by M. Murenu,
D. Cuccu, M. C. Follesa, A. Sabatini & A. Cau
During
the Medits ITM2 survey 1999 (17th
May to 2nd July, 123 valid hauls), a total of 170 species were
caught and identified in seas around Sardinia (M2 region, 133 zone). Of the
species, 122 were fishes, 27 crustaceans, and 21 cephalopods. Based on the
reference lists, 41 species of fishes (24.1 % of the total), 7 species of
crustaceans (4.1 % of the total), and 5 species of cephalopods (2.9 % of the
total) were identified.
For the
37 species included in the short reference list (Medits Target Species) the length frequency distributions and
abundance indices (number and weight) were analysed singularly for each depth
stratum. The results of the analysis are here reported.
Considering
the whole Medits ITM2 area and
the species from the reference list, only 3 species yielded more than 50
km/kmē. They were in decreasing order: Merluccius
merluccius (BI=113.2, CV=12.9), Octopus
vulgaris (BI=60.9, CV=18.4) and Spicara
smaris (BI=48.4, 59.8). Important biomass values (BI>30) were also
obtained for Raja clavata (BI=39.5,
CV=17.2), Scyliorhinus canicula
(BI=37.8, CV=20.6), Zeus faber
(BI=31.8, CV=59.7) and Mullus barbatus
(BI=30.2, CV=22.9).
With
regard to the number of individuals, M.
merluccius still showed the highest value of abundance (DI= 3494,CV=14.4).
Other target species that showed high density values (more than 500 N/kmē) were
in decreasing order: Trisopterus minutus
capelanus (DI=1512, CV=18.1), Sardina
pilchardus (DI=918, CV=37.5), M.
barbatus (DI=851, CV=22.9), Parapenaeus
longirostris (DI=815, CV=32.1), Trachurus
trachurus (DI=610, CV=28.3), S.
canicula (DI=583, CV=32.9) and Aspitrigla
cuculus (DI=502, CV=48.9).
M. merluccius, O.
vulgaris, S. smaris, Z. faber and M. barbatus were the most abundant species in biomass also on the
continental shelf. At this depth, Sardina
pilchardus and T. minutus also
showed high densities.
On slope
bottoms with the exception of M.
merluccius (BI=76.7, DI=3860), biomass indices greater than 30 kg/kmē were
obtained for two non-commercial species
Galeus melastomus and Lepidopus
caudatus, which also showed high densities (BI=55.6 and BI=44.0
respectively). Among the commercial species high biomass and density values
were obtained for three crustaceans, P.
longirostris, Aristaeomorpha foliacea
and Aristeus antennatus (BI=19.4, 10.6, 7.2 and DI=1714, 527, 402
respectively), for the fish Phycis
blennoides (BI=26.1, DI=1150) and for the cephalopod Illex coindetii (BI=26.1, DI=183).
Species
such as Pagrus pagrus, Trigla lucerna, Spicara maena, Eutrigla
gurnardus, and Squilla mantis
showed very low abundance indices (BI<1.0, DI<6) in the whole region and
at all bathymetric levels.
The most
remarkable difference in catches between 1998 and 1999 is the important
increase in overall biomass and density indices for most of the target fish,
for some cephalopods (O. vulgaris, S.
officinalis, E. cirrhosa and I. coindetii)
and for P. longirostris. The other
target crustaceans slightly decrease both in biomass and density.
A total
of 122 species of fish (104 teleosts and 18 selachians) were collected during
the survey. About one third of the species (31%) was included in the reference
list.
The highest
biomass index (133.2 kg/kmē) was registered for M. merluccius. High values (more than 98 kg/kmē) were also observed
for Capros aper and Glossanodon leioglossus. The most
abundant in number (more than 2500 N/kmē) were species that are not included in
the reference list: Chlorophthalmus
agassizii, Gadiculus argenteus, C. aper, and Macrorhamphosus scolopax. Among the species included in the
reference list the most abundant was M.
merluccius (3500 N/kmē).
Aspitrigla cuculus
This
species mainly occurred between 50 and 200 m of depth (shelf BI=19.1
CV=25.3; shelf DI=786, CV=49.3), but few specimens were also caught between 200
and 371 m. A. cuculus was
particularly abundant in the Gulf of Asinara (northern Sardinia, stratum 133
13) where the highest biomass (BI=150.8, CV=32.1) and density indices
(DI=14466, CV=34.3) at depth of 100-200 m were recorded.
The
specimens (n=3607) collected ranged from 6 to 23 cm TL with few specimens
(n=43) of 29 cm TL. Two cohorts could be well identified at 7-8 and
17-18 cm respectively.
Citharus linguatula
According
with the previous findings on the biology of the species Citharus linguatula was only present on the continental shelf
(shelf BI=2.5 CV=29.0; shelf DI=108, CV=30.2) off the western and southern
coasts (sub regions d, e, f and g). C.
linguatula was mainly caught at depths between 50-200 m. The highest
biomass index was obtained for the stratum 13317 (off western north coasts, at
depth of 50-100 m). High indices, ranging from 11.0 kg/kmē to 14.0 kg/kmē,
were also obtained in strata 13323, 13322 and 13327.
Sizes
ranged from 6 to 23 cm of total length. The modal class was 12 cm.
Eutrigla gurnardus
Only ten
specimens of Eutrigla gurnardus were
caught in the first bathymetric stratum.
Helicolenus dactylopterus
Only
found from 100 m downward in the overall strata, Helicolenus dactylopterus showed a low regional biomass value
(BI=3.7, CV=21.6). The highest biomass (BI=34.9) was recorded at depth of
500-800 m in stratum 13325 (western Sardinia). Lower indices were obtained
for strata 13324 and 13319 in the previous bathymetric level.
Lengths
ranged from 3 to 29 cm, and three evident cohorts (length classes of 5, 9
and 16 cm) could be identified. However more than 70 % of the specimens
were juveniles, ranging from 3 to 10 cm TL.
Lepidorhombus boscii
Lepidorhombus boscii was mainly found at depths greater
than 100 m. It showed low abundance values in the whole zone (BI=1.8,
CV=11.9; DI=26, CV=11.6), although the highest index (15.8 kg/kmē) was recorded
in stratum 13325.
The
lengths of the 259 specimens collected ranged homogeneously between 7 and
34 cm TL.
Lophius budegassa
Only few
specimens (n=70) were mainly caught in the depth strata over 100 m. The
overall biomass index (zone 133) was of 6.3 kg/kmē (CV=27.2). The highest
biomass values (BI=58.2, CV=44.0) were recorded for stratum 13319
(200-500 m off western Sardinian coasts).
The
lengths of the specimens were widely distributed from 10 to 72 cm TL.
Lophius piscatorius
Only
fifty-two specimens were caught in the overall zone. Abundance indices were
BI=10.3 (CV=25.3) and DI=7 (CV=18.1). The highest biomass values (75.3 kg/kmē,
CV=41.1) occurred in the deepest bathymetric level, off the southern coasts
(stratum 13335). A significant index was also obtained in stratum 13335.
Lengths ranged
from 11 to 100 cm TL.
Merluccius merluccius
Merluccius merluccius was the most abundant species in
the whole 133 zone (BI=113.2, DI=3494). This species was particularly abundant
on the continental shelf where the BI was
134.3 (CV=16.2). Higher yields (ranged from 429 to 547 kg/kmē) were
obtained at depths between 50 and 200 m off the western and southwestern
coasts, in strata 13317, 13322 and 13323.
The
species was widely distributed in the investigated area. The 29994 specimens
(19708 specimens more than the previous years) were collected during 94 hauls
(76.4 % of the total). The lengths, ranging from 4 to 69 cm TL, were
evenly distributed in the whole region and at all depths. The size frequency
distribution showed at least 3 different cohorts (12-13, 20 and 31 cm
respectively), however more than 50 % were juveniles (less than 12 cm TL).
The
largest specimen (69 cm of total length) was caught below 500 m of
depth.
Micromesistius poutassou
Micromesistius poutassou was only caught at depths greater
than 100 m. The highest abundance indices (BI=146 CV=25.5; DI=2842,
CV=3.4) were observed in stratum 13303. High indices were also observed from
200 to 500 m of depth off the eastern and northeastern coasts.
The length ranged between 8 and 39 cm TL
although most of the specimens caught were juveniles (90 % under 16 cm
TL). One modal class could be clearly identified on 13-14 cm.
Mullus barbatus
Mullus barbatus was caught exclusively on shelf bottoms in
which the following abundance indices were calculated: 1343 N/kmē (CV=22.9),
47.6 kg/kmē (CV=22.9).
High BI
were found off northern and southern-west coasts (BI=232.4, 193.6 and 188.8,
DI=6710, 6132, 5566 in strata 13311, 13326 and 13312 respectively). However
significant biomass values (BI>40) were observed at different depths in west
and south sub regions.
The
overall range of the length frequency distribution was 7-24 cm TL (modal
class=12-13 cm) in the whole zone. At depths lower than 100 m small
sizes (less than 14 cm TL) represent a quota of 72.0 %.
Mullus surmuletus
Mullus surmuletus was mainly caught at depths from 10 to
500 m (regional BI=30.2, CV=29.6), but also relatively abundant shallower
than 200 m (shelf BI=33.7, CV=31.6). The highest indices of the whole zone
were recorded in stratum 13313 (BI=204.0, CV=43.2; DI=2044 CV=43.1) and stratum
13322 (BI=185.7, CV=40.7; DI=3317
CV=40.7) off the northern and the western coasts respectively. High indices
were also obtained off the northern-east coasts.
The 1885
specimens ranged from 7 to 31 cm in total length, showing a definite modal
class between 16 and 18 cm.
Pagellus acarne
Pagellus acarne was only caught down to 500 m. The
regional index was 3.7 kg/kmē (CV=48.8). The highest biomass value was recorded
in stratum 13314 (BI=76.0, CV=47.1). However significant catches (BI~20) were
also recorded in shallower bottoms (strata 13301 and 13322).
A
different lengths frequency distribution was observed among shelf and slope
bottoms. On the shallower depth strata (0-100 m) sizes of specimens ranged
from 7 to 19 cm and two cohorts (9 and 16 cm TL) could be identified.
At depth of 200-500 m lengths range shifted to 18-31 cm with only one
modal class (20-21 cm).
Pagellus bogaraveo
Only 82
specimens were collected at depths from 47 to 652 m. The highest indices
(BI=11.3 CV=23.6; DI=36, CV=26.7) were obtained in the deepest bathymetric
level of the southwest sub region (13330).
Lengths ranged from 13 to 57 cm of total
length.
Pagellus erythrinus
Was
mainly caught in the shallower strata (between 10 and 100 m of depth),
although few specimens were collected in the third bathymetric stratum
(100-200 m).
Biomass
indices varied from a minimum of 0.6 kg/kmē (stratum 13313) to a maximum value
of 26.3 kg/kmē (stratum 13311). The
regional abundance indices calculated for the continental shelf were of 8.7 kg/kmē (CV=21.4) and 164 N/kmē
(CV=26.5).
Lengths
showed a rather wide range (from 7 to 28 cm) in which two modal classes of
11 and 16 cm could be clearly identified.
Pagrus pagrus
Few
specimens (N=26) were collected off the eastern, northeastern and western coast
on shelf bottoms only (shelf BI=1.5, CV=56.9). However biomass indices were
rather high in the eastern regions in strata 13301 (BI=9.0, CV=36) and 13302
(BI=11.3, CV=33.4).
Lengths
ranged from 12 to 58 cm of total length.
Phycis blennoides
It was
mainly caught at depths greater than 200 m. However low biomass
(BI<3.6) and density (DI<34) indices were obtained between 100 and
200 m of depth. The regional BI calculated for the slope resulted of 23.0
kg/kmē (CV=11.5). The higher biomass indices were observed in the deepest strata and ranged from 14
to 33 kg/kmē, excluding the 13315 stratum (BI=51, CV=0) in which for technical
problem only one haul was made.
The most frequent lengths were 10 and
23 cm. They ranged from 5 to 54 cm.
The modal class was 10 cm of total length.
Spicara flexuosa
According
with the biology of the species S.
flexuosa was only caught on shelf bottoms (slope BI=21.4, CV=23.5; slope
DI=638, CV 24.6). It was particularly abundant off the southwestern and western
strata in which the highest biomass index was 115 kg/kmē (CV=25.5,
stratum 13333).
Spicara smaris
Occurred
in the continental shelf only, although was caught both in high density (shelf
DI=2016, CV=51.8) and biomass (shelf BI=76.4 CV=59.8) below 100 m of
depth. The extremely high biomass index (BI=1188, CV=31.4) obtained for stratum
13331 was due to a single haul that yielded 138 kg in half an hour. High
biomass indices (from 124 to 263 kg/kmē) were obtained off the northern coast
for strata 13311 and 13312.
The
total lengths of specimens (N=5937) ranged from 10 to 20 cm TL. The most frequent lengths were 14 and
17 cm.
Solea vulgaris
A very
low number of specimens (N=95) were collected on bottoms shallower than
100 m of depth. Density and biomass indices calculated for the continental
shelf were 42.0 N/kmē (CV=82.0) and 3.6 kg/kmē (CV=36.0) respectively. The
highest biomass index (BI=25.0, CV=24.6) was found in stratum 13326.
Specimen sizes ranged from 7 to 37 cm.
Trachurus mediterraneus
Trachurus mediterraneus was rarely caught and occurred
mainly on the continental shelf bottoms (DI=204, CV=60.1; BI=3.8, CV=44.0). The
highest biomass indices were recorded in strata 13318 (BI=32,CV=40.6) and 13326
(BI=13, CV=26.5).
Total
lengths ranged from 6 to 39 cm in total length. Most of them (80%) were
juveniles (less than 13 cm of total length).
Trachurus trachurus
Trachurus trachurus was only caught down to 280 m of depth.
The overall shelf density and biomass indices were 610 N/kmē (CV=28) and 9.7
kg/kmē (CV=32) respectively. The highest biomass index was registered off the
northern coast (strata 13314, BI=568,CV=47.1).
Lengths of the specimens collected (N=4148)
were distributed from 5 to 35 cm around two cohorts (10 and 23 cm
TL). A quota of 67.6 % of these
specimens was juvenile.
Trigloporus lastoviza
This
species was mainly caught above 100 m of depth. Generally abundant in the
whole area, it showed the higher biomass off the eastern, the northeastern and
the southwestern coasts. These indices ranged from 24 to 33 kg/kmē.
Specimens
varied between 6 and 22 cm with a modal class of 14-15 cm TL.
Trisopterus minutus capelanus
The poor
cod was caught both in large quantities and numbers at depths between 50 and
200 m mainly. The regional density and biomass indices calculated for
shelf bottoms were 2384 (CV=18.1) and 16.4 (CV=14.7) respectively.
Catches
were abundant in the third bathymetric stratum (100-200 m). The highest
biomass index was found for stratum 13323 (BI=100, CV=9.9).
Sizes
ranged from 3 to 25 cm. Most of the specimens (85.2%) were juveniles (less
than 10 cm of total length).
Zeus faber
Zeus faber was generally abundant in the whole area at
depths between 10 and 342 m, and showed very high biomass values (BI=47.9,
CV=62.5). It was mainly abundant on shelf bottoms (shelf BI=47.9, CV=62.5)
while down to 200 m of depth was caught off the northeastern coasts only
(sub region 133 b).
The
extraordinary BI values of 933 (CV=30.7) and 118 (CV=100.6) observed in strata
13317 and 13323 respectively are mainly due to single hauls which yielded 106.5
and 15.0 kg in half an hour. High biomass indices were also observed from 100
to 200 m of depth off the eastern and the north eastern coasts in which
strata 13303 and 13308 showed biomass indices of 60 (CV=28) and 55 (CV=4.3) respectively.
Total
lengths ranged from 3 to 60 cm. Three cohorts could be clearly identified
(11, 17 and 49 cm of total length respectively).
Galeus melastomus
6355
individuals of Galeus melastomus were
caught below 200 m of depth. Considering slope areas it showed the second
biomass values among the Medits
species (slope BI=55.6 CV=20.2). It was particularly abundant off the western
and the northeastern coasts. The highest biomass indices were found for strata
13324 and 13323 (BI=344, CV=3.1 and BI=146, CV=36.5 respectively).
The size
of the specimens ranged from 8 to 60 cm TL. Juveniles were mainly
distributed at depths below 500 m (modal class=17 cm).
Raja clavata
Raja clavata was caught at depths between 50 and
450 m. In relation to biomass it was the 3rd target species.
The regional biomass index was 39.5 kg/kmē (CV=17.2). High biomass and density
indices were obtained on the continental shelf of the northeast coast and on
slope bottoms of the north and northwest coasts. The highest biomass value was
found in stratum 13308 (BI=242, CV=1.8).
Sizes ranged from 6 to 85 cm TL.
Scyliorhinus canicula
It was
caught above 500 m of depth and particularly abundant between 100 and
500 m. High abundance indices were computed either on shelf (shelf BI=41.3
CV=26.3; shelf DI=496, CV=48.2) or slope bottoms (slope BI=31.8 CV=30.7; slope
DI=734, CV=43.8). The highest density (DI=5935, CV=44; BI=175, CV=44) and the
highest biomass values (BI=179, CV=39.7; DI=2678, CV=65.9) were obtained for
strata 13323 and 13319 respectively.
The size
of the 4803 specimens ranged from 11 to 94 cm of total length. Small
individuals were mainly caught on slope bottoms (modal class=20-21 cm TL).
Twenty-seven
species of crustaceans were caught and identified during the survey. Excluding Squilla mantis and Penaeus kerathurus all the target species were found.
The most
abundant species was Parapenaeus
longirostris, caught either in large quantity or number (7.0 kg/kmē and 815
N/kmē). However, Aristeus antennatus
and Aristaeomorpha foliacea showed
rather high values of biomass too (BI=3.9
and 2.6 kg/kmē respectively).
As for
the non-target species, catches of Plesionika
martia, Palinurus elephas and Plesionika edwardsii were also worthy of
note due to their economic value (BI=1.6,
0.6 and 0.4 kg/kmē respectively). Excluding Palinurus
elephas, these species were also caught in high numbers (regional indices
> 230 N/kmē).
Aristaeomorpha foliacea
A total
of 2736 specimens were collected between 443 and 675 m. Catches were
particularly abundant in the deepest bathymetric stratum. The overall indices
calculated for the slope were BI=10.6 (CV=16.1) and DI=527 (CV=16.1). The
highest biomass value (43 kg/kmē, CV=16.6) was observed in stratum 13335.
Specimens
ranged from 17 to 69 mm. Four main distinct cohorts were observed (25-26,
33-34, 43-44 and 56 mm of carapace length).
Aristeus antennatus
A total
of 2318 specimens of Aristeus antennatus
were caught between 505 and 675 m of depth.
For
slope bottoms the mean density and biomass values were 402 N/kmē (CV=54.5) and 7.1 kg/kmē (CV=49.5) respectively. The
most significant biomass index (BI=41.0, CV=63.9) was obtained in the stratum
13330.
Lengths
ranged from 18 to 59 mm CL. Three distinct cohorts were observed on
classes at 30, 39 and 48 mm of carapace length.
Nephrops norvegicus
This
species caught below 273 m of depth, showed high biomass values especially off
the western costs; in strata 13324 and 13325 biomass indices were of 23 kg/kmē
(CV=47.9) and 55 kg/kmē (CV=8.8) respectively. The overall regional abundance
indices calculated for slope bottoms were BI=5.2 (CV=22.17) and DI=118
(CV=25.7).
Observed
lengths ranged from 18 to 66 mm of carapace length.
Parapenaeus longirostris
The 8757
specimens collected were found at depths from 109 to 595 m. This species was
particularly abundant on slope bottoms (slope BI=15.4, CV=38.4), although was
occasionally caught between 100 and 200 m and below 500 m off the
eastern, the northern and the western coasts. The regional biomass index was
6.9 kg/kmē (CV=33.2). The highest biomass values were calculated at strata
13328, and 13325 (B.I of 14.0 and 10.3 respectively).
The
carapace ranged from 9 to 38 mm CL, with a modal class of 23-24 mm.
A total
of 21 different species of cephalopods were collected. All target species were
present.
Among
cephalopods the most abundant species, caught either in large quantity or
number, were Octopus vulgaris (BI=61.0), Eledone cirrhosa (BI=19.2)
and Illex coindetii (BI=18.5).
Among
the species not included on the Medits
reference list Loligo forbesi was
worthy of note due to his economic value. It was caught in high numbers (DI=60,
CV=28.1) and quantities (BI=4.5, CV=31.2).
Eledone cirrhosa
Eledone cirrhosa was caught in the whole area at depths between
33 and 588 m. This species showed high biomass values on continental shelf
fishing grounds, at depths between 50 and 200, although rather high BI were
also observed in some strata of the
deepest and shallower bathymetric level. The highest biomass indices were
observed at strata 13307 (BI=65 CV=15.3), 13332 (BI=54.8 CV=9.9), 13327
(BI=47.1 CV=9.9).
Sizes
ranged from 1 to 19 cm in mantle length, with two cohorts of 2-3 and
7-8 mm. A high percentage of small individuals (28.9 % of 2-3 mm ML)
were caught in the third bathymetric level (100-200 m).
Eledone moschata
Excluding
strata 13312 and 13317, Eledone moschata
was only caught in eastern, northern-east, southern-west and southern sub
region (133a, b, f, g) above 100 m of depth. For shelf bottoms of the whole
M2 region the mean biomass value was 4.03 kg/kmē (CV=24.3). Strata 13302 and
13307 showed the highest indices (BI=32.6, CV=0.3 and BI=13.5, CV=30.2
respectively).
Mantle
lengths of the 61 individuals caught were distributed from 4 to 18 cm.
Illex coindetii
Illex coindetii was caught at all bathymetric levels with the
highest values from 100 to 500 m. The
mean regional biomass index was 18.6 kg/kmē (CV=31.3)
and the highest value (BI=315.1,
CV=41.0) was observed in stratum 13314 (northern Sardinia, 200-500 m of
depth).
Length
distribution was from 4 to 25 cm with three cohorts of 5-6, 15-16 and
19-20 cm.
Loligo vulgaris
Loligo vulgaris was mainly caught at depths between 10 and
100 m, this species showed highest biomass indices above 50 m of
depth off the south-western (BI=16.1, CV=10.1), the northern (BI=11.3, CV=15.1)
and the southern coasts (BI=10.8, CV=30.9).
Lengths
ranged from 4 to 25 cm. Three modal classes were observed at 7-8, 15 and
19 cm mantle length.
Octopus vulgaris
One of
the most abundant species caught on the shelf (BI=96.1, CV=18.4) Octopus vulgaris was caught in all the
strata above 100 m of depth although some catches were made on deeper
bathymetric levels till 316 m. The highest biomass values were obtained above
50 m of depth. Strata 133g and 133c showed the highest values (BI=615
CV=19.6 and BI=396, CV=4.2 respectively).
The
length of the mantle varied from 3 to 19 cm and the most frequent values
ranged from 9 to 11 cm.
Sepia officinalis
Few
specimens (N=82) of Sepia officinalis
were collected between 26 and 300 m in the subregions 133a, 133b, 133e and
133g. The highest biomass values were observed off the east and the south
coasts (BI=47.5, CV=8.6 and BI=37.8, CV=11.5 respectively).
Mantle
length varied from 4 to 24 cm.
Trawling
20 hauls a total of 84 different species were caught. Of these, 71 were fishes,
12 cephalopods, and 1 crustacean. The 48 % of the catches was represented by
species belonged to the reference Medits
list of which 33 species were fishes and 7 were cephalopods. In this stratum no
target crustaceans were collected at all.
The
highest abundances, in terms of biomass and in terms of density, were observed
for S. smaris (BI=1188, CV=31.3; DI=26612, CV=31.0), which was caught
particularly off the southern coast.
In terms
of biomass high values (more than 100 kg/kmē) were also obtained, in decreasing
order of importance, for O. vulgaris,
M. barbatus, Raja polystigma, Diplodus
annularis and Raja asterias. The
biggest quantities were caught off the southern and the northern basins.
In terms
of density, the most significant indices (more than 2000 N/kmē) were found for S. smaris, M. barbatus, M. surmuletus,
D. annularis, S. pilchardus, Serranus
cabrilla, M. merluccius and S. flexuosa.
In a
total of 22 hauls, 84 species were caught. Forty species belonged to the Medits reference list (33 fishes and 7
cephalopods).
In the
whole area, the highest value of biomass in the second bathymetric level was
observed for Z. faber (BI=932). It was mainly caught off the
northwestern coast (133d zone). Both high biomass and density indices were
observed for a non-target species, Centracanthus
cirrus, especially off the southern coast (133g zone).
High
density values of M. merluccius were
calculated particularly off the western, the south western, and the southern
coasts (133d, e, f, g zones).
Other
species with considerable values of biomass (more than 100 kg/kmē) were M. barbatus (133c zone), M. surmuletus (133e) S. pilchardus (133f), O. vulgaris (133b,c), and R. clavata (133b).
In this
stratum the highest number of different species (n=97) was caught trawling 22
hauls. 49.0 % of these species were on the reference list: 30 were fishes and 8
cephalopods. Among the target species no crustaceans were fished at all.
In this
stratum, big quantities of non-commercial species were caught. The highest
values of density were calculated for Macrorhamphosus
scolopax, off the southern coasts (133g sub region), and for Glossanodon leioglossus off the northern
and the southern-west coasts. High values were also observed for M. merluccius and, off the northeast
coast, for R. clavata.
In this
stratum 24 valid hauls were carried out and a total of 95 different species
were collected. From this stratum downward a visible increase of crustaceans
was observed. With regard to the reference list species, fishes, cephalopods,
and crustaceans represent a quota of 25.3 %, 5.3 %, and 3.2 % respectively.
G. argenteus, Ch.
agassizii and C. aper, three
non-commercial species that are not included in the Medits target species, showed the highest biomass in most of
the sub regions (133a, b, f, g). Among the species of the reference list the
highest biomass indices were observed for T.
trachurus M. merluccius, S. canicula, G. melastomus, Lepidopus
caudatus and R. clavata. In the
northern subregion (133c) biomass of I.
coindetii was also high.
In these
deep strata, in which 26 hauls were carried out, an increase of crustaceans
occurred. Of the 74 species found, 42 were fishes, 11 cephalopods, and 21
crustaceans. Regarding target species, fishes, cephalopods and crustaceans
represent percentages of 17.6 %, 2.7% and 6.8 % respectively.
A
non-commercial species, G. melastomus,
showed the highest biomass in most of the subregions (133e, f, g, b). In
western Sardinia significant indices were also observed for N. norvegicus (BI=54.4, CV=8.7), I. coindetii (BI=48.5, CV=1.6), and G. argenteus (BI=47.7, CV=12.5).
As regard
density, the highest values were observed for Ch. agassizii (DI=10400,
CV=) and G. argenteus (DI=4490) off the western coast, and for P. blennoides off all Sardinian coasts
(DI>1000).
Worthy
of note due their very important economic value are two demersal crustaceans: A. foliacea and A. antennatus. Their biomass indices (BIŧ41) were higher respectively in the
western and southwestern subregions.