Foraging ecology and fisheries interactions of common bottlenose dolphins (Tursiops truncatus) inferred from strandings in western iberian atlantic waters

The common bottlenose dolphin (Tursiops truncatus) is a resident species along the Portuguese mainland coast, yet knowledge of its stranding patterns and feeding ecology is scarce. This study presents a comprehensive assessment of strandings (n=264, from 1980 to 2019) and feeding ecology based on stomach content analysis (n=43 from 1997 to 2019) along the Portuguese mainland coast. Strandings were more frequent in the first half of the year and have increased in recent decades, particularly along the northwestern and southern coasts, likely reflecting improved monitoring efforts. Dietary analysis revealed a predominantly piscivorous diet (>85% by number and weight), with prey including pelagic, meso-pelagic, and demersal fish species. Hake (Merluccius merluccius), conger eel (Conger conger), and blue whiting (Micromesistius poutassou) emerged as the most important prey items. Despite a preference for demersal and mesopelagic fish, dolphins exhibited dietary plasticity, foraging across diverse habitats, likely adapting to local prey availability. The substantial dietary overlap with commercially targeted species, particularly by small-scale and coastal fisheries, suggests potential interactions and competition for shared resources. These findings provide valuable insights into the trophic ecological role of bottlenose dolphins in the region and highlight the need to consider this species in ecosystem-based fisheries management and conservation planning.