In.ternational Council of
the Exploration of the 8ea
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HYDROGRAPHIC FEATURES AND DYNAMICS OF BLUE WHITING, MACKEREL
AND HORSE MACKEREL IN THE BAY OF BISCAY, 1994-1996.
A MULTIDISCIPLINARY STUDY ON SEFOS.
Porteiro.C.(1}. Cabanas, J.(1}. Valdes. L.(2}, Carrera, P.(3), Franco,C.(4), Lavin, A.(2)
•
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(1)
(2)
(3)
(4)
Instituto Espafiol de Oceanografia. P.O. Box 1552, Vigo, Spain
Instituto Espafiol de Oceanografia, P.O. Box 240, Santander, Spain
Instituto Espafiol de Oceanografia, P.O. Box 130, A Corufia, Spain
Instituto Espafiol de Oceanografia, Avda Brasil 31, Madrid, Spain
ABSTRACT
Hydrographie and elimatie eonditions have been found to be one
of
the most
important
faetors
that
can
influence
the
distribution and behaviour of adults, juveniles and early stages
of fish. This relationship, which has been pointed out by
several authors, is also the main, objective of the SEFOS
project,
which
studies
the
relationship
between
the
distributions and migrations of commercially important fish
species and the oceanography of the European shelf edge. Within
this framework, the Bay of Biscay presents special oceanographic
and climatic conditions that could influence the aggregations of
food and larvae in retention areas throughout this area, which
is one of the most important, nursery areas for several fish
species and seasonal migrations of blue whiting, horse maekerel~
and mackerei.':"
This paper presents the results of a multidiseiplinary study of
the relationship between thc oceanographic eonditions of the Bay
of Biscay and the distribution of both early stages - eggs' and
larvae - and adult fish of horse mackerei, mackerel and blue
whiting for the period 1994-1996.
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INTRODUCTION
A eentral aim in pelagic ecology is to identify the spatial
,distribution patterns of species and to understand the causa1
meehanisms that lead to them. In the pelagic domain these
'patterns are a result of complieated interactions between
attributes of the biology of the organism and the environmental
charaeteristics of the ocean.
Specific attributes
include
behaviour,
predator-prey
interaetions,
diel' and
ontogenie
•
vertical migration, etc. Environmental characteristics include
the physical-chemical and biological features of a region. The
nature of this dispersive environment and the behaviour of the
organisms within it has an important influence on the survival
and recruitment of populations.
The Shelf Edge Fisheries Oceanography Study
(SEFOS) is a
multi-disciplinary project which studies the interaction of
physical processes at the shelf edge with commercially important
fish species such as mackerel (Scomber scombrus, L), horse
mackerel (Trachurus trachurus, L), blue whiting (~cromesistius
poutassou, R) and hake (Merluccius merluccius sp, L). One of the
main objectives ,in the SEFOS project was to detect the
hydrographical features that determine
the distribution of
eggs, larvae, recruits and adults and to explore the effects of
the observed dynamies on the planktonic forms during the
spawning season of the fish species that spawn on the shelf edge
in the Bay of Biscay.
Meteorological conditions determine to a great extent thc
formation and evolution of the hydrological structurcs of the
Bay of Biscay. In winter the Azorcs high pressure cell is
situated on the northwestern coast of Africa and a deep low
pressure arca is located in Grecnland. This system forces wind
of a wmq component onto the western cdges of the Iberian
peninsula and Bay of Biscay. In summer the Azores high pressurc
moves to the central Atlantic and produces fluxes from the NE in
the north and northwest of the peninsula. This pattern causes
upwelling in summer in the north and west of the Iberian
Peninsula (Blanton et al., 1984).
In the ,upper layers of the oceanic region surrounding the
Iberian Peninsula, three water masses can be distinguished:
Surface Water, highly variable and influenced by meteorological
conditions and coastal runoff;
Northern Atlantic Central Water
(NACW), seasonally variable and found between approximately 60
and 600· m depth; and
Mediterrancan Intermediate Water (MIW)
(Cabanas et al., 1992; Lavin et al., 1992).
The general circulation in theBiscay arca is weak because there
are no density gradients which might produce potential currents
in the south of the Bay, although the flow suggcsts a weak
clockwise circu1ation (Pingree, 1993). Ovcr the shelf-break of
the Iberian peninsula and Armorican shelf a current drives
mainly poleward and castward. The currents on the continental
shelfs are affected by strong fluctuations on different time
scalesi the current regime changes seasonally in surface layers
over the Continental Shelf and coastal area. In autumn-winter a
poleward flux from 'the western Iberian Peninsula. appears
(Pingrce & Le Cann, 1990, Haynes & Barton, 1990; Frouin et al.,
1990). It produces winter warming in the area arid may cause the
development of eddies. The circulation over the continental
slope may become unstable, especially in the southern part of
2'
•
•
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tpe Bay of Biscay. These instabilities have been detected in the
proximities of topographie accidents such as the canyon of Cap
Ferret and Cabo Ortegal (Pingree et al., 1992). '
f
","
.-.,t:o. : \i',,~,:
In the Bay of Biscay, the important dynamic features that govern
the exchange of properties between regions include Ekman
currents, mesoscale rings, fronts and filaments. These patterns
affect the spatial displacement (e.g. advection, diffusion,
retention) of larvae and determine the observed distribution of
these early life stages until their recruitment.
•
•
Available data on blue whiting eggs and larvae distribution in
the Bay of Biscay are,scarce as most of the literature refers to
the Porcupine and surrounding area between the south and west of
Ireland and the west of Scotland (Bainbridge & Cooper, 1973;
Coombs, 1974, 1979; Coombs & Pipe, 1978; Bailey, 1974, 1982). In
the Bay of Biscay only very sparse patches of larvae were
described (Arbault & Boutin, 1969; Sola & Franco, 1984; Sola &
Franco, 1985) .
Mackerel and horse mackerel eggs and larvae have been sampled
periodically almost every year from 1987 and their abundances
and distribution studied in the context of the ICES triannual
egg surveys as weIl as in other plankton surveys in the
Cantabrian Sea and off Galicia during the spawning seasons of
both species, and the results have already been published (Anom
1996). To the North of Spain, spa~ing takes place in spring
(Sola et al., 1990, 1994; Lago de Lanzos et al., 1993) and that
the patterns in the observed distribution are consistent through
the years studied, however, as most of the surveys were carried
out in the contest of the evaluation of spawning stock biomass,
no attempt of relate observed distributions with hydrographical
features were undertaken be fore the present SEFOS project .•
Horse mackerel and mackerel are highly migratory species, . and
there are many references to their movements in northeastern
Europe (Macer, 1977; Lockwood,' 1988; Walsh & Martin, 1986;
E1tink ct al, 1986; Anon, 1990a; Walsh, 1994; Borges et al.,
1995), as weIl as in the Bay of Biscay in the case of mackerel
(Uriarte, 1995; Villamor et al., 1996). The blue whiting has a
widesprcad distribution along the continental slope in the North
Atlantic ocean (Zilanov, 1980). This species has been studied by
means of acoustic methods since 1972 (Anon, 1982; Anon, 1996).
One of the most important features of this species is its
ability to migrate from feeding areas to spawning ones and viceversa (Carrera et al., 1996). Mackerel and horse mackerel are
important species for the Spanish fishing fleet operating in .the
Bay of Biscay. The average yearly catch in 'the ,Bay of Biscay
during the period 1992-1995 (Anon, 1993, 1995a, ,1996) 'was 22 500
tons of mackerel and 35 500 tons of horse mackerel. For blue
whi ting the catch has remained stable over the last 20 years,
with approximately 30 000 tonslanded each year.
3
MATERIAL AND METHODS
Surveys
In the spring of 1994, from 15th Mareh to 14th April, and in
1996 from 11th Mareh to 13th April, two joint
aeoustie,
hydrographie and iehthyop1ankton survcys (SEFOS 0394 and SEFOS
0396) were carried out on board R/V "Cornide de Saavedra", in
order to identify the spawning, 1arvae retention and reeruitment
areas of blue whiting, and to study the oceanographic conditions
in the Bay of Biscay during the spawning season. The area
covered for both surveys was from 41 ° 50' N , 9°38 'w (north
Atlantic coast of Spain) to 47°40'N, 7°W (French Brittany coast)
(Fig.la,b).
.
In 1995 two surveys were performed: the first survey (MPH/95)
from 25 March to 15 April, covered the area from Lisbon up to
45°N (Arcachon, France), while the second survey (SEFOS/95) from
28 May to 18 June, covered the northern Cantabrian area and the
west of France (Fig.lc,d). In both surveys the sampling grid was
designed in accordance wi th the procedure described by AEPM
(Anon, 1994) in cross-shelf transects every 15-30 nm and with
CTD & plankton stations 15 nm apart.
Physical
procedures
In the SEFOS 0394 survey, 113 CTD stations and 5 SSS (SEFOS
Standard Sections) were performed. In the two cruises of 1995,
there were 112 CTD stations and 6 SSS in the MPH/95, and
122
CTD stations and 4 SSS in SEFOS/ 95. In SEFOS 0396 114 CTD
stations and 7 SSE were samp1ed. The
CTD cast (SBE 25 and
Falmouth Scientific) was performed, SEFOS Standard Sections were
sampled (Turrell et al,· 1995) and water samples were taken for
CTD salinity calibrations ..
stations
Sefos St.Sect.
CTD
•
1994
SEFOS 0394
113
5
1995
MPH/95 SEFOS/95
112
122
6
4
1996
SEFOS 0396
114
7
Continuous
recording
of
thermohaline
and
f1uorescence
charaeteristics of surface water, and satellite images of the
area were taken into account for further analysis. Also three
current meter lines were moored from February 1995 to February
1996 in the shelf, shelf-break and slope waters in the Southern
part of the Bayof Biscay ( Diaz deI Rio et al, 1996).
4
•
~lankton
sampling
In the SEFOS 0394 survey a total of 113 plankton stations were
made on a zig-zag line. iThe.stations were situated every 8-12 nm
and distributed as foliows: 37 stations over the shelf (depth
<200 m), 34 stations over the shelf break (depth 200-1000 m),
and 42 stations over the ocean basin (depth >1000 m). In 1995 a
total of 112 and 120 stations were sampled in the MPH/95 and
SEFOS/95. In both surveys the sampling grid was designed in
accordance with the procedure described by AEPM (Anon, 1994) in
cross-shelf transects every 15-30 nm and with plankton stations
15 nm apart.
:.i ..
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In SEFOS 0394, plankton sampling was carried out at each station
using a Bongo net (50 cm diameter and mesh size of 200 mm) on
double oblique tows in water shallowcr than 300 m and vertical
tows in deeper water. In the 1995 surveys (MPH/95 and SEFOS/95),
plankton sampling was carried out using a Bongo net (20 cm
diameter and mesh size. of 250 mm) which was hauled in double
oblique tows down to a maximum depth of 200 m, or 5 m above the
bottom in shallower water. In thc three surveys tows were worked
at a ship's speed of 2-3 knots and a depth recorder was fixed to
the net cable in order to register the maximum depth reached. A
GeneralOceanics flowmeter was used to determine the water
volume sampled. Sampies were immediately sorted and counted for
target
species.
Sampies
were
preserved
in
4 % buffered
formaldehyde, and once in the laboratory all fish eggs and
larvae were counted and classificd to species level .. Mackerel
and hor~e mackerel eggs were staged (Lockwood et al.·, 1977; Pipe
& Walker, 1987) and the larvae of all target species mcasured to
the
nearest
0.1
mm
for
information
on
size
frequency
distribution. Abundances were converted to number per square
metre following standard techniques (Smith & Richardson, 1977).
Acoustic sampling
Thc survey grid was designed to provide the best' coverage for
acoustic sampling. In SEFOS 0394 the survey grid consisted of a
zig-zag track design with 20 nautical miles between peaks, with
random start, whereas a parallel track design wi th 24 nautical
miles between transects was performed in SEFOS 0396. The main
transect direction, in both cases, was normal to the isobath
contour, over .the shelf break. In addition, in SEFOS 0396, in
. thc Spanish area, extra transects were allocated in order to
evaluate the Spanish fraction of sardine. The distance between
transects varied between 12 milcs as a general distance and 6
miles in specific areas.
A Simrad EK-500
echointegrator with a. 38kHz split bcam
transducer was used. In. 1994, due to bad weather .conditions, it
was not possible to calibrate' this equipment and' the results of
the previous ca libration (November·93) were assumed. In 1996 the
calibration was performcd before the survey. Both surveys wcre
5
conducted day and night at a ship speed of 10 knots. Integrated'
values (SA values) (Bodholt, 1990) were directly collected every
nautical mile and stored in a PC, which controlled the main
settings of the echosounder. Geographical position was also
taken by GPS. Total SA va lues were allocated to different
species, according to the information obtained at both pelagic
and bottom fishing stations.
RESULTS
HYDROLOGY
In the Bay of Biscay shelf and slope surface waters (down to a
depth of 200 m) the thermohaline characteristics, during the
months of April and May, are greatly influenced by the presence,
during the winter months, of the poleward current in the west
and by a large influx of fresh water in the east.
•
For each cruise, salinity at sigma-t 26.9 and 27.1 (fig. 2),
temperature (fig. 3) and salinity at 100 m depth (fig. 4) was
presented as indicatives to show the dynamic and termohaline
characteristics .
In 1994 most of the water in the Bay came from higher latitudes,
which also gave rise to a flux towards the Spanish coast. There
was a more superficial haline front in the Bay due to the
presence cf large runoffs of fresh water and that of a pocket of
water at 6: > 26.9 which recirculates in the Bay (Fig. 2a). At
the level of upper NACW (180m) the waters are homogeneous
between Finisterre and La Rochelle, except for in the corner of
the Bay of Biscay, where salinity is lower and the temperature
is higher, (Fig. 3a, 4a).
In April 1995 the situation of the haline fronts in the Bay was
similar tc that found in 1994, although temperatures were higher
and salinity lower in the SE corner of the Bay, extending as far
as 4°W. Incipient eddies were also found. In the surface layers
a frontal zone appeared at the northwest corner of the Iberian
peninsula
which
separated
the
Cantabrian
and
Atlantic
circulations, and a second frontal zone in the eastern part of
the Cantabrian Sea isolated the inner part of the Bay. The
thermohaline circulation in the gulf was limited, in contrast to
that of 1994 (Fig. 3b, 4b).
In May-June a frontal zone with steep temperature and saline
gradients appeared over the French slope along all i ts length,
\oJhich led to the formation of eddies, especially in the inner
areas of the Bay. The thermohaline characteristics at the level
of upper NACW (100m) showed a gradient Qver the whole area, with
warmer and less saline water between SOW and 45°N and the SE
6
41
corner of the Bay, and indications of connection with colder and
more saline waters around 6°W. In the lower NACW (500m) the same
charaeteristics could be observed between the Asturias-Cape
Ortegal zone and the Armorican ßhelf. "Over, the Cantabrian shelf
the circulation is westward . and parallel
to
the coast.
Measurements of the eurrent taken at a depth of 75m on the slope
off Cape Penas (Diaz deI Rio et al., 1996) show a steady eurrent
with an average speed of 10cm/s flowing westward (Fig. 3e, 4c).
In 1996 a higher level of salinity than that of previous years
was reeorded in the whole of the Cantabrian, whieh indicates a
greater influence of southern Atlantic waters (winter poleward
current). The layer of water eorresponding to NACW (100-500m)
indicated an association of the ecntral parts of the Freneh and
Spanish shelf and the Ortegal-Corufia area with colder and less
saline waters, although there was a lack of continuity off Cape
Ortegal. A pocket of warmer and more. saline water was found
between this zone and the SE corner of the Bay (Fig. 3d, 4d) •
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With regard to surfaee waters, in 1994 there was a strong
eirculation in the SE corner of the Bay towards the Spanish
eoast and a frontal zone in Finisterre; in 1995 there was a
greater homogenei ty and in 1996 the influence of the winter
poleward eurrent was notieeable and a front was deteeted in
Ortegal. In addition to this a mainly haline front assoeiated
with the French slope appcared in all the cruises.
The most noticeable differenees between the three years were the
greater influcnee'of the northern part of the Bay and a net flow
towards the south in 1994, a lesser degree of circulation and
regular thermohaline charaeteristics in 1995 and a grcater
influenee of the southern part of the Bay (west Iberian
Peninsula) in 1996, due to the greater intensity of thewinter
cireulation. In addition to this, thc cyclonic circulation in
the SE corner of the Bay and the appearance of fronts in Ortegal
produee an interannual variation over the period studied whieh
is refleeted in the biological eommunities .
EGGS AND LARVAE
The first observation that arises from our results is that more
than 50% of the larvae remain in the spawning areas and the
other half are transported equally to inshore as weIl as
offshore waters. So, al though the bulk of the population is
retained over the spawning grounds, there is still a large
proportion of the larvae whose spatial distribution seems to be
in some way related to hydrographie features .(Fig. 5a, b, c).
7
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Blue whi ting:
Blue whiting Iarvae were identified in 57 of the 113 plankton
sampling stations during the SEFOS94 cruisc (March/April).
A
total of 852 blue whiting larvae wcre sorted and measured. The
most intensc spawning area appeared in the north (west of
France, betweeen 46° and 47° N) where relatively high numbers
were recorded even quite far offshore, with a maximum value of
137.34 larvae/m2 • Significant spawning also occurred in a small
area off Cape Penas. These two main arcas account for 88.92% of
total blue whi ting larvae. The rest !Jf the sampled area shows
very low abundances.
Blue whiting Iarvae collectcd were in the size range of 2 to 24
mm. The size frequency distribution was bimodal with peaks at
4.5 and 9.5 mm. In thc" area west of France there was a
significantly higher abundance of ncwly hatched larvae in the
smaller range (2-6 mm) which corresponded to an arca where quitc
strong spawning was ta king place or had recentIy occurred (Fig.
..
6) •
Mackerel:
Thc egg and larvac abundanccs for thc whole arca samplcd in each
survey are shown in Figures. 7 & 8. Mackerci eggs were qui te
abundant and widely distributed over the continental shelf,
particularly on thc shelf edge. Mackerel larvac were found at
greater depth in the offshorc stations, du ring March-April in
the SEFOS 94 and MPH 95 surveys when first spawning took place.
Thc highcst conccntration of mackcrei eggs was found in April
1995 (MPH/95) off the northern coast of Galicia with a maximum
value of 3 072 eggs/m2 , coinciding with the highest concentration
of the smallest larvae (886 larvac/m2 ) . In the SEFOS95 survey
carried out in June,
eggs were less abundant, and very few
larvae were found. Howcver, some important concentrations of
larvae appearcd in thc northern area covered (47 oN) and in the
furthermost offshore stations coinciding wi th an area of high
fluorescence. Plankton data support the hypothesis that the
spawn occurs while adults move into the Gulf of Biscay folloving
the coastiine of France and Spain in the same way the adult
population does.
The size of larvae ranged from 2.8 to 17 mm, while the most
abundant were
from 5 to
7.5 mm
(excluding the highest
concentration of these feund recently hatched off Galicia). A
pattern in larval distribution can be observed, from spawning
areas in the shclf break, where the highest abundance ef eggs
and larvae was found, to offshore areas, where the abundance of
larger sized larvae was greater (Figures 9 & 12).
8
.
•
.
Horse Mackerel:
•
The egg and larvae abundanees for the whole area sampled in eaeh
survey are shown in Figure,., 10,,: & ;11.,Exeept for an important
nueleus of eggs found off the west eoast' of Franee (47°N) during
SEFOS/94 (March/April) very few eggs and larvae were found that
year. However, eggs and larvae of horse maekerel appeared in
great abundanees in the SEFOS/95 survey (May/June). At this
time, there were two areas of high abundanee of eggs on the
eontinental shelf, one being found off the Cape Ortegal coast
with a maximum value of 1 252 eggs/m2, and the other off the
French coast. This differenee between the first survey in 1994
and the later survey in 1995 indieates that the main spawning
oeeurs later in the year, at late spring, and that spawning
progress northwards from waters in the South of Portugal to the
North of Spanish and West of France. Larvae seem to be
distributed in a similar pattern to that of eggs throughout the
eontinental shelf, but high densi ties were found elose to the
shelf break (Fig. 11) .
ADULTS
Figure 13 shows SA values for blue whiting for eaeh transeet and
survey, split by age group, and figure 14 shows the maps with
the SA values for each nautieal mile. Both surveys show more or
less the same distribution pattern. Important ehanges of density
were found along transeets, with the greatest density in North
Franee and North Galieia and the Iowest in East Cantabrian. In
addition, there was an area in West Cantabrian with searee
density.
•
In 1994 age group 111 was the most abundant in the whole area,
whereas age group 11 was also important in North Franee and age
group I was only found, with a low density, in West Cantabrian .
In 1996 age groups land 11 were the most abundant. Age group 11
was the most abundant in North Franee and in the easternpart of
North Galieia whereas age group I was the most important in West
and East Cantabrian and in thc western part of North Galieia. In
East Cantabrian only age group I was found.
In Freneh waters blue whi ting was mainly distributed along the
eontinental sheIf-break and its distribution spreads further
offshore in a pelagie Iayer at 200-300 m depth, but in Spanish'
watcrs it was mainly distributed over the eontinental shelf,
elose to the slope, wi th only a small proportion in a pelagie
layer, mainly in the inner part of the Bay of Biseay.
Blue whiting juveniles were found in 1994 in the corner of the
Bay of Biseay (East Cantabrian ,md South Franee) .. They had, a
mean of 3.7 em (0.6 s.d.) and formed large pelagie schools elose
9
to the sea surface over 1000-2000m. water depth. In addition,
juveniles of 10.7 cm (0.6 s.d.) were found at 46°40' N, 5°40'W,
at 100-150 m depth close to the shelf-break. In 1996 juveniles
were detected in the corner of the Bay of Biscay, but their
density was lower than in 1994.
DISCUSSION
In several fish species that spawn offshore, the postlarvae and
early juveniles recrui tinshore, so at some cri tical moment in
the early fish stages, eggs and/or larvae should be transported
from offshore
spawning areas
to
the
nearshore nurseries
(Koutsikopoulos et al., 1991). Transport from the spawning
grounds to the nearshore region is not weIl understood, and many
authors have encouraged active collaboration between physical
oceanographers and biologist in the hope that this will lead to
a better understanding of this keystone of marine fish ecology.
Spawnings of SEFOS target species are spatially related to the
shelf-break, and early life stages are found all along the Bay
of Biscay during the sampling months, so for this reason they
can be used as good tracers for comparing spatio/temporal
observations of ·hydrographic features and larvae and adult
distribution.
When considering the circulation of the upper layers of the
southern part of the Bay of Biscay a distinction has to be made
between that which takes place over the shelf-break and that
over deep waters. The latter is markedly anticyclonic due to the
influence of the North Atlantic flow (Pingre 1993), and gives
rise to an influence of the northern waters of the Bay on the
central area of the Cantabrian Sea. Superimposed on this general
pattern of circulation is the influence of the topography of the
sea-bottom (shelf-break) and seasonal atmospheric conditions
(sunshine, rainfall, wind stress) and runoff, all of which
affect circulation in the upper layers.
Other noticeable
seasonal influences are those of upwelling (spring-summer), the
poleward current (winter) in the western part of the Iberian
Peninsula and runoff in the eastern part of the Bay. These all
combine to
induce
a
front
in
Finisterre-Ortegal
and
a
circulation cell in the . SE corner of the Bay, which together
with thc formation of eddies are the most outstanding features
of the surface waters of the Cantabrian Sea.
Over the
continental slope there is a countercurrent with net eastward
flow, although seasonal changes of direction occur due to the
aforementioned factors.
Variability in the observed distribution of eggs and larvae
obtained in the SEFOS project can be reasonably explained by the
. biological behaviour of the spawning stock (which was shown to
10
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spawn close to the shelf-edge) and
features that occured in these years
41
by
the
hydrographical
The distribution of the larvae in. the central region of the
Cantabrian sea suggests some llmit'eef "~a'stward ,transport of a
fraction of the spawning during this period when very few larvae
were found in the outer stations in this area. This feature was
consistent in our results and the continuity in the distribution
of rnackerel and horse mackerel eggs and larvae suggests little
net displacement of the planktonic stages from the· spawning
grounds to offshore.
In those areas where circulation is
governed by topography,
wind forcing will tend to favour
alongshore movements of the larval population rather than crossshelf movements. In fact, circulation in
these areas was
characterized by weak eastward currents (10-15 cm/s) ( Diaz deI
Rio, 1996) generated by dominant SW and NW winds and also the .
intrusion of water from the centre of the Bay of Biscay
detected du ring the period studied. These features are coherent
with the spatial larvae distribution observed in the central
part of the Cantabrian.
Some large larvae of mackerel and horse mackerel were found
further off the coast. These larvae were distributed across the
oceanic waters in two areas: off the Armorican platform (47°N)
and off Cape Ortegal (SoW) .This front was detected in June-95
when the biological
and
environmental
conditions
changed
abruptly in the cross-shelf direction, and both phytoplankton
(measured as fluorescence) and zooplankton (displacement volume)
increased their abundance. Hydrographical measurements also
suggest a displacement of waters off the coast, and quite high
numbers of mackerel and horse mackerel larvae in very heal thy
conditions were caught. Abundant information about the Armorican
shelf front is available in the literature, and a revision on
the physical,
chemical and biological processes has been
published recently (Sournia et al., 1990).
•
At 8 0 W the forcing was more energetic and resul ted in a much
larger and more continuous displacement of the larvae compared
to the Armorican platform where larvae were not continuously
distributed·over and off the shelf. This pattern of distribution
in Cape Ortegal has been repeatedly observed in previous years
since 1992 (Lago de Lanzos et al., 1993; Franco et al. 1993) and
it seems to be associated with the connection between Atlantic
and Bay of Biscay waters. The hydrographical processes described'
in the Armorican platform and in Cape Ortegal may explain' the
large numbers of planktonic stages of different fish. Moreover,
these dynamics in Cape Ortegal. have an. important influence on
food availibity and its .quality for, adult fish. Abaunza et al
(1995) have found different infestation 'levels
of
Anisakis
simplex (Nematoda: Ascaridata) for horse mackerel 'westward . and
eastward of Cape Ortegal; since this fish, species feeds on
zooplankton arid planktonic crustaceans among others, the high,
hydrodynamic activity 'at west Cape Ortegal gives a high primary
11
production, ensuring favourable conditions for the development .
of the life-cycle of Anisakis simplex and, therefore, a grcater
abundance of this'parasite may occur in Galician waters.
The SE corner of the Bay has pcculiar oceanographic and climatic
conditions which set it apart from the rest of the Cantabrian
Sea. The main features are the prescnce of thermohaline fronts
and a cell of cyclonic circulation, which differentiate this
area for larvae as weIl as for juveniles and adults. The
thcrmohaline front and the cyclonic circulation lead to a
concentration of larvae, and make th.;. Bay an important nursery
arca (Schmidt, 1909; Maucorps, 1979;' Bailey, 1982;
Porteiro,
1996). In 1994the presence of a strong southwards thermohaline
current in the eastern sector of the Bay could explain the largc
concentration of juvenile blue whiting found in this zone. On
the other hand, in both 1994 and 1996 the density of adult blue
whiting surveyed in this zone was low in comparison to other
sectors of the Bay, the only noticeable feature being the
presence of specimens in age group I.
..
Adult blue whiting wcre unevenly distributed horizontally, with
areas of high density alternating with others of scarcity. One
feature of note was thc difference in density found in the
western corner of the Iberian Peninsula (North Galicia) in both
1994 and 1996, but especially in the latter, in comparison with
the adjacent zone of the Cantabrian Sea (bctween 6° and 7°W).
This difference may be explained by the thermohaline features
and the dynamies of the NACW. In 1996 a break in continuity was
discernible off Cape Ortegal , which coincided wi th low numbers
of blue whiting in thc area. On the other hand the density of
blue whiting in the central arca of thc Cantabr.i.an Sea was lower
in 1994 than in 1996, which mayaiso correspond to the lower
salinity found in this zone in 1994 eompared to 1996; this
sector of the Cantabrian Sea was also more stable and
homogeneous in 1996 than in 1994.
Blue whiting is a migratory speeies whose patterns of ,behaviour
are still not completely understood. Neverthcless, the grcatest
ehanges in distribution at this time of year are to be found in
north France (Carrera, 1996), and therefore thc differenee in
spatial distribution to be found in the rest of the Cantabrian, ,
Sca mayaiso be explained by changes in hydrographie conditions.
The vertieal distribution of blue whiting' is 'reasonably
homogeneous, with an average depth of 200-250 m, whieh coincides
with its ideal depth (Bailey, 1982). However its behaviour in
French waters varies radieally from that in Spanish waters. In
French waters blue whiting was found from 200 m downwards on the
'slope, with almost no prescnee on thc shelf, and in 1996
extended as far as 6-10 miles offshore from the shelf in a
pelagic layer' at around 200-300 m.' However in Spanish" watcrs
blue whiting was found from 150 m downwards, with' maximum
abundance from 200 ID, but always over the shelf,' with almost no
12
4t
1---'-- extension in a pelagic layer like that found in France except
for in the SE corner of the Bay. The Spanish shelf is narrower
than the French shelf, but it is also deeper, going down as far
as 250m in comparison to,the. 150m of "the;..French shelf before the
slope begins. This topographical difference may explain the
presenee of blue whiting over the Spanish shelf, but it would
not explain its lack of extension in a pelagic layer like that
in Freneh waters. The higher degree of hydrodynamic activity in'
the NW of the Iberian peninsula, which spreads eastwards into
the Cantabrian Sea, makes this area less stable and homogeneous
than the SE corner of the Bay and its Freneh waters, which could
be the reason for a differenee in the behaviour of blue whiting
in the two waters.
•
On the other hand, the presenee of a eireulation eell in the SE
corner of the Bay of Biscay, whieh reaehes into both French and
Spanish waters and produees a coneentration of larvae and the
early stages of different speeies, casts doubt on the whose
argument that the Cape Breton Canyon marks a dividing linefor
the distribution of species. In the light of the present
results, at least as far as the early stages of the species
studied are coneerned, the definition of the so-called Southern.
stocks of different species (horse maekerel, blue whiting or'
mackerei), whose distribution is said to begin at the Cape
Breton Canyon, is not eonsistent wi th the real distribution of.·
juveniles and larvae of these speeies.
REFERENCES
•
Anon.' 1994. Report of the maekerel/horse maekerel egg production
workshop. lCES GM 1994/H:4, 58 pp .
Abaunza, P., B. ViiIamor & J.R. Perez 1995.
Infestation. by
larvae of Anisakis simplex (Nematoda: Asearidata)
in horse
mackerei, Trachurus trachurus, and Atlantic mackerei, Scornber
scombrus, in ICES Divisions' VllIb, Vllle and Ixa (N-NW of
Spain). Sei. Mar. 59(3~4), 223-233
Bailey, R.S. 1974. The life history and biology of blue whiting
in the northeast Atlantie. Mar.Res., 1: 29 pp.
Bai1ey, R.S. 1982. The population biology of blue whiting in the
North Atlantie. Adv. Mar. Bioi., 19: 257-355.
Bainbridge, V.and Cooper, G.A. 1973. The distribution and
abundance of the larvae of the b1ue whiting, . Micromesistius
poutassou (Risso), in the north-east Atlantie 1948-1970. Bull.
Mar. Eeol., 8: 99-114.
13
Blanten, J.O., K.R. Tenore, F. Castillejo, L.P. Atkinson, F.B.
Sehwing & A. Lavin 1987. The relationship of upwelling to musseI
production in the Rias on the western eoast of Spain. J.
Mar.Res., 45, 497-511.
Cabanas, J .M., G. Diaz DeI Rio & T Nunes. 1992. Hydrographie
eonditions off the Galieian coast, NW of Spain, during an
upwelling event. Bol. Inst. Espanol Oceanog., 8(1), 27-40.
Carrera, P.,
M. Meixide, C. Porteiro & J. Miquel. 1996. Does
Blue Whiting migrate from Porcupine Bank to Bay of Biseay after
the spawning season? lCES C.M. 1996/S:14. Poster
Carrera, P., C. Porteiro, L. Valdes. 1996. Depth and spatial
distribution of Blue Whiting juveniles in Bay of Biscay.
lCES/C.M. 1996/S:15. Poster.
Coombs, S.H. 1974. The distribution of eggs and early laivae of
the blue whiting, ~cromesistius poutassou (Risso) in the north
east Atlantie. ICES CM 1974/H:35.
..
Coombs, S.H. 1979. An estimate of the size of the spawning stock
of the blue whiting (Mücromesistius poutassou) based on egg and
larval data. lCES CM 1979/H:41.
Coombs, S.H. and Pipe, R.K. 1978. The distributon, abundanee and
seasonal oceurrence of the eggs and larvae of blue whiting,
}.Ücromesistius poutassou (Risso), in the eastern North Atlantie.
lCES CM 1978/H:45.
Diaz DeI Rio, G., A. Lavin , J. Alonso,
J .M. Cabanas & X.
Moreno-Ventas. 1996. Hydrographie variability in Bay if Biseay
Shelf and Slope waters in spring 1994, 1995, 1996 and relation
to biologieal drifting material. lCES C.M. 1996/S.18 Poster
Franco, C., L. Motos, A. Sola & A. Lage de Lanzos .1993. Horse
maekerel ( Trachurus trachurus L.) egg distribution and stage I
egg production estimates in division Vlllb, c and lXa in 1988,
1990 and 1992. lCES C.M. 1993/H:43, 7pp.
Frouin R., A. F. G. Fiuza, I. Ambar & T. J. Boyd. 1990 .
.Observations of a poleward surface current off the coast of
Portugal and Spain during winter. J. Geophysical Res., 95, Cl,
679-691.
Haynes, . R., E.D. Barton And Y. Pilling (1993) Development,
persistence and variability of upwelling filaments off the
Atlantic ceast of lberian Peninsula. J. Geophysical Res., 98, n°
C12.
14
•
Koutsikopoulos, C., L. Fortier & J.A.Gagne. 1991. Cross-shelf
dispersion of Dover sole ( Solea solea) eggs and larvae in
Biscay Bay and recrui tment to inshore nurseries . J. Plankton
Res., 13 (5): 923-945.
,
.~:\'
Lago de Lanz6s A., Sola A, Motos L. & Franco C. 1993. Mackere1
(Scomber scombrus L.)
egg distribution and stage
I
egg
production estimations in division Vlllb, c and lXa in 1988,
1990 and 1992. lCES C.M. 1993/H:44, 7 pp.
Lavin, A., G. Diaz DeI Rio, J .M. Cabanas & R. Carballo 1992.
SARP area cruise. Hydrography and nutrients. Bol. lnst. Espanol
Oceanog., 8(1), 7-26.
Maucorps, A.
1979. Le Merlan
Bull.lnst. Peches marit., n° 294,
41
Bleau.
Science
Lockwood,
S.J.,
J.H.
Nichols
&
W.A.
Dawson,
development rates of mackerel (Scomber scombrus L.)
range of temperatures. lCES CM 1977/J:13.
et
Peche
,
1977.
The
eggs over a
Pingree, R. D. 1993. Flow of surface waters to the west of the
British lsles and in the Bay of Biscay. Deep Sea Res., 40 . N°
1/2, 369-388.
Pingree, R. D. & B. Le Cann. 1992. Three anticyclonic slope
water occanic eddies (swoddies) .in the southern Bay ofBiscay.
Deep Sca Res~, 39,no7/8, 1147-1175.
Pingree, R. D. & B. Le Cann .1990.
Structure, strength and
seasonali ty of thc slope currents in the in the Bay of Biscay
region. J.Mar~Biol.Ass.U.K., 70, 857-885.
•
Pipe, R.K. & P. Walker, 1987. The cffect of temperature on
development and hatching of scad, Trachurus trachurus L., eggs.
J. Fish BioI., 31: 675-682 •
Schmidt, J. 1909. The distribution of the pelagic fry and the
spawning regions of the gadois in the North Atlantic from
lceland to Spain. lCES. Rapp. et P.V des Reun. 10 (pt4) 229 pp.
Smith, P.E. & S.L. Richardson. 1977. Standard techniques for
pelagic fish eggs and larval surveys. FAO Fish. Tec. Paper, No.
175, 100 pp.
Sola, A & C. Franco. 1984. lchthyoplankton survey of interesting
commercial specics of the Cantabric and Galician she1ves (N, NW,
Spain) .. lCES CM 1984/H: 42.
Sola, A .& C. Franeo. 1985. Contribuci6n al estudio deI
ictioplancton de especies de interes comercial de 1a plataforma
cantäbrica. Bol. lnst. Esp. Oceanog., 2(3}: 1-15.
15
Solei, A., L. Motos
C. Franco & A. Lago de Lanzos. 1990.
Seasonal ocurrence of pelagic fish eggs and larvae in the
Cantabrian Sea (Vlllc) and Galicia (IXa) from 1987 to 1989. ICES
C.M. 1990/H:26.
Sola, A., A. Lago de Lanzos & C. Franco 1994. Seasonal ocurrence
of mackerel and horse mackerel eggs and larvae in the Cantabrian
Sea (Vlllc) and Galicia (IXa) from 1990 to 1992. W.D. Mackerel /
Horse Mackerel Egg Production Workshop, Vigo (February, 1994).
Sournia, A., J.M. Brylinski, S. Dallot, P. Le Corre , M. Leveau,
L. Prieur & C. Froget . 1990. Fronts hydrologiques au large des
cates francaises: Les sites-ateliers du programme frontal.
Oceanologica Acta, 13 (4) 413-438
Turrell, W.R., A. Jorge Da Silva, C. Mohn, C. Griffiths, A.
Lavin, A. Svendsen & M. White 1995. A quasi-synoptic survey of
the european continental shelf edge during the Sefos proyect.
ICES. GM 1995!C:IO
•
ACKNOWLEDGEMENTS
We would like to thank all those who helped with this project,
especially the crew of the R/V Cornide Saavedra. We also express
our sincere thanks to many friends who made this study possible,
especially our colleagues from
the Instituto Espanol de
Oceanografia (Labs. of Vigo, La Coruna, Santander, Baleares and
Madrid) , Plymouth Marine Laboratory and Universidad de Vigo.
This research has been supported by the Commission of the
European Communities
(Project No. AIR2!1105)
and Instituto
Espanol de Oceanografia (Project No. 115).
16
•
100
9°
8°
7°
6°
5°
4°
3°
2°
1°
0°
Fig 1a,b: Acoustic track and fishing stations during SEFOS 0394 (above) and SEFOS0396 (below) cruises
•
•
•
•
•
"-.--. '~
•
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Fig ] c, <I: CTO & Plankton stations du ring .\IPH/95 (abo\ e) anti SEFOS/95 cruis('s.
•
...
A
43.
42.
-800
-800
".00
·2.00
0.00
·10.00
SEFOS 0394. SALINlY AT SGT 26.9
-8.00
-8.00
".00
-2.00
0.00
SEFOS 0394. SALlNlY AT SGT 27.1
45.
44.
•
B
41.
40.
~.
·10.00
-8.00
-8.00
".00
-2.00,
·10.00
0.00
-8.00
-8.00
".00
-2.00
0.00
MPH 95. SAUNllY AT OOT 27.1
MPH95. SAlINIlY AT SGT 26.9
...
c
•
,
-8.00
0.00
-8.00
-4.00
·200
0.00
SEFOS 95. SAlINlTY AT SGT 27.1
SEFOS95. SALINITY AT SGT 26.9
...
o·
43.
,: .
.... 00
-8.00.
".00
-2.00
SEFOS 0396. SAUNITY AT OOT 26.9
0.00
-8.00
-8.00
".00
·2.00
SEFOS 0396. SAlINITY AT SGT 27.1
Fig. 2.- Salinity at sigma-t 26.9 and 27.1
0.00
12.90
12.80
12.70
b
a
12.60
\~I
1
12.50
12.40
~ I'
12.30
12.20
I
12.10
12.00
I
I
11.90
l
11.80
11.70
11.60
:~~~~ 11.50
11.40
40°
::;;;':.i
Ii
!
I
I
11.30
11.20
-10°
-10°
-6°
SEFOS 0394. Temperature 100 m
-8°
-6°
-4°
o
00
f
I
MPH-95. Temperature 100 m.
11.10
11.00
12.2C
H12.0C
LJ 11.8C
12.70
12.60
13.8C
c
d
13.6C
12.50
13.4C
12.40
1320
12.30
12.20
12.80
12.10
12.60
12.00
-
12.40
12.20
1
11.80
q
!
I
I'..
-8°
11.70
11.60
SEFOS 95. Temperature 100 m.
-6°
SEFOS 0396. Temperature 100 m,
0°
Figure 3.- Temperature distribution at 100 m. for the cruises a) SEFOS 0394
b) MPH-95, c) SEFOS 95, d) SEFOS 0396
12.00
1·::· J11.80
·U
U
I
~11.5O
.1
11.60
11.40
~11.20
c
35.75
35.74
35.73
35.72
35.71
35.70
35.69
35.67
35.66
35.65
35.64
35.63
35.62
_ 35.61
".-".: 35.60
a
b
35.9:
35.9C
I
35.8E
~
35.8:
35.8~
35.8C
r
35.7f.
I
I
35.75
35.7'L
35.7C
. ~"'"
rI
::,,''': 35.59
,,,:c::: 35.58
35.56
35.55
35.54
35.53
L-J35.52
-10°
SEFOS 0394. Salinity 100 m
35.67
-8°
35.65
35.63
0°
35.60
SEFOS MPH-95. Salinity 100m
35.58
35.55
035053
35.50
35.88
c
d
35.86
35.84
I
I
35.82
I
35.80
II
.55
35.78
35.76
I
35.74
l
35.72
I
·35.70
I
35.68
35.66
I
I"'~
~
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H35.46
n
35 .44
0°
SEFOS 95. Salinity 100m
SEFOS 0396. Salinity 100 m
H35.43
I
0
135.42
35 .40
= 35.64
Figure 4.- Salinity distribution at 100 m. for the cruises a) SEFOS 0394
b) MPH-95, c) SEFOS 95, d) SEFOS 0396
I
. 35.62
0°
35.60
tj35.58
35.56
I
135 .54
!
1
35 .52
---------------------------------------------SEFOS MARCH-APRIL 1994
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Figura 5a. Scatterplots of eggs and larvae abundance of the target
species vs. topographie and environmental variables (survey:
SEFOS XXX).
MPH APRIL 1995
_...
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"
1200
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..0
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se
Figura 5b. Seatterplots of eggs and larvae abundanee of the target
speeies vs. topographie and environmental variables (survey:
SEFOS XXX).
SEFOS JUNE 1995
'-
I
150
1'00
~". '.. -'~ :.
l
50
o
I
I
r
40
40
30
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..
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160
12.5
13.5
14.5
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o
w
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18.5
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400 . ~_._--"--_._. _"_.
1I
i I
I 1
300
I 300
,
'
300
-40
'
•
40
.....
80
120
.
100
!
~-+_"..JZ ~- ...----+._-_--..A-.4
•• ,..;.. h~"
','
,
o -- ..-.-~~--U-J . ~_.:..:_~~,~_.::.fe.-_t.+_
1&0
I
12.5
13.5
14,5
15,5
18.5
17,5
18.5
33
'e
M
.
Figura 5c. Seatterplots of eggs and larvae abundanee of the target species vs.
topographie and environmental variables (survey: SEFOS XXX).
.._.._,.
~
•__. _•..._.,
C
200
-80
J
35
800
400
o ..
~
1200
I!
800
I ': -- -
1800
Twnp.. "".
1200
o
16,5
1600
2OO"cOO'ltOl.-h
J
15,5
'0
1600
...
_
J20
': I....." -_ -----_
."
,",
o·
.
~
:I~'-­
I:: 1
"
..:,. '.:'
- . - - _•••
~
35
~
48.
+
47.
•
46.
0
0,1 - 10
10,1 - 25
25,1 - 100
100
>
45.
44.
•
43.
SEFOS94
42.01....--L4-,-.L----a::r:.oc-----=-7'-.o----6-:J".-=-o---:_5:r:.0;----:l-4-;:;-.0----3:<:.0;:-----;-2r;.0;-----~1-;:;-.0---;;l:0.0
Figure 6. Distribution and abundance ofblue larvae larvae/rn2
48.Ur----'---....L------'------'---~-~--:'------'----.l------'----_+
.
I
SEF0S94
B1uewhiting larvae
42.QJ------='-=----::r::----::r::-----:r~_:__:_:r::------:r-:---__:rc------:.----_r__--_1_
-8.0
- .0
-6.0
.0
-4.0
-3.0
• 0
Figure 7. Distribution ofblue whiting larvae rnean sizes (only positive stations)
-1.0
0.0
47.
46.
45.
44.
43.
SEF0S95.
~.o
-4.0
-3.0
-2.0
Figure 8. Distribution and abundance ofmackerel eggslm2
-1.0
0.0
48Or--~-~~---";--~--~--~~-;;--~--~--~--1
47.
46.
45.
44.
43
SEF0S94
42.oL--Lf.-:.-~---:.s'7.0---.7;r.0=-----:-6r.;.0:-----57.0;;-----;-4r;;.0:-----3~.0;;----;;.2n.O---.l:;r;.O,------;tO.O
•
o
•
•
•
•
0,1 - 10
10,1 - 25
25,1 - 100
>
100
MPH95
•
.s.0
•
·7.0
-6.0
-5.0
-4.0
-3.0
·2.0
·1.0
••
SEF0S95
-8.0
-7.0
-6.0
.
-6.0
.0
-3.0
-2.0
Figure 9. Distnöution and abundance ofmackerellarvae/m2
·1.0
0.0
480'r--~--"""'-"'""-~--~---~-""-;:---~---~
__~__- t
SEF0S94
-7.0
-50
.{j.0
-4.0
-3.0
-2.0
-1.0
0.0
•
45.
44.
43.
o
•
42.
•
•
•
0.1 - 50
50,1 - 500
500,1 - 1000
>
1000
MPH95
-9.0
-7.0
-5.0
-40
-3.0
-2.0
-1.0
46
SEF0S95
-7.0
-5.0
-4.0
-3.0
-2.0
-1.0
Figure 1Q Distribution and abundance ofhorse mackerel eggs/m2
0.0
•
480'r--~---;,-~-~--~
~---<:--
~
_ _~
~
.......
~
470
SEF0S94
-80
-7.0
~.o
-50
-4.0
-30
-50
-4.0
·20
-1.0
00
•
o
•
•
•
•
0,1 - 10
10,1 - 25
25,1 - 100
>
100
MPH95
-10
-90
-8.0
-7.0
-30
-2.0
-1.0
•••
•
SEF0S95 .
-8.0
-1.0
Figure l;I.Distribution and abundance ofhorse mackerellarvae/m2
0.0
WH95
fv1ackerellalVae
rvPH95
Horse rrackerellarvae
SEF0S95
Horse rrackerellarvae
FigureIZ Distribution ofmackerl and horse mackerel larvae mean sizes (only positive stations)
43° N·g·W
25CXXJ ,.------
44° N -7°W
44° N _2°W
47°::J:J N·'" W
---------r
I
Cage2
lZIage3
1500J
1CXXXl
3
5
7
9
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
Transects
North Galicia
West C l E a s t C.
I
South France
North France
4El
51
~ON-goW
44° N. 7°W
44° N ·2'W
47° '::ß N· 7" W
----------_._----_._--..-
CAge1
DTotal
CAge2
1500:)
1CXXlO
o
il
I~ .~
.~
.1
12345
North Galicia
~ 1ft.J
6
7
8
.nrn
9
n
1011
West Cant.
.~
1213
i:
nrn
.nfll
14TtahsJas 17
East C.
1
I
r1'i'l
181920
212223
I South France
24
25
26
I I J
272829
North France
30
43°
•
(1576)
0
(51)
1 - 100
o 100 - 500 (234)
500 - 1000 (92)
>1000
(58)
0
8
42°
10°
9°
8°
7°
5°
60
4°
3°
48°
o
o
o
o
(878)
1 - 100
(93)
100 - 500 (232)
500 - 1000 (77)
>1000
(90)
Figure 14: Echointegrated values by nautical mile during SEFOS 0394 (above)
and SEFOS 0396 (below) cruises .
2°
1°
0°