Diet of bottlenose dolphins (Tursiops truncatus) from the Gulf of Cadiz: Insights from stomach content and stable isotope analyses

The ecological role of species can vary among populations depending on local and regional differences in diet. This is particularly true for top predators such as the bottlenose dolphin (Tursiops truncatus), which exhibits a highly varied diet throughout its distribution range. Local dietary assessments are therefore critical to fully understand the role of this species within marine ecosystems, as well as its interaction with important ecosystem services such as fisheries. Here, we combined stomach content analyses (SCA) and stable isotope analyses (SIA) to describe bottlenose dolphins diet in the Gulf of Cadiz (North Atlantic Ocean). Prey items identified using SCA included European conger (Conger conger) and European hake (Merluccius merluccius) as the most important ingested prey. However, mass-balance isotopic mixing model (MixSIAR), using δ13C and δ15N, indicated that the assimilated diet consisted mainly on Sparidae species (e.g. seabream, Diplodus annularis and D. bellottii, rubberlip grunt, Plectorhinchus mediterraneus, and common pandora, Pagellus erythrinus) and a mixture of other species including European hake, mackerels (Scomber colias, S. japonicus and S. scombrus), European conger, red bandfish (Cepola macrophthalma) and European pilchard (Sardina pilchardus). These contrasting results highlight differences in the temporal and taxonomic resolution of each approach, but also point to potential differences between ingested (SCA) and assimilated (SIA) diets. Both approaches provide different insights, e.g. determination of consumed fish biomass for the management of fish stocks (SCA) or identification of important assimilated prey species to the consumer (SIA).The study was funded by Fundación Loro Parque, CEPSA (Compañía Española de Petroleos S.A.), EcoCet Project [CGL2011-25543], SafeSea EEA-Grants and European Commission’s Life Programme [MarPro NAT/PT/00038]. J.G. and R.dS. were funded by the Spanish Ministry of Economy and Competitiveness through the Severo Ochoa Programme for Centres of Excellence in R+D+I [SEV-2012-0262]. A.M. and L.N. were partly supported by the Portuguese Foundation for Science and Technology [SFRH/BPD/64889/2009 and SFRH/BD/51416/2011]. Project ECOBOGUE-P11RNM7467 was funded by “Consejería de Economía, Innovación y Ciencia – Junta de Andalucía. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript