This paper not to bc

International Council ferthe Exploration of the Soa

roferonce to thc authors

C.M. 1969/Lg19Plankton Committee

Rof. Goal' and Behaviour Committoe

•

•

Comparativo tests with high-speed plankton samplors

by

D. Harding, J. M. Nicqols and D. S. Tungate

INTRODUCTImr

Hieh-speed plankton samplors are being usod incroasingly to study

tho abundaneo and distribution of fish larvae. Those oporated ll1 the

;y-oarly international survoy of thD lme,'m herring spmming grounds in the

North Sca,at the peak of hatching, are oxclusively variations ofthe all

metal Gulf III sampler dcscribed by Gehringer (1952).

GEAR AHD l1EtrHODS

Thc Louestoft version of this sanpIer in 0. fibroglass tube 7 ft long

and 20 in in dianeter and doos not have tho charactoristic roduced real'

soction of tho Gulf IIr sampIer. It has a rcunded fibreglass nOSG 'cono

with an aporturo 14 in in dianoter and a 6 foot cenical nylon 60 mpi

plaructon net is nounted inside the tube. A ncchanicalflow metor fitted

with 14 in dianotor blades is rnountod in the noso cone to record the amount

of water filtorod by tho net.

Experinents have been carricd out during tho past two years to osti­

mato the filtration efficicncy of this sa~pIor andto comparo its catches

with two of the international nets. Calibrntion of tho Lowestoft 20 in

sampler w::os dono in the N.P.L. circulnting \'Iator chnnncl VJhich is' 58 ft

long, 8 ft Ylide, 12 ft deop c:md has a vlorking depth of 8 ft of water.

Thc samplor VJaS mountodcentrally ,in tho vmtor chaimol and moasuroinonts

made at unter spoeds ranging from 3 to 9 ft pOl' second. Forthis series

of tosts tho flow notor uns fittcd uith an olectrical sensor and ~as cali­

brntcd (0.) in IfroEl-strcam" mounted on a rißid streamlincd bnr outside tho

snr:lplor, (b) in "freo-flO\';'1I mountod in tho nase cone cf thc sDJilplcr li/ith­

out a hot and (c) Dountod in tho noso cone of tho sampIer Viith n 60 mpi

nylon plnnl~ton nGt, 0.3 it isnor~ally u3ed nt soa.

1

•

,"

Filtration cfficicncy (F) is thc ratio of watcr filtercd by a

plank.ton, samplcr.. to thc voluID.O 9f. water SVlcpt by thc rnouth .and has. bocn

estim~tod from tho flow meter readings in two waysg (i) Bridgcr (1956). usod c/b = E and (ii) Trantor and Horon (1965) usod c/a = F. Ii alb >1

as Tranter and.Heron (1965) and l~llen and Hompol (in press) suegest for

an cncased net, then e/a undcrcstioatcs the density of anioals in the

water. If alb = 1, thon e/b = cla and tho dcnsity is proporly estinatod

by oithcr calibration.

Thc first scrics of tests at Gca was carriod out using a fibreglass

version of thc 30 inch diametor oultipurposo plankton sanpIer (Bcvorton

and Tungato 1961), but non fitted with n rounded fibreglass noso cone

vlith c.n 18 in diameter aporture and an eloetronic flovl r.1ctor. Tho chief

aims of these trials nt sen wore to estimate (i) thc period of time tho

st~dard samplor could bo fishod at a constant filtration effieicney,

(ii) how rapidly cloggL~g occurred in different water conditicns, and 4It(iii) tho sizo rango of organisms retall10d by thc net. In tests (i) and

(ii) nots nith mcsh sizos of 30, 40, 50 end 60 mpi were fishod nt five

knots until they had completely clogged, nnd the rate at which tho wator

was filtored was rccordod continuously by tho flow meter. Finnlly, in

tost (iii) 'the sane mosh sizes were usod und tho organisms escapL~g

through tho neshes were colloctod in a 100 mpi cover mounted on the roar

of the sampling tube. Uoasurements of Sagittn rotainod by, and oscaping

through these nets into tho covor were usod to estirr.ato the mean reten-

tion length in each nosh.

In tho socond serios of tests ut seu tho 20 in saopler ~as fished

in turn c.gainst a otc.ndard Scottish Gulf III and tho now Gorr.1M lTackthai,

end in theso cor.~arntiv0 hauls each pc.ir of sampIers weo towod side by

s,ido on the sarae i'iarp at an avoro.ge speed of 5 Imots. Tho Scottish Gulf

III hasn nose cono nperturo of 8 in, nas fittod with 40 nnd 60 opi monel

conical nets, nnd had ito flow netor mountcd in the 16 in diarnetor.tail

soction. The Gernan Nnckthai 0.100 had an 8 in dianeter nose cono apor-

ture, but \iCS used with two 40 mpi perlon nots,onQ of \'ihich VIaS a

stando.rd conc,nnd thc othor fittod I'lith '?- cylindrical extension piece

which incronsod its filtration area by 50 per cOnt. In this sampler the

mechanicnl flow moter was mo~~ted in tho noso cone. Ta complote tho tests,

tho Nackthc.i fittod with Cl. 60 npi nylon net, "jeD fishod C(j2inst tho Lowestoft

somplcr '1ith rm 8 in, instend of its usunl 14 in, aporture and a 60 mpi

nylon not to ansoss the cffeot of oncascmGnt on tho catoh.

2

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\

RESULTS

The caIibr~tion of the Lowestoft s~mpler in the N.P.L. flume shouod

thore w~s no nignificant differenco betnoon tho free-stream ~d freo-flow

measuremcnts for 11 rango of speeds betueen 3 end 9 ft per secend (Figure 1

and Table 1). This moens that alltho pator presented to tho opcning in

tho nose cono in accopted by tho sampling tube. . When. 0. 60 mpi net in

fittod, the saffipler has an opon eron r~tio (R) of 6.73 (Trantor 1969)nnd enIy 83 per cent of tho nntcr presontod to tho nose cono is nccepted

by tho not. Tho vo.luo of 83 per cont is Bridgor I s oxprGssion of offj.cioncy

and is cc.Iculntod from floVJ rD..to VJith not.;. floVi rnte \'1ithout net x 100 =E

end in this case is oquivelont to F in curront terminology (Tranter 1969).In thc cloc.n nator of tho flume this is 0. maximum ~.luo whichwould bo

reducod progrossivo~ by clogging cf tho moshes in tho soa.

Thc filtration and clogging rntos were studiod at sea using tho

30 in sc.mplor fittod nith an eloctronic flon motor. Thoso studios showod

that a not may filtor at 0. constant but roduced officionoyfor.somo timo

bofore clogSing complotoly. ClogginC dopends on throo factors, (i) the

mosh 8izo, (U) tho ratio R and (Hi) tho· amount of pla.nkton in tho rJater.

Ono sorios of tests with nots of difforent mosh sizcs is illustro.tod

(Figuro 2) and showod tha.t oaoh mosh sizo filtorod at a difforont and

constant rato for vo.ryine poriods of timo, boforo clogging rnpidly

rcducou. the flo,"J to zero. Tho sto.ndo.rd 60 mpi not uscd in this tost had

a vo.luo of R =.6.03 and filtorod nt 0. constnnt efficicncy of 78 per cent

for 10 Plinuton, r.ftor i"Jhich thG flo\'3 re,to decreascd rnpidly cmd tho not .cIoggad

complotoly i"lithin thc nO.xt 4 minutos fishing. Othor noto with lnrgor

Boshes or incronsed D.r.l0untS of notting filtered for longor periods at

tho So.m0 or higher officioncios~ thus tho 40 mpi not nith R = 5.85filtorod nt 90 per cent officiency for 20 minutos and tha 30 mpi not

uith R = 4.1 wns ntill filtoring nt 90 par cent efficioncy after

40 minutes.

In the compc.rativo hauls betwoon the throo sanplors whioh wore of

10-14 13inUtcs duration, all had R vo.luos in excoss of 6.03 and uould

thoreforo bo GA~octod to filter ~t constant rates during oach test run.

CloBt~ing only oocurrod on one sorios of ho.uls botVJoen tho l1ackthai nnd

tho LowostoftsQr.1plor (TabIo 2) w110n riD.tor \1ith a high phytoplankton

population "m.a doliboratoly sought to tost tho cfficiency of tho Hackthai

Viith 0.11 onlargod net (R = 24.71). In this Gorios of lmuls only the

Lowosto~ snnplorshonod signs of sevoro clogging.

The mean catches of organisms frorn tho comparativo hauls are listod

(Table 3 and 4) nnd aro also oxprossod as 0. porcont~gc of tho moan catch

of tho LOTIo~toft samplor. Tho LPD.n size range ofSagitta is givon for

cach samplo, and plots of tho lonGth frequoncy distribution illustratod

(Figuro 3). Sasitta was tho only largecrganism COl:J[;10n to both serios

of tosts and is.usod to sho~ mosh soloction in tho absonco of suitablo

fish larvae.

Tho two sorios of hauls with tho Scottish Gulf 111 saDplcr were

:.,carried out in tho southorn Uorth Soa in llarch 1968 nnd containod only

plaico oggs and larvno and S~itta in significant numbors. Th~rc TIns vory

littlo difforonco botTIoon thocatchos in oithor sorios and cyan tho

Sagitta lw.d vory sinilar length distributions (Tnblo 3 nnd Figure 3).

Tho cor::rparativo hauls bctvloon tho !bckthai nnd the Lowostoft sarilpler

were carriod out in tho southern Rorth Sen in June 1969 and bad a mOl'O

variod catch. In tho throo series of hauls tho IJackthai caUßht moro fish

oggs ranging froD109 to 127 per cent of tho Lowostoft catch, but tho

reverse was truo for fish larvao whoro tho rnnge was from 31-72 per cont

of the LO'flOStoft co.tch. Sngitta C3.tchos varied, boineS aloost equal in

nur;lbors in tho first series but in the second c.nd third series thoy wore

Doro abundant in tho Lowostoft sampIer. Tho size range of Sagitta also

vßl'i~d, tho longth distributions Vloro tho sanG whon 60 mpi nats wore used

in both sarJplarn, but tho hO r:.pi not in tho Ibckthai caught a lßrgcr sizo

range than the 60 mpi not in the Lo\~ostoft sc::.mpler (Table 4 and Figura 3).

Tho Dosh solection oA~crimont sunmnrizod in Tablo 5 ~as cnrriod out

in tho nar.1O plo.nkton pntch in 1969 and ahovJOdthat numGrical cc::.tch end.

size rangoof Sngitta vo.ried \'Iith the Dosh sizo usod. Tho lcngth fro­

qucncy distributions illustrated (Figurc4 end To.blo 6) show tho nizo

ro.ngo rotainod by tho different Doshos nnd tho siZQ range lost through

tho L1Gshus. A noloction curvo for onc11 not 11o.s boon constructod fror1

thc nunbors of Sr1ßitta in oach I:lillinotro group rotainod by tho Dain net

oxprossod o.n aporcontago of the totnl numbors rotainod in eo.ch nilli­

motrG group in tho ra~in not nnd thc covor (Figuro 5) o.nd tho moan rotGntion

IGl1ßth for o<:1.ch not can thon bo roo.d frof.1 tho curvcs. ThoGe VIHI vnry

with difforent populntions out in tho series illustratod, tho rotention

lcngtl1 ia Ghown to inareaso Ylith I:lOsh size fron 6.0 J:lIl1 in tho 60 I:1pi net

to 13.5 mr.1 in. tho·30 mpi not. Tho criticnl. size govorning tl!o roleaso of

4

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•

olongato organisos such as Sagitta (or fish lnrvao) through tho moshes

YJould bc thc raaxinum girth, and this can bo more conveniontly cxprcssod

in teros of a mcasuremcnt of n~~imun diameter. The relationship betwocn

ooan longth and Dünn diameter of S~gitta caught in these samplos in sho\7.n

to bo linear (Figure 6) nnd by interpolation a mean diameter cnn bo calcu­

lated for each mann retention longth. rlhonthic monn retenticn diameter

is plott'3d nßoü11st tho dingonnl of mesh' a linear rolationship SllOUld rasul t

as shownin tho graph (Figure 7).

DISCUSSIOlJ }JJD COlTCLUSIOITS

The rosults cf tho calibration of thc LODestoft 20 in plankton sar.~lor

in a flW:1O clonrly ohowod thnt thc tube ncceptod 0.11 tho v,'o.tor prcsentcd

at thc nose cono aporturo, but timt Cl. stondard 60 mpi not roducod this flow

to 83 per cont in clean VIa. tor. Tho motor usod to DOo.sure tho flOlll through

• tho noso cone:: lw.d bl2.dos cqua.l in dio.raotor to thc cross sectional area of

tho aporturo, end thus ga.vo an accurato measure of the wntor entoring

tho sat~ling tube with nnd without tho not. It is tho mcasuro offlow

ontorL'lJ.g thrcueh tho noso cone ,vhich is requirod to ostmato accuratoly

tho truo filtra.tion of thG encloood not nnd so tho true donsity.of nni­

mals cont~inod thorein.

•

Similnr flo\'1 motors noasuring tho total flo\'1 into the l?-0t (Unckthai)

or tho dischargo fron thc not (Culf lIlA) shc"led th~t bath these saoplcrs

3ccoptod :Loss w3tcr than tho Lowostcft 20 in s<:>..mplor fittod VJith n 14 in

naso cono, Gxcopt during sovoro ologging.

Tho tests doscribod showod that tho Gulf IIIA, and thc Eackthni and"

Lowostoft samplors with 8 in nase ceno nporturos and 60 mpi nots nIl fil­

tor at oll1ilar conotnnt Qnd high officioncies (TabIo 2) confirning

Bridgor1s o~lior findings (nridger 1956). Tho Lcwootoft samplor with

a 14 in noso cono aporturo c.ccopts tao much w~tor ~nd is not Guitnblo fcr

prolongod hnulo or uso in donse pl~nkton. This ncans that the difforonces

in tho cntches of fish l~rvao and S~gitta,in tho Inst two sorios of hnuls,

betvJOün the LOVlostoft samplor cmd tho Unckthai nro renl. Thio ma.y be

simply nttributod to tho 1000 of omallor fish la.rvo.o nnd Sagittn through

thc l~rgor moshes of tho 40 mpi porlon not uscd in thc Nackthai. Thora

was no significant difforencc botwoon tho nuobors or tho oizo rango cf

organisms taken in thc first serics whorü both samplors were fitted with

8 in nose conos nnd 60 mpi nylon nato. In both sorios of hauls with tho

5

J

Gulf lIlA samplor thora was no significant diffcronco bctwoon tho nwnbers

and sizo r~1go of orgnnisms caught cven though more wator was strainod

by tl~ Lowostoft samplcr at lo~or officiencies.

It 'ilould seom desirable thereforo·to uso c. 60 mpi nylon plankton

not to be cortain of sampling the prolarvc.e af fish adequatoly. The size

cf the nase cone nay only affect tho catch in very dense plankton patches

where clogging might roducc the efficiency to an unacceptably low level

beforo the Imul is complotod. This VJould of course result in an under­

cstimG.te :in the cntch und may be overcomo by ch~ging tho naso cone to

one TIith a snallor aperture.

REFERb1:TCES

BEVERTON, R. J. H. and TUNGATE , D. S., 1961. A mult i-purpose plankton

sanplcr. J. Cons. int. Explor. ~Icr, 21, No. 2, 145-151.

BRIDGER, J. P., 1956. On efficiency tests mado with a Dodified.Oulf 111

high-speed tow not. J. Cons. int. Dxplor. Mor, 23, 351-365.

GEHRI1TGER, J. ;!., 1952. An all metal plankton sampler, Spoc. Scient.

Rep. U.S. Fish Wildle Serv., Fisheries No. 88, 7-12.

lT.GLLTII,.W. r.::cl H!}'PLL, G" V:Jrsuc~:.::l. ~ur Fangigkeit dos 'Hai' und des

modifizierten Gulf-V-Plankton-Snh~lers INackthai'. (In press).

TRANTER, D. J. (editor) 1969. Zooplankton sar:~ling mcthods m'~sco

llonographs on Oceanographic mothodology 2.

TbUUJTER, D. J. und HERON, A. C., 1965. Filtration chnrc.cteristics of

Clarke Bu.r:lpuS Plcmkton Sm;lplors.

6

•

•

,Table 1 Calibration data for the 20-inch Lowestoft sampIer

in the N.P.L. flume

FlUItle' . . Cmlsecsetting

• 3

44.22

56

...~ ".... ,' 6;'33 ..··· .._ " ..

7~" .. "" ".~ " _.. , ~.'

8............ ' '8.44

9.12

84.95

113.03 .

119.23

141.20

169.38"178.68 .

197·56

225.73

238.13'

257.25

•Regression equations

Free flow

Free stream :

SampIer with60 mpi net

~ c rcvolu~ion per second

y = 0.1935x + 0.0556

. y = 0.2048x - 0.0127

.. y = 0.1834x - 0.1284

x = flume setting

Table 2 Filtration efficiency and calculated volumes fil tered

(a) Gulf lIlA vs Lowestoft 20-inch fibreglass plankton sampler

Series Station Gulf IIIA Lowcstoft"20-inch

EfficienC\y(%)

Cubicmetref?

Efficiency(%)

Cubicmetres

14-inch nose cone and60 mpi net

61. 758 8055.260 7552~687 ·7751. 736 76

..55.)15. . . 76: _..

1 102103104105106

8-inch nose cone and40 mpi net

10098989696 .

150.572128.508125.906124.412133.019

.. Mean . 97.6, .._" ••.• _' ....~.~__•.• , •. _ • hr"-'~.·_· ... _. - .•.. , '" ...

55.351 76.8

2

8-inch nose cone and 14-inch nose cone and60 .1?Pi net " .... "..- . 60 mpi. net:

107 90 50.696 69 118.224 •108 90 45.955 76 117.565109 92 38.811 70 89.946110 90 55.972 68 127.606111 80 51.937 66 118.211------- ---------- ------ ---------- -------Mean 88.4 48.674 70 114.310

(b) German Nackthai vs Lowestoft 20-inch fibreglass plankton sampler

Series qto.tion Nackthai LOWQstoft 20-inch

Cubicmetres

Efficienny(10)--_ _---

Efficioncy(%)

.......- .;.. - ..........•...............-.-

Cubicmetres

8-inch nose cone and60 mpi net

8-inch.nose cone and.... "60"riiprriet"~'

1 49, 49A.

.49B49C49D

Mean

98.381.472.488.491.6

66.36355.29849.18t1.60.20367.031

59.616

97·791.9

:87.687.991.4

91.3

65.95862.43159.51063.20866.885

63.598

•8-inch nose cone und40 mpi not

14-inch nose cone and60 mpi net

2 6364656667

Mean

90.189.190.992.092.5

90.9

56.63457. 28758.29161.40959.317

58.588

77.273·973·975.876.8

75.52

145.908143·499145.764151.192148·737

147.020

Table 2 (continued)

(b) German Nackthai vs Lowestoft 20-inch fibreglass plankton sampIer (cont.)

•

•

Series

3

Station

7576

. ·777879

Mean

Nackthai Lowcstoft 20-inch

Efficiency Cubic Eff;iciency Cubic.. (%) metres (%y metres

8-inch nose cone and 14~inch nose cone and40 mpi net : 60 'mpi net

90.5 53.120 72.3 144.08695.6 68.745 34.2 74·27390.1 62.504 . 23.6 49·44493.4 61.395 28.6 56.77792.5 64.169 29·9 62.643

---------- ------ ---------- -------92.4 61.987 37.'7 77·445

,.......

Table 3 Aberdeen Gulf lIlA vs Lowestoft 20-inch fibreglass planktoni

sampl~r

Series 1 %cf Ser1es 2 %cfLt 20-inch Lt 20-inch~

Gulf IrIA Lt 20-inch Gulr IIIA Lt 20-inch

Filter material Monel Nylon Monel NylonMesh 40 60 60 ·60Mesh size (microns) 420 270 ? 270Nosecone aperture 8-inch 14-inch 8-iJ;lch 14-inchMean %filtration efficiency 97.6 76.0 90.0 70.0Mean volume strained (m3) 55.35 132.48 41.8 48.67 114.31 ;42.6Mean numbers/1 000 m3

Pleuronectes platessa ova 1 358 1 483 91.6 1 360 1 470 92.5Pleuronectes platessa larvae 15 26 57.7 52 61 85.2Clupeid larvae 0 2 0.0 :4 5 80.0Sagitta sp. 955 1 087 87.7 2501 2 331 107.3

(mm)i

Mean length of Sagitta 9.13 9.24 8.,6 8.94Standard deviation 2.64 2.74 3·tO 3.89

•

Table 4 CORELLA cruise 10/69. Nackthai va Lawcstoft 20-inch fibregluss plankton samplor. Numbera carrected far ef!iciencyand expressed as numbers per 1 000 m3 cf water filtered

....... - . .. . - Series 1 ... - .... Nackthai- ., "Series'2 . ... ~ . _.... "-Nackthai'" " SeriesJ' ......... Nackthaias %cf as %af as %cf

Nackthai Lt Lt Nackthai Lt Lt Nackthai Lt Lt

Filter material Nylon Nylon Nylon Nylon Nylon NylonMesh 60 60 40 60 40 60Mesh size (microns) ..... 270 270 363 270 363 270Nasecone aperture 8-inch 8-inch 8-inch 14-inch 8-inch 14-inchMean %filtration efficiency' 86.5 91.3 90.9 75·5 . 92.4 37.7Mean volume strained 59.•_61 .5 63.598 93.7 58.587 147·02 39.8 61.986 77.444 80.0

. .,-----------------------------------------------------------------------------------------------------------------------Ova , .",.......

"

Caramc trachurus .; 50 62 80.6 24 9 266.0 6 60 10.0Clupea snrattus 6 063 5817 104.2 0 2 0.0 2 362 1 810 130.5~ merlan.gus 411 226 181.8 154 111 .138.7 321 539 59.6Litlanda limanda 1 209 1 100 109.9 306 214 142.9 1 440 567 254.0Rhombus maximus 66 94 70.2 85 59 144.1 138 97 142.3Scomber scombrus 557 319 174.6 2 786 2 253 123.7 1 951 2 232 87.4Other fish ova 44 71 61.8 62 44 140.9 211 264 79.9--------------------------- -------- ------ -------- -------- ------- -------- -------- ------- --------

8 400 7 689 109.2 3 417 2 692 126.9 6 429 . 5 569 115.4. . .-----------------------------------------------------------------------------------------------------------------------Larvae

Clupea sprattus 3 086 4 548 67.9 274 308 89.0 683 2 060 33.2Gadus merlangus 259 271 95.6 1 051 1 385 75.9 411 893 46.0Limanda limanda '. 1 781 1 761 101.1 898 . 1 310 68.6 1 272 4 761 26.7---

668other fish larvae 114 17 .1 97 541 17.9 77 199 38.7----------------------------" ,. . ." ._------- -------, ._------- -------_. -----_ .. --------- -------- . "------- --------

' .. 5 240 7 248 "'72.3 2 320 3 544 . 65.5 2 443 7 873 31.0

Sagitta sp.Mean length cf SaRitta (mm)Standard deviation

6 80712.223.46

5 521 123.311.543.79

12 46612.743.39

25 2139.523.30

49.4 15 35810.631.75

21 8659.292.07

Table 5 - CORELLA- cruisc-10/69. Sagitta - mesh selection experiment

Filter material Nylon Nylon Nylon Nylon Nylon-- --- Nominal mesh size (mpi) 60 60 50 40 30

_._.- _.. _- -·Manufacturer' s number 62 GGN 62 GGN 56 GGN 44 GGN 34 GGN_...... ~ . ~

Manufacturer's aperture size (p) 275 275 308 414 563%open area 46 46 47 46 50

. Measured warp/weft diameter· (r) 122 122 131 240 230Measured apcrture used net (~ . 283 283 304 380 .- 570Measured diagonal used net Ü,) 390 390 425 575 800

--- --- Internal circumference of mesh 1 132 1 132 1 216 1 520 2 280(open area) (~)

Mean length of Sagitta in main 12.07 10.32 10.95 11.93 13.78.~ ...._.. . " -net (mm)

_.- - Standard deviation 3.91 3.22 3.15 3.09 4.25Median length of Sagitta in 11.6 10.7 10.2 11.5 12.0

main net (mm)Median length of Sagi tta in -- 5.7 8.5 6.7 10.4 11.2

cover (mm)50 per cent retention length 6.5 3.8 7.6 8.8 - 14.0

of Sagitta (rnm)

Equivalent diameter (J.!.) 460 270 530 610 980

-Calculated.·circumference 445 --·848 - 1 665 -·---1 917 - 3 079

%Sagitta retained - - . - 80 -97·· 93 14 45-

~ . .- . . .

Table 4 CORELLA cruise 10/69. Nackthai vs Lowcstoft 20-inch fibreglass plankton samplcr. Numbers corrected for ef!iciencyand expressed as numbers per 1 000 m3 of water filtered

-,-" Series 1

Uackthai Lt

- Nackthai­as %ofLt

Series 2 - '-Nackthai-. as %of

Nackthai Lt Lt

Series"3

Nackthai Lt

Nackthaias %ofLt

80.0

Nylon60

27014-inch

'37.777.444

Nylon40

3638-inch92.461-.98639.8

Nylon60

27014-inch75·5

147·02

Nylon40

3638-inch90.958.58793.7

Nylon60

2708-inch91.363.598

Nylon60

2708-inch

"86.5.5~.~.§15 . -'-----------------------------------------------------------------------------------------------------------------------

Filter materialMe6hMesh size (microns)Nosecone apertureMean %filtrationefficiencyMean volume strained

Ova

Caranx trachurus' 50 62 80.6 24 9 266.0 6 60 10.0Clupea sprattuß 6 063 5817 104·2 0 2 0.0 2 362 1 810 130.5Gadus merlangus 411 226 181.8 154 111 138.7 321 539 59.6Limanda limanda 1 209 1 100 109.9 306 214 142.9 1 440 567 254.0Rhombus maximus 66 94 70.2 85 59 144.1 138 97 142.3Scomber scombrus 557 319 174.6 2 786 2 253 123.7 1 951 2.232 87.4Other fioh ova 44 - 71 61.8 62 44 140.9 211 264 79·9--------------------------- -------- ------ -------- -------- ------- -------- -------- ------- --------

8 400 7 689 109.2 3 417 2 692 126.9 6 429 5 569 115.4

Larvae

Clupea sprattuo 3·086 4 548 67.9 274 308 89·0 683 2 060 33.2Gadus merlangus 259 271 95.6 1 051 1 385 75.9 411 893 46.0Limanda limanda 1 781 1 761 101.1 898 1 310 68.6 1 272 4 761 26.7Other fish larvae 114 668 17 .1 97 541 17·9 77 199 38.7---------------------~--~--- ._------- . . _----- -------- .. -------- ------- -------- -------- ------- --------

-5 240 7 248 -72.3 2 320 3 544 65.5 2 443 7 873 31.0-----------------------------------------------------------------------------------------------------------------------Sagitta sp.Mean length of SaRitta (mm)

. Standard deviation

6 80712.223.46

5 521 123.311.543.79

12 46612.743.39

25 2139.523.30

49·4 15 35810.63

1. 75

21 8659.292.07

70.2

Table 5 CORELLA cruisc 10/69. Sagitta - mesh selection experiment

74'" .... ' 45

Filter material.. Nominal mesh sizc (mpi)... Manufacturer Is number

"Manufacturer Isaperture size (l!)%open area

Measured warp/weft diameter (~)Measured aperture.used net (p)

. Measured diagonal used net (!c.:). Internal circumference of mesh.. (open area) (I-!-)

. Mean length of Sagitta in main......... net (mm)

Standard deviationMedian length of Sagitta in

main net (mm)Median length of Sagitta in

cover (mm)50 per cent retention length

cf Sagitta (mm)

Equivalent diameter (~)

..... Calculated.circumference .

%Sagitta retained·

Nylon60

62 GGN275

46

122283390

1 132

12.07

3·9111.6

5.7 .

6.5

460

.. 1 445'"

80·

Nylon60

62 GGN275

46

122283390

1 132

10.32

, 3.2210.7

8.5

3.8

270

-848 .

Nylon50

56 GGN308

47

131 .304425.

1 216

10.95·

3.15 .10.2

6.7

7.6

530

1 665'

'93

Nylon40

44 GGN414

46

240380575

1 520

11.93

3.0911.5

. 10.4'

8.8

610

1 917'

Nylon30

34 GGN56350

230570800

2 280

13.78

4.2512.0

11.2

980 :

3 079'

. ,,

Flg. I. Calibration Curvcs For 'hf Lowestoft 20"

Flbre Glass Samplu With A 14" Nosecone

c Fr«:«: St re amo Fru Flow (Sampler Without Nd)x Sampleto With 60 mpi (270 mlc) Mesh

.~

1IlN

lI')N

11)...oc~

I/l

u

"CI)

..........eu

98765

X : Flume Setting

432

.,>-

11)

co

-o

....J

o0°5 ~

er:

•

3000 CLOGG ING EX·PC:RIM.ENT FREE OW

60 HPI

_.-A-.....- 40HPI

60MPI EHl"RGED HEl

{> 0 11 PIST" ND" Il. 0 NE T

2000

Flowm(t~r

Rfvolut Ions

1000

10 20 30 40"'---'---.------11----- --L ..L 1

"

•

I

Duratlon Of Haul In MlnuUs

Gulf mA V Lowutoft 20"

r-------

20

SUIClS I.

SAGITTA 0/0'/t Fro", Movmg AVfroge M3

Lowutoft •• • 14" N.C, 60,Net

Gulf mA _ 8" NC 40Net

•

10

~ - wo wo

20

10

Serlcs 2, Low 14" NC 60 Net

G ulf 8" N C 60 Net

10

20

10

Geormon Nachthai V

SCrt~S I,

..... -., ..., ..5~rl~s 2. -,' ' ...., "-, ..,,.,,,

".-

Lowutoft 20"

Low • • S"NC 60 Net

Nachthai~ 8" NC 60 Net

Low 14'"N C 60 NetNachthai 8" NC 40 Net

•Low 14" NC 60 Nd

Nachthai 8" Ne 40 Nd

20

10

.I

II

I.,,,I

",.'--5 10 15 20

100

F.g. 5_

so

Sclcction Curvcs ForFor Dlffncnl Muh

SAGITTA spptlZCS • 30 mpi Nct

100 mp' Covcr

•

•• • •

•

so mpi ·Nft

100 mpi Cover

60 mpi Net

100 I'Ilpi Cover

•• •

o

10

50

/mm

100 0

• •"

5 10

o 50

3-3 mm

5

mm

Lcn 9th10

in. Millim~t~rs

15

60 mpi N

100 I'Ilpi Cour

20

O'S

•

•

SAGITTA LENGTH V .DIAMETER

•

D iamctcrIn

MM

Lcngth in M M

F.g.7.

RETENTION OF SAGITTA SV DIFFERENT MESH SIZES

20

1000 M,erons

800

600

Mcan Diameter

400

. .200

Dla·gonal Mcsh' Snc in M lerons400 5 0