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ABSTRACT Investigating the foraging ecology and trophic interactions of threatened marine predators is critical to assess how community changes due to anthropogenic activities will affect predator–prey relationships. Two species of threatened coastal dolphins, the Indian Ocean humpback dolphin (Sousa plumbea) and the Indo‐Pacific bottlenose dolphin (Tursiops aduncus), occur off Nosy Be, north‐western Madagascar, in a region where artisanal fisheries are ecologically and socioeconomically important. Here, we investigated the feeding ecology of these two coastal dolphins and their trophic interactions with four other odontocetes using bulk stable carbon and nitrogen isotope analysis (δ¹³C andδ¹⁵N). Humpback dolphins had significantly enrichedδ¹³C values, reflecting a preference for coastal/benthic prey. Bottlenose dolphins had a broader isotopic niche, suggesting a broader range of prey and foraging habitats. The overlap in isotopic niche of all six odontocete species was limited, indicating partitioning of resources and habitats. Bayesian mass‐balance isotopic mixing models revealed that humpback dolphins forage primarily on reef planktivores (38.9%) and inner reef mesopredators (20.5%), while bottlenose dolphins had a broader diet, including reef‐associated (15%–32%) and pelagic prey (12%–23%). Our study reveals that the reliance on inshore prey by humpback dolphins may place them in competition with coastal fisheries.