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Intemationat Coundl for theExptoraUon of the Sea

CM 1997/ HH:22Pelaglc Fish Commlttee

ntE REPRODUCT1YE BIOlOGY OF THE PATAOONIAN SPRAT (Spmtua fuegensla):SEVERAL FACTS AND STILL SOME SPECULATIONS

R.P. ~nch8Z, A. Madirolas, R. Reta, M. P6jaro, M. O. Ehrlich, G. AJvarez Colombo and G. Macchilndtu1D N8cionaI de 1nYMtig8c:i6n Yo..roIlo peeqlHM'O

P.O. Box 175,~ del PIlIta 7600, ARGENTlNA

l8i~--------------------------INIDEP

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7M.v rnrrr i.v IInl In "r cile,[ \I";thnrlf l"l/w re/i·relle,. In Ih,. mllhnr.'

Inlernational COllncil rOr theExploration cf tho Sea

THE REPRODUCTIVE BIOlOGY9F,T~~EPATAGONIAN SPRAT.(Sprattus fuegensis):SEVERAl FACTS AND STIll SOME SPECUlATIONS

R.P. Sanchez, A. Madirolas, R. Rela, M. Pajaro, M.D. Ehrlich, G. Alvarez Coiombo and G. Macchi

Instituto ~Jacional de Investigaci6n y Desarrollo PesqueroP.O. BOl( 175, Mar deI Plata, 7600, ARGENTINA

ABSTRACT: TWo populations of Spral;us fuege;lsis have been recognized in the SW Atlantic, one inhabiting lhecoaslal area off Malvinas Islands and another on the continenlal coast in the soulhern extreme of South America.Previous reports supported the idea of two separate spawning populations and led to the inference that reproduction offsoutherri Patagonia should take place during the spring in the straits arid channels of the Fireland. In autumn, winterand spring 1996 three acoustic-icthyoplankton surveys covered the spawnirig grounds of. each population. Theprevailingoceanographic conditions, and plankton components in each of thern are described. Reproduction aroundMalvirias ,lslands wasobserved in shelf waters to lhe south of the archipelago in late September. Histological analysisof ripe females showed that the species is a.serial spawner Batch fecundity estimates based on the hydrated ooctytemethod are reported for the first time. Mean relative fecundity was estimated at 288 oocytesl gram The assumedexistence of the spawning grounds off the Firelandwas confirmed. Egg and early larvae of the species were collected .in severat stations along the Beagle Channel, the Strait of Le Maire, and the southern Patagonian shelf in lateNovember. The existence of an extended nursery ground alorig the southern Patagonian coast, was corroborated. AGompertz equation (5.75exp[2.194(1-exp(.O.0195t))1l was fitted to describe larval and posl-Iarval growth. Back­calculated birthdates indicate that the spawning season ofthis population began during the firstweek of Oetober. Theacoustically estimated biomass of the species. along the shores of southern Patagonia was 323,400 t

Kevwords: spral, SW Allanlic, fisli reproducliol1. ichlhyopfan1<lori. Sprallus fuegensis.

INTRODUCTION

Sprals, genus Sprattus, cornprise five species wilh acharacteristic anlilropical distribution, four of lheminhabiling the Soulhern Hemisphere. Sprals are marine pelagic schooling fishes, occurring especially incoaslal waters, orten close inshore. sornelimes loleraling very low salinilies (Whilehead, 1985).

S. fuegensis, lhe palagonian. spral, is dislribtlled along the Atlantic and Pacific ceasls of nie soulhernextreme of the Soulh American continenl. The habilat of the Palagonian spral is lhe sotJlhernmost occupiednol only by lhe gemis Sprattus. bul byall Clupeoid fishes of the world. Two populations of S. fllegensis havebeen recognized in the SW Allanlic, one inhnbiling lhe coastal area off Malvinas Istands and anolher on the .coast of Sanla Cruz and Tierra dei Fuege Provinces in the soulhern conlinental exlreme üf South America.The oceanographic characteristics of lhe spral habilat in lhe SW Atlantic have been doscribed by Sanchezand Ciechomski (1995). The arens inhabiled by the speCies also include, the Beagle Chanrlel, Straits of LeMaire and Magellan and Burdwood Bnnk (See Figure 1 .ror lopography and geographical references). On

. lhe Pacific coasl the spedes has been found 10 exlend 10 laliludes as low as33'S (Manrl, 1954), thOlJghlhis record may possibly refer 10 lho sympalric Stratlgomera benticl<i (Whilehead, 1985).

Previous reports, reviewed by Sanchez ~t af. Hi93, gave fragmentarY evidence on lhe dislribullon aridabundance of early li.re hislorY stages of lhe species, sllpportinglhe idea of lwo separale spawningpopulations. Resul's of the first pelagic slIrvey on the SOIJlhern Palagonian Shclf carried out in aulumn1992, revealed the exislence of a rrHljor ntJrserY ground of.lhe Palagoniari spral' on the coaslat region offSanla Cruz and Ti~ma dei Fuego, leadingto the inference that reproduction off sOIJlhern Palagonia shouldlake place during the spring in lhe slmils and channels cf Tierra dei FlIego (Sänchez et al. 1995) .

.Seascimil acous!iciichlhyoplanklon cruises were organlzed in H~96 wilh lhe objective to sllrvey the spawningand mirsery grounds of bolh poplliatiofls, and assess lhe adult spawning concenlrations. This paper reportson the resulls of lhose sllrveys, with special reference to progress in the underslandinq of lhe reproduclivebiology of the species..

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The physiciJl setting

The coastal region off Southern Patagonia, and .the adjaeent oceanic area are bolh under Ihe prevailinginfillence (70%) of western winds (W,. SW, amI NW). The territorial extension of the allstml extreme of theSoutharnerican continerlt is insufficient to develop Gontinental air masses, hut inrluences, on aeeount of its

'topography, tlle loeal rain regime and wind strength and directiein.

The region is located within the natural, corridor of extratropical cycions know as ihe low pressure bett.Characteristic of this region is the constant penelratiori of cold and wet air masses from Antarelica eomingfrom Ihe Pacific dragged bythe West Wind Drift. The atmospheric pressure attains ~nnlJal mean vahjes of1,000 hpa. Monthly averages are higher during summer, and lower in wintertime.

Air temperalure varies 'ittte both dally and annualy, on account of the oceanic infllJence. AI 55° S the lowestmea" temperatures are about O°C, .whereas ,at the same latitudein the 'northern hemisphere lowest mean .temiJeratures reach-2S"C. The warmest annual period usually extends from late JanlJary to early Februarywith mean temperaturesof abotlt 16"C. .

Maximum wind speed (30 km/h) is attained in winter. Storm frequency (sea condition ? 8) is highest in earlyspring (September-October) and lowest in early summer (Deeember-January). From February önwardswind speed and storms frequency inerease signifieanUy.

Two major tidal waves of semidiljrnal regime h~lVe beeri described. Aprogressive wave from the Paeifie,surrounds, Cape Heirri, penetrales. the Argentine sea, between tlie continent and Malvinas Isrands aridpropagah~s northwards along the Argentine coast up to Ihe, Rio de la, Plata, developing in 24 hours twocomplete tidal, cyeles~ The second wave of a stationa,rY nature, comes. from the Atlanlic. After refractingagainst the slope interferes with the previous one along the eontim3nÜll shelf, originales two amphidromicsyslems, one near Gulf San Jorge and another at abeiut 41 0 to the south of Sahia Blanca.

On {he Patagonian coast there is a sauthwards (5i-S5~S) decrease of mean (8.4~2.7m) and maximumamplitudes (13-4.0 m) of semidiurnal tides. Tidal current has a WNW directlon al high arid ESE at low,and velocities that reach 1m/s in neap tides and 1.am/s in spring tides (Servicio Hidrografia Naval, 1995).This wide Iidal amplitudes generäte high energy dissipation ,caused by bollorn frietion ihal coincides wilh

. the loeation of shelf ses. frants as described by Glorioso and Flather (1995) based or; Ihe Simpson-Hunlerparatemer. They also show that frontal zones located to the south of 47"S have simil:lr characterislics 10those off Peninsula Valdes (GIarioso and Simpson, 1994). '

Water circlliation on the Argentine Sh~lr has been recenÜy reviewed by Pioia rind RiV~5 (in i:mlss). Thetopogräphy, saHen gEwgraphical features and sürrace circulalion wilhin the study are<l are shown in Figure 1.Shelf waters have a Subantaretic origin, entering the shelf through a passage delimil~d by Malvinas andTierra dei Fuego Islands. Wah~r masses cin the northen eXtreme of the Drake Pas5aqe. 10 lhe north of theSlIbantarctic front, are diluted due to an excess of rainfall on the SE Pacific and a conlinental dischartealong ttie W coast of SOllthamerica. The f10w towards the Atlantic known as. Cape Horn Gurrent, showschMacteristic salinities of about 33.5 psu. The Malvinas Current also originates as :1 north bound branch ofthe Antarclic Circumpolar ClIrreht, but due 10 its hightransport capacity, the impar.t of r:ontinental Olltrlow5is less significant. and typieal salinity values are 33.75 or higher.

Subantaretic waters on the Ärgenline, shelf are modified by eonlinental run-offs ;-ind as a resuli of ,Iheinterchange of mass and heat with the atmosphere. Sased on, salinity ranges. Bianehi ef al. (1982)recognized three water massas on the southern Patagonian shelf: Malvinas Clirrenl (33 8-34.2 psu) CoastalWaters «33.2 pSll). and Shelf Waters (33.2-33.8 psu). Wilhin our study area Ihf' rno<;1 import:mt riversdiseharging on the shelf are Santa Cruz, Coig, Gallegos and Grande. Their eonlrihillion , has only localizedeffects, and, is negligible as compared to the intrusion of waters from the Magellan <;Irailinto the shelLSeveral basins drain along this strait collecting the abundant rainfall (>2,000 mm/yp.~r) and thaw duringsummer. The penetration of lhe Magellan run-off into the shelf dilutes SlIh;lIll~rr:lic water, wilh aeharaeteristic value of 33.2 psu, traceable several miles off-share due to Ihe, efff>clc; of diffusion (Krepper,1977) ,and advecticiii of Ihe' Ekman layer callsed by the prevailing W winds Shf>lf walers differ fromMalvinas Current not only in, temperature and salinity butalso in velocity wilh flow V:llues 10-15% lower.Circulation seems to be. topographically induced by the tiathymetrie depression.. hl'tween the islands ofTierra dei Fuego and Malvinas.

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MATERIAL AND METHODS

Surveys were eondueted on board FRV's "Dr. EDUARDO L. HOLMBERG" and "CAPITAN OCA BALDA".Table 1 summarizes eruise delails, number of sl<llions oeeupied, oeeanographic, plankton. juvenile andadult fish sampiers ulilized.

TABLE 1. Summary of survey dala.

C~UISE.DETAJL~ ..•.•.

725 2627EH-O~/96

C~U1SE' C~ÜISE '. di5·-:kibi&Hii I~U;>' oe.'LAGiC' .. ' .' ' .. : .. ,; .:: '."

__+.-,-,N""UM=~§L._..:O::~A~::-,TI::::;:S,-:'+_':...:.'::::...:"'--'--I---'--c..:.:..;.;.--"-"--f-:.:..:,"::;:...:.... .......;._f-'---'-'TRA~W-'-'·l",S,_19/04/9601/05/96

FRV;::; ~.

HOLMBERG

OCII BIlLOll OB-11196 12/09/9601/10/96

57 48 11

OCA BI\LDA OB-13/96 23/11/96

06/121961\7 53 4 14

The surveyed area

The area eovered by eruise EH-04/96 extended along Ihe eoasts of Santa Cruz and Tierra dei Fuego (50" to55"S), from the shoreline to the 50-m deplh eontour. The same latitudinal range was surveyed in spring(OB-13/96), but extending the geographieal eoverage to the 90-m depth eountour. In winter (OB-11/96) thesurveyed area covered the outer eontinental shelf and slope off southern Patagonia and Malvinas Islands,from 52· to 55·, ineluding Burdwood Bank.The geographieal references, lopographieal features and surfacecirculalion pattern in the study area is shown in Figure 1.

Data collection

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Acoustic instruments, calibration procedures and data processing were similar for the three surveysanalyzed. Acollstic sampling was carried out using a SIMRAD EK-500 scientific echo-sounder operatingwilh a 38 KHz split beam transducer. The dala processing method was echointegration (Forbes and Nakken,1972). A SIMRAD BI500 post-proeessing system was employed for data logging and analysis (Foote ef a/.,1991). The system operated at a working frequeney of 38kHz. Eehosounder ealibration was performedbefore or during eaeh eruise, aeeording to the eentered sphere method wilh standard targets (Foote el al.,1987).

Oeeanographie (CTD) and planklon (NACKTHAll) stations were reglllarly distributed along the acollstietransects, in order to cover the study area uniforrnly (Figure 2). Based on previous informalion Ihe Ihesampling of post-Iarvae and juveniles wilh IKMT was restricled 10 in-shore stations. The NACKTHAIsampier was fitled with a 400~-mesh nel The dislanee Iravelled by the sampier was estimaled by means ofa meehanieal f10wmeler mounted 10 its 20-em moulh. Sampling depth was adjusted lIsing a SCANMARdepth sensor mounted 10 Ihe NACKTHAI frame. The sampier was towed obliquely from bollom to surfaee inshallow waters, and from up to SOO-m deplh 10 surface in off-shore stalions. Towing speed was mainlainedat 0.5 m/s. IKMT tows were made obliquely through the water column from bollom to surfaee, exeept instations where boltom deplh was below 40 m. In these shallow stations IKMT tows were made in equalstepped intervals_ The distance between sleps was 10m, duralion of the horizontal trawl 5 minules. Forbolh sampiers ship speed was 3.5-4 kn.

Plankton sampies were analyzed 011 board and preserved in 5% buffered formalin. Sprat eggs werereeognized from descriptions given by Ciechomski (1971). Sprat specimens of the whole size-rangecollected were sorted out and kepl in aleohol (95 % ethanol) for age determination. During Ihe spring eruise,Ihe main zooplankton components were sorted, dried and weighted prior to fixation.

Adult fish sampies were collected wilh a NICHIMO mid-water trawl net. Fu/l delails of adult sampling duringthe autllmn and spring sprat surveys are given by Hansen (in press). During the winter cruise 56 hydraledfernales were collected for fecul1dity determination. Speeimens were preserved in individual plastic bags. Alaleral ineision was praclised to insure the penetration of Ihe fixative into the body cavity. Olle 10 thelimitation imposed by the time interval in wl1icl1 l1ydrated females may be collecterl, hateIl fecundity estimateswere based on eounlings of hydrated oocytes from a single pelagic trawl.

_._------_._._---, The NACKTHI\I sampier is a Germ"n modification 01 the GULF V high speed sampier (NelIen and Hempel. 1969)

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Laboratory procedures

Acoustics

Eehointegration va/ues were assigned 10 speeies by mean of the pos-proscessing software, in unils ofeolumn scaltering values, Sl\ (Knudsen, 1990). To eonvert the echointegration values to fish densilies,aproper target strength relationship must be established (Clay & Medwin, 1977). In view of fhe lack ofprevious information about the acoustie target strength for the Patagonian sprat and the diffieulties to obtainin situ TS measurements due 10 its sehooling behaviour, a generalised TS-fish length relationshipdeveloped for elupeoid fish (Foote, 1987) was employed to convert the seattering values 10 fish densities.The formulae are as follows,

TS =20IogL-71.9dB

(T.,. = 1O(T 511 0) (Tt>s = (T 1(411:)

n = s" (1/411:). (T.,.)"'

o = 10-3 . s" . (1/411:) . (Tt><; ~g)"l

where:

s" column scattering strength coefficient (EK500 output), in (m?/nm2)

TS fish acoustic target strength, in [dB)

er equivalent acoustic scattering cross section of fish, in (m2].

(Tb, : equivalent acoustic backscattering cross section of fish, in Im?).

""".kQ equivalent acoLJstic backscattering cross section, normalised by kilogram of fish, in [m?/Kg}

L : fish totallength, in [ern]

W fish weight, in (Kg).

r fish density, in (1/nm?).

R fish biomass density, in [Unm 2)

Larvae and juveniles

In the laboratory specimens were sorted out and their standard and total lengths were measured to thelowest mm. In total 119 aleohol preserved specimens were disseeted and the sagitta pair of otolilhsextracted for age determination. At a first stage otoliths were read with optical microseope using transmittedlight under 1000 X magnificalioll. Otoliths were mounted in Pro-Texx mounting medium. Visibility ofmicrostructures was enhanced after treatment with 3M polishing paper (1 0 ~lm).

The duration of the embryonie and yolk-sac stages were eslimated from results reported, respectively, byThompson et a/. (1981) and Alshuth (1988), for Sprattus sprattus. Mean density of earty juveniles eaught bythe IKMT was calculated applying the minimum variance unbiased estimator of !he -distribution (Aitehisonand Brown, 1957). The biomass of post-Iarvae and juvenile sprat was calculated applying the length/weightrelationship estimated by Sanchez ef al. (1995) to the production eurve. Larval production at age, wasestimated by dividing the abundanee of eaeh size group by the time spent in the size eCllegory. Duration ofeach size category was the inverse of the instantaneous growth rate for the category, which in turn wasobtained from the derivative of the growth eurve. The Laird Gompertz growth model (Zweifel and Lasker,1976) was used to describe sprat larval. post-larval and early juvenile growth. Full details of the model andderivation are given by Sanehez ef al. 1995.

Fecundity studies

In the laboratory, specimens were measured to the lowest mm (TL) and weighed. Ovaries were disseetedand weighed and stored in individual vials. 5 ovaries were selected to analyze Ihe distribution of ooeytediameter. The diameters of 416 mahl ring oocites (> 100 ~m) were measured with a rnicrometric eye piece.Batch fecundity of the Patagonian sprat was estimated gravimetrically, using fhe hydraled oocyte method(Hunter et al., 1985). Only hydrated ovaries whieh have not lost oocytes cr, whieh after histologiealexamination did not show postovulatory follicles, were used for fecundity estimalion. Linear regressionswere filted to des"ribe the relations between bateh fecundity and gonad-free weigt,t, and bateh fecundilyand totallength.

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RESULTS

The autumn cruise (EH-04/96)

Meteorological conditions during the autumn survey fell within the general trend described above. Meanatmospheric pressure was 1,004 h Pa (range: 993-1,012), winds prevailed from NW (mean value 22 km/h).Air temperature was 0.8°C higher in average than sea water temperature.

Temperatures were homogenously distributed withiin the water column. Figure 3 (Ieft) shows a horizontaltemperature gradient, decreasing coastwards ,md more pronounced on the EN coast of Tierra dei Fuegowhere values ranged between 7.8 and 8.6 °C. The surface salinity field shows the less haline valuescharacteristic of the outflows frorn Magellan Strait and the Fuegan Channels. This low salinity tongue nowsnorrthwards along the continental shelf and forms a salinity front with the more haline shelf waters, notshown in Figure 3 (right) due to the restricted geographical coverage of the cruise. Salinity values rangedbetween 30.9 and 33.0 psu. The coastal region, from 50 0 S to the north of Tierra dei Fuego, was includedwithin the 32.8 salinity contour. Minimum salinity values were recorded in the mouth of the Beagle Channel(30.9 psu) an in the estuary of the Santa Cruz River (31.8 psu) to the north of the study area.

The largest zooplankton concentrations were recorded to the North of Bahia Grande (-500 and 1000 mg.m-3) gradually decreasing southwards (-300 mg.m-3) The biomass of calanoid copepods predominated notonly over the smaller-sized fraction, but also over the larger specimens (Fig. 4). Hyperiid amphipods andmysids alternated as prevailing groups within the last fraction. Intermediate biomass values (-100-150mg.m-3), were generally recorded n the Atlantic coast of Tierra dei Fuego, except for a maximum value(1200 mg.m-3) corresponding to astation to the south of Magellan Strait were mysids predominated. Theregion to the SE of Tierra dei Fuego showed typically low plankton concentrations « 100 mg.m-3) with theexception of high euphausiid biomass (3500 mg.m-3) measured to the north of Picton. an island in themouth of the Beagle Channel.

A total of 2,480 sprat post-Iarvae and juveniles (size range 15-63 mm SL) were eollected in 25 NACKTHAI(Fig. 5a) and 26 IKMT stations (Fig. Sb). Over 80% of all post-Iarvae caught by the NACKTHAI sampierwere smaller than 36 mm SL. Conversely over 90% of all juveniles eolleeted by the IKMT were larger than39 mm SL (Fig. Sc). Positive stations lay mostly within the 50-m depth contour. Peak densities wereoblained off the Santa Cruz river estuary and in the southern Atlantic coast of Tierra dei FlIego. Post-Iarvaeand juveniles were collected within narrow temperature (7.6-8.6·C) and salinity (32.3-32.9 psu) ranges,always within the domain of coastal waters. The inserts in Figure 5 b show the laditlldinClI variation in thelength frequency distribulion of sprat in representative stations at 50· and 54°S. There is a change in ranges(26-62 mm SL; 34-63 mm SL) and an increase modal values (40 mm SL; 47 mm SL) of the specimenscollected, from north to south.

Mean density of juvenile sprat over a survey area of 4,607 n mi2 was 18.09 individurlls/100 m2. with

confidenee intervals (-15%, +26%). The total number of posHarvae and and juveniles collected by thesamplers( largely pre and post-metamorphic stages) can be eslimated at 2.86 • 10P Applying thelenglh/weight relation to the size distribution within the nursery ground, the biomass of post-Iarvae and pre­juveniles ean be estimated at 916.9 t.

The analysis of pelagic trawls indicated the existence of two distinct areas, to the north and south of theStrait of Magellan. The former extended from 50·5 and comprised sma" sized specimens (post-Iarvae andjuveniles). The laUer ineluded larger juveniles and adults. Figure 7 shows the acoustic densities of spratduring the survey. The estimated biomass. total and per stratum, and lhe corresponding coefficients ofvariation is presented in Table 2.

Table 2 Acollstic biomass dllring the autumn survey

.

.-:: .

Nörtheth stratümt·I:, ....

Biomass C. V. Biolll3SS C. V.

45,197t (i.1 % 7.6 %

TOTAL BIOMASS: 104,431 t

5

The winter cruise (08-11/96)

A completc analysis clf the oceanograpllic dala of Ihis survey is given by Madirolas cf <1/. (1997) in relationto the distribution and abundance of soulhern blue whiling (Micromesistius <lllstmlis). DlJe 10 Ihe reslrieledoccurrcnce of sprat durintg this cruise, wc shall not include a similar antllysis herein.

Figure 7 shows lhe sprat eggs distribulion irl laIe winter. -rhe presencc of eggs is rcslricted 10' the shelfregion to Ihe south of Malvinas Islands. Surface temperatures and salinities in posilive st<ltions ranged 5.5­5.6 °C)and 33.7-33.8 pSll, respectively. The percentage of positive sampies was low (6.3%), but densities inIhese stationswere high (1,001-10,000 eggs/l0 m").

The gonad analysis of ripe females collecled dllring the crllise, showed that the species is a partial spawner.Hislological ovary analysis showed tlle concurrent presence of. yolked oocytes in malllration and posl­oVlllatory follicles from previous spawnings. The frequency dislribution of maturing oociles (Fig. 8a) showsthe exislence of two principal groups: a larger one comprising hydrated oocytes wilh ditlmalers ranging 900­1400 pm, and a smaller one which includes several batehes of oocytes undergoing maturalion, wilhdiameters ranging 120-800 pm.

The estirnales of batch fecundity are based on the analysis of 44 females with hydrated ovaries Ihai showno indication of recent post-ovulatory follicles. The length range of specirnens analyzcd was 168 - 202 nimTL. Mean values of lenglh and weight were 184.2 mm and 54.6 g, n~speclively.

Mean bateh fecundity was estimated at 13,039.20 (± 58%). Mean relative fecllndily w~s 235.68 (±36%), andthe mean ovary-free relative fecundily was 287.78 (±39%) (Fig. 8 b). Balch fecundity was related to lotalovary:free weight and totallenglh (Fig. 8 c (md d). The regression curves filled were:

BF = - 5,734 + 419.23 TW (r = 0.76)

BF = -45,814 + 319.42 TL . (r = 0.72)

The spring cruise (08-13/96)

Prevailing W winds allained an <lverage inlensily or 44 km/ho Atmosphcric pressure rnnged betweerl 981­1,009 hPa (mean=l,004 hPa). There was a heal transference from lhe almospherc as air lernperalure wnsin average 3.14oe higher than ttint of sea sLlrface.

TemperatlIre and salinily surface .lnd bollom fjelds are shown in Figure 9. Sl/rface lemperalures mngedbelween 7~9·C, wilh minimum values off the Strait of Magellan. Most of the she'f slnlions showed a weakseasonal lherniocline. The.vertical lemperaluro gradient increased eastwmds mid northwards. Themaximum vertical gradient (0.2 °C/m al 25 rn deplh) was registered in asIation <11 50"S <lnd 65 n rn fromshore. Stations comprised by lhe 40-m deplh contour, between 50-52°S, showed very weck slratiricalion inspite of slrong tidal currents of abolli 1.5 rn/so In sÜllions along the littoral of Tierra dei Fuego the walerCOllllTlIl was complelely homogenized. . . .

Surface salinity ranged belween 32.2 and' 33.4 psu. Minirnum val~es were recorded off Ihe Stmil ofMagellan whereas highest salinilieswere characteristic of shelf waters in more off-shore slations. The moreinlense horizontal gradients were observee! in lhe vicinily of the Slraits MClgellan <111(1 Le Maire, wlwlecoaslal waters meet the Cape Horn Currenl (Fig. 9). The IitloraI of Tierra dei FUf'!lo shows salinities ofabollt 32.6 psu. Haloclines at aboul 20 rn deplh were recorded off lhe Santa Cruz estuClry (0.01 pSll/m) andoff Magellan Slrait (0.03 psu/m). .

TempereÜllre and salinily profiles. along lhree selected transects at 50 0 S, 52"S amI il1 Ihe Bengle Chmlllei .from lhe UshuClia cove 10 the ilOrlh of Nue\m Island, me presenled in Figures 10, 11 ,md 12, respectively.Distnnce between stations was 20 11 rn npproxirnntelY. .

The northern profile (Fig. 10) shows n slight wmming of the surface layer füClChil1g 20 m depth. Thegradient inlensifies in lhe more olfshore. slnlions. The rise of the thermocline Cll 25 n rn froin Ihe COClstoriginales a surface tempemlllle front. Salinity increases gradually, from Ihe coasl .(32.65 psu) 10approximalely 40 n rn (33.35pSII), were il becomes slabilized. The densily profile delines a cOClslal regionwilh 'vertical slralific<llion slrongly inflllenced hy surfcice salinily, which COlIlllN<lctS lhe effecl lhehomogenizing effecls of highly energelic lides. Tho coaslal region is separaled hy lhe 25.8 isopycne fromIhe more oceanic region, where vertical slralificalion is induced by tempemlure. nnd density grndient isalocaled al 3D-rn deph in average, sinking to the bollom at 35 n m from shore.

Off the Strait of Magellan (Fig. 11) ihe consinl station is highly homogenized wilh temperalures below rc.Ther'e is a slighl wmming (8.5°C) in the surface layer of more oceanic stations, where lhe vertical gradie,nt,is .more pronounced. Theinjeclion of the Magellan runoff is evident by a decrease in salinity wilh a minimumcore of 32.2 psu. -rhe direction of the f10w is topographically induced. Density is slrongly dependent onsalinity. The 25.8 isopycne delimits the coastal from t1H~ shelf regime.

lha Beagle Charmel extends .. some. 120 miles along lha southern .. coast of Ihe Grande isiand ':md Ihonorthern coast of Navarino and Haste Islands. Tho average width of the charmel Is 2 miles, with sevcralnarrowings where width decreases to 700 m. Botlom topography along the. Channel isrTHukedly rUg(jed.Deph increases w~stwards, from, abolji 50 m in the eastern part to about 160 m in Ihe vicinity of the. Ushuai~cove. Current direction is always towards the E. Tides influenco current velocity in the channel. bllt not itsdirection which is always towards the E. Current velocity ranges betweim 0.5 m/s and 1.5 m/s. inerensing aiIhe areas of eonstriction. . .

TerTlperalure arid salinities profiles (Fig. 12) define two regions wilhiri the charmeL The inner region isdeeper, waters are stralifiod .as a, resull of wenk tempemture vertieal variation nnd a slronger salinitygradient. A haloeline was observed at about 80 mdepth. The lipper layer showed the lowest salinities in lhewhole sUrVey, (31.0 psu) whereas iri the bollorn layer salinily reached,32.0 psu. The external region, isshallower. Bottom topograpl;y is more regul~r than in the inner region. A very eon5piclloS haline front was·registered in Sl. 868. To the east of lhis station the water eolumn was homogeneous.

Walers running eastwards from theBeaglo Ch~mnel f10w along the eoast ot Tierra dei Fuego. transversingtho Strait of Lo Maire and penetraling Ihe Argentine Shelf. Off the SE tip of. TiE?rra der Fuego. this waterlayer mailains a width of about 60 m and salinities. of about 32.4 psu. The bollorn Iclyer showed a clearsignal of walors from Ihe northern extremo of tho Drake Passage with salinities of ahollt 33.5 psu.

zo~plankion biomass values inereased in relation to thos~ measuH~d during the autlJllHl survoy.The smarierorganism fraction reached maximum densilies in Grande Bay. and off the Straitof Magellan. Densities forthe larger fraction were generally low, wilh the exception of SI. 868 where high concenlralions of juvenileslages of Mlmida sp. ware eollecled. Crllslacean larvae were presc,;t in the wholp. sllloy arca in bolh sizefractions. usually prevailing over the larger grollp (Fig. 13).

Of all NACKTHAi sampies eolloeted 15. t % were positive for sprat eggs, arid 45.3 %forlarvae. Eggs warecollected of lhe coasl of Tierm dei FlIego, moslly .in the Beagle Channel arid souIllern eoast wherelhelargest densilies wore registered (534.1/10m'), but also in the Slrait of Lo Mairp. ~lld 10 the north ofPeninsula Mitre (F;ig. 14).Sprat larvae were collecled in the same stations that WNP positive for eggs, bulalso in large densilies all along lhe Fliegeln Allarltic Iiltoral, off Magellan, and to a minor f'xlpnl in tho coaslalregion of Snnta Cruz. The highest larval sprat densilies (1,361.6/10 rTl') were oblaincd alollg a longitudinal(65°W) transeel to Ihe north of the Slrnit of Le Maire.Otherfish larVae ealleeled chirinfj Ihe cruiso includedCareproelus pallidus, Agollopsis eIJi/oellsis. Salifola ai,slralis. Mieromesistius a,/sfmlle;. SP./);}sles oeulalus,and several Myetophiid speeies.

The distribiJtion of sprat egg5 is eneompassod by the7.S ,0C isotllerm. Salinity gmdieill<; seem to playanimportant role~ MaximllrTl densities are eomprised belween the salinity front describC'd fm SI. 868 and thearea influEmced by waters from Ihe Drake Passage. SI 868 also rnarks the weslern lirnii nf sprnt larvne intolhe Beagle Channel. The temperature and salinily ranges al which larvae were colleclpcl Wf>le slighlly wider(7.0 - 7.5°C; 31.4 - 33.6 psu) eh~raCleristic of eoaslnl and shelf walers. .

Growth increments iri ololilhs were used to estimate Ihe age of Patagonian sprat I'HVap. Malerial trom thespring and autum cruise was pooled in order to fil a Laird-Gompertz curve Ihat cornplf'If'ly deseribes spratgroWth during the larval, post-larval and met~morphie juvenile stages (size range 6 0 . 40rnm SL. N =119).The filted equation was: .

SL = 5.75expI2.194(1-exp(-0.0195t))J (r= 0.94)

This rnodel implies lilat lhe maximllm groWth rate (0.37 mm/d) is altained at age 40 ci whf'1l size is 19 mmSL. The asymrtotie length prcdicted by the model is 51.4 min SL. .

In order to esiimalethe birthdalos of larvne cOlrected during cruise OB-13/96 cl:lily periodicity of ringdeposition, and initial increment formation at the onset of exogenous feeding were :lC;C;llll1P(j The Illimber ofdays elapsed ouring the embryonie and yolk sae larval slages was estimated from p.xpPlirnf'ntal data for theNorth Sea sprat. Figure 15 b shows lIle clistriblltioil of birthdates of spratlarvae (sin'; r:lIiqe 6.0 - 20 rnin SL,

. N = 63) collecled during lhe spriiig cruise. Over 40% of,the specimeris arialyzed Wp.rfl horn during the third

7

part of October, but the birthdate frequency distribution shows that spawning on the Patagonian coast startsat the beginning of that month.

Juveniles collected by IKMT showed a c1ear southwards increase in median values from 42 mm SL (52° S),55 mm SL ( 53°S) to 60 mm SL at 54°S. Mature adults were collected in the Strait of Le Maire and BeagleChannel, the area where the 'argest specimens (maximum size 168 mm TL) were obtained . Histologicalanalysis showed however that in spite of the fact that several ripe females had been caught, this material,collected mostly at dawn, was not suitable for the application of the hydrated oocyte method for batchfecundity estimates.

Similar to the autumn cruise the acoustic survey indicated the existence of two zones, a northern one wheremostly immature juveniles prevail, and a second one to the south where larger specimens were recorded.The protracted nursery ground that in autumn extended from 50 0 S to the Magellan Strait, appears in springdisplaced southwards, with maximum concentrations in the Atlantic coast of Tierra dei Fuego. Very fewadult sprat were caught to the northe of Mitre Peninsula. Adult concentrations, coincident with eggdistribution, were largely recorded in the Strait of Le Maire and Beagle Channel (Fig. 16). Table 3 gives theacoustic biomass estimates corresponding to each stratum during cruise OB-13/96

Table 3. Acoustic biomass during the spring survey

:.::!/t:.'.::;,.::;::.::.:.:::::::: ..::::·.. g~~J~:F:A@'1~ f~:~:::::::::::::::m. :;::;::=\;:;:.:;;:;:.:; .:}

:)f/?Norlhefhslraltim::/::;:::::\:::::::I::::$~9Jij~#j:~d:J:t.: .. ·:::·::~.:::::::·::::P,:::::.·•••::::t:::r::::::::::~(:{:~t::::.::::~t~tfrtr~::rt~~:·~: :;:::;:;:; ~r ::;: :::':';::':';:;"':':"':'::: ::::::::::: ::::::::::::::;:::::::: . ;::::::;::

Biomass

155,207t

cv.5.1%

Biomass

16~, 193 t

cv.21.4 %

TOTAL BIOMASS: 323,400 t

DISCUSSION AND CONCLUSIONS

Contemporary research along the Patagonian litloral, Magellan and Fuegan regions is surprisingly scarce,as compared to the wealth of information deriving from these areas during the 18th, 19th and early 20thcentury, particularly dUl ing the period of great circunmavegation voyages and inland expeditions.

Three recent surveys have recently reversed this trend. The Argentine-Russian survey on board RV DmitryStefanov, specifically aimed at the Patagonian sprat, has already been referred to (Sanchez et al.,1995).Reports of two multidiciplinary projects have recently been published. Magazzu et al. (1996) reported on thedistribution of phytoplankton biomass and primary production during three oceanographic cruises carried outin spring, summer and autumn in ihe Strait of Magellan. Although plankton has been collected during thesesurveys no reference is yet available as to the presence of planktonic stages of sprat in the region. Arntzand Gorny (1996) published a eruise report on a joint Chilean-German-Italian survey carried out in thespring of 1994 in the Strait of Magellan, Fuegan channels and straits including the Beagle Channel. Table 1(lbid.) indicates the presence of unidentified fish larvae in several locations. There is no reference to thepresence of fish eggs in the Bongo net sampIes.

The previous sprat survey in southern Patagonia had len several unanswered questions. It was thenhypothesized that spring spawning cOllld take place in the inlets and channels of the Fireland. This surveyhas confirmed this assumption, and also the observation that reproductive activity or this population, thattakes place through spring and earty summer, starts in early Oetober. The oceanographic analysis pointedout the importance of frontal regions. particularly those created by salinity gradients, on the concentration orplanktonic preys, adult sprat and early life history stages of the species.The reslllls of the longitudinaltransect to the north of the Strait of Le Maire corroborates the assumed linkage between larval distributionand circulation pattern in the area. The resulls of the winter survey showed that the spawning activity of theMalvinas population starts in late winter. The histological analysis of ripe females confirmed that the speeiesis aserial spawner. Also as a reslllt or this survey, batch fecundity estimales based on the hydrated ooctytemethod are reported rar the first time. The existence of extended nursery grolInd along the southernPatagonian coast, reported by Sanchez et al. (1995) was corroborated. Results presented here showedsimilar mean juvenile densities as those reported for 1992. The difference in absolute abundance are due toa larger estimate of the extension of the nllrsery grollnd.

olf··..

----------

niere are no previous reports referring to zooplankton sampling of the type reported here, in the coastal andinshore waters, characteristic of the Patagonian sprat habitat. With similar methodology, Sabatini et al.(1996) showed that in the habitat of Micromesistius [wsfralis and Macruronus mage//anicus, shelf and slopewaters at about 51°S, lhe larger organism fraction (>5 mm) prevailcd in autumn ovcr the smaller fraction«5 mm) mainly due to the abundance of the amphipod hyperiid TIlemisto gaudichaudii (Alvarez ColomboMS). Results reported here' for the aulumn survey (EH-04/96), indicate larger densilies for the <5m~fraction. This contrasting result may be attributed to differences in sampling depths, that in the course of thissurvey never exceeded 60 m.

The significance of results on the zooplankton distributions reported here may be discussed in view of therole of these groups on the feeding ecology of the Patagonian sprat. Ramirez (1976) had reported changesin the diet composition of the species in relation with seasonal changes in ttie availability of differentzooplankton. groups. In summer the main food item wEne mysids (Arthromysis mage/lanica) , whereas inautumn the diet was rnostly composed by copepods (Ca/anus. australis, Drepanopus rorcipatus,Centropages brac/lYatus and Acartia fonsa). Angelescu (unpubl. data) analised the stomach .contents ofadult sprat(N=170) caught off Peninsula Mitre during the spring surveY,showing a high prevalence (up to70%) of larval stages of Anomura and Brachyura crustaceans. A similar analysis carried out in juvenile sprat(N=45) showed a diet predominance of up to 100% of the calanoid copepod Centropages brachyafus(Ramirez, unpubl. data).

The biomass 01. the juvenile and adult sprat was assessed for the first time. in the course of the springsurvey. These assessment may be considered preliminary due to some methodological constraints. In thecourse of the analysed surveys, the necessary condilions for reliable in sifu measurements of TS werefound only once. It was a low density layer of fish scaltered near surface at night, during the autumn survey.This field. measurement agrees wilh the utilised TS relationship. In spite of this limitation it is clear that thesize of the population is such that may encourage the establishment of regional fisheries in Tierra deIFuego.

To achieve this aim several research activities need to be pursued and others implemented. Someremaining queries on the species distribution should be addressed: the western extreme of the geographicalrange of the Patagonian stock needs to be. established; all channelsand strails of the Fireland regionshould be surveyed during spring to delimil the spawning grounds of that stock; the nursery grounds of theinsular stock must be located. Adult concentrations of both populations need to be further assessed:methodological advances should include the confirmation/development of a specific TS model, and theconcurrent application of Ihe DEPM. Finally, transference of technology in such fields of fishing gears andindustrial utilization will be required in order to establish a regional commercial fisheries.

, ~ _.

ACKNOWLEDGEMENTS

This shidy was partly supported by the Program of Fisheries Technicai Cooperation wilh the EU (PROJECT03.06: SARDINA FUEGUINA). The collaboralion of the authorities of the Province of Tierra deI Fuego,Antartida elslas dei Allantico Sur and Ihe Argentine Navy Prefecture, that greally facilitated sampling in theBeagle Channel, is gratefully acknowledged. The aulhors wish to express their gralilude to RV's officials,crews and technical staff that ässistE~d in Ihe different stages of this research.

9

.e

~,- ,l

REFERENCESALsHuTH, S. 1988. Daily groWth increments. cin otoliths of laboratory-reared sprat, Sprattus sprattus L, larvae.

Meeres(orschung. Rep. Mar. Res., 32:23-29.

AlTCHISON, J. & BROWN, JAC. 1957. The log-normal distribution. Cambridge Univ. Press.• London, 176 pp.

ALVAREZ COLOMBO, G.L.Variaci6n estacional en, la . distribuci6n y abundancia, deThemisto, gaudichaudii(Amphipod~:Hyperiidea)En el mar epicontin~ntalargentino, al sur de los 45° LS. !n: Inf. CONICET, 1996.

ARNTZ, W. & GORNY, M. (Ed.). 1996. Cruise report of the Joint Chilean Gemlan-Italian Magellan ·Victor Hensen"Campaign in 1994. Ber. Polarforsch., 190. 113 PP: o. ' .

OIANCHI, A., MASSONNEAU, M., & OLIVERA, R. M. 1982. Analisis estadrstico de las caracterrsticas T-S dei sectoraustral (je la Plataforma Continental Argentina. Acta Oceanografica Arg. 3:.93-118.

CIECHOMSKI, JoD. deo 1971, Estudios sobre los huevos yiarvas de Ja sardina fueguina, Sprattus fuegensis y deMau.rolieus mu!!"eri, hallados an aguas,~dyä~entes al sect?r patag6nico a~gentino. Physis, XXX (81): 557-567.

CLAY, C.L. & H. MEDWIN. 1977. Acoustical oceanography: principles and applications. In: J.W1ley, N. Y., 544 pp.FOOTE K.G. 1987. Fish target strengthos for use in echo-integration surveYs. J. Aeoust. Soe. Am,. 82 (3): 981-987.FOOTE, K.G.,KNUDSEN, H. P.,VESTNES, G.,MacLENNAN, D. N. & SIMMONDS, E. J. 1987. Calibration of acoustic

instruments for fish density estimation:, A practical guide. ICES Cooperative Research Reporl N· 144, 69 pp.FOOTE, K.G., KNUDSEN, H.P.. & KORNELlUSSEN, RJ. 1991. Postprocesslng system for echo sounder d~ta. J. Aeoust.

Soe. Am. 90 (1): 37-47.FORBES, S. T. & NAKKEN. 0. 1972. Manual of methods for ,fisheries resources surveys and appraisal: Part 2. The use of

acoustic instruments for fish detection and abundance estimation. In: F.A.O.• MarlUal in Fisheries Seience N° 5,138 pp. , .

GLORIOSO, P.D. & FLATHER, RA 1995. A barotropic model of the currents of SE South America. Journal ofGeophysical Research, 100 (C7): 13427-13400. •

GLORioso, P.D. & SIMPSON, J.H. 1994. Numerical modelling of the M2 on the northern Patagonian Seil. Cont. Shel.. Res., 14: 267-278.. .

HANSEN, J.E. 1997. Estimaci6n de parametros poblacionales dei efectivo de sardina fueguina (Sprattus fuegensis) de laCosta Continental Argentina Inf. Tee. INfDEP. (In press).

~ilJNTER, J.R., LO, N.C.H& LEONG, R.J.H',1985. Batch fecundity in multipie spawning fishes. In: An Egg ProductionMethod (or Estimating Spawning biomassof Pelagle Fish: Aplieation to the Norlhern Anchovy. Engraulis mordax .Lasker R. (Ed..) NOAA Tee. Rep. NMSF: 36 (67-77).

KNUDSEN, H.P. 1990. The Bergen echo integrator: An introduction. J.Co':'s. Exp. Mer, 47: 167-174.KREPPER, C.M. 1977. Difusi6n dei agua proveniente dei Estrecho de Magallanes en las aguas de la Plataforma

Continental. In: Acta oceänogratica Arg., 1 (2): 49-65.. <', " r:

MADIROLAS, A., GUERRERO, R, SANCHEZ, RP., PRENSKI, L.B., SABATINI, M. PAJARO, M & MACHINANDIARENA,L. .1997. Acouslic, oceanographic and ichthyoplankton surveys on the spawning grounds of the austral bluewhiting (Mieromesistius austrafis ), off southern Patagonia, 1994-1996. ICES CM 1997/ Y:26

MANN. F: G. 1954. La vida de los peces ~n Aguas Chilenas. Ministerio de AgricUltura, Universidad de Chile. 342. pp.MAGAZZU, G., PANELLA, S. & DECEMBRINI, F. 1996. Seasonal variability of fractionaated phytoplanctori. biomass and

primary production in the Straits of Magellan. J. Mar. Syst. 9 (3-4): 249-267.PIOLA, A.R. &. RIVAS, A.L. Corrientes e'n la Plataforma Continental. In: EI mar Argentino y sus reeursos pesqueros. 1:

121-134. (In press).

RAMIREZ, F.C. H~76. Contribuci6n al conocimiento dei espectro alimenticio de 113 sardina fueguina rCLlJPEIDAE, Sprattusfuegensis (Jenyns»). Neotropie8, 22 (68): 137-142.

SABATINI, M.E., ALVAREZ COLOMBO, G.L. 8. RAMIREZ, F.C. 1996. Zooplankton biomass in the reproductive area ofthe southern blue whiting (Micromesistius australis). In: Reproductive habitat. biology and aeoustie biomassestimates of the southern blue whiting (Micromesistius australis) in the sea off southern patagonia. Informepresentado en la VIII Reuni6n dei Subcomite Cientrfico de la Comisi6n de Pesca dei Atlantico Sur, Junlo, 1996.

SANCHEZ, RP. & CIECHOMSKI. J.D. 1995.. Spawning and nursery grounds of pelagic fish species in the sea-shelf offArgentina and adjacent areas. Sei. Mar., 59 (3-4): 455-478.

SANC~~EZ. RP., REMESLO, A, MADiROLAS. A & CIECHOMSKI, j. D. 1993. Distribution and abundance of postlarvaearid juveniles of the Patagonian sprat, Sprattus fuegensis, arid related hidrographic condltions ICES. C. M.19931 L: 22.

SANCHEZ, RP., REMESLO, A., MADIROLAS, A. & CIECHm.1SKI, J.D. 1995.' Distribution and abundance of post-Iarvaeand juveniles of the Patagonian sprat, Spraffus fuegensis, arid related hydrographie condltions Fisher. Res. 23:47-81.

SERVICIODE HIDROGRAFIA NAVAL. 1995 Publieo H-203. Derrotere Argentino. Parte 111. Archipielago fueguino elslasMalvinas.

niOMPSON, B M.. MILUGAN, S.P. & NICHOLS, J.H. 1981. The development rates of sprat (Sprat1us sprattus L.) egssover a range of temperature. ICES Pe/agic fish Cornm., CM 1981/ H: 15.

WHITEHEAD, P.J.P. 1985. King herring: his piaces among the c1upeoids. Ca':'. J. Fish.8cuat.Sci. 42 (1) 3-20.ZWEIFEL, J.R. 8. LASKER, R., 1976. Prehatch arid posthatch groWl'; of frshes. A gerieral model' Fish Bull. 74: 609-621.

10

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Figure 1. Topography, geographical references and surface circulation in the studyarea.

.,. ·-·-_···_-...··_···'--:::1 ...s

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Figure 2. Location of CTD (Iett) and plankton stations (centre), acoustic tracks and pelagic trawls (right),during the autumn (top), winter (middle) and spring surveys (bottom).

--~~---,...-- - - .- Surface Temp. (OC)

- -485urface Sal. (psu).

-48

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Figure 3. Sea surface temperature and salinity in automn 1996.

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Figure 4. Survey H-04/96. Results fram the biomass analysis of the zooplankton sampledwith Nackthai sampier showing the densities (mg/m3) found for the two fractions analized.

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A B20 ~400 °00°c:Pi35Q N=44 °l16 N =416 °='

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• ~50,.t:f'

IJ

--51

~52

.- -~.>

-s. -.~",.

•

i

68

,'. ::

66 64

:: ::".::: ::.<.: ::.<::.: _::: . ,.!------48E3o~rrtSaW[psul:../

1··)~.': . :! //'-::»> .J

I":::::

70

54

"~531

J11~54

-,

52

+53,

i1

151

iI-1-52j

\ ~50•

( --49

f I

.h f (. ~ 150----

,I I...-. ~

"I~) ~)

I

~

j~:.• ,- -""'8.s 1 51. '----....... ]- . •

_--,--,---'-~'--""~_l-.1-1-=,-::-1.J...l_. _ .~

66 64

• < " " ~-'~.s ----~ - -48ZSurface;Temp, rC]~ =

< • .--

I,,,'

.r

Figure 9. Sea surface and botton temperature and salinity in spring 1996

839 837 836 835

70

70835

70835

60

60

60

50

50836

50836

40

40

40

7.00-----

30

30

30

20

20837

20837

10

10

o

o839

o839

8

2

Distance from the coast (nm)

Figure 10. Temperature. salinity and density profiles along a transect at 50 oS

70

70

835

60

6050

836

4030

30 40 50

Distance trom the coast (nm)

20

20

837

10

10

839

o

o

2

E4-ß.Q)

o

E4-oeä.~ 6

839 837 836 835

8.00~f>O'//,. 00,.

-54

ß.Q)

0 6

8

10 20 30 40 60 70

837 835

Figure 11. Temperature, salinity and density profiles along a transect at 52° S

865

865

80

lI

----..1

7080

ll68

<.

50

ll68

870872 870876

E---tQ)

o

sal (psu): ....

:' ..

110 20 30 40 50 60 70 80

878 872 87. 8?0 869 ll68 865

I

ulT~I,I U-~~~'" _25 20P-

IeS J"'-....... 8 .

:fj \

2foAO~~'40 <It~ jl:.:. :

~'---

I ~2UO

= U0. ~~IOQ)

0 1

-~: Sigma T:

160 10 20 30 40 50 60 70 80

Distoneetrom thll COMl (r<n)

160 10 20 30

876 872 87. 870 869

I I• '---~

~

I=0.Q)

0 1

Figure 12. Temperature. salinity and density profiles along a transect at Beagle Channel (55 0 S)

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

56'

55

,54'

53

,.a"I

,'0 '-"'-. 10 m<2

.~

•• '1.100

• lQ1.1CXX)

• l<Xl1. ooסס'

_ ooסס'·

+ Plankton station

08·13/9626·11·96 to 03·12·96

604'

. I.1

-h......-r......-r......-r--,--,-M--'--'''''''''''''--''--'r-T"""',..--,-,..--,-,..--,-..-h.56

-70W -69 -68 -67 -66 -65 -64

54'

52'

54

55

53

5"

• 11-100

• 101-1000

• OOסס1001-1

_ ooסס1<

.~

+ Plankton station

08-13/969S 08-13/96

9S

Fraction< 5mm Fraction> 5mm

10m""') 10 "'WIIIJ

50 50IOD "'11""'3 100 ""1""3

500 lftfMt J • 500",••3 •51 51

1000 ....'.10ll0~.'.

52 52

08-13196 .26-11-96 to 03-12·96

,.".- -, .a"1

Figure 14. Distribution and abundance of Sprat eggs and early larvae in spnng.

Figure 13. Survey 08-13/96. Results fram the biamass analysis of the zooplankton sampledwith Nackthai sampIer showing the densities (mglm3) found for the two fractionsanalized.

nrw 68'

-70W -69 -68 -67 -66 -65 -64

A

Figure 15. A. Larval and post-larval growth of Sprattus fuegensis.8. 8irthdate distribution of sprat larvae collected incruise 08-13/96

8

12090

21-31 1-10 NOV 11-20OCT NOV

Date

60

Daily Increments

30

50

oo

140

~3O.!!'E 20

! 10

N = 63

50

40

l>. 30~!I 20~~

10

01-10 OCT 11-20

OCT

Figure 16. Geographical distribution of Sprattus fuegensis trom the spring survey acoustic data(color scale made proportional to the square root of column scattering).