Survey Results for Italy - area M2 - Sardinia
Results of a biological analysis of findings obtained in subregion M2 (Seas surrounding Sardinia, strata 13301-13335) during the Medits-IT 97 trawl survey are reported below. Length frequency distributions and abundance indices (number and weight) of catches concerning the 31 Medits reference species were analysed singly and at each depth stratum. Results for the most important species on the reference list were compared. Collected data were also compared with those which emerged in the same zone during previous international trawl surveys.
From June to the beginning of August, a total of 126 hauls were carried out using the commercial trawler "Nuovo Splendore". In 125 valid hauls one hundred and thirty-four species were identified: 84 fishes, 32 crustaceans and 18 cephalopods.
Considering the entire M2 region, the most abundant target species regarding weight (more than 10 kg/kmē) were, in descending order, Merluccius merluccius, Raja clavata, Sardina pilchardus, Octopus vulgaris, Argentina sphyraena, Scyliorhinus canicula, Spicara smaris, Spicara flexuosa, Mullus barbatus, Zeus faber and Eledone cirrhosa. Numerically speaking, the most important species were Spicara smaris, Sardina pilchardus, Argentina sphyraena, Merluccius merluccius, Spicara flexuosa and Lepidotrigla cavillone.
A more detailed analysis of abundance indices and size frequency distribution of reference species (Medits list of 30 species) is given below.
Found mainly on the continental shelf of western Sardinia (d, e, f and g zones). The regional abundance index was 1.4 kg/kmē and the highest biomass value of 26.3 kg/kmē was found in stratum 13317. Concerning the size-frequency distribution, lengths ranged from 5 to 21 cm.
Only nine specimens were caught along the northern and western coasts (c, d, f, g zones). The highest biomass value was 1.8 kg/kmē.
Caught at depth of between 100 and 800 m, with a regional index of 4.6 kg/kmē. The highest biomass index (77.5 kg/kmē) was recorded in stratum 13314. Specimens ranged from 3 to 32 cm, and the most frequent were 6 cm length.
L. boscii was caught frequently in all sub zones below 100 m (regional index 2.1 kg/kmē). The highest biomass index (10.8 kg/kmē) was recorded in stratum 13319. The most frequent specimens had a total length of 15 cm. Lengths ranged between 6 and 38 cm.
Few specimens were caught in an area covering almost all the Sardinian coasts (regional indices of 9 Ind/kmē and 7.7 kg/kmē). The highest abundance index (68.3 kg/kmē) occurred in stratum 13317. Lengths ranged between 9 and 71 cm.
These were few in number (24 specimens only) at all the bathymetric levels. The highest biomass index (32.4 kg/kmē) occurred in stratum 13308. The regional biomass index was 8.5 kg/kmē. Lengths varied from 29 to 84 cm.
The reference species M. merluccius has the highest abundance index in the Sardinian zone (regional index 837 N°/kmē, 38.4 kg/kmē). It was found at all the bathymetric levels, although it was very abundant at depths between 50 and 500 m. The highest indices (more than 140 kg/kmē) were recorded along the north-western coast (strata 13317 and 13318). The 5545 specimens obtained in the M2 region ranged from 4 to 68 cm in total length. The few adult specimens were found mainly below a depth of 500 m. The maximum length value recorded was 68 cm. Juveniles (less than 13 cm total length) were caught in great numbers at depths between 100 and 200 m.
M. poutassou was caught below 200 m. The highest indices of 15.3 and 11.8 kg/kmē were found in the strata 13319 and 13314 respectively. Specimens ranged from 23 to 38 cm length.
M. barbatus occurred on the continental shelf only. The highest biomass index was 121.9 kg/kmē (stratum 13327). The biomass index of the zone 133 was 14.6 kg/kmē. Analysis of size-frequency distribution showed that the mean value was 13-14 cm, with sizes ranging from 4 to 31 cm in total length.
Found above a depth of 500 m (regional index 9.8 kg/kmē), it was particularly abundant between 10 and 50 m. The highest biomass indices were recorded in strata 13316 and 13306 (128.7 and 126.8 kg/kmē respectively). At depths less than 50 m, specimens ranged from 5 to 25 cm and two modal classes (6 and 16 cm) could be distinguished; below this depth, lengths varied from 13 to 25 cm.
P. acarne was caught at depths between 10 and 500 m. The regional index was 1.3 kg/kmē, and the highest biomass value (28.0 kg/kmē) occurred in stratum 13306. Lengths ranged from 13 to 20 cm and one modal class of 14-15 cm was found.
A total of nine specimens of P. bogaraveo were collected at depths from 50 to 800 m. Lengths ranged from 13 to 28 cm, while abundance indices varied from 0.2 to a maximum of 2.3 kg/kmē.
Found above a depth of 100 m, it was especially abundant along the western coast. In fact, the highest biomass values ranged from 17.6 to 26.0 kg/kmē in strata 13317, 13322, 13327 and 13316. Lengths ranged from 4 to 33 cm. The most frequent length was 18 cm.
Although found starting from a depth of 100 m, it was more abundant (up to 13 kg/kmē) between 500 and 800 m. The regional abundance index was 5.5 kg/kmē. The highest index was 33.6 kg/kmē in stratum 13305. Lengths ranged from 5 to 55 cm, with many specimens having a total length of 11-12 cm.
R. clavata was caught at depths between 100 and 500 m, with the greatest abundance in strata 13328 and 13309 (142.5 and 105.0 kg/kmē respectively). The abundance index for the whole zone was 31.4 kg/kmē. The length frequency distribution ranged from 17 to 83 cm.
Caught mostly above a depth of 100 m, it showed the highest indices in strata 13326 and 13322 (58.9 and 45.4 kg/kmē respectively). Only seventy specimens were collected and these ranged from 8 to 38 cm in length.
Many specimens (Ind=3502) were found at depths between 10 and 200 m. In particular, higher indices (above 70 kg/kmē) were observed on the western and southern coasts (133e, f, g). The regional biomass index was 15.8 kg/kmē. Analysis of the size-frequency distribution showed that the mean value was 11 cm and size ranged from 8 to 23 cm in total length.
This species was caught in larger numbers on the entire continental shelf (10-200 m). The regional index (0.5 kg/kmē) was very low. However, the most significant biomass index was observed at strata 13322 and 13307 (4.0 and 2.3 kg/kmē respectively). Size frequency distribution ranged from 6 to 26 cm in total length.
Found mainly at a depth from 100 to 200 m, some specimens were also collected between 50 and 100 m and between 200 and 500 m. The highest biomass index was observed on the western coast (strata 13318, 13323 and 13328). The regional index was 0.9 kg/kmē. Size frequency distribution varied from 5 to 32 and showed two modal classes (9 and 16 cm in total length).
It was absent along the east coast (strata 133a and 133b) and at depths greater than 500 m. It was, however, particularly abundant between 50 and 200 m (more than 17 kg/kmē). Mean abundance values for the whole M2 zone was 4.4 kg/kmē. A large number of specimens (n=2164) were caught. The lengths ranged from 3 to 20 cm, in which two modal classes of 5 and 14 cm can be observed.
Found at depths from 10-500 m, this species is particularly abundant on the continental shelf of the western coast (zone 133d), in which the highest indices of 29.5, 38.1 and 47.3 were found in strata 13316, 13317 and 13318 respectively. Lengths were widely distributed - from 2 to 56 cm - and were divided into three modal classes (5, 11-15, and 49 cm).
This species was caught between 200 to 800 m. It was particularly abundant in the deepest bathymetric stratum (500-800 m). The abundance index of the M2 region was 3.0 kg/kmē. The highest biomass values, 21.7 and 19.9 kg/kmē, were observed in strata 13330 and 13320. The carapace lengths ranged from 16 to 58 mm and the mean value was 24-26 mm.
Although generally abundant at depths from 500 to 800 m, small numbers were also caught between 200 and 500 m. For the entire M2 region the mean abundance value was 1.9 kg/kmē. The most significant abundance indices were 29.6 and 28.8 kg/kmē (13330 and 13335 strata respectively). Length ranged from 18 to 65 mm. Three main distinct cohorts were observed (26-28, 35-36 and 51 mm of carapace length).
N. norvegicus was relatively abundant (1.7 kg/kmē) from 200 to 800 m. The highest biomass values, 59.1 and 42.8 kg/kmē, were obtained in strata 13309 and 13319 respectively. Observed lengths ranged from 16 to 64 mm. The most frequent specimens were from 36 to 38 mm of carapace length.
This species was mostly found at depths from 200 to 500 m, although it was occasionally caught between 100 and 200 m and below 500 m. The regional index was 1.7 kg/kmē. The highest biomass values were found in strata 13324 and 13329 (10.0 and 8.5 kg/kmē respectively). The length frequency distribution ranged from 3 to 40 mm, with a mean value of 17-19 mm.
Well represented at all bathymetric levels, this species had a mean abundance value of 10.7 kg/kmē. The species was particularly abundant in the south-east, where the highest index (38.6 kg/kmē) occurred in stratum 13309. Length distribution was from 1 to 14 cm, the most frequent being 2 cm.
E. moschata was abundant in all the strata at depths of less than 100 m. The regional index was 5.6 kg/kmē. Length varied from 3 to 13 cm and the most frequent was 6-7 cm.
Caught at all depths. The highest biomass indices were obtained for strata 13323 and 13328 (53.8 and 14.1 kg/kmē respectively). Lengths ranged from 4 to 26 cm. One modal class was evident at 7 cm of mantle length.
This species was caught at depths between 10 and 200 m. The regional index was 2.9 kg/kmē and the highest indices (over 8 kg/kmē) were recorded along the western coast in strata 13326, 13322 and 13327. Length varied from 5 to 27 cm and the modal class was 12 cm.
Caught in large numbers and weights at depths of less than 100 m (24.8 kg/kmē). The highest biomass indices were obtained in strata 13316, 13311 and 13306 (234.5, 135.3 and 117.1 kg/kmē respectively). Sizes varied from 3 to 17 cm, the most frequent being 7 cm in mantle length.
Limited numbers of specimens were collected in strata 13301, 13306, 13331 and 13306 only. Biomass values were 7.9, 1.3, 19.7 and 8.2 kg/kmē respectively. Length varied from 3 to 13 cm of mantle length.
A total of 120 species were collected, 42 of which were target species (Medits list of 57 species).
The most abundant were two non-target species, Glossanodon leioglossus and Capros aper, which were fished in large quantity and number (regional index 92.3 and 68.0 kg/kmē respectively). As concerns target species, M. merluccius, R. clavata, S. pilchardus and A. sphyraena were the most abundant in biomass; in number the most abundant were S. pilchardus, A. sphyraena and M. merluccius.
|
SPECIES |
kg/kmē |
CV |
N°/kmē |
CV |
|
M. merluccius |
38.4 |
12.9 |
837 |
15.2 |
|
R. clavata |
31.4 |
22.9 |
59 |
28.0 |
|
S. pilchardus |
31.3 |
46.2 |
3081 |
63.3 |
|
A. sphyraena |
22.6 |
35.5 |
1932 |
53.8 |
|
S. canicula |
20.7 |
18.4 |
279 |
22.9 |
|
S. smaris |
18.4 |
32.0 |
646 |
29.8 |
|
S. flexuosa |
15.8 |
21.4 |
710 |
23.7 |
|
M. barbatus |
14.6 |
27.9 |
391 |
31.3 |
|
Z. faber |
12.7 |
36.9 |
36 |
20.9 |
A total of 28 different crustaceans were identified. All crustacean target species were fished.
The largest catches were, in decreasing order of weight, A. antennatus, A. foliacea, N. norvegicus and P. longirostris, the abundance indices of which ranged from 3.0 to 1.7 kg/kmē. The most abundant in number were, in decreasing order, P. longirostris, N. norvegicus, A. antennatus and A. foliacea. Considering all non-target species, the catches of Plesionika martia (233 Ind/kmē and 1.1 kg/kmē) were also worthy of note.
|
SPECIES |
kg/kmē |
CV |
Ind/kmē |
CV |
|
A. antennatus |
3.0 |
21.1 |
192 |
27.6 |
|
A. foliacea |
1.9 |
19.2 |
139 |
17.7 |
|
N. norvegicus |
1.7 |
21.9 |
43 |
20.8 |
|
P. longirostris |
1.7 |
26.3 |
277 |
27.1 |
|
P. martia |
1.1 |
18.4 |
233 |
26.1 |
Twenty-one different species of cephalopods were identified. Of these, 7 species were in the Medits list.
The highest biomass value was calculated for O. vulgaris. However, catches of the species E. cirrhosa, I. coindetii and E. moschata were also significant. Regarding non-target species, Loligo forbesi and Todaropsis eblanae were also relatively abundant. Also noteworthy was the abundance in number of I. coindetii (250 Ind/kmē).
|
SPECIES |
kg/kmē |
CV |
Ind/kmē |
CV |
|
O. vulgaris |
24.8 |
13.7 |
63 |
11.0 |
|
E. cirrhosa |
10.7 |
9.9 |
177 |
13.0 |
|
I. coindetii |
5.8 |
23.0 |
250 |
33.6 |
|
E. moschata |
5.6 |
19.2 |
55 |
17.8 |
|
L. forbesi |
4.4 |
27.7 |
172 |
51.5 |
|
L. vulgaris |
2.9 |
37.3 |
32 |
45.3 |
|
T. eblanae |
2.0 |
26.0 |
22 |
17.2 |
|
S. orbignyana |
1.2 |
13.3 |
55 |
19.4 |
|
S. officinalis |
0.9 |
34.7 |
6 |
33.9 |
|
T. sagittatus |
0.7 |
28.6 |
2 |
28.0 |
A total of 75 hauls were carried out, one of which was not valid and for this reason was repeated. A total of 107 species were fished. Thirty-six were target species, of which 29 were fish and 7 were cephalopods. No one crustaceans on the reference list was caught.
S. pilchardus was the most abundant target species, both in number and weight (4861 N°/kmē, 49.3 kg/kmē respectively). Considering biomass, the highest values (more than 20 kg/kmē) were calculated for M. merluccius, O. vulgaris, R. clavata, S. smaris, S. flexuosa, S. canicula, M. barbatus and A. sphyraena. Significant indices were also observed for Zeus faber, M. surmuletus, S. cabrilla and E. cirrhosa (more than 11 kg/kmē).
In terms of number, the most significant indices (more than 1000 Ind/kmē) were found for A. sphyraena, S. flexuosa, S. smaris and M. merluccius.
|
SPECIES |
kg/kmē |
Ind/kmē |
|
S. pilchardus |
49.3 |
4861 |
|
M. merluccius |
47.1 |
1006 |
|
O. vulgaris |
39.0 |
99 |
|
R. clavata |
33.8 |
51 |
|
S. smaris |
29.1 |
1019 |
|
S. flexuosa |
24.9 |
1120 |
|
S. canicula |
23.6 |
286 |
|
M. barbatus |
23.1 |
616 |
|
A. sphyraena |
21.2 |
2389 |
In this stratum 24 valid hauls were made, with a total of 94 different species being caught. Considering the target list, 31 species, 22 fishes, 5 cephalopods and 4 crustaceans were classified.
At this depth, both in numerical abundance and biomass, very high values (more than 46000 N°/kmē and more than 200 kg/kmē) were observed for many species not included in the reference list (Chlorophtalmus agassizii, C. aper, Galeus melastomus, Gadiculus argenteus, G. leioglossus, etc.).
Considering only species on the reference list, R. clavata, M. merluccius, H. dactylopterus and E. cirrhosa had the highest biomass values (more than 38 kg/kmē), while the highest abundance value was for M. merluccius.
|
SPECIES |
kg/kmē |
Ind/kmē |
|
R. clavata |
105.0 |
483 |
|
M. merluccius |
86.4 |
2598 |
|
H. dactylopterus |
77.5 |
1304 |
|
E. cirrhosa |
38.6 |
308 |
In twenty-seven valid hauls, a total of 81 different species were identified. Of these, only 18 (12 fishes, 2 cephalopods and 4 crustaceans), were on the target list,
In numerical abundance, the highest indices (more than 1800 Ind/kmē) were calculated for A. foliacea, Ph. blennoides and A. antennatus. In terms of biomass, the highest values (more than 50 kg/kmē) were for species not included in the reference list. The most important commercial species was P. martia. Considering the reference species only, the most significant were in descending order of biomass Ph. blennoides, A. foliacea, L. piscatorius, A. antennatus and M. merluccius (mean values ranging from 36.6 kg/kmē to 13.4 kg/kmē).
|
SPECIES |
kg/kmē |
Ind/kmē |
|
P. martia |
81.3 |
81 |
|
Ph. blennoides |
36.6 |
1887 |
|
A. foliacea |
29.6 |
2223 |
|
L. piscatorius |
29.3 |
4 |
|
A. antennatus |
21.7 |
1873 |
|
M. merluccius |
13.4 |
201 |
|
M. merluccius |
13.4 |
201 |
A general analysis of the Medits 97 data relating to the geographic distribution and the length size frequencies confirms those collected so far, while data on abundance varied from species to species.
Different biomass values along the western and southern coasts (133d,e,f,g) as far as along the east coast (133a,b) were observed this year as in the past. In particular, for most species the highest indices were calculated in the western zone, although some species (M. surmuletus, L. piscatorius, P. acarne, O. vulgaris, R. clavata, N. norvegicus, E. moschata, E. cirrhosa) were also abundant along the north and north-east coast.
In the eastern zone, significant values were calculated for Ph. blennoides, M. barbatus, P. longirostris, E. cirrhosa, S. officinalis and I. coindetii only.
Comparing 1996 and 1997 biomass and abundance values, we observed increases for L. vulgaris, P. longirostris, E. moschata, I. coindetii, E. cirrhosa and R. clavata. In particular, the increase in I. coindetii was due to a large number of juveniles. On the contrary, a decrease in indices, by order of importance of biomass, was detected for P. bogaraveo, T. mediterraneus, M. poutassou, T. minutus, N. norvegicus, T. trachurus and M. merluccius. For the latter, abundance decreased much more than did biomass.
For the Mullidae, M. barbatus and M. surmuletus, and for L. boscii, biomass increased while abundance in number decreased. The opposite situation was found for two species, H. dactylopterus and A. foliacea.
No significant difference in biomass or abundance resulted for other species in the reference list.
Analysis of the results of the Medits 97 survey confirms that the western part of the island (133d, e, f) was generally richer than the other subzones (133a, b, c, g) in term of number of species, abundance and biomass. This can be explained as follows:
The most noteworthy differences between 1996 and 1997 are an important decrease in biomass index for M. merluccius and an important increase in biomass for L. vulgaris, P. longirostris and E. moschata.
For some species the 1996 - 1997 variation of the abundance index is due to the change in the length class of the catches. For instance, the increase in indices shown for I. coindetii was caused by the rise in the number of juvenile length classes. Similarly, variations in the indices for M. merluccius were caused by decreases in the smaller length classes.
In any case, on analysing the biomass trend over the four-year period, we can observe that this index is constant or positive for most reference species.