by A. Souplet
In the
91 hauls of the survey Medits FR
99, 176 animal species have been identified. Most of them have been only rarely
seen: 55 % occurred in less than 10 % of the hauls and 15 % occurred in only
one haul. The most frequent species in the different strata, only in terms of
presence / absence, are (in decreasing order) Merluccius merluccius, Eledone
cirrhosa, Serranus hepatus, Trachurus trachurus, Alloteuthis media, Lepidotrigla cavillone, Eutrigla gurnardus, Trisopterus minutus
capelanus, Scyliorhinus canicula and
Capros aper which were present in
more than 50 hauls.
Some
species of the list of reference show very high values of abundance indices
(more than 30 kg/kmē) in the Gulf of Lions. These are (in decreasing order) Micromesistius poutassou, Trisopterus minutus capelanus, Eledone cirrhosa, Trachurus trachurus, Merluccius merluccius,
Galeus melastomus and Lophius budegassa. On the other hand,
the other species of the list of reference exhibit low or even very low abundance
indices in that area.
In the
eastern Corsica the most abundant species of the list of reference are Spicara smaris, Scyliorhinus canicula,
Galeus melastomus and Mullus barbatus.
All
species in the reference list have been caught at least in one area.
Taking
into account the spatial heterogeneity of the fish populations, all abundance
estimates given in the text are mean estimates by stratum raised to the surface
unit (kmē). In all strata which have been sampled (in fact all except the three
strata mentioned in the technical report) the estimates are the mean of at
least two hauls. The sections below deal with the species of the reference list
modified for the 1998's survey. This list contains 36 species.
Aspitrigla cuculus
This
species exhibits low abundances in the Gulf of Lions (9.2 kg/kmē, 193 N/kmē)
and in Corsica (8.4 kg/kmē, 194 N/kmē). It is mainly located on the shelves
(10-200 m) in both areas. The relative abundant numbers of individuals are
explained by their very small sizes (around 6 or 7 cm).
Citharus linguatula
This
species is only present in the Gulf of Lions, with very low relative abundances
(3.36 kg/kmē, 97 N/kmē) only on the shelves (10-200 m).
Eutrigla gurnardus
This
species is rather abundant in the Gulf of Lions down to 500 m with a
maximum biomass index of 87.4 kg/kmē, far above the last year value. The
maximum density indices are 1649 and 1673 N/kmē in the strata 50-100 m and
100-200 m respectively in the western Gulf. The length frequencies show
that the mean length increases with the depth from around 9 cm in the
strata 10-50 m to around 18 cm in the strata 100-200 m. It is
nearly absent in Corsica as well as in the rest of the Medits area.
Galeus melastomus
This
species newly introduced in the reference list is more abundant in Corsica than
in the Gulf of Lions (43.9 kg/kmē, 803 N/kmē vs. 36.25 kg/kmē, 148 N/kmē). It
occurs at depths greater than 200 m.
Helicolenus dactylopterus
Due to
only some hauls, it appears to be abundant in the French waters in the stratum
200-500 of the western Gulf (121.4 kg/kmē, 1139 N/kmē). The length
distributions show several modes.
Lepidorhombus boscii
This
species is more abundant in the Gulf of Lions than in Corsica at depths greater
than 50 m but it never exceeded a relative abundance of 27.8 kg/kmē.
Lophius budegassa
This
monk fish has been found in big abundance in the stratum 100-200 m in the
eastern Gulf (101.5 kg/kmē, 87 N/kmē) although there has been caught greater
quantities of smaller individuals in the stratum 50-100 m in the western
Gulf (40.2 kg/kmē, 125 N/kmē). It is nearly absent from Corsica.
Lophius piscatorius
It is
more widely distributed than the previous one with a maximum apparent abundance
in the stratum 200-500 in the eastern Gulf (254.0 kg/kmē, 40 N/kmē). It should
be noted that very big individuals (more than 100 cm and 20 kg) have been
caught in this stratum as well as small recruits (less than 10 cm).
Merluccius merluccius
Merluccius merluccius is widely distributed over the
whole studied area. In the Gulf of Lions this species is present at all depths
with biomass indices reaching 89.2 in the stratum 100-200 (2972 N/kmē). On the
other hand, in Corsica, it is less abundant with significant densities only for
depths deeper than 200 m. in the north and than 100 m in the south.
The biomass indices in Corsica do not exceed 16.8. Nevertheless, it should be
noted that the biomass indices, both for the Gulf of Lions and Corsica are much
lower than in 1998.
The most
important part of the catch of Merluccius
merluccius has been made of juveniles below 20 cm. The calculated
histograms allow to identify more or less precisely the first two age groups
with respective mean length around 9-10 cm and 19-20 cm. These two
age groups make the greater part of the catches. Length frequency distributions
according to the depth show that the smallest individuals (smaller than
10 cm) have been caught in all strata between 10 and 500 m. From
200 m downwards bigger individuals have been caught together with the
smaller. In the deepest stratum (500-800 m) mainly big individuals have
been caught. As noted in the previous years of the survey, this distribution
strongly suggests a spatial segregation between juveniles and adults according
to the depth, the adults living mainly at depths deeper than 200 m. It
should be noted that the early period in the year of the survey (May and early
June), due to national constraints, did not allow to catch very young
individuals in the beginning of the survey. During the last two weeks, very
small individuals (4-5 cm) appeared in the catches, probably because of
the beginning of the demersal life at this period of the 0-group hakes.
Micromesistius poutassou
Micromesistius poutassou was significantly observed at depth
below 50 m in the Gulf of Lions and below 200 m on the Corsican
coasts. The highest biomass indices have been reported between 100 and
500 m with maximum values of 415.6 (100-200 m) and 493.9
(200-500 m) in the eastern Gulf of Lions (density index of 64158 and 13460
respectively) and of only 54.6 (almost the third than last year) in the
northern Corsica (density index of 468).
The
youngest individuals (at age 1) with a mean length between 10 and 15 cm
are mainly found on the shelves at depth less than 200 m and on the upper
slope between 200 and 500 m. The older fish (from 20 cm, age group 2
and more) are more widely distributed on the slopes either in the Gulf of Lions
or alongside the Corsican coasts. It should be noted that no 1-group fish have
been caught at all in Corsica.
Mullus barbatus
Mullus barbatus was observed on all the studied shelves, from
10 to 200 m depth. In the Gulf of Lions, the maximum biomass index is 44.0
(density index of 1234) in the stratum 100-200 m) while in Corsica this
index reach 131.4 (4 384 N/kmē) in the stratum 50-100 m.
In both
areas, the length of caught Mullus
barbatus is in general between 10 and 20 cm. As the first maturity
length is 12.5 cm for males and 13 cm for females, the majority of
these individuals can be considered as adults.
Mullus surmuletus
This
species is much less abundant in the French waters than M. barbatus. The maximum biomass index is 46.0 kg/kmē (844 N/kmē)
in the stratum 50-100 m in south Corsica.
Pagellus acarne
It is
present in medium or low abundance (maximum of 46.9 kg/kmē, 389 N/kmē) in the
strata 10-200 m in the western Gulf, in the strata 10-500 m in the
eastern Gulf (maximum 36.1 kg/kmē, 114 N/kmē) in the eastern Gulf, while it is
nearly absent in Corsica. It should be noted that in only one haul of half an
hour in the western Gulf, unfortunately invalid because of technical problems,
215 kg of P. acarne have been caught.
The length frequencies show two modes at 19 and 25 cm.
Pagellus bogaraveo
As last
year this species was caught in significant quantities between 200 and
500 m in the eastern Gulf of Lions (113.5 kg/kmē and 179 N/kmē) and
between 500 and 800 m in southern Corsica (108.4 kg/kmē and 104 N/kmē).
The main catches were made by large individuals, between 30 and 40 cm in
the Gulf, and between 40 and 50 cm in Corsica.
Pagellus erythrinus
In
general the catches of this species have been rather poor, except in the
stratum 10-50 m in the western Gulf (41.32 kg/kmē, 524 N/kmē) and in the
stratum 50-100 m in south Corsica (110.6 kg/kmē, 1627 N/kmē).
Phycis blennoides
This
species has been caught in significant quantities only at depths below
200 m and mainly in the Gulf of Lions. The maximum apparent densities have
been reported in the stratum 500-800 m in the western Gulf (53.8 kg/kmē,
1206 N/kmē).
Raja clavata
Raja clavata was mainly caught on the majority of the
grounds between 50 and 500 m in the eastern part of the Gulf of Lions,
with a maximum biomass index of 23.8 (21 N/kmē) in the stratum 100-200 m,
far below the previous year value of 69.5, but was nearly absent in the western
part. The biomass index is significantly higher in Corsica between 100 and
200 m in the north (53.7 kg/kmē) and between 50 and 100 m in the
south (47.8 kg/kmē) again far below the last year value of 384.8. The dramatic
decrease of this species, since at least two decades, as described by Y.
Aldebert in the Pisa symposium, seems to continue.
The
length frequencies, ranging between 10 and 75 cm, show that the different
age groups live in mixture on the whole area.
Scyliorhinus canicula
This
species is present between 50 and 500 m. The highest indices have been
reported between 50 and 100 m in south Corsica (133.08 kg/kmē and 814
N/kmē) and between 200 and 500 m in the same area (142.4 kg/kmē, 454
N/kmē). It should be noted that in north Corsica a density of 1454 N/kmē has
been reported due to catches of numerous small individuals (less than
25 cm).
Solea vulgaris
The
design of the Medits trawl has
not been made to catch efficiently this benthic species. That explains probably
why its abundance indices are very low all over the Medits areas. In the French waters the highest abundance
indices has been observed in the stratum 10-50 m in the eastern Gulf of
Lions (6.9 kg/kmē, 16 N/kmē).
Spicara flexuosa
This
shallow water species is rather abundant alongside the Corsican coasts between
50 and 100 m: 131.2 kg/kmē in the north and 71.7 kg/kmē in the south
(4619 and 2877 N/kmē respectively). In the Gulf of Lions, the catches were
negligible.
Spicara smaris
Once
again this species has been mainly found in Corsica in the strata 50-100 m
both in the north and in the south (respectively 122.0 kg/kmē, 73620 N/kmē and
122.1 kg/kmē, 4339 N/kmē). Obviously the length frequencies are very different
between this two areas, the biggest individuals having been caught in the
south.
Trachurus mediterraneus
This
year, the catches of Trachurus
mediterraneus on the shelf in the Gulf of Lions exhibit the same magnitude
as in the last year (maximum biomass index of 20.4). The biomass indices were
far higher off Corsica, especially in the stratum 50-100 m with biomass
and density indices of 158.4 and 9071 N/kmē in the stratum 50-100 m in the
north.
Catches
are mainly constituted of immature fish with a length between 9 and 22 cm
but a not negligible part of the catches in the strata 10-50 m and 50
-100 m in the Gulf are made of mature individuals reaching 30 cm. The
sexual maturity for this species is at 4 years old (mean length of around
23 cm).
Trachurus trachurus
This
species is present in the Gulf of Lions between 10 to 500 m with much
higher biomass indices reaching 146.7 (density index of 2364) in the stratum
50-100 m. On the other hand a big number of juveniles has been caught in
the stratum 10-50 m in the western Gulf (6953 N/kmē for only 52.7 kg/kmē).
In Corsica it has been caught in similar quantities (74.3 kg/kmē and 8428
N/kmē) in the stratum 100-200 m in the north.
The
caught individuals have in general a length less than 15 cm in the
shallowest strata (10 to 100 m) with a secondary pick around 20 cm in
the Gulf of Lions The length at first maturity is around 20 cm. In deeper
waters the mean length of the catches increases and reaches 42 cm in the
strata 200-500 m. Once again it is possible to see a segregation according
to the depth between the different age groups. It is remembered that this
species is not strictly speaking demersal. That should be kept in mind to
interpret the exposed results.
Trigloporus lastoviza
The
catches of this species in the French waters are insignificant.
Trisopterus minutus capelanus
Absent
in Corsica, Trisopterus minutus capelanus
was caught in all strata from 10 to 200 m in the Gulf of Lions. The
biggest indices were reported between 100 and 200 m in the eastern part of
the Gulf (152.6 kg/kmē and 23 309 N/kmē).
The
youngest individuals (mean length around 7 cm) are predominant or even
exclusive in the shallowest waters (10-50 m) and at least one other age
group (mean length around 16 cm) was caught between 50 and 200 m.
Zeus faber
This
highly valuable species has been caught in rather small quantities in some
strata: 100-200 m in the eastern Gulf (29.6 kg/kmē, 85 N/kmē),
50-100 m in south Corsica (25.2 kg/kmē, 15 N/kmē) and 100-200 m in
south Corsica again (27.1 kg/kmē, 19 N/kmē).
Aristaeomorpha foliacea
This
shrimp is only present in Corsica (in the French waters), below 200 m
depth, with very low abundance indices.
Aristeus antennatus
This
species was only caught in the Gulf of Lions and at depths between 200 and
800 m. The highest biomass index was reported in the western part of the
Gulf (10.7 kg/kmē). The spatial distribution of this species is highly variable
(horizontal and vertical migrations) and the sampled area does not probably
cover the whole population distribution area.
As it
has previously been observed in the same area, the catches are mainly made of
adult females. The range of cephalo-thoracic lengths (between 20 and
60 mm) indicates that the catches are approximately made of 3 age groups.
Nephrops norvegicus
In the
studied areas, Nephrops norvegicus
lives mainly on the slopes. It has mainly been observed on grounds deeper than
200 m. The biomass indices are high: 85.3 in the eastern Gulf of Lions and
51.0 in the southern Corsica, both in the stratum 200-500 m.
In all
strata where this species was present the cephalo-thoracic length lies between
15 and 64 mm.
Parapenaeus longirostris
This
species is mainly present below 500 m in the Gulf of Lions (279 N/kmē) and
between 200 and 500 m in Corsica (357 N/kmē and 202 N/kmē in the north and
the south respectively).
Eledone cirrhosa
Eledone cirrhosa has been caught in almost all strata both in
the Gulf of Lions and in Corsica. The most important catches have been made in
the Gulf of Lions between 50 and 100 m with maximum biomass index of 86.2
in the stratum 50-100 m. In general the mantle length never exceeds
10 cm.
Eledone moschata
This
species is significantly present in the shallowest stratum in the Gulf of Lions
(10-50 m) with a maximum biomass index 37.3. In Corsica, it is very
scarce. As for the former species, the mantle length never exceeds 10 cm.
Illex coindetii
Illex coindetii was found at depths that have been increasing
from the western Gulf of Lions (50-100 m) to the southern Corsica
(200-800 m). The biomass indices never exceeded 17.0.
Loligo vulgaris
No
significant catches of this species have been made in the French waters
Octopus vulgaris
Octopus vulgaris seems to be a coastal species. In the Gulf of
Lions, the most important catches have been made at depths smaller than
200 m (261.2 kg/kmē, 291 N/kmē in the strata 10-50 m).
Sepia officinalis
This
species has been caught in very low quantities essentially in the stratum
50-100 m in south Corsica (18.5 kg/kmē, 105 N/kmē).
It should
be remembered that the comments on these strata concern only the Gulf of Lions
because this stratum is not trawlable in Corsica.
In these
strata height species have been caught in significant quantities at least in
one part of the Gulf of Lions. Their abundances, both in terms of biomass and
density are given below
|
|
Western
Gulf |
Eastern
Gulf |
||
|
Species code |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
|
Merluccius merluccius |
22.3 |
1417 |
23.8 |
540 |
|
Pagellus acarne |
49.9 |
389 |
1.9 |
21 |
|
Trachurus mediterraneus |
11.1 |
375 |
20.4 |
720 |
|
Trachurus trachurus |
52.7 |
6953 |
9.6 |
1212 |
|
Trisopterus minutus capelanus |
27.1 |
12069 |
5.1 |
1228 |
|
Eledone cirrhosa |
18.8 |
263 |
2.5 |
32 |
|
Eledone moschata |
37.3 |
392 |
24.5 |
191 |
|
Octopus vulgaris |
73.4 |
90 |
261.2 |
291 |
In these
strata 12 species show a particular importance in at least one of the four
areas. They are as follow:
|
|
Western
Gulf |
Eastern
Gulf |
North
Corsica |
South
Corsica |
||||
|
Species code |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
|
Merluccius merluccius |
34.2 |
2312 |
49.8 |
1187 |
2.9 |
33 |
0.0 |
0 |
|
Micromesistius poutassou |
149.6 |
25439 |
1.7 |
323 |
0.0 |
0 |
0.0 |
0 |
|
Mullus barbatus |
19.4 |
578 |
2.1 |
72 |
100.1 |
3603 |
131.4 |
4384 |
|
Pagellus erythrinus |
1.2 |
10 |
3.5 |
20 |
40.8 |
763 |
110.6 |
1627 |
|
Raja clavata |
3.7 |
6 |
0.2 |
2 |
384.8 |
159 |
80.4 |
27 |
|
Scyliorhinus canicula |
12.5 |
43 |
8.9 |
25 |
95.7 |
438 |
133.1 |
814 |
|
Spicara flexuosa |
0.5 |
9 |
0.0 |
0 |
131.2 |
4619 |
71.7 |
2877 |
|
Spicara smaris |
0.2 |
5 |
0.0 |
0 |
1122.0 |
73620 |
122.1 |
4339 |
|
Trachurus mediterraneus |
0.1 |
2 |
1.8 |
20 |
158.4 |
9071 |
5.8 |
105 |
|
Trachurus trachurus |
22.7 |
819 |
146.7 |
2364 |
1.2 |
126 |
3.3 |
241 |
|
Trisopterus minutus capelanus |
135.7 |
15628 |
124.8 |
18256 |
0.0 |
0 |
0.0 |
0 |
|
Eledone cirrhosa |
84.0 |
796 |
86.2 |
504 |
1.6 |
13 |
25.7 |
121 |
In these
strata, 11 species have been caught in significant abundance in at least one
sub-area.
|
Western
Gulf |
Eastern
Gulf |
North
Corsica |
South
Corsica |
|||||
|
Species code |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
|
Eutrigla gurnardus |
87.4 |
1673 |
28.0 |
592 |
0.0 |
0 |
0.0 |
0 |
|
Lophius budegassa |
17.2 |
55 |
101.5 |
87 |
0.0 |
9 |
0.0 |
9 |
|
Merluccius merluccius |
20.2 |
1392 |
89.2 |
2972 |
16.8 |
342 |
2.8 |
75 |
|
Micromesistius poutassou |
242.3 |
29305 |
415.6 |
64158 |
0.0 |
0 |
0.0 |
0 |
|
Mullus barbatus |
44.0 |
1234 |
19.2 |
500 |
32.3 |
874 |
68.0 |
2044 |
|
Raja clavata |
0.0 |
0 |
23.8 |
21 |
53.7 |
40 |
27.8 |
75 |
|
Scyliorhinus canicula |
42.3 |
130 |
50.1 |
303 |
86.6 |
522 |
41.1 |
254 |
|
Trachurus mediterraneus |
0.0 |
0 |
1.3 |
13 |
74.4 |
3958 |
0.5 |
35 |
|
Trachurus trachurus |
1.0 |
103 |
80.5 |
1242 |
74.3 |
8428 |
0.5 |
19 |
|
Trisopterus minutus capelanus |
90.7 |
10607 |
152.6 |
23309 |
0.0 |
0 |
0.0 |
0 |
|
Eledone cirrhosa |
60.7 |
706 |
71.3 |
482 |
24.6 |
161 |
7.0 |
28 |
In these
strata deep-water species, such as Galeus
melastomus, Helicolenus dactylopterus
or Nephrops norvegicus, occurred.
This year only seven species have been caught in significant quantity:
|
Western
Gulf |
Eastern
Gulf |
North
Corsica |
South
Corsica |
|||||
|
Species code |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
|
Galeus melastomus |
147.0 |
424 |
497.2 |
2273 |
32.7 |
501 |
196.1 |
6366 |
|
Helicolenus dactylopterus |
52.3 |
475 |
121.4 |
1139 |
11.6 |
142 |
3.2 |
66 |
|
Lophius
piscatorius |
14.9 |
5 |
254.0 |
40 |
14.4 |
3 |
0.0 |
0 |
|
Micromesistius
poutassou |
63.5 |
600 |
493.9 |
13460 |
54.4 |
468 |
51.6 |
246 |
|
Pagellus
bogaraveo |
0.1 |
2 |
113.5 |
179 |
0.4 |
2 |
0.0 |
0 |
|
Scyliorhinus canicula |
52.7 |
176 |
5.7 |
14 |
108.5 |
1454 |
142.4 |
454 |
|
Nephrops norvegicus |
45.7 |
1271 |
85.2 |
1752 |
36.0 |
1467 |
51.0 |
1131 |
In these
strata, only 6 species have been caught in significant quantity. One can note
the catch of some very big individuals of Lophius
piscatorius in the western Gulf of Lions and a very important catch of Pagellus bogaraveo in southern Corsica.
|
Western
Gulf |
Eastern
Gulf |
North
Corsica |
South
Corsica |
|||||
|
Species code |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
kg/kmē |
N/kmē |
|
Galeus melastomus |
110.0 |
382 |
|
|
73.9 |
615 |
32.4 |
239 |
|
Lophius piscatorius |
74.0 |
15 |
|
|
0.0 |
0 |
74.3 |
5 |
|
Micromesistius poutassou |
71.4 |
5192 |
|
|
0.0 |
0 |
2.1 |
10 |
|
Pagellus bogaraveo |
0.0 |
0 |
|
|
2.2 |
8 |
108.4 |
104 |
|
Phycis blennoides |
53.8 |
1206 |
|
|
24.7 |
234 |
11.8 |
338 |
|
Eledone cirrhosa |
50.1 |
103 |
|
|
0.0 |
0 |
0.0 |
0 |