Survey Results for Italy - area M3 - South Tyrrhenian Sea and Strait of Sicily
The results of the Medits survey carried out in the South Tyrrhenian Sea and in the Strait of Sicily in the period 3rd June-6th July 1997 are discussed.
The survey was conducted using the professional trawler SANT ANNA and the Medits gear. A total of 141 hauls was carried out according to the calendar reported below.
|
Sub-region |
Code |
N° of hauls |
Survey period |
|
South Tyrrhenian Sea: Volturno River - Cape Suvero |
M3a |
57 |
23rd June-6th July |
|
South Tyrrhenian Sea: Cape Suvero - Cape San Vito |
M3b |
28 |
16th June-22nd June |
|
Strait of Sicily |
M3c |
56 |
3rd June-14th June |
Abundance indices per stratum, both in number (N°/kmē) and weight ( kg/kmē) as well as length frequency distributions were calculated (using the IndMed 4 program) and analysed for the 31 Medits target species. Before analysing data, errors were checked using the CheckMed program. Both programs were developed and distributed by A. Souplet.
It has to be pointed out that even if efforts were made to present results at a regional level, since the M3 zone encompasses totally different sub-zones, no joint analysis seems sensible and results per sub-region will be mostly presented and discussed.
A total of 209 different species (150 fishes, 35 crustaceans, 24 cephalopods) was identified. Among the 31 species of the reference list, Solea vulgaris and Sepia officinalis did not occur in the catches in the sub-region M3a whereas Lepidorhombus boscii and Raja clavata were not fished in the sub-region M3b. One species of the reference list, Eutrigla gurnardus, was absent from the catch in the whole area excepting one specimen found in the Strait of Sicily.
The ten most abundant species, if mean biomass indices over the whole area are considered, were Trachurus trachurus (24.92 kg/kmē), Spicara flexuosa (20.79 kg/kmē), Merluccius merluccius (19.20 kg/kmē), Aristaeomorpha foliacea (6.72 kg/kmē), Raja clavata (6.40 kg/kmē), Parapenaeus longirostris (5.80 kg/kmē), Mullus surmuletus (5.52 kg/kmē), Mullus barbatus (5.06 kg/kmē), Trachurus mediterraneus (4.23 kg/kmē) and Octopus vulgaris (4.06 kg/kmē). The species list as well as the abundance indices change if the species depth and space distribution is considered. For example, it has to be pointed out that the presence in the list of Mullus surmuletus and Raja clavata was mainly due to the high catches coming from the Sicilian Strait, being these species rare in the South Tyrrhenian Sea. On the other hand, Pagellus spp. which represent an important resource in the South Tyrrhenian Sea, especially region M3b, showed negligible or low yields in the Strait of Sicily. As far as depth distribution is concerned, in the continental shelf (10-200 m), higher yields were obtained for all the species of the above list excepting the two crustaceans which were substituted by Eledone moschata (7.36 kg/kmē) and Zeus faber (7.11 kg/kmē). A value of 11.04 kg/kmē was observed for Aristaeomorpha foliacea in the depth range 200-800 m.
The species was mainly caught in the Strait of Sicily where abundance indices of 4.56 and 2.50 kg/kmē were found in the second and the third stratum respectively. Yields less than 2 kg/kmē were observed in the South Tyrrhenian Sea.
Eutrigla gurnardus was not fished in the whole area excepting one specimen found in the Sicilian Strait.
Helicolenus dactylopterus was caught at depth greater than 100 m. In the Strait of Sicily the abundance indices were 6.32 kg/kmē in the fourth stratum (200-500 m) and 6.81 kg/kmē in the last one (500-800 m). In the South Tyrrhenian Sea the highest yields both in weight and number were observed in stratum D (200-500 m) (4.40 and 2.10 kg/kmē in sub-regions M3a and M3b respectively). Mean size of specimens was found to increase from sub-region M3a (9.9 cm) to sub-region M3b (12.5 cm) and finally to sub-region M3c (16 cm). On the whole, length ranged from 3.5 to 33 cm.
The species was caught at depths between 100 and 800 m. Very low abundance indices (less than 1 kg/kmē) were observed in sub-regions M3a and M3c whereas they were zero in the sub-region M3b. Specimen size ranged from 4.5 to 32 cm.
Low yields of Lophius budegassa were observed in the whole area at depth from 50 to 800 m. The highest yield (3.42 kg/kmē) was obtained in the sub-region M3a. Specimens having length between 7 and 66 cm were caught.
Yields of Lophius piscatorius did not exceed the value of 5 kg/kmē in the whole area excepting the 43.18 kg/kmē observed in the stratum 100-200 m in the sub-region M3a due to the presence of a large specimen of 104 cm in length. On the whole, specimen size ranged from 8.5 to 104 cm.
Merluccius merluccius was one of the most abundant species in the whole area (mean biomass index = 19.20 kg/kmē). It was fished at any depth and showed the highest concentration between 50 and 500 m where biomass indices ranging from 15.27 to 46.59 kg/kmē were observed. A high value of 33.09 kg/kmē was also observed in the first stratum (10-50 m) of the sub-region M3a. On the whole, lengths ranged from 5 to 70 cm. Most of the catch was represented by juveniles (less than 20 cm). The older specimens rarely occurred in the catches and were mainly found in the deepest stratum of the Sicilian Strait. The population structure of the adult fraction was not well represented by the samples.
The species was caught at depth greater than 200 m with rather low yields (0.25-2.19 kg/kmē). Observed length ranged from 21 to 39.5 cm.
Generally abundant in the whole area at depth less than 200 m, the species showed different yields in the three sub-regions. The highest indices, both in number and weight, were observed in the sub-region M3b: 44.26 kg/kmē in stratum 10-50 m, 112.32 kg/kmē in stratum 50-100 m and 10.40 kg/kmē in stratum 100-200 m. A high abundance index (33.09 kg/kmē) was also obtained in the shallow water of the sub-region M3a but it decreased to a value of 6.41 kg/kmē in stratum B and 2.04 kg/kmē in stratum C. The same distribution pattern was observed in the Sicilian Strait where yields, decreasing with the depth, ranged from 10.14 to 4.58 kg/kmē. Observed length ranged from 9.5 to 25 cm.
A great difference between the Sicilian Strait and the South Tyrrhenian Sea was observed as regards Mullus surmuletus. Very low yields (less than 1 kg/kmē) were obtained in the sub-regions M3a and M3b at depth between 10 and 200 m. Instead, the species was abundantly fished in the Strait of Sicily where it was found at any depth. Highest abundance indices were 27.50 kg/kmē in stratum 50-100 m and 12.50 kg/kmē in stratum 100-200 m. Most of the catch was represented by juveniles (mean length = 7 cm) in the sub-region M3a whereas the size of specimens ranged from 13.5 to 26 cm in the other sub-regions.
The species showed an irregular spatial and depth distribution. The highest yields were obtained in the sub-region M3b: 88.30 kg/kmē in the stratum A (10-50 m), 12.32 kg/kmē in stratum B (50-100 m), 21.74 kg/kmē in stratum D (200-500 m). A high abundance index (10.31 kg/kmē) was also found in the shallow water (10-50 m) of the sub-region M3a where a prevalence of small specimens (9-11 cm) was observed. Finally, low catches were obtained in the Strait of Sicily (0.02- 2.59 kg/kmē). On the whole, specimen length ranged from 7.5 to 23 cm.
The catches of Pagellus bogaraveo, not uniformly distributed in the depth strata of the different sub-areas, were negligible (less than 1 kg/kmē) in the sub-regions M3a and M3c. Instead, a high abundance index (32.72 kg/kmē) was obtained in the sub-region M3b at depth between 50 and 100 m. The yield decreased to 1.67 kg/kmē in the stratum 100-200 m and to 0.29 kg/kmē in the stratum 500-800 m. On the whole, specimen length was ranging from 6 to 25 cm.
Pagellus erythrinus was mainly fished at depths less than 100 m. Very high catches were obtained in the sub-region M3b of the South Tyrrhenian Sea: 55.83 kg/kmē in stratum 10-50 m and 71.43 kg/kmē in stratum 50-100 m. Yields of about 7 kg/kmē were found in the first two strata of the sub-region M3a. Finally, abundance indices of 1.63 and 8.18 kg/kmē were found in the first and second stratum of the Sicilian Strait. The specimens mean size was found to increase with depth and the lengths ranged from 10 to 37 cm.
This species was mainly fished at depths greater than 100 m. The highest yields were obtained in the strata D and E of the sub-region M3a (11.07 and 8.48 kg/kmē respectively). Abundance indices ranging between 4.93 ad 5.69 kg/kmē were found in the same strata of the other sub-regions. Length was ranging from 6 to 51 cm.
This species was mainly concentrated in the Sicilian Strait where it was caught in all the strata except the first one. Yields were found to decrease with depth and were ranging from 21.05 kg/kmē (32 N°/kmē) in stratum B to 2.46 kg/kmē (2 N°/kmē) in stratum E. Observed length ranged from 22.5 to 81.0 cm. No specimen of Raja clavata was found in the sub-region M3b whereas in the sub-region M3a the species was caught only in the stratum 200-500 m with abundance indices of 4.84 kg/kmē and 5 N°/kmē.
This species was not fished at all in the sub-region M3a of the South Tyrrhenian Sea. Very low catches (less than 1 kg/kmē) were also observed in the other sub-regions excepting a value of 5.45 kg/kmē found in the stratum B (50-100 m) of the sub-region M3b. Specimen length ranged from 27.5 to 42.5 cm.
This species was abundantly fished in the whole area at depth less than 200 m (mean abundance indices: 20.79 kg/kmē and 1060 N°/kmē). Especially high yields were obtained in the second stratum (50-100 m). The range of the abundance indices were: 2.45-24.78 kg/kmē in the sub-region M3a, 17.62-155.40 kg/kmē in the sub-region M3b, 19.21-113.51 kg/kmē in the Sicilian Strait. Specimens having length between 4.5 and 20.5 cm were found.
This species, abundant in the whole area, showed rather different yields in the various strata of the three sub-regions. In the sub-region M3a the highest abundance index (31.45 kg/kmē) was observed in the first stratum (10-50 m) whereas it occurred in the stratum 50-100 m in the sub-region M3b (27.81 kg/kmē). Moreover in the sub-region M3b a value of 9.87 kg/kmē was observed in the stratum 100-200 m opposite to the negligible or null value found in the other sub-regions. Finally, indices of 55.26 and 3.89 kg/kmē were obtained respectively in the first two strata of the Sicilian Strait. Observed length ranged from 4.5 to 29.5 cm.
Trachurus trachurus, distributed from 10 to 500 m, was the most abundant species in the whole area (mean abundance indices: 24.92 kg/kmē and 828 N°/kmē). Biomass indices were in the ranges: 1.64-18.99 kg/kmē in the sub-region M3a, 2.92-21.81 kg/kmē in the sub-region M3b and 13.14-107.86 kg/kmē in the Strait of Sicily. Individual size ranged from 4 to 40 cm.
Similar catches of Trisopterus minutus capelanus were observed in the Strait of Sicily and in the sub-region M3a of the South Tyrrhenian Sea. In these sub-regions, abundance indices of 5.52 and 3.44 kg/kmē respectively were found at depth between 50 and 100 m whereas yields were less than 1 kg/kmē in the stratum C (100-200 m) due to the prevalence of small specimens. On the other hand, in the sub-region M3b the species was caught in the second stratum only and a very high yield was obtained (16.36 kg/kmē). Observed length ranged from 3.5 to 21 cm.
This species was mainly caught in the first three strata (10-200 m). Biomass indices were found to increase with depth due to the large individuals found in the deepest strata. The highest yields were 9.45 kg/kmē in the sub-region M3a, 4.85 kg/kmē in the sub-region M3b, 22.61 kg/kmē in the Strait of Sicily. Individual length ranged from 2.5 to 57 cm.
Aristeus antennatus was fished in the deep waters (500-800 m) with very different yields, both in number and weight, in the three sub-regions: 3.44 kg/kmē and 138 N°/kmē in the sub-region M3a, 10.17 kg/kmē and 1276 N°/kmē in the sub-region M3b, 1.02 kg/kmē and 36 N°/kmē in the sub-region M3c. Carapace length ranged from 19 to 60 mm.
This species was abundantly caught in the deep waters (500-800 m) of the whole area. Abundance indices were: 26.86 kg/kmē in the sub-region M3a, 23.14 kg/kmē in the sub-region M3b and 16.67 kg/kmē in the Strait of Sicily. Observed carapace length ranged from 17 to 69 mm.
Found at depth greater than 200 m, the species showed the highest yields in the stratum D (200-500 m) of the sub-region M3a (2.56 kg/kmē) and the Sicilian Strait (4.10 kg/kmē). A similar yield of about 1.8 kg/kmē was obtained for these sub-regions in the stratum E (500-800 m). Abundance indices less than 1 kg/kmē were observed in the sub-region M3b. Carapace length was ranging from 16 to 69 mm.
Parapenaeus longirostris was abundantly fished at depths between 100 and 500 m in the Strait of Sicily with yields of 13.10 and 15.81 kg/kmē. In the South Tyrrhenian Sea yields ranged from 2.51 to 8.30 kg/kmē. Most of the catch was represented by recruits (6-20 mm) in stratum C. On the whole, carapace length ranged from 6 to 43 mm.
This species was mainly fished at depths between 50 and 500 m. Ranges of abundance indices were: 3.59-6.56 kg/kmē in the sub-region M3a, 2.18-3.04 kg/kmē in the sub-region M3b and 1.28-4.73 kg/kmē in the Strait of Sicily. Individual length was ranging from 1 to 19 cm.
Low yields (not exceeding 1.6 kg/kmē) were observed for this species in the sub-region M3a. Instead, it was abundantly caught in the Sicilian Strait (10.76 and 21.32 kg/kmē in the first two strata respectively) and in the sub-region M3b of the South Tyrrhenian Sea (10.91 kg/kmē in stratum B and 5.06 kg/kmē in stratum C). Observed length ranged from 1.5 to 16.5 cm.
This species was fished at depth between 10 and 500 m. The highest biomass indices were found in the stratum 100-200 m: 12.40 kg/kmē in the sub-region M3a, 5.51 kg/kmē in the sub-region M3b, 9.09 kg/kmē in the Sicilian Strait. Yields less than 2 kg/kmē were observed in the other strata. Specimens having length between 3.5 and 18.5 cm were found.
Depth distribution of Loligo vulgaris was not homogeneous in the three areas. In the sub-region M3a it was fished in strata A and C with yields not exceeding 1.13 kg/kmē. Most of the catch in this area, was represented by very small specimens (mean lenght=3.8 cm). In the sub-region M3b the species was found in strata A (6.33 kg/kmē) and D (1.92 kg/kmē). Finally in the Sicilian Strait Loligo vulgaris was caught in strata A and B with yields of 6.82 and 5.60 kg/kmē respectively. Specimen size ranged from 1 to 19.5 cm.
Found at depths less than 500 m, Octopus vulgaris was abundantly caught in the first two strata where the following yields were obtained: 24.32 and 5 kg/kmē in the sub-region M3a, 11.8 and 20.69 kg/kmē in the sub-region M3b, 12.96 and 25.72 kg/kmē in the Sicilian Strait. Length ranged from 3 to 19 cm.
No specimen of Sepia officinalis was caught in the sub-region M3a of the South Tyrrhenian Sea. The highest abundance indices (1.13 and 6.40 kg/kmē) were observed in the first two strata of the Sicilian Strait whereas yields of about 1 kg/kmē were found in the sub-region M3b. Length ranged from 7 to 17.5 cm with a mean value of about 11 cm.
If Trachurus spp. is excluded, Merluccius merluccius, Mullus barbatus and Spicara flexuosa were the most abundant species in the whole area. High catches of Mullus surmuletus were obtained in strata B and C of the Strait of Sicily (27.50 and 12.50 kg/kmē respectively) whereas they were negligible in the South Tyrrhenian Sea. Yields around 20 kg/kmē were also observed in some strata of the Sicilian Strait for Zeus faber and Raja clavata (absent in the sub-region M3b and rare in the sub-region M3a). In the sub-region M3b of the South Tyrrhenian Sea very high catches were obtained for Pagellus erythrinus (65.83 and 71.43 kg/kmē) at depths between 10 and 100 m, for Pagellus bogaraveo (32.72 kg/kmē) in stratum 50-100 m and for Pagellus acarne (from 12.32 to 88.30 kg/kmē) at depths below 500 m. Pagellus spp. were not so important species in the other sub-regions. A yield above 10 kg/kmē was also observed in the sub-region M3b for Trisopterus minutus capelanus (16.36 kg/kmē at 50-100 m). In the sub-region M3a, besides the species mentioned at the beginning, abundance indices above 10 kg/kmē were observed for Lophius piscatorius (43.18 kg/kmē at 100-200 m), Pagellus acarne (10.31 kg/kmē in the shallow water) and Phycis blennoides (11.07 kg/kmē at 200-500 m).
The remaining fish species presented yields below 10 kg/kmē in each stratum of the whole area.
Aristaeomorpha foliacea, present in the deepest stratum, was the only crustaceans species which occurred with high yields in the whole area: 26.86 kg/kmē in the sub-region M3a, 23.14 kg/kmē in the sub-region M3b and 16.67 kg/kmē in the Sicilian Strait. High abundance indices were also observed, in the Sicilian Strait, for Parapenaeus longirostris (13.10 and 15.81 kg/kmē in the third and fourth strata respectively) whereas it did not exceed the yield of 8.30 kg/kmē in the sub-region M3b and 4.67 kg/kmē in the sub-region M3a. Yields of Aristeus antennatus ranged from 1.02 kg/kmē in the Sicilian Strait to 10.17 kg/kmē in the South Tyrrhenian Sea. Finally, Nephrops norvegicus was more abundant in the Strait of Sicily where nevertheless it did not exceed the yield of 4.10 kg/kmē.
Among Cephalopods, Octopus vulgaris was the most abundant species (in weight) in the whole area with yields ranging from 5.00 to 25.72 kg/kmē in the first two strata. High abundance indices, both in weight and number, of Illex coindetii were obtained at depth between 100 and 200 m in the three sub-regions. Eledone moschata was particularly abundant in the first two strata of the Sicilian Strait (10.76 and 21.32 kg/kmē respectively) as well as in the stratum 100-200 m of the sub-region M3b. On the contrary, Eledone cirrhosa was more abundant in the sub-region M3a with yields ranging from 3.59 to 6.56 kg/kmē. Loligo vulgaris was mainly fished at depth below 50 m in the South Tyrrhenian Sea (1.13 and 6.33 kg/kmē) and between 10 and 100 m in the Strait of Sicily (6.82 and 5.60 kg/kmē). Finally, Sepia officinalis occurred with a maximum yield of 6.40 kg/kmē in the second stratum of the Sicilian Strait whereas it was rare in the sub-region M3b and absent in the sub-region M3a.
A total of 18 species, among those of the reference list, was found in this stratum; crustaceans were absent while 12 fish species and 6 cephalopods were caught.
|
M3a |
M3b |
M3c |
||||
|
SPECIES |
kg/kmē |
N°/kmē |
kg/kmē |
N°/kmē |
kg/kmē |
N°/kmē |
|
Mullus barbatus |
33.09 |
1050 |
44.26 |
1249 |
10.14 |
299 |
|
Pagellus acarne |
10.31 |
370 |
88.30 |
1076 |
0.56 |
6 |
|
Spicara flexuosa |
14.77 |
1257 |
23.02 |
875 |
19.21 |
1853 |
|
Trachurus mediterraneus |
31.45 |
1573 |
0.58 |
52 |
55.26 |
2158 |
|
Octopus vulgaris |
24.32 |
16 |
11.80 |
40 |
12.96 |
68 |
Catches were not homogeneous among sub-regions in this stratum. The most abundant species in the whole area were Mullus barbatus, Spicara flexuosa, and Octopus vulgaris. Important yields of Pagellus acarne, Pagellus erythrinus, and Trachurus trachurus were obtained in the South Tyrrhenian Sea, especially in the sub-region M3b, whereas they were negligible in the Sicilian Strait. High abundance indices were also observed for other species in the different sub-regions: Merluccius merluccius (33.19 kg/kmē) and Trachurus mediterraneus (31.45 kg/kmē) in the sub-region M3a; Trachurus mediterraneus (55.26 kg/kmē), Eledone moschata (10.76 kg/kmē) and Merluccius merluccius (7.04 kg/kmē) in the Strait of Sicily. Among cephalopods, also Loligo vulgaris was present in this stratum with yields of 6.33 and 6.82 kg/kmē in the sub-regions M3b and M3c respectively. Catches were negligible for the remaining species.
23 of the 31 target species were fished in this depth range: 17 fishes, 1 crustacean and 6 cephalopods.
|
M3a |
M3b |
M3c |
||||
|
SPECIES |
kg/kmē |
N°/kmē |
kg/kmē |
N°/kmē |
kg/kmē |
N°/kmē |
|
Merluccius merluccius |
36.70 |
2548 |
15.27 |
169 |
34.97 |
429 |
|
Mullus barbatus |
6.41 |
193 |
112.32 |
4564 |
9.67 |
265 |
|
Spicara flexuosa |
24.78 |
1641 |
155.40 |
5458 |
113.51 |
4328 |
|
Pagellus erythrinus |
6.81 |
93 |
71.43 |
649 |
8.18 |
93 |
|
Trachurus trachurus |
5.04 |
552 |
21.81 |
1570 |
13.14 |
514 |
Merluccius merluccius, Mullus barbatus, Spicara flexuosa, Pagellus erythrinus and Trachurus trachurus were the most abundant species in this stratum as regards the whole region. However, three other species were abundantly caught in the whole area: they were Trachurus mediterraneus (3.89-27.81 kg/kmē), Octopus vulgaris (5.00-25.72) and Trisopterus minutus capelanus (3.44-16.36). Instead, very different catches were observed for the remaining species in the various sub-regions. High yields were obtained for: Pagellus acarne (12.32 kg/kmē), Pagellus bogaraveo (32.72 kg/kmē), and Eledone moschata (10.91 kg/kmē) in the sub-region M3b; Mullus surmuletus (27.50 kg/kmē), Eledone moschata (21.32 kg/kmē) Raja clavata (21.05 kg/kmē) and Zeus faber (22.61 kg/kmē) in the sub-region M3c.
A total of 26 different target species were fished in this stratum: there were 20 fishes, 1 crustacean and 5 cephalopods.
|
M3a |
M3b |
M3c |
||||
|
SPECIES |
kg/kmē |
N°/kmē |
kg/kmē |
N°/kmē |
kg/kmē |
N°/kmē |
|
Merluccius merluccius |
46.59 |
4572 |
28.96 |
1563 |
32.65 |
1915 |
|
Spicara flexuosa |
2.45 |
72 |
17.62 |
450 |
38.30 |
2880 |
|
Trachurus trachurus |
3.88 |
538 |
10.12 |
153 |
107.86 |
3592 |
|
Parapenaeus longirostris |
4.67 |
1353 |
8.30 |
2205 |
13.10 |
3642 |
|
Illex coindetii |
12.40 |
635 |
5.51 |
310 |
9.09 |
186 |
Three fishes (Merluccius merluccius, Spicara flexuosa, Trachurus trachurus), 1 crustacean (Parapenaeus longirostris) and 1 cephalopod (Illex coindetii) were the most abundant species in this stratum if the whole area is considered. Other important catches were: Lophius piscatorius (43.18 kg/kmē, due to the presence of large specimens), Zeus faber (9.45 kg/kmē) and Eledone cirrhosa (6.56 kg/kmē) in the sub-region M3a; Mullus barbatus (10.40 kg/kmē) and Trachurus mediterraneus (9.87 kg/kmē) in the sub-region M3b; Mullus surmuletus (12.50 kg/kmē) and Raja clavata (19.56 kg/kmē) in the sub-region M3c.
24 of the 31 target species were found in this stratum: 16 fishes, 3 crustaceans and 5 cephalopods.
|
M3a |
M3b |
M3c |
||||
|
SPECIES |
kg/kmē |
N°/kmē |
kg/kmē |
N°/kmē |
kg/kmē |
N°/kmē |
|
Merluccius merluccius |
22.08 |
1117 |
15.56 |
553 |
26.65 |
815 |
|
Phycis blennoides |
11.07 |
443 |
5.39 |
339 |
4.93 |
183 |
|
Helicolenus dactylopterus |
4.40 |
250 |
2.10 |
63 |
6.32 |
120 |
|
Trachurus trachurus |
1.64 |
9 |
2.92 |
17 |
35.44 |
806 |
|
Parapenaeus longirostris |
2.51 |
205 |
7.70 |
818 |
15.81 |
2887 |
As in stratum C, Merluccius merluccius, Trachurus trachurus and Parapenaeus longirostris were among the five most abundant species. They showed the highest yields in the Sicilian Strait. Besides these species, Pagellus acarne (21.74 kg/kmē) was again abundant in the sub-region M3b. As far as crustaceans are concerned, Nephrops norvegicus was the other species caught in the whole area (2.56, 0.83 and 4.10 kg/kmē in the sub-regions M3a, M3b and M3c respectively) whereas Aristaeomorpha foliacea (1.51 kg/kmē) was fished in the sub-region M3a only. Finally, yields of Eledone cirrhosa (2.41-4.73 kg/kmē) were rather homogenous among the sub-regions.
The lowest proportion of target species was caught in this stratum: there were 11 fishes, 4 crustaceans and 1 cephalopod.
|
M3a |
M3b |
M3c |
||||
|
SPECIES |
kg/kmē |
N°/kmē |
kg/kmē |
N°/kmē |
kg/kmē |
N°/kmē |
|
Helicolenus dactylopterus |
1.20 |
15 |
1.04 |
10 |
6.81 |
35 |
|
Phycis blennoides |
8.48 |
125 |
5.42 |
134 |
5.69 |
42 |
|
Aristeus antennatus |
3.44 |
138 |
10.17 |
1276 |
1.02 |
36 |
|
Aristaeomorpha foliacea |
26.86 |
3154 |
23.14 |
2223 |
16.67 |
690 |
|
Nephrops norvegicus |
1.87 |
48 |
0.33 |
6 |
1.74 |
48 |
Three crustaceans (Aristeus antennatus, Aristaeomorpha foliacea, Nephrops norvegicus) and two fishes (Phycis blennoides, Helicolenus dactylopterus) were among the most abundant species in the deepest stratum. Catches were rather low with the exception of Aristaeomorpha foliacea, abundant in the whole area. Cephalopods did not occur in this stratum excepting a negligible catch of Eledone cirrhosa (0.12 kg/kmē) in the sub-region M3a.
An analysis of the Medits 97 survey results essentially confirms the spatial distribution of the species, both in depth and among zones, observed in the 1996 survey. However, no comparison can be done between the overall biomass indices in the two years since in no case the increases or decreases of species abundance reflect a general trend in the whole area. Rather they can be explained by abundance variations in specific areas. Moreover, it can also happen that steady overall indices hide important differences occurring at a sub-regional level.
In the following, the most important cases are described for each sub-region.
Sub-region M3a: a considerable increase of biomass was observed in 1997 for Lophius piscatorius, Merluccius merluccius, Spicara flexuosa, Trachurus mediterraneus and Aristaeomorpha foliacea. An abundance increase was also recorded for Pagellus acarne, Phycis blennoides, Aristeus antennatus and Parapenaeus longirostris, whereas a remarkable decrease was found for Trachurus trachurus .
Sub-region M3b: several important differences were observed in this sub-region between the two years. In particular, remarkable abundance increases were observed in 1997 for Lophius budegassa, Pagellus acarne, Trachurus mediterraneus, Aristeus antennatus and Aristaeomorpha foliacea. Higher catches were also recorded for Lophius piscatorius, Trisopterus minutus capelanus and Parapenaeus longirostris whereas a decrease of abundance was detected for Trachurus trachurus and Eledone cirrhosa. Finally, important increases or decreases of biomass, depending on the strata, were observed for the following species: Merluccius merluccius, Mullus barbatus, Pagellus erythrinus and Spicara flexuosa.
Sub-region M3c: in the Sicilian Strait the differences between the two years were less important than in the South Tyrrhenian Sea. In 1997, the yields generally increased for Merluccius merluccius and Trachurus mediterraneus whereas they decreased for Phycis blennoides, Nephrops norvegicus and Parapenaeus longirostris. The abundance variation was depending on the strata for Mullus barbatus, Mullus surmuletus, Spicara flexuosa, Trachurus trachurus and Illex coindetii.