ICES 1997 '~"' __ PAPER. C.M. 1997/EE:07Environmental Factors

Polish acoustic survey on pelagic fish distributionin leES Subdivisions 24, 25 and 26 in the Baltic Sea

carried out in October 1996

BY

Andrzej Orlowski, Wlodzimierz Grygiel,

Ryszard Grzebielec and Miroslaw Wyszynski

Sea Fisheries InstituteP.O. BOX 345, ul. Koll~taja 1

81-332 Gdynia, POLAND

ABSTRACT

The paper presents the results of the acoustic survey carried out on board r/v "Baltica" in

Gctober 1996 with the use of the EK 400 and QD echo-integrator linked to the Hewlett­

Pack~d Vectra computer working as a data server. The biomass ofherring, sprat and cod was

estimated in ICES Subdivisions 24, 25 and 26, including Danish and Swedish waters and the

whole Polish EEZ.

. The biomass of herring estimated in the above-mentioned area was 151 thousand tons,

with a mean surface density of9.1 t/n~l.Ayear before, herring biomass surface density (lCES

Subdivisions 25 and 26) was estimated at 26.4 t/nm2• The biomass of sprat stocks was

estimated at 388 thousand tons, with a mean surface density of23.3 t/nm2 (41.9 t/nm2 in 1994,

and 27.9 t/nm2 in 1995). A substantial decrease in herring biomass densities in the surveyed

area was observed. Mean total biomass density (herring and sprat together) equaled 32.4 t/nm2

and was considerably lower than during the autumn 1995 survey (56.1 t/nm2).

The estimated herring and sprat biomass was recalculated into numbers at age using age­

length key and mean weight for each ICES rectangle. Numerous charts and tables giving a

broad review of the research materials and pelagie fish resouree characteristics ~e also

enclosed.

INTRODUCTIONTbe third cruise ofr/v "Baltica" devoted to the hydroacoustic stirvey ofBaltic commercial fishresources and coordinated by the ICES Baltic International Fisheries Survey \Vorking Group(Anon. 1996) took place on October 5-24,1996.

Tbe area surveyed from aboard r/v "Baltica" covered ICES Subdivisions 24 (13.6% ofthetotal area), 25 (80.4%) and 26 (50.8%), including the Polish EEZ (Exclusive Economic Zone)below a 20 m isobath. The surireys were carried out in the fisheries zones of Poland, Swedenand Denmark.

MATERIALS AND METHODSThe schematic track ofhydroacoustic transects and the distribution ofpelagic control hauls arepresented in Figure 1. In total, 1,930 nm of hydroacoustic tfansects were covered, out ofwhich 1,496 nm, lying within the regular research grid, were selected after, analysis forcomputations. Surveys covered 16,654 iun2 below a 20-m isobath. This yielded a coverageindex of 11.1 nm2 ofslicveyed area per one mile ofa irririsect. In the previous year, 1,788 nmofacoustic transects were covered, and 1,450 nm were selected; the actual surveyed area withICES rectangles identified by control hriuls was 20,386 "nm2 "(a coverage index of 14.1nm2/nm).

In covering hydroacoustic trarisects, the EK 400 echo sounder and digital QD echointegrator were used linked to the Hewlett-Packard 386s/25 Vectra computer and the researchnetwork of the vessel providing supplementary data ahout the 10cation, time, speed of thevessel and the depth of the sea hottom. The computer was also used as a manipulator of theQD echo integration system and a serVer of datri in the tranSitional forrilat supplementing thestandard of the QD-SIMRAD system by navigational data iridispensable to performhydroacoustic estimates of fish resources. Echo iritegratiori was performed with the QDintegrator along one-mlle sections, 24 hours a day. For each integration channel, ci. thresholdequivalent to a minimum target strength of-68 dB was applied. ,

The calibration of the hydroacoustic system of the vesSei was performed off the HögönIsland, near Västervik (Sweden), With the participation ofMr. N. Hakansson from the InstituteofMarine Research in Lysekil. The calibration constant equaled SL + VR = 128.55 dB. As themeasured value of the calibration constarit differed only slightly (by Iess than 1%) from theresult obtained during the calibration in 1994 (SL + VR = 128,5 dB), the same recalculatedconstant as in the previous years, equal to -64.54 dB, was used for the computations ofbiomass. The obtained results of calibration confirmed very high stability of acouSticparameters ofthe SIMRAD system, fully verifYing the value ofthe 1995 biomass estimate.

Conversion ofthe readouts ofthe EK 400 + QD integration system irito values ofcolumnscattering strength Svcwas performed by methods presented iri papers by Orlowski (1989,1990, 1993, 1994, 1996) and Grzebielec ef al. (1995). In these papers, ri.lsO technicalparameters used during measurements were presented iri greater detail.

Biomass ofparticular:fish species in the given ICES rectangle was computed by separatingintegration values, taking into account the mean share of:fish in the hauls. For each ICESrectangle, mean target strength of one kilogram of:fish TS~was computed based on the

known mean weight and Iength of the specimens of herring, sPrat and cod. These data wereestimated by analyzing and trarisforming the resuits of control hauls in the quantified areas(Grygiel ef al. 1996). Computations were performed for the rireas of ICES rectanglescorresponding to the area of a bottom depth of over 20 m. Mean fish target strength wascomputed (according to the ICES recommendations, Anori. 1990, 1994) from the followingformula:

•

.•

•

[1]

2

•

where: TS i!. is the target strength of a speeunen of the j-th speeies iIi the i-th ICES reetangle[dB], and llJ is the rriean length ofsi:>ceimens ofthe j-th species in the i-th ICES rectangle [ern].In the case of cod, the target strength of orie kilogram of fish was adopted according to the'fonnula given by K. Foote (1986). The target strerigth of one specimen in an ICES rectanglewas computed by TS-LENGTH regression: .

TS = 2010gL-67.5. . [2]In tbe acoustic survey area, 44 pelagic control hauls were made, of which 38 were

considered to be representative biological sampies (Table 1; Grygiel et al. 1996). Tbe hauISwere perfonned with the midwater herring trawl WP53/64x4 type, ofa mesh bar length of 11mril in the coderid. Mean trawling speed ranged from 3.1 to 4.2 knots. Along the acotistictranseets,the vessel went at 7-9 knots. Tbe tirile of trawling varied from 30 to 60 minutes.Most hauls were made during the day. Four hauls were perfonned in the everung hours, andone-:-in the night. . '. Lerigth eornposition and mean body weight of herring aitd sprat in the catch were

deterinined based on the mei:t.surements of 8,108 and 12,006 speeimens, respeetively (Grygielet al. 1996). Detailed iehthyological analyses, ineluding age arid popUlation determinations,were penorined oril,989 hemng from 35 hauls imd 1,187 si:>rat from 30 haulS. The totalnumber offish was divided irit<? herring arid sprat arid age groups, aceording to, thespeeies aridage cornposition ofthe catch. ALKs were made for eaeh Subdivision arid bOth the species.

. ,

RESULTSDistribütion or column scatteririg strength (Sve) , .A relatively Uniform pattern of aeoustie transects, similar to that repeated since 1981, made itpossible to deternune a eornparable geographie distribution of resourees.. Similarly to previouSyears, for the final deterinination of the fish resomee distribution the values of iIitegrationaveraged for 4-mile sections of the vessel's route were used. In Figures 2 and 3, the Iririps ofthe distribution of the main cornmereial flSh resourees in 1996 arid 1995 are presented,expresSed with, tbe use of the acoustic parameter, caned column scattering strength-Svc.Drita used for the eomputations ofthe values ofparameters Svc, L, SA and.thebioniaSs offishresomees and their riiunbei- are listed along with the other ciuise data in Tables 2 rind 3.

The highest Value~ of colurnn scattering strength (class N: -48+-44 dB) eneornpasSed rifew eornpaet areas, different with regard to size. The largest area covered, shaIlower watersbeiween Norra Midsjöbariken arid Södra Midsjöbanken, extending as far as tbe western slopesof Hoburgs Bank. Tbe second moSt important area of fish coneentration covered tbe eastemslopes cif the Gdailsk Deep arid the eastern pan: of the Gulf 0f Gdail.sk. The lafgest area 0f themap (Figure 2) correspcmded to the values of Svc ofclass L, rariging from -52 dB to -48 dB.ThiS c1ass also compfised the mean value ofcolumri scattering strength iri tbe cruise area, equalto -51.36 dB. The general pattern of fish distribution in 1996 exhibited sinall d}1lamics, aridthe total range of the values of column seattering strength eneornpassed only four claSses ofvalues (H, J, L, N). .

The pattern ofresoui-ee distribution deterrillned in 1995 (Fig. 3) differed considerably frointhe one obserVed in 1996.Tbe fust important differeriee was found in the rarige ofvanation inthe parameter Syc,whieh iri 1995 erieompassed six classesofvalues (0, H, J, L, N, P: fonn thevalue beIow -64'dB to the values above -44 dB; Orlowski et al. 1996). lri 1995, aS many asfour cireas ofhigher bioinriss densities (c1ass P: -44+-40 dB) were observed. In 1996, no areawith such a high concentration of fish waS foUrid. Tbe traditionally large coneeritrations of theclupeoids,in the Gda6.sk Deep, betWeeri the Gdarisk Deep and Gotland Deep, or iIi the.SlupskFurrow. did not oeeUf. Tbe mam fISh resoUfees moved eonsiderably in the northerIy directiori(beyond the bOundary ofthe Polish EEZ) without reachiIig the concentration density of 1995.

3

Tbe mean value of Svc for the whole cruise area amounted to -51.36 dB, at a eonfideneeintervaI of 0.336 dB. In 1995, this value was higher (-50.53 dB), at a higher eonfideneeinterval (0.435 dB), eonfirining greater dynamies of the geographie distnbution of fishresourees..

, The quantitative eharaeteristies ofherring, sprat and eod resourees in the whole cruise areadivided into ICES Subdivisions and rectangles are given m Table 2.

Herring resources . .Herring biomass in the surveyed area of 16,654 nm2 amounted to 151.2 thousand tons, with amean density of 9.11 t/nm2 (Table 2). In the eomparable area, eomprising ICES Subdivisions25 (80%) and 26 (around 50%), there oeeurred asubstantial, almost threefold, deerease in thebiomass density ofthe discussed speeies relative to 1995 (Orlo\vski et al. 1996). Tbe share ofherring in the resourees of eommereial pelagie fishes in the Surveyed area was eonsiderably

. . 2smaller (27.3%) than the share ofsprat (69.8%), whose mean densitywas 23.27 t1nm .

The geographie distribution ofherring resourees in the whole research area is presented inFigirre 4. Tbere were no sites of eonsiderable eoneentrations of fish of this speeies obserVed,and the maximum biomass densities did not exeeed, exeept for onesmatl area (Darlowo fishinggroimd), a densityof40 t1rim2 (mark "M" in Figure 4). In most ofthe area (and partieularly inits eastern part), densities under 14 t1nm2 oecurred. In the Polish EEZ ofthe Baltie Sea, higherherring densities--exeeeding 14 t1nm2-were reeorded in the area southwest 0 f the meridian18°E. Similar densities were found in Hanö Bayand in the.eastern part ofthe GulfofGdafisk.

Tbe greatest ehanges in. herring distribution sinee 1995 oeeurred in the eastern Baltie,where fIsh resourees east ofthe meridian 18°E have deereased notieeably. In 1995 (Orlowskiet al. 1996), herring eoricentrations exeeeded here everi 120 t/nm2

, whereas in 1996 they didnot reaeh 4 t1nm2

• Coneentrations of this species have also disappeared eompletely from theGdansk Deep and the southern slopes ofthe Gotlaild Deep. .

Ir, in 1995, ICES reetangle 3964 showed reeord values \vith regard to herring biomass(70.5 thousand tons), in 1996, aeeording to estimates, only 2.3 thousand tons eould be foundthere. In 1996, the largest herring resourees were reeorded in the followmg ICES reetangles:4060 (18.9 thousand tons), 3861 (16.7 thousand tons), 3962 and 4059 (13.1 thousand tonseaeh). Tbe area ofthe most repeatable distnbution ofherring eoneentrations in 1995 and 1996eneompassed the southern part of the Polish EEZ, partieularly the area lying east of theDarlowo fishing grounds as far as the Slupsk Furrow.

Sprat resourcesSprat biomass in the surveyed area was estimated at 387.5 thousand tons, with a mean densityof23.27 t1ni:n2 (Table 2). Tbe share ofsprat in the biomass ofthe species examined eonstitutednearly 70%. Consequently, this species was clearly predominant in numbers in the iehthyofaunaof the southern Baltie. A year before(Orlowski er al. 1996), in the eomparable area, sprritbiomass amounted to 335.6 thousand tons, with a mean densitY of21.4 tlnm2

• Large relativestability ofthe biomass ofthis species eould thus be observed in the years 1995-1996. .

Tbe geographie distribution of sprat resomees is presented in Figure S. A relatively highdensity of sprat bioniass (claSs M: 40-120 t/nm2

) was estimah~d in a few areas of the Baltiesituated mainly in the vieinity ofthe northern border ofthe Polish EEZ. This area eomprisedshallower waters betWeen Norra Midsjöbanken and Södra Midsjöbanken, extending as far asthe western slopes of Hoburgs Bank. Tbe seeond most importUnt area of sprat eoncentrationwas found on the southeastern slopes ofthe Gdansk Deep. Smaller areas ofconceritration werereeorded in the Slupsk Furrow, on the eastern slopes ofthe Bomholrri Deep arid in the westernpart ofthe BornhoIm-S fishing ground.

4

. ,

•

e.

~ _.,•

Tbc general pattern of sprat distribution in 1996 exhtbited a very large simiIarltY to 1995.Only a certain shift of this species iri the northerly direction by aroU11d 16 nm relative to thehypothetical center ofgravity could be observed.

In comparing sprat distrIbution by particuIaf ICES rectrißgles~ it can be noticed that, in1996, considerable.decreases in the densitY of resources occtirred solely iri the Gdaiisk Deep(lCES rect8ngle 3864). Sprat concentrations in the rerilaining part of the southern Balticbehaved iri a much more stable maniter.

The. gi-eatest sprat resources were located in the followrng ICES recuingles: 4162 (43.7th01isand tons), 4163 (36.4 thouSand toris) and 4061 (35.1 thousarid tons). A year before, thelargest si>rat resourees were estinlated in the following reetangles: 4362 (86 thouSänd tonS)~

4462 (55.9 thousand ions) arid 3864 (50 thousand tons).

Cod resOllrces '. . ,The assessment of eod resourees by aeoustic methods performed while estimating peIagic fishresciÜIces is burdened with errors; nonetheless, it can be regarded as comparable Within theframework of identically performed research procedures used duririg the ci-uise (Grzebielec elal. 1995, Orlowski el al. 1996, Grygiel el al. 1996).

Cod biomass for the whole surveyed area, estimated according to the procedure deScribed(see Afaterials and Afeihods; Tables 2 arid 3), amourited to 15..9 ± 1.1 thoUsand tons, with amean density of 0.97 t/nm2

• A year before, particularly in ICES Subdivision 25, conside~ablyhigher derisities of this species were recorded; rriean cod denSity in the whole southein Baltiewas then equal to 1.79 tlnm2 (3.37 tlnm2 in 1994, GrZebielec el al. 1995).

Cod resourees in the Polish EEZ in 1996 \vere eStimated at barely, 6.9 thoUsciitd tons, withamerin density of 0.91 tlrim2

; they were Substaßtially small6i than in 1995 (22.9 thousaridtons). In 1995-1996~eod biomass greater thrin mean was located only in ICES rectaDgle 3961,comprisirig the eastem slopes of the Bornholm Deep arid the western part of the SlupskFurrow.

The characteristfcs of fish control haulsIn October 1996" merin catch-per-hour of all the fish species along the traek of echoiritegration was 61 kg (254 kg in 1995). Cateh-per-hour ranged from 0.4 to 271.6 kg (Table 1,

. ,.' ." . ,.'. "',,,., 2 'Grygiel et al. 1996). One control haul corresponded on the average to an area of 438 nm , ascompared With 566 nm2 in 1995. . "

Herrmg cateh rate during the ciuise rariged from 0 to 80.5 kglh (a meari of 14.7 kglh), andsprat catch nite-from 0.02 to 243.5 kglh (a mean of 48.5 kglh). Sprat, in different numbers,oceurred in all the control hau1s; at the same time, they predommated in Dumbers in as many as31 hauls. ,. Cod oceurred in pelagic hauls as bycatch. The geographie exterit of oecurrenee was

lirIlit6d alrnost exclusivelyto the Bornholnt Deep (wheie they were preserit in 10 hauls, Grygielel al. 1996). Cod were also caught in orie haul perforrned in the Gulf of GcIansk. Catch-per­hour ranged from 1.0 to 13.8 kg. In the bycatch; apart from ,eod, there occtirred the followingspecies: smelt, ee!, flourider, turbot, lurnpfIsh, arid only occasionally-stickleback.

The bioiogical characteristies of herriög arid sprat ,In the cutches made in the Gdaiisk Basin; herring 15-19 ein in length and ofa mean weight 6f27-32 g prevalled (Table 5). in the Gulf ofGdrinsk and over the eustein slopes ofthe GdanskDeep, herring from the youngest 1996 year~claSs, mostly 10.5-11.0 cm in length, oecurredre1atively numerously. In the hriuls made in the other stirveyed areas, herring from the ah()vc­mentioned year-class were seldom obserVed (Table 4). Over the easterri slopes of theBörnholm Deep and on the Kolobrzeg fIshing ground, specimens 14-27 cm in length were

5

-----

-------------------------------------

eaught. In the hauls made in Subdivision 25, herring from age groups 2 and 4-5 weredominant. .

Among sprat eaught in the Gdarisk Basin, speeimens 10.0-12.5 em in length, of a meanweight of6.1-11.8 g and from age groups 1-4 prevailed (Tables 6 and 7; Grygiel et al. 1996).In the Bornholm Basin, sprat from length-classes of 11.5-13.0. em, of a mean weight of9.6-13.8 g and from age groups 2-4 and 1 were predominrint. It was alarming that in theeatehes (exeept for ICES reetangle 3863) there were no sprat from the 1996 yerir-class (Table6). .

CONCLUSIONS[J Tbe total biomass ofthe elupeoids in the surveyed area in Getober 1996 was estimated at

539 thousand tons (mean biomass density was 32.31 t/nin2). Tbe mean share by weight of

sprat, herring and eod in the biomass ofthe fish species exillnined amounted to 69.8, 27.3and 2.9%, respeetively. A year before, the predominanee of sprat over herrlng was only3.3%. In 1996, the highest total fIsh biomass densities were reeorded in the foUmving ICESreetangles: 4162 (51.43 t/rim2

), 4061 (43.63 t/nm2) arid 4062 (40.63 t/nm2

). In 1995,reetangle 3864, eorrespondinf- to the Gdarisk Deep, exhIbited reeord values with regard tobiomass density (117.13 t/nm). .

[J In 1996, herririg and sprat resourees in the research area eomparable with 1995 wereestimated at 151 and 388 thousand tons, respeetively. In 1995, resourees ofthese speciesamounted to 420 and 336 thousand tons, respeetively. In 1996, a sharp deerease wasreeorded in herring resourees (down to 36% ofthe 1995 state), along with a slight inereasein sprat resourees.

[J In 1995-1996, in the surveyed areas ofthe Baltie, the largest deerease in fish resourees wasreeorded in the southeastern part of the sea. Tbe deereaSe in herring biomass was alsoeonfirmed by low eateh rates of eontrol hauls performed from aboard r/v "Baltiea". Tbeprobable reason for such astate was the geographie movement of fIsh eonneeted to anatypieal hydrological situation (deseribed below after Grygiel et al. 1996), heing aeonsequenee ofthe frosty 1995/96 ,vinter arid the eooUy '96 summer. .

[J In Oetober 1996, sea water temperature iri the surfaee layer ofthe surveyed Baltie area \vasclearly lower (by 1.61°C on the average) than in 1995, and slighdy 10wer (by 0.38°C onthe average) than the long-term mean. Also water temperature in the deep layer waseharaeterized by re!atively low values. In the Sh.:ipsk Furiow and Gdarisk Deep, wiriterwater remained, and its temperature was 4-5°C and 4°C, respeetively. Gnly in theBornholm Deep was the inflow of warmer water from the western Baltie marked, and thetemperature there averaged 7°C. In Getober 1996, the salinity ofthe waters ofthe southernBaltic deereased relative to the long-term mean-bOth in the deep layer (partieularly in theSlupsk Furrow) and in the surfaee !ayer (by 0.47 PSU on the average). In Getober 1996,the oxygen eontent in the deep !ayer of the Gdarisk Deep, Slupsk Furrow and BornholmDeep increased relative to the long-term mean by 2.19, 1.33 and 0.37 m1Il, respectively.

ACKNOWLEDGMENTSThe authors would like to thank Dr. Tiit Raid from the Estonian Marine Institute inTallinn, Mr. Sergej Shirokov from the Latvian Fisheries Research Institute in Riga,and all the colleagues from the Sea Fisheries Institute in Gdynia for very efficientand friendly scientific cooperation during the October 1996 hydroacoustic survey onboard r/v "Baitica".

6

•

•

•

•

•

REFERENCESAnon. 1990. Report of the Planning Group for Hydroacoustic Surveys in the Baltic. ICES

C.M.1990/J:34.Anon. 1994. Report of the Planning Group for Hydroacoustic Surveys in the Baltic. ICES

C.M.1994/J:4. .Anon. 1996. Report ofthe Baltic International Fisheries Survey \Vorking Group. ICES C.M.

1996/J:l, B.F.C.Foote, K. 1986. Measurement of fish target Stfength With a .split-beam echosounder. J.

AcouSt. Soc. ArD.. 80(2): 612-621. .Grygiel, W., A. Orlowski, M. Wysz)rnski, A. Kurowicki. 1996.Wst~pneWyniki hydroakll­

stycznych badan rozmieszczenia i wielkoSci zasob6w sledzi, szprot6w i dorszY w 24,25 i 26 podobszaIze ICES (na podstawie rejsli r/v "Baltica", 5-24.1 O. 1996 r.).[preliminary results ofthe hydroacoustic surveyon the distribution and size ofherring,sprat and cod resources in ICES Subdivisions 24; 25 and 26 (based on the eruise ofr/v"BaItica", Oet. 5-24, 1996)]. Mor. Inst. Ryb. Gdynia (mimeo, in Polish).

Grzebielec, R, A. Paciorkowski, M. Wyszynski, W. Grygiel. 1995. Polish hydroaeoustieassessment survey ofherring, sprat and eod stocks in ICES Subdivisions 25 and 26 ofthe Baltic eonducted in Oetober 1994. ICES C.M. 1995/J:18, B.F.C.

Orlowski, A. 1989. Zastosowanie akustyeznyeh metod do badania rozmieszezenia ryb iwarstw rozpraszajacych na tle Srodowiska morskiego (Application ofacoüstic methodsfor study ofdistribution of fish and scattering layers vs the marine environment). Studiai Materialy, sero B, nr 57; Mor. Inst. Ryb. Gdynia.

Orlowski, A; 1990. Distribution arid size offish stocks in the Polish fishery zone determi-. nated by the acoustie method (eruise of r/v "Profesor Siedlecki", October 5-23, 1989).

Bull. SeaFish. Inst., 1-2(117-118), Gdynia; 2-12. ,Orlowski, A. 1993. Distribution of the fish stocks vs environ mental factors in the Polish

fishery zone, determined by the acoustie method (cruise of r/v "Profesor Siedlecki",Oct. 2-24, 1990). Bull. Sea Fish. Inst., 1(128), Gdynia; 29-44.

Orlowski, A. 1994. Rozmieszczerue i wielkosc zasob6w ryb poludniowego Baltyku wlatach 1988-1992. [The distributiOll and size offish resomees in the southern Baltie in1988-1992]. StiIdia i Materialy, sero B, nr 57, Mor. Inst. Ryb., Gdynia.

Orlowski, A. 1996. Increase of cod biomass in the southern Baltie observed during 1994/5autUmn aeoustic surveys. In: Scientifie Papers Presented at the Polish-Swedish Symposiwnon Baltie. Cod. Gdynia 21-22 March, 1995, IMR Repoit No. 327, LYSekil; 49-58.

Orlowski, A; W. Grygiel, R Grzebielee; M. WyszyD.ski. 1996. Polish aeoustie survey of .fish stock abundanee in the ICES Subdivisions 21, 26, arid 27 ofthe Baltie Sea earriedout in Oetober 1995. ICES C.M. 1996/J:34, B.F.C.

7

14

41

40

39

38

37

17 18 19 20 21

55

Figure 1. Cruise track (location of end points of one-mile sections of integration)and the location of pelagic control hauls.

• •

14

41

40

39

38

37

59

15

60 61

17

62

18 19 20 21

56

55

Figure 2. Map of the distribution of the values of eolumn scattering strength SVCin the area surveyed from aboard r/v "Baltica" in Oetober 1996. Seale ofgraphieal marks of map:SVC: D: < --64, H: -60+-56, J: -56+-52, L: -52+-48, N: -48+-44, P: >-44 [dB]

14

41

40

39

38

37

15 16 17 18 19 20 21

56

55

-...o

Uo......_----=:z.L.---'-- 1..- ---'-- 1..- --J.- 1..- ---1 5459 60 61 62 63 64 65

Figure 3. Map ofthe distribution ofthe values of column scattering strength SVCin the area surveyed from aboard r/v "Baltica" in October 1995. Scale ofgraphical marks of map:SVC: D: < -64, H: -60+-56, J: -56+-52, L: -52+-48, N: -48+-44, P: >-44 [dB]

•

62

AEIM

56

55

2120191817

6160

15

59

14

38

40

37

39

41

Figure 4. Distribution of herring resources (surface density of biomass) in thearea surveyed from aboard r/v "Baltica" in Gctober 1996. Gra~hical scale ofmap: A: 0-4, E: 4-14, I: 14-40, M: 40-120, Q: 120-360 [t/nm ].

--- -----

14

41

40

39

38

37

59

15

60 61

AEltvl

19 20 21

56

55

Figure 5. Distribution of sprat resourees (s rfaee density of biomass) in the areasurveyed from aboard r/v "Baltiea" in Oetober 1996. Gr~hieal seale of map: A:0-4, E: 4-14, I: 14-40, M: 40-120, Q: 120-360 [t/nm ].

•

•Table 1. Catch data. rlv BALTICA, October 1996

No Date Time Latilude Longilude Duration Speed Water Headrop Ne! Total Validity

start depth depth opening catch(UTe) (ddmm.m N (ddmm.m E) (min) (kn) (m) (m) (m) (kglh)

1 05.10 11.30 5435.4 1852.8 40 4.6 69 21 32 20.7

2 05.10 13.30 5430.2 1854.3 30 4.0 62 25 26 82.6

3 05.10 15.00 5427.9 1902.4 30 4.2 68 22 24 38.7

4 05.10 16.40 5427.0 1921.3 40 3.9 69 23 26 12.7

5 06.10 6.10 5435.7 1920.1 30 3.6 80 10 24 21.6

6 06.10 9.40 5450.8 1918.9 60 3.9 107 40 27 231.7

7 06.10 14.50 5512.5 1859.5 60 3.8 79 18 28 122.3

8 07.10 6.10 5540.9 1840.0 60 3.6 97 47 30 54.0

9 07.10 10.30 5601.7 1840.7 40 3.4 105 51 28 57.5

10 07.10 15.00 5618.7 1832.8 30 4.0 78 28 30 104.4

11 08.10 6.20 5539.9 1820.2 30 4.0 98 30 30 37.9

12 08.10 9.15 5527.6 1830.0 40 3.5 86 50 30 26.0

13 08.10 16.00 5454.9 1846.5 30 3.9 95 60 30 1.0• 14 09.10 6.10 5538.7 1759.5 30 3.5 66 25 30 110.4

15 09.10 12.00 5608.9 1758.1 60 2.9 55 23 28 3.2 unsuccessful

16 09.10 14.40 5602.5 1743.4 90 3.2 61 20 26 137.6

17 10.10 6.20 5529.0 1741.3 40 3.2 61 27 28 0.5

18 10.10 9.40 5519.3 1801.3 60 3.9 75 40 30 19.0

19 10.10 14.45 5514.9 1740.7 60 3.6 66 25 28 79.0

20 11.10 6.20 5514.4 1720.4 60 3.1 92 50 30 15.8

21 11.10 12.10 5541.8 1743.8 30 3.7 58 30 28 225.0

22 11.10 14.35 5552.3 1738.9 60 3.7 59 27 28 215.7

23 12.10 6.15 5523.8 1700.1 30 3.6 57 23 27 1.5

24 12.10 10.20 5511.3 1700.3 35 3.3 90 50 30 66.3

25 12.10 13.35 5512.5 1838.5 60 3.7 67 35 30 23.5

26 13.10 6.30 5518.2 1632.3 30 4.1 62 35 28 2.9

27 13.10 10.20 5535.6 1636.3 60 3.9 58 30 28 271.6

28 13.10 13.20 5540.7 1621.0 60 3.6 67 30 30 33.8

29 14.10 6.30 5514.2 1617.8 60 3.6 68 40 27 46.8

30 14.10 10.20 5504.6 1621.7 60 3.8 60 38 27 69.5

31 14.10 13.30 5457.6 1606.7 60 3.6 70 38 28 21.3

32 15.10 6.25 5512.4 1549.6 30 3.1 93 37 30 117.5

33 15.10 13.30 5453.3 1540.4 30 3.4 77 39 30 31.1• 34 15.10 13.30 5442.4 1539.6 30 3.4 64 35 25 46.6

35 15.10 16.00 5429.8 1540.7 60 3.2 54 25 27 77.236 16.10 6.10 5445.5 1454.9 30 3.6 56 22 28 2.6

37 16.10 7.50 5444.8 1505.9 30 3.6 62 26 29 1.8

38 16.10 15.25 5539.2 1517.3 30 4.1 69 35 27 24.5 intercalibration

39 16.10 21.40 5522.6 1544.6 30 4.0 93 10 28 61.5 intercalibration

40 20.10 11.15 5532.2 1520.8 60 3.3 73 37 29 64.2

41 20.10 16.10 5535.5 1443.3 60 3.6 74 24 28 10.9

42 21.10 6.25 5445.0 1446.5 60 3.9 51 13 27 15.7

43 21.10 11.50 5429.3 1527.7 60 3.8 48 15 26 6.2

44 22.10 11.00 5459.5 1834.8 60 3.0 81 274.1 bottom trawl

45 22.10 16.10 5455.1 1842.7 60 4.1 93 22 26 74.4

46 23.10 9.40 5550.7 1809.9 30 4.0 66 25 27 0.4 intercalibration

47 23.10 11.40 5546.9 1813.3 30 3.9 74 25 30 162.2 intercalibration

48 23.10 15.20 5556.3 1819.5 30 3.9 88 24 29 169.1 intercalibration

Note: hauls 44, 46, 47and 48 have not been included in assessment

13

Table 2. Characteristics of fish stocks in the surveyed areas by lCES subdivisions and rectangles.

-biornass BiornassSD' lCES Surface < SA > <Svc> Surface density

SQ. [nrn2 1 [rn 2 /nrn 2 1 [dB 1 [t/nrn2 1 [tl

Herring Sprat Cod Herring Sprat Cod

24 3859 838,5 270 -52,03 0,13 23,37 0,00 112,3 19594,2 0,0Surn 838,5 0,13 23,37 ° 112 19594 °25 3760 372,3 245 -52,45 19,99 6,29 0,33 7441,0 2343,3 121,5

3860 1035,8 199 -53,37 11,56 7,62 0,15 11971,7 7894,4 160,23861 789,4 392 -50,41 21,19 15,76 3,29 16724,5 12440,2 2597,93862 371,4 412 -50,21 13,12 21,71 0,00 4873,0 8061,4 0,03960 976,9 393 -50,41 9,54 24,49 0,84 9319,9 23919,7 824,33961 1026,4 306 -51,50 7,52 18,00 3,02 7715,4 18474,7 3101,33962 1032,2 398 -50,35 12,69 21,01 0,00 13097,9 21690,6 0,04059 579,2 370 -50,67 22,54 12,35 5,03 13054,8 7155,1 2910,64060 1012,5 350 -50,91 18,66 14,06 3,13 18892,1 14231,6 3173,54061 1019,3 535 -49,06 9,16 34,47 1,02 9334,1 35133,6 1042,24062 961,4 550 -48,95 6,91 35,35 0,00 6647,1 33983,1 0,04162 989,5 689 -47,97 7,75 44,23 0,00 7668,6 43764,3 0,0

Surn 10166.3 12,47 22,53 1,37 126740 229092 13931

26 3764 138,0 576 -48,75 38,42 16,14 0,00 5301,8 2227,3 0,03863 541,4 398 -50,36 9,15 19,25 3,66 4951,3 10422,5 1981,63864 883,4 465 -49,67 9,00 26,46 0,00 7947,1 23377,4 0,03963 1032,2 267 -52,09 2,16 18,21 0,00 2233,1 18794,1 0,03964 1032,2 233 -52,68 2,26 15,26 0,00 2331,4 15755,5 0,04063 1019,3 425 -50,07 0,43 31,17 0,00 434,7 31767,9 0,04163 1002,9 527 -49,13 1,66 36,34 0,00 1665,3 36441,7 0,0

Surn 5649,4 4,40 24,57 0.35 24865 118787 1982

16654,2 9,11 23,2 0,96 151717 387472 15913

• ..

Table 3. Survey statistics. r/v BAlTICA, October 1996.

SO leES Area Mean Sa Sigma Total Species Abundace in millioll$

rectangle abundance composition <%>2

m2

/nm2 m2 .10-4

nrnin millions herring sprat herring sprat

24 3859 838.5 270 1.59 1424 0.32 99.68 5 1420

25 3760 372.3 245 2.36 386 50.2 49.76 194 1923860 1035.8 199 2.03 1010 35.92 64.08 363 6473861 789.4 392 2.12 1459 29.46 70.44 430 10283862 371.4 412 1.59- 962 15.35 84.65 148 8143960 976.9 393 1.7 2260 14.62 85.36 330 19293961 1026.4 306 1.69 1848 11.47 88.48 212 16353962 1032.2 398 1.59 2588 15.34 84.66 397 21914059 579.2 370 2.33 916 39.49 60.11 362 5504060 1012.5 350 2.17 1628 33.06 66.72 538 10864061 1019.3 535 1.59 3436 9.5 90.49 326 31094062 961.4 550 1.56 3386 7.06 92.94 239 31474162 989.5 689 1.62 4207 7.12 92.88 300 3908

26 3763 0 0 0 0 0 0 0 03764 138 576 1.83 433 42.83 57.17 185 2473863 541.4 398 1.21 1770 17.05 82.92 302 14683864 883.4 465 1.19 3453 10.91 89.09 377 30763963 1032.2 267 1.33 2059 3.92 96.08 81 19783964 1032.2 233 1.28 1878 4.65 95.35 87 17904063 1019.3 425 1.31 3293 0.55 99.45 18 32754163 1002.9 527 1.39 3792 1.94 98.06 74 3719

-lo

lJ1

,

Table 4. Estimated number (millions) of herring. r/v BALTICA, October 1996

SO Rectangle Total age 0 age 1 age 2 age 3 age 4 age 5 age 6 age 7 age 8 age 9 age 10+

24 3859 5 0 2 0 0 0 0 0 0 0SUM 5 0 2 0 0 0 0 0 0 0

25 3760 194 4 13 31 22 41 38 25 16 3 1 03860 362 0 33 74 42 82 67 38 21 4 1 03861 430 1 26 70 45 90 89 58 37 9 3 23862 148 0 13 30 16 32 29 16 9 2 1 03960 330 3 39 82 40 73 56 24 11 2 1 03961 212 0 15 40 23 44 42 26 17 4 1 13962 397 0 34 80 42 85 78 43 25 5 2 14059 362 3 27 63 38 79 72 44 27 6 1 14060 539 6 43 97 58 116 106 64 38 9 2 14061 327 1 34 72 36 73 59 32 16 2 1 04062 239 1 26 61 27 48 41 21 11 2 1 04162 300 2 35 83 34 59 48 24 12 2 1 0SUM 3838 21 338 783 421 824 726 415 238 50 15 6

26 3763 0 0 0 0 0 0 0 0 0 0 0 03764 185 16 12 24 19 34 36 27 13 3 1 03863 302 159 18 32 18 28 24 15 6 2 0 03864 377 101 28 52 37 58 52 33 12 3 1 03963 81 1 7 15 10 17 15 10 3 1 0 03964 87 2 9 17 12 18 16 10 3 1 0 04063 18 0 2 4 2 4 3 1 1 0 0 04163 74 0 10 18 12 15 11 6 2 0 0 0SUM 1049 279 77 144 99 159 146 96 38 9 2 0

• •

•Table 5. Estimated mean weight (gramm~ of herring. rlv BAlTICA , October 1996

SD Rectangle Total age 0 age 1 age 2 age 3 age 4 age 5 age 6 age 7 age 8 age 9 age 10+

24 3859 24.3 8.6 24.2 24.0 26.4 29.7 26.7 38.6 0.0 0.0 0.0 0.0

25 3760 38.4 10.5 24.1 29.1 38.4 37.1 38.2 42.1 47.4 53.8 54.0 90.13860 33.0 14.2 25.0 26.2 32.2 32.2 33.7 38.8 44.4 52.7 52.8 89.33861 38.9 9.9 25.7 29.0 38.0 37.2 39.1 42.2 48.5 59.2 63.1 96.13862 33.0 15.6 25.0 26.7. 31.9 32.2 34.6 38.4 44.9 62.2 62.3 98.73960 28.2 10.6 24.2 23.8 26.5 27.7 31 34.6 42 57.1 59.2 85.53961 36.4 10.2 24.9 27.5 35.2 35.1 37.9 41.2 47.7 73.7 72.4 102.53962 33.0 15.6 25 26.7 31.9 32.2 34.6 38.4 44.9 61.2 62.3 98.74059 36.1 10.4 25.2 28.1 35.1 34.7 38.3 40.9 46.3 56.0 57.3 82.24060 35.1 10.4 24.9 27.5 34.5 34.1 37.7 40.4 45.5 55.5 55.4 80.04061 28.6 12.4 24.9 25.6 28.6 29.2 30.6 35.3 39.5 47.4 47.5 69.44062 27.8 12.6 23.4 23.9 27.8 29.2 31.9 36.4 40.5 55.1 55.4 86.84162 25.6 12.4 22.7 23.1 26.9 28.7 30.6 36.0 40.0 54.7 50.2 69.4

26 3763 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.03764 28.6 7.1 20.2 23.6 27.6 29.5 30.3 33.8 37.6 48.5 37.4 0.03863 16.4 7.4 18.1 19.8 23.8 28.4 28.7 34.2 38.8 49.9 41.7 0.03864 21.1 7.3 19.4 21.5 24.2 26.6 27.7 31.4 37.6 39.3 37.3 0.03963 27.7 9.2 19.9 22.3 24.4 26.5 27.7 32.2 37.4 46.9 35.5 943964 26.7 9.2 19.5 21.8 23.6 25.3 27 31.1 37.3 44.2 34 04063 24.1 11.8 18.4 20.7 22.5 25.5 27.2 33.3 41.5 42.7 42.7 0.04163 22.6 0.0 19.1 20.3 21.6 24.6 25.3 29.1 35.4 39.8 40.7 0.0

Table 6. Estimated number (millions) of sprat. r/v BALTICA, October 1995

SD Rectangle Total age 0 age 1 age 2 age 3 age 4 age 5 age 6 age 7 age 8+

24 3859 1418 0 149 601 166 244 185 54 14 6SUM 1418 0 149 601 166 244 185 54 14 6

25 3760 192 0 32 80 34 32 9 4 1 03860 646 0 95 254 126 118 34 15 3 13861 1027 0 138 393 205 198 61 27 5 13862 815 0 239 363 115 76 16 6 1 03960 1931 0 239 756 388 370 116 48 10 43961 1635 0 327 639 289 263 77 33 5 23962 2193 0 642 977 309 204 44 15 2 o·4059 550 0 50 211 117 115 36 16 3 14060 1086 0 88 399 237 242 79 33 7 24061 3109 0 581 1293 547 469 143 59 12 34062 3147 0 588 1224 579 522 157 63 9 34162 3911 0 406 1426 848 844 254 106 20 8

SUM 20243 0 3426 8016 3794 3455 1027 424 77 26

26 3763 0 0 0 0 0 0 0 0 0 03764 247 0 84 74 46 33 8 2 0 03863 1466 6 870 336 144 85 18 6 1 03864 3076 0 1836 649 323 206 46 15 0 03963 1978 0 477 649 439 311 77 20 4 23964 1789 0 600 593 317 211 50 14 2 24063 3272 0 596 1143 802 567 124 33 3 34163 3719 0 561 1179 963 744 208 52 7 4

SUM 15547 6 5025 4622 3034 2156 532 143 18 11

• .. ..

Table 7. Estimated mean weight (gramme$ of sprat. rlv BALTICA , October 1995

SO Rectangle Total age 0 age 1 age2 age 3 age 4 age 5 age6 age 7 age 8+

24 3859.0 13.8 0.0 11.9 13.0 14.0 14.4 14.6 14.2 16.2 21.0

25 3760 12.2 0.0 9.4 10.8 12.2 13.5 14.4 15.4 17.2 16.03860 12.2 0.0 9.4 10.9 12.4 13.5 14.2 14.9 17.2 15.93861 12.1 0.0 9.4 11.0 12.4 13.5 14.4 15.1 17.3 16.23862 9.9 0.0 8.7 10.5 11.6 12.7 13.6 13.9 20.2 15.03960 12.4 0.0 9.6 11.1 12.4 13.5 14.3 15.1 17.0 15.73961 11.3 0.0 9.0 10.8 12.3 13.4 14.2 14.9 17.1 15.63962 9.9 0.0 8.7 10.5 11.6 12.7 13.6 13.9 20.2 15.04059 13.0 0.0 9.9 11.2 12.5 13.5 14.4 15.4 17.1 16.34060 13.1 0.0 9.9 11.3 12.6 13.6 14.4 15.4 17.0 15.84061 11.3 0.0 9.2 10.8 12.1 13.5 14.6 15.7 19.1 15.74062 10.8 0.0 8.9 10.9 12.3 13.5 14.3 15.0 17.0 15.54162 11.2 0.0 9.6 11.2 12.6 13.5 14.2 14.8 17.0 15.7

26 3763 8.3 0.0 6.9 7.9 10.4 11.2 12.1 12.4 14.2 0.03764 9.0 0.0 6.9 7.9 10.4 11.2 12.1 12.4 14.2 0.03863 7.1 1.5 5.8 7.6 9.7 10.8 12.6 11.7 13.4 0.03864 7.6 0.0 6.5 9.2 10.0 11.5 12.3 20.0· 20.0 0.03963 9.5 0.0 6.9 8.0 9.9 11.9 12.0 15.6 0.0 0.03964 8.8 0.0 6.7 9.6 9.7 11.8 12.0 16.5 20.0 0.04063 9.7 0.0 7.8 9.4 11.1 12.4 13.3 13.8 0.0 18.64163 9.8 0.0 8.1 9.2 12.2 13.6 14.1 18.3 0.0 0.0