Unravelling the ecological role and trophic relationships of uncommon and threatened elasmobranchs in the western Mediterranean Sea

16 pages, 7 figures, 4 tables, supplementary material http://dx.doi.org/10.3354/meps11494Deficiencies in basic ecological information on uncommon and endangered elasmobranch fishes impair the assessment of their ecological role in marine ecosystems. In this study, we examined the feeding ecology (diet composition and trophic level) and trophic relationships of 22 elasmo branchs (2 Carcharhiniformes, 1 Hexanchiformes, 1 Lamniformes, 3 Myliobatiformes, 6 Rajiformes, 6 Squaliformes and 3 Torpediniformes) present in the western Mediterranean Sea. To obtain a comprehensive view of the feeding ecology of these species, we combined different approaches: stable isotope analyses (δC and δN values), stomach content analyses and published sources. Our results revealed differences in feeding strategies among elasmobranch groups: skates (Rajiformes) mainly consume crustaceans; sharks (Carcharhiniformes, Hexanchiformes, Squaliformes and Lamniformes) prefer mixed diets composed of cephalopods, crustaceans and fishes; electric rays (Torpediniformes) feed mostly on fishes; and the diet of stingrays (Myliobatiformes) varies between species. Sharks and electric rays show higher trophic positions than skates, and the former occupy similar positions to other apex predators. Skates are more similar to other mesopredator fishes. These new findings offer essential information on the ecological role of several elasmobranchs in the western Mediterranean Sea and provide useful data for managers for future conservation strategiesC.B. was supported by a predoctoral fellowship CONICYT-Becas Chile. M.C. was partially supported by the Marie Curie Career Integration Grant Fellowships of the BIOWEB project and by a postdoctoral contract of the Ramon y Cajal Program (Spanish Ministry of Economy and Competitiveness). J.N. was supported by the projects Estación Biológica de Doñana-Severo Ochoa (SEV-2012-0262) and ESFRI-Life-Watch. This study forms a contribution to the project ECOTRANS (CTM2011-26333, Spanish Ministry of Economy and Competiveness, Spain) and to the PhD thesis of C.B.Peer Reviewe