Discards of elasmobranchs in a trammel net fishery targeting cuttlefish, Sepia officinalis Linnaeus, 1758, along the coast of Sicily (central Mediterranean Sea)

Abstract

Several species of elasmobranchs are commonly found as bycatch or discard in both artisanal and industrial fisheries. In particular, in the Mediterranean Sea, only few studies are available about bycatch and discards of elasmobranchs in artisanal coastal fisheries. In this study, we focus our attention on elasmobranch catches in a trammel net fishery targeting cuttlefish (Sepia officinalis) in the southeastern Ionian coast of Sicily (central Mediterranean Sea). In 2017, during the peak S. officinalis fishing season (February–May), four species of the infraclass Batoidea (Raja radula, Dasyatis pastinaca, Torpedo marmorata and Torpedo torpedo) constituted the total elasmobranch catches of the 16 survey days. Catch per unit effort (CPUE) of T. torpedo, in both number of specimens and biomass terms, showed the highest value, accounting for about 50% of the total. Except for the three larger specimens of R. radula (1.7% of R. radula specimens caught), all elasmobranchs were discarded. An ANOVA showed significant differences (P<0.05) between monthly CPUE values of the four species; while, for each species, the chi-square test failed (P>0.05) to show a significant difference in monthly CPUE values. Average disc width of the specimens caught showed the overall presence of a large number of juveniles. Chi-square test for sex ratio showed a significant difference (P<0.05) only for T. torpedo. For D. pastinaca, survival rate was equal to 0. Local traditions play an essential role in fishermen’s choice to discard or retain fishes. Monitoring the impact of fishing on populations of these vulnerable or potentially vulnerable species is of fundamental importance for the development of management strategies.