Survey Results for Italy - area M1 - Ligurian and Tyrrhenian Seas
Below is a report on the abundance indices and size distribution data obtained during the Medits '97 - M1 Region - trawl survey. It deals with the Ligurian Sea (strata 13201 -13205), the northern Tyrrhenian Sea (strata 13206 - 13210), the central Tyrrhenian Sea (strata 13211 - 13215) and the southern Tyrrhenian Sea (strata 13216 - 13220).
In the M1 region the 1997 Medits survey was carried out from June 3 to July 31 using the professional trawler "Francesco Padre". A total of 153 hauls were carried out.
A total of 221 animal species were identified, 145 of fishes, 29 of Cephalopods and 47 of Crustaceans, and a lot of non commercial species.
The species which were most abundant in the hauls during the Medits '97 trawl survey of the M1 zone were, in order of numerical abundance, Merluccius merluccius (mean value 3.366 Ind/kmē over the whole area), Trachurus trachurus (mean value 1.616 Ind/kmē), Trisopterus minutus (mean value 360 Ind/kmē), Mullus barbatus (mean value 330 Ind/kmē), Loligo vulgaris (mean value 269 Ind/kmē) and Trachurus mediterraneus (mean value 222 Ind/kmē).
From the point of view of biomass, the most significant species in the M1 area is M. merluccius (mean value 37.7 kg/kmē over the whole area), followed by Eledone cirrhosa (mean value 11.3 kg/kmē), Mullus barbatus (mean value 11.9 kg/kmē), Trachurus mediterraneus (mean value 7.7 kg/kmē) and T. trachurus (mean value 6.9 kg/kmē).
Species as Eutrigla gurnardus, Solea vulgaris and Sepia officinalis exhibit very low abundance indices in the area.
In the Ligurian Sea the most abundant species of the reference list were Merluccius merluccius, Mullus barbatus, Eledone cirrhosa. Trachurus trachurus, Phycis blennoides, Pagellus erythrinus, Spicara flexuosa, Eledone cirrhosa, Loligo vulgaris.
In the Northern Tyrrhenian Sea the most abundant species of the reference list were Merluccius merluccius, Mullus barbatus, Trachurus mediterraneus, Eledone cirrhosa, Lophius budegassa, Pagellus erythrinus, Nephrops norvegicus, Phycis blennoides, Trachurus trachurus.
In the Central Tyrrhenian Sea the highest abundances were recorder for Merluccius merluccius, Mullus barbatus, Eledone cirrhosa, Octopus vulgaris, Trachurus mediterraneus, Trachurus trachurus, Spicara flexuosa, Trisopterus minutus capelanus, Nephrops norvegicus.
In the Central Tyrrhenian Sea the highest abundances were recorder for Merluccius merluccius, Octopus vulgaris, Eledone cirrhosa, Mullus barbatus, Phycis blennoides, Trisopterus capelanus, Illex coindetii, Aristaeomorpha foliacea.
It must be pointed out that the catches of these species were made up largely of young fish.
As far as crustaceans are concerned, the mean biomass values were highest for Nephrops norvegicus (mean value 4.3 kg/kmē), followed by Aristaeomorpha foliacea (mean value 1.6 kg/kmē), Aristeus antennatus (mean value 1.2 kg/kmē) and Parapenaeus longirostris (mean value 0.89 kg/kmē).
There were also relevant catches of species which were not being targeted by the trawl survey, such as Plesionika martia and P. edwardsii.
As far as cephalopods are concerned, the mean biomass values were highest for Eledone cirrhosa (mean value 11.3 kg/kmē), followed by Octopus vulgaris (mean value 4.9 kg/kmē), Illex coindetii (mean value 2.3 kg/kmē), Loligo vulgaris (mean value 1.5 kg/kmē), Eledone moschata (mean value 0.7 kg/kmē) and Sepia officinalis (mean value 0.1 kg/kmē).
Among the species which were not being targeted by the trawl survey but which were present, we can mention Loligo forbesi, Pteroctopus tetracirrhus and Octopus salutii.
The areas with the most abundant biomass inside the M1 region were the central and northern Tyrrhenian Sea in the upper strata (10-200 m) while in the deeper strata (200 - 800 m) abundant biomass values were also in the Ligurian Sea and Southern Tyrrhenian Sea.
Below is a report on the data obtained for the reference list species.
Citharus linguatula occurred relatively commonly in the central and southern Tyrrhenian Sea between 10 and 50 m (1.9 kg/kmē) and between 50 and 100 m (1.6 kg/kmē). Mean biomass values for the M1 region were very low (0.32 kg/kmē).
This species was caught mainly in the 100-200 m stratum. Biomass values in the region were low (0.16 kg/kmē) and 2.08 kg/kmē in the northern Tyrrhenian Sea were the highest values. Absent from the Ligurian Sea and the southern Tyrrhenian Sea.
Helicolenus dactylopterus was present from 100 to 800 m and more abundant between 500 - 800 m. H. dactylopterus had high biomass in the northern Tyrrhenian Sea (12.67 kg/kmē) and Ligurian Sea (17.18 kg/kmē), but also in the southern Tyrrhenian Sea between 200 and 500 m (2.07 kg/kmē). The lengths ranged from 3 to 28 cm with 3 or 4 distinct cohorts.
More abundant in the strata 200 - 500 m in the northern Tyrrhenian (3.59 kg/kmē) and the Ligurian Sea (2.99 kg/kmē). It was found also abundant in the 500-800 m stratum in the northern Tyrrhenian Sea (1.75 kg/kmē). The lengths ranged from 5 to 35 cm with 3 or 4 distinct cohorts.
Lophius budegassa was relatively abundant between 100 and 500 m particularly in the northern Tyrrhenian Sea (up to 23.64 kg/kmē). Important catches of this species in the 10-50 stratum in the Ligurian Sea (6.03 kg/kmē). The lengths ranged from 4 to 62 cm.
Almost absent in the Ligurian Sea, Lophius piscatorius was abundant between 500 and 800 m in the northern Tyrrhenian Sea (up to 13.32 kg/kmē) and in the central Tyrrhenian Sea (16.15 kg/kmē).
The lengths ranged from 30 to 83 cm.
M. merluccius was caught in larger numbers between 100 and 200 m in the Central Tyrrhenian (18.720 Ind/kmē) and in the southern Tyrrhenian Sea (6.215 Ind/kmē) and between 200 and 500 m in the central Tyrrhenian Sea (7.377 Ind/kmē). From the biomass point of view Hake was more abundant in the central Tyrrhenian Sea between 100 and 200 m (146.8 kg/kmē) and between 200 and 500 m (58.3 kg/kmē) but high values are for all the areas. Mean biomass values for the M1 region of 37.6 kg/kmē was given by this species.
M. merluccius had a length frequency distribution which was homogeneous over the whole region. The greatest proportion (between 40 and 90%) of the specimens present in the hauls was up to 20-22 cm in length over the whole area. Specimens exceeding 30 cm length were present below 200 m. The biggest measured individual was of 74 cm.
M. poutassou was relatively abundant between 200 and 500 m in the northern Tyrrhenian Sea (205 Ind/kmē) and in the Ligurian Sea (87 Ind/kmē). M. poutassou gave high biomass values in the northern Tyrrhenian Sea (14.2 kg/kmē between 200 and 500 m). Mean biomass values for the M1 region of 1.86 kg/kmē was obtained for this species.
The length frequency of this species was distributed according to depth, with smaller individuals found between 100 and 200 m and adults found below 200 m. The lengths ranged from 7 to 38 cm. Juveniles were caught mainly in the northern and central Tyrrhenian Sea.
Mullus barbatus was particularly abundant between 10 and 50 m in the central (132.8 kg/kmē) and northern Tyrrhenian Sea (43.1 kg/kmē) and between 50 and 100 m in the Ligurian Sea (60.7 kg/kmē). The mean biomass value for this species in the M1 region was 11.9 kg/kmē.
At the time of the survey there were no young specimens of M. barbatus in the M1 region. The normal sizes for fish of this species in the hauls were between 10 and 27 cm with almost two distinct cohorts.
Mullus surmuletus was caught in limited numbers between 10 and 100 m with a relatively high abundance in the central-northern areas of the Tyrrhenian Sea (up to 3.08 kg/kmē) and in the Ligurian Sea (2.12 kg/kmē) at depth of 100 - 200 m.
Juveniles were caught in the Ligurian Sea, northern and southern Tyrrhenian Sea.
Was very abundant in some hauls between 10 and 50 m in the Ligurian Sea (1.487 Ind/kmē and 31.45 kg/kmē). Very low the biomass in the other areas, occurring principally in the central and northern Tyrrhenian Sea. Mean biomass values for the M1 region of 1.54 kg/kmē was given by this species. The smallest individuals (6-15 cm) are located between 10 and 50 m mainly in the Ligurian Sea, but also in the northern and central Tyrrhenian Sea.
There were significant numbers of juveniles of Pagellus erythrinus at depths between 10 and 50 m in the southern Tyrrhenian (2.371 Ind/kmē). The species was caught at depth from 10 m to 200 m. The mean biomass value in the area was 3.61 kg/kmē.
Young specimens (2-20 cm) of P. erythrinus occurred at 10-50 m mainly in the central Tyrrhenian Sea. Total Lengths seam to increase according to depth.
Was common in the northern Tyrrhenian at depths between 100 and 200 m (8.29 kg/kmē) and 200 and 500 m (13.01 kg/kmē), in the Ligurian Sea (3.03 kg/kmē) and with a large number of juveniles in the northern Tyrrhenian Sea at depths between 10 and 50 m (150 Ind/kmē). Large specimens (40 - 46 cm) of P. bogaraveo were found at depths between 200 and 500 m in the northern Tyrrhenian Sea.
Phycis blennoides was abundant between 200 and 500 m in the southern Tyrrhenian Sea (10.06 kg/kmē), in the Ligurian Sea (15.7 kg/kmē) and between 500 and 800 m in the northern Tyrrhenian Sea (20.8 kg/kmē) and in the Ligurian Sea (18.75 kg/kmē). The mean biomass value for this species in the M1 region was 5.26 kg/kmē.
P. blennoides was also found in three and more distinct cohorts, which were distributed according to the depth in all the zones. The lengths ranged from 4 to 56 cm.
Raja clavata was present in significant numbers only in the northern Tyrrhenian Sea between 50 and 200 m (up to 33.8 kg/kmē). A mean biomass value of 4.97 kg/kmē (4 Ind/kmē) was found for the whole M1 region. Absent from the hauls made on the Ligurian Sea and southern Tyrrhenian Sea. The lengths ranged from 16 to 93 cm.
Solea vulgaris was found principally in the central Tyrrhenian Sea between 10 and 50 m (2.42 kg/kmē). A mean biomass value of 0.18 kg/kmē was found for the M1 region. Absent from the hauls made in the Ligurian Sea and in the southern Tyrrhenian Sea.
Occurred between 10 and 200 m, more commonly in the central Tyrrhenian Sea (between 10 and 50 m) and the Ligurian Sea (between 50 and 100 m), less so in other Tyrrhenian areas (between 10 and 100 m). A mean biomass value of 2.50 kg/kmē (170 Ind/kmē) was found for the M1 region.
The lengths ranged from 4 to 18 cm. Juveniles were caught mainly in the central and southern Tyrrhenian Sea.
Common in the northern (101.26 kg/kmē) and central Tyrrhenian Sea (87.53 kg/kmē) between 10 and 50 m but also between 50 and 100 m. A mean biomass value of 7.75 kg/kmē (222 Ind/kmē) was found for the M1 region.
The lengths ranged from 5 to 43 cm. Several distinct cohorts (with an important cohort of juveniles) were found in the central Tyrrhenian Sea.
T. trachurus gave high biomass values between 10 and 100 m (up to 25.62 kg/kmē in the Ligurian Sea) and in the 100-200 stratum in the central Tyrrhenian Sea (39.64 kg/kmē). High number of juveniles were caught mainly in the central Tyrrhenian Sea (16.352 Ind/kmē) between 100 and 200 m. The juveniles were dominant also in the catch of the shallowest strata in the Ligurian Sea and north Tyrrhenian Sea. A mean biomass value of 6.92 kg/kmē (1.616 Ind/kmē) was found for the M1 region.
Nearly absent in the Ligurian Sea, this species was found in the central Tyrrhenian Sea (23.94 kg/kmē between 100 and 200 m) and in the southern Tyrrhenian Sea (13.0 kg/kmē between 100 and 200 m). Also from the numerical abundance point of view T. minutus was more abundant between 100 and 200 m in the southern Tyrrhenian (1374 Ind/kmē) and in the central Tyrrhenian Sea (1614 Ind/kmē).
T. minutus was found in at least 2 distinct cohorts (the first one between 2 and 10 cm TL).
Occurred mainly between 100 and 200 m in the northern Tyrrhenian Sea (17.4 kg/kmē) and in the southern Tyrrhenian Sea (9.23 kg/kmē).
The lengths ranged from 2 to 49 cm.
A. antennatus was slightly less common than Aristaeomorpha foliacea. Caught in good numbers in depths more than 500 m only in the Ligurian Sea (13.4 kg/kmē) and in the southern Tyrrhenian Sea (5.31 kg/kmē). A mean biomass value of 1.19 kg/kmē (54 Ind/kmē) was found for the M1 region. The lengths ranged from 17 to 62 mm. The catches are mainly made of adult females, but this year several juveniles were caught.
Absent from the Ligurian Sea, more abundant in the central-southern Tyrrhenian Sea (respectively 10.2 and 11.9 kg/kmē). A mean biomass value of 1.65 kg/kmē (66 Ind/kmē) was found for the M1 region.
The lengths ranged from 20 to 69 mm; three or four distinct cohorts were evident. Also for this species, the catches are mainly made of adult female, but this year several juveniles were caught.
As far as crustaceans are concerned, one of the species which was present with a relatively high biomass was N. norvegicus (4.33 kg/kmē over the whole area and up to 18.2 kg/kmē in the northern Tyrrhenian Sea). This species was caught in the central and northern Tyrrhenian Sea and in the Ligurian Sea but it was less common in the southern Tyrrhenian Sea.
The lengths ranged from 14 to 61 mm.
A very low mean biomass value of 0.89 kg/kmē (138 Ind/kmē) was found for the whole M1 region. The species was fished in depths between 100 and 500 m. The specimens were mainly caught in the southern (2.5 kg/kmē) and central Tyrrhenian Sea (2.2 kg/kmē). The lengths ranged from 6 to 41 mm.
The species of cephalopod which occurred with the highest biomass was E. cirrhosa. It was particularly common in depths up to 500 m (29.51 kg/kmē) between 200 and 500 m in the northern Tyrrhenian Sea (27.6 kg/kmē) and between 100 and 200 m in the central Tyrrhenian Sea.
A mean biomass value of 11.27 kg/kmē was found for the M1 region.
The population of E. cirrhosa was set up with two cohorts (1-6 cm and 6-17 cm).
Absent from the Ligurian Sea, a very low mean biomass value of 0.72 kg/kmē was found for the whole M1 region. Caught at depths between 10 and 200 m, this species was found mainly in the central and southern Tyrrhenian Sea.
The mean biomass value of 2.31 kg/kmē was found for the region M1. Fished at depths between 50 and 200 m, this species was found mainly in the Ligurian Sea.
Lengths ranged from 1 to 19 cm with almost 3 distinct cohorts. Juveniles were found mainly between 50 and 100 m.
Found in relatively greater numbers in the Ligurian Sea between 10 - 50 m (35.67 kg/kmē). Small specimens less than 10 cm length were found mainly in the Ligurian and northern Tyrrhenian Sea at depths between 10 and 50 m.
O. vulgaris (4.95 kg/kmē in the whole M1 region) was found at depths down to 200 m and was more common in the central-southern Tyrrhenian Sea between 10 and 50 m (up to 51.28 kg/kmē) and between 50 and 100 m in the central Tyrrhenian Sea (10.6 kg/kmē). Lengths ranged from 2 to 16 cm.
Biomass of Sepia officinalis was low and relatively more common in the central and northern Tyrrhenian Sea in depths less than 50 m (biomass up to 3.56 kg/kmē). This species was absent from the waters of the southern Tyrrhenian and Ligurian Sea. The mean biomass value of 0.10 kg/kmē was found for the whole M1 region.
The coastal species Sardina pilchardus (17.7 kg/kmē), Engraulis encrasicolus (9.2 kg/kmē), Diplodus annularis (9.1 kg/kmē) and the deeper species Galeus melastomus (17.6 kg/kmē), Glossanodon leioglossus (3.7 kg/kmē) and Gadiculus argenteus (4.9 kg/kmē) were the more common species between those not present in the reference list.
Sardina pilchardus was very abundant in the Ligurian Sea (140 kg/kmē) between 50 and 100 m and in the Northern Tyrrhenian Sea (135 kg/kmē) between 10 and 50 m.
Engraulis encrasicolus was very abundant in the Ligurian Sea between 50 and 100 m (576 kg/kmē) and between 100 and 200 m (15 kg/kmē).
Galeus melastomus was very abundant in the northern Tyrrhenian Sea, with biomass up to 100 kg/kmē between 500 and 800 m.
Gadiculus argenteus was abundant in the Ligurian Sea (26 kg/kmē) and in the northern Tyrrhenian Sea (34 kg/kmē) between 200 and 500 m.
Biomass of Diplodus annularis were high between 10 and 50 m in the Ligurian Sea (250 kg/kmē) and central Tyrrhenian Sea (65 kg/kmē).
A total of 41 of the 43 Medits reference list species were collected. The most abundant species was Merluccius merluccius in all the depths. In the 10 - 200 m stratum the most abundant species were three non target species: Sardina pilchardus, Diplodus annularis and Engraulis encrasicolus. In the 200 - 500 m stratum Galeus melastomus, Phycis blennoides and Gadiculus argenteus were abundant.
With regard to the number of individuals, Merluccius merluccius was the most important species mainly due to the large number of juveniles. In the 10 - 200 m stratum important catches were for Trachurus trachurus, with important number of juveniles, and for not target species as S. pilchardus, E. encrasicolus, Macroramphosus scolopax and Glossanodon leioglossus. In the 200-500 m stratum important number of M. merluccius, G. argenteus, Chlorophtalmus agassizi, G. melanostomus and juveniles of Phycis blennoides.
All the 6 target species of crustaceans were collected. The highest catches were observed for Nephrops norvegicus, Aristaeomorpha foliacea and Aristeus antennatus. In some areas the indices of abundance of Plesionika spp. and Palinurus mauritanicus were interesting.
In number of individuals, the most abundant species were Plesionika martia, P. edwardsii and N. norvegicus.
All the 7 cephalopods species of the Medits list were fished. The highest biomass values were calculated for Eledone cirrhosa, Octopus vulgaris and Illex coindetii, but also Todaropsis eblanae shown interesting biomass.
In the 10-200 m stratum the species with the highest biomass indices were Merluccius merluccius, Mullus barbatus, Sardina pilchardus, Diplodus annularis, Trachurus mediterraneus and Engraulis encrasicolus among the fishes, Octopus vulgaris and Eledone cirrosa among the cephalopods and Parapenaeus longirostris among the crustaceans.
In the 200-800 m stratum the species with the highest biomass indices were Galeus melanostomus, Merluccius merluccius, Gadiculus argenteus, Phycis blennoides, Conger conger, Helicolenus dactylopterus and Lophius piscatorius among the fishes, Eledone cirrhosa and Todaropsis eblanae among the cephalopods and Nephrops norvegicus, Aristaeomorpha foliacea and Plesionika edwardsii among the crustaceans.
Important nurseries areas have been identified in the Ligurian Sea (for L. budegassa, M. barbatus, P. acarne, T. trachurus, A. antennatus, E. cirrhosa, I. coindetii, L. vulgaris), in the Northern Tyrrhenian Sea (for H. dactylopterus, L. vulgaris, T. trachurus), in the Central Tyrrhenian Sea (for M. merluccius, P. blennoides, S. flexuosa, T. trachurus, T. capelanus) and in the Southern Tyrrhenian Sea (for H. dactylopterus, P. erythrinus, P. blennoides, T. capelanus, P. longirostris).
In this stratum the catches were made by a significant quantity of juveniles of 5 - 6 species, some of them with low economic value.
The most abundant species in weight in this stratum are Mullus barbatus, Trachurus mediterraneus, Octopus vulgaris, Pagellus erythrinus and Spicara flexuosa.
M. barbatus, S. flexuosa and O. vulgaris show a higher biomass in the central Tyrrhenian Sea, P. erythrinus in the Ligurian Sea, T. mediterraneus in the northern Tyrrhenian Sea. The most important species in number are Loligo vulgaris (juveniles abundant in the Ligurian Sea), Mullus barbatus (mainly in the central Tyrrhenian Sea), Trachurus mediterraneus (juveniles mainly in the central Tyrrhenian Sea), Spicara flexuosa (mainly in the central Tyrrhenian Sea), Trachurus trachurus (abundant in the northern Tyrrhenian Sea) and Pagellus erythrinus (abundant in the southern Tyrrhenian Sea).
|
10 - 50 m |
Ligurian S. |
North T. S. |
Central T. S. |
South T. S. |
||||||
|
Species |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
||
|
Trachurus mediterraneus |
7.7 |
121 |
101.3 |
2889 |
87.5 |
3212 |
10.9 |
71 |
||
|
Mullus barbatus |
17.6 |
563 |
43.1 |
1447 |
132.8 |
4199 |
8.2 |
180 |
||
|
Pagellus erythrinus |
31.2 |
1105 |
27.1 |
795 |
29.0 |
683 |
8.2 |
2371 |
||
|
Octopus vulgaris |
3.9 |
20 |
0.7 |
11 |
51.3 |
104 |
46.9 |
110 |
||
|
Pagellus acarne |
31.5 |
1487 |
11.5 |
679 |
7.5 |
138 |
2.7 |
81 |
||
In this stratum the most abundant species are Merluccius merluccius (particularly abundant in the northern Tyrrhenian Sea), Mullus barbatus (abundant in the Ligurian Sea), Trachurus trachurus (in the Ligurian Sea), Eledone cirrhosa (abundant in the Ligurian Sea) and Spicara flexuosa (abundant in the Ligurian Sea). Large quantities in number are for Trachurus trachurus (in the central Tyrrhenian Sea), Merluccius merluccius (mainly in the Ligurian Sea), Loligo vulgaris (abundant in the Ligurian Sea), Illex coindetii (abundant in the Ligurian Sea) and Mullus barbatus (abundant in the Ligurian Sea). A lot of animals in the Ligurian Sea and in the central Tyrrhenian Sea are juveniles.
|
50 - 100 m |
Ligurian S. |
North T. S. |
Central T. S. |
South T. S. |
||||
|
Species |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
|
Merluccius merluccius |
30.39 |
1013 |
37.38 |
830 |
33.12 |
1684 |
16.91 |
471 |
|
Mullus barbatus |
60.69 |
1560 |
28.73 |
858 |
1.68 |
46 |
0.88 |
25 |
|
Trachurus trachurus |
18.85 |
3272 |
5.02 |
1303 |
14.93 |
5135 |
2.25 |
123 |
|
Spicara flexuosa |
8.20 |
281 |
8.10 |
435 |
2.18 |
69 |
7.24 |
366 |
|
Eledone cirrhosa |
11.01 |
217 |
8.58 |
64 |
10.71 |
36 |
2.43 |
60 |
In this stratum the most abundant species in biomass are Merluccius merluccius, Eledone cirrosa and Trachurus trachurus (mainly in the central Tyrrhenian Sea). Then we find Mullus barbatus and Raja clavata (abundant in the northern Tyrrhenian Sea).
The most important species in number are Merluccius merluccius (mainly in the central Tyrrhenian Sea), Trachurus trachurus (particularly abundant in the central Tyrrhenian Sea), Trisopterus minutus (mainly in the central Tyrrhenian Sea), Illex coindetii (mainly in the Ligurian Sea), Parapenaeus longirostris (abundant in the southern Tyrrhenian Sea). In this stratum too, the large numbers of animals are juveniles.
|
100 - 200 m |
Ligurian S. |
North T. S. |
Central T. S. |
South T. S. |
||||||
|
Species |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
||
|
Merluccius merluccius |
26.2 |
1442 |
71.1 |
3286 |
146.8 |
18720 |
58.4 |
6215 |
||
|
Eledone cirrhosa |
22.0 |
406 |
27.1 |
349 |
27.6 |
146 |
6.7 |
94 |
||
|
Trachurus trachurus |
2.0 |
145 |
10.7 |
342 |
39.6 |
16352 |
2.6 |
330 |
||
|
Mullus barbatus |
1.5 |
24 |
31.5 |
721 |
9.2 |
165 |
9.4 |
202 |
||
|
Raja clavata |
0.0 |
0 |
33.8 |
20 |
15.5 |
8 |
0.0 |
0 |
||
The most abundant species in biomass in this stratum are Merluccius merluccius (abundant in the central Tyrrhenian Sea), Phycis blennoides (mainly in the southern Tyrrhenian Sea) and Nephrops norvegicus (abundant in the northern Tyrrhenian Sea). Then we have Lepidorhombus boscii (abundant in the Ligurian Sea) and Parapenaeus longirostris (mainly in the southern Tyrrhenian Sea)
Large quantities in number are of M. merluccius, Eledone cirrhosa, N. norvegicus, P. blennoides and Micromesistius poutassou.
|
200 - 500 m |
Ligurian S. |
North T. S. |
Central T. S. |
South T. S. |
||||
|
Species |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
|
Merluccius merluccius |
10.73 |
180 |
55.22 |
5123 |
58.30 |
7377 |
34.16 |
3546 |
|
Eledone cirrhosa |
14.68 |
87 |
29.51 |
171 |
24.89 |
141 |
11.06 |
61 |
|
Phycis blennoides |
15.67 |
438 |
8.31 |
263 |
7.98 |
409 |
10.06 |
479 |
|
Micromesistius poutassou |
9.34 |
87 |
14.24 |
205 |
3.52 |
33 |
0.84 |
7 |
|
Nephrops norvegicus |
8.56 |
239 |
18.20 |
471 |
12.55 |
336 |
4.91 |
147 |
In the deepest stratum, the most abundant species in biomass are Phycis blennoides (mainly in the northern Tyrrhenian Sea) and Helicolenus dactylopterus (in the Ligurian Sea). Then we have Nephrops norvegicus (mainly in the northern Tyrrhenian Sea), Lophius piscatorius (mainly in the central Tyrrhenian Sea), and Aristaeomorpha foliacea (mainly in the southern Tyrrhenian Sea).
The largest quantities in number were for P. blennoides (mainly in the northern Tyrrhenian Sea), A. antennatus, N. norvegicus, A. foliacea and H. dactylopterus.
|
500 - 800 m |
Ligurian S. |
North T. S. |
Central T. S. |
South T. S. |
||||||
|
Species |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
kg/kmē |
Ind/kmē |
||
|
Nephrops norvegicus |
9.75 |
298 |
14.40 |
355 |
9.94 |
281 |
2.29 |
68 |
||
|
Phycis blennoides |
18.75 |
322 |
20.80 |
390 |
5.55 |
203 |
8.65 |
300 |
||
|
Helicolenus dactylopterus |
17.18 |
203 |
12.67 |
150 |
8.87 |
64 |
2.41 |
18 |
||
|
Lophius piscatorius |
0.00 |
0 |
13.32 |
2 |
16.15 |
3 |
0.00 |
0 |
||
|
Aristaeomorpha foliacea |
0.00 |
0 |
0.70 |
19 |
10.24 |
357 |
11.97 |
540 |
||
As we told the last year, the results of these Medits surveys show spatial and temporal trends that seem to be well defined.
As far as the spatial distribution is concerned, some geographical areas, such the central and northern Tyrrhenian Sea, and some hauls in particular, show relatively high biomass indices during the four surveys.
With regard to the temporal trend, some species show steady abundance indices during the 1994-97 surveys (Lepidorhombus boscii, Mullus surmuletus, Pagellus bogaraveo, Helicolenus dactylopterus); other species show abundance indices strictly correlate with the catch of juveniles (Merluccius merluccius, Micromesistius poutassou, Pagellus acarne, P. erythrinus, Spicara flexuosa, Trachurus mediterraneus, T. trachurus, Trisopterus capelanus).
To get straight to the point, we can see how several species showed higher biomass indices during the Medits '94 - 96 surveys than during the '97 one: Citharus linguatula, Eutrigla gurnardus, Lophius piscatorius, Micromesistius poutassou, Pagellus erythrinus, Solea vulgaris, Spicara flexuosa, Trachurus trachurus, Eledone cirrhosa, Illex coindetii, Octopus vulgaris, Sepia officinalis. In particular some of these species show a very evident decrease of abundance indices: M. poutassou, S. flexuosa, T. mediterraneus, O. vulgaris.
Some species showed higher biomass indices during the Medits 97 survey than during the 1994-96 surveys: Merluccius merluccius, Pagellus acarne, Phycis blennoides, Raja clavata, Aristeus antennatus, Aristaeomorpha foliacea, Loligo vulgaris.
Other species show higher biomass indices during the '97 survey than during the 94-96 survey but with a less number of specimens: H. dactylopterus, L. boscii, M. merluccius, P. blennoides, N. norvegicus.
In the last survey report, we wrote that the densities variation (total number) of some species was mainly due to the number of juveniles caught in the region. This is confirmed for the 1997 survey. Some species show higher densities during the '97 survey than during the 94-96 surveys (in biomass) due to the higher number of juveniles caught (M. merluccius, P. acarne, L. vulgaris) but other species present a decrease of abundance indices during the '97 survey due to the less number of juveniles found (M. poutassou, P. bogaraveo, S. flexuosa, T. mediterraneus).
Some species show a less number of adult specimens during the '97 survey: P. bogaraveo, T. mediterraneus, Lophius piscatorius, Solea vulgaris, Zeus faber.
As we told about the '94-96 surveys, it is difficult to make out if the higher biomass of some species was due to an effective increase of the biomass of these species.
The situation is however complex: the same species shows different trends in mean biomass or number of individuals in different areas or depths. As a general trend, we can point out that the decrease of the biomass indices of some species was probably due to the lower catches of juveniles (Micromesistius poutassou and Spicara flexuosa) while for other species the increase (Aristaeomorpha foliacea, Aristeus antennatus, Nephrops norvegicus) or decrease (Raja clavata, Eledone cirrhosa, Illex coindetii, Loligo vulgaris) were probably caused by a real change of the abundance of the species.
In the Medits '97 survey, the areas of more abundance for some species and the areas of concentration of juveniles, already highlighted for the Medits '94 - '96 surveys, were pointed out.
Citharus linguatula: slight lower biomass indices during the past four years.
Helicolenus dactylopterus: constant biomass indices during the '94-'97 surveys.
Eutrigla gurnardus: decline of the biomass indices during the '94-'97 surveys.
Lepidorhombus boscii: nearly steady during the past three years.
Lophius budegassa: slight rise of biomass index during the past three years but a steady during the '97 survey.
Lophius piscatorius: decline in biomass indices during the past four years.
Merluccius merluccius: high biomass indices during the '94-'95 surveys because of great recruitments. During the '96 survey a less abundant catch of juveniles caused a lower biomass index. A slight rise of the biomass index during the '97 survey.
Micromesistius poutassou: high biomass indices during the '94-'95 surveys because of the great recruitments. During the '96 and '97 surveys a less abundant catch of juveniles caused lower biomass indices.
Mullus barbatus: rise of biomass index in the '96 and 97 survey than '95 and '96 survey.
Mullus surmuletus: nearly steady during the four surveys.
Pagellus acarne: slight rise of biomass index, and a higher number of juveniles, during the '97 survey respect the '94-'96 surveys.
Pagellus bogaraveo: a new decline of the catch of the bigger specimens.
Pagellus erythrinus: general decline of the biomass index during the '97 survey.
Phycis blennoides: from the '95 survey a slight rise of biomass indices.
Raja clavata: slight lower biomass indices during the past three years but a rise of biomass during the '97 survey.
Solea vulgaris: slight lower biomass indices during the four years
Spicara flexuosa: higher biomass index and higher number of juveniles in the '96 survey than '94-'95 surveys but a decline during the '97 survey.
Trachurus mediterraneus: constant lower biomass indices during the four years.
Trachurus trachurus: fall in biomass indices during the past three years but a slight rise of biomass in the '97 survey.
Trisopterus minutus capelanus: constant lower biomass indices during the four years because of a lower number of juveniles.
Zeus faber: lower biomass indices during the four years.
Aristeus antennatus: constant slight rise biomass indices during the four years.
Aristaeomorpha foliacea: constant rise of biomass indices during the four years.
Nephrops norvegicus: increase of biomass indices during the four years.
Parapenaeus longirostris: slight decline during the '94-'96 surveys but a slight rise in the biomass index during the '97 survey.
Eledone cirrhosa: slight decline during the four years.
Illex coindetii: in decline during the '94-'97 surveys.
Loligo vulgaris: decrease of the biomass indices during the '94-'97 surveys, but a slight increase during the '97 survey.
Octopus vulgaris: constant rise of biomass indices during the '94-'96 surveys but an evident decline during '97 surveys.
Sepia officinalis: constant decline of biomass indices.