Project 5 Final160209 - bycatch.orgbycatch.org/sites/default/files/Partan&Ball_2016.pdf · Rope-less fishing gear has long been discussed as a possible approach to reducing entanglement

BycatchConsortium–FinalReport#NA10NMF4520343

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Project5FinalReport

Rope-lessFishingTechnologyDevelopment

JimPartanandKeenanBall

[email protected],[email protected]

WoodsHoleOceanographicInstitutionWoodsHole,MA02543

Abstract:Thistechnicalreportdescribesthedesignandfabricationofprototyperope-lessfishingsystems.Theprototypesconsistofnewdesignsintendedasacontributiontowardsevaluating thepotential of rope-less fishing in theGulf ofMaineoffshore lobster fishery.Threeprototypeunitswerefabricatedforuseinfuturetesting.

Rope-less fishinggearhas longbeendiscussedasapossibleapproach toreducingentanglement of North Atlantic Rightwhales, othermarinemammals, and sea turtles. Arope-lesssystemsecures thevertical linesof fixed fishinggearon theseaflooruntil theyarereleasedtothesurfaceforhauling.

The focus of this project was on the offshore fishery for several reasons: (1)Previousdemonstrationsofrope-lessfishinggearwerenotdesignedtooperateinthehighcurrentsanddeepwateroftheoffshoreNewEnglandandGulfofMainelobsterfishery;(2)Weaklinksandropesofreducedbreakingstrengtharenotlikelytobeviableforthelargeandheavytrawlsofupto fifty trapsthatareusedoffshore;and(3)While lobster fishinggear ingeneral isamajorsourceofentanglements,heaviergearsuchas thatused in theoffshorefisheryappearstopresentalargerriskforNorthAtlanticRightwhales.

Design requirementswere derived from discussionswith offshore fishermen andpreviousstudiesofrope-lessgear.Theoffshorelobsterfisheryhaswaterdepthsupto300meters,andsurfacecurrentsofup to1-2knots.Linescopeswillneed tobebetween2:1and3:1,withabout140-180poundsofbuoyancyinordertobringthelinetothesurface.To be compatible with existing hauling equipment, gear weights, and dimensions onoffshorefishingvessels,designrequirementsincludedaunitthatcouldbeusedwithalinediameter of at least ½”, has a maximumweight of about 180 pounds, and a maximumlengthofaboutfourfeet.

Tosecurethelineontheseafloor,theprototypeusesalinespoolwithcapacityfor900metersof½”line.Flotationfoamprovides180poundsofbuoyancyinthespool.Therelease is controlled by a timer with a release time set by the user, providing a cost-effectivemeans (relative to acoustic releases) to reduce the time of exposure of verticallines in thewater column tomarine animals. The design ismodular to allow scaling todifferentfishingenvironments,suchasshallowerinshorewaters.

This study also performed a preliminary investigation of passive acousticdetectability of rope-less fishing gear. Without surface buoys, an alternate method fordetectingrope-lessgearisneededtoreducegearconflictswithotherfixedgearaswellasmobile gear. Extrapolating the results of an echo-sounder dock test in 14meters to 300meters depth will be somewhat inconclusive. Echo-sounder detection of the rope-lessendlinespoolsin300metersislikelyfeasible,butdistinguishingpassiveacousticreflectorsonlobstertrapsfromtheseafloorwilllikelybechallengingwithstandardechosounders.

Thisstudyfabricatedthreeprototyperope-lessfishinggearunits.Thenextstepsarecontinuedtesting tovalidaterobustunspooling, followedbytesting incollaborationwithoperationalfishingvessels.Funding Acknowledgement: This investigation was supported by The Consortium forWildlife Bycatch Reduction at the New England Aquarium under NOAA / NMFS GrantAwardNA10NMF4520343.


Section1:OperationalInformationDerivedfromOffshoreFishingVessels

Anexcellentsummaryoflobsterpotgearconfigurations,asdeployedinthewater,isprovided in the report “LobsterPotGearConfigurations in theGulfofMaine” (McCarronandTetreault,2012).Thatreportdoesnotcoverdeckoperationsonoffshorelobsterboats,however.Tounderstandcompatibilitywithexistingdeckoperationsanddeckequipmentof offshore vessels,we visited two lobster boats in July 2015.One of the boats operatesnearapotentialGearDevelopmentArea--thathavebeendiscussedpreviouslyforoffshoreareas suchas theGreatSouthChannelRestrictedArea (NMFS,2010)--and theotherwasnominally an inshore boat, but fishes trawls of up to 20 traps about 20miles offshore.Everyfishermanoperatesslightlydifferently,andwedescribetheoperationsofthesetwoparticularboatsinthesectionsbelow.

Section1.1:OffshoreBoatoperatingnearpotentialoffshoreGearDevelopmentArea

The offshore boat we visited is 75’ long and has a crew of four plus a captain.Offshoreboats in similarwaters canbeup toabout90’ long.Twoboatsunder the sameownershippartnership service1600 traps, set in50-trap trawls.They spend3-4daysatseapertrip,andfishprimarilyalongthe100-fathomline(200meterbathymetryline)neartheContinentalShelfbreak,fromHydrographer’sCanyoninthewesttotheHagueLineintheeast,andinparticulareastofOceanographer’sCanyonwherethefishingisapparentlybetter. Traps are set for about 3-7 days, depending upon the season. They haul 10-15trawlsperday.Theyoperate24hoursperdaywhenatsea.Inadditiontolobster,theboatfishesforJonahcrabswithessentiallythesamegear.

Thereisaverticalline,5/8”,withbuoysoneachendofthetrawl.Thebuoysonthisboat were two LD-3 Polyform floats (40.7 liters each, about 91 pounds rated buoyancyeach)oneachoftheverticallines.Thehigh-flierwithradarreflectorwasnotalwaysused,especiallywhen currentswere high, because it could get dragged under, the foam buoycrushed,andthensinkthevertical line.ThepairofLD-3Polyformfloatsoneachverticallinesometimesgetsdraggedunderaswell,butnotdeepenoughtocrushthefloats.

Trawls generally are set “downhill” (with the tide), and generally hauled “uphill”(intothetide).Thatisthemainreasonthatthereisaverticallineonbothendsofthetrawl.Ifthetidalcurrentisstrong,thebuoyscanbepulledunder,andtheyhavetowaituntilthetideslackenstohaul.

Duringhaulingoperations,thegearcomesthroughasmalldoor/openingintherailandontothedeck,throughapothauler.Thehaulerplatesgetwornoutfrequentlyduetosediment in the sinking groundlines, and need to be re-planed every few trips. It takesaboutanhourtohaulatrawlof40-50traps.Asthetrawlishauled,thetrapsarestackedondeck,and the linegoes intoa line locker (examplesize:4’x6’x6’high).Therecanbeacrew member assigned to the line locker to make sure the line goes in neatly. Thatparticularsizelinelockercanfitlinesforaboutthreetrawlsiftheyarepackedneatly.After

theentiretrawlisrecoveredondeck,itisredeployed,generallyinthesamelocationifthefishingwasgood.

Theoffshoretrapseachweightabout100poundswhenempty.Ateachendofthetrawlisa180-pound“anchorsled”madeofsteel.Theverticallinesareputtogetherof50-fathom(100-meter)shots,withabigknotjoiningtheshots.Somefishermenuse75-fathom(150-meter)shots.In100-fathom(200-meter)waterdepths,theverticallinesare175-300fathoms(350-600meters).

Due to chafing of the sinking groundlines, in particular with storms, sometimestrawls or parts of trawls are lost. If a trawl is lost, they will grapple for it. They cansometimesseetheverticallineontheechosounder(FurunoFCV-292).

Thegearconflictbetweenfixed-gearfishermenanddraggermobile-gearfishermenis inpartdealtwith throughwhatappears tobeanhistorical informalagreement:Fixedgear is set on certain LORAN time-differences (“TDs”), and mobile gear is dragged ondifferent LORANTDs. Even though LORAN is no longer active, the historical agreementsappeartobecontinuing.Apparently,differentGPSmanufacturersgeneratelegacyLORANTDs differently, some more accurately than others, and the discrepancies can causepotentialconflictsbetweenfixedandmobilegears.

Picturesofhaulingequipment,line,andfloatationfromtheoffshorelobsterboatareonthefollowingpages.

Figure1.1:300fathoms(600meters)of5/8”line,coiledin50-fathomshots,withonePolyformLD-3float.This isthetypicalamountanddiameterof lineusedforoneofthevertical lines inanoffshoretrawlin100fathomsofwaterwithhighsurfacecurrents.OftentwoPolyformLD-3floatswillbeusedforincreasedfloatation.


Figure1.2:Two180-poundsteelanchorsleds.Theanchorsledsweighmorethantheemptylinepackspool(about135pounds),i.e.thelinepackspoolweightiscomparabletoweightsofexistinggear.

Figure1.3:PotHaulerwithplatesadjustedfor5/8”rope.

Figure1.4:Openinginrailthroughwhichgearishauled.Thelinepackspoolis32”wideand43”tall.


Figure1.5:Ropelockerandpothauler.Thisropelockerisabout4’x6’x6’andcanholdthelineforthreecompletetrawlsof50trapseach.Duringhauling,sometimesacrewmemberisstationedintheropelockertoensurethatthelinecomingintothelockeriscoiledneatly.

Figure1.6:Pothauler,pothaulerplates,ropelocker,anchorsleds,line.


Section1.2:InshoreBoatFishing20-TrapTrawlsinMassachusettsBay

Our primary goal for this technology development is the offshore lobster fishery,includingpotentialoffshoreGearDevelopmentAreas.InshoreareassuchasCapeCodBayandpartofMassachusettsBay,however,havehadseasonalfisheryclosuresduetocriticalhabitat forNorthAtlanticRightwhales, and fishermen in those regions couldpotentiallybenefit from availability of rope-less gear. In particular, inshore fishermen with longertrawlswouldbetheonesmostlikelytotoconsiderinvestinginrope-lessgear.

WevisitedaninshoreboatthatfishesinMassachusettsBayeastofStellwagen.Theboatisabout38’longandhasacaptainplusasternman.Theyservice800traps,allsetin20-trap trawls. All of their trips are day trips, often around 12 hours on the water orsometimesmore.Thesettimesrangefrom2daysupto14daysinthewinter.Theyhaulabout 15 trawls per day (300 traps per day). It takes about 20minutes to haul a trawl,typicallyin75’(25meters)ofwaterwith200’(65meters)ofline.Theyoperateupto300’(100meters)depth, inwhichcasetheygenerallyuse400’of line.Whentherearehighercurrents,theywilluse300’endlinesfor75’waterdepth.Theendlinesare3/8”,with5/16”groundlines. The trapsweigh 60-70 pounds each.With their echosounder (Furuno FCV-528L)theycanseetheverticallineasitgoesdownwiththetraps.

The captain was very conscious of avoiding whale entanglements, and uses noknots in his endlines, but rather splices everything. The endlines are orange line withoccasionalorangeflaggingtoimprovepotentialvisibilityforrightwhales.Theyuseswivelbreakawayswithabouta600-poundbreakingstrength.Thebottomthirdoftheendlineispolyfloatingline.

Section2:Rope-lessFishingTechnologyBackgroundandRelatedWork

Endangered whales and turtles are known to become entangled in vertical linesusedinfixed-gearfisheries.Heavierlines,asintheoffshoreGulfofMainelobsterfishery,are a particular risk for endangeredNorthAtlanticRightwhales (Knowlton et al, 2015).Reducingthenumberofverticallinesinthewatercolumnatanygiventimeistheprimarymotivationbehinddevelopingrope-lessfishingtechnology.Arope-lessfishinggearsystemsecures the vertical linesused in fixed fishingon the seaflooruntil they are released forhauling.

Ourmain goalwith this projectwas to design a research prototype for rope-lessfishinggear for theoffshoreGulfofMaine lobster fishery.We fabricated threeprototypeunits thatwill enable researchdeployments fromoperational fishingvessels, to evaluatethepotentialofrope-lessfishingfortheGulfofMaineoffshorelobsterfishery.Atthisstage,these units are not being proposed as a commercially viable product, but mainly as aresearch project to evaluate how such a systemmight be developed toworkwithin theoperational fishing circumstances of the offshore lobster fishery. While design-for-manufactureandlargerproductionnumberswillreducecosts,theinitialprototypebatchofthreeunitscostapproximately$13,000each.

Although initiallydesignedfortheoffshore fishery,akeydesigngoalwastomakethe system modular, so that various components can be scaled from the moreoceanographicallychallengingoffshoreenvironmenttoshallowerinshoreareas.Asysteminitially designed for the challenging offshore environmentwill likely scale down to theinshorefishery,whereasstartingwiththeinshorefisherycouldpotentiallyendupwithadesignthatmightnotscalesuccessfullytooffshoreconditions.

Oursystemwasdesignedfortheoffshorelobsterfisheryforseveralreasons.First,themostpromisingexistingentanglementmitigationapproachesfortheinshorefishery–namelyweak linksandweak lines–arenotviable for theheavyoffshore lobster fishingtrawlsofup to fifty traps.Second,noneof thepreviouslydemonstratedrope-less fishingsystemshaveadequatebuoyancytooperate in theoffshore lobster fishery,wherestrongsurfacecurrentsanddeepwaterrequireflotationontheorderof140-180poundssimplytobringtheropetothesurface.Finally,thisresearchcancontributetopotentialrope-lessfishingGearDevelopmentAreas.

Figure 2.1 shows a standard offshore lobster trawl of traps (McCarron andTetreault, 2012). The groundlines are sinking ropes, and the entanglement hazard ispresumedtobemainly fromthevertical lines.Theweights, rope lengths,andnumberoftrapspertrawlaretypicalofsomeoffshoreareasintheMainefishery.Theoffshorefisheryalong the edge of the Continental Shelf has similar configurations, but generally withheaviergear,longerlines,andmoretrapspertrawl.


Section2.1:OverviewofRope-lessFishingTechnology

There are several key design questions for categorizing rope-less fishing systems andreleasesystems.Eachofthecategoriesisexplainedinfurtherdetailbelow.

• Howistheropesecuredontheseafloor?o Maintypesconsistofalinecanister(ormeshbag),andlinespool.

• Howisthereleasetriggered?o Maintypesaregalvanicaction,timer,andacousticcommands.

• Whatisthereleasemechanism?o Maintypesarecorroding“burn”wire,solenoid,andmotor.

Figure 2.1: A standard configuration for an offshore lobster trawl, shown for a Maine fishery(McCarron and Tetreault, 2012). The offshore fishery along the edge of the Continental Shelf isgenerallysimilar,butwithheaviergearandmoretrapspertrawl.

Section2.1.1MethodsofSecuringtheRopeontheSeafloor

To secure the rope on the seafloor, a “line pack” has been used. The mainapproaches for designing a line pack are to use a line canister or a line spool. In a linecanister, the line is packed into a container, then pulled to the surface with a float.Generally, the line is randomly packed into the canister, and usually uses a torque-freebraided rope to avoid kinks. Mesh bags can also be used as line canisters (Liggins andWestley,2011).Althoughtheyarenominally“randomly-packed”,caremustbetakenwhenpackingalinecanister.Ifthepackingistooloose,theropecanbemovedinsidethecanisterbywatercurrents,causingtanglesandreleasefailures.Ifthepackingistootight,thefloatmightnotpulltheropeoutofthecanister.Figure2.2showstwolinecanisterapproaches,acommercial systemfromOREOffshoreandameshbag fromLigginsandWestley(2011)from the New South Wales Australian lobster fishery, and a line spool developed byFioMarine.

Alinespool iswhatwechoseforourprototypedesign.Linespoolsareoftenusedforlongerlengthsof line,ontheorderof300metersor longer.Typically,oneachrowofwrapsaroundalinespool,amasticoradhesivesecuresthewrapsinplacebeforethenextrowofwrapsisputontothespool.Siliconeadhesiveisoftenusedasthemastic,althoughalternatematerialssuchasbiodegradablecornstarch-basedmasticsareconceivable.NovellinepacksarealsocurrentlybeingdevelopedbyEOMOffshoreandotherswherethereisnocentralspool inthelinepack,butratherthecoiledlineis“cast”withanadhesiveintothedesired form.Toreducea fishingvessel’s timeonsite for turningaroundarope-lessfishing trawl, one possibility we considered for our line spool approach is an onshoreservice industry that provides pre-spooled line spool cartridges to fishing vessels. Linepacks thatarecast into formswithadhesivemightalsobeanapproachtoproviding linespoolcartridgesthatcanquicklybeusedforre-spoolingtheline.

Figure 2.2:Three line packmethods. Left: Line canister (ORE Offshore). Middle: Mesh bag as linecanister(LigginsandWestley,2011).Right:LineSpool(FioBuoy,FioMarine).


Section2.1.2MethodsofTriggeringtheRelease

Thesecondmaincategorizationofrope-lessfishingsystemsandreleasesishowthereleaseistriggered.Thesimplestandleastexpensiveapproachistouseagalvanictimedrelease,where the corrodingmetal is sized toprovide an approximate release time.Therelease time isnotveryaccurate, if thesurfaceof themetalbecomes fouledwithoilorabiofilm. A timer-based approach is what we chose for our prototype system, as a cost-effective method to provide accurate release times without requiring fishing vessels topurchasepotentiallyexpensiveacousticreleasedeckgear.Atimer-basedreleasecanbesetsuchthatthelineisonthesurfacereadyforhaulingwhenthefishingvesselisexpectedtobebackonsite.Finally,addinganacoustically-commandedreleaseinparallelwithatimer-based release allows flexible hauling times in the event of changing weather or fishingvesselschedules.Acousticreleases,andinparticulartheassociatedacousticdeckgear,canberelativelyexpensive,primarilybecauseoftheverysmallandspecializedmarket.Iftheywere ina largecommercialmarket, acoustic releasesanddeckgearcould comedown inunitcostsandbesoldonparwithoraspartoffish-findingsonarsorechosounders,rangingfrom about $500 for low-end consumer models to around $5000 for higher-endcommercialinstrumentsandtransducers.

Section2.1.3TypesofReleaseMechanisms

Thefinalcategorizationofrope-lessfishingsystemsisthereleasemechanismitself.Typically there is a lever system to provide the appropriate amount of mechanicaladvantagesothattheactuator’sforceortorquecanberelativelysmalltoreleasealargerload.Themeansbywhichtheleverisreleasedcanbeacorrodingburnwire,asolenoid,oramotor.Acorrodingburnwire isgenerallyassumedtobe the leastexpensive, though itmeansaconsumablereleaselinkneedstobereplacedeachtimethesystemisrecovered.The expense of the consumable links could be considerable for commercial fishingoperations.Forexample,SubSeaSonicssellsreleaselinksfor$8or$12each,forloadsof40-90 pounds or up to 200 pounds, respectively. The offshore rope-less system designdescribed in this technical report would require a 150-pound release link ($12). Anoffshorefishermanwith30trawlsandayear-roundaveragesoaktimeoffivedayswouldconsumeabout2000 release linksperyear, costingabout$24,000peryear for the linksalone. Burnwires also have potential biofouling concerns, and the tension on the burnwirehastobedesignedappropriately–wellunderitsratedtensilestrength,butenoughtoensurethatthereleasetriggersreliably–asthisisacommonfailuremodeforburn-wiresystems.

Manycommercialreleasesusesolenoidsas thereleaseactuator. Inasolenoid, theactuator ismoved by applying electrical current, creating amagnetic field. The actuatormotion can be linear or rotary; rotary solenoids are often used for releasemechanisms.Rotarysolenoidsusuallyareinternallyalinearsolenoidwithatorsionalspringtranslatinga linearmotion into a rotarymotion. To conserve energy, releasemechanisms generallyusealatchingsolenoid,wherecurrentonlyhastobeappliedtoreleasethedevice,rather

than traditional solenoids where current would be applied continuously to hold theactuator’s position in thenon-released state.Most solenoids are single-shot devices, andmust be reset manually, without any provision for a second release attempt if the firstattemptfails.

The approach thatwe chose for our prototype system is to use a DCmotorwithmotor encoders. The encoders provide feedback to themicrocontroller, which can thenreversemotor drive directions and continue to drive themotor back and forth to try torecoverfromareleasefailure.

Section2.1.4SummaryofTop-LevelDesignDecisions

Inalldesigndecisionsforthisrope-lessprototypesystem,weselectedtheapproachthatwebelievetobemostrobustandreliable–alinespoolratherthanalinecanister,atimerwithacousticoptionratherthangalvanicaction,andamotorratherthanburnwireor solenoid. These more robust options are generally slightly more expensive, but notdramaticallyso,especiallyforaprototyperesearchsystemwherethegoalsaretoevaluatea reliable rope-less fishing in theGulfofMaine lobster fisheries, rather than todrive themanufacturingcostaslowaspossible.

Section2.2:PreviousRelatedWorkinRope-lessFishing

Previous related work in rope-less fishing products, demonstrations, and designstudies are summarized in Table 2.1. That table also compares previous work with therequirementsfortheoffshoreNewEnglandlobsterfishery.Inparticular,thebuoyancyofpreviously-demonstrated rope-less fishing systems, with a maximum buoyancy of 38pounds, is inadequate for deployment with the high currents and deep water of theoffshorefishery(180poundsneededfor½”linewith3:1scope).

Less buoyancy would be required for smaller line diameters. We set ½” as theminimum line diameter for several reasons. The line diameter for pot haulers is set byadjustingtheseparationoftwosteelplates;thelinediametersettingisnoteasilyadjustedonthefly.Thesinkinggroundlinesinatrawlcanbeupto2500’(750m)long,whichwouldcomprise roughlyhalfof theoverall lengthof linehauled in300mofwaterwitha scopebetween 2:1 and 3:1 (600m-900mof vertical line). Sinking groundlines gather sedimentthat abrades the rope fiber as it is forced between the hauler plates, and so offshoregroundlinesare typically5/8” line to increase the longevityof therope.Thevertical linecannot have a dramatically smaller diameter than that of the groundline, since the pothaulerplatesarenoteasilyadjusted.Inaddition,smalldiameterropessuchas¼”poseapotential injury hazard for fishermen that can cause loss of fingers if the line breaks orcomesoffthepothauler.Therefore,wehaveset½”lineasarequirement,inturnrequiringhigherbuoyancyforthelinespoolflotation.


Summary

Wearetargetingtheoffshorelobsterfisherybecauseheavierlinesappeartoposeahigher risk for endangered North Atlantic Right Whales, and because potential inshoremitigationapproachessuchasweaklinksandweaklinesarelessviableforlargeoffshoretrawls.Wesurveyedthepreviousworkonrope-less fishinggear,andnoneof itprovidesanywhere near the required buoyancy to bring a line to the surface (38 pounds for thebest-documented prior work, versus 140-180 pounds required for the offshore fisheryalong the edge of the Continental Shelf). For an initial prototype design, our designdecisions were based on what we believe will be the most robust approaches to eachcomponentofarope-lessfishingsystem.

Table2.1:Anoverviewofrelatedworkinrope-lessfishingproducts,demonstrations,andstudies.ThebuoyancyrequiredtoreturnaropetothesurfaceinthehighcurrentsoftheoffshoreNewEnglandlobsterfishery,atabout180pounds,isseveraltimeshigherthanthebuoyancyprovidedbypreviousrope-lessfishingsystems.

Name Depth Buoyancy LineCapacity ReleaseType

LinePackType

FioBuoy,FioMarine,Australia

Twomodels,100metersand200meters

Upto18pounds,air-filledplasticspool

Approx.250mof½”line

Timeroracoustic

Linespool

DeAlteris1999;Allen&DeAlteris2007

200meters 38pounds(14”trawlfloat)

300mof3/8”line

Acoustic(Benthos)

Random-packcanister

Hopkins&Hoggard2006

Testedin20meters

Notspecified Notspecified Acoustic(SubSeaSonicsAR50)

Linecanister

Liggins&Westley,2011,NewSouthWales,Australia

120meters Twosmalltrawlfloats(estimated<50pounds)

Notspecified Acousticwithgalvanicactionbackup

Meshbaglinecanister

Turneretal1999(designstudy)

1200’(365m)

8pounds(plastictrawlfloat)

1400’(425m)of1/8”rope

Acousticmock-upwithfish-findersonar

Linespool

OffshoreNewEnglandlobsterfishery(thisstudy)

300meters(andatShelfbreak,needsafetymargin)

Need180lbin2-knotcurrentin300mdepthwith3:1scopeformarginwithwind,waves,andsurfacelayer.

Needscopeof2:1to3:1,i.e.600mto900mline.Needatleast½”lineforpothaulercompatibility.

Timedrelease,oracousticrelease

Linespool


Section3:BuoyancyModelingandLineSpoolDesignDecisions

Significant timewasspentresearchingvarious linepackspreviouslyused inrope-less fishingandother release systems.A linepackholds thevertical lineon the seaflooruntilitisreleased,atwhichpointafloatbringsthelinetothesurfaceforrecovery.Thetwomain types of line packs are line spools and line lockers. For an offshore system, wedetermined that a line spool would bemore reliable, and that is what we used for ourprototype design. For inshore systems with less rope, however, a line locker might bereliableenoughwithlesscomplexityandcost.Themodularityofourdesignwouldallowafutureinshoreversiontousealinelockerapproach.

Inalinelocker,thelineiscoiledinacanisterormeshbagthatsitsonorneartheoceanbottom.Uponrelease,thelineispulledfromthecanisterviaaflotationdevice.Forrelatively short lengths of line, freely-packed line canisters can work well withappropriatelychosenrope,suchastorque-freebraidedropes.Forthelonglengthsofline(600-900meters)andtherelativelylargeminimumropediameter(1/2”)requiredfortheoffshore lobster fishery, however, a freely-packed line canisterwouldbecome increasinglarge, increasing the danger of tangling and release failures. Line canisters cannot bepackedtooloosely,becausetheropecanmoveandtangleinsidethecanisterduetowatermotion. Line canisters also cannot be packed too tightly, because the line might notsuccessfully pull out of the canister. Additionally, since the line locker would remainrelativelyclosetothetrawlanchors,thecanistercouldpotentiallyincreasethedifficultyofretrievingthetrawlanchorsonboardthefishingvessel.Oneof the largestcautionsfromexperts in these technologieswas the care required in coiling the line in the locker.Anysort of improper twist in the line, knots, or slack in the packing could create potentialtangles in the line, preventing the float from reaching the surface. This risk of failure inusingthelinelockerapproachwastoogreatandwasabandoned.

Expertsinthesedeviceshavebeenutilizingvariousincarnationsoflinespoolsoverthe course of thousands of deployments with excellent success. Several well-knownpracticesandproceduresare inplace forwinding linepacks for reliability.Basedon theexpertiseavailableatWHOI,itwasdeterminedthatpursuingalinespoolarrangementwasthelowest-risksolution.Intermsofhandling,theflotationandtheemptylinespoolcometo the surface first, are recovered by the fishing vessel, and then the fishermenhaul thetrawl as normal. Getting the flotation spool on board and out of the way earlier in theprocess also provides time while the trawl is being recovered to reset the spool andprepareitforredeployment.

Our visit with Massachusetts offshore lobster fishermen revealed some criticalinformation beyond that the information provided by the report “Lobster Pot GearConfigurations in the Gulf of Maine” (McCarron and Tetreault, 2012). The offshorefishermen reported theywereworking on the 100-160 fathom (180-300m) bathymetrycontourlinesattheedgeofthecontinentalshelfnearvariouscanyons.Thewaterdepthsintheareassurroundingthedeepercontourchangedrasticallyovershortdistances,reaching

up to 200-400 fathoms (365-731m) over a distance of less than one nautical mile (seeGeorges Bank and Vicinity Bathymetric Chart). Additionally, they were often deployingtheir gearwhere eddies from the Gulfstreamwould induce strong currents of 1-2 knotsthatwouldsubmergeapairofPolyformfloats thatwereproviding~180lbsofbuoyancy.Tocompensateforthedrasticchangesinbottomtopographyandstrongcurrent,theyuseascope of vertical line equal to three times that of the water depth. Additionally thefishermenwereusinga5/8”diameterlineratherthanthe½”lineinordertoincreasethelongevityof the line.The sinkingground line inparticularpicksup sedimentgrains thatthenabradeas it issqueezedthroughthepothaulerplates.Similarly,saltcrystals in linethathasdriedoutwithoutafreshwaterrinsecanabraderopefibers.Usinglargerdiameterlineincreasestheusefullifeoftheline.

Duringthevisitwiththefishermenthefollowingdesignparametersweregeneratedforthesystem:

1. Theflotationdepthratingneedsasafetymargingreaterthanoriginal300-meterdepthspecificationdue to thedrastically changingbottomcontour.Having theflotationfailatdepthwouldresultinlostgear.

2. Thesystemneedstobesized(physicaldimensionandweight)foreasyhandlingwhere minimal hauling gear is available (no A-frames or cranes). The fishingvesselsdidnothavethefullsuiteofliftingequipmentthatisoftenavailableonoceanographicresearchvessels.Assuchthedeviceneedstobesizedcomparablyto existing fishing gear for fishermen to lift and maneuver the device withlimitedmechanicalassistance.

3. Thespoolwouldneedtoholdsufficientlinesuchthattheavailablebuoyancycanovercome the water currents at the continental shelf. The offshore fishermenreportedusing200%-300%scope as opposed to the150%scope reportedbyMcCarronandTetreault(2012).

4. Thespoolsystemshouldminimizethetimerequiredatseaforredeployment.Atpresent a crewman is often dedicated to figure-eight the line coming aboardfromthetrawldowninthelinelockerofthefishingvessel.Thissamemancouldpossibly be trained to properly spool line onto a line pack but it would takesignificantlymoretimewhileonsite. Inasystembasedonanacousticrelease,theacoustictransducershouldbeprowedabovetheflotationtoprovideaclearline of sight to the surface. Flotation acts as an acoustic baffle that preventssound from passing through the material due to the acoustic impedancedifferences.

5. The system should be rugged enough to handle the rigorous handling of gearthat is typical on board fishing and oceanographic research vessels, and withminimal mechanical assistance. There is not ample room on the deck of anoffshorefishingvessel,andtypicallygeargetsdroppedanddraggedaroundonthedeck.


Initial design concepts used 14” trawl floats attached on top of a line pack spoolsimilar to existing line pack arrangements. Trawl floats are inexpensive and readilyavailable. However, the amount of flotation required for the operational area of interestduetothedepthandwatercurrentswouldhaverequiredmultipletrawlfloats,makingtheoverall size of the systemunwieldly,whether as a single component or as two separatecomponentsasinatypicalmooringarrangement.

AmongtheexistingdesignsthatareinuseatWHOI,thelinespoolapproachseemedthemostpromising.AlinespooldesignedatWHOIthatincorporatesflotationintothespoolitselfisshowninFigure3.1.

Figure3.1:ExistingWHOI-designedflotationspoolusingsyntacticfoamandacommerciallyavailablerelease.

Having the spool include the flotation makes the design more compact whileallowing for a significant volume of otherwise unused space for flotation material.Installing the acoustic release in the center of the flotation spool allows the acoustictransducer to have an unblocked signal path to the ocean surface. Traditionalmooringshavetheacousticreleaseunderneaththeflotationspheresandarethereforesubjecttoanacousticdeadzone,throughwhichacousticsignalscannotpropagate.Thedeadzonecausesa lossofcommunicationwith therelease incertainorientations, reducingreliability.ThedownsidesoftheexistingWHOIlinespoolwerethesize,weightandthecost.Traditionalsyntactic foam is very heavy to achieve a given buoyancy. Flotation buoyancy of 190poundshasanairweightofabout200poundsforthefoamalone.Theuseofcommerciallyavailableacousticreleasesdrivesthecostsbeyondwhatislikelysupportableinthefishingindustry.

To determine the amount of flotation required for this application, themodelingpackageWHOI Cable (Gobat and Grosenbaugh, 2000) was utilized to simulate a simplebuoy, catenary cable, and anchor system.Water current information for the operational

area in questionwas extracted from the University ofMassachusetts Dartmouth Gulf ofMaineandGeorgesBanktidalsimulationdatabase(http://fvcom.smast.umassd.edu/research_projects/GB/tidal_simulation.html).

TheWHOI Cable simulations utilized a simple cylindrical buoy, neutrally buoyantline, and an anchor. Variables such aswater currents,wind speed,wave conditions, linelength, and line diameterweremodified between simulations to determine the primarydriversfortheflotationrequirements.Whenabuoyisfullysubmerged,thetensionintheverticallinewillbeequaltothetotalbuoyancyofthebuoy.Byselectingabuoysizethatislarger than required, it is possible to look at the tension in the line relative to variousparameterstoobtainanunderstandingoftheforcesinvolved.

Table3.1:Comparisonofverticallinetensionforvariouswatercurrents.

VerticalLineDiameter(inches)

VerticalLineLength(m)

WaterCurrents(m/s–Surface,Bottom)

WindSpeed(m/s)

WavesAmplitude(m),Period(s)

MaxLineTension(N)

MaxLineTension(lbs)

0.5 600 0.2–0.1 5 0.5,7 80 180.5 600 0.4–0.1 5 0.5,7 150 340.5 600 0.6–0.15 5 0.5,7 310 700.5 600 0.8–0.15 5 0.5,7 500 1120.5 600 1.0–0.2 5 0.5,7 770 173

At the edge of the Gulf Stream, surfacewater currents can be as high as 2 knots(1m/s).Inthecomparisonofverticallinetensionversuswatercurrentsforafixedlengthofline,asignificantincreaseinlinetensionresultsfromanincreaseinwatercurrents.Thelast result in Table 3.1 closely matches what was reported to us by offshore lobsterfishermen.OffshorefishermenhaveobservedtwoPolyformLD-3floats(with180poundsofbuoyancy)becomingsubmergedincurrentsintherangeof2knots.Herewecanseethatthe tension in the line is approximately 173 pounds. Accounting for other simulationvariables shown below, it is easy to imagine the situations local fishermen wereexperiencing.


Table3.2:Comparisonofverticallinetensionsforvariousverticallinelengths.




WindSpeed(m/s)


MaxLineTension(N)

MaxLineTension(lbs)

0.5 450 1.0–0.2 5 0.5,7 875 1960.5 600 1.0–0.2 5 0.5,7 770 1730.5 750 1.0–0.2 5 0.5,7 650 1460.5 900 1.0–0.2 5 0.5,7 580 1300.5 1050 1.0–0.2 5 0.5,7 500 112

Localoffshorefishermenreportusing600m-900moflineinwatersof300mdepthto try to prevent their surfaces floats from becoming submerged. In the comparison ofvertical line tension for various line lengths, shown inTable3.2, it canbe seen that linetensiondecreasessignificantlyasthelinelengthinincreased.In300mofwaterwith1m/sof surface current and 750m-900m of line length the tension decreases below the 180poundsofbuoyancythatthePolyformfloatsprovide,allowingthefloatstoremainontheoceansurfaceasconfirmedbythefishermen.

Table3.3:Comparisonofverticallinetensionsforvariouswindspeeds.




WindSpeed(m/s)


MaxLineTension(N)

MaxLineTension(lbs)

0.5 600 1.0–0.2 5 0.5,7 770 1730.5 600 1.0–0.2 10 0.5,7 ~770 ~1730.5 600 1.0–0.2 15 0.5,7 ~770 ~173

Inthecomparisonofvertical linetensionforvariouswindspeeds,showninTable3.3,WHOICabledoesnot showa significant change in line tension as thewind speed isincreased.Thewatercurrentsappeartobethemaindriverinthesimulation.

Table3.4:Comparisonofverticallinetensionsforvariouswaveconditions.




WindSpeed(m/s)


MaxLineTension(N)

MaxLineTension(lbs)

0.75 600 1.0–0.2 5 0.5,7 880 1970.75 600 1.0–0.2 5 1.0,7 930 2090.75 600 1.0–0.2 5 1.5,7 950 2130.75 600 1.0–0.2 5 2.0,7 1000 224

Tworesultscanbeseeninthecomparisonofverticallinetensionforvariouswaveconditions,showninTable3.4.Herethelinediameterhasbeenincreased.Comparisontopreviousresultsshowsanincreaseinverticallinetensionasthediameterincreasesduetothe added hydrodynamic drag. Additionally we can see that as the wave amplitude isincreasedasmallincreaseinverticallinetensionisgenerated.

The empirical information provided by local offshore fishermen regarding howmuchbuoyancytheyusedprovidedareferenceagainstwhichtocomparetheWHOICablesimulations.Fromthesimulationsitwaspossibletonearlyreplicatethesituationswhichthefishermenwereexperiencingwiththeirexistingfishinggear,forexamplethatgenerallytheyused180poundsoffloatationtobringthelinetothesurface,butthatsometimeswithstrongcurrents, even180poundsof floatationwaspulledunderwaterby the tensionontherope.Thesimulationresultsalsoprovidesomereasonableboundsontheoperationalparametersinordertodesigntheflotationspool.

Amodulardesignapproachwaschosenfortherope-lessfishingsystemasshowninFigure3.2.Aflotationcoreissandwichedbetweentwospoolcheekcages.Bothcheekcagesprovideasmoothsurface tosecure the linepackandprovidean interinteruptedpay-outpathfortheline.Thecheekcagesalsoprovideameanstohandlethefullassemblyaswellasprotectthereleasemechanismandacoustictransducer.Thecagesweredesignedsuchthattheflotationspoolassemblycouldsitflatonthethedeck,toeasehandlingrelativetoanassemblythatcannotsitflatandmustbeheldatalltimes.Thereleasemechanismandelectronicsareinstalledinthecenteroftheflotationcorewiththetransducerremotedtothe top of the flotation spool, such that it has a clear acoustic line of sight to the oceansurface.


Figure3.2:ModularLinePackSpool

Aninternalspineassemblysecuresthereleasemechanismandflotationtothetopspool cheek cage evenwhen thebottomspool cheek cage is removed.Thebottomspoolcheekcagecanbequicklyremovedviafourboltsandapre-woundlinepackcartidgecanbeloadedontothespool.Oncethenewlinepackcartridgeisloadedontothefloationcore,thebottomspoolcheekplatecanbereinstalled,securingthelinepackontothespool.

Althoughspoolingtherecoveredlineontotheflotationspoolviatraditionalmeans(byspinningthespoolandwindingtheline)ispossible,itwouldbeburdensomeandtimeconsumingtohandlethesetaskswhileonsite,addingprecioustimeandlabortoeachtrawlrecovery. Utilizing a prewound line pack spool allows for a quick turn-around on site.Cartidgescouldbewoundbyfishermenwhileonshoreorviaaserviceindustrythatcouldbe created to collect recovered lines from fishermen as they return to port and thenreplacedwithcustomlengthlinepackcartridges.

The flotation spool prototypes that were generated (Figure 3.3 and Figure 3.4)during the period of performance were designed to accommodate a line pack cartridgecontaining approximately 900m (or less) of ½” diameter neutrally-buoyant line. Theoverallsystemdimensionsareapproximately32”diameterbyapproximately43”tall.Theflotationspoolassemblyweighsapproximately130poundsinairunloadedandasmuchas340poundsinairwhenfullyloadedwith900mof½”line.Theavailablebuoyancyofthesystemasbuiltis145pounds.Positivelybuoyantlinecouldbeusedasaddedbuoyancyatthecostofrequiringaheavieranchor.Largerdiameter linescouldalsobeutilizedat thecostreducingthetotallinelengththatthespoolcansupport.

Figure3.3:Fullyassembledmodularflotationspools.Left:Loadedwith900m1/2"line;Right:Unloaded.

To keep the system’s overall weight down and the available buoyancy up, theflotation core is constructed from sheets of Divinycell HCP-70 foam. HCP-70 is a lowdensity foam that has an operational depth rating of 450m and a crush depth rating of700m.Utilizinga lowdensity foamalsokeepstheoverallsizeof thesystemsmallerthanwouldotherwisebepossible.Lowerdensityfoamsareavailable,butatthecostofreducedoperatingdepth.

Figure3.4:ModularFlotationSpoolPrototypes

Air filled flotation mechanisms were investigated but ultimately proved to be asourceofriskintermsoffabricationcostsandreliability.Someothersimilarsystemslike


theFioBuoy(FioMarine,Australia)useaplasticair-filledhousingastheprimaryflotationmechanism, but are limited in the operational depth that can be achieved in terms ofphysical strength and line capacity, require a completely different assembly, and havelimitedbuoyancyofapproximately18poundsforthe200-metermodel.

Themodularnatureofourdesignallowsforscalabilitytoaccommodateavarietyofdifferent environmental parameters without having to modify the entire design. Forexampleifalighterweightsystemwererequiredtooperateinshallowerwaters,thefoamcorecouldsimplebeswappedout fora lowerdensity foamto reduce theoverallweightwhileincreasingtheavailablebuoyancy.

Basedonthesimulationresultsandtheempiricalobservationsfromlocaloffshorefishermentheprototypesystemsthatweredesignedandbuiltshouldbeabletooperatein300mwaterdepthutilizing900mof lineincurrentsofupto2knots(1m/s).Thesystemsize and weight should be manageable based on existing equipment that the offshorefishermenarecurrentlyhandling.Thecostsof theprototypesystems isrelativelyhighatabout $13,000 per timer-based unit, but the cost can be addressed with volumemanufacturingprocesses,includingpotentiallymanufacturingmoldedfoamunits.

Section4:ReleaseMechanismDesignDecisionsandDescription

Commercially available acoustic releases are can be quite expensive with pricesrangingfrom$6,500to$15,000,notincluding~$15,000inrequiredtopsidedeckgear.Therope-less fishing system needs to be a lower cost device (< $10,000) to aid in adoptionrates. As such it was decided to leverage our existing expertise in acoustic modemtechnologyandelectromechanicalsystemstodevelopalowercostreleasesystem(Freitagetal2005;Gallimoreetal2010).

Thereareseveraltechniquesavailableforretrievingheavyloadssuspendedbelowtheoceansurface.Allrequireasystemthatprovidessomeformofmechanicaladvantageandareleasecomponent.Thereleasecomponentcancomeinavarietyofstyles,andthesewere investigated for use in the rope-less fishing system. We consulted with the mostexperiencedWHOI engineers andmooring operations personnel to discuss the pros andcons of various release types. Collectively, these engineers and operational technicianshave designed and fabricatedmore than a dozen differentmodels of releases, producedhundredsofunits,andmadethousandsofdeployments.

Burnwires use an electrical current passing through awire exposed to seawaterthatcausesittocorrode.Theburnwireisoftenusedtosecuretheendofalever.Oncethewirecorrodesawaytheleverisallowedtomovefreelyandreleasetheloadhangingfromitsotherend.Burnwiresareelegantbecausetheyareinexpensivetoreplacebuttheydorequirethatstockiskeptonhand.Burnwiressometimesfail tocorrodeas intendedandare consideredaone-shotdevice (use it once then replace).Ultimately, burnwireswereconsideredareliabilityriskforthisproject.

Rotary and linear solenoids are used quite frequently in commercially availableacoustic releases. The solenoid usually restrains one endof a leverwith a spring-loadedlockingmechanismwhiletheotherendofaleversecurestheload.Anelectricalcurrentissuppliedtothesolenoidcausingthesolenoidshafttounlockthemechanism.Toovercomepotential biofouling or corrosion that may have accumulated on the release lever orrestraint catch, a powerful spring is often incorporated into the mechanism inside thehousingtoensurethattherestraintcatchsuccessfullyfreestheleverarm.Oncetheendofthe lever is free to move, the load is released. Rotary and linear solenoids are usedcommonly in the industrywithhighreliability.However, thesizeandone-shotnatureofthedeviceswereconsideredundesirable forthisapplication. Increasedmechanismsizesrequirelargerhousing,andoneofourgoalswastokeepthesystemsizetoaminimum.Intheeventofa releasemechanismgetting fouledandnot releasingon the firstattempt, aone-shotdevicedoesnotallowforaremotereset.Amanualtoolisoftenrequiredtoresetthedevice.

Ultimately, itwas decided to utilize a small DC gearheadmotorwith an attachedrotary encoder. Themotor is attached to a shaft that secures one end of a lever systemwhile the other end of the lever secures the load. Once the motor is energized, a shaftrotates a key that preventsmovement of the lever system.Once the key is no longer anobstruction, the leversystem is free tomoveand the load is released.Bymonitoring theencodersignalsasthemotorisenergized, itcanbedeterminedifthemotorismovingascommanded.Themotor state canbe reportedback to theuser evenwhen the system isremote(ifproperlyequipped,forexamplewithacousticcommunications).Themotorcanalsobecommandedtorotatemultipletimesorinopposingdirectionsintheeventthatthekeyisobstructedinoneorientationbutnottheother.Althoughthecostsforthemotorsareoftenhigherthanotherreleasetypes,thefeedbackandprovenreliabilityjustifytheaddedcosts.

Thereleasemechanismandassembly(Figure4.1)wasalsodesignedasamodularcomponent. The housing is one of theWHOI Acoustic Communication Group’s standardaluminumDraw-Tightdesigns,andisratedto1000m.Thehousingaccommodatestimer-based or acoustic modem-based release hardware, a rechargeable Lithium-Ionrechargeablebatterypack,batterychargerwithpowerdistributionandthereleasemotor.On the endcap, connectors for a remote acoustic transducer and physical consoleconnection to the controller are available, as well as a rotary power switch and statusviewport.TheviewportallowstheusertoseeLEDindicatorswithoutopeningthehousing.


Figure4.1:ModularReleaseSystem

Manycommerciallyavailablesystemsuse thepressurehousingof thereleaseasastrength member, with the full mechanical load of the system applied directly on thepressurehousing.Thisaddscostandcomplexitytothehousingdesign.Inourdesign,thehousingismountedtothelowerspineplateoftheflotationspoolassemblysuchthattheloads are transferred to the spine rather than to the housing. This allows for a smallerelectronicshousingandformodularreleasecomponents.

Figure4.2showstheexternalreleasecomponents.Theexternalreleasecomponentsconsistofthelowerspineplate,tworeleasecheekplates(turquoise),twoleverarms(redandyellow),andamotorshaftreleaselatch(green).Theloadisattachedinthehookofthelower leverarm (red) forcing it to rotate clockwiseabout itspivot.The topof the lowerlever arm (red) makes contact with the upper lever arm (yellow) forcing it to rotatecounterclockwiseaboutitspivot.Theendoftheupperleverarm(yellow)makescontactwith the release latch attached to theDCmotor shaft.When themotor shaft rotates thelatch(green)theupperleverarmisfreetorotate,allowingthelowerleverarmtorotatetorelease the load. As built, the mechanical advantage of the release mechanism isapproximately300:1,requiringonlyasmallamountoftorquefromtheDCmotortorotatethe key. Requiring less torque requires less battery capacity and smaller electroniccomponentssizes,andallowsforareducedpackagingfootprint.

Theexternalreleasecomponentsaresimpleshapesthatcanbecutonawater-jetorcomparablemachine to keep component costs down.Bymaking the designmodular theassemblycouldeasilybeusedinotherdesigns,suchasontheendofacagewherethecagetakes the load rather than the housing as it does in a traditional mooring design. Thescalabilityofthedesignsallowsforflexibilityinpackagingsizeandmechanicaladvantageneeds.

Agearhandlingrequirementforarope-lessfishingsystemisthatitnotrollaroundonthedeck,sothecylindricalendsofthelinespoolneedtobeabletositflatonthedeckofthe fishingvessel.Mostexistingreleasesystemshavearelatively large leverarmprofile,extending significantly beyond the pressure housing endcap. Using an existing releasemechanismwiththerequirementofsitting flatonthedeckwouldhaverequireda largerlinespoolcage,inturnincreasinggearhandlingdifficultyforthefishermen.Tomaintainascompact a systemaspossible, the external release componentsweredesigned tohave alowerprofilethanexistingreleases.

Figure4.2:ModularReleaseMechanism

In field deployments, it is recommended that the release be floated at a nominalheightof5mabovetheanchorandtheoceanbottom,inordertoavoidfoulingwithbottomand other residual gear that may be present. This 5-meter length of line between theanchor and the releasewill also be of use during deployment, as itwill allow the spool


assembly tobesecured to thedeckwith temporaryquick-releasegear-handling lines(orsimilar)whilethetrawlisstreamingoutbehindthefishingvessel.Whenthevesselisatthetarget deployment location for the line spool (the “rope-less” endline), the quick-releaselinesontheflotationspoolarereleasedandtheweightanddragofthetrawlwillpullthespooloffthebackofthevesselwithminimalhandlingbeingrequiredbythecrew.

Additionally, having the flotation spools set 5meters above the bottommay alsoincrease passive acoustic visibility, to aid with gear conflicts if active acoustics are notutilized.

Section5:ReleaseElectronicsDesignDecisionsandUserInterface

Themain electronics design goal for this project was to produce a robust timer-basedreleasedrivercapableofactuatingthereleasemechanismataspecifiedreleasetime.Thereleasetimeneedstobeconfigurableviaauserinterface.Whileatimer-basedreleaseprovidesacost-effectivemethodmeanstoreleasethelinespool,itlackstheflexibilityofanacoustically-commanded release to react to changes in weather or fishing schedules.Therefore,asecondarydesigngoalwastoconsiderfutureacousticreleasecapability,and,where feasible, include the electronics support necessary to enable that capability in afuturesoftwareandhardwarerevision.Additionalaspectsoftheelectronicsdesignincludebattery selection and battery controller, as well as provisions for an acoustic poweramplifierandtransducerinfuturerevisions.

The electronics consist of several circuit boards, namely amicrocontroller circuitboard, a release driver board, a battery charging board, and a distribution board. Inaddition, thehousingandcircuitboardstackcan immediatelyacceptanacousticmodemandacousticmodempoweramplifierinordertoimplementanacousticreleaseoptioninparallel,andinadditiontothetimer-basedoptionthatwouldremainactive.

The microcontroller circuit board is pictured in Figure 5.1. The microcontrollerimplementstheuserinterfaceoveranRS-232serialport,setsthereleasetimeinamicro-power battery-backed real-time clock, switches the power supply to a low-power“hibernate” state when not releasing or interacting with the user, controls the releasemotorandmonitorsitsencoders,andincludestheanalogsignalconditioningcircuitsforafutureacousticlow-powerdetectortodetectacousticreleasecommands.

The release driver board is a separate circuit board that is quite simple and onlyincludesaswitchablepowersupplyandamotordriverchip.Thereleasedriverboardisaseparateboardfortworeasons:first,toreduceriskfortheprototypebuild,andsecond,toincorporatemodularity. If a future version of the prototype uses a differentmotor or adifferent actuator (such as a solenoid or a galvanic burn wire), the only circuit boardrevisions required would be to revise the relatively simple release driver board, ratherthanhavingtorevisethemicrocontrollercircuitboardhardware.ThereleasedriverboardisshowninFigure5.2.

Theprototypedesignalsoincludesseveralfeaturestohelpevaluateanddebugthereleaseandlinespoolunspoolingperformance.Forexample,anorientationmotion-sensorchip is integrated in order to record the motion of the release prototype’s line spoolthroughthewatercolumn,tohelpdiagnoseprototypereleasefailures.Inaddition,duringoperationaluse,themotionsensorwillenablethemicrocontrollertodeterminewhetherornot the linespoolhassuccessfullyreleasedfromitsanchor,andhencewhetherornot tocontinuetryingtoactuatetherelease.Fortheprototype,amicro-SDmemorycardslot isincluded to record sensor measurements for diagnostic analysis. The power supply isprotected against over-voltage, under-voltage, and reverse-voltage, and against incorrectbatteryconnections.Thebatteryisrechargeablesothattheuserdoesnothavetoopenthepressurehousing,whichcouldpotentiallycompromisetheO-ringseals.

Figure 5.1: The microcontroller circuit board that implements the user interface, the timerfunctionality,motorcontrol,andacousticsignaldetectionforafutureacousticreleaseoption.


Figure 5.2: Release Driver circuit board and release motor with integrated motor encoders. Thereleasedriverboardissimpleandcanberevisedeasilyifusedwithadifferentmotororanalternatereleaseactuator,suchasasolenoidoraburnwire.

Section5.1:UserInterface

The user interface is implemented over an RS-232 serial port, with parameters19200bitspersecond,8bitwords,noparity,and1stopbit(“19200,8N1”).Thefirsttimethesystemisused,theclockneedstobeset.Insubsequentdeployments,theuserneedstore-armthereleaseandsetthedesiredreleasetime,thenputthesysteminits low-powerstateuntilitsreleasetime.Futuresoftwarerevisionscanallowmorecomplexbehaviors,aswellasallowingcontroloveraWiFiorsimilarwirelesslinkfromcommoditysmartphonesorcomputers,thatwouldreducethecostofrequireddeckgear.

Theuserinterfacemenucommandsarelistedbelow:

s Status:Printcurrenttime,unit’sacousticcommandIDnumber,releasetime,armed/notarmedstatus,andremainingbatteryvoltage.

t Time:Setcurrenttime.i ID:setunit’sacousticcommandIDnumber.c Correction: Set motor encoder count correction to avoid release motor

overshoot.r ReleaseTime:Setdesiredreleasetime.a Armrelease.

h Hibernate now: go into low-power state to wait for release time or userinteraction.

n releaseNow:forresettingmechanicalreleasestate.v Version:displayfirmwareversionandhardwareversionnumbers.? help:displayhelpmenu.

The microcontroller we selected, an ARM M4-based Atmel SAM4S, includes hardwarecryptographic support that would enable eventual cryptographic signatures that onlyauthorizedfishingvesselscouldrelease.Anyfishingvesselcouldqueryarope-lesssystemontheseafloor,whichwouldthenreplywithanacknowledgmentsignaltoalertthevesselthat rope-less gear is set in that location. The reply signalwould need to be very short(henceasmallamountofbatteryenergy)sothatrepeatedgear-conflictquerieswouldnotsignificantlydeplete itsbattery. If the reply togear-conflictqueries consumedsignificantenergy, a malicious fishing vessel could repeatedly query rope-less gear to deplete itsbattery. Since thegear isdesigned to releasewhen itsbattery isbelowa certain level toavoid permanent loss of gear, a malicious fishing vessel could potentially force gear toreleasebydepletingitsbattery.Byminimizingtheenergyconsumedbythereplytoagear-conflict query, the goalwould be tomake a repeated-query gear theft attack to becomeextremelytimeconsumingandmoretroublethanitisworth.

Section5.2:BatteryandBatteryController

Weselecteda14.4V rechargeableLithium-Ionbatterypack from InspiredEnergy.Webelievethatarechargeablebatteryisimportanttominimizethenumberoftimesthattheelectronicshousingneedstobeopened.Everytimethehousingisopened,itsO-ringsandsealingsurfacesneedtobehandledcarefully topreventnicks,dirt,or inadequateO-ring lubrication fromcausing leaks.Witharechargeablebattery, there isnoneed for theendusertoopenthehousing.

Theenergycapacityofthebattery(20.4Amp-Hoursat14.4Vnominal)ismorethanadequate for a timer-based release. The batterywas sized to provide approximately sixmonthsofbattery life forasystemwithanacousticrelease,wherea low-poweracousticdetector is runningconstantly, aswell asoccasionally transmitting shortacoustic repliesfor gear conflict “ping”queries fromother fishingvessels, or acoustic release commandsfromthegear’sowner.

Section6:EvaluationofPassiveAcousticstoDetectGearatDepth

Fixed fishinggearsuchas lobsterpot trawlscanhaveconflictseitherwithmobilefishinggeardraggedoverit,orwithotherlobstergearsetontopofit.Fishinggearbuoysprovide visual cues for other fishing vessels that fishing gear is below.Rope-less fishing


gearwouldnothaveavisualcueonthesurface,whichcouldincreasethelikelihoodofgearconflicts. In addition to surface buoys, other existingmethods help reduce gear conflictssuchassettingtrawlsinconsistentorientations(e.g.north-south),orsharedfishinggroundunderstandings(e.g. fixedgearsetonparticularagreed-uponLorantime-differences,andmobile gear dragged on different Loran time-differences, as is currently done along theedgeoftheContinentalShelfintheoffshoreGulfofMainelobsterfishery,usingGPSunitstodisplaylegacyLoranlocations).

Acoustic methods could also provide ways to allow fishing vessels to detect thepresenceof rope-less fishinggear.Anacoustic transmittercouldbe integrated intorope-lessgear,andsendrepliestoacousticqueriessentfromfishingvessels.Thiswouldlikelyrequire an additional acoustic transducer and electronic instrument for fishing vessels.Althoughalmostallfishingvesselsincludeanechosounderwithavisualdisplay,thereisnostraightforwardwayforarope-lessfishingsystemontheseafloortoreplytoechosounderpingsanddisplayusefulinformationwithexistingunits.

Forthisproject,wemadeapreliminaryevaluationofpassiveacousticdetectabilityof rope-less fishinggearand traps thatwouldnot requireanacoustic transmitteron therope-less system at the seafloor. Even if a rope-less system did include an acoustictransmitter,replyingtoechosounderpingsoracousticinterrogationswouldconsumesomeofthelimitedbatteryenergyonthereleasesystem,andsoasystemequippedwithactiveacousticswouldbenefitfrompassiveacousticdetectability.

For the evaluation of passive acoustic detectability, we used a fish-finding depthsounderat theWHOIdock to record returns frombothaprototype line spoolaswell astrapsoutfittedwithvariousacousticreflectors.ThegearwasdeployedintotheinstrumenttestingwellattheWHOIdock(Figure6.1).

BoatscannotgointothewellattheWHOIdock,sothedepthsounderthatweusedwas a Vexilar SP200A T-BOX SonarPhone (http://www.sonarphone.mobi), which has adual-frequency 83kHz/200kHz transducer with a 20°/40° beamwidth. The display isshownonasmartphone,fromwhichwemadetheimagecaptures.Weusedagainof41%forallthemeasurements,andsetthedepthrangeto0-60feetratherthanauto-ranging.

We performed six experimental treatments, with the group of six experimentaltreatmentsprecededandfollowedbycontrolrecordingswherenogearandnoropeswerein the water. The experimental reflectors are shown in Figure 6.2. The experimentsrecorded echosounder plots of the line spool, a bare lobster trap, and various acousticreflectors zip-tied to the lobster trap: PVC pipe reflectors, metal tube reflectors, a steelplate,andtrawlfloats.

Foroffshoredeployments,thelinebetweentheanchorandthelinespoolwouldbeabout5metersratherthantheapproximately1.5metersoflineusedhere.Thelobstertrapwas 22” x 48” x 14”, andwas previous used in Cape Cod Bay. Offshore traps would besomewhat larger. There were six PVC pipe reflectors, each ¾” x 12”, with the endcaps

cementedinplace.Schedule80PVCpipewith¾”diameterhasaratedworkingpressureof690psi,whichprovides roughlya50%safetymarginat the targetdepthsof300meters.Themetal tube reflectorsusedwere inabundleof seven1.5” x24”pipeswith theendswelded shut. The steel platewas½” thick, and approximately 7” x 20”. Therewere twotrawlfloats,eachwitha7”diameter.

Intermsofoperationaldeployment,trapsarestackedontopofeachotherwhenonthefishingvessel,andtwotrapreflectordesignsinparticularseempotentiallywell-suitedtoallowstacking.CappedPVCpipescouldbezip-tiedon the insideof the traps,ora flatreflective plate could be attached on top of them. In order to significantly increase thestrengthofthereturnsignalfromaflatplate,syntacticfoamorperhapsmetalcouldbecastwitharetro-reflectorsurfacesimilartoabicyclereflector,whichincorporatesmanyretro-reflectorsintoaflatsurface.Eachretro-reflectorsectionwouldlooklikethehollowcornerinside of a cube, as in a sailboat’s passive radar reflector. For a deep-water (~300m)echosounderfrequencyofabout50kHz(wavelengthabout3cm),theretro-reflectorfacetswould likelybeontheorderof5-10cmacross,whichwouldmakeanextendedstructurerelatively thick. Alternatively, a few larger retro-reflector hollow cube corners could beplaced inside the trap facing up. If capped PVC pipes provide adequate return strength,theywouldbeaveryinexpensiveoptionandeasytoattachtotraps.

Figure 6.1 Left: The well at the WHOI dock where the experiments were performed. It isapproximately45-50 feetdeep,withacraneandanopeningthat is18 feetwide.Right:TheVexilarSonarPhoneused for the sonar imaging, showing the “towfish”weight thatwasused todepress thesonartransducerandtowitbackandforthacrossthewell.


Figure6.2:Differentexperimentaltreatmentsmeasured.Fromlefttoright,top:Linepackspoolandanchor;barelobstertrap(22”x48”x14”,previouslyfishedinCapeCodBay);lobstertrapwithsix¾”x12”PVCpipereflectors.Bottom:lobstertrapwithsevengrouped1.5”x24”metaltubereflectors;lobstertrapwith7”x20”x½”steelplate;lobstertrapwithtwo7”trawlfloats.

The recorded echosounder images are shown and discussed below. The sonartransducerwaspulledmanuallyonatowfishataslowwalkingpace,backandforthacrossthewellopening.Theimageswererecordedwhenthetowfishwasatthesouthernendofanorth-to-south transit. The left-most side ofmost images show the end of the south-to-north transit. The towfish depthwas approximately 6feet below thewater surface, andwasmaintainedatanapproximatelyconstantdepthbykeepingaknotinthelinelevelwiththesteelbeamthatdefinesthewesternedgeofthewellopening.Thenominaldepthinthewellisabout45-50feet.Forthecontrolrecordings,nogearorlinewasinthewaterexceptfor the towfish and transducer. For all other experimental recordings, the rope from thecrane,aswellasitshookandshackle,wereinthewateraswellastheexperimentalgear.Schools of baitfish (3”-6” in length) were visible on and off throughout the experiment.Forklifts,generators,trucks,othercranes,motorboatsandferrieswereactiveonthedockandinnearbywatersthroughouttheexperiment.

Figure6.3:Oneof thecontrolbaselinemeasurementstakenat thebeginningof theexperiment.Nogearorropeswereinthewater,andthereturnfromthebottomisclean,atabout40-42feetbelowthetransducer,inturnatadepthofabout6feet(46-48feetwaterdepth).Beamwidthisrecordedas40°(83kHzfrequency),whereasallotherrecordingsusedabeamwidthof20°(200kHzfrequency).

Figure6.4:Oneoftheechosounderrecordingstakenwiththelinespoolatthebottomofthewell.Weinterpretthestrongreturnsaround6feetoffthebottom(greenarrow)as likelybeingfromthelinespool,althoughthatisnotconclusive.


Figure6.5:Oneoftheechosounderrecordingstakingwiththebarelobstertrapwithnoreflectorsatthebottomofthewell(returnsinterpretedasbaretrapindicatedwithgreenarrow).Theverticallinefromthecraneanditshookandshackleareinthewatercolumn,andwillcontributetothereturnsignal(returnsinterpretedasthehookandshackleindicatedwithbluearrow).

Figure6.6:OneoftheechosounderrecordingstakenwiththelobstertrapwithPVCpipereflectorsatthebottomofthewell.Thereturnsthatareabout2feetoffthebottom(greenarrow)areconsistentwithapproximatelywherewewouldexpectreturnsfromthePVCpipesontopofthetrap,butarenotconclusive.

Figure 6.7: Echosounder recordings taken with the lobster trap with metal tube reflectors at thebottomofthewell.Thereturnsthatareabout2feetoffthebottomareconsistentwithapproximatelywherewewould expect returns from themetal tubeson topof the trap (greenarrow), butarenotconclusive.

Figure 6.8: Echosounder recordings taken with the lobster trap with steel plate reflector at thebottomofthewell.Thereturnsthatareabout2feetoffthebottomareconsistentwithapproximatelywherewewould expect returns from the steel plate on top of the trap (green arrow), but are notconclusive.


Figure6.9:Oneoftheechosounderrecordingstakenwiththelobstertrapwithtwotrawlfloatsatthebottomofthewell.Thereturnsthatareabout2feetoffthebottomareconsistentwithapproximatelywhere we would expect returns from the floats on top of the trap (green arrow), but are notconclusive.

AsshownbelowinthecaptionforFigure6.10,thecontrolechosounderrecordingsmadeattheendoftheexperimentwereverydifferentfromthecontrolrecordingsattheendoftheexperiment.Therecordingstakenattheendoftheexperimentwithoutanygearin the water show returns approximately where they would have been expected fromreflectorsplacedon topof the lobster trap, sowe cannot conclude that the experimentswithacousticreflectorsdefinitivelyshowedreturnsfromthereflectorsorfromsomethingelseinthewater,suchassediment,orfishfeedingonsedimentthatmayhavebeenstirredupbytheexperiment.

Thedepthintheinstrument-testing“well”sectionoftheWHOIdockthatwewereable touse isabout45-50 feet (13-15m). It isdifficult toextrapolate fromadock test in13mofwatertoestimatepassivedetectabilityin300mofwater,inparticularbecauseofthehighresolutionthatwouldberequiredtodistinguishapassivereflectorabout50cmabovetheseafloor(ontopofatrap)fromtheseaflooritself. Inaddition,thewidthoftheopening of the well on the WHOI dock is about 18 feet. With a 20° beamwidth, theechosounder beam at the bottom (45-50’ depth) is about the same as the width of theopeningofthewell,andsoourexperimentsdidnotresolvetheedgesofthelinespoolortraps.

The resolution required to distinguish a passive reflector on top of a lobster trapthat is 50cmhigh from the seafloor is achievable for a perfect pencil-beam sonar – it isabout 15-20wavelengths at 50kHz and requires a very achievable timing resolution ofseveralhundredmicroseconds.Butforatypicalsonar,evenwithanarrowbeamwidthof10°,thebeam’s“spotsize”ontheseafloorat300mdepthisroughly20mindiameter.Thesurroundingseafloorwouldhavetobeflatenoughthatthe50cm-hightrapswouldbethehighestpointwithinseveralsonarspotsizes–meaningthattherecouldnotbeanysmallmounds,rises,ormedium-sizedrocks.There’sa tradeoffofanarrowenoughbeamtobeabletodistinguishatargetfromtheseaflooraroundit,butawideenoughbeamsothatthefishingvesselwouldnotneedtobedirectlyontopofthetraptodetectitacoustically.

Figure6.10:Oneof thecontrolechosounderrecordingstakenattheendof theexperimentwithnogearorropeinthewaterasidefromthetowfishandtransducer.Thecontrolrecordingstakenattheend of the experiment are very different from the control readings taken at the beginning of theexperiment,inthattherearesignificantreturnsatabout2feetoffthebottom(orangearrow).Thesecontrol recording unfortunately invalidate any conclusions that could be drawn from the otherexperimentalrecordingswiththelobstertrapreflectors,makingitimpossibletodeterminefromtheseresultswhethertheexperimentalreturnsareduetothereflectors,orsomethingelsesuchassedimentstirredupbythelobstertrapsorfishattractedtosomethingstirredupbytheexperiments,ortothedifferenceinresolutionandscatteringstrengthbetweenreturnsat83kHzand200kHz.


Based on this preliminary trial, subsequent evaluations of passive acoustic detectabilityshould:

• Ensure thatallmeasurementsaremadeat thesame frequency,and ideally repeateachexperimentaltreatmentateachfrequency,83kHzand200kHz.Althoughthebeamwidth is wider at 83kHz than it is at 200kHz, 83kHz would be morerepresentative of the frequency used in deepwater. 200kHz has the benefit of a(slightly)narrowerbeamaswellasshowingmorestructure(thoughalsonoise)inthewatercolumn.

• Performcontrolrecordingswithnogearinthewaterbetweeneveryexperimentaltreatment,ratherthanjustatthebeginningandendoftheoverallexperiment.Iftheadditional sonar returns were being caused by sediment stirred up in the watercolumn,wewouldbeabletotellmorequickly,andperhapsdeterminethesettlingtimerequiredaftereachtimethebottomisdisturbedbeforeameasurementcanbemade (i.e. make control recordings at both frequencies, deploy experimentaltreatment,determinetimeforneededforsedimenttoresettle,makeexperimentalrecordingsatbothfrequencies,recover,determinetimeforneededforsedimenttoresettle,repeat).

Section7:ConclusionsandFutureWork

Under thework described in this technical report,we have designed a prototyperope-less fishing system functionally appropriate for the challenging environment of theNewEnglandoffshorelobsterfishery.Wehavefabricatedthreeprototyperope-lessfishingunitsthatcanbefurthertestedunderat-seaconditions,includingonboardoffshorelobsterfishingboats.Wewanttoemphasizethatatthisstagetheseunitsshouldnotbeconsideredcommercially ready, but as a contribution to advancing the research into a system thatmighteventuallybeusedintheGulfofMaineorinotherpartsoftheworldtoreducewhaleentanglement risk while being practical for fishing. The first three prototypes wereproduced at a cost of approximately $13,000 each.We believe that through design-for-manufactureandincreasedproductionnumbers,thatcostcouldcomedownsignificantly,butatthispointwedonothaveaper-unitcostestimateunderlargerscaleproduction.

The logicalnextstep is toperformdocktestingof theunit itself toverify that lineunspoolingisrobust,andtocharacterizeotherperformancefactors.Followingdocktestingand subsequent design refinement to correct release issues and performancecharacterization, sea trials should be carried out from a research vessel to validate linespool unspooling in deeper water. These are the critical testing steps required beforebeginninga collaborationwith fishermenand fishing industry associations todeploy therope-lessgearoperationallyandevaluateitspotentialinthefishery.Lookingfurtherahead,atsomepointitmightbehelpfultoestablishaGearDevelopmentAreainwhichanareasclosedtolobsterfishingmightpermitthetestingofrope-lessfishingsystemssuchasthis

one.ThisideahasbeensuggestedwithintheALWTRT(NMFSConceptPaperonALWTRT,Nov.2010).

We believe a timer-based system provides good cost-effectiveness to reduceexposure of animals to vertical lines in the water column, without requiring moreexpensive acoustic deck gear on fishing vessels. Furthermore, timer-based releases canallowthelinetobeatthesurfacewhenthefishingvesselarrivesonsite,savingtimebynothavingtowaitforthesystemtofloattothesurface(ontheorderof10minutesacousticallysummoned in 300m of water depth). Nevertheless, we do not rule out that an acousticreleasemightbeeventuallypreferablegiventhebetteron-sitetimingofgearretrievalthatit provides for fishermen. Our system design includes provisions for straightforwardintegrationofanacousticmodemandtransducer,andtheexistingmicrocontrollerboardhas the hardware capability (but not yet the software) to performas a relatively simplelow-cost,low-poweracousticmodem.

Another reason to include active acoustics capability is thatwe believe it will bedifficulttodetectpassiveacousticreflectorsonlobstertrapsontheseafloorat300mdepth.Our preliminary dock experiment, however, did not conclusively prove this point, and ifacousticdeckgearremainsprohibitivelyexpensive,passiveacousticexperimentswillneedto be revisited. To reduce gear conflictswith rope-less fishing trawls, an active acousticqueryfromfishingvesselsmaybethebestsolution,withareplyfromtherope-lesssystemontheseafloorindicatingthatgearhasbeensetinthatlocation.Ifacousticdeckgearwereacquiredamongfishingfleetsoperatinginthesamearea,theacousticreplyfromtherope-less systemcanbe integrated intodisplays, for exampleby showing the location, length,andcompassheading(butnotowner’sname)ofatrawl,toreducegearconflicts.

To minimize the time required at sea to redeploy gear, we have proposeconsideration of an onshore re-spooling industry, providing pre-spooled line cartridgesthatfishermencanrapidlyinstallontoanemptylinespool.Thereareanumberoftechnicalhurdles to this idea, including that a large volume of linewould be difficult to store onmany fishing vessels, which argues for an onboard re-spooling machine rather than anonshoreserviceindustry.Iftheminimumlinediameterallowablecanbereducedfrom½”to perhaps 3/8”, design requirements would be eased significantly, allowing a smallersystem with a lower buoyancy requirement, and easier storage of pre-spooled linecartridges.

After future dock testing and research vessel sea trials are performed, the threeexisting prototypes will be available for operational testing in collaboration withfishermen. The prototype designs all exist as electronic design files, and additionalprototypeunitscanbefabricatedasrequired.Theultimategoalofthisresearchprojectistoenableevaluationofthepotentialofrope-lessfishingfortheoffshorelobsterfisheryintheGulfofMaine.


Acknowledgements

ThisinvestigationwassupportedbyTheConsortiumforWildlifeBycatchReductionattheNewEnglandAquariumunderNOAA/NMFSGrantAwardNA10NMF4520343.

TimWerner fromNewEnglandAquariumwasan integralpartneron thisproject,providingguidanceonthehigher-levelmanagerialdecisions,inparticularforustofocusonthe offshore lobster fishery due to its heavier gear that poses a larger risk to entangledanimalsaswellas the lackofotherentanglementmitigationapproaches for theoffshorefishery.

LoriCaron,DennyColbert,andRobMartinwereextremelygenerouswiththeirtime

during our visits to their fishing vessels and follow-up questions by email and phone.Jeffrey Brodeur of Woods Hole Sea Grant was very helpful in providing additionalbackground for theGulfofMaine lobster fishery.LeeFreitagprovidedvaluable technicalandprojectmanagementadvice.JeffreyBrodeurandAndyGirardlentusgearforthedocktest evaluations. Robin Littlefield, Jim Dunn, John Kemp, Ben Allen, and Bob McCabeprovided advice, ideas, and cautions from their cumulative decades of experience withvariousreleasemechanismsand linepacks.TomAustinrecommendedpursuinga timer-basedreleasefortheprototypeunitsasacost-effectivealternativetoanacousticrelease.Eric Gallimore provided feedback on the circuit designs. Michael Moore providedreferences to thepreviouslysuggestedGearDevelopmentArea forrope-less fishinggear.AlexBocconcelliandTomHurst,aswellasTomAustinandBenAllen,providedideasandfeedbackinearlymeetingswithTimWerner.

References

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Gallimore,E.,J.Partan,I.Vaughn,S.Singh,J.Shusta,L.Freitag.2010TheWHOIMicromodem-2:AScalableSystemforAcousticCommunicationsandNetworking.Proc.IEEEOceans2010.Gobat,J.,andGrosenbaugh,M.2000.WHOICablev2.0:TimeDomainNumericalSimulationofMooredandTowedOceanographicSystems,WoodsHoleOceanographicInstitution,TechnicalReportWHOI-2000-08.http://iop.apl.washington.edu/~jgobat/cable.pdf

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Knowlton,A.R.,Robbins,J.,Landry,S.,McKenna,H.A.,Kraus,S.D.,andWerner,T.B.2015(inpress).Implicationsoffishingropestrengthontheseverityoflargewhaleentanglements.ConservationBiology.Liggins,G.,andS.Westley.2011.“Acousticreleasetechnology:Applicationinlobsterfisheries:theNewSouthWalesExperience”,Powerpointpresentation,24pp.

McCarron,P.,andH.Tetreault,2012.LobsterPotGearConfigurationsintheGulfofMaine.ConsortiumforWildlifeBycatchReduction,36pp.http://www.bycatch.org/sites/default/files/Lobster_Gear_Report_0.pdfNMFSConceptPaperonALWTRT,Nov2010.ProposaltoOpenaManagementAreaPresentlyClosedtoTrap/PotFisheriestoStimulateDevelopmentofRopeless[BuoyLineless]Fishing.http://www.greateratlantic.fisheries.noaa.gov/whaletrp/trt/meetings/Mid-Atlantic_Southeast_ALWTRT_Materials/Final%20Lineless%20Concept%20Paper%20Nov2010.pdfSubSeaSonics,http://subseasonics.com/Turner,H.,DeCrew,J.,Goldsmith,D.,andBrimlow,S.1999.BLT:acousticallytriggeredBuoylessLobsterTraprecoverysystem.UniversityofNewHampshire/UniversityofMaineSeaGrant,89pp.

Project 5 Final160209 - bycatch.orgbycatch.org/sites/default/files/Partan&Ball_2016.pdf · Rope-less fishing gear has long been discussed as a possible approach to reducing entanglement

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