Investigating gear and seasonal effects in experimental trawl surveys: the case of Galeus melastomus Rafinesque, 1810 (Chondrichthyes, Scyliorhinidae) in the South of Sicily (Central Mediterranean)

Mediterranean young-fish oriented experimental bottom trawl surveys represent a precious source of information on both past and current standing stocks and their life history traits and exploitation state. In the present note, taking the occasion of the same vessel employed in the South of Sicily (Central Mediterranean), an indirect approach has been implemented to compare MEDITS (Mediterranean International Bottom Trawl Survey) and GRUND (Gruppo Nazionale Demersali) abundance and biological features of the blackmout catshark Galeus melastomus Rafinesque, 1810 to highlight gear and season effects if any. Data were gathered between 1994 and 2006, in spring-summer (MEDITS) and autumn (GRUND). The density and biomass indexes and occurrences were substantially lower in spring than in autumn. On the contrary, the biological traits were more similar, although significant differences were detected in the length frequency distribution. The homogeneity of life traits between seasons and the critical features showed in this study demonstrate that an annual experimental trawl survey can be enough to monitoring G. melastomus. Similar analysis could be useful to highlight seasonal and gear effects on the other demersal stocks to better figure out limits and possibility of Mediterranean young-fish oriented experimental bottom trawl surveys data.