FISHERIES RESEARCH BOARDO:f CANADA

MANUSCRIPT REPORT SERIES

(BIOLOGICAL)

No. 724

TITLE

Fishing Effici ency Trials with a HydraulicClam (Mya) Rake - 1961

AUTHORSHIP

J. S. MacPhail and J. C. Medcof

Establishment

Biological Station,St. Andrews, N. B.

Dated July 1962

FISHING EFFICIENCY TRIALS WITH A HYDRAULICCLAM (MYA) RAKE - 1961

CONTENTS

INTRODUCTION

PHYSICAL PRINCIPLE INVOLVED INHYDRAULIC RAKING

Laboratory experimentsDiscussion of results

DESIGN CHANGES IN HYDRAULIC RAKE

WORK SITE

COLLECTING RAKEDesignEfficiency of collection raking

HYDRAULIC RAKING TRIALSOperating conditionsPreparation and fishing of test plots

DISCUSSION OF RESULTSI. Collection raking2. Raking speed3. Recovery rate40 Harvesting rate5. Manoeuverability of hydraulic rake6. Effect of water pressure on raking7. Scattering of clams$0 Breakage of clams9. Rake track on beach

100 Comparison of hydraulic raking withother harvesting methods: harvestingcapacity; ease of operation and team­work; costs; cond:lt ion of catch;conservation aspects; precautions

SUMMARY

LITERATURE REFERRED TO

TABLES

FIGURES

PageNo.

1

112

2

3

444

445

66677$$$

101010

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FISHING EFFICIENCY TRIALS WITH A HYDRAULICCLAM (MYA) RAKE = 1961

By

J 0 So MacPhail & Co Medcof

INTRODUCTION

While we were completing our work with the hydraulicescalator ha.rvesteri9 DroDoB Quayle told us about. one"'man 9

hydraulic 9 soft-shell clam harvesters that are used in theState of Massa.chus etts 9 Uo S oAo 9 particularly inareas.aboutCape Codo These machines (Figo Ii were examined and observedi noperati on <in tid.al ponds <at Martha vsVineyardin October1959t,hrougll th.e kin~Liassistanceof Mro'Foi Co Wilbourj.Jro. andDro Go Co Matt,hienssen 9 Department of Natural Resources, Stateof Massachusetts 9 UoSoAo

Building and testing a copy the prototypeMassachusetts hydraulic cla.mrake. (tlle machine resembles anordinary garden rake in general pattepn 1. were undertaken in1960 with the help of Mro Ho Yo Brownrigg of this Station andfinancial assistanc.~ fromt,he Industrial DeyelopmentServiceof the Department of Fisheries (MacPhai1 9 MS 9 1961)0 It wascontinued in 1961 at Fisheries Research Board expense by thesenior author with hired assistants as a project of the StoAndrews Biological StationVs Molluscan Shellfish Investiga­tions under the supervision of Dro Jo Co Medcof o

PHYSICAL PRINCIPLE INVOLVED INHYDRAULIC RAKING

In describing. th e functioning o.f the hydraulic rakeit is often stated that it ffwashes clams out of the soil tt 0This statement is true but it is too vague to satisfy the gearresearchervs interestso Whenever possible .. he likes· to. under­stand .the mechanics of operation of any gear he is asked tostudyandi/ improve 0 For this reason we carried out· the twofolloydngsimple experimentsio

Laboratory Experiments

In the first experiment a glass...sided aquarium2 ft x 1 ft x 1 ft was filled to a depth of 8 inches with sandoClams whose shells were numbered with VolgerVs ink were killedin formaldehyde and then buried in the sand a tttnormal ffpositions and depths (Medcof 91950} 0

Tjlese clams were all dead clams but th ey were not allalikeo Some were just dead clams 0 Others had had a few orseveral or manysli vers of lead slipped intoth.eir mantle

cavities through the pedal opening in the mantleo In the lasttests in the two experiments two living clams were added to thetest lots of clams 0 . The numbers, sizes a~dspecific gravitiesof all these animals are reported in Table VITo

After the clams were buried 9 the aquarium was filledto overflowing with watero A spray nozzle of a hose was thenheld below the water surface arid moved slowly from one end ofthe aquarium to the other several timeso By watching throughthe glass we could see something of what was happening insideoWe thenremovedi thehose 9 drainedoffithe isupernatantwater andsearched the sand for the clams and recorded the findings 0

The experiment was performed three times 0

the end of each test some clams were always at thesurface, some were buried at intermediate depths in the sand andsome were on the bottom of the aquarium under the sand 0

In th eisecond .. e:xpe!"iment the. san'le ..materialswere usedand the same proc:durewasf9110wed except that the clams werenot buriedo .. '1'hey"wereipla~~d9n surface of the sand beforefilling the aquarium withwater b

This three

The results of thi s experimentsame as from the firsto

Discussion of Results

VII) were . the

These experirne~ts\tllerenot ..e:Xhaustive but they weresufficient to convince ius~hat.inhydrauli.c raking of clamswe were dealing with a floatation phenomenono The jets fromthe rake apparently create a fluid soil-water suspension witha high specific gravi~y-=probably" ranging BiDout 105 to 1 0 6 0 Inthis heavyi suspension the low-specific"'gravity clams rose tothe surface like) corkso

From the point of view of the gear researcher theexperimemts> show thatiithe essentia.lifunctionof· the nozzles %ndwater jets is to convert theiupperstrata of soil .. from a solidinto a fluido Presumably the size, shapel/force a.nd spacing ofthe jets could be varied a great deal and still be effective aslong as they perform thi's converting function 0 In of,heY'iwoirds,it should be possib1~.. to vary the design .. .of' ..the prototype rakea good deal without .. sacrifice of effectiveness 0

DESIGNi)GHANGES IN HYDRAULIC RAKE

In 1961we used the same hydrau.licunit as in 19600It consists of a i 2-inch x2....inch .. self -prirning 9 centrif'Uga1force pump powered by a I-cylinder ~6 h opo~ air-cooled ~gasoliIle

=3-

engine 0 But further changes from the prototype design were madein the body of the rake (see Figo 1 and 2 and compare withFig 0 in MacPhai1 9 MS 9 1961) 0 The discharge .hose was attacheddirectly to the manifold and a "Dn-type steel handle fastenedto its opposite side (Figo 2)0 These changes facilitatedhandling and.fishingo The new handle is lighter than the oldand the operator9whilefishing~ now faces the boat and pumpwhich isanadvantage(Figo 5Jo

Besides these changes ~ nozzle lengthswerealtered~

Four comple.te 9 interchangeables ets of·$ nozzles 2 9 3 ~'7ana 9inches long were constructed in the workshop at the BiologicalStationo The 2-inch nozzles just touched the surface of thesoil but the 3- 9'7-and 9...inchnozzlespenetrated1 9 5 and '7inch E3s respectiveHyintothe soil o Each '7-and 9"..inchiDozzlehad threet-inchdiameter. holes drilled into its leading faceto wash away the soil in the direction therakemoveso Thefree ends of all typesJofnozzleswereitapered or flattened· to~ive.a flat~. fan-" spray effect to the <j etsofwater (Fig 0 3)

The effects of these nozzle changes were tested ina series of hydraulic raking trials

Changes were. made in the method of collecting clamsthat· wer.e.fished by the hydraulic rake but these did.notaffect the designofth e •rake i.tself''''''''see s ectionheaded 9vtCollecting raketto

WithJ.al1 nozzles operating? the average workingpressure was. about 25 pounds per square inch and the volume ofwater delivered approximately 130 gallons perminuteo

WORK SITE

The 1961 tria1swereca.rried out at Clam Harbour 9NoSo 9 on the same flat where similar tests had been conducted

~~~ ~~~01~3gr1~:c~~~ii~el~~~)~Ul~~i:s~~~~t~~:~~~:~t{~v~~andcomposed of uniformly fine sand and contains a scatteredpopulation of <.clams (MyaarenariaJo It was chosen beCause ofthe uniformity of its conditions 9.· because it is similar to manyof the. clam producing areas on<the outer coast of< Nova Scotiaand in the·GulfofStoLawrenceandbecauseit afforded anopportunitytomakedirectcomparisonsoftheifishing efficiencyof the hydraulic rake with that (of the escalator harvesterwhich was test.ed there a few years previous {Medcof 9 1961 andMacPhail 9 1961) 0

The tidal amplitude at Clam Harbour is apprOXimately5 feet and the run-off is slow compared wi th that in the Bay ofFundy 0 On the average 9 the rise or fall of the water level isabout I foot per. hour 0

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COLLECTING RAKE

Design

In 19609 when working wi ththehydraulic rake atSto Andrews II NoB" 9we picked the clams from the track by handafter the tide recededo But in Clarn Harbourit·wasnecessaryto collect them while they were still submerged or theyburied themselves before the tide fell low enough· to exposethe fla tso For thispurpos e we designed a rake with a bow­shaped head (Fig "4),,

The rake ris24incheswideand crescent shaped tofit.thecontours of the tracko The teeth were inches longat the outer extremities and decreased gradually to 5 inchesat the centre" They were covered most to .theirtips withk-inchmesh<wirescreening" bow was backed with similarscreening that extended the <handle a distance of about 14,inches and formed a collecting pocket for the raked clams 0

Efficiency of collection raking

To test ··theefficiency oftherake>llweresorted toa fi eld tagging experiment 0 One hundred market-sizeclams weremarked with·arfilerather>than<ink so that they could not beconspicuous enough to be id entifi ed among nativestockwhileraking in 2 to 3 feet of water o Three runs? each about 30 feetin length ?were <then made through ana turally stocked clam bedin sandy soilmearthe experimentaL plots 0 The marked clamswere scatteredramongth enativ.e < clams in the track and on •theverges throughout their length o Three persons were involvedin the raking tests ll each working one tracko By working care­fully the rakers gathered 95 11 <99 and 100% of the marked clams 0

HYDRAULTGRAKING .. TRIALS

Opera t i %.conditio.ns

EoIIowing <. our estab li~l1~<c:l»p:ra.ct:i.(':ell>fishi ng trialswerercarried .out as the tide was falling while the flats werestill >coveredwith water from a·. depth 01'3 f.eet < to·$ inches(MacPhailj) MS,196l1o Ordinarily this enabled us to worksteadilyon·the<.plotsfOr 2hoursbefor·ethey were exposed 0

,We wore chest-height.ll<rubber ffwadersf\' which.are a necessityfor this kind ofrwork The pump--motorassembly was floatedin a dinghy behind the rake and the operator w'alked <slowlybackwards exerting a steady pull on the handle (Figo

Inthis<pure saridysoil the clams were .floated>upfrom their burrows by the water jets and as soouas the rakepassed j) they settled onto the sando They were < quite free ofthe fine black sediment which often settled over clams fishedfrom the muddy flats at Sto Andrews 0

Preparation andf'oishing. of t~stplots

The most time-consuming.task in measuring the efficiencyof the hydraulic rake was <setting up.thetest.<plotso Clams forstocking wet'e fj.shedwi.;th the rake and sorted. into a size groupsui tablefortheparticlllartesto We. then established plotsmeasuring 3 ft x 10 ft withth~ .long .axis of th.eplot in linewith the prevailing direction of tidal currents across the flato

For precision in planting th.e >iClams at a density of 9per square foot 9 we used a grid frame 9 3 ft x 5 ft 9 which hadbeen strung lengthwise and crosswise with cotton twine to give4-inch squareso Wl1en planting 9 this frame wasl.aici on the soi1 9a hole made in the centre of each square with a wooden spike aridaclamplaced 9 siphop;-endllP9 ip.the holeoThe dep;thof the holewas.sucht):la'trthe upper<endo£, the. clam was about 2 inches belowthe surf'a.ce of?'the soiloV.rwenty-four plots Gontaininga totalof6 94.80. clams <wi.th}.a.n.averag<elength of\l~ <inches (mabIe. V) ·'W'ereplant:, .edinthisfashiono

Fishing tests were?conductplanting which.is suffic:ientt im e. forselves at approximately normal depths1944) ..

days or morEl aft€!rclams to establish them­in their burrows (Medcof 9

Thepurposepf''th~. rf'irst tests.was to show the effectsof nozz length on raking speed.frecoveryrate9harvesting ratbreakage andma!loeuverability of? the. hydraulic rake (Table IloA single91engthwis e/strip was;f'ishedthrougheach iplotand?fouror more.plpts were fished in 'testing each nozzle length" Collec~~

tion raking was done as soon.as the water cleared after hydraulicraking 0

Other tests werelllade wi ththe.2-inchnozzles todetermine the effects of increasing water pressure on fishingefficiency (Table 11)0 To achieve the higher pressure 9 2 Of the8 jets were closed offo

Inafew(tests the} angle of th enozzles was adjusted.Table and IIlto;s~eifthis .a.ffectedth~ rake. VsperformanceoIn someth e..(. nozzle swereperpendicularto'the. surfac e of.thefla to.. Inotheps.the free .ends of th enozzle s were canted t.owardthe operator.approximately? 6(> from perpendicularo,

The .effect.s of .hydraulic>r'a.king/on. cla.ms that are toosmall to be of commercial use were also examined 0 In some testsdead (formalin-killed) clams were used (because they do notburrow) to. s ee how. (young clams are seattered.? :bythe rakei and bythe tide after therak.epasses(Table IIIlo In. other tests liveclams were used to see how many and where the young clamsre-established themselves (Table IV) 0 These plots were. plantedin the same way as those set up for the escalator harvester in1958 (Medcof 9 1961)0 One thousand and eighty (1 9 °80) clams 9

1 inch in length (Table VI) were tagged with VolgerVs Ink andplanted at a density of 9 per square foot in four plots 3 ft x10 fto

In fishing the plots of sm~nl, clams~2...inchnozzleswere used and raking was begun 10 feet down-tide from the plot 9continued up to and >through the<plotand 10 feet beyond 0 • Noattempt was made to gather these with thec?2Llecting rakeoThey were left where they were 9 as small clams would be incommercialfishingoperationsci Their position was examined assoon as the tide fell and exposed theiflatso

DISCUSSION OF RESULTS

I. Collection raking

Rakingiwi th the collecting rakeisarfessential part ofclam harvesting wit~thehydraulicrakeo" And if it.hadnot.beenuniformly done 9 itl-lOuld have been impossi bletoform reliableopinions of, the way the hydraulic rake performed when operated indifferent ways 0 Our tests showed that with care the collectingrake recovered, 98% of marketable clams from the verges .a.nd trackin the sandy soils at ClamHarbour~ i From this we decided thatno serious error would heintrodllcedif(fortliepurposes of thisstudy 9we assumed the collecting rake to be 100% efficient inrecovering clams that the hydraulic rake brought to. the surfaceo

To·' minimize erforiIl Our' experiments we had one man dothe collecti0D; raking and made isureithat ,workedwith ithegreatest careo This slowed down the workoWefoundthat ourexperimental· collection raking occupied roughly80to/85% andhydraulic rakiIlg 15 to 20% of the total plot 'harvestingtimeo·Insimulatedcommercial fishing operations we found collectionraking could be done more quickly and took 70 to 80% of thetotal harvesting time. "But we suspect that under these conditionsthe per cent· recovery sufferedo

2. Raking speed

In tests with nozzles more than 2. inches long9 thesteady pull on the" handle. of the rake bytllefisherman forcedthe rake<ahead as fast as/it would gowith01J.tttjumping"it outof it strack. The result 8 «Table I )~howed<that/thi8.maximumraking sp eed'in sandysoilvariedinver~elywith ·nozzle .·length 9being 19.2 9 9 0 6 and 5.2 feet per minute with and9-inchnozzles. ,This maxim1J.m speed seemed to be, determin,ed by the rateat which the soil was washed away from the subsurface 9 leadingfaces of the nozz leso

The 2-inchnozzles did not enter the soil so there wasnosoilimpedence it olimitth e··. raking speed ,as with .i the longernozzleso The fisherman could wheel the rake as fast or asslow as he pleased.

3., Recovery rates

If the combinatibn of hydraulic. raking and ... i co11ectionraking had been c()mpletely effective?/ l~Ocl§tmswo'Uld.ha.ve be.enrecovered from eachplot..;~theclamswere planted 9. per square.foot ~ the plots were 10 feet long a.nd the flat.bottom of therake track through the plo.tswas .2.4incheswidea~thoughithe

distance between centres of the 0l..1t side nozz~E!El was. only 21inches (Fig., 2}0 (This was not true for the plots referred toin Table 110 In these the bottom of the <track. was 21 incheswideCind the ideal recov~rywouldhave been15cLclarnsper plot 0)It was on this basis of an ideal retuI'n. of 188 .clams that .w-eestimated·per cent recoveries •. listed·in Tab~eIo Theseshow

~~~ .. ·.1~~~95%j·. ~iidari~t96~~i~11~~~ z·~ife~~:dPb~ ···~b~~l~ef~hZih? wasraking· speed or angle of nozzle to the surface of the flato

In contrast ~ the per cent recovery with the 2..;inchnozzles varied greatly with raking speed~

At high speeds (40 ft. per min)Jhe recovery .was 10'W--53%0 Apparently it takes.a certainamol.1nt of time for th7 waterjets to create a. favourable cOllsisteIlcyofsoil-Yia.ter mixtureand this consistency has to be.maintaine(j1o:nK enough to al~ow

the clams to float upt() thestlrfaceo Raking Cit 40 feet perminute does not seem to meet these requirementso

At intennediate speeds (20-30 ft. perlltin) the recoverywas higho Neglecting the results for the foul cut through plot3? it averaged 90 to 95% (Table I) 0

At low speeds (10.,5Ttperm:i.11)th~ ecoverywasveryhigh-"'120%o This is believed to haVE! been caused by fYborder:effectsf'lo . At. low spe7ds th7 track may have been deeper a l1d mayhave lead to excessivetmdElrcut,tingof.the verge~ of .the trackby the flat 9 fan-spray Ilozzles (Fig~ 3)a:nd thevergescru.mbledoWhatever the .cCiuse? theres11l~ was all increase inthe effectivewidth of the track because more clams were recoveredo

40 Harvesting rate

To estimate the harvesting efficiency of the hydraulicrake (number of' clams caught in l.lnit harvesting .time Jthe percent recovery and the raking speed mustboth be c<)llsidered.o Onthis basis the rake performedbest when equipped with 2-inchnozzles and .at intermediate rCik:ing speeds (20-30 f't .per min).,At 25 fe.et per minute it covered 50 squCire.feet per minute andrecovered 95% of the.. marketable clams 0 Some. were found in thetrack and some on the verges (Table T) .,Experimentalcollectionraking of a 25-foot cut ordinarily occupied 4 t05 minutesbringing the. total harvesting time to .5 to 6 minutes and theharvesting rate to 8 to 10 square feet per minute o

50 Manoeuverab~o~ hydraulic rake

Hanciling t.he rak[8whf.!n equippedwith 2-inchnozzleswas veryrasyo .•...•. Itcouldb.e wheel~.dfor.:wardsor.backwards •likeala'Wnmoweras q1.lick1y or.s1mdyasthe ~isherman.pleased

regardless of whethe.Y' thf'... wat€!r .pump 'Was on or.. 0££'0 ThismanoeuyerabiT~tywouldbea grf'Jat.?dllantage in .C()rmne:rcialoperations/bec.au~e.th.eIf? p()s~~i()nil1g of. the rake on.productiveparts of natural beds .he c()mes. important 0

With. noz~lesm()rethan 2. inches. in length ~ there wasa great loss~!1.man?euverabi:i.ity 0 ... As soon asth~.water pumpwas s~tltofr the·· nozz lest C?ught. so. ~irrnly in the~oiLthatt.herake.could.notbe.hauledo .•.•. It. had. to beliftedandcarriedo< Thiswas diff:icult when.:worf<:ing .. in2 ()T 3 fyet of.. 'Wat.er<becaus~ therake it$elf weighsplpo1.lnds and tlle Bose is an extra.burdeno

60 Effect of water pressure 0lJ.~ rakin,K

Increases in pressure appeared increaseefficiency. {Table.I.I}.Pllt this .. eff.ectwc9.snot tooclearo Thereas()ni~ that inthissyri.es ofi:,ests o111y.6 nozzles were used(the t'W0 01.lter. f ...incB ... no:z;zles. wereplugged)a.nd .• the width of thetrask wfis redtlpecl.to31 ~ncheso.Thi~ gave the desired. 5 posoiincre?$e irlwatyr. prEH,su:ryo ThisClrrangem~nt:,.tended t() exag­gerate 'lYborder effects.~.intlle Beirne waY.eis l0'W... speed raking(Item 3)0 That is to saY9 the number of wwashouts'IY on the sidesof the track beqame .reiative:ty< larg;er.in proportion to the totalcatch than when the. track was .24 inches wideo

If some other means of increasing the pressure hadbeen devis.ed 9 we'W()uld .ha"ehada.better basis for. judging thetrue effect 13 of pr~B~mre.. qhanges and the per cent recovery mighthave be€!n (lJ.oser to the 9.5% recorded for 25 posoio pressurewith the 8n.ozzles inop€!J:"ationoNyvertheless.weareinclinedtobelieve from theway.. themachine.pehaved 9 that the 5 posoioincreasydid indeed effect:, •• sOmer€!al<increase in ef'fici~ncy0It is doubtful.wheth er il1s:refiBesbey()ndJO po s 0i o would. provideimportant overall advantages in sandy soils but it might beworth while in compact mud or clayey soilso

70 Scattering of clams

The seatter Mtternof small $ formalin-killed clamscaused py ~he. hyd:raulicrake ShOlATsthat60%. w.ereleft on thesoft soil of. the digg.er·· track and.tBa t .mostof .thesewer.ewithinlOfeet 0:f. t.he.pl()to The r~st, (40%) were on theundisturbed fJ.at o.<.~heseweresprea.dforadistance oflOOfeet down-tide fromth.e.plots but most ..of them were within60 feet of. the. plots (Ta.ble III) 0

Clam Harb.our~ like most clam-producing inlets ineastern Nova Scotia~ has a comparatively small opening to thesea and a large basin that fills and empties each tidal cycleoThis causes vigorous tidal currents in portions of the inletoThe particular flat on which we were working was opposite the

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mouth of the harbour and bounded on two sid esby channels 0

ConsequentlY9 at. half-tide 1e17e1 9 strong currents 9. at.a rateof about 2 knots 9 .were running seaward across the rlat. and hada great inrluenc e on the drift of the formalin-killed seed clams 0

In other parts of the . harbour currents were. muchweaker andwhen·fishing was carried on there 9 living .se.edclamswere observed to drift only 20 feet or less down~tide from thetrack of the hydraulic rakeo From this we conclude that mostof' the scattering of test plot stocks was caused by tidalcurrents not by the rake itselfo

In weighing the results listed in Table 111.9 it mustbe recalled that these anirIl<3.ls wer~dead a l1d. incapable of bllrrow:"ing so they were exposed to tidal action for the whole period 9

frpm fishing u l1til the flats were exposed bJT the falling tideoThis was approximately 2 hours o Many small living clams burythemselves within 20 minutes (Medcof 9 1961) and presumably undernormal fishing conditions these would be carried only shortdistances before burial 0 This supposition is· supported byresults listed in Table IVo

An average of 78% .of the formalin-killed clams plantedinth.etwo· small-clam test .ptlots •.• w<3.s recovered (TableJII YoThis value. isl()w. compared -withrecoyeries reported in Table Tand 110 One .. reason for this is tqatduring theprocess()f'hydraulic· raking considerClble·. numbers of. tagged 9 deadclarns .wereobs~rved floating onth.~ surface()f the. water and being .~arried

away by the tide" Thisphenomenotlhas been observed onpreviollsoccasions and we bel.ieve it. i s callsed by the clams closil1gtheirshells .. quickly· and ··trapping air when they are first immersed inthe formalin batho

The twop~ots of smal~. tagged living clams. weresubj ected to· .the. same. fishi ngprocedures with the. hydraulic rake(Table IV) as tho.~e. that were 1'0 rmal in-killed 0 • Only 25% of theclams in the path of the r<3.ke were recovered and most ()f thesewere obtained by probing in the soft soil in the tra9ko .. Themost striking featureo{ tqese tests was that on the averagethe living clams found on the surface constituted only 5% ofthe total di~t.llrbed.9Y the. hydraulic rake 0 . Presumably th e resthad buried thE3mselV~s completely in the track or in the un­disturbed flat~ in a period of less than. 2 hours after d.igging 0

In other words 9 95% of the stock had reburied and would surviveo

Our impression was that the sca~tering of the smallliving clams (Table IV) was much less than that of the formalin ...killed animals and essenti~lly like that observed in parts ofthe harbour where tidal currents were weako

EL Breakage. of clams

Th.ere.wasVirtuallynobr13ak~geof>ITlarketa"bleclamsfishedwith2... ipchnozzles. and they camel1Pv~ry.cleano However~in gathering them under water with the collecting rake~ 3% werebroken (Table I and 11)0 This was .mostlycaused by the rakernotseeingal:L. the clams in the murky water and walking on andcrushing some that .had >been waE)hedup on.th~ verges of th~

track 0

With longer nozz s ~ breakage rates were as high as 11%0We conclude that most of this increased damage was caused by thenoz.zles themselves~probab:LYbyc:ru.E)hing theclams<while they weres~ill •. in theirbu:r'rows •• becalls e)theopE:rator exerted .. a steady pullon the rak to>.move the noz.zle.s through the soilo

Breakage among small cams was aand IV) averaging less than 1%0

90 Rake track on beach

slight

The track made by the hydraulic rake was inspected ass90n§tS thef1at.was< exposed by the falling tide (Figo 6) 0 Inappearance it r~sembledthe track made by. the. escalator harvester(Medcof9 1961 )0 ... WhE:n the water> pressure .w~s> .25 po S 0 i 0 t.he fourtypes of n9zzleE; Pr9ducedsimiJ,.ar tracks 0 The •. bottom of thetracks>'W'p-s) 24iIlchesW'ideandtb.evergEe...to-vergew-idth of thetrClckat th..elevelof the undis'turbed flat W'as 33 inches 0Gru.mbliIlg 0 fW e .verges.g.f'the ."l;.rack accounts for. 'the dif f.erenc ..~bE:tweenthes widths 0 No. doubt the tidal currents. a.id.ed> in .thiscru.rnb1Jng pcesso . The flat p0't't0m of the track was 2! inchesbelow the surface of the undisturbed flato

The verges were bu.ilt up §tQout 1 inch above theunp.istW'pedfl§l- t<. 'W'i th. sang fromthe track 0 The thicknessofth.ebuild-up tapered off so as to be indistinguishable at a distanceof lOto :L2 ~ncll es.:rrom.th everge>o After 24 hgurs.the< soi:L inthe tra~k w§l-s> quite firm but the depressions in the flat wouldlikely. last for <. s~veral. mop.'thsas is .the case following ... opera­tions of escalator harvesters. or clam. hacks 0

Wh.en theTa}{ waE) operated with a 'W'aterpressure 9f30 posoi o• thetrack.was deeper.Jabout 4ino) whichrnay haveincre§1se<i the number of ... "washout sn .and the verges were. built uphigher (about 2 inches)o Presumably a longer period would berequi r~cifor.natural levelling of.th beaches when higher waterpresstlres are used· in hyp.raulic raking 0

100 Compa on of hydraulic raking withother harvesting methods

1001 Harvesting capacityo A fisherman with a hydraulic rakeharvests 9 square feet per minute (Item 4) 0

A two-man escalator harvester like the one we used onMoBo Cyprina harvests 50 square feet per minute or 25 square

feet per man per minuteo The recovery ratesf'or'cthE!set'WOharvesting.tools aret.oughly ~qual (see Item<4 and MacPhail 9

1961.) Thus 9 in terms of :'clamsproducedper man perminute of fishing 9 >.thehatvesting power of the escalatorharvester isaIDproximately three >timesthat of the hydraulicrake 0

per,mi~u~;s~~::~~~~~lab~~a~eh~~~o~~~e~~~y56~~u:~et~:etmarketable clams in thesoilo Thus 9 >in terms· of clamspr.oduc edper<manper minute. of' fishing 9 the harvesting. powerof»a.man »wi thahack is .only one third that .of.a manrwith ahydraulic rake 0

In studying harvesting capacity,thenlength of<timegear> can be rOIDeratedmustbe consid~redaswell/as rharvestingrateduring.therfishingrperiod Clam Harbour$Mith uits·sandysoils,.' is>rity picalrof'manyiclamgrowing>areas wherefi:shingrisca.rried out with clam·. ha cks on.:i.ntertidal· flats" . Productivegroundsuare exposed f'or r)ab out 5 yhoursat each.low..;tideperiodand clam fishermen are able to work y·thedryflatsduring thistime 0 Ordinarily a fisherman works only one tide per daybecause clamrdigging·istiri.ng work and >becaus eone of. thelow..tide periods of"t,enoccurs:atnight 0

Hydraulic. raking requires that the beaches be coveredwith.watero Thus 9 i.nmostplaces} <the rak.er.ca,n beginfishing earlier and continue la"ter, if he is f'ishingonafalling tide 9 or vice versa 9 if he is fishing on a risingtide{thantheclam.;..hackf.ishermano And there isa periodof' abou.t ·2hours.athigh.water'andat lowwaterwhen·hydraulicraking is not possible Wh:Vchwould.gi.ve the rfishermananoPIDortunityto rest·which in l11any cases would be. quit ewelcomeoOur·experimental work was done ?-"t,ebbtide and.at onebe'achlevelo Water depths permitted raking continuously.f'pr2....ho1lrIDeriodso In our opinion it would have been IDossible to workdownand>uID thebeach.with ebb and flood tides at ClamHarbour and .be able to rake at least' 5hours)onproductivegroundsi:nany one.t idal .cycle

In the shelteredlagoohs in the southern Gulf of StoLawrence which contain most of the productive clam groundsof that region , thetidaleff~ctl3a:r'~slig1:ltarl.d ~I'ratic 0

Many clam be ds .arepermane:ntlysu9merged •and .•.. others a reexposed only at periods. of sp:r'ing,tides" In these areaslong..;handled ·garden >ordungfo'rksorplumbervs helpers aretypicalmanualfishingtool$o HYdraulic raking.co:W-dbecarried out for long periods there but dif'ficultiesmightbeencountered.with collection raking because the turbiditycaused by the hydraulic rake would persist since often tidalcurrentsaresluggish "or. •practi cally non- exis tant ~

IntheBayof.Fundyth e reverseconditions.obtainoTidal run-off is fast and usually clams·are f'ound<onlyatintermediate beach levels 0 Some areas could be raked for

-12=

4 hours on the ebb and flood tides ~ others for less~ Anotherdisadvantage\ofhydraulic raking ofFundyclamb~dsisthe<mu.ddytype of soil that is generally found there 0 . From <:mr experiencewith the· rake in·. these soils. we wouldexpect>harvesting.. efficiencyto drop to about 60% {MacPhaiMS ~l96lloHowever9insome\partsof the Fundy area it might be worth while to combine the two typesof fishing 9 hydraulic raking and clam-hack fishingo

In Minas <Basin 9 \particularly the Five Islands and Economyareas, there are good quantities of clams harvested eachyear oHowever~·thetidalamplitude at neap tides is over 40 \feet> and therun-off so rapid over the clam beds that hydraulicrakingw6uld notbe practicalo

The escalator iharvestermustalsobeus edwhenthe flats arecovered with water andrequiresgreaterdepths.thanthehydraulicrake be cause. theremus t be enough waterto.floatamoderate.;.;sizeb6at.o Therefore fishingcanpeginearlieron<the/ebb·.tide /andcontinuelater.onfloodtideithan hydraulic raking or clam;...hackf'ishing,<although a4-houriiriterruptiongenerally occurs at thelow....slackphaseof the tid e~

Thus in\areaswhereit is practicable· to use all three clamharvesting devices it appears that fishing times/for anyone low­tide period would be about the same for all these appliancesoThiswould >meant hat thei I' daily harvesting capa citycouldordinarilybegaugedfronitheirharvesting rates during·thefishingcperiod" '

From the <point of view of the ordinq:ry-··clam fisherman thereis little prospect of ·conver;;~ngfrom/clam-hackfishingto

escalator harvesting (seesuo"""it.emlO.;3 below}o But many couldconvert tohydraulic·raking andr if they did, they should ibe ableto at·least treble their harvesting capacity and hence theirearning powero

Becau.se of their greater harvesting power it seems ikelythat clamfishermenwitn 'hy'draulic rakes may be willing to fishareas that are too sparsely stocked to attract clam"'ha.ckfis;her­meno This would raise the industryts harvesting capacity andshould insure fuller us eof ourclamresourc es 0

10 0 2 Eas.eof operationandteam.;.;work 0 Clamfishingwithhydraulicrakes.. :i.!scomparativelylightwork 0 The rake can be . hauled over theflats like a lawn.;.;mower 9 positionedon the clambed 9 and thedig;gingoperationcarriedoutat·aslow steady-paceo Forthisreason converting to hydraulic rakingfromclam-hackefishing shouldbe attractive to those fishermen who still try to supplementth eirannual incomes by fishing clams nthewarmmonths

The collection raking phase of harvesting/mayoccupy 5 or 6times as much time as hydraulic raking itself (Item 4)0 Thismeans that one man operating a •hydraulic rake could keep as manyas 4 or 5 persons busy·with collectingrakeso From this wernightexpect that hydraulic raking would encourage team-work among clamfishermen 0 The family group is the simplest and most likely team

-13-

to form and we think of clam harvesting with hydraulic>rakesas likely to·develop family enterprises

1003CostsoA hydraulic rake ,completewithp1.1.mp-:motor,hoses and attachments can be built for $400 to $500(MacPhail, MS,t 1961) 0 It. can be operated from a small oaredboat costing>tp50to)$IOO and the operator needs a etofchest-11.igh >ffwaders vt 0 ··.·Anescalator harvester co sts$5 ,000and requires a $4,>500 boat to operate it (MacPhail, 1961) 0A clam hack costs Tess than $5000 and aclam=hack fishermanmayor may not need small boat to goc.lamfishing 0

It . clear that almOst. anyone can equip himself/forclarn-hack)fishingo. But when other harvesting methods areconsidered werealiz e' that ··few ··clam.fisherrnen are·in·.iapositio ri>tb invest)i:na.nescalator·harvester Howeverthere are many who could finance a hydraulic rake andamortize i/the)iinvestment> in ss .than •.. one season ~ 'From ourexperience we judge )that the lifetime of the engine is about5 years but the pump .and rake should be ·.serviceable foramuch longer periodo

10~i4 Condition of catcho Since clams fished by the hydraulicrake haveL>hot:been handled by processors in the Maritimes, wehave no opinions ·.fromis11.ucking plant operators>onthe condi­tion of clams harvested by this .method.; However, Jbreakagerates are lower than those fished With clam hack which mean;sthat few cla.mswould discardedby.ishuckers ·.and 9 ··coinse-quently,that .... higheriJ)foportion of the catch) would beprocessed (Item 8 and Medcof<and MacPhail 9 1952) 0

We did fi·nd>that while outwardly the catch was verycleaIJ., there vvas more than the normal .amount of sand andgrit in the mantle cavity of clams fished with the hydraulicl:'ake~.. This >wbuldi probably Jrequire ishucking iplants to carryout a more careful andlong;erwashing.processthanhasrbeencustomarl in~hepastbut,.sofaras we can> judge ,ithiswouldnot adversely affect the quality of the finished product 0

I005i~()ris>ervatioriaspectso Thehydra.ulicra.ke has threefeatures that recommend its use from the cons ervati on stand­pof~t''\iVhich((s~?tild>increasetheiannual per-:acre yields ofclams from areas where.it can beusedo

First 9 hydra.ulicrakesdo>little damage to theismallclams left behind in the soil" Breakagewasle.ssthanl%(Item 8) and it appears that losses from this and othercauses would not exceed 5% (Item 7) 0 In contrast clam hacksdestroy 50% of the young clams left behind in the soil(Needler and Ingalls, 1944) 0

Second, at a single fishing a hydraulic rake harvestsalmost all the marketable clams from the ground worked(Item 3)0 Therefore there is little inducement for fisher­men to return to and refish the same ground until the clams

-14=

have grown sufficiently to.. make it worth whileo By comparisonclam-hack fishermen take only .60%.ofthe clams from the groundthey turn (Reed, 1952) and the survivors of the 40% they missoft.entattpact .themback>.to re..fishthe,same 'grounds everaltimesinra singleseasono

Third,twheretidal pun-off ap.pr.oximat~s.lfoot per;.hourhydraulic. raking must ceasetabout.three.quartersof an. hourbeforetheflatsarfilexposed ,which isrample time for clamslinch and. leas in length. to burt'ow pack into the soil beforethe flatsare.expos ..ed o . Moreover~,mQst,·of the clams. (of allsiz es left behind are deposited in the track of the rake andcovered <with water (Fig 0 ,61 for.tan.e.ven longer.periodo There

s ampletopportunity.forthemtot re.;;bury" Thus ,>only"asmallper.centage of the clams disturbed. by ,the rake are,exposed togull predation or to the effects of heat orfreezingo

10.,6 Precautions 0 Althoughwe e hydraulic rake asapproaching the idealcla.mharvesting.devic e 9 improperhandling ..canbe.damagingtoclam. flats and c.lam stockso

First, novices or careless rakers can cause damage by~wellingftthef1ats therake.is(l ef.''t .s'ta'tJ..onal'Ywiththe jets facing downward 'and the pump engine running wellis excavatedinrthe soi·1., We1lafil1iints1owly.,.and aci;,>astraps>rforsmall clams,whic.h 'could·caus emortaliti es or. otherundesirableeffectsirby overcrowdi.ng" at.fishermanworkingalonehe.canpreventwel1tl1.gipy,turning the rakfil onits side .!when.starting orsto.ppiqg ith.epumprengined Ifworking inatea.m 9 he.continues tmoving attthe normal fishingrate until his assistant shuts off the pump engineolneither'c.ase~welling9'lune.ed.inot;be.a;problemo

Second~a coll.ection (rakerimay bring.up a rakefulofclams ,pick out (thfil markei;,abletsizesand empty the discardsin.,one •.spot.alongside ia.,stati()narywire ·.ibasket imila.rtypeofcontainero Eveni;,uaEly aheap.oftsIllall clams willbuildupito)such an extentt1:lat some will> fail tore-buryand those that do will suffer from overcrowdingo We havedeveloped and a trongTI..y,recommend. <th~uSfil Qf~,lV'iI"~basket

or cagewithfloatsfastenfild to thetrimo Therakertiesthis container to his. waders withashortilineo Byi;,hisarrangement the c ontainer;i.s.alwaysathandtoreceiv~hismarketable clams and with a swinging motion of the rake hecan return the smallclJamsto the portiqnof the track fromwhichtheyhad.befiln>gatheredo

SUMMARY

Lab61"atory;.exPtrimentsindfcat~thathydraul:ic.I'akingdoes not "washout wclams 0 It merely liquif'iesthe. upper s~rata

of' the soil by turning it into a soil-water suspension with ahigh specif'icg;ravityo ....In ~hi~.~ediu~? ic~<:ullswith thtir lowspecific gravity floa.t to the Slurface where they can be collectedo

Fie~dtrials~how.tllatinsflndy so~ls our 1961model()fthe hydraulic rake ?.equ;i.ppedwitl1"\t{heels.and2-in.?h>noz ziJ.yes?is amanoeuverable ··andefficient .toolforharvesting.sqf.t-shell.clams 0

It harvests three times as fast as clam-hack fishing? coveringabout.9..~.quarf; fee~ peI'.mil1u~E!oIthBrves~sCl.t.. one~l1ird thespeed()fthf;escal~Borhfl:r"Ve.ster;iF~cove1"sQQto95.~ of.~hemarketablecTamsinits path; damages less than 5.% of tb..e m~rketableclams and destroys 5.% or less of the small clams left behind inthe soi.~oIn.c()nt..ra,Slt.?a.clam.hack.•90versaQout 5. squ;are feetper min.utf;;··'r~9overs60%,of.thema1"~etable.. clam.s •.• in >thesOilturned; breaks 10 to I 5.% oftheh.arvE3stedclamSl..an.d.smqt.heFs orotherwise destroys 50% of the small clams left behindo

Commercia.l .MS e ,of '. hyd raulic ralces .lPlpuld '. prodllcE!° o cla.msthat are a.cceptableto processorS! and should increase ,the annualyields from our clam flatso

SbmE3.·precal1:tions .. sholl~9~epbserved ·in.opeF~tfnghydraulic rakes to ,avoidcl.amage toclamfla,.tS!andclamstockso

Thf; >capitala.rldoperatipg c:Rsts of hydraulic rakes aresufficientlylowtha~.marlY . clfl~ ff~her~E!n .should •tJeaple, toacquire themo Conservationwise we regard them as approachingthe ideal clam harvesting tool and we think of them as wellsuited to the needs of family or small team operationso~

Hydraulic raking is not drudgery and the adoption ofhydraulic rakes in preference to clam hacks should make clamfishing more attractive to those fishermen who supplement theirannual earnings by fishing clams in the warm monthso

We believe we could make further improvements in thehydraulic rake by study and performance tests but we have doneenough to demonstrate its potentialities and its likely effects 9

if widely used? on clam stockso If it were used for commercialfishing 9 clam fishermen would find their own ways of makingthese improvements and of adapting it to suit. the special localconditions in which they are workingo

-16-

LITERATURE REFERRED TO

MacPhail, JoSo MS,.196.lo Building and 't(';sting a.hydraulicclam rakeo Fisho.Reso Bd •. Canada, MSRept. (.Biol., 1,No. 711, lOpp.

1.9610 A hydraulic escalator shellfish harvester.Bull 0 Fisho Reso Bd. Canada, No. 128, 24 pp.

Medqof ,Jo •. MS~194lyo 1944 Inv 13f)tigatfons, Oysters andClams.o Fish. • Ref) 0..l?d.Canada , .. :MSRe.r>toiBiol~ StaNoo 378, .95ppo .

19500.. Bl1rr.oWing.h~bitsandmovementsofsoft-shelledclams 0 Fish • Res. Bd.o canaga, Atlantic.Prog 0 Rept 0, :NOD5Q,pp 17-.22

1.9€>10. Effect.of hydra.ulic.escalatorharvester Onunger7siz e> soft....shel~.qlarnso 1959Proc o National.Shell...fisheries Assoc 0,5Q~15l-1910

Medcpf, J~ C., and uJo So>~acPhailo 1.952. BreCikage GO the bugbear in clam handling. Fisho ILeso Bdo Canadp., AtlanticFrog. Rept., Noo 54, pp 19-250

Needler, A.Wo ..Ho ,and RoAo Ingallso. 1944. Ex:per1Inents inthe prQciucti9n off)oft7shelled >qJ.ams(Mya) 0 Fish. Res. BdoCanada, Atlantic Prog. Rept., Noo 35, pp 3~80

Reed, Go. E. <1952 • Annual RePPFt oT.the Fisheries ResearchBoard .o.f ...Ganada ..forthe year 1951, PP..19-210

Table 1. Hydraulic raking for clams with a pressure of 25 posoi. and $ nozzles in3 ft x 10 ft plots, planted 9 per square foot at Clam Harbour, NoSo, inJuly 1961 (1$0 clams in path of digger - width of cut 24 in.). Nozzlessloping slightly toward operator in all tests unless otherwise stated.

RakingPlot speed Clams Clams Av. Av.

No. Nozzle ft per min broken recovered recovered breakage Remarks'.

Av. % % % %1 2 in. 40.0 - 6.3 53.32 ft 2$.6 ) 3.7 90.0)3 ft 26.1) 2.5 66.7) Foul cut; digger missed corner4 ft 24. 0) 4.9 90.0) of plot5 ft 22.9) 2) .1 1.9 $$.3 ) 91 3.56 ft 20.3 ) 3.1 $$.9)7 ft 19.4) 4.0 97.2) Nozzles perpendicular to soil$ ft 10.5 - 1.$ 120.·5

9 3 in. 21.4) 5.4 93.3 )10 ft 20.0) 19 2 2.3 97.2)11 ft 17.7) • 9.7 $6.1 ) 92 6.512 ft 17.6) $.6 90.6 )

13 7 in. 10.3 ) 13.7 76.1)14 " 10.2) 10.0 72.2)15 " 9.3 ) 9.6 10.4 91.1) 79 11.316 ft $.5) 12.1 7$.3 )

17 9 in. 5.9) 11.6 $1.1)1$ ft 5.2) 6.$ 90.0)19 " 5.0) 5.2 13.1 $$.9) 90 10.120 ft 4.$) 9.0 9$.3)

Table II. Hydraulic rake fishing for clams with a pressure of 30 p.s.i. and 6 nozzlesin 3 ft x 10 ft plots, planted 9 per square foot at Clam Harbour, N.S.,July 1961 (158 clams in path of digger - two outside nozzles shut off ­width of cut 21 in.).

Raki~

Plot speed Clams Clams Av. Av.Noo Nozzle ft per min brok~n_ recover~9 __ ~~~9Y~TY pr~~k~ge Remarks

21

22

23

24

2 in.

"

"

"

% %13.6 1.8 10Ul

)11.8 4.5 112.7 )

16.2 0.7 96.8 l)

15.4 0.0 101. 9 )

%

110.4

99.3

%

3.0

0.4

Nozzles sloping slightlytoward operator

Nozzles slopi~ slightlytoward operator

Nozzles perpendicular tosurface of soil

Nozzles perpendicular tosurface of soil

Table III. Scatter pattern caused by hydraulic raking with 2-inch nozzles throughplots of small, tagged, formalin-killed clams planted 9 per square footat Clam Harbour, N.Se, August 1961. Count~ made next low tide afterdigging. "T" indicates clams found ~n track; "8" indicates clams foundon undisturbed soi1 0 The raked area extended from a point10 feet up-tide to a point 10 feet down-tide from the plot.

Disposition of clams Distance behind

Plot No. 25

Surface

Plot No. 26

Surface Av.

Raked ground

Plot

Raked ground

Unraked ground

n

n

n

___ jllot (feet)

-10 - 0

oo - 10

10 - 35

35 - 60

6 - 85

85 - 110

T

3

8

gg

S

11

40

7

T

22

22

34

S

23

13

8

2

Total number recovered

Distribution of clams recovered

No. recovered-No. in path- of digg-er

No. brokenNo 0 recovered

99 58

63% 37%

m 87%

2ill 1.3%

78

63%

121,I80

o124

46

37%

69%

0%

78%

<1%

Table IV. Scatter pattern caused by hydraulic raking with 2-inch nozzles throughplots of small, tagged, living clams planted 9 per square foot atClam Harbour, N.S., August 1961. Counts made next low tide afterdigging! "Tn indicates clams found in trackj "3" indicates clams foundon undisturbed soil. There was no search for buriedclams outside the track. The area raked extended from a point 10 feetup-tide from the plot to a point 10 feet down-tide from the plot.

Plot No. 27 Plot No. 28•

-Disposition of .clams - iilstl'nce behind Surface Buried Surface Buried

_______n'2lot (feet) T S T T S T Av.

Raked ground -10 - 0 4 - 0 0 - 0

Plot 0 2 - 0 5 - 0

Raked grou nd o - 10 4 - 36 7 - 30

Un~aked ground 10 - 35 - 1 - - 1

Total number recovered 10 1 36 12 1 30

No. dead (included in totals) 4 1Distribution of clams recovered 21% 2% 77% 28% 3% 69%

No. reeovered & 26% ~ 24%tlo.in '-path of digger 25%

No. living clams on surface r10 4% 127% 5.5%No. in path of digger 180

No. broken 0 0

Table V. Length frequency distribution of marketable-sizedclams used in digging efficiency tests withhydraulic rake.

Length Frequencymm

33 13435 136 337 138 539 114D 1641 1742 1843 1044 1145 1146 1247 1048 949 750 651 752 253 254 155 156 160 163 1

*Number of clams 165

Av. size 44.2 mm or H in.

*Random s~mple of 165 taken from total lot of 6,480 planted.

Table VI. Length frequency distribution of seed clams usedto determine scatter pattern and damage to non­marketable clams by hydraulic rake.

Length Frequencymm

22 2

23 4

24 3

25 7

26 5

27 6

2$ 7

29 $

30 12

31 6

32 6

33 1

34 1

35 2

*Number of clams 70

Av. size 2$.3 mm or 1 1/$ in.

*Random sample of 70 taken from total lot of 1,0$0 planted.

Table VII. How specific gravity of clams in an aquariumaffects their reaction to hosing (1) when theyare buried and (2) when they are on the surfaceof the soil. "S" means that they were on thesurface after hosi~. "Bs" means they wereshallowly buried. "Bd" means they were deeplyburied.

Clam Length Specific Clams buried Clams on surface

no. nun gravity 1 2 3 4 5 6

9* 50 1.35 s s10* 50 1.38 S S

1 56 1.38 S S S S S

2 51 1.21 S Bs S S s

3 54 1.60 B Bs S S Bs

4 50 1.76 Bd Bs B B Bs

5 47 2.11 Bd Bs B B Bd

6 49 2.28 Bd Bd B B Bd

7 49 2.56 Bd Bd B B Bd

8 46 2.88 Bd Bs Bd B Bd

*These clams were livingj no. 1-8 were dead.

Fig. 1.

Fig. 2.

Fig. J.

LEGENDS FOR FIGURES

Prototype Massachusetts, U.S.A., hydraulic clamrake. The basic design of this rake was incorpora_ted into the machine built at the Biological Station,St. Andrews, N.B. (Drawing Frank Cunningham)

Perspective drawing of hydraulic rake designed forfishing soft-shell clams. A 6 h.p. engine poweringa 2-inch x 2-inch centrifugal force pump deliversabout 130 gallons per minute at a pressure of 25pounds per square i~ch to the nozzles on the manifold.The jets of water apparently form an emulsion withthe soil which stratifies as it settles, the heavierparticles first. Since the specific gravity of clamsis low, they are found on the surface of the soilafter the rake passes. The complete unit, less thedinghy which floats the pump assembly, costs about$500. (Drawing P.W.G. McMullon)

The hydraulic rake equipped with J-inch nozzles,at normal water pressure and gallonage per minute,showing flat spray effect of tapered nozzles.

Fig. 4. The crescent-shaped metal rake designed to fit thecontours of the hydraulic rake's track and gatherthe clams before they dig into the soil.

Fig. 5. Fishing clams in about 2, feet of water with thehydraulic rake. The pump assembly is floated in adinghy and the operator walks slowly backwarddrawing the hydraUlic rake over the clam bed. Manon left is using collection rake.

Fig. 6. Experimental clam plots showing tracks made byhydraulic rake. The 80il in the track is about2; inches lower than the undisturbed flats and theverges are built up about 1 inch.

•"''"

< • ,<:< "110<> --f'<"

,

..

Fig. 2.

I" 3 "'2 to 8"

Mild Steel

20"

Handle Adjustment

•o·

f:." Moo",ld

25 lb. Weight

I 1.",

,. .11'2 3~ 0' I ' I .1 Reducing Coupling

.-- '_..,...:-:':''-1-. 3'4-. 3'i ,,,.I'--..~.2,07'--- ~ .. X 2" Nozzle

2" D. Fire Hose 4~'2 1_,' •Coupling

Perspective drawing of hydraulic rake designed for fishingsoft-shell clams. A 6 h.p_ engine powering a 2-inch x 2-inchcentrifugal force pump delivers about 130 gallons per minuteat a pressure of 25 pounds per square inch to the nozzles onthe manifold. The jets of water apparently form an emulsionwith the soil which stratifies as it settles, the heavierparticles first. Since the specific gravity of clams is low,they are found on the surface of the soil after the rakepasses. The complete unit, less the dinghy which floats thepump assembly, costs about $500.

(Drawing P.W.G. McMullon)

Fig. 3.

Fig. 4.

Fig. 5.

7

Fig. 6.

J

•