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In trawl fisheries, elasmobranchs are commonly caught as bycatch and discarded, including the lesser-spotted dogfish (Scyliorhinus canicula) and the marbled electric ray (Torpedo marmorata). This study examined their feeding ecology in the Gulf of Cádiz and tested the hypothesis that S. canicula would display a broader and more diverse diet than T. marmorata, with diet composition in both species varying according to body size and environmental factors, and Levin's index indicating opportunistic feeding. A total of 303 individuals were analyzed between 2019 and 2022. The two species showed clear habitat segregation, with S. canicula more frequent at greater depths and T. marmorata in shallower waters, while both were more abundant during nighttime hauls. Diet analysis revealed higher prey diversity in S. canicula compared to T. marmorata, with crustaceans and teleosts as dominant prey in both species. T. marmorata showed a higher vacuity index, suggesting reduced feeding activity or more specialised foraging. In S. canicula, diet composition varied with body size, depth, and time of day, whereas no effects of sex or parasite presence were detected. Levin's index indicated a relatively narrow trophic breadth in both species. These results highlight species-specific differences in trophic ecology and the influence of biological and environmental factors on feeding strategies in discarded elasmobranchs. They underscore the ecological relevance of bycaught species in demersal food webs and support their inclusion in ecosystem-based fisheries management frameworks.
Fernández-Oliveras et al. (2026) studied this question.