ICES 1991 PAPER C.M. 19911H:50 Pelagic Fish Cttee

AUTUMN SPAWNING HERRING AROUND FAROES DURING SUMMER 1991

by

Jan Arge Jacobsen

Fiskiranns6knarstovan N6at6n, FR-IOD T6rshavn

• ABSTRACT

Investigations in 1990 indicated that concentrations of herring feeding in the Faroese area from May through July were similar to North Sea herring. Again in 1991 North Sea type herring was distributed in Faroese waters in May-July and approximately 16.000 tonnes fished. Results from an exploratory fishery and a research vessel survey showed, as in 1990, that the herring might be an adult part of the auturnn spawning herring in the north-western North Sea migrating into the Faroese area to feed from May to late July. However, in 1991 more by-catch of herring was reported from the mixed industrial fishery than previous years. •

2

INTRonucnoN

At prcsent two different groups of hcrring can be id~ntified as occurring at Faroes, one group of Iocal summer spawners found in the fjords', (Täning 1943), and one group of autimm spawners migrating into the Faroese area from May to late July, probably from the north-western North Sea around Shetland isles (Jacobsen 1990). A new fishery on this herring has been established south-east of the isles. The catch figure for 1990 was 5.500 tonnes and the preliminary catch in 1991 amounted to 'over 16.000 tonnes. ,' , ,I".' • In 1991 Fiskiranns6knarstovan received several re ports' on by-ciltches of herring in various fisheries for othcr species arourid the Faroes during the 'spring, and the reported herring was all of the Nortll-Sea type. There might be one exception to this, a sampIe of 22 herring caught north-east of the isles in March was exceptionally hirge herring with a mean length of 35 cm and mean weight of 400 g, all with maturation stage IU. This herring could be of Icelandic origin belonging to the Icelandic summer spawners. I increasing effort has been put ioto the research for herr~g the last few years. In 1988 during e an exploratory fishery with a Faroese purse-seiner, herring was found distributed in the south-eastern corner of the Faroese EEZ. Also in 1989 herring was found in the same area. Iri both years the distribution was liinited to a rather small area around 600 30'N and 6°00'W. , In June 1990 tbe Faroese research vessel Magnus Heinason carried out a siUVey in the Faroese area south-east of the isles, and herring was fourid to bc distribllted over a comparatively large area south and south-east of the isles. I • I . I In 1991 acommercial purse-seiner was hired to survey the area east and south-east of the isles from mid May to mid June, and RlV Magnus Heinason contiriued the research two wecks in June in thc same area. The aim of the investigations is firstly to deterrnine the origin ofthe herring and secondly to clarify when the h'erring enters the Faroese area, when it Icaves the area, and the abundarice in the Faroese ar~a during that pedod. j

MATERIAL AND METHOnS .,'

Magnus Heinason is equipped with a Simrad SU-2 15 kHz sonar and the new simi-hd • EK-500 38 kHz sounder. Both sonar and echo sounders were run continllously durmg the survey and echo intensities were integrated along the co'urse and mean integrator values (SA) were recorded for every 1 nm. I '. !' Sampies of herrlng were collected from the commercial purse-seine catches and analyzed for the followi.~g bioIogic~1 arid meristlc charactcrs: length, ,weight, otoliths, sex, maturi~y ~tage, and number of vertebrae. i'" .

I I' ,I

RESULTS :.

t The survey area was limited to the eastern south-east~rn part of the Faroese EEZ. Cruise tracks with bottom trawl stations arid hydrographical stations are shown in Fig. 1. Magnus Heinason is not equipped with a purse seine, and sampIes were therefore collected from commercial purse-seiners fishing for herring in the same area (Fig. 1). I 3

, " The cruise tracks of the exploratory purse-seine fishery in May and June is shown iri Fig. 2, and positions with herring catches are indicated on the figure. .

Thetcmpcrature eC) at io m, 50 m, and 100 m dcpth is shown in Fig. 3a-c respeciively~ South-east of the Faroes the warmer North Atlantic watcr from south-west meets the colder water coming southward east of the isles (mixed North Atlantic arid Icelaridic water). This is the sccond year of investigations in this area in June, and the temperature at 10 m dcpth (Fig. 3a) is betweeri 1-2 °Ccolder in 1991 as compared to 1990 (Jacobsen 1990). The tcinperature at 50 m depth (Fig. 3b) where the main bulk of herring was observed (ref. Fig. 4) was 1 °C colder thm the sUrface temperature, with no clear thermocIine. The temperature at 109 min 1991 (Fig. 3c) was apinoximately the sarne as in the 1990 sUlveY. Iri Fig. '4 is shown tbe distribution and dens'ities of herring from the survey in 1991. COInmercial by-catch of herring at bottom are shown as dotted areas, and areas with herrmg schools are hatched, while areas with large numbers of schools or significmt pw-se-seine .

" catches äre einphasized (crosshatched) on the figure. The herring schools were disii-ibuted in the upperinost 5-50 in below sea surface in riumerous rather small schools (10-40 toriries), with a few large schools up to 300 tonnes as measured by commercial purse-seiners. Herring . • was caught in the bottom trawloperated by Magnus Heinason in areas where no schools were observed and far outside the areas where the purse-seiners were operating, refcr to the dotted areas in Fig. 4.

The biological resuits are divided into two parts, the first part is from the arialysis of the sarnples provided by the commercial purse-seiners from mid May to mid July 1991; arid the sccond part isfrom the analysis of the sampIes caught with bottom trawl, mainly as by-ciltch in the indusmal fishery in April 1991. Thc reason to divide the sarnples is thai tbe räiher . small sampIes, a total of 347 herring in April, is not representative for the mam purse-seiric fishery later in theseason. also the total by-catch of herring during tbe spring is thought to be insignificani. Therefore the results arid the discussion later in the paper will mainly be on the bäsis of the daia from the purse-seine catches while the other results will be meniioned only briefly.

Tbc length distribution of the recorded herring from the purse-seine catches is shown in Fig. 5. The length ranged from 26-38 cm with mean length of 30.0 cm and a mean weight of 244 g (Table I, first part). The length distribution of thc hcrring from the bottom trawl catchcs • is shown in Fig. 6. Tbe length ranged from 25-37 cm with mean length of 30.8 cm and a mean weight of 220 g (Table 1; second part). The size distribution was generally slightly larger in the noI-them part.of the surveyed ärea. The age distribution (nurnber of winter rings) from the purse-seine fishery arid from the by-catch is shown in Fig. 7 arid 8 respectiv­ ely. Approximatelyone third of the herring was 4 ringers and orie forth was 5 ringers while praciically no small herring less than 3 winter rings was observed.

Maturity stages by montb is given in Fig. 9. The shift from stages VIII arid 111 domiriäiirig in April and May towards maturity stages iv and V in June and July is evident from Fig. 9. Th6 average vertebral coUnt of 823 herring was 56.63 vertebrae (Fig. 10). The weighi distribution from purse-seine catches in june is depicted in Fig. 11 and from boitom trawl catches in April in Fig. 12.' .

Tbc mean iength and mean weight by age is give~ iri Tabie 1. It ls notlceable that the meän wcight by äge for ages 3 and 4 in June 1991 is father high compared to similar figw-es given for previous years (Anon. 1991a) and also compared to the Faroese investlgations last ycar (Jacobsen 1990). I' 4 ~ No attempt was made to estiinate the biomass of herririg from the acoustlc recordings, the reuson for this will be dealt with in the discussion. I' I I ! DISCUSSION I I . ''', ,,'" i' ",', ', ,""' The areal distribution of herring schools iri 1991 (Fig.,4) was limited to the south-eastem part of the Faroese area, approxiniately the same distribution as in 1990 (Jacohsen 1990). ' However, i.It 1990 good herring catches were obtairied 'on Sandoyarbanka east of the isles and the northem limit of distribution iri 1990 was up to 62°N while the limit was aplnoxi­ mately 61~0'N in 1990 with no schools over SandoYarbankti. One reason to the more southerly distribution of th6 herring might be fOUnd iri the temperature distribution this year (Fig. Ja-b). As the temperatUre at 10 indepth was generally I-2°C colder in 1991, in addition io the steady wind conimg from north~easi duririg late spring and early sUmmer, the herdng mighi have stopped its migration fuIther south' this year. An analysis of plllI1kton sarnples taken with aHensen net during the sUrVey shows that plenty of copepods in several stages and other plankton was available further north ririd east of the isles. Therefore it'is not assWned that insufficient amount of prey is' the reason to this more southerty distribution (the herring was mairily fee ding on copepods). On the contrary to this the areal distributiori at bottom was much wider than th6 distribution of the schools, refer to doited areas mFig. 4. It is not elear why tl1e areal distributiori of pelagic herring schools is different from the distribution at bottom. .; " I . , I The mean vertebral count (VS) of 56.63 veitebrae (N=a947) in 1991 give evidence ofhigh resemblance io th6 reported VS ofwest of Scotland herrißg between 56.4-56.7 (Anon. 1969), arid the Norwegian sarnples of North Sea herring in Divisiori IVa west und in Division VIa riorth with a VS betweeri 56.3-56.6 (Dahl arid 0stvedt 1975, 1986. 0stvedt and Dahl1984. 1985, 'Anon 1991). However. thc VS is iri th6 higher c'nd of the riutunln spawning herring in the North Sea. hut ilO spring spawning herring was obserVed in our ~arnples. This is also confmned by the dcveloping trend in the inaturity stages from stages VIII arid III in April to stages IV and V in July (Fig. 9). '

A sampIe of herririg from the Farocse ärea (Vb) wäs ~alyzed 1>y the method described by Johannessen and Jßrgenseri (1990)' and rei;ults show\ elose similarities with North Sea l sampIes (Anon. 1991 a), also sarnples from Divisiori VIa noith have been analyzed and could • not be separaied from the other sarnples of North Sea hcrring (Jßrgensen. pers. COmln.).' . : I The stäte of the herring stocks in the North Sea (inciuding IVa) and west of Scotland (VIa) is describcd as good in Arion. (1991a). The rapidly increasirigspawnmg stock biomass during recent years coincides in time with th6 incrcased biomass of herring observed in the Faroese area during the last threc years. A wider distribution of adult herring riUght be expected as a consequence of the incre'ased stock size. However, Corteri arid Kamp (1991) rirgued that a possible reason for the northem shift of herdng might be changes of water transport in the shelf edge CUtTent west of Scotl:irid and in Orkney/Shetland'area. They also püi forwärd the hypothesis that the iritensification ofthe 'shclfedge cuITent during the 1980's might have resulted in an. incrcased rruxing iri this area; and a subsequent increase· in biological pröductivity. With the result fiÜit adult heri-ing has moved further north arid nortb­ west iri recerit ycars~ This hypothesis can not. however. cxplain that the herring migratcs past thc shelf edge into the shetf edge region in thc Faroes area~ If the shelfedge eurrentgoing northwaeds is strong it is expected·that this would act 'as abarrier to the herrmg to move across the Faroe Shetland Channcl, to the contrary if. the shelf edge cUrrcnt is slow, a 5

migration of herring over the channel could beexpected. Recent hydrographie work has iridicatcd that the flow of Atlantie water through the Faroe Shetland Channel may have been reduced in recerit years (Hansen and Jakupsstovu 1991). At present the foimdations of Ws hypothesis is not strong cnough to draw any conelusion but research which is origoing should establish whether the herring migration can be linked to this phenomenon;

Comparing the age distribution of the herring caught in Faroese waters with heiTing from other ICES areas (Fig. 13 and Table 2), shows that the age distribution found is most elose to the age distribution from ICES area IVa west. This is a sampie of 221 herring from th6 . nOrWegian herring survey in July 1991. Tbe Faroese herring fishery is characterized by the small aIlloimt (10%) of herring of age 3 (winter rings) and the absence of small iffimatui-e herring. It seems as the age distribution iri the northern North Sea and in the Faroese area constitlites the ölder age groups from the North Sea (ref. Fig. 13).

As in 1990 the herring schools were distributed in the upper 5-50 ni below sea surface arid were difficult to detect on the hull mounted transducer onboard RlV Mag;uls Heinason, even if we tried to. sieer on them. There were two reasons to this, firstly a malfllOction of thc sonar as th6 titt angle of the sonar beam was not displayed, and secondly the problem of vessel induced avoidance reaction which is thought to be a significant source oferror in thc preserii surVey (ref. Olsen et al. 1983a and b, Aglen 1985, Misund 1987; Ona 1988a arid b, and Aglen arid Misund 1990). As much as 30% of the herring schools obserVed in front of a surveyirig vessCi have been reported to avoid the vessel, hence the echo integration system (Aglen and Misund 1990). Therefore, the author consider an acoustic assessment io be of limited value~ arid would not yield a reliable biomass estimate in the Faroese area.

If the herring found inarea Vb origiriates in the North Sea, the question arises wllether this herring is iric1uded in the biomuss estirriates obtained during the combined acoustie surveys iri July in thc North Seä and west of Scotlarid (Anon. 199Ib).

In last yeai-s sUrVey trials with a towed side 100king 38 kHz transducer were done, and it was argulnented that this method could give better results than conventional echo integration from huH mouöted transducers (Jacobsen 1990). However, after a test of this system iri 1991, it became dear that in order to get satisfying results, thc transducer in the. towed body has to be of the same power and size as the hull mounted transducer (i.c. an 38 kHz split beam • transducer). Such a towed system is not available to Fiskiranns6knarsiovan.

CONCLUSIONS

Again in 1991 herring of North Sea type has been found distributed iri an area south-est of the Faroes originating from the nOrtb-westem North Sea, migrating into the Faroese area to feed from early Mai to late July; It seems as the age distribution in the northern North Sea und in the Faroese area constitutes the older age groups from the North Sea'..

An acoustic assessment is considen~d to be of Ümited value, arid would not yield ä reliabie' biomass esÜrriate in the Faroese area. 6

ACKNOWLEDGEMENT : :. 1 ~ , , The skippers and the crew onboard the five Faroese purse-seiners are greatly appreciated for their help to provide herring sampIes to me on the field or to Fiskiranns6knarstovan rind Marit Pctersen is appreciated for the vertebral coUnts and age readings of the herrit1g sarnples. I

REFERENCES. '

• , . ~ .' 1 Aglen. A. 1985. Sonar observations of the behavior of herring schools in relation to a fishing vessel. ICES, Fisheries Acoustics Science and Technology Working Group, Troms". May 1985. I I Aglen. A. and Misund. O.A, 1990. Swinuning behaviour of fish schools in the North Sea during acoustic surveying and pelagic sampling trawling. ICES, C.M. 1990(B:38): 1-22 [Mimeo). • . , .. . " ' ., . Anon. 1969. Report on the State of the Herring Stocks around Ireland an North-West of Scotland. ICES, CM 1969(Assess): 1-23 [Mimeo). .

Anon. 1991a. Report of the Herring Assessment Working Group for the Area South of 62~. . 2 - 12 April 1991. ICES. C.M. 1991(Assess:15): 1-192 [Mimeo). I . . Anon. 1991 b. Report of the Planning Group on Acoustic S~rveys in Sub-area IV and Division lIla. Aberdeen. 9 - 10 January 1991. ICES.'C.M. 1991(H:40): 1·55 [Mimeo). . . : Corten. A. and Kamp. G.van 1991. Natural changes in pelagic fish stocks of th~ North Sea in the 1980·s. ICES. Variability Symposium. No.27/session 3. Mariehamn. ' , ,I . , Dahl. O. and 0stvedt. O.J. 1975. Tbc Norwegian herring fisheries in the North Sea and Skagerrak. 1973. ICES. Anna!. BioI.. 30: 136-139. : ' .

Dahl. O. and 0stvedt. O.J. 1986. The Norwegian herring fisheries in the North Sea and Skagerrak in 1983. ICES, Anna!. Biot.. 40: 122-124. ,!

Hansen. B. and Jakupsstovu. S.H.i 1991. Availability of blue whiting (Micromesistius poutassou) in Faroese waters in relation to hydrography. ICES; Variability Symposium. No.28/session • 3. Mariehanin. I I . Jacobsen. J.A. 1990. A survey on herring south of the Faroes in June 1990.' ICES. C.M. 1990(H:34): 1-18 [Mimeo). 1

Johannessen. A. and Jargensen. T. 1990. Stock structure; ~nd classificaii~n of herring (Clupea harengus L.) in the North Sea. SkagerrakiKattegat and western Baltlc based on a multivariate analysis 'of mörphometric and me'ristic characters. Proceedings of the International Herring Symposium. Anchorage. Alaska. October 23-25. 1990. [Mimeo.) . i . j Misund. O.A. 1987. Sonar observations of horizontal extension. swirnming behavior. and vessel aod purse-seine avoidance of herring schools. International Symposium on Fisheries Acoustics. June 22-26. 1987. Seattle. Wash. USA, [Mirneo.] I 7

Olsen, K., AngeH, J., Pettersen, F. and L0Vik, A. 1983a. Observed fish reactions to a surveying vessel with special reference to herring, cod, capelin and polar cod. In O. Nakken and S.C. Venema (eds) Selected papers to the ICESIFAO Symposium on Fisheries Acoustics, , , 21-24 June 1982. FAO Fish. Rep., 300: 131-138.

Olsen, K., AngeH, J. and Lovik, A. 1983b. Quantitative estimations of the influence of fisb behavior on acoustically determined fish abundance. In O. NaUen and S.C. Venema (eds) Selected papers to the ICESIFAO Symposium on Fisheries Acoustics, Bergen, Norway, 21-24 June 1982. FAO Fish. Rep., 300: 139·149.

Ona, E. 1988a. Herring avoidance during trawling, studied by scanning sonar. ICES, Fisheries Acoustics Science and Tecbnology Working Group, Ostende, April 1988.

Ona, E. 1988a. Sonar observations of herring vessel avoidance. ICES. Fisheries Acoustics Science and Technology Working Group, Ostende, April 1988.

Täning, Ä.V. 1943. Fiskeri- and Havunders0gelser ved Fltf0eme. Skrifter fra Komm. f. Danm. • Fiskeri- and Havunders0gelser. 12, Copenhagen 1943: 92-94. 0stvedt, O.J. and Dahl, O. 1984. The Norwegian herring fisheries in the North Sea and Skagerrak in 1981. ICES. Annal. Biol., 38: 141-144.

0stvedt, O.J. and Dahl, O. 1985. Norwegian herring fisheries in the Nortb Sea and Skagerrak in 1982. ICES. Annal. Biol., 39: 127-130•

• 12" 10" 8" 6" 4" 2" 0" 6 3" 1r==~~=:;:P::=~~=r::p:=p:::JF==:C::P~=F==L--PPr::1J_=t:L::Il:=F===f:Do:::x:::q:===J==:=::c:f163" -~ ~ '\ ._) ~---- '0. 62' 62" .

61" 61" 00

Bottom trawl • 60' 60" • Purse-seine sampIes •+ Hydrographical station

~ , ,jP ~ ~l~'''' 0) ° ::cl 0" 59' 59" 4' 2" 0" 12' 10" 8" 6"

Figure 1. Cruise tracks with trawl and hydrographical stations, RJV Magnus Heinason June 1991. Herring sampIes were obtained from commercial purse-seinerso • 2· O· 63° 63·

-)---. ~ ·0 62' 62·

61" 61",

4

60·, X Purse seine

"f -( , ,jI' , .•i#" !lt' " ... ±.=H:::cd==:d:::J==::l===r±=~9·:3:IJf~'!'=:d:::J==:±===!l5 9' 59· 0 .::r=cr 4° 2° O· 12· 10'° s· 6°

Figure 20 Cruise tracks of the exploratory purse-seine fishery with M/S Skuvanes in the periode 17/5 to 17/6 1991. An x indicate positions with herring catches oe herring observations. 10

eo'

<,~. 59' 111' 12' 10' s· S' 4' 2' O'

12' 10' s· 6' 4' 2' O' 63' er •

59' 111' 12' s· 6' 4' 2' O'

O' 12' 10' s· 6' 4' 2' 63' 113' • 62'

·f 60' < • -: 111' 59' 12' 10' s· 6' 4' 2' O'

Figure 3. Temperature (0C) at 10 m (a), 50 m (b), and 100 m (c) depth in June 1991. 1.------•

12· 4· 2· O· 63·Ir:='='='::CIPI,=,=,=,:q::x=::c:q== ~==F~=i====c:p:==f===I==::Cf:==t==:c:Il6 3·

62'

61" 61" -

60· 60·

,f -< ;Ir' {0 ~,:l)l. Off • 59· 59· 12· 10· 8· 6· 4· 2· O·

Figure 4. Distribution and densities of herring around the Faroes from May to mid July 1991. Areas of distribution at bottom are dotted, areas with schools are hatched, and areas with significant purse-seine catches are double hatchedo Based on data from R1V Magnus Heinason, commercial purse-seine vessels, and mixed industrial fishery. 12

35 30

(1) 25 C) 20 Sc Cl) e 15 Cl) Q. 10

5 o • 1- • 24 26 28 30 32 34 36 38 Length (ern)

Figure 5. Length distribution of herring from purse-seine catches within the south-eastem area of the Faroese EEZ in JOlle and July 1991.

35 30

Cl) 25 C) S • c 20 Cl) ~ 15 Cl) Q. 10 5 0 24 26 28 30 32 34 36 38 Length (ern)

Figure 6. Length distribution of herring from bottom trawl catches (industrial fishery) around the isles on the Faroe plateau in April 1991. 13

40..------,

35~----

CIJ 30 E25~---­

5i 20'+-----­ (.) ~ 15-+-----­ Q. 10-+---- 54---­ 04----.. • . 1 2 3 4 5 6 7 8 9 10 Winter rings·

Figure 7. Age distribution (no. of winter rings) of herring from purse-seine catehes within the south-eastem area of the Faroese EEZ in June and July 1991.

40,..------, 35-f------l

CIJ 30 S 254----- • ~ 20+-----­ U ~ 15i-+-----­ Q. 10+------5,-+---­ 0-+----.--.. 1 ,2 3 4 5 6 7 8 9 10 Winter rings

. Figure 8. Age distribution (no. of winter rings) of herring from bottom trawl catehes (industrial fishery) around the isles on the Faroe plateau in April 1991. 14

C1.) C) ~ 60 C1.) E 40 a.C1.) 20'.J--""O'

April May June .' I Month ~ I .I t Figure 9. Matudty stages ofherring per rnorim in the south-easiem area of the Faroese EEZ in 1991. .

I

60,..---;:::======1"="==;:--, I Mea" vertebral count: 56.63., (N= 823) .1 50

~ 40+-----­ ca ·e 'EQJ 30f------E & 20-+------

10-+------

01+-----..--.... 54 . 55 . ~6 57 I 58 59 Vertebral count I I Figure 10. Vertebral count of hemng horn b~ttorn trawl catches in April and purse~seine catchcs in June 1991 within the south-eastem urea of the Faroese EEZ. : I I 15

14,-r------, 12-+------1------1

~ 10'-r------= Cl 5 8~---- I c (I) ~ 6-+-----.1111 (I) a. 4-+-----111111

2~--~ Hltll U

o-+---'-T'T'T"1'""'f"fI/ 1111111 H 100 150 200 250 300 350 400 450 500 Weight (g)

Figure 11. Weight distribution of herring from purse-seine catches within the south-eastem area of the Faroese EEZ in June and July 1991.

14,------, 12-+----.---=------l

(I) 104---­ Cl 5c 8-+---- ~ ~ 6-+---- QJ a. 4-+----1

2-+---' 0+-...... ,., 100 150 200 250 300 350 400 450 500 Weight (g)

Figure 12. Weight distribution of herring from bottom trawl catches (industrial fishery) around the isles on the Faroe plateau in April 1991. 16

50.------;======~ 50'-Y---;======iI I Vb East, June I IVa North-west, July 40.J------.!=====~

C) C) ~ 30+--­ ~ 30+--­ C C ~ U ~ t 20-+--- u 20+--­ n. n. 10 10+--- • o 3 4 5 6 7 8 9+ 3 4 5 6 7 8 9+ Winter rings Winter rings

50.-----;;::::======1 50.-----;:======" Via North, at spw. I North Sea, at spw. I 4Qt-----======l 40-l----======~ C) C) ~ 30 ~ 30+----==------1 C C ~ ~ u 20 ..u n. n. 10 o 3 4 5 6 7 8 9+ 3 4 5 6 7 8 9+ Winter rings Winter rings

Figure 13. Comparison of age distributions (%) of herring in different ICES areas during summer 1991. 17

Table 1. Mean length and mean weight by age (no. of winter rings) ofherring from purse- seine catches in June and July 1991 (first part of table), and from bottom trawl catches in April 1991 (second part of table).

Age (no. of winter rings) 2 3 4 5 6 7 8 9 10 Mean

Purse-seine: June/July Mean length 26.5 28.9 29.6 30.3 30.7 31.0 31.4 31.4 30.0 Mean weight 196 225 240 248 257 253 260 262 240 No. of herring meas. 2 52 140 111 34 39 11 5 394

Bottom trawl: April Mean length 29.8 30.1 31.8 30.8 30.9 30.7 31.7 30.8 Mean weight 202 211 257 214 206 201 229 220 • No. of herring meas. 14 46 37 21 25 10 2 155

Table 2. Comparison of age distributions (%) of herring in different ICES areas, during summer 1991.

Winter Div. VIa Div. Vb Div. IVa Total North- rings north 1) east north-west 2) Sea 1)

3 31 13 6 25 4 14 36 36 29 5 33 28 33 28 6 8 9 17 12 7 5 10 2 3 8 3 3 6 2 9+ 6 1 0 1

1) From tab1e 2.8.3 and 5.1.12 in lCES CH 1991/Assess:15. 2) From Norwegian herring 8urvey, Ju1y 1991.