International Council for the of thc Sea · ' '\ , C.M. 1910jH:4 Pelagic Fish (Northern) Committee Reuort on the of Herring Larvae in North Sea und Adjacent Waters in 1969/70 by R. J. llood X ) The international herrinff larval ourvoys which were otarted in 1961 wero continucd durins thc autumn and winter of 1969/10 with a total of six countrios Tho countrieo und their rcspective research vessols were England - EVo "Corella ll a..'"ld IlClione", Germany - RV "Anton Dohm", Netherlands - RVs "Tridens" end "i'!illom J3eukeloz", Norway - RV "G.O. Sars", Sweden - RV "Thetis", and Scotland - R70 "Scotia" and "Clupea". Details of the sampling goar used, i ts operation and the ourvey axeas have alrcady boen described in oarlier roports by Saville (196S) and J3oötiuo (1969). The areao which \'lore ourveyed during 1969/10 were again oimilax to t.hoce uhich \,rore coverod in the previous two ycars and they included the north-weotern end western-contral North Sea betwecn latitudes 53 0 30 l N and 61 0 12'N, tho Jutland the Kattegat from 56°0S I N to 51°52 1 N and the southern Uorth Sen. und em:torn Channel between 49 0 30 l N and 53°30 I N. The first survey 3rd September 1969 and the last was completed 15th Januar,y 1910. Tho rosulto of all the surveys have again been presonted here, 0.0 in earlier yoaro, 0.3 the calculn.tod numbors of herring larvae beneath one'square metre of curface at each of the stationo worked. They are shown in three size groups, 1.0. leoo than 10 mm., from. 10-15 mm and greator than 15 mm. vJhere more than one haul wao made at particular station position only the highest number of herring larvae caught in any single haul has been plotted on the accompanying oharts. In order "to clearly both the total area of herring larval distribution and also the centres of donsity of these charts only contours at lcvelo of 1 and 25 larvae per oquare metre have boen drawn in. However, for the actual calculation of the larval abundance eotimates, which are diocusoed in the concluding section of thio report, only laree-scale charts of eithor 1 or 1 have 1,000,000 1,250,000 been used, and these were contoured and planimetered at appropriate levels of densit;r. Irorth-1leoto:!:n lTorth Sen. \-ras carriod out in the north-weotern' North Sea botween 4th-16th September 1969 by English end Scottish research vessols working both to the oast and wont of thc Orkney and Shotland Inlandn and aLoo off tho north-enst coast of Scotlnnd. The diot:dbutions of horrinß' larvao in this region durinß' the period are shmffi noparately for the three size ß'roups in Figures 1-3. It will be seen at thio time hiß'h densitieo of recently hatched herring larvae less than 10 mm in le!lB'th were confined to thc area situated within an arc from south-west to nor-:;h--caot of \'1i th denoi tieo excoedi!lß' 100 larvae per square metre at a nunber of t.hc highcot being 351 per square metre to the north of Thc dietribution of herring larvaa- largor than 10 mm. wae 80mewhat more eÄtcnoiyo ui emaIl n':1mboro 0.100 occurring at the stations worked up tho wootern nidc of Shotland and round to thc north-east of the islands. Some of thc larger laT.VD.e 0.100 found to thc eaot of Orkney and in the Moray Firth off Clytlmoss. uensitiec aoongot thc larger larvae were 226 per square metre for those 10..15 mm in lC'ngth and 36 per square metre for those larger than 15 mm, '00":;11 ::011.!l.d at positions to the south-west of Orkney. Tbe contours for all three g:::-ouJ;>::: of h'JrrinG larvae \'lere not cOIDplete1y closed along the western eide of. ::n=vey aran. du:t'in.ß' the period 4th-16th September 1969 and the ful1· extent of .. the larval concontration to the \'leet of Orkney and Shetland at this time could ::lot bo determined. Numbero of herring 1arvae of all sizes were insignificant eloenlhcre in the reffion. X)Pish'Jries Laboratory, Lo...;estoft, Suffolk. Engle..nd.
Transcript
International Council for theEx?loratio~ of thc Sea
·''\,C.M. 1910jH:4
Pelagic Fish (Northern) Committee
Reuort on the of Herring Larvae in
~pe North Sea und Adjacent Waters in 1969/70
by
R. J. lloodX)
The international herrinff larval ourvoys which were otarted in 1961 werocontinucd durins thc autumn and winter of 1969/10 with a total of six countrios~articipatincr. Tho countrieo und their rcspective research vessols were England- EVo "Corellall a..'"ld IlClione", Germany - RV "Anton Dohm", Netherlands - RVs "Tridens"end "i'!illom J3eukeloz", Norway - RV "G.O. Sars", Sweden - RV "Thetis", and Scotland R70 "Scotia" and "Clupea". Details of the sampling goar used, i ts operation andthe ourvey axeas have alrcady boen described in oarlier roports by Saville (196S)and J3oötiuo (1969). The areao which \'lore ourveyed during 1969/10 were againoimilax to t.hoce uhich \,rore coverod in the previous two ycars and they includedthe north-weotern end western-contral North Sea betwecn latitudes 530 30 l N and61012'N, tho Jutland J3ar.L~, the Kattegat from 56°0S IN to 51°52 1N and the southernUorth Sen. und em:torn Channel between 490 30 lN and 53°30 IN. The first surveyco~~enced 3rd September 1969 and the last was completed 15th Januar,y 1910.
Tho rosulto of all the surveys have again been presonted here, 0.0 in earlieryoaro, 0.3 the calculn.tod numbors of herring larvae beneath one'square metre ofcurface at each of the stationo worked. They are shown in three size groups, 1.0.leoo than 10 mm., from. 10-15 mm and greator than 15 mm. vJhere more than one haulwao made at a..~r particular station position only the highest number of herringlarvae caught in any single haul has been plotted on the accompanying oharts.In order "to cho~., clearly both the total area of herring larval distribution andalso the centres of donsity of these charts only contours at lcvelo of 1 and 25larvae per oquare metre have boen drawn in. However, for the actual calculationof the larval abundance eotimates, which are diocusoed in the concluding sectionof thio report, only laree-scale charts of eithor 1 or 1 have
1,000,000 1,250,000been used, and these were contoured and planimetered at appropriate levels ofdensit;r.
Irorth-1leoto:!:n lTorth Sen.
S~:plinß' \-ras carriod out in the north-weotern' North Sea botween 4th-16thSeptember 1969 by English end Scottish research vessols working both to the oastand wont of thc Orkney and Shotland Inlandn and aLoo off tho north-enst coast ofScotlnnd. The diot:dbutions of horrinß' larvao in this region durinß' the periodare shmffi noparately for the three size ß'roups in Figures 1-3. It will be seenth~t at thio time hiß'h densitieo of recently hatched herring larvae less than10 mm in le!lB'th were confined to thc area situated within an arc from south-westto nor-:;h--caot of Or~mey, \'1ith denoitieo excoedi!lß' 100 larvae per square metre ata nunber of positio~3, t.hc highcot being 351 per square metre to the north ofC:'.:'~::noy. Thc dietribution of herring larvaa- largor than 10 mm. wae 80mewhat moreeÄtcnoiyo uit~l emaIl n':1mboro 0.100 occurring at the stations worked up tho wooternnidc of Shotland and round to thc north-east of the islands. Some of thc largerlaT.VD.e w~re 0.100 found to thc eaot of Orkney and in the Moray Firth off Clytlmoss.~~e ~ig~90t uensitiec aoongot thc larger larvae were 226 per square metre for thosete-i;:!cc~ 10..15 mm in lC'ngth and 36 per square metre for those larger than 15 mm,'00":;11 ::011.!l.d at positions to the south-west of Orkney. Tbe contours for all threeoi~c g:::-ouJ;>::: of h'JrrinG larvae \'lere not cOIDplete1y closed along the western eideof. t~e ::n=vey aran. du:t'in.ß' the period 4th-16th September 1969 and the ful1· extentof ..the larval concontration to the \'leet of Orkney and Shetland at this time could::lot bo determined. Numbero of herring 1arvae of all sizes were insignificanteloenlhcre in the reffion.
Part of thc north-weatcrn rcgion 1'lac rcoampled froIJ leth September - 4thOetober 1969 by English, Seottioh und Gor.uan renoareh vosDole ~~t this tinostationc werG eonfinod to tho oaat of tbD Orlaloy und Shotl~1 Inlands anuSeottioh mainland. Thc distributiono of hcrring larvao durinG tr~c neeondporiod aro shown in Figuree 4-6. The stations ,·rhieh wore ,.,.or:ccd to tho castof Orlmcy by the RV tlJmton Dohrn" on 21nt-22nd Soptenbor are chov,'Il oopa.::atelyon a largo-eealo ehart (Fie;ureo 7-9) boec.uoo nest of then ilore very eloDetogother. Owing to the nature of the distribution of theoe otc.tions on1 thofaet that they ,.,.ere 'lorked in un area eovered s~rsto:':latieallyby the R7 "Sootic::ourvey, thoy have not bcen used in thc final ealeulation of total larval nb~Q~ccdealt with in thl) eoneluding seetion of thia report. I·I; "laD hmlovor, firoJ.;aocortainod that thoir oxelusion would not oiGDifieantly affeet the larvalootimatos arrived at for the period. During thio oeeond poriod fnirly lowdeneities of rcecntly h'J.tchcd herring la-ryac less than 10 m::il in longth ,..c:::efound to tho eaot of both Orlmoy and Shotland, tho maximu.-n dcnoity at c-votation boing only 61 lCl,rvao per oquaro notro. La.rgor horrin&, 10X'Tac ,:eroconfinod to tho oamo localitioo and dcnoitios \'Toro aloe lou, tho oflXimU!:l nunbcrboing 29 per cq,uaro I:lotro ::or larvao bot,·;een 10-15 tl!l in lenGt!! a..'"ld 14 !lcr ct:.v.nrcDetre for larvn.o largor than 15 mn.
To oUIrrIln.riso, in tho north-weoto::n Horth Soa during tho firot half ofSoptombor 1969 mn.jor concontrations of horring larvao wero only loeated in thcaroa to tho woot of tho Orlmey a..'"ld Shetland Is1ands. Durin{! tho seeond half ofSeptembcr, up to and ine1uding 4th Oetobor 1969, far losn donne concent:::ation3were found to the east of both Orlmoy and Shotland. Uo signifieant eoneon·~=at5.ono
of herring larvae were locatod elsewhcre, but, becauDe no sru:npling vlas carr5-ecl outto tho west of Orlmey and Shetlund during the soeond period, it is an open questio::lao to whothor tho oa.in contre of herring larval diotribution was otill oiJ.;uc.todthora at that time, as wac the eano in both 1967 and 1968. It is a fact hm-loverthat herring larvae appcarcd to be abundant a few mi1es to thc north-wost 0:: rc.ir~
lsle during thc night of Oetobor 4th~5th when vertical diotributicn oDIDpling 'l~n
carriod out there by RV "Coro11a". Unfortunate1y it uas impo:::oiblo to eonycrttho numbero caught in tho vertical distribution hau1s to nUl1boro benoath C:JC o~:u.o:co
metro of surfaco.
lt wou1d soem to be of considerable importance to obtain sampIes, cortainlyto tho wont of Orknoy, during DI1Y futaro horring larval surveys earried out in tlüoregion in 1ato Soptember und October. It must be of ncme conce~ that in the nor~h
westom region durinß' tho autur:m of 1969 tho overall extont of tho aron. in ,,!hiehhorring larvao ,.,oro found to tho eaot of tho Orlmey and Shetland Islands c.ßOinshowod a roduetion for the socond yoar in succession.
Centra1 North Soa
During tho poriod 3rd-25th September 1969 a very good eovorage of tho westompart of the central North Sea vTas obtained by Duteh, Gormnn and Scottinh rooearchvom::c1s working betwoen latitudos 53°30 1U and the northorn boundury of the region(Le. 57°30'U), tho area off the Scottish cast eoast bcing particu1nr1y \1011covered by both tbo Gorman and Seottioh veeselo. Tbo dintributions of herrir~
1arvao in this reffion durine thc period aro chmm for tho throo size eroups inFigures 10-12. Dctuoen 9th-11th September s~a11 nm1bers of rocently hatchedherring 1arvae ' ....ero found to the eant of 'Vlhitby at a total of four stationo buttho highost density at that time was only 14 1arvao per squaro cotro for thoso1ess thnn 10 !lJTIl in length nnd four :per oqu~e I:letro for larvao botwoen 10-15 I:"JJl.
Ovor the reID::l.index of tho vory largo aron. uhieh was surveyod bctwcen 3rd-25thSeptembor 1969 horrincr larvao were almoot conp1etoly abnent .from tho planI::toncatches although a fm'l odd individua10 "lOro eaught off tho Scottinh coaot, I:ln.inlyto the eant of tho Abordoen :SanI'.:, whoro the higheot dennity for all nizcs of1arvao wao o~r four per oquare metro.
A second o:ctonsive survoy '"as comp1oted by Duteh and Enc1ish rcnearch v8nse1~
in tho wostern part of the eentral lTorth Sen. bet"'tQon latimdeo 53°30'!T und 56 OOIU
during the period 6th-14th Oetobor 1969. The larval diotributions at this time aroshown in Figures 13-15. Small r.umbora of reeent1y hatched horrinG la--vae leso ~~10 mm in lollß'th were found in two loealitios. They ,.,rere preoe~t up to a deneity of19 larvae per oquaro metre off Scarborough nnd up to oight lo....-vao per oqun.re metreoast of the ill.vor Hutlber in tho vieinity of the Outer Dowsing Light Vensole He::::TingIn.rvae largor than 10 I::JI:l 'loro however caught in far greator nu."J.bers, up to 69 persquaro metro for 1arvao from 10-15 mm in 1ength off Jnamborough IIead nnd 20 persquare metro for 1arvao largor than 15 mm near tho Outor Dowsinc;. Those largorhcrring larvae ,,,oro distributod over a wide area extonding somo 60 mi1es fron thc
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English coaotline between approximately latitudes 5,O,O'N and 54°40 ' N. The contoursnlong the southem edge of the survey area however were not completely clooed. ll..very emaIl lmv denoity patch of herring larvae mainly from 10-15 IDI:l in length '\-TaS
also locatod betwecnllth-13th October off the lTorthumberland coast to the south ofthe Loncstone area, but the higheot density was only four larvae per square metrefor all cizcc combinod.
To o~arisc, the only nubotantial concentrationo of herrine larvae in thewcotern part of the central Uorth Sea in the autumn of 1969 were found duringSeptember-October in thc iihitby-Flcoborough-Dowsing area. It oeemo ominouo thatthere was apparently a completc abcenco of herring larval production in the areaof the H.E. Banl\: and that only conccntrationo of very minor importance were foundin the vicinity of the Abcrdcen Bank ond thc Longotonc, although it must bc addcdthat catchen of ripc hcrring (in mo.turity otaßC VI) wcrc otill beine landcd byEnglioh vennelo fiching the Lonestone grounds ac late as 9th October 1969 so thathatching of herring larvao must ctill have occurred after thc last survey endcd.In addition ·the very small numbers of horring larvae, mainly from 10-15 mm inlength, whioh were found round the weste~"Il. ond south;"western ed.eos of tho DoggerBank in Ootober nay have been derived from spawning which took place in that nreatoo.
The Jutlond Bank: ond Kobborß'EUE.d 1J:ea
Sampling here was carried out by rooearoh vesselo of No~ and Swcden betweenl6th~28th Octobor 1969. Norway surveyed the Jutlond :Bank on 16th-17th Octobor andthe Kobbergrund area frou 20th-23rd October. Swedon 0.100 curvoyed the Kobbergrundarea at this time, Le. 20th-28th October with all but four stationo beL'"lg completedbotweon 20th-24th October. San.pling was again carried out by Norway with both thcJuday and Clarke-Bumpun nets while Sweden used 0. Gulf II!. All but 0. very smallnumber of herring larvae caught during these survoys were omallor than 10 mm inlength. Uouo.lly the Clarkc-Bumpuo net gave higher numbors of larvae por squaremetro of surface than the Juday not and in the accompa.nying charts only the higheotnumber of larvae caught by eithor goar at ony otation has beon plotted. Theresecmed gonero.lly to bo good agreement betwe~n the numbers of herring larvaecalculated benoath ono square metre of curface for both tho Clarke-:Bu:opuo ondGulf III samplero4
. The results of the Norwegion and Swodish survoys during Octobor 1969 aro givenin Figuren 16 and 11. As in 1961 and 1968 no herring larvae were found over theJutland Bank but in the Kobborgrund aroa recently hatchcd herring larvao loss than10 Dm in lcngth were taken at oeveral stations in numbers excoeding 25 larvao persquare oetro, the highest being 48 per square oetro. Small numbers of herringlarvao Were prcsent at stations llorked over 0. considorable part of thc Kattegatbut unfortunatoly beoause of the way in which the southernmost stations ware spacedit wao impoooible to contour the distribution accuratcly.
To sumInarise, there were again no catches of herring larvao ovcr the JutlnndBank in tho autumn of 1969 for the third yoar in succossion, but i t is possiblethat herring larval production in the Kattegat was of approximatoly the samemagnitude as in the previouo two yoars.
Southorn North Sen and Eastorn Channel
Although i t was not originally spcoified that the spawning groundo of tho Lm\'nsstock chould bo includcd whcn the international larval surVeyc "Tere sot up, ncvertbelose the results of surveys of these grounds carried out by research vesoels of theNetherlands have becn made available for incluoion in both the previous repo-rt fo::1961 and 1968. Du::ing the l·Tinter of 1969/70 thore was a ouch botter coveragc of'tho Downs spawning areas than for 0. numbcr of yeurs and i t has been posoiblo toinclude 11ll tho results in this roport.
Rcocarch vessels ofthe Nethcrlands cnrried out two extensive surveys, thefirst in Deceober 1969 and tho second in Januo.ry 1970. In addition 0. survey W.:1:Joade by Englond during curly January 1910 covcring both the southern North Sea andeastem Channel. lrhile 0. curvey by Germany in the sane month extendod ovar parts ofthe couthern and contral Ho:rth Sea.
The dictributions of the herring larvae caught during the first survey wllic~
W3.S carried out by the RV "Tridenc" from 8th-19th December 1969 are shown in Ficrur~~
18-20 for tho three size groups. A number of additional otationo were worked ~~
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a few of the earlier ones resat:lpled bet,,,een 19th-23rd Dl3cember and these c.re shmm.soparately in Figures 21 and 22. During tho ,,,hole of tho period 8th-23rd LocemooremaIl numbers of reccntly hatched herri..'>lg larvne less thL'.n 10 r'lil in 10ngth werelocated in three general areas:-
1) . in tho Bay of the Seino, with concentrationo of up tosix larvao per square metre;
2) off Point d'1I.illy with concentrations of up to 11 larvaeper square ~etre;
3) in thc Sandetti6 area "rhere the density was only one larva.per square metre.
Very snall nurabers of hcrring larvae bet,,,een 10-15 mm in:.length were also caught inthese sa~e localities but nowhere did they exceed six larvae per square metro ~d
only 0. single larva lareer than 15 mm ",as caught during the whole of the Doccmbor::mrvey.
The second survey I:lade bet~·:cen 3rd-6th January 1970 by RV "Clione" producorlomall numbero of herring larvae at approximately half of the stations '·lOrked. Thodistributions of these larvae are sho~~ in Figures 23-25 for the three size groupo.Recently hatched herring larvae less than 10 mm in length were scattered.throUßhoutthe Southern Bight and eaotem Channel but at no point did their density exce~d
5 per square metre. The pieture was very similar for those larvae betwecn 10-15 w'~
in length and these bad a m~~ density of only 8 larvae per square metre. ~g~~n,
os during thc Dec~mbcr survey, only 0. oinglc larva larger thanY .15 mm mtS caugb:t;.
The third and most productive survey of all was made betwcen 5th-15th .TDJ'1";:::"'-:Y1970 by the RV "''!i11em Bcuke1sz". Recent1y hatched herring 1arve.e 1ess tha.l1. 10 :";1",:,.
in length were found not only in thc Sandettio area where densitieo of up to 25larvae per square metre occurrcd~ but 0.100 in the Charmel off Point d 1Ailly ".Therethe maximum density ,,,as 22 1arvae per square metre and in tho Bay of thc SC~-:lO
whcre up to 75 larvD.O por square metre were obtained. Evon higher concentra'~ion8
occurred onongst the 1arger larvae from 10-15 mm in lcngth at oevcral of thestations in the CharmeI, the highest of all being one of 200 por squaro metresome 25 mIes 1m of Point d'Ailly. The fu11 extent of the herring larval concontrationo both at Sandottio and in the Bay of the Seine could not be determinedbecauoe moot of the contours remained open in these two areas. Dxring tho wholoof this survey no herring larvao largor than 15 mm woro caught. SDlllpling ''1hichwao done during tho same period by tho RV "...mton Dohm" in the northcrn part ofthis survoy aroa and 0.100 in tho contral North Sea produced only 0. single larva Figure 28.
To summarise, for tho firot tioe in 0. nunber of yoars very approciable herringlarval production occurrod during tho winter of 1969/70 in the eastern Channel, thedcnsest concentrations being found during January 1970 in the Bay of tho Seino a.~d
off Point d1Ailly. Horring larval production of some importance also took place inthe Sandotti6 area during the SaI:lO period.
Discussion
One of tho chief objectives of the intornnt; on~l herring larval ourvuyo into obtain ootimntcs .fron yoo.r to year of the changos which are tnkL'"1g place intho size of each of tho major opnwning otocks. In Tablo 1 larval abundnncoeotimateo ara eivcn fo= the throo oize eroups of herrine larvae soparately byeither areD. or otock~ together with total production fieureo. (see page 8).
Tlle ~reoentation of the data relcting to thc area wost of Orkney and Shetlandprescnted OOI:lothing of a problem. A emaIl number of stationo 1'lerO ,·ro:rked btS" RY"Sootiall during the firot half of Septomber 1969 to tho west of longitudo 4 '.....Ogtin ICES Region VIa nnd at thene otationo high dcnoitieo~ particularly o.f =eccntlybatched herrin/! larvae, "TOre obtained. There are good reanons for not inclu1L'"l.ethese horring l~vao i~ production ontimato9 with those found closor to Orlcncy inICES Region VIa. Thc autUI:l.~ spa,ming g.round off Capo llrath hao been "rell Y.nmmror many yearo (o.s. Clark 1933) and the herring which spawn thore ~y ~ell beassociated more OloDOly with the Hebridos autumn spa~mero (oee "Tood 19680.) Jlihanwith those of tho north-''1eotem Horth Sea. In Table 1 the abunda."lce cstioatesfor herring larvae surveyod in ICES Region VIa during the period 4th-16th September1969 have thorefore been shown separately. The total abundance eotimate for these
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1arvae of 281.1 x 109 is ver,y considerab10 and it cust be noted also that bocauseof the ver,y emaIl nu::nber of sta.tiono ,'[orked in tha·~ area the true ovor.D.1 ä.i:::tri~
bution pictoxo connot be doducod. Tho abovo figuro io thoroforc rroba.bly a VCr'J
considerab10 underestiIJa.te of the total herring larval production off Ca"?o ;'!::c;{.hin tho first half of Septomber 1969.' -
The horring larval eetimates for tho north-westorn North Sea ure s~oNn inTab1e 1 for the two periods 4th-16th September und 18th September .~ 4th October1969. Inc1uded in these is a total production figure of 3.1 x 109 for hGr::ir~1arvae found in thc traditional Buchon area off the Soottish east coast (cainlyncar to Ab9rdeen Bank) in ICES Region !Vb. T'no total abundance estm.o;to of157.8 x 10. herring 1arvao for the period 4th-16th Soptember 1969 is al~oot
identica1 to that of 762.1 x 109 given by S~vil1e (1968) for tho ?uc~gn :::tockduring the period 6th-24th Septcnbor 1967. The figure of 180.2 x 10 hc::ring1arvao for the period 18th September - 4th October 1969 is conoider~bly 1eosthan that of 888.8 x 109 for th€ period 25th September - 13th Octob0r 1967 butaS,was pointod out ear1ier in this report no stations wero worked to the 'fost ofOrkney or Shetland during the 1ator period in 1969 v~lile the ~ajor part of the1967 abundance estimate for thc period 25th September - 13th October was eori\edfrom a number of ver,y high density stations to tho south-woot of Orknoy. Thoproduction figuren for thc Buchan stock in 1968 (Boötius 1969)were no~ewhat10wor than those in both 1961 and 1969, but the timing of the survoyo in 1968was slightly difforent and tho covorago, particularly during the firat half ofSeptember, not so extensive.
It thus seem3 reasonabl0 to conc1ude fro!:l thooo larval abundaneo ostioatosthat thcre has been no appreciablo chango in the overall oize of the :::pmminC!herring population in the north-wcotcm North Sea ao a ""halo during the yen.ro1967-1969. Thoro haß howovor beon a markod change in tho diotribution of hO::r.::'l:lC1arvae in thio aroa during tho throo yoars. In 1967 significant nU::::!.bern of :'2o:;:J:5.ng1arvae wero found over a considorablo aroa to tho oast of both Orknoy and Shet1rW1~
and off the Scottish cast coast in addition to tho main concentrations fUrther totho wost ~ In 1969 howevor production in the north-'footorll North Sea ,V'a3 ycrJ la=gelyconfined to the aroa wost of tho Orknoy and Shetland Is1ando.
For the Bank stock in Tab1e 1 larval ootimatos have been made for tho twaperiods 3rd-25th September and 6th-14th October 1969. As statod ear1ier theSeptember survey was ver,y extensive and covered the whole of the we::::tom portio::lof the contra1 North Sea. It io probable however that this ourvey wns in thotlain timed too oar1y to cover herring larval production over all tho npnwninggrounds in the region as Herape1 and Schnack (1968) deduced that tho oajor hatchingof herring 1arvae on the N.E. Bank in 1967 commenced on 22nd Septembe::, a~d. tllinarea was ourveyed by RV !tAnton Dohm" in 1969 bctween 12th-19th September. A f'~11
patch of recent1y hatched herring 1arvae wao on.r:ap1od off Whitby by RV "Tridcns:lbetwecn 9th-11th September und togethor ,üth thc fm'[ odd larvao caught 011:.'011:10:::-::
this gave a total abun~ce ostimate for the Bank otock bct~~en 39d~25th S~pte~ber
1969 of on1y 11.4 x 1c};1 herring 1arvao. The fiß'lll'c of 184.8 x 10 herring l~::,v[\cduring tho period 6th-14tli'Octobor 1969 for 1arvae caught almoot entiroly in thevnnitby/Flamborough/Dow~ingarea io notabIo and of thc same order ofmagnitudo cethat for the survey carried out in thc same area by RV "Emest Holt" bot"won11th-21st October 1968. During the second survey period in 1969 thc li.B. B~~~
was again surveyed, this tiDe by RV nTrideno", but no herring larvae "Tere ca.u~n~;
. thero. Horring larval production in tho Bank otock in both 1968 and 1969 ~OCI'lfJ ';;0
havo boen alraoot ontire1y confinod to the \lhitby/F1cmborough/Dowoing n=ea ~nd ~2eabundaneo eotimates for theso yoaro aro very much lower thnn thone "Th::'ch wereobtainod in 1967. In 1961 there was considerab1e production in the vicini~y ofthc N.E. Bank whi10 nono haG been in evidence thora in cithcI' of tho t~'10 cuceccd.il~g
ycars. The figure givcn by Savi110 (1968) of 400.5 x 109 :for the B:ml:: otock du::inSthe period 6th-24th Septembor 1961 was however for 1arvao caught in tho m:1il1 offllhitby and it in therefore perhaps roughly cooparablo vlith tho f'ieuro oi.' 184.8 ::': 109herring larvao for tho poriod 6th-14th October 1969. It wou1d thus a:ppCa:J: th3.·;;during tho threo years 1967-1969 production of herring larvao bao virtlla11y cC3.sedover the N.E. Bank, haD been conniderably reducod in tho \olhitby axea X'lct bccn (I.tan extrOOlely 10w love1 in the Doggerj\fe11 Bank area.
Tbe total abundanoo estiDate of herring larvae in .the Kobbergrund aren forthe period 16th-28th October 1969 io 29.2 x 109 • This figure io obviously nnundorestimate and pcrhaps a considerab1e one, for the main larval concentrationwao only partial1y covored by the survey grid of stationo and in addition thoreworo indicationo that herring larvae were l1idoly distributed to thc nou·th oi' the
•
- 6-
mai.n survoy aroa. In spitc of this thc abundance estimate is more than double thc11.5 x 109 for 1968 (Boötius 1969) although considerably lowar thrin the 59.5 x 109in 1961 (Saville 1968).
Because of tho incomplate coverago of the autumn hcrring larval distributionin tho Kattogat it would bo Unwise to draw a:ny conclusions from tho abovo estimatos.
Tbe rosults cf the survoys' carriod out ovor tho spaw:ning grounds of tho Dow.r.:::stock during Decombor 1969 and Januar,r1910 nro. porhaps tho most intorostine of tllOsorios covorod by this report. Abundance ostimatos are. givon in Tablo 1 for Downsliorring larvao in separato poriods; A total of 25.0 x 109 horring larVae was obtninodfrom the first survey which Was carried out betWoen 8th-23rd Docomber 1969, ar..d th~.O
figura may be comparedwith that of 5.3 x 109 given by Savi110 (1968) for tho po:dod11th-20th Decombor 1961 and an English ostimato of 36.8 xl0~ for a survoy c~-=icdout betwoen 8th.;.18th December 1961 during which tho IllO.i.D. larval patch off Boacr.yHead was covored more extonsivoly. Boötius (1969) did not includo an estiI:lato forDowns 1arvaa surVeyod botwee~ 9th.;.11th Docombor 1968 but tlio figure wou1d appcar ~obe of tho order of 20.0 x 10 and therofore fair1y simi1ar to that of Doccobcr 1909;
Two abundance ostimates ware dorived from tho survoys carriod out duringJanliary 1910; the first being 39.0 x 109 for tho period 3rd-6th Jariuary and thosacond 259.0 x 109 for thc poriod 5th-15th January. Tbe 1attor figUro is ro1ativo1ylargo and as has already boan pointod out iSt oven so, an underostimata of totalabundnnco bocausc only parts of two of tho mo.in larval concontrations woro covorod.by tho DUrVoy grid.
Somo rocontEnglish abtlndanco ostimatos (mainly dorivcd from p1aico O{;g arid.larVal surVoys) aro avai1ab1e for Downs horring larvac during the ear1y part of tJ.'1eyoar. These are aB fol10ws:-
Survey Period
2n.d':'10th January 1968
23rd-31st January 1968
9th-20th Fobruar,y 1968
18th-23rd January 1969
Total Abundance of LarVae
49.8 x 109
10.0 x 109
11.5 x 109
10.0 x 109•. __ f.,• It io quito cloar that,tho estimato of 259.0 x 109 herring larvao for the poriod
5th-:-15th January 1910 is exccptionally high, arid in fact no cOm;Parablc abundancoostimato has becn obtlrlncd for English surveys carriod out ovor the Downs spaWningaroas since a figUro of 609 x 109 for tha period 2nd':'1th JanUnry 1952.
Only one conclusion can bo drawn from the high January 1910 abUndance estion.toand,that i8.that thc sizo of the Downs spa~~ stock during the 1969/10 Boasen,particularly in thc castorn Charmol, was vory much larger thari. for a nuobcr of ye2:'::paste It might appear unwisc to draw this. conclusion from only one high abunda.nooestimato, but cortainly Burd and Holford (1968) havc commontod on tho fact thatalthough herriDg larval production in thc Downs stock roo.ched an oxtremoly 10w levelin, thc mid 1950 1s, therowas; aftor aperiod of only l~ght fishing offort, a cj~.:'j.
cant recovery in larval production by the 1961/68 spawning Season. "Tood (196Gb;moreover found a marked increasa in tho abUndanca of o.:.group herring of tho provieuo(1966/61) year-class thought to havo been derivcd from thc spawning groundc of thoDowns stock, and Wood and Parnell (1910) havo roccntly rcported that a signif'icantproportion of thc rocruit herring of the 1966/61 year-c1ass caught during the Ent;J.ir.hdrif'tnot f'ishery ofr North Shiolds in 1969 wero almost cortainly mcrabers of .thc DmmsHorring Stock.
It will bc .extromoly interesting during the noxt scrios of survo~ to obcorvewhether the recovery cf the DownS stoc~ shows siens of' continuing.
- 7 -
References
Boätius, I. 1969 "A report of the international surveysof herring larvae in the North Sea in1968". lCES, Dcc. C.M. 1969/H:34, pp. 1-4.·(mimeoJ.
Burd, A.C. 1968 "Decline in the abundance of Downs herring&Holfom B.H. larvae". ICES, C.M. 1968. Symposium on
"The Biology of Early Stages and Recruit -ment Mechanisms of Herring". Doc. No. 11,pp. 1-2. (mimeo).
Clark, R.S. 1933 "Herring larvae. The mixing of the Broodsin Scottish Waters". Rapp. P.-V. Reun.Cons. perm. int. Explor. Mer, .§2 (3): 11-18.
Hempel, G. 1968 "On the AbUndance of Larvae in Spawning• &Schnack, G. areas of Bank and Downs lierring". lCES,C.M. 1968. Symposium on "The Biology ofEarly Stages and Recruitment Meohanismsof Herring". Doo. No. 34, pp. 1-12. (mimeoJ.
Saville, A. 1968 "A report on the international surveys ofherring larvae in the North Sea 1967". lCES,Doc. C.M. 1968/H:20, pp. 1-6. Appendix 4 pp.(mimeo.) •
"lood, R.J. 1968a "Autumn-spawning grounds of herring to thowest of Sootland". lCES, C.M. 1968, Symposiumon "The Biology of Early Stages and Recruit-ment Meohanisms of Herring". Doo. No. 8,pp. 1~9. (mimeoJ.
'''ood, R.J. 1968b "Whitebait herring on the English EastCoast". lCES, C.M. 1968, Symposium on"The Biology of Early Stages and Reoruit-ment Meohanisms of Herring". Doo. No. 9,pp. 1-5. (mimeo~.
"lood, R. J. 1970 "The English herring fisheries in 1969".&Parnell, W.G. 1lnnls. biol., Copenh., 26 (1969), pp. 1-3.
- 8 -
Table 1
1Area or Stock Survey
-I Ahtmdance of herring larvae x , ()9 --r, . [
. < 10 mm 10-15 mm > 15 mm Total_Cape Wrath 4th-16th Sept. 161.8 113.3 6.6 281.7(Region VIa) 1969
North-western North Sea 4th-16th Sept. 348.1 327.6 82.1
-~~J(Region IVa) 1969
18th Sept.-4th Oct. 74.9 65.3 40.0 180.2 I1969
Bank 3rd-25th Sept. I 8.4 2.9 0.1 11.41969 ----6th-14th Oct. 12.7 138.6 33.5 184.81969 --
Kobbergrund 16th-28th Oct. 28.1 1.1 - 29.21969
I I8th-23rd Dec. I 13.0 I 12.0 - 25.0~
~9I I
3rd-6th Jan. 16.7 22.3 - 39.0 iDowns 1970 I-----1
15th-15th Jan. 73.1 185.9 - 259.0 I1970 j
•
•
+
oo
20,/
. ... .... ".-
,"",,,'
KEY TC EIGURES 1 - 28
Less thon 0-5 herring larvae b<aneath one squaremiltre of surface.
Station. workGd twicca during survey period.
Station VIOrkod three tknes durlng survey ~riod.
Number of larvae indicated caught at positionmarmd by point of arrow.
1 hel"ring larvQe bQneath one square mew 016urface.
25 herring larvaQ bQllGQth one squ~ ~tre of
surface.
--------_._---------
Numbers of herring larvae <10 mm long beneath 1 square metreof surface. North-western North Sea. 4-16 September 1969.
o
o
o
o
o
o·
o
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o
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[Q]O 00 O[Q],}
Numbers of herring larvae 10-~.~ mm long beneath 1 square metreof surface•.. North-western North Sea. 4-16 September 1969.
~, Figure,12 Numbers of herring larvae >15 mm long ben.eath 1 square metre"r~ of surface. Western central North Sea. 3-25 September 1969.H-,tirio\q(.\'\.)
.~~~1:&..;1",,,,
.. '
~lli}Jr· ---"-...........t
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~i
t~
1~~
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o . M~rld...... .
\". .... m/o ~\'ic\.
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o 0 0
o 0 0
o 0
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Numbers of herring larvae <10 mm long beneath 1 square metreof surface. Western central North Sea. 6-14 October 1969.
0 0 0
0 0 0
0 0
0 0
0 0
0
0
00
0
Figure 13
~r--_"'-".--......
.i~t:
'it,-_!::
~ln:.
mhl"-'I~
o 10 Merlal1äii 1'" . rl 3· •4.~.••.' - ~55iEl~2iii1::lllC~IIIEiiiI:::!IiiiiIe:liiiiaiii:ZSiIl5i-lIIIlilill-E°ii:LiiiGTIii:1i~nijB:tili.ieh__llllSi:iiilI!IIiiiil!!Ei1.5iI!lIE!!iiiiill!Ei3!!lE!!!5L3!!!Eii!!!!!B!!D\LiiCfiiiillll:liiil:li.1a::5ieliiiil::liiiil::li;;iil::e~.fJ '--r.'~~ ~ ~ eei:;;:;:;: ::;: ~ !!!!: lIiiI ~ I ;! , ; pi.. -= t1 H M rl rs c:
\.~\:3Ö I ßL 11"4 . ~.'b} SJ" Figure 14 'Numbers of herring larvae 10-15 mm, long beneath 1 square metre ~"
tI of surfaee. Western eentral NorthSea. 6-14 Oetober 1969. ill':.
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