This study analyzed the exploitation and sharing of coastal resources in Swahili maritime society, where many ethnic groups intersect. Bantu people and people of Arab/Persian descent have long coexisted in the use of fishery resources on Kilwa Island in Tanzania. The study area included three ecological sea zones (ecozones): mangrove inland sea, open sea with fringing reef, and intermediate sea. Because of the diversity of sea products in these ecozones, each ethnic group has been able to monopolize its own fisheries, thus reducing intergroup conflict. This has contributed to the maintenance of harmonious multi-ethnic coexistence on the island. A clear understanding on the current status of use/sharing of maritime resources by local people is a necessary component for avoiding social disorder caused by the environmental conservation policy.