Preprint volume - SIBM

Pre-print Volume –Oral presentations
Topic 4: THE ELASMOBRANCHS
0.34, p = 0.0064), while no correlations emerged for Scyliorhinus spp. and “Asià”
group with any environmental variable (sea water temperature, annual mean Po river
discharge, NAO, WeMO).
During the surveys at the fish market, 2770 individuals were sampled, 2339 sharks and
431 skates, belonging to 13 species: Alopias vulpinus, Galeorhinus galeus, Mustelus
asterias, M. mustelus, M. punctulatus, Scyliorhinus canicula, S. stellaris, Squalus
acanthias, S. blainville, Raja asterias, R. clavata, R. miraletus, Myliobatis aquila. The
smooth-hound, M. mustelus, represented 61.15% of the samples, while A. vulpinus, G.
galeus, M. asterias, S. stellaris, S. blainville, R. miraletus and M. aquila, were
sporadically recorded. The attribution of sexual maturity to males highlighted, for the
most frequent species, that from 33.9% (R. clavata) to 86.7% (S. canicula) of sampled
males were sexually immature.
The developed demographic models were able to fit well landing data from 1997 to
2008, setting the fishing mortality at 0.23 for M. mustelus, and 0.39 for S. canicula.
Without management, the models forecast a reduction of 80%, for M. mustelus, and
90%, for S. canicula, in the next 50 years. From these models, a management strategy
that reduces fishing effort of one day a week stabilizes the population of M. mustelus
and significantly slows down the decline of S. canicula. A management measure
banning the landing of immature individuals allowed a significant increase of the
populations of both species.
Fig. 1 - Yearly landing data for the three categories reported at Chioggia’s fish market from 1945 to
2008.
Dati annuali di sbarcato presso il mercato ittico di Chioggia dal 1945 al 2008.
Conclusions – The analyses of fishery data highlighted an impressive decline in
landing, particularly for skates and Scyliorhinus spp., and the negative trend was even
stronger in the last fifteen years. The data presented here mirror the worldwide scenario
of decline or even collapse of elamobranch fishery (Bonfil, 1994), including the
Mediterranean (Jukic-Peladic et al., 2001; Ferretti et al., 2008). The documented
decrease in landings likely reflects real population decrease, given that elasmobranchs
represent mainly by-catch, market demand did not substantially change and fishermen
did not change their fishing grounds. Variations in environmental conditions are not
able to fully explain landing trends, even for skates whose landings correlated with
environmental factors, namely WeMO and NAO. Such correlations can reflect species
migration, likely to the southern Adriatic, due to the occurrence of unfavorable
conditions. The surveys at the fish market showed how elasmobranch catch is
41 st S.I.B.M. CONGRESS Rapallo (GE), 7-11 June 2010
200