Seasonal distribution of young sole (Solea solea (L.)) in the nursery ground of the bay of Vilaine (Northern bay of Biscay)

297

Netherlands Journal of Sea Research 27 (3/4): 297-306 (1991)

S E A S O N A L D I S T R I B U T I O N O F Y O U N G S O L E ( S O L E A S O L E A (L.)) IN T H E N U R S E R Y G R O U N D O F T H E BAY O F V I L A I N E ( N O R T H E R N BAY O F B I S C A Y )

DIDIER DOREL 1, CONSTANTIN KOUTSIKOPOULOS 1, YVES DESAUNAY 1 and JOCELYNE MARCHAND 2 ~IFREMER, B.P. 1049, 44037 Nantes cedex 01, France 2Universite de Nantes, Laboratoire de Biologie marine, 2 rue de la Houssiniere, 44072 Nantes cedex 03, France

ABSTRACT The distribution of young sole was studied in the bay of Vilaine nursery ground as a function of age and season for the 0, 1 and 2-groups. During 1988 and 1989, bimonthly trawl surveys were carried out from the estuary to the 50-m-isobath along a 65-km transect. A regular seasonal pattern demonstrated two combined trends. An offshore movement is observed with increasing age; this general trend is marked by an inshore migration in spring and an offshore one in winter. The fluctuations of the distribution pattern are discussed in relation to sedimentary characteristics, to trophic requirements and to hydroclimatic variations. The main conclusion is that young soles are concentrated inside a closed nursery area. In their third winter some participate in spawning migration and they get mixed, to a certain extent, with newly recruted soles from nearby nursery grounds. 1. INTRODUCTION The distribution of young flatfish as a function of their age and environmental conditions has already been described (RILEY et al., 1981; LAGARDERE, 1982; MILLER et al., 1984; LOCKWOOD & LUCASSEN, 1984; BERGHAHN, 1986; KOUTSlKOPOULOS et al., 1989a, 1989b; ROGERS, 1989a). Some of these studies are more restricted in time and in space: BERGHAHN (1987) considered 0-group and 1-group plaice movements from muddy flats to tidal channels along short transects (about 2 km), within depths less than 3 m. GREER WALKER & EMERSON (1990) studied seasonal migrations of adult soles on a larger scale in an offshore deep (50 m) area. The fact that seasonal migration patterns are very species-specific (LAGARDERE, 1982; GUNDERSONet al., 1990) and that factors controlling these migrations operate on both local and regional scales (ALLEN & BARKER, 1990) led us to study the distribution in a wider area. The present study deals with young sole (Solea solea (L.)) in the Northern Bay of Biscay, from their

settlement on the bottom, mainly concentrated in the estuaries (MARCHAND, 1989), tO their maturity, about three years later. Sole in Biscay Bay spawns from January to April at 70 to 90 m depth (GUILLOU, 1978). Eggs and larvae are found between 30 and 70 m from south to north of the Biscay Bay (ARBAULT et al., 1984). The first concentration of juveniles on the bottom occurs in late spring, in isolated nurseries located in bays and estuaries (DESAUNAYet al., 1981). This study describes the distribution of the pre-recruits spreading on a given nursery ground as a function of age and season. The main factors involved are depth, grain-size distribution and annual variations of temperature and salinity. A model describing the seasonal displacements of a cohort is proposed. The results will be checked against Heincke's law and the estuarine-dependent concept. 2. MATERIALS AND METHODS The bay of Vilaine nursery ground (Fig. 1) is well defined geographically, between an estuarine dam (Arzal dam, 9 km up in the estuary) and the 50-m-isobath taken as the eastern margin of the offshore spawning grounds. This area can be divided into three sectors: the estuarine zone (0 to 9 km from the dam), the bay (9 to 30 km) and the offshore zone (30 to 65 km); shallows in this area, represent only 3% of the total surface. It is characterized by a quite regular slope, a grain-size distribution dominated by muddy sediments (Fig. 2), according to LE BRIS (1988) and rather weak tidal currents (less than 50 cm.s -1 in spring tide, according to SALOMON & LAZURE, 1988). The tidal range varies between 0.2 and 6 m in spring tide and between 2.1 and 3.9 m in neap tide. The surface temperature varies from 6 ° to 9°C in winter and from 17° to 23°C in summer. This study is based on a two-year survey (1988-1989) on a 65-km-long transect between the Arzal dam and the offshore zone (Fig. 1). This transect was prospected every two months by bottom trawling. Trawling in the shallow ( < 5 m deep) estuary required two different types of gears. A 3-m beam trawl,

D. DOREL, C. KOUTSIKOPOULOS, Y. DESAUNAY & J. MARCHAND

298

Depth (m) 0 Fine and medium muddy sand

~

10 ~.~'~ 20

0

~

30

Sandy mud

B

. ~ 1

E

S~OtOmud t

Co rse and medium medi Jm clean el, sa d 50

J

60 km

45

30

15

Dam

Fig. 2. Depth profile and grain-size distribution along the transect. E=estuarine sector, B=bay and O=offshore area.

I

J °I0 3o

o

40

2030

Fig. 1. Map of the area studied. I(x) is the coast-to-coast distance at a point (~) with coordinates (x,y) relative to the transect, d i is the distance between this point and an interpolated point on the transect. with 20-mm mesh size in the cod end, was towed by a small ship (9 m length, 95 h.p.), for sampling the estuary and the upper part of the bay. This gear was previously used for the survey of the sole nursery ground in the Bay of Vilaine (DESAUNAYet al., 1981). The mean trawling duration was 20 min and the mean sampled surface was about 3000 m 2. In the deeper offshore area a 25-m otter trawl (20-mm mesh size in the cod end) was operated by the R.V. 'Gwen Drez' (25 m, 600 h.p.) with a mean duration of 30 min and a mean sampled surface of 40 000 m 2. The efficiency of both gears was compared with an ANOVA carried out on 1-group catches of 13 paired hauls performed on May 1989 in the bay. No significant differences were observed (F=1.0158 for 1 and 24 d.f.). Trawls had no tickler chains before the foot rope. Tows were made against the tidal current, at right angles to the isobaths, according to POXTON et al. (1982). Inside the estuary only the channel was sampled. Temperature and salinity vertical profiles were made along the transect on every cruise. Dates of cruises and number of hauls are given in Table 1. 0-group catches were not considered before July, because of the gear selectivity (20-mm mesh size). All samples were sorted and the soles measured. Otoliths were collected for every cruise in order to provide a length-at-age distribution. A growth curve was built up from the mean sizes observed. Catches were converted into the number of individuals per unit surface area by: Ci -

Ni

si. lO4

where N i is the catch for each age group and S i is the sampled surface in m 2, without correction for net efficiency. In restricted sectors, the number of individuals per unit surface area depends on the area available between the sector boundaries. Indeed, the limitation of the area increases the fish concentration. Thus, for the same level of abundance, higher densities are observed in restricted areas (up to 1400 ind.10 000 m -2 in the estuary). To compensate for this influence, the coast-to-coast distance of the sector, at a given point of the transect, was used to weight the raw population densities; C i is thus transformed into Z i by:

z,=c,J= where Ix is the coast-to-coast distance at the point with coordinates x,y relative to the transect (Fig. 1). In this way the true representation of the population is figured along the transect. These weighted population densities were then expressed as a percentage W i of the total catches observed during the cruise. In this way, only information concerning the spatial distribution is conserved and the comparison between cruises and age groups is not affected by the differences in the catches: TABLE 1 Dates of cruises and number of hauls Dates

number of hauls 3-m beam trawl

6- 2 tO 15- 2-1988 7- 5 tO 9- 5-1988 30- 6 tO 6- 7-1988 23- 9 to 29- 9-1988 7-12 tO 14-12-1988 1- 2 tO 10- 2-1989 26- 4 tO 4- 5-1989 27- 6 to 1- 7-1989 18- 9 tO 28- 9-1989 6-12 to 12-12-1989 Total

7 14 17 14 13 12 25 13 14 11 140

25-m otter trawl

13 19 21 29 45 68 54 27 30 33 339

YOUNG SOLE IN THE BAY OF VILAINE, FRANCE

Salinity (%)

Temperature ('C.) 22

2o

299

B

February

\

18 16 14 12 10

~

p

2 20

February

i

i

~

L

i

i

i

[

B

i

i

~

i

i

[

B

May

18 16 14 12

J

f

J

/

lO May

J

2: 2o

J

J_

i

/

• i,, ,~u,x

i

i

B

i

i

i

i

J

i

i

i

/ B

/z

16 14 lO

July

8

B

6 L

22 20

i

I

i

i

]

i

~ "beplemoer "

i

B

i

i

i

i

i

i

i

i

~

i

i

i

i

~

f

16 12 10 September

•

i

i

i

i

i

[

i

i

i

i

i

i

B

J

i

i

~

i

2 December

20

B

18 16 14 12

w

~

10

-%%

December

B

\ i

|

60 krn

i

i

i

45km

i

i

i

30km

i

I

15km

i

i

Arzal dam

i

60 km

i

45 km

Fig. 3. Temperature and salinity profiles. 1988: solid line, 1989: d a s h e d line. B = b a y .

30 km

15 km

Arzal dam

300

D. DOREL, C. KOUTSIKOPOULOS, Y. DESAUNAY & J. MARCHAND

w j=

zi

.lOO

n

12Zj i=1

The local weighted values W i were then projected on the onshore-offshore axis. The spatial distribution of a given age group on the axis (x coordinate of the sample location) was smoothed by an inverse distance squared method: n

W(X)= i=1 di 2 n 1

decreased in the estuary and in the bay from December to May, with a steeper slope in 1988. The offshore waters were very stable, the bottom temperature ranging from 10° to 13°C and the bottom salinity staying higher than 35 S throughout the year. 3.2. AGE-GROUP DISTRIBUTION The 0-group was concentrated in the vicinity of the estuary during its first summer. In December the young soles left the estuary and spread out in the bay, a few of them reaching the 45-m isobath (50 km from the dam). The distribution was similar in both years (Fig. 4). The 1-group, with a mean age of 11 months and a mean length of 13 to 14 cm, was

E;--

Population density (%)

i=1 di 2

I

35 where d r is the distance between the interpolated point and the location of the sample i (xi,Yi). Bottom temperature and salinity were smoothed in the same way. For a given age-group and a given cruise the pattern distribution is summarized by its barycentre (centre of gravity of the distribution) and the dispersion of the samples

30

July:0-Group

25 20 15 lO 5

n

x~, Wj ~_

B

i=1

r

i

i

~

E

35

n

30

B

September:0-Group

t~

i=1

25 n

E ( x - ~ )2 . wi var (x) = i=1

I i

20 15 lO

i=1

5

where ,~ is the coordinate of the centre of gravity on the offshore-onshore axis and var(x) is the dispersion of the samples around this centre. 3. RESULTS

r

i

i

I

i

35

December:0-Group

30 25 20

3.1. HYDROGRAPHICAL CONDITIONS Important differences in hydrographical conditions were observed between the two years (Fig. 3) mainly due to differences in rainfall. 1988 was a very rainy year, whereas a severe drought occurred in 1989 (MARCHAND, 1991). The winter 1988 was colder than 1989. The offshore gradient of bottom temperature exhibited an inverted trend in winter, compared with the rest of both years, when coastal waters were warmer than offshore waters. The bottom salinity

15 lO 5 o

L

i

60 km

45 km

30 km

15 km

Fig. 4. 0-group sole distribution. 1988: solid line, 1989: dashed line. B=bay.

,

Arzal dam

YOUNG SOLE IN THE BAY OF VILAINE, FRANCE

Population density (%)

301

Population density (%)

T---'--I

2O 17,5

February:l -Group

B

February:2-Group

/ /

f', !

15 12,5 10 7,5 5

/

2,5

17,5

May:2-Group

B

May:l-Group

/

15I

/\

12,5 10 7,5

/

,J

51

/ /

2,5 20 17,5

July:l -Group

B

July:2-Group

B

15

12,5 10

lO

7,5

7,5

5

5

2,5

2,5

2O

20

I

17,5

September:l -Group

17,5

15

15

12,5

12,5

Q

10 7,5 5 2,5

December:2-Group /\

B

,5 5 ,5 ~.0

December:l -Group

,5

f\

12,5

/

15

15 12,5 10

10

7,5

7,5

5

5

2,5

2,5

0

B

IO

2o 17,5

September:2-Group

60 km

45 km

30 km

15 km

Arza;dam

0

\

I

'

60 km

45 km

Fig. 5. 1- and 2-group sole distribution. 1988: solid line, 1989: dashed line. B=bay.

i

30 km

15 km

Arzaldam

302

D. DOREL, C. KOUTSIKOPOULOS, Y. DESAUNAY & J. MARCHAND

Distance to the dam 60

-

•

5O

• --

19BS

2-GROUP

1989

ModeJ

40

1-GROUP 30

2O

10 1st of March t

0 0

2

4

6

8

10

12

14

16

18

20

22

24

26

J

J

28

30

32

34

Age (months)

Fig. 6. Time-related changes in the position of the distribution barycentre of the sole juveniles and the fitted model. Vertical segments above and below represent one standard deviation (i.e. dispersion of individuals around the barycentre). Age is expressed in months with a assumed birth date of 1 March.

dam, a g e is the mean age in months with an assumed birth date on the 1st of March, and k, I, m, n are constants (k=0.572,/=13.369, m =-1.4, n =5.61). This model explains 89.9% of the total variance. The offshore displacement of the barycentre is accompanied by an increase of the standard deviation which corresponds to the dispersion of the individuals around the centre of the distribution. Although less clear, the time-related changes in the standard deviation showed the same general trend: a continuous increase with age and a seasonal periodicity. The dispersion increases in winter and seems reduced in summer. This evolution may be compared with the growth curve of sole (Fig. 7). Higher growth rates corresponded to the summer period in the inshore area and the winter offshore movement was marked by reduced growth rates. This periodicity was considered in the fitted model which has the following form: L = s-(1 - e ( - r.(age - u) + q. cos(age-p) 112.27r)

present in February within the same limits as the December 0-group but was less regularly distributed. In May, a major part of the population was concentrated in the bay and the estuary. Then limited seaward progressive movements occurred, and in December the 1-group was found outside the bay (mean age 21 months, mean length 20 to 22 cm) (Fig. 5). In February the 23-month-old 2-group showed a tendency to inhabit the offshore part of the study area. During the following summer of their third year of life, these immature soles had a wide distribution and the proportion of individuals found outside the bay increased. In December, the observed movement towards the offshore zone did not yet allow the young soles to reach the spawning grounds (mean age 33 months, mean length 26 to 28 cm) (Fig. 5).

where the total length (L) is a function of a g e (in months with an assumed birth date of 1 March, and p, q, r, s, u are constants (p=2.050, q--0.064, r=0.034, s =37.411, u =-2.208). This model explains 99.7% of the total variance. 4. DISCUSSION 4.1. BOUNDARIES AS DEFINED BY SEDIMENTS ROGERS (1989b) demonstrated that young soles prefer muddy grounds and have a patchy distribution within a given nursery ground. Indeed, muddy sediments largely dominate the bay of Vilaine (LE BRIS, 1988). Two sandy sectors are found along the tran-

3.3. SEASONAL EVOLUTION OF THE BARYCENTRE Lengtr~ (cm) 30 . .

Fig. 6 sums up the displacements of the sole population. An alternating movement of the barycentre between the shallow areas in summer (May, July and September) and offshore sectors in winter (December and February) was combined with a general offshore movement. Generally, juveniles were mainly concentrated within the estuary and the bay until they were 19 to 20 months old. This regular pattern can be summarized by a model taking into account both the annual oscillations and the general offshore trend. The model is expressed by the following formula:

25 i l~ - -

Distance to the dam (kin) .

.

Growth curve

.

60

"~1/t i'

1-GROUP

Mo,.,

,

,50

T-T _ j ~ /

20

~- ~- /

O-GROUP

,}"

~ 40

/J;

2-GROUP , , i3° /

15!i'! 10

i20

5

10 1st of March

0 I'/ 0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

32

34

Age (months)

x = k . a g e + I + c o s ( ( a g e - m)112.2~r).n

where x is the distance of the barycentre from the

Fig. 7. Bay of Vilaine sole growth curve in parallel with the

model of Fig. 6 describing the movements of juveniles in the nursery.

YOUNG SOLE IN THE BAY OF VILAINE, FRANCE

303

sect (Fig. 2). The first is situated at the very mouth of the estuary and can be regarded as a small delta. The fluvial regime may modify the superficial grainsize distribution (LE BRIS, 1988) (Fig. 8), and the balance between the muddy channel and the less deep sandy bank is continually altered. The reference transect pass through this sandy delta. In the present study no decrease in abundance over this sandy area was observed because sampling carried out in both channels, where the 0-group densities were higher, was projected on the transect. Nevertheless this discontinuity does exist (DOREI, et al., 1989). It makes up, in association with hydrographical parameters, the inshore limit of the distribution of the 1- and 2-groups. In contrast, the second sandy area, 45 km from the estuary, exhibits a drastic and definite change, into a wide plateau of coarse and medium clean sand (VANNEY, 1965). This external limit of prerecruit distribution is only just reached during the first winter. These observations agree with those of ROGERS (1989b). Consequently, the distribution of juveniles may be defined by the sedimentary facies which constitute stable boundaries in both space and time. 4.2. HEINCKE'S LAW AND THE ESTUARINE-DEPENDENT CONCEPT The most noticeable finding is the progressive drift towards the offshore area with age and thereby with length. This is an illustration of Heincke's law (1905 in BERGHAHN, 1987): older individuals are found in deeper areas. In addition, young soles first exhibit an onshore drift, which involves either passive or active behaviour (CHAMPAI_BERT& CASTELBON, 1989; KOUTSIKOPOULOS et al., 1989a). This scheme agrees with the 'estuarine-dependent' concept proposed by MII,I,ER et al. (1983). Many flatfish species illustrate this principle: European species such as Solea solea (RILEY et al., 1981; DOREL, 1983), Pleuronectes platessa (LOCKWOOD, 1974), Platichthys flesus (MASSON, 1984; VAN DER VEER & GROENEWOI_D, 1987), the American Pacific pleuronectiform, Parophrys vetulus, (ROGERS et al., 1988), the Japanese flounder, Platichthys olivaceus (TANAKA et al., 1989), the South African sole, Solea bleekeri, (CYRUS & BLABER, 1987). For other species (Buglos-

sidium luteum, Scophthalmus rhombus, Scophthalmus maximus), nursery grounds may be found in coastal open marine waters but not in estuaries (RII,EY etal., 1981). Some species, on the other hand, stay in offshore waters: in Biscay Bay, Microstomus kitt, Lepidorhombus whiffiagonis and Lepidorhombus boscfi were never found inshore of the 30-m isobath. As far as sole in Biscay is concerned, this 80- to 100-km displacement of pre-recruits from the spawning area to the coast, seems to be a 'sole-

NW

SE

A

B

Fig. 8. Modifications of the sediment distribution in the upper part of the bay (from LE BRIS, 1988) and the bottom profile along the indicated transect AB (from VANNEY, 1965). specific' route, with a 'compulsory crossing' of an estuarine sector. 4.3. PERIODICAL RETURN TO THE ESTUARINE NURSERY In addition to the general offshore trend, yearly movements towards the coastal area occur in May, thus repeating the first benthic phase of behaviour. Even though this periodical return decreases with age, a recall of the 'compulsory crossing' is obvious. Atrophic appeal and a search for a given category of amino acid were proposed by MACKIE et al. (1980), for several species, including sole juveniles. APPELBAUM & SCHEMMEL (1983) studied the elaborated sense organs of sole and stressed their efficiency for identifying prey at a distance. Thus the chemosensitive ability would induce the concentration of young sole in the estuarine area, when the appropriate food is available. Despite the lack of an established relation between benthic fauna and the food of young sole in the bay and the estuary of Vilaine, this linkage might

304

D. DOREL, C. KOUTSIKOPOULOS, Y. DESAUNAY & J. MARCHAND

act as a 'baited trap' out of which juveniles could not easily escape, even if the environment was modified, Such a concentration in the estuarine system has already been observed by COGGAN & DANDO (1988) in the Tamar estuary. According to MILLER et a1.(1984): 'emigration from the primary nursery may be related to ontogenical sensitivity to salinity changes or decreasing food resources'. Consequently, the winter decrease of productivity of invertebrates in an estuarine community would decrease the olfactive attractiveness for young soles. In the following spring, the recovery of benthic productivity would reinforce this attraction. With increasing age, trophic requirements become less selective in prey species and prey size. Older fish are able to exploit bigger prey from the benthic community as shown by LE MAO (1986) for sole, POXTON et al. (1982) for dab and plaice and HOGUE & CAREY (1982) for Oregon coastal flatfish. Nevertheless, in winter, juveniles move offshore to flee the unfavourable hydrographic conditions in coastal waters. This movement to offshore areas where food is rather scarce affects growth rate. As observed by LOCKWOOD (1974) in young plaice, hydroclimatic cues and trophic behaviour act very closely together. The distribution pattern of the young fish thus results from a continuous adjustment in search for the optimal location in terms of growth and survival. 4.4. LOCAL EFFECTS OF ENVIRONMENTAL EVENTS The best scheme leads to a maximization of the time spent in the coastal nursery ground. It may be modified by random changes of local environmental features. In the area studied, the coastal hydroclimate is marked by an increase in water temperature and salinity from February to September (Fig. 3). The two parameters probably do not affect the sole distribution in the same way. A threshold temperature of about 10° to 12°C reached in May and in late autumn, may directly induce movements. LAGARDERE (1982) has shown that temperature is not the only factor responsible for seasonal migrations in Dicologoglossa cuneata. In fact, several climatic factors influence the behaviour of young soles simultaneously, as indicated by KOUTSlKOPOULOSet al. (1989a) in the bay of Vilaine. Physical factors or climatic changes are correlated with seasonal migration, but no clear evidence has been found of one particular factor responsible for a drastic change in behaviour and distribution. The estuary has a wide salinity range, fluctuations decrease in the bay and offshore salinity remains stable throughout the year. This situation would limit the penetration of young soles into estuarine waters (MARCHAND& MASSON,1989), by an ontogenic decrease of euryhalinity. Nevertheless, even if a saline preference exists for the 0-group, ranging from 10 to 30 S (RILEYet al., 1981), the same authors

do not attribute a definite role to salinity: 'The relationship of abundance to salinity is observed and in most cases may be indirect'. 4.5. EXTREME CONDITIONS AND SMALL-SCALE CHANGES IN YOUNG SOLE DISTRIBUTION In a coastal environment, the combination of a strong water stratification, a possible nutrient discharge from the river, and a weak tidal current may lead to anoxic conditions. This happened in the Bay of Vilaine in July 1982, (ROSSlGNOL-STRICK,1985). An other extreme situation was observed in the AmocoCadiz oil spill in northern Brittany in 1979 inducing very unfavourable conditions in a nursery ground (DESAUNAY, 1981). According to KOUTSlKOPOULOSet al. (1989b), it seems that 0-group soles are not able to escape from the disturbed area, whereas the older ones can reach deeper waters. Thus, the general migration pattern may be locally but drastically changed for the youngest fish. A clear description of this phenomenon was given by ROGERS & LOCKWOOD (1990) after an algal bloom in the coastal waters of the eastern Irish Sea. 4.6. THE MOVEMENTS OF SOLE JUVENILES AND ESTIMATION OF RECRUITMENT The overall life cycle may be described in three stages: firstly, transport of eggs and larvae from the offshore spawning area to the coast by diffusive mechanisms (KOUTSIKOPOULOSet al., 1991); secondly, a specific attraction by estuarine waters; thirdly, an offshore movement towards spawning grounds. During the first three years of their life young soles periodically migrate between the inshore, sheltered, productive but variable ecosystems and the offshore stable but less productive areas. Immature soles migrate inside a 'restricted' sector delimitated either by sediment types or by hydrographic features. But the 'restriction' gets less and less effective and some mixing of cohorts migrating from nearby nurseries is likely. Such time-related changes have to be considered for the abundance estimation of young sole in a given nursery, which can be merely seen as a temporary figure of the recruitment to come. Because of such movements and according to RIJNSDORPet al. (1985) and VAN DER VEER (1986), one may wonder whether 'recruitment' is best estimated by the number of young fish migrating out of a nursery or by the number of the entering 0-group. 5. REFERENCES ALLEN, D.M. & D.L. BARKER,1990. Interannual variations in larval fish recruitment to estuarine epibenthic habitats.--Mar. Ecol. Prog. Ser. 63: 113-125.

YOUNG SOLE IN THE BAY OF VILAINE, FRANCE

APPELBAUM, S. & CH. SCHEMMEL, 1983. Dermal sense and their significance in the feeding behaviour of the common sole, Solea vulgaris.--Mar. Ecol. Prog. Ser. 13: 29-36. ARBAULT, S., P. CAMUS & C. LE DEC, 1984. Estimation du stock de sole (Solea vulgaris, Quensel) dans le golfe de Gascogne et partir de la production d'oeufs.--J. appl. Ichthyol. 4: 145-156. BERGHAHN, R., 1986. Determining abundance, distribution and mortality of 0-group plaice (Pleuronectes platessa L.) in the Waddensea.--J. appl. Ichthyol. 2: 11-22. , 1987. Effects of tidal migration on growth of 0-group plaice (Pleuronectes platessa L.) in the North Frisian Waddensea.--Ber. dt. wiss. Kammn Meeresforsch. 31: 209-226. CHAMPALBERT, G. & C. CASTELBON, 1989. Swimming activity rhythms in Solea vulgaris (Q) juveniles.--Mar. Behav. Physiol. 14: 201-209. COGGAN, R.A. & PR. DANDO, 1988. Movements of juveniles Dover sole Solea solea (L.) in the Tamar estuary, South-western England.--& Fish Biol. 33(A): 177-184. CYRUS, D.P & S.J.M. BLABER, 1987. The influence of turbidity on juvenile marine fishes in estuaries. Part 1. Field studies at lake St Lucia on the South-eastern coast of Africa.--& exp. mar. Biol. Ecol. 109: 53-70. DESAUNAY, Y., 1981. Evolution des stocks de poissons plats darts la zone contaminee par I'Amoco-Cadiz. In Amoco-Cadiz, Consequences d'une pollution accidentelle par les hydrocarbures.--Actes du Colloque International Centre Oceanologique de Bretagne, Brest (France), 1979: 727-735. DESAUNAY, Y., J.B. PERODOU & P. BEILLOIS, 1981. Etude des nurseries de poissons du littoral de la LoireAtlantique.--Sci. Peche, Bull. Inst. P~ches Maritimes 319. DOREL, D., 1983. Etude des nurseries de deux secteurs c6tiers de la Manche en 1980.--Ann. Biol. 37: 292-297. DOREL, D., Y. DESAUNAY & J. MARCHAND, 1989. Prise en compte des migrations saisonnires des soles juveniles pour I'estimation d'abondance des prerecrues sur une nourricerie. (Golfe de Gascogne, France) CIEM, Comite des Poissons Demersaux. CM/1989/G 30:1-7 (mimeo). GREER WALKER, M. & L. EMERSON, 1990. The seasonal migration of Soles (Solea solea) through the Dover strait.--Neth. J. Sea Res. 25: 417-422. GUILI_OU, A., 1978. Biologie et niveau d'exploitation des stocks de langoustine, de merlu, des baudroies et de sole clans le proche Atlantique.--Rev. Trav. Inst. P~ches marit. 42: 115-157. GUNDERSON D.R., D.A. ARMSTRONG, Y. SHI & R.A. MC CONNAUGHEY, 1990. Patterns of estuarine use by juvenile English sole (Parophrys vetulus) and Dungeness crab (Cancer magister).--Estuaries 13: 59-71. ROGUE, E.W. & A.G. CAREY, 1982. Feeding ecology of 0-group flatfishes at a nursery ground on the Oregon coast.--Fish. Bull. P. 80: 555-565. KOUTSIKOPOULOS, C., Y. DESAUNAY, D. DOREL & J. MARCHARD, 1989a. The role of coastal areas in the life history of sole (Solea solea L.) in the Bay of Biscay. In: J.D. ROS. Topics in Marine biology.--Scient, mar. 53: 567-575. KOUTSIKOPOULOS, C., M. KARAKIRI, Y. DESAUNAY & D.

305

DOREL, 1989b. Response of juvenile sole (Solea solea L.) to environmental changes investigated by otolith micro-structure analysis.--Rapp. P-v. Reun. Cons. perm. int. Explor. Mer 191: 281-286. KOUTSIKOPOULOS, C., L. FORTIER & J.A. GAGNE, 1991. Cross-shelf dispersion of Dover sole eggs and larvae (Solea solea) in Biscay Bay and recruitment to inshore nurseries.--& plankt. Res. (in press). LAGARDERE, E, 1982. Environnement peri-estuarien et biologie des Soleidae dans le golfe de Gascogne (zone sud) & travers I'etude du ceteau (Dicologoglossa cuneata, Moreau 1881). These de Doctorat d'Etat. Universite d'Aix-Marseille: 1-303 + annexes. LE BRIS, H., 1988. Fonctionnement des ecosystemes benthiques c6tiers au contact d'estuaires: la rade de Lorient et la bale de Vilaine. These de Doctorat. Universite de Bretagne occidentale, Brest: 1-311. LE MAC, P., 1986. Feeding relationships between the benthic infauna and the dominant benthic fish of the Rance estuary (France).--& mar. biol. Ass. U.K. 66: 391-401. LOCKWOOD, S.J., 1974. The settlement, distribution and movements of 0-group plaice Pleuronectes platessa L. in the Filey Bay, Yorkshire.--& Fish Biol. 6: 465-477. LOCKWOOD, S.J. & W. LUCASSEN, 1984. The recruitment of juvenile plaice (Pleuronectes platessa L.) to their parent spawning stock.--J. Cons. perm. int. Explor. Mer 41 : 268-275. MACKIE, A.M., J.W. ADRON & RT. GRANT, 1980. Chemical nature of feeding stimulants for the Dover sole, Solea solea (L.).--J. Fish Biol. 16: 701-708. MARCHAND, J., 1989. Interannual comparison of the settlement conditions of the 0-Group sole (Solea solea) in the Vilaine estuary (1986-1989). Fish population biology. The Fisheries Society of the Bristish Isles, University of Aberdeen. , 1991. Influence of environmental conditions on the settlement, the distribution and the growth of the 0-group sole (Solea solea) in a macrotidal estuary.-Neth. J. Sea Res. 27: 307-316. MARCHAND, J. & G. MASSON, 1989. Process of estuarine colonization by 0-group sole (Solea solea): hydrological conditions, behaviour and feeding activity in the Vilaine estuary.--Rapp. P.-v. Reun. Cons. perm. int. Explor. Mer 191: 287-295. MASSON, G., 1984. Bioecologie d'un poisson plat migrateur: le flet (Platichthys flesus L.) dans I'estuaire de la Loire et ses milieux annexes.--CIEM, Comite Poissons demersaux, CM/G:42. MILLER, JM., L.B. CROWDER & M.L. MOSER, 1983. Migration and utilization of estuarine nurseries by juvenile fishes: an evolutionary perspective.--Contr. Mar. Sci. 27 (suppl.): 338-352. MILLER, J.M., J.P. NEED & L.J. PIETRAFESA, 1984. Patterns, mechanisms and approaches to the study of migrations of estuarine dependent fish larvae and juveniles. In: J.D. Mo CI,EAVE, J.P. ARNOLD, J.J. DODSON & W.H. NEILL. Mechanisms of migration in fishes. Plenum Publishing Corporation-New York: 209-227. POXTON, M.G., A. ELEFTHERIOU & A.D. MCINTYRE, 1982. The populations dynamics of 0-group Flatfish on Nursery Grounds in the Clyde Sea area.--Estuar, coast. Shelf Sci. 14: 265-282.

306

D. DOREL, C. KOUTSIKOPOULOS, Y. DESAUNAY & J. MARCHAND

RIJNSDORP, A., M. STRATEN& H.W. VAN DER VEER, 1985. Selective tidal transport of North Sea plaice (Pleuronectes platessa) in coastal nursery areas.Trans. Am. Fish. Soc. 114: 461-470. RILEY, J.D., D.J. SYMONDS& L. WOOLNER, 1981. On the factors influencing the distribution of 0-group demersal fish in coastal waters.--Rapp. P.-v. Reun. Cons. perm. int. Explor. Mer 178: 223-228. ROGERS, C.W., D.R. GUNDERSON& D.A. ARMSTRONG,1988. Utilization of a Washington estuary by juvenile English sole, Parophrys vetulus.--Fish. Bull. 86: 823-831. ROGERS, S.l., 1989a. The ecology of juvenile Dover sole: a review of the litterature.--Progr. Underw. Sci. 14: 53-66. ----, 1989b. Characterizing the nursery grounds of the Dover sole So/ea solea using selected biological and physical criteria. Fish populations biology. The Fisheries Society of the British Isles. University of Aberdeen. ROGERS, S.I. & S.J. LOCKWOOD, 1990. Observations on coastal fish fauna during a spring bloom of Phaeocystis pouchetii in the Eastern Irish Sea.--J. mar. biol. Ass. U.K. 70: 249-253.

ROSSIGNOL-STRICK,M., 1985. A marine anoxic event on the Brittany coast, July 1982.--J. Coast. Res. 1: 11-20. SALOMON, J.C. & P. LAZURE, 1988. Etude par modele math~matique de quelques aspects de la circulation marine entre Quiberon et Noirmoutier.--Rapp. IFREMER-DERO-88-26-EL, Brest: 1-104. TANAKA, M., T. GOTO, M. TOMIYAMA& H. SUDO, 1989. Immigration, settlement and mortality of flounder (Paralichthy$ ofivaceus), larvae and juveniles in a nursery grounds, Shijiki bay, Japan.wNeth. J. Sea Res. 24: 57-67. VANNEY, J.R., 1965. Etude sc~climentologiquedu Mot Braz, Bretagne.--Mar Geol. 3: 195-222. VEER, H.W. VAN DER, 1986. Immigration, settlement and density-dependent mortality of a larval and early postlarval 0-group plaice (Pleuronectes p/atessa) population in the Western Wadden Sea.--Mar. Ecol. Prog. Set. 29' 223-236. VEER, H.W. VAN DER & A. GROENEWOLD, 1967, The ecology of 0-group flounder (P/atichthys f/esus) in the Western Wadden Sea.--ICES C.M. 1987/L:41.