Abstract
The time series of elasmobranch catch rates off the Tuscany coasts (NW Mediterranean) were investigated by means of min/max auto-correlation factor analysis in order to estimate variations in population abundance and evaluate the influence of environmental and anthropogenic factors. The analyses highlighted a general decreasing trend in the catch rates of sharks and skates from 1961 to the mid-1990s, mainly influenced by the increase in fishing effort. Since the 1990s, the EU Common Fishery Policy for the Mediterranean has promoted the reduction of fishing fleets through incentives to vessel demolition. The Porto S. Stefano trawl fleet has decreased by about 50%, leading to a decrease in fishing effort which seemed to be the most relevant factor affecting the increasing trend shown by the catch rates of Galeus melastomus, Scyliorhinus canicula and skates from 1991 to 2009. The elasmobranch assemblage did not undergo major shifts but the weighted frequency of occurrence shows that elasmobranchs were more frequent in the past. Particular caution should be paid in interpreting the recent rebound of some species as an early sign of recovery: trawl survey data and landing data show that over the last 50 years elasmobranch fauna have undergone a drastic decline and that recent rebounds are still far from a recovery to historical levels.
Highlights
For thousands of years fishing activities has fundamentally altered marine ecosystems
The catch rate time series of sharks and skates obtained from the Italian official fisheries statistics for the period 1961-2009 seem to follow a general decreasing pattern (Fig. 2), while the total engine power and the number of vessels increased until 1990 and started
sea surface temperature (SST), wind and WeMOi showed oscillating behaviours (Fig. 4), but no significant auto-correlation was found, so the time series were analysed without applying smoothing by means of seasonal decomposition (Loess smoothing)
Summary
For thousands of years fishing activities has fundamentally altered marine ecosystems. The removal of certain species of predators reduces environmental heterogeneity; elasmobranch overexploitation can have a detrimental effect on the whole ecosystem by disturbing the complex equilibrium that these predators provide (Gouraguine et al 2011). For these reasons, understanding the ecological role, distribution, and life histories of elasmobranchs is considered as a fundamental step towards the preservation of marine biodiversity, and the impact of fishing on elasmobranch stocks and the consequences of their decline on the ecosystem are currently raising considerable international concern (Stevens et al 2000, Myers and Worm 2003, Ferretti et al 2010)
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