Feeding ecology of the highly threatened common bottlenose dolphin of the Gulf of Ambracia,Greece, through stable isotope analysis

The Gulf of Ambracia, in northwestern Greece, hosts a highly threatened community of about 150 common bottlenose dolphins (Tursiops truncatus). Until now, information on their feeding habits was derived exclusively from fish scale samples collected during surface-feeding events targeting small schooling epipelagic fish. The aim of this study was to determine the diet of bottlenose dolphins living in the Gulf of Ambracia through the application of Bayesian isotopic mixing models. Skin biopsy samples of 16 dolphins were analyzed and no difference related to sex or age-class was found in δ¹³C and δ¹⁵N values. Results suggested that the dolphin diet was mainly based on Trachurus trachurus, species belonging to the family Sparidae: Diplodus annularis, Lithognathus mormyrus, and Sepia officinalis, which represented together about 42% ± 15% of the biomass ingested, followed by species belonging to the order Clupeiformes (Engraulis encrasicolus, Sardinella aurita, and Sardina pilchardus) and the genus Gobius (37% ± 17%). A better understanding of the feeding habits of these dolphins sheds light on the feeding ecology of this highly threatened population by, for instance, evidencing interactions with artisanal fisheries sharing the same target species, and is key for identifying adequate management measures consistent with an ecosystem-based approach.