Fishing communities constantly change and adapt to modifications in the environment, and are reflected in changes to variables related to the dynamics of a fishery. Such changes in a fishery could involve a decline in fish stocks, market failure or the loss of an important species. The effects of such changes on the social dynamics of artisanal fishing communities have been poorly investigated in the Western Indian Ocean region. This article examines how communities have been affected by recent environmental, technological and socio-cultural changes in fisheries in five coastal villages in the Mtwara rural district, Tanzania, and the mechanisms whereby people cope with these changes. Data were derived from 103 semi-structured interviews, 15 focus group discussions, nine oral interviews, participant observations, and reviews of literature and policy documents. Overall, nearly 80% of respondents declared that there were significant changes in fishing techniques, strategies and the social organisation of the fishers. Almost 60% of the respondents admitted that traditional fishing gear such as traps and hand lines have increasingly been replaced by fishing nets operated from powered boats, especially since the 1980s, to compensate for declining fish catches. There is a shift from collective communal fisheries to individual and private fishing groups due to weakening of social structures and increased monetisation in the fishery activities. New values and perspectives are now being integrated into the communities. Approaches required for understanding and promoting development of fishing communities should include objectives that recognise how social structures adapt in the face of extreme conditions of the fishery.