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Figure 1. Numerical grid, bathymetry (isobaths every 50 m), and meteorological stations. Initial particles location in southern Lake Michigan is also shown.

Conclusions• Firstphysical-biologicalmodelforlarvalfishintheGreatLakeswasbuilt.•Modelresultsshowsignificantinterannualvariabilityinlarvaltransportandgrowth.•ModelresultsareconsistentwithmanyrecentobservationsinLakeMichigan.• Physicalmodelresultscanbeusedforotherlarvalfishmodelingin1998-2003.

Modeling the Transport of Larval Yellow Perch in Lake Michigan

Objectives• SimulatelarvalyellowperchtransportinLakeMichiganusing3Dcirculationmodelresults.

•Developcoupledbiophysicalmodeltopredictlarvaltransport,larvalgrowth,settlementandsurvivalin6years(1998-2003).

• Explaininter-annualvariabilityinlarvalsurvivalandrecruitmentduetotemperatureandlake-widecirculation.

ApproachHydrodynamic Model- Princeton Ocean Model (Blumberg and Mellor, 1987)• Fully3DnonlinearNavier-Stokesequations• Freeuppersurfacewithbarotropic(external)mode• Baroclinic(internal)mode•Mellor-Yamadaturbulencemodelforverticalmixing• Terrainfollowingverticalcoordinate(sigma-coordinate)

A3-dimensionalcirculationmodelofLakeMichigan(Beletskyetal.,2006)isusedtocalculatelakecirculationona2kmgrid(Figure1).

Particle Trajectory Model• 3DmodelisbasedonthePOMsubroutineTRACE(byJ.Berntsen).• Particlesarepassiveandneutrallybuoyant.

Individual Based Perch Growth ModelGrowth=Consumption-Losses(Losses=Respiration,Egestion,Excretion)

•Determineslengthoftimelarvaecandriftuntilsettlementat30-50mm.• Consumptionisafunctionoftemperature,larvalweightandzooplanktonpreydensity.

• Preydensitiesareconstantintimeandspace(notenoughinformationonspatialandtemporalvariability).

•Nomortality.

ResultsPhysicsMonthlyaveragesurfacetemperaturepatternsforeachsummerin1998-2000arepresentedinFigure2a.Thereisageneralnorth-southtemperaturegradientseeninallmonthsinallyears.Anotherprominentfeatureoflaketemperaturepatternsisawind-drivenupwellingatthewestcoasttypicalofsummerconditionsinLakeMichigan(BeletskyandSchwab,2001).InsouthernLakeMichigan,surfacetemperaturesteadilyincreasedfromabout17oCinJuneto22oCinJulyto23oCinAugustofboth1998and1999.Inallsummermonthsof2000lakesurfacetemperaturewasabout1-2oClowerwhichshouldhaveimportantimplicationsonlarvalgrowthaswillbeshowninthenextsection.ModelresultswereevaluatedwithsurfacetemperatureobservationsatNOAAbuoys45002and45007,andlake-widesatellitetemperatureobservations(Figure2b).

ThecirculationpatterninsouthernLakeMichiganoftenconsistedoftwogyreswiththecyclonicgyreconfinedtothedeepareaandtheanticyclonicgyreintheshallowsouthernmostarea(Figure3).Duringsomemonths(August1998,JuneandAugust2000),astrongnorthwardcurrentfromsouthernLakeMichiganpenetratedthenorthernbasinwithsignificantimplicationsforlarvaltransport.Thespeedofmeansurfacecurrentsvariedfrom10to20cm/s.

Intheparticletrajectorymodel,246particleswerereleasednorthofChicago(Figure1)atbathymetricdepthsoflessthan10m.Particlesweredistributeduniformlywithdepth:nearthesurface,at1/3andat2/3ofagridcell’sdepth.ParticlemodelrunsbeganonJunefirstofeachyear(1998,1999,and2000)andendedintheendofAugust.ParticlelocationsattheendofeachmonthareshowninFigure4.Becauseallparticleswerereleasedinveryshallowwaterstheyhaveatendencytostayrelativelyclosetothesurface(0-20m).Overall,particlemovementmatchesthemonthlymeansurfacecurrentpatternratherwell:particlesinitiallymoveoffshoreandthencontinuetocirculateinsouthernLakeMichiganinananticyclonicfashion.Undercertainconditions(likeacaseofaparticularlystrongnorthwardcoastalcurrentinAugust1998)asignificantnumberofparticlesescapethesouthernbasinandpenetratethenorthernbasinofLakeMichigan.TheproximityofparticlestoshoreattheendofthemodelruninAugustcanalsobecriticalforlarvalsurvival.Larvaeaboutthistimebegintometamorphoseintotheiradultcharacteristicsandmoveintoadulthabitat,whichisnearbottomandnearshore.Asmodelresultsshow,in1998thenumberofparticlesreachingnearshorewatersinAugustwassignificantlyhigherthanin1999and2000whichmayprovideasignificantadvantageforsurival.

BiologyAlllarvaewereassumedtohaveinitiallengthof6mmathatching.Movementandgrowthoflarvaeinthemodelwerefollowedfromhatchingto30-50mm,thelengthatwhichtheysettleandbecomedemersal;larvaemetamorphoseintojuvenilesat20mm,andby30mmtakeonthecharacteristicsofadultfish.Growthratesandtimetosettlementwerepredictedassumingtwodifferentfoodavailabilityscenarios.Thiswasdonebymultiplyingmaximumconsumptionby1.0(Scenario1)and0.5(Scenario2).Inallbiologicalmodelrunsweassumedthatthereisnospatialgradientinfood(zooplankton)availableforlarvalyellowperch.Locationsoflarvaewhichreached30mmlengthunderthemaximumconsumptionconditions(Scenario1)areshowninFigure5.Nolarvaereached30mmbeforetheendofthefirstmonthexceptasmallnumberin1999.Onthecontrary,alllarvaereached30mmbytheendofthesecondmonthandthereforeJulyandAugustlocationsmatchexactlythoseofFigure4.Incaseofthereducedconsumptionscenario2(moretypicalofrealisticLakeMichiganconditions)thesituationchangesdramatically.Asexpected,nolarvaereached30mmbytheendofJunebutbytheendofJulyonlyafewlarvaereached30mmin2000whilein1998and1999morethan60%oflarvaegrewtotheirsettlementlength(Figure6).Thisisundoubtedlytheresultofmuchcoolerwatertemperaturesin2000predictedbythehydrodynamicmodelandconfirmedbysurfacetemperatureobservationsattheNDBCbuoy45007.Biophysicalmodelperformancewasevaluatedbycomparingmodelresultswithindependentobservationsofage-0yellowperchabundancefrom1998to2003(Beletskyetal.,2007).

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Figure 2a. Modeled lake surface temperature in 1998-2000.

Figure 2b. Modeled (black) versus observed (red) lake surface temperature at 45002, 45007 and lake-averaged in 1998-2003.

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Figure 3. Surface currents in 1998-2000.

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Figure 4. Particle transport in 1998-2000, total number of particles shown.

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Figure 5. Larval transport and growth, Scenario 1 (see explanation in text). Total number of larvae reached 30 mm also shown.

Figure 6. Larval transport and growth, Scenario 2 (see explanation in text). Total number of larvae reached 30 mm also shown.

6/30/1998Day = 181

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Problem StatementYellowperch(Percaflavescens)isecologicallyandeconomicallyimportantspeciesinLakeMichiganthathassufferedrecruitmentfailuresoverthelastdecade(Francisetal.,1996).Causesforpoorrecruitmentarenotunderstood,butarebelievedtobearesultofhighmortalityduringthelarvalstage.ThegoalofthisprojectistobeginexploringtheeffectsofphysicalfactorsonrecruitmentvariabilityofimportantLakeMichiganfishesinordertogaininsightintothedeclineintheyellowperchpopulationsandfactorscausingpoorrecruitment.Inthisproject,weapplyamodel-basedLangrangianapproachthatutilizes3-Dcirculationandthermalprocesses,physiologyandecologyoffishlarvae,andtrophodynamicsforunderstandingrecruitmentdynamicsinLakeMichiganspecifically,andtheotherGreatLakesingeneral.IntheinitialsetofnumericalexperimentswefocusonthetransportoflarvalyellowperchhatchedintheareainsouthernLakeMichiganknownforhighconcentrationsofrockyhabitatpreferredbyyellowperchspawners(Figure1).

Dmitry Beletsky1, David Schwab2, Doran Mason2, Edward Rutherford2, Michael McCormick2, Henry Vanderploeg2, John Janssen3, David Clapp4, and John Dettmers5 1Cooperative Institute for Limnology and Ecosytems Research, Ann Arbor, MI, 2NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI,

3Great Lakes Water Institute, Univ. of Wisconsin-Milwaukee, 4Michigan DNR, Charlevoix, MI, 5Lake Michigan Biological Station, Zion, IL

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Cooperative Institute for Limnologyand Ecosystems Research

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