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.

LAMBERT66

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

salinitysurfacelayerwhichhasawideannualrangeintemperatureandalowerlayer

Fig 1 MapoftheBrasd’OrLakesindicatingplacesmentionedinthetext.

67FISH ECOLOGY

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’

LAMBERT68

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

69FISH ECOLOGY

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.

LAMBERT70

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

71FISH ECOLOGY

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

LAMBERT72

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).

73FISH ECOLOGY

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

LAMBERT74

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).

79FISH ECOLOGY

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

0

1

2

3

4

5

20

1967

Plaice

Winter

floun

derCod Ska

te

Yellow

tail

White

hake

Window

pane

Perc

ent

0

1

2

3

4

5

20

401999 - 2000

Perc

ent

0

1

2

3

4

5

20

40

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

89FISH ECOLOGY

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,

LAMBERT90

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).

91FISH ECOLOGY

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

LAMBERT92

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

93FISH ECOLOGY

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.

LAMBERT94

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.

references

Beacham, T.D. 1982.Biologyandexploitationofwinterflounder(Pseudopleuronectes americanus) in the CanadianMaritimes area of theNorthwestAtlanticOcean.Can. Tech. Rept. Fish. Aquat. Sci. No.1113,33p.

Beacham, T.D. 1983a.Variabilityinsizeandageatsexualmaturityofwhitehake,pollock, longfin hake and silver hake in theCanadianMaritimes region of theNorthwestAtlanticOcean.Can. Tech. Rept. Fish. Aquat. Sci. No.1157,43p.

Beacham, T.D. 1983b.VariabilityinsizeandageatsexualmaturityofAmericanplaiceandyellowtailflounderintheCanadianMaritimesregionoftheNorthwestAtlanticOcean.Can. Tech. Rept. Fish. Aquat. Sci. No.1196,74p.

Bigelow, H.B. and Shroeder, W.C. 1953. FishesoftheGulfofMaine.Fish. Bull. US Fish Wildl. Serv.53,viii+577p.

Black, W.F.1958.BiologyofmysidsoftheGreatBrasd’Or.MS. Rept. Fish. Res. Board Can.#671.

Black, W.F. 1976.Aspects of themarine biology of theGreat Bras d’Or. INThe proceedings of the Bras d’Or Lakes aquaculture conference, Sydney, Cape Breton.(Ed.M.G.McKay)CollegeofCapeBretonPress,Sydney,N.S.,44-53.

Bousfield, E.L.and Thomas M.L.H.1975.PostglacialchangesindistributionoflittoralmarineinvertebratesintheCanadianAtlanticregion.Proc. N.S. Inst. Sci.27,Suppl.3:47-60.

Bratty, J.1990.Effectoftemperatureonegghatchinginthreeascaridoidnematodespeciesfromseals. IN Population biology of sealworm (Pseudoterranova decipiens) in relation to its intermediate and seal hosts.(Ed.W.D.Bowen).Can. Bull. Fish. Aquat. Sci.222:27-39.

Bratty, J. and Stobo W.T. 1990.GroupReport2: InfectionofDefinitiveHosts. In Population biology of sealworm (Pseudoterranova decipiens) in relation to its

95FISH ECOLOGY

intermediate and seal hosts.(Ed.W.D.Bowen).Can. Bull. Fish. Aquat. Sci.222:139-145.

Crawford, R.H., Webber, D.M.andBoutilier, G.1982.ThebiologyofherringfromBrasd’OrLake,CapeBreton.Nova Scotia. MS and Tech. Rept. N.S. Dept. Fish.82-04,66p.

Dennis, C. 2001.(EskasoniFishandWildlifeCommission,Eskasoni,N.S.)Personalcommunication.

Denny, S.,Clark, K.J., Power, M.J.andStephenson, R.L.1998.ThestatusoftheherringintheBrasd’OrLakesin1996-1997.Can. Stock Asses. Sec. Res. Doc.98/80,32p.

Denny, S.2001.(EskasoniFishandWildlifeCommission,Eskasoni,N.S.)Personalcommunication.

Drinkwater, K.F., Colbourne, E.andGilbert D.1999.OverviewofenvironmentalconditionsintheNorthwestAtlanticin1998.NAFO SCR. Doc.99/36,Ser.No.N4094.

Ekman, S.1953.Zoogeography of the sea.SidgwickandJacksonLtd.,London.Fournier, J. A.and Pocklington,P.1984.ThesublittoralpolychaetefaunaoftheBrasd’OrLakes,NovaScotia,Canada.INProc. First Int. Polychaete Conf., Sydney.(Ed.P.A.Hutchings)LinneanSoc.N.S.Wales,254-278.

Geen, G.H.1965.Primary production in Bras d’Or Lake and other inland waters of Cape Breton Island, Nova Scotia.Ph.D.thesis,DalhousieUniversity,Halifax,N.S.,187p.

Geen, G.H.and Hargrave, B.T.1966.PrimaryandsecondaryproductioninBrasd’OrLake,NovaScotia,Canada.Verh. Inter. Limnol.16:333-340.

Krauel, D.1976.Asummaryof thephysicaloceanographyof theBrasd’OrLakesystem.INThe proceedings of the Bras d’Or Lakes aquaculture conference, Sydney, Cape Breton.(Ed.M.G.McKay)CollegeofCapeBretonPress,Sydney,N.S.,29-43.

Leim, A.H.andScott, W.B.1966.FishesoftheAtlanticcoastofCanada.Bull. Fish. Res. Bd. Can.155,485p.

MacDonald, K.F.1968.FishpopulationassessmentBrasd’OrLake,CapeBretonIsland. N.S. Dept. Fish., Resource Development Div., Pictou,16p.

MacIsaac, A.2001.(Dept.FisheriesOceans,EasternN.S.SydneyOffice)Personalcommunication.

McKay, M.G. (Ed.)1976.Proceedings of the Bras d’Or Lakes Aquaculture Conference, held in Sydney, Cape Breton, 1975.CollegeofCapeBretonPress,Sydney,N.S.xvii+312p.

McLachlan, J. and Edelstein, T. 1971. Investigations of themarine algae ofNovaScotia.IX.ApreliminarysurveyofthefloraofBrasd’OrLake,CapeBretonIsland.Proc. N.S. Inst. Sci.27:11-22.

McLelland, G.1990.Larvalsealworm(Pseudoterranova decipiens)infectionsinbenthicmacrofauna. IN Population biology of sealworm (Pseudoterranova decipiens) in relation to its intermediate and seal hosts.(ed.W.D.Bowen).Can. Bull. Fish. Aquat. Sci.222:47-65.

McLelland, G., Misra,R.andMarcogliese, D 1983. Variationsinabundanceoflarvalanisakines,sealworm(Phocanema decipiens)andrelatedspeciesincodandflatfishfromthesouthernGulfofSt.Lawrence(4T)andtheBretonshelf(4Vn).Can. Tech. Rep. Fish. Aquat. Sci.1201:ix+27p.

McLelland, G., Misra,R.andMartell, D.1990.LarvalanisakinenematodesinvariousfishspeciesfromSableIslandBankandvicinity.IN Population biology of sealworm (Pseudoterranova decipiens) in relation to its intermediate and seal hosts.(Ed.W.D.Bowen).Can. Bull. Fish. Aquat. Sci.222:83-118.

Nelson, J.A., Tang, Y.andBoutilier, R.G.1994.Differencesinexercisephysiology

LAMBERT96

betweentwoAtlanticcod(Gadus morhua)populationsfromdifferentenvironments.Physiol. Zool.67(2):330-354.

Nelson, J. A., Tang, Y.andBoutilier, R.G.1996.TheeffectsofsalinitychangeontheexerciseperformanceoftwoAtlanticcod(Gadus morhua)populationsinhabitingdifferentenvironments.J. Exp. Biol.199:1295-1309.

O’Brien, L., Burnett, J.andMayo, R.1993.MaturationofnineteenspeciesoffinfishofftheNortheastcoastoftheUnitedStates,1985-1990.NOAA Tech. Rept. NMFS113.

Petrie,B.andBugden,G.2002.ThePhysicalOceanographyoftheBrasd’OrLakes.Proc. N. S. Inst. Sci . 42:11-38.

Pogson, G.H., Taggart, C.T., Mesa, K.A.andBoutilier, R.G.2001.IsolationbydistanceintheAtlanticcod,Gadus morhua,atlargeandsmallgeographicscales.Evolution55(1):131-146.

Scott, D.M.1952.TheGreenlandcod(Gadus ogac)inCapeBretonIsland.Can. Field Nat.66(5):123-124.

Scott, D.M.and Black,W.F.1960.Studiesonthelife-historyoftheascaridPorrocaecum decipiensintheBrasd’OrLakes,NovaScotia,Canada.J. Fish. Res. Bd. Can.17(6):763-774.

Scott D.M. and Fisher,H.D.1958.IncidenceoftheascaridPorrocaecum decipiensin the stomachsof three species of seals along the southernCanadianAtlanticmainland.J. Fish. Res. Board Can.15:495-516.

Shih, C.-T., Marhue L., BarrettN.and Munro,R.1988.PlanktoniccopepodsoftheBrasd’OrLakessystem,NovaScotia,Canada.Hydrobiologica167/168:319-324.

Sinclair, M., Stobo, W.T. and Simon, J.1980.1979-19804Vnherringassessment.CAFSACRes.Doc.80/50.

Strain, P.andYeats, P.2002.TheChemicalOceanographyoftheBrasd’OrLakes.Proc. N .S. Inst. Sci . 42:39-66.

Tremblay, M.J.2002.LargeEpibenthicInvertebratesintheBrasd’OrLakes.Proc. N. S. Inst. Sci . 42:xx-yy.

Vilks, G.1967.QuantitativeanalysisofforaminiferaintheBrasd’OrLakes.Report of Bedford Institute of Oceanography.67-1,84p.

Wright, R.A.1976.SomeproductionparametersatselectedBrasd’Orsites.InThe proceedings of the Bras d’Or Lakes aquaculture conference, Sydney, Cape Breton.(ed.M.G.McKay)CollegeofCapeBretonPress,Sydney,N.S.,54-66.

Young,J.1976.AquacultureandchemistryofBrasd’Or.INThe proceedings of the Bras d’Or Lakes aquaculture conference, Sydney, Cape Breton. (Ed. M.G. McKay) College of Cape Breton Press, Sydney, N.S., 17-28.

(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