Not 10 be cited without prior rerercncc to the authors.
c.M.
ICES STATUTORY MEETING 1993
1993fL:22
Rer. H.
Biological Oceanography Commillee
DISTRIBUTION AND ABUNDANCE OF POST-LARVAE AND JUVENILES OF TUE
PATAGONIAN SPRAT, Sprattusfuegetrsis, AND RELATED
HYDROGRAPHIC CONDITIONS
"
by
R.P. Sanchez (INIDEP. P.O.Box 175, Mnr dcl Plnln. Argcntina)
A. RemcsJo (AllnntNJRO, Kaliningrad, Russin)
A. MadiroJns (INIDEP. Argclllina)
J. de Ciecholllski (INIDEP/CONICET, Argenlina)
••
'.
~:C"0'
..... ..
. ,t':t
\~.
~
1"
~
~
:'
A talge shoaI of Spraltusjuegensis stranded in the port ofUshuaia.
Not to bc cited without prior reference 10 the nuthors.
C.M. 19931L:22
Ref. H.
Biologieal Oceanogmph)' Committee
ICES STATUTORY MEETING 1993
DISTRIBUTION AND ABUNDANCE OF POST-LARVAE AND JUVENILES OF THE
PATAGONIAN SPRAT,Spratfus/uegcm;s, AND RELATED
HYDROGRAPHIC CONDITIONS
by
R.P. S:inchez (INIDEP, P.O.Dox 175, Mar dcl Plata, Argentina)
A. Remeslo (AtlantNIRO, Kaliningrad, Russia) .
A. Madirolas (INIDEP, Argentina)
& J. de Cicchomski (lNIDEP/CONICET, Argentina)
I.
I
I
ABSTRACT
This paper reports on the first pelagic surve)' on the Southcrn Patagonian shclf. As a result of a joint
Argentine-Russian cmise on board the RfV "Dmitr)' Stcfanov" carricd out in the earl)' autumn of 1992, a major
nursery ground of the Sprattus!uegensis was located in the coastal aren olT Santa Cmz nnd the Fircland,
Fort)'-nine ichthyoplankton stations :l1ong 14 tmrisects :md 7 intertransccts were occl~pied. Biological
snmples were taken with :md 1KMT equippcd with a net soundcr and Oowmcter for the determination of the
sampIer dcpth and distance travelled. Hydrologieal data were obtaincd in 78 CTD stations. lvfctcorologieal
observations were made concurrently. Real time SST images from NOAA s,1tellites were recch'cd on board,
twice per da)', cloudiness permiUing. Positive stations lay mostly within the 50-m depth contour. Of all
coastal stations 71 % were positive for sprat post-Ian'ae and juvenilcs. The dcnsity and size of the specimcns
collccted increased southwards. Median valucs of the juvenile distribution va ried from 23.6 mm SL to the
north of the study region to 38.5 mm for stations at 5~ oS. Highest biomass densities (> 2.8 tln mi 2) were
found to the south of Magellan strait, corresponding to IKfl.rr densities of over 1000 specimens per haut Other
important components of the Isaaes-Kidd collections were thepost-Ian'al altd juvenile stagcs of Sebastes
oculallls and Patagonotothen tessel/ata. '
.
_
In order to obtain a higher resolution vicw of the distribution and abundance ofjuvcnile sprat, the aren ~vas
simullancously sun'cyed using an EK-400 eeho-sounder with a SIORS echo integrator. A significant
eorrclation (r=0.95; 0.<0.01) was obtained bctween acoustically dcrived abundance estimates and those
resulting from the IKMT snmpling.
The large amount of post-laf\'ae and juvcniles eollectcd and the very high values' of echointegration
registered particularly in the area of the strait and channeIs, are indic.:itive of a major nursery ground of the
species in the Patagonian coast. Post·laf\'al and earl)' juvenile production in the area was cstimated at over 1.5
x 109 itldividuals. DilTcrences in the diel patterns of the ,'crtical migration of adult and earl)' juveniles are
dcscribCd.
'
Gro\\1h inercmcnts in otoliths werc uscd to cstimate the age of sprat post-Iarvae and juvcniles. A LairdGompcrtz model was fitted to the lcngth-at-age d1ta. The spawning periodicity of the specics was deternlincd
by exnmining the tempoml distribution of birthdntcs from otolith-ngcd specimcns. There \vas indicntion of a
major spawning peak on Inte Deeember, and a secondary Olle on mid-January. Available information on the'
rcproduction' and earl)' Iife histor)' of the species is analyzed in view the obtained rcsulls. The importance of
the Mageltan strait low-salinity watcr outnow for cgg dispcrsal :md Inr\"nl retention is discussed,
of
INTRODUCTION
'Tlie Patagonian sprat, Sp'rattusluegensis, is frequently referred to as the largest potential pelagi~ resource
on the austral extreme of the sea shclf olT Argentina. The existence of two dilTerent populations, one on thc
Patagonian coast and another on the coast of Malvinas, has been postulated on the basis of dilTerences in
grO\\1h parameters (Gru & Cousseau, 1982) and sonle nlorphollletCic characteristics (Cousscau, 1982).
. Lnrgeshoals ofadults ofthe specks strandcd on the Patagonian eoasts or entering the coves, inlcts and even
the ports ofUslniaia (Frickart, 1942) :md Port Stanley (Norman, 1936) have been frequently reported in the
course of this centurY. These events seern to oceur at a mesoscale spatial pattern. Lloris & Rucabado. (1991)
report on two reeent simultaneous arrivals of several hundred tons of fish occurring at locations distant 300
km.
..
NOh,·lthstanding, the, Occurrence of sprat in shclf waters has only occasionall); been reported in the
cxploratory cruises carried out in the
mostly directed to the detcction and assessmcnt of demers:tl
resources (sec COUSSC.1U (1982) for a re\·iew). Additional information is given by Gru & COUSSC.1U (1982) "ho
refer to some sampIes collected in the coastal region of the Patagonian Province of Santa Cruz, by sniall pilfse .
seiners of the artisanal coastal fleet.
arca,
In contrast ,,,ith the erratle presenee of adults in our surveys, planktonic collections sho\,' that larme of the
specics are major compcinent of the icthyoplallkton assemblage of the austral extreme of the Argentillc sen
dui"ing summer (Cieehomski et al., ,1973, 1981).
a
. This paper reports on the first pclagic survey Oll the Southeril Patagonian shclf, a joint Argentine-Russian
cmisc on board the RIV "Dlnitry Stef..1nov~ carried out ili the emly autunln of 1992, with the general objecti\"e
of assessing the population of sprat inhabiling the coasts olT Patagonia.
The study region.
The Argeotine shelf is the largest in the sauthern helllisphcre with Cl total area of about 1,000,000 km2 and a
vCr)' smooth dcpth gradient (00°02'30" on the a\"erage) in contrast "'ith Cl verY stcep coritinental slopc of up to
4°. Thc ,,,idth and mc.1n deplh of the continental shclf increase southwards. The a\"erage distance from shore ,
to the 180m-depth reaches 800 knl in the southern Patagonian region. Mean depth olT the Rio de la Plata is
less than 181ß, gradually inCrc.1sing to 90m to the south of45°S.
Waters o\"er the Argentine Silelf are predominantly of Subantarctic origin. Soui!1 of 45°S (Fig. I) shclf
"'aters are formed as a result of mixing beh\'een Subaiiiarctic waters of the Mal\"inas (=Falkland) Current
nowing northwards nlong the continentnl slope nod of the Magellan Strait rlm-olT, a 100\'er salinity water
tangue (Soüthern Coastnl Water) flowing along the Patagonian coast to the San lorge Gulf (Dianchi ct aL.
1982)..The three wnter mnsses are recognized by their s.~linity ranges. Mnl\'inas ,,'nters nre niore hnlinc \rith
ranges bet\"een 33.8-3·t,2 ppt. Coasial waters sho\" values belo,,, 33.2 ppt. Shclf ,,'nters 5.1linity vnlues range
betwcen those two extreilles. Water circulation in the Argeniinc Shclf has been estirilnted scvcral times by
rilCans of, theoretical nlOdels based on surface wind stress nnd horizontal dcnsity gradieflts (Zyryailov &
Se,'erov, 1979; Lusquifios & SchroU, 1983; Forbes & Gnrrafo, 1988). Surf..1ce ,;e!ocities show in all cases a
NNE oriefltation rind niagnitüdes ranging between 10 :ind 20 cntls. The progression ofbimonthly distributions
of surface Ekma" transport presentcd by Dakun and Parrish (1990), show that nca;' the coast of Patagonia the
ocean surface layer trnnsport respoflding 10 the Sc.1solial variability of wind stress is gencrally directcd toward
shore, "'ith a northernly oriclitation.
Mesoscalefron131 zones are' extrcmCly impOrtant fcatures or'Argentine shclf. having \'ery strong locaiized
elfect
hydrogmphy and fish spawnirlg distributions. In the Patagonian regioil they inchide: a) a permanent
shclf break front near the 200 isobath in the boimdary bctwecn outer shclf and slope; b) tidal fronts of vnf)'ing.
intcnsitics occurring olT Valdes Pcninsula and southwards from earl}' spring to aiJllimn; c) a thermo-haline
front associated wHh intrusion of southern coustal ,,,ater to the south of Sa!l Jorge Gutf; and d) the prcscllce of
anticydonic fing currcnt around the Mal\'iilas Islmids (Sc\'cro\'. 1990).
.
on
2
Fig. I-B.
Fig. I-A.
\ 'L -c...
\~~".t
\.
\
I
\
.... \{
\
J
.
.
--
bs....,.in..
I
-,,-,.t~:'
.Sft1..~
,.
"
~~~t1ii~'~I
. .-.
····1·----
\
I
65'
60'
55'
Fig.I-C.
Fig. 1. A. Location oflhe study are3.
B. Watcr ll1asscs and circulation pattems
on the southcm I'atagonian shelf
(Frolll lIart, 1946).
C. Surface salinily distribution in carly
alllllllln (Frolll Krepper & Rivas, 1979)
Rclativcly high valucs of nitrates and chlorophyll-a
are found lhroughoul lhe year. A peak in nitrales
concenlralion (2.5-14.5 ~M) is followed by a single
phytoplanklon maximum in spring and summer (2.3 2.7 mg/m3). As regards primary produclion values
allained in the region around Malvinas Islands
(1.3gC/m 2/day) are among the highest reported for
the Argcnline Sca (Angclescu & Prenski, 1987). High
values of zooplankton biomass are attained during
summer time wiLh densities belween 101-1000
mm3/m3 over mosl of the conlinenlal shelf 10 Lhe
soulh of 48°S with densily maxima 10 Lhe north of
Malvinas Islands (Ciechomski & Sanchez, 1983).
...
•.
...
...
..
...
••
..
••
..
...
....
Ir"
Reproduction snd early life history of the Patagonian sprat.
Early developmenlal stages of the specics havc beCIl dcscribed by Ciecholllski (1971) and Cassia & Lasta
(unpubl. manusc.).
3
Available information on the spawning aclivily of Ihe Patagonian sprat is at presenl fragmenlary as neilhcr
the coastal regions off Palagonia nor Ihose off Malvinas have been adequalely sampled during spring. Ripe
females have been collected off the North and WesI coasls of Malvinas during laIe September. Shirokova
(1978) studied Ihe malurity cyde of spral adults off Malvinas. Her results show Ihat the species is a partial
spawncr, wilh a 4-monlh reproductive season from September to Deeember. Planktonic eggs of the sprat have
been collected o\er a mueh shorter time span, (12 - 29 Octobcr) during the spawning seasons of 1969 and
1978. In both eases higher concentralions (about 1000 eggs/IO 111 2) were obtained in an area to the North of
Malvinas Islands (Ciechomski, ] 97]; Ciechomski et al. 1981).
Conversely, sprat larvae are abundant through oul the summer showing and e:xtended spatial distribution
over lhe Patagoni:m shd f. Aecording to Ciechomski et al. (1981) sprat Iarvae cOlnprise 57% of all larvac
colleeted in the area in summer. The distribution and abundanee of sprat larvae, sizes and monlh combined,
have been mapped by Ciechomski et al. (1975 and (981).
]n addition to Ihese reports, an examinaliOll of lhe iClhyoplankton collections of Ihe INIDEP carried oul
during the preparalory slages of this projecl, showed Ihat sprat larvae and juveniles have been obtained in all
exploralory cruises surveying the area during laIe spring, summer and early autumn (April, 1969; OcloberNovember 1969; January, 1970; December-January 1973/4; DeeemberlMarch 1978/9: January 1987; February
(992). These surveys cm ered the shelf from the coast 10 Ihe 200-m depUI conlour extending southwards to
Burdwood's Bank, some 100 Km 10 the south of Malvinas. A chronological arrangement of Ihis information is
presented in Figures 2.
October
~
Dceembcr
~
100..
100..
~
0
~
0
0
~
:s
. \..~
~
o.ooClDa
"
t""Q~'
"t.\. ......
r
~
H
~
~
.
&e
6'2
".......
oe
l~
"
a
o
:s
0
o
0
'" \ ..
0
~1000
....,.. _,0-
0' ......
...
(?
}
66
7.
68
62
66
LCl\GITLDE
68
62
LCl\GITLDE
January
Fcbruary
~
. ..
100..
~
• '0
0
~
~
H
11-100
101-1000
0
~f!,.~f.
~0.
.J
,~
.1"
r.
0
66
7.
-
6'2
S4
66
\..,
6GI
::J
~
H
~
\
S4
0
O. ci.:o
6GI
0.:
0 ...
OaD o
l-
~
~
c··..•
.f
. D '0..
. }
00
0
\.._."
m'
'" ,,'
. '"
~\.
."iJI
-0.)
.~
100..
~
:.
.J
,,.......
.t.
~
.. \...:..:.
.
6GI
'~."
::J
~
H
I-
<
-.J
0
62
\
mr:
. ,.,.c···.·,
".;.#
.......
°
....'
'., "......!
••• 1
S4
0
66
78
66
62
68
78
LCl\GITLDE
66
62
68
LCl\GITLDE
Fig. 2. Spatial and tempor.1 distributions of Patagonian spm! (Sprarrll.f jilegensis) eggs. larvae and juveniles
(tll. sizcs cOlnbillcd), on thc southcnl Patng(ll1i~n shcl[ All "nlues are in Il\unhcrs per 10111 2 orw:1ter surf:.1ce.
4
1 - 10
Sprat larvae were particularly abundant in Dcccmbcr and January. Positive stalions were observed in the
strails and channeIs and such distanl locations as Burdwood's Bank. SprattlJs !lJegensis larvae were colleclcd
between 47-55°S; the main concentrations were silualed bctween 50-54.30 S wilh an imaginary axis along Ihe
lOO-m isobath ofT Ihe Argentine coast. In February larger densities are observed 10 the south of 52 S also
along the IOO-m depth contour, allhough no coastal sampling ofT Malvinas or Palagonia was carried out during
this month.
0
0
U:NGTH rRECUENCV OISTRIBUTlON
11 - I' oelOBER 1'73
'I
.
N -
1e59
..
'00
.0
St. (mrn)
LEHC-H rREOUE/Je'f OISTRIOUTION
17 - '0 OECU4BER 19n
n
U _
1451
:n
n
..
,.
.0
"
'0
\0
11
1..\
l't
l'
.,
;'t
:1.>
n
I'
ZI
)1
J4 ), "
..:>_
9.. (mm)
LEHeTll rREQUENeV DISTRIBUTION
I~
-
29 JANUARY I 9 I!! 7
r"
~N!....=.=.::'.3=..:,27
..
JO
"
JO
os
The Icngth frequenc)' dislributions of the specimens
collected is presented in Figure 3. Larvae collected in
Oclober were in all cases smaller than 10 mm SL.
Very fcw larvae were collected in November, with sizes
ranging from 7-16 mm SL. In December the sizes of
collected larvae ranged mosll)' from 8 to 26 mm SL,
with peak in 1I mm. In January larvae 9 10 37 mm
have been obtained, over 23% of which were 17 mm
SL. Larvae from the February collections ranged from
11 10 37 nun SL with peak also in 17 mm SL. In
March, the range is also very wide, from ]6 10 38 mm
SL, bul the distribution shows a marked peak (>22%)
in Ihe 23 mm size calegory.
Smaller larvae (6-9 111m SL) were present from
Octobcr 10 Januar)'. The 10-14 film SL size range was
found from November to February. Larger size groups
were found from Decembcr 10 March. Metamorphosing
juveniles (>35mm SL) wcre first obscrved in the
January collections and were present throughout the
sUl11mcr till April. The presence of Ihese larger-sizcd
specimens in our sampies musl be considered
incidenlal as colleclions were made wilh Bongo and
Nacklhai sampIers, which are nol efficient for larvae
larger lhan 20 111m SL.
"
,
•
11
JJ U
"
l'
J,
:'J
!,
11
n
SI
~3
35 .". J_
SI- (Wllt)
LeHen, rR[QUCNCV OISlP.IBUTION
~ - 21 TCBRUAR'f 1979
: r-.
.::N-=~~24~3 ,.
"
1
•
"
IJ ~J "
t.
21
'3
,~
''t ,. ." .,..
,~
'\,
~J
5t. (... m)
lENG1H rRE:QUENCY DISTRIBUTION
3 - 2' WA~H 19l,
~,.~==__!.l~UV ,~
,. "'
'0
On Ihe basis of this background information, and
laking inlo consideration the dale of lhe cruise, our
specific objective was 10 locate and assess the nursery
grounds of Ihe spral in the coasts ofT Patagonia. The
wide lnrval size-ranges encountered during lhe summer
months may be indicalive of a more protracled
spawning season Ihan could be deduced from reports
011 planklonic eggs and seemed to be in doser
agrecment with the period reported by Shirokova
(1978). To check lhis hypolhesis we planned 10 oblain
eSlimales of the daily growth of post-Iarvae and
juveniles in the fjeld, and back-calculate Ihe duralion of
Ihe reproductive period, from Ihe frequency distribution
of birthdates during Ihe spawning season.
Other
objeclives of Ihis Sludy were to gain information on the
transport roules of sprat post-Iarvae in the area, on
their distribulion in the waler column and on Iheir dicl
pallerns of migration.
'0
..
•
I1
l'
')
"
."
:n 1J 2" 71 a S,
JJ ~ J.~ 19
Fig.J. Lcnglh fr~qll~ncy histograms of Patagonian spral larvae
and juveniles. groupcd by monlh. Data d~rived from
5 exploratory cmiscs carricd out frol11 197310 1987.
5
MATERIAL AND METHODS
The survey was conducted between 23 March aud 10 April 1992, in the coaslat area olT Palagonia from
47°20'S 10 54°30'S. Before delimiting the easlcrn border of lhe sampting area, an acoustic survey was
conducled along the she1f from Ushuaia 10 tJle soulhern extreme of Gutf San Jorge.
Hydrologicat data were oblained in 78 CTD stations distribuled along 14 transects. Dislance between
adjacent stations was 25 miles. Meteorotogical observalions were made concllrrently. Real time SST images
from NOAA satellites were received on board, lwiee per day, cJolidiness permilting, with a SU-8 FURUNO
receiver. Maximum resolving ability accounted for was 2 Km2.
In order to oblain a higher resolution view of lhe distribution and abundance of juvenile spral. the arca was
simultaneousty surveyed using an EK-400 echo-sounder wilh a SIORS echo integralor.
Table 1. Parameters ofthe acollstic systcl1lllsed dllring the cmise.
Eehosounder
Echoinlegralor
Transducer
Frequency
Pulse length
Atlenualor
Band-widlh
SL+VR
Instrument constant (CI)
78
66
LONGI TUDE
62
STMRAD EK400
(ES400 transmitter).
SIORS
ES38
38kHz
Ims
IOdB
3.3kHz
: 131.5dB
-57.6dB
Fig. 4. SlIrvey acollstic trackline followed dllring the cmisc
ofRlV Dmitr)' Ster.~nov, 21 March· 14 April 1992.
Acoustic sampling was carried out along the trackline shown in Figure 4. The echosignal from the
ealibrated oulput of a 38 kHz scientil'ic echosounder, was processed in real time wHh a digilal eehoinlcgrator.
The echoinlegmtion averaging interval was 5 n mi. Echosounder calibration was performcd before cruise and
according to the centered sphere method wHh standard targets (Foote and MacLennan. 1983; Foote el al.,
1987). The sealing faetor of the eehoinlegralor was included together wHh the eehosounder parameters into an
instrument eonstant (Dalen and Nakken, 1983). The chnracteristics of lhe aeouslic system are given in Table I.
In order to obtain Iish densities per unil of volume and per unit of area, the echointegrator outputs were
expressed in terms of volume baekscaUering coefficient (Sv) (Clay and Mcdwin, 1977) and column
backseaUering eoefficient normalized per squared nautical mille (sa) (Dalen and Nakken. 1983; Foote et al..
1991). Conversion of scattering coefficient values or acoustic dcnsities to fish densitics was carried out by
using a target strenght model derived from c1upeoids data, including Sprattl1s sprattus (Foole 1987):
TS = 20 (oglO L -71.9 dB
where:
TS= fish aeoustie target strength, in dB.
L = fish total length, in cm.
The TS "alues obtained from this model are also in agreement wilh olher in situ Illcasurcments for sprat
(Degnbol et al., 1985).
Forty-nine ichthyoplankton stations along 14 transects and 7 inlertransects were occupied from March 28 to
April 9, 1992. Distance between the three stalions (co<lslal, cenlral and olTshore) on e<lch transeet was 50 n rni.
In eoastal intertranseets, one slation was oecupied al h,1If way belween adjacent Iransects (Fig. 5).
6
46
.7
70
-
68
66
)-.
"0
--'
o
.
6
6.
+
.,.
Q
+
0
... 0
<f+o+o
<9
+ 0
Ci)
Fig. 5. Oceanogrnphic and lK~IT stations oceupied during the enoise or
RJV Dmitry Ster.,nov. 21 March - 14 April 1992.
Sampling of posl-Iarvae and early juveniles was earried oul by means of
an lsaacs-Kidd midwaler trawl.
An echo-sounder for genr depth
determination. and a nowmeter for estimalion of distance lravelIed, were
mounled on the sampIer. IK tows were made obliquely through the waler
column from boltom 10 surf(lee. cxcept in stations where boltom deplh was
below 40 111. In these shallow st(ltions IK tows were made in equal stepped
intervals (dislanee bctween steps 10m. duration of Ihe horizonlal trawl 5
min.). Sampies were preserved in 5% buffcred formalin. Spral specimens
of Ihe whole size-range collecled were soried oul and kepl in alcohol (96 %
ethanol) for age delerminnlion.
In thc Inboralory spccilllcns wcrc sortcd oul and Ihcir standard and totnl
lengths werc rncasurcd to Ihe lowest mm. To convert this dala to real size
o +
lhe equalion o[ Theil(leker (1980) was IIsed. In order 10 provide some
Q ""' • .....
adjuslemelll of lhe dala for daylime avoidanee of Ihe nel. ralios of night 10
'--_ _-'-'''--_ _..L-+_'''''_ _-' day abundances were calculated for Ihe I-null Icngth cIasses that were
derived from the eSlimntes of mcnn dcnsily. Post-Iarvae and juveniles
(N= 175) werc washed in distilled water aud weighed with precision of 0.1 mg.
In lolnl 115 alcohol preserved spccimens were dissccled and Ihe sagilla pnir of ololiths extraclcd for age
determination. At a first sl(lge ololiths were read wilh oplical microscope IIsing transmilled light under 1000
X magnifie(ltion. Ololilhs were 1ll0llnled in Pro-Texx mounling medium. Visibilily of microstruclures wns
enlmneed aller Irealment wilh 3M polishing pnpcr (I 0 ~tm).
Larval production nt age was estimaled by dividing lhe nbundnnce of each size group by Ihe lime spenl in
the size category. Duration of eaeh size eategory was the inverse of the instantaneous growlh rate (IGR) for
the eategory, whieh in lurn was oblnined from the derivative of lhe growth curve. The Laird GOlllpertz growth
model (Zweifel and Lasker, 1976) was used to describc spral posl-lan'al and carly juvenile growlh. The model
may bc formulated as:
SL(t) = La exp{G[1-cxp(-al)l}
wherc SL is stnndnrd length and I is nUlllbcr of daily incretllenls.
LO= lenglh at I = 0;
G= AOI 0.
Aa= specifie growlh rnle at 1=0; alld
0.= rnle of exponenlial decHy
Inslnnt gro\\th rale for sizc ealegory LSi, is givcn by
IGRLSi = 0. LS [In (LSilLo) -
GI
Duralion of size dass was estitllnted as:
LSi = I/lGRLSi
Thc duralion of Ihe embryonie (Ind yolk-sac slnges werc eslimnled from results rcporlcd, respeclivcly. by
Thompson & Nichols (1980) and Alshuth (1988), for Sprnltlls .Wrnltus.
Time at halching was eslimalcd by Ihc equ<llion:
l(h) = -1.259 111 (T) + 7.509
7
where t(h) is time in hours and T is temperature (oC). Duration of the yolk sac stage was assumed to be six
days.
Mean dcnsity of early juveniles caught by the IKMT was calculated applying the minimum variance
unbiased estimator ofthe ~-distribution (Aitchison & Brown, 1957).
The c1assic allometry equation was used to describe the increase in wet weight with length. Age/Length and
Weight/Length models were fiUed by Marquardt's algorithm for non linear least squares regression.
RESULTS
The Physical Setting.
Meteorological conditions during the sllrveyed pcriod were delincd by the inleraction and reciprocal localion
of the Soulh American pressure maximum and cyclones coming from the Drake Strait. Frolll March 23 10
April 2 the area was influenced by 3 crest of the South Atlantic anlicyclone. As a result, moderate north and
north-west winds prevailed. During this period calm weather and fog were recorded. Frolll April 3 10 April 9
cyclonic activity intensified, and storm winds were registered.
Intensity of zonal western air 1I13SS transport in the Southwest AtI~lIltic was on the whole dose 10 the longtime allllual mean, whereas sOllthern Iransport was a liule below average. Air telllperalure and pressure
r3nged from 8.2-16°C and 1009.8-1027.0 mb, respectively. In all stations d;Jily mcans of air temperalure ovcr
Ihe sllrveyed area exceeded sea surface temperalure.
fig.6-A
46
70
-66
68
52
11/
70
i
i
I
48
. ~,\~..
~"-'
'0,
•
/ ...o .. ~
49 .
~r,.
~'~--'
.
~~.:-.
/-""~.'~
-::::W.;:-~
-~""'/.~
-'/(~)'F4'
~\ "~"-
54
\J',. {f' /,\
55
-::---....r-,. . . . . . 1
5J
46
~~~.
%-
49
-
62
47
~"
48
51
- 64
-,,-
47
50
fig.6-8.
..
t
:;J
1".
I'~
~
0°
5fi L -
56
...:..i-=---
fig. 6. Sea-surfuce waler tcmpcrature (A) and salinity (0) distributions
on the Patagonian shelf(28 March· April 4, 1992).
8
_
,_.r--
Fig.7-B.
fig.7-A.
16
47
-
70
66
6~
61
62
46
~-r-r-
"-
70
68
66
61
62
47 -
48
18
49
19
30
50
:;'1
51
52
52
53
54
56 L _ _--=::..i::------------'
Fig. 7. Bollol1l waler ICl1lperature (A) and S.1linity (D) distributions
OIIlhe Palagonian shclr (28 March - April 4, J992).
Differences in the basic hydrographieal parameters were largcly defined in Ihe meridional direclion.
Temperature decreased from north 10 south, from the coastline to Ihe open sea and from surface to bollom.
Similarly, salinity increased witll depth and distance from shore (Figs. 6-& 7).
Maximum sea surface temperalure values (> 12°C) were found in the northern part of Ihe surveyed area.
Minimum temperature «6.5 0c) was recorded 10 Ihe NE of Slal.en Island in walers of Ihe conlinenlal slope of
deplh below 450m. The areas adjacent to the Magellan Strait showed more hOll1ogeneous water temperature
distributions, both in the vertieal plane and in the olT-shore direclion. Values observed ranged from 9.2°C in
surface coastal waters to 8.0°C in off-shore bottom waters.
The encounter of the cold runolT from the Strait of Magellan and warmer waters from Ihe Grande Bight in
the southern eoast of Santa Cruz province, originate a gradient zone, that ma) be clearly seen in SST satellite
images. The trasport ofMagellan strait water is also evident from Ihe temperature distribution ofbottom water
shown in Figure 7. The front is loealed between 50°30'5 and 51 °30'5. Divergence and subsequent upwelIing
originated a loea] area of low temperature centered at 51 ° 15'5 and 66°30'W (Figs. 6-A & 7-A).
A more pronounced decrease of water temperatures wHh deplh and distance frol11 shore was observed to the
north of 51 ° latitude, where va lues ranged uniformi)' bctween 12°C and 7°C from surf.1ce coastal to off-shore
boltom waters.
The dislributions of surface and bottom waler S<llinilies are quile similar (Figs. 6-8 & 7-8). The position of
lhe 33.0 ppt isohaline coineides with the configuralion of the 100-111 depth contour. Less haline waters «32.0
ppt at surface and <32.45 ppt on Ihe bollom) are found along a narrow strip along the 50-rn deptlt contour
belwcen 49°00'5 and 51°15'5. Minimum salinity ,alues (31.l6 and 32.38 ppl, at surface and bottom,
respectively) were recorded at 50°00'5 in relation with the outflow of the Santa Cruz River. Coaslal Walers
(saJinity <33.2 ppt) covered most of the study region from the southcrn extreme of San Jorgc's Gulf 10 the Hp of
9
Tierra deI Fuego. The core of this water mass could be identified at a temperature of 8. 9°C and s'llinity of 32.7
pp!.
While moving away from the Magellan strait, coastal waters gradually modify their characteristics and
transform into shelf waters. This \vater mass was observed in the NE part of the study area. with temperatures
o"cr 12°C and S<1linilies ranging between 33.3-33.6 ppt. and a weil marked Ihermocline. To the sOllth of 52°S
shelfwaters were characterized by similar saIinilies (33.3-33.7 ppl) 'lnd lower temperalures (7.8-8.8°C).
Highest salinity registers (>33.8 ppt) were obtained in illl area to the NE of Staten Island over the slope,
where waters of M'lIvinas Current could be identified. On the surfilce temperalures ranged bctween 6.4-7.8°C
and salinities bctween 33.8-34.0 pp!. At 490 m deplh tempcrature decreased to 4.JoC whcrens salinity
increased to 34.2 pp!.
Temperature and salinity profiles along transects made in the northern, central, and soulhern parIs of the
surveyed area are presented in Figure 8. In the northern pnrt of the study region the mean horizontal salinily
gradienl (ppt/km) observed was 4.6 :< 10-3 for surface waters nnd 4.4 :< 10- 3 for bottOlll w<lters. Minim<ll
gradients were observed in the area adjacent to the Milgelliln Slrait (3.3 :< 10-3 and 3.6 x 10- 3, at surface and
büttoln. respectively) whereas milxilllllm gradienls where observed at the south of the st.lIdy area re<lching
values of 5.9 x 10-3 both on Ihe Sllrf.1ce and bollom lilyers. The intense horizonlill salinity gmdient. obseryed on
bolll layers is the result of the interilclion bct.ween Western Malvinas Walers ilnd Shelf Walers. The 33.8 ppt.
isoline, whieh delimits both water masses, is located on the boltom at 250 m deplh rising sharply to lhe surface
as bottom depth inereases (Fig. 8-F).
Temperature and salinity verticaI distribut.ions were largcly independent of deplh in the region ofT Ihe Slrait
of Magellan (Fig 8- E), where similar structures could be traced from the coast to mid- shelf at bottom dcpth of
about 100m. To the north of the slrait, small variations in temperalure and salinily are observed p<lrticularly
along the coast within the 50-rn depllt contour. However in some cases, within the narrow range of values.
ternper<lture and salinity inversions could be observed. On the other hand. temperature and particlllarly salinity
inversions were typical for stations loc:lted outside de 100-111 eonlour.
Fig.8-A.
Fig.8-B.
47 10~
65.32,.
4120c
6.\.10..
15
1)
f),------r--r--~:.---.
49 :!Or.
67.JOw
-10 .
-20
-20
-JO
-30
-40
:-'0
31
56....
3l
_
-4U
-50
-50
-GO
-60
-70
··70
-80 ..
··80
-90
-100
-90
-100
-110
-120 '--
-=:::::z:...
41.20.
63.10...
14
15
-110
-120 1- - - - - - - - - - - - - - - - - - '
---1
47.20.
65.32..
IJ
12
49.21),
67.30...
49.20,
64.56.
o 2;~8",.,-,-".,_,2-9,._.,-"""-]-O-~,_-_31_ _,..-_32
11
Or-------.,r-.....- , . - -__----,--.,-,-"
10
-50
f}4
29
"r-.,----,------,....--..,.-----,.--,
-10 -
-20
-30
-40
49.10"
28
11
-10
-20
-30
-40
..... 50
\
-6n
-60
-70
-80
-70
·80 .
-90
-100
:::
\
-90 -Inl)
-110
-110 .
-qO ' - - - - - - - - - - - - - - - - - - - -
-120
10
Fig.8-D
Fig.8-C.
50.Ja.:
50.JOo
66.~~..
39
6fi.20w
40
4\
42
4J
o """'-""'--,-_::='='-:"'-_-.-._~"""::-.-.,--,-..-/"".,.-,...,/,....-/,-..r--r-.-:>/- . - ' - - '
-10
,a
-20
~.
........ -.........
'0..1 _ --~~~ ....,... ..-'/
""'----~'.• --.........4~~:::::::--!),o
......
~~ ~.. _~~-
-WU
-110
-1201----------------------'
5O.JO.
68.55.
39
~.-'09
52.JO.
G6.20.
66.2Ow
40
~
1
4J
42
o6~·,-,--,___r~.,_-_r.......:'_T,1\-··
O,----r-----r--.----r-....-----,--r,
-'0
-10
-20
,1f'
-10
-30
-40 .
-50
-JO
-40
·50
-60
-60
-70
-70
-60
-SO
~
-9U
-100
-110
-120 .
-130_
_ t4ln l -
-90
100
110·
•20 ' - - - - - - -
_
Fig.8-F.
Fig.8-E.
~•.} JO.
t;7.~7 ..
6~•.
7J
72
75
5~
:;4 JO"
5.3.30.
6fi ()8w
1 I...,
83
/6
0.----....,--------,.---,.--,--,--.,...---.----,
3D!:
"w
1i2....
64
8:>
86
87
81:!
" ,-----,----==...-;----..,-,rr-,---,-777T77TT1.Fm'
··10 .
-20
-030·
.."!
-150 .
-40
-~O
-100
-50
-70
-250
-JOO
-80
-90
-100
-110
-120
-350 -400
-450
-------------_..... -
_5001-.
'-'.JOs
o
~4 .30.
66.08..
67.57.
72
-"
~4 .JO.
6?.~J..
o 8r3:-..._.::...:.-o;~~::a_""";:r:;r-:-~,..""'-8~7=--:;T77T.n81l8
-10
-20
-50
-JO
-100
-40
-50
-150
-200
-60
-2'0
·70
-60
-90
-100
110
-120
-.100
- 350
-400
-450
'''\.. -,-"\..
,
-500L-----------------~
Fig. 8. TCll1peraturc and salinity profilcs along five latitudinal transccts on lhe ratagonian shelf
A) 47"20' S; B) 49"20' S; C) Soo30'S; D) 52°30'S; E) S3°30'S; and F) 54°30'S.
11
The seasonal thermocline was more e1emly seen in the northwcstern part of Ihc surveyed area. The upper
limit of the thermocline marked by a tel11peratnre gradient of O.05/0.06°C/m, generally occurred between 40
and 60 m depth. In the central part of the study region a rise in the thennoc1ine was observed. with lIpper limit
at about 10-15 m depth. In the southeastern region the thermoc1ine cOl1ld be found al dcplhs belween 16 and
40m. In general terms the width of the gradient layer did not exeeed 20 111.
The characteristics of the water dynamics in the survcyed area can be studicd through lhe distributions of
temperature and salinity. As illllstraled by Figure 8 B-C, leaking of warmer, Icss haHnc, :lnd consequenlly Icss
dense waters on a more dense subsurface water mass could be observed <llmosl throllgholll Ihe study are<l. The
high-gradient zone on the continental slope may be regarded as a high velocity indicator or the Weslern
Malvinas Current (Fig. 8-F). Impinging of comparatively colder watcr from the south mny be traced throllgh
the characteristic bend of surface layer isotherms (Fig. 8-C), llnd by a rise of isothenllS 10 lhe surfacc at bollom
.
deplhs below t 00 m (Fig. 8 A-B).
IKMT sampling.
A lotal of 3209 sprat posl-larvae, pre and post-melamorphosis juvenilcs (size r;lIlge 18-48 111m SL) were
collccted in 17 IKMT stations (Fig.9-A). Positive stalions lay moslly within the 50-11\ depth contour. Of all
coastal stalions 71 % were posilive for spral posl- larvac and juveniles. Ovcr 95% of all specimens collecled
were caughl to the soulh of 51 ° lalilude. Peak dcnsilies (> 1000 specimens per haul) were oblained in Ihe
vecinity of Magellan slrait and in the coast off Tierra dei Fuego.
Other important components of the tsaacs-Kidd collcctions were the post-larval ;lIld juvenile stages of
Sebnsles oCli/alus (7 o(f-shore and central stCllions), Pnfngol1ofofhen lessellnfa (15 stations, penk densities in
coastal stations) and Rnmnognsfer arcl/nln in 6 coastal stations. Occurrence of Ihese three species is presented
in Figure 9-B.
-4
,------r---------,
-16
: 6lh
*
. . . * *Q *
n
oo *
o
-41
-..
-58
-
~
S
....
....
I-
~
.,
.:'.1
-1;2
-IM
"
'.
I-
~
-""
-11'4
-56
-61
_
'--~_L.:::...II:....!:........Jl_.
__'_ _--J
-711
LeN:;I n..a::
Fig.9. A. Dislrihlllion and abundance (Nil 03 m3) of Patagonian sprat post-Iarvae al\(l juveniles collcctcd with IKMT
dllring the cmisc of R/V Dmitry Stcr:,nov, 21 March-14 April 1992.
O. OcclIrrence of(Ll) Ralllllogasler arCllala. (0) f'aragaaorollwn lessel/ara and
(f.t) SebaSles oelllallls inlhe IKMT sal1lJlles.
LENCll-l fREOUENCY OIS1FlIBUTIOt-.
LATITUO(:48--4S' S
Fig. 10. 1..:ltiludinal variation inlhc Icngth frcqucncy
dislribu(ions ofPatngonitlll sprnt post-Inrvne nnd
juvcnilcs during the CTllise of R/V [)1llilry Stcfanov,
24 March - 9 April 1992.
-.::N'---......:'_~:.;O
.. ;=.,,
.,
Jl
2.
~O
Z':
;J3
.s.
...
4!
Sprat post-Iarvae and early juveniles were
coHected within a narrow range of temperatures
(9.0-12.0°C, 64% between 9.0 and 9.2°C) and
salinities (32.5-33.0 ppt). Temparatures in the
stations where post-Iarvae were coHected were in
the upper extreme of the range observed (l1.212.0°C). All positive stations for sprat were
locnted within the same water Illnss (southern
coastal water). No specimen was coHected nt
bottom deptlls over 100m, almost 98% were
caught at depths below 60m, and 66% in shallow
waters, at deptlls under 40 m.
1ft
<lS
$\ (mml
LENGTlI rRf.CUENCY DIS IIlIUUTION
L"rrrVOI:, :;1' S
;:.~
--'-N_-_~,SO
•
.l~1
il,..
".
, ,+......-1
•• +--1..........
,
6
,.
24
17
;:0
<I:
3~
:sC
;)J
,I
Ir.
.....
(mm:
LEHC1H r~[QUEI~CY DISTRlaUlIOIl
LAnrU::l[: sr 5
"
Length frequencies distributions of post-larval
and juvenile sprat armnged by latitude are
presented in Figure 10. The size of specimens
coHected increased southwards. Post-Iarvae
(preserved sizes: 18-27 mm SL) were coHected
only in the northern part of the surveyed region.
The lengtl\ of individunls caught between 48°·
49°8 ranged from 18 to 35 mm SL (median=
23.6 mm).
In the rest of the study area
specimens within a similar size-range (mostly
31-45 n1l11 SL) were obtained. Median lengths
calculated for specimens colleeted between 51 °
and 53° S were quite similar (34.5 111m, 34.7
111m, and 34.6Il1m), but increased signilicantly
(38.5 mm SL) for specimens collected in OIe
southernmost transects.
.:..:N-:=::.....:...l':--::;tlJ >0
=1-
,u
"
'0
'0:[
1.
"
~..-+-.--r-h-~
n
J<4
3J
:-,fl
JI
~2
3t
.. )
48
Sl ~mrr.)
LENGTH fREQUEIlCY DISTlUOUTIOH
u..nruo[: 5Y 5
:>s
;,'t_.
--'-Ne----=.3'-;
... 1 15
,u
'0
1ft
Isnaes-Kidd stations were 1I\0stly (65%)
carried out during night hours, 23% of the
st<ltions were occllpied during daytime, and 12%
either at dusk or dawn. Cateh ratios calculated
from mean va lues for nighl stations against aH
olhers, for each size categol}', gave v111ues around
J for specimens between 24 and 36 nun SL (Fig.
J I). SmaHer specimens were 11l0stly calight at
dllsk or dawn, whereas for large sized specimens
the genr seeIlIed to operate more emciently
during night !lOUfS.
!'
LENGlH FI1f.OUf.NCY DISTRlfLrrlCN
LA1ITUOC: ~-4' S
N _
"
'OA~
-----~-
::ll
.,
_0
,
u
"
.
,
-h-,-l-,-,-,,,,,,,,,~~
24
"
.30
33
,.
Jo.
41
..
...
SL (mm)
J3
Nie c&lch ratio
...-~~---------------------,
3.5
3
2.5
2
'.5
.
::>5
"
-~
o L - - ' -_
t _•L·8
•
20
..
------. "
&.
.---...::::----
' - - - ' - _ - - ' - _ - ' - - _ . _ - ' - _ - - ' - _.........- ' - _ - ' - _ ,
22
24
26
28
3e
32
34
3e
38
4
SL (mm)
UD
~
:)Ob9 exp (:J081'SL)
Fig. 11. eatch ratios I>ased onlllcan abunduncc ofnight and day IKMT sUllIl'lcs of
post-larval and juvenile Patagonian sprat by size groups.
Acoustic survey.
46
100,'1
..
(.. /'.~'
.'"
~.~'\~~~:'
47
The degrec of coverage of the acoustic sampling in
the coaslal area prevenled us from estimating accuratcly
the juvenile producliOlI from the echoinlegration dnta.
However an approximate abundance of 1.5x 10 9
indh iduals may be obtained by t1Iultiplying the area of
the nurscry ground by its corrcsponding lTIean colut11n
backscallcring cocfficient.
48
49
0.:.
W
0
=:J
e
IH
<"2.........
··>·
.-
51
.'
)-
I-
:
<{
-1
i
.......
50
52
Fig. 12. Abundancc dislribution ofl'ost-Iarvaeand juvcnile
Palagonian sprat, obtaincd frolll lhc echointegralor
readings. References: minimulll contour = I O~ lish/m J
maximulll contour = 106 lish/m J .
, '.
,
Isolines of dcnsity distribution werc calculaled from
the echoinlcgmlion datn and lhe TS model previously
mentioned. Figure 12 shows lhe reslllti ng abllndmlce
distribution l1l;Jp of posl-lan'ae and juveniles of Sprafflls
fllcgcns;s.
53
Different pallerns of vertical distribulion were fOtlnd
for individu:JIs with si7.e range 25-50111111 ~llId for lhose
54
wilh sizes abave 70mm. The echogram shown in Figure
13-A corresponds 10 nighl Station No. 42, where
36.6111111 menn lenglh early juvenile spral dominated the
55
IKMT haul. A wide spread layer covering mosl of lhe
w;Jler COltllllll can be observed. represcnling the night
56 '--'---"'-'--'--'-'l.....I.-':....L-'----'---.L-'--J--l-'--'--'
vertical distribution of the smaller fish. In daytime this
70 69 68 67 66 65 64 63 62
pallem lransfonns inlo a lhinncr layer and lhal is placed
LONGITUDE
doser 10 the bollom. Figure 13-8 corresponds 10 lhe
larger fish, sampled with an ENGEL pelagic lrawl. The dicl pnllem observed at sunrise corrcsponds to
indi\ iduals wilh l11ean lengtll 74.4111111. Al niglh lhese fishes concenlrale in a very shallow layer partially
above lhe transducer depth, al abaul Sm. In light hours, this surface layer Illoves deeper <Ind splits into small
midwater schools. constitttting the d;Jytime vertical distribution of ngc 0/ I group Cish.
14
Fig. 13-A.
I
......
,.
I
I
I
t'"
I
'I
.,',1.' "
: I,
,"
"11
,I
I.
,ship
stopped
Fig. 13-8.
''''l'
1,1'1
~'I
I'
~o tn
I
'I'
.,1
t~
I
l
,/
I
"
..' Ir
li
.",
!
~ r. ,I
"
~·I~ '~
1
-
.
, "I~' ,
I
, .
:j
I
11
';. 'li'
• Il'~
'I', I"
:' ~'Ji"' ,
I
~
'
:
I P'I~ "1/'1 "t1i'l,r
Hr
;'
11
1,1
i
,L
1-
,
I I Ik ,I,'
, , I~I , 'I, t
-' 1-11
11'1 11]' 11.",
'l-l,I'\!lr'l
.f" '! , ,I r' jjYlt ~
,lu'Udl
I
J
"
I
I, .
r
~Om
,I:'jI ,(,,',
',I' '
'I : ":'\
I, , 'I i I
,,
I
i
'1'
I
, '",
-
30m
I
I,
"
; I I
,
"
,.1
I
I
I'
. I
"
Fig. 13, Echograms showing the vertical distribution pattcms ofearly juvcnile and nge Oll group I'atagonian sprat:
A Nightime vertical dislribution pallem ofthc posl-larvac and carly juveniles (arrows indicate
ship stopping for CTD station).
B. Verticalrnigration ofthe age Oll sprat frorn nightirnc to da)1imc distribution, at da\\1,.
15
.--_------------------------------------------~-----------~----~---
It has been demonstrated that, under certain circumstances, fish Illay rcacl 10 lhe prescnce of lhe research
vesscl (Ona & Godo, 1990; Olsen, 1990). An example of this type of re..1clion was obscrved at night during a
CTD station carricd out in very shallow water. The 110rmal night-lime distribution pallern for post-Ian'ae and
early juvenile sprat was clearly altered, as can be apprcciatcd at the right end of Figure 13-A. Thc fish rcactcd
soon aOcr the ship stopped to oeeupy the station and concentrated in a decpcr layer on the bollom. As obscn'cd
from the haul transducer, mounted at approximately middle ship Icngth, such areaction could bc stimulated by
light from the shipts deck, by noise from shipts machinery or by a combination of these two sources.
The fish density values obtaincd from
the IKMT collcctions and the densitics
derivcd
from
the
eorresponding
echointegrator outputs wcre compared. A
simple rcgression analisys was performed
over the data of the coastal stations.
Those stations with significant abundances
of oUter fish specics, particularly
Ral1lllogaster arcllata and Patagonotothen
tessellata, wcre discarded for this analysis.
The sealler diagram and the rcgression
line are shown in Figure 14.
"-r------------------------,
ECItO... 0.03
r .. 0.95
..
II(UT IR.... 'tnnn m:n
+ t.24IKMT
Fig. 14. Relation hetwecnli~h dcnsity "alues,
derived from IKMT collections and
from the corresrontling echoilllcgrat(lr
(lUlput.
.
Studies on Patl1gonil1n sprl1t post-Iarvae ami juveniles.
In order to express juvenile productiOll in terms of biomass, the grO\\ th in wcight of the different size
categorics was calculaled. As the c1assic allomell)' equation filted data very weil (Fig. 15), no other model was
tricd. Estin13les of the parameters, confidence inten'als and the ANOVA for model significance are presented
in Table 2.
Taille 2. Power cqualion and estimated rarameters dcserihing growth of Spral/lls
ji,egellsis lX'~t-larvae and juveniles. 11le growth model \\as fitted using
nonlineat lea~t-sqllares regre~sion. ASE = aS)lllptotie standard crror of
rarameter estimates; CI = arrroximate conlilknce interval ofrarameter
estimates.
WEIGHTILENGTH GROWTH EQUATION
W=aLb
Parameter
ASE
(95%) CI
a = 0.926
0.205E-06
b = 3.562
0.0587
ANOVATABLE
Sourcc
DF
SS
Model
2
38.05
Residual 173
0.31
Total
175
38.35
16
0,926
3.44 - 3.68
MS
19.02
().()02
<0.001
Fig. 15. Rclationship betwccn body weight
and standard lellgth for post-Iarvae
and juveniles of Spralllls fiwgensis,
and fitted power growth curve.
LENGTH/WEIOHT RELATIONSHIP
Spraltu~
fuegen••
/UWHlfle~
'.lrW--'("'gI
"_"-,"·I.,
.
,
0.1
0.1
Mean density of juvenile sprat over a
nursery ground of 2400 n mi 2 , was
estimated at 16.06 individuals/100 m2.
Confidence intervals of the estimate are
-31 % and +43%. Hence, the total
number of juveniles in the study area
can be estimated at 1.32 x 109 .
0.1
0.'
0.1
oL-~-~-~-~-~~-~-'o
•
"
~
11
~
M
SL I....,,)
4&
"
"
BIOt-lASS ESTlt-lArtS/LENGTH CLASS
80 Welghl (tO"S)
Expanding the length frequency
distribution in the sampIes to the whole
nursery ground, and applying the
length/weight relation calculated in Fig.
15, the biomass of post-Iarvae and
juveniles can in turn be eSlimated al
423.2 t (Fig. 16).
80
10
70
1;(,
50
....
'.
50
40
.0
Ja
,.
'0
• 4-.-+->~_--'-h"""
11
'0
17
,.
2.
71
10
12
M
,J.
.)I
.0
.2
Sl (mm)
Fig. 16. ßiomass ofthe different sizcc1asses collccled wilh IKMT.
Growth increments in otholits were used to eSlimate the age ofPatagonian spratjuveniles. Daily periodocity
of ring deposition, and initial increment formation at tJle onset of exogenous feeding were assllmed. Backcalculation of daily rings has been used to determine the temporal distribution of birthdates during the
spawning season.
AGE/LENGTH RELATIONSHIP
Spraffus fuegensis juveniles
50
-
SL
(mm)
r-~--=------------------------,
40
50
r2
=
0.84
N
=
109
20
10
01
40
,'
50
60
70
80
90
100
110
12.0
Number of increments
- - Gompertz Qrowth functlon
Fig. 17. Relationship belwecn standard lenglh and number of growlh incrcmcnts
on sagiUae for posl-Iarvac and juvenilcs of Spralllls filegensis, and fiUed
Gompcrtz growlh curvc.
Three models that had been applied to dcscribe the post-larval growth of cold-temperature waters c1upeoids
were fitted to the set of data: The Laird-Gompetz (Zweifel & Lasker. 1976; Lough et aJ. 1982), and von
Bertalanffy (Saila & Lough, (981) growth models and Ihe power equalion (Castillo cl al., 1985; Aguilera et al.,
1986). The three models gave good and similaI' lits to the data (1'2=0.84 for the Gompertz, 1'2=0.83 for the von
Bertalanffy, and 1'2=0.81 for the power equalion), but only results on the Laird-Gompertz are presented (Fig.
17
17, T<lble 3) <lS the model fitted the daL::l wiLh ::l lower rcsidual
(SSR=871, 887, 994, respeclively).
SUI1l
squares Ihan Lhe other regression tesled
Tahle 3. (~,ird-GOInp"r1z equation and eslirn"lcd p"rHlneler
dcscribing growth of Spmlllls jilCgen.ris post-Im'vae
and juveniles. The gro\\1h model was litted using
nonlil1ear leasr-squares rcgres!ööion.
ASE = as)",ptolie slandard error ofparameter eslim"les;
CI = approximate eonfidenee inter"al ofparameler eslimates.
AGEfLENGTH GROWTH MODEL
SLt = LO exp{GIl-exp(-ut)]}
Parameter
ASE
(95%) Cl
LO=0.132
0.254
-0.376 - 0.640
G=5.871
1.862
2.147-9.595
(X. =0.035
0.00652
0.022 - 0.048
ANOVA TABLE
u
Source
DF
SS
MS
Modcl
3 106571.6 35523.9 <O.OOJ
871.4
8.30
Residual 106
Total
109 J07443.00
Aller correcting for d<lY avoidance of the lIel :llld dividing the abund:lnee of each size cal.egory by its
duralioll, ealculaLed as the inverse of Lhe growth rate for Ihe c:llcgory. Icngl.h frequcneies were aged aecording
to the :lgc/length model described <lbove. As nUl1lber of increrncnLs W::lS supposed to represenL age sinee first
feeding, to estim::ttc the age frOI11 ferl.ilization of the juveniles eollceted during the eruise, the number of days
e1apsed during the embryonic and yolk sae larvac slages were added.
BACK -CALCULATED SPAWNING DATE
%
-
I:;
-
5
10
'0
')
5
o
0
11:l::>24:l12:.,)lY·'I::>U'l
1tl !::!
t)
.t
•
:lY:lbLJ:lJIII~
lx:ct",O(,:;
I:S
J 2615 8 23-:.2.1
....,OV
OCl.
Fig. 18. Reproduclive aelivily orlhe l'''lagoni:rn spral, during 'ate spring and early
summer, based on baek-ea\cnlated dales orsp"wning. O"le ofinitial
inercmenl fonnalion was ealeulaled fromlhe numher ofring eounlings.
-111e dnralion orthe embryonie and yolk-sae slages were cslimaled Irom
eqnalions given by '\1lOml'son & Nichol~ (1980) and I\I~hlllh (1988).
Figure 18 shows that spawning of the Patngonian spraL ocellrred over four monLhs from Oelober to Janllary.
A major spawning peak is estimated to have laken plClce nround the end of Deeembcr 1991, ami a seeondary
one on 19 Janunry 1992. The final age dass of the histogram. rcprcscnts thc fcw specimens collected of sizes
over 45mm SL, whieh are assumed to have beeil spawllcd before Oetober 23.
18
DlSCUSSION
Although thc small and middle-sizcd 1:If\'ae of the Sprattusfucgcl1sis show an extcndcd distribution o\'cr thc
southern Patagoni:m shelf during summcr, results rcportcd hCfc, :md thosc obtaincd from thc analysis of thc
ENGEL net sampling (Hanscn, unpub. manusc,) dcmonstratc that thc bulk of the O-group sprat, rcmains from
mctamorphosis onwards in the southcrn Patagonian shelf, in assodation with southern coastal waters, mostly
at bollom deptlls below 50m. Satcllitc imagcs of thc stud)' arca for mid-Fcbruar)' show thc -lO-milc widc cold
Magellan watcr tonguc, sprcading northwards from the Strait arca to San Jorgc's Gulf, in good corrcspondance
with the deseriptions ofKrcppcr (1977), Krepper & Rivas (1979) and Dianchi ct al. (I9ß2). During the cmise,
howe\'er, the con\'erse situation was obscr\'ed, Thc coastal region was co\'ered by warmer - and as the CTD
sampling indicated lower salinity - water impinging from San Jorge's Gulf. mo\'ing southwards down to 51 oS,
probably as a consequcnee of the Magellan nJllolT s1:lckcning and displadng olTshore. A similar warm coastal
countcreurrcnt has been rcfcrred to by Hart (1946) as "old shc1fwate( (Fig, 1-0).
In thcir analysis on the comparati\'e c1imatology of reproducti\'c habitats of neritic pelagic fishcs, Oakun &
Parrish (1991) point out se"eral phJsieal :llld biologieal eonligurations of spawning and nnrsery grounds that
ser\'e to seeure lan'al survi"al. Reeurrcnt featnres of these scenarios are mechanisms tcnding to produee (i)
stability of the water eolumn by strong "crtieal stratilieation, (ii) nutdent enriehment cmlsed by upwelling and,
(iii) retention of spawn within a f.1\'ourable habitat.
The nursery ground of thc Patagonian sprat shares features in cOliullon with ~ther neritic fish rcproducth'e
habitats, Stability of the water eolumn induced by the formation of picnoc1ines is a cmeial mcch:l1lisll1 for food
partic1e accumulation, In the study area. piclloc1ines arc mainly deperidcnt on salinity gradicnts, although
dnring the cmise tcmpcratnre also conlributcd to the lowcr dcnsit)' of thc' uppcr waler laycr.
Sourccs of nutrient enrichment are gi\'en by the impinging of eomp:uath'c1)' colder sub:l1ltarctic walcr
e"ident by the risc of hottom thermoc1ines to sub-surfaec laJers, alld by cireulalion charactcristics of thc
encountcr of the Magellan' runolT and shelf waters, \\ hieh dnring the cmise origin:ltcd dh'crgenee and
subscqucnt upwelling. Thcse rcsults arc conlirmcd by thc direct obsen':llions on chlorophJII-a distribulion
carricd out b)' thc Coastal Zone Color SC:l1lner, a radiometcr wilh \'isible and infrarcd speetral channels that
opcrate on NASA's Nimbus-7 rescarch satcllitc. Summer images sho\\' "ery high pigment conccntrations in
relation wilh the penetration of Magellan \"ater o\'cr the shc1f mid in the frontal zone betwecn the two watcr
masses.
Rctcntion ofjuvcniles within the eoasta! habitat, ma)' be seeured by oce:lII surf.,ce layer transport caused by
wind strcss that in the mea is generally directed shorcwards, and by the southwards drin of coasta! water from
San Jorgc's Gulf, that in combination with tidal circulation and migralory habits of post-Iaf\'ac and jU\'cniles
. may sen'c to countcracting the gcncral pattern of NNE transport charactcristic of the Argcntinc shclf.
Acoustic sampling combincd with IKMT s:lIupling pro\'cd to gi\'c vcr)' uscful information on abundance and
distribution ofju"enile sprat. 1I0wc\'er a higher salllpling elTort, both acoustic and IKMT, should be allocated
in the coastal area to ohtain accuratc estimatcs ofjuvcnilc productiOll.
From the rcgrcssion analysis bctwcen IKMT and echointcgration data. it can be concluded that the fish
dcnsitics obtaincd from both lIlelhods show a good corrclation. Adcquate s:ullpling conditions -with a
prcdominanee of night stations, and emdent salllplcrs for the size-ranges eneountcred· lead us to conclude
that the IKMT catehes are representative of the real abundanee of early juvenile sprat. Thc obiained regression
line (interccpt dose to 0 and slope dose to I), supports rcasonably weil thc assumption of applieability of thc
adopted TS model. IIowe"er the use of a shorter wa\'clength in the aeoustic salllpling, as for cxalllple 120 or
200kHz, ShOltld be cxpcrilllcnted in order to aceount for possible unstabilitics in the TS of post-Ian'ac and carly
ju\'eniles fish duc to thc frequeile)' dcpcnd:lI1ce of thc backscallering I frequeue)' function near or at the
. R.1ylcigh zone (Clay & Medwin, 1977~ llolliday, 1983).
.
Thc fact that the sehools of post-Iaf\':lc and c1rly ju\'eniles and thosc of :lgc 0/1 group sprat wcre in
oceasions distinctly scpparatcd, pcrlllilled to conclude that bolh age groups show dilTerent dicl Illigr:ltor)'
patterns. Variations in the yertical distributions of young alld auult stages of one specics inhabiting thc saine
arca h:l\'c becn reported by Raid (1985) for ßallic herring, but contrar)' to his results our obscrvations indicate
that during the day post-Ian'ae and early jm'enilcs eoncentrate Bear the bottom from \\hcre the)' Illigratc to
19
occupy the whole water column in nighttimc. Older stages on the other hand, moye to the surface during the
night, migrating to mid-depths and breaking into small schools, at sunrise. Night distributions of post-Ian'ae
and earl)' juycniles gcncrally rcported in the litcrature, dcscribe an asccnd of specimens aflcr dusk, and a
migration towards the bollom as illumination progrcsses (Le. Sjöblom & Parmanne, 1978; Munk, 1988).
The 'avoidance reaction obscn'cd when the ship stopped to occupy the slation could be duc, at least partiaIly,
to the ship's illumination at thc working station. Thus, the utili7d1tion of deck Iigths during rcgular sampling
(trawling or acoustic stlf\'eying) should bc restrictcd to a minimum 10 avoid possible bias in the data. Taking
into consideration that most of the study area lays in shallow waters, a smaller and more quict ship should be
.
employcd in order to redllce vesscl introdllced perturbations.
D:lck-calcul:ltion of otoliths eountings to determine lan'al birthd:ltes dllring the spawning se:lson, h:ls been
rcportcd for sevcral c1upcoids (Towndscnd & Graham; 1981; Mcthot, 1983; Jones, 1985; Thorrold, 1988;
Alhcit & D:lkun 1991). Patagonian sprat sccm to spawn over 01 period of at least 4 months, "hieh comp:lres
weIl with results reported for the M:llvin:lS popul:ltion. Results presented here are limited by the fact th:lt
duration of the cgg and yolk sac stagcs had to be calculated on the b:lsis of v:llues reported for Sprattus
spratt/ls. The duration of the pcriod from hatching to initial ring deposition, nwy be underestilllJted as Alshuth
(1988)'s experimental valucs were obtaincd at highcr tempcratures than those cncountered b)' the P:lt:lgoni:ln
sprat. Age detcrmination with optic:ll microscopy sccmcd to be adcquate for spccimcns smaller th:lIl 40 mm
SL. Largcr specimens wcre somcwhat difficult to rcad, :lnd othcr tcchniqucs (i.e. SME) will be uscd in the
future.
Two qucstions rcmain unanswcrcd: (a) "here does the Patagoni:1Il stock sp:lwn?; and (b) is there a nursery
ground of the type describcd hcre on the coasts of Malvin:ls Islands? We bc1ieve that sprat eggs present in our
historie collections corrcspond to the sp:lwning of the Malvinas stock. Although not completcl)' discarding the
f.1Ct that vcr)' coastal sp:nrnings ofT Patagonia could have c1uded prcvious plankton suryeys during early
summer, it may be hypothesized t1wt the reprodllctive acth-ily could take place in inlcts :lIld ch:lnncls, amI that
early de\'c1opmental slagcs could be transported to the shc1f by the MagcIlan strait mnofT. The fact that POStlan'ae during summcr monlhs, appeared aggregatcd along the 100-m depth contollr, which as slated :lbO\'e
corrcsponds wilh tk 33.0 psu isohaline, seem to indicate an associalion bcl",een these earl)' sl:lges and Ihe
frontal zone crealed by the mecting of lcss-haline Magellan ",alcrs :md shclf ",alcrs. Ad\'ection towards the
coast could be cfTectcd by surface Ekman transport, that during Ihe reproduclive scason is gener:lIly direcled
toward shore (Dakun & Parrish, 1991).
As to the second quest ion, there is no information available from that area about the prescnce of post-Ian'ae
and carl)' juvcniles resulting from spring spawning. Howevcr, assuming that this is a gencticalIy distinct stock,
as morphometrics and population attribulcs indicate, we can speculate, foIlowing IIcs & Sindair (1982) upon
the existence of a gcographically st:lble lan'al rctention area. The wcll-dclimiled arca around I\.1:llvin:lS as a
result of anlic)'cloninc cuncnt circulation and sinking of shclf waters dcscribed by Scvcrov (1990), may be the
physic.11 feature involved in maintainig the inlegrity of the individual population.
•
ACKNOWLEDGEI\1ENTS
We would like to exprcss our sin..:~re gratitude to our Argcntinc, Russian and Ucraninn collcagues and crew
mcmbcrs for constant support during the cmisc. Spccinl thanks are due to Dr. 1. IIanscn for his active
participation during the prep:lratory stages of this projcct. Wc are :llso thankful to Mr. D. Brown for his
technieal support in the Iaboratory analysis ofthe ichlhyoplankton samplcs.
This is Contribulion No. 772 of the Inslituto Nacional de Invcstig:lci6n y Desarrollo Pesquero, Mar dcl
Plata.
20
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