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 prefere..., Study area and data collection 
Boat-based surveys for dolphins were conducted along the south coast of South Africa within the Agulhas Bioregion in 2014–15. When a dolphin or groups of dolphins were encountered, they were identified and photographed, the position of the sighting was recorded and the behaviour of the dolphins were categorised. The surveys occurred between the western boundary of the Goukamma MPA and the eastern boundary of the Tsitsikamma MPA (Figure 1). The area is strongly influenced by the warm Agulhas Current [22] and wind-driven upwelling results in high levels of primary productivity and associated high prey biomass for predators [22]. 
The surveys were designed as a transect line of 145 km distance, running parallel to the coast (approximately 100 m from the coastline), corresponding with the known coastal preferences of both dolphin species [16,23]. A full survey was defined as transect completed within a calendar month between April 2014 and October 2015 (n: ..., R programme and Microsoft ExcelÂ