The feeding ecology of eight demersal elasmobranchs, three sharks (Etmopterus spinax, Scyliorhinus canicula and Galeus melastomus) and five batoids (Myliobatis aquila, Leucoraja naevus, Raja polystigma, R. miraletus and R. clavata), from the Balearic Sea (western Mediterranean) was analyzed. For each species, the diet and feeding habits were characterized by depth strata using quantitative indices such as diet overlap, diet breadth and prey diversity. Diet variation with size and depth were also tested for the most abundant species. For shelf-living species, natantian and reptantian crustaceans together with teleosts were the most important preys. On slope bottoms, euphausiids were the preferential prey for S. canicula and G. melastomus, while E. spinax fed mainly on cephalopods. The most specialist and generalist diet corresponded to G. melastomus living on the upper slope and S. canicula from the continental shelf, respectively. High overlap was found between all the skates on the continental shelf and the sympatric sharks S. canicula and G. melastomus on the slope. Significant overlap was also found between S. canicula and R. clavata on the continental shelf. Size was found to significantly affect the diet of S. canicula, G. melastomus and R. clavata, whereas depth affected exclusively S. canicula.

Selectivity studies usually describe the effects on target species, whereas information on by-catch and discards is scarce. Nevertheless, large quantities of undersized individuals and invertebrates are discarded in the Mediterranean multi-species bottom trawl fishery. The present work analyses the data from two surveys carried out on the shallow and deep continental shelf (50–78 m, and 147–189 m, respectively) off the Balearic Islands (western Mediterranean). In these surveys, the traditionally used 40 mm diamond mesh codend and an experimental square mesh codend were used under commercial conditions. Catch composition, yields, size selectivity of both target and by-catch species, and discards were compared between the two mesh types. The mean selection length (L 50) clearly increased for most species when using square mesh, escaping many more individuals under their minimum landing size. Yield of Spicara smaris was significantly lower by using the square mesh, changing the composition of the retained catch. Escapement ratio and economic loss were significantly higher with square mesh, although economic loss was almost negligible for both meshes on the deep continental shelf. The use of square mesh significantly reduced the discards of algae in the shallow waters and fish on the deep continental shelf. The results confirmed that square mesh codend reduces the fishing pressure on small specimens as well as the impact of trawling on the ecosystem. These benefits would not lead to a reduction of the yields neither of the main target species, the fishes Merluccius merluccius, Mullus surmuletus, Zeus faber, and the cephalopods Loligo vulgaris and Octopus vulgaris, nor of the rest of commercial categories, except for Spicara smaris. Des études de sélectivité décrivent habituellement les effets sur une espèce-cible où les informations sur les captures accessoires et les rejets sont rares. Cependant, de grandes quantités de poissons et d'invertébrés de petites tailles sont rejetés dans les pêcheries plurispécifiques benthiques. Cette étude analyse les données de deux campagnes de pêche sur la plateau continental entre 50 et 78 m, et en zone plus profonde entre 147 et 189 m, respectivement, au large des îles Baléares. Durant ces campagnes, le chalut traditionnel, à mailles de 40 mm, montées en losange et un chalut expérimental à mailles montées en carré ont été utilisés en conditions commerciales. La composition des captures, les rendements et la sélectivité des tailles, à la fois des espèces-cibles et de celles des rejets ont été comparés entre ces deux types de mailles. La taille moyenne de sélection (L 50) augmente clairement pour la plupart des espèces en utilisant la maille carrée, laissant échapper davantage d'individus de taille inférieure à la taille autorisée pour les débarquements. Les rendements en Spicara smaris sont significativement inférieurs en utilisant la maille carrée, changeant la composition des captures retenues. La proportion des captures échappées et la perte économique sont significativement plus élevées avec la maille carrée bien que la perte économique soit presque négligeable pour les deux types de mailles en zones profondes du plateau continental. L'usage de maille carrée réduit significativement les rejets d'algues en eaux peu profondes, ainsi que les rejets de poissons en zones profondes du plateau continental. Les résultats confirment que les mailles de culs de chalut, montées en carré, réduisent la pression de pêche sur les petits individus ainsi que l'impact du chalutage sur l'écosystème. Ces avantages ne conduisent pas à une reduction des rendements ni ceux des principales espèces-cibles, les poissons Merluccius merluccius, Mullus surmuletus, Zeus faber, et les céphalopodes Loligo vulgaris and Octopus vulgaris, ni à ceux des autres catégories commerciales, à l'exception de Spicara smaris.

Chondrichthyans are a vulnerable group that has been overexploited for almost half a century in the Mediterranean. Since in this area most chondrichthyans are rarely incorporated into international statistics, the impact of fishing on their populations is difficult to assess. Here, we evaluate temporal trends in order to understand the recent history of chondrichthyans in the western Mediterranean. Fishery-independent data were obtained from scientific surveys carried out from 1994 to 2015 in three geographical sub-areas. Our results reflect fairly stable populations in terms of diversity, with some increase in density and standardized biomass of some species dwelling on the continental shelf, and even for some species dwelling on the slope. In contrast, decreasing trends were observed in some deep-water species. This can be explained by the reduction of the trawling effort on the continental shelf over the last few decades, and the shift of the fleet towards deep waters, along with the greater resilience displayed by some species. Furthermore, a decreasing trend in maturity ofScyliorhinus caniculawas detected, suggesting an evolutionary response to overfishing. These results improve scientific knowledge for developing true adaptive management in the Mediterranean that will implement measures to strengthen or initiate the recovery of chondrichthyans.