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  • ICES WKNEPH REPORT 2009 ICES ADVISORY COMMITTEE

    ICES CM 2009/ACOM:33

    Report of the Benchmark Workshop on Nephrops (WKNEPH)

    26 March 2009

    Aberdeen, UK

  • InternationalCouncilfortheExplorationoftheSeaConseilInternationalpourlExplorationdelaMer

    H.C.AndersensBoulevard4446DK1553CopenhagenVDenmarkTelephone(+45)33386700Telefax(+45)33934215www.ices.dkinfo@ices.dk

    Recommendedformatforpurposesofcitation:

    ICES.2009.ReportoftheBenchmarkWorkshoponNephrops(WKNEPH),26March2009,Aberdeen,UK.ICESCM2009/ACOM:33.156pp.

    Forpermissiontoreproducematerialfromthispublication,pleaseapplytotheGeneralSecretary.

    ThedocumentisareportofanExpertGroupundertheauspicesoftheInternationalCouncilfortheExplorationoftheSeaanddoesnotnecessarilyrepresenttheviewsoftheCouncil.

    2009InternationalCouncilfortheExplorationoftheSea

  • ICES WKNEPH REPORT 2009 | i

    Contents

    Executivesummary................................................................................................................3

    1 Openingofthemeeting................................................................................................4

    2 Adoptionoftheagenda................................................................................................5

    3 Backgroundtomeeting.................................................................................................6

    4 Commentsfromexternalreviewers...........................................................................8

    5 RecentProgresswithUWTV.....................................................................................10

    5.1 2007:WKNEPTVWorkshop on the Use of UWTV Surveys forDeterminingAbundanceinNephropsStocksthroughoutEuropeanWaters...................................................................................................................10

    5.2 2008: WKNEPBID: Workshop and training course on Nephropsburrowidentification.........................................................................................10

    5.3 2009:SGNEPS......................................................................................................11

    6 Alternativedatasources.............................................................................................12

    6.1 Fisherydependent..............................................................................................12

    6.2 TrawlSurvey.......................................................................................................12

    6.3 Lifehistoryandbiologicaldatasources..........................................................16

    6.4 Modellingapproaches........................................................................................206.4.1 Anagestructuredsimulationmodel..................................................206.4.2 SCA..........................................................................................................21

    7 Uncertaintyandpotentialbias..................................................................................22

    8 Methodologyfordeterminationofstockstatus.....................................................35

    8.1 Surveyasarelativeindex..................................................................................36

    8.2 Surveyasanabsoluteindex..............................................................................37

    9 Agreedmethodologyforproductionofcatchoptions..........................................39

    9.1 StepprocessforgenerationofcatchoptiontableinWGreports.................39

    9.2 Assumptionsregardingsurveyselectivity......................................................40

    9.3 Assumptionsregardingdiscardproportion...................................................41

    10 Futureresearchneeds..................................................................................................45

    Annex1: Listofparticipants................................................................................47

    Annex2: Agenda....................................................................................................51

    Annex3: References..............................................................................................52

    Annex4: Recommendations................................................................................55

    Annex5: SCA..........................................................................................................56

  • ii | ICES WKNEPH REPORT 2009

    Annex6: StockAnnex:FU6,FarnDeeps...........................................................62

    Annex7: StockAnnex:FU7,FladenGround....................................................69

    Annex8: StockAnnex:FU8,FirthofForth........................................................77

    Annex9: StockAnnex:FU9,MorayFirth..........................................................85

    Annex10: StockAnnex:FU10,Noup....................................................................95

    Annex11: StockAnnex:FU11,NorthMinch....................................................103

    Annex12: StockAnnex:FU12,SouthMinch....................................................111

    Annex13: StockAnnex:FU13,Clyde.................................................................119

    Annex14: StockAnnex:IrishSeaWestNephrops(FU15)..............................129

    Annex15: StockAnnex:FU17,AranGrounds..................................................137

  • 3 ICES WKNEPH REPORT 2009

    Executive summary

    TheBenchmarkWorkshoponNephropsassessment,heldinAberdeen,Scotlandfromthe26March2009,addressedtheproblemsencounteredwhilegeneratingTACadvice forNephrops in 2008.Theseproblems arose fromdifferent approaches inhandlinguncertaintyandpotentialbiaswhenusingunderwaterTVsurveystoestimatetheabundanceofNephropspopulationsinFunctionalUnits(FUs=thesubdivisionalgeographicalscaleonwhichNephropsareassessed).

    TheWorkshopfocusedFUs:6(FarnDeeps,DivisionIV),7(FladenGround,DivisionIV),8(FirthofForth,DivisionIV),9(MorayFirth,DivisionIV),11(NorthMinch,DivisionVI),12(SouthMinch,DivisionVI),13(Clyde,DivisionVI),15(IrishSeaWest,DivisionVIIa)and17(AranGrounds,DivisionVIIb).

    ExpertsonNephropsstockassessmentandlifehistory,industryrepresentatives,andapanelofthreeindependent,externalexpertswerepresent.ThemeetingwaschairedbyKevinStokesbury.Themeetingopenedwithpresentationscoveringtheevolutionof theNephropsTV surveys, theiruseand recentdevelopments inanalysisandassessment,Nephropslifehistoryandinformationonthefishery.

    ThefirstdecisionforthegroupwaswhethertheTVsurveyindicesshouldbeusedasrelative or absolute indices of abundance. Initially the group consideredusing thesurveysasarelativeindextherebyavoidingtheestimationofbiascorrectionfactors.Thebias foreachFU is listed inaTableofUncertainty.However thisstill requiressomecouplingofthesurveytoabsoluteTACadviceandnoobviousroutetomakingthislinkcouldbefound.Theuncertaintyinhistoricallandingsinformationwascriticallylimiting.ThegroupthereforerevertedtousingtheTVindexasanabsoluteindex andmade initial estimates of the various potential sources of bias. For eachsurvey,eachpotentialsourceofbiaswastabulatedandquantified.

    PreviouslytheTVsurveyswereassumedtohavethesameselectivityasthefishery.A comparisonof fisherydependent and independentdata in the IrishSeademonstrated that there was a portion of the population which was physically on theground and available to fishing gear butdoes not appear in the sampled catches.ThesesmallerNephropsarecapableofconstructing theirown independentburrowsandthissuggeststhattheTVsurveylikelyobservedburrowsofindividualsareconsiderablysmallerthanthefisheryselects.Usingacombinationofexpertknowledgeandonscreenmeasurements,thegroupsuggestedaknifeedgedetectionselectivityof17mmforallareas.ThisrevisionofTVsurveyselectivityrequiredarevisionofthesustainableharvestrate.Newharvestratescorresponding to fishingatF0.1andFmaxwerecalculatedforeachFunctionalUnit.

    Standardprotocols for thehandlingofTV surveydataand thegenerationof ICEScatchoptiontableswereproducedandincorporatedintotheStockAnnexesforeachFunctionalUnit.Research recommendationswereprovide that should improve theestimatesofuncertaintyinthenextfewyears.

  • 4 | ICES WKNEPH REPORT 2009

    1 Opening of the meeting

    Themeetingopenedwithpresentations covering the evolutionof theNephropsTVsurveys,theiruseandrecentdevelopmentsinanalysisandassessment,Nephropslifehistoryandinformationonthefishery.

  • ICES WKNEPH REPORT 2009 | 5

    2 Adoption of the agenda

    Theagendawasadoptedwithoutquestion.

  • 6 | ICES WKNEPH REPORT 2009

    3 Background to meeting

    Since2001therehasbeenaprogressionofchangesinthedevelopmentofadviceonNephropsfisheries.(Seetexttablebelow).

    YEAR ICES GROUPS ADVICE BASIS ADVICE DEVELOPMENTS

    2001 WGNEPH Indicators/trendsIncXSA&ICA

    Averagelandings

    2002 WGNEPH(amixtureofassessmentandstudygroup)

    Indicators/trendsIncXSA

    AdviceforAreasVIIIandIXa(FUs2331)

    2003 WGNEPH Indicators/trendsIncXSA&ICA

    Averagelandings

    2004 WGNEPH(amixtureofassessmentandstudygroup)

    Indicators/trendsIncXSA

    AdviceforAreasVIIIandIXa(FUs2331)

    EvaluationofPredictions

    2005 WGSSDS,WGNSDS,WGHMM,WGNSSK

    Indicators/trendsincludingXSA

    Averagelandings

    MixedFisheriesMTACAgebasedVPAswerecalledintoquestion

    2006 WKNEPH(workshoponNephropsmaturity)

    WGSSDS,WGNSDS,WGHMM,WGNSSK

    STECF0.1/TVharvestratioIndicators/trendsIncXSA(forFUswithoutTVsurveys)

    Noincreaseineffort

    2007 WKNEPHTV

    Simulationofexploitation.Uncertaintytablesinthecontextofusingthesurveyasrelativeorabsolute

    WGSSDS,WGNSDS,WGHMM,WGNSSK

    WhereUWTVsurveysexisteda15%harvestratewasapp