Niche variation in sympatric delphinids: Indo-Pacific bottlenose and Indian Ocean humpback dolphins on the south-east coast of South Africa

The ecological interactions and mechanisms that mediate coexistence among species are often poorly understood, despite its relevance to conservation management. A case in point is the Indo-Pacific bottlenose dolphin (Tursiops aduncus) and Indian Ocean humpback dolphin (Sousa plumbea) that occur sympatrically along the south-east coast of South Africa. To improve on our understanding of their coexistence, data on spatial distribution and habitat use were collected using boat-based surveys during 2014-15 along 145 km between Goukamma and Tsitsikamma MPAs. During 235 hours of survey effort, 55 and 42 encounters with T. aduncus and S. plumbea were recorded respectively. We investigated differences in their space use and habitat preferences. There was a strong overlap of the core areas used by both species, located mainly along Goukamma MPA and the eastern section of Plettenberg Bay. For both species, foraging was observed in mornings and travelling in afternoons. T. aduncus showed a preference for rocky areas in the afternoon while S. plumbea preferred estuarine and sandy habitats. We demonstrated that coexistence among dolphins with overlapping distributional patterns can be driven by fine-scale spatial segregation in feeding activities. Spatial conservation management measures such as the protection of sandy and estuarine habitats are recommended.