Indigenous ecological knowledge and customary sea tenure may be integrated with marine and social science to conserve the bumphead parrotfish (Bolbometopon muricatum) in the Roviana Lagoon, Western Solomon Islands. Three aspects of indigenous ecological knowledge in Roviana were identified as most relevant for the management and conservation of bumphead parrotfish, and studied through a combination of marine science and anthropological methods. These were (1) local claims that fishing pressure has had a significant impact on bumphead parrotfish populations in the Roviana Lagoon; (2) the claim that only small bumphead parrotfish were ever seen or captured in the inner lagoon and that very small fish were restricted to specific shallow inner-lagoon nursery regions; and (3) assertions made by local divers that bumphead parrotfish predominantly aggregated at night around the new moon period and that catches were highest at that time. The research supported claims (1) and (2), but did not support proposition (3). Although the people of the Roviana Lagoon had similar conceptions about their entitlement rights to sea space, there were marked differences among regional villages in their opinions regarding governance and actual operational rules of management in the Lagoon. Contemporary differences in management strategies resulted from people's historical and spatial patterns of settlement across the landscape and adjoining seascapes, and the attendant impact of these patterns on property relations. This was crucial in distinguishing between those villages that held secure tenure over their contiguous sea estates from those that did not. Indigenous ecological knowledge served to (1) verify that the bumphead parrotfish was a species in urgent need of protection; (2) explain how different habitats structured the size distribution of bumphead parrotfish; (3) identify sensitive locations and habitats in need of protection; and (4) explain the effect of lunar periodicity on bumphead parrotfish behaviour and catch rates. Secure customary sea tenure identified locations best suited to bumphead parrotfish management programmes, with a greater likelihood for local participation and programme success. The information was used to establish two marine protected areas in the region for bumphead parrotfish conservation.