Feeding ecology of Mediterranean common dolphins: the importance of mesopelagic fish in the diet of an endangered subpopulation

The Mediterranean subpopulation of common dolphin (Delphinus delphis) is classified as endangered by the IUCN. Still, information about their diet in the Mediterranean is scarce. Stomach contents of 37 common dolphins stranded in the Alboran Sea and Strait of Gibraltar were analyzed. A total of 13,634 individual prey of 28 different taxa were identified. For fish, Myctophidae was the most important family as indicated by the highest index of relative importance (IRI = 8,470), followed by the family Sparidae (IRI = 609). The most important Myctophidae species was Madeira lantern fish (Ceratoscopelus maderensis) and for Sparids, the bogue (Boops boops). Cephalopods, instead, were found in low quantities only with 31 prey from the Loliginidae, Ommastrephidae, and Sepiolidae families. Overall, our results indicate that common dolphins are mainly piscivorous (99.77%N, 94.59%O, 99.73%W), feeding mostly on mesopelagic prey. Although common dolphins inhabit mainly coastal waters in the study area, the narrow continental shelf seems to facilitate the availability of Myctophids and other members of the mesopelagic assemblage to dolphins when the assemblage migrates to the surface at night. Our results represent the first attempt at quantifying the diet of this predator in the Alboran Sea and Strait of Gibraltar

This work was supported by Fundación Loro Parque, CEPSA (Compañía Española de Petróleos S.A.) and EcoCet Project from the Spanish Ministry of Economy and Competitiveness [CGL2011-25543]. JG and RdS were funded by a predoctoral and postdoctoral fellowship from the Severo Ochoa Programme for Centres of Excellence in R+D+I [SEV-2012-0262]. AM was funded by a postdoctoral fellowship from the Portuguese Foundation for Science and Technology [SFRH/BPD/64889/2009]. Thanks are due to the “Consejería de Agricultura, Pesca y Medio Ambiente” and the “Agencia de Medio Ambiente y Agua” of the “Junta de Andalucía” for the sample collection as a part of their program “Gestión sostenible del medio marino andaluz” and to CREMA (Centro de Recuperación de Especies Marinas Amenazadas). Special thanks to Carlos Gutiérrez-Expósito and Pauline Fabre for their help during the stomach content processing, Gema Hernandez-Milián and Lidia Nicolau for their help and advice with stomach content analysis, Silvia Monteiro for her statistical advice and Juan Moles for his valuable comments on the manuscript. Finally, we want to thank the anonymous reviewers for their comments that greatly improved the manuscript. The authors declare no competing financial interests.

Peer reviewed