Biol. Mar. Mediterr. (2010), 17 (1): 254-255
C. Manfredi, E. Ciavaglia, I. Isajlović*, C. Piccinetti, N. Vrgoč*
Laboratory of Marine Biology and Fisheries of Fano, University of Bologna,
Viale Adriatico, 1 – 16132 Fano (PU), Italy.
[email protected]
*Institute of Oceanography and Fisheries, Split, Croatia.
TEMPORAL AND SPATIAL DISTRIBUTION
OF SOME ELASMOBRANCHS IN THE NORTHERN
AND CENTRAL ADRIATIC SEA
DISTRIBUZIONE SPAZIO-TEMPORALE DI ALCUNI
ELASMOBRANCHI IN ALTO E MEDIO ADRIATICO
Abstract – Data collected from trawl survey, carried out in the Northern and Central Adriatic Sea,
were analysed in order to know about the spatial distribution of Myliobatis aquila, Mustelus mustelus
and Squalus acanthias. Distribution areas with relation to different seasons were discussed.
Key-words: Elasmobranchs, Adriatic Sea, geographical distribution.
Introduction - Myliobatis aquila (L., 1758), Mustelus mustelus (L., 1758) and Squalus
acanthias (L., 1758) are three demersal elasmobranchs species widely distributed in
the Mediterranean. In the Adriatic Sea the eagle ray lives on sand and soft substrates
up to 100 m in depth, but most often down to 50 m. The smooth-hound lives on
sandy and muddy-sandy bottom of the continental shelf up to 200 m depth. The
spiny dogfish lives in shallow waters, especially at 10-200 m depth, but exceptionally
it can be also found up to 900 m (Jardas, 1984). The aim of this work is to analyse
their spatial distribution and to consider possible seasonal changes.
Materials and methods – Data were collected in the Northern and Central
Adriatic from 2001 to 2007; in summer in the framework of the MEDITS project
(Bertrand et al., 2002) and in autumn-winter in the framework of GRU.N.D. project
(Relini, 2000) and FAO/AdriaMed Trawl Surveys Program. The sampling gear was
an experimental bottom trawl in summer surveys and an Italian commercial gear
in autumn surveys. In both surveys, a depth-stratified random scheme of sampling
was applied. Four depth-strata were explored (10-50 m, 50-100 m, 100-200 m and
200-500 m). Catches data were standardised per km2. In both seasons abundances
per stratum in the three sub-area (North Adriatic, Central Adriatic and Croatia), as
provided in the Medits project, were calculated. Statistical comparison of catches per
stratum were carried out by means of the non-parametric test of Kruskal-Wallis; in
the event of the H0 hypothesis being refused, a pairwise comparison procedure (test
of Mann-Whitney) was used to check significant differences between strata. Seasonal
distribution area were also mapped by means of geostatistical analysis using the
Indicator Kriging method. All spatial analysis and variography studies were carried
out using GStat; Arcview GIS 3.2a (Esri) was used for maps production.
Results – M. aquila was found up to 90 m depth. In summer, highest abundance
indices were estimated in the stratum 10-50 Croatia; catches in this stratum were
significantly higher respect to catches in the strata 10-50 North Adriatic and 50-100
Croatia (posthoc Mann-Withney test, p<0.01). In autumn catches also occurred
in the strata 50-100 North Adriatic and 50-100 Central Adriatic; in this season,
Kruskal-Wallis test did not show significant differences among strata. M. mustelus
was found up to 170 m. In summer, highest abundance indices were recorded in the
Temporal and spatial distribution of some elasmobranchs in the Northern and Central Adriatic Sea
255
stratum 10-50 Croatia, followed by the 10-50 North Adriatic; catches deeper than
50 m occurred only in Croatia. Catches of stratum 10-50 Croatia were significantly
higher than catches in other positive strata (posthoc Mann-Withney test, p<0.01).
In autumn, it was also caught in the strata 50-100 North and Central Adriatic and
100-200 Central Adriatic; Kruskal-Wallis test did not highlight significant differences
among strata. S. acanthias was found up to 240 m. In both seasons highest abundance
indices were estimated in the stratum 10-50 North Adriatic followed by the 50-100
North Adriatic and 50-100 Croatia.
Fig. 1 - Distribution area for the studied species in summer (above) and autumn (below).
Area di distribuzione delle specie indagate in estate (sopra) ed autunno (sotto).
Conclusions – Vertical distribution of the studied species agreed with the
bathymetric range reported by Jardas (1984). S. acanthias showed no significant
differences of distribution area between seasons. M. aquila and M. mustelus pointed
out a different distribution per stratum, also confirmed by the geostatistical analysis;
in summer, their distribution areas were limited to the North Adriatic and Croatia
while in autumn they also extended to the Central Adriatic. According to Jardas
(1984) their distribution depends on both depth and granulometric composition
of the bottom sediments but it probably also depends on other ecological and/or
environmental factors.
References
BERTRAND J.A., GIL DE SOLA L., PAPACONSTANTINOU C., RELINI G., SOUPLET A.
(2002) – The general specifications of the MEDITS surveys. Sci. Mar., 66 (Suppl. 2): 9-17.
JARDAS I. (1984) – Horizontal and vertical distribution of benthos Selachia (Pleurotremata,
Hypotremata) in the Adriatic. FAO Fish. Rep., 290: 95-108.
RELINI G. (2000) – La ricerca sulla pesca: le risorse demersali. Biol. Mar. Mediterr., 7 (4): 13-45.