by (cf. below)
M3 Co-ordinator: D. Levi -
Istituto di Ricerche sulle Risorse Marine e l’Ambiente – IRMA – CNR - Via Luigi
Vaccara, 61, 91026, Mazara del Vallo
(TP), Italy.
Sub region M3a: M.T. Spedicato, G.
Lembo, P. Carbonara, T. Silecchia, M. Contegiacomo, G. Costantino - COISPA Tecnologia
e Ricerca S.c.l.r., SS 16 km 818.8, Complanare Est, Strada Padovano, CP
6270042, Mola di Bari (Bari), Italy.
Sub region M3b: S. Greco, P.
Rinelli, F. Perdichizzi, D. Giordano, T. Romeo, G.Cannavò, A. Drogo –
Istituto Sperimentale Talassografico – CNR, Spianata S. Raineri, 86, 98123,
Messina, Italy.
Sub region M3c: S. Ragonese, F.
Fiorentino, G. Norrito, M.G. Andreoli, G. Garofalo, G. Bono, P. Rizzo, G.B.
Giusto, S. Gancitano - Istituto di Ricerche sulle Risorse Marine e
l’Ambiente – IRMA – CNR -Via
Luigi Vaccara, 61, 91026, Mazara del
Vallo (TP), Italy.
The
results of the Medits survey
carried out in the South Tyrrhenian Sea and in the Strait of Sicily (Region M3;
Region 1.3.4) in the period 3rd May – 10th June 1999, are
presented and discussed.
The Medits-ITM3 1999 survey (hereby defined
as Medits’99) was conducted, as
the previous years, using the professional stern trawler “S. ANNA” and the Medits gear. A total of 140 hauls were
carried out according to the calendar reported below:
|
Sub
region |
Code |
Number of hauls |
Survey
period |
|
South Tyrrhenian Sea: Volturno River - Capo Suvero |
M3a |
57 |
3rd May-18th May |
|
South Tyrrhenian Sea: Capo Suvero – Capo San Vito |
M3b |
27 |
19th May-25nd
May |
|
Strait of Sicily |
M3c |
56 |
26th May-10th
June |
Mean
abundance were estimated and length frequency distributions (LFD) were computed
by IndMed 4 program and analysed for the 37 Medits
target species (short list); before analysing data, errors were checked by
CheckMed program. According to the Medits
“Manual of protocols”, the overall range of the length frequency distribution
are expressed as total length (TL; cm), carapace length (CL; mm) and
mantle length (ML; cm) for fish, crustaceans and cephalopods,
respectively.
Practically,
the observed catches, both in number (N) and weight (kg), are referred to a
standardised region of 1 km², and hereby expressed as “Density index” (DI=
N/km²) and “Biomass index” (BI= kg/km²) by each stratum (sub regional and
regional level), and for shelf (10-200 m; i.e., 1st, 2nd
and 3rd stratum combined; hereby defined as shelf-index) and slope
(200-800 m; i.e., 4th and 5th stratum combined;
hereby defined as slope-index) bottoms (at regional level) and for the overall
region.
Results
will be mostly presented and discussed at sub regional level; in fact, it is
well known that the specific representativeness as well as the abundance
indices may be influenced by the sampling period, and may change when species
depth and space distribution are considered.
For
example, catches of Mullus surmuletus and
Raja clavata were recorded, almost
exclusively, in the Strait of Sicily (Sub region M3c), being these species rare
or lacking at all in the other two sub regions (M3a and M3b).
On the
other side, Pagellus acarne and Pagellus bogaraveo still represent an
important catch in the South Tyrrhenian Sea (especially in M3b), whereas
negligible yields generally resulted in the Strait of Sicily.
Given
the heterogeneity of the three M3 sub regions, and the lack of joint
comparative analysis, the abundance estimates and the overall length structure
at the regional level must be considered as indicative only.
Furthermore,
it must be pointed out that the abundance estimates at regional level for those
species showing restricted bathymetric distribution (such are the cases of the
deep water red shrimps and common octopus) underestimate the true “biological”
abundance, given the inclusion in the computations of the strata where the
species has never occurred. Splitting abundance between shelf and slope bottoms
partially reduces this problem. Nevertheless, inter years comparison can be
obviously done given the invariance of the statistical design and strata
sampling frequencies.
A total
of 239 different species (167 fish,
39 crustaceans, and 33 cephalopods) was identified in the catch. Among the
first 37 species of the reference (“short”) list (hereby defined as “target”
species, or more simply targets), 36 were represented in the catch, in one sub
region at least.
Likewise
to the Medits’98, no specimen of Eutrigla gurnardus was caught during the
Medits’99 (by the way, only one
specimen of this species had been found in the Medits’97).
Considering
the sub regions, Sparus pagrus was
not collected in the M3a while Aspitrigla
cuculus, Raja clavata and Trachurus
mediterraneus were not caught at all in M3b.
With
regards to the new catches in M3, four species of bony fish (Schedophilus medusophagus, Microichthys
coccoi, Sudis hyalina and Brama brama)
and one decapod crustacean (Liocarcinus
vernalis) were added to the “FM list”, following the procedure indicated in
the “Manual of protocols”.
For sake
of simplicity, only the numeric values of the mean abundance, both as density
index (DI) and biomass index (BI), as previously defined, are hereby presented
and discussed; the presence of the decimal in BI (whereas DI is an integer)
allows an immediate distinction between the two indices. When some confusion
may arise, the corresponding units, kg or N follows the figures, but 1/km² is
always omitted. Corresponding coefficient of variation (CV = sd/Mean) are
expressed as %.
Considering
the regional scale and the fish targets, only 9 species yielded BI higher than
5.0 kg, sometimes with high values of the coefficient of variation: Trachurus trachurus (BI= 47.5 kg;
CV=53.1), Spicara flexuosa (20.5;
CV=35.2), Merluccius merluccius
(20.2; CV=11.3), Parapenaeus longirostris.
(17.0; CV=12.9); Galeus melastomus
(12.3; CV=16.8); Raja clavata (8.8;
CV=39.5), Aristaeomorpha foliacea
(8.5; CV=15.4); Mullus barbatus (5.7;
CV=30.8) and Phycis blennoides (5.2;
CV=10.3).
Considering
the abundance in number, regional DI higher than 100 N were also observed in 9
fish species: Trachurus trachurus
(DI= 5762 N; CV=57.4), Parapenaeus
longirostris (3526; CV=15.7); Spicara
flexuosa (821; CV=40.9), Merluccius
merluccius (586; CV=14.2),
Aristaeomorpha foliacea (410; CV=15.5); Phycis
blennoides (191; CV=9.4), Mullus
barbatus (153; CV=33.1), Trachurus
mediterraneus (145; CV=30.3) and Helicolenus
dactylopterus (107; CV=25.5).
With
regards to the sub regional level, the important target fish which showed
considerable abundance in M3a (> 10 kg, at least in one stratum) were Galeus melastomus, Merluccius merluccius, Mullus
barbatus, Pagellus acarne, Pagellus erythrinus, Phycis blennoides, Spicara flexuosa, Spicara smaris, Trachurus mediterraneus, Trachurus
trachurus and Zeus faber.
For the
sub region M3b, the target fish which showed considerable level of abundance
(> 10 kg, at least in one stratum) were Galeus
melastomus, Merluccius merluccius,
Mullus barbatus, Pagellus bogaraveo, Pagellus
erythrinus, Spicara flexuosa and Trachurus trachurus.
Speaking
about the M3c sub region, the important target fish which showed considerable
level of abundance (> 10 kg, at least in one stratum) were Galeus melastomus, Lophius piscatorius, Merluccius merluccius, Phycis blennoides, Raja clavata, Spicara flexuosa, Trachurus mediterraneus, Trachurus trachurus and Zeus faber.
When
crustaceans are considered, only 2 species yielded abundance higher than 5.0 kg
and 100 N, with relatively low values of the coefficient of variation: Parapenaeus longirostris (BI= 11.3 kg;
CV=14.6; DI= 2456 N; CV=17.4) and Aristaeomorpha
foliacea (6.6; CV=15.8; 317; CV=16.4). For this category, it is worth to
note the very deep localisation of Aristeus
antennatus, found only in the deepest stratum in all sub-regions with
almost equal abundance (few kg).
At sub
regional level, in M3a Aristaeomorpha
foliacea was the most abundant, followed by Parapenaeus longirostris and Nephrops
norvegicus. The rose shrimp (Parapenaeus
longirostris) and the red shrimp (Aristaeomorpha
foliacea) were also the most abundant target in the sub regions M3b and
M3c. The Norway lobster (Nephrops
norvegicus) was well represented in M3c, but it occurred only marginally in
the catches of M3b.
Talking
about the cephalopods, no species went above the arbitrary limit of 5.0 kg or
100 N mean catch at regional level. Some species resulted in very high
abundance when strata were considered: such were the cases for Octopus vulgaris and Illex coindetii.
Considering
the sub region M3a, Eledone cirrhosa,
Illex coindetii, Octopus vulgaris and Sepia
officinalis yielded abundance in weight higher than 5 kg (at least in one
stratum).
As far
as the sub region M3b is concerned, only Eledone
cirrhosa, Illex coindetii and Octopus vulgaris reached the threshold
in abundance.
In the
Strait of Sicily (M3c), beside the three species common to the other sub
regions (Eledone cirrhosa, Illex coindetii and Octopus vulgaris), Eledone moschata and Loligo
vulgaris gave biomass index higher than 5 kg.
Aspitrigla cuculus
This
species was collected only on the shelf in M3a (depth range: 115-184 m) and M3c
(27-138 m), whereas in the M3b the species was not found at all. In the
whole region, this species gave BI of 1.1 kg (CV=31.5) and DI of 27 N
(CV=31.2). Considering that Aspitrigla cuculus was absent on the slope, the
shelf indices were 2.8 (CV=31.5) as BI, and 70 (CV=31.2) as DI. At sub regional
level, the highest indices, 5 (CV=31.2) and 120 (CV= 31.2) were obtained, in
the 3rd stratum, in M3c.
The
range of the total length was 6-24 cm (mean=15.9) in the whole region, and
15-20 (mean=17.5) and 6-24 (mean=15.5) for M3a and M3c, respectively.
Citharus linguatula
This
species was collected only on the shelf in M3a (68-160 m) and M3c (52-143
m), whereas in the M3b was found also along the slope (81-596 m), practically
within the 2nd and 5th stratum (50-800 m). The
regional BI resulted 0.7 kg (CV=36.4) with a DI of 25 N (CV=41.8); however, the
species was found almost exclusively on the shelf (1.7 and 63) with indices for
the slope being negligible. Considering the sub regional level, the highest
abundance (3.3; 122) was observed in the 2nd stratum of the M3c
region (Strait of Sicily).
The
overall range of the total length was 9-24 cm (mean=15); sub regional
length ranges were 13.5-20.5 (mean=16.2), 9-24 (mean=17.1) and 10-19.5
(mean=14.5) for M3a, M3b and M3c, respectively.
Eutrigla gurnardus
No
specimen of Eutrigla gurnardus was
fished in the M3 region during the Medits’99.
Helicolenus dactylopterus
The
black mouth rockfish was collected both in the shelf and slope, without
differences among sub regions (113-650 m), with higher abundance in the 5th
stratum. The overall BI and DI were 3.1 kg and 107 N with CV of 37.1 and 25.5,
respectively. As a matter of fact, this species resulted more abundant on the
slope (5.0 and 134) than the shelf (0.2 and 63). Considering the sub regional
level, the highest BI and DI were observed in the Strait of Sicily (6.6, 5th
stratum and 320, 4th stratum, respectively). Catches by strata were
generally lower in the South Tyrrhenian Sea (M3b).
The
range of the total length was 3-30 cm (mean=8.6) in the whole region, and
3-25 (mean=8.3), 3.5-19 (mean=6.2) and 3-30 (mean=9.5) in M3a, M3b and M3c,
respectively.
Lepidorhombus boscii
This
species was collected in the 4th and 5th stratum (i.e.,
on the slope), without differences in the depth range among sub regions
(302-640 m), but always with low catches. At regional level, considering
the slope, the index of abundance was 0.7 kg and 7 N (values further reduced by
combining shelf and slope regions: 0.4, CV=31.6, and 4, CV=32.0). This flatfish
was observed in all M3 sub regions, although sporadically in the South
Tyrrhenian Sea (M3b).
The
range of the total length was 10.5-35 cm (mean=21.3) in the whole region,
and 10.5-32.5 (mean=20.8), 12-34.5 (mean=24.5) and 11-35 (mean=21.2) for M3a,
M3b and M3c, respectively.
Galeus melastomus
This
shark, a new entry in the reference list, was collected only in the slope,
without differences in the depth ranges among sub regions (292-704 m).
Considering only the slope, good index of abundance were obtained: the BI was
20.3 kg (CV=16.8) and the DI was 154 N (CV=16.7). Obviously, for the whole
region, these values are strongly reduced (12.3 kg, CV=16.8; 94 N, CV=16.7). At
sub regional level, the highest indices, 41.7 (CV=44.9) and 520 (CV= 49.7) were
obtained, in the 4th stratum, in M3a.
The
range of the total length was 7-54.5 cm (mean=31) in the whole region, and
10.5-54.5 (mean=29.9), 7-53 (mean=33.6) and 10-53 (mean=33.4) for M3a, M3b and
M3c, respectively.
Lophius budegassa
This
species was collected, mainly as medium size specimen, both on the deepest
shelf and slope of M3a (166-420 m) and M3c (152-434 m), whereas in the M3b
it showed a wider depth range (40-596m). Considering the whole region, this
Anglerfish yielded BI of 0.9 kg (CV=31.2) and DI of 4 N (CV=23.1); however, the
catch in weight was mainly concentrated on the slope than the shelf resulting
1.0 and 0.7 kg, respectively. At sub regional level, the highest indices were
observed in M3b: in particular, in the 2nd and 3rd
stratum for BI (6.3 kg; CV=41.9) and DI (13 N; CV=30.0), respectively.
The
range of the total length was 7-42 cm (mean=25.5) in the whole region, and
8-41.5 (mean=22.5), 10-41.5 (mean=22.4) and 7-42 (mean=22.6) for M3a, M3b and
M3c, respectively.
Lophius piscatorius
This
species was found only on the shelf in M3a (84-172 m), and both on the shelf
and the slope in M3b (81-355 m) and M3c (27-640 m). On the overall,
this anglerfish gave indices of 3.3 kg (CV=66.7) and 4 N (CV=28.4), mainly as
medium size specimens. Considering the BI, the abundance on the shelf was lower
than that on the slope (0.6 vs. 5.1), whereas the opposite occurred for the DI
(8 vs. 2). At sub regional level, the highest BI, 13.4, resulted in the deepest
stratum of M3c; furthermore, it is worth noting that this species occurred in
the 1st stratum only in the sub region M3c, with appreciable
captures (BI=2.0; DI=28).
The
range of the total length was 6-111.5 cm (mean=19.3) in the whole region,
and 10.5-29.5 (mean=20.0), 6-27 (mean=12.2) and 6-111.5 (mean=23.7) for M3a,
M3b and M3c, respectively.
Merluccius merluccius
The
Mediterranean hake was fished at any depth showing, however, a preference for
bottoms between 50 and 500 m. In the M3a (16-576 m) and in the M3c (34-636
m) it was found in all strata, whereas in the M3b it was not caught in the 1st
and in the 5th strata (76-395 m). This species showed, on the
overall region, BI and DI of 20.2 kg (CV=11.3) and 586 N (CV=14.2),
respectively. The shelf-indices, both as BI and DI, were higher than the
slope-indices (26.7 vs. 16.0 and 852 vs. 414). At sub regional level, the
highest captures were observed in the 3rd stratum of M3a (54.9,
CV=25.5; 4111, CV=21.4).
The
range of the total length was 3.5-74 cm (mean=13.9) in the whole region,
and 3.5-56.5 (mean=12.8), 5.5-40.5 (mean=15.8) and 5-74 (mean=14.9) for M3a,
M3b and M3c, respectively.
Micromesistius poutassou
Only one
specimen of Blue whiting was caught in the M3b at 355 m; for the other sub
regions, the species was found both on the deepest shelf and in slope in M3a
(121-456 m) and M3c (143-576 m). In the whole region, this species gave BI of
1.1 kg (CV=50.4) and DI of 49 N (CV=66.1). The shelf-indices, both as BI and
DI, were lower than the slope-indices (0.5 vs. 1.5 and 30 vs. 61). At sub
regional level, the highest stratum values (6.3, CV=49.9; 180, CV=108.7) were
observed in the 4th stratum, but in two different sub regions: M3a
and M3c for BI and DI, respectively.
The
range of the total length was 8.5-38 cm (mean=17.1) in the whole region,
and 8.5-38 (mean=24.1), 25 and 9-32.5 (mean=13.3) for M3a, M3b and M3c,
respectively.
Mullus barbatus
The Red
mullet was caught exclusively on the shelf in M3a (19-184 m) and in M3b
(32-120 m), whereas in M3c the species was also found in the upper slope
(27-368 m). Considering the whole region, the resulting indices were 5.7 kg
(CV=30.8) and 153 N (CV=33.1). However, referring to the “true” distribution
region of the species (the shelf), higher indices are obtained: 14.5 (CV=30.9)
and 391 (CV=33.2). At sub regional level, the highest indices, 54.4 (CV=36.2)
and 2028 (CV= 37.8) were obtained, in the 1st stratum, in M3a.
The range
of the total length was 8.5-25.5 cm (mean=14.5) in the whole region, and
8.5-22 (mean=13.9), 9-25.5 (mean=14.9) and 10.5-25 (mean=15.2) for M3a, M3b and
M3c, respectively.
Mullus surmuletus
This
species was caught both on the shelf and the slope in M3a (40-358 m) and in M3c
(66-704 m), whereas in the M3b the Stripped red mullet was found only in the
shelf (112-158 m). In the whole region, this species gave BI of 2.2 kg
(CV=38.6) and DI of 29 N (CV=36.6). The shelf-indices were 5.4 (BI) and 70
(DI), quite higher than the slope-indices (0.2 and 3). Considering the sub
regions, Mullus surmuletus was caught
almost exclusively in the M3c, with the highest indices in the 2nd
stratum (19.1, CV=27.5; 254, CV= 26.1).
The
range of the total length was 13-25.5 cm (mean=18.7) in the whole region
and 16.5-20.5 (mean=18.4), 15.5-22 (mean=18.0) and 13-25.5 (mean=18.8) for M3a,
M3b and M3c, respectively.
Pagellus acarne
This
species showed an irregular (highly contagious) spatial and depth distribution
and was practically fished on the shelf in all sub regions, between 19 and
250 m depth (very few specimens were caught on the upper slope bottoms).
At regional level, an overall BI of 1.3 kg (CV=35.4) and DI of 23 N (CV=41.1)
resulted for this species; however, the bulk of the catch was concentrated
within the 100 m (shelf-indices: 3.3 and 59). At sub regional level, the
highest values were obtained in the 1st stratum of M3a, resulting a
BI of 18.1 (CV=40.1) and a DI of 466 (CV=40.6).
The
range of the total length was 13-22.5 cm (mean=16.2) in the whole region,
and 13.5-19.5 (mean=15.7), 13-20 (mean=16.1) and 15-22.5 (mean=17.7) for M3a,
M3b and M3c, respectively.
Pagellus bogaraveo
This
species was found both on the shelf and the slope in all sub regions, but it
was mainly caught between the 2nd and 4th stratum. The
widest depth range of occurrence was observed in M3a (40-571 m), whereas quite
similar depth range resulted in M3b (81-395 m) and M3c (52-387 m). P. bogaraveo showed, on the overall
region, BI and DI of 1.2 kg (CV=54.6) and 25 N (CV=63.3), respectively.
Shelf-indices were 2.6 (BI) and 62 (DI), values quite higher than the
slope-indices (0.4 and 2). The highest catches were found in the 2nd
stratum in M3b, where BI was 43.7 (CV=42.1) and DI was 1048 (CV=42.1).
The
range of the total length was 4.5-30 cm (mean=15.3) in the whole region,
and 4.5-30 (mean=19.4), 12.5-27 (mean=14.9) and 12.5-25.5 (mean=17.3) for M3a,
M3b and M3c, respectively.
Pagellus erythrinus
A
typical neritic species, this sparid was fished on the shelf of all sub
regions, between 16 and 142 m depth, the bulk of the catch occurring in the
first two strata (10-100 m). The overall indices of abundance were 2.3 kg
(CV=26.5) and 29 N (CV=20.6). However, when only the shelf catches are
considered, the indices increase up to 5.9 kg (CV=26.5) and 73 N (CV=26). The
highest mean value by stratum, as BI, was found in the 2nd stratum
in M3b, with a value of 36.6 kg (CV=36.1) while the maximum DI was obtained in
the 1st stratum of the same sub region, with a value of 408 N (CV=
20.6).
The
range of the total length was 7-28.5 cm (mean=17.4) in the whole region,
and 7-24.5 (mean=16.3), 10-27 (mean=18.2) and 10.5-28.5 (mean=18.0) for M3a,
M3b and M3c, respectively.
Sparus pagrus
Only few
specimens of this species were fished in shallow waters in the sub regions M3b
(two hauls at about 40 m) and M3c (only one positive haul at 42 m depth);
even considering only the shelf strata, the resulting mean abundance indices
are inconspicuous (<0.05 kg, BI, and 2 N, DI). The highest values by stratum
were found in the 1st stratum in M3b: 0,9 (CV=29.8), as BI, 16
(CV=28.2), as DI.
The
range of the total length was 6.5-17.5 (mean=12) in the whole region.
Phycis blennoides
This
species was found both on the shelf (with the exception of the 1st
stratum) and slope in M3a (80-656 m), M3b (76-596m), and M3c (130-704 m). By
combining strata and sub regions, indices were 5.2 kg (CV=10.3) and 191 N
(CV=9.4). Higher indices resulted considering only the slope captures: 8.0
(CV=10.8) and 279 (CV=10.1). By comparing the low indices of the shelf (0.7 kg
and 53 N), it is evident the preference of this species for the slope bottoms.
The highest BI (10.9 with CV=25.4) was obtained in the 5th stratum
(where the bigger animals were also found) in the M3c sub region. With regards
to the density indices (DI), the highest value, 1222 (CV=16.5), was observed in
the 4th stratum of M3b.
The
range of the total length was 4.5-53 cm (mean=11.1) in the whole region,
and 4.5-52 (mean=11.2), 5.5-39 (mean=9.9) and 5-53 (mean=12.8) for M3a, M3b and
M3c, respectively.
Raja clavata
This
skate was caught both on the shelf and the slope in M3a (160-411 m) and in M3c
(70-628 m), whereas in the M3b the species was not found at all. Considering
the abundance indices at regional scale, the values were 8.8 kg (CV=39.5), as
BI, and 7 (CV=49.2), as DI. The overall shelf-indices in the region were 12.9
(BI) and 7 (DI), higher than the slope-indices (6.2 and 6). At sub regional
level, the highest values were obtained in the 2nd stratum of M3c,
resulting a BI of 26.8 (CV=39.6) and a DI of 17 (CV=49.9).
The
range of the total length was 27.5-82.5 cm (mean=50.7) in the whole
region, and 30-63.5 (mean=40.7) and 27.5-82.5 (mean=53.5) for M3a and M3c,
respectively.
Scyliorhinus canicula
This
small size shark was found on the slope in M3a (250-440 m) and M3b
(although only in one haul at 344 m), while both in shelf and slope in M3c
(66-576 m). In the whole region, this species gave BI of 3.0 kg (CV=33.7) and
DI of 31 N (CV=47.0). The shelf-indices, as BI, 5.1 (CV=41.5) were higher than
the slope-ones, 1.6 (CV=57.7), but this result mainly reflects some quite good
catches realised in the M3c sub region. On the contrary, the DI were higher in
the slope (34, CV=65.0) than the shelf (25, CV=48.0). At sub regional level,
the highest stratum BI value was 18.4 (CV=27.2) in the 2nd stratum
in M3c, otherwise the highest DI index, 104 (CV=82.4) was recorded in the 4th
stratum in the same sub region.
The
range of the total length was 9.5-56 cm (mean=23.9) in the whole region,
and 14.5-43 (mean=31.5), 46-56 (mean=51) and 9.5-48.5 (mean=23.2) for M3a, M3b
and M3c, respectively.
Solea vulgaris
Likewise
to the results of the previous trawl surveys (Medits’98),
this coastal species is almost disappeared from the bottoms of the M3 region.
Only one specimen was caught in M3b (at 81 m depth) and M3c (52 m), whereas in
sub region M3a few individuals were fished between 16 and 121 m. Even
considering only the shelf captures, the abundance indices were quite low (<
0.6 kg and 2 N). The highest value by stratum, as BI, was found in the 2nd
stratum in M3b (3.5 with CV=42.1), otherwise the maximum DI was obtained in the
1st stratum of M3a (11 with CV=41.3).
The
range of the total length was 25-39.5 cm (mean=31.6) in the whole region.
Spicara flexuosa
This
species was fished in all sub regions, but only on the shelf, between 16 and
172 m depth. The bulk of the catch occurred in the 2nd stratum
(50-100 m). Considering the overall depth range at regional scale, the
abundance indices were 20.5 kg (CV=35.2) and 821 N (CV=40.9). The
shelf-indices were, obviously, higher: 52.3 kg (CV=35.2) and 2098 N (CV=40.9)
respectively. The 2nd stratum of the sub region M3c yield the
highest indices (127 kg with CV=27.3 and 3650 N with CV=28.2).
The
range of the total length was 3.5-21 cm (mean=12.8) in the whole region,
and 3.5-18 (mean=11.7), 8-21 (mean=13.4) and 9-19.5 (mean=13.3) for M3a, M3b
and M3c, respectively.
Spicara smaris
As the
congeneric species, S. smaris was
caught in all sub regions and only on the shelf, between 32 and 152 m depth;
also in this case, the bulk of the catch occurred in the 2nd stratum
(50-100 m). Considering the overall depth range at regional scale, the
abundance indices were 1.1 kg (CV=35.1) and 52 N (CV=34.6). The shelf-indices
were 2.9 kg (CV=35.1) and 134 N (CV=34.6), respectively. At sub regional level,
the highest indices, 41.7 (CV=26.7), as BI, and 1906 (CV= 25.3), as DI, were
obtained in the 2nd stratum of M3a.
The
range of the total length was 10-20 cm (mean=13.8) in the whole region,
and 10-19 (mean=14), 10-20 (mean=13.1) and 11-19 (mean=13.8) for M3a, M3b and
M3c, respectively.
Trachurus mediterraneus
This
species was caught only on the shelf of M3a (16-87 m) and M3c (27-82 m); on the
contrary, no specimens was gathered in the M3b sub region. In the whole region
this species gave BI of 2.6 kg (CV=21.1) and DI of 145 N (CV=30.3). The
shelf-indices resulted in BI of 6.6 (CV=21.1) and DI of 372 (CV=30.3),
respectively. At sub regional level, the highest stratum BI and DI values were
recorded in the same sub region (M3a) and stratum (1st): 50.0 kg
(CV=18.3) and 3366 N (CV=21.8).
The
range of the total length was 6.5-25.5 cm (mean=12.5) in the whole region,
and 6.5-25.5 (mean=12.8) and 6.5-24 (mean=11.4) for M3a, M3b and M3c,
respectively.
Trachurus trachurus
It was
the most abundant target species in the whole region. Considering the different
sub regions this species was caught both on the shelf and the slope in M3b
(32-328 m) and in M3c (27-434 m), while it was found only on the shelf in M3a
(38-140 m). Considering the overall depth range at regional scale, the
abundance indices were 47.5 kg (CV=53.1), as BI and 5762 N (CV=57.4), as DI.
Keeping shelf and slope separate, shelf-indices were 118.6 (BI) and 14708 (DI),
quite higher than the slope-indices (1.9 and 11). At sub regional level, the
highest values were obtained in the 2nd stratum of M3b, with a BI of
251.5 (CV=41.0) and a DI of 41289 (CV=43.0).
The
range of the total length was 4-43 cm (mean=10.2) in the whole region, and
5-35.5 (mean=9.7), 6-35 (mean=11) and 4-43 (mean=10.4) for M3a, M3b and M3c,
respectively.
Trigloporus lastoviza
This
species was caught exclusively on the shelf in all sub regions. It was found
only in one haul (80 m) in the M3a, between 40 and 112 m depth in M3b, and
between 27 and 92 m in M3c. Considering the whole region, this species showed
BI of 0.9 kg (CV=46.5) and DI of 21 N (CV=43.1). As only the shelf indices were
considered, a BI of 2.3 (CV=46.5) and a DI of 54 (CV=43.1) were obtained. At
sub regional level, the highest indices, 8.0 (CV=32.5) and 155 (CV= 29.4),
resulted in the 2nd stratum of M3c.
The
range of the total length was 5.5-32 cm (mean=15.5) in the whole region,
and 13.5-32 (mean=22.6) and 5.5-22.5 (mean=14.2) for M3b and M3c, respectively.
Just one fish of 17 cm total length was caught in M3a.
Trisopterus minutus capelanus
The poor
cod was found in a narrow depth range (50-200 m). In M3a the species
occurred between 84 and 171 m depth, in M3b it was caught only in one haul (81
m) and in M3c between 52 and 152 m. The abundance indices, combining all
strata, were 0.8 kg (CV=55.4), as BI, and 52 N (CV=78.9), as DI. Considering
the shelf, the indices were 2.0 kg (CV=55.4) and 134 N (CV=78.9). At sub region
level, the highest value by stratum, as BI, was found in the 2nd
stratum in M3b (14.7 with CV=42.1), otherwise the maximum DI was obtained in
the 3rd stratum of M3c (313 with CV=64.5).
The
range of the total length was 3-24 cm (mean=12.7) in the whole region, and
3-21.5 (mean=14.6), 14-24 (mean=18.7) and 5-16.5 (mean=9.3) for M3a, M3b and
M3c, respectively.
Zeus faber
This
species was caught both on the shelf and in the upper edge of the slope in M3a
(85-160 m), in M3b (32-120 m) and in M3c (27-258 m). Considering the
regional level and combining all strata, the abundance indices were 3.3 kg
(CV=36.3) and 9 N (CV=17.7). The shelf indices were 8.5 (CV=36.4) and 24
(CV=17.9). The highest values by stratum were found in the 3rd of
M3a, as BI (15.9 with CV=54.8), and in the 1st stratum in M3b, as DI
(48 with CV=14.2).
The
range of the total length was 5-54 cm (mean=20.8) in the whole region, and
8.5-41.5 (mean=24.3), 6.5-53 (mean=17.6) and 5-54 (mean=19.6) for M3a, M3b and
M3c, respectively.
Aristeus antennatus
The blue
and red shrimp was fished only in the deepest stratum (5th:
500-800 m), occurring in a narrow depth range (550 – 704 m). Combining all
strata in the whole region, a BI of 0.5 kg (CV=32.0) and DI of 26 N (CV=28.3)
was observed. The slope values, however, were slight higher: 0.8 kg (CV=32.0),
as BI, and 42 N (CV=28.3) as DI. At sub regional level, the highest indices,
3.8 (CV=56.5) and 218 (CV= 55.7) were obtained in M3b.
The
range of the carapace length was 17-59 mm (mean=35) in the whole region, and
17-57 (mean=33), 22-59 (mean=36) and 20-59 (mean=40) for M3a, M3b and M3c,
respectively.
Aristaeomorpha foliacea
The red
shrimp was mainly caught in the deep waters (500-800 m), although this
species occurred also at the lower edge of the 4th stratum. The
depth ranges were 355-656 m in M3a, 548-596 m in M3b and 387-704 m in M3c. The
overall indices at regional scale were 8.5 kg (CV=15.4) and 410 N (CV=15.5),
but become quite higher (13.9, CV=15.4; 673, CV=15.5) when only the slope
strata are considered. At sub regional level, the highest indices were obtained
in the 5th stratum, but in different sub region: 25.6 kg (CV=27.9)
in M3c, and 1811 N (CV= 38.8) in M3a.
The
range of the carapace length was 13-69 mm (mean=33) in the whole region,
and 13-66 (mean=31), 20-68 (mean=38) and 17-69 (mean=40) for M3a, M3b and M3c,
respectively.
Nephrops norvegicus
Norway
lobster was collected almost exclusively on the slope; only few specimens were
gathered on the outer edge of the shelf in M3c sub region. The depth ranges
were 338-650 m, 555-595 m and 164-704 m in M3a, M3b and M3c, respectively.
Combining all strata in the whole region, a BI of 3.1 kg (CV=35.3) and DI of 97
N (CV=27.4) were observed. The slope values were 5.1 (CV=35.9), as BI, and DI
of 157 (CV=27.7). At sub regional level, the highest indices, 9.0 (CV=69.7) and
312 (CV= 46.6), were obtained in the 4th stratum of M3c.
The
range of the carapace length was 17-61 mm (mean=35) in the whole region
and 17-60 (mean=37), 22-61 (mean=35) and 18-56 (mean=34) for M3a, M3b and M3c,
respectively.
Parapenaeus longirostris
The rose
shrimp was found both on the shelf and in slope in M3a (68-529 m), M3b (76-584
m) and M3c (92-657m). The preferential depth range was, however, between 100
and 500 m. On the overall region, the abundance indices were 17.0 kg
(CV=12.9) and 3526 N (CV=15.7). The shelf-index, as BI, was lower than the
slope-index (13.0 vs. 19.6); otherwise DI was higher in the shelf (3855) than
in the slope (3315). The abundance by stratum in the Strait of Sicily (up to
55.0 kg, with CV=22.3, and 9661 N, with CV=28.3, in the 4th stratum)
overcame those corresponding to the other sub regions.
The
range of the carapace length was 5-42 mm (mean=20) in the whole region,
and 7-42 (mean=22), 5-39 (mean=21) and 8-38 (mean=19) for M3a, M3b and M3c,
respectively.
Eledone cirrhosa
This
species was found both on the shelf and the slope in M3a (121-619 m) and M3c
(92-387 m), while in the M3b it was caught only in the shelf (32-158m). At
regional scale, the overall abundance indices were 3.2 kg (CV=32.7) and 24 N
(CV=32.6). Both BI and DI for the shelf were higher than the slope-indices (6.1
vs. 1.3 kg, and 47 vs. 10 N). The highest abundance was found in the 3rd
stratum, no matter the sub regions considered. With regards to the BI, the
highest value was obtained in M3c (12.8 kg with CV=36.9), while the maximum of
DI was found in the M3a (117 N with CV=33.5).
The
range of the mantle length was 1.5-13.5 cm (mean=6.5) in the whole region,
and 1.5-12 (mean=5.4), 2-12 (mean=7.2) and 1.5-13.5 (mean=7.6) for M3a, M3b and
M3c, respectively.
Eledone moschata
A more
“coastal” species than the congener, this species was caught exclusively on the
shelf in M3a (only one haul at 40 m depth) and M3c (27-131 m), with the
exception of M3b, where this octopus was found between 40 and 383 m.
Considering the overall region, indices were 2.5 kg (CV=17.8) and 22 N
(CV=24.4). Shelf-indices, however, were quite higher: 6.3 kg (CV=18.1) and 56 N
(CV=24.7). The highest abundance indices were recorded in the 2nd
stratum of M3c, resulting 20.0 kg (CV=12.9) and 174 N (CV=18.7).
The
range of the mantle length was 1.5-19 cm (mean=6.9) in the whole region
and 7-10 (mean=8.5), 1.5-15.5 (mean=5.4)) and 2.5-19 (mean=7.3) for M3a, M3b
and M3c, respectively.
Illex coindetii
This
squid was found both on the shelf and the upper slope in M3a (68-440 m),
in the M3b (76-344 m) and M3c (34-434 m). Considering the abundance indices at
regional level, a preference for the shelf was quite evident: in fact, the
shelf-indices, both BI and DI, were higher than the slope-indices (6.7 vs. 0.8
and 109 vs. 7). Combining all the depths and sub regions, the following indices
were derived: 3.1 kg (CV=13) and 47 kg (CV=14). Generally, the highest
abundance occurred in the 3rd stratum; with regards to the BI for
this stratum, the highest value was obtained in M3c (11.0 kg with CV=15.4),
while the maximum of DI was found in the M3b (235 N with CV=25.0).
The
range of the mantle length was 4.5-25 cm (mean=13) in the whole region,
and 5-25 (mean=13.3), 5-20.5 (mean=13.7) and 4.5-25 (mean=12.4) for M3a, M3b
and M3c, respectively.
Loligo vulgaris
This
highly prized squid was fished only on the shelf in all sub regions, between 32
and 81 m depth, and almost exclusively in the M3b and M3c sub regions.
Shelf-indices were 1.5 kg (CV=36.3) and 31 N (CV=38.3); on the contrary,
considering all strata and the overall region, indices decreased to 0.6 kg
(CV=36.3) and 15 N (CV=38.3). The highest abundance indices were recorded in
the 1st stratum, but in different sub regions: 5.4 kg (CV=27.4) in
M3c, and 439 N (CV=27.5) in M3b.
It is
worth noting that the catch was represented only by small size specimens; in
fact, the range of the mantle length was 2.5-21 cm (mean=6.7) in the whole
region, and 2.5-9 (mean=5.3), 3-16 (mean=5.5) and 4.5-21 (mean=11.1) for M3a,
M3b and M3c, respectively.
Octopus vulgaris
The
common octopus was caught exclusively on the shelf at depth between 19-171 m
(M3a), 43 m (M3b; only one haul) and 27-71 m (M3c). Abundance indices of the
shelf were 8.3 kg (CV=31.9) and 16 N (CV=32.4), which, obviously, reduced to
lower values considering the combined strata on the overall region (3.2 kg,
CV=31.9; 6 N, CV=32.4). The highest abundance was recorded in the 1st
stratum. As far as the BI is concerned, the highest value was obtained in M3b
(23.8 kg, CV=37.0), while the maximum of DI was found in the M3c (51 N,
CV=30.1).
The
range of the mantle length was 3-19 cm (mean=8.7) in the whole region, and
4-15 (mean=9.3), 4.5-16 (mean=7.3) and 3-19 (mean=8.9) for M3a, M3b and M3c,
respectively.
Sepia officinalis
This
cuttlefish was caught only exclusively on the shelf with slight differences
between the depth ranges: 16-87, 40-43 and 27-138 m for M3a, M3b and M3c,
respectively. At regional scale and considering all strata, this species showed
BI of 0.8 kg (CV=49.2) and DI of 5 N (CV=49.1). When only the shelf catches are
considered, the indices increase up to 2.0 kg (CV=49.2) and 13 N (CV=49.1). At
sub regional level, the highest indices, 16.6 kg (CV=41.3) and 129 N (CV=
41.3), were obtained in the 1st stratum of M3a.
The
range of the mantle length was 8-16.5 cm (mean=10.5) in the whole region,
and 8-15 (mean=9.9), 8.5-16.5 (mean=13.8) and 9.5-13 (mean=10.9) for M3a, M3b
and M3c, respectively.
The five
most abundant target species by stratum were sorted considering the average of
the mean biomass index (BI; kg/km²) by stratum previously computed in each sub
region; the corresponding density index (DI; N/km²) were also presented along
with the respective coefficient of variation (CV; %).
A total
of 23 species, among those considered as targets, was found in this stratum
with a minimum abundance (BI>0.05); target crustaceans were absent (as the
case of Medits’98), while 17 bony
fish species and 6 cephalopods were caught. Mullus
barbatus is found in the “pole position”: the other most abundant targets
are 3 bony fish and 1 cephalopod, which data are presented, by sub region, in
the following tables:
|
|
M3a |
M3b |
M3c |
|||
|
species |
kg/km² |
CV% |
kg/km² |
CV% |
kg/km² |
CV% |
|
Mullus barbatus |
54.4 |
17.4 |
41.8 |
20.3 |
7.2 |
15.7 |
|
Trachurus
mediterraneus |
49.8 |
18.3 |
0 |
0 |
13.4 |
13.7 |
|
Pagellus
erythrinus |
14.9 |
17.3 |
26.7 |
21.5 |
3.4 |
14.6 |
|
Spicara flexuosa |
15.9 |
20.7 |
16.0 |
21.5 |
11.8 |
22.5 |
|
Octopus vulgaris |
1.8 |
32.5 |
23.8 |
37.0 |
13.6 |
41.5 |
|
|
M3a |
M3b |
M3c |
|||
|
species |
N/km² |
CV% |
N/km² |
CV% |
N/km² |
CV% |
|
Mullus barbatus |
2028 |
37.8 |
1308 |
19.2 |
194 |
12.4 |
|
Trachurus
mediterraneus |
3366 |
21.8 |
0 |
0.0 |
935 |
27.5 |
|
Pagellus
erythrinus |
298 |
13.8 |
408 |
20.6 |
57 |
8.6 |
|
Spicara flexuosa |
1281 |
16.2 |
683 |
19.4 |
895 |
30.7 |
|
Octopus vulgaris |
11 |
25.2 |
32 |
37.0 |
51 |
30.1 |
In this
stratum, abundance was not homogeneous among the subregions; in particular,
absence of Trachurus mediterraneus
must be noted in the catches realised in the subregion M3b. With the exception of O. vulgaris, M3c showed lower yields
than the other two subregions, with regards to the top five.
In the
whole region, only nine species, among the other targets, yielded more than 1
kg. The most relevant species were Sepia
officinalis (BI=6.8; DI=50), Pagellus
acarne (6.0; 155), Trachurus
trachurus (5.4; 792), Merluccius
merluccius (5.0; 68), Eledone
moschata (3.8; 24) and Loligo
vulgaris (3.7; 235). In all cases, some variability between the sub regions
was evident; for example, Merluccius
merluccius was not caught at all in the 1st stratum of M3b.
Among
the “minor” species (those included in the “Complementary list”), indices
higher than 5 kg resulted only in 5 species: Sardina pilchardus (104.7 kg), Engraulis
encrasicolus (40.6), Diplodus
annularis (29.4), Squilla mantis
(6.5) and Raja asterias (5.5); it is
worth noting that the first three species were the same of the Medits’98 survey, but with higher
catches in Medits’99.
Again,
some variability among sub regions were evident: for example, M3c yielded the
highest mean BI for Sardina pilchardus
(192.6 kg vs. 88.4 and 33.1 of M3b and M3a, respectively), whereas the biggest
catches of Diplodus annularis were
realised in M3a (68.0 kg vs. 7.9 and 12.2 of M3b and M3a, respectively).
Furthermore, M3b and M3c yielded the same amount of Engraulis encrasicolus (57.2 and 55.6), overwhelming the catch of
the same species in M3a (only 9.0 kg).
A total
of 28 target species, 21 fish (19 bony and 2 cartilaginous), 1 crustacean and 6
cephalopods, were fished within this depth range. It is worth noting that only
fish (and of the same species of the “top five” previously observed in Medits’98) are represented in the most
abundant species reported below:
|
|
M3a |
M3b |
M3c |
|||
|
species |
kg/km² |
CV% |
kg/km² |
CV% |
kg/km² |
CV% |
|
Trachurus trachurus |
17.5 |
42.6 |
251.5 |
40.9 |
209.1 |
54.3 |
|
Spicara
flexuosa |
25.3 |
27.1 |
44.7 |
21.6 |
127.0 |
27.3 |
|
Merluccius merluccius |
34.4 |
27.4 |
54.3 |
32.6 |
26.0 |
18.9 |
|
Mullus barbatus |
17.4 |
33.1 |
36.5 |
30.8 |
18.1 |
46.3 |
|
Pagellus erythrinus |
17.3 |
21.5 |
36.6 |
36.1 |
7.5 |
28.7 |
|
|
M3a |
M3b |
M3c |
|||
|
species |
N/km² |
CV% |
N/km² |
CV% |
N/km² |
CV% |
|
Trachurus trachurus |
2427 |
45.3 |
41289 |
43.0 |
27065 |
57.9 |
|
Spicara
flexuosa |
1496 |
27.9 |
1856 |
13.9 |
3650 |
28.2 |
|
Merluccius merluccius |
681 |
24.1 |
1141 |
24.7 |
348 |
29.8 |
|
Mullus barbatus |
503 |
35.1 |
868 |
29.6 |
426 |
50.2 |
|
Pagellus erythrinus |
250 |
22.1 |
295 |
33.7 |
77 |
28.3 |
The
abundance indices of the above reported species were generally lower in the M3a
sub region. It is remarkable the high variability in the indices of Trachurus trachurus (which was mainly
caught in M3b and M3c). Among the other target species, only two (Phycis blennoides and Eledone cirrhosa) yielded less than 1 kg
(BI=0.1). Conversely, the other most relevant captures, always ranked in order
of abundance, were Trachurus
mediterraneus (16.2 kg; 622 N), Spicara
smaris (15.5; 684), Pagellus
bogaraveo (14.8; 358), Octopus
vulgaris (10.0; 12) and Raja clavata
(8.9; 6).
Among
the catches included in the “Complementary list”, 8 species yielded BI over the
threshold of 5 kg: Sardina pilchardus
(52.0), Engraulis encrasicolus
(43.9), Boops boops (23.5), Lepidotrigla cavillone (15.7), Serranus cabrilla (14.4), Diplodus annularis (11.8), Mustelus mustelus (11.0) and Lepidopus caudatus (8.8).
With
regards to the sub regions comparison, it was evident an high geographic
variability: for example, considering only the 2nd stratum, Diplodus annularis was caught
exclusively in M3b, and Sardina
pilchardus almost exclusively in M3a (108.1 kg) and M3c, (46.4), with a
minimum yield in M3b (1.6). The bulk of the catch of Boops boops was realised in M3b, whereas no specimen of Mustelus mustelus was gathered in M3a
and M3b.
A total
of 29 target species were fished in this stratum: 22 fish (20 bony and 2
cartilaginous), 2 crustaceans and 5 cephalopods. Four fish and one crustacean
yielded the highest abundances:
|
|
M3a |
M3b |
M3c |
|||
|
species |
kg/km² |
CV% |
kg/km² |
CV% |
kg/km² |
CV% |
|
Trachurus trachurus |
17.9 |
35.7 |
22.5 |
32.5 |
145.4 |
58.2 |
|
Merluccius merluccius |
54.9 |
25.5 |
54.2 |
35.7 |
23.2 |
16.3 |
|
Spicara flexuosa |
0.7 |
45.6 |
7.3 |
30.9 |
42.6 |
53.0 |
|
Parapenaeus longirostris |
11.2 |
18.1 |
9.7 |
12.1 |
29.8 |
16.0 |
|
Zeus faber |
15.9 |
54.8 |
0.5 |
51.5 |
13.3 |
34.9 |
|
|
M3a |
M3b |
M3c |
|||
|
species |
N/km² |
CV% |
N/km² |
CV% |
N/km² |
CV% |
|
Trachurus trachurus |
2073 |
39.4 |
908 |
16,2 |
16354 |
62,5 |
|
Merluccius merluccius |
4111 |
21.4 |
1764 |
24.5 |
750 |
23.1 |
|
Spicara flexuosa |
14 |
44.2 |
175 |
31.3 |
2411 |
59.2 |
|
Parapenaeus longirostris |
2501 |
18.8 |
3732 |
13.7 |
8591 |
18.2 |
|
Zeus faber |
46 |
37.0 |
10 |
26.0 |
33 |
16.7 |
The
first position of T. trachurus is a
consequence of the great catches realised in the M3c sub region. Merluccius merluccius showed a higher
abundance in M3a and M3b than M3c, whereas the contrary occurred for S. flexuosa and P. longirostris. It is worth noting that the Medits’99 abundance for the latter
species is more than twice that realised in the Medits’98 (BI=12.4 kg)
Considering
the other important target species for this stratum, only 5 yielded more than 5
kg, and among these the most represented in the catches were Eledone cirrhosa (BI=9.1; DI=77), Illex coindetii (7.9; 167) and Mullus barbatus (6.8; 150).
Among
the catches included in the “Complementary list”, only 3 species yielded BI
over the threshold of 5 kg: Lepidopus
caudatus (67.9 kg), Lepidotrigla
cavillone (12.4) and Mustelus
mustelus (7.6). A few species (7) yielded regional BI means in this stratum
ranging between 1 and 5 kg; among these the most relevant were Boops boops (4.9), Sardina pilchardus (4.6), Argentina
sphyraena (3.1) and Conger conger
(2.7).
However,
in some cases the overall indices by stratum reflects geographical variability
in the catches: for example, high mean values were obtained for Lepidopus caudatus in M3a (55.6) and M3c
(147.7), but the overall BI was reduced by the low catches gathered in M3b (0.3
kg). Furthermore, only an average of 0.5 kg of Boops boops was obtained in M3a, whereas the corresponding yields
in the other sub regions were quite higher (6-8 kg).
On the
overall, 23 of the target species were found in this stratum, but only 14
yielded more than 1 kg. Fish species were the most numerous (14 bony and 3
cartilaginous), whereas crustaceans and cephalopods contributed with the same
number of species (3). In this stratum, however, the most abundant captures
belonged to 1 crustacean and 4 fish; for the latter it is worth noting the presence
of the black mouth shark (G. melastomus), a new entry for Medits’99:
|
|
M3a |
M3b |
M3c |
|||
|
species |
kg/km² |
CV% |
kg/km² |
CV% |
kg/km² |
CV% |
|
Parapenaeus longirostris |
8.7 |
20.3 |
22.1 |
13.1 |
55.0 |
22.3 |
|
Merluccius merluccius |
24.6 |
83.0 |
23.7 |
39.4 |
30.4 |
20.9 |
|
Galeus melastomus |
41.7 |
44.9 |
6.3 |
58.6 |
1.3 |
47.1 |
|
Phycis blennoides |
10.3 |
25.3 |
9.9 |
17.8 |
4.6 |
20.5 |
|
Raja clavata |
2.9 |
113.7 |
0 |
0.0 |
15.1 |
115.0 |
|
|
M3a |
M3b |
M3c |
|||
|
species |
N/km² |
CV% |
N/km² |
CV% |
N/km² |
CV% |
|
Parapenaeus longirostris |
824 |
26.1 |
2652 |
15.8 |
9661 |
28.3 |
|
Merluccius merluccius |
706 |
91.0 |
546 |
60.8 |
1033 |
33.7 |
|
Galeus melastomus |
520 |
49.7 |
57 |
44.9 |
49 |
56.1 |
|
Phycis blennoides |
522 |
17.7 |
1222 |
16.5 |
359 |
24.9 |
|
Raja clavata |
7 |
110.0 |
0 |
0.0 |
16 |
116.2 |
As
expected, the presence and contribution of the different species has changed in
comparison to those observed in the shelf strata; Parapenaeus longirostris and Merluccius merluccius represent the bulk
of the catch among the target species, with a clear prevalence in the M3c. It
is worth noting the high catch of G.
melastomus in M3a and the lack of R.
clavata specimens over M3b bottoms.
Concerning
the other target species, only 9 yielded more than 1 kg, and among these the
most abundant were: Nephrops norvegicus
(BI=5.3 kg; DI=162 N), Helicolenus
dactylopterus (3.9; 188), Micromesistius
poutassou (3.1; 74), Trachurus
trachurus (2.8; 14) and Scyliorhinus
canicula (2.4; 38). For these species, it is interesting to note that
present weight values are almost the same as the ones of the previous survey (Medits’98).
Among
the catches included in the “Complementary list”, all species but Lepidopus caudatus (49.5 kg of BI),
yielded inconspicuous catches (less than 0.1 kg). The index for Lepidopus caudatus was, however,
affected by the geographical variability: M3a and M3b yielded about the same
means BI (15.9-22.0 kg), whereas the bulk of the catch was obtained in M3c
(110.5).
By
comparing the Medits’99 results
(for the same category of species) with Medits’98,
the most remarkable difference concerns the strong reduction for Argentina sphyraena (0.9 vs. 5.0 kg).
The
lowest proportion of target species was caught in this stratum, both as
frequencies and abundance: as a matter of fact, only 17 targets (10 bony fish,
3 cartilaginous fish and 4 crustaceans) were recorded.
No
target cephalopod was caught in Medits’99
at these depths in significant amount (BI less than 0.05 kg). Catches were
generally poor (half of the species yielded less than 1 kg) with the exception
of Galeus melastomus and Aristaeomorpha foliacea, homogeneously
present in the three sub regions. The most abundant five species were:
|
|
M3a |
M3b |
M3c |
|||
|
species |
kg/km² |
CV% |
kg/km² |
CV% |
kg/km² |
CV% |
|
Galeus melastomus |
27.7 |
51.7 |
21.2 |
35.1 |
31.2 |
33.3 |
|
Aristaeomorpha foliacea |
25.1 |
26.1 |
20.2 |
37.7 |
25.6 |
27.9 |
|
Phycis blennoides |
6.9 |
42.5 |
6.8 |
6.5 |
10.9 |
25.4 |
|
Lophius piscatorius |
0 |
0.0 |
0 |
0.0 |
13.4 |
97.8 |
|
Merluccius merluccius |
0.8 |
81.4 |
0 |
0.0 |
8.4 |
69.0 |
|
|
M3a |
M3b |
M3c |
|||
|
species |
N/km² |
CV% |
N/km² |
CV% |
N/km² |
CV% |
|
Galeus melastomus |
174 |
59.0 |
180 |
38.6 |
169 |
32.7 |
|
Aristaeomorpha foliacea |
1811 |
38.8 |
883 |
35.8 |
1019 |
28.6 |
|
Phycis blennoides |
134 |
27.5 |
428 |
20.5 |
67 |
25.4 |
|
Lophius piscatorius |
0 |
0.0 |
0 |
0.0 |
2 |
72.4 |
|
Merluccius merluccius |
1 |
80.5 |
0 |
0.0 |
10 |
82.0 |
By
comparing the above reported densities in weight and number, it is evident that
the catch of Lophius piscatorius and Merluccius
merluccius is composed by few larger size fish, mainly or only trawled
within the M3c sub region.
The
other target species of some relevance (but always with low BI and DI) were one
fish (Helicolenus dactylopterus; 2.8
kg; 19) and two crustaceans (Aristeus
antennatus; 2.4; 132; and Nephrops
norvegicus; 2.1; 58). The distribution by sub regions remains in some cases
quite variable: for example, the captures of Aristeus antennatus were mainly concentrated in Tyrrhenian Sea (M3a
and M3b).
Cephalopods
did not occurred in this stratum, excepting negligible catches of Eledone cirrhosa (BI=0.12 kg), in the
sub region M3a, and Illex coindetii
(BI= 0.06 kg) in the sub region M3c.
Among
the catches included in the “Complementary list”, only 3 species were caught: Centrophorus granulosus (9.0 kg), Conger conger (2.2) and Lepidopus caudatus (0.4).
With
regards to the geographical variability, it must be noted that both Centrophorus granulosus and Conger conger were not gathered in M3b
sub region, whereas the catch of Lepidopus
caudatus occurred only in M3a.
One of
the basic goals of experimental trawl surveys, such those implemented within
the Medits project consists in
monitoring the level of abundance of the standing stocks. To be more effective,
however, the comparison among years should consider not only the single
species, but also the stocks assemblages. Furthermore, when different regions
are surveyed, it can also happen that steady overall indices hide important
differences occurring at a sub regional level, but always without any apparent
direction.
In the
specific case, a qualitative comparison of biomass indices (BI; kg/km²)
relative to the different Medits
surveys, which have been carried on in the M3 region since 1994, was done
considering only the 9 most abundant species, i.e., those which yielded BI
higher than the arbitrary threshold of 5 kg.
Furthermore,
the abundance of the species, which were consistently found among the 5 most
relevant captures in each stratum, were also compared in order to get an idea
of the sub regional and depth variation in the last three years.
Considering
the overall region, the results of the qualitative comparison of the BI can be
summarised as follows:
Trachurus trachurus – more than 100 kg/km² were estimated in the
first two Meditss surveys (Medits’94 and Medits’95), with the maximum BI in Medits’95. An abrupt decline was observed in Medits’96, and then BIs progressively
increased up to 47.5 kg (Medits’99).
No general trend is observable in M3 region.
Spicara flexuosa – the maximum abundance was registered in the
first survey (Medits’94). In the
following years, more or less the same BIs (about 20-30 kg) were obtained, with
the exception of Medits’98, when
a very low BI (9.4 kg) was estimated. The graphs do not show any general trend.
Merluccius merluccius – the current BI (20.2 kg) is
almost the same of the previous years, with no trend evident.
Parapenaeus longirostris – with the only exception of Medits’97, a positive trend is
appreciable for this crustacean. It is worth to note that Medits’99 yielded the highest BI (17.0
kg).
Galeus melastomus – for this small size shark, the abundance
level has been remained the same (at about 12 kg) since the first survey, with
no trend evident.
Raja clavata – the maximum abundance for this skate were
registered in the first (Medits’94)
and last (Medits’99) survey.
Between these years, the BI first declined (Medits’95)
and then began a progressive increase up to about 9 kg (Medits’99), so evidencing a slight
positive trend, at least after 1995.
Aristaeomorpha foliacea – this deep-water shrimp showed the
maximum abundance in the first survey (Medits’94).
An abrupt decline occurred in the successive year (Medits’95); then the BIs increased more or less regularly up
to 8.5 kg (Medits’99), showing a
slight positive trend.
Mullus barbatus – the relative abundance for this coastal fish
has not been changed since the first survey, with only slight irregular
variations around 6-8 kg.
Phycis blennoides – the picture emerging for the great fork beard
is analogous to that observed for the red mullet; i.e., only slight irregular
variations around 5-7 kg are evident.
The
above reported results indicate that neither substantial changes nor particular
trend can be detected on the most relevant targets on the base of the biomass
indices of the M3 region. However, a clearer picture of the temporal evolution
of the abundance of the demersal resources could be derived on the base of the
analysis of the data, gathered in all the Medits
regions in the different years.
Coming
back to M3 region, it remains the possibility that abundance variations
occurred in specific sub regions or depth levels.
In order
to give an idea of such modifications in the distribution pattern (if any),
some remarks concerning the variation in the catches by stratum and sub regions
are reported (not taking into account the precision degree of the means).
This
comparison refers to the surveys Medits’97,
Medits’98 and Medits’99, and it is limited to those
species which consistently resulted among the five most abundant targets.
In the 1st stratum, only 3 species have been always
found in the five targets in the 3 years considered, and their BI are presented
in the following table:
|
|
M3a
(kg/km²) |
M3b
(kg/km²) |
M3c
(kg/km²) |
||||||
|
species |
1997 |
1998 |
1999 |
1997 |
1998 |
1999 |
1997 |
1998 |
1999 |
|
Mullus barbatus |
33.1 |
4.4 |
54.4 |
44.3 |
60.5 |
41.8 |
10.1 |
7.0 |
7.2 |
|
T. mediterraneus |
31.4 |
12.9 |
49.8 |
0.6 |
0.9 |
0 |
55.3 |
65.1 |
13.4 |
|
Octopus vulgaris |
24.3 |
65.0 |
1.8 |
11.8 |
23.6 |
23.8 |
13.0 |
30.4 |
41.5 |
It is
interesting to note that Spicara flexuosa
was found between the five top species, both in Medits’97 and Medits’99.
Other relevant species were the two sea breams, Pagellus erythrinus and P.
acarne; the former has occurred in ’98 and ’99 surveys, whereas the latter
was found in ’97 and ’98 surveys.
Beside
the consistent presence of some species, the data in the table indicate a high
variability in the abundance both in time and in space. T. mediterraneus represents a good example of both geographical
(almost nil catch in M3b) and temporal (differences of ten of kg within the
same sub regions in different years) variation.
Finally,
the striking fluctuations are remarkable in the catches in this stratum,
concerning the common octopus.
Referring
to the 2nd stratum, the top five targets have been maintained
unchanged in the three years, although with different ranks. The results are:
|
|
M3a
(kg/km²) |
M3b
(kg/km²) |
M3c
(kg/km²) |
||||||
|
species |
1997 |
1998 |
1999 |
1997 |
1998 |
1999 |
1997 |
1998 |
1999 |
|
T. trachurus |
5.0 |
7.0 |
17.5 |
21.8 |
6.8 |
251.5 |
13.1 |
121.3 |
209.1 |
|
Spicara flexuosa |
24.8 |
27.8 |
25.3 |
155.4 |
36.7 |
44.7 |
113.5 |
51.3 |
127.0 |
|
M. merluccius |
36.7 |
14.2 |
34.4 |
15.3 |
14.7 |
54.3 |
35.0 |
25.2 |
26.0 |
|
Mullus barbatus |
6.4 |
13.2 |
17.4 |
112.3 |
79.6 |
36.5 |
9.7 |
8.5 |
18.1 |
|
P. erythrinus |
6.8 |
4.1 |
17.3 |
71.4 |
31.7 |
36.6 |
35.0 |
25.2 |
7.5 |
The
increase in the captures of T. trachurus is
astonishing: the BI for this species doubled in M3c and changed of two orders
of magnitude in M3b. Not considering this species, it is remarkable how the
mean abundance appear to be more balanced in M3a than the other two sub regions.
Within
the 3rd stratum, only two species have been consistently included in
the top five captures, in the three years (1997-’99). The BIs, presented below,
indicate a quite stable distribution both in time and space for the hake,
whereas a strong variability characterises the abundance of T. trachurus. For this benthopelagic
species, in fact, the catches were always higher in M3c than M3a, showing a
strong fluctuation (of one order of magnitude) in M3b.
|
|
M3a
(kg/km²) |
M3b
(kg/km²) |
M3c
(kg/km²) |
||||||
|
species |
1997 |
1998 |
1999 |
1997 |
1998 |
1999 |
1997 |
1998 |
1999 |
|
T. trachurus |
3.9 |
8.6 |
17.9 |
10.1 |
264.1 |
22.5 |
107.9 |
116.2 |
145.4 |
|
M. merluccius |
46.6 |
33.6 |
54.9 |
29.0 |
18.5 |
54.2 |
32.6 |
23.1 |
23.2 |
Among
the other relevant species, it is remarkable the higher affinity between Medits’99 and Medits’97 (two other species in common: Spicara flexuosa and Parapenaeus
longirostris) than Medits’98
(no other species in common). On the contrary, in Medits’97 and Medits’98,
Illex coindetii was found among the
five top species.
Talking
about the 4th stratum, the top species can be individuated in the
hake, rose shrimp, great fork beard and black mouth shark. The relevance for
the latter species (which was included in the main list at the end of 1998) was
assumed on the base of the comparison of the overall index of abundance. The
BIs for these common species are summarised in the following table:
|
|
M3a
(kg/km²) |
M3b
(kg/km²) |
M3c
(kg/km²) |
||||||
|
species |
1997 |
1998 |
1999 |
1997 |
1998 |
1999 |
1997 |
1998 |
1999 |
|
P. longirostris |
2.5 |
5.5 |
8.7 |
7.7 |
15.0 |
22.1 |
15.8 |
30.9 |
55.0 |
|
M. merluccius |
22.1 |
9.9 |
24.6 |
15.6 |
25.4 |
23.7 |
26.6 |
28.4 |
30.4 |
|
G. melastomus |
- |
- |
41.7 |
- |
- |
6.3 |
- |
- |
1.3 |
|
Phycis blennoides |
11.1 |
11.4 |
10.3 |
5.4 |
6.0 |
9.9 |
4.9 |
9.8 |
4.6 |
It is
worth noting the homogeneous increment in the index of abundance of the rose
shrimps: for this high prized crustacean, the BI of Medits’99 is almost three times higher than the corresponding
values of Medits’97.
More or
less stable indices characterise both Phycis
blennoides and M. merluccius.
Among the other most important species in this stratum, Helicolenus dactylopterus and
Trachurus trachurus appeared in Medits’97,
whereas they have been replaced by Lophius
budegassa and Raja clavata in Medits’98. However, it must be pointed
out that the relevance of the skate is the consequence of the high abundance in
the M3c, being almost absent in the other two sub regions.
In the 5th
stratum, only three top species resulted common to the three surveys, black
mouth shark, red shrimp and great fork beard, all showing more or less stable
indices of abundance. As indicated by the following values, however, only the
first two species have contributed mostly to the catches:
|
|
M3a
(kg/km²) |
M3b
(kg/km²) |
M3c
(kg/km²) |
||||||
|
species |
1997 |
1998 |
1999 |
1997 |
1998 |
1999 |
1997 |
1998 |
1999 |
|
G. melastomus |
- |
- |
27.7 |
- |
- |
21.2 |
- |
- |
31.2 |
|
A. foliacea |
26.9 |
18.9 |
25.1 |
23.1 |
19.7 |
20.2 |
16.7 |
19.4 |
25.6 |
|
Phycis blennoides |
8.5 |
8.5 |
6.9 |
5.4 |
5.8 |
6.8 |
5.7 |
6.6 |
10.9 |
Among
the other target species, Aristeus
antennatus and Helicolenus
dactylopterus were found in the Medits’97
and Medits’98, but were replaced
by L. piscatorius and M. merluccius in Medits’99. The lower rank in the red and blue shrimp in 1999,
however, is the consequence of a general reduction in the index of abundance
observed in M3 region, particularly evident in the M3c sub region (1.6 and 0.8
kg in ’98 and ‘99 surveys, respectively).
On the
contrary, the high rank of Lophius
piscatorius in Medits’99 was
determined by the relevant catches realised in M3c.
Finally,
the analysis of the Medits’99
results tends to confirm the spatial distribution and the abundance levels
observed in the previous surveys, at least for the most relevant species.
Variations among sub regions and strata are, however, important in some cases,
but of difficult interpretation when the analysis is based on a qualitative comparison
of single species in a limited region of the Mediterranean Sea.
Present
results, although useful to get a first picture about the variation degree of
the biomass between years, and of the different contributes of the target
species, must be treated with caution, also taking into account the relatively
shortness of the time series of available data.