RONALD JOEL SMOLOWITZ

MFR PAPER 1310

ABSTRACT-This paper presents an assessment of ghost fishing in the NewEngland lobster fishery by reviewing trends in trap design, loss rates, lost-trapcatch rates, and related factors. Preventative solutions are discussed.

Trap Design and GhostFishing: Discussion

the lowest cost, that catches and retainsthe greatest amount of legal-sizedlobsters in good condition. The designparameters are interrelated with theoverall economics of the fishing opera­tion as well ea with each other. Thissection will focus on the various designfactors in order to predict which waytrap design may go.

SizeThe size of the pot is usually dictated

by handling problems, deck space, andexpected catch rate. In the inshorefishery, where the availability of legal­sized lobsters is low and the boats aresmall, the pots are small. A lobstermanwho hauls his pots every other day in­stead of daily might use a slightly largerpot if he expects a larger catch.

In the offshore fishery the pots arelarger due to the larger vessels, longersoak periods, and higher availability oflegal-sized lobsters.

Both inshore and offshore, largerpots are claimed by many fishermen tocatch more lobsters. This may occurbecause lobsters have a more difficulttime finding their way out of the pot dueto the increased area to be searched.Another reason may be a lobster­density limitation, which we will coverlater on in this discussion.

The deck space limiting factor oflarge pots can be dealt with by usingcollapsible or stackable pots (Munro,1973).

Shape

The shape of the pot is important indetermining its resistance to stormdamage. Improper shape can cause potsto turn over and roll along the oceanbottom when subject to wave action.Prudden (1962:44) makes the followingsuggestions to reduce pot losses: I) Anyreduction in the height of a pot from thepresent 18 inches would reduce theleverage tending to overturn a pot; and2) The construction of a pot with in­clined sides like a pyramid wouldchange the side pressure of a wave froman overturning effect into a force press­ing the pot down on the ocean floor.

Proper settling of the pot on the bot-tom is also a function of shape. Drag

Ronald Joel Smolowitz is with theNortheast Fisheries Center, NationalMarine Fisheries SerVice, NOAA,Woods Hole, MA 02543.

'Interview sheets on file at the Woods HoleLaboratory. Nonheasl Fisheries Center. NationalMarine Fisheries Service. NOAA. Woods Hole.MA 02543

were about 72,000 pots being fished byISO vessels. Roughly two-thirds ofthese pots were of wood-frame con­struction, the remaining third were allmetal with nylon heads (NMFS, un­pub!. data'). The loss rate offshore hasvaried considerably from year to yearand vessel to vessel. Annual loss ratesof 100 percent were common in 1971­72 but decreased to 20-30 percent by1974. Based on confidential informa­tion gathered from logbooks and othersources, there may be as many as40,000 all-metal pots lost on theoffshore grounds since 1971. Approx­imately 180,000 wood-frame pots werelost offshore during the same period.

Offshore losses are mostly caused byvessel propellers, dragged gear, gearmechanical failure, and storms. Ex­perience gained by fishermen has cutthese losses to where, in many cases,they are equal to inshore loss rates.

Loss rates, both inshore andoffshore, will probably remain in the20-30 percent range. However, thenumber of pots in both fisheries is in­creasing, thus the absolute number ofpots lost will probably increase also.

POT TYPE

Pot type, as speci fied by design andmaterials, is one of the key indicators ofwhether a ghost-fishing situation willbe created. The pot-design problem, asdefined by history, can be simply statedas: To build the most durable pot, for

NUMBER OF POTS LOST

By 1973, the number of lobster(Homarus americanus ) pots beingfished along the Atlantic seacoast ex­ceeded 2 million. The annual inshoreloss rate is claimed by many fishermento be between 20 and 30 percent; onepublished estimate is 33 percent (Prud­den, 1962:43). Most of these pots areall wood or wood framed and were ef­fective fishing units when lost.

There are many reasons why pots arelost in the inshore fishery. Gear failureincludes the pot warp parting, the buoyseparating from the pot warp, and thebuoy breaking up. This gear failure c~n

be caused by normal wear and tear,powerboat propellers, pot "wars"among lobstermen, sea gulls chewingup buoys, fish biting the warp, andmany other causes. Losses are alsocaused by operational mistakes such assetting too deep and improper ballast­ing. Storm surge can cause the pot toroll on the bottom, wrapping up itsbuoy line, and becoming unrecovera­ble.

In the offshore fishery in 1976, there

The studies presented in this issue ofMarine Fisheries Review (40:5-6) areultimately concerned with developingpreventive measures to avoid a ghost­fishing problem. In researching pre­ventive measures, information has beenobtained which enables us to make apreliminary assessment of the ghost­fishing situation as it exists today andwhat may occur in the future. This dis­cussion presents this assessment andreviews preventive measures.

May-JI/Ile' 1978 59

Figure I.-Lobster escaping from an offshore trap that landed upside down.

forces acting on the pot as it settlesthrough the water column determinehow the pot is going to land. Stability, afunction of weight and shape, deter­rrtines how the pot will remain on thebottom (Burgess, 1969). If the pot doesnot assume the correct position on thebottom, the entrance heads can becomeobstructed or ineffective (Fig. I).

Pot shape also determines whatshape the heads will take. The reasonthat most pots are high and long as theyare is to allow for a more effective headdesign.

Head Design

As the catch rates fell in the inshorefishery, the soak periods increased inorder to maintain an economically via­ble catch. The 15-rrtinute soaks of hoopnets gave way to the full-day soaks ofthe single-compartment pot. The parlorpot became necessary when soaks ex­ceeded I day.

The key problem with longer soaktimes is how to prevent escapementonce the lobster enters the pot. Theanswer, for the past century, has beenbetter head design. Rathbun (1887) de­scribes variations in head design basedon reorienting the position of the headring, e.g., the opening facing slightlyup instead of straight into the pot. Healso describes pots with tandem headsmade of wood laths, two types that arestill seen today.

Thomas (1959) has conductednumerous experiments to improve theefficiency of pots. He has shown that: I)Lobsters enter a pot more readily if thelower half of the head is lined withfine-mesh netting, 2) high-rigged headsinhibit escape better, and 3) head­opening size affects the number andsize of lobsters caught, as does thefitting of nonescapement devices. Hefurther states that the effects of pot vari­ations differ with the size and composi­tion of the population being fished andother fishing conditions.

Leakey (1965) feels parlor pots are awaste of space and materials. His solu­tion to the retention problem is an es­cape inhibitor that he has patented. Thisinhibitor, as with many similar devicesknown generally as triggers, allows thelobster to enter through the head butprevents its escape back out. Triggershave been tried or are in use in many

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areas but there is still quite a bit ofcontroversy as to their effectiveness.

Spurr2, after comparison fishing five

different types of pots, believes that theprincipal factor affecting pot efficiencyis not pot shape but parlor-head design.He believes that the parlor head shouldhave a long steep slope terminating in asmall opening very close to the end ofthe pot and near the top. This agreeswith Thomas' (1959) findings thathigh-rigged heads deterred escape. Ourfield data con firms Spurr's andThomas' observations and furtherdemonstrates the degree of sensitivityparlor head design parameters have thataffects ingress and retention.

Moody (1965), from a pot­escapement experiment, obtained re­sults that showed 90 percent of thelobsters caught in unbaited pots escap­ing within 3 days. In baited pots, theescapement rate was 90 percent in 8days. While it is difficult to make adirect comparison of Moody's workwith our field experiments, it seems hehad a higher escapement rate. Wehypothesize that this is due to the factthat he used wood-lath parlor headswhich may be less efficient in retaininglobsters than our nylon-twine skate­mouthed heads. On the other hand,wood-lath heads may allow morelobsters into the parlor in that they pro-

'Spurr. E. 1972. Lobster research project: Finalreponof3-I05-R.July I969-June 1971. Unpubl.manuscr .. 22 p. Fish. Div .. New Harnp~hire FishGame Dep.

vide better footing than nylon netting(Prudden, 1962:41).

The way the entrance head is at­tached to the bottom of the pot may alsobe important. Wilder3 (p. 5) found thatwide spaces along the lower sides of thepot made it difficult for the lobster tofind the head and thus enter the pot.

Materials

For the purposes of this discussionwe have grouped pots into three cate­gories: wood and wood-framed, metal,and plastic.

Degradation

Wood borers are probably the pri­mary degrading force acting on woodpots. Borer damage can destroy a woodpot as an effective fishing unit in as littletime as 4 weeks. On the other hand, atreated wood pot may last upwards of 2years on the bottom in areas with lowborer acti vity. Wood borers do not af­fect metal or plastic pots.

Corrosion affects metal fastenings onwood pots, wire mesh on wood andmetal pots, and wire mesh and struc­tural frames on metal pots. There aremany ways to cut down the corrosionrates, such as plastic coatings, design­ing against galvanic corrosion, anodiz­ing aluminum, etc. Leakey (1965) re­ports zinc-coated metal-framed pots

"Wilder. D. G. 1956 Experiments to improvelobster Irap~. Unpubl. manuscr. Fi~h. Res. BoardCan .. BioI. Sin .. 51. Andn·w~. New Bnmswick.

Marini' Fisheries Rel'ie,,'

lasting over 5 years and some lasting 7years. Proper anticorrosion design canprobably extend a metal pot's lifebeyond 10 years. Plastic pots do notcorrode.

Weight

Metal pots have weight advantagesfar exceeding wood pots. They arelighter out of water and heavier in wa­ter. In tests conducted at the NortheastFisheries Center (New England MarineResources Information Program, 1972:2), one metal and one wood pot wereweighed in and out of water. The wate.r­logged wood pot weighed 22 pounds mwater and 115 pounds out of water. Thewire-mesh metal pot weighed 33pounds in water and 53 pounds ~ut ofwater. Metal pots are thus easier tohandle on deck and have better anchor-ing qualities on the bottom. .

Plastic pots vary, in regard to weJg~t

and buoyancy, with the type of plasticused and the construction method.

Swrm Damage

Metal pots are probably more resis­tant to storm damage than wooden potsof the same size and shape because oftheir greater weight on the bottom andless surface area exposed to stormforces.

In a series of comparison-fishing ex­periments. Wilder (footnote 3, p. 23)reports that during a severe st~rm helost 14 out of 19 wood pots With theremaining 5 damaged almosl beyondrepair. Only lout of 19 metal pots waslost during the storm. Similar resultsoccurred during several other stormsthroughout his experiments. ~etal-pot

Iusses that did occur were attnbuted tobuoy line failures.

Experiments by Spurr (footnote 2)provide the same results: wire-meshpots moved less in current and stormaction than wood-lath pots.

Costs

The material to build an inshorewood pot costs from $4 to $6. To buy apot already constructed costs from $8 to$14. Inshore metal pots cost about $20.

Offshore double-parlor wood potscost $18 in 1972. In 1974 the cost was$27. Metal pots of the same designwere $24 in 1972, $35 in 1974, andclose to $40 in 1977.

May-JillIL' /978

Efficiency

There is a traditional belief amonglobstermen that metal pots are not aseffkient as wood pots. Some of thereasons why lobsters are said to be re­pelled by metal pots are: .1) Me~al wirevibrates in the water fnghtenmg thelobsters away, 2) lobsters do not like thefeel of bare metal, 3) lobsters are sensi­tive to sharp metal edges, 4) lobsterssense an electric field set up by galvalllcaction, and 5) lobsters sense chemicalsproduced by galvanic action.

There are many variables that affect apot's efficiency, though li.ttle is know.nabout how or why. Very little compan­son fishing has been performed anddocumented. Experiments that havebeen done have not had ample controlsto determine if metal construction aloneaffected pot efficiency. We can say thatthe five objections to metal pots statedabove have been overcome by properconstruction and plastic dipping. Manyfishermen have reported plastic coatedand aluminized metal pots fished well.

Adaptability

Metal and plastic are more adaptablethan wood in pot designs that are eithercollapsible or stackable.

Handling

Wood and wood-framed pots cantake a lot more abuse in handling thanwire pots. This can be compensated forby building the wire pots stronger andmore rigid by addition of a s~ructural

metal frame. Shipboard handlmg sys­tems can also be modified to be lessabusive to the pots as they comeaboard.

Wire pots have a handling advantageover wood in that they offer less resIs­tance when being hauled up through thewater.

Catch Condition

The catch suffers a signi ficant degreeof claw damage and loss in wood potsdue to claws protruding between thelaths and being hit when hauled aboard.This problem is eliminated in wire­mesh metal pots.

Pot-Type Summary

Researchers generally agree thatlobster-pot design has not been op-

timized. The preceding discussion onpot design and materials demonstratesthe fact that pots can now be designedthat are more durable and efficient thanthe ones being fished commonly today.The probability of a long-term. ghost­fishing situation being created will onlyincrease.

LOCATION WHERE LOST

Biological Deterioration

Since most lobstermen use synthetictwine in pot construction, the mainform of biological deterioration of con­cern is wood-destroying organisms. Inthe lobstering areas the organisms areusually Teredo navalis in the shallowdepths and Xylophaga atlantica in thedeeper part of the range.

Teredo navalis spawns about July.The larvae settle onto the wood trapsand can destroy a trap in less than 2months. Offshore Xylophaga atlanticaspawns about October and can destroy atrap just as fast.

It is generally thought that most lob­ster areas are subject to wood-borer ac­tivity, though not of the same mag­nitude. In most inshore and offshoreareas an untreated wood trap wouldprobably not make it through thewinter.

Corrosion

Location-dependent factors thatinfluence corrosion are temperature,dissolved oxygen, and current velo­cities. Our trap-release study dem­onstrated the significant difference infailure rates that occurred with testsamples in different areas. Corrosionrates are probably higher inshore thanoffshore.

Storm Surge

Storm surge and wave action areknown to destroy many pots in shallowinshore waters. Though pots withoutbuoy lines are less susceptible to stormaction, they too probably move on thebottom in depths less than 20 m. It IS

generally believed by lobstermen thatpots moved by storms tend to break upagai nst rocks on the bottom ..

Summer fishing is usually m shallowdepths. As fall and winter approach,pots are usually moved farther offshoreinto deeper water to follow the lobsters

6/

Figure 2.-Lobster trap partially buried in sand after several weeks on the bottom.

and also to reduce storm losses. Potsthat were lost during the summer in theshallow water probably do not survivethe winter storms on exposed coasts.

Substrate Burial

Pots sometimes become buried in thesubstrate by the action of storms andcurrents. This is commonly referred toas "sanding down" or "mudding up."Sanding down is quite common, indepths shallower than 16 m, in the westcoast Dungeness crab fishery (Hipkins,1972:9). In this fishery a pump is car­ried on board with a special hose ar­rangement that can be lowered to thepot and water pressure applied to freethe pot, sometimes buried to a depth of4 m.

To what degree this problem exists inthe lobster fishery is unknown. We canassume that a pot only needs to beburied about 15 cm in the substrate be­fore its heads become relatively ineffec­tive. There are many areas, inshore andoffshore, where the bottom conditionsof substrate and current are right forpartial burial to occur (Fig. 2).

Destruction byDragged Gear

Offshore lobstermen set their potsfollowing the migrations of lobstersfrom the deep canyons in winter up ontothe shallow shelf in summer. Many potsare lost in areas that are not continu­ously pot-fished. When the pot fisher­men move out, the draggers move in,fishing the bottomtish in the area. Thesedraggers haul back many lost pots andquite possibly destroy many others onthe bottom. Only pots in the canyonsthemselves probably escape being de­stroyed by draggers.

CATCH RATES

Ingress minus escapement and trapmortality equals retention or, in otherwords, the catch. Catch rate is a timefunction; in trap fishing the time isdefined in set-over days.

Set-Over Days

Set-over days are probably very im­portant in determining rates of trap­related injury and mortality, in additionto their importance in catch/effort rela­tionships. Unfortunately our data is not

sufficient to perform a statisticalanalysis because we cannot isolate theeffects of temperature, fishing pres­sure, and moulting from those of set­over days. (Our surface-hauled trapshad set-over periods varying from I to13 days).

We divided set-over days into threebasic periods. The first is the baitedperiod, in which some of the initial baitis still in the trap and is effective. Thesecond is the transition period, in whichthe bait is recently gone and the lobsterscaught are highly active in attempts toescape. The third period is the ghost­tishing period. The limits of the transi­tion period cannot be exactly described,but in most cases the trap probably en­tered the ghost- fishing period by theend of the second week.

There may be times of increased in­gress to the trap during the ghost­fishing period. This may be caused bythe trap self-baiting, a lobster migra­tion, or some seasonal event. Thismakes it very difficult to relate ghost­catch rate to set-over days. This isfurther compounded by the low ghost­fishing period catch rates, in our exper­iment equal to 10 percent of thesurface-hauled catch rate.

Availability and Catchability

Ingress is a function of availabilityand catchability. A good example of thevariation in availability of lobsters to apossible ghost trap can be found in thefishing strategy used offshore. As the

bottom water temperature changes, thelobster population migrates and thefishermen correspondingly move theirtraps. A trap lost in a location wherethere were good catches one week maynot have lobsters available to it forweeks or months afterwards.

Many factors affect catchability butprobably the most important are tem­perature and other seasonal variations.Since ghost traps are on the bottom forlong periods, the lobsters available tothem will have a wide range of catcha­bility coefficients varying with time.

In summation, availability andcatchability cannot readily be used foran assessment of ghost-fishing periodcatch rates due to their variability.However, during the initial baitedperiod these factors can be used forestimating the initial catch, which dur­ing our experiment was more than 50percent of the overall ghost catch.

Escapement

In our Phase III experiment, 81lobsters were classified as missing fromthe ghost traps, this being 33 percent ofthe known ingress. Two-thirds of thisnumber were missing by the 30th day.Only six of these lobsters were recap­tured. We conclude that the escapementrate from ghost traps, after the initialbaited and transition periods, is lessthan 30 percent. This rate decreaseswith time. This figure is in basic agree­ment with that of Sheldon and Dow(1975).

"\1urille Fis"aies Rel'inl'

Bait

There are a number of arti ficiaJ lob­ster baits on the market; they have beenused by fishermen with varying degreesof success. One of the goals of the ar­ti ficial bait manufacturers is to producea product that is long-lasting in the trap.Accomplishment of this goal wouldimprove the trapping efficiency forlonger set-over periods. Correspond­ingly this would increase ghost- fishingcatch rates.

Behavior

The most interesting question abouttrap-related lobster behavior is why dolobsters enter traps? We must addressthis question to fully understand trap­ping efficiency and thus normal andghost-fishing catch rates.

We know that lobsters primarilyenter traps to get food (bait). We alsoknow that lobsters enter unbaited traps,and this is usually thought to beshelter-seeking behavior. In the naturalenvironment inshore lobsters are con­sidered sol itary. rarely sharing the sameshelter. Offshore, on relatively flatfeatureless bottom, two or more lob­sters have been observed to share thesame shelter, usually a depression inthe bottom. This observation is the ex­ception though.

This natural solitary behavior is op­posite what is observed in trapping. Ourfield experiment catch data shows manyinstances, especially in Phase III,where 15 or more lobsters were foundin a trap, sometimes after 8 set-overdays. Many of those lobsters enteredthe trap after the bait was gone. Thesame observation is demonstrated byour "lost" trap inventories. There isingress to unbaited traps with largenumbers of others lobsters present.This is in an area with plenty of availa­ble shelters.

We assume that a lobster entering atrap with 10 other individuals alreadythere is aware of their presence beforeentering. Lobsters possess visual,chemical, and possibly sonic means ofcommunication. The lobster may be en­tering for some social interaction withits conspeci fics.

To determine the effects of socialbehavior on catchability, Edward

;War-jlll//' /97ti

Leger, a Boston University MarineProgram graduate student, conducted apreliminary experiment at the North­east Fisheries Center in 1973. Sixteeninshore lobsters (70 mm ±2 mmcarapace) and 16 offshore lobsters (74mm ±2 mm) were tested in 2-m diame­ter circular tanks under three differentconditions. Capture time was recordedfor each lobster placed in the tank with:I) Trap and bait alone, 2) trap with baitand one lobster, and 3) trap and bait andtwo lobsters. During I-hour testperiods, 14 of 16 lobsters tested enteredthe trap with bait alone; 26 of 32 lob­sters entered the trap containing baitand I lobster; none of 6 tested enteredthe trap with bait and 2 lobsters. Thisexperiment indicated a possible densitylimitation factor in trap behavior.

Evidence exists that some form ofsocial behavior, other than feeding andshelter related, is affecting catchabilityof lobsters. Leger's experiment seemsto conflict with the field data, indicatingthe need for more closely controlledexperiments to validate the social be­havior hypothesis.

Another hypothesis is that lobstersenter unbaited traps because they havebeen conditioned to do so. Every weeklobstermen place millions of pounds ofbait into the water via lobster traps.This may constitute the major foodsource of lobsters who thus relate feed­ing with traps. Upon seeing a trap alobster enters expecting a food source.Probably small (sublegal) lobsters havebeen repeatedly caught and disgardedby fishermen as they became con­ditioned to traps being effectively afeeding station. Lobsters repeatedly re­turn to the trap as a food source, muchas birds return to window feeders.Lobsters may enter unbaited pots sim­ply to "check-it-out" for food.

Injury and Mortality

Emmel (1905) reported that 7 to 25percent of lobsters caught in Rhode Is­land were missing one or both claws.Scarralt (1973) found incidence of clawloss from 5 to 19 percent in Canadianwaters. Other wounds ranged from I toII percent in the lobsters sampled.Krouse (1977) analyzed Maine catchdata which indicated 6.5 percent oflobsters caught were missing at least

one claw and 21 percent had missingand/or regenerate claws.

Our field data for all three phasescombined (surface hauled) shows 11.2percent of the lobsters caught missingone or both claws. The overall inci­dence of lobsters with one or moretypes of damage is 27.6 percent. Thisfield data may not truly reflect what isoccurring in the actual fishery due toour longer set-over periods. Our datadoes show that the number of injuriesmight increase with longer set-overperiods, increases in water tempera­ture, increases in fishing pressure, andpossibly be related to moulting. Morecontrolled experiments are needed todetermine the effects of each of theabove factors.

Incidence of newly damaged lobstersduring a portion of the Phase III studywas similar for vented and nonventedpots. Due to the larger number oflobsters caught in the nonvented traps,more lobsters were injured than in vent­ed traps. Total new damage amountedto 9 percent of the lobsters caught; 42percent had old damage.

There were 10 I instances of majordamage to lobsters in our ghost pots, 25percent occurring within the first 15days and 69 percent occurring beforethe 30th day of entrapment. Mortalitiesamounted to 24.6 percent of the totalghost catch, 30 percent of the mor­talities having major injuries prior totheir deaths.

There is considerable evidence thatthe greater part of major damage tolobsters is trap-related. Despite thereputation of lobsters being aggressive,it seems aggression-related injuries innature may be rare. Scrivener (1971)conducted behavior experiments with700 pairs of lobsters and never onceobserved damaging aggression. Writ­ing about decapods, and then hislobsters specifically, he states: "In­frequently fighting leads to physicaldamage of one individual. This may berarer under natural conditions for somespecies, because many of the studieshave been done under crowded labora­tory conditions. Damaging aggressionhas occurred among the lobsters in thesmall holding tanks when the dividerhas been pushed over but has neverbeen observed in the 6-foot diameterobservation tanks."

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Stein et al. 4 conclude that the lobsteris much less aggressive than previouslythought as long as the lobsters haveadequate space and shelter. Duringtheir experiments, observing lobsterbehavior in seminatural habitats inlarge aquaria, there may have been oneor two damage-inducing interactionsbetween lobsters.

We have data showing that many in­juries are sustained by lobsters in traps.These injuries are mostly induced byconspeci fics in the .stress conditionscaused by the entrapment. There is alsoevidence from many sources that on­board handling of traps and lobsters in­duces injuries. Lobsters roughly han­dled, such as being dumped intoa checker, will open their claws and bitedown on the first thing contacted, usu­ally another lobster.

The causes of trap-related mortalityare harder to define. Many lobstersprobably die directly from the injuliessustained in the traps, i.e., they arecannibalized by healthier lobsters orbleed to death. Lobsters that moult in atrap probably don't stand much of achance for sUIvival. McLeese (1956)reported that lobsters near moult areless able to withstand stress, thus theymay also be subject to mortality in thetrap even before moulting.

Toward the end of our Phase III studythere were mass mortalities in the ghosttraps. One possible cause would havebeen gaffkemia, a lobster disease.Rabin (1965) found that it is endemic inthe natural lobster populations in theWoods Hole area. He also states thatvirulence may be a condition of theholding impoundment. There are noobvious signs of the disease though it isknown to be transmitted throughwounds. Higher temperatures speed theprogress of the disease (Stewart et a!.,1969). It can be shown that when ourmass mortalities occurred. conditionswere ideal for a gaffkemia epidemic.

Another cause of trap mortality maybe predation by other species, espe­cially if the lobsters were recent moults

·Stein, L.. S, Jacobson. and J, Atema, 1975,Behavior of lobsters (Honwrt/s americonLls) in asemi-natural environment at ambient tempera­tures and under thermal stress, Unpubl. man­user., 49 p, Woods Hole Oceanogr. Insl. Tech,Rep. 75-48,

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or weakened by injuries. It is generallyconsidered that healthy hard-shelledlobsters of trapable sizes are not com­monly preyed upon. The predatorwould have to get into the trap and thatlimits the possibilities further. Scar­rall's (1965) work indicates thatweakened lobsters con fined in trapsmay be subject to predation by am­phipods.

Lobsters probably do not starve todeath in traps but may be weakenedand stressed by starvation. Morgulis(1916) found that lobsters starved for56 days showed no outward signs ofemaciation and the greatest weight losswas 2.89 percent. The lobsters ab­sorbed water making up for the loss oforganic and mineral matter; the weightloss would have exceeded 34 percentotherwise. Stewart et al. (1967) heldstarved lobsters for 140 days that suf­fered physiological changes butshowed no outward signs of stress orincreased cannibalism. McLeese(1956) reported that the lethal limitsestablished for temperature, salinity,and oxygen did not change after 57 daysof starvation.

ASSESSMENT OF LOSSES

In this section we will make an as­sessment of ghost-pot mortality andclaw loss for 1976; 1973 through 1975are similar. The number of traps andlobster landings are preliminary figuresgathered by NMFS.

The inshore fishery landed25,812,000 pounds (11,615,400 kg)using 2,100,000 traps; an annual land­ings per trap of 12.3 pounds (5.53 kg).The offshore trap fishery landed4,220,000 pounds (1,899,000 kg)using 72 ,000 traps; an annual landingsper trap of 58.6 pounds (26.4 kg). Theannual landings per trap is a roughfigure as many traps are only in thefishery for a few months. Another pointis that the landings, especially from in­shore, represent only a small part of theactual catch, i.e., 20 percent where thethrowback ratio is 4 to I.

Twenty- five percent is presently themost accepted average figure for annualinshore trap loss rate. To see if we coulduse this figure for the offshore fishery,the port interview data from offshorelobster boats were analyzed.

Port interviews are conducted by

NMFS port agents when a fishing ves­sel returns from a trip. We surveyed the1976 interviews from Massachusettsand Rhode Island ports; these two statesaccount for 53,000 of the 72,000 trapsbeing fished offshore. The average ves­sel fished 400 traps having 25 to 50traps per trawl. The soak times aver­aged 4-7 days.

Twenty-nine vessels were listed asfishing 13,040 wood traps. (Many ofthese vessels fish some wire traps.) Onehundred and forty-nine interviews wereconducted and a loss of 1,025 pots wasreported; a 7.8 percent loss rate.

Eleven vessels fished 4,920 all-metalor plastic pots. During 40 interviews aloss of 121 traps was reported; a 2.4percent loss rate.

These loss rates at first appear verylow but this is due to the fact that manyvessels were only interviewed once ortwice. We next grouped all vessels thatwere interviewed six or more times. Inthis group there were 16 vessels, fishinga total of 7,290 traps, that were inter­viewed 134 times for an average of 8.3interviews each. They lost 908 traps fora loss rate of 12.4 percent. From theport weigh-out sheets we determinedthat these vessels were averaging 20trips annually so the annual averageloss rate was 29 percent. We will use 25percent for the purposes of this assess­ment.

Annual inshore trap losses: 525,000ghost traps.

Annual offshore trap losses: 18,000ghost traps.

Another category of ghost traps is thecumulative trap losses. From the inter­view data we found that about one-thirdof the traps offshore are all-metal orplastic. If we give these traps a 3-yearghost fishing life span, there will be12,000 additional traps ghost fishingoffshore each year. Due to lack of dataon inshore trap types lost, we will notevaluate inshore cumulative ghostfishing, but it may be significant.

To determine what the inshore mor­tality per ghost trap should be, we as­sumed that half the lobsters in the mis­sing category in our experiments died inthe traps. This gives us 0.5 pounds(0.23 kg) per trap in Phase I, 1.3pounds (0.58 kg) per trap in Phase II,4.2 pounds (I .9 kg) per trap in Phase IIInonvented, and 1.0 pounds (0.45 kg)

Marine Fisheries Re\'ielV

per trap in Phase III vented. Annualghost-trap mortality would be higherfor the following reasons: I) Therewere lobsters still entrapped at the endof each phase of the experiments. 2)Many of the lobsters were releasedfrom our traps when catch escapepanels opened and when our traps wereraided. 3) Our experiments did not con­tinue into the fall when greater mortll.l­ity was probable.

We conclude that a conservativefigure for the inshore annual ghost­fishing mortality rate would be 2.5pounds (1.12 kg) per nonvented trapand 1. 5 pounds (0.67 kg) per vented (45rnrn) trap. (For this assessment we areneglecting legal size differences be­tween states.) We can derive similarfigures by taking landings per inshoretrap, assume a throwback ratio of 4 to 1for nonvented traps, and arrive at acatch of 61.5 pounds (27.7 kg) per trap.A ghost trap fishes at 10 percent of thisrate (our field experiments) for a ghostcatch of 6 pounds (2.7 kg) per trap.Using a 40 percent mortality rate(known mortality plus one-half themissing category) gives us 2.4 pounds(1. I kg) per nonvented trap.

By an intuitive process we assumed amortality rate of 6 pounds (2.7 kg) peroffshore nonvented trap based onoffshore catch rates.

Anuual inshore ghost trap mortality:525,000X2.5=1,312,500 pounds(590,625 kg).

Landed value: $2,179,000.00 (1976average price: $1.66 per pound).

Annual offshore ghost trap mortality:(18,000 +12,000) x6.0 = 180,000pounds (81,000 kg).

Landed value: $299,000.00.To assess claw loss we used 10 per­

cent for the number of lobsters with oneor more missing or small regenerateclaws. We used 15 percent as theweight reduction per cull lobster. Using30,000,000 pounds (13,500,000 kg) asthe annual trap caught landings, we get450,000 pounds (202,000 kg), for avalue of $747,000.00, lost due to mis­sing and/or regenerate claws.

There are additional losses that can­not be evaluated here. These are thepossible decrease in moult frequencyand growth increments due to injuriesand claw loss sustained in the traps bysublegals.

May-June /978

PREVENTIVE SOLUTIONS

Reduced Effort

It becomes obvious that the best wayto reduce trap-related injury and mortal­ity is to reduce the number of traps. Anyreduction in the number of traps willcause a corresponding reduction in traplosses and thus in ghost-fishing mortal­ity. If the same landings can be sus­tained with a 50 percent reduction intraps inshore, then close to 700,000pounds (315,000 kg) of lobsters will besaved from unprofitable deaths; over$1. I million in landed value.

Cutting Losses

It may be possible to decrease potlosses both inshore and offshore sub­stantially below levels of 20-30 per­cent. To do this the first step needed tobe undertaken is a survey to identifyquantitatively the causes of pot lossesand the methods developed by lobster­men to reduce losses.

As mentioned previously, there aremany areas in the lobstering operationthat can be improved upon to reducelosses. Trapezoidal pots may be lesssusceptible to loss than half-round pots.Many lobstermen may be using in­sufficient ballast or an inferior potwarp. There are indications that sometypes of buoys are better than others(Spurr, footnote 2, p. 19). Multipottrawls may suffer fewer losses thansingle pots inshore.

Degradable Sections

To prevent a long-term cumulativeghost fishing problem, the solutionmight be to have all virtually nonde­gradable pots contain a section thatwould rot out in about a year's time.When this section fails it should leavean opening with a minimum dimensionat least equal to the diameter of the headopening. The degradable section couldconsist of wood, natural fiber, or un­treated iron wire. As mentioned in theintroductory paper (Smolowitz, 1978),this approach has been taken in severalfisheries already.

To solve the short-term ghost fishingproblem is more difficult. Since the de­gradable mechanism would be requiredto fail sooner, it would be more bother­some for the fishermen to keep replac­ing them. If the fisherman is not fully

convinced of the value of this exercisehe may replace the degradable mech­anism with a nondegradable one. In thesablefish (blackcod) pot fishery, somefishermen laced up the escape vent withnylon instead of cotton twine.

Sublegal Escape Vents

It has been demonstrated many timesthat sublegal escape vents reduce thecatch of sublegals. Pots that retainfewer lobsters are less destructive to thecatch both in the normal and ghost­fishing modes. If all traps inshore usedsublegal escape vents of 45 mm. theghost-catch mortality rate would drop1.0 pound (0.45 kg) per trap for a sav­ing of 525,000 pounds (236,250 kg), orroughly $870,000 in landed value. Themany additional advantages of sublegalescape vents have already been re­viewed elsewhere.

Catch Escape Panels

The sublegal escape vent and the de­gradable section could be combinedinto one unit. Our catch escape panel is8X8 inches (20.3X20.3 cm) and con­tains a I ¥I-inch (45 mm) high x6-inch(15.2 cm) long sublegal escape vent.This panel is affixed over a 6- x 6-inch(15.2- x 15.2 cm) hole cut into the par­lor end of the pot and is attached by twohog-ring hinges on the bottom and adegradable link on the top.

In the closed state the panel allowssublegal-sized lobsters to escapethrough the vent. After a period of timethe degradable link fails, allowing thepanel to drop open so all trappedlobsters can escape.

The choice of panel material wouldprobably depend on whether the panelis provided by the State or made by thelobsterman. The choice of degradablelink would depend on the failure-timerequired.

For the purposes of this discussion,we will assume that the panels would bemass-produced by the States, similar tothe way auto license plates are, andcontain a stamped license number.Lobstermen could, for example, be re­quired to buy one panel annually foreach pot fished. Double-parlor potswould be required to have two panels,one on each parlor.

The possible advantages of the catch

65

HAB/PQT - wilhaul head funnel

Figure 3.-Basic tire habipot design with two entrance vents and drainage holes. The tires were notnegatively buoyant enough and had high drag characteristics during hauling.

escape panel are analyzed in the follow­ing discussion.

I. Allows the State to have moreaccurate knowledge of the number ofpots being fished. If the State issues thepanels, not only will it have a solidestimate of the number of pots beingfished but also of how many are beinglost.

2. Easier to enforce regulations dueto the high visibility of the panel on thepot. This is one of the major advanatgesover lath spacing as a means to regulatesublegal catch. All the enforcementofficer has to do is to see the panel andhe knows it has the correct vent size.

3. Uniform size of sublegal vent al­lows more accurate control of pot selec­tivity. The sublegal vent can be accu­rately sized and constructed so as not toswell or be worn away.

4. Decreases damage to sublegallobsters. This is an advantage of anysublegal venting mechanism.

5. Decreases illegal sales of sublegallobsters. This is not known for sure,because many lobsters just under legalsize will still be retained. These are thelobsters a dishonest lobsterman wouldsell.

66

6. Reduces and eventually endsghost fishing. A sublegal escape vent,by reducing the number of lobsters re­tained, should reduce ghost-fishingmortality. When the degradable linkfails, the pot will no longer fish.

7. Improves quality of catch. Fewerlobsters in the pot should cause lessconspecific-inflicted injuries, e.g.,claw loss.

8. Controls bycatch. Pots with sub­legal vents let out most crabs. This maybe more of a problem where the crabsare sold commercially.

9. Increases pot efficiency. In areaswhere there is a large population oflegal lobsters, the sublegal escape ventshould allow more of them to becaught.

Habipots

During this project we constructedand started to test several designs ofhabipots, but time and money consider­ations did not allow for completion ofthe work. Two types of habipots con­structed out of old automobile tires(Figs. 3 and 4) were fished with limitedsuccess; they caught sublegallobsters.

A lot more work is necessary to developa selective nonentrapment type of pot.

CONCLUSIONS

I. The main ghost-fishing danger liesin the cumulative effect on the inshorefishery if the majority of fishermen startusing all-metal and/or plastic traps, atrend that is well under way. We re­commend that all traps be required tohave one untreated wood lath in theirconstruction which, upon rotting out,leaves an opening equal to or greaterthan 75 x I50 mm.

2. Any reduction in the total numberof traps used will have positive resultsin reducing ghost fishing and trap­related injuries and mortality even if thefishermen increase effort.

3. We recommend field tests with a47-mm escape vent, as indications arethat this size vent will substantially in­crease the overall bene fits to the fisheryattributed to sublegal venting, withonly a negligible reduction in legalcatch.

4. We recommend that a study beundertaken to determine the causes oftrap losses and the means to prevent orreduce them.

Murine Fisheries Rel'in\,

Figure 4.-A head funnel was incorporated into the basic design to preventescapement during hauling.

SECTION A-A

HOmLJrus americanus, in commercial and re­search catches off the Maine coast. Fish. Bull.,U.S. 74:719-724

Leakey, R. D. 1965. Folding traps built to beescape proof. Natl. Fisherman, October 1965,p. 13.

McLeese, D. W. 1956. Effects of temperarure,salinity and oxygen on the survival of theAmerican lobster. J. Fish. Res. Board Can.13:247-272.

Moody, J. A. 1965. Pilot studies in Saco Bay,Maine on chemical bait, phototropism, andescape of the American lobster. Bio­Dynamics, Inc., Cambridge, Mass., 16 p.

Morgulis, S. 1916. The influence of fasting onlobsters. Trans. Am. Fish. Soc. 45:198-201.

Munro, J. L. 1973. Large volume stackable fishtraps for offshore fishing. Gulf Caribb. Fish.Inst. Proc. 25:121-128.

New England Marine Resources InformationProgram. 1972. Forget the mice' It's a betterlobster trap that's needed. New Eng/. Mar.Res. Inf. 34: 1-2. Sea Grant No. RIU-2-72-34.

Prudden, T. M. 1962. About lobsters. BondWheelwright Co., Freepon, Maine, 170 p.

Rabin, H. 1965. Srudiesongaffkemia, abacterialdisease of the American lobster, HOmLJrusamericanus (Milne-Edwards). J. Invenebr.Pathol. 7:391-397.

Rathbun, R. 1887. The crab, lobster, crayfish,rock lobster, shrimp, and prawn fisheries. InGeorge Brown Goode (editor), The fisheriesand fishery industries of the United States, Sec.V, vol. II, p. 627-810. Gov. Print. Off.,Wash., D.C.

Scarralt, D. J. 1965. Predation of lobsters(Homarus americanus) by Anonyx sp. (Crus­tacea, Amphipoda). J. Fish. Res. Board Can.22: 1103-1104.

____. 1973. Claw loss and other wounds incommercially caught lobsters (Homarusamericanus). J. Fish. Res. Board Can.30: 1370-1373.

Scrivener, J. C. E. 1971. Agonistic behavior ofthe American lobster HOmLJrus americanus(Milne-Edwards). Fish. Res. Board Can.,Tech. Rep. 235, 128 p.

Sheldon, W. W., and R. L. Dow. 1975. Trapcontribution to losses in the American lobsterfishery. Fish. Bull., U.S. 73:449-451.

Smolowitz, R. 1. 1978. Trap design and ghostfishing: An overview. Mar. Fish. Rev.40(5-6):2-9.

Stewan, J. E., J. W. Cornick, D. M. Foley, M.F. Li, and C. M. Bishop. 1967. Muscle weightrelationship to serum proteins, hemocytes. andhepatopancreas in the lobster, Homarusamericanus. 1. Fish. Res. Board Can.24:2339-2354.

- , , and B. M. Zwicker.1969. Influence of temperature on gaffkemia, abacterial disease of the lobster, Homarusamericanus. J. Fish. Res. Board Can.26:2503-2510.

Thomas, H. 1. 1959. A comparison of somemethods used in lobster and crab fishing. Scott.Fish. Bull. 12:3-8.

MFR Paper 1310. From Marine Fisheries Review, Vol. 40, No. 5·6, May-June1978. Copies of this paper, in limited numbers, are available from D822, UserServices Branch, Environmental Science Information Center, NOAA. Rockville.MD 20852. Copies of Marine Fisheries Review are available from the Superin­tendent of Documents, U.S. Government Printing Office. Washington. DC20402 for $1.10 each.

LITERATURE CITED

Burgess, J. 1969. Crab trap with anchor. Fish.News (Lond.) No. 2932, 15 August, 6.

Emmel, V. E. J905. The regeneration of lostpans of the lobster. Commissioners of InlandFisheries of Rhode Island, 35th Annu. Rep., p.81-117.

Hipkins, F. W. 1972. Dungeness crab pots. U.S.Dep. Commer., NOAA, Natl. Mar. Fish.Serv. Fish. Facts-3, 13 p.

Krouse, J. S. 1977. Incidence of cull lobsters.

tough job of typing the annotated bib­liography.

HABIPOT - wilh head funnel

5. We recommend that all research­ers, where applicable, use a standard­ized trap to eliminate variable of selec­tivity and trap efficiency and thus allowfor better comparisons of data collectedthroughout the lobster areas.

ACKNOWLEDGMENTS

Dozens of people were involved inthe collection of data used in this report,among them lobstermen, port agents,statisticians, divers, boat operators,and students. Hopefully the authorshave done justice to this hard-earneddata.

We would like to especially acknow­ledge John Lamont who performed thenear-endless task of preparing the il­lustrations for this report. MargaretMehmel also deserves praise for the

May-JI/ne /97R 67