3 International Stock Assessment and Data Needs

26 EIFAC/ICES WGEEL Report 2008

3 International stock assessment and data needs

3.1 Introduction on stock assessment and data needs

TheȱEuropeanȱUnionȱhasȱdecidedȱonȱaȱprotectionȱandȱrestorationȱplanȱ(EelȱRegulaȬ tion)ȱinȱ2007,ȱaimingȱatȱtheȱprotectionȱofȱ40%ȱofȱtheȱsilverȱeels,ȱrelativeȱtoȱaȱsituationȱ withoutȱ humanȱ influence.ȱ Atȱ theȱ heartȱ ofȱ theȱ Regulationȱ isȱ theȱ obligationȱ forȱ allȱ MemberȱStatesȱtoȱdevelopȱaȱ(nationalȱorȱriverȱbasinȱspecific)ȱmanagementȱplanȱforȱtheȱ eelȱ stockȱ andȱ fisheries,ȱ aimingȱ atȱ theȱ agreedȱ 40%ȱ target.ȱ Eachȱ managementȱ planȱ shouldȱcontainȱanȱassessmentȱofȱtheȱcurrentȱstatusȱofȱtheȱlocalȱstock,ȱaȱdescriptionȱofȱ futureȱmonitoringȱandȱregistrationȱofȱcatchȱandȱfisheriesȱforȱfutureȱassessmentsȱofȱtheȱ stockȱandȱanthropogenicȱimpacts.ȱ

Theȱ WGEELȱ considersȱ itsȱ tasksȱ (ICESȱ andȱ EIFACȱ ToRs)ȱ toȱ assessȱ andȱ evaluateȱ theȱ overallȱstatusȱofȱtheȱstock,ȱandȱtheȱimpactȱofȱprotectionȱmeasuresȱtaken.ȱThereȱisȱanȱ apparentȱoverlapȱwithȱtheȱobligationȱinȱtheȱEelȱRegulation,ȱtoȱreportȱonȱtheȱstatusȱofȱ theȱstockȱinȱindividualȱEelȱManagementȱUnits,ȱandȱwithȱtheȱevaluationȱbyȱtheȱComȬ mission.ȱHowever,ȱtheȱassessmentȱofȱtheȱworkingȱgroupȱwillȱfocusȱonȱtheȱtotalȱpopuȬ lation,ȱindependentȱofȱtheȱsplitȱoverȱjurisdictionsȱandȱmanagementȱunits.ȱOnlyȱwhereȱ theȱbiologicalȱprocessesȱareȱinherentlyȱspatiallyȱdiversified,ȱwillȱtheȱassessmentȱofȱtheȱ workingȱgroupȱgoȱintoȱdisaggregateȱanalyses.ȱ

Thisȱchapterȱwillȱelaborateȱtheȱconceptsȱofȱanȱinternationalȱassessmentȱofȱaȱregionallyȱ managedȱstockȱ(Sectionȱ3.2),ȱandȱderiveȱcriteriaȱforȱaȱminimallyȱrequiredȱdatasetȱonȱ eelȱ(Sectionȱ3.3).ȱ

3.2 International stock assessment

3.2.1 International management and stock assessment

TheȱEUȱRegulationȱonȱeelȱsetsȱaȱcommonȱtargetȱforȱtheȱescapementȱofȱsilverȱeels,ȱatȱ 40%ȱ ofȱ theȱ naturalȱ escapementȱ inȱ theȱ absenceȱ ofȱ anthropogenicȱ impacts.ȱ Inȱ accorȬ danceȱ withȱ theȱ precautionaryȱ adviceȱprovidedȱ byȱ ICESȱ (2002),ȱitȱ isȱ assumedȱ thatȱ aȱ stockȱrecruitmentȱrelationshipȱexists.ȱMemberȱStatesȱareȱobligedȱtoȱimplementȱprotecȬ tiveȱmeasuresȱtoȱachieveȱtheȱescapementȱtarget,ȱandȱshouldȱprovideȱaȱtimeȱscheduleȱ forȱ theȱ attainmentȱ ofȱ thisȱ target.ȱ Thisȱ timeȱ scheduleȱ isȱ certainlyȱ muchȱ moreȱ deterȬ minedȱbyȱtheȱslowȱbiologicalȱrestorationȱofȱtheȱstockȱ(decades;ȱÅströmȱandȱDekker,ȱ 2007),ȱ thanȱ byȱ theȱ timeȱ requiredȱ to ȱ implementȱ theȱ protectionȱ measuresȱ completelyȱ (years?).ȱTheȱRegulationȱsetsȱnoȱlimitȱonȱtheȱtimeȱframeȱforȱrestoration.ȱImplicitly,ȱthisȱ rulesȱoutȱtheȱhypothesisȱthatȱtheȱstock–recruitmentȱrelationshipȱisȱdeterminedȱbyȱdeȬ pensatoryȱprocesses,ȱasȱtentativelyȱfoundȱinȱhistoricalȱdataȱ(Dekker,ȱ2004;ȱICESȱ2007).ȱ Asȱ anȱ alternativeȱ toȱ theȱ depensationȱ hypothesis,ȱ itȱ hasȱ beenȱ hypothesized,ȱ thatȱ theȱ declineȱofȱtheȱstockȱmightȱhaveȱbeenȱcausedȱbyȱclimateȱfactorsȱ(Chapterȱ7ȱofȱthisȱreȬ port),ȱpollutionȱorȱparasitismȱ(chapterȱ6ȱofȱthisȱreport),ȱandȱothersȱactingȱinȱtheȱoceȬ anicȱphase.ȱ

NotingȱthatȱtheȱEUȱEelȱRegulationȱhasȱsetȱtargetsȱforȱtheȱquantityȱ(biomass)ȱofȱsilverȱ eelsȱescapingȱfromȱtheȱcontinent,ȱandȱobligesȱMemberȱStatesȱtoȱtakeȱprotectiveȱmeasȬ uresȱprimarilyȱfocusingȱonȱtheȱquantitiesȱescaping,ȱbutȱhasȱnotȱsetȱtargetsȱandȱdoesȱ notȱobligeȱtoȱtakeȱactionsȱwithȱrespectȱtoȱotherȱprocessesȱ(relatedȱtoȱsilverȱeelȱquality,ȱ orȱ climateȱ change)ȱ in ȱ relationȱ toȱ eelȱ managementȱ (ifȱ possible),ȱ theȱ internationalȱ asȬ sessmentȱofȱtheȱstatusȱofȱtheȱstockȱwillȱpresentlyȱfocusȱonȱtheȱdynamicsȱofȱstockȱinȱ numbersȱ andȱ quantities,ȱ andȱ onȱ theȱ effectȱ ofȱ protectionȱ andȱ restorationȱ measuresȱ taken.ȱThisȱdoesȱnot,ȱinȱprinciple,ȱruleȱoutȱpotentialȱeffectsȱofȱotherȱfactors, ȱincludingȱ silverȱ eelȱ qualityȱ and/orȱ climateȱ factors.ȱ However,ȱ sinceȱ theȱ mechanismsȱ involvedȱ EIFAC/ICES WGEEL Report 2008 27

haveȱnotȱbeenȱclearedȱup,ȱandȱtheȱquantitativeȱimpactȱonȱtheȱstockȱisȱunclear,ȱthereȱisȱ noȱ wayȱ forwardȱ toȱ includeȱ theseȱ aspectsȱ inȱ internationalȱ stockȱ assessmentȱ atȱ thisȱ momentȱinȱtime.ȱFurtherȱresearchȱwillȱbeȱneeded,ȱtoȱelucidateȱtheȱprocesses,ȱtoȱquanȬ tifyȱtheȱimpacts,ȱtoȱfindȱmitigationȱmeasures,ȱtoȱadviseȱmanagementȱtargets,ȱandȱtoȱ assessȱ theȱ netȱ effectsȱ ofȱ measuresȱ takenȱ onȱ theȱ eelȱ stock.ȱ Untilȱ thatȱ hasȱ beenȱ done,ȱ primeȱ focusȱ inȱ theȱ stockȱ assessmentȱ willȱ necessarilyȱ restȱ withȱ “classical”ȱ fishȱ stockȱ assessment,ȱwhichȱforȱtheȱeelȱcase,ȱwillȱbeȱcomplexȱenough.ȱ

Underȱ theȱ EUȱ Eelȱ Regulation,ȱ an ȱ internationalȱ assessmentȱ willȱ beȱ requiredȱ ofȱ theȱ populationȬwideȱstatusȱofȱtheȱstock,ȱandȱanȱassessmentȱofȱtheȱimpactȱofȱtheȱmanageȬ mentȱmeasuresȱtaken.ȱTheȱRegulationȱfocusesȱonȱstockȱdynamicsȱinȱtermsȱofȱquantiȬ tiesȱandȱbiomassȱandȱthusȱtheȱassessmentȱleavesȱasideȱscientificȱdebatesȱonȱtheȱimpactȱ ofȱspawnerȱqualityȱand/orȱclimateȱfactors.ȱAȱdecisionȱtreeȱdiagramȱforȱthisȱassessmentȱ isȱpresentedȱinȱFigureȱ3.1.ȱTheȱindicatedȱstepsȱareȱelaboratedȱinȱtheȱtextȱbelow;ȱ

START

1. Trend in recruitment? increase 1.a increase continues over a long period (decades)? yes Success !!

Recruitment does not restore, despite increasing silver eel escapement. decrease, or This is NOT consistent with the precautionary assumption of a minor increase (standard) stock-recruitment relationship. Several hypotheses arise: - incorrect assessment of trends in recruits or silver eels - stock-recruitment relationship is non-standard (e.g. depensatory) - unaccounted anthropogenic impacts (e.g. pollution, parasites, ...) 2. Global trend in silver eel increase - external pertubating processes (e.g. climate, ...) Further research will be required in order - to correct monitoring deficiencies, - to resolve the cause of the apparent mismatch between trends decrease - to develop mitigation measures, if possible - to set targets for cause, mitigation measure and effect on the eel stock - to post-evaluate net effects of these measures on the eel stock.

3. Local trend in silver eel escapement ? Locally successful management, encourage other areas to do the same, increase Assess by River Basin District! and consider stronger measures to speed up the recovery process!

decrease Density dependence generally occurs where stock density is close to the potential maximum (carrying capacity). If local silver eel escapement declines, while available habitat does not, this indicates that that maximum is NOT reached anymore. 4. Is density dependence dominating Consider the following: the current local silver eel escapement? yes - incorrect assessment of trends Assess by River Basin District! - density dependence was actually not dominating the stock dynamics - unaccounted (non)-anthropogenic impacts, changing the carrying capacity. Research will be required, to find cause and remedy. Meanwhile, a further no precautionary reduction in anthropogenic impacts will be required.

5. Is relative survival (spawner per recruit) Await slow recovery, according to your local time schedule, consistent with your local time schedule? yes or take stronger measures to speed up the recovery process! Assess by River Basin District!

"Standard" fish stock assessment tools, including cohort-models, length-based assessments, etc. Tool-box development and standardisation of post-evaluation techniques is recommended. Development of standard targets for survival and time schedule is recommended. Escapement and survival below expectation, much stronger protective measures required!!

Figureȱ3.1:ȱDecisionȱtreeȱforȱinternationalȱassessmentȱofȱtheȱimpactȱofȱprotectiveȱmeasuresȱtakenȱ underȱ theȱ EUȱ Eelȱ Regulation.ȱ Internationalȱ issuesȱ areȱ depictedȱ inȱ aȱ singleȬlinedȱ box,ȱ whereasȱ RiverȱBasinȱSpecificȱissuesȱareȱinȱaȱdoubleȬlinedȱbox.ȱ 28 EIFAC/ICES WGEEL Report 2008

3.2.2 Only recruitment and escapement trends?

Takingȱaȱsuperficialȱ viewȱonȱ firstȱ examinationȱ ofȱ theȱ taskȱ ofȱinternationalȱ stockȱ asȬ sessment,ȱitȱmightȱappearȱthatȱtheȱtimeȬseriesȱdataȱonȱspawnerȱemigrationȱandȱglassȱ eelȱ recruitmentȱ areȱ theȱ onlyȱ dataȱ itemsȱ ofȱ informationȱ essentialȱ toȱ internationalȱ asȬ sessmentȱofȱeelȱstockȱandȱrecruitment.ȱThisȱview,ȱhowever,ȱignoresȱtheȱrealityȱofȱtheȱ currentȱ andȱ probableȱ futureȱ situation.ȱ Onlyȱ ifȱ recruitmentȱ wereȱ toȱ recoverȱ rapidlyȱ followingȱmeasuresȱtoȱincreaseȱspawningȱstock,ȱresultingȱinȱconfidenceȱthatȱrecoveryȱ isȱunderway,ȱwouldȱtheseȱtwoȱdataȱitemsȱsuffice.ȱSuchȱaȱrapidȱrecoveryȱisȱanȱunlikelyȱ scenario,ȱgivenȱthatȱourȱabilityȱtoȱincreaseȱspawningȱstockȱescapementȱsignificantlyȱ willȱ beȱ limitedȱ forȱ atȱ leastȱ anȱ eelȱ generation,ȱ asȱ aȱ consequenceȱ ofȱ theȱ pastȱ 15ȱ toȱ 25ȱ yearsȱofȱlowȱrecruitmentȱyetȱtoȱfeedȱthroughȱtoȱspawnerȱemigrationȱ(Chapterȱ2ȱofȱthisȱ report).ȱ Itȱ isȱ quiteȱ probable,ȱ therefore,ȱ thatȱ recruitmentȱ willȱ continueȱ toȱ declineȱ forȱ someȱtime,ȱandȱitȱwillȱbeȱalmostȱunavoidableȱthatȱsilverȱeelȱescapementȱwillȱalsoȱdeȬ clineȱconsiderablyȱfurtherȱforȱatȱleastȱsomeȱyears.ȱTheȱeffectivenessȱofȱprotectionȱandȱ restorationȱ measuresȱ takenȱ underȱ theȱ EUȱ Eelȱ Regulationȱ willȱ thereforeȱ haveȱ toȱ beȱ judgedȱonȱaȱrelativeȱscale:ȱtheȱrelativeȱimprovementȱofȱsurvivalȱ fromȱrecruitȱtoȱsilverȱ eel.ȱThisȱnecessitatesȱtheȱanalysisȱofȱtheȱfullȱcontinentalȱphaseȱofȱtheȱlifeȱcycle.ȱ

3.2.3 Issues of time-scale

TheȱprincipalȱobjectiveȱofȱWGEELȱatȱitsȱfutureȱmeetingsȱwillȱbeȱassessment,ȱrenewedȱ annually,ȱofȱtheȱstateȱofȱtheȱstockȱandȱrecruitmentȱatȱanȱinternationalȱlevel.ȱTheȱdeȬ siredȱobjectiveȱofȱcurrentȱmanagementȱisȱclearlyȱthatȱmeasuresȱtakenȱtoȱprotectȱandȱ enhanceȱspawnerȱescapementȱresultȱinȱincreasedȱrecruitment.ȱTheȱtimeȬscaleȱforȱfullȱ evaluationȱ ofȱ suchȱ successȱ isȱ long,ȱ andȱ forȱ assuredȱ confidenceȱ thatȱ recoveryȱ isȱ unȬ derway,ȱanyȱrecoveryȱwillȱhaveȱtoȱbeȱsuccessfullyȱtrackedȱthroughȱtheȱgenerations,ȱ thatȱis:ȱoverȱdecades.ȱ

3.2.4 If recruitment continues to decline

Shouldȱrecruitmentȱnotȱrespondȱpositivelyȱtoȱincreasedȱspawnerȱbiomass,ȱandȱconȬ tinueȱ toȱ fallȱ whereasȱ spawningȬstockȱ biomassȱ isȱ rising,ȱ thenȱ thereȱ areȱ otherȱ factorsȱ operatingȱthanȱthoseȱincludedȱinȱtheȱassumptionsȱ(thatȱeelȱwillȱfollowȱclassicalȱstock– recruitmentȱrelationships).ȱ

Whereȱsuchȱconclusionȱisȱreached,ȱatȱanyȱpointȱinȱtheȱassessmentȱandȱstudyȱofȱeel,ȱitȱ wouldȱ beȱ evidentȱ thatȱ unknownȱ factor(s)ȱ areȱ actingȱ onȱ theȱ stock–recruitmentȱ relaȬ tionship.ȱThisȱbringsȱinȱpossibilitiesȱsuchȱasȱaȱproblemȱinȱoceanicȱprocessesȱaffectingȱ migration,ȱ eelȱ “quality”ȱ factorsȱ affectingȱ spawningȱ ability,ȱ geneticȱ issues,ȱ orȱ aȱ newȱ andȱunforeseenȱproblemȱresultingȱinȱdepensationȱinȱtheȱSȬRȱprocess.ȱTheseȱscenariosȱ wouldȱ allȱ forceȱ anȱ urgentȱ searchȱ throughȱ researchȱ programmesȱ onȱ possibleȱ addiȬ tionalȱ causesȱ ofȱ decline,ȱ whichȱ isȱ ofȱ courseȱ anȱ optionȱ atȱ anyȱ stageȱ whereȱ newȱ eviȬ denceȱofȱdetrimentalȱfactorsȱarises.ȱTheseȱ“new”ȱproblems,ȱhowever,ȱhaveȱalwaysȱtoȱ beȱresearchedȱthroughȱaȱprocessȱinvolvingȱdataȱgathering,ȱcorrelation,ȱquantificationȱ ofȱcauseȱandȱeffect,ȱdevelopment,ȱproposalȱandȱadoptionȱofȱmitigationȱmeasures,ȱandȱ postȱ evaluationȱ beforeȱ theyȱ canȱ beȱ fullyȱ builtȱ inȱ toȱ theȱ assessmentȱ ofȱ SȬRȱ orȱ RȬSSBȱ processes.ȱItȱisȱthereforeȱnecessaryȱthatȱtheȱ“new”ȱlinesȱofȱpotentialȱimpactȱresearchȱ areȱcontinuallyȱprogressedȱthroughȱresearchȱprogrammesȱalongsideȱtheȱannualȱstockȱ assessmentȱprocess,ȱsoȱthatȱwhenȱandȱifȱnumericalȱestimatesȱofȱtheirȱimpactȱareȱavailȬ able,ȱtheseȱcanȱbeȱtakenȱintoȱaccount.ȱ

Ifȱ recruitmentȱ doesȱ notȱ respondȱ toȱ spawnerȱ enhancementȱ measures,ȱandȱ spawningȱ stockȱcontinuesȱtoȱdecline,ȱthenȱtheȱassessmentȱprocessȱisȱrequiredȱtoȱinvestigateȱbioȬ logicalȱ andȱ mortalityȱ processesȱ atȱ aȱ spatiallyȱ disaggregatedȱ level.ȱ Inȱ principle,ȱ theȱ analysisȱcouldȱproceed,ȱatȱaȱbiologicallyȱmeaningfulȱdisaggregatedȱlevel.ȱInȱpractice,ȱ EIFAC/ICES WGEEL Report 2008 29

however,ȱtheȱRBDȱlevelȱwillȱbeȱmuchȱmoreȱeasilyȱachievable.ȱAtȱthisȱlevel,ȱmanageȬ mentȱmeasuresȱhaveȱbeenȱtaken,ȱandȱdataȱonȱstock,ȱfisheriesȱandȱotherȱanthropogenicȱ impactsȱhaveȱbeenȱgathered.ȱIndeed,ȱtheȱprobableȱsituationȱoverȱtheȱcomingȱtwoȱdecȬ adesȱisȱatȱbestȱcontinuedȱlowȱspawnerȱemigrationȱprotectedȱtoȱsomeȱdegreeȱbyȱmeasȬ uresȱtoȱbeȱtakenȱunderȱmanagementȱplansȱrequiredȱtheȱeelȱregulation,ȱwithȱglassȱeelȱ recruitmentȱ atȱ bestȱ displayingȱ aȱ slowȱ recoveryȱ butȱ perhapsȱ continuingȱ itsȱ decline.ȱ Managementȱplansȱmayȱfailȱtoȱgenerateȱanyȱincreaseȱinȱspawners,ȱsomeȱthroughȱnoȱ faultȱofȱtheȱplansȱbutȱsimplyȱasȱaȱconsequenceȱofȱtheȱhistoryȱofȱlowȱrecruitment,ȱandȱ someȱ throughȱ inadequacyȱ inȱ theȱ plan.ȱ Inȱ thisȱ scenario,ȱ itȱ willȱ becomeȱ necessaryȱ toȱ carryȱ outȱ aȱ spawnerȬperȬrecruitȱ analysesȱ atȱ theȱ internationalȱ levelȱ (thatȱ isȱ probablyȱ theȱsimpleȱsumȱofȱriverȱbasinȱspecificȱanalyses)ȱtoȱdistinguishingȱbetweenȱtheseȱtwoȱ possibleȱ causesȱ ofȱ unpredictedȱ lowȱ spawnerȱ production.ȱ Thisȱ analysisȱ willȱ requireȱ accessȱtoȱdataȱtoȱexamineȱprocessesȱoperatingȱatȱleastȱatȱtheȱeelȱmanagementȱunit,ȱandȱ preferablyȱtheȱriverȱbasinȱlevel.ȱ

3.3 Data requirement

Anȱ internationallyȱ coordinatedȱ internationalȱ stockȱ andȱ recruitmentȱ assessmentȱ forȱ Europeanȱ eelȱ hasȱ aȱ minimumȱ dataȱ requirement,ȱ whichȱ isȱ notȱ yetȱ met.ȱ Theȱ dataȱ neededȱforȱfutureȱinternationalȱstock–recruitmentȱassessmentȱareȱaȱminimumȱof:ȱ

1ȱ) EscapementȱestimatesȱfromȱallȱEelȱRiverȱBasins,ȱinȱabsoluteȱtermsȱ(biomassȱ andȱnumbers,ȱbyȱsex),ȱcombinedȱwithȱ 2ȱ) Recruitmentȱindicesȱindicativeȱofȱrecruitmentȱstrengthȱoverȱ theȱwholeȱdisȬ tributionȱarea.ȱ

3.3.1 River Basin vs. international uses of data

TheȱsumȱofȱtheȱescapementȱestimatesȱoverȱtheȱdistributionȱareaȱprovidesȱaȱproxyȱesȬ timatorȱ ofȱ theȱ spawningȱ stockȱ size,ȱ whereasȱ recruitmentȱ indicesȱ quantifyȱ theȱ offȬ spring.ȱ Theȱ combinationȱ ofȱ spawningȱ stockȱ sizeȱ andȱ recruitmentȱ indexȱ facilitatesȱ assessmentsȱ ofȱ stockȱ statusȱ andȱ analysisȱ ofȱ theȱ stock–recruitmentȱ relationshipȱ andȱ potentialȱeffectsȱofȱclimaticȱfactorsȱonȱtheȱoceanicȱlifeȱphase.ȱ

Theȱanalysisȱofȱtheȱstockȱdynamicsȱinȱtheȱcontinentalȱphase,ȱi.e.ȱaȱspawnerȬperȬrecruitȱ analysis,ȱrequiresȱdataȱfromȱtheȱcontinentalȱphase,ȱwhichȱresidesȱwithinȱnationalȱwaȬ ters,ȱ withinȱ Eelȱ Managementȱ Unitsȱ (EMUs).ȱ Sinceȱ theȱ biologicalȱ characteristics,ȱ asȱ wellȱasȱtheȱanthropogenicȱimpactsȱonȱtheȱstockȱvaryȱfromȱregionȱtoȱregion,ȱaȱsingleȱ unifiedȱ assessmentȱ ofȱ theȱ statusȱ ofȱ theȱ stockȱ willȱ notȱ beȱ feasible,ȱ otherȱ thanȱ onȱ anȱ EMUȱbyȱEMUȱbasis.ȱ

NeitherȱtheȱEelȱRegulation,ȱnorȱtheȱWaterȱFrameworkȱDirectiveȱprogrammesȱobligeȱ MemberȱStatesȱtoȱmakeȱtheȱbasicȱdataȱavailable,ȱthoughȱtheyȱdoȱcontainȱanȱobligationȱ toȱreportȱonȱtheȱresultsȱtoȱtheȱCommission.ȱTheȱDataȱCollectionȱRegulation,ȱinȱconȬ trast,ȱdoesȱrequireȱMemberȱStatesȱtoȱmakeȱdataȱavailableȱuponȱrequest,ȱbutȱnoȱcentralȱ databaseȱexists.ȱAȱfutureȱWGEELȱmightȱhaveȱtoȱspeciallyȱrequestȱtheseȱdataȱfromȱtheȱ Commission.ȱAsȱindicatedȱabove,ȱpartialȱspatialȱcoverageȱmayȱallowȱforȱanȱanalysisȱ ofȱtrendsȱinȱrecruitment,ȱbutȱneitherȱtheȱassessmentȱofȱtheȱtrendȱinȱsilverȱeelȱescapeȬ ment,ȱnorȱtheȱassessmentȱofȱtheȱrelativeȱsurvivalȱoverȱtheȱcontinentalȱlifeȱstages,ȱwillȱ beȱfeasible.ȱAȱformalȱrequirement,ȱandȱaȱpracticalȱprocedureȱtoȱpresentȱandȱstoreȱtheȱ data,ȱwillȱhaveȱtoȱbeȱdeveloped.ȱDevelopmentȱofȱprotocols,ȱexchangeȱproceduresȱandȱ databasesȱwillȱnotȱbeȱfeasibleȱwithinȱtheȱframeworkȱofȱtheȱinternationalȱassessmentȱ workingȱgroup.ȱ 30 EIFAC/ICES WGEEL Report 2008

3.3.2 Use of yellow eel data

Therefore,ȱdataȱonȱtheȱgrowingȱyellowȱeelȱphaseȱareȱnotȱdirectlyȱapplicableȱtoȱtheȱfirstȱ levelȱofȱanȱinternationalȱscaleȱstockȱassessment.ȱTheyȱare,ȱhowever,ȱessentialȱtoȱindiȬ vidualȱ memberȱ states,ȱ orȱ regions,ȱ forȱ exampleȱ asȱ inputsȱ toȱ modellingȱ silverȱ eelȱ esȬ capement,ȱ orȱ forȱ providingȱ interimȱ dataȱ checkȱ pointsȱ duringȱ theȱlongȱ growthȱtermȱ betweenȱ recruitmentȱ andȱ silverȱ eelȱ production.ȱ Ifȱ theȱ nationalȱ orȱ regionalȱ stockȱ asȬ sessmentsȱ areȱ toȱ beȱ checkedȱ atȱ anȱ internationalȱ level,ȱ theȱ dataȱ onȱ whichȱ theseȱ areȱ basedȱmustȱbeȱavailableȱinȱanȱaccessibleȱform.ȱ

3.3.3 The EU Eel Regulation

TheȱEUȱeelȱrecoveryȱregulationȱrequiresȱspecificȱnationalȱactionsȱincludingȱtheȱgatherȬ ingȱofȱsomeȱeelȱdata,ȱandȱtheȱsupplyȱofȱtheseȱdataȱtoȱtheȱEUȱCommissionȱuponȱreȬ quest.ȱItȱdoesȱnotȱspecifyȱorȱrequireȱthatȱthisȱinformationȱisȱdirectlyȱavailableȱtoȱtheȱ WGEELȱorȱtoȱanyȱorganizationȱexceptȱtheȱEUȱcommission.ȱFurthermore,ȱtheȱdataȱtoȱ beȱgatheredȱasȱpartȱofȱtheȱmanagementȱplanȱandȱsubsequentȱreportingȱtoȱECȱunderȱ theȱstockȱrecoveryȱregulationȱisȱtoȱbeȱsuppliedȱtoȱtheȱECȱatȱrelativelyȱlongȱintervalsȱofȱ atȱleastȱthreeȱyears.ȱTheȱreportingȱcycleȱstartsȱwithȱtheȱdetailȱofȱmanagementȱplansȱbyȱ theȱendȱofȱ2008,ȱwithȱsubsequentȱreportingȱeveryȱthreeȱyears,ȱreducingȱinȱfrequencyȱ toȱeveryȱsixȱyearsȱafterȱ2021.ȱTheȱCommissionȱitselfȱwillȱmakeȱitsȱfirstȱreportȱtoȱtheȱEUȱ Parliamentȱinȱ2013.ȱ

NotwithstandingȱtheȱfactȱthatȱthereȱisȱnoȱbuiltȬinȱobligationȱtoȱreportȱtheseȱdataȱtoȱtheȱ WGEELȱforȱstockȱassessment,ȱtheȱintervalsȱinȱtheȱreportingȱcycleȱunderȱtheȱEUȱReguȬ lationȱ areȱfarȱ tooȱ longȱ toȱenableȱ anyȱ rapidȱ progressȱ byȱWGEEL.ȱ Forȱ anȱ assessmentȱ workingȱ groupȱ toȱ makeȱ significantȱ progressȱ towardȱ bringingȱ eelȱ inȱ lineȱ withȱotherȱ internationalȱ speciesȱ stockȱ assessments,ȱ annuallyȱ updatedȱ dataȱ are ȱ required.ȱ Theȱ crossȬcomplianceȱrequirementȱbetweenȱtheȱrecoveryȱregulationȱandȱtheȱCFPȱfisheryȱ dataȱ collectionȱ regulationȱ obligesȱ countriesȱ toȱ makeȱ someȱ dataȱ availableȱ annually.ȱ However,ȱtheȱDCRȱdoesȱnotȱ(yet)ȱcoverȱallȱdataȱsourcesȱrequiredȱforȱanȱassessmentȱofȱ theȱstatusȱofȱtheȱstock,ȱeitherȱatȱEMUȱorȱwiderȱscales.ȱ

3.3.4 Checklist of actions required under the Eel Regulation and associated guidelines

Whereȱdataȱmayȱbeȱusefulȱtoȱinternationalȱstockȱassessmentȱthisȱisȱdisplayedȱinȱboldȱ text.ȱ

x Establishmentȱofȱmanagementȱplansȱbyȱcountryȱorȱotherȱeelȱmanagementȱ unitȱbyȱendȱ2008,ȱincluding:ȱ x Aȱlistȱofȱmanagementȱunitsȱandȱauthoritiesȱresponsible.ȱ x Anȱinventoryȱorȱindividualȱbasinsȱinȱeachȱmanagementȱunit.ȱ x Justificationȱforȱtheȱuseȱofȱaȱnationalȱscaleȱplanȱifȱthisȱoptionȱisȱselected.ȱ x MapsȱrevealingȱeelȱmanagementȱunitsȱinȱrelationȱtoȱWFDȱriverȱbasinȱdisȬ tricts.ȱ x Annualȱcatch,ȱifȱfished,ȱinȱKgȱforȱeachȱRBDȱofȱglass,ȱyellowȱandȱsilverȱ eel.ȱ (thisȱ isȱ notȱ includedȱ inȱ theȱ regulationȱ itselfȱ but ȱ isȱ includedȱ inȱ theȱ Commissionȱimplementationȱguidelines).ȱ x Quantitativeȱandȱqualitativeȱdescriptionȱofȱeelȱfisheryȱunits.ȱ x Aȱlistȱofȱfishers,ȱlicences,ȱvesselsȱlicensedȱtoȱlocalȱandȱEUȱwaters,ȱplusȱaucȬ tioneersȱandȱlicensedȱdealers.ȱ x Quantitativeȱandȱqualitativeȱdescriptionsȱofȱeelȱfisheryȱeffortȱreflectingȱ localȱsituationȱandȱanyȱreductionsȱimposed.ȱ EIFAC/ICES WGEEL Report 2008 31

x Aȱquantitativeȱdescriptionȱofȱrecreationalȱeelȱfishing,ȱi.e.ȱnumbersȱofȱfishersȱ andȱtheirȱcatchesȱofȱeels.ȱ x Statementȱ ofȱ whichȱ optionalȱ method(s)ȱ isȱ usedȱ toȱ defineȱ silverȱ eelȱ esȬ capementȱofȱtargetȱ40%.ȱ x Aȱdescriptionȱofȱtheȱsilverȱeelȱ40%ȱescapementȱtargetȱmodeȱofȱmeasureȬ mentȱsystemȱusedȱincludingȱits ȱprecisionȱandȱaccuracy.ȱ x Aȱ descriptionȱ ofȱ habitatȱ condition,ȱ includingȱ nonȱ fisheryȱ mortalitiesȱ e.g.ȱ causedȱbyȱpollution,ȱmigrationȱobstaclesȱ(quantifyȱthisȱmortalityȱifȱpossiȬ ble).ȱ x AnȱindicationȱofȱtheȱproportionȱofȱeachȱlifeȱstageȱaffectedȱbyȱcontamiȬ nants,ȱpathogens,ȱparasitesȱandȱdegreeȱofȱcontamination.ȱ x Qualitativeȱandȱquantitativeȱdescriptionsȱof ȱpastȱrestockingȱandȱanyȱinȬ tendedȱasȱpartȱofȱtheȱmanagementȱplan,ȱwithȱstockedȱareas.ȱ x Aȱquantitativeȱestimateȱofȱhowȱstocking,ȱifȱtoȱbeȱused,ȱwillȱcontributeȱtoȱ achievingȱtheȱ40%ȱescapement.ȱ x Theȱproportionȱofȱcapturedȱlessȱthanȱ12ȱcmȱeelȱtoȱbeȱusedȱforȱrestocking.ȱ x Actualȱorȱestimatedȱescapementȱrelativeȱtoȱtheȱ40%ȱtarget,ȱatȱtimeȱofȱplanȱ submissionȱ(2008)ȱwithȱdescriptionȱofȱestimationȱmethodsȱused.ȱ x Priceȱmonitoringȱforȱglassȱeelȱmarkets.ȱ x Descriptionȱ ofȱ theȱ samplingȱ systemȱ forȱ catchesȱ andȱ effortȱ concerningȱ allȱ lifeȱstagesȱofȱeel,ȱwithȱregardȱtoȱRegulationȱ(EC)ȱNoȱ1639/2001ȱ(DCR).ȱ x Measuresȱtoȱidentifyȱoriginȱandȱtraceabilityȱofȱliveȱimportsȱandȱexports.ȱ x Determinationȱthatȱeelȱimportedȱandȱexportedȱfromȱterritoryȱareȱcapturedȱ withinȱnationalȱ(EMP)ȱandȱinternationalȱ(CITES)ȱrules.ȱ

Inȱsummary,ȱthisȱchecklistȱidentifiesȱseveralȱitemsȱofȱpotentialȱuseȱtoȱfutureȱworkingȱ groups,ȱ assumingȱ thatȱ theȱ WGsȱ haveȱaccessȱ toȱ allȱ data,ȱ preferablyȱ inȱ theȱ yearȱ proȬ duced,ȱ ratherȱ thanȱ havingȱ toȱ waitȱ forȱ theȱ reportingȱ cycle.ȱ Byȱ farȱ theȱ mostȱ relevantȱ dataȱforȱinternationalȱuseȱwillȱbeȱtheȱsilverȱeelȱpotentialȱandȱactualȱescapementȱestiȬ mates.ȱ

Thereȱare,ȱhowever,ȱveryȱsignificantȱdeficienciesȱinȱthisȱdataȱsourceȱasȱanȱaidȱtoȱinterȬ nationalȱstockȱassessment.ȱPerhapsȱtheȱmostȱobviousȱgapȱisȱtheȱfailureȱofȱtheȱregulaȬ tionȱtoȱsecureȱaȱfisheryȬindependentȱglassȱeelȱrecruitmentȱdataseries.ȱTheȱrelianceȱonȱ catchȱmonitoringȱfocusesȱtheȱrelevantȱpartȱofȱtheȱregulationȱonȱcommercialȱglassȱeelȱ fisheries,ȱwhichȱmayȱchangeȱmarkedly,ȱresultingȱinȱlossȱofȱindividualȱ dataseries.ȱAsȱ outlinedȱabove,ȱtheȱreportingȱcycleȱofȱthreeȱyearsȱisȱatȱintervalsȱtooȱlongȱforȱanyȱrapidȱ progressȱtoȱbeȱmadeȱonȱinternationalȱscaleȱstockȱassessment.ȱManyȱofȱtheȱdataȱhighȬ lighted,ȱwhileȱofȱsupportingȱinterest,ȱareȱnotȱcoreȱrequirements.ȱTheȱabsenceȱofȱaȱreȬ quirementȱforȱeelȱquality ȱdataȱareȱnoted.ȱ

3.3.5 Data Collection Regulation

TheȱcrossȬcomplianceȱlinkȱbetweenȱtheȱEelȱregulationȱandȱtheȱDCRȱprocessȱisȱaȱusefulȱ provisionȱforȱstockȱassessmentȱpurposes.ȱTheȱDCRȱdrivenȱdataȱprovisionȱis,ȱhowever,ȱ dependentȱonȱcontinuationȱofȱcommercialȱandȱrecreationalȱeelȱfisheries.ȱThereȱisȱnoȱ requirementȱ forȱ anyȱ fisheryȬindependentȱ eelȱ samplingȱ inȱ theȱ DCRȱ orȱ forȱ anyȱ samȬ plingȱ toȱ continueȱ whereȱ andȱ whenȱ fisheriesȱ close.ȱ Continuationȱ ofȱ commercialȱ eelȱ fishingȱisȱfarȱfromȱguaranteedȱgivenȱtheȱcontinuingȱdownwardȱtrendsȱinȱcatches,ȱtheȱ possibilityȱ ofȱ approachingȱ economicȱ extinction,ȱ andȱ theȱ probabilityȱ ofȱ widespreadȱ 32 EIFAC/ICES WGEEL Report 2008

cutsȱinȱeelȱfishingȱactivityȱasȱaȱconsequenceȱofȱMSȱorȱRBDȱscaleȱfailureȱtoȱmeetȱtheȱ “40%”ȱsilverȱescapementȱtargetsȱrequiredȱinȱtheȱeelȱregulation.ȱ

EvenȱwhileȱtheȱDCRȱdoesȱapplyȱandȱforcesȱdataȱcollection,ȱtheȱminimumȱprescribedȱ samplingȱisȱunlikelyȱtoȱprovideȱsufficientȱdataȱtoȱcompileȱaȱmeaningfulȱinternationalȱ scaleȱeelȱstockȱassessment,ȱasȱitȱdoesȱnotȱcontainȱyellowȱeelȱsurveys.ȱAlthoughȱthereȱ willȱbeȱsomeȱsilverȱeelȱdataȱwhereȱfisheriesȱstillȱexist,ȱmostȱDCRȱdataȱwillȱbeȱonȱyelȬ lowȱeelȱfisheries,ȱandȱasȱsuchȱwillȱbeȱofȱindirectȱvalueȱtoȱinternationalȱstockȱassessȬ ment.ȱ Silverȱ eelȱ fisheriesȱ areȱ alsoȱ likelyȱ toȱ beȱ theȱ firstȱ targetȱ forȱ closureȱ whenȱ escapementȱtargetsȱareȱfailed.ȱ

Accordingȱ toȱ theȱ DCRȱ minimumȱ stipulationȱforȱ dataȱ precisionȱ level,ȱ theȱ “fallback”ȱ optionȱisȱtoȱmeasureȱ100ȱeelsȱforȱeveryȱ20ȱtȱlanded.ȱAȱdedicatedȱworkshopȱonȱnationalȱ dataȱcollectionȱofȱEuropeanȱeelȱ(Dekkerȱetȱal.,ȱ2005)ȱconcludedȱthatȱ“…ȱoneȱsampleȱ perȱ20ȱtȱcatchȱ…ȱwasȱfoundȱtoȱbeȱinadequateȱ…”ȱandȱrecommendedȱthatȱ“15ȱsamplesȱ perȱlifeȱstage,ȱperȱmanagementȱunitȱwouldȱbeȱmoreȱappropriate”.ȱThisȱworkshopȱalsoȱ statedȱthatȱ“Theȱnumberȱofȱindividualsȱperȱsampleȱforȱlengthȱanalysisȱwasȱexaminedȱ andȱthereȱhasȱbeenȱnoȱanalysisȱtoȱdateȱdeterminingȱtheȱpreciseȱlevelsȱrequired.ȱComȬ monȱpracticeȱwouldȱindicateȱthatȱ100ȱindividualsȱperȱsampleȱmayȱnotȱbeȱadequateȱforȱ lengthȱandȱthisȱshouldȱbeȱincreasedȱtoȱ200ȱperȱsample.ȱSGRNȱ(STECF)ȱhaveȱstronglyȱ endorsedȱ thisȱ recommendationȱ inȱ itsȱ Decemberȱ 2007ȱ meeting.ȱ However,ȱ forȱ someȱ RBDsȱwithȱsmallȱfisheries,ȱtheȱDCRȱsamplingȱrequirementȱexceedsȱtheȱtypicalȱannualȱ catchȱofȱyellowȱorȱsilverȱeel,ȱbutȱasȱtheȱEUȱEelȱRegulationȱconstitutesȱanȱinternationalȱ recoveryȱplan,ȱnormalȱexemptionȱrulesȱdoȱnotȱapply.ȱ

TheȱDCRȱonȱitsȱownȱwillȱnotȱprovideȱaȱframeworkȱtoȱestimateȱtheȱsizeȱofȱtheȱspawnȬ ingȱ stockȱ asȱ theȱ programmeȱ doesȱ notȱ provideȱ estimatesȱ ofȱ eelȱ abundanceȱ inȱ smallȱ fisheriesȱorȱinȱthoseȱwatersȱnotȱfished.

3.3.6 Recruitment dataseries are not secured

EUȱconcertedȱactionȱ98/076ȱ(Dekker,ȱ2002)ȱbroughtȱtogetherȱtheȱEuropeȬwideȱdataserȬ iesȱ ofȱ recruitmentȱ samplingȱ whichȱ nowȱ formȱ theȱ basisȱ ofȱ theȱ recruitmentȱ dataȱ reȬ portedȱ annuallyȱ toȱ thisȱWG.ȱ Itȱ wasȱ concludedȱatȱ theȱ timeȱ thatȱ betterȱ coverageȱ wasȱ neededȱandȱproposalsȱwereȱmadeȱtoȱestablishȱnewȱsites.ȱOnlyȱtwoȱofȱtheseȱnewȱsitesȱ (researchȱsitesȱinȱGreece)ȱhaveȱbeenȱstarted,ȱandȱsomeȱofȱtheȱformerlyȱactiveȱsitesȱareȱ nowȱeffectivelyȱstoppedȱasȱaȱconsequenceȱofȱtheirȱdependenceȱonȱfisheriesȱnowȱnotȱ commerciallyȱviableȱorȱaȱlackȱofȱglassȱeelȱproducedȱforȱrestocking.ȱ

3.3.7 Water Framework Directive

Theȱ WGEELȱ hasȱ notedȱ onȱ manyȱ occasionsȱ thatȱ theȱ requirementȱforȱ MSȱ toȱ monitorȱ eelsȱasȱpartȱofȱinlandȱfishȱpopulationsȱunderȱWaterȱFrameworkȱDirectiveȱprovisionsȱ mayȱalsoȱaidȱstockȱassessment.ȱSuchȱmonitoringȱisȱlikelyȱtoȱgatherȱsomeȱdataȱonȱyelȬ lowȱeelȱandȱasȱsuchȱwillȱbeȱaȱdataȱinputȱtoȱsilverȱeelȱoutputȱmodels.ȱHowever,ȱgivenȱ theȱ broaderȱ aimsȱ ofȱ theȱ Waterȱ Frameworkȱ Directive,ȱ thereȱ isȱ aȱ highȱ riskȱ thatȱ theȱ monitoringȱrelatedȱtoȱtheȱWFDȱwillȱbeȱinadequateȱforȱtheȱassessmentȱofȱtheȱeelȱstock.ȱ Inadequateȱspatialȱcoverage,ȱlowȱselectivityȱforȱeel,ȱunderreportingȱactualȱeelȱcatchesȱ andȱnonȬ reportingȱforȱeel,ȱhaveȱbeenȱobserved.ȱ

3.3.8 Data availability for international analyses

Tableȱ3.1ȱsummarizesȱtheȱassistanceȱthatȱcurrentlyȱactiveȱinitiatives,ȱincludingȱtheȱeelȱ regulation,ȱDCRȱprovisions,ȱandȱWFDȱmonitoring,ȱmayȱbringȱtoȱinternationalȱstockȱ assessment.ȱItȱisȱconcludedȱthatȱthese,ȱwhileȱwelcome,ȱwillȱnotȱprovideȱanyȱrapidlyȱ availableȱ sourceȱ ofȱ dataȱ forȱ aȱ fullȱ internationalȱ eelȱ stockȱ assessment.ȱ Thisȱ objectiveȱ EIFAC/ICES WGEEL Report 2008 33

canȱonlyȱbeȱachievedȱbyȱtheȱestablishmentȱofȱnationallyȱmaintainedȱdatabase,ȱmadeȱ availableȱforȱinternationalȱcompilation,ȱofȱtheȱkeyȱstockȱdescriptors.ȱTheseȱdescriptorsȱ areȱemigratingȱsilverȱeelȱnumbers,ȱbiomassȱandȱsexȱratio,ȱandȱrecruitmentȱinȱtermsȱofȱ glassȱeelȱorȱyoungȱofȱtheȱyearȱnumbersȱandȱbiomass.ȱTheȱcomponentȱandȱcompiledȱ dataȱmustȱbeȱannuallyȱupdatedȱtoȱenableȱexaminationȱofȱanyȱstock–recruitmentȱrelaȬ tionship.ȱOnlyȱwhenȱsuchȱdataȱexistȱwillȱitȱbeȱpossibleȱtoȱbringȱeelȱpopulationȱandȱ stockȬȱrecruitmentȱassessmentsȱtoȱtheȱlevelȱgivenȱtoȱmostȱotherȱmajorȱinternationallyȱ exploitedȱfishȱspecies.ȱ

TheȱlistȱofȱdataȱelementsȱandȱsupplyȱinȱTableȱ3.1ȱincludesȱtheȱEMUȱorȱRBDȱlevelȱdataȱ asȱaȱrequirement,ȱoverȱandȱaboveȱtheȱsimpleȱneedȱforȱaggregatedȱtotalȱspawnerȱemiȬ grationȱandȱglassȱeelȱrecruitmentȱindices.ȱInȱalmostȱallȱcases,ȱtheseȱdataȱdoȱnotȱcurȬ rentlyȱ existȱ andȱ newȱ dataseriesȱ needȱ toȱ beȱ commenced,ȱ withȱ internationalȱ coordinationȱ ensuringȱ aȱ compatibleȱ approachȱ endȱ allowingȱ futureȱ analysesȱ ofȱ theȱ disaggregatedȱindividualȱareaȱcomponentsȱofȱtheȱaggregatedȱspawnerȱproductionȱperȱ recruitȱrelationship.ȱ

Tableȱ3.1:ȱSummaryȱofȱpotentialȱdataȱprovisionȱasȱrequiredȱbyȱEUȱandȱotherȱinternationalȱlegislaȬ tiveȱinstruments,ȱandȱWGȱdataȱrequirementsȱforȱpostȬevaluationȱofȱtheȱRegulation.ȱ

GUIDANCE CITES REQUIRED REQUIRED NOT IN DEQUATE ECEEL DOCUMENT REQUIREMENT A FOR STOCK– FOR ASSESSMENT COVERAGE RECOVERY FOR (IF INTER- ? RECRUITMENT SURVIVAL (FURTHER REGULATION PREPARATION NATIONAL OK ANALYSIS ANALYSIS RESEARCH DATA ELEMENT 1100\2007 OF EMPS DCR WFD TRADE EXISTS) NOT OK. (OCEAN) (CONTINENT) REQUIRED).

EMUsȱandȱ Yȱ YȱȱYȱ (Y)ȱ Listavailableȱ ȱ +ȱȱ RiverȱBasinsȱȱ 2009ȱ Listȱ Yȱȱ ȱȱ(Y)ȱȱ ȱ ȱ ȱ commercialȱ Fishermenȱȱ Catchȱbyȱ Yȱȱ Yȱȱ ȱ TriȬannualȱ ȱ +ȱȱ recreationalȱ insufficientȱ fishersȱ Listȱofȱ Yȱȱ ȱȱ(Y)ȱȱ ȱ ȱ ȱ primaryȱ sellersȱ Traceabilityȱ Yȱ YȱȱȱYȱȱ ȱ ȱ ȱ inȱtradeȱ Fishingȱ ȱ Yȱ Yȱȱ (Y)ȱȱ ȱ ȱ ȱ Capacityȱ Silverȱeelȱ Yȱ Yȱȱȱ(Y)ȱ TriȬannualȱ +ȱ +ȱȱ escapementȱ insufficientȱ PotentialȱSEȱ Yȱ Yȱȱȱ(Y)ȱ Oneȱoffȱȱȱ +ȱ +ȱȱ escapementȱ inȱ2008/9ȱ Fishingȱ Yȱ Yȱ Yȱȱ (Y)ȱ FromȱDCRȱȱ +ȱȱ effortȱbyȱ métierȱ Landings,ȱ Yȱ Yȱ Yȱȱ (Y)ȱ FromȱDCRȱȱ +ȱȱ glassȱeelȱȱ Landings,ȱ ȱ Yȱ Yȱȱ (Y)ȱ FromȱDCRȱȱ +ȱȱ yellowȱeelȱ Landings,ȱ ȱ Yȱ Yȱȱ (Y)ȱ FromȱDCRȱȱ +ȱȱ silverȱeelȱ 34 EIFAC/ICES WGEEL Report 2008

GUIDANCE CITES REQUIRED REQUIRED NOT IN ECEEL DOCUMENT REQUIREMENT ADEQUATE FOR STOCK– FOR ASSESSMENT RECOVERY FOR (IF INTER- COVERAGE? RECRUITMENT SURVIVAL (FURTHER REGULATION PREPARATION NATIONAL OK ANALYSIS ANALYSIS RESEARCH DATA ELEMENT 1100\2007 OF EMPS DCR WFD TRADE EXISTS) NOT OK. (OCEAN) (CONTINENT) REQUIRED). Catchȱ ȱȱ (+)ȱȱ ȱ FromȱDCRȱȱ +ȱȱ compositionȱ ȬLengthȱ Biologicalȱ ȱȱ +ȱ (Y)ȱȱ DCR,ȱbutȱ ȱ +ȱȱ samplingȱforȱ onlyȱwhereȱ length,ȱage,ȱ fisheriesȱ sex,ȱmaturity existȱ Recruitmentȱ ȱȱ ȱȱȱ Incomplete,ȱ +ȱ +ȱȱ surveysȱ andȱnoȱ obligation!ȱ Yellowȱeelȱ ȱȱ ȱYȱȱ WFD,ȱȱlowȱ ȱ +ȱȱ surveysȱ coverageȱandȱ detailȱ Silverȱeelȱ ȱ Yȱȱȱȱ TriȬannualȱ +ȱ +ȱȱ ”surveys”ȱȱ insufficientȱ Hydropowerȱ ȱ Yȱȱ ȱ Yȱ (Y)ȱ EMPȱ,WFDȱȱ ȱ +ȱȱ mortalityȱ–ȱ Hydromorphȱ NoȱStationsȱ dataȱȱ Hydropowerȱ ȱ Yȱ–ȱIfȱinfoȱ ȱȱ (Y)ȱ Notȱforȱallȱ ȱ +ȱȱ mortalityȱ availableȱ sitesȱ Predationȱ ȱ Yȱ–ȱIfȱȱinfoȱ ȱȱ (Y)ȱ onlyȱpartialȱ ȱ +ȱȱ Lossesȱ availableȱ coverageȱ EelȱQualityȱ ȱ Yȱȱȱȱ Onlyȱlocalȱ ȱ +ȱȱ data1ȱ dataȱ

1ȱe.g.ȱfatȱcontent,ȱcontaminants,ȱparasitesȱandȱdiseases.ȱ Yȱ =Requiredȱ asȱ aȱ primaryȱ function;ȱ (Y)=Requiredȱ asȱ crossȬcompliance;ȱ +ȱ =Adequatelyȱ covered;ȱȱ(+)ȱ =Partiallyȱcoveredȱbutȱinadequate;ȱentriesȱinȱboldȱindicateȱdataȱdeficiencies,ȱwhileȱentriesȱinȱitalicsȱmeetȱ requirements.ȱEelȱqualityȱincludesȱpollution,ȱparasites,ȱpathogensȱandȱfatȱlevels.ȱ

3.4 Stock assessment vs. research needs

TheȱEUȱRegulationȱonȱeelȱaimsȱatȱtheȱrestorationȱofȱtheȱspawningȱstockȱandȱrecruitȬ ment.ȱImplicitly,ȱitȱassumesȱthatȱaȱstock–recruitmentȬrelationȱ(ofȱtheȱstandardȱtype)ȱ existsȱforȱtheȱtotalȱstock. ȱInȱFigureȱ3.1,ȱaȱdecisionȱtreeȱdiagramȱisȱpresented,ȱinȱwhichȱ theȱinternationalȱassessmentȱofȱtheȱstateȱofȱtheȱstockȱandȱofȱtheȱimpactȱofȱprotectiveȱ measuresȱunderȱtheȱEUȱRegulationȱareȱevaluated,ȱonȱtheȱbasisȱofȱtrendsȱobservedȱatȱ theȱglobalȱandȱlocalȱlevel.ȱ

TheȱEUȱEelȱRegulationȱhasȱsetȱtargetsȱforȱtheȱquantityȱ(biomass)ȱofȱsilverȱeelsȱescapȬ ingȱfromȱtheȱcontinent,ȱandȱobligesȱMemberȱStatesȱtoȱtakeȱprotectiveȱmeasuresȱpriȬ marilyȱfocusingȱonȱtheȱquantitiesȱescaping.ȱNoȱtargetsȱhaveȱbeenȱsetȱwithȱrespectȱtoȱ otherȱprocessesȱ(e.g.ȱrelatedȱtoȱsilverȱeelȱquality,ȱorȱclimateȱchange)ȱinȱrelationȱtoȱeelȱ managementȱ (ifȱ possible).ȱ Theȱ internationalȱ assessmentȱ ofȱ theȱ statusȱ ofȱ theȱ stockȱ thereforeȱfocusesȱonȱtheȱdynamicsȱofȱstockȱinȱnumbersȱandȱquantities,ȱandȱonȱtheȱefȬ fectȱofȱprotectionȱandȱrestorationȱmeasuresȱtaken.ȱ

However,ȱtheȱevaluationȱprocessȱdepictedȱinȱFigureȱ3.1ȱ(leftȱhandȱcolumn),ȱprovidesȱ diagnosticsȱatȱseveralȱpointsȱinȱtheȱevaluationȱprocess,ȱjudgingȱtheȱadequacyȱofȱtheȱ focusȱonȱquantitiesȱescapingȱonly.ȱWhenȱtheseȱdiagnosticsȱindicateȱaȱdeviationȱfromȱ expectation,ȱfurtherȱ researchȱ willȱ beȱ requiredȱ toȱ clearȱ upȱ theȱ processes,ȱ toȱ quantifyȱ EIFAC/ICES WGEEL Report 2008 35

theirȱimpacts,ȱtoȱfindȱmitigationȱmeasures,ȱetc.ȱTheȱrightȱhandȱcolumnȱofȱtheȱdecisionȱ diagramȱ ofȱ Figureȱ 3.1ȱ presentsȱ aȱ bareȱ skeletonȱ forȱ theȱ decisionȱ processesȱ forȱ theseȱ cases.ȱ

TheȱfinalȱtwoȱcolumnsȱinȱTableȱ3.1ȱreflectȱtheȱcurrentȱstateȱofȱdevelopmentȱofȱdataȱ andȱquantitativeȱknowledgeȱofȱhowȱtheyȱaffectȱprocesses,ȱseparatingȱthoseȱdataȱitemsȱ essentialȱnowȱforȱdatabaseȱbuildingȱtoȱfeedȱSPRȱanalysesȱfromȱthoseȱwhereȱthereȱmayȱ beȱanȱimpactȱonȱeelȱbiologyȱbutȱwhereȱcurrentȱandȱfurtherȱresearchȱprogrammesȱneedȱ toȱ beȱ completedȱ toȱ quantifyȱ impactsȱ andȱ toȱ allowȱ theseȱ toȱ beȱ incorporatedȱ intoȱ mathematicallyȱbasedȱanalysesȱofȱstockȱandȱrecruitmentȱprocesses.ȱ

3.5 Stock assessment

3.5.1 Mortality based management targets

Ifȱ andȱ whenȱ recruitmentȱ continuesȱ toȱ declineȱ andȱ silverȱ eelȱ escapementȱ isȱ notȱ imȬ provedȱ(whichȱsituationȱisȱquiteȱlikelyȱtoȱoccurȱinȱtheȱcomingȱyears)ȱaȱcriticalȱassessȬ mentȱ ofȱ theȱ stockȱ statusȱ willȱ beȱ requiredȱ forȱ eachȱ Riverȱ Basinȱ District,ȱ indicatingȱ whetherȱorȱnotȱtheȱtargetsȱofȱtheȱEUȱEelȱRegulationȱhaveȱbeenȱmet.ȱTheȱtargetȱofȱtheȱ EelȱRegulationȱhasȱbeenȱsetȱinȱtermsȱofȱsilverȱeelȱescapementȱbiomassȱ(40%ȱinȱrelationȱ toȱaȱnotionalȱpristineȱproduction).ȱThereȱareȱmanyȱareasȱwhereȱthatȱtargetȱcanȱnotȱbeȱ reachedȱinȱtheȱforeseeableȱfuture,ȱasȱaȱconsequenceȱofȱtheȱlow ȱrecruitmentȱinȱrecentȱ years,ȱ evenȱ ifȱ allȱ anthropogenicȱ mortalityȱ wouldȱ haveȱ beenȱ removedȱ immediately.ȱ Additionally,ȱaȱphasedȱimplementationȱofȱprotectiveȱmeasuresȱmightȱslowȱdownȱtheȱ recoveryȱinȱtheȱearlierȱyearsȱfollowingȱimplementationȱofȱtheȱRegulation.ȱ

However,ȱtheȱRegulationȱalsoȱrequiresȱMemberȱStatesȱtoȱspecifyȱaȱtimeȱscheduleȱforȱ theȱattainmentȱofȱtheȱtarget.ȱTheȱRegulationȱdoesȱnotȱspecifyȱwhatȱtimeȱschedulesȱwillȱ beȱaccepted.ȱRestorationȱtimesȱareȱmoreȱlikelyȱtoȱbeȱinȱtheȱorderȱofȱdecadesȱorȱcentuȬ ries,ȱthanȱinȱtermsȱofȱyearsȱ(ÅströmȱandȱDekker,ȱ2007);ȱifȱtotalȱanthropogenicȱmortalȬ ityȱremainsȱaboveȱaȱcriticalȱthresholdȱ(fisheryȱmortality ȱFȱplusȱotherȱanthropogenicȱ mortalityȱHȱisȱ0.08ȱinȱthatȱanalysis),ȱnoȱlongȬtermȱrecoveryȱisȱexpected.ȱPreliminaryȱ reȬassessmentȱofȱtheȱtimeȱtillȱrecoveryȱforȱspecificȱpartsȱofȱtheȱdistributionȱareaȱ(notaȬ blyȱ theȱ southernȱ areasȱ withȱ higherȱ growthȱ rates),ȱ presentedȱ duringȱ theȱ workingȱ groupȱ meeting,ȱ confirmsȱ aȱ decadalȱ orȱ centennialȱ recoveryȱ period,ȱ andȱ aȱ thresholdȱ mortalityȱlevelȱforȱlongȬtermȱrecovery,ȱthoughȱtheȱresultsȱdifferȱinȱabsoluteȱvalues.ȱ

SinceȱtheȱEelȱRegulationȱbiomassȱtargetȱisȱnotȱachievableȱinȱtheȱnearȱfutureȱinȱmanyȱ areas,ȱtheȱmortalityȱthresholdȱforȱrecoveryȱisȱexpectedȱtoȱrepresentȱtheȱeffectiveȱtargetȱ toȱwhichȱtheȱstocks,ȱtheȱanthropogenicȱimpactsȱandȱtheȱprotectionȱmeasuresȱwillȱhaveȱ toȱbeȱjudged.ȱTheȱimplicitȱcharacterȱofȱthisȱmortalityȱthresholdȱ(beingȱderivedȱfromȱ theȱtimeȱschedule,ȱasȱanȱunacceptableȱ“keepȱsteady”ȱlimit)ȱpleadsȱforȱtheȱderivationȱ ofȱanȱexplicitȱmortalityȱtarget,ȱcorrespondingȱtoȱtheȱtimeȱscheduleȱrequirementȱand/orȱ theȱ biomassȱ targetȱ ofȱ theȱ EUȱ Eelȱ Regulation.ȱ Aȱ general,ȱ areaȬindependentȱ targetȱ isȱ recommendable,ȱe.g.ȱ%SPR.ȱWhetherȱthisȱindexȱofȱlifeȱtimeȱmortalityȱactuallyȱsufficesȱ forȱeel,ȱneedsȱtoȱbeȱinvestigated.ȱ

3.5.2 Density dependence and stock assessment

Theȱ longȱ continuedȱ andȱ widespreadȱ declineȱ ofȱ theȱ Europeanȱ eelȱ stockȱ hasȱ ledȱ toȱ adoptionȱofȱaȱprotectionȱandȱrecoveryȱplan,ȱbasedȱonȱclassicalȱconceptsȱinȱfisheriesȱ biologyȱforȱprecautionaryȱreasons.ȱȱThisȱconcerns,ȱfirstȱandȱforemost,ȱtheȱassumptionȱ ofȱ aȱ classicalȱ stock–recruitmentȱ relationshipȱ inȱ theȱ oceanicȱ phase.ȱ Inȱ itsȱ continentalȱ phase,ȱhowever,ȱtheȱeelȱisȱscatteredȱoverȱaȱmultitudeȱofȱsmallȱwaterȱbodiesȱ(Dekker,ȱ 2000),ȱinȱalmostȱallȱEUȱMemberȱStatesȱandȱsurroundingȱareas,ȱoftenȱunderȱlocalȱmanȬ agement.ȱBiologicalȱcharacteristicsȱofȱtheȱcontinentalȱwatersȱvary,ȱbothȱatȱshortȱdisȬ 36 EIFAC/ICES WGEEL Report 2008

tanceȱ(e.g.ȱfromȱtheȱcoast,ȱviaȱriversȱandȱlakes,ȱtoȱheadwaters,ȱmarshesȱandȱditches)ȱ andȱbetweenȱgeographicalȱareasȱ(fromȱproductiveȱlagoonsȱinȱtheȱMediterranean,ȱviaȱ denselyȱpopulatedȱriversȱinȱtheȱBayȱofȱBiscay,ȱtoȱextensiveȱcoldȱwatersȱinȱtheȱBaltic,ȱ producingȱlowȱdensitiesȱofȱlargeȱoldȱfemales).ȱBecauseȱofȱtheȱwideȱvarietyȱofȱecosysȬ temsȱinȱtheȱcontinentalȱphase,ȱnoȱsingleȱuniformȱapproachȱtoȱprotectionȱandȱassessȬ mentȱ willȱ suffice.ȱ Someȱ localȱ stocksȱ willȱ beȱ adequatelyȱ representedȱ byȱ classicalȱ populationȱ modelsȱ suchȱ asȱ lifeȱ tableȱ models,ȱ butȱ othersȱ willȱ not.ȱ Perhapsȱ theȱ mostȱ conspicuousȱ deviationȱ isȱ foundȱ inȱ placesȱ whereȱ densityȬdependenceȱ dominatesȱ theȱ localȱstockȱdynamics.ȱWhereȱthisȱoccurs,ȱanȱincreaseȱinȱrecruitment,ȱasȱstrivedȱforȱbyȱ theȱrecoveryȱplan,ȱwillȱnotȱresultȱinȱaȱ(proportional)ȱincreaseȱinȱtheȱstockȱandȱinȱtheȱ silverȱeelȱescapement.ȱWhereȱandȱwhenȱthisȱoccurs,ȱtheȱclassicalȱmodelsȱofȱ(densityȱ independent)ȱstockȱdynamicsȱwillȱnotȱbeȱapplicable.ȱLossȱofȱproductionȱpotentialȱcanȱ occurȱinȱtheseȱwatersȱasȱaȱconsequenceȱofȱhabitatȱloss,ȱorȱlossȱofȱaccessibilityȱ(migraȬ tionȱbarriers).ȱOtherwise,ȱtheȱpresenceȱofȱdensityȬdependenceȱindicatesȱthatȱtheȱstockȱ isȱatȱor,ȱcloseȱto,ȱitsȱmaximumȱdensityȱ(carryingȱcapacity),ȱandȱrestrictionsȱofȱanthroȬ pogenicȱimpactsȱwillȱprobablyȱnotȱincreaseȱsilverȱeelȱescapementȱveryȱmuch.ȱConseȬ quently,ȱ managementȱ actionsȱ shouldȱ primarilyȱ focusȱ onȱ mitigationȱ ofȱ habitatȱ loss.ȱ However,ȱweȱdoȱnotȱknowȱinȱhowȱmanyȱriversȱdensityȬdependenceȱisȱevident,ȱandȱ theȱ continuedȱ decreaseȱ inȱ recruitmentȱ willȱ decreaseȱ theirȱ numberȱ overȱ theȱ years.ȱ WhereȱandȱwhenȱdensityȬdependenceȱisȱinsignificant,ȱclassicalȱconceptȱinȱfishȱstockȱ dynamics,ȱsuchȱasȱlifeȱtimeȱsurvival,ȱspawnerȱperȱrecruit,ȱandȱmaximumȱsustainableȱ yieldȱ canȱ beȱ applied.ȱ Derivationȱ ofȱ (standardized)ȱ criteriaȱ forȱ densityȬdependence,ȱ andȱadaptationȱofȱ(standard)ȱfishȱstockȱassessmentȱmodelsȱtoȱtheȱpeculiaritiesȱofȱtheȱ eelȱforȱdensityȱindependentȱscaseȱ isȱrequired.ȱ

3.5.3 Assessment tools

Theȱ EUȱ Eelȱ Regulationȱ obligesȱ Memberȱ Statesȱ toȱ assessȱ theȱ currentȱ stateȱ ofȱ theirȱ stocks,ȱandȱtoȱassessȱtheȱexpectedȱimpactȱofȱproposedȱmanagementȱactions.ȱTheȱinȬ ternationalȱ stockȱ assessment,ȱ asȱ discussedȱ here,ȱ willȱ postȬevaluateȱ theȱ statusȱ ofȱ theȱ stock,ȱandȱtheȱnetȱeffectȱofȱmanagementȱmeasuresȱtaken.ȱThatȱis:ȱtheȱfocusȱisȱonȱtheȱ actualȱstateȱofȱtheȱstock,ȱratherȱthanȱonȱexpectedȱimpacts.ȱTheȱfieldȱofȱfishȱstockȱasȬ sessmentȱisȱparticularlyȱwellȱdevelopedȱforȱmarineȱfishȱstocks,ȱincludingȱtechniquesȱ suchȱ asȱ cohortȱ analysis,ȱ lengthȱ frequencyȱ basedȱ assessments,ȱ surveyȱ basedȱ assessȬ ments,ȱetc.ȱExistingȱexperienceȱinȱpostȬevaluationȱassessmentȱtechniquesȱforȱeelȱfishȬ eriesȱisȱextremelyȱlimitedȱ(seeȱDekkerȱetȱal.,ȱ2006ȱforȱanȱoverview).ȱTakingȱadvantageȱ ofȱ theȱ experiencesȱ inȱ marineȱ fishȱ stockȱ assessments,ȱ theȱ constructionȱ ofȱ adequateȱ postȬevaluationȱtechniquesȱforȱeelȱstocksȱisȱanȱachievableȱchallenge.ȱInȱcontrastȱwithȱ “standard”ȱ marineȱ fishȱ stockȱ assessmentȱ techniques,ȱ anthropogenicȱ impactsȱ otherȱ thanȱfisheriesȱ(e.g.ȱpredation,ȱhydropower,ȱeelȱquality),ȱtheȱspatialȱdistributionȱofȱloȬ calȱstocksȱwithinȱriverȱsystems,ȱmigrationȱandȱmigrationȱbarriersȱshouldȱalsoȱbeȱtakenȱ intoȱaccount.ȱItȱisȱrecommendedȱtoȱdevelopȱtheseȱtoolsȱinternationally,ȱmakingȱoptiȬ malȱ useȱ ofȱ availableȱ expertiseȱ andȱ funding,ȱ andȱ involvingȱ dataȱ andȱ expertsȱ fromȱ variousȱgeographicalȱareas.ȱ

Theȱ adoptionȱ andȱ implementationȱ ofȱ theȱ EUȱ Eelȱ Regulationȱ willȱ setȱ anȱ unpreceȬ dentedȱbreakpointȱinȱeelȱstockȱmanagement,ȱandȱwillȱitȱisȱtoȱbeȱhopedȱleadȱtoȱaȱmajorȱ breakpointȱ inȱ stockȱ trends.ȱ Consequently,ȱ theȱ applicationȱ ofȱ theȱ aboveȱ mentionedȱ postȬevaluationȱ assessmentȱ techniquesȱ willȱ haveȱ toȱ copeȱ withȱ unprecedentedȱ dataȬ sets.ȱItȱisȱthereforeȱsuggestedȱtoȱexploreȱtheȱuseȱofȱconstructedȱreality,ȱthatȱis:ȱtoȱapplyȱ theȱtoolsȱbeingȱdevelopedȱonȱdataȱderivedȱfromȱ(other)ȱsimulationȱmodels.ȱ EIFAC/ICES WGEEL Report 2008 37

3.6 Conclusions and recommendations for Chapter 3: International stock assessment and data needs

Theȱ absenceȱ ofyȱ an ȱ internationallyȱ drivenȱ requirementȱ toȱ maintainȱ aȱ recruitmentȱ dataseriesȱ needsȱ toȱ beȱ corrected,ȱ withȱ referenceȱ toȱ theȱ recommendationsȱ ofȱ theȱ EUȱ contractȱ98/076:ȱEstablishmentȱofȱaȱrecruitȱmonitoringȱsystemȱforȱglassȱeel.ȱ

InternationallyȱcoordinatedȱeelȱrecruitmentȱmonitoringȱshouldȱbeȱincludedȱinȱtheȱreȬ quirementsȱforȱtheȱDCR.ȱ

TheȱWGEELȱnotesȱthatȱforȱfutureȱmeetingsȱitȱwillȱneed:ȱ

x Theȱ meansȱ toȱ compileȱ dataȱ onȱ spawnerȱ emigrationȱandȱ glassȱ eelȱ recruitȬ ment,ȱ x Theȱ meansȱ toȱ assessȱ RBDȱ levelȱ spawnerȱ outputȱ perȱ recruitȱ relationshipsȱ withȱtheȱfullȱaccessȱtoȱEMUȱlevelȱdataȱthatȱentails.ȱ

TheȱWGEELȱfurtherȱnotesȱthat:ȱ

x CurrentȱlegislativeȱinstrumentsȱincludingȱtheȱEelȱRegulation,ȱDCR,ȱCITESȱ andȱWFDȱdoȱnot,ȱeitherȱindividuallyȱonȱinȱcombination,ȱcontainȱsufficientȱ provisionsȱtoȱensureȱadequateȱdataȱsupplyȱforȱsuchȱassessments.ȱ x ThereȱisȱanȱurgentȱneedȱtoȱdevelopȱassessmentȱandȱpostȬevaluationȱtoolsȱ adaptedȱtoȱtheȱeelȱcase.ȱ 38 EIFAC/ICES WGEEL Report 2008

4 Assessing stocks and management actions

4.1 Background theory on population dynamics

4.1.1 Introduction

Theȱreproductiveȱprocessȱisȱoneȱofȱtheȱmainȱmechanismsȱthatȱcontrolsȱandȱmaintainsȱ fishȱpopulations.ȱInȱfisheriesȱscience,ȱtheȱphaseȱfromȱadultȱspawningȱstockȱtoȱnewȬ bornȱrecruitsȱcontributingȱtoȱtheȱstockȱisȱknownȱasȱStockȬRecruitmentȱ(S/R)ȱrelationȬ ship.ȱ Itȱ isȱ theȱ evolutionaryȱ mechanismȱ byȱ whichȱ fishȱ stocksȱ “buffer”ȱ theȱ effectȱ ofȱ varyingȱ foodȱ andȱ spatialȱ resources.ȱ Theȱ S/Rȱ relationshipȱ isȱ mostȱ oftenȱ exploredȱ byȱ examiningȱtheȱempiricalȱrelationshipȱbetweenȱtheȱspawningȱstockȱsizeȱ(orȱitsȱproxy)ȱ andȱtheȱsubsequentȱrecruitmentȱoutputȱwhichȱresultsȱfromȱaȱcomplexȱchainȱofȱeventsȱ throughȱ spawning,ȱ ovaȱ depositionȱ andȱ larvalȱ andȱ juvenileȱ growthȱ andȱ survival.ȱ Inȱ fishȱ stocks,ȱ theȱ S/Rȱ relationȱ isȱ oftenȱ theȱ mainȱ resilientȱ mechanismȱ bufferingȱ theȱ exȬ ploitationȱmortality.ȱ

TheȱmechanismsȱthatȱdetermineȱtheȱS/RȱrelationshipȱcanȱbeȱcategorizedȱasȱdensityȬ dependentȱ andȱ densityȱ independent.ȱ Densityȱ independentȱ mechanismsȱ implyȱ thatȱ theȱindividualȱchanceȱofȱsurvivalȱforȱaȱyoungsterȱisȱindependentȱofȱitsȱparent’sȱstockȱ sizeȱandȱtheȱnumberȱofȱeggsȱproduced,ȱgivingȱriseȱtoȱaȱlinearȱrelationshipȱbetweenȱ theȱ spawningȱ stockȱ sizeȱ andȱ theȱ numberȱ ofȱ recruitsȱ producedȱ acrossȱ theȱ rangeȱ ofȱ spawningȱstockȱsizes.ȱThisȱmodelȱmustȱhaveȱlimitsȱsinceȱnoȱpopulationȱcanȱincreaseȱ indefinitelyȱ givenȱ thatȱ resourcesȱ areȱ finite,ȱ andȱ fullyȱ densityȱ independentȱ relationsȱ areȱnotȱobservedȱinȱpractice.ȱAtȱhighȱspawningȱstockȱsize,ȱcompensatoryȱmechanismsȱ ultimatelyȱlimitȱpopulationȱsizeȱbyȱmaintainingȱsomeȱceilingȱonȱtheȱlevelȱofȱrecruitȬ ment,ȱ i.e.ȱ densityȬdependenceȱ becomesȱ dominating.ȱ Severalȱ mathematicalȱ modelsȱ haveȱbeenȱusedȱtoȱdescribeȱtheȱshapeȱofȱS/Rȱmodelsȱ(i.e.ȱBevertonȬHolt,ȱRicker)ȱbutȱ theseȱallȱtakeȱaȱsimilarȱgeneralȱshapeȱatȱlowȱstockȱsizesȱandȱlargelyȱonlyȱdifferȱinȱtheȱ upperȱrangesȱofȱstockȱsize,ȱwhichȱisȱofȱlittleȱconcernȱforȱdepletedȱstocks.ȱ

Figureȱ4.1ȱdescribesȱaȱtheoreticalȱS/RȱrelationshipȱofȱtheȱBevertonȬHoltȱtype.ȱTheȱsolidȱ lineȱ describes ȱ theȱ relationȱ betweenȱ theȱ numberȱ ofȱ spawnersȱ andȱ theȱ subsequentȱ numberȱofȱoffspringȱ(recruits).ȱThisȱhasȱanȱalmostȱdensityȱindependentȱphaseȱ(nearlyȱ linear)ȱatȱlowȱstockȱdensityȱ(spawningȱstocksȱofȱ0ȱtoȱ10,ȱrecruitmentȱofȱ0ȱtoȱ40)ȱandȱanȱ upperȱdensityȬdependentȱphase,ȱwhenȱtheȱcurveȱlevelsȱoffȱ(seeȱ above).ȱ

Itȱisȱrelativelyȱsimpleȱtoȱunderstandȱthisȱrelationshipȱforȱlocalȱstocksȱsuchȱasȱsalmonȱ orȱseaȱtroutȱwhereȱtheȱspawningȱeffortȱandȱjuvenileȱproductionȱtakesȱplaceȱinȱindiȬ vidualȱcatchmentsȱandȱwhereȱdensityȬdependentȱfactorsȱsuchȱasȱspaceȱforȱspawningȱ andȱfoodȱavailabilityȱareȱclearlyȱfiniteȱresources.ȱItȱisȱmuchȱmoreȱdifficultȱtoȱenvisageȱ howȱ thisȱ mightȱ operateȱ forȱ eelȱ whichȱ hasȱ anȱ oceanicȱ spawningȱ andȱ larvalȱ phase,ȱ givenȱtheȱlackȱofȱknowledgeȱofȱtheȱspawningȱandȱearlyȱlifeȱhistoryȱofȱtheȱeelȱinȱtheȱ Sargasso.ȱ EIFAC/ICES WGEEL Report 2008 39

Fcurrent Flim pristine 100 limit

60 F=0

Recruitment 40

Rcurrent Blim BF=0 0 0 20 40 60 80 100 Spawning Stock Biomass ȱ

Figureȱ4.1:ȱHypotheticalȱStockȬRecruitmentȱrelationship,ȱshowingȱaȱBevertonȱandȱHoltȬtypeȱrelaȬ tionship,ȱtheȱsolidȱlineȱindicatesȱwhatȱrecruitmentȱisȱproducedȱatȱwhatȱspawningȱstockȱsize;ȱtheȱ brokenȱlinesȱindicateȱwhatȱspawningȱstockȱcanȱbeȱderivedȱfromȱaȱgivenȱrecruitment,ȱatȱnoȱfisheryȱ

(F=0,ȱ dashesȱ line),ȱ atȱ maximal,ȱ justȱ sustainableȱ fisheryȱ (Flim,ȱ dottedȱ curve)ȱ andȱ currentȱ nonȱ susȬ

tainableȱ fisheryȱ (andȱ otherȱ anthropogenicȱ sourcesȱ ofȱ mortality)ȱ (Fcurrent,ȱ dotȬdashedȱ curve).ȱ Bothȱ RecruitsȱandȱSpawningȱStockȱBiomassȱareȱgivenȱinȱarbitraryȱunits.ȱTheȱEUȱRegulationȱsetsȱtheȱ minimumȱ targetȱ atȱ 40%ȱ ofȱ theȱ pristineȱ spawningȬstockȱ biomass,ȱ whichȱ willȱ keepȱ recruitmentȱ closeȱtoȱitsȱmaximum,ȱbutȱonȱtheȱbrinkȱofȱimpairedȱrecruitment.ȱTheȱintersectionsȱbetweenȱtheȱ twoȱtypesȱofȱcurvesȱdetermineȱequilibriumȱbiomassesȱ(densities).

So,ȱ populationȱ dynamicsȱ andȱ resultingȱ equilibriumȱ levelsȱ canȱ beȱ analysedȱ throughȱ theȱuseȱofȱcurvesȱforȱSSBȬ>Rȱ(fromȱSpawningȱStockȱBiomassȱtoȱRecruitment)ȱandȱRȬ >SSBȱ(fromȱRecruitmentȱtoȱSpawningȱStockȱBiomass)ȱ(seeȱFigureȱ4.1)ȱwhere:ȱ

x Recruitmentȱinȱthisȱcontextȱisȱassumedȱtoȱbeȱ theȱbiomassȱ(orȱnumber)ȱofȱ glassȱ eelsȱ thatȱ successfullyȱ arriveȱ toȱ continentalȱ watersȱ afterȱ havingȱ surȬ vivedȱjuvenileȱdensityȬdependentȱmortalityȱinȱtheȱoceanicȱphase.ȱAnȱalterȬ nativeȱcouldȱbeȱtoȱdefineȱrecruitsȱasȱaȱsomewhatȱlaterȱstageȱlike:ȱglassȱeelsȱ settlingȱ(orȱelvers)ȱinȱcontinentalȱwaters,ȱandȱthusȱincludeȱtheȱpossibleȱloȬ calȱdensityȬdependenceȱinȱtheȱearlyȱprocessesȱwhenȱglassȱeelsȱarriveȱatȱtheȱ continent.ȱ x Spawningȱstockȱbiomassȱisȱtheȱmagnitudeȱofȱtheȱeffectiveȱspawners,ȱi.e.ȱtheȱ onesȱthatȱareȱsuccessfullyȱreachingȱtheȱSargassoȱSeaȱandȱactuallyȱspawnȬ ing.ȱ

Equilibriumȱ pointsȱ correspondȱ toȱ intersectionsȱ pointsȱ betweenȱ theȱ twoȱ typesȱ ofȱ curves.ȱ

TheȱSSBȬ>Rȱcurveȱdependsȱuponȱoceanicȱfactorsȱsuchȱasȱspawner,ȱsuccess,ȱcurrents,ȱ foodȱavailability,ȱetc,ȱwhereasȱtheȱRȬ>SSBȱcurveȱdependsȱuponȱmortalityȱcumulatedȱ duringȱ continentalȱ lifespan.ȱ Particularly,ȱ mortalityȱ ratesȱ F+Mȱ (anthropogenicȱ andȱ natural)ȱcumulatedȱinȱtheȱlifespanȱ(fromȱglassȱeelȱtoȱspawner)ȱdeterminesȱtheȱslopeȱofȱ theȱRȬ>SSBȱrelationshipȱdan ȱconsequentlyȱtheȱequilibriumȱlevel.ȱHigherȱlevelsȱofȱmorȬ talityȱratesȱdetermineȱequilibriumȱpointsȱcorrespondingȱtoȱlowerȱvaluesȱofȱbothȱRȱandȱ SSB.ȱ 40 EIFAC/ICES WGEEL Report 2008

NoteȱthatȱspawnerȱqualityȱmightȱbeȱexplicitlyȱincludedȱinȱtheȱSSBȬ>Rȱrelationshipȱasȱ anȱ additionalȱ mortalityȱ consideredȱ thatȱ “badȱ spawners”ȱ dieȱ beforeȱ spawning,ȱ butȱ afterȱleavingȱtheȱcontinent,ȱorȱsimplyȱproduceȱlessȱoffspring.ȱ

4.1.2 Eel stock and stock decline

Inȱ recentȱ years1,ȱ theȱ developmentȱ ofȱ theȱ precautionaryȱ approachȱ inȱ fisheriesȱ manȬ agementȱandȱtheȱexploitationȱofȱstocksȱhaveȱreceivedȱmuchȱattentionȱalongȱwithȱtheȱ developmentȱ ofȱ fisheriesȱ managementȱ toolsȱ andȱ theȱ provisionȱ ofȱ scientificȱ advice.ȱ TheȱprecautionaryȱapproachȱdictatesȱaȱriskȬaverseȱstrategy,ȱinȱwhichȱnoȱfishȱstockȱisȱ exploitedȱatȱaȱrateȱhigherȱthanȱoneȱthatȱgeneratesȱmaximumȱyield,ȱandȱnoȱspawningȱ stockȱ isȱ reducedȱ toȱ lowȱ levels,ȱ atȱ whichȱ recruitmentȱ impairmentȱ occurs.ȱ Inȱ theȱ abȬ senceȱofȱpertinentȱknowledgeȱtoȱtheȱcontrary,ȱaȱS/Rȱrelationshipȱshouldȱbeȱassumedȱ toȱexist,ȱevenȱforȱeel.ȱTheȱexistingȱtrendsȱinȱeelȱlandingsȱandȱrecruitmentȱindicesȱsupȬ portȱthisȱview,ȱalthoughȱtheȱexactȱformȱofȱtheȱS/Rȱrelationshipȱhasȱnotȱbeenȱpossibleȱ toȱdetermineȱsoȱfar.ȱ

RecruitmentȱofȱEuropeanȱeelȱhasȱbeenȱinȱdeclineȱsinceȱtheȱearlyȱ1980s,ȱandȱisȱbelowȱ 5%ȱofȱtheȱhistoricalȱlevel,ȱsinceȱ2000.ȱTotalȱlandingsȱhaveȱrevealedȱaȱgradualeȱdeclin ȱ sinceȱtheȱ1960s,ȱdownȱtoȱapprox.ȱ25%ȱofȱtheȱformerȱlevelȱ(Dekker,ȱ2003).ȱTheȱcausesȱofȱ theȱ declineȱ inȱ recruitmentȱ areȱ notȱ wellȱ known,ȱ butȱ mightȱ wellȱ beȱ relatedȱ toȱ aȱ lowȱ spawningȱstock.ȱGivenȱtheȱcontinuouslyȱdecliningȱtrend,ȱdataȱsuggestȱthatȱtheȱpreȬ sentȱequilibriumȱpointȱcorrespondsȱtoȱextinctionȱorȱveryȱcloseȱtoȱextinction.ȱTheȱecolȬ ogyȱ ofȱ eelsȱ makesȱ itȱ difficultȱ toȱ demonstrateȱ aȱ stock–recruitmentȱ relationship.ȱ However,ȱ theȱ precautionaryȱ approachȱ requiresȱ thatȱ suchȱ aȱ relationshipȱ shouldȱ beȱ assumedȱ toȱ exist.ȱ Therefore,ȱ ICESȱ (1999)ȱ advisedȱ toȱ restrictȱ fisheriesȱ andȱ otherȱ anȬ thropogenicȱimpactsȱtoȱtheȱlowestȱlevelȱpossible,ȱ inȱorderȱtoȱensureȱthatȱtheȱspawningȱ stockȱreturnsȱtoȱthenȱremainsȱaboveȱtheȱcriticalȱlevelȱBlim,ȱaboveȱwhichȱrecruitmentȱisȱ notȱimpairedȱbyȱtheȱsizeȱofȱtheȱspawningȱstock.ȱClassicalȱfisheryȱmanagementȱsetȱtheȱ criticalȱspawningȬstockȱbiomassȱlevelȱ(Blim)ȱatȱ30%ȱofȱthatȱinȱabsenceȱofȱfishery.ȱDueȱtoȱ theȱ fundamentallyȱ differentȱ biologyȱ ofȱ theȱ eelȱ (semelparousȱ withȱ highȱ longevity,ȱ panmicticȱ andȱ scatteredȱ overȱ theȱ wholeȱ continent),ȱ theȱ WGEELȱ suggestedȱ aȱhigherȱ Blimȱofȱ50%ȱforȱeels,ȱandȱEUȱRegulationȱoptedȱforȱaȱ40%ȱobjective.ȱ

AsȱanȱalternativeȱstrategyȱtoȱsettingȱSSBȱtargetȱatȱanȱuncertainȱ(30,ȱ40ȱorȱ50%?)ȱperȬ centageȱofȱtheȱnotionalȱpristineȱSSBȱ(whichȱisȱnotȱeasilyȱestimated),ȱwithȱanȱunknownȱ correspondingȱlevelȱofȱrecruitment,ȱanotherȱapproachȱmightȱbeȱtheȱfollowing:ȱInȱtheȱ 1970s,ȱrecruitmentȱofȱglassȱeelȱwasȱstillȱatȱhistoricallyȱhighȱlevels.ȱThisȱindicatesȱthatȱ SSBȱwasȱnotȱlimitingȱtheȱproductionȱofȱrecruitsȱatȱthatȱtime.ȱQuantificationȱofȱtheȱpreȬ 1980ȱ spawnerȱ escapementȱ thereforeȱ isȱ theȱ simplestȱ derivationȱ ofȱ aȱ referenceȱ level.ȱ Noteȱthatȱinȱthisȱcase,ȱtheȱfullȱescapementȱ(100%)ȱofȱtheȱsilverȱeelsȱinȱtheȱ1970sȱ(givenȱ theȱ anthropogenicȱ mortalityȱ ofȱ thatȱ time)ȱ thenȱ isȱ assumedȱ toȱ correspondȱ toȱ theȱ esȬ capementȱlevelȱadvisedȱbyȱICESȱ(2002).ȱThatȱis,ȱoneȱcouldȱeitherȱsetȱthisȱinterimȱreferȬ enceȱthresholdȱatȱ100%ȱpreȬ1980ȱsilverȱeelȱescapementȱwhereȱtheȱdataȱareȱavailable,ȱorȱ inȱtheȱabsenceȱofȱdata,ȱatȱaȱpercentageȱofȱtheȱnotionalȱpristineȱstate.ȱ

ȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱȱ

1ȱUnitedȱNationsȱConventionȱonȱLawȱofȱtheȱSeaȱ(1982).ȱ

UNȱConferenceȱonȱEnvironmentȱandȱDevelopmentȱ(RioȱdeȱJaneiro,ȱ1992).ȱ

FAO,ȱCodeȱofȱConductȱforȱResponsibleȱFisheriesȱ(1995).ȱ EIFAC/ICES WGEEL Report 2008 41

4.2 Targets

InȱgeneralȱitȱcanȱbeȱexpectedȱthatȱachievingȱtheȱtargetȱdefinedȱbyȱtheȱEuropeanȱCounȬ cilȱ (councilȱ regulationȱ Noȱ 1100/2007)ȱ throughȱ managementȱ actionsȱ willȱ takeȱ aȱ veryȱ longȱ time.ȱ Åströmȱ andȱ Dekker,ȱ 2007ȱ estimatedȱ theȱ timeȱ toȱ fullȱ recoveryȱ ofȱ recruitȬ mentȱ(theȱultimateȱgoalȱofȱtheȱmanagementȱofȱtheȱeel)ȱtoȱbeȱatȱleastȱ80ȱyears,ȱifȱallȱeelȱ fisheriesȱwereȱclosedȱandȱnoneȱofȱtheȱotherȱmortalityȱissuesȱaddressed.ȱTheȱlongȬtermȱ targetȱdefinedȱbyȱtheȱECȱthenȱbecomesȱhardȱtoȱapplyȱinȱpracticalȱmanagementȱterms.ȱ So,ȱ forȱ practicalȱ reasonsȱ shortȬterm,ȱ managementȱ unit ȱ based,ȱ interimȱ targetsȱ (hereȱ calledȱinterimȱtargets)ȱneedȱtoȱbeȱdefinedȱinȱconnectionȱwithȱmanagementȱmeasuresȱ toȱbeȱtakenȱ(Figureȱ4.2).ȱ

TheseȱinterimȱtargetsȱneedȱthenȱtoȱbeȱtranslatedȱintoȱsubȬtargetsȱforȱactionȱonȱtheȱloȬ calȱscale,ȱwhichȱcanȱrangeȱinȱgeographicalȱscaleȱfromȱaȱpointȱsourceȱ suchȱasȱaȱhydroȬ powerȱplantȱorȱfisheryȱtoȱtheȱcatchmentȱorȱtheȱscaleȱofȱtheȱEelȱmanagementȱUnit.ȱThisȱ isȱrequiredȱasȱtheȱefficiencyȱofȱmanagementȱactionȱhasȱtoȱbeȱevaluatedȱinȱaȱshortȱtermȱ compatibleȱwithȱtheȱtimeȬscaleȱofȱtheȱresponsibleȱmanagersȱandȱthisȱisȱshorterȱthanȱ theȱexpectedȱtimeȱspanȱforȱtheȱrecoveryȱofȱtheȱeelȱstock.ȱThereforeȱshortȬterm,ȱsubȬ targetsȱareȱneededȱtoȱoptimizeȱregionalȱmanagementȱaccordingȱtoȱtheȱlongȬtermȱobȬ jectiveȱofȱfullȱstockȱrecoveryȱ(Figureȱ4.2).ȱTheȱsubȬtargetsȱwillȱbeȱsplitȱintoȱmanageȬ mentȱsubȬtargetsȱdirectlyȱlinkedȱtoȱtheȱsetȬupȱofȱmanagementȱandȱintoȱeelȱsubȬtargetsȱ aimingȱatȱincreasingȱtheȱproductionȱofȱeelȱonȱaȱlocalȱorȱregionalȱscale.ȱManagementȱ subȬtargetsȱmayȱbeȱdefinedȱasȱtheȱnumberȱorȱmagnitudeȱofȱactionsȱtaken,ȱi.e.ȱnumberȱ ofȱdamsȱwithȱpassesȱinstalled,ȱreductionȱofȱfishingȱmortality,ȱnumberȱofȱhabitatsȱandȱ amountȱofȱeelȱstocked.ȱInȱcontrastȱanȱeelȱsubȬtargetȱcould,ȱasȱanȱexample,ȱbeȱrelatedȱ toȱtheȱabundanceȱorȱdensityȱforȱ0+ȱeelȱinȱpredefinedȱsectionsȱofȱaȱcatchment.ȱ

European level (several decades) EU target: 40% of the pristine escapement

MS, RBD, EMU level (decade or less)

Interim target … Interim target … Interim target % of current escapement

Local level (several years)

Mngt sub-target Eel sub-target … Mngt sub-target Eel sub-target Mngt sub-target Eel sub-target N of equipped dams Density of yellow eel

Management set-up Post Evaluation ȱ

Figureȱ4.2:ȱSchematicȱrepresentationȱofȱdifferentȱtargets,ȱinterimȱtargetsȱandȱeelȱandȱmanagementȱ subȬtargets.ȱ

ȱ 42 EIFAC/ICES WGEEL Report 2008

Bothȱtypesȱofȱtargetȱ(eelȱlifeȱstageȱsubȬtarget;ȱmanagementȱsubȬtarget)ȱshouldȱbeȱposȬ sibleȱtoȱpostȬevaluate,ȱi.e.ȱitȱshouldȱbeȱpossibleȱtoȱempiricallyȱmeasureȱtheȱoutcomeȱofȱ theȱmanagementȱeffortȱrelativelyȱsoonȱafterȱitȱhasȱbeenȱapplied,ȱandȱmemberȱstatesȱ areȱ requiredȱ toȱ collectȱ relevantȱ dataȱ toȱ achieveȱ this.ȱ Forȱ eachȱ typeȱ ofȱ managementȱ measuresȱ differentȱ timeȬscalesȱ forȱ theȱ responseȱ inȱ theȱ relevantȱ eelȱ lifeȱ stageȱ canȱ beȱ expected.ȱ

AȱlinkȱbetweenȱtheȱoutcomeȱofȱtheȱpostȬevaluationȱandȱfutureȱmanagementȱrestricȬ tionsȱshouldȱbeȱestablished.ȱInȱprinciple,ȱoneȱcouldȱuseȱaȱqualitativeȱlink;ȱi.e.ȱwhenȬ everȱ theȱ spawnerȱ productionȱ isȱ belowȱ theȱ subȬtarget,ȱ theȱ managersȱ increaseȱ theirȱ restrictions.ȱHowever,ȱaȱquantitativeȱlinkȱisȱpreferable,ȱifȱnotȱaȱprerequisiteȱasȱtheȱECȱ targetȱisȱdefinedȱinȱquantitativeȱterms;ȱi.e.ȱtheȱpostȬevaluationȱmethodȱshouldȱindiȬ cateȱwhatȱlevelȱofȱrestrictionsȱisȱrequiredȱtoȱachieveȱtheȱsubȱtarget.ȱ

TheȱlevelȱofȱtheȱinterimȱandȱsubȱtargetsȱshouldȱbeȱdefinedȱsoȱthatȱtheȱlongȬtermȱtargetȱ definedȱbyȱtheȱcouncilȱregulationȱNoȱ1100/2007ȱ(Ȉ…ȱreduceȱanthropogenicȱmortalitiesȱ soȱasȱtoȱpermitȱwithȱhighȱprobabilityȱtheȱescapementȱtoȱtheȱseaȱofȱatȱleastȱ40%ȱofȱtheȱ silverȱeel ȱbiomassȱrelativeȱtoȱtheȱbestȱestimateȱofȱescapementȱthatȱwouldȱhaveȱexistedȱ ifȱnoȱanthropogenicȱinfluencesȱhadȱimpactedȱtheȱstock.ȱȈ),ȱ(orȱotherȱrelevant,ȱstricter,ȱ targets),ȱ hasȱ aȱ highȱ probabilityȱ ofȱ beingȱ reached,ȱ inȱ reasonableȱ time.ȱ Theȱ expectedȱ differencesȱinȱtimeȱuntilȱdifferentȱmeasuresȱresultȱinȱincreasedȱspawnerȱescapementȱ haveȱtoȱbeȱconsideredȱinȱthisȱcontext.ȱ

IfȱreachingȱtheȱlongȬtermȱtargetȱisȱnotȱpossible,ȱbasedȱonȱtheȱcurrentȱeelȱstockȱwithinȱ anȱEelȱManagementȱUnitȱ(EMU),ȱandȱtheȱtimeȱscheduleȱforȱtheȱattainmentȱofȱtheȱtarȬ getȱ levelȱ ofȱ escapementȱ cannotȱ beȱ calculatedȱ (althoughȱ suchȱ aȱ timeȱ scheduleȱ isȱ reȬ quiredȱ byȱ theȱ councilȱ regulationȱ Noȱ 1100/2007),ȱ managersȱ mightȱ considerȱ usingȱ aȱ stepwiseȱapproachȱwithȱincreasinglyȱmoreȱambitiousȱinterimȱtargetsȱinȱsequenceȱoverȱ time.ȱ Thisȱ couldȱ meanȱ startingȱ outȱ withȱ interimȱ targetsȱ andȱ shortȬtermȱ measuresȱ basedȱonȱcurrentlyȱachievableȱimprovementsȱinȱtheȱeelȱstock,ȱgivenȱtheȱcurrentȱlowȱ recruitmentȱ(e.g.ȱaȱhighȱ%ȱofȱcurrentȱpossibleȱescapement)ȱthenȱmovingȱtoȱanȱinterimȱ targetȱrelatedȱtoȱescapementȱofȱpreȬ1980ȱ(e.g.ȱ40%ȱofȱpossibleȱ(withoutȱanthropogenicȱ impact)ȱescapementȱofȱtheȱpreȬ1980),ȱthenȱincreasingȱtheȱrequiredȱpercentageȱofȱpreȬ 1980ȱescapementȱ(e.g.ȱ100%ȱofȱescapementȱpreȬ1980)ȱtoȱfinallyȱbeȱableȱtoȱaimȱdirectlyȱ forȱ40%ȱofȱpristineȱescapement.ȱ

Itȱwillȱneedȱtoȱbeȱrememberedȱthatȱwhenȱcalculatingȱexpectedȱspawnerȱescapementȱ fromȱeachȱRBD/EMU,ȱinȱresponseȱtoȱmanagementȱmeasures,ȱitȱmustȱbeȱemphasizedȱ toȱconsiderȱinformationȱonȱtheȱrecentȱrecruitmentȱdecline,ȱwhichȱinȱmostȱcasesȱwillȱ imposeȱaȱdecreasing ȱlocalȱstockȱofȱeelsȱinȱtheȱnearȱfuture,ȱandȱconsequentlyȱaȱdeclinȬ ingȱspawnerȱescapement,ȱwhichȱneedȱtoȱbeȱcounteractedȱbyȱtheȱlevelȱofȱtheȱmanageȬ mentȱ measures.ȱ Thisȱalsoȱ raiseȱ theȱ riskȱ ofȱ gettingȱ aȱsituationȱ whereȱ anȱ escapementȱ targetȱmightȱbeȱreachedȱoneȱyear,ȱjustȱtoȱdropȱbelowȱtheȱnextȱyearȱbeingȱinȱtheȱriskȱofȱ aȱcontinuedȱdeclineȱdespiteȱtheȱmanagementȱmeasuresȱtaken.ȱ

4.3 Estimation of spawner escapement

TheȱRegulationȱsuggestsȱthreeȱoptionsȱforȱdeterminingȱtheȱtargetȱlevelȱofȱescapementȱ (Articleȱ2.5):ȱ (a) using data collected in the most appropriate period prior to 1980 to estimate silver eel escapement, provided these are available in sufficient quantity and quality; (b) a habitat-based assessment of potential eel production, in the absence of anthropogenic mortality factors; (c) extrapolating with reference to the ecology and hydrography of similar river systems. EIFAC/ICES WGEEL Report 2008 43

4.3.1 Estimation of silver eel escapement pre- and post-1980

Theȱdefinitionȱofȱsilverȱeelȱneedsȱtoȱbeȱstandardizedȱforȱescapementȱestimates.ȱTheȱ differenceȱbetweenȱsilveringȱandȱsilverȱeelsȱhasȱtoȱbeȱclearȱandȱtheȱadoptionȱofȱtheȱ sameȱcriteriaȱallȱoverȱEuropeȱisȱthereforeȱrequired.ȱTheseȱdistinctionsȱhaveȱbeenȱmadeȱ clearȱbyȱsomeȱauthorsȱ(e.g.ȱAcouȱetȱal.,ȱ2005;ȱDurifȱetȱal.,ȱ2005)ȱandȱfollowingȱthemȱweȱ proposeȱthreeȱcriteria,ȱwhichȱincludeȱeyeȱdiameter,ȱstateȱofȱlateralȱlineȱ(presenceȱofȱ blackȱcorpuscles)ȱandȱbodyȱcolourȱcontrast.ȱItȱisȱessentialȱthatȱaȱstandardizedȱmethodȱ ofȱsilverȱeelȱidentificationȱisȱadoptedȱforȱescapementȱstudies.ȱ

Estimationsȱofȱsilverȱeelȱescapementȱareȱavailablemȱfro ȱaȱnumberȱofȱstudies;ȱtheseȱareȱ summariesȱinȱTablesȱ4.1aȱandȱbȱforȱassessmentsȱpreȱandȱpostȱ1980,ȱrespectively.ȱTheȱ geographicalȱdistributionȱofȱ theȱ studiesȱ dataȱareȱshownȱ inȱ Figureȱ 4.3.ȱSilverȱeelȱ esȬ capementȱisȱdefinedȱasȱtheȱtotalȱnumberȱorȱweightȱofȱsilverȱeelȱthatȱleftȱtheȱ catchment,ȱ expressedȱperȱunitȱwettedȱareaȱavailableȱtoȱeelȱforȱcomparisonȱbetweenȱcatchments.ȱ Potentialȱsilverȱeelȱescapementȱisȱdefinedȱasȱtheȱnumber,ȱorȱweight,ȱofȱsilverȱeelȱthatȱ wouldȱleaveȱtheȱcatchment,ȱwithoutȱanthropogenicȱmortality,ȱandȱforȱTablesȱ4.1aȱandȱ b,ȱthisȱhasȱbeenȱcalculatedȱasȱtheȱsumȱofȱsilverȱeelȱescapementȱandȱtheȱcatchesȱofȱsilȬ verȱandȱyellowȱeelȱandȱanyȱmortalityȱfromȱotherȱcausesȱ(hydropower,ȱillegalȱfishing,ȱ etc).ȱ

PreȬ1980ȱ dataȱ areȱ availableȱ fromȱ 25ȱ locationsȱ (Tableȱ 4.1a).ȱ Forȱ riverȱ systemsȱ whereȱ lakesȱ areȱ aȱ smallȱ proportionȱ ofȱ theȱ availableȱ habitatȱ forȱ eelȱ productionȱ estimatesȱ rangedȱfromȱ 1.9–49ȱkg/haȱ(n=4).ȱForȱcatchmentsȱwhereȱthereȱisȱaȱsizeableȱlakeȱcomȬ ponentȱ toȱ theȱ overallȱ wettedȱ areaȱ (>50%)ȱ theȱ estimatesȱ rangedȱ fromȱ 0.3–17.4ȱ kg/haȱ (n=4).ȱForȱlakes,ȱwithȱtheȱexceptionȱofȱtheȱIjsselmeerȱwhereȱproductionȱwasȱestimatedȱ atȱ40ȱkg/haȱonlyȱminimumȱestimatesȱbasedȱonȱsilverȱeelȱyieldsȱfromȱ fisheriesȱsuggestȱ aȱrangeȱofȱ0.1–11.7ȱkg/haȱ(n=14).ȱForȱmarshȱtypeȱhabitatȱthereȱisȱaȱminimumȱestimateȱ ofȱ43.7ȱkg/haȱandȱforȱlagoonsȱoneȱestimateȱofȱ20ȱkg/ha.ȱ

PostȬ1980,ȱ theȱ numberȱ ofȱ assessmentsȱ ofȱ productionȱ hasȱ increased,ȱ butȱ remainsȱ dominatedȱbyȱlakeȱstudiesȱfromȱSweden;ȱ66%ȱofȱtheȱ50ȱstudiesȱ(Tableȱ4.1b).ȱEstimatesȱ ofȱpotentialȱsilverȱeelȱescapementȱforȱriversȱvariedȱfromȱ2.7–16.4ȱkg/haȱ(n=3),ȱforȱlakeȱ dominatedȱcatchmentsȱfromȱ0.2–6.4ȱkg/haȱ(n=4)ȱandȱforȱlakesȱfromȱaȱminimumȱ(basedȱ onȱsilverȱeelȱyield)ȱofȱ0.04–4.4ȱkg/haȱ(n=35).ȱOfȱtheȱ35ȱlakeȱstudies,ȱtwoȱtheȱShannonȱ andȱ Ijsselmeerȱ provideȱ anȱ estimateȱ ofȱ potentialȱ silverȱ eelȱ productionȱ ofȱ 2.7ȱ andȱ 4.4ȱ kg/ha,ȱrespectively.ȱThereȱareȱthreeȱlagoonȱstudiesȱwithȱestimatesȱrangingȱfromȱ6.2– 30ȱkg/ha.ȱ 44 EIFAC/ICES WGEEL Report 2008

Tableȱ4.1a:ȱEstimatedȱsilverȱeelȱyieldȱandȱproductionȱ(inȱkg/haȱwettedȱarea),ȱpreȬ1980.ȱ

ȱ EIFAC/ICES WGEEL Report 2008 45

Tableȱ4.1b:ȱEstimatedȱsilverȱeelȱyieldȱandȱproductionȱ(inȱkg/haȱwettedȱarea),ȱpostȬ1980.ȱ 46 EIFAC/ICES WGEEL Report 2008

Pre - 1980

Post - 1980

Figureȱ4.3:ȱTheȱlocationȱofȱtheȱcatchmentsȱforȱwhichȱhistoricalȱȱ(preȬ1980ȱblack)ȱandȱrecentȱsilverȱ eelȱproductionȱestimatesȱ(postȬ1980ȱred)ȱareȱpresentedȱinȱtheȱTablesȱabove.ȱ

4.3.2 Modelling approaches

AȱnumberȱofȱmodellingȱapproachesȱhaveȱbeenȱmadeȱtoȱestimateȱescapementȱorȱaȱrefȬ erenceȱconditionȱtoȱassessȱcomplianceȱwithȱtheȱEUȱescapementȱtarget.ȱ

Theȱmodelsȱare:ȱ

x ReferenceȱConditionȱModelȱ(RCM)ȱ x EelȱLengthȱStructureȱAnalysisȱ(ELSA)ȱ x ScenarioȬbasedȱModelȱforȱEelȱPopulationsȱ(SMEP)ȱ x GlobalȱAnguilleȱ(GLOBANG)ȱ x LengthȬbasedȱVirtualȱPopulationȱAnalysisȱ(LVPA)ȱ x SwedishȱAnalyticalȱModelsȱ(SWAM)ȱ x DemographicȱModelȱofȱtheȱCamargueȱ(DEMCAM)ȱ x Glassȱeelȱmodelȱtoȱassessȱcomplianceȱ(GEMAC)ȱ

Theseȱ modelsȱ andȱ theirȱ potentialȱ toȱ supportȱ theȱ EMPsȱ haveȱ beenȱ describedȱ byȱ EIȬ FAC/ICESȱWGEELȱandȱDekkerȱetȱal.,ȱ2006.ȱInȱadditionȱduringȱtheȱmeetingȱaȱnumberȱ ofȱ otherȱ approachesȱ haveȱ beenȱ presentedȱ toȱ theȱ WGEELȱ asȱ nonȱ peerȬreviewedȱ workedȱexamples.ȱ EIFAC/ICES WGEEL Report 2008 47

4.3.2.1 Elbe population dynamic model (Oeberst et al., submitted)

AnȱageȱbasedȱmodelȱhasȱbeenȱdevelopedȱbyȱOeberstȱetȱal.,ȱsubmittedȱtoȱexamineȱtheȱ populationȱdynamicsȱofȱeelȱinȱtheȱRiverȱElbeȱ(Germany)ȱandȱestimateȱtheȱnumberȱofȱ eelȱ emigratingȱ fromȱ theȱ catchment.ȱ Theȱ modelȱ inputsȱ areȱ quantityȱ ofȱ immigratingȱ youngȱ eel,ȱ numberȱ (andȱ weight)ȱ ofȱ eelȱ stocked,ȱ naturalȱ mortalityȱ andȱ mortalityȱ causedȱbyȱcommercialȱandȱrecreationalȱfishing,ȱcormorants,ȱandȱhydropowerȱplants.ȱ TheȱstructureȱofȱtheȱmodelȱallowsȱtheȱsensitivityȱofȱtheȱparametersȱtoȱtheȱoverallȱesȬ timateȱ toȱ beȱ examined.ȱ Theȱ modelȱ mayȱ beȱ usedȱ toȱ developȱ managementȱ strategiesȱ andȱtoȱassessȱtheȱeffectivenessȱofȱdifferentȱmanagementȱoptionsȱtoȱmeetȱtheȱEUȱtarget.ȱ Itȱhasȱtheȱadvantageȱofȱsimpleȱadjustmentȱbyȱbeingȱmodularȱconstructedȱandȱcanȱbeȱ furtherȱdevelopedȱusingȱMSȬEXCEL.ȱ

Theȱmodelȱassumesȱthatȱeelȱremainȱinȱfreshȱwaterȱforȱaȱmaximumȱofȱ20ȱyears.ȱTheȱ availableȱdataȱforȱdescribingȱtheȱdifferentȱfactorsȱwhichȱinfluenceȱtheȱstockȱdynamicsȱ haveȱdifferentȱquality.ȱTotalȱcatchȱ(kg)ȱperȱyearȱisȱestimatedȱforȱtheȱcommercialȱfishȬ ersȱandȱangler.ȱTheȱmeanȱweightȱofȱtheȱcatchȱ(g)ȱandȱage–lengthȱbasedȱsamplesȱareȱ onlyȱavailableȱfromȱsomeȱareasȱofȱtheȱElbeȱandȱshortȱperiods.ȱLengthȱbasedȱestimatesȱ existȱforȱtheȱtransformationȱofȱyellowl ȱee ȱtoȱsilverȱeelȱandȱforȱtheȱeelȱwhichȱareȱtakenȱ byȱcormorantsȱbasedȱonȱstomachȱsamples.ȱToȱcombineȱtheȱdifferentȱdataȱtypesȱaȱproȬ cedureȱisȱnecessaryȱforȱtransferringȱlengthȱbasedȱdataȱintoȱageȱbasedȱdata.ȱ

Forȱtheȱmodelȱitȱwasȱassumedȱthatȱeelȱageȱ>8ȱwereȱfullyȱrecruitedȱtoȱtheȱfishery,ȱthisȱisȱ basedȱonȱaȱminimumȱsizeȱlimitȱofȱ45ȱcmȱforȱcommercialȱandȱrecreationalȱfishers.ȱReȬ cruitmentȱisȱcomposedȱofȱnaturalȱimmigrationȱofȱglassȱ/ȱyellowȱeelȱbasedȱonȱmonitorȬ ingȱestimatesȱandȱstockedȱeelȱfromȱpublishedȱreports.ȱNaturalȱmortalityȱisȱassumedȱ toȱbeȱconstantȱat%ȱ13 ȱ(M=0.14)ȱperȱyearȱ(Dekker,ȱ2000).ȱForȱrecreationalȱanglersȱtheȱ totalȱ weightȱ ofȱ eelȱ caughtȱ wasȱ theȱ productȱ ofȱ theȱ totalȱ numberȱ ofȱ anglersȱ andȱ theȱ meanȱweightȱofȱtheȱcatch.ȱTheȱamountȱofȱeelȱconsumedȱbyȱtheȱcormorantȱpopulationȱ wasȱ estimatedȱ basedȱ onȱ theȱ numberȱ ofȱ cormorants,ȱ theirȱ residencyȱ time,ȱ theȱ dailyȱ foodȱ intakeȱ andȱ theȱ averageȱ proportionȱ ofȱ eelȱ inȱ theirȱ dietȱ (Brämickȱ andȱ Fladung,ȱ 2006).ȱTheȱtotalȱcatchȱofȱtheȱcommercialȱandȱrecreationalȱfishersȱandȱtheȱconsumptionȱ ofȱeelȱbyȱcormorantsȱwereȱconvertedȱfromȱaȱweightȱbasedȱestimateȱtoȱaȱnumberȱperȱ ageȱusingȱweightȱtoȱlengthȱconversionsȱandȱaȱvonȱBertalanffyȱgrowthȱmodel.ȱAȱlengthȱ basedȱlogitȬfunctionȱwasȱusedȱtoȱestimateȱtheȱproportionȱofȱsilverȱeelȱinȱtheȱcatchȱofȱ eelȱbyȱfishersȱandȱinȱtheȱeelȱconsumedȱbyȱcormorants.ȱ

Inȱaddition,ȱsomeȱgeneralȱassumptionsȱwereȱusedȱforȱestimatingȱtheȱcatchȱinȱnumberȱ byȱage ȱgroupȱandȱyearȱbecauseȱappropriateȱdataȱareȱlacking:ȱTheȱageȱfrequencyȱofȱtheȱ catchesȱbyȱfishersȱandȱanglersȱisȱsimilarȱtoȱtheȱageȱfrequencyȱofȱtheȱstockȱcombinedȱ withȱtheȱrequirementȱthatȱeelȱyoungerȱthanȱeightȱyearsȱareȱnotȱlanded;ȱsilverȱeelȱareȱ notȱlandedȱbyȱfishersȱorȱtheȱlandingsȱcanȱbeȱneglected.ȱ

Evenȱthoughȱtheȱmodelȱisȱadjustedȱtoȱtheȱconditionsȱinȱtheȱriverȱsystemȱandȱtoȱtheȱ availabilityȱofȱdata,ȱitȱalsoȱincludesȱseveralȱassumptionsȱandȱuncertainties.ȱTherefore,ȱ theȱresultsȱofȱtheȱmodelȱwillȱhaveȱtoȱbeȱvalidatedȱbyȱmonitoringȱtheȱstock,ȱespeciallyȱ byȱsilverȱeelȱmonitoring.ȱ

4.3.2.2 Irish model to estimate silver eel escapement (Ó’Néill and Poole, in prep.)

Catch based estimates of historic/pristine escapement

Theȱcalculationȱofȱpristineȱproductivityȱforȱexploitedȱcatchmentsȱrequiresȱestimatesȱofȱ silverȱ eelȱ escapementȱ alongȱ withȱ historicȱ silverȱ andȱ brownȱ eelȱ catchesȱ (Figureȱ 4.4).ȱ Historicalȱcatchȱrecordsȱforȱsilverȱeelȱfisheriesȱwereȱavailableȱforȱtheȱfiveȱcatchmentsȱ ofȱ theȱ Corrib,ȱ Moy,ȱ Garavogueȱ andȱ Erne.ȱ Theȱ efficienciesȱ ofȱ theȱ fisheriesȱ hadȱ beenȱ 48 EIFAC/ICES WGEEL Report 2008

previouslyȱ estimatedȱ forȱ theȱ Shannon,ȱ Corribȱ andȱ Erneȱ silverȱ eelȱ fisheries.ȱ Whereȱ fisheryȱefficiencyȱwasȱnotȱmeasuredȱanȱapproximatelyȱaverageȱvalueȱofȱ33%ȱwasȱusedȱ toȱcalculateȱescapement.ȱInȱadditionȱtoȱtheȱcatchȱatȱtheȱrecordingȱstationȱandȱescapeȬ mentȱpastȱtheȱrecordingȱstationȱtheȱbrownȱeelȱandȱsilverȱeelȱcatchesȱmadeȱupstreamȱ wereȱincludedȱtoȱestimateȱpristineȱproductivity.ȱInȱtheȱabsenceȱofȱhistoricalȱȱdataȱforȱ theseȱlatterȱparametersȱ(brownȱandȱsilverȱeelȱcatchesȱupstreamȱofȱtheȱrecordingȱstaȬ tion)ȱ itȱ wasȱassumedȱ thatȱ theȱ yieldsȱ wereȱ equalȱ toȱ thoseȱ currentlyȱ observedȱ (2001– 2007).ȱ

Brownȱeelȱyieldȱwasȱassumedȱtoȱbeȱequivalentȱtoȱtheȱsameȱweightȱofȱpotentialȱsilverȱ eel.ȱThisȱassumptionȱwasȱbasedȱonȱtheȱlogicȱthatȱinȱaȱsystemȱsubjectȱonlyȱtoȱnaturalȱ mortality,ȱmigrationȱwouldȱonlyȱbeȱdelayedȱsuchȱthatȱfecundityȱ(relatedȱtoȱweight)ȱ wouldȱbeȱmaximized.ȱConsequently,ȱitȱisȱunlikelyȱthatȱthereȱwouldȱbeȱaȱnetȱlossȱofȱ weightȱ inȱ subsequentȱ yearsȱ fromȱ aȱ cohort.ȱ Finally,ȱ theȱ productivityȱ estimatesȱ wereȱ correctedȱbyȱtheȱlevelȱofȱunreportedȱandȱillegalȱfishing.ȱUnreportedȱyieldȱwasȱderivedȱ asȱtheȱratioȱofȱunreportedȱlicencesȱtoȱlicencesȱissuedȱwithinȱtheȱrelevantȱRiverȱBasinȱ Districtȱbetweenȱtheȱyears ȱ2001–2007.ȱTheȱproportionȱofȱtheȱfisheryȱyieldȱtakenȱilleȬ gallyȱwasȱassumedȱtoȱbeȱequalȱtoȱthatȱestimatedȱforȱtheȱShannonȱbyȱtheȱDEMCAMȱ (SLIME)ȱmodelȱ(Dekkerȱet.ȱal.,ȱ2006).ȱȱForȱthoseȱcatchmentsȱwithȱhydropower,ȱanȱesȬ timateȱofȱtheȱimpactȱwasȱderivedȱbyȱimposingȱaȱ28.5%ȱmortalityȱperȱturbine ȱpassageȱ (WGEEL,ȱ2002).ȱTherefore,ȱtheȱprobabilityȱofȱsurvivingȱpassageȱthroughȱ‘n’ȱnumberȱ ofȱhydropowerȱinstallationsȱisȱ(0.715)n.ȱ

Theȱestimatedȱpristineȱspawnerȱescapementȱrangedȱfromȱ0.9–5.4ȱkg/haȱwithȱaȱmeanȱ ofȱ3.9ȱkg/haȱ(Tableȱ4.2).ȱ

Index catchment Index catchment current escapement potential escapement

Hydropower impact

Total fishing impact EIFAC 2002 report – mean of estimated hydro- National authorisation statistics Proportion unreported Proportion illegal power mortalities

Reported fishery impact Estimate of illegal catch for the Shannon lakes based on DEMCAM Silver catch model

Input variables Brown catch Calculated variables National catch statistics Target

Figureȱ4.4:ȱDescriptionȱofȱhowȱpotentialȱproductionȱ(escapement)ȱwasȱderivedȱfromȱtheȱcurrentȱ escapementȱofȱcatchmentsȱwhereȱestimatesȱofȱsilverȱeelȱescapement,ȱfisheryȱyieldȱandȱtheȱimpactȱ ofȱhydropowerȱareȱavailable.ȱ EIFAC/ICES WGEEL Report 2008 49

Tableȱ 4.2:ȱ Estimatedȱ pristineȱ spawnerȱ productivityȱ fromȱ fiveȱ Irishȱ catchmentsȱ basedȱ onȱ eitherȱ directȱmeasurementȱand/orȱcatchȱdata.ȱ

MOY GARAVOGUE ERNE CORRIB BURRISHOOLE

1942– 1955– 1976– ȱȱ1952ȱ 1962–1975ȱ 1982ȱ 1982ȱ 1971–1980ȱ Silverȱeelȱcatchȱatȱ recordingȱstationȱ (t)ȱȱ3.4ȱ 0.9ȱ 9.2ȱ 19.4ȱ 0.0ȱ Escapementȱpastȱ recordingȱstationȱ (t)ȱȱ6.8ȱ 4.4ȱ 51.3ȱ 38.8ȱ 427.5ȱ Brownȱeelȱyieldȱ upstreamȱ(t)ȱ Reportedȱȱ 4.0ȱ 1.7ȱ 13.4ȱ 9.0ȱ 0.0ȱ ȱBrownȱeelȱyieldȱ upstreamȱ(t)ȱ Unreportedȱ 3.0ȱ 1.2ȱ 23.4ȱ 6.5ȱ 0.0ȱ Silverȱeelȱyieldȱ upstreamȱ(t)ȱ Reportedȱȱ ȱ 0.0ȱȱ18.6ȱ 0.0ȱ ȱSilverȱeelȱyieldȱ upstreamȱ Unreportedȱ 29.1ȱ 1.2ȱ 9.2ȱ 13.4ȱ 0.0ȱ Hydropowerȱ impactȱ(t)ȱȱ 0.0ȱ 0.0ȱ 25.4*ȱ 0.0ȱ 0.0ȱ Wettedȱareaȱ(ha)ȱȱ 8418.0ȱ 1783.0ȱ 25.9ȱ 28869.0ȱ 475.0ȱ Productivityȱ (kg/ha)ȱȱȱ 5.3ȱ 5.4ȱ 4.5ȱ 3.4ȱ 0.9ȱ

*occursȱfollowingȱrecordingȱstation.ȱ

Potential production based on habitats of similar characteristics

Theȱ methodȱ involvedȱ determiningȱ theȱ relationshipȱ betweenȱ productivityȱ andȱ theȱ geologicalȱcharacteristicsȱofȱtheȱcatchment.ȱ

Growthȱrateȱofȱeelȱwereȱavailableȱforȱ17ȱcatchmentsȱ(Moriarty,ȱ1988,ȱCentralȱFisheriesȱ Board).ȱTheȱwettedȱareaȱwithinȱeachȱcatchmentȱwasȱquantifiedȱusingȱaȱgeographicalȱ informationȱsystemȱandȱclassifiedȱaccordingȱtoȱtheȱproportionȱofȱtheȱcatchmentȱareaȱ comprisingȱnonȬcalcareousȱgeology.ȱForȱ17ȱcatchmentsȱgrowthȱrateȱwasȱfoundȱtoȱbeȱ closelyȱ negativelyȱ relatedȱ toȱ theȱ proportionȱ ofȱ theȱ catchmentsȱ comprisingȱ nonȬ calcareousȱgeologyȱ(Figureȱ4.5)ȱ(r2=0.67;ȱp<0.0001).ȱ 50 EIFAC/ICES WGEEL Report 2008

Growth rate compared with geological classification

40 35 30 25 20 15 10 Growth Rate (mm/yr) Rate Growth 5 0 0 102030405060708090100 Proportion of catchment non-calcareous ȱ

Figureȱ4.5:ȱTheȱrelationshipȱbetweenȱgrowthȱrateȱandȱtheȱproportionȱofȱtheȱcatchmentȱcomprisingȱ nonȬcalcareousȱgeology.ȱ

Theȱ fourȱ catchȬbasedȱ productionȱ estimatesȱ alongȱ withȱ theȱ directȱ estimateȱ forȱ theȱ Burrishooleȱ(Tableȱ4.2)ȱwereȱplottedȱagainstȱtheȱproportionȱofȱnonȬcalcareousȱgeologyȱ withinȱtheȱcatchmentȱ(Figureȱ4.6).ȱTheseȱhistoricȱestimatesȱsuggestȱthatȱinȱexclusivelyȱ nonȬcalcareousȱ catchmentsȱ silverȱ eelȱ productivityȱ wasȱ approximatelyȱ 0.9kg/haȱ whereasȱ inȱ predominantlyȱ calcareousȱ catchmentsȱ silverȱ eelȱ productivityȱ averagedȱ aboutȱ4.5kg/ha.ȱ

AnȱobviousȱweaknessȱinȱtheȱrelationshipȱpresentedȱinȱFigureȱ4.6ȱisȱtheȱdistributionȱofȱ theȱ data,ȱ withȱ veryȱ fewȱ dataȱ forȱ intermediateȱ orȱ nonȬcalcareousȱ catchments.ȱ Toȱ inȬ creaseȱtheȱrobustnessȱofȱtheȱmodelȱtheȱ5ȱavailableȱproductivityȱestimatesȱwereȱusedȱtoȱ convertȱ theȱ growthȬrateȱ estimatesȱ forȱ 17ȱ catchmentsȱ intoȱ pristineȱ productionȱ estiȬ mates.ȱ

Potentialȱ silverȱ eelȱ productivityȱ wasȱ regardedȱ asȱ aȱ productȱ ofȱ recruitment,ȱ naturalȱ survivalȱandȱaverageȱsilverȱeelȱweight.ȱNaturalȱmortalityȱwasȱimposedȱatȱaȱconstantȱ rateȱofȱ14%ȱperȱannum.ȱThisȱrateȱwasȱchosenȱbecauseȱtheȱaverageȱageȱof ȱIrishȱsilverȱ eelsȱisȱapproximatelyȱ18ȱyearsȱandȱtheȱcumulativeȱnaturalȱmortalityȱoverȱtheȱcontiȬ nentalȱlifeȱstagesȱisȱapproximatelyȱ2.5ȱ(Dekker,ȱ2004).ȱTheȱresidenceȱtimeȱwasȱtheȱtimeȱ requiredȱforȱglassȱeelsȱ(70ȱmm)ȱtoȱgrowȱtoȱtheȱIrishȱaverageȱsilverȱeelȱlengthȱofȱ480ȱ mmȱ(sexesȱcombined).ȱ EIFAC/ICES WGEEL Report 2008 51

Historic productivity estimates

6 5 4 3

(kg/ha) (kg/ha) 2 1 Silver eel productivity Silver eel productivity 0 0 20 40 60 80 100 Percentage of catchment non-calcareous

Corrib Garavogue Moy Burrishoole Erne ȱ

Figureȱ4.6:ȱCatchȱbasedȱproductivityȱestimatesȱplottedȱagainstȱtheȱpercentageȱofȱcatchmentȱwithȱ siliceousȱ(nonȬcalcareous)ȱgeology.ȱ

Forȱeachȱofȱtheȱ17ȱcatchmentsȱtheȱproportionȱofȱfishȱsurvivingȱ(S)ȱwasȱthusȱestimatedȱ asȱfollows:ȱ

Sȱ=ȱ(1Ȭ0.14)((480Ȭ70)/G)ȱ

WhereȱGȱ=ȱȱgrowthȱrateȱ(mm/yr)ȱ

Forȱthoseȱfiveȱcatchmentsȱdataȱonȱsilverȱeelȱproductionȱwasȱalsoȱavailableȱ(Tableȱ4.2)ȱ andȱtheseȱwhereȱusedȱasȱindexȱcatchmentsȱtoȱestimateȱpotentialȱspawnerȱescapementȱ asȱfollows:ȱ

Spawnerȱproductionxȱ=ȱ(Survivalx/Survivali)ȱ*ȱSpawnerȱproductivityiȱ

Whereȱȱi=ȱ“index”ȱriver;ȱxȱ=ȱriverȱwhereȱnoȱestimateȱofȱspawnerȱproductionȱisȱavailȬ able.ȱ

Thisȱcalculationȱwasȱrepeatedȱusingȱtheȱsurvivalȱandȱspawnerȱproductivityȱforȱeachȱ ofȱtheȱfiveȱ“index”ȱcatchmentsȱandȱtheȱmeanȱcomputed.ȱTheȱrelationshipȱbetweenȱtheȱ estimatedȱproductivityȱandȱgeologyȱforȱtheȱ17ȱcatchmentsȱisȱshownȱinȱFigureȱ4.7ȱtoȬ getherȱ withȱ theȱ estimateȱ forȱ thoseȱ fiveȱ catchmentsȱ whereȱ productivityȱ hadȱ beenȱ measuredȱeitherȱfromȱcatchesȱofȱbyȱdirectȱmeasurement.ȱ 52 EIFAC/ICES WGEEL Report 2008

Pristine productivity

1 Silver eel productivity (kg/ha) productivity Silver eel 0 0.00 20.00 40.00 60.00 80.00 100.00 Proportion of catchment comprising non-calcareous geology

Average productivity based on growth rates (calibrated with direct count and historic fishery data) Productivity based on direct count (n = 1) or historic fishery data (n = 5).

Figureȱ4.7:ȱRelationshipȱbetweenȱsilverȱeelȱproductivityȱ(kg/ha)ȱandȱpercentageȱofȱcatchmentȱwithȱ siliceousȱ(nonȬcalcareous)ȱgeology.ȱTheȱpinkȱpointsȱareȱbasedȱonȱcatchȱbasedȱorȱdirectȱestimatesȱ ofȱ productivity.ȱ Theȱ blueȱ pointsȱ areȱ basedȱ onȱ theȱ relativeȱ productivityȱ ofȱ theȱ catchȱ basedȱ estiȬ matesȱbutȱtheseȱareȱnotȱincludedȱinȱtheȱregression.ȱ

Theseȱdataȱnowȱallowȱforȱcalculationȱofȱpristineȱproductivityȱ(kg/ha)ȱbasedȱonȱeither:ȱ

1ȱ) Theȱ relationshipȱ betweenȱ silverȱ eelȱ productivityȱ (basedȱ onȱ fourȱ historicȱ catchȱ recordsȱ andȱ oneȱ historicȱ totalȱ count)ȱ andȱ theȱ proportionȱ ofȱ nonȬ calcareousȱgeologyȱinȱtheȱcatchmentȱusingȱtheȱregressionȱequation:ȱ

Productivityȱ(kg/ha)ȱ=ȱȬ0.041*(percentageȱofȱcatchmentȱnonȬcalcareous)ȱ+ȱ5.18ȱ

2ȱ) Theȱrelationshipȱbetweenȱsilverȱeelȱproductivityȱ(basedȱonȱ17ȱgrowthȱratesȱ calibratedȱwithȱfourȱhistoricȱcatchȱrecordsȱandȱoneȱhistoricȱtotalȱcount)ȱandȱ theȱ proportionȱ ofȱ nonȬcalcareousȱ geologyȱ inȱ theȱ catchmentȱ usingȱ theȱ reȬ gressionȱequation:ȱ

Productivityȱ(kg/ha)ȱ=ȱȬ0.030*(percentageȱofȱcatchmentȱnonȬcalcareous)ȱ+ȱ4.97ȱ

ForȱIrelandȱpristineȱspawnerȱproductionȱisȱestimatedȱatȱ641ȱ928ȱkgȱ(4.17ȱkg/ha)ȱusingȱ theȱregressionȱbasedȱonȱhistoricalȱcatchȱorȱtotalȱcountȱdataȱandȱ651ȱ092ȱkgȱ(4.23ȱkg/ha)ȱ usingȱ theȱ regressionȱ basedȱ onȱ growthȱ ratesȱ calibratedȱ withȱ historicalȱ catchȱ orȱ totalȱ countȱdata.ȱ

Asȱ reliableȱ dataȱ becomesȱ availableȱ thisȱ approachȱ willȱ beȱ takenȱ toȱ extrapolateȱ fromȱ dataȱrichȱtoȱdataȱpoorȱsituationsȱwhereȱapplicable.ȱThisȱapproachȱisȱwellȱestablishedȱ forȱsalmonȱmanagementȱinȱIreland.ȱTheȱregressionȱapproach,ȱasȱdescribed,ȱallowsȱtheȱ transferȱ ofȱ dataȱ fromȱ indexȱ catchmentsȱ withȱ productionȱ estimatesȱ toȱ catchmentsȱ whereȱlittleȱorȱnoȱdataȱexistsȱonȱtheȱbasisȱofȱgeologicalȱproxyȱforȱproduction.ȱ EIFAC/ICES WGEEL Report 2008 53

4.3.2.3 French methodology to estimate silver eel production (Hoffman, unpublished)

Theȱ evaluationȱ ofȱ theȱ biomassȱ ofȱ silverȱ eelȱ producedȱ inȱ continentalȱ watersȱ atȱ theȱ Frenchȱ scaleȱ isȱ basedȱ onȱ modellingȱ theȱ yellowȱ eelȱ abundance.ȱ 20ȱ000ȱ electrofishingȱ operationsȱwereȱusedȱtoȱfitȱtheȱmodel.ȱTheyȱcorrespondedȱtoȱ9000ȱstationsȱandȱcoverȱ theȱperiodȱ1980–2005.ȱTheȱmodelȱdescribesȱpresenceȱabsenceȱandȱabundanceȱofȱtotalȱ densitiesȱandȱdensitiesȱperȱclassȱsizeȱofȱ15ȱcm.ȱ

Fourȱ categoriesȱ ofȱ variablesȱ wereȱ used:ȱ environmentȱ (distanceȱ toȱ theȱ sea,ȱ temperaȬ tures,ȱaltitude,ȱgeographicalȱarea),ȱtemporalȱ(month,ȱyear),ȱvariablesȱlinkedȱwithȱanȬ thropogenicȱ pressureȱ (habitatȱ quality,ȱ obstacles,ȱ glassȱ eelȱ andȱ yellowȱ eelȱ fisheries)ȱ andȱvariablesȱassociatedȱwithȱelectrofishingȱ (fishingȱmethod).ȱ

Theȱ workȱ isȱ basedȱ onȱ aȱ GISȱ databaseȱ ofȱ theȱ Frenchȱ riverȱ network,ȱ whichȱ hasȱ beenȱ analysedȱtoȱextractȱsomeȱenvironmentalȱparametersȱ(distanceȱtoȱtheȱsea,ȱcumulatedȱ riverȱlengthȱupstream,ȱriverȱwidth,ȱStrahlerȱrank).ȱEnvironmentalȱparametersȱareȱexȬ tractedȱandȱdensitiesȱareȱpredictedȱinȱallȱpointsȱofȱtheȱnetwork.ȱSettingȱanthropogenicȱ parametersȱtoȱzero,ȱitȱisȱpossibleȱtoȱpredictȱtheȱactualȱpristineȱproductions.ȱTemporalȱ variablesȱallowȱtheȱpredictionȱofȱpastȱdensities.ȱTheȱcombinationȱofȱbothȱprovidesȱaȱ figureȱofȱpastȱpristineȱproductions.ȱDensitiesȱareȱconvertedȱintoȱnumbersȱbyȱmultiplyȬ ingȱbyȱtheȱwaterȱsurfaces.ȱ

TheȱaimȱisȱtoȱcompareȱtheȱestimatedȱȈpristineȈȱ1989ȱdensitiesȱwithȱthoseȱdeterminedȱ duringȱtheȱ1960sȱandȱ1970sȱandȱifȱtheȱlatterȱareȱhigherȱadjustȱtheȱpristineȱ1989ȱestiȬ mateȱbyȱaȱfactor.ȱThisȱdensityȱwouldȱthenȱbeȱcomparedȱwithȱcurrentȱestimatesȱ(FigȬ ureȱ4.8).ȱ

Theȱyellowȱstandingȱstockȱwillȱthenȱbeȱcomparedȱwithȱactualȱestimatesȱofȱsilverȱeelȱ production.ȱ 54 EIFAC/ICES WGEEL Report 2008

Figureȱ 4.8:ȱ Modelȱ predictionȱ inȱ Loireȱ Bretagneȱ ofȱ theȱ spatialȱ variationȱ inȱ yellowȱ eelȱ densitiesȱ (nb/100ȱm²).ȱSurfacesȱareȱnotȱyetȱcalculatedȱsoȱtheȱmedianȱofȱeelȱdensitiesȱisȱshownȱonȱeachȱgraph.ȱ Pristineȱcorrespondȱtoȱpredictionsȱwithoutȱdamȱandȱwithȱnoȱglassȱeelȱfishery.ȱ

Theȱpredictedȱtemporalȱtrendȱinȱyellowȱeelȱdensitiesȱestimatedȱatȱtheȱmouthȱofȱtheȱ riverȱinȱtheȱabsenceȱofȱdamsȱforȱtheȱperiodȱ1982–2005ȱisȱshownȱinȱFigureȱ4.9.ȱAfterȱ 1989ȱ thereȱ isȱ aȱ steadyȱ declineȱ inȱ density.ȱ Itȱ shouldȱ beȱ notedȱ thatȱ priorȱ toȱ 1989ȱ theȱ methodȱofȱdataȱcollectionȱdiffered,ȱandȱtheȱdifferenceȱmayȱreflectȱtheȱlowerȱdensityȱ estimates.ȱ EIFAC/ICES WGEEL Report 2008 55

Figureȱ 4.9:ȱ Modelȱ predictionȱ ofȱ theȱ temporalȱ trendȱ inȱ yellowȱ eelȱ densitiesȱ (nb/100ȱ m²)ȱ inȱ Loireȱ Bretagne.ȱ Theȱ yearȱ effectȱ wasȱ classifiedȱ asȱ categoryȱ inȱ bothȱ presenceȬabsenceȱ andȱ abundanceȱ whenȱpresentȱmodels,ȱtheȱdensitiesȱareȱthoseȱpredictedȱatȱtheȱmouthȱofȱtheȱriver,ȱinȱtheȱabsenceȱofȱ anthropogenicȱimpact.ȱ

Forȱeachȱobstacleȱtheȱseverityȱofȱtheȱobstructionȱwasȱestimatedȱonȱaȱscaleȱofȱ0–5ȱandȱ forȱobstaclesȱinȱseriesȱtheȱimpactȱwasȱestimatedȱtoȱbeȱcumulative.ȱObstaclesȱhaveȱtheȱ effectȱofȱreducingȱtheȱdensityȱofȱeelȱupstreamȱ(Figureȱ4.10).ȱThereȱisȱaȱrapidȱdeclineȱinȱ densityȱwithȱanȱincreaseȱinȱtheȱnumberȱandȱseverityȱofȱtheȱobstructionȱfallingȱtoȱapȬ proximatelyȱaȱthirdȱatȱaȱcumulativeȱobstructionȱscoreȱofȱ50.ȱ

Theȱmodelȱalsoȱpredictedȱthatȱeelȱdensityȱdeclinesȱwithȱdistanceȱfromȱtheȱseaȱ(Figureȱ 4.11).ȱ 56 EIFAC/ICES WGEEL Report 2008

Figureȱ4.10:ȱModelȱpredictionȱinȱLoireȱBretagneȱofȱtheȱcumulatedȱeffectȱofȱobstacles.ȱTheȱeffectȱofȱ obstaclesȱisȱexpressedȱasȱaȱscoringȱ(fromȱ0ȱtoȱ5ȱimpassable).ȱDensitiesȱ(nb/100ȱm²)ȱareȱpredictedȱatȱ theȱsea,ȱinȱ1995,ȱinȱtheȱLoire,ȱwithoutȱanthropogenicȱimpact.ȱ

Figureȱ4.11:ȱModelȱpredictionȱinȱLoireȱBretagneȱofȱtheȱeffectȱofȱtheȱdistanceȱtoȱtheȱsea.ȱDensitiesȱ (nb/100ȱm²)ȱareȱpredictedȱinȱ1995,ȱinȱtheȱLoire,ȱwithoutȱanthropogenicȱimpact.ȱ EIFAC/ICES WGEEL Report 2008 57

4.3.2.4 Silver eel production in Danish streams (Pedersen, pers.comm.)

Silverȱ eelȱ productionȱ inȱ Kogeȱ Lellingeȱ streamȱ wasȱ estimatedȱ toȱ beȱ 105ȱ kg/haȱ riverȱ (wettedȱ area)ȱ (Rasmussenȱ andȱ Therkildsen,ȱ 1979).ȱ Theȱ estimateȱ wasȱ basedȱ onȱ theȱ densityȱ ofȱ residentȱ yellowȱ eels,ȱ observedȱ growthȱ (derivedȱ fromȱ ageȱ reading)ȱ andȱ mortalityȱwithȱdataȱcollectedȱduringȱtheȱperiodȱ1965–1968.ȱTheȱestimateȱisȱthereforeȱ basedȱ onȱ glassȱ eelȱ recruitmentȱ duringȱ theȱ periodȱ theȱ lateȱ 1950sȱ andȱ earlyȱ toȱ midȬ 1960s.ȱTheȱpopulationȱconsistedȱmostlyȱofȱmalesȱwithȱmeanȱweightȱofȱ100ȱgramme.ȱ Theȱexperimentȱwasȱundertakenȱinȱtheȱlowestȱpartȱofȱtheȱstreamȱandȱdownstreamȱofȱ aȱweir,ȱtheȱestimateȱthereforeȱcanȱnotȱbeȱtakenȱasȱrepresentativeȱofȱsilverȱeelȱescapeȬ mentȱforȱtheȱcatchmentȱasȱaȱwholeȱbutȱonlyȱtheȱlowerȱpartȱofȱtheȱriver.ȱ

SilverȱeelȱproductionȱinȱRiverȱBredeȱwasȱestimatedȱtoȱbeȱ49ȱkg/haȱriverȱ(wettedȱarea)ȱ (Nielsen,ȱ1982).ȱTheȱsilverȱeelȱwereȱcaughtȱinȱautumnȱ1981ȱusingȱfykenetsȱwithȱtheȱ escapementȱestimatedȱusingȱmarkȬrecaptureȱandȱisȱthusȱbasedȱonȱtheȱrecruitmentȱofȱ glassȱ eelȱ duringȱ theȱ periodȱ 1965–1975.ȱ Theȱ populationȱ ofȱ silverȱ eelȱ wasȱ 82%ȱ malesȱ andȱ18%ȱfemales.ȱAverageȱweightȱwasȱ120ȱgrammes.ȱ

SilverȱeelȱproductionȱinȱtheȱRiverȱBjornsholmȱwasȱestimatedȱinȱ1988ȱtoȱbeȱinȱtheȱ rangeȱ 9–39ȱ kg/haȱ riverȱ (wettedȱ area)ȱ (Bisgaardȱ andȱ Pedersen,ȱ 1990).ȱ Densitiesȱ ofȱ residentȱ yellowȱeel,ȱobservedȱgrowthȱrateȱ(derivedȱfromȱageȱreading)ȱandȱmortalityȱproducedȱ anȱ estimateȱ ofȱ 39ȱ kg/haȱ riverȱ (wettedȱ area).ȱȱThisȱ comparesȱ withȱ anȱ estimateȱ ofȱ 9ȱ kg/haȱriverȱ(wettedȱarea)ȱfromȱmarkȬrecaptureȱonȱsilverȱeelȱ carriedȱoutȱinȱAugustȱandȱ Septemberȱandȱthereforeȱshouldȱbeȱconsideredȱaȱminimumȱestimateȱofȱescapement.ȱ Sexȱratiosȱofȱsilverȱeelȱwereȱ40%ȱmalesȱandȱ60%ȱfemalesȱwithȱanȱaverageȱweightȱofȱ 280ȱgrammes.ȱ

InȱDenmark,ȱitȱisȱproposedȱthatȱ50ȱkg/haȱ(wettedȱarea)ȱrepresentsȱ“pristine”ȱescapeȬ mentȱforȱtheȱfreshȬwaterȱenvironment.ȱThisȱtranslatesȱintoȱtheȱEUȱescapementȱtargetȱ ofȱ20ȱkg/haȱ(wettedȱarea).ȱ

4.3.2.5 Quebec approach (Verreault and Lambert, pers. comm.)

AȱCanadaȬFranceȬQuébecȱresearchȱprojectȱwasȱsetȱupȱtoȱevaluateȱimpactsȱofȱbarriersȱ openingȱinȱtermsȱofȱescapementȱandȱnetȱproductivityȱgainȱinȱtheȱfreshȬwaterȱhabitatsȱ ofȱtheȱSt.ȱLawrenceȱwatershed.ȱThisȱGISȱdecisionȱtoolȱwillȱbeȱbasedȱonȱeelȱhabitatȱsurȬ faceȱandȱeelȱdistributionȱinȱaȱwatershed.ȱMoreȱprecisely,ȱtheȱmodelȱisȱbasedȱonȱtheȱ exponentialȱ decreaseȱ ofȱ potentialȱ yellowȱ eelȱ abundanceȱ withȱ distanceȱ fromȱ marineȱ waters.ȱThenȱtheȱpotentialȱyellowȱeelȱdensityȱforȱeveryȱriverȱstretchȱisȱmodulatedȱbyȱ theȱ cumulativeȱ mortalityȱ andȱ passiblityȱ ofȱ downstreamȱ barriersȱ thenȱ convertedȱ inȱ absoluteȱabundanceȱofȱsilverȱeelȱescapingȱtheȱsystem.ȱTheȱmodelȱfinalȱoutputȱwillȱbeȱ anȱestimateȱofȱpotentialȱproductionȱofȱoocytesȱbyȱusingȱaȱsizeȬfecundityȱrelationship.ȱ

4.4 Future methods for silver eel escapement (yellow eel proxies)

Itȱisȱessentialȱtoȱadoptȱstandardizedȱmethodsȱtoȱestimateȱescapement,ȱpotentialȱbioȬ massȱ(e.g.ȱbiomassȱavailableȱinȱtheȱriverȱsystem)ȱandȱalsoȱeffectiveȱbiomassȱ(thatȱwillȱ escapeȱandȱthatȱhasȱreasonableȱprobabilityȱtoȱreproduce)ȱderivedȱfromȱsilverȱeelȱqualȬ ityȱ andȱ mortalityȱ withinȱ theȱ riverȱ catchment.ȱ Possibleȱ methodologiesȱ areȱ outlinedȱ belowȱ andȱ inȱ theȱ INDICANGȱ methodologicalȱ guideȱ (Adamȱ etȱ al.,ȱ inȱ press)ȱ notȱ yetȱ seenȱbyȱtheȱWGEEL.ȱ

Silverȱ eelsȱ biomassȱ productionȱ isȱ aȱ primaryȱ managementȱ targetȱ toȱ beȱ urgentlyȱ achievedȱ forȱ startingȱ theȱ restorationȱ ofȱ theȱ Europeanȱ eelȱ (Anguilla anguilla)ȱ populaȬ tion.ȱ Anȱ assessmentȱ ofȱ theȱ proportionȱ ofȱ individualsȱ actuallyȱ escapingȱ fromȱ catchȬ mentsȬandȱableȱtoȱreproduceȬcomparedȱtoȱaȱtheoreticalȱpristineȱproductionȱunderȱnoȱ humanȱintervention,ȱisȱofȱcriticalȱimportanceȱforȱpreservingȱthisȱresource,ȱandȱtheȱEUȱ 58 EIFAC/ICES WGEEL Report 2008

obligesȱMemberȱStatesȱtoȱimplementȱmeasures.ȱHowever,ȱthereȱisȱcurrentlyȱveryȱlittleȱ informationȱonȱsilverȱeelȱescapementȱandȱevenȱlessȱinformationȱonȱsilverȱeelȱqualityȱ (e.g.ȱdefinedȱbyȱparasiteȱburdens,ȱmetallicȱandȱorganicȱcontaminationȱofȱtissues,ȱfatȱ content).ȱ Inȱ orderȱ toȱ estimateȱ effectiveȱ breedingȱ biomassȱ inȱ dataȬpoorȱ catchments,ȱ researchȱ isȱ requiredȱ toȱ developȱ andȱ implementȱ methodsȱ andȱ protocolsȱ describingȱ reliableȱproxies.ȱSuchȱresearchȱhasȱrecentlyȱstartedȱduringȱtheȱEUȱprogrammeȱINDIȬ CANGȱthatȱproposesȱtoȱclarifyȱsomeȱofȱtheȱbasicȱconceptsȱneededȱtoȱimplementȱasȬ sessmentȱ toolsȱ forȱ aȱ characterizationȱ ofȱ theȱ productionȱ ofȱ spawningȱ biomassȱ inȱ aȱ catchment.ȱ Theseȱ conceptsȱ relyȱ mostlyȱ onȱ theȱ influenceȱ ofȱ theȱ catchmentȱ contextȱ (conditionsȱforȱ theȱ eelȱgrowth)ȱ onȱ theȱ silverȱ eelȱ populationȱ characteristicsȱ (biomassȱ andȱnumbers,ȱsexȱratio,ȱsizeȱandȱageȱstructure,ȱconditionȱindices)ȱbeforeȱmigration.ȱ Theȱeffectiveȱbreedingȱbiomassȱ(escapementȱofȱhighȱqualityȱfutureȱspawners)ȱisȱthenȱ estimatedȱ byȱ attributingȱ anthropogenicȱ mortalityȱ ratesȱ (fisheries,ȱ hydroelectricȱ turȬ bines,ȱdamsȱandȱreservoirs).ȱRiskȱanalysisȱisȱalsoȱneededȱtoȱdefineȱtheȱproportionȱofȱ eelsȱthatȱareȱhealthyȱenoughȱ(lowȱparasiteȱburdens,ȱhighȱconditionȱandȱfatȱcontentȱasȱ wellȱasȱlowȱchemicalȱcontaminationȱlevels)ȱforȱsuccessfulȱmigrationȱandȱtoȱcontributeȱ toȱtheȱgeneȱpool.ȱAsȱaȱfirstȱstep,ȱthisȱeffectiveȱbreedingȱpotentialȱshouldȱbeȱestimatedȱ atȱ theȱ catchmentȱ areaȱ levelȱ fromȱ theȱ sourcesȱ toȱ theȱ sea.ȱ Then,ȱ regionalȱ approachesȱ needȱtoȱbeȱdevelopedȱandȱimplementedȱtoȱmodelȱrelationsȱbetweenȱcatchmentȱcharȬ acteristicsȱandȱsilverȱeelȱpopulationȱcharacteristicsȱ(Acouȱetȱal.,ȱinȱpress).ȱ

Hereȱweȱreviewȱdifferentȱapproachesȱwhichȱhaveȱbeenȱimplementedȱorȱproposedȱtoȱ estimateȱsilverȱeelȱescapement.ȱTheȱmethodsȱwillȱsoonȱbeȱavailableȱandȱtranslatedȱinȱ fourȱ languagesȱ (French,ȱ English,ȱ Castillano,ȱ Portuguese)ȱ inȱ Chaptersȱ 8ȱ andȱ 9ȱ ofȱ aȱ “GuideȱbookȱforȱEuropeanȱeelȱmonitoring”ȱproducedȱfromȱINDICANGȱprojectȱ(webȬ siteȱreferences).ȱPartsȱofȱtheȱresultsȱareȱalsoȱpresentedȱinȱRobinetȱetȱal.,ȱ2008.ȱInȱaddiȬ tionȱ toȱ beingȱ ableȱ toȱ quantifyȱ theȱ statusȱ ofȱ theȱ stockȱ informationȱisȱ alsoȱ neededȱ onȱ processes,ȱparticularlyȱgrowthȱandȱmortality,ȱasȱsuchȱthereȱisȱaȱrequirementȱtoȱensureȱ standardizationȱofȱtheȱmethod(s)ȱusedȱtoȱestimateȱage.ȱ

4.4.1 At the catchment level

4.4.1.1 Estimating silver eel biomass escapement

Direct estimates intercepting silver eel runs

a.ȱCommercialȱsilverȱeelȱfisheriesȱcan,ȱdependingȱonȱtheirȱlocationȱandȱscale,ȱprovideȱ goodȱ opportunitiesȱ forȱ directȱ estimationȱ ofȱ theȱ numbersȱ andȱ biomassȱ ofȱ silverȱ eelsȱ escapingȱfromȱhydrosystems,ȱbyȱanalysesȱofȱannualȱvariationȱinȱeitherȱyieldȱorȱcpueȱ providedȱthatȱitȱisȱpossibleȱtoȱdetermineȱtheȱefficiencyȱ(proportionȱofȱrunȱcaptured)ȱofȱ theȱeelȱcaptureȱsystemsȱinvolved.ȱExamplesȱofȱsuchȱinvestigations,ȱofȱpopulationȱdyȬ namicsȱandȱseasonalȱpatternsȱofȱseawardȱmigratingȱeels,ȱincludeȱthoseȱundertakenȱonȱ theȱ Riverȱ Loire,ȱ Riverȱ Shannonȱ andȱ Corrib,ȱ Riverȱ Bannȱ (Loughȱ Neaghȱ outlet),ȱ theȱ RiverȱImsa,ȱtheȱBalticȱbasinȱandȱtheȱStȱLawrence.ȱDifficultiesȱcanȱoccurȱwhenȱtheȱfishȬ ingȱseasonȱdoesȱnotȱcoverȱtheȱfullȱmigrationȱperiodȱorȱwhenȱthereȱisȱsignificantȱeelȱ productionȱdownstreamȱofȱtheȱfisheryȱarea.ȱUseȱofȱmark/ȱrecaptureȱmethodsȱforȱestiȬ mationȱofȱfisheryȱcaptureȱefficiencyȱallowsȱforȱestimationȱofȱtheȱnumbersȱandȱbiomassȱ ofȱ migratingȱ eelsȱ atȱ theȱ fishingȱ sites.ȱ Thisȱ canȱ involveȱ useȱ ofȱ aȱ varietyȱ ofȱ tagsȱ andȱ marksȱ(seeȱConcertedȱActionȱforȱTaggingȱofȱFish:ȱwww.hafro.is/catag).ȱExperimentalȱ fisheriesȱcouldȱbeȱestablishedȱinȱdataȱpoorȱareasȱandȱusedȱtoȱimproveȱfisheryȱmoniȬ toringȱmethodologies.ȱ(VollestadȱandȱJonsson,ȱ1988;ȱCaronȱetȱal.,ȱ2000;ȱFeunteunȱetȱal.,ȱ 2000;ȱFeunteunȱetȱal.,ȱinȱpress;ȱAllenȱetȱal.,ȱ2006;ȱWGEELȱBalticȱsea;ȱandȱMcCarthyȱetȱ al.,ȱ2008).ȱ EIFAC/ICES WGEEL Report 2008 59

b.ȱWolfȱtraps,ȱorȱrelatedȱsystems,ȱorȱuseȱofȱwingedȱnetsȱdeployedȱforȱresearchȱpurȬ posesȱcanȱprovideȱpreciseȱestimatesȱofȱmigratingȱeelȱpopulationȱdynamicsȱandȱunderȱ someȱcircumstancesȱallȱsilverȱeelsȱcanȱbeȱcountedȱandȱweighed.ȱHowever,ȱthisȱisȱusuȬ allyȱonlyȱpossibleȱinȱsmallerȱriverȱsystemsȱwhereȱdischargeȱpatternsȱallowȱforȱsilverȱ eelȱtrappingȱthroughoutȱtheȱmigrationȱseason.ȱExamplesȱofȱthisȱtypeȱofȱsilverȱeelȱesȬ capementȱ estimationȱ includeȱ theȱ studiesȱ undertakenȱ onȱ theȱ Norwegianȱ Riverȱ Imsaȱ (VollestadȱandȱJonsson,ȱ1988),ȱtheȱFrenchȱRiversȱFrémurȱ(Feunteunȱetȱal.,ȱ2000)ȱandȱ Oirȱ(Acouȱetȱal.,ȱinȱpress),ȱtheȱBurrishooleȱ(Pooleȱetȱal.,ȱ1990;ȱ1994)ȱandȱtheȱoutletȱofȱ LoughȱEnnelȱinȱtheȱRiverȱShannon,ȱIrelandȱ(McCarthy,ȱunpublishedȱdata).ȱ

c.ȱCountersȱandȱvariousȱacousticȱtechnologiesȱcanȱallowȱforȱtheȱestimationȱofȱsilverȱ eelȱ escapementȱ inȱ locationsȱ whereȱ eelȱ captureȱ isȱ notȱ possible.ȱ Forȱ example,ȱ hyȬ droacousticȱmethods,ȱsuchȱasȱdwereȱuse ȱbyȱMcCarthyȱetȱal.,ȱ2008ȱtoȱinvestigateȱvariaȬ tionsȱ inȱ numbersȱ ofȱ silverȱ eelsȱ migratingȱ downstreamȱ inȱ theȱ headraceȱ canalȱ ofȱ theȱ Ardnacrushaȱ hydropowerȱ plantȱ inȱ theȱ Riverȱ Shannon,ȱ andȱ resistivityȱ countersȱ andȱ DidsonȱacousticȱcamerasȱtrialledȱforȱcountingȱemigratingȱsilverȱeelȱinȱtheȱUKȱ(M.A.ȱ Aprahamian,ȱ pers.ȱ comm.).ȱSuchȱ eelȱ counts,ȱandȱ linkedȱ dataȱ onȱsizeȱfrequenciesȱ ofȱ theȱmigratingȱeels,ȱareȱonlyȱpossibleȱinȱlocationsȱwhereȱotherȱfishȱspeciesȱ(withȱtargetȱ strengthsȱinȱtheȱsameȱrangeȱasȱtheȱsilverȱeels)ȱareȱnotȱalsoȱmigratingȱdownstreamȱatȱ theȱsameȱtimeȱasȱeels.ȱWorkȱisȱinȱprogressȱinȱIreland,ȱUK,ȱPolandȱandȱotherȱEuropeanȱ countriesȱthatȱshouldȱleadȱtoȱimprovedȱsamplingȱprotocolsȱandȱtoȱmoreȱwidespreadȱ useȱofȱthisȱmethodȱforȱestimationȱofȱeelȱescapementȱrates.ȱ

Indirect estimates using yellow eel proxies

Inȱmanyȱwaterȱbasins,ȱlackȱofȱdataȱconcerningȱsilverȱeelȱestimates,ȱrequiresȱtheȱuseȱofȱ alternativeȱapproachesȱtoȱmeetȱtheȱdemandsȱofȱCouncilȱRegulationȱ1100/2007ȱforȱesȬ timatingȱsilverȱeelȱescapement.ȱTheȱuseȱofȱproxyȱindicatorsȱfromȱsedentaryȱeelsȱandȱ habitatȱpopulationȱmodelsȱseemȱtoȱbeȱtheȱmostȱpromisingȱapproachesȱ(Feunteunȱetȱ al.,ȱ2000;ȱAprahamianȱetȱal.,ȱ2007;ȱLobonȬCerviaȱandȱIglesias,ȱ2008;ȱFeunteunȱetȱal.,ȱinȱ press,).ȱTheseȱproceduresȱshouldȱneverthelessȱbeȱstandardizedȱsoȱthatȱmethodologiesȱ usedȱcanȱprovideȱrepresentativeȱestimatesȱofȱsilverȱeelȱproduction,ȱe.g.ȱsamplingȱatȱ theȱbeginningȱofȱtheȱmigratoryȱseasonȱ(lateȱsummerȱinȱsouthernȱlatitudesȱandȱmiddleȱ summerȱinȱnorthernȱlatitudes).ȱ

MarkȬrecaptureȱ orȱ otherȱ moreȱ locallyȱ adequateȱ methodsȱ couldȱ beȱ usedȱ toȱ estimateȱ densityȱofȱyellowȱandȱsilverȱeels.ȱSeveralȱhabitatȱtypesȱrepresentativeȱofȱeachȱcatchȬ mentȱshouldȱbeȱevaluatedȱinȱorderȱtoȱbeȱableȱtoȱextrapolateȱforȱtheȱwholeȱcatchmentȱ andȱincludeȱitȱinȱhabitatȱpopulationȱmodels.ȱ

Eelȱ mortalityȱ ratesȱ needȱ toȱ beȱ determinedȱ throughoutȱ theȱ riverȱbasinȱ includingȱ theȱ estuaryȱasȱwellȱasȱfreshȬwaterȱhabitatȱ(seeȱalsoȱChapterȱ3).ȱ

Inȱsomeȱcountries,ȱlackȱofȱdataȱonȱbothȱyellowȱandȱsilverȱeelsȱrequiresȱaȱdifferentȱapȬ proachȱinȱwhich,ȱhabitatȱdataȱcollectedȱwithinȱtheȱWFDȱshouldȱbeȱusedȱinȱconjuncȬ tionȱwithȱeelȱpopulationȱdataȱfromȱsimilarȱregionalȱareas.ȱHowever,ȱEMPsȱbasedȱonȱ thisȱ provisionalȱ approachȱ shouldȱ alsoȱ includeȱ detailsȱ ofȱ samplingȱ programmesȱ toȱ provideȱaȱbasisȱforȱfutureȱdeterminationȱofȱspawnerȱescapement.ȱ

Estimating effective silver eel biomass escapement

Effectiveȱsilverȱeelȱbiomassȱ{proportionȱofȱtheȱpotentialȱsilverȱeelȱbiomassȱ*ȱmortalityȱ (Fishery,ȱHydropower,ȱNatural)ȱ*ȱquality}ȱestimationȱisȱessentialȱifȱtheȱactualȱcontriȬ butionȱmadeȱbyȱparticularȱrivers,ȱriverȱbasinȱdistrictsȱorȱlargerȱscaleȱEuropeanȱregionsȱ isȱtoȱbeȱevaluatedȱnowȱandȱduringȱpostȱevaluationȱofȱEMPs.ȱThisȱintegrationȱofȱdataȱ onȱpopulationȱdynamicsȱandȱeelȱqualityȱhasȱnotȱbeenȱsubjectȱtoȱtheȱdetailedȱlevelȱofȱ 60 EIFAC/ICES WGEEL Report 2008

discussionȱtoȱwhichȱotherȱelementsȱofȱtheȱEUȱeelȱrecoveryȱplanȱhaveȱbeenȱsubjected.ȱ However,ȱaȱmoreȱstandardizedȱapproachȱtoȱthisȱtopicȱisȱrequiredȱifȱresultsȱofȱongoingȱ studiesȱonȱcontaminants,ȱparasitesȱandȱdiseasesȱofȱsilverȱeelsȱareȱtoȱbeȱintegratedȱatȱaȱ Europeanȱlevel.ȱ

4.4.1.2 Quality

Monitoringȱqualityȱofȱsilverȱeelsȱshouldȱaimȱtoȱestablishȱtheȱproportionȱofȱmigratingȱ eelsȱthatȱhaveȱsufficientȱqualityȱtoȱreachȱtheȱspawningȱgrounds,ȱbreedȱandȱproduceȱ adequateȱnumbersȱofȱviableȱlarvae.ȱInȱanalysesȱofȱsilverȱeelȱpopulationsȱtheȱextentȱofȱ qualityȱ monitoringȱ willȱ beȱ moreȱ limitedȱ forȱ eelsȱ releasedȱ followingȱ captureȱ andȱ measurement.ȱ Forȱ releasedȱ eels,ȱ theȱ lifeȬhistoryȱ stageȱ determination,ȱ andȱ theȱ usualȱ lengthȱandȱweightȱmeasurements,ȱmustȱbeȱrecordedȱforȱrepresentativeȱsubsamples.ȱ

Observationsȱofȱsignificantȱdecreasesȱinȱfatȱlevelsȱinȱyellowȱeelsȱoverȱ15ȱyearsȱinȱBelȬ giumȱandȱtheȱNetherlandsȱraisesȱseriousȱconcernsȱaboutȱtheirȱreproductiveȱpotentialȱ (Belpaireȱetȱal.,ȱinȱpress),ȱandȱwarrantȱtheȱinclusionȱofȱeelȱqualityȱestimatesȱwithinȱtheȱ quantitativeȱtargetsȱforȱescapement.ȱ

Considerablyȱ moreȱ parametersȱ shouldȱ beȱ requestedȱ onȱ aȱ subsampleȱ ofȱ silverȱ eels.ȱ Theseȱcanȱinvolveȱdataȱonȱcontaminationȱlevelsȱofȱmetalsȱandȱorganicȱ(forȱmethodsȱ referȱtoȱqualityȱsection),ȱfatȱcontentȱandȱconditionȱfactor,ȱotolithȱageȱreading,ȱA.ȱcrasȬ susȱandȱEVEXȱandȱotherȱviralȱdiseases.ȱInformationȱonȱlifeȬhistoryȱtraitsȱandȱpopulaȬ tionȱ characteristicsȱ shouldȱ alsoȱ beȱ providedȱ forȱ sampledȱ silverȱ eelȱ populationsȱ andȱ thisȱcanȱinvolveȱsexȱratioȱestimatedȱfromȱsizeȱfrequenciesȱ(withȱcalibrationȱusingȱsacȬ rificedȱeels).ȱThereȱisȱaȱneedȱtoȱestablishȱaȱsizeȬageȱrelationshipȱandȱalsoȱanȱindexȱreȬ latingȱeelȱqualityȱtoȱbreedingȱsuccess.ȱ

4.4.2 At the regional level

Itȱ isȱ anticipatedȱ thatȱ theȱ EMPsȱ areȱ developedȱ underȱ theȱ Riverȱ Basinȱ Districtȱ (RBD)ȱ level.ȱTheȱsuccessȱofȱEMPsȱdependsȱonȱaȱgoodȱcoordinationȱandȱconsistencyȱbetweenȱ measuresȱtakenȱunderȱRegulationȱ1100/2007ȱandȱEuropeanȱDirectivesȱhavingȱimpactȱ inȱtheȱriverȱbasin.ȱTherefore,ȱtoȱmakeȱEMPsȱmoreȱeffective,ȱitȱisȱdesirableȱthatȱcatchȬ mentȱbasedȱmodelsȱareȱalsoȱdevelopedȱatȱaȱregionalȱlevelȱ(involvingȱeachȱRBD),ȱaimȬ ingȱatȱpredictingȱsilverȱeelȱescapement.ȱ

4.5 Methods for evaluation of management measures

AȱcloseȱlinkȱbetweenȱbothȱmanagementȱandȱeelȱsubȬtargetȱwillȱbeȱestablishedȱinȱtheȱ followingȱsectionsȱwithȱregardȱtoȱselectedȱmanagementȱmeasuresȱ(Tableȱ4.3).ȱTheȱreȬ lationshipȱbetweenȱmanagementȱandȱeelȱsubȬtargetsȱwillȱallowȱforȱaȱdirectȱfeedbackȱ toȱmanagementȱifȱmeasuresȱareȱnotȱachievedȱand/orȱtheȱlocallyȱtargetedȱeelȱpopulaȬ tionȱ responded,ȱorȱfailedȱtoȱrespond,ȱinȱtheȱpredictedȱmannerȱ(e.g.ȱanȱincreaseȱinȱyelȬ lowȱeelȱdensity).ȱTheȱmethodsȱtoȱevaluateȱmanagementȱmeasuresȱandȱtheȱresponseȱofȱ theȱtargetedȱeelȱlifeȱstagesȱshouldȱbeȱappliedȱlocallyȱandȱthereforeȱgiveȱaȱfeedbackȱtoȱ theȱ authoritiesȱ inȱ theȱ eelȱ managementȱ units.ȱ Byȱ thisȱ feedbackȱ loopȱ localȱ managersȱ willȱbeȱableȱtoȱadaptȱtheirȱmanagementȱapproachȱwithoutȱregardȱtoȱtheȱdelayedȱreȬ sponseȱofȱtheȱwholeȱeelȱstockȱ(e.g.ȱchangesȱinȱrecruitment).ȱHoweverȱtheȱproposedȱ managementȬȱandȱeelȬtargetsȱareȱnotȱintendedȱtoȱbeȱanȱexhaustiveȱlistȱofȱallȱpossibleȱ managementȱmeasures.ȱItȱshouldȱbeȱtakenȱasȱaȱfirstȱstepȱinȱfillingȱtheȱgapȱbetweenȱ localȱmanagementȱandȱtheȱlongȬtermȱrecovery.ȱ

ItȱisȱalsoȱrecognizedȱthatȱmethodsȱforȱevaluatingȱtheȱoutcomeȱofȱmanagementȱmeasȬ uresȱonȱtheȱpopulationȱlevelȱ(eelȱsubȬtargets)ȱareȱnotȱalwaysȱfullyȱavailableȱandȱneedȱ furtherȱresearch.ȱTheȱsameȱholdsȱtrueȱforȱtheȱdefinitionȱofȱdifferentȱquantitativeȱlevelsȱ EIFAC/ICES WGEEL Report 2008 61

ofȱeelȱsubȬtarget.ȱTheȱlevelsȱhaveȱtoȱbeȱrelatedȱtoȱtheȱactualȱstatusȱofȱtheȱeelȱpopulaȬ tionȱwithȱrespectȱtoȱtheȱglobalȱobjectiveȱofȱfullȱrecoveryȱ(e.g.ȱ40%ȱofȱspawnerȱescapeȬ mentȱ withoutȱ anthropogenicȱ impact).ȱ Theȱ levelȱ ofȱ theȱ managementȱ actionȱ finallyȱ dependsȱonȱhowȱfarȱaȱcertainȱmanagementȱunitȱisȱawayȱfromȱtheȱobjectiveȱ(referȱtoȱ Figureȱ4.2).ȱ

4.5.1 Management measures and methods for evaluation

4.5.1.1 Commercial fishery

EMP´sȱwillȱinvolveȱfisheriesȱregulationȱmeasuresȱthroughoutȱtheȱdistributionalȱareaȱ andȱacrossȱallȱcontinentalȱlifeȱstages.ȱAȱrangeȱofȱdifferentȱmeasuresȱcanȱbeȱidentifiedȱ andȱappliedȱtoȱtheȱdifferentȱlifeȱstages.ȱEvaluatingȱtheȱeffectsȱmayȱrequireȱdifferentȱ approachesȱandȱtimeȱframes.ȱ

ManagementȱsubȬtargetȱ1.1:ȱEffortȱrestrictions.ȱForȱallȱlifeȱstages,ȱtheȱregulationȱandȱ limitationȱofȱtheȱaccessȱtoȱtheȱfisheryȱisȱaȱcommonȱmeasureȱthatȱcanȱbeȱapplied.ȱ

4.5.1.2 Glass eel fishery

Quotasȱandȱpartialȱorȱtotalȱclosureȱofȱfishingȱactivitiesȱareȱtheȱmostȱplausibleȱmethodsȱ inȱmanagingȱaȱglassȱeelȱfishery.ȱ

ManagementȱsubȬtargetȱ1.1;ȱAchievementȱofȱQuota.ȱAȱdefinedȱproportionȱofȱtheȱreȬ cruitsȱtoȱaȱmanagementȱunitȱisȱexcludedȱfromȱtheȱlocalȱfishery.ȱEvaluationȱshouldȱbeȱ basedȱonȱknowledgeȱofȱvariationȱinȱabundance/catchabilityȱoverȱtimeȱinȱtheȱseasonȱ andȱmonitoringȱofȱlandedȱquantities.ȱ

ManagementȱsubȬtargetȱ1.2;ȱTotalȱorȱpartȱtimeȱclosure.ȱAȱgivenȱdegreeȱofȱclosureȱreȬ sultsȱinȱaȱpredeterminedȱreductionȱofȱfisheryȱmortality.ȱThisȱtargetȱmustȱbeȱbasedȱonȱ theȱknowledgeȱofȱglassȱeelȱabundanceȱoverȱtimeȱinȱtheȱfishingȱareaȱandȱmayȱbeȱmoniȬ toredȱbyȱfieldȱcontrolȱofȱfishingȱactivities.ȱ

4.5.1.3 Yellow eel fishery

Quota,ȱtotalȱorȱpartȱtimeȱclosure,ȱsizeȱlimitsȱandȱclosedȱareasȱareȱmeasuresȱapplicableȱ inȱregulatingȱmostȱfisheries,ȱincludingȱfishingȱforȱyellowȱeel.ȱTechnicalȱregulationsȱofȱ theȱ fisheryȱ forȱ yellowȱ eelȱ mayȱ haveȱ differentȱ effectsȱ dependingȱ onȱ whereȱ theyȱ areȱ imposedȱinȱaȱcatchment.ȱIfȱtheyȱareȱimposedȱdownstream,ȱinȱanȱestuaryȱorȱnearȱtheȱ areaȱofȱprimaryȱrecruitment,ȱtheyȱmayȱhaveȱanȱeffectȱonȱdensityȬdependentȱmigrationȱ andȱthusȱproliferateȱupstreamȱinȱtheȱriverȱbasin.ȱOnȱtheȱotherȱhand,ȱifȱtheyȱareȱintroȬ ducedȱupstreamȱ inȱaȱsystem,ȱ whereȱ theȱ subpopulationȱ hasȱaȱ higherȱ degreeȱ ofȱ resiȬ dence,ȱ theȱ expectedȱteffec ȱ willȱ primarilyȱ concernȱ demographyȱ andȱ mortality.ȱ Theȱ statementsȱaboveȱsuggestȱdifferentȱdesignsȱofȱmonitoringȱandȱshortȬtermȱevaluation.ȱ

ManagementȱsubȬtargetȱ1.3;ȱQuota.ȱAȱdefinedȱproportionȱofȱtheȱyellowȱeelȱstockȱinȱaȱ managementȱunitȱisȱexcludedȱfromȱtheȱlocalȱfishery.ȱEvaluationȱshouldȱbeȱbasedȱonȱ knowledgeȱofȱtheȱlocalȱproductionȱinȱtheȱareaȱandȱeffectsȱofȱaȱregulationȱcanȱbeȱmoniȬ toredȱinȱlandedȱquantities.ȱ

ManagementȱsubȬtargetȱ1.4;ȱTotalȱorȱpartȱtimeȱclosure.ȱAȱgivenȱdegreeȱofȱclosureȱreȬ sultsȱ inȱ aȱ predeterminedȱ reductionȱ ofȱ fishingȱ mortality.ȱ Evaluationȱ ofȱ thisȱ targetȱ needsȱstockȱassessmentȱmodels,ȱwhichȱareȱoftenȱdependentȱofȱanȱexistingȱfishery.ȱAȱ totalȱclosureȱthusȱisȱeasierȱtoȱevaluate.ȱ

ManagementȱsubȬtargetȱ1.5;ȱSizeȱlimits.ȱImposingȱsizeȱlimitsȱisȱtargetingȱreductionȱofȱ fishingȱmortality.ȱEvaluationȱofȱthisȱtargetȱneedsȱstockȱassessmentȱmodels,ȱwhichȱareȱ oftenȱdependentȱofȱanȱexistingȱfishery.ȱ 62 EIFAC/ICES WGEEL Report 2008

ManagementȱsubȬtargetȱ1.6;ȱProtectedȱareas.ȱAȱmanagementȱtargetȱforȱprotectedȱarȬ easȱcouldȱbeȱevaluatedȱasȱtheȱproportionȱofȱtheȱavailableȱhabitatȱorȱproductiveȱpotenȬ tialȱ thatȱ isȱ takenȱ outȱ ofȱ fishery.ȱ Inȱ thisȱ case,ȱ asȱ inȱ mostȱ otherȱ cases,ȱ theȱ properȱ managementȱ targetȱ isȱ aȱ certainȱ reductionȱ ofȱ fishingȱ mortalityȱ inȱ theȱ managementȱ unit.ȱ

4.5.1.4 Silver eel fishery

Theȱmostȱplausibleȱtoolsȱtoȱmanageȱaȱsilverȱeelȱfisheryȱareȱtotalȱorȱpartȱtimeȱclosureȱ andȱsizeȱlimits.ȱProtectedȱareasȱmayȱalsoȱbeȱconsidered.ȱ

ManagementȱsubȬtargetȱ1.7;ȱTotalȱorȱpartialȱclosureȱshouldȱfulfilȱtheȱtargetȱtoȱreduceȱ mortalityȱbyȱaȱpredeterminedȱvalue.ȱEvaluationȱmustȱbeȱbasedȱonȱaȱgoodȱestimateȱofȱ theȱnumberȱofȱeelȱthatȱwouldȱbeȱcaughtȱifȱfishingȱwasȱopenȱandȱtheȱtotalȱcatchȱinȱtheȱ openȱseason.ȱThisȱtargetȱmayȱbeȱmonitoredȱusingȱlandingsȱandȱhistoricalȱinformationȱ onȱdistributionȱofȱcatchesȱoverȱtheȱentireȱseason.ȱ

ManagementȱsubȬtargetȱ1.8;ȱLegalȱsizeȱlimitsȱmayȱincludeȱexclusionȱofȱtheȱsmallestȱasȱ wellȱasȱtheȱbiggestȱindividualsȱfromȱtheȱlandedȱpartȱofȱtheȱcatch.ȱThisȱtargetȱshouldȱ beȱsetȱbearingȱinȱmindȱtheȱtotalȱeffectȱonȱeffectiveȱSSB.ȱEggȱproductionȱmayȱnotȱbe/isȱ notȱ linearlyȱ relatedȱ toȱ bodyȱ weightȱ (Verreault,ȱ 2002).ȱ Complianceȱ withȱ theȱ targetȱ mustȱrelyȱonȱsamplingȱofȱtheȱsizeȱdistributionȱinȱtheȱtotalȱcatch,ȱdiscardsȱincluded.ȱ

ManagementȱsubȬtargetȱ1.9.;ȱProtectedȱareas.ȱTheȱeffectȱofȱprotectedȱareasȱshouldȱtarȬ getȱaȱcertainȱproportionȱofȱtheȱsilverȱeelȱproductionȱinȱaȱmanagementȱunitȱandȱshouldȱ beȱ restricted/closedȱ forȱ allȱ typesȱ ofȱ fishingȱ activity,ȱ i.e.ȱ F=0ȱ forȱ x%ȱ ofȱ theȱ potentialȱ production.ȱ

4.5.1.5 Recreational fishing

InȱpartsȱofȱEuropeȱrecreationalȱfisheryȱgeneratesȱaȱmajorȱpartȱofȱtheȱfishingȱmortality.ȱ Thisȱkindȱofȱfishingȱisȱtoȱaȱgreatȱextentȱfocusingȱonȱtheȱyellowȱeelȱstageȱbutȱcapturingȱ silverȱeelȱmayȱalsoȱoccurȱ(Staas,ȱ2006).ȱTheȱmeasuresȱavailableȱforȱmanagingȱthisȱsecȬ torȱ ofȱ fisheryȱ areȱ primarilyȱ theȱ sameȱ asȱ thoseȱ forȱ theȱ commercialȱ fishery.ȱ Thusȱ theȱ biologicalȱtargetsȱareȱsimilarȱtoȱthoseȱpresentedȱaboveȱunderȱyellowȱeelȱfishery.ȱAllȱ managementȱactionsȱdescribedȱinȱtheȱsameȱsectionȱcouldȱbeȱappliedȱtoȱrecreationalȱ fishery.ȱTheȱpresenceȱofȱpoachingȱthough,ȱmayȱintroduceȱtheȱneedȱforȱofficialȱcontrol.ȱ

Managementȱtargetȱ1.10.;ȱControlȱofȱeffort.ȱThisȱtargetȱshouldȱbeȱtheȱcontrolȱofȱeffortȱ takenȱinȱaȱmanagementȱunitȱorȱinȱpredefinedȱpartsȱofȱaȱmanagementȱunit.ȱ

4.5.1.6 Actions to make rivers passable and enhance habitat quality

Upstream migration

ManagementȱsubȬtargetȱ2.1;ȱnumberȱofȱdamsȱwhereȱeelȱladdersȱwillȱbeȱinstalled,ȱesȬ peciallyȱinȱandȱnearȱtheȱzoneȱofȱactiveȱcolonization:ȱ

ManagementȱsubȬtargetȱ2.2;ȱsurfaceȱareaȱofȱriverȱchannelsȱandȱlakesȱinȱaȱcatchmentȱorȱ aȱpercentageȱofȱlostȱhabitatsȱthatȱcouldȱbecomeȱrecolonizedȱbyȱeels.ȱ

EvaluationȱofȱmanagementȱsubȬtargetȱ2.1ȱandȱ2.2ȱcouldȱbeȱachievedȱannuallyȱbyȱlistȬ ingȱofȱtheȱrecentlyȱequippedȱdamsȱcombinedȱwithȱGISȱtechniquesȱofȱupstreamȱsurȬ faceȱmeasurement.ȱ

TheȱconversionȱofȱtheȱmanagementȱtargetsȱintoȱanȱeelȱsubȬtargetȱassumeȱthatȱallȱhabiȬ tatsȱwithinȱaȱriverȱsystemȱareȱequallyȱproductiveȱperȱunitȱsurfaceȱareaȱandȱeelsȱwereȱ totallyȱexcludedȱupstreamȱofȱmanȬmadeȱobstaclesȱ(Verreaultȱetȱal.,ȱ2004;ȱICESȱ2007).ȱ EIFAC/ICES WGEEL Report 2008 63

ManagementȱsubȬtargetȱ2.3;ȱnumberȱofȱfishȱpassingȱoverȱtheȱobstacles.ȱToȱdetermineȱ theseȱnumbersȱanȱeelȱladderȱshouldȱbeȱequippedȱwithȱaȱfishȱcountingȱdeviceȱ(trap,ȱ videoȱcameraȱetc.).ȱHowever,ȱpassageȱofȱfishȱmayȱfluctuateȱaȱlotȱwithȱseveralȱpeaksȱ duringȱ theȱ migrationȱ period.ȱ Forȱ example,ȱ inȱ theȱ Riverȱ Couesnon,ȱ 75%ȱ ofȱ theȱ fishȱ trappedȱoccurredȱwithinȱfourȱweeksȱwhereasȱ17ȱweeksȱcontributedȱtoȱlessȱthanȱ10%ȱ ofȱtheȱtotalȱcatchȱ(Legault,ȱ1994).ȱTheȱtargetȱinȱabsoluteȱnumbersȱcouldȱbeȱdifficultȱtoȱ achieveȱinȱtheȱshortȱtermȱespeciallyȱwhenȱaȱdecreasingȱrecruitmentȱtrendȱisȱobserved.ȱ Itȱisȱprobablyȱbetterȱtoȱdefineȱaȱrelativeȱtargetȱi.e.ȱpercentageȱofȱfishȱthatȱsucceedȱtoȱ migrateȱupstream.ȱBriandȱetȱal.,ȱ2005aȱundertookȱaȱsurveyȱofȱarrivalȱnearȱtheȱobstacleȱ byȱusingȱaȱmarkȱandȱrecaptureȱtechniqueȱbutȱthisȱkindȱofȱapplicationȱisȱdifficultȱtoȱ executeȱandȱrepeatȱforȱaȱlongȱperiod.ȱ

Downstream migration

Currentȱpracticeȱofȱstockingȱandȱtheȱ(recent)ȱconstructionȱofȱfishȱpassesȱhaveȱledȱtoȱ theȱ establishmentȱ orȱ maintenanceȱ ofȱ yellowȱ eelȱ populationȱ inȱ habitatsȱ situatedȱ upȬ streamȱ ofȱ hydropowerȱ plants.ȱ Inȱ manyȱ casesȱ theseȱ areasȱ willȱ beȱ includedȱ intoȱ theȱ naturalȱeelȱhabitat.ȱButȱwhenȱreachingȱtheȱsilverȱeelȱstageȱaȱfairlyȱlargeȱproportionȱofȱ theseȱeelȱareȱlostȱasȱaȱconsequenceȱofȱturbinesȱpassagesȱandȱorȱimpingement.ȱPossibleȱ mitigationȱmeasuresȱconsistsȱofȱinstallingȱbypassȱsystems,ȱswitchingȱoffȱhydropowerȱ turbinesȱtemporarilyȱandȱcapturingȱdownstreamȱmigratingȱsilverȱeelsȱ(andȱincidenȬ tallyȱyellowȱeels)ȱbeforeȱenteringȱhydropowerȱturbines.ȱ

ManagementȱsubȬtargetȱ2.4;ȱnumberȱofȱobstaclesȱwhereȱappropriateȱbypassȱsystemsȱ willȱbeȱinstalled,ȱorȱwhereȱhydroelectricȱpowerȱturbinesȱshouldȱbeȱswitchedȱoffȱtemȬ porarily,ȱorȱwhereȱtrapȬandȬtransportȱmeasuresȱwillȱbeȱcarriedȱout.ȱ

EvaluationȱofȱthisȱmanagementȱtargetȱcouldȱbeȱachievedȱannuallyȱbyȱlistingȱtheȱreȬ centlyȱequippedȱdams.ȱ

4.5.1.7 Reduction of environmental contamination

ManagementȱsubȬtargetȱ2.5;ȱreductionȱofȱpollutantȱdischargeȱuntilȱtotalȱprohibitionȱofȱ useȱforȱtheȱmostȱdangerousȱcontaminants.ȱ

Theȱdirectȱevaluationȱofȱsuchȱtargetȱisȱnotȱsimpleȱbecauseȱitȱisȱdifficultȱtoȱestimateȱtheȱ quantityȱofȱpollutantsȱbeingȱinputȱtoȱtheȱriver,ȱespeciallyȱwhenȱsourcesȱofȱpollutantȱ areȱdiffuse.ȱ

4.5.1.8 Increase of habitat quality

ManagementȱsubȬtargetȱ2.6;ȱWettedȱsurfaceȱareaȱofȱriverȱwhereȱeelȱhabitatȱqualityȱisȱ improved.ȱ

Asȱwithȱcontaminantsȱtheȱdirectȱevaluationȱofȱsuchȱaȱtargetȱisȱnotȱsimpleȱbecauseȱitȱisȱ difficultȱtoȱestimateȱtheȱhabitatȱqualityȱandȱtheȱrelationshipȱwithȱtheȱquantityȱofȱeel.ȱ

4.5.1.9 Stocking of glass eel or pre-grown (farmed) yellow eels

IfȱstockingȱisȱtoȱbeȱusedȱasȱaȱmanagementȱmeasureȱaccordingȱtoȱtheȱEUȬRegulation,ȱitȱ hasȱtoȱbeȱassumedȱthatȱstockingȱisȱperformedȱatȱtheȱactualȱstateȬofȬtheȬartȱ(decisionȱ treeȱandȱstockingȱprotocolsȱareȱavailable;ȱseeȱChapterȱ5)ȱwithȱrespectȱtoȱcarryingȱcaȬ pacityȱandȱsufficientȱqualityȱofȱtheȱchosenȱhabitatsȱ(seeȱrelevantȱdataȱcollectedȱunderȱ theȱWFD).ȱTheȱhealthȱstatusȱofȱmaterialȱusedȱforȱstockingȱwithȱspecialȱregardȱtoȱparaȬ sites,ȱ virusesȱ andȱ otherȱ pathogensȱ hasȱ toȱ beȱ checked.ȱ Additionallyȱ silverȱ eelsȱ proȬ ducedȱfromȱsuchȱstockingsȱshouldȱbeȱableȱtoȱescapeȱfromȱtheȱhabitatsȱwithoutȱmajorȱ lossesȱasȱaȱconsequenceȱofȱpumpingȱstationsȱorȱhydropowerȱturbines.ȱ 64 EIFAC/ICES WGEEL Report 2008

ManagementȱsubȬtargetȱ3.1ȱDefinedȱproportionȱofȱhabitatȱwithȱlowȱrecruitmentȱinȱtheȱ managementȱunitȱforȱsupplementationȱofȱeelsȱandȱnumberȱofȱeelsȱstockedȱperȱsurfaceȱ unitȱ(ha)ȱaccordingȱtoȱavailableȱeelȱsurplusȱforȱstocking.ȱ

Managementȱ subȬtargetȱ 3.2ȱ Definedȱ proportionȱ ofȱ naturalȱ eelȱ habitatsȱ withoutȱ reȬ cruitmentȱandȱnumberȱofȱeelsȱstockedȱperȱsurfaceȱunitȱ(ha)ȱaccordingȱtoȱavailableȱeelȱ surplusȱforȱstocking.ȱ

Stockingȱ activitiesȱ willȱ inȱ futureȱ relyȱ onȱ theȱ assumptionȱ thatȱ aȱ surplusȱ ofȱ glassȱ eelȱ fromȱatȱleastȱsomeȱEuropeanȱestuariesȱisȱstillȱavailable.ȱInȱviewȱofȱhighȱpricesȱforȱglassȱ eelȱtheȱlocallyȱavailableȱbudgetȱmayȱlimitȱstockingsȱmoreȱthanȱbiologicalȱorȱlogisticalȱ aspects.ȱ

4.5.1.10 Measures related to aquaculture for stocking

AȱgreatȱproportionȱofȱglassȱeelȱcapturedȱinȱEuropeȱisȱcurrentlyȱusedȱforȱeelȱproducȬ tionȱinȱaquaculture.ȱThisȱproportionȱisȱassumedȱtoȱdiminishȱinȱtheȱnextȱyearsȱasȱacȬ cordingȱtoȱtheȱEUȬRegulationȱupȱtoȱ60%ȱofȱallȱeelȱbelowȱ12ȱcmȱshouldȱbeȱreservedȱforȱ stocking.ȱOnȱtheȱotherȱhandȱstocking,ȱasȱaȱconservationȱmeasure,ȱcanȱincludeȱeelsȱupȱ toȱ 20ȱ cmȱ inȱ length.ȱ Thisȱ isȱ inȱ accordanceȱ withȱ currentȱ stockingȱ practiceȱ usingȱ preȬ grownȱeelsȱfromȱaquacultureȱforȱreleaseȱinȱnaturalȱeelȱhabitats.ȱAsȱpricesȱofȱglassȱeelȱ tendedȱ toȱ beȱ highȱ inȱ recentȱ yearsȱ andȱ glassȱlee ȱ areȱ assumedȱ toȱ faceȱ aȱ highȱ naturalȱ mortalityȱinȱtheȱfirstȱyearsȱthisȱpracticeȱwillȱprobablyȱcontinueȱinȱcomingȱyears.ȱAsȱaȱ consequenceȱofȱrearingȱconditionsȱthereȱisȱaȱconcernȱaboutȱtheȱqualityȱofȱsuchȱeelȱreȬ leasedȱafterȱaȱtimeȱinȱconventionalȱeelȱaquacultureȱwithȱregardȱtoȱhealth ȱstatusȱandȱ geneticȱdiversityȱ(seeȱChapterȱ5.4.2.3).ȱ

ManagementȱsubȬtargetȱ4.1ȱEnsureȱtheȱproductionȱofȱsufficientȱnumbersȱofȱeelsȱ(forȱ stocking)ȱ withȱ aȱ goodȱ healthȱ statusȱ withȱ respectȱ toȱ parasitesȱ (Ang.ȱ crassus),ȱ virusesȱ (HVA,ȱEve,ȱEVEX)ȱandȱotherȱpathogens.ȱ

Managementȱ subȬtargetȱ 4.2ȱ Ensureȱ theȱ productionȱ ofȱ eelsȱ fromȱ aquacultureȱ withȱ aȱ minimumȱ geneticȱ selectionȱ andȱ avoidȱ stockingȱ ofȱ slowȱ growingȱ individualsȱ sortedȱ outȱfromȱaquaculture.ȱ

4.5.2 Eel sub-target

4.5.2.1 Glass eel sub-target

EelȱsubȬtargetȱ1.1;ȱDensityȱtargetȱforȱwildȱ(andȱstocked)ȱ0+ȱinȱpredefinedȱsectionsȱofȱaȱ catchment.ȱ

Thisȱ canȱ beȱ monitoredȱ inȱ laddersȱ and/orȱ byȱ electroȬfishingȱ andȱ toȱ beȱ evaluatedȱ againstȱhistoricalȱdata.ȱAȱshortȬtermȱresponseȱisȱexpectedȱ(fewȱmonths).ȱ

Timeȱframeȱforȱrevisionȱmanagementȱaction:ȱ1ȱyear.ȱ

Indicators;ȱn/ha,ȱabsence/presence,ȱfrontȱofȱcolonization.ȱ

4.5.2.2 Yellow eel sub-target

Eelȱ subȬtarget:ȱ Profileȱ ofȱ eelȱ occurrenceȱ accordingȱ toȱ longitudinalȱ positionȱ inȱ theȱ catchment.ȱ Moreȱ precisely,ȱ thisȱ targetȱ canȱ beȱ expressedȱ inȱ distanceȱ fromȱ theȱ seaȱ whereȱtheȱprobabilityȱofȱeelȱpresenceȱisȱ50%.ȱ

NoȱinformationȱonȱtimeȬscaleȱofȱresponse,ȱprobablyȱfewȱyearsȱdependingȱonȱlatitude.ȱ EIFAC/ICES WGEEL Report 2008 65

Example of application

Thisȱ methodologyȱ isȱ basedȱ onȱ anȱ analysisȱ electroȬfishingȱ dataȱ withȱ logisticȱ regresȬ sions.ȱLasneȱandȱLaffaille,ȱ2007ȱestimatedȱthatȱstudyȱofȱtemporalȱtrendsȱofȱ“eels’ȱloȬ gisticȱ profilesȱ alongȱ theȱ longitudinalȱ gradient”ȱ allowȱ theȱ assessmentȱ ofȱ theȱ improvementȱofȱcolonizationȱafterȱmitigationȱofȱlocalȱimpacts.ȱ

EelȱsubȬtarget:ȱDensityȱofȱyellowȱeelȱinȱtheȱupstreamȱreaches.ȱ

AȱshortȬtermȱtargetȱcouldȱbeȱsetȱasȱaȱspecificȱincreaseȱinȱdensityȱonȱaȱcertainȱlevelȱinȱaȱ riverȱsystemȱafterȱaȱcertainȱperiodȱofȱtime.ȱComplianceȱcanȱbeȱmonitoredȱbyȱmarkȬ recapture,ȱcountingȱinȱladders,ȱbyȱelectrofishing,ȱwithȱfykenetsȱorȱotherȱkindsȱofȱfishȬ eryȬindependentȱ methodsȱ (ICESȱ 2007)ȱ andȱ canȱ beȱ evaluatedȱ referringȱ toȱ historicalȱ dataȱorȱexpectedȱdensitiesȱfromȱmodels.ȱ

NoȱinformationȱonȱtimeȬscaleȱofȱresponse,ȱprobablyȱfewȱyearsȱdependingȱonȱlatitude.ȱ

Indicators

Numbersȱpassing,ȱn/ha,ȱcpue.ȱ

Example of application

AnȱillustrativeȱexampleȱisȱgivenȱbyȱtheȱreopeningȱofȱtheȱVilaineȱwatershedȱ(Briandȱetȱ al.,ȱ2005b).ȱTheȱconstructionȱofȱtheȱeelȱladderȱresultedȱinȱhighȱdensitiesȱ(>1ȱeels/mȬ2)ȱinȱ theȱ downstreamȱ andȱ middleȱ streamȱ areasȱ afterȱ twoȱ orȱ threeȱ yearsȱ after.ȱ Theseȱ changesȱremainȱclearȱandȱtheȱexaminationȱofȱfiveȱyearsȱofȱdataȱhasȱchangedȱlittleȱofȱ theȱconclusionsȱexpressedȱafterȱonlyȱtwoȱyears.ȱNumberȱofȱglassȱeelsȱclimbingȱtheȱfishȱ ladderȱ ledȱ toȱ theȱ colonizationȱ ofȱ theȱ entireȱ basinȱ andȱ aȱ possibleȱ saturationȱ inȱ theȱ downstreamȱandȱmiddleȱstreamȱareas.ȱButȱdecreaseȱofȱglassȱeelȱarrivalȱandȱdensityȬ dependantȱmortalityȱcouldȱcomplicateȱtheȱinterpretationȱofȱtheȱresults,ȱbyȱinducingȱaȱ decreaseȱinȱdensityȱinȱsomeȱpartsȱofȱtheȱcatchmentsȱ(Briandȱetȱal.,ȱ2005b).ȱAȱsimilarȱ approachȱwasȱperformedȱonȱtheȱFremurȱRiverȱandȱstressedȱagainȱtheȱimportanceȱof maintainingȱlongitudinalȱconnectivityȱinȱrivers.ȱ

EelȱsubȬtarget;ȱDegreeȱofȱhabitatȱsaturationȱofȱyellowȱeel.ȱ

Responseȱinȱdistribution/habitatȱsaturationȱlevelȱinȱtheȱentireȱcatchmentȱcanȱvaryȱinȱ timeȱframesȱaccordingȱtoȱlatitude,ȱaltitude,ȱclimate,ȱetc.ȱAȱreasonableȱestimateȱisȱthatȱ aȱsubȬtargetȱlikeȱthisȱcouldȱbeȱsetȱtoȱ3–5ȱyearsȱinȱtheȱcentralȱareaȱofȱdistribution.ȱTheȱ targetȱfulfilmentȱcanȱbeȱevaluatedȱagainstȱhistoricalȱdataȱorȱdensitiesȱfromȱmodels.ȱ

Indicators

Ratioȱbetweenȱsaturatedȱandȱunsaturatedȱsurface,ȱrationȱbetweenȱactualȱdensityȱandȱ carryingȱcapacity.ȱ

EelȱsubȬtarget:ȱSexȱdistribution.ȱ

AnȱincreaseȱinȱdensityȱinducedȱbyȱaȱreducedȱfishingȱmortalityȱmayȱresultȱinȱaȱdenȬ sityȬdependentȱchangeȱinȱsexȱratios.ȱEvaluationȱofȱtheȱappropriateȱtargetȱlevelȱwillȱbeȱ difficult,ȱbutȱmayȱbeȱbasedȱonȱhistoricalȱdata.ȱ

Example of application

TheȱBalticȱeelȱstockȱdeclinedȱsharplyȱinȱtheȱ1960sȱandȱtheȱ1970sȱfollowingȱaȱprecedingȱ declineȱ inȱ recruitmentȱ ofȱ youngȱ yellowȱ eelȱ intoȱ theȱ Balticȱ Sea.ȱ Theȱ hypothesisȱ wasȱ raisedȱthatȱtheȱreducedȱrecruitmentȱwasȱdueȱdensityȬdependentȱprocessesȱinȱtheȱarȬ easȱofȱprimaryȱrecruitment,ȱi.e.ȱtheȱKattegattȱandȱtheȱDanishȱstraitsȱ(Svärdson,ȱ1976).ȱ 66 EIFAC/ICES WGEEL Report 2008

FollowingȱthisȱmaleȱeelȱalmostȱcompletelyȱdisappearedȱinȱSWȱSweden.ȱAnȱeffectȱofȱ densityȱonȱsexȱratioȱwasȱalsoȱobservedȱinȱLoughȱNeaghȱinȱNorthernȱIrelandȱ(Rosellȱetȱ al.,ȱ2005).ȱ

TheȱtimeȱframeȱforȱaȱresponseȱinȱdensityȬdependentȱsexȱdifferentiationȱisȱuncertain,ȱ asȱthereȱisȱaȱperiodȱofȱtimeȱbetweenȱrecruitmentȱandȱsexualȱdifferentiation.ȱ

Indicator

Proportionȱofȱsexesȱperȱsizeȱgroup.ȱ

EelȱsubȬtarget:ȱShortȱtermȱresponseȱinȱmortalityȱrate.ȱ

Localȱ estimateȱ ofȱ globalȱ mortalityȱ(fishingȱ mortality,ȱ otherȱ sourceȱ ofȱ anthropogenicȱ mortality)ȱrateȱcanȱinformȱonȱpressureȱonȱtheȱstock.ȱ

Example of application

TheȱLVPAȱassessmentȱmodelsȱquantifyȱtheȱpopulationȱstateȱandȱtheȱimpactȱofȱfishing,ȱ forȱtheȱdataȱyearsȱDekker,ȱ1996ȱ#865}.ȱAȱminimumȱofȱassumptionsȱandȱaȱmaximumȱofȱ dataȱensureȱaȱcloseȱtrackingȱofȱtheȱtrueȱpopulationȱstateȱinȱrecentȱyears;ȱinȱparticular,ȱ estimatesȱofȱbothȱtheȱpopulationȱnumberȱandȱtheȱfishingȱmortalityȱbyȱlengthȱclassȱareȱ updatedȱannually.ȱTheȱBevertonȱandȱHoltȱmethodologyȱeasilyȱallowsȱforȱsimulationȱ ofȱalternativeȱfishingȱregimes,ȱandȱderivationȱofȱreferenceȱpoints.ȱApplicationȱonȱtheȱ yellowȱeelȱfisheriesȱinȱLakeȱIjsselmeerȱdemonstratedȱthatȱthisȱfisheryȱoverexploitȱtheȱ localȱstockȱofȱeel.ȱCurrentȱfisheriesȱreduceȱmaleȱspawner ȱescapementȱtoȱoneȱinȱsevenȱ partsȱandȱreduceȱfemaleȱspawnerȱescapementȱtoȱoneȱinȱsevenȱhundredȱpartsȱofȱtheȱ unexploitedȱsituationȱ(Dekker,ȱ2000).ȱ

ELSAȱisȱaȱmodellingȱapproachȱbasedȱonȱeelȱlengthȱtakenȱintoȱaccountȱrelativeȱchangeȱ inȱrecruitment,ȱsexȱratio,ȱgrowth,ȱnaturalȱandȱfishingȱmortalityȱandȱrateȱofȱsilvering.ȱItȱ isȱusefulȱtoȱestimateȱtotalȱmortalityȱrateȱfromȱaȱsimpleȱlengthȱstructureȱaboveȱ30ȱcmȱ (Lambertȱetȱal.,ȱ2006).ȱTheȱinformationȱaboutȱeelȱstockȱstatusȱprovidedȱbyȱanȱapplicaȬ tionȱonȱtheȱGirondeȱestuaryȱpresentȱanalysisȱurgesȱtoȱimplementȱmanagementȱactionsȱ inȱfreshȬwaterȱpartȱofȱtheȱestuary.ȱ

Time frame for revision management action

Twoȱtoȱfiveȱyearsȱ(shouldȱbeȱrevised).ȱ

4.5.2.3 Silver eel sub-target

Eelȱtarget:ȱlevelȱofȱmortalityȱrateȱforȱeachȱobstacle,ȱmaximumȱdelayȱforȱmigration.ȱForȱ globalȱriverȱmanagement,ȱcumulativeȱmortalityȱandȱdelayȱcanȱbeȱtargeted.ȱ

Anȱ approximateȱ estimateȱ ofȱ turbineȱ mortalityȱ canȱ beȱ obtainedȱ usingȱ empiricalȱ forȬ mulaȱfromȱliteratureȱ(LarinierȱandȱTravade,ȱ1999).ȱMoreȱaccurateȱestimationsȱofȱeelȱ mortalityȱratesȱcanȱbeȱobtainedȱbyȱtelemetryȱprocedureȱalthoughȱtheyȱareȱdifficultȱtoȱ obtainȱasȱaȱconsequenceȱofȱtheȱuncertainȱbehaviourȱofȱeelsȱduringȱtheirȱdownstreamȱ migrationȱ(ICESȱ2007).ȱ

Evaluationȱ ofȱ suchȱ targetȱshouldȱ takeȱ intoȱ accountȱ theȱ variabilityȱ inducedȱ byȱenviȬ ronmentalȱfluctuationsȱandȱthereforeȱaȱmultiȬannualȱsurveyȱisȱadvised.ȱ

Time frame for revision management action

Twoȱorȱthreeȱyears.ȱ

Eelȱtarget:ȱNumberȱofȱsilverȱeelsȱescapingȱ EIFAC/ICES WGEEL Report 2008 67

Thisȱcanȱbeȱmonitoredȱbyȱcatchȱstatistics,ȱdirectȱcountingȱmethods,ȱorȱmark–recaptureȱ experimentsȱ(ICESȱ2007).ȱ

Theȱ potentialȱ productionȱ ofȱ silverȱ eelsȱ canȱ beȱ deducedȱ byȱ convertingȱ theȱ reȬ establishedȱyellowȱeelȱpopulationȱorȱproductionȱ(dataȱfromȱelectroȬfishing)ȱintoȱsilverȱ eelȱusingȱsimpleȱ populationȱ models.ȱWhereȱ downstreamȱ damsȱ areȱ present,ȱ escapeȬ mentȱ estimatesȱ shouldȱ beȱ adjustedȱ toȱ accountȱ forȱ cumulativeȱ mortalityȱ fromȱ damȱ passage.ȱ

Time frame for revision management action

Oneȱtoȱfiveȱyears.ȱ

4.5.2.4 All life stage sub-targets

EelȱsubȬtargetȱ4.1:ȱLevelȱofȱcontaminantȱloadȱinȱeel.ȱMeasurementsȱinȱfishȱareȱpossibleȱ forȱmanyȱcontaminants,ȱespeciallyȱforȱlipophilicȱonesȱsinceȱeelsȱareȱparticularlyȱsensiȬ tiveȱtoȱbioaccumulationȱofȱsuchȱcontaminants.ȱEelȱmeasuresȱgiveȱbetterȱresponsesȱ(%ȱ ofȱ detection)ȱ thanȱ measurementsȱ inȱ waterȱ orȱ inȱ sedimentȱ (Belpaireȱ andȱ Goemans,ȱ 2007a)ȱandȱanȱadaptationȱofȱtheȱFlemishȱsurveyȱ(BelpaireȱandȱGoemans,ȱ2007a)ȱtoȱtheȱ relevantȱscaleȱofȱtheȱstudiedȱsourceȱofȱpollutionȱshouldȱbeȱadvised.ȱ

Theȱtimeȱresponseȱofȱtheseȱmanagementȱactionsȱdependsȱmainlyȱonȱtheȱpersistenceȱofȱ theȱcontaminantȱinȱtheȱfield.ȱForȱexample,ȱinȱFlandersȱlindaneȱloadȱdecreasedȱrapidlyȱ afterȱitsȱbanȱinȱ2002,ȱwhereasȱDDTȱcontinuesȱtoȱ slowlyȱdecreaseȱ30ȱyearsȱafterȱprohiȬ bitionȱ(Maesȱetȱal.,ȱ2008).ȱ

EelȱsubȬtargetȱ4.2;ȱLevelȱofȱqualityȱindex.ȱAnȱindexȱofȱ(yellowȱorȱsilver)ȱeelȱqualityȱisȱ importantȱforȱevaluatingȱtheȱnetȱeffectȱofȱsilverȱeelȱescapementȱonȱreproduction.ȱ

FatȱcontentȱcouldȱalsoȱbeȱgoodȱproxyȱindicatorȱofȱtheȱcontaminationȱlevelȱandȱaȱsubȬ sequentȱdecreaseȱinȱyellowȱeelȱfatȱcontentȱhasȱbeenȱtentativelyȱlinkedȱtoȱtheȱcapabilityȱ ofȱsilverȱeelsȱtoȱperformȱtheȱmigrationȱtoȱtheȱSargassoȱ(Belpaireȱetȱal.,ȱ2008).ȱHealthȱ statusȱofȱeelsȱusedȱforȱstockingȱespeciallyȱwithȱregardȱtoȱA.ȱcrassusȱandȱvirusesȱsuchȱ asȱHVA,ȱEVEȱandȱEVEXȱcanȱcompleteȱthisȱindex.ȱ

ȱ 68 EIFAC/ICES WGEEL Report 2008

Tableȱ4.3:ȱLinkingȱmanagementȱsubȬtargetȱandȱeelȱsubȬtarget.ȱRelationȱinȱaȱshortȱtermȱbetweenȱmanagementȱsubȬtargetsȱ(levelȱorȱmagnitudeȱofȱactionȱinȱlocalȱmanagement)ȱandȱeelȱsubȬ targetsȱ(responseȱofȱtheȱeelȱpopulationȱtoȱmanagement)ȱ(GE:ȱglassȱeelȱYE:ȱyellowȱeel;ȱSEȱsilverȱeel).ȱ

Eel sub-target GE YE SE 1.1; 2.1 2.2 : 2.3.; 2.4. Sex 2.5 3.1; 3.2 4.1 4.2; Den Occur- Density Habitat Distri- Mortality Obstacle Escapee Conta- Quality sity rence saturation bution. rate mortality number minant index load 1.1 ; GE Quota 99 1.2; GE time closure 99 1.3; YE Quota 99 9 9 9 1.4; YE time closure 9999 1.5; YE Size limits 9999 1.6; YE Protected Fishery Fishery areas 99 9 9 1.7; SE time closure 9 Management sub-target 1.8; SE size limits 9 1.9. SE protected

areas 9 1.10. Control effort 9 ȱ EIFAC/ICES WGEEL Report 2008 69

Tableȱ4.3:ȱcontinued.ȱ

2.2; Opened surface area 99 9 9 2.3; Fish passing

Upstream migration number 99 9 9 2.4 No. of obstacles

mig.

stream 99 Down- 2.5; Pollutant reduction 99 2.6; Improved Pollution habitat surface 99 3.1 Surface of habitat with low o recr. and N . of 99 9 9 stocked

Stocking 3.2 Surface of habitat without recr. and No. of stocked 99 9 9 4.1 No. of produced eels with a good health status 9 9 4.2 No. of produced eels with minimum Aquaculture genetic selection 9 9

ȱ 70 EIFAC/ICES WGEEL Report 2008

4.6 Conclusions and recommendations for Chapter 4: Assessing stocks and management actions

4.6.1 Conclusions

Itȱisȱsuggestedȱthatȱmanagersȱdefineȱinterimȱtargetsȱforȱtheȱmanagementȱmeasuresȱinȱ orderȱ toȱ integrateȱ localȱ actionȱ efficientlyȱ toȱ theȱ aimȱ ofȱ longȬtermȱ recoveryȱ ofȱ theȱ Europeanȱ eelȱ stock.ȱ Forȱ thisȱ purposeȱ managementȱ subȬtargetsȱ definingȱ theȱ magniȬ tudeȱ ofȱ actionsȱ (e.g.ȱ numberȱ ofȱ damsȱ removed)ȱ willȱ beȱ linkedȱ withȱ eelȱ subȬtargetsȱ reflectingȱtheȱexpectedȱshortȬtermȱresponseȱofȱtheȱlocalȱeelȱpopulation.ȱEelȱsubȬtargetsȱ shouldȱthereforeȱallowȱaȱfairlyȱrapidȱevaluationȱofȱtheȱmanagementȱmeasuresȱtakenȱ butȱsensitivityȱandȱtimeȱresponseȱofȱsomeȱofȱtheȱproposedȱeelȱsubȬtargetsȱwouldȱneedȱ furtherȱinvestigationȱbeforeȱtheirȱapplicationȱwouldȱbeȱoperational.ȱ

Eelȱ subȬtargetsȱ shouldȱ finallyȱ beȱ integratedȱ intoȱ theȱ evaluationȱ ofȱ theȱ statusȱ ofȱ theȱ wholeȱeelȱstock.ȱHoweverȱitȱhasȱtoȱbeȱrecognizedȱthatȱadequateȱmethodsȱorȱmodellingȱ approachesȱforȱdoingȱthisȱexerciseȱareȱstillȱlacking.ȱ

ImplementationȱofȱEMPsȱrequiresȱtheȱdevelopmentȱofȱmethodologiesȱtoȱobtainȱthoseȱ data.ȱTheyȱcanȱincludeȱeitherȱdirectȱ(e.g.ȱmarkȬrecapture)ȱorȱindirectȱmeasuresȱ(yellowȱ eelȱproxiesȱtoȱdetermineȱsilverȱeelȱproductionȱandȱeelȱhabitatȱmodellingȱproduction).ȱ Itȱisȱimportantȱtoȱensureȱstandardizationȱandȱqualityȱcontrolȱofȱtheȱmethod(s)ȱusedȱtoȱ estimateȱage.ȱ

Useȱofȱdirectȱmethods,ȱthoughȱpreferableȱinȱmanyȱrespects,ȱwillȱbeȱseverelyȱrestrictedȱ by:ȱ unevenȱ distributionȱ ofȱ silverȱ eelȱ fisheriesȱ withinȱ andȱ betweenȱ regions;ȱ limitedȱ fisheryȱmonitoringȱresources;ȱandȱinȱextremeȱfluctuationsȱinȱlargeȱriverȱflows.ȱHowȬ ever,ȱwhereȱpossible,ȱuseȱofȱdirectȱmethodsȱshouldȱbeȱprioritized.ȱ

Aȱvarietyȱofȱindirectȱmethods,ȱmostlyȱdependantȱonȱyellowȱeelȱdproxiesȱan ȱmodelȬ ling,ȱareȱavailableȱforȱareasȱwhereȱdirectȱmeasurementsȱofȱsilverȱeelȱescapementȱareȱ notȱpossibleȱandȱshouldȱbeȱextensivelyȱusedȱtoȱestimateȱregionalȱandȱnationalȱsilverȱ eelȱescapement.ȱSelectionȱofȱmodelsȱshouldȱtakeȱaccountȱofȱSLIMEȱconclusionsȱandȱ adviceȱ givenȱ elsewhereȱ inȱ thisȱ reportȱ (Dekkerȱ etȱ al.,ȱ 2006).ȱ Validationȱ ofȱ indirectȱ methodologiesȱshouldȱbeȱundertakenȱonȱanȱongoingȱbasisȱforȱaȱnetworkȱofȱriverȱsysȬ temsȱwhereȱreliableȱdirectȱestimationȱofȱsilverȱeelȱescapementȱbiomassȱisȱpossible.ȱ

EstimationȱofȱeffectiveȱspawnerȱbiomassȱshouldȱbeȱundertakenȱinȱallȱEMPsȱ(i.e.ȱatȱloȬ cal,ȱregionalȱandȱnationalȱlevels)ȱandȱthisȱwillȱrequireȱquantificationȱofȱadverseȱeffectsȱ ofȱcontaminants,ȱlowȱfatȱlevels,ȱnonȬlethalȱturbineȱdamage,ȱviralȱdiseases,ȱalongȱtheȱ linesȱ previouslyȱ proposedȱ forȱ A.ȱ crassusȱ asȱ wellȱ asȱ otherȱ anthropogenicȱ mortalityȱ ratesȱȱalongȱtheȱriverȱcatchment.ȱLocalȱmanagementȱdecisionsȱshouldȱthenȱbeȱmadeȱ byȱreferenceȱtoȱeffectiveȱsilverȱeel ȱescapementȱratherȱthanȱtotalȱspawnerȱbiomassȱesȬ timates.ȱ

Thereȱareȱveryȱfewȱquantitativeȱestimatesȱofȱpristineȱ(preȬ1980)ȱandȱcurrentȱsilverȱeelȱ productionȱtoȱallowȱcomparisonsȱtoȱbeȱmadeȱbetweenȱsystemsȱandȱthereȱisȱveryȱfewȱ dataȱ onȱ theȱ importanceȱ ofȱ estuarineȱ andȱ coastalȱ populationsȱ toȱ overallȱ production.ȱ Modellingȱwillȱbeȱneededȱtoȱtransferȱestimatesȱfromȱdataȱrichȱtoȱdataȱpoorȱsystems.ȱ Someȱ approachesȱ haveȱ beenȱ outlinedȱ byȱ thisȱ Workingȱ Groupȱ whichȱ complementsȱ thoseȱfromȱpresentedȱinȱpreviousȱworkingȱGroupȱreportsȱandȱinȱDekkerȱetȱal.,ȱ2006.ȱ EIFAC/ICES WGEEL Report 2008 71

4.6.2 Recommendations x wellȱ definedȱ subȱ targetsȱforȱ shortȬterm,ȱ localȱ managementȱ effortsȱ shouldȱ beȱ used,ȱ andȱ thatȱ dataȱ shouldȱ beȱ collectedȱ soȱ thatȱ theyȱ canȱ beȱ postȬ evaluatedȱbothȱregardingȱtheȱfulfilmentȱofȱtheȱmanagementȱeffortsȱandȱtheȱ anticipatedȱeffectsȱonȱeel;ȱ x populationȱmodel(s)ȱshouldȱbeȱusedȱtoȱassessȱtheȱstatusȱofȱstock,ȱcompliȬ anceȱwithȱ(sub)ȱtarget(s),ȱtoȱevaluateȱmanagementȱactionsȱandȱtoȱevaluateȱ theȱ influenceȱ ofȱ bioticȱ andȱ abioticȱ factorsȱ onȱ theȱ stockȱ atȱ aȱ rangeȱ ofȱ geoȬ graphicalȱscales;ȱ x adaptiveȱ feedbackȱ linksȱ areȱ establishedȱ betweenȱ postȬevaluationȱ resultsȱ andȱresultingȱchangesȱinȱmanagementȱefforts;ȱ x careȱshouldȱbeȱtakenȱsoȱthatȱlocallyȱestablishedȱ(shortȬterm)ȱsubȱtargetsȱenȬ sureȱ longȬtermȱ recovery,ȱ eventuallyȱ leadingȱ toȱ theȱ restorationȱ ofȱ theȱ spawningȱstockȱsoȱthatȱtheȱeelȱreachȱfullȱrecruitmentȱcapacity.;ȱ x sinceȱshortȱtimeȱevaluationȱofȱmanagementȱactionsȱurgesȱforȱaȱlistȱofȱmoniȬ toringȱactivities,ȱfisheryȱdependentȱasȱwellȱasȱfisheryȬindependent,ȱmethȬ odsȱ forȱ monitoringȱ inȱ connectionȱ toȱ theȱ subȱ targetsȱ presentedȱ byȱ theȱ WGEELȱ inȱ thisȱ reportȱ andȱ inȱ theȱ reportȱ ofȱ 2007ȱ shouldȱ beȱ implementedȱ ASAPȱwithinȱtheȱDCRȱandȱelsewhereȱandȱthatȱwhereȱpossibleȱtheseȱactiviȬ tiesȱshouldȱbeȱcoordinatedȱnationallyȱwithȱrelatedȱmonitoringȱactivities,ȱi.e.ȱ regardingȱbiodiversityȱwithinȱtheȱWFD;ȱ x theȱ conceptȱ ofȱ effectiveȱ spawnerȱ biomassȱ escapementȱ shouldȱ beȱ adoptedȱ forȱallȱEMPsȱandȱcomprehensiveȱprotocolsȱforȱintegrationȱofȱstandardizedȱ eelȱqualityȱdataȱshouldȱbeȱdevelopedȱforȱapplicationȱofȱthisȱconcept;ȱ x standardizedȱterminology,ȱandȱidentificationȱcriteriaȱbeȱadopted,ȱforȱuseȱinȱ allȱEuropeanȱeelȱprogrammes;ȱ 72 EIFAC/ICES WGEEL Report 2008

5 Stocking and aquaculture

5.1 Introduction

StockingȱandȱtransfersȱofȱjuvenileȱeelȱhaveȱbeenȱdiscussedȱatȱlengthȱbyȱtheȱWorkingȱ Groupȱ(mostȱrecentlyȱICES,ȱ2006ȱandȱ2007).ȱTheseȱdiscussionsȱhaveȱcoveredȱtheȱprinȬ ciplesȱandȱextentȱofȱstocking,ȱstockȱtransferȱpracticesȱandȱtheirȱcontributionsȱtoȱfisherȬ ies.ȱ Theirȱ effect ȱ onȱ escapementȱ hasȱ beenȱ discussedȱ mainlyȱ inȱ conceptualȱ andȱ theoreticalȱframeworksȱasȱaȱconsequenceȱofȱaȱlackȱofȱhardȱdata.ȱTheȱWGȱ2007ȱrecomȬ mendedȱthatȱ“guidelines,ȱorȱbestȱpracticeȱmanuals,ȱshouldȱbeȱestablishedȱforȱmethȬ odologiesȱforȱ…….ȱstockingȱofȱeel”.ȱ

ToRȱb)ȱdevelopȱmethodologiesȱforȱtheȱassessmentȱof ȱtheȱstatusȱofȱtheȱeelȱstock,ȱtheȱ impactȱ ofȱ fisheriesȱ andȱ otherȱ anthropogenicȱ impactsȱ andȱ ofȱ implementedȱ manageȬ mentȱmeasures;ȱthisȱmightȱinclude,ȱforȱexample,ȱsupportȱforȱEMPsȱonȱtheȱdeterminaȬ tionȱofȱȈpristineȈȱspawnerȱproductionȱlevelsȱandȱrelativeȱcontributionȱofȱstocking.ȱ

Extractȱfromȱ2006ȱWGEELȱreportȬtheȱchangingȱscientific ȱadviceȱregardingȱstocking.ȱ

ȈScientificȱadviceȱonȱreȬstockingȱhasȱchangedȱoverȱtheȱyears,ȱfromȱclearlyȱinȱfavourȱ (Moriartyȱ andȱ Dekker,ȱ 1997),ȱ toȱ againstȱ onȱ precautionaryȱ groundsȱ (ICES,ȱ 2000).ȱ Inȱ ourȱpreviousȱreportȱ(ICES,ȱ2005b),ȱtheȱrisksȱinvolvedȱwereȱdiscussed,ȱbalancingȱpoȬ tentialȱgeneticȱeffectsȱagainstȱtheȱriskȱthatȱtheȱcurrentȱstockȱmightȱsufferȱfromȱdepenȬ satoryȱeffectsȱinȱtheȱreproductiveȱphase,ȱforȱwhichȱreȬstockingȱmightȱbeȱoneȱsolution.ȱ

Clearly,ȱargumentsȱ bothȱ proȱ andȱ contraȱ reȬstockingȱ remainȱ valid,ȱ andȱ noȱ finalȱandȱ scientificȱadviceȱcanȱbeȱderived.ȱHowever,ȱtheȱpreviousȱadviceȱwasȱbasedȱonȱtheȱpoȬ tentialȱforȱdepensationȱoccurringȱinȱtheȱreproductiveȱphase.ȱAllȱargumentsȱproȱandȱ conȱbeingȱasȱtheyȱareȱaȱmoreȱpracticalȱandȱnearbyȱargumentȱhasȱcomeȱtoȱtheȱforeȱinȱ thisȱ report:ȱ thatȱ seedȱ stockȱ areasȱ mightȱ progressivelyȱ becomeȱ depletedȱ asȱ aȱ conseȬ quenceȱofȱaȱcontinuedȱdeclineȱinȱglassȱeelȱimmigration.ȱOptionsȱforȱpotentiallyȱsucȬ cessfulȱrestorationȱofȱtheȱstockȱbyȱglassȱeelȱrestockingȱareȱfading.ȱReȬstockingȱofȱglassȱ eel,ȱeitherȱinȱsouthernȱareasȱrapidlyȱcontributingȱtoȱsilverȱeelȱproduction,ȱorȱinȱnorthȬ ernȱareasȱwithȱaȱlongȱpostponedȱandȱlongȱlastingȱcontributionȱtoȱsilverȱeelȱproducȬ tion,ȱthereforeȱneedsȱurgentȱconsideration.Ȉȱ

TheȱWorkingȱGroupȱrevisitedȱthisȱtopicȱinȱ2008ȱinȱorderȱtoȱprovideȱupdatesȱonȱstockȬ ingȱfiguresȱandȱpracticalȱinformationȱtoȱsupportȱstockingȱbestȱpracticeȱandȱwillȱproȬ videȱsupportȱtoȱEMP’sȱandȱtheȱEUȱCommission.ȱ

5.2 Methods to assess the relative contribution of stocking to the regeneration of the European stock, and for EMPs

5.2.1 Source of glass eel

AdviceȱfromȱICESȱtoȱtheȱEUȱcommissionȱ(ICES,ȱ2005a)ȱwasȱthatȱtheȱrecentȱglassȱeelȱ catchȱ(ca.ȱ100ȱtonnes)ȱisȱlessȱthanȱthatȱrequiredȱ(150ȱtoȱ1000ȱtonnes)ȱtoȱsupplyȱtheȱtotalȱ potentialȱ productiveȱ habitatȱ (aboutȱ40ȱ000ȱ km2),ȱ andȱACFMȱfurtherȱconcludedȱthatȱ fullȬscaleȱ restockingȱ aloneȱ isȱ unlikelyȱ toȱ achieveȱ theȱ EUȱ objectivesȱ inȱ theȱ mediumȱ termȱ(ICES,ȱ2006).ȱ

Therefore,ȱtheȱadviceȱremainsȱthatȱthereȱareȱlikelyȱtoȱbeȱinsufficientȱglassȱeelȱavailableȱ fromȱtheȱfisheryȱtoȱmeetȱtheȱdemandsȱforȱstockingȱatȱtheȱEuropeanȱlevel.ȱHowever,ȱ theȱRegulationȱEU:ȱ1100/2007,ȱrequiresȱthatȱfisheriesȱmakeȱatȱleastȱ35%ȱofȱeelȱ<12ȱcmȱ availableȱforȱstockingȱinȱ2009,ȱrisingȱtoȱ60%ȱbyȱ2013.ȱTheȱimplementationȱofȱEMPsȱinȱ 2009ȱmayȱeffectȱtheȱreductionȱinȱsomeȱglassȱeelȱfishingȱeffort,ȱeitherȱasȱpartȱofȱlocalȱ EIFAC/ICES WGEEL Report 2008 73

ManagementȱPlansȱorȱasȱaȱconsequenceȱofȱtheȱ50%ȱcutȱrequiredȱwhereȱplansȱareȱnotȱ submittedȱandȱapproved.ȱThisȱoutcomeȱwillȱnotȱbeȱknownȱuntilȱtheȱEMPsȱareȱpubȬ lished.ȱHere,ȱweȱconsiderȱtheȱpotentialȱeffectȱ(benefit)ȱofȱthisȱstockingȱmaterial.

5.2.2 Yield potential

TheȱyieldȱpotentialȱcanȱbeȱcalculatedȱfromȱYield/Recruitȱ(Y/R)ȱestimates.ȱMostȱofȱtheȱ dataȱonȱY/RȱavailableȱareȱobtainedȱfromȱstockingsȱinȱlakesȱandȱanȱItalianȱlagoon.ȱTheȱ dataȱ forȱ lakesȱ rangeȱ fromȱ 5–72ȱ g.stockedȱ eelȬ1,ȱ butȱ mostȱ areȱ inȱ theȱ rangeȱ 20–50ȱ g.stockedȱ eelȬ1.ȱ Theȱ yieldȬperȬrecruitȱ inȱ theȱ Italianȱ lagoonȱ appearsȱ toȱ beȱ moreȱ thanȱ twiceȱasȱhigh.ȱIfȱtheȱtotalȱcatchȱofȱglassȱeelsȱinȱEuropeȱisȱinȱtheȱregionȱofȱ100ȱtonneȱ (ICES,ȱ2005)ȱofȱglassȱeels,ȱwithȱ3000ȱglassȱeelsȱperȱkilo,ȱandȱ35%ȱ(minimumȱrequestedȱ byȱtheȱEelȱRegulation)ȱprovidedȱinȱ2009ȱforȱstocking,ȱthisȱwouldȱhaveȱaȱproductionȱ potentialȱforȱapproximatelyȱ2000–5000ȱtonsȱofȱsilverȱeelȱafterȱoneȱeelȱgenerationȱtime.ȱ Whenȱ60%ȱofȱtheȱcatchȱbecomesȱavailableȱinȱ2013,ȱitȱwillȱhaveȱaȱlifetimeȱpotentialȱforȱ 3500–8500ȱtonsȱofȱsilverȱeelsȱgivenȱnoȱanthropogenicȱmortality.ȱICESȱ 2006ȱproducedȱ comparableȱ resultsȱ (10ȱ000ȱ tonsȱ ofȱ silverȱ eelsȱ whenȱ stockingȱ 100ȱ tonsȱ ofȱ glassȱ eels)ȱ whenȱ usingȱ populationȱ dynamicȱ calculationsȱ andȱ dataȱ fromȱ Moriartyȱ andȱ Dekker,ȱ 1997.ȱTheȱaboveȱestimatesȱareȱmaximumȱestimates,ȱbasedȱonȱtheȱassumptionȱthatȱtheȱ catchȱofȱglassȱeelȱwillȱbeȱinȱtheȱregionȱofȱ100ȱtons.ȱThereȱisȱofȱcourseȱtheȱpossibilityȱ thatȱthereȱmayȱbeȱnoȱsurplusȱofȱglassȱeelsȱinȱtheȱnearȱfutureȱ(ICES,ȱ2007).ȱ

Glassȱeelȱareȱcaughtȱusingȱmovingȱandȱstationaryȱfishingȱgears.ȱThereȱisȱevidenceȱthatȱ handlingȱmortalityȱofȱsomeȱofȱtheseȱgears,ȱe.g.ȱtrawlsȱmayȱbeȱup.ȱtoȱ40% ȱReductionȱofȱ theseȱ mortalitiesȱ wouldȱ leadȱ toȱ theȱ moreȱ efficientȱ useȱ ofȱ theȱ limitedȱ andȱ decliningȱ resourceȱofȱglassȱeels.ȱ

5.3 Review of stocking activity across Europe

BeforeȱtheȱWGȱmeeting,ȱaȱsimpleȱquestionnaireȱwasȱsentȱtoȱtheȱWGȱmembersȱinȱorderȱ toȱobtainȱadditionalȱinformation.ȱTheȱresponsesȱtoȱthisȱquestionnaireȱareȱbrieflyȱdeȬ scribedȱinȱtheȱfollowingȱsection.ȱInformationȱfromȱ17ȱcountriesȱisȱincluded.ȱForȱthisȱ purpose,ȱUKȱandȱNorthernȱIrelandȱwereȱconsideredȱasȱtwoȱcountries,ȱsinceȱthereȱisȱaȱ considerableȱtransferȱofȱglassȱeelsȱfromȱtheȱ“UK”ȱtoȱNorthernȱIreland.ȱ

A. Does your country buy eels for stocking?

Yes:ȱ 11ȱ(DE,ȱPL,ȱN.Irl,ȱSE,ȱNL,ȱBE,ȱFI,ȱEE,ȱLT,ȱLV,ȱDK)ȱ

No:ȱ 6ȱ(FR,ȱES,ȱPT,ȱUK,ȱIE,ȱNO)ȱ

Aȱclearȱgeographicalȱpatternȱcanȱbeȱseen.ȱCountriesȱatȱtheȱAtlanticȱcoastȱdoȱnotȱbuyȱ eelsȱwhereasȱcountriesȱfurtherȱeastȱofȱtheȱAtlantic,ȱandȱinȱparticularȱaroundȱtheȱBalticȱ Sea,ȱusuallyȱpurchaseȱeelsȱforȱstocking.ȱ

Itȱhasȱtoȱbeȱnotedȱthatȱthisȱisȱaȱdynamicȱpicture,ȱwhichȱmayȱchangeȱfromȱyearȱtoȱyearȱ dependingȱonȱseveralȱfactorsȱ(availabilityȱandȱpriceȱofȱglassȱeels,ȱsituationȱofȱtheȱfishȬ eryȱinȱtheȱrespectiveȱcountry,ȱpoliticalȱandȱadministrativeȱdecisions).ȱ

B. If so which life stage, glass or yellow eels? (only countries with “Yes” under question 1)

Glassȱeels:ȱȱȱȱ6ȱ(DK,ȱLT,ȱEE,ȱFI,ȱSE,ȱN.Irl)ȱȱ

Yellowȱeelsȱ(elvers,ȱpreȬgrownȱeels):ȱ 1ȱ(LV)ȱ

Both:ȱȱȱȱȱ4ȱ(BE,ȱNL,ȱPL,ȱDE)ȱ 74 EIFAC/ICES WGEEL Report 2008

Clearȱchangesȱinȱtheȱstockingȱstrategiesȱhaveȱoccurredȱinȱtheȱpastȱandȱwillȱprobablyȱ reȬoccurȱinȱtheȱfutureȱdependingȱonȱseveralȱfactors,ȱinȱparticularȱtheȱavailabilityȱandȱ priceȱofȱglassȱeelsȱvs.ȱpreȬgrownȱeelsȱfromȱfarms.ȱNewȱscientificȱresultsȱmayȱalsoȱinȬ fluenceȱtheȱdecisionȱforȱoneȱofȱtheȱstockingȱtypesȱ(e.ȱg.ȱsurvivalȱandȱgrowthȱratesȱofȱ glassȱeelsȱvs.ȱpreȬgrownȱeels,ȱgenderȱselectionȱbasedȱonȱfarmȱdensitiesȱandȱriskȱofȱinȬ fectionȱ withȱ diseasesȱ fromȱ theȱ farms).ȱ Thereȱ areȱ risksȱ andȱ benefitsȱ forȱ eachȱ type,ȱ whichȱareȱconsideredȱinȱanotherȱsectionȱofȱthisȱreport,ȱandȱwhichȱshouldȱbeȱconsidȬ eredȱinȱtheȱstockingȱstrategy.ȱ

C. How much stock was purchased in 2008?

Theȱdataȱforȱ2008ȱwereȱnotȱcompleteȱandȱdidȱnotȱallowȱaȱusefulȱanalysis.ȱTherefore,ȱ theȱdataȱforȱ2007ȱwereȱconsideredȱhere.ȱ

Totalȱglassȱeelsȱ2007:ȱ 5.7ȱMillionȱindividualsȱ

Totalȱyellowȱeelsȱ2007:ȱ 5.6ȱMillionȱindividualsȱ

ThereȱareȱuncertaintiesȱinȱtheseȱnumbersȱandȱtheȱdataȱareȱnotȱcompleteȱforȱallȱcounȬ triesȱ (butȱ allȱ 11ȱ countriesȱ whichȱ answeredȱ “yes”ȱ underȱ questionȱ A,ȱ areȱ included).ȱ Therefore,ȱtheseȱnumbersȱmustȱbeȱconsideredȱasȱminimumȱvalues.ȱTheȱcalculationȱisȱ difficult,ȱsinceȱsomeȱcountriesȱbuyȱglassȱeelsȱandȱrearȱthemȱinȱfarmsȱforȱaȱwhileȱbeforeȱ stocking.ȱInȱsomeȱofȱtheseȱcases,ȱtheȱoriginalȱnumbersȱofȱimportedȱglassȱeelsȱareȱnotȱ availableȱ(justȱtheȱnumbersȱofȱyoungȱyellowȱeelsȱstocked).ȱ

Aȱ roughȱ estimateȱ wasȱ madeȱ aboutȱ theȱ totalȱ amountȱ ofȱ glassȱ eelsȱ finallyȱ usedȱ forȱ stocking.ȱForȱthatȱpurpose,ȱyellowȱeelȱnumbersȱwereȱtranslatedȱintoȱglassȱeelȱnumȬ bersȱ(glassȱeelȱequivalents)ȱbyȱcorrectionȱfactors ȱusuallyȱusedȱinȱDenmarkȱ(1ȱfarmedȱ eelȱequalsȱ1385ȱglassȱeels;ȱM.ȱI.ȱPedersen,ȱpers.ȱcomm..)ȱandȱGermanyȱ(1ȱfarmedȱeelȱ equalsȱ3ȱglassȱeels;ȱe.ȱg.ȱKnöscheȱetȱal.,ȱ2004).ȱ

Basedȱonȱtheseȱfactors,ȱtheȱtotalȱnumbersȱofȱglassȱeelȱ(equivalents)ȱusedȱforȱstockingȱ rangedȱfromȱ13.5ȱMillionsȱ5toȱ22. ȱMillions.ȱIfȱaȱmeanȱweightȱofȱ0.3ȱgȱforȱglassȱeelsȱisȱ assumed,ȱtheseȱnumbersȱtranslateȱintoȱbiomassesȱofȱ4.5ȱtȱtoȱ7.5ȱt.ȱEvenȱthoughȱtheseȱ areȱroughȱestimates,ȱtheyȱmayȱindicateȱtheȱorderȱofȱmagnitudeȱofȱglassȱeelsȱusedȱforȱ stockingȱofȱnaturalȱwatersȱinȱEurope.ȱIfȱthisȱisȱcomparedȱtoȱtheȱtotalȱglassȱeelȱcatchȱinȱ Europe,ȱwhichȱwasȱbetweenȱ50–60ȱtonsȱinȱ2007,ȱaȱproportionȱofȱ7.5–15%ȱofȱtheȱtotalȱ glassȱeelȱcatchȱwasȱusedȱforȱstocking.ȱThisȱisȱinȱtheȱsameȱorderȱofȱmagnitudeȱasȱpreȬ viousȱestimates.ȱTheseȱfiguresȱmayȱbeȱinfluencedȱbyȱincompleteȱrecordingsȱofȱstockȬ ingȱasȱwellȱasȱofȱglassȱeelȱcatches.ȱ

D. From where or whom?

Itȱ doesȱ notȱappearȱ possibleȱ toȱ provideȱveryȱ clearȱ analysesȱ aboutȱtheȱ tradeȱ pathsȱ ofȱ glassȱeelsȱsinceȱtheȱsituationȱisȱveryȱdynamicȱorȱpoorlyȱreportedȱ(Figureȱ5.1).ȱGlassȱ eelsȱ areȱ mainlyȱ purchasedȱ fromȱ Franceȱ orȱ fromȱ theȱ UK.ȱ However,ȱ evenȱ glassȱ eelsȱ boughtȱ fromȱ theȱ UK,ȱ mayȱ previouslyȱ haveȱ beenȱ importedȱ fromȱ France.ȱ Whenȱ preȬ grownȱeelsȱfromȱfarmsȱareȱusedȱforȱstocking,ȱtheyȱareȱeitherȱimportedȱasȱglassȱeelsȱ andȱrearedȱinȱfarmsȱwithinȱtheirȱownȱcountryȱ(e.ȱg.ȱDK,ȱNL,ȱpartlyȱDE,ȱLT)ȱorȱdirectlyȱ importedȱ asȱ youngȱ yellowȱ eelsȱ (mainlyȱ fromȱ NL,ȱ DE,ȱ butȱ possiblyȱ alsoȱ DKȱ andȱ inȱ smallerȱamountsȱfromȱotherȱcountries).ȱTheȱinformationȱisȱprobablyȱincomplete.ȱ EIFAC/ICES WGEEL Report 2008 75

23 + Europe (Aquaculture 15 restocking) restocking) 11 China

85 23

47 27 8

Figureȱ5.1:ȱMeanȱtradeȱvolumesȱofȱglassȱeelȱ(T)ȱ1996–2006ȱinȱEuropeȱanalysedȱfromȱEUROSTATȱ database.ȱ

Theȱ analysisȱ ofȱ theȱ questionnaireȱ demonstratedȱ thatȱ atȱ presentȱ itȱ isȱ notȱ possibleȱ toȱ traceȱtheȱoriginȱandȱtradeȱpathsȱofȱglassȱeelsȱandȱyoungȱyellowȱeels.ȱHowever,ȱasȱaȱ consequenceȱofȱtheȱobligationsȱinȱ2009ȱfromȱCITESȱandȱfromȱtheȱEUȱCouncilȱRegulaȬ tionȱ(1100/2007Ȭtheȱ“EelȱRegulation”),ȱMemberȱStatesȱhaveȱtoȱdevelopȱsystemsȱforȱtheȱ traceabilityȱ ofȱ tradedȱ eels.ȱ Consequently,ȱ theȱ availabilityȱ ofȱ informationȱ onȱ numȬ bers/biomassesȱofȱeelȱtradedȱandȱtheirȱtradeȱpathsȱareȱexpectedȱtoȱimproveȱinȱtheȱfuȬ ture.ȱ

E. Does your country have a protocol in place by which it stocks its waters?

Yes:ȱȱȱȱ6ȱ(DE,ȱES,ȱSE,ȱUK,ȱEE,ȱDK)ȱ

No:ȱȱȱȱ7ȱ(PT,ȱPL,ȱLT,ȱLV,ȱIE,ȱNO)ȱ

Willȱbeȱdeveloped:ȱȱ 1ȱ(BE,ȱNL)ȱ

Noȱinfo/unclearȱstatus:ȱȱ 3ȱ(FR,ȱFI,ȱN.Irl)ȱ

Theȱinformationȱshownȱhereȱcontainsȱsomeȱuncertainties.ȱTheȱtypeȱofȱprotocolȱmayȱ beȱveryȱdifferentȱbetweenȱcountries.ȱItȱmayȱcontainȱjustȱrulesȱonȱwereȱtoȱplaceȱtheȱeelsȱ andȱatȱwhatȱdensityȱwhereasȱinȱotherȱcasesȱaȱscreeningȱforȱdiseasesȱorȱparasitesȱmayȱ beȱincluded.ȱOtherȱcountriesȱareȱatȱtheȱstageȱofȱdevelopingȱprotocolsȱatȱpresent.ȱTheȱ situationȱ mayȱ evenȱ differȱ withinȱ oneȱ countryȱ ifȱ regionalȱ authoritiesȱ orȱ governmentȱ areȱresponsibleȱforȱ fisheriesȱissuesȱasȱisȱtheȱcaseȱinȱGermany.ȱAȱconsiderableȱnumberȱ ofȱcountriesȱdoȱnotȱhaveȱprotocolsȱinȱplaceȱsuggestingȱroomȱforȱfurtherȱimprovementȱ inȱthisȱarea.ȱ

F. Does your country intend using stocking as a tool in its eel management plans?

Yes:ȱȱȱȱ12ȱ

No:ȱȱȱȱ1ȱ(NO)ȱ 76 EIFAC/ICES WGEEL Report 2008

Stillȱinȱdiscussion:ȱȱ 2ȱ(IE,ȱFR)ȱ

Unclear/noȱinformation:ȱȱ 2ȱ(PT,ȱFI)ȱ

TheȱmajorityȱofȱcountriesȱintendȱtoȱuseȱstockingȱasȱanȱoptionȱinȱtheȱEelȱManagementȱ Plans.ȱThisȱraisesȱtheȱquestionȱif,ȱgivenȱtheȱpossibilityȱofȱaȱfurtherȱdeclineȱinȱglassȱeelȱ catchesȱ andȱ theȱ obligationȱ toȱ achieveȱ theȱ managementȱ targetsȱ alsoȱ inȱ theȱ donorȱ catchments,ȱsufficientȱnumbersȱofȱglassȱeelȱwillȱbeȱavailableȱtoȱreachȱtheȱstockingȱtarȬ gets.ȱ However,ȱ theȱ decisionȱ whetherȱ theȱ exportȱ ofȱ glassȱ eelȱ fromȱ thoseȱ catchmentsȱ (mainlyȱinȱFranceȱandȱtheȱUK)ȱtoȱotherȱcountriesȱforȱstockingȱwillȱbeȱpermitted,ȱinȬ cludesȱanȱeconomicȱand ȱpoliticalȱdimension,ȱwhichȱisȱdifficultȱtoȱassess.ȱ

5.4 Decision framework

TheȱWGȱhasȱpresentedȱandȱmadeȱuseȱofȱvariousȱdecisionȱframeworksȱinȱourȱearlierȱ reportsȱ(ICESȱ2006ȱandȱ2007;ȱWilliamsȱandȱAprahamian,ȱ2004;ȱSymonds,ȱ2006;ȱMontȬ realȱreportȱ(WilliamsȱandȱThreader,ȱ2007)).

5.4.1 Management policies

5.4.1.1 Objectives

“Wheneverȱstockingȱofȱfishȱisȱtoȱbeȱconsidered,ȱtheȱaimsȱandȱspecificȱobjectivesȱofȱtheȱ exerciseȱmustȱbeȱclearlyȱdefinedȱandȱadheredȱto”ȱ(Cowx,ȱ1999).ȱ

Onlyȱmoreȱrecentlyȱhasȱstockingȱbeenȱdoneȱtoȱmainlyȱenhanceȱlocalȱstocksȱinȱorderȱtoȱ improveȱorȱprovideȱtheȱbasisȱforȱaȱprofitableȱfishery.ȱInȱsomeȱcircumstancesȱstockingȱ wasȱdoneȱtoȱmitigateȱorȱcompensateȱforȱdepletedȱstocks,ȱasȱaȱresultȱofȱupstreamȱdamsȱ relatedȱ toȱ hydropower.ȱ Suchȱ stocksȱ mayȱ beȱ depletedȱ asȱ aȱ consequenceȱ ofȱ damsȱ asȱ migrationȱ obstaclesȱ forȱ youngȱ ascendingȱ eelsȱ andȱ asȱ turbineȬinducedȱ mortalitiesȱ inȱ silverȱeels.ȱ

ConcurrentlyȱwithȱtheȱawarenessȱofȱtheȱseriousȱdeclineȱinȱtheȱEuropeanȱeelȱstockȱandȱ inȱ connectionȱ withȱ theȱ preparationȱ ofȱ eelȱ managementȱ plans,ȱ stockingȱ hasȱ becomeȱ oneȱmeasureȱtoȱimproveȱtheȱstock.ȱThisȱtimeȱstockingȱisȱdoneȱwithȱtheȱmainȱpurposeȱ ofȱincreasingȱtheȱproductionȱofȱsilverȱeelsȱleavingȱtheȱmanagedȱunitȱandȱcontributingȱ toȱtheȱspawningȱbiomass,ȱi.e.ȱnotȱtoȱsupportȱaȱfishery.ȱ

COMȱ hasȱ proposedȱ stockingȱ inȱ watersȱ withȱ freeȱ accessȱ toȱ theȱ seaȱ asȱ oneȱ measureȱ amongȱothersȱtoȱenhanceȱlocalȱstocksȱwithȱtheȱultimateȱgoalȱaimȱtoȱincreaseȱtheȱbioȬ massȱ ofȱ spawnersȱ toȱ produceȱ aȱ sufficientȱ numberȱ ofȱ recruitingȱ glassȱ eelsȱ (COMȱ 1100/2007).ȱ

Stockingȱasȱpartȱofȱmanagementȱplansȱmayȱalsoȱoccurȱinȱnewȱwaterȱbodies,ȱorȱareasȱ whereȱeelȱareȱabsent,ȱinȱorderȱtoȱproduceȱadditionalȱpotentialȱspawnersȱwhereȱaccessȱ toȱtheȱseaȱisȱopen.ȱ

Anotherȱ objectiveȱ mightȱ beȱ toȱ restoreȱ localȱ stocksȱ inȱ orderȱ toȱ improveȱ orȱ preserveȱ biodiversityȱ(Verreault,ȱpers.ȱcomm.)ȱandȱthisȱalsoȱmightȱbeȱbeneficialȱifȱthereȱisȱanȱ olfactoryȱ cueȱ toȱ upstreamȱ migration.ȱ Alternativeȱ strategiesȱ toȱ stockingȱ haveȱ toȱ beȱ consideredȱ andȱ analysed.ȱ Improvingȱ theȱ possibilitiesȱ forȱ eelsȱ toȱ migrateȱ upstreamȱ mightȱbeȱaȱsufficientȱmeasureȱwhereȱdamsȱareȱobstructingȱupstreamȱmigration,ȱgivenȱ that ȱtheȱemigrationȱrouteȱisȱsecured.ȱImprovedȱenvironmentalȱconditionsȱinȱeelȱgrowȬ ingȱwaters,ȱthusȱincreasingȱsurvivalȱandȱgrowth,ȱmayȱalsoȱbeȱanȱalternativeȱorȱaddiȬ tionȱtoȱstocking.ȱ

Asȱthereȱisȱaȱgeneralȱlackȱofȱstockingȱmaterialȱ(glassȱeels)ȱthereȱisȱnoȱroomȱforȱaȱmisȬ useȱ ofȱ thisȱrestrictedȱ resource.ȱ Thereforeȱ stockingȱshouldȱ onlyȱ beȱ doneȱasȱ partȱ ofȱaȱ EIFAC/ICES WGEEL Report 2008 77

managementȱplanȱensuringȱaȱsignificantȱescapeȱofȱsilverȱeels.ȱTheȱpotentialȱavailabilȬ ityȱofȱcentralȱfundingȱthroughȱtheȱEuropeanȱFisheriesȱFundȱ(EFF)ȱtoȱsupportȱstockingȱ forȱenhancementȱpurposes,ȱmayȱensureȱparityȱwithȱotherȱcompetitorsȱforȱseedȱstockȱ (e.g.ȱaquaculture,ȱfisheriesȱenhancements).ȱ

5.4.2 Ecological considerations

5.4.2.1 What size of eel should be stocked?

Thereȱareȱthreeȱmainȱoptions;ȱstockingȱofȱglassȱeel,ȱyoungȱyellowȱeelsȱandȱongrownȱ eelȱ fromȱ aquaculture.ȱ Apartȱ fromȱ thatȱ thereȱ isȱ theȱ optionȱ ofȱ movingȱ eelsȱ“overȱ theȱ dam”ȱinȱcasesȱofȱmigrationȱobstructionsȱ(assistedȱmigration).ȱTheȱlatterȱoptionȱisȱnotȱ dealtȱwithȱhere.ȱ

Theȱrisksȱconcernedȱwithȱdiseases,ȱparasites,ȱbiasedȱsexȬratiosȱandȱgeneticȱselectionȱ mayȱbestȱbeȱavoidedȱbyȱstockingȱwithȱeelsȱthatȱareȱasȱyoungȱasȱpossibleȱfromȱaȱnatuȬ ralȱstate.ȱStockingȱwithȱyellowȱeelȱcaughtȱinȱtheȱwildȱposesȱtheȱadditionalȱriskȱofȱtheirȱ beingȱ contaminated.ȱ Ifȱ ongrownȱ eelsȱfromȱ aquacultureȱ areȱ consideredȱ forȱ stocking,ȱ thereȱareȱrisksȱofȱdiseaseȱspread,ȱreducedȱgeneticȱfitnessȱ(Sectionȱ5.4.2.3)ȱandȱskewedȱ sexȱratios.ȱWhenȱpurposelyȱinfectedȱwithȱherpesȱvirusȱinȱaquaculture,ȱasȱseemsȱtoȱbeȱ widelyȱpractised,ȱwhenȱtheseȱeelsȱareȱstockedȱtheȱspreadȱofȱdiseaseȱisȱaȱcertainty,ȱnotȱ aȱrisk.ȱHowever,ȱstockingȱofȱhealthyȱongrownȱeels ȱwillȱresultȱinȱcomparableȱgrowthȱ ratesȱandȱmortalitiesȱcomparedȱtoȱtheȱstockingȱofȱglassȱeelsȱ(ICES,ȱ2007).ȱ

Anotherȱriskȱassociatedȱwithȱusingȱongrownȱeels,ȱisȱtheȱstockingȱofȱAnguillaȱrostrata.ȱ StockingȱofȱA.ȱrostrataȱseemsȱtoȱhaveȱoccurredȱinȱtheȱpastȱ(GermanȱCountryȱReport,ȱ 2008;ȱUblȱandȱFrankowski,ȱ2008),ȱA.ȱ rostrataȱisȱgrownȱinȱEuropeanȱaquacultureȱandȱ discriminationȱbetweenȱA.ȱrostrataȱandȱA.ȱAnguilla,ȱwhenȱgrownȱup,ȱisȱnotȱpossibleȱinȱ practice.ȱ

5.4.2.2 Contaminants

Oneȱofȱtheȱpotentialȱecologicalȱandȱenvironmentalȱrisksȱwhichȱstockingȱprogrammesȱ shouldȱconsiderȱisȱcontaminationȱasȱaȱpotentialȱriskȱtoȱproduceȱ(inȱstockedȱsystems)ȱ reproducersȱnotȱableȱtoȱreachȱspawningȱgroundsȱatȱtheȱSargassoȱSeaȱand/orȱproduceȱ enoughȱgametesȱofȱhighȱquality.ȱ

Considerationȱ shouldȱ beȱ givenȱ toȱ pollutionȱ withȱ PCBs,ȱ flameȱ retardants,ȱ pesticidesȱ andȱheavyȱmetals.ȱPriorityȱshouldȱbeȱgivenȱtoȱthoseȱsitesȱwhereȱsuchȱcontaminantsȱ areȱabsentȱorȱatȱpermissibleȱlevelsȱ(informationȱavailableȱthroughȱtheȱEuropeanȱEelȱ QualityȱDatabaseȱChapterȱ6).ȱ

Detrimentalȱeffectsȱofȱpollutionȱonȱfitnessȱandȱfecundityȱhaveȱbeenȱsuggestedȱearlierȱ onȱ (Larssonȱ etȱ al.,ȱ 1990),ȱ butȱ recently,ȱ thereȱ areȱ indicationsȱ thatȱ poorȱ qualityȱ ofȱ theȱ spawners,ȱnamelyȱtheȱsilverȱeelsȱmigratingȱtoȱtheȱoceanicȱspawningȱgrounds,ȱmightȱ beȱaȱkeyȱfactorȱinȱtheȱdecline,ȱe.g.ȱdecreaseȱofȱbodyȱfatȱcontent.ȱPalstraȱetȱal.,ȱ2006ȱarȬ guedȱ thatȱ gonadalȱ levelsȱ ofȱ dioxinȬlikeȱ contaminants,ȱ includingȱ PCBs,ȱ in ȱ eelsȱ fromȱ mostȱ Europeanȱ locationsȱ impairȱ embryonicȱ development.ȱ Pollutionȱ mightȱ alsoȱ imȬ pactȱreproductiveȱsuccessȱthroughȱeffectsȱonȱgenotype:ȱaȱsignificantȱnegativeȱcorrelaȬ tionȱbetweenȱheavyȱmetalȱpollutionȱandȱeelȱgeneticȱvariabilityȱwasȱreportedȱbyȱMaesȱ etȱ al.,ȱ 2005.ȱ Insufficientȱ conditionȱ andȱ energyȱ resourcesȱ (Svedängȱ andȱ Wickström,ȱ 1997),ȱ highȱ bioaccumulationȱ ofȱ persistentȱ organicȱ pollutantsȱ (especiallyȱ polychloriȬ natedȱbiphenylsȬPCBs)ȱ(Larssonȱetȱal.,ȱ1990;ȱRobinetȱandȱFeunteun,ȱ2002;ȱPalstraȱetȱal.,ȱ 2006)ȱ andȱ pathologicalȱ agentsȱ (Palstraȱ etȱ al.,ȱ 2007)ȱ haveȱ beenȱ reportedȱ asȱ potentialȱ restrictiveȱ factors,ȱ disablingȱ longȱ distanceȱ migrationȱ andȱ successfulȱ reproductionȱ withȱprimeȱqualityȱgametes.ȱ 78 EIFAC/ICES WGEEL Report 2008

Whereȱspawnerȱqualityȱisȱpoorȱandȱlipidȱcontentȱlow,ȱsilverȱeelsȱmayȱnotȱcontributeȱ toȱtheȱoverallȱspawningȱandȱrecruitmentȱofȱtheȱEuropeanȱstock.ȱAccumulationȱofȱenȬ ergyȱthroughȱlipidȱstorageȱmayȱbeȱaffectedȱbyȱdifferentȱenvironmentalȱfactorsȱsuchȱasȱ diseaseȱagents,ȱchangesȱinȱfoodȱavailability,ȱotherȱglobalȱchangesȱinȱtheȱenvironment,ȱ changesȱinȱ(densityȬdependent)ȱsexȱratiosȱevenȱlifeȬhistoryȱcharacteristics,ȱi.e.ȱrestockȬ ingȱ itselfȱ andȱ pollutionȱ pressureȱ asȱ aȱ consequenceȱ ofȱ disruptionȱ ofȱ theȱ endocrineȱ processes.ȱ

5.4.2.3 Genetics, diseases and health issues

Genetics

TheȱimportanceȱofȱmaintainingȱgeneticȱdiversityȱcanȱbeȱdividedȱintoȱaȱshortȬtermȱimȬ pactȱ (inȱ theȱorderȱ ofȱfewȱgenerations),ȱbyȱ avoidingȱinbreedingȱ andȱ fitnessȱ decreaseȱ (populationȱsurvival)ȱandȱaȱlongȬtermȱimpactȱ(overȱdecadesȱorȱevenȱcenturies),ȱandȱ byȱconferringȱtheȱpossibilityȱtoȱadaptȱtoȱchangingȱconditionsȱ(speciesȱsurvival).ȱGeȬ neticȱdataȱmayȱhelpȱtoȱassessȱspeciesȱintegrityȱwithinȱtheȱNorthȱAtlantic,ȱevaluateȱtheȱ geneticȱstockȱstructureȱofȱtheȱEuropeanȱeel,ȱclarifyȱtheȱspatioȬtemporalȱstabilityȱofȱtheȱ geneticȱ structure,ȱ defineȱ theȱ influencesȱ ofȱ oceanicȱ conditionsȱ onȱ geneticȱ variability,ȱ monitorȱandȱguideȱtheȱstockingȱpolicyȱinȱEurope,ȱandȱevaluateȱtheȱeffectȱofȱpopulaȬ tionȱdeclineȱandȱhabitatȱdegradationȱonȱgeneticȱvariabilityȱandȱtheȱoverallȱfitnessȱofȱ eelsȱ(seeȱalsoȱAnnexȱ4ȱforȱaȱmoreȱdetailedȱreview).ȱ

Genetic consequences of stocking practices

BelowȱareȱlistedȱsomeȱimportantȱpointsȱtoȱconsiderȱinȱregardsȱtoȱgeneticsȱwhenȱplanȬ ningȱstockingȱmeasuresȱandȱprovideȱsomeȱadviceȱforȱsustainableȱstocking.ȱ

1ȱ) Decidingȱonȱmassȱstockingȱpracticesȱtoȱsupplementȱpopulationsȱcanȱleadȱtoȱ theȱrapidȱintroductionȱofȱnonȬnativeȱgeneticȱmaterialȱfromȱnonȬindigenousȱ eelȱ species.ȱ Monitoringȱ theȱ correctȱ speciesȱ identityȱ (tracing)ȱ isȱ thereforeȱ crucialȱtoȱpreserveȱgeneticȱintegrityȱofȱtheȱEuropeanȱeel.ȱExamplesȱofȱthisȱ phenomenonȱhaveȱalreadyȱbeenȱobserved,ȱmainlyȱinȱGermanyȱ(Trautnerȱetȱ al.,ȱ2006),ȱwhereȱA.ȱrostrataȱwereȱfound,ȱpromptingȱforȱupȱtoȱdateȱmolecuȬ larȱ identificationȱ methodsȱ forȱ speciesȱ discriminationȱ (Maesȱ etȱ al.,ȱ 2006a).ȱ TheȱEuropeanȱeelȱhasȱbeenȱlistedȱunderȱCITES,ȱpotentiallyȱleadingȱtoȱinȬ creasedȱ importationsȱ ofȱ otherȱ eelȱ species.ȱ Suchȱ exoticȱ eelȱ introductionsȱ haveȱbeenȱaȱmajorȱproblemȱinȱAsia,ȱwhereȱEuropeanȱeelsȱwereȱintroducedȱ toȱsupplementȱJapaneseȱeelȱstocksȱ(Okamuraȱetȱal.,ȱ2002;ȱ2004).ȱ 2ȱ) Aquacultureȱgrownȱglassȱeelsȱ(grownȱfromȱglassȱeelsȱtoȱ10ȱcms)ȱareȱoftenȱ usedȱforȱstockingȱpurposes.ȱAlthoughȱatȱfirstȱsightȱnoȱsignificantȱproblemȱ isȱexpectedȱfromȱtheȱgeneticȱdiversityȱpointȱofȱviewȱ(glassȱeelsȱareȱnaturalȱ recruits),ȱ potentialȱ consequencesȱ couldȱ beȱ otherȱ thanȱ expected.ȱ Indeed,ȱ keepingȱglassȱeelsȱtooȱlongȱinȱsuchȱfacilitiesȱwillȱadaptȱthemȱtoȱaquacultureȱ conditionsȱ (suchȱ asȱ artificialȱ foodȱ andȱ temperatureȱ regimes),ȱ andȱ willȱ lowerȱtheirȱcompetitivenessȱinȱtheȱnaturalȱenvironment.ȱCurrentlyȱjuvenileȱ eelsȱareȱdeliberatelyȱexposedȱtoȱwaterȱcontaminatedȱwithȱtheȱhighlyȱviruȬ lentȱHerpesȱvirusȱanguillarumȱ(HVA)ȱinȱorderȱtoȱinduceȱaȱlimitedȱinfectionȱ which,ȱalthoughȱcausingȱsomeȱmortality,ȱwillȱautovaccinateȱtheȱfishȱpriorȱ toȱ themȱ meetingȱ theȱ infectionȱ atȱ theȱ mostȱ vulnerableȱ fastȱ growingȱ stage.ȱ Thisȱprocessȱcausesȱaȱsignificantȱdropȱinȱfoodȱintakeȱandȱgrowthȱrateȱbutȱisȱ consideredȱtheȱlesserȱevilȱbyȱtheȱindustryȱatȱpresentȱinȱtheȱabsenceȱofȱanȱ approvedȱ commercialȱ vaccine.ȱ Asȱ such,ȱ ongrownȱ eelsȱ usedȱ forȱ stockingȱ whichȱ haveȱ beenȱ rearedȱ underȱ suchȱ practicesȱ poseȱ anȱ epidemiologicalȱ EIFAC/ICES WGEEL Report 2008 79

threatȱ givenȱ thatȱ theyȱ canȱ infectȱ naturalȱ populations.ȱ Additionally,ȱ suchȱ practicesȱcreateȱaȱhighȱselectiveȱpressureȱonȱglassȱeels,ȱreducingȱtotalȱgeȬ neticȱdiversityȱandȱdirectionallyȱselectingȱatȱtheȱfunctionalȱlevelȱforȱspecificȱ diseaseȱresistanceȱgenesȱ(suchȱasȱMHC).ȱThisȱhasȱbeenȱrevealedȱtoȱhaveȱaȱ veryȱdetrimentalȱeffectȱinȱsalmonidsȱwhenȱsuchȱindividualsȱareȱreleasedȱinȱ theȱwild,ȱasȱaȱconsequenceȱofȱaȱlowerȱfitnessȱforȱnaturalȱpathogens.ȱTimingȱ ofȱ stockingȱ shouldȱ beȱ carefullyȱ consideredȱ inȱ orderȱ toȱ optimizeȱsurvival.ȱ StockingȱmaterialȱshouldȱnotȱbeȱcomposedȱofȱtheȱslowȱgrowersȱofȱaquaculȬ ture,ȱwhichȱhaveȱbeenȱrevealedȱtoȱexhibitȱaȱlowerȱfunctionalȱgeneticȱdiverȬ sityȱandȱcouldȱdemonstrateȱlowerȱsurvivalȱratesȱandȱskewedȱsexȱratios.ȱ 3ȱ)Atȱtheȱpopulationȱlevel,ȱstockingȱpracticesȱcanȱhaveȱmajorȱconsequencesȱonȱ intraspecificȱbiodiversity,ȱasȱaȱconsequenceȱofȱtheȱmixingȱofȱgeneticallyȱdifȬ ferentiatedȱ populations.ȱ Noȱ stableȱ geographicalȱ differentiationȱ hasȱ beenȱ detectedȱtoȱdateȱ(WirthȱandȱBernatchez,ȱ2001;ȱDannewitzȱetȱal.,ȱ2005;ȱMaesȱ etȱal.,ȱ2006).ȱHowever,ȱgivenȱlongȬtermȱstockingȱpracticesȱsinceȱtheȱ1950s,ȱitȱ isȱpossibleȱthatȱtheseȱmightȱcontributeȱtoȱaȱhomogenizationȱofȱpopulationsȱ asȱaȱconsequenceȱofȱmassiveȱtranslocations.ȱIndeed,ȱtheȱpresenceȱofȱonlyȱaȱ smallȱlevelȱofȱgeographicalȱgenetic ȱdifferentiationȱatȱneutralȱgeneticȱmarkȬ ersȱmayȱleadȱtoȱseriouslyȱunderestimatingȱofȱquantitativeȱandȱadaptiveȱdifȬ ferentiationȱ betweenȱ populations.ȱ Fromȱ recentȱ studiesȱ onȱ marineȱ fishȱ populationsȱweȱknowȱthatȱadaptiveȱdifferencesȱmightȱbeȱpresentȱbutȱnotȱ detectableȱwithȱtheȱcurrentȱmolecularȱmarkers.ȱIndeed,ȱapartȱfromȱanalysȬ ingȱneutralȱgeneticȱvariationȱtoȱassessȱtheȱdemographicȱindependenceȱandȱ stabilityȱofȱfisheriesȱstocks,ȱknowledgeȱofȱgeographicȱandȱtemporalȱscalesȱ ofȱadaptiveȱgeneticȱvariationȱisȱcrucialȱtoȱspeciesȱconservationȱ(Conoverȱetȱ al.,ȱ2006;ȱMaesȱandȱVolckaert,ȱ2007).ȱIfȱdistinctȱpopulationsȱexist,ȱtheȱintroȬ ductionȱofȱgeneticallyȱdifferentȱglassȱeelsȱcanȱpotentiallyȱbreakȱupȱanyȱexȬ istingȱ adaptationȱ inȱ localȱ stocksȱ andȱ haveȱ majorȱ fitnessȱ consequencesȱ onȱ lifeȬhistoryȱtraits,ȱsuchȱasȱmigrationȱdurationȱandȱtiming,ȱtemperatureȱreȬ sistanceȱ andȱ sizeȱ atȱ maturationȱ sizes.ȱ Theȱ homogenizationȱ ofȱ theseȱ traitsȱ canȱleadȱtoȱaȱdecreaseȱinȱdiversityȱandȱtheȱlossȱofȱimportantȱtraitsȱforȱsurȬ vival.ȱHowever,ȱgivenȱtheseȱconcernsȱandȱtheȱabsenceȱofȱdataȱtheȱfollowingȱ adviceȱforȱdifferentȱlevelsȱofȱnaturalȱrecruitmentȱisȱthereforeȱprecautionary.ȱ

Regionsȱwithȱnoȱrecruitment:ȱstockȱwithȱglassȱeelsȱinȱhighȱqualityȱhabitatsȱoriginatingȱ inȱifȱpossibleȱtheȱsameȱmainȱhydrographicalȱregionȱ(NorthernȱEurope,ȱWestȱAtlantic,ȱ SouthernȱEurope,ȱMediterranean).ȱ

Regionsȱ withȱ lowȱ recruitment:ȱ Preserveȱ naturalȱ recruits,ȱ whileȱ preferablyȱ stockingȱ glassȱeelsȱfromȱestuariesȱorȱneighbouringȱriverȱbasinsȱinȱhighȱqualityȱupstreamȱhabiȬ tats.ȱ

Regionsȱ withȱ highȱ recruitment:ȱ careȱ shouldȱ beȱ takenȱ notȱ toȱ overfishȱ glassȱ eelsȱ forȱ stockingȱpurposes,ȱasȱthisȱwillȱweakenȱtheȱdonorȱregionȱandȱdepleteȱtheȱriversȱfromȱ escapees.ȱ

IfȱneitherȱneutralȱnorȱadaptiveȱdifferencesȱcanȱbeȱdetectedȱinȱtheȱEuropeanȱeel,ȱstockȬ ingȱpracticesȱmayȱhaveȱaȱbeneficialȱeffect.ȱHowever,ȱtheȱquestionȱremains,ȱwhetherȱ stockedȱindividualsȱwillȱfindȱtheirȱwayȱtoȱtheȱSargassoȱSeaȱandȱultimatelyȱcontributeȱ toȱtheȱspawningȱstock.ȱTheȱmostȱimportantȱissueȱis ȱthenȱtoȱpreserveȱtheȱtotalȱgeneticȱ diversityȱtoȱallowȱadaptationȱtoȱaȱchangingȱenvironment.ȱKeepingȱtheȱhighestȱlevelȱofȱ biodiversityȱinȱphenotypicȱ(quantitative)ȱandȱgeneticȱtraitsȱisȱcrucialȱtoȱtheȱsurvivalȱofȱ theȱentireȱspecies.ȱ 80 EIFAC/ICES WGEEL Report 2008

Pathogens and parasites

Theȱoccurrenceȱofȱdiseasesȱandȱparasitesȱinȱeelsȱhasȱbeenȱrecordedȱforȱsomeȱtime.ȱUpȱ toȱnow,ȱconsequencesȱonȱtheȱabilityȱofȱeelsȱtoȱcarryȱoutȱtheirȱlongȬdistanceȱmigrationȱ andȱ reproductionȱ wereȱ unknown,ȱ althoughȱ theseȱ haveȱ beenȱ suggestedȱ asȱ potentialȱ causesȱforȱtheȱdeclineȱinȱeelȱpopulations.ȱAvailableȱinformationȱonȱtheȱintroductionȱ andȱ spreadȱ ofȱ A.ȱ crassusȱ inȱ Europeȱ illustratesȱ howȱ throughȱ liveȬtransportȱ ofȱ eels,ȱ withinȱ andȱ betweenȱ countries,ȱ andȱ throughȱ stockingȱ programmesȱ theȱ parasiteȱ hasȱ beenȱrapidlyȱdispersedȱtoȱallȱmajorȱspawnerȱproducingȱareas.ȱ

InȱtheȱproceedingsȱofȱaȱrecentȱworkshopȱheldȱinȱMontrealȱ(Canada)ȱinȱ2007,ȱtheȱriskȱ ofȱ diseaseȱ transferȱ whenȱ stockingȱ eelȱ wasȱ specificallyȱ addressedȱ (Williamsȱ andȱ Threader,ȱ 2007)ȱ becauseȱ eelȱ transfersȱ increaseȱ theȱ riskȱ ofȱ pathogenȱ introduction.ȱ Inȱ herȱ review,ȱ Symonds,ȱ 2007ȱ describedȱ severalȱ parasites,ȱ viruses,ȱ bacteriaȱ andȱ fungiȱ thatȱhaveȱbeenȱfoundȱinȱeelȱcommunitiesȱinȱNorthȱAmerica.ȱInȱEurope,ȱmanyȱstudiesȱ onȱeelȱparasitesȱandȱdiseasesȱindicateȱthatȱstockingȱandȱtransfersȱhaveȱbeenȱresponsiȬ bleȱforȱrapidȱspreadingȱofȱtheirȱfellowȱtravellersȱ(Szekely,ȱ1994;ȱVanȱGinnekenȱetȱal.,ȱ 2004;ȱEELREPȱ2005).ȱTheȱrapidȱspreadȱofȱA.ȱcrassusȱthroughoutȱEuropeȱindicatesȱthatȱ eelȱtransferȱorȱstockingȱdoneȱwithoutȱscreeningȱisȱaȱpracticeȱthatȱcanȱbeȱdetrimentalȱ forȱtheȱpopulationȱandȱaquaticȱcommunity.ȱ

InȱCanadaȱeelȱstockingȱandȱtransfersȱmustȱbeȱdoneȱunderȱȈTheȱNationalȱCodeȱonȱInȬ troductionsȱ andȱ Transfersȱ ofȱ Aquaticȱ OrganismsȈȱ toȱ avoidȱ risksȱ toȱ aquaticȱ animalȱ healthȱ fromȱ theȱ potentialȱ introductionȱ andȱ spreadȱ ofȱ pathogensȱ andȱ parasitesȱ thatȱ mightȱaccompanyȱeelsȱbeingȱmoved.ȱScreeningsȱareȱroutinelyȱdoneȱforȱelversȱbeforeȱ theirȱ stockingȱ inȱ freshȬwatersȱ locations.ȱ Screeningsȱ forȱ virusesȱ (IHNV,ȱ ISAV,ȱ IPNVȱ andȱEVH)ȱandȱA.ȱcrassusȱinȱindividualsȱpriorȱtoȱstockingȱwereȱnegativeȱsinceȱtheȱiniȬ tiationȱofȱtheȱstockingȱprogrammes,ȱfourȱyearsȱago.ȱ

Inȱ spiteȱ ofȱ warningsȱ concerningȱ virusesȱ andȱ diseasesȱ issuedȱ fromȱ WGEELȱ inȱ 2006,ȱ thereȱisȱstillȱnoȱcommonȱprotocolȱforȱparasiteȱandȱdiseaseȱscreeningȱpriorȱtoȱstocking.ȱ Eachȱ countryȱ appliesȱ itsȱ ownȱ regulationȱ andȱ screeningȱ procedureȱ forȱ stocking.ȱ Forȱ example,ȱSwedenȱpractisesȱquarantineȱforȱimportedȱglassȱeelȱpriorȱtheirȱstockingȱinȱ brackishȱandȱfreshȬwaterȱareasȱwhereasȱnoȱspecificȱproceduresȱareȱinȱplaceȱforȱotherȱ countries.ȱTableȱ5.1ȱshowsȱwhatȱisȱdoneȱforȱeachȱEuropeanȱcountryȱpriorȱtoȱglassȱeelȱ and/orȱelverȱstockingȱtoȱpreventȱtheȱintroductionȱofȱparasites,ȱvirusesȱandȱpathogens.ȱ

Itȱappearsȱthatȱfewȱcountriesȱhaveȱputȱinȱplaceȱproceduresȱtoȱpreventȱtheȱintroductionȱ andȱspreadingȱofȱparasitesȱandȱdiseasesȱwhenȱstockingȱyoungȱeels.ȱThisȱcouldȱbeȱveryȱ detrimentalȱforȱtheȱfutureȱofȱeelȱpopulationsȱsinceȱstockingȱwillȱpresumablyȱbeȱpartȱofȱ manyȱ nationalȱ Managementȱ Plans.ȱ Aȱ robustȱ protocolȱ forȱ screeningȱ stockedȱ stocksȱ shouldȱbeȱputȱinȱplaceȱasȱsoonȱasȱpossible.ȱ

Tableȱ5.1:ȱCurrentȱproceduresȱforȱstockingȱglassȱeel/youngȱeelȱtoȱEuropeanȱcountries.ȱ

SCREENING FOR PARASITES, VIRUSES COUNTRY STOCKING AND PATHOGENS QUARANTINE

Belgiumȱ Yesȱ Noȱ N0ȱ Denmarkȱ Yesȱ Yesȱ Yesȱ Estoniaȱ Yesȱ Yesȱ Noȱ Finlandȱ Yesȱ Yes/Noȱ Yesȱ Polandȱ Yesȱ Noȱȱ Franceȱ Yesȱ Noȱ Noȱ Germanyȱ Yesȱ Yes/Noȱ Noȱ EIFAC/ICES WGEEL Report 2008 81

SCREENING FOR PARASITES, VIRUSES COUNTRY STOCKING AND PATHOGENS QUARANTINE Irelandȱ Yes1ȱ Noȱ Noȱ Italyȱ NoȱȬȱ Ȭȱ Latviaȱ Yesȱ Noȱ Noȱ Lithuaniaȱ Yesȱ Noȱ Noȱ Netherlandsȱ Yesȱ Noȱ Noȱ Norwayȱ NoȱȬȱ Ȭȱ Portugalȱ NoȱȬȱ Ȭȱ Spainȱ Yesȱ YesȱȬȱ Swedenȱ Yesȱ Yesȱ Yesȱ UKȱ Yesȱ Yes*/Noȱ Noȱ

1Stockingȱrestrictedȱwithinȱtheȱsameȱwaterȱcatchment.ȱ *ȱForȱEnglandȱandȱWalesȱonly.

5.4.3 Fisheries considerations and considerations for other users

Generationȱ timesȱ ofȱ eelsȱ decreaseȱ withȱ temperatureȱ andȱ increaseȱ withȱ latitudeȱ andȱ mayȱbeȱ2–3ȱtimesȱlowerȱinȱtheȱmostȱSouthernȱpartsȱofȱtheȱdistributionȱrangeȱasȱcomȬ paredȱ toȱ theȱ Northernȱ partsȱ ofȱ Scandinavia.ȱ Growthȱ ofȱ eelsȱ variesȱ betweenȱ 14–62ȱ mm.yearȬ1ȱwithinȱitsȱdistributionȱrangeȱ(ICES,ȱ2006)ȱandȱthisȱmeansȱthatȱforȱmaleȱsilȬ verȱeelsȱofȱ37ȱcmȱitȱwillȱtakeȱthenȱ5–21ȱyearsȱtoȱreachȱthatȱsize.ȱForȱfemaleȱeelsȱofȱ67ȱ cmȱitȱwillȱtakeȱtwiceȱasȱlong,ȱwhileȱforȱlongerȱfemalesȱitȱwillȱtakeȱevenȱlonger.ȱIfȱtheȱ glassȱeelsȱwereȱstockedȱinȱ2009,ȱtheȱeffectsȱonȱsilverȱeelȱescapementȱcouldȱbeȱexpectedȱ fromȱ2014ȱ(atȱtheȱearliest)ȱtoȱapproximatelyȱ2050,ȱdependingȱpartlyȱonȱstockingȱlocaȬ tionȱandȱpartlyȱonȱsexualȱdifferentiationȱandȱeelȱgrowth.ȱThereforeȱthisȱisȱaȱmeasureȱ thatȱmightȱbeȱvaluableȱoverȱaȱlongerȱtime Ȭscale.ȱIfȱtheȱstockedȱeelsȱareȱnotȱhamperedȱ byȱanthropogenicȱfactors,ȱtheyȱcouldȱcontributeȱsignificantlyȱtoȱsilverȱeelȱescapementȱ afterȱ10ȱyearsȱorȱmore.ȱEelsȱstockedȱinȱsuitableȱhabitatsȱmayȱwellȱgrowȱfasterȱthanȱifȱ leftȱinȱsituȱand,ȱtherefore,ȱmatureȱearlierȱ(Aprahamian,ȱ1988).

5.4.3.1 Effects on recipient eel populations

Theȱ surfaceȱ areaȱ ofȱ availableȱ habitatsȱ inȱ Europeȱ isȱ estimatedȱ atȱ 5–10*106ȱ haȱ (ICES,ȱ 2005).ȱAȱpossibleȱstockingȱofȱ60ȱtonneȱ(atȱmost)ȱwhenȱwellȱspreadȱoverȱtheȱavailableȱ habitat,ȱ willȱ haveȱ noȱ significantȱ negativeȱ effectȱ onȱ theȱ growthȱ ofȱ theȱ existingȱ eelȱ populations.ȱHowever,ȱifȱhighȱstockingȱratesȱareȱappliedȱlocally,ȱthisȱwillȱbeȱdifferentȱ becauseȱofȱdensityȬdependentȱgrowthȱratesȱ(reviewedȱbyȱICES,ȱ2007).ȱ

Effectsȱonȱexistingȱpopulationsȱmayȱoccurȱwhenȱstockedȱeelsȱareȱdiseased.ȱChangeȱinȱ sexȱratiosȱ(asȱdemonstratedȱonȱLoughȱNeaghȱunderȱdifferingȱrecruitmentȱandȱstockȬ ingȱpatternsȱ(Rosellȱetȱal.,ȱ2005)),ȱinȱfavourȱofȱmales,ȱpotentiallyȱaffectingȱtheȱyearlyȱ productionȱofȱtheȱnonȬstockedȱeels.ȱEffectsȱonȱtheȱwholeȱstockȱmayȱoccurȱifȱtheȱgeȬ neticȱfitnessȱofȱtheȱstockedȱeelsȱisȱfurtherȱreduced.ȱTheȱlatterȱmightȱoccurȱwhenȱstockȬ ingȱ eelsȱ fromȱ aquacultureȱ withoutȱ additionalȱ careȱ forȱ reducingȱ possibleȱ geneticȱ effects.ȱ

5.4.3.2 Effects on the remainder of the exploited fishery

Theȱeffectsȱonȱtheȱfisheryȱdependȱlargelyȱonȱtheȱtotalȱquantityȱofȱeelsȱtoȱbeȱstocked.ȱIfȱ theȱaforementionedȱ35–60ȱtonsȱwouldȱbeȱstocked,ȱitȱhasȱaȱyieldȱpotentialȱinȱtheȱsameȱ orderȱ ofȱ magnitudeȱ asȱ theȱ eelȱ aquacultureȱ productionȱ inȱ Europeȱ orȱ theȱ currentȱ eelȱ landingsȱinȱEurope.ȱThisȱpotentialȱwouldȱbeȱfullyȱrealizedȱafterȱoneȱgenerationȱtime.ȱ Ifȱnotȱfishedȱatȱall,ȱthisȱwouldȱincreaseȱtheȱproductionȱofȱsilverȱeelsȱ(ICES,ȱ2006).ȱTheȱ 82 EIFAC/ICES WGEEL Report 2008

quantityȱofȱ35–60ȱtonsȱofȱglassȱeelsȱisȱmoreȱorȱlessȱequalȱto,ȱorȱmoreȱthanȱtheȱhistoricalȱ maximumȱofȱstockingȱratesȱ(40ȱtons).ȱ

5.4.3.3 Effects in mixed-stock fisheries

ThereȱareȱnoȱadditionalȱeffectsȱexpectedȱinȱmixedȬstockȱfisheries.ȱ

5.4.4 Implementation constraints

5.4.4.1 Introduction

Cowx,ȱ1999ȱrecognizedȱaȱnumberȱofȱpotentialȱconstraintsȱassociatedȱwithȱanyȱstockȬ ingȱ programme,ȱ andȱ posedȱ theseȱ asȱ aȱ seriesȱ ofȱ checksȱ forȱ managers,ȱ regardingȱ theȱ availabilityȱof:ȱ

x sufficientȱquantityȱandȱqualityȱofȱfish;ȱ x suitableȱmethodsȱofȱtheȱtransportationȱandȱexpertise;ȱ x sufficientȱfunds;ȱand,ȱ x haveȱtheȱaccessȱrightsȱbeenȱdefined.ȱ

Theȱ issuesȱ ofȱ fundingȱ forȱ stockingȱ programmes,ȱ andȱ accessȱ toȱ donorȱ andȱ recipientȱ watersȱ areȱ politicalȱ ratherȱ thanȱ scientificȱ issues,ȱ andȱ soȱ weȱ willȱ notȱ considerȱ themȱ here.ȱTheȱfirstȱtwoȱbulletȱpointsȱhaveȱbeenȱconsideredȱpreviouslyȱbyȱICESȱ(2006,ȱ2007)ȱ andȱothersȱ(WilliamsȱandȱAprahamian,ȱunpublished;ȱSymonds,ȱ2007;ȱMontreal,ȱ2008).ȱ Here,ȱweȱsummarizeȱtheȱoutcomesȱandȱupdateȱsupportingȱmaterialsȱwhereȱtheyȱhaveȱ becomeȱavailableȱsinceȱtheȱ2007ȱreportȱwasȱcompiled.ȱ

5.4.4.2 Are sufficient quantities of eel available for stocking, at the local level?

Atȱtheȱlocalȱorȱcatchmentȱlevel,ȱthereȱmayȱbeȱaȱsurplusȱstockȱofȱglassȱeel,ȱarisingȱasȱaȱ resultȱ ofȱ densityȬdependentȱ mortalityȱ beingȱ higherȱ inȱ theȱ absenceȱ ofȱ fishingȱ (ICES,ȱ 2006).ȱTheȱprimeȱassumptionȱforȱaȱlocalȱsurplusȱofȱeelȱisȱthatȱremovingȱtheȱeelȱhasȱnoȱ impactȱonȱtheȱdonorȱpopulationȱ(onȱsilverȱeelȱoutput).ȱThatȱis,ȱreductionsȱinȱdensityȬ dependentȱ mortalityȱ(orȱ otherȱ limitingȱeffectsȱsuchȱasȱ growthȱ ratesȱ andȱ genderȱ deȬ termination)ȱ resultȱ inȱ enhancedȱ productionȱ ofȱ silverȱ eelȱ inȱ theȱ stockedȱ populationȱ exceedingȱtheȱputativeȱlossȱ(fromȱfishingȱelvers)ȱinȱproductionȱfromȱtheȱdonorȱpopuȬ lation.ȱ

LobónȬCerviáȱandȱIglesias,ȱ2008ȱstudiedȱlongȬtermȱvariationsȱinȱtheȱdensityȱofȱeelsȱinȱ theȱ Rioȱ Esvaȱ (northwesternȱ Spain)ȱ atȱ anȱ estuaryȱ siteȱ andȱ atȱ nineȱ sitesȱ distributedȱ amongȱ threeȱ tributariesȱ (1986–2006).ȱ Mortalityȱ ratesȱ calculatedȱ forȱ ageȱ cohortsȱ reȬ vealedȱaȱconsistentȱpositiveȱtrend,ȱwithȱ53.3%ȱofȱtheȱvariationȱinȱcohortȱmortalityȱrateȱ explainedȱbyȱvariationȱinȱglassȱeelȱabundance.ȱNote,ȱhowever,ȱthatȱthisȱpopulationȱisȱ characterizedȱbyȱfastȱgrowingȱandȱearlyȱmaturingȱeels,ȱalmostȱallȱofȱwhichȱbecomeȱ male.

AlthoughȱtheȱRegulationȱ(1100/2007)ȱdoesȱnotȱspecificallyȱrequireȱthatȱeelȱforȱstockingȱ areȱsourcedȱonlyȱfromȱcatchmentsȱwhereȱsuchȱa ȱsurplusȱexists,ȱitȱisȱprudentȱtoȱfocusȱ collectionȱ onȱ suchȱ catchments.ȱ However,ȱ previousȱ ICESȱ reportsȱ andȱ otherȱ reviewsȱ haveȱprovidedȱlittleȱguidanceȱonȱhowȱmanagersȱcouldȱassessȱwhetherȱaȱsurplusȱexȬ ists,ȱandȱthereafter,ȱquantificationȱofȱthisȱsurplus.

Theȱdirectȱmeansȱforȱthisȱassessmentȱisȱtoȱquantifyȱtheȱsizeȱofȱtheȱdonorȱpopulation,ȱ typicallyȱglassȱeel,ȱandȱcompareȱthisȱwithȱestimatesȱofȱtheȱamountȱofȱsettledȱelverȱreȬ quiredȱtoȱproduceȱtheȱtargetȱsilverȱeelȱoutput.ȱTheȱEUȱInterRegȱprogramme,ȱIndicang,ȱ consideredȱ methodsȱ forȱ theȱ absoluteȱ quantificationȱ ofȱ glassȱ eelȱ inȱ estuaries,ȱ recomȬ mendingȱfluxȱquantificationȱ(filtration)ȱorȱmarkȱrecaptureȱexercises,ȱbutȱnotingȱthatȱ EIFAC/ICES WGEEL Report 2008 83

theseȱmethodsȱareȱdifficultȱinȱlargeȱandȱstratifiedȱestuariesȱ(Feunteun,ȱpers.ȱcomm.).ȱ Alternatively,ȱanȱindirectȱassessmentȱcanȱbeȱmadeȱbasedȱonȱstudyingȱtheȱassociatedȱ yellowȱeelȱpopulationȱunderȱconditionsȱofȱvaryingȱglassȱeelȱexploitationȱtoȱestablishȱ lackȱofȱimpactȱofȱsaidȱfishery.ȱForȱexample,ȱaȱglassȱeelȱfisheryȱinȱtheȱSevernȱestuary,ȱ England,ȱ doesȱ notȱ yetȱ seemȱ toȱ haveȱ hadȱ anyȱ measurableȱ negativeȱ impactȱ onȱ upȬ streamȱstocksȱofȱeelȱ(SeeȱUKȱcountryȱreportȱ2006).ȱ

ICES,ȱ2006ȱdiscussedȱtheȱconceptȱofȱtheȱcarryingȱcapacityȱofȱeelȱinȱrelationȱtoȱdecidingȱ whetherȱ toȱ stockȱ eelȱ inȱ aȱ waterȱ body,ȱ butȱ itȱ shouldȱ beȱ consideredȱ alsoȱ inȱ decidingȱ whetherȱaȱpotentialȱdonorȱwaterȱbodyȱcanȱsustainȱtheȱlossȱofȱeelsȱtoȱbeȱstockedȱelseȬ where.ȱ

Thereȱareȱtwoȱconsiderations;ȱimmediateȱeffectsȱofȱlossȱtoȱtheȱestuary,ȱandȱsubsequentȱ effectsȱtoȱtheȱyellowȱeelȱpopulationȱandȱsilverȱeelȱoutputȱfromȱtheȱriverȱbasin.ȱ

AȱmethodȱofȱcalculatingȱcarryingȱcapacityȱofȱaȱriverȱorȱlakeȱforȱeelȱhasȱnotȱbeenȱidenȬ tified;ȱinȱpartȱasȱaȱconsequenceȱofȱtheȱdifficultyȱinȱassessingȱdensityȱand/orȱbiomassȱofȱ eelȱaccuratelyȱinȱaȱgivenȱbodyȱofȱwaterȱ(WilliamsȱandȱAprahamian,ȱ2004).ȱWhetherȱaȱ siteȱisȱatȱcarryingȱcapacity ȱisȱlinkedȱtoȱeaseȱofȱaccessȱforȱcolonizationȱandȱtheȱproducȬ tivityȱofȱtheȱwater.ȱ

InȱtributariesȱofȱtheȱlowerȱSevern,ȱAprahamian,ȱ2000ȱfoundȱeelȱdensityȱrangedȱfromȱ 0.12Ȭ1.14ȱmȬ2ȱandȱbiomassȱfromȱ2.56–25.24ȱgmȬ2.ȱTheȱabsenceȱofȱanyȱrelationshipȱbeȬ tweenȱgrowthȱandȱeitherȱdensityȱorȱbiomass,ȱsuggestsȱthatȱtheȱsitesȱwereȱlimitedȱbyȱ theirȱproductivityȱandȱmayȱindicateȱthatȱtheyȱwereȱcloseȱtoȱorȱatȱtheirȱcarryingȱcapacȬ ity,ȱdefinedȱasȱtheȱmaximumȱdensityȱorȱbiomassȱthatȱtheȱhabitatȱcanȱsustainȱunderȱ averageȱconditions.ȱ

InȱtheȱsouthernȱpartȱofȱtheirȱrangeȱtheȱcarryingȱcapacityȱisȱlikelyȱtoȱbeȱhigherȱasȱaȱconȬ sequenceȱofȱhigherȱtemperaturesȱandȱproductivityȱresultingȱinȱaȱshorterȱgenerationȱ time,ȱevenȱifȱextremelyȱvariableȱamongȱsites.ȱNoȱrecentȱevaluationsȱareȱavailable,ȱbutȱ givenȱtheȱpotentialȱforȱspawnerȱproductionȱofȱthoseȱenvironments,ȱtheȱenhancementȱ ofȱevaluationȱstudiesȱonȱthisȱaspectȱisȱrecommended.ȱGreaterȱimportanceȱshouldȱbeȱ givenȱtoȱbiomassȱwhenȱtryingȱtoȱassessȱwhetherȱaȱsiteȱisȱorȱisȱnotȱatȱcarryingȱcapacity.ȱ Thisȱisȱbecauseȱthereȱisȱaȱsmallerȱvariationȱinȱbiomassȱwhenȱcomparedȱtoȱdensityȱbothȱ withinȱandȱamongȱriverȱsystemsȱ(Aprahamian,ȱ1986)ȱandȱitȱisȱmoreȱrelatedȱtoȱcarryȬ ingȱcapacityȱ(Knightsȱetȱal.,ȱ2001).ȱ

Theȱ analysisȱ ofȱ eelȱ fisheryȱ ‘outputs’ȱ fromȱ L.ȱ Neaghȱ inȱ relationȱ toȱ glassȱ eelȱ stockedȱ (ICESȱ 2007)ȱ suggestsȱ aȱ densityȬdependentȱ relationshipȱ withȱ aȱ negativeȱ exponentialȱ betweenȱinputȱstockȱandȱeventualȱoutput.ȱThatȱis,ȱoutputsȱareȱmaximalȱforȱinputsȱinȱ theȱrangeȱofȱ150ȱtoȱ200ȱglassȱeelȱperȱhectare.ȱ

Similarly,ȱKnöscheȱetȱal.,ȱ2004ȱgiveȱaȱformula,ȱhowȱtoȱestimateȱtheȱrecaptureȱrateȱinȱ theȱfisheryȱafterȱstockingȱforȱaȱrangeȱofȱcommonȱstockingȱdensitiesȱforȱGermanȱwaȬ tersȱ(50–00 ȱglassȱeelȱequivalentsȱperȱhectare).ȱ

Recaptureȱrateȱ(%)ȱ=ȱ611ȱ*ȱstockingȱdensityȱȬ0.81ȱ

Thus,ȱatȱaȱstockingȱdensityȱofȱ50ȱglassȱeels/ha,ȱthisȱwouldȱresultȱinȱaȱrecaptureȱrateȱofȱ 26%,ȱwhereasȱatȱ500ȱglassȱeels/haȱitȱwouldȱdecreaseȱtoȱ4%.ȱ

However,ȱ theȱ generalȱ lackȱ ofȱ informationȱ onȱ carryingȱ capacityȱ inȱ eelȱ populationsȱ notedȱbyȱICESȱ2006ȱcontinuesȱtoȱthisȱday.ȱ

AȱmethodȱofȱcalculatingȱcarryingȱcapacityȱofȱaȱriverȱorȱlakeȱforȱeelȱhasȱnotȱbeenȱidenȬ tified,ȱinȱpartȱasȱaȱconsequenceȱofȱtheȱdifficultyȱinȱassessingȱdensityȱand/orȱbiomassȱofȱ 84 EIFAC/ICES WGEEL Report 2008

eelȱaccuratelyȱinȱaȱgivenȱbodyȱofȱwaterȱ(WilliamsȱandȱAprahamian,ȱ2004).ȱWhetherȱaȱ siteȱisȱatȱcarryingȱcapacityȱisȱlinkedȱtoȱeaseȱofȱaccessȱforȱcolonizationȱandȱtheȱproducȬ tivityȱofȱtheȱwaterȱandȱrecruitment.ȱHowever,ȱtheȱgeneralȱlackȱofȱinformationȱonȱcarȬ ryingȱcapacityȱinȱeelȱpopulationsȱnotedȱbyȱICESȱ2006ȱcontinuesȱtoȱthisȱday.ȱTheȱmostȱ likelyȱsourcesȱofȱeelȱforȱstockingȱ(andȱseedingȱongrowingȱfacilities)ȱareȱglassȱeelȱfishȬ eriesȱinȱestuaries,ȱandȱtrapsȱwhereȱupstreamȱmigratingȱeelȱareȱconcentrated,ȱsuchȱasȱ eelȱpassesȱonȱweirsȱandȱdams.ȱInȱconsideringȱtheȱeffectsȱofȱremovingȱglassȱeelȱfromȱ estuariesȱandȱlowerȱreachesȱofȱrivers,ȱtheȱcarryingȱcapacityȱofȱtheȱestuaryȱmayȱbeȱimȬ portant.ȱ Thereȱ is,ȱ however,ȱ noȱ informationȱ currentlyȱ onȱ this,ȱ andȱ itȱ isȱ anȱ areaȱ thatȱ shouldȱbeȱaddressed.ȱAȱstudyȱgroupȱtoȱaddressȱthisȱareaȱhasȱbeenȱproposedȱtoȱtheȱ DiadromousȱFishȱCommitteeȱ2008.ȱ

5.4.4.3 Potential indirect impacts on donor stock

ICES,ȱ 2006ȱ notedȱ thatȱ underȱ theȱ currentȱ situationȱ ofȱ criticallyȱ lowȱ stockȱ levels,ȱ reȬ movalȱofȱglassȱeelȱfromȱanyȱsiteȱtoȱstockȱanotherȱshouldȱonlyȱbeȱdoneȱwithȱaȱfullȱasȬ sessmentȱofȱtheȱeffectȱonȱrecruitmentȱintoȱtheȱgrowingȱareasȱdependentȱonȱthatȱdonorȱ site.ȱInȱadditionȱtoȱtheȱdirectȱeffectsȱonȱtheȱsizeȱofȱtheȱlocalȱpopulation,ȱthereȱareȱtwoȱ otherȱpotentialȱrisksȱwithȱremovingȱglassȱeelȱfromȱtheȱdonorȱsite,ȱaȱreductionȱofȱdisȬ persalȱofȱjuvenileȱeelȱtoȱupstreamȱhabitats,ȱandȱpossibleȱalterationsȱtoȱsexȱratioȱofȱsilȬ verȱeel.ȱ

Upstreamȱmigrationȱmayȱbeȱdrivenȱby ȱintraspecificȱcompetitionȱandȱhigherȱdensitiesȱ downstream.ȱForȱexample,ȱtheȱconstructionȱofȱanȱestuarineȱdamȱonȱtheȱVilaineȱpreȬ ventedȱrecruitmentȱofȱeelsȱforȱ25ȱyears,ȱbutȱtheȱinstallationȱofȱanȱeelȱpassȱresultedȱinȱaȱ densityȬdependentȱmigrationȱbehaviour;ȱ1+ȱgroupsȱbeingȱforcedȱintoȱtheȱperipheryȱofȱ theȱhighȬdensityaȱare ȱ(aboutȱ0.8ȱeelsȱmȬ2),ȱwhichȱextendedȱfurtherȱupstreamȱinȱsuccesȬ siveȱyearsȱ(Feunteun,ȱ2002).ȱNote,ȱhoweverȱthatȱthisȱ“wave”ȱtypeȱmigration,ȱisȱinȱconȬ trastȱ toȱ thatȱ reportedȱ byȱ Ibbotsonȱ etȱ al.,ȱ 2002ȱ forȱ eelsȱ colonizingȱ theȱ Riverȱ Severnȱ whereȱ upstreamȱ migrationȱ wasȱ mainlyȱ throughȱ diffusion.ȱ Removalȱ ofȱ stockȱ fromȱ downstreamȱareasȱmayȱreduceȱtheȱpropensityȱforȱcolonizationȱofȱupstreamȱareas.ȱ

Althoughȱ theȱ physiologicalȱ mechanismsȱ forȱ genderȱ differentiationȱ inȱ eelȱ (reviewedȱ byȱDaveyȱandȱJellyman,ȱ2005)ȱareȱstillȱunclear,ȱevidenceȱsupportsȱtheȱconceptȱthatȱitȱisȱ densityȱdriven.ȱThereȱisȱaȱriskȱthatȱremovingȱglassȱeelȱfromȱestuariesȱwillȱaffectȱsubȬ sequentȱ genderȱ differentiationȱ andȱ sexȱ ratioȱ ofȱ yellowȱ eelȱ (andȱ henceȱ silverȱ eel).ȱ Transportingȱundifferentiatedȱeelsȱfromȱhighȱtoȱrelativelyȱlowȱdensityȱhabitatsȱmayȱ wellȱ influenceȱ ultimateȱ sexȱ ratioȱ ofȱ theȱ silverȱ eelȱ output,ȱ andȱ byȱ association,ȱ theȱ weightȱofȱoutputȱandȱdistributionȱacrossȱtime.ȱ

5.4.4.4 Issues of ownership

Inȱconsideringȱwhereȱtoȱstock,ȱmanagersȱmustȱevaluateȱtheȱsubsequentȱpotentialȱexȬ ploitationȱandȱotherȱmortalitiesȱofȱtheȱeel,ȱe.g.ȱfisheries,ȱturbines,ȱetc.ȱThereȱmayȱbeȱaȱ numberȱ ofȱ usersȱ whoȱ potentiallyȱ benefitȱ fromȱ theȱ stocking,ȱ andȱ therefore,ȱ theyȱ shouldȱallȱcontributeȱtoȱfundingȱofȱtheȱstocking.ȱ

5.5 Artificial reproduction of eel

5.5.1 Introduction

SummaryȱofȱtheȱmainȱfindingsȱrelevantȱtoȱWGEELȱfromȱtheȱEuropeanȱAquacultureȱSoȬ cietyȱThematicȱGroupȱWorkshopȱonȱEuropeanȱEelȱReproductionȱ(Octoberȱ24th,ȱ2007,ȱIstanȬ bul).ȱ

Givenȱtheȱcomplexȱnatureȱofȱtheȱeelȱlifeȱcycleȱandȱthatȱmaturationȱoccursȱduringȱtheȱ oceanicȱphaseȱthereȱisȱveryȱlittleȱinformationȱonȱnaturalȱmaturationȱandȱreproduction.ȱ EIFAC/ICES WGEEL Report 2008 85

Consequentlyȱmuchȱofȱthisȱworkȱisȱderivedȱfromȱlaboratoryȱstudiesȱwhichȱexamineȱ theȱenvironmentalȱeffects,ȱendocrineȱcontrolȱandȱartificialȱreproductiveȱtechniquesȱonȱ theȱproductionȱofȱlarvalȱEuropeanȱeel.ȱDetailsȱofȱabstractsȱonȱthisȱworkȱcanȱbeȱfoundȱ atȱhttp://www.easonline.org.ȱ

Theȱonsetȱofȱsexualȱdifferentiationȱinȱeels:ȱ

Studiesȱ fromȱ Israelȱ intoȱ theȱ hormonalȱ developmentȱ inȱ youngȱ farmedȱ eelsȱ <25ȱ cmsȱ foundȱ aȱ differenceȱ inȱ theȱ hormonesȱ releasedȱ fromȱ theȱ pituitaryȱ glandȱ dependingȱ uponȱtheȱdensityȱofȱeelsȱheldȱinȱtanks.ȱThoseȱwithȱfewerȱeelsȱinȱthem,ȱdevelopedȱintoȱ femaleȱ eelsȱ associatedȱ withȱ theȱ hormoneȱ releaseȱ ofȱ theȱ femaleȱ hormoneȱ estradiol,ȱ whileȱthoseȱinȱhigherȱdensitiesȱbecameȱmaleȱassociatedȱwithȱtheȱreleaseȱofȱtheȱmaleȱ hormoneȱ12ȱKetoȬtestosterone.ȱ

5.5.2 Silver eels

SeveralȱstudiesȱpresentedȱevidenceȱthatȱsilverȱeelsȱleavingȱcontinentalȱEuropeȱshouldȱ beȱconsideredȱasȱbeingȱinȱaȱpreȬpubertalȱstateȱgivenȱthatȱswimmingȱappearsȱtoȱbeȱaȱ strongȱ naturalȱ triggerȱ forȱ theȱ developmentȱ ofȱ advancedȱ maturation.ȱ Duringȱ theȱ swimmingȱphaseȱlipidȱstoresȱinȱtheȱeelȱareȱutilizedȱforȱtheȱproductionȱofȱenergyȱtoȱ fuelȱtheirȱmigrationȱandȱtoȱproduceȱgametesȱthroughȱaȱvarietyȱofȱhormonallyȱinducedȱ metabolicȱpathways.ȱResearchȱintoȱtheȱthermodynamicȱinfluenceȱofȱhydrostaticȱpresȬ sureȱonȱswimmingȱabilityȱfoundȱthatȱtheȱmetabolismȱofȱtheȱeel’sȱfatȱstoresȱwasȱmuchȱ moreȱefficientȱatȱdepthȱthusȱoptimizingȱtheirȱenergyȱexpenditureȱduringȱmigration.ȱ Onceȱ theyȱ haveȱ arrivedȱ atȱ theȱ spawningȱ groundsȱ severalȱ studiesȱ intoȱ theȱ olfactoryȱ capabilitiesȱofȱsilverȱeelsȱandȱtheirȱreactionsȱtoȱspecificȱeelȱodoursȱsuggestedȱthatȱolȬ factionȱmaybeȱcrucialȱtoȱsynchronizingȱfinalȱmaturationȱinȱbothȱsexes.ȱ

5.5.3 Embryo and larval development

Theȱnaturalȱdevelopmentȱofȱembryosȱappearsȱtoȱbeȱinfluencedȱbyȱhydrostaticȱeffectsȱ (thatȱhadȱnotȱbeenȱusedȱpreviouslyȱduringȱartificialȱattemptsȱatȱfertilization)ȱwhichȱ induceȱaȱslowerȱeggȱcleavageȱrateȱandȱthusȱembryoȱdevelopmentȱperiod.ȱIt’sȱlikelyȱ thatȱ thisȱ mayȱ beȱ causedȱ byȱ theȱ pressureȱ influenceȱ onȱ thermodynamicsȱ andȱ orȱ meȬ chanicalȱstressȱonȱeggȱmembranesȱandȱwaterȱtransferȱthroughȱthemȱatȱtheseȱdepths.ȱ

Despiteȱ manyȱ previousȱ attemptsȱ toȱ artificiallyȱ breedȱ Europeanȱ eelȱ theȱ hatchingȱ ofȱ larvaeȱ hasȱ onlyȱ beenȱ achievedȱ onȱ aȱ fewȱ occasionsȱ withȱ aȱ maximalȱ larvalȱlifeȱ ofȱ 3.5ȱ days.ȱTheȱmainȱobstructionȱhasȱbeenȱtheȱintricateȱhormonalȱcontrolȱmechanismsȱthatȱ inhibitȱgonadalȱmaturationȱatȱtheȱonsetȱofȱpuberty.ȱRepeatedȱhormonalȱtreatmentsȱtoȱ produceȱgametesȱhaveȱbeenȱsuccessfullyȱappliedȱtoȱproduceȱviableȱeggsȱandȱlarvaeȱofȱ theȱ Japaneseȱeel.ȱ Similarȱmethodsȱ haveȱ beenȱappliedȱ toȱ theȱ Europeanȱ eel,ȱ butȱ defiȬ cienciesȱ inȱ genitorȱ qualityȱ causingȱ fertilizationȱ failureȱ had ȱ hamperedȱ theȱ abilityȱ toȱ produceȱlarvaeȱinȱtheȱpast.ȱInvestigationsȱintoȱtheȱfailureȱfoundȱthatȱanȱessentialȱfattyȱ acidȱwasȱmissingȱfromȱtheȱfeedȱgivenȱtoȱtheȱbroodstockȱwhichȱwhenȱincludedȱproȬ ducedȱfertileȱeggs.ȱMassȱhatchingsȱfromȱtheseȱeggsȱhaveȱbeenȱachievedȱandȱtheȱlarvaeȱ wereȱfullyȱdevelopedȱandyȱread ȱtoȱfeedȱ12ȱdaysȱpostȬhatching.ȱHoweverȱfurtherȱdeȬ velopmentȱ ofȱ theȱ larvaeȱ pastȱ thisȱ stageȱ failedȱ asȱ aȱ suitableȱ feedȱ hasȱ yetȱ toȱ beȱ found/developed.ȱ

5.5.4 Artificial reproduction techniques

Theȱ hormonalȱ inductionȱ ofȱ maturationȱ isȱ aȱ fundamentalȱ requirementȱ forȱ artificialȱ reproductionȱbutȱthisȱpresentsȱdifficultiesȱinȱtermsȱofȱsynchronizingȱtheȱdevelopmentȱ ofȱmalesȱandȱfemales.ȱToȱaidȱthisȱcryopreservationȱtechniquesȱhaveȱnowȱbeenȱdevelȬ opedȱforȱeelȱspermȱwhichȱyieldedȱviableȱeelȱspermȱseveralȱmonthsȱafterȱdeepȱfreezeȱ 86 EIFAC/ICES WGEEL Report 2008

storage.ȱPriorȱtoȱstorageȱtheȱhormonalȱinductionȱofȱtheȱmalesȱyieldedȱspermȱafterȱfourȱ weeksȱtheȱqualityȱandȱquantityȱofȱwhichȱincreasedȱupȱtoȱeightȱweeksȱafterȱinduction.ȱ Developmentsȱinȱtheȱmaturationȱofȱfemalesȱhaveȱfoundȱthatȱlowȱinitialȱtemperaturesȱ increaseȱ theȱ sensitivityȱ ofȱ theȱ femaleȱ andȱ thatȱ temperaturesȱ <17°Cȱ duringȱ gonadalȱ maturationȱproducedȱbetterȱresults.ȱ

5.5.5 The Japanese Experience

Japaneseȱ glassȱ eelȱ wereȱ successfullyȱ producedȱ inȱ captivityȱ inȱ 2005ȱ (Kagawaȱ etȱ al.,ȱ 2005),ȱandȱsinceȱthenȱthisȱworkȱhasȱprogressedȱtoȱproduceȱhybridȱlarvaeȱofȱEuropeanȱ (male)ȱandȱJapaneseȱeelȱ(female).ȱTheȱsuccessȱofȱthisȱworkȱhasȱreliedȱheavilyȱuponȱtheȱ productionȱofȱaȱsuitableȱfeedȱforȱtheȱlarvalȱstage,ȱdetailsȱofȱwhichȱareȱcurrentlyȱconȬ tainedȱinȱaȱJapaneseȱGovernmentȱregisteredȱpatent.ȱ

5.6 Conclusions for Chapter 5: Stocking and aquaculture

5.6.1 Potential benefit of stocking to regenerate the stock

Atȱ present,ȱ itȱ isȱ estimatedȱ thatȱ aroundȱ 7.5ȱ toȱ 15%ȱ ofȱ theȱ glassȱ eelȱ catchȱ isȱ usedȱ forȱ stocking,ȱeitherȱdirectlyȱorȱasȱonȬgrownȱeels.ȱEstimatesȱsuggestȱanȱinsufficientȱsupplyȱ ofȱglassȱeelȱfromȱtheȱtotalȱfisheryȱforȱstockingȱtoȱfullȱcapacityȱatȱtheȱEuropeanȱlevel.ȱ Nevertheless,ȱtheȱRegulationȱ1100/2007ȱrequiresȱthatȱ35%,ȱrisingȱtoȱ60%,ȱofȱglassȱeelȱ catchesȱ areȱ madeȱ availableȱ forȱ stockingȱ toȱ enhanceȱ theȱ stock.ȱ Ifȱ theseȱ percentagesȱ wereȱappliedȱtoȱrecentȱannualȱcatchesȱofȱglassȱeel,ȱtheȱpotentialȱlifetimeȱeffectȱofȱthisȱ increasedȱlevelȱofȱstocking,ȱinȱtheȱabsenceȱofȱanthropogenicȱmortalities,ȱcouldȱbeȱinȱ theȱsameȱorderȱofȱmagnitudeȱasȱcurrentȱfisheriesȱorȱeelȱculture.ȱHowever,ȱthereȱisȱaȱ continuingȱandȱurgentȱrequirementȱforȱrobustȱevidenceȱofȱtheȱextentȱtoȱwhichȱstockȬ ingȱandȱtransfersȱonȱlocal,ȱnationalȱandȱinternationalȱscalesȱcanȱincreaseȱsilverȱeelȱesȬ capementȱandȱspawnerȱbiomass.ȱ

Theȱgeneralȱlackȱofȱ informationȱonȱcarryingȱcapacityȱinȱeelȱpopulationsȱnotedȱbyȱICESȱ 2006ȱisȱstillȱanȱissueȱhamperingȱmanagementȱofȱeel.ȱ

5.6.2 Identifying local surplus

Itȱ isȱ anticipatedȱ thatȱ assessmentsȱ conductedȱ forȱ EMPsȱ willȱ decideȱ whetherȱ orȱ notȱ thereȱisȱaȱlocalȱsupplyȱofȱeelȱsufficientȱtoȱmeetȱdemandsȱforȱstockingȱ(eitherȱwithinȱ catchment,ȱRBD,ȱnationȱorȱelsewhereȱinȱEurope).ȱHowever,ȱthereȱisȱaȱlimitedȱunderȬ standingȱonȱmethodsȱbyȱwhichȱtoȱmakeȱassessmentsȱofȱaȱlocalȱsurplusȱonȱaȱquantitaȬ tive,ȱbiologicalȱbasis.ȱ

5.6.3 Post-evaluation of the net benefit of stocking

TheȱassessmentȱpostȬevaluationȱofȱtheȱcontributionȱofȱstockingȱtoȱsilverȱeelȱproducȬ tionȱ isȱ stillȱ hinderedȱ byȱ theȱ limitedȱ quantitativeȱ informationȱ availableȱ onȱ surȬ vival/mortalityȱ ratesȱ (stageȱ specificȱ andȱ glassȱ eelȱ toȱ silverȱ eel),ȱ bothȱ forȱ stockedȱ eelȱ andȱwild/naturalȱeelȱforȱcomparativeȱpurposes,ȱforȱhabitatsȱrepresentingȱtheȱvarietyȱ availableȱacrossȱEurope,ȱandȱespeciallyȱforȱstockingȱinȱrivers.ȱ

5.6.4 Risks of stocking

Itȱ appearsȱ thatȱ fewȱ countriesȱ operateȱ proceduresȱ toȱ preventȱ theȱ introductionȱ andȱ spreadingȱofȱparasitesȱandȱdiseasesȱwhenȱstockingȱyoungȱeelsȱandȱthisȱcouldȱbeȱdetȬ rimentalȱforȱtheȱfutureȱofȱeelȱpopulationsȱsinceȱstockingȱwillȱpresumablyȱbeȱpartȱofȱ manyȱnationalȱManagementȱPlans.ȱTheȱrisksȱremainȱofȱdiseaseȱandȱparasiteȱtransferȱ viaȱstockedȱmaterial,ȱpotentiallyȱbothȱfromȱtheȱ‘wild’ȱandȱonȬgrownȱinȱaquaculture.ȱ Forȱ example,ȱ theȱ practiceȱ ofȱ aquacultureȱ inȱ termsȱ ofȱ viralȱ inoculationsȱ needsȱ toȱ beȱ EIFAC/ICES WGEEL Report 2008 87

addressed.ȱAȱrobustȱprotocolȱforȱscreeningȱstockedȱstocksȱshouldȱbeȱputȱinȱplaceȱasȱ soonȱasȱpossible.ȱ

Newȱtechniquesȱareȱcurrentlyȱusedȱforȱgeneticȱanalysesȱofȱtheȱeelȱstockȱandȱresultsȱ areȱexpectedȱinȱaȱfewȱyears.ȱTheseȱresultsȱmayȱpromptȱaȱreȬassessmentȱofȱtheȱpotenȬ tialȱrisksȱassociatedȱwithȱstocking.ȱ

Thereȱisȱaȱclearȱneedȱforȱassuranceȱthatȱdonorȱpopulationsȱareȱnotȱimpairedȱbyȱtheȱ removalȱofȱglassȱeel.ȱNotwithstandingȱtheȱpotentialȱrisksȱtoȱtheȱdonorȱpopulation,ȱitȱisȱ anticipatedȱthatȱassessmentsȱconductedȱforȱEMPsȱwillȱdetermineȱwhetherȱorȱnotȱthereȱ isȱaȱlocalȱsupplyȱofȱeelȱsufficientȱtoȱ meetȱdemandsȱforȱstockingȱ(eitherȱwithinȱcatchȬ ment,ȱRBD,ȱnationȱorȱelsewhereȱinȱEurope).ȱ

5.6.5 Aquaculture/on-growing to support stocking for enhancement

SpawnerȱqualityȱinȱtermsȱofȱlevelsȱandȱcompositionȱofȱlipidsȱandȱcontaminantsȱapȬ pearsȱ toȱ beȱ aȱ keyȱ issueȱ forȱ theȱ successȱ ofȱ bothȱ naturalȱ andȱ artificialȱ reproduction.ȱ GivenȱtheȱfutureȱrequirementsȱforȱstockingȱglassȱeelȱorȱdecidingȱtoȱstockȱonȬgrownȱ eel,ȱtheȱimplicationsȱofȱtheȱfindingsȱonȱhormonalȱreleaseȱandȱsubsequentȱgenderȱdeȬ velopmentȱdependingȱuponȱstockingȱdensitiesȱmustȱbeȱconsidered.ȱ

Spawnerȱqualityȱinȱtermsȱofȱlipidȱlevelsȱandȱcontaminantsȱappearsȱtoȱbeȱaȱkeyȱissueȱ forȱtheȱsuccessȱofȱbothȱnaturalȱandȱartificialȱreproduction.ȱ

5.7 Recommendations

5.7.1 Methods to support the basis of stocking for enhancement purposes

TheȱWGȱrecommendsȱthatȱdevelopingȱmethodsȱtoȱmakeȱassessmentsȱofȱlocalȱsurplusȱ ofȱstockingȱmaterialȱonȱaȱquantitative,ȱbiologicalȱbasisȱisȱaȱpriorityȱforȱresearchȱinȱtheȱ nearȱ future.ȱ Dataȱ toȱ postȬevaluateȱ theȱ relativeȱ contributionȱ ofȱ stockingȱ toȱ silverȱ eelȱ productionȱcanȱonlyȱbeȱsuppliedȱbyȱexperimentalȱstudies,ȱandȱalthoughȱacknowledgȬ ingȱthatȱsomeȱstudiesȱareȱongoing,ȱweȱrecommendȱconcertedȱactionȱtoȱaddressȱthisȱ area,ȱespeciallyȱwithȱregardȱtoȱstockingȱinȱrivers,ȱandȱtheȱrelativeȱperformanceȱandȱ yieldȬperȬrecruitȱofȱstockedȱculturedȱeelsȱcomparedȱwithȱglassȱeels.ȱ

Aȱ studyȱ groupȱ toȱ addressȱ eelsȱ inȱ salineȱ habitatsȱ hasȱ beenȱ proposedȱ toȱ theȱ DiadroȬ mousȱFishȱCommittee.

5.7.2 Risks associated with stocking

TheȱeelȱshouldȱbeȱincludedȱinȱtheȱEuropeanȱfishȱdiseaseȱpreventionȱpolicyȱinȱorderȱtoȱ minimizeȱtheȱrisksȱofȱtransferȱofȱdiseasesȱassociatedȱwithȱstocking.ȱ

AȱrobustȱprotocolȱforȱscreeningȱstockedȱstocksȱshouldȱbeȱputȱinȱplaceȱasȱsoonȱasȱposȬ sible.ȱ

Purposelyȱ infectedȱ eelsȱ inȱ aquacultureȱ withȱ pathogensȱ (viruses,ȱ etc.)ȱ shouldȱ notȱ beȱ usedȱforȱstockingȱpurposes.ȱ

Theȱ cultureȱ ofȱ A.ȱ rostrataȱ inȱ Europeanȱ aquacultureȱ willȱ makeȱ itȱ impossibleȱ toȱ disȬ criminateȱbetweenȱstockingsȱofȱA.ȱanguillaȱandȱA.ȱrostrataȱandȱshouldȱbeȱavoided;ȱtheȱ sameȱappliesȱtoȱpossibleȱgrowingȱofȱotherȱeelȱspeciesȱinȱtheȱfuture.ȱTheȱimprovedȱsysȬ temsȱ toȱ traceȱ glassȱ eelȱ trade,ȱ forȱ CITESȱ andȱ theȱ Regulationȱ (EUȱ 1100/2007),ȱ shouldȱ facilitateȱthis,ȱandȱtheȱWGȱstronglyȱsupportȱtheseȱdevelopmentsȱalsoȱtoȱaddressȱtheȱ risksȱ highlightedȱ here.ȱ Besidesȱ theȱ Eelȱ Regulationȱ andȱ CITES,ȱ theȱ followingȱ EUȱ CouncilȱRegulationȱ(EC)ȱN°ȱ708/2007ȱconcerningȱtheȱuseȱofȱalienȱandȱlocallyȱabsentȱ 88 EIFAC/ICES WGEEL Report 2008

speciesȱinȱaquacultureȱisȱalsoȱlikelyȱtoȱallowȱbetterȱcontrolȱofȱfarmedȱalienȱspeciesȱlikeȱ A.ȱrostrata.ȱ

DespiteȱlimitedȱevidenceȱandȱaȱcomplicatedȱvarietyȱofȱpossibleȱimpactsȱofȱenvironȬ mentalȱ factors,ȱ suchȱ asȱ contaminants,ȱ onȱ silverȱ eelȱ quality,ȱ conservativeȱ adviceȱ reȬ mainsȱ thatȱ stockingȱ forȱ stockȱ enhancementȱ purposesȱ shouldȱ notȱ beȱ conductedȱ inȱ watersȱheavilyȱpollutedȱwithȱsubstancesȱthatȱmightȱposeȱrisksȱforȱspawnerȱquality.ȱ EIFAC/ICES WGEEL Report 2008 89

6 Eel quality

6.1 Introduction

Inȱrecentȱyearsȱ(e.g.ȱICES,ȱ2006)ȱtheȱWorkingȱGroupȱhasȱdescribedȱtheȱrisksȱofȱdeteȬ rioratedȱbiologicalȱqualityȱofȱeels.ȱInȱ2005ȱtheȱEUȬEELREPȱprogrammeȱ(Estimationȱofȱ theȱreproductionȱcapacityȱofȱEuropeanȱeel)ȱconcludedȱthatȱcontaminationȱwithȱPCBsȱ impairedȱfertilityȱwhileȱinfectionsȱwithȱpathogensȱandȱparasitesȱwereȱdevastatingȱforȱ swimmingȱeels.ȱ

TheȱrecommendationsȱofȱtheȱWGȱEELȱ2006ȱhighlightedȱtheȱneedȱtoȱmonitorȱandȱtoȱ collectȱinformationȱonȱ(1)ȱpollutionȱandȱdiseaseȱtoȱbeȱableȱtoȱdesignateȱareasȱproducȬ ingȱhighȱqualityȱspawnersȱ(e.g.ȱwithȱlowȱcontaminantȱandȱparasiteȱburdensȱinȱorderȱ toȱmaximizeȱprotectionȱforȱtheseȱareas;ȱandȱ(2)ȱtheȱchemicalȱstatusȱofȱeelȱunderȱtheȱ implementationȱofȱtheȱWFD.ȱ

AnȱincreasingȱlevelȱofȱevidenceȱonȱtheȱdetrimentalȱimpactȱofȱcontaminationȱandȱdisȬ easesȱonȱtheȱeelȱhasȱbeenȱmadeȱavailable.ȱ

ICESȱ2007ȱreportedȱonȱtheȱadvancesȱmadeȱinȱtheȱcollection ȱofȱdataȱonȱcontaminants,ȱ parasitesȱ andȱ fatȱ levelsȱ inȱ eel,ȱ andȱ reportedȱ thatȱ manyȱ Memberȱ Statesȱ startedȱ theȱ monitoringȱofȱeelȱquality.ȱInȱ2007,ȱtheȱWGEELȱinitiatedȱtheȱsetȬupȱandȱdevelopmentȱ ofȱaȱEuropeanȱEelȱQualityȱDatabaseȱ(EEQD),ȱallowingȱtheȱcompilationȱofȱaȱcompreȬ hensiveȱ overviewȱ onȱ theȱ contaminantȱ loadȱ inȱ eelȱ overȱ itsȱ distributionȱ area.ȱ Resultsȱ fromȱtheȱEEQDȱdemonstratedȱthatȱconsiderableȱvariationȱinȱcontaminantȱloadȱexistsȱ withinȱ riverȱ basinȱ districts,ȱ accordingȱ toȱ localȱ anthropogenicȱ pollution,ȱ linkedȱ withȱ landȱ use.ȱ Thereȱ isȱ evidenceȱ that,ȱ onȱ aȱ panȬEuropeanȱ scale,ȱ largeȱ differencesȱ inȱ eelȱ qualityȱoccursȱbetweenȱcatchments.ȱFurthermore,ȱ‘blackȱspots’ȱwithȱlowȱqualityȱeelsȱ wereȱdetected.ȱLipidȱcontent,ȱwhichȱisȱbelievedȱtoȱbeȱanȱimportantȱindexȱofȱfitness,ȱ wasȱ highlyȱ variableȱ betweenȱ sites.ȱ Newȱ evidenceȱ (Geeraerts,ȱ etȱ al.,ȱ 2007)ȱ wasȱ preȬ sentedȱonȱtheȱnegativeȱimpactȱofȱcertainȱcontaminantsȱonȱtheȱfitnessȱofȱeel.ȱ

TheȱrecommendationsȱofȱtheȱWorkingȱGroupȱ2007ȱ(ICESȱ2007)ȱproposedȱthat:ȱ

1ȱ)MSȱshouldȱfurtherȱdevelopȱandȱmaintainȱtheȱEuropeanȱEelȱQualityȱDataȬ base.ȱ 2ȱ)MSȱ shouldȱ initiateȱ harmonizedȱ monitoringȱ strategiesȱ toȱ developȱ aȱ EuroȬ peanȱEelȱQualityȱMonitoringȱNetwork,ȱtoȱcollectȱtheȱrelevantȱdataȱtoȱbeȱfedȱ intoȱ theȱ EEQD.ȱ Nationalȱ eelȱ managementȱ plans,ȱ shouldȱ takeȱ accountȱ ofȱ theseȱdataȱforȱevaluationȱofȱtheȱqualityȱofȱspawners.ȱ 3ȱ) UnderȱtheȱimplementationȱofȱtheȱWFDȱeelȱspecificȱextensionsȱshouldȱbeȱinȬ cluded,ȱ usingȱ theȱ eelȱ asȱ anȱ indicatorȱ ofȱ riverȱ connectivityȱ andȱ ecologicalȱ andȱchemicalȱstatus,ȱandȱmakingȱcostȬeffectiveȱuseȱofȱcollectedȱdata,ȱalsoȱ forȱtheȱbenefitȱofȱtheȱEUȱEelȱRegulationȱandȱrecoveryȱofȱtheȱeelȱstock.ȱ

DuringȱtheȱWGEELȱ2008ȱsession,ȱnewȱscientificȱevidenceȱofȱeelȱqualityȱasȱanȱimporȬ tantȱ factorȱ inȱ theȱ declineȱ ofȱ theȱ speciesȱ hasȱ beenȱ presentedȱ andȱ discussed.ȱ Theȱ WGEELȱ2008ȱalsoȱupdatedȱtheȱEEQD.ȱInȱtheȱlightȱofȱtheȱintroductionȱofȱtheȱEUȱReguȬ lationȱinȱ2007,ȱtheȱWGEELȱproposedȱrecommendationsȱandȱdiscussedȱurgentȱresearchȱ needs/demonstratedȱgapsȱinȱeelȱqualityȱknowledge.ȱ 90 EIFAC/ICES WGEEL Report 2008

6.2 Contaminants

6.2.1 Introduction

Dueȱ toȱ specificȱ ecologicalȱ andȱ physiologicalȱ traits,ȱ eelsȱ areȱ particularlyȱ sensitiveȱ toȱ bioaccumulationȱofȱlipophilicȱcontaminants.ȱFromȱrecentȱscientificȱevidenceȱ(Belpaire,ȱ 2008)ȱthereȱisȱreasonȱforȱseriousȱconcernȱasȱtheȱlevelȱofȱmeasuredȱconcentrationsȱofȱ someȱcontaminantsȱhasȱbeenȱdemonstratedȱtoȱhaveȱadverseȱeffectsȱonȱtheȱreproducȬ tionȱsuccessȱofȱtheȱsilverȱeel.ȱ

Currentȱ gonadalȱ levelsȱ ofȱ dioxinȬlikeȱ contaminants,ȱ includingȱ PCBs,ȱ inȱ eelsȱ fromȱ mostȱEuropeanȱlocationsȱimpairȱnormalȱembryonicȱdevelopmentȱandȱthatȱPCBsȱandȱ otherȱcontaminantsȱmayȱhaveȱcontributedȱtoȱtheȱdeclineȱofȱeelȱrecruitmentȱobservedȱ sinceȱ1980ȱ (vanȱ denȱ Thillartȱ etȱ al.,ȱ2005;ȱ Palstraȱ etȱ al.,ȱ 2006),ȱ aȱ conclusionȱ consistentȱ withȱtheȱfactȱthatȱtheȱemissionȱofȱPCBsȱinȱtheȱenvironmentȱ(vanȱLeeuwenȱandȱHerȬ mens,ȱ1995)ȱprecededȱtheȱdeclineȱofȱEuropeanȱeel.ȱ

Anȱextensiveȱdatasetȱofȱcontaminantsȱhasȱbeenȱanalysedȱbyȱstatisticalȱmodelling,ȱtoȱ demonstrateȱrelationshipsȱbetweenȱfitnessȱ(lipidȱcontentȱandȱeelȱcondition)ȱandȱvariȬ ousȱ environmentalȱvariablesȱandȱPCBsȱ(especiallyȱtheȱhigherȱchlorinatedȱones)ȱandȱ DDTsȱwereȱrevealedȱtoȱhaveȱaȱnegativeȱimpactȱonȱtheȱlipidȱcontentȱofȱtheȱeel.ȱ(GeerȬ aertsȱetȱal.,ȱ2007).ȱ

ExtensiveȱinformationȱhasȱalreadyȱbeenȱprovidedȱinȱtheȱWGEELȱ2006,ȱandȱ2007ȱreȬ portsȱ(ICESȱ2006;ȱ2007).ȱRecently,ȱBelpaire,ȱ2008 ȱcompiledȱanȱoverviewȱofȱresearchȱonȱ contaminantsȱinȱFlandersȱ(Belgium).ȱTheȱstatusȱandȱtrendsȱofȱeelȱqualityȱfactorsȱandȱ theȱpotentialȱroleȱofȱcontaminationȱinȱtheȱcollapseȱofȱtheȱstockȱareȱpresentedȱandȱdisȬ cussedȱhere.ȱ

6.2.2 The eel and the Water Framework Directive

Theȱ EUȱ Waterȱ Frameworkȱ Directiveȱ requiresȱ monitoringȱ ofȱ aȱ selectionȱ ofȱ priorityȱ substancesȱinȱtheȱaquaticȱphase,ȱincludingȱlipophilicȱsubstances.ȱHowever,ȱthereȱareȱ strongȱargumentsȱforȱmeasuringȱtheȱlatterȱinȱbiotaȱ(BelpaireȱandȱGoemans,ȱ2007a,ȱb).ȱ Yellowȱeelȱisȱaȱgoodȱcandidateȱbecauseȱitȱisȱwidespread,ȱsedentaryȱandȱaccumulatesȱ manyȱlipophilicȱsubstancesȱ inȱitsȱ muscleȱ tissue.ȱSeveralȱ authorsȱ haveȱ describedȱ theȱ indicativeȱ valueȱ ofȱ measuredȱ concentrations,ȱ yetȱ fewȱ studiesȱ haveȱ investigatedȱ theȱ extentȱ toȱ whichȱ theȱ spectrumȱ ofȱ contaminantsȱ presentȱ characterizesȱ theȱ localȱ enviȬ ronmentalȱpollutionȱpressure.ȱToȱevaluateȱtheȱvalueȱofȱtheȱpollutionȱprofileȱofȱanȱeelȱ asȱ aȱ fingerprintȱ ofȱ theȱ chemicalȱ statusȱ ofȱ theȱ localȱ environment,ȱ twoȱ datasetsȱ wereȱ selectedȱ fromȱ theȱ Flemishȱ Eelȱ Pollutantȱ Networkȱ database.ȱ Oneȱ setȱ fromȱ aȱ smallȱ catchmentȱareaȱtoȱinvestigateȱsiteȬspecificȱprofiles,ȱandȱoneȱfromȱsevenȱlargeȱFlemishȱ riversȱtoȱinvestigateȱriverȬspecificȱprofiles.ȱTheȱpollutionȱprofilesȱofȱpersistentȱorganicȱ pollutantsȱinȱindividualȱeelsȱalongȱaȱriverȱ(evenȱatȱdistancesȱ<5ȱkm)ȱprovedȱtoȱbeȱsigȬ nificantlyȱdifferentȱ(Figureȱ6.1).ȱAnalysisȱofȱpooledȱcontaminantȱdataȱfromȱmultipleȱ sitesȱandȱsamplingȱyearsȱwithinȱriversȱallowsȱcharacterizationȱofȱriverȬspecificȱchemiȬ calȱpressures.ȱTheȱresultsȱhighlightȱtheȱusefulnessȱofȱeelȱasȱaȱbioȬindicatorȱforȱmoniȬ toringȱ pollutionȱ withȱ lipophilicȱ chemicalsȱ likeȱ polychlorinatedȱ biphenylsȱ andȱ organochlorineȱ pesticidesȱ inȱ riversȱ (Belpaireȱ etȱ al.,ȱ 2008).ȱ Itȱ wasȱ concludedȱ that,ȱ asȱ such,ȱeelȱmayȱbeȱusedȱeffectivelyȱwithinȱtheȱmonitoringȱprogrammeȱforȱaȱselectionȱofȱ priorityȱsubstancesȱreferredȱtoȱinȱtheȱ WaterȱFrameworkȱDirectiveȱ(Tableȱ6.1).e ȱSom ȱ countriesȱ reportedȱ planningȱ reportingȱ eelȱ qualityȱ dataȱ withinȱ theȱ WFDȱ chemicalȱ statusȱreport.ȱ EIFAC/ICES WGEEL Report 2008 91

GN4 GN5 20

GN2 15 GN3 KN2 Dimension 1 KN1 10

KN3 0 KN4

-10 -5 0 5 10 Dimension 2 ȱ

Figureȱ6.1:ȱCanonicalȱdiscriminantȱanalysisȱofȱeelsȱcollectedȱatȱeightȱsitesȱinȱtheȱGroteȱNeteȱandȱ KleineȱNeteȱonȱtheȱbasisȱofȱtheirȱPCBȱandȱOCPȱconcentrationsȱ(N=ȱ61).ȱDistanceȱbetweenȱlocaȬ tionsȱvariedȱbetweenȱ4ȱandȱ20ȱkm.ȱ

Tableȱ6.1:ȱWFDȱsubstancesȱmentionedȱunderȱCECȱ(2007),ȱandȱavailableȱdataȱfromȱmeasurementsȱ ofȱFlemishȱeels.ȱAllȱdataȱareȱexpressedȱinȱngȱg–1ȱwetȱweight.ȱDL,ȱdetectionȱlimitȱ(fromȱBelpaireȱandȱ Goemans,ȱ2007).ȱ

NO. RANGE OF SUBSTANCE NOTE MIN –MAX (MEAN) %

Benzeneȱ aȱ 1.2–18.9ȱ(5.7)ȱ 0ȱ 20ȱ 1996–1998ȱ jȱ Brominatedȱdiphenylethersȱ aȱ 6.9–5ȱ284.4ȱ 0ȱ 18ȱ 2001ȱ lȱ (369.1)cȱ Cadmiumȱandȱitsȱcompoundsȱ aȱ D.L.Ȭ151.4ȱ(11.7)dȱ 19ȱ 357ȱ 1994–2005ȱ kȱ 1,2ȬDichloroethaneȱ aȱ D.L.Ȭ4.9ȱ(1,2)ȱ 55ȱ 20ȱ 1996–1998ȱ jȱ Hexachlorobenzeneȱ aȱ D.L.Ȭ61.6ȱ(5.7)ȱ <1ȱ 357ȱ 1994–2005ȱ kȱ Hexachlorobutadieneȱ aȱ D.L.Ȭ12.2ȱ(1.8)ȱ 50ȱ 20ȱ 1996–1998ȱ jȱ AlfaȬHexachlorocyclohexaneȱ aȱ D.L.Ȭ13.7ȱ(0.8)eȱ 13ȱ 357ȱ 1994–2005ȱ kȱ (gammaȬisomer,ȱLindane)ȱ aȱ 0.1–2ȱ076.4ȱ(46.9)ȱ 0ȱ 357ȱ 1994–2005ȱ kȱ Leadȱandȱitsȱcompoundsȱ aȱ D.L.Ȭ1ȱ744.2ȱ(56.6)fȱ 3ȱ 357ȱ 1994–2005ȱ kȱ Mercuryȱandȱitsȱcompoundsȱ aȱ 10–535.4ȱ(113.5)gȱ 0ȱ 355ȱ 1994–2005ȱ kȱ Naphthaleneȱ aȱ 1.5–63ȱ(5.8)ȱ 20ȱ 20ȱ 1996–1998ȱ jȱ Nickelȱandȱitsȱcompoundsȱ aȱ D.L.Ȭ2ȱ944.7ȱ 16ȱ 297ȱ 1994–2005ȱ kȱ (186.2)hȱ (1,2,4ȬTrichlorobenzene)ȱ aȱ D.L.Ȭ30.9ȱ(6.0)ȱ 15ȱ 20ȱ 1996–1998ȱ jȱ Trichloromethaneȱ aȱ D.L.Ȭ96.0ȱ(13.4)ȱ 25ȱ 20ȱ 1996–1998ȱ jȱ (chloroform)ȱ DDTȱtotalȱ bȱ 6.6–1ȱ102.7ȱ(90.2)iȱ 0ȱ 357ȱ 1994–2005ȱ kȱ p,p’ȬDDTȱ bȱ D.L.Ȭ62.6ȱ(2.9)ȱ 38ȱ 357ȱ 1994–2005ȱ kȱ Aldrinȱ bȱ D.L.Ȭ11.4ȱ(1.3)ȱ 33ȱ 96ȱ 1994–2005ȱ kȱ 92 EIFAC/ICES WGEEL Report 2008

NO. RANGE OF SUBSTANCE NOTE MIN –MAX (MEAN) %

aȱPriorityȱsubstances.ȱ

bȱOtherȱpollutants,ȱwhichȱfallȱunderȱtheȱscopeȱofȱDirectiveȱ86/280/EECȱandȱwhichȱareȱincludedȱinȱListȱIȱ ofȱ theȱ Annexȱ toȱ Directiveȱ 76/464/EEC,ȱ areȱ notȱ inȱ theȱ priorityȱ substancesȱ list.ȱ Environmentalȱ qualityȱ standardsȱforȱtheseȱsubstancesȱareȱincludedȱinȱtheȱCommission’sȱproposalȱtoȱmaintainȱtheȱregulationȱofȱ theȱsubstancesȱatȱCommunityȱlevel.ȱ

cȱTheȱdataȱpresentȱtheȱSumȱofȱ10ȱBDEs.ȱ

dȱCd.ȱ

eȱalphaȬhexachlorocyclohexane.ȱ

fȱPb.ȱ

gȱHg.ȱ

hȱNi.ȱ

iȱSumȱofȱp,p’ȬDDD,ȱp,p’ȬDDT,ȱandȱp,p’ȬDDE.ȱ

jȱDataȱfromȱRooseȱetȱal.ȱ(2003).ȱ

kȱINBOȱEelȱPollutantȱMonitoringȱDatabase.ȱ

lȱDataȱfromȱdeȱBoerȱetȱal.ȱ(2002)ȱandȱBelpaireȱetȱal.,ȱ2003.ȱ EIFAC/ICES WGEEL Report 2008 93

6.2.3 Eel pollution monitoring networks-status and trends

MostȱofȱtheȱcountriesȱsubmittedȱdataȱonȱcontaminantsȱtoȱtheȱEEQDȱ(seeȱAnnexȱ5ȱforȱ Countryȱreviews).ȱInȱmanyȱsamplingȱsites,ȱconcentrationȱofȱcontaminantsȱfellȱandȱthisȱ probablyȱ reflectsȱ decreasingȱ contaminantȱ exposure.ȱ However,ȱ theȱ monitoringȱ doesȱ notȱevaluateȱtheȱpresenceȱofȱnewȱcontaminantsȱnotȱtoȱmentionȱtheȱincreasingȱnumberȱ ofȱ nonȬnativeȱ species.ȱ Neverthelessȱ thereȱ areȱ widespreadȱ industrializedȱ regionsȱ whereȱcontaminantȱloadsȱstillȱexceedȱreferenceȱlevels.ȱ

SomeȱcountriesȱareȱoperatingȱEelȱPollutionȱMonitoringȱNetworksȱonȱaȱnationalȱscale.ȱ TheȱnetworksȱallowȱtheȱfollowȬupȱofȱcontaminationȱinȱeelsȱandȱallowȱdetailedȱanalyȬ sesȱofȱtheȱstatusȱandȱtrendsȱforȱaȱspecific ȱcontaminant,ȱorȱaȱgroupȱofȱcontaminants.ȱ Theyȱalsoȱallowȱdetailedȱanalysisȱofȱstatusȱandȱtrendsȱofȱcontaminationȱonȱaȱcertainȱ spatialȱ scaleȱ (site,ȱ river,ȱ catchment,ȱ town,ȱ province,ȱ region).ȱ Inȱ someȱ countriesȱ (e.g.ȱ Belgium)ȱtheseȱtrendsȱcanȱbeȱviewedȱinȱreportsȱviaȱpredefinedȱqueriesȱonȱaȱnationalȱ databaseȱavailableȱonȱtheȱ Internet,ȱandȱmapsȱareȱavailableȱforȱcontaminationȱinȱeelȱforȱ PCBs,ȱpesticidesȱandȱheavyȱmetalsȱ(e.g.ȱGoemansȱetȱal.,ȱ2008).ȱAsȱanȱexampleȱtheȱdisȬ tributionȱofȱPCBȱ156ȱinȱeelȱfromȱFlandersȱ(Belgium)ȱisȱrepresentedȱinȱFigureȱ6.2.ȱThisȱ allowsȱtheȱindicationȱofȱgoodȱandȱbadȱqualityȱeelȱareas.ȱ

Eelsȱfromȱdifferentȱriverȱbasinsȱdifferȱinȱcontamination.ȱBelpaireȱetȱal.,ȱ2008ȱpresentedȱ PCBȱandȱOCPȱcontaminationȱprofilesȱforȱsomeȱbasinsȱinȱBelgium.ȱEelsȱfromȱtheȱriverȱ YserȱareȱcharacterizedȱbyȱhighȱOCPs,ȱespeciallyȱdieldrinȱandȱlindaneȱ(·ȬHCH),ȱandȱ lowȱPCBȱlevels.ȱInȱtheȱRiverȱMaas,ȱPCBȱconcentrationsȱear ȱhigh,ȱandȱareȱdominatedȱ byȱtheȱhigherȱchlorinatedȱ(andȱhigherȱtoxic)ȱPCBs.ȱ

Figureȱ6.2:ȱDistributionȱofȱPCBȱ156ȱinȱyellowȱeelȱinȱFlandersȱ(2002–2005);ȱmeansȱonȱmuscleȱwetȱ weightȱbasis,ȱclassifiedȱfollowingȱtheȱdeviationȱfromȱtheȱreferenceȱvalueȱ(Goemansȱetȱal.,ȱ2008).ȱ

Highȱconcentrationsȱofȱsomeȱsubstancesȱinȱeelȱtissueȱconfirmedȱtheȱpreviouslyȱknownȱ highȱpollutionȱloadȱofȱsomeȱspecificȱareas,ȱbutȱinȱmanyȱcasesȱhowever,ȱeelȱanalysesȱ revealedȱ unknownȱ environmentalȱ problems.ȱ Inȱ aȱ fewȱ casesȱ analysisȱ ofȱ eelsȱ fromȱ aȱ specificȱlocationȱhasȱdemonstratedȱunsuspectedȱhighȱpollutionȱlevelsȱofȱseveralȱconȬ taminants.ȱButȱseveralȱcontaminantsȱ(e.g.ȱBTEXȱ(benzene,ȱtoluene,ȱethylbenzeneȱandȱ 94 EIFAC/ICES WGEEL Report 2008

theȱxylenes)ȱcompounds,ȱPCBsȱandȱsomeȱveryȱpersistentȱOCPsȱlikeȱDDTs)ȱareȱwideȬ spreadȱinȱcertainȱcountries.ȱ(Rooseȱetȱal.,ȱ2003)ȱ

ResultsȱofȱmeasurementsȱofȱdioxinsȱonȱeightȱlocationsȱinȱBelgiumȱ(Flanders)ȱindicateȱ someȱ reasonȱ forȱ concern.ȱ Dioxinȱ concentrationsȱ inȱ eelȱ varyȱ considerablyȱ betweenȱ samplingȱsites,ȱsuggestingȱthatȱeelȱmayȱbeȱgoodȱindicatorsȱofȱlocalȱpollutionȱlevels.ȱ TheȱEuropeanȱCommissionȱhasȱsetȱmaximumȱlevelsȱofȱ4ȱpgȱTEQȱgȬ1ȱfreshȱweightȱforȱ theȱsumȱofȱdioxinsȱ(WHOȬPCDD/FȱTEQ)ȱandȱ12ȱpgȱTEQȱgȬ1ȱfreshȱweightȱforȱtheȱtotalȬ TEQȱi.e.ȱtheȱsumȱofȱdioxinsȱandȱdioxinȬlikeȱPCBsȱ(WHOȬPCDD/FȬPCBȱTEQ)ȱinȱmusȬ cleȱmeatȱofȱeelȱandȱproductsȱthereofȱ(Directiveȱ2002/69/EC).ȱHalfȱofȱtheȱsamplingȱsitesȱ inȱ Belgiumȱ demonstrateȱ DLȬPCBȱ levelsȱ exceedingȱ theȱ Europeanȱ consumptionȱ levelȱ (withȱaȱfactorȱthreeȱonȱaverage).ȱTheȱlevelsȱofȱPCDD/FSȱandȱDLȬPCBSȱmeasuredȱinȱ someȱsitesȱgaveȱriseȱtoȱseriousȱconcernȱaboutȱtheȱreproductionȱpotentialȱofȱtheȱeelsȱ fromȱtheseȱsites.ȱHumanȱconsumptionȱofȱeels,ȱespeciallyȱinȱtheseȱhighlyȱcontaminatedȱ sites,ȱseemsȱunwiseȱ(Geeraertsȱetȱal.,ȱinȱpress).ȱ

TrendȱanalysisȱinȱaȱBelgianȱstudyȱ(Maesȱetȱal.,ȱ2008)ȱoverȱtheȱperiodȱ1994–2005ȱindiȬ catedȱthatȱthereȱwereȱsignificantȱdecreasesȱinȱtheȱaverageȱwetȱweightȱconcentrationȱofȱ allȱ PCBȱ congeners,ȱ nearlyȱ allȱ pesticidesȱ andȱ fourȱ metals.ȱ Theȱ observedȱ declineȱ ofȱ PCBsȱ inȱ eelȱ tissueȱ wasȱ inȱ agreementȱ withȱ otherȱ studiesȱ reportingȱ onȱ timeȬseriesȱ ofȱ contaminantsȱinȱfish.ȱPCBsȱwereȱbannedȱfromȱtheȱEUȱinȱ1985ȱandȱsinceȱthen,ȱseveralȱ timeȬseriesȱhaveȱindicatedȱdecreasingȱlevelsȱofȱcontamination.ȱAlsoȱconcentrationsȱofȱ mostȱpesticidesȱdecreasedȱsignificantlyȱoverȱtime.ȱThisȱwasȱespeciallyȱevidentȱforȱ΅Ȭ HCHȱandȱlindane,ȱdemonstratingȱthatȱtheȱbanȱofȱlindaneȱinȱ2002ȱhasȱpositiveȱeffectsȱ onȱ theȱ accumulationȱ inȱ biota.ȱ Similarȱ reductionsȱ wereȱ modelledȱ forȱ HCB,ȱ dieldrinȱ andȱendrin;ȱhoweverȱtheseȱcompoundsȱwereȱbannedȱmanyȱyearsȱago.ȱUnexpectedly,ȱ concentrationsȱofȱp,p’ȬDDTȱincreasedȱwhileȱatȱtheȱsameȱtime,ȱp,p’ȬDDDȱandȱp,p’ȬDDEȱ demonstratedȱsignificantȱdecreases.ȱ

Theȱ ratioȱ ofȱ DDEȱ overȱ DDTȱ wasȱ >1ȱ inȱ allȱ eelsȱ analysed,ȱ normallyȱ suggestingȱ thatȱ DDTȱ hadȱ notȱ beenȱ recentlyȱ reapplied.ȱ Atȱ someȱ locationsȱ inȱ Flanders,ȱ however,ȱ theȱ ratioȱofȱDDEȱoverȱDDTȱrapidlyȱdecreasedȱbyȱanȱorderȱofȱmagnitudeȱofȱthreeȱoverȱaȱ fewȱyears.ȱSuchȱaȱsteepȱdecrease,ȱevenȱifȱtheȱratioȱwasȱhigherȱthanȱone,ȱprobablyȱindiȬ catesȱ recentȱ applicationȱ ofȱ DDTȱ andȱ demonstratesȱ thatȱ notȱ allȱ stockȱ wasȱ depleted.ȱ ThisȱurgedȱregionalȱpolicyȬmakersȱtoȱmakeȱaȱseriousȱattemptȱinȱorderȱtoȱcollectȱtheȱ remainingȱstockȱofȱbannedȱpesticides.ȱ

Someȱ heavyȱ metalȱ concentrationsȱ decreasedȱ inȱ theȱ eel,ȱ inȱ particularȱ lead,ȱ arsenic,ȱ nickelȱ andȱchromiumȱwereȱnotablyȱreduced.ȱTheȱconcentrationȱofȱleadȱinȱeelȱmuscleȱ tissueȱwasȱconsistentlyȱdecreasingȱbetweenȱ1994ȱandȱ2005,ȱwhichȱpossiblyȱisȱrelatedȱ toȱtheȱgradualȱchangeoverȱfromȱleadedȱtoȱunleadedȱfuelsȱandȱaȱreductionȱofȱindusȬ trialȱ emissions.ȱ Forȱ arsenic,ȱ nickelȱandȱ chromium,ȱ theȱ trendȱ mayȱ beȱ biasedȱ asa ȱ dat ȱ wereȱ availableȱ onlyȱ sinceȱ 2000.ȱ Cadmiumȱ andȱ mercury,ȱ however,ȱ didȱ notȱ demonȬ strateȱdecreasingȱtrendsȱandȱremainȱcommonȱenvironmentalȱpollutantsȱinȱtheȱindusȬ trializedȱregionȱofȱFlanders.ȱ

FollowingȱtheȱveryȱhighȱlevelsȱofȱBFRsȱencounteredȱinȱeelsȱfromȱOudenaarde,ȱnewȱ measurementsȱwereȱcarriedȱoutȱinȱ2006ȱ(Roosensȱetȱ al.,ȱ2008).ȱAȱdescendingȱtrendȱinȱ theȱcontaminationȱwithȱBFRsȱwasȱobservedȱfromȱ2000ȱtoȱ2006ȱonȱthisȱsite.ȱForȱPBDEs,ȱ levelsȱhaveȱdecreasedȱbyȱaȱfactorȱ35ȱ(26ȱ500ȱtoȱ780ȱngȱgȬ1ȱLW),ȱwhereasȱforȱhexabroȬ mocyclododecaneȱ(HBCD),ȱtheȱdecreaseȱwasȱlessȱconspicuous,ȱ(35ȱ000ȱtoȱ10ȱ000ȱngȱgȬ1ȱ LW).ȱBasedȱonȱtheseȱresultsȱweȱcanȱconcludeȱthatȱinȱ2006,ȱfishȱseemȱtoȱbeȱlessȱexposedȱ toȱPBDEsȱthanȱ6ȱyearsȱearlier.ȱThisȱisȱprobablyȱasȱaȱconsequenceȱofȱtheȱrestrictionȱreȬ gardingȱ theȱ useȱ ofȱ theȱ pentaȬBDEȱ technicalȱ mixtureȱ (sinceȱ 2004),ȱ aȱ betterȱ environȬ mentalȱ managementȱ andȱ aȱ raisingȱ awarenessȱ concerningȱ PBDEs.ȱ However,ȱ sinceȱ EIFAC/ICES WGEEL Report 2008 95

thereȱareȱnoȱrestrictionsȱregardingȱitsȱusage,ȱHBCDȱcanȱstillȱbeȱdetectedȱinȱlargeȱquanȬ tities,ȱespeciallyȱinȱaquaticȱenvironmentalȱsamplesȱtakenȱnextȱtoȱindustrializedȱareas,ȱ whereȱitȱisȱusedȱinȱspecificȱapplications.ȱTheȱtextileȱindustryȱisȱlikelyȱtheȱcauseȱofȱeleȬ vatedȱBFRȱlevelsȱinȱfishȱonȱthisȱpartȱofȱtheȱriverȱScheldt,ȱbutȱfurtherȱstudiesȱshouldȱbeȱ setȱupȱtoȱdetermineȱtheȱexactȱoriginȱandȱhowȱfarȱthisȱcontaminatedȱareaȱextendsȱoverȱ theȱwholeȱriver.ȱ

ItȱwasȱconcludedȱthatȱEelȱPollutionȱMonitoringȱNetworks,ȱsuchȱasȱtheȱonesȱoperatedȱ inȱ Belgiumȱ andȱ Theȱ Netherlands,ȱ allowȱ gettingȱ aȱ comprehensiveȱ overviewȱ ofȱ conȬ taminantsȱ indicatingȱ environmentalȱ pressure,ȱ andȱ theyȱ areȱ ableȱ toȱ documentȱ theȱ temporalȱevolutionȱofȱsomeȱofȱtheseȱpressures.ȱTheseȱnationalȱmonitoringȱnetworksȱ shouldȱbeȱupscaledȱatȱtheȱEuropeanȱlevel.ȱTheȱintensityȱofȱpollution,ȱatȱleastȱatȱsomeȱ sites,ȱmayȱwellȱindicateȱpotentialȱnegativeȱeffectȱonȱtheȱhealthȱofȱthese ȱcontaminatedȱ eels.ȱTheseȱdataȱunderlineȱtheȱlargeȱvariationȱinȱqualityȱstatusȱofȱtheȱeelȱoverȱitsȱdisȬ tributionȱrange.ȱItȱisȱbelievedȱthatȱthisȱvariationȱinȱqualityȱisȱindicativeȱwithȱaȱvariaȬ tionȱinȱreproductionȱpotentialȱ(Belpaireȱetȱal.,ȱinȱpress).ȱ

6.2.4 Contamination in eel and its role in the decline of the stock

Weȱsummarizeȱtheȱmainȱfindingsȱofȱworkȱinȱthisȱfieldȱ(seeȱalsoȱBelpaire,ȱ2008)ȱinȱtheȱ followingȱsectionȱandȱdrawȱsomeȱconclusionsȱrelatedȱtoȱtheȱpotentialȱroleȱofȱcontamiȬ nationȱinȱtheȱcollapseȱofȱtheȱstock.ȱ

Asȱ aȱ consequenceȱ ofȱ theȱ increasedȱ internationalȱ concernȱ aboutȱ theȱ declineȱ ofȱ theȱ stocks,ȱalsoȱresearchȱactionsȱhaveȱpaidȱincreasingȱattentionȱtoȱanalyseȱcontaminantsȱ inȱtheȱeelȱandȱtoȱinvestigateȱtheȱeffectsȱofȱtheseȱsubstancesȱinȱtheȱeel.ȱAsȱaȱresultȱaȱ largeȱandȱgrowingȱquantityȱofȱinformationȱbecameȱavailable,ȱandȱasȱsuggestedȱICESȱ 2007ȱaȱreviewȱonȱtheȱeffectsȱofȱcontaminantsȱisȱunderway.ȱManyȱstudiesȱhaveȱexamȬ inedȱtheȱimpactȱofȱaȱwideȱvarietyȱofȱxenobioticsȱonȱvariousȱaspectsȱofȱfishȱbiochemisȬ try,ȱ physiologyȱ andȱ populationȱ structure.ȱ Inȱ someȱ casesȱ ofȱ acuteȱ pollution,ȱ directȱ effectsȱareȱclearlyȱvisibleȱasȱfishȱmayȱbeȱmoribundȱorȱdying.ȱButȱcontaminantȱexpoȬ sureȱcanȱleadȱtoȱaȱdecreaseȱinȱgrowthȱorȱaȱloweredȱorȱdeficientȱimmunologicalȱsysȬ tem,ȱcausingȱanȱincreasedȱsensitivityȱtoȱinfectiousȱdiseasesȱandȱparasites.ȱButȱinȱmostȱ cases,ȱtheseȱeffectsȱhaveȱbeenȱinducedȱbyȱeffectsȱonȱmolecularȱandȱsubcellularȱlevel.ȱ Theȱlastȱ20ȱyears,ȱanȱincreasingȱnumberȱofȱreportsȱdealȱwithȱstudyingȱcausalityȱbeȬ tweenȱpressureȱofȱxenobioticsȱandȱresponseȱatȱtheȱsubcellularȱlevel.ȱInȱtheȱeel,ȱtheȱimȬ pactsȱofȱcontaminantsȱonȱmetabolicȱfunctionsȱandȱonȱbehaviourȱofȱtheȱeelȱareȱwidelyȱ divergentȱandȱ actȱ throughȱ variousȱ mechanisms.ȱ Figureȱ6.3ȱ showsȱ aȱ simplifiedȱ conȬ ceptualȱmodelȱofȱtheȱeffectsȱofȱpollutionȱexposureȱonȱtheȱpopulationȱstructureȱofȱtheȱ Europeanȱeelȱ(afterȱGeeraertsȱetȱal.,ȱinȱprep,ȱadaptedȱfromȱLawrenceȱandȱElliott,ȱ2003).ȱ

Aȱsignificantȱnegativeȱcorrelationȱbetweenȱheavyȱmetalȱpollutionȱloadȱandȱconditionȱ wasȱobserved,ȱsuggestingȱanȱimpactȱofȱpollutionȱonȱtheȱhealthȱofȱsubadultȱeelsȱ(Maesȱ etȱal.,ȱ2005.ȱInȱgeneral,ȱaȱ reducedȱgeneticȱvariabilityȱwasȱobservedȱinȱstronglyȱpollutedȱ eels,ȱasȱwellȱasȱaȱnegativeȱcorrelationȱbetweenȱlevelsȱofȱbioaccumulationȱandȱallozyȬ maticȱmultiȬlocusȱheterozygosityȱ(Maesȱetȱal.,ȱ2005).ȱ

VanȱCampenhoutȱetȱal.,ȱ2008ȱstudiedȱtheȱeffectȱofȱmetalȱexposureȱonȱtheȱaccumulationȱ andȱ cytosolicȱ speciationȱ ofȱ metalsȱ inȱ liversȱ ofȱ Europeanȱ eelȱ byȱ measuringȱ metalȬ lothioneinsȱ (MT)ȱ induction.ȱ Thisȱ researchȱ wasȱ carriedȱ outȱ inȱ fourȱ samplingȱ sitesȱ inȱ Flandersȱ revealingȱ differentȱ degreesȱ ofȱ heavyȱ metalȱ contaminationȱ (Cd,ȱ Cu,ȱ Ni,ȱ Pbȱ andȱZn).ȱItȱwasȱconcludedȱthatȱtheȱmetals,ȱratherȱthanȱotherȱstressȱfactors,ȱareȱtheȱmaȬ jorȱ factorȱ determiningȱ MTȱ induction.ȱ Theȱ effectsȱ ofȱ perfluorooctaneȱ sulfonicȱ acidsȱ (PFOS)ȱinȱFlemishȱeelsȱwereȱstudiedȱbyȱHoffȱetȱal.,ȱ2005,ȱindicatingȱthatȱPFOSȱinducesȱ liverȱdamage.ȱ 96 EIFAC/ICES WGEEL Report 2008

InȱFrance,ȱmigratingȱsilverȱeelsȱA.ȱanguillaȱwereȱcollectedȱinȱaȱriverȱsystemȱwhereȱalȬ galȱbloomsȱoccurredȱyearly.ȱFiftyȱperȱcentȱofȱeelȱliversȱwereȱcontaminatedȱbyȱmicroȬ cystinȬLRȱ (theȱ mostȱ commonȱ andȱ toxigenicȱ compoundsȱ associatedȱ withȱ cyanobacterialȱblooms).ȱContaminatedȱsilverȱeelsȱhadȱlowerȱfishȱconditionȱcomparedȱ toȱnonȬcontaminatedȱeels.ȱConsequencesȱofȱthisȱimpactȱforȱtheȱbreedingȱpotentialȱofȱ theseȱmigratingȱeelsȱareȱdiscussed,ȱinȱparticularȱtheȱimportanceȱofȱlipidsȱandȱenergyȱ reserveȱallocation.ȱTheȱconsequencesȱofȱcontaminationȱbyȱmicrocystinsȱonȱtheȱbreedȬ ingȱpotentialȱofȱsilverȱeelsȱshouldȱbeȱfurtherȱinvestigatedȱ(Acouȱetȱal.,ȱ2008).ȱ

Figureȱ6.3:ȱAȱsimplifiedȱconceptualȱmodelȱofȱtheȱeffectsȱofȱpollutionȱexposureȱonȱtheȱpopulationȱ structureȱofȱtheȱEuropeanȱeel,ȱA.ȱanguilla.ȱAdaptedȱfromȱLawrenceȱandȱElliott,ȱ2003.ȱNumbersȱreferȱ toȱ references:ȱ (1)ȱ Vollestad,ȱ 1992;ȱ (2)ȱ Tuurulaȱ andȱ Soivio,ȱ 1982;ȱ Svobodovaȱ etȱ al.,ȱ 1994;ȱ Azzalisȱ etȱ al.,ȱ 1995;ȱStohsȱandȱBagghi,ȱ1995;ȱSanchoȱetȱal.,ȱ1997;ȱIbukiȱandȱGoto,ȱ2002;ȱPachecoȱandȱSantos,ȱ2002;ȱ(3)ȱ Nigroȱetȱal.,ȱ2002;ȱJha,ȱ2004;ȱMaesȱetȱal.,ȱ2005;ȱNogueiraȱetȱal.,ȱ2006;ȱ(4)ȱMcKinneyȱandȱWaller,ȱ1994;ȱVerȬ sonnenȱetȱal.,ȱ2004;ȱ(5)ȱJoblingȱetȱal.,ȱ2002;ȱ(6)ȱJimenezȱandȱBurtis,ȱ1989;ȱSanchoȱetȱal.,ȱ1998;ȱFernandezȬ Vegaȱetȱal.,ȱ1999;ȱRobinetȱandȱFeunteun,ȱ2002;ȱHuȱetȱal.,ȱ2003;ȱPierronȱetȱal.,ȱ2007;ȱ(7)ȱRocheȱetȱ.al ,ȱ2002;ȱ (8)ȱSuresȱandȱKnopf,ȱ2004;ȱSures,ȱ2006;ȱ(9)ȱSanchoȱetȱal.,ȱ1997;ȱ(10)ȱGony,ȱ1987;ȱ(11)ȱCeronȱetȱal.,ȱ2003;ȱvanȱ denȱThillartȱetȱal.,ȱ2005;ȱ(12)ȱVanȱGinnekenȱetȱal.,ȱ2005;ȱ(13)ȱJohnsonȱetȱal.,ȱ1998;ȱPalstraȱetȱal.,ȱ2007;ȱ(14)ȱ Sures,ȱ2006;ȱ(15)n ȱVa ȱGinnekenȱetȱal.,ȱ2005;ȱ(16)ȱCorsiȱetȱal.,ȱ2003;ȱ(17)ȱVanȱCampenhoutȱetȱal.,ȱ2008;ȱ(18)ȱ Ahmadȱetȱal.,ȱ2006;ȱMariaȱetȱal.,ȱ2006;ȱ(19)ȱJha,ȱ2004;ȱMaesȱetȱal.,ȱ2005;ȱ(20)ȱBelpaireȱetȱal.,ȱ2003ȱ(afterȱGeeȬ raertsȱetȱal.,ȱ2008,ȱinȱprep).ȱ

Geeraertsȱ etȱ al.,ȱ 2007ȱ analysedȱ anȱ extensiveȱ datasetȱ ofȱ contaminantsȱ byȱ statisticalȱ modellingȱ andȱ concludedȱ thatȱ PCBs,ȱ especiallyȱ theȱ higherȱ chlorinatedȱ ones,ȱ andȱ DDTs,ȱhaveȱaȱnegativeȱimpactȱonȱlipidȱcontentȱofȱtheȱeel.ȱItȱwasȱfurtherȱdemonstratedȱ thatȱfatȱstoresȱandȱconditionȱdecreasedȱsignificantlyȱduringȱtheȱlastȱ15ȱyearsȱinȱeelsȱinȱ FlandersȱandȱinȱTheȱNetherlandsȱ(Belpaireȱetȱal.,ȱ2008),ȱjeopardizingȱaȱnormalȱmigraȬ tionȱandȱsuccessfulȱreproduction.ȱInȱBelgiumȱandȱTheȱNetherlandsȱoverȱtheȱpastȱ15ȱ years,ȱlipidȱcontentsȱdroppedȱbyȱaboutȱoneȬthirdȱ(fromȱca.ȱ20%ȱtoȱ13%)ȱ(Figureȱ6.4).ȱ Alsoȱ theȱ conditionȱ(Leȱ Cren’sȱ relativeȱconditionȱfactor)ȱ ofȱ theȱ eelsȱ decreased.ȱ Lipidȱ reservesȱareȱessentialȱtoȱcoverȱenergeticȱrequirementsȱforȱsilverȱeelȱmigrationȱandȱreȬ production.ȱ Onȱ theȱ basisȱ ofȱ theȱ somaticȱ energyȱ reserves,ȱ reproductiveȱ potentialȱ ofȱ eelsȱfromȱvariousȱlatitudesȱoverȱEuropeȱwasȱestimated,ȱassumingȱfatȱlevelsȱinȱyellowȱ eelȱ areȱ indicativeȱ ofȱ thoseȱ inȱ silverȱ eels.ȱ Onlyȱ largeȱ individuals,ȱ femalesȱ asȱ wellȱ asȱ males,ȱ withȱhighȱ lipidȱ contentȱ seemȱ toȱ beȱ ableȱ toȱ contributeȱ toȱ theȱ spawningȱ stockȱ (Belpaireȱetȱal.,ȱ2008).ȱBelpaireȱetȱal.,ȱ2008ȱargueȱthatȱtheȱdecreaseȱinȱfatȱcontentȱinȱyelȬ EIFAC/ICES WGEEL Report 2008 97

lowȱeelsȱmayȱbeȱaȱkeyȱelementȱinȱtheȱstockȱdeclineȱandȱraisesȱseriousȱconcernsȱaboutȱ theȱchancesȱofȱtheȱstockȱtoȱrecoverȱ(Figureȱ6.4).ȱ

Itȱisȱthereforeȱimportantȱtoȱgainȱinsightȱofȱtheȱquality,ȱlipidȱreservesȱandȱconditionȱofȱ theȱeelsȱleavingȱcontinentalȱwatersȱandȱtoȱincludeȱqualityȱaspectsȱinȱeelȱstockȱmanȬ agement.ȱBothȱmuscleȱlipidȱcontentȱandȱconditionȱfactorȱseemȱtoȱbeȱimportantȱinteȬ grativeȱ indicatorsȱ inȱ anȱ overallȱ estimateȱ ofȱ theȱ qualityȱ ofȱ theȱ eelsȱ escapingȱ toȱ theirȱ spawningȱgrounds.ȱ

Contaminantȱpressureȱisȱaȱplausibleȱconcernȱforȱtheȱrecoveryȱofȱeelȱstocksȱandȱhereȱ weȱsummarizeȱargumentsȱandȱhypothesesȱtoȱunderpinȱthis:ȱ

1ȱ) Contaminationȱhasȱbeenȱdemonstratedȱasȱtheȱcauseȱofȱpopulationȱcollapseȱ ofȱmanyȱotherȱbiotaȱfromȱtheȱ1970sȱonȱ(e.g.ȱtheȱcollapseȱofȱseveralȱbirdsȱofȱ preyȱinȱtheȱ1960sȱasȱaȱconsequenceȱofȱDDT).ȱ 2ȱ) Manyȱchemicalsȱhaveȱbeenȱdevelopedȱandȱputȱonȱtheȱmarket,ȱsimultaneȬ ousȱwithȱtheȱintensificationȱofȱagriculturalȱandȱindustrialȱactivitiesȱduringȱ theȱ 1970s.ȱ Theȱ timingȱ ofȱ thisȱ increaseȱ inȱ theȱ productionȱ andȱ releaseȱ ofȱ chemicalsȱmayȱfitȱwithȱtheȱtimingȱofȱtheȱdecreaseȱinȱrecruitmentȱfromȱ1980ȱ on.ȱ 3ȱ) Eelsȱbioaccumulateȱmanyȱchemicalsȱtoȱaȱhighȱextent.ȱ 4ȱ) Theȱ moreȱ orȱ lessȱ comparableȱ decreasesȱ inȱ recruitmentȱ inȱ theȱ NorthernȬ hemisphereȱAnguillaȱspecies,ȱlikeȱA.ȱrostrataȱandȱA.ȱjaponica,ȱduringȱtheȱlastȱ 30ȱ years,ȱ mightȱ suggestȱ thatȱ someȱ newȱ contaminantsȱ quicklyȱ spreadingȱ overȱtheȱindustrializedȱworld,ȱmightȱhaveȱcontributedȱtoȱtheȱdecline.ȱ 5ȱ) Manyȱreportsȱhaveȱbeenȱdealingȱwith ȱdirectȱadverseȱeffectsȱofȱcontaminaȬ tionȱonȱindividual,ȱpopulationȱandȱcommunityȱlevelȱinȱfish.ȱInȱeel,ȱmanyȱ detrimentalȱ effectsȱ ofȱ contaminantsȱ onȱ theȱ individualȱ levelȱ haveȱ beenȱ demonstrated,ȱ includingȱ impactȱ onȱ cellular,ȱ tissueȱ andȱ organȱ level.ȱ Alsoȱ geneticȱdiversityȱseemsȱtoȱbeȱloweredȱbyȱpollutionȱpressure.ȱ 6ȱ) Consideringȱtheȱhighȱ levelsȱofȱcontaminationȱinȱeelsȱfromȱmanyȱareas,ȱenȬ docrineȱ disruptionȱ inȱ matureȱ silverȱ eelsȱ mightȱ beȱ expected,ȱ jeopardizingȱ normalȱ reproduction.ȱ DioxinȬlikeȱ contaminantsȱ haveȱ beenȱ reportedȱ toȱ hamperȱnormalȱlarvalȱdevelopment.ȱ 7ȱ) Lipidȱ levelsȱ inȱ eelsȱ haveȱ decreasedȱ considerablyȱ overȱ theȱ pastȱ 15ȱ years.ȱ Thisȱdecreaseȱinȱlipidȱlevelsȱ isȱmainlyȱinducedȱbyȱcontamination.ȱLowȱlipidȱ levelsȱmayȱhaveȱcontributedȱtoȱaȱreductionȱinȱmigrationȱandȱreproductionȱ success.ȱ

ȱ 98 Joint EIFAC/ICES WGEEL REPORT 2008

n = 59 n = 370 n = 83 n = 65 n = 71 n = 112 n = 99 n = 147 n = 66

a a

b Condition factor Condition Muscle lipid content (% w.w.)

Muscle lipid content(% w.w.) b c

c 12 14 16 18 20 0.94 0.96 0.98 1.00 1.02 1.04 1.06 1.08

1994-1998 1999-2003 2004-2006 12 14 16 18 20 22 1977-1981 1982-1986 1987-1991 1992-1996 1997-2001 2002-2004

40 1000,00 25,0 IJsselmeer, Medemblik 35 Meuse, Eijsden Roer, Vlodrop y = - 0,0 12 1 x2 + 47,956x - 47371 Twentekanaal, Hengelo R2 = 0,867 20,0 30

25 100,00

15,0

Fat (%content w.w.) 10,0

10,00 Muscle lipid content (% w.w.) content lipid Muscle

10 value 1979-1994 of Percentage Glass eel recruitment 5,0 5 Muscle lipid content

0 1975 1980 1985 1990 1995 2000 2005 2010 1,00 0,0 Year 1950 1960 1970 1980 1990 2000 2010

Figureȱ6.4:ȱTemporalȱtrendȱinȱfatȱcontentsȱ(%ȱofȱwetȱmuscleȱweight)ȱofȱyellowȱeelsȱinȱBelgiumȱ(upperȱleftȱpanel)ȱandȱTheȱ Netherlandsȱ(upperȱrightȱpanel)ȱ(means,ȱbarsȱindicatingȱstandardȱerrors).ȱTheȱnumberȱofȱsitesȱisȱindicated.ȱMeansȱofȱperiodsȱ withȱtheȱsameȱletterȱareȱnotȱsignificantlyȱdifferentȱfromȱeachȱother.ȱForȱtheȱBelgianȱeelsȱalsoȱconditionȱfactorȱisȱpresented.ȱ Lowerȱleftȱpanel:ȱTemporalȱtrendsȱinȱfatȱcontentsȱinȱyellowȱeelsȱfromȱfourȱwaterȱbodiesȱofȱdifferentȱtypology.ȱTimeȱtrendȱofȱ theȱfatȱcontentȱinȱmuscleȱtissueȱ(pooledȱsamples)ȱfromȱyellowȱeelsȱinȱaȱlakeȱ(IJsselmeer),ȱaȱlargeȱriverȱ(Meuse),ȱaȱsmallȱriverȱ (Roer)ȱandȱaȱcanalȱ(Twentekanaal)ȱinȱTheȱNetherlands.ȱLowerȱrightȱpanel:ȱTimeȬseriesȱofȱglassȱeelȱrecruitmentȱinȱEuropeȱ (ICESȱ2007)ȱandȱofȱmuscleȱlipidȱcontentsȱinȱyellowȱeelsȱfromȱTheȱNetherlands.ȱDataȱofȱtheȱtimeȬseriesȱofȱglassȱeelȱrecruitȬ mentȱareȱgeometricȱmeansȱofȱmonitoringȱdataȱofȱrecruitingȱbiomassesȱinȱ21ȱEuropeanȱrivers,ȱeachȱseriesȱbeingȱscaledȱtoȱitsȱ 1979–1994ȱaverage.ȱDataȱofȱmuscleȱlipidȱcontentsȱareȱmeansȱofȱpooledȱyellowȱeelȱsamplesȱfromȱTheȱNetherlandsȱbetweenȱ 1977ȱandȱ2004ȱ(Belpaireȱetȱal.,ȱ2008).ȱ

Note:ȱinȱtheȱlowerȱrightȱpanel:ȱrecruitmentȱisȱonȱaȱlogȱscaleȱandȱmuscleȱlipidȱisȱonȱaȱnormalȱscale.ȱ

ȱ EIFAC/ICES WGEEL Report 2008 99

6.3 Parasites/pathogens

A.ȱcrassusȱcanȱbeȱconsideredȱwidespreadȱthroughoutȱEuropeȱandȱthereȱisȱaȱgrowingȱ evidenceȱthatȱA.ȱcrassusȱisȱspreadingȱfurtherȱintoȱnewȱareas.ȱNewȱdataȱinȱ2008ȱindiȬ catedȱtheȱpresenceȱofȱtheȱnematodeȱinȱCanadaȱ(notȱincludedȱinȱtheȱEEQDȱyet)ȱforȱtheȱ firstȱtime.ȱFurtherȱprocessȱresearchȱisȱrequiredȱbeforeȱtheȱimpactȱofȱcontaminantsȱandȱ parasitesȱcanȱbeȱincludedȱinȱtheȱquantitativeȱstockȱassessments.ȱ

6.4 Quality assessment of spawners using genomic tools

Eelȱdeclineȱmightȱdependȱnotȱonlyȱonȱtheȱquantityȱofȱadultȱeelsȱleavingȱtheȱcontinent,ȱ butȱalsoȱuponȱtheirȱquality.ȱGoodȱqualityȱspawnersȱareȱthoseȱthatȱsucceedȱinȱcrossingȱ theȱAtlanticȱOceanȱandȱreproduce.ȱParasites,ȱsuchȱasȱtheȱexoticȱswimbladderȱnemaȬ todeȱA.ȱcrassusȱcanȱimpairȱeelȱviabilityȱbyȱbothȱincreasingȱcontinentalȱmortalityȱandȱ affectingȱtheȱswimmingȱabilityȱofȱadultȱeels.ȱOrganicȱandȱinorganicȱpollutantsȱmayȱ significantlyȱreduceȱtheȱqualityȱandȱreproductiveȱcapacityȱofȱvertebrates.ȱThisȱisȱespeȬ ciallyȱtheȱcaseȱinȱfish,ȱwhereȱpollutantsȱmayȱaccumulateȱinȱtheȱwaterȱandȱsedimentȱ andȱinȱtheȱbenthicȱbiotaȱ(food).ȱAdditionally,ȱinfectionsȱandȱpollutionȱhaveȱbeenȱreȬ vealedȱ toȱ impairȱ stronglyȱ theȱ survivalȱ andȱ reproductiveȱ capacityȱ ofȱ eelsȱ inȱ experiȬ mentalȱ trials,ȱ resultingȱ inȱ anȱ evenȱ strongerȱ responseȱ toȱ pollutionȱ andȱ viceȬversaȱ (Palstraȱetȱal.,ȱ2006;ȱ2007).ȱAȱthoroughȱanalysisȱofȱpollutantsȱandȱpathogenȱstressȱlevȬ elsȱand ȱaȱbetterȱunderstandingȱofȱtheȱbiologicalȱresponseȱ(besidesȱmeasuresȱofȱcondiȬ tionȱindex)ȱareȱmissing.ȱPujolarȱetȱal.,ȱ2005ȱandȱMaesȱetȱal.,ȱ2005ȱassessedȱwhetherȱtheȱ geneticȱ backgroundȱ ofȱ Europeanȱ eelsȱ couldȱ beȱ linkedȱ toȱ twoȱ fitnessȱ traits,ȱ earlyȱ growthȱ andȱ pollutantȱ bioaccumulation.ȱ Summarizingȱ bothȱ studiesȱ here,ȱ thereȱ wasȱ strongȱ evidenceȱ ofȱ aȱ relationȱ betweenȱ geneticȱ diversityȱ andȱ fitnessȱ measuresȱ (alsoȱ calledȱHeterozygosityȬFitnessȬCorrelationsȱorȱHFCs).ȱItȱmightȱbeȱexplainedȱeitherȱbyȱ anȱeffectȱofȱdirectȱoverdominanceȱatȱfunctionalȱmarkers.ȱRecently,ȱitȱbecameȱpossibleȱ toȱreliablyȱquantifyȱtheȱgeneȱandȱproteinȱexpressionȱlevelsȱduringȱexposureȱtoȱpollutȬ antsȱ andȱ parasites,ȱ allowingȱ theȱ earlyȱ detectionȱ ofȱ decreasedȱ fitnessȱ andȱ survival.ȱ Suchȱ knowledgeȱ wouldȱ provideȱ theȱ chanceȱ forȱ earlyȱ warningȱ systems,ȱ facilitatingȱ managementȱ actionsȱ beforeȱ majorȱ mortalityȱ eventsȱinȱ naturalȱ populationsȱandȱ proȬ videȱaȱlongȬtermȱassessmentȱofȱsuccessȱratesȱofȱconservationȱmeasures.ȱUsingȱsuffiȬ cientȱ backgroundȱ informationȱ onȱ theȱ identityȱ andȱ concentrationȱ ofȱ pollutant,ȱ thisȱ approachȱmayȱyieldȱbetterȱinsightsȱintoȱtheȱfactorsȱinfluencingȱtheȱrecentlyȱobservedȱ decreaseȱinȱfatȱcontent,ȱaȱpotentiallyȱcrucialȱmeasureȱforȱeelȇsȱabilityȱtoȱreachȱtheȱSarȬ gassoȱSea.ȱTheȱongoingȱanalysesȱofȱnorthernȱ(Belgium)ȱandȱSouthernȱ(Italy)ȱeelȱpopuȬ lationsȱforȱtheirȱgeneȱexpressionȱlevelȱandȱhealthȱstatusȱwillȱallowȱaddingȱaȱqualityȱ statusȱtagȱonȱsilverȱeels,ȱwhileȱidentifyingȱgoodȱqualityȱhabitatȱforȱpreservation.ȱ

6.5 The European Eel Quality Database

6.5.1 Introduction

Inȱ 2006ȱ theȱ EELȱ WGȱ recommendedȱ thatȱ furtherȱ samplingȱ andȱ ongoingȱ monitoringȱ intoȱ eelȱ qualityȱ wasȱ urgentlyȱ required.ȱ Memberȱ countriesȱ shouldȱ setȱ upȱ aȱ nationalȱ programmeȱonȱRBDȱscaleȱtoȱevaluateȱtheȱqualityȱofȱemigratingȱspawners.ȱThisȱshouldȱ includeȱ atȱ leastȱ bodyȱ burdenȱ ofȱ PCBs,ȱ BFRs,ȱ infestationȱ levelsȱ withȱ A.ȱ crassus,ȱ andȱ EVEX.ȱItȱshouldȱbeȱincludedȱinȱtheȱnationalȱmanagementȱplansȱwhileȱspecialȱemphaȬ sisȱshouldȱbeȱgivenȱtoȱstandardizationȱandȱharmonizationȱofȱresultsȱ(unitsȱandȱmethȬ ods).ȱToȱthisȱeffectȱtheȱEuropeanȱEelȱQualityȱDatabaseȱwasȱcreatedȱinȱBelgiumȱinȱ2007ȱ andȱ circulatedȱ amongȱ membersȱ ofȱ theȱ EELWGȱ requestingȱ dataȱonȱ fatȱ composition,ȱ contaminantȱanalysisȱandȱinfectionȱparametersȱofȱA.ȱcrassus.ȱDuringȱtheȱintersessionȱ periodȱandȱduringȱtheȱWorkingȱGroupȱmeetingȱ2008ȱeelȱqualityȱdataȱhasȱbeenȱproȬ videdȱandȱincludedȱinȱtheȱEEQD.ȱ 100 EIFAC/ICES WGEEL Report 2008

Theȱ databaseȱ isȱ coordinatedȱ byȱ theȱ Researchȱ Instituteȱ forȱ Natureȱ andȱ Forestȱ (BelȬ gium)ȱandȱincludesȱdataȱonȱeelȱqualityȱelements,ȱsuchȱasȱcondition,ȱcontaminantȱconȬ centrationsȱandȱepidemiologicalȱparameters,ȱinȱadditionȱtoȱtheȱrelevantȱdescriptorsȱofȱ dateȱ andȱ placeȱ ofȱ samplingȱ andȱ sampleȱ characteristicsȱ (eelȱ lifeȱ stage,ȱ numberȱ andȱ morphometrics).ȱTheȱdatabaseȱwasȱinitiallyȱrestrictedȱtoȱaȱlimitedȱnumberȱofȱqualityȱ elementsȱ(lipidȱcontent,ȱca.ȱ30ȱchemicalsȱandȱA.ȱcrassusȱinfectionȱparameters).ȱDuringȱ WGEELȱ2007ȱsomeȱcountriesȱreportedȱonȱsomeȱmoreȱelements,ȱandȱtheȱlistȱofȱICES7ȱ (CB28,ȱCB52,ȱCB101,ȱCB118,ȱCB138,ȱCB153ȱandȱCB180)ȱcongenersȱwasȱextendedȱwithȱ nonȬorthoȱandȱmonoȬorthoȱcongeners,ȱasȱtheyȱexhibitȱtheȱhighestȱdioxinȬlikeȱtoxicityȱ andȱcontributeȱmostȱtoȱtheȱTEQȱ(toxicȱequivalency).ȱAlsoȱoneȱpesticide,ȱseveralȱmetalsȱ andȱsomeȱbacterialȱdiseaseȱagentsȱwereȱadded.ȱ

DuringȱtheȱWGEEL,ȱ2008ȱevidenceȱhasȱbeenȱpresentedȱthatȱconditionȱfactorsȱareȱimȬ portantȱelementsȱforȱestimatinglȱee ȱqualityȱ(Acouȱetȱal.,ȱ2008;ȱBelpaireȱetȱal.,ȱ2008).ȱItȱ wasȱ recommendedȱ thatȱ conditionȱ shouldȱ beȱ includedȱ inȱ theȱ EEQD,ȱ thisȱ requiresȱ howeverȱaȱstandardizedȱmethodologyȱ(Froese,ȱ2006).ȱ

6.5.2 Analysis of the EEQD

Duringȱ theȱ Workingȱ Groupȱ session,ȱ newȱ dataȱ wereȱ compiledȱ andȱ theȱ EEQDȱ nowȱ containsȱ informationȱ fromȱ 14ȱ countriesȱ reviewedȱ inȱ Tableȱ 6.2.ȱ Dataȱ fromȱ Norway,ȱ FranceȱandȱEstoniaȱalsoȱareȱavailableȱandȱwillȱbeȱincludedȱinȱ2008.ȱDataȱsourceȱisȱhetȬ erogeneous,ȱ dataȱ derivingȱ mostȱ fromȱ nationalȱ orȱ localȱ levelȱ surveys,ȱ butȱ alsoȱ fromȱ ecoȬtoxicologicalȱstudies.ȱBelgiumȱhasȱpresentedȱtheȱmostȱexhaustiveȱinformation,ȱasȱ aȱconsequenceȱofȱtheȱavailabilityȱofȱdataȱfromȱtheȱFlemishȱeelȱpollutionȱnetwork,ȱinȱ placeȱ sinceȱ 1994ȱ (Belpaireȱ andȱ Goemans,ȱ 2007).ȱ Norwayȱ alsoȱ providedȱ aȱ longȱ timeȱ monitoringȱ seriesȱ inȱ theȱ Grenlandȱ fjordsȱ (S.ȱ Norway)ȱ followingȱ theȱ discoveryȱ ofȱ PCDF/PCDDsȱinȱedibleȱorganismsȱafterȱaȱ99%ȱreductionȱinȱtheȱloadȱofȱwasteȱcompoȬ nentsȱfromȱtheȱHydroȱPorsgrunnȱmagnesiumȱfactoryȱ(Knutzenȱetȱal.,ȱ2001).ȱHowever,ȱ theȱlongestȱdataseriesȱforȱbioaccumulationȱofȱcontaminantsȱisȱfromȱtheȱNetherlands,ȱ becauseȱinȱthisȱcountryȱaȱmonitoringȱnetworkȱforȱPCBs,ȱOCPSȱandȱmercuryȱinȱeelȱisȱ inȱplaceȱsinceȱtheȱ1979s,ȱlinkedȱtoȱtheȱsafetyȱforȱconsumptionȱnorms.ȱGermanyȱandȱ UKȱhaveȱprovidedȱdataȱonȱconcentrationȱofȱpollutantsȱandȱcontaminantsȱrelativeȱtoȱ someȱriverȱbasins,ȱcarriedȱoutȱwithinȱlocalȱmonitoringȱprogrammes.ȱSomeȱcountriesȱ (Italy,ȱPortugal,ȱSpain)ȱdidȱreportȱdataȱdrawnȱfromȱecoȬtoxicologicalȱstudiesȱcarriedȱ outȱwithinȱspecificȱresearches.ȱSomeȱcountriesȱ(e.g.ȱFranceȱandȱtheȱNetherlands)ȱhaveȱ publishedȱ reportsȱ demonstratingȱ thatȱ considerableȱ informationȱ isȱ available.ȱ Atȱ theȱ presentȱmomentȱthisȱinformationȱisȱnotȱaccessibleȱforȱinclusionȱinȱtheȱEEQD.ȱOnȱtheȱ whole,ȱ eelȱ qualityȱ dataȱ wereȱ providedȱ forȱ approximatelyȱ 600ȱ differentȱ sitesȱ overȱ Europe;ȱatȱtheȱpresentȱhowever,ȱtheȱdatabaseȱisȱoverbalanced,ȱmostȱofȱtheȱsitesȱbeingȱ situatedȱ inȱ Belgium.ȱ Mostȱ informationȱ isȱ availableȱ forȱ heavyȱ metalsȱ (771ȱ records),ȱ PCBsȱ(695ȱrecords)ȱandȱorganochlorineȱpesticidesȱ(OCPs)ȱ(656ȱrecords)ȱwhileȱ566ȱobȬ servationsȱonȱlipidȱcontentȱwereȱalsoȱincluded.ȱApartȱfromȱsomeȱobservationsȱonȱbacȬ terialȱ diseasesȱ availableȱ forȱ threeȱ sitesȱ inȱ Spainȱ andȱ oneȱ siteȱ inȱ UK,ȱ diseaseȱ agentsȱ includedȱinȱtheȱdatabaseȱareȱrestrictedȱtoȱtheȱswimbladderȱnematodeȱA.ȱcrassus,ȱwithȱ epidemiologicalȱdataȱfromȱ335ȱsitesȱacrossȱEurope.ȱ

Givenȱtheȱimportanceȱofȱlipidȱlevelsȱasȱanȱenergyȱresourceȱutilizedȱgdurinȱ theȱeels’ȱ migrationȱ andȱ forȱ theȱ productionȱ ofȱ gametes,ȱ disturbingȱ dataȱ areȱ seenȱ inȱ Europe.ȱ Fourȱoutȱofȱtwelveȱcountriesȱhaveȱaȱfatȱpercentageȱaboveȱ20%ȱ(Figureȱ6.5,ȱtheȱminimalȱ lipidȱ storageȱ neededȱ forȱ aȱ successfulȱ reproductionȱ (Boëtiusȱ andȱ Boëtius,ȱ 1980;ȱ Vanȱ denȱThillartȱetȱal.,ȱ2004;ȱ2005).ȱ

Researchȱonȱtheȱfatȱcontentȱinȱyellowȱeelsȱhasȱbeenȱdoneȱonȱtwoȱ(independent)ȱlargeȱ datasetsȱofȱlipidȱcontentsȱinȱyellowȱeelsȱfromȱBelgiumȱandȱtheȱNetherlands.ȱAȱ7.7%ȱ EIFAC/ICES WGEEL Report 2008 101

decreaseȱinȱlipidȱcontentȱonȱwetȱweightȱbasisȱoverȱaȱ13ȱyearȱperiodȱhasȱbeenȱrevealedȱ inȱBelgium.ȱWhereasȱinȱtheȱNetherlandsȱbeforeȱ1990ȱtheȱmeanȱfatȱcontentȱwasȱgenerȬ allyȱ superiorȱ toȱ 20%,ȱ aȱ clearȱ andȱ significantȱ decreaseȱ occurredȱ afterȱ 1990.ȱ NotwithȬ standingȱ theȱ differencesȱ inȱ bothȱ networkȱ concepts,ȱ andȱ largeȱ variationȱ inȱ lipidȱ contentsȱofȱeelsȱfromȱvariousȱwaterȱbodies,ȱsimilarȱtrendsȱwereȱobviousȱinȱBelgiumȱ andȱtheȱNetherlands:ȱaȱdropȱinȱlipidȱcontentsȱoverȱtheȱpastȱ15ȱyearsȱbyȱaboutȱoneȬ thirdȱ(fromȱca.ȱ20%ȱtoȱ13%)ȱ(Belpaireȱetȱal.,ȱinȱpress).ȱ

Table 6.2: Overview of the number of records of eel quality data compiled during the WGEEL 2008 and incorporated in the European Eel Quality Database.ȱ

HEAVY COUNTRY FAT PCB PESTICIDES METALS A. CRASSUS BFR DIOXIN PFOS

Belgiumȱ 409ȱ 408ȱ 373ȱ 373ȱ 140ȱ 24ȱ 8ȱȱ Denmarkȱ 7ȱ 6ȱ 6ȱȱ3ȱ 4ȱȱ12ȱ Estoniaȱȱȱȱȱȱȱȱȱ Finlandȱȱȱȱȱȱȱȱȱ Franceȱȱ12ȱȱ 3ȱȱȱȱȱ Germanyȱ 14ȱ 12ȱ 23ȱ 23ȱ 26ȱȱ2ȱȱ Irelandȱ 13ȱ 9ȱ 7ȱȱ6ȱ 7ȱ 7ȱȱ Italyȱ 24ȱ 24ȱ 20ȱ 7ȱ 10ȱȱȱȱ Latviaȱȱȱȱȱȱȱȱȱ Lithuaniaȱȱȱȱȱȱȱȱȱ NorthernȱIrelandȱ 2ȱȱ ȱ ȱ 3ȱȱȱȱ Norwayȱ 8ȱ 8ȱ 8ȱȱ ȱȱȱȱ Polandȱȱ 7ȱ 7ȱ 7ȱ 7ȱ 21ȱȱ7ȱȱ Portugalȱ 1ȱ 1ȱȱ 12ȱ 8ȱȱȱȱ Spainȱȱ 18ȱ 60ȱ 73ȱ 52ȱ 52ȱȱȱȱ Swedenȱȱ 25ȱ 10ȱ 1ȱ 179ȱ 51ȱȱ7ȱȱ TheȱNetherlandsȱ 37ȱ 99ȱ 99ȱ 76ȱȱȱȱȱ UKȱ 1ȱ 39ȱ 39ȱ 39ȱ 16ȱȱȱȱ TOTALȱ 566ȱ 695ȱ 656ȱ 771ȱ 335ȱ 35ȱ 31ȱ 12ȱ

30.00 N= 2 N= 1 N= 19 N= 5 N= 11 N= 16 N= 409 N= 30 N= 1 N= 15 N= 12 N= 1 25.00

20.00

15.00

10.00

5.00 Mean fat percentage of eel 0.00 SPAIN ITALY NORTH POLAND SWEDEN UNITED IRELAND IRELAND BELGIUM THE KINGDOM DENMARK GERMANY PORTUGAL NETHERLANDS ȱ

Figureȱ 6.5:ȱ Variationsȱ inȱ meanȱ muscleȱ lipidȱ contentȱ (%)ȱ inȱ yellowȱ endȱ silverȱ eelsȱ inȱ Europe.ȱ Nȱ indicatesȱtheȱnumberȱofȱsitesȱonȱwhichȱtheȱmeanȱvaluesȱareȱcalculated.ȱ 102 EIFAC/ICES WGEEL Report 2008

6.5.3 Future development of the database

TheȱdevelopmentȱofȱaȱEuropeanȱEelȱQualityȱDatabaseȱinȱtheȱWGEELȱ2007ȱhasȱbeenȱ updatedȱduringȱtheȱ2008ȱsessionȱandȱnowȱformsȱtheȱbasisȱforȱcompilingȱaȱcompreȬ hensiveȱpanȬEuropeanȱoverviewȱofȱeelȱqualityȱdata.ȱ

ThereȱisȱaȱwideȱrangeȱofȱinformationȱwidelyȱscatteredȱoverȱEuropeȱbyȱlocationȱandȱ collectingȱagency.ȱTheȱcollectionȱandȱreportingȱofȱeelȱqualityȱdataȱareȱrecommendedȱ withinȱtheȱinternationalȱframeworkȱforȱtheȱrestorationȱofȱtheȱspeciesȱ(DataȱCollectionȱ Regulation)ȱasȱproposedȱbyȱtheȱWorkingȱGroupȱonȱEelȱ(ICES,ȱ2006)ȱandȱtheȱScientific,ȱ TechnicalȱandȱEconomicȱCommitteeȱforȱFisheriesȱofȱtheȱECȱ(STECF,ȱ2006).ȱTheȱcollecȬ tionȱofȱsuchȱdataȱareȱnowȱalsoȱincludedȱinȱtheȱguidelinesȱforȱtheȱpreparationȱofȱEelȱ ManagementȱPlans.ȱ

Someȱ informationȱ isȱ missingȱ andȱ theȱ databaseȱ hasȱ toȱ beȱ expandedȱ andȱfurtherȱ upȬ datedȱ inȱ theȱ future.ȱ Forȱ instanceȱ someȱ countriesȱ (e.g.ȱ Franceȱ andȱ theȱ Netherlands)ȱ haveȱ publishedȱ reportsȱ thatȱ demonstrateȱ considerableȱ informationȱ isȱ availableȱ butȱ dataȱ wereȱ notȱ presentedȱ forȱ inclusionȱ inȱ theȱ EEQD.ȱ Itȱ isȱ alsoȱ presumedȱ thatȱ manyȱ unpublishedȱresultsȱareȱavailableȱinȱsomeȱcountriesȱandȱshouldȱbeȱutilizedȱbyȱincluȬ sionȱinȱtheȱdatabase.ȱSomeȱwereȱprovidedȱduringȱtheȱWorkingȱGroupȱmeeting,ȱbutȱ couldȱnotȱbeȱincludedȱinȱtheȱdatabaseȱatȱtheȱtime.ȱ

Consideringȱthatȱeelȱqualityȱcouldȱbeȱaȱmajorȱelementȱinȱtheȱdeclineȱofȱtheȱspecies,ȱtheȱ databaseȱmayȱbecomeȱaȱusefulȱtoolȱforȱtheȱ(inter)nationalȱeelȱconservationȱmeasures.ȱ Theȱ databaseȱ allowsȱ theȱ identificationȱ andȱ designationȱ ofȱ goodȱ qualityȱ sitesȱ whereȱ specialȱmeasuresȱforȱmaximumȱprotectionȱofȱstocksȱandȱemigratingȱspawnersȱofȱgoodȱ qualityȱ canȱ beȱ proposedȱ (e.g.ȱ restrictionȱ ofȱ fisheries,ȱ priorityȱ placesȱ forȱ restocking,ȱ priorityȱforȱhabitatȱrestorationȱmeasures,ȱetc).ȱFromȱpreliminaryȱanalysesȱitȱwasȱclearȱ thatȱmanyȱcontaminantsȱandȱlipidȱreservesȱvariedȱaȱlotȱoverȱtheȱdistributionȱareaȱofȱ theȱeelȱ(ICES,ȱ2007)ȱandȱtheȱpresenceȱofȱȇblackȱspotsȇȱwasȱidentified.ȱEEQDȱdataȱonȱ diseaseȱ agentsȱ suchȱ asȱ A.ȱ crassusȱ demonstratedȱ aȱ widespreadȱ distributionȱ overȱ Europe.ȱFromȱanȱenvironmentalȱpointȱofȱviewȱitȱisȱclearȱthatȱtheȱdatabaseȱwillȱgiveȱ informationȱaboutȱspecificȱenvironmentalȱchemicalȱpressuresȱandȱwillȱindicateȱpolluȬ tionȱ areasȱ forȱ specificȱ contaminants.ȱ Theȱ databaseȱ willȱ allowȱ anȱ overviewȱ andȱ inȬ depthȱanalysisȱofȱeelȱqualityȱonȱaȱEuropeȱwideȱscaleȱandȱfollowȬupȱofȱemergingȱprobȬ lemsȱ ofȱ aȱ chemicalȱ orȱ epidemiologicalȱ natureȱ andȱ couldȱ alsoȱ beȱ usedȱ asȱ anȱ earlyȱ warningȱsystemȱforȱtheȱspreadȱofȱnewȱeelȱdiseasesȱorȱcontaminants.ȱYellowȱeelsȱhaveȱ beenȱproposedȱasȱaȱsentinelȱorganismȱforȱevaluatingȱtheȱchemicalȱqualityȱofȱpriorityȱ hazardousȱsubstancesȱinȱbiotaȱinȱaccordanceȱwithȱtheȱWFD.ȱEEQDȱcanȱintegrateȱtheseȱ dataȱandȱmakeȱthemȱavailableȱforȱeelȱstockȱmanagement.ȱTheȱdatabaseȱwillȱpinpointȱ sitesȱwhereȱtheȱqualityȱofȱeelsȱisȱbelowȱthatȱdeemedȱsuitableȱforȱhumanȱconsumption,ȱ soȱadequateȱfisheriesȱmanagementȱmeasures,ȱlikeȱclosingȱfisheriesȱorȱpreventingȱconȬ sumptionȱofȱeels,ȱcanȱbeȱtakenȱinȱtheseȱareas.ȱ

6.6 Conclusions and recommendations for Chapter 6: Eel quality

6.6.1 Conclusions

Estimationȱofȱeffectiveȱspawnerȱbiomassȱrequiresȱquantificationȱofȱtheȱadverseȱeffectsȱ ofȱcontaminants,ȱparasites,ȱdiseases,ȱlowȱfatȱlevels,ȱnonȬlethalȱturbineȱdamage,ȱalongȱ theȱlinesȱpreviouslyȱproposedȱforȱA.ȱcrassus,ȱasȱwellȱasȱotherȱmortalityȱratesȱthroughȬ outȱtheȱriverȱbasin.ȱPresentȱknowledgeȱdoesȱnotȱfullyȱpermitȱquantitativeȱassessmentȱ ofȱtheȱeffectsȱofȱtheseȱfactorsȱonȱtheȱoverallȱstock.ȱ

TheȱEuropeanȱEelȱQualityȱDatabaseȱ(EEQD)ȱhasȱbeenȱupdatedȱwithȱdataȱonȱcontamiȬ nants,ȱ parasitesȱ andȱ fatȱ levelsȱ inȱ eel,ȱ allowingȱ theȱ compilationȱ ofȱ aȱ comprehensiveȱ EIFAC/ICES WGEEL Report 2008 103

overviewȱ ofȱ theȱ contaminantȱ loadȱ inȱ eelȱ overȱ itsȱ distributionȱ area.ȱ Resultsȱ demonȬ strateȱ highlyȱ variableȱ dataȱ withinȱ riverȱ basinȱ districts,ȱ accordingȱ toȱ localȱ anthropoȬ genicȱ pollution,ȱ linkedȱ withȱ landȱ use.ȱ Persistentlyȱ elevatedȱ contaminationȱ levels,ȱ aboveȱ humanȱ consumptionȱ standards,ȱ areȱ seenȱ inȱ manyȱ Europeanȱ countries.ȱ Theȱ mostȱimportantȱreportedȱimpactȱisȱseenȱonȱtheȱfatȱcontentȱofȱtheȱyellowȱeelsȱ(i.e.ȱinȱ BelgiumȱandȱtheȱNetherlands)ȱwhichȱhasȱdecreasedȱoverȱtheȱlastȱnumberȱyearsȱandȱ whichȱraisesȱconcernȱregardingȱtheȱmigratoryȱandȱreproductoryȱsuccessȱofȱsilverȱeels.ȱ ThereȱisȱgrowingȱevidenceȱthatȱA.ȱcrassusȱisȱspreadingȱfurtherȱintoȱnewȱareasȱandȱnewȱ dataȱindicateȱtheȱpresenceȱofȱtheȱnematodeȱinȱCanadaȱ(notȱincludedȱinȱtheȱEEQDȱyet)ȱ forȱtheȱfirstȱtime.ȱ

Clearȱecotoxicologicalȱeffectsȱofȱcontaminantsȱhaveȱbeenȱdemonstrated.ȱTheȱmostȱimȬ portantȱimpactȱisȱseenȱonȱtheȱfatȱcontentȱofȱtheȱeelsȱwhichȱisȱdecreasingȱoverȱtheȱlastȱ numberȱof ȱyearsȱandȱwhichȱmayȱjeopardizeȱmigrationȱandȱreproductionȱsuccess.ȱ

TheȱvalueȱofȱmonitoringȱcontaminantsȱinȱeelȱforȱenvironmentalȱissuesȱhasȱbeenȱdemȬ onstrated.ȱButȱtheȱeelȱasȱaȱbioȬindicatorȱisȱnotȱrecordedȱinȱtheȱWaterȱFrameworkȱDiȬ rectiveȱ andȱ theȱ numberȱ ofȱ contaminantsȱ recordedȱ isȱ insufficientȱ forȱ safeguardingȱ sufficientlȱee ȱhealth.ȱ

6.6.2 Recommendations

TheȱWorkingȱGroupȱrecommendsȱtheȱcontinuationȱonȱaȱlocalȱscaleȱofȱtheȱlongȬtermȱ monitoringȱofȱqualityȱ(contaminants,ȱparasitesȱandȱdisease)ȱinȱeelȱwithȱanȱemphasisȱ onȱstandardizingȱtheȱmethodologicalȱapproach,ȱanalysisȱofȱnewȱcompounds,ȱanȱapȬ propriateȱ communicationȱ systemȱ andȱ robustȱ dataȱ management.ȱ Theȱ Europeanȱ Eelȱ QualityȱDatabaseȱshouldȱbeȱdevelopedȱandȱmaintained.ȱMemberȱStatesȱshouldȱinitiȬ ateȱharmonizedȱmonitoringȱstrategiesȱaimedȱtowardȱtheȱdevelopmentȱofȱaȱEuropeanȱ EelȱQualityȱMonitoringȱNetwork,ȱtoȱcollectȱtheȱrelevantȱdataȱtoȱbeȱfedȱintoȱtheȱEEQD.ȱ

Theȱ Workingȱ Groupȱ recommendsȱ investigationsȱintoȱ eelȱ qualityȱ ofȱ theȱ eelsȱ leavingȱ continentalȱ watersȱ soȱ asȱ toȱ includeȱ qualityȱ aspectsȱ inȱ eelȱ stockȱ managementȱ andȱ evaluationȱofȱeffectiveȱspawningȱescapement.ȱ

CarryȱoutȱaȱEuropeȱwideȱstudyȱtoȱcomprehendȱrelationshipsȱbetweenȱcontaminationȱ andȱeelȱstockȱdecline.ȱAnȱimportantȱfocusȱshouldȱbeȱtoȱstudyȱtheȱeffectsȱofȱcontamiȬ nantsȱonȱlipidȱmetabolismȱandȱcondition.ȱ

TheȱWorkingȱGroupȱrepeatsȱitsȱrecommendationȱthatȱcontaminantȱmonitoringȱinȱeelȱ shouldȱbeȱincludedȱasȱaȱtoolȱforȱmeasuringȱtheȱchemicalȱstatusȱofȱourȱwaterȱbodiesȱasȱ definedȱinȱtheȱWaterȱFrameworkȱDirective.ȱ 104 EIFAC/ICES WGEEL Report 2008

7 Oceans, climate and recruitment

7.1 Introduction

TermȱofȱReferenceȱc.ȱtaskedȱtheȱWorkingȱGroupȱto,ȱ“reviewȱhypothesesȱandȱinformaȬ tionȱonȱtheȱpossibleȱrelationshipsȱbetweenȱtheȱEuropeanȱ(andȱAmerican)ȱeelȱstock(s),ȱ recruitmentȱpatternsȱandȱclimaticȱandȱoceanicȱfactors”.ȱ

EuropeanȱA.ȱanguillaȱandȱnorthȱAmericanȱA.ȱrostrataȱeelȱspawnȱin ȱtheȱSargassoȱSea.ȱ Thisȱpartȱofȱtheȱlifeȱcycleȱhasȱnotȱbeenȱwitnessedȱorȱquantifiedȱandȱthereforeȱtheȱfullȱ stock–recruitmentȱrelationshipȱcircleȱcannotȱbeȱclosedȱatȱpresent.ȱOceanicȱfactors,ȱbioȬ logicalȱandȱphysical,ȱmayȱinfluenceȱtheȱrecruitmentȱofȱeelȱthroughȱimpactingȱonȱbothȱ theȱmigratingȱsilverȱeelsȱandȱonȱtheȱsubsequentȱreturnȱofȱjuvenileȱrecruits.ȱOverlaidȱ onȱthis,ȱrecruitmentȱofȱEuropeanȱeelȱhasȱdecreasedȱbyȱapproximatelyȱ95%ȱsinceȱ1982ȱ (Dekker,ȱ2003)ȱandȱisȱbelowȱ5%ȱsinceȱ2000ȱ(ICES,ȱ2007).ȱ

InȱaddressingȱthisȱToR,ȱtheȱWGȱinȱitsȱpreȬmeetingȱundertookȱaȱliteratureȱreviewȱandȱ invitedȱsubmissionsȱtoȱthisȱreview.ȱTheȱWGȱwouldȱlikeȱtoȱacknowledgeȱinputsȱfromȱ Beaulaton,ȱBonhommeau,ȱCairns,ȱDekker,ȱFriedland,ȱKettle,ȱKnights,ȱandȱMiller.ȱ

7.2 Review of ocean change/controlling mechanisms

LongȬtermȱclimateȱvariationȱinȱtheȱNorthȱAtlanticȱhasȱbeenȱrevealedȱtoȱcorrelateȱwithȱ observedȱtrendsȱinȱaquaticȱandȱterrestrialȱecosystemsȱthroughoutȱEuropeȱ(Ottersenȱetȱ al.,ȱ2001).ȱSSTȱ(seaȱsurfaceȱtemperature)ȱdifferencesȱmayȱbeȱtheȱmainȱdriversȱofȱtheȱ NorthȱAtlanticȱOscillationȱ(NAO)ȱandȱassociatedȱcontinentalȱclimateȱchange.ȱCyclesȱ ofȱ changeȱ couldȱ resultȱ fromȱ slowȱ transfersȱ ofȱ warmer/colderȱ waterȱ byȱ theȱ majorȱ thermohalineȱ andȱ windȬdrivenȱ gyreȱ currentsȱ (Hurrell,ȱ 1995).ȱ Changesȱ inȱ theȱ NAOȱ winterȱindexȱ(NAOI)ȱsinceȱtheȱ1820sȱappearȱtoȱfollowȱcyclesȱwithȱperiodsȱvaryingȱinȱ theȱrangeȱ7ȱtoȱ13ȱyears.ȱInȱadditionȱtoȱtheȱNAOȱthereȱareȱotherȱnaturalȱlongerȱperiodȱ climateȱcyclesȱi.e.ȱtheȱapproximatelyȱ60ȱyearȱAtlanticȱMultidecadalȱOscillationȱ(AMO,ȱ SuttonȱandȱHodson,ȱ2005)ȱ(Figureȱ7.1).ȱSuperposedȱonȱtheȱnaturalȱclimateȱoscillationȱ isȱtheȱsteadyȱanthropogenicȱincreaseȱofȱglobalȱtemperature.ȱ

TheȱwidelyȱusedȱNAOȱindexȱquantifiesȱalterationsȱinȱatmosphericȱpressureȱbetweenȱ theȱsubtropicalȱAtlanticȱ(Azores)ȱandȱtheȱArcticȱ(Iceland).ȱAnȱincreasedȱAzoresȱHighȱ indicatesȱmoreȱandȱstrongerȱwinterȱstormsȱcrossingȱtheȱAtlanticȱinȱaȱmoreȱnortherlyȱ track,ȱandȱshiftsȱtheȱGulfȱStreamȱtoȱaȱmoreȱnortherlyȱposition.ȱAȱnumberȱofȱalternaȬ tiveȱindicesȱhaveȱbeenȱdefined,ȱvaryingȱinȱtheȱmonthsȱincluded,ȱtheȱanalysisȱproceȬ dureȱ andȱ theȱ exactȱ locationsȱ measuredȱ (Dekker,ȱ 2004a).ȱ Theȱ NAOȱ winterȱ indexȱ isȱ alwaysȱused,ȱbecauseȱitȱprovidesȱtheȱmostȱpronouncedȱsignal.ȱTheȱNorthȱAtlanticȱSSTȱ demonstratesȱaȱlongȬtimeȱdownwardȱtrendȱexpressingȱtheȱcombinedȱeffectsȱofȱNAOȱ andȱAMOȱfromȱtheȱearlyȱ1940sȱuntilȱtheȱearlyȱ1970sȱfollowedȱbyȱaȱgradualȱincreaseȱ untilȱtheȱmidȱ2000s,ȱamplifiedȱbyȱtheȱanthropogenicȱwarming.ȱTheȱmostȱrecentȱdataȱ indicateȱtheȱbeginningȱofȱaȱcoolingȱperiod.ȱTheȱunusualȱwarmingȱofȱtheȱNorthȱAtlanȬ ticȱisȱalsoȱindicatedȱbyȱtheȱrelationshipsȱtoȱtheȱSargassoȱSeaȱSurfaceȱTemperatureȱ(SSȬ SST)ȱ(Figureȱ7.2).ȱOtherȱparametersȱhaveȱalsoȱbeenȱanalysedȱbyȱvariousȱauthorsȱandȱ theirȱputativeȱeffectsȱareȱdescribedȱinȱTableȱ7.1.ȱ EIFAC/ICES WGEEL Report 2008 105

Figureȱ7.1:ȱTheȱeffectȱofȱtheȱnaturalȱclimateȱoscillationsȱoverȱtheȱNorthȱAtlanticȱareaȱonȱtheȱmeanȱ yearlyȱseaȱtemperatureȱofȱtheȱKolaȱsectionȱinȱtheȱBarentsȱSeaȱillustratingȱtheȱinteractionȱbetweenȱ decadalȱandȱmultidecadalȱtimeȬscales.ȱFromȱSveinȱSundbyȱpresentedȱatȱFisheriesȱManagementȱandȱ ClimateȱChangeȱinȱtheȱNortheastȱAtlanticȱOceanȱandȱtheȱBalticȱSea,ȱBergenȱ17–18ȱAprilȱ2008.ȱ

7.3 Review of recruitment patterns in eels

Leptocephaliȱ larvaeȱ ofȱ Europeanȱ eelȱ areȱ transportedȱ alongȱ theȱ Gulfȱ Streamȱ andȱ NorthȬAtlanticȱ Driftȱ forȱ aȱ journeyȱ takingȱ somewhereȱ betweenȱ anȱ estimatedȱ 8–9ȱ monthsȱ(LecomteȬFiniger,ȱ1992)ȱandȱ2–3 ȱyearsȱ(Tesch,ȱ2003;ȱKettleȱandȱHaines,ȱ2006;ȱ Bonhommeauȱ etȱ al.,ȱ 2008)ȱ toȱ arriveȱ backȱ toȱ theȱ easternȱ Atlanticȱ coastȱ whereȱ theyȱ metamorphoseȱtoȱglassȱeels,ȱascendȱriversȱandȱgrowȱasȱyellowȱeelsȱuntilȱreachingȱparȬ tialȱ maturityȱ (Tesch,ȱ 2003).ȱ Americanȱ eelȱ leptocephaliȱ mustȱ alsoȱ reachȱ theȱ Floridaȱ CurrentȱorȱGulfȱStream,ȱalthoughȱtheyȱlaterȱhaveȱtoȱleaveȱthatȱcurrentȱsystemȱtoȱreȬ cruitȱtoȱtheȱcoastȱofȱNorthȱAmerica.ȱLeptocephaliȱgrowȱlargerȱandȱhaveȱaȱlongerȱlarȬ valȱdurationȱthanȱmostȱfishȱspecies,ȱtakingȱupȱtoȱaȱyearȱorȱlongerȱbeforeȱtheyȱrecruitȱ toȱfreshȬwaterȱhabitatsȱasȱglassȱeelsȱorȱelvers.ȱThisȱlongȱlarvalȱdurationȱisȱthoughtȱtoȱ makeȱ leptocephaliȱ particularlyȱ susceptibleȱ toȱ changesȱ inȱ oceanȱ currentsȱ andȱ foodȱ availabilityȱ(Friedlandȱetȱal.,ȱ2007).ȱ

Aȱfundamentalȱquestionȱinȱresolvingȱtheȱroleȱofȱoceanȱcirculationȱinȱlifeȱcycleȱofȱtheȱ Europeanȱ eelȱ isȱ theȱ durationȱ ofȱ theȱ larvalȱ migration.ȱ Schmidt,ȱ 1923ȱ madeȱ aȱ carefulȱ analysisȱofȱtheȱageȱcohortȱsizeȱstructureȱforȱleptocephaliȱcapturesȱacrossȱtheȱAtlanticȱ Oceanȱandȱconcludedȱthatȱtheȱpassiveȱtransatlanticȱmigrationȱlastsȱtwoȱyearsȱwithȱtheȱ metamorphosedȱglassȱeelsȱenteringȱfreshȱandȱbrackishȱwatersȱinȱspringȱatȱtheȱendȱofȱ theirȱ thirdȱ year.ȱ Directȱ Lagrangian ȱ simulationsȱ (Hardenȱ Jones,ȱ 1968)ȱ indicatedȱ thatȱ theȱmigrationȱshouldȱtakeȱ2.5–3ȱyears.ȱAȱmoreȱrecentȱLagrangianȱstudyȱ(Kettleȱandȱ Haines,ȱ 2006)ȱ suggestedȱ thatȱ theȱ durationȱ ofȱ theȱ larvalȱ eelȱ migrationȱ wasȱ probablyȱ aboutȱtwoȱyears.ȱOnȱtheȱotherȱhand,ȱglassȱeelȱotolithȱringȱcountsȱhaveȱindicatedȱanȱ oceanicȱmigrationȱtimenȱofȱlessȱtha ȱaȱyearȱ(LecomteȬFiniger,ȱ1992),ȱbutȱthereȱisȱdebateȱ aboutȱwhetherȱtheȱgrowthȱringsȱareȱdepositedȱdaily.ȱKnights,ȱ2003ȱandȱFriedlandȱetȱ al.,ȱ2007ȱsuggestȱthatȱthereȱmayȱonlyȱbeȱaȱoneȱyearȱtimeȱdelayȱoceanicȱperturbationsȱ representedȱbyȱtheȱNAOȱandȱtheȱDenOeverȱglassȱeelȱindex,ȱimplyingȱaȱoneȱyearȱmiȬ grationȱperiod.ȱTheȱmostȱrecentȱstudyȱbyȱBonhommeauȱetȱal.,ȱ2008ȱhasȱindicatedȱthatȱ thereȱisȱaȱ2–3ȱyearȱtimeȬlagȱbetweenȱperturbationsȱofȱoceanȱtemperatureȱandȱprimaryȱ 106 EIFAC/ICES WGEEL Report 2008

productivityȱinȱtheȱSargassoȱSeaȱandȱglassȱeelȱrecruitmentȱindicesȱinȱAtlanticȱFrance,ȱ andȱthereȱisȱaȱconvergenceȱofȱopinionȱthatȱtheȱdurationȱofȱtheȱlarvalȱmigrationȱmayȱbeȱ approximatelyȱtwoȱyears.ȱ

Tableȱ7.1.ȱOceanicȱparametersȱthatȱhaveȱbeenȱanalysedȱbyȱvariousȱauthorsȱandȱtheirȱputativeȱefȬ fectsȱonȱeels.ȱ

OCEANIC FACTOR MECHANISM OF INFLUENCE AUTHOR

NorthȱAtlanticȱoscillationȱ NAOȱquantifiesȱtheȱalterationȱinȱ Dekker,ȱ2004ȱ NAOȱȱ atmosphericȱtemperaturesȱbetweenȱtheȱ AzoresȱandȱIceland.ȱȱ

Itȱindicatesȱaȱmoreȱnortherlyȱpositionȱofȱ theȱGulfȱStream.ȱImpactsȱlarvalȱ migrationȱ SargassoȱSeaȱSeaȱSurfaceȱ Theȱmarineȱproductionȱincreasesȱwithȱ Bonhommeauȱetȱal.,ȱ2008ȱ Temperaturesȱ seaȱsurfaceȱtemperatureȱinȱtheȱcoolerȱ (SSȬSST),ȱaverageȱ0Ȭ100ȱmȱ watersȱfromȱtheȱNorthȱAtlanticȱbutȱ deepȱ decreaseȱinȱwarmerȱwaters.ȱThisȱeffectȱisȱ asȱaȱconsequenceȱofȱaȱreducedȱverticalȱ mixingȱandȱlowerȱmarineȱproductionȱ thusȱimpactingȱlarvalȱfeedingȱ SargassoȱSeaȱWindsȱ Surfaceȱcurrent,ȱcausedȱbyȱtheȱcombinedȱ Friedlandȱetȱal.,ȱ2007ȱ effectȱofȱwindȱandȱCoriolisȱforces,ȱhaveȱ diminished,ȱreducingȱtheȱwestwardȱ transportȱtowardsȱtheȱFloridaȱcurrentȱ intoȱtheȱGulfȱStream–couldȱaffectȱ transportȱofȱleptocephaliȱ MeanȱTemperatureȱofȱtheȱ Wouldȱreflectȱclimateȱchangeȱandȱitsȱ Knightsȱandȱ northernȱhemisphereȱ impactȱonȱprimaryȱproductionȱinȱtheȱ Bonhommeau,ȱ (NHT)ȱ oceanȱandȱlarvalȱfeeding.ȱ unpublishedȱ GulfȱStreamȱIndexȱ(GSI)ȱ LatitudeȱofȱtheȱGulfȱStream,ȱfromȱ Bonhommeau,ȱ2008ȱ monthlyȱchartsȱofȱtheȱnorthȱwallȱ Transportȱindexȱ(TI)ȱ StrengthȱofȱtheȱGulfȱStreamȱandȱNorthȱ Bonhommeau,ȱ2008ȱ Atlanticȱcurrentȱsystemȱ(baroclinicȱgyreȱ circulationȱinȱtheȱNorthȱAtlantic)ȱ Calculatedȱfromȱpotentialȱenergyȱ anomaliesȱ(PEA)ȱbetweenȱBermudaȱandȱ Labradorȱbasinȱ–ȱcouldȱaffectȱtransportȱ ofȱleptocephaliȱ PPȱ(Bermudaȱbiologicalȱ Primaryȱproduction.ȱConsideredȱasȱaȱ Bonhommeau,ȱ2008ȱ station,ȱNorthȱofȱspawningȱ goodȱproxyȱforȱleptocephaliȱfood.ȱ area)ȱ Seaȱsurfaceȱtemperaturesȱ Foodȱavailabilityȱforȱleptocephaliȱwouldȱ Knights,ȱ2003ȱ anomaliesȱ(SSTA)ȱ beȱexpectedȱtoȱbeȱreducedȱduringȱwarmȱ highȱSSTAȱperiodsȱasȱaȱconsequenceȱofȱ reducedȱspringȱmixing,ȱnutrientȱ recirculationȱandȱproductivityȱ Surfaceȱexpressionȱofȱtheȱ Theȱ22.5ȱ°Cȱisothermȱisȱaȱusefulȱindicatorȱ Friedlandȱetȱal.,ȱ2007ȱ 22.5°Cȱisothermȱ ofȱtheȱnorthernȱlimitȱofȱspawningȱbyȱ bothȱspeciesȱofȱeelsȱinȱtheȱAtlantic.ȱȱ Therefore,ȱchangesȱinȱtheȱlatitudeȱorȱ intensityȱofȱtheseȱfrontsȱmayȱaffectȱbothȱ theȱspawningȱlocationȱandȱtheȱ subsequentȱtransportȱofȱtheȱleptocephaliȱ toȱcontinentalȱhabitats.ȱ EIFAC/ICES WGEEL Report 2008 107

AȱveryȱshortȱtimeȬlagȱcomparedȱtoȱtheȱdriftȱestimatesȱseemsȱunlikelyȱconsideringȱtheȱ swimmingȱabilityȱofȱtheȱleptocephalusȱlarvaeȱ(Bonhommeau,ȱ2008).ȱToȱgainȱoneȱyearȱ inȱtheȱtransatlanticȱmigrationȱtheȱlarvaeȱhasȱtoȱsustainȱaȱcontinuous,ȱdirectedȱswimȬ mingȱ velocityȱ ofȱ 15ȱ toȱ 20ȱ cm/sec,ȱ orȱ 3–5ȱ bodyȬlengths/sec.ȱ Aȱ typicalȱ anguilliformȱ swimmingȱspeedȱisȱofȱtheȱorderȱ0.5ȱbodyȬlengths/secȱ(Ellerbyȱetȱal.,ȱ2001).ȱ

MetaȬanalysesȱofȱmanyȱlocalȱdataseriesȱhaveȱrevealedȱcommonȱtrendsȱinȱtheȱpopulaȬ tion.ȱTheȱbreakpointȱinȱtheȱrecruitmentȱseriesȱinȱsouthȱandȱmiddleȱEuropeȱfromȱ1980ȱ pointsȱtoȱaȱsharedȱprocessȱcausingȱtheȱdeclineȱthereafter.ȱRecruitmentȱseriesȱofȱyoungȱ yellowȱeelȱinȱnorthernȱEuropeȱdeviatesȱfromȱthis,ȱwithȱanȱearlierȱdeclineȱstartingȱdurȬ ingȱtheȱ1950s.ȱThisȱcouldȱbeȱinterpretedȱasȱaȱdifferentȱclimaticȱeffectȱonȱtheȱnorthȬȱandȱ southȬȱ goingȱ branchesȱ ofȱ theȱ Northȱ Atlanticȱ drift,ȱ whichȱ splitsȱ intoȱ theȱ Northȱ Eastȱ Atlanticd ȱan ȱtheȱCanaryȱcurrentsȱtoȱtheȱsouthwestȱofȱIreland.ȱ

7.4 Review of hypotheses of causal linkages between oceanic factors and recruitment patterns

Theȱ mechanismȱ orȱ mechanismsȱ behindȱ theȱ observedȱ correlationȱ betweenȱ glassȱ eelȱ recruitmentȱandȱclimateȱoscillationsȱareȱunknown.ȱTheȱmigratoryȱphaseȱofȱadultsȱandȱ larvae,ȱasȱwellȱasȱtheȱeggȱandȱlarvaeȱproductionȱmightȱhaveȱbeenȱinfluencedȱbyȱcliȬ mateȱvariation.ȱCurrentlyȱitȱisȱdifficultȱtoȱseparateȱoutȱtheȱimpactȱofȱoceanȱandȱclimateȱ onȱspawnerȱmigrationsȱandȱonȱsubsequentȱmigrationsȱofȱlarvaeȱandȱrecruitingȱglassȱ eels.ȱ

Itȱhasȱlongȱbeenȱrecognizedȱthatȱthereȱmayȱbeȱaȱdirectȱlinkȱbetweenȱlarvalȱmigrationȱ successȱandȱtheȱdensity,ȱorȱthermohalineȱcirculation,ȱofȱtheȱocean.ȱTheȱNAOȱmightȱ impactȱtheȱlarvalȱmigrationȱbyȱchangingȱtheȱoceanȱcurrentsȱorȱbyȱinfluencingȱoceanȱ productivityȱandȱfoodȱavailabilityȱforȱtheȱmigratingȱlarvaeȱ(Knights,ȱ2003).ȱTheȱlongȬ termȱvariationsȱinȱglassȱeelȱrecruitmentȱindicesȱmayȱbeȱmodulatedȱbyȱcharacteristicȱ timeȬscaleȱofȱtheȱNAOȱindex,ȱwhichȱvariesȱinȱperiodicityȱbetweenȱ7ȱandȱ13ȱ years.ȱThisȱ hadȱ importantȱ implicationsȱ inȱ explainingȱ theȱ longȬtermȱ declineȱinȱ glassȱ eelȱ recruitȬ mentȱacrossȱEuropeȱsinceȱtheȱlateȱ1970sȱasȱitȱhasȱbeenȱrecognizedȱthatȱtheȱNAOȱindexȱ hadȱbeenȱinȱaȱprolongedȱpositiveȱphaseȱoverȱthisȱperiodȱ(ICES,ȱ2001;ȱFriedland,ȱ2007).ȱ

Focussingȱ onȱ theȱ longȱ termȱ DenOeverȱ glassȱ eelȱ index,ȱ Friedlandȱ etȱ al.,ȱ 2007ȱ estabȬ lishedȱtheȱexistenceȱofȱsignificantȱcorrelationsȱwithȱenvironmentalȱparametersȱinȱtheȱ NorthȱAtlanticȱduringȱtheȱspawningȱperiodȱbetweenȱFebruaryȱandȱMay:ȱtheȱsurfaceȱ expressionȱofȱtheȱ22.5°Cȱisotherm,ȱtheȱeastwardȱwindspeeds,ȱandȱtheȱNAO.ȱExplanaȬ tionsȱ forȱ theȱ observedȱ relationshipsȱ focusedȱ onȱ theȱ possibleȱ influenceȱ ofȱ windȬ inducedȱ geostrophicȱ transportȱ inȱ advectingȱ larvaeȱ intoȱ theȱ Gulfȱ Streamȱ andȱ onȱ theȱ impactȱ ofȱ interannualȱ variabilityȱ ofȱ theȱ mixedȱ layerȱ depthȱ onȱ nutrientȱ supplyȱ andȱ oceanȱproductivityȱinȱprovidingȱfoodȱtoȱtheȱdevelopingȱlarvae.ȱ

AȱcloseȱnegativeȱrelationshipȱhasȱbeenȱfoundȱoverȱtheȱlastȱfourȱdecadesȱbetweenȱlongȬ termȱ fluctuationsȱ inȱ recruitmentȱ andȱ inȱ seaȱ temperatureȱ (Tableȱ 7.2).ȱ Byȱ contrast,ȱ variationsȱ inȱ integrativeȱ indicesȱ measuringȱ oceanȱ circulation,ȱ i.e.ȱ latitudeȱ andȱ strengthȱofȱtheȱGulfȱStream,ȱdidȱnotȱseemȱtoȱexplainȱvariationsȱinȱglassȱeelȱrecruitȬ mentȱ(Bonhommeauȱetȱal.,ȱ2008).ȱ

TheȱimpactȱofȱfoodȱavailabilityȱinȱtheȱSargassoȱSeaȱonȱtheȱsuccessȱofȱtheȱlarvalȱeelȱmiȬ grationȱwasȱsuggestedȱandȱrejectedȱbyȱDesaunayȱandȱGuerault,ȱ1997.ȱUsingȱinformaȬ tionȱaboutȱtheȱlengthȱofȱtheȱoceanicȱmigrationȱfromȱotolithsȱtheȱconclusionȱwasȱthatȱ theȱnumberȱandȱphysicalȱconditionȱofȱglassȱeelsȱ arrivingȱonȱtheȱcoastȱofȱFranceȱwasȱ linkedȱ toȱ chlorophyllȱ concentrationȱandȱ foodȱ availabilityȱ inȱ theȱSargassoȱSeaȱatȱ theȱ timeȱofȱspawning.ȱTheȱlargestȱglassȱeelsȱnearȱtheȱspringȱarrivalȱpeakȱinȱcoastalȱFranceȱ 108 EIFAC/ICES WGEEL Report 2008

wereȱ assumedȱ toȱ haveȱ startedȱ inȱ theȱ Sargassoȱ Seaȱ duringȱ theȱ springȱ chlorophyllȱ bloomȱofȱtheȱpreviousȱyear.ȱ

Bonhommeauȱ etȱ al.,ȱ 2008ȱ usedȱ aȱ shortȱ timeȬseriesȱ toȱ demonstrateȱ aȱ correlationȱ beȬ tweenȱ recruitmentȱ andȱ primaryȱ productionȱ inȱ theȱ Sargassoȱ Seaȱ demonstratingȱ aȱ strongȱ bottom–upȱ controlȱ ofȱ leptocephaliȱ survivalȱ andȱ growth.ȱ Onȱ aȱ longerȱ timeȬ scale,ȱSSTȱisȱusedȱasȱaȱproxyȱforȱprimaryȱproductionȱandȱrelatedȱtoȱrecruitmentȱindiȬ ces.ȱSeaȱwarmingȱinȱtheȱeelȱspawningȱareaȱsinceȱtheȱearlyȱ1980sȱmayȱhaveȱmodifiedȱ marineȱproductionȱandȱeventuallyȱaffectedȱtheȱsurvivalȱrateȱofȱEuropeanȱeelsȱatȱearlyȱ lifeȱstagesȱ(seeȱFigureȱ7.2).ȱDirectȱmeasurementsȱofȱprimaryȱproductivityȱinȱtheȱnorthȬ ernȱSargassoȱSeaȱwereȱalsoȱfoundȱtoȱbeȱcorrelatedȱwithȱaȱthreeȬyearȱlagȱtoȱtheȱLoireȱ Riverȱ recruitmentȱ timeȬseriesȱ inȱ France,ȱ butȱ notȱ thoseȱ atȱ theȱ otherȱ locationsȱ (BonȬ hommeauȱ etȱ al.,ȱ 2008).ȱ Changesȱ inȱ oceanȱ productivityyȱ ma ȱ alsoȱ beȱ associatedȱ withȱ changesȱinȱtheȱlengthȱandȱconditionȱofȱglassȱeelsȱrecruitingȱtoȱEuropeȱ(Desaunayȱandȱ Guerault,ȱ1997;ȱDekkerȱ1998;ȱ2004b).ȱ

Kettleȱetȱal.,ȱ2008ȱhaveȱdemonstratedȱthatȱtheȱNAOȱrepeatȱcycleȱisȱpresentȱbothȱinȱtheȱ glassȱeelȱcatchesȱandȱtheȱFAOȱeelȱlandingȱstatistics. ȱThisȱmeansȱthatȱthereȱmayȱbeȱaȱ resonantȱamplificationȱbetweenȱsilverȱeelȱescapementȱandȱglassȬeelȱrecruitment.ȱAllȱ stagesȱofȱtheȱlifeȱcycleȱappearȱtoȱrespondȱtoȱinterannualȱclimateȱvariabilityȱassociatedȱ withȱtheȱNAO,ȱbutȱitȱisȱnotȱclearȱifȱtheȱlarvalȱmigrationȱsuccessȱisȱimpactedȱdirectlyȱbyȱ meteorologicalȱconditionsȱoverȱtheȱSargassoȱSeaȱorȱifȱitȱisȱmodulatedȱbyȱtheȱnumberȱ ofȱ silverȱ eelsȱ thatȱ areȱ triggeredȱ toȱ spawnȱ byȱ NAOȬassociatedȱ rainfallȱ patternsȱ inȱ Europe.ȱ

Tableȱ7.2:ȱCorrelationsȱbetweenȱvariousȱglassȱeelȱrecruitmentȱseriesȱandȱoceanicȱparameters.ȱ

TIME LAG RECRUITMENT SERIES OCEANIC PARAMETER CORRELATION (YEARS) AUTHOR

Transportȱrelatedȱparameterȱ SeriesȱfromȱLoire,ȱ NAOȱ(winterȱindex)ȱȬ0.13ȱ 0ȱ(maxȱ1ȱ Dekker,ȱ2004ȱ LȇEmsȱ&ȱDenȱOever,ȱ andȱ6ȱ 1950–2001ȱ years)ȱ DenOeverȱ1938–2005ȱ NAOȱ(winterȱindex)ȱȬ0.35ȱ 0ȱ(maxȱ0ȱ Friedlandȱetȱal.,ȱ2007ȱ andȱ8)ȱ 10ȱseriesȱ NAOȱ(winterȱindex)ȱ GAMȱmodelȱ ȱ Beaulaton,ȱ2008ȱ significantȱeffectȱbutȱ noȱlinearȱtrendȱ 26ȱseriesȱ NAOȱ(winterȱindex)ȱ AnticorrelatedȬ 1ȱtoȱ4ȱ Kettleȱetȱal.,ȱ2008ȱ significantȱ Drakkarȱmodel,ȱ NAOȱ(winterȱindex)ȱ 0.5ȱ 0ȱ Bonhommeau,ȱ2008ȱ particlesȱthatȱ GSIȱ 0.73ȱ succeedingȱinȱreachingȱ PEAȱ 0.57ȱ theȱ20ȱWȱȱ Mercatorȱmodel,ȱ NAOȱ(winterȱindex)ȱ 0.78ȱ 0ȱ Bonhommeau,ȱ2008ȱ particlesȱsucceedingȱ GSIȱ 0.80ȱ inȱreachingȱtheȱ20ȱWȱȱ TIȱ 0.47ȱ Drakkarȱmodel,ȱ NAOȱ(winterȱindex)ȱ Ȭ0.57ȱ 0ȱ Bonhommeau,ȱ2008ȱ minimumȱmigrationȱ GSIȱ Ȭ0.75ȱ durationȱ TIȱ Ȭ0.48ȱ 21ȱseriesȱ NAOȱȬ0.28ȱ 2ȱ Knightsȱandȱ 1935–2007ȱȱ Ȭ0.31ȱ 3ȱ Bonhommeau,ȱ Ȭ0.35ȱ 7ȱ unpublishedȱ 7ȱseriesȱ TIȱ NSȱ 3ȱ Bonhommeauȱetȱal.,ȱ2008ȱ EIFAC/ICES WGEEL Report 2008 109

TIME LAG RECRUITMENT SERIES OCEANIC PARAMETER CORRELATION (YEARS) AUTHOR 7ȱseriesȱ GSIȱ NSȱ 3ȱ Bonhommeauȱetȱal.,ȱ2008ȱ DenOeverȱ1947–2004ȱ Latitudeȱofȱtheȱ Ȭ0.15ȱtoȱȬ0.39ȱ 1ȱ Friedlandȱetȱal.,ȱ2007ȱ surfaceȱexpressionȱofȱ accordingȱtoȱmonthȱ theȱ22.5°Cȱisothermȱ andȱlongitudeȱ inȱtheȱSargassoȱSeaȱ DenOeverȱ1949–2003ȱ WindsȱȬ0.09ȱtoȱȬ0.48ȱ 1ȱyearȱ Friedlandȱetȱal.,ȱ2007ȱ Productionȱrelatedȱparametersȱ 1955–2007ȱ SSȬSSTȱ NSȱ 1–6ȱ Knightsȱandȱ yearsȱ Bonhommeau,ȱ unpublishedȱ 1935–2007ȱ NHTȱ NSȱ 2–3ȱ Knightsȱandȱ yearsȱ Bonhommeau,ȱ unpublishedȱ Loireȱseriesȱfromȱtraderȱ PPȱ 0.74ȱ 2.5ȱyearsȱ Bonhommeauȱetȱal.,ȱ2008ȱ 1994–2004ȱ EmsȱDenOever,ȱLoireȱ SSȬSSTȱȬ0.88ȱ 2.5Ȭyearȱ Bonhommeau,ȱ2008ȱ Nalonȱȱ 1960–2005ȱ DenOeverȱ(3ȱyearȱ SSTȱanomalyȱatȱ100– Ȭ0.47ȱ 0ȱyearȱ Knight,ȱ2003ȱ average)ȱ1952–1995ȱ 250ȱmȱ Ȭ0.30ȱ 1ȱyearȱ DenOeverȱ(1960–1996)ȱȱ Sizeȱofȱglassȱeelsȱ 0.7ȱ 0ȱyearȱ (Dekker,ȱ1998)ȱ

ȱ 110 EIFAC/ICES WGEEL Report 2008

Figureȱ7.2:ȱTimeȱseriesȱofȱDenOeverȱrecruitmentȱindexȱ(5Ȭyrȱmovingȱaverage;ȱsolidȱlineȱwithȱcirȬ cles)ȱandȱtemperatureȱ(°C;ȱ5Ȭyrȱmovingȱaverage;ȱsolidȱlineȱwithȱsquares)ȱinȱtheȱSargassoȱSeaȱfromȱ 1960ȱtoȱ2003.ȱBoldȱlinesȱindicateȱregimeȱshiftȱdetectionȱ(RodionovȱandȱOverland,ȱ2005)ȱandȱvertiȬ calȱdashedȱlineȱindicatesȱtheȱregimeȱshiftȱinȱtemperatureȱinȱ1979.ȱ(ReproducedȱfromȱBonhommeauȱ etȱal.,ȱ2008).ȱ

7.5 Ocean factors as reason (or contributory factor) for recruitment decline (1980s onwards)

Theȱhistoricȱrecordȱshowsȱstrong ȱevidenceȱthatȱtheȱabundanceȱandȱsizeȱofȱglassȱeelsȱ recruitingȱ toȱ theȱ continentȱ haveȱ theȱ sameȱ periodicityȱ asȱ naturalȱ climateȱ oscillationsȱ (Figureȱ7.3).ȱEvidentlyȱNAO,ȱandȱotherȱclimateȱcycles,ȱareȱprimarilyȱmeteorologicalȱ indicesȱthat,ȱatȱmost,ȱcanȱbeȱproxiesȱtoȱthoseȱecologicalȱandȱhydrographicȱchangesȱinȱ theȱNorthȱAtlanticȱthatȱcouldȱbeȱtheȱprimaryȱcausesȱforȱvariationsȱofȱeelȱrecruitment.ȱ Severalȱparametersȱareȱpossibleȱcandidatesȱforȱtheȱcauseȱofȱtheȱdeclineȱe.g.ȱseaȱsurfaceȱ temperatureȱanomaliesȱandȱchangesȱinȱproductivityȱlinkedȱtoȱtemperature.ȱ

Aȱshiftȱinȱseaȱtemperatureȱinȱ1979ȱmarkedȱtheȱbeginningȱofȱchangesȱinȱtheȱSargassoȱ Seaȱenvironmentȱandȱwasȱfollowedȱbyȱtheȱlargeȱshiftȱinȱeelȱrecruitmentȱdetectedȱinȱ 1982ȱ inȱ mostȱ ofȱ theȱ Europeanȱ riversȱ thatȱ haveȱ beenȱ analysedȱ (Bonhommeauȱ etȱ al.,ȱ EIFAC/ICES WGEEL Report 2008 111

2008).ȱCorrelationȱanalysisȱofȱtheȱglassȱeelȱcatchesȱrevealedȱthatȱalmostȱallȱtheȱmoniȬ toringȱindicesȱacrossȱEuropeȱvaryȱinȱphase,ȱprovidingȱsupportȱthatȱtheyȱareȱmoduȬ latedȱ byȱ aȱ largeȬscaleȱ meteorologicalȱ disturbanceȱ (i.e.ȱ asȱ previouslyȱ suggestedȱ byȱ Knightsȱ 2003;ȱ Friedlandȱ etȱ al.,ȱ 2007).ȱ However,ȱ measuringȱ ascendingȱ youngȱ eelsȱ (youngȱofȱtheȱyear,ȱandȱolder),ȱtheȱdropȱinȱrecruitmentȱinȱnorthernȱEuropeanȱriversȱ wasȱ observedȱ considerablyȱ earlier.ȱ Thisȱ leavesȱ theȱ possibilityȱ openȱ thatȱ conditionsȱ closerȱtoȱtheȱEuropeanȱshelfȱmayȱbeȱimportantȱorȱthatȱtheȱdeclineȱinȱsouthernȱEuropeȱ startedȱearlierȱalsoȱ(seeȱl’AdourȱandȱGirondeȱseries,ȱChapterȱ2).ȱ

Temperatureȱ mayȱ beȱ oneȱ ofȱ theȱ mainȱ governingȱ factorsȱ influencingȱ eelȱ larvaeȱ surȬ vivalȱbyȱdecreasingȱfoodȱavailabilityȱinȱtheȱSargassoȱSeaȱ(Bonhommeauȱetȱal.,ȱ2008).ȱ Theȱ sizeȱ ofȱ glassȱ eelsȱ isȱ positivelyȱ correlatedȱ withȱ abundanceȱ andȱ withȱ theȱ NAOȬ cycle.ȱThisȱalsoȱpointsȱtoȱaȱroleȱofȱoceanȱprimaryȱproductionȱonȱtheȱfeedingȱofȱglassȱ eelȱandȱpossibleȱstarvationȱofȱleptocephali.ȱ(Dekker,ȱinȱprep,ȱFigureȱ7.3).ȱ

-6

8 NAO Glass eel length -3 . index (reversed) NAO winter

7 Glass eel length (cm) (cm) length eel Glass

6 6 1950 1960 1970 1980 1990 2000 2010 ȱ

Figureȱ7.3:ȱTrendsȱinȱglassȬeelȱlengthȱenteringȱLakeȱIJsselmeerȱ(shortȱdash),ȱandȱtheȱNAOȱwinterȱ indexȱ(longȱdash).ȱ(DataȱfromȱDekker,ȱ1998ȱandȱHurrell,ȱ1995).ȱ(FromȱDekker,ȱinȱprep).ȱ

Changesȱinȱoceanȱcurrents,ȱparticularlyȱinȱtheȱSargassoȱarea,ȱmayȱhaveȱalsoȱaffectedȱ glassȱeelȱrecruitment.ȱThisȱassertionȱisȱsupportedȱbyȱtheȱcorrelationȱbetweenȱrecruitȬ mentȱseriesȱandȱNAO.ȱItȱisȱalsoȱsupportedȱbyȱresultsȱfromȱmodellingȱdemonstratingȱ theȱpositiveȱeffectȱofȱtransportȱindicesȱonȱbothȱsuccessȱandȱtimeȱofȱmigration.ȱHowȬ ever,ȱwhenȱlookingȱatȱindicesȱrelatedȱtoȱtheȱstrengthȱofȱtheȱGulfȱStreamȱ(TIȱandȱGSI),ȱ noȱsignificantȱcorrelationȱwasȱfoundȱ(Bonhommeau,ȱ2008).ȱ

Theȱsteepȱdeclineȱinȱrecruitmentȱbetweenȱ1980ȱandȱ1983ȱandȱtheȱcontinuedȱlowȱandȱ stillȱ decliningȱ recruitmentȱ sinceȱ thenȱ cannotȱ beȱ easilyȱ explainedȱ byȱ oceanicȱ factorsȱ alone.ȱTheȱdemonstrationȱofȱaȱpossibleȱstockȱrecruitmentȱrelationshipȱ(Dekker,ȱ2003;ȱ 2004b;ȱ updatedȱ byȱ WGEELȱ 2007)ȱ demonstratesȱ strongȱ evidenceȱ ofȱ aȱ depensatoryȱ mechanismȱinȱtheȱrelationship.ȱInȱthisȱS/Rȱrelationship,ȱlandingsȱhaveȱbeenȱusedȱasȱaȱ proxyȱforȱcontinentalȱstockȱandȱitȱisȱassumedȱthatȱcontinentalȱstockȱvariesȱinȱparallelȱ withȱSSB.ȱItȱisȱpossibleȱthatȱthisȱrelationshipȱbetweenȱstockȱandȱSSBȱisȱnotȱconstantȱ andȱthatȱSSBȱhasȱdeclinedȱfasterȱthanȱtheȱstock,ȱpossiblyȱasȱaȱconsequenceȱofȱaȱbreakȬ downȱinȱtheȱmigratoryȱphase,ȱtheȱspawningȱprocessȱand/orȱtheȱqualityȱofȱtheȱspawnȬ ers,ȱleadingȱtoȱaȱsmaller ȱnumberȱofȱrecruitsȱperȱspawnerȱthanȱobservedȱpriorȱtoȱtheȱ 1980s.ȱIsolationȱorȱfragmentationȱofȱspawningȱeffortȱasȱaȱconsequenceȱofȱlowȱSSBȱmayȱ 112 EIFAC/ICES WGEEL Report 2008

haveȱexacerbatedȱthis.ȱTheȱsteepȱstockȱrelatedȱdeclineȱinȱrecruitmentȱcouldȱbeȱoverȬ laidȱonȱtheȱoceanicȱinfluencesȱandȱmightȱhaveȱdrownedȱoutȱtheȱoceanȱsignalsȱinȱlatterȱ years.ȱ

Aȱ differentȱ viewȱ toȱ thisȱ isȱ proposedȱ byȱ Knightsȱ andȱ Bonhommeau,ȱ unpublished.ȱ TheyȱfoundȱthatȱcombinedȱandȱgeographicalȬareaȱstockȱtrendsȱareȱmoreȱmeaningfulȱ thanȱlandingsȱdataȱforȱuseȱinȱformulatingȱstock–recruitmentȱhypothesesȱandȱmodelȬ lingȱ andȱ inȱ developingȱ managementȱ targets.ȱ Theirȱ resultsȱ predictȱ thatȱ glassȱ eelȱ reȬ cruitmentȱwouldȱtoȱbeȱableȱtoȱrecoverȱinȱlessȱthanȱ10ȱyearsȱfromȱveryȱlowȱlevelsȱifȱ oceanȬclimateȱ conditionsȱ becomeȱ moreȱ favourable.ȱ Thisȱ conflictsȱ withȱ theȱ lifeȱ cycleȱ modellingȱstudyȱofȱAstromȱandȱDekker,ȱ2007ȱwhichȱconcludedȱthatȱstockȱrecoveriesȱ couldȱtakeȱ>80ȱyears.ȱAlso,ȱDekkerȱetȱal.,ȱ2003ȱandȱDekker,ȱ2004bȱassumedȱtheȱgeneralȱ declineȱinȱcombinedȱlandingsȱwasȱaȱproxyȱforȱstocksȱandȱhenceȱspawningȱstockȱandȱ thatȱdepensationȱcouldȱhaveȱledȱtoȱtheȱfallsȱinȱrecruitmentȱ20ȱyearsȱlater.ȱTheȱstudyȱ byȱKnightsȱandȱBonhommeau,ȱunpubl.ȱhowever,ȱsuggestsȱthatȱfluctuationsȱinȱenviȬ ronmentalȱfactors,ȱbothȱoceanicȱandȱnearȬcontinent,ȱareȱtheȱmainȱdeterminantsȱofȱreȬ cruitmentȱoverȱshorterȱperiodsȱandȱthatȱclassicalȱstock–recruitmentȱmodelsȱcannotȱbeȱ appliedȱ toȱ theȱ Europeanȱ eel.ȱ Itȱ alsoȱ debatedȱ theȱ assumptionȱȱthatȱ largeȱ femaleȱ eelsȱ producedȱinȱtheȱBalticȱmakeȱaȱmajorȱcontributionȱtoȱoverallȱproductionȱofȱtheȱEuroȬ peanȱeelȱ(e.g.ȱTesch,ȱ2003),ȱasȱNorthȱAtlantic/NorthȱSeaȱglassȱeelȱrecruitmentȱwasȱrelaȬ tivelyȱveryȱhighȱaroundȱ1980,ȱdespiteȱtheȱmajorȱdeclinesȱinȱBalticȱstocksȱbeginningȱinȱ theȱ1950–1960s.ȱInȱconclusion,ȱKnightsȱandȱBonhommeau,ȱunpubl.ȱsuggestȱthatȱcomȬ binedȱEuropeanȱlandingsȱdataȱcannotȱbeȱusedȱasȱaȱsimpleȱdirectȱproxyȱforȱstocks,ȱcerȬ tainlyȱ inȱ differentȱ regionsȱ inȱ NWȱ Europe.ȱ Theȱ lackȱ ofȱ anyȱ clearȱ recoveryȱ inȱ recruitmentȱduringȱtheȱlowȱNAOȱperiodsȱinȱthe ȱlateȱ1990sȱledȱDekker,ȱ2004aȱtoȱquesȬ tionȱtheȱroleȱofȱtheȱNAOȱinȱaffectingȱglassȱeelȱrecruitment.ȱHowever,ȱtheȱcontinualȱ warmingȱ ofȱ theȱ Nȱ Atlanticȱ signalledȱ byȱ theȱ risingȱ SSȬSSTȱ andȱ NHTȱ hasȱ probablyȱ overriddenȱtheȱeffectsȱofȱtheȱNAOȱ(KnightsȱandȱBonhommeau,ȱunpubl.).ȱ

7.6 Conclusions and recommendations for Chapter 7: Oceans, climate and recruitment

7.6.1 Conclusions x SufficientlyȱlongȱtimeȬseriesȱofȱglassȱeelȱrecruitment,ȱcoveringȱseveralȱperiȬ odsȱ ofȱ theȱ naturalȱ climaticȱ oscillationȱ overȱ theȱ Northȱ Atlantic,ȱ reflectȱ theȱ sameȱperiodicity.ȱ x Theȱcausalȱlinkȱbetweenȱclimateȱandȱrecruitmentȱstrength,ȱisȱunknown.ȱ x Itȱisȱunknownȱwhereȱandȱwhenȱduringȱtheȱoceanicȱlifeȱofȱtheȱeelȱlarvaeȱtheȱ climateȱeffectȱoperates.ȱItȱmayȱbeȱinȱtheȱSargassoȱSeaȱorȱcloserȱtoȱtheȱEuroȬ peanȱcoastalȱarea.ȱ x Theȱrecent,ȱprolongedȱstrongȱdeclineȱinȱeelȱrecruitmentȱisȱoutȱofȱphaseȱwithȱ theȱdominatingȱclimateȱcycle,ȱtheȱNorthȱAtlanticȱOscillation,ȱalthoughȱconȬ tinualȱwarmingȱhasȱprobablyȱoverriddenȱtheȱeffectsȱofȱtheȱNAO.ȱ

Asȱlongȱasȱtheȱcausalȱfactorsȱofȱoceanicȱinfluenceȱareȱunknown,ȱitȱisȱnotȱsafeȱtoȱasȬ sumeȱthatȱtheȱdeclineȱisȱexplainedȱbyȱclimateȱalone,ȱespeciallyȱwhileȱweȱknowȱthatȱ theȱanthropogenicȱinfluencesȱduringȱtheȱcontinentalȱlifeȱstageȱofȱtheȱeelȱareȱlargeȱandȱ betterȱunderstood.ȱTheȱfactȱthatȱoceanicȱclimateȱmayȱcontributeȱtoȱrecruitmentȱvariaȬ tionȱ isȱ notȱ groundsȱ forȱ abstainingȱ fromȱ allȱ possibleȱ measuresȱ toȱ increaseȱ silverȱ eelȱ escapementȱ toȱ boostȱ spawningȬstockȱ biomass.ȱ Atȱ someȱ levelȱ theȱ stock/recruitmentȱ relationȱwillȱalwaysȱbeȱimportantȬthereȱisȱnoȱrecruitmentȱwithoutȱeggs.ȱOceanȱenviȬ ronmentalȱfactorsȱcanȱneverȱjustifyȱaȱlackȱofȱconservationȱmeasures.ȱ EIFAC/ICES WGEEL Report 2008 113

TheȱoptionsȱandȱexpectationsȱforȱmanagementȱoutcomesȱcanȱbeȱsummarizedȱinȱTableȱ 7.3ȱthatȱcanȱbeȱusedȱinȱaȱriskȱanalysis:ȱ

Tableȱ7.3:ȱOptionsȱandȱexpectationsȱforȱmanagementȱoutcomes.ȱ

HYPOTHESIS ABOUT CAUSE OF DECLINE Pureȱstock/recruitmentȱ Oceanȱenvironmentȱ

ACTION TAKEN Improvingȱ Deterioratingȱ

Reduceȱ Recoveryȱifȱmeasuresȱ Recoveryȱfasterȱthanȱ Noȱrecoveryȱorȱslowerȱ anthropogenicȱ areȱsufficientȱȱ expectedȱ thanȱexpectedȱ mortalityȱȱ Noȱactionȱ Noȱrecoveryȱ Possibleȱrecoveryȱ Fasterȱcontinuedȱ declineȱ

7.6.2 Recommendations

ToȱaddressȱtheȱdifficultiesȱcomparingȱoceanȱenvironmentalȱcyclesȱwithȱbiologicalȱcyȬ clesȱofȱeelȱitȱisȱnecessaryȱtoȱimproveȱourȱknowledgeȱofȱtheȱoceanicȱphasesȱofȱtheȱeelȱ lifeȱcycle.ȱThisȱwillȱallowȱusȱtoȱbetterȱunderstandȱwhichȱoceanicȱfactorsȱareȱbehindȱtheȱ climateȱ effects.ȱ Thisȱ inȱ turnȱ willȱ allowȱ forȱ aȱ moreȱ sophisticatedȱ analysisȱ thanȱ mereȱ correlationsȱandȱtheȱweightingȱofȱtheȱroleȱofȱclimateȱeffectsȱonȱreproductiveȱsuccess,ȱ comparedȱtoȱcontinentalȱfactors.ȱSomeȱkeyȱquestionsȱare:ȱ

x TheȱquestionȱofȱtheȱinteractionȱbetweenȱleptocephaliȱmortalityȱandȱdisperȬ sion.ȱ x Theȱroleȱofȱleptocephaliȱinȱtheȱecosystem,ȱincludingȱfeedingȱandȱpredation.ȱ

WGEELȱ proposesȱ thatȱ anȱ ICESȱ Studyȱ Groupȱ isȱ establishedȱ toȱ coordinateȱ andȱ planȱ researchȱonȱtheȱoceanicȱeffectsȱonȱleptocephaliȱandȱmetamorphosisȱtoȱglassȱeel.ȱ 114 EIFAC/ICES WGEEL Report 2008

8 Research needs

8.1 Introduction

Theȱ Workingȱ Groupȱ onȱ Eelȱ identifiedȱ aȱ considerableȱ needȱ forȱ newȱ researchȱ onȱ eelȱ populationȱdynamicsȱandȱitsȱinfluencingȱfactors.ȱDueȱtoȱtheȱcurrentȱimplementationȱ ofȱtheȱEUȱeelȱrecoveryȱplanȱ(EUȱRegulationȱ1100/2007),ȱtheȱprimaryȱfocusȱofȱdiscusȬ sionsȱonȱresearchȱrequirementsȱatȱWGEELȱ2008ȱwasȱonȱsupportingȱtheȱassessmentȱofȱ theȱstockȱandȱitsȱrecoveryȱasȱsoughtȱbyȱtheȱimplementationȱofȱthisȱregulation.ȱWGEELȱ 2008ȱdidȱnot,ȱhowever,ȱloseȱsightȱofȱtheȱcontinuingȱlackȱofȱknowledgeȱofȱtheȱfundaȬ mentalȱbiologyȱ(i.e.ȱcarryingȱcapacityȱandȱdensityȬdependence)ȱandȱofȱtheȱEuropeanȱ eel’sȱ oceanȱ phaseȱ (includingȱ spawnerȱ qualityȱ andȱ migrations).ȱ Itȱ isȱ recognizedȱ thatȱ methodsȱ forȱ evaluationȱ ofȱ theȱ outcomeȱ ofȱ managementȱ measuresȱ areȱ notȱ yetȱ fullyȱ availableȱeitherȱatȱtheȱpopulationȱ(internationalȱtarget),ȱorȱlocalȱ(subȱtarget)ȱlevel.ȱ

8.2 Priority research needs

WGEELȱbelievesȱthatȱtheȱbestȱapproachȱisȱaȱseriesȱofȱintegratedȱandȱinternationallyȱ coordinatedȱprojectsȱandȱisȱsetȱoutȱinȱFigureȱ8.1.ȱAȱprogrammeȱofȱresearchȱisȱneededȱ toȱaddressȱgapsȱinȱknowledge,ȱgatherȱdataȱtoȱevaluateȱtheȱstatusȱofȱtheȱstock,ȱandȱfurȬ therȱdevelopȱstockȱassessmentȱmethodsȱtoȱdetermineȱcomplianceȱwithȱtargetsȱandȱtheȱ effectivenessȱofȱmanagementȱactionsȱatȱtheȱinternationalȱandȱlocalȱlevel.ȱ

Eel Research Needs

Model for international stock assessment this will need to be based on SLIME models EMU estimates these need to be interpreted in Data transfer quantative manner over Europe from data rich to • Stock assessment (incl. coastal) data poor EMUs Methodologies • Quality INDICANG 2 • Habitat quality • Mortality Density EELIAD – natural, anthropogenic dependence • Growth • Migration • Ocean effects ȱ

Figureȱ8.1:ȱFlowȱdiagramȱshowingȱlinkagesȱbetweenȱresearchȱneeds.ȱ

Theȱprioritiesȱforȱintegratedȱresearchȱareȱasȱfollows:ȱ

x InternationalȱStockȱAssessmentȱandȱtrendȱmonitoringȱ x LocalȱstockȱassessmentȱandȱpostȬevaluationȱofȱmanagementȱactionsȱ x Processȱ basedȱ researchȱ onȱ biologicalȱ parametersȱ requiredȱ forȱ estimatingȱ escapement.ȱ EIFAC/ICES WGEEL Report 2008 115

8.2.1 International stock assessment and trend monitoring

Improvedȱannualȱtrendsȱonȱrecruitment,ȱstockȱandȱyieldȱ

Emigratingȱsilverȱeelȱbiomass,ȱnumbersȱandȱsexȱratioȱ

Theȱaggregationȱofȱriverȱbasinȱspecificȱdataȱandȱassessments,ȱintoȱstockȬwideȱassessȬ mentsȱinȱsupportȱofȱstockȱtoȱrecruitmentȱ(SȬR)ȱandȱrecruitmentȱtoȱspawnerȱstockȱbioȬ massȱ(RȬSSB)ȱassessmentȱandȱmodellingȱ(e.g.VPA).ȱ

Theȱfurtherȱdevelopmentȱofȱmodelsȱtoȱassessȱcomplianceȱwithȱtheȱrecoveryȱtargetȱandȱ evaluateȱmanagementȱactionsȱ

Theȱinternationalȱassessmentȱofȱrecruitmentȱandȱstockȱtrendsȱtoȱassessȱtheȱresponseȱofȱ theȱ stockȱ toȱ managementȱ actionsȱ underȱ theȱ Regulation,ȱ notingȱ theȱ WGEELȱ recomȬ mendationȱonȱaccessibilityȱtoȱnationalȱeelȱmanagementȱplansȱandȱsupportingȱeelȱdata.ȱ

8.2.2 Local stock assessment and post-evaluation of management actions

TheȱdevelopmentȱofȱlocalȱstockȱassessmentȱproceduresȱandȱestimatesȱofȱsilverȱeelȱesȬ capementȱ

Theȱfurtherȱdevelopmentȱofȱmodelsȱandȱmethodologiesȱtoȱassessȱcomplianceȱatȱtheȱ localȱscaleȱwithȱtheȱrecoveryȱtargetȱandȱevaluateȱmanagementȱactionsȱ

Theȱdevelopmentȱandȱtestingȱofȱmethodsȱtoȱcharacterizeȱandȱquantifyȱeelȱstocksȱinȱ deeperȱareasȱofȱrivers,ȱlakes,ȱestuariesȱandȱcoastalȱwatersȱ

Theȱtestingȱofȱrelationshipsȱbetweenȱhabitatȱcharacteristics,ȱeelȱqualityȱandȱeelȱproȬ ductionȱasȱindicatorsȱofȱtheȱrelativeȱproductionȱpotentialȱforȱdifferentȱhabitatsȱ

Toȱdevelopȱmethodsȱforȱquantitativeȱassessmentȱofȱtheȱavailabilityȱofȱlocalȱsurplusȱforȱ stocking,ȱandȱforȱtheȱcontributionȱofȱstockingȱtoȱescapementȱ

ImplementationȱofȱEMPsȱrequiresȱtheȱdevelopmentȱofȱmethodologiesȱtoȱobtainȱestiȬ matesȱofȱescapement.ȱTheseȱcanȱbeȱdirectȱ(e.g.ȱmarkȬrecaptureȱorȱacousticȱcounting)ȱorȱ indirectȱmethodsȱ(e.g.ȱyellowȱeelȱproxiesȱtoȱdetermineȱsilverȱeelȱproductionȱandȱeelȱ habitatȱmodellingȱproduction).ȱValidationȱofȱindirectȱmethodologiesȱisȱrequired.ȱ

8.2.3 Process based research on biological parameters required for estimating escapement

QuantifyȱtheȱpossibleȱdensityȬdependenceȱeffectsȱinȱvariousȱprocessesȱincludingȱmorȬ tality,ȱgrowth,ȱmovement,ȱmaturationȱandȱsexȱdifferentiation.ȱ

Quantifyȱtheȱimpactsȱofȱpathogens,ȱparasites,ȱdiseases,ȱandȱlowȱchemicalȱqualityȱonȱ effectiveȱsilverȱeelȱescapementȱandȱspawningȱsuccess.ȱThisȱshouldȱincludeȱtheȱrelaȬ tionshipȱbetweenȱeelȱqualityȱandȱbodyȱfatȱcontent.ȱ

Quantifyȱanyȱimpactȱofȱaquaculture,ȱtransportȱandȱstockingȱofȱeelȱinȱtermsȱofȱreducedȱ spawnerȱproductionȱ

Researchȱisȱrequiredȱonȱtheȱrelativeȱimportanceȱofȱtheȱhabitatȱtypesȱusedȱbyȱeelsȱandȱ whatȱdemographicȱcharacteristicsȱtheyȱexhibitȱinȱtheseȱhabitats,ȱsuchȱbetweenȱfreshȱ (riversȱandȱlakes)ȱandȱsalineȱ(brackish/salt)ȱwaters.ȱ

Recentȱresearchȱhasȱsuggestedȱthatȱprocessesȱinȱtheȱoceanicȱphaseȱ(includingȱspawnerȱ quality)ȱmayȱbeȱimportantȱinȱdeterminingȱrecruitmentȱlevels.ȱImprovedȱknowledgeȱofȱ theȱoceanicȱphasesȱofȱtheȱeelȱisȱneededȱtoȱfurtherȱtheȱinitialȱsearchȱforȱcorrelationsȱbeȬ tweenȱeelȱrecruitmentȱandȱoceanicȱprocesses.ȱ 116 EIFAC/ICES WGEEL Report 2008

8.3 Other research needs

WGEELȱ2008ȱfocusedȱheavilyȱonȱtheȱrequirementsȱofȱtheȱEUȱRegulationȱandȱtheȱneedȱ forȱinternationalȱandȱnationalȱstockȱassessment.ȱAdditionalȱresearchȱwillȱbeȱrequiredȱ inȱorderȱtoȱfillȱmanyȱgapsȱinȱtheȱbiologyȱandȱmanagementȱofȱeel.ȱ

ResearchȱonȱoptimumȱcollectionȱandȱtransportȱmethodsȱforȱglassȱeelȱtoȱreduceȱmorȬ talityȱforȱstockingȱ

Timingȱandȱfrequencyȱofȱstockingȱ

Relatedȱeelȱhealthȱissuesȱ

PostȬevaluationȱmethodsȱforȱtheȱnetȱbenefitȱofȱstockingȱforȱconservationȱ

Investigationsȱexaminingȱtheȱcompetitiveness,ȱsurvivalȱandȱreproductiveȱcapacityȱofȱ stockedȱglassȱeels,ȱcomparedȱwithȱtheir ȱnaturallyȱrecruitedȱcounterpartsȱbyȱmarkingȱ theȱstockedȱindividualsȱandȱcomparingȱtheirȱrecaptureȱatȱsexualȱmaturityȱ

Quantifyȱtheȱrelationȱbetweenȱfatȱcontentȱandȱeelȱquality,ȱtheȱeffectsȱofȱspecificȱconȬ taminantsȱandȱparasitesȱonȱfatȱmetabolismȱandȱaȱpossibleȱrelationshipȱbetweenȱeelȱfatȱ contentȱandȱenvironmentalȱvariablesȱsuchȱasȱchangingȱtemperature,ȱchangingȱtrophicȱ status,ȱandȱfoodȱavailabilityȱ

Predatorȱpreyȱrelationshipsȱ(e.g.ȱcormorants).ȱ

8.4 Proposals for study groups

WGEELȱ proposesȱ thatȱ anȱ ICESȱ Studyȱ Groupȱ isȱ establishedȱ toȱ coordinateȱ andȱ planȱ researchȱonȱtheȱoceanicȱeffectsȱonȱleptocephaliȱandȱmetamorphosisȱtoȱglassȱ eel.ȱ

WGEELȱnotesȱandȱapprovesȱtheȱproposalȱforȱanȱeelȱageȱcalibrationȱworkshop.ȱ

WGEELȱnotesȱandȱapprovesȱtheȱproposalȱtoȱtheȱDFCȱ(2008)ȱforȱaȱstudyȱgroupȱonȱanȬ guillidȱeelsȱinȱsalineȱ(brackish/salt)ȱwaters.ȱ EIFAC/ICES WGEEL Report 2008 117

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