Preprint volume - SIBM

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Pre-print Volume –Oral presentations
Topic 4: THE ELASMOBRANCHS
days at sea (Porto S. Stefano) hours at sea (shelf, Viareggio)
hours at sea (slope, Viareggio)
Jan-91 Jan-93 Jan-95 Jan-97 Jan-99 Jan-01 Jan-03 Jan-05 Jan-07
months
Fig. 2 – Time series plot of the mean monthly values of the explanatory variables.
Serie temporali delle variabili esplicative.
From the Porto S. Stefano data set, an increasing common trend was extracted by
means MAFA, positively correlated to all the response variables and SST, and
negatively correlated to the fishing effort (Fig. 3). As concerns Viareggio, two trends
were computed: the first trend significantly related to S. canicula, R. asterias, and the
fishing effort, the second to G. melastomus and the NAO index (Fig. 4).
Conclusions – The application of MAFA highlighted the presence of three trends
underlying in the multi-species data sets. The available evidence suggests that the
reduction of fishing effort should have mainly driven these trends. The trawl fleet
capacity in Porto S. Stefano decreased of almost 50% since 1990s (Sbrana et al., 2006).
This reduction was mainly due to the Common Fishery Policy. The Viareggio trawl
fleet suffered a less sharp decrease in capacity, whereas the fishing effort showed a
sharp shift from the continental shelf to the slope. The reduction of fishing effort on the
shelf favoured the biomass increase of S. canicula and R. asterias. The trend of the
deep-water species G. melastomus was influenced by the NAO index. The influence of
NAO on marine resources has been already highlighted (Solow, 2002). The SST was
positively correlated to the evolution of LPUEs of Porto S. Stefano fleet. A warming
process of the upper and intermediate water layers of the western Mediterranean
occurred since 1950s (Briand, 2000; Vargas-Yánez et al., 2009), and it may favoured
the population biomass increase. Further investigations are requested to combine
different sources of data (surveys, landings, log-books, interviews, etc.), in order to
face with an accurate scenario of the spatial and temporal evolution of chondrichthyan
communities, and to get suitable protection and conservation measures. The depletion
of the elasmobranchs in the Mediterranean could be largely underestimated and
requires an immediate large scale reassessment (Ferretti et al., 2005).
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010
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