Preprint volume - SIBM
Preprint volume - SIBM
Preprint volume - SIBM
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Pre-print Volume –Oral presentations<br />
Topic 4: THE ELASMOBRANCHS<br />
C. PINTO, A. MANNINI, G. RELINI<br />
Centro Biolmar<br />
DIP.TE.RIS., Università degli Studi di Genova, V.le Benedetto XV, 3 – 16132 Genova, Italia.<br />
pinto.cecilia85@gmail.com<br />
REMARKS ON GALEUS MELASTOMUS<br />
IN THE NORTHERN LIGURIAN SEA<br />
OSSERVAZIONI SU GALEUS MELASTOMUS NEL NORD DEL MAR LIGURE<br />
Abstract – Galeus melastomus (Chondrichthyes, Scyliorhinidae) is a deep sea elasmobranch that is fished<br />
as a by-catch species of the bottom trawl fishery targeted to norway lobster and red shrimps. The mapping<br />
of its distribution shows that adults and juveniles occupy bottoms at different depths. Analyses of<br />
abundance doesn’t show significant trends in MEDITS while a decrease is detected in GRUND surveys.<br />
Key-words: Galeus melastomus, Selachians, trawl surveys, GIS, Ligurian Sea.<br />
Introduction – The study of by-catch species is considered significant in those kinds<br />
of fisheries that capture a wide range of species, as bottom trawling fishery does.<br />
Elasmobranchs are often part of by catch species and are reckoned as more vulnerable<br />
than other species, due to their biological and reproductive characteristics (Walker,<br />
1998). This group is characterised by a slow growth, late attainment of sexual maturity<br />
and long life spans (Stevens et al., 2000), moreover they are often top predators in the<br />
trophic web, that is why they are taken in account as good indicator, both, of the “topdown”<br />
effect of the trophic chain, and of populations variations due to overfishing<br />
(Carbonell et al., 2003; Serena et al., 2002; Baum et al., 2003). The main objective of<br />
this work is the identification of areas of distribution of a deep sea elasmobranch,<br />
Galeus melastomus, in the northern Ligurian Sea, dividing the population into adults<br />
and juveniles to verify if the last ones have preferential habitats. Having a 15 years<br />
time series of data derived from seasonal bottom trawl surveys, we got the chance to<br />
observe the trend of abundance, biomass, mean weight and lengths distribution, to<br />
determine the population status of adults and juveniles. This species has been studied<br />
in the past, in the same area, concerning reproduction and feeding patterns (Orsi Relini<br />
and Wurtz, 1975).<br />
Materials and methods - The study area is the Northern Ligurian Sea, from the<br />
French borderline to the North Gorgona Isle (belonging to Tuscany Archipelago). The<br />
dataset used was made taking data from GRUND (autumn season) and MEDITS<br />
(spring season) scientific trawling campaigns based on a random stratified sampling<br />
scheme, using a dataset of 15 years, from 1994 to 2008. A total number of 248 and 213<br />
hauls were carried out on bathyal grounds respectively in GRUND and MEDITS<br />
surveys. To realize the cartography representing the species distribution, we used mean<br />
points of trawling transects, representing them through ArcGIS 9.2. To have a more<br />
robust representation of the distributions using abundances of species, we put together<br />
abundances of all the 15 years for each fishing point and then realized an interpolation<br />
through the IDW technique building different maps for adults and juveniles (when data<br />
were available). Our interpolation has been limited to fishing points comprised<br />
between 200 m and 80 0m, since this species has never been found in shallower waters.<br />
We built trends to observe fluctuations of the population trying to assess the population<br />
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010<br />
206