shock and awe! es4ma4ng mysis density and catch avoidance ... · - we sampled on quarter and full...

Background

SampleDesign•  Our sampling scheme followed that of Wiebe et al. (2004, 2013) for krill

aggregaAonsindeepoceansoffAntarcAcaandinNorthAtlanAcOcean.•  WeconductedpoweranalysisofWiebeetal.(2013)’skrilldensityesAmatesto

esAmatenumbersofreplicates(n=4)neededtodetectsignificantdifferencesinMysisdensitybetweenstrobeonandstrobeoff.

WELLS,D.1,PSAROUTHAKIS,Z.1,RUTHERFORD,E.2,CHIN,T.1,VANDERPLOEG,H.2,CAVALETTO,J.2,GLYSHAW,P.1,andMason,D.2

1CooperaAveInsAtuteforLimnologyandEcosystemsResearch,2NOAAGLERL

ShockandAwe!Es4ma4ngMysisDensityandCatchAvoidanceusingtheMOCNESSinSELakeMichigan

Results

Acknowledgments:ThisworkissupportedbyNOAAGLERL.

Mysis diluviana (opossum shrimp) is a key member of Great Lakes aquaAc foodwebs and an important prey for pelagic fish. Mysis are visual predators ofzooplankton,andundergodiel verAcalmigraAon from the lakebo_om (day) intothewatercolumnatnight.MysisbiomassesAmatesarehighlyvariablebutcriAcalfor food web models that inform salmonid stocking decisions. In 2016, weevaluated catch efficiency of Mysis in a MulAple Opening/Closing Net andEnvironmentalSensingSystem(MOCNESS)withLEDstrobelighAngthatisusedtosample Euphausid shrimp (krill), plankton and fish larvae in marine waters. WemadereplicatetowsinthermallystraAfieddepthlayersduringnight,andcomparedMysis densiAes sampled with the LED strobe on vs strobe off. There were nosignificantdifferences inMysisdensityor size in sampleswith strobeonoroff inanymonth.MysisdensiAeswerehighestinthemetalimnionatnight.WeconcludethatthestrobeflashlighthadnoeffectoncatchavoidancebyMysis.

Abstract

WhynodifferenceinMysisdensityorsizeinnetswithstrobeon/off?•  Toomuchambientlight!

-Wesampledonquarterandfullmoonphases.-WaterclarityinLakeMichiganishigherthaninoceansduetoLM’slowerproducAvityandintensefiltraAonbyinvasivedreissenamussels. -Our samplesites inLakeMichiganwereshallowerandcloser toshore.Wiebe et al. (2013) sampled krill in deep, remote ocean sites far fromland.

•  PerhapsMysisaremorelightsensiAvethankrill.

WhywasMysisdensityhighestinmetalimnion?–Theymigrateatnighttoareasofhighzooplanktonpreydensity.

ResearchObjec4veandHypothesis•  EsAmatecatchavoidancebyMysisinLakeMichiganatamiddepthand

offshorestaAon(M45,M110)usingMOCNESSwithLEDstrobelights.

Figure1.MapofsamplingsitesoffMuskegon,MIinS.E.LakeMichigan.

Wiebe,P.E.,Ashjian,C.J.,Gallager,S.M.,Davis,C.S.,Lawson,G.L.,andCopley,N.J.2004.Usingahigh-poweredstrobelighttoincreasethecatchofAntarcAckrill.MarineBiology144:493–502.

Wiebe,P.E.,Lawson,G.L.,Lavery,A.C.,Copley,N.J.,Horgan,E.,andBradley,A.2013.ImprovedagreementofnetandacousAcalmethodsforsurveyingeuphausiidsbymiAgaAngavoidanceusinganetbasedLEDstrobelightsystem.ICESJ.MarineScience70:650-664.

ArebiggerMysiscaughtwithstrobeflash?

StudyAreaMysiswerecollectedfromS.E.LakeMichiganata45msite(M45)inJune,anda110msite(M110)inJulyandSeptember,2016(Figure1).

Methods

FieldCollecCons

Methods

Discussion&FutureDirec4ons

LiteratureCitedandAcknowledgments

Results

FutureWork

AremoreMysiscaughtwithLEDstrobeflash?

•  Sampleduringnewmoon.In2016,wesampledonquartermoon(June,July)andfull

moon(Sept.)phaseduetoshipavailability.•  TestwhetherMysiscatchabilityvariesbyLEDstrobeintensity,duraAonorpulse.

•  Evaluate catchability of fish larvae in nets with LED strobe on/off. Will larval fishcatchabilitybesuscepAbletostrobeflash“shockandawe”?We hypothesizedMysis densi4es sampled byMOCNESS would be higher

withtheLEDstrobelightonvs.off.

Figure2.AboveleI-VerAcalprofileoftemperatureatthe45mstaAoninJuly,andexampleofMOCNESSsampletrackinthemetalimnionwithLEDstrobeflashon(inwhite)andoff(inred).Aboveright–LaseropAcalplanktoncountershowshighestzooplanktondensityinthemetalimnion.BoLom-HydroacousAcsprofileshowshighestMysisdensiAesat18minthemetalimnion(1kmscreenimage).

Mysisdensityinthewatercolumn Figure3(ler).Mysis

collectedatnightatthe45msiteinJuneandthe110msiteinJulyindicatedmean(±s.e.)Mysisdensitywashigherinthemetalimnionthanintheepilimnion(p>0.236).ThehypolimnionwasnotsampledineithermonthbecauseoflackofAme.

Figure4(ler).Datafromallsitesandmonthsindicatetherewasnosignificantdifference(P>0.36)inmeandensity(±s.e.)ofMysiswithstrobeonoroff.

Figure5(ler).Datafromthe45msiteinJuneindicatetherewasnosignificantdifference(P>0.53)inmeanlength(±s.e.)ofMysiscaughtbetweenstrobeonoroff.

Mysis:arecold-watershrimp-likeorganismsthatfeedopportunisAcallyonplanktonandbenthos.Withtwostalkedcompoundeyes,MysisdielverAcalmigraAonishighlysensiAvetolightlevelandtemperature.

MOCNESSwithstrobeisaMulApleOpeningClosingNet,withanEnvironmentalSensingSystemplusLEDstrobelights.OurMOCNESSsystemhas9,1-m2nets;eachnetcanbeclosedandopenedindependentlyatdepthsothatitsamplesadiscretepatchofwater.TheMOCNESSrecordstemperature,depth,chlorophyll,oxygenandlightlevelsduringeachsample.TheLEDstrobelightshavebeenshowntoimprovecatchabilityofkrillinmarinesystems(Wiebeetal.2013)

WetargetedthermalstratawherelaseropAcalcountsofzooplanktonwerehighandbacksca_erfromfisheriesacousAcsshowedpotenAallyhighdensiAesofMysis.Wetow-yo’dMOCNESSnets(totalnumberofnetsamples=40)for10minuteseachwithinthermalstrata.Werandomizedtheon/offsequenceofLEDstrobelightsforeachnet.Allsampleswerepreservedinethanol,andMysiswerelatercountedandmeasuredinthelaboratory.

On

Off

Depth(m)

Amplitu

de(Db)