonthecontinentalshelfcanrarelybetrackedformorethanafewdays.Thelowflushing,combinedwiththefactthattheLakescontainresidentmarinepopulations,providesauniqueopportunityforquantitativestudiesofallstagesofthelifehistoryofanorganism.ThroughouttheNorthwestAtlantic,manycodstocksweredecimatedinthelate1980sandhavefailedtorecoveraftertenyearsormore.Whythesestocksarenotrebuildingisanopenquestion.AstudyoftheresidentcodpopulationintheBrasd’OrLakescouldprovidevaluableinsightsintothepopulationdynamicsofthisspecies.

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AswehaveseenwithintheBrasd’OrLakes,onecanfindspecieswhichnormallywouldbefoundonlybytravellingsouthtoVirginiaandintheoppositedirectionnorthtoBaffinIslandintheArctic.Amazingly,over30ooflatitudearerepresentedwithindistancesoflessthan10kminCapeBreton’sinlandsea.Certainly,asMcLachlinandEdelstein(1971)noted,“ThegreatdiversityofhabitatsintheBrasd’OrLakespresentsauniqueopportunityforextensiveecologicalobservations.”

acknowledgements

MysincerethankstoBobCrawfordfortrackingdowntheMacDonaldmanuscriptontheBrasd’OrLakessurvey.ThanksalsotomyableEFWCfieldtechniciansaboardtheCCGCNavicula:KyleDicks,LisaPaul,BertLewis,AllisonMacIsaac,VivianBushellandespeciallytoCaptainJoeBrayandCook/DeckhandJoeRandallfortheircheerfulcooperation.IamindebtedtoJeffMcRuer,andparticularlyScottWilson,oftheMarineFishDivisionattheBedfordInstituteofOceanographyforprovidinglogisticsupport.Mostimportantly,IwishtorecogniseCharlieDennis,DirectoroftheUnama’kiInstituteofNaturalResourcesforinitiatingtheBrasd’OrLakesresearchprogrammeandforhiscontinuingsupport.Finally,thanksareduetoBrianPetrie,JohnTremblayandtwoanonymousreviewersforsuggestionsforimprovementofthemanuscript.

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(Received 1 March 2002)

97FISH ECOLOGY

appendix

Table AI NumberofsetsmadebylocationinthreetrawlsurveysintheBrasd’OrLakes.DatafromBlack(1976),MacDonald(1968)andLambert(thisstudy).

Location 1951-1952 1967 1999-2000

GreatBrasd’OrChannel 6 8 1BaddeckBay 78 - 1St.Patrick’sChannel 9 6 4NyanzaBay - - 2WhycocomaghBay 42 4 4St.Andrew’sChannel - 34 5NorthBasin 36 17 7Brasd’OrLake - 16 9DenysBasin - 11 2WestBay - 11 2St.Peter’sInlet - - 2EastBay - 8 4

Total 171 115 43

Table AII Meancatch(numbers/tow)ofselectedspeciesbylocationinBrasd’OrLakes.1951&1952combined(Black,1976).

Location Cod Winter Window Yellow Plaice White Skate Total flounder pane tail hake flounder flounder

Gt.Brasd’OrChn. 11.3 222.7 - 17.8 - 0.7 0.5 253.0BaddeckBay 12.1 43.2 1.3 2.4 1.7 32.6 0.6 93.9St.Patrick’sChn. 1.8 8.3 0.2 0.1 0.1 0.6 0.1 11.2WhycocomaghBay 18.5 13.7 <0.1 <0.1 0.1 1.0 <0.1 33.5KemptHead 19.3 46.0 0.2 0.3 58.5 56.1 0.3 180.6

Average 12.6 66.8 0.4 4.1 12.1 18.2 0.3 114.4

Table AIII Meancatch(kg/naut.mile)persetofselectedspeciesbylocation–1967survey(MacDonald,1968).(Note,thesedatahavenotbeenadjustedforgeardifferenceswiththe1999/2000survey.)

Location Cod Winter Window Yellow Plaice White Skate Total flounder pane tail hake flounder flounder

GreatBrasd’OrChn. 4.99 14.49 0.09 1.83 0 0.43 1.72 23.91St.Patrick’sChannel 5.02 17.98 0.04 0.33 0 0.54 0.15 24.20WhycocomaghBay 1.10 23.77 0.10 0 0 0.02 0 25.35St.Andrew’sChannel 6.77 1.44 0 0.01 20.67 0.01 0.10 29.00NorthBasin 8.45 11.45 0.04 0.53 6.20 0.03 1.27 28.13Brasd’OrLake 4.40 7.74 0.15 0.42 0.03 0.02 0.30 13.64DenysBasin 19.45 13.66 0.17 0 0 0.01 0.18 34.11WestBay 5.20 9.02 0 0 0.88 0 0.86 15.96EastBay 9.30 12.14 0.03 0 5.59 0 0 27.15

AverageofLocations 7.19 12.41 0.07 0.35 3.71 0.12 0.50 24.60

AverageofallSets 7.52 8.98 0.28 7.51 0.07 0.49

LAMBERT98

Table AIV Meancatch(kg/naut.mile)persetofselectedspeciesbylocation-1999/2000surveys.

Location Cod Winter Window Yellow Plaice White Skate Total flounder pane tail hake flounder flounder

GreatBrasd’OrChn. 0 0.80 0 0.06 0 0.10 0.20 1.16BaddeckBay 0 1.40 0.40 0 0 0.50 0 2.30St.Patrick’sChannel 6.70 20.04 1.89 0 0 21.17 4.76 54.86NyanzaBay 0 6.30 0.64 0 0 0.00 0.17 7.11WhycocomaghBay 30.60 20.89 0.49 0 0 0 1.88 53.86St.Andrew’sChannel 29.26 18.92 0.41 0.52 7.21 0.08 0.06 57.00NorthBasin 64.31 4.11 1.50 0.21 0 2.29 3.00 75.42Brasd’OrLake 46.70 29.35 3.11 0.22 0.68 5.82 0.73 86.61DenysBasin 9.10 22.30 0.50 0 0 1.30 3.40 36.60WestBay 50.80 218.90 0.35 0 0 0.79 0 270.84St.Peter’sInlet 60.00 87.20 1.10 0 0 0.20 1.90 150.40EastBay 21.90 114.80 1.00 0 0 0.92 0.79 139.41

AverageofLocations 26.53 45.75 0.95 0.08 0.66 2.76 1.45 78.13

AverageofallSets 34.25 39.77 1.38 0.15 1.08 3.48 1.53