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.