Preprint volume - SIBM

Pre-print Volume –Oral presentations
Topic 4: THE ELASMOBRANCHS
A. LIGAS, D. BERTOLINI, C. MANCUSI * , B. REALE, M. RIA * , P. SARTOR, M. SBRANA,
F. SERENA * , A. VOLIANI * , S. DE RANIERI
Centro Interuniversitario di Biologia Marina ed Ecologia Applicata “G. Bacci”,
V.le N. Sauro, 4 - 57128 Livorno, Italia.
ligas@cibm.it
* A.R.P.A.T., Area MARE - 57126 Livorno, Italia.
TEMPORAL EVOLUTION OF LANDINGS
OF ELASMOBRANCHS IN TUSCANY (MEDITERRANEAN SEA)
EVOLUZIONE TEMPORALE DELLO SBARCATO
DI ELASMOBRANCHI NEI MARI TOSCANI
Abstract – The time series of landings per unit of effort of some elasmobranch species/category by the
Porto S. Stefano and the Viareggio bottom trawl fleets were analyzed by means of Min/Max Autocorrelation
Factor Analysis. This approach was useful to highlight the increasing trend of such species
during the investigated period (1991-2008). The trends were positively affected by the reduction of fishing
effort in both Porto S. Stefano and Viareggio trawl fleets. The effects of the environmental variables were
significant as well.
Key-words: bottom trawling, shark fisheries, landings, time series, Mediterranean Sea.
Introduction – Sharks and rays appear to be particularly vulnerable to fishing
exploitation. The biological characteristics of elasmobranchs, such as low fertility, low
growth rate and late maturity, make them vulnerable to drastic increases in mortality
rates. Shark depletion, however, often goes unnoticed and the capture may continue for
many years, as fisheries are sustained by the more productive target fishes). Given the
mainly artisanal and semi-industrial aspects of Mediterranean fisheries, and the
relatively low economic value of elasmobranchs, fishery statistics are rarely adequately
reported (Ferretti et al., 2005). Notwithstanding these problematics, previous studies
carried out in different Mediterranean areas highlighted that shark species diversity and
biomass have decreased in the last century due to fishing pressure (Abella & Serena,
2002; Ferretti et al., 2005).
The present study aims to investigate the temporal variations of landings per unit of
effort (LPUE) of elasmobranchs in Tuscany through the analysis of the time series of
data obtained from landing and effort monitoring surveys. In addition, the temporal
evolution of LPUEs was related to three explanatory variables: overall fishing effort
indices, superficial seawater temperature (SST) and North Atlantic Oscillation (NAO)
index.
Materials and methods – During the period 1991-2008, landing and effort data were
collected monthly at the auctions of Porto S. Stefano and Viareggio. Monthly landings
per unit of effort (LPUE) were calculated (as kg/day/vessel) for the Black mouth
catshark, Galeus melastomus, the Small-spotted catshark, Scyliorhinus canicula, the
Longnosed skate, Dipturus oxyrinchus, and for the commercial category “Rays” from
the Porto S. Stefano data. As concerns Viareggio data, the LPUE were computed (as
kg/h) for the Black mouth catshark, the Small-spotted catshark, and the Starry ray,
Raja asterias. To investigate the effect of hydrological conditions on LPUEs, mean
monthly values of SST (°C) and NAO index were collected from www.pfeg.noaa.gov
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