Equipment failure or operational errors are behind three out of four farmed salmon escapes. Two out of three escapes are due to holes in sea cage nets according to a new study.
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March | April 2013
Escapes primarily caused by equipment failure
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Equipment failure or operationalerrorsarebehindthreeoutoffourfarmedsalmonescapes.Twooutofthree escapes are due to holes in
seacagenetsaccordingtoanewstudy.
Researchers working on the SECUREproject (Securing fish – farming technologyandoperationstoreduceescapes)haveana-lysedallescape incidentsbetween2006and2009reportedbyNorwegianfishfarms.Theirefforts provide the industry and researcherswith new insights into the factors leading tolossatNorwegianproductionfacilities.
Structural failures most commonEquipmentfailureordamage isthemajor
factor behind the escape of farmed salmon.Figures from theSECUREproject show that68 percent of escapes occurred because ofstructural failure. An additional 8 percentwere able to escape due to human errorduringoperations.Elevenpercentofescapestook place from land-based facilities and anequalpercentageescapedduetoexternalfac-tors.All inall, the researchershave revealedclearexplanationsfor96percentofthetotalescapesreportedfrom2006to2009.
Factors changing over time“Commonstructuralfailuresincludeprob-
lems with mooring lines, collapsed floatingcollarsandholestorn inthenettingofaseacage. Badweather is another factor contrib-uting to structural failure and escape. Wehavealsodocumentedincidentsofautomaticfeedingdevices loosenandcausingdamage,”says Østen Jensen, research manager withSINTEFFisheriesandAquacultureandprojectmanageroftheSECUREproject.
The escape incident reports reveal thatequipment suppliers and fish farmers havemanaged to solve some of the equipmentproblemsthatpreviouslyledtoahighnumberofescapes.
“Escapes caused by mooring or floatingcollar failure have become more and morerare.The greatest challengenow facingpro-ducersofsalmonandtroutishowtopreventwear and tear to the netting. Holes formedfromchafingcontactbetweenthenetandthesinker tubechainwereresponsible formorethan 50 percent of total escapees between2008and2010,”DrJensensays.
delousingormaintenance,combinedwithfishtransfer, account for close to 20 percent oftheescapefigures.Thelastlarge-scalesalmonescapeevent, inwhich175,000 fishescapedaproductionfacilityinTrøndelag,occurredinconnectionwithdelousing.
“Large-scaleescapeeventsinwhichmorethan 10,000 fish are involved comprise 19percentofthetotalnumberofescapesduringthe period studied. As much as 91 percentof all fish that escaped can be attributed tolarge-scaleevents,”saysDrJensen.
The reduction in the number of largeescape events is the most significant fac-tor behind the substantial reduction in thenumberofproductionsalmonescapeesfrom2006to2009.
“Incontrasttosalmonandtrout,codwilloften bite the netting and tear the netwall.The cod also display more interest in suchholesandarefarmoreeagerthansalmonortrouttotrytoswimthroughthem,”addsDrJensen.
The Houdinis of the seaCod are better escape artists than other
species of production fish, opting to swimthroughobstaclesratherthanaroundthem.
AspartoftheSECUREproject,research-ers at Norwegian Institute of Food, Fisheryand Aquaculture (Nofima) have analysedthe behavioural characteristics of cod whichmakethemmorelikelytoescapethanotherproduction species. Using controlled experi-ments, researchers have studied how theybehaveinseacages.
Codconstantlybiteandnibbleonthenetthreads, showinggreat interest in investigat-ing anything that appears unnatural to theirenvironment. This affects how net repairshould be approached at cod-productionfacilities. Repairs are most effective whencolours and shapes of the repaired nettingconformtotheoriginal.Theendsofthreadsneedtobeaffixedsothattherepairwillnotdeviate in appearance from the rest of thenetting.
Improved reportingFish farmers are required to report all
escapeevents to theDirectorateofFisheries.Jensensaysthatescape incidentreportinghasimproved substantially since the Norwegian
Placing responsibility on suppliersTwoproblemareasstandoutintheefforts
to reduce the risk of escapes in Norwegianaquaculture. Jensen believes that both canbe solved by the suppliers of aquacultureequipment.
“If the aquaculture industry is ever goingtorealisticallyrealiseitsvisionofzeroescapesfrom sea-based production facilities, it mustsolve two big challenges. The first is thatweightingsystemscurrentlyinusetomaintainthe shape and volume of the net pens leadtowearand tear in thenetting.The secondis finding ways to decrease the incidence ofoperational–orhuman–error.”
Solutions can be developedDr Jensen points out that the key to
solving both challenges can be found in thesupplierindustry.
“Improvedproductdesignandprocedurescanmitigateand, inpart,preventbothwearandtearaswellashumanerrorduringopera-tionsatsea.Muchoftheequipmentinuseinsea-based facilities shouldbe redesignedandsimplifiedtomakeitdifficultorimpossibletouse incorrectly. Under the SECURE projectwehaveacquired theknowledgeneeded todevelop better and more secure solutions.Thenextstepisuptothesuppliers.”
Suppliers have already begun applyingthe documented findings from the SECUREproject to test new solutions. The ResearchCouncilofNorwayallocated funding to twonewresearchprojectsthisyear(Towardssus-tainable fish farming at exposedmarine sites[SUSTAINFARMEX2011-2014]andExposedFarming)thathavecarriedoutmodellingtestsusingnetswithintegratedsinkertubes.
Certification scheme improves safety
The SECURE project has documented anumberof factorssignificant foravoidingnetabrasionandtearing:• Insufficient weighting of net-cages, use
of exceedingly large nets, sea-currentconditions and biofouling lead to netdeformation and risk of abrasion andtearing.
• Washing nets by machine reduces thestrengthofnetthreadsby10-20percentafter4-5washings.
• Attachingthesinkertubetothenethasproven to be a more secure solutionthanusingslidingconnectors.
• Conic net pens create more distancebetweenthenetandthechain,reducingtheriskofabrasionandtearing.Inspiteof this, the majority of net pens arecurrentlycylindricalinshape.
“Fish producers are able to buy freely
on the market and can purchase nets andfloating collars separately. It is by no meansautomatic that the net chosen will suit theselected floating collarwhenassembled.Weneedtohaveamoreintegratedapproachtothe design of fish-farming systems to ensurethatcomponentsarecompatible,”explainsDrJensen,whobelievestheintroductionoffacil-itycertificationisastepintherightdirection.
Providing input for regulations
Asof January1, 2013, all fish-productionfacili-ties in Norwaymust have cer-tification statingthatthefacilityisusingcompatiblecomponents.
“TheSECUREprojecthas providedknowledge ofimportance tothe design ofregulations thatthat will formthe basis forfacility certifica-tion, amongother things.We have seenthat the layoutofafacilitycom-binedwithwavesize can haveunforeseen con-sequences. Thehighest wave
doesnotalwayscarrythegreatestforce.Wehave found examples where a low-crestedwaveexertsmuchgreater forceona facilitythan a steep wave. Twice the force is notunusual,andthisshouldobviouslybeincorpo-ratedintothespecificationsforthedesignanddimensions of a production facility,” Jensenconcludes.
More information: www.forskningsradet.no
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