Rapp. Comm. int. Mer Médit., 36,2001
282
Introduction
Small-scale fisheries are of primary social and economic importance to
Greece, accounting for 87.5% of the mean number of boats and 47.7% of
the mean value of landings (1). In the present study, multivariate tech-
niques were used to identify gear competition and overlap, in terms of total
length, weight and value, between gillnets and longlines for Diplodus
annularisandSerranus cabrilla.
Materials and Methods
Overall, 46 fishing trials were carried out in the coastal waters off Naxos
Island (Cyclades), from October 1997 to October 1998, with gillnets (mesh
sizes : 22, 24, 26 and 28 mm bar length; G
22
, G
24
, G
26
and G
28
, respec-
t ively) and longlines (“Mustad” round bent spade hooks of sizes
11>12>13>15; H
11
, H
12
, H
13
and H
15
, respectively). 1000 m of each mesh
size and 250 hooks of each hook size were used. Fishing with all gears
took place on the same day, at the same general area and at depths ranging
from 4 to 90 m. Wholesale values are from reference 2, whereas market
values were collected locally. Data were grouped in classes with different
step per parameter (total length, TL : 0.5, 1, 2 and 3 cm; weight : 5, 10, 15,
20 and 25 g; wholesale and market value : 2, 5, 10 and 15 drh). The (num-
ber per class)¥(fishing gears) matrices were transformed to triangular
matrices using the Bray-Curtis similarity index (3) and subjected to both
clustering (group-average linking) and non-metric multi-dimensional scal-
ing (MDS) techniques, using PRIMER (4).
Results and Discussion
Overall, 284 individuals of D. annularisand 466 individuals of S.
cabrillawere caught. Both cluster (Fig. 1) and MDS (figures not shown)
indicated the same groups per species for all parameters examined (weight
and values : figures not shown), irrespectively of class step. Three groups
(G
22
+G
24
; G
26
+G
28
+H
15
; and H
11
+H
12
+H
13
) were identified for D. annu-
laris(Fig. 1a) and two (G
24
+G
26
+G
28
; and G
22
+H
11
+H
12
+H
13
+H
15
) for S.
cabrilla(Fig. 1b).
Figure 1. Dendrograms of group-average clustering for (a) Diplodus annu-
l
a
r
i
sand(b)Serranuscabrilla,usingBray-Curtissimilaritymatrices
(based on length, step=1 cm), Cyclades 1997-1998. G
2
2
, G
2
4
, G
2
6
, G
2
8
:
gillnets with mesh sizes 22, 24, 26 and 28 mm, respectively; H
11
,
H
1
2
, H
1
3
,
H
15
: longlines with hook sizes 11, 12, 13 and 15, respectively.
ForD. annularis, group G
26
+G
28
+H
15
generally caught larger individ-
uals of higher value when compared to those of the remaining ones (Fig.
2). The greatest fishing pressure was expended on small sized and valued
classes (Fig. 2). The percentages of individuals with TL<TL
m50
(i.e.,
length at 50% maturity) caught in groups G
22
+G
24
and H
11
+H
12
+H
13
were
35.3 and 15.0%, respectively, whereas that of group G
26
+G
28
+H
15
was the
lowest, 1.9% (Fig. 2).
Figure 2. Diplodus annularis. Cumulative frequency distributions of
total length, weight, wholesale value and local market value, for the
groupsidentifiedbymultivariateanalysis:G
2
2
+
G
2
4
(---------),
G
26
+G
28
+H
15
(---------- ), and H
11
+H
12
+H
13
(- - -) (for symbols see Fig. 1),
Cyclades 1997-1998. Vertical line indicates length at 50% maturity
(L
m50
=12.5 cm; from reference 5).
ForS. cabrilla,group G
24
+G
26
+G
28
caught larger individuals and of
higher value when compared to group G
22
+H
11
+H
12
+H
13
+H
15
(Fig. 3).
Although both groups competed for some size classes (Fig. 3), group
G
24
+G
26
+G
28
caught considerably fewer individuals with TL<TL
m50
than
group G
22
+H
11
+H
12
+H
13
+H
15
(21.6 and 58.0%, respectively).
Figure 3. Serranus cabrilla. Cumulative frequency distributions of total
length, weight, wholesale value and local market value, for the groups
identifiedbymultivariateanalysis:G
2 4
+
G
2
6
+
G
2 8
(---------)and
G
22
+H
11
+H
12
+H
13
+H
15
(- - -) (for symbols see Fig. 1), Cyclades 1997-
1998. Vertical line indicates length at 50% maturity (L
m50
=17.5 cm; from
reference 1).
The results clearly indicated the strong multi-gear nature of the Greek
small-scale fisheries, one of the main factors responsible for the failure of
the technical regulations currently in force, and thus the importance of
Marine Protected Areas as one of the most promising management tool
(for an extended discussion see : 1, 6).
References
1.Stergiou K.I., Christou E.D., Georgopoulos D., Zenetos A. and
Souvermezoglou C., 1997. The Hellenic Seas : Physics, Chemistry, Biology
and Fisheries. Oceanogr. Mar. Biol. Ann. Rev., 35 : 415-538.
2.Smirnioti E., 1998. HAFD A.E. Statistical data of fish catch distribution.
Total for wholesale markets 1997. Greek Fish. News, 208 : 85-88 (in Greek).
3.Bray J.R. and Curtis J.T., 1957. An ordination of the upland forest
communities of southern Wisconsin.Ecol. Monogr., 27 : 325-349.
4.Clarke K.R. and Warwick R.M., 1994. Change in marine communities : an
approach to statistical analysis and interpretation. Natural Environment
Research Council, UK.
5.Froese R. and Pauly D., 2000. FishBase 2000 (online).
SMALL-SCALE GEAR COMPETITION AND OVERLAP FOR DIPLODUS ANNULARIS
ANDSERRANUS CABRILLA
P. K. Karachle* and K. I. Stergiou
Aristotle University of Thessaloniki, School of Biology, Department of Zoology, Laboratory of Ichthyology,Thessaloniki, Greece -
kstergio@bio.auth.gr
Abstract
In the present study, multivariate techniques were used to analyse competition and overlap between different fishing gears (gillnets : 22,
24, 26 and 28 mm bar length; longlines with hook sizes : 11>12>13>15), in terms of total length, weight and value, for Diplodus annularis
andSerranus cabrilla. Cluster and multi-dimensional scaling analyses clearly indicated that gillnets with mesh sizes 26 and 28 mm and
hook size 15, for D. annularis, and gillnets with mesh sizes 24, 26 and 28 mm, for S. cabrilla, caught larger individuals of higher value,
the vast majority of which were sexually mature, than the remaining gears.
Keywords : fisheries, Aegean Sea
