Many traditions of coastal peoples may be viewed as traditional forms of marine conservation because, like modern fisheries management, they restrict fishing gear, fishing times, and places, but their effects are little studied in practice. A study was undertaken of human culture and fisheries resources in an area of southern Kenya, designated as a national marine reserve, to determine the effect of the existing 'traditional management' on fisheries yields and on the ecological condition of the fished reefs. This area has one of the oldest and most elaborate cultural traditions concerning sacred sites and rituals of sacrifice along the Kenyan coast. The purpose of the customs is, however, to appease spirits rather than to regulate fish stocks which are traditionally seen to fluctuate independently of fishing effort. Many of these traditions have decayed in recent times as Islamization of the culture has occurred, and authority has shifted towards national organizations, weakening the effectiveness of the traditional leaders. Coincidentally, fishers have adopted new or foreign gear, colleagues, and traditions. Two adjacent landing sites (Mvuleni and Mwanyaza) have, however, successfully stopped pull seiners from landing their catch at their sites for over 20 years through passive means. Other landing sites have adopted pull seining. Both landing areas use arguments based on tradition to justify their use of gear. The two landings that restrict pull seining have higher per capita fish catches than those that do not. Nonetheless, there were no obvious differences in the ecological condition of the reefs at these two management areas; both areas were amongst the most degraded reefs reported in East Africa. Biological diversity and coral cover were reduced greatly in all these areas compared to other fished or fully-protected marine park or reserve sites established by the national government. Presently, traditional management is not effective in protecting species diversity or ecological functions, which was probably never the intention of the customs. The conflict between national organizations and local fishers arises because some resource users are concerned that the management proposed by the national organizations will eventually lead to the total loss of access to, and control of the resource by local fishers. There is, therefore, a need to resolve conflicts concerning gear use and regulation, and a need to increase awareness of the expectations and management programmes among the national and local organizations. Many of the traditional forms of management are compatible with the policies of national organizations, but confusion and conflict occur concerning enforcement and its benefits. To solve these conflicts discussions are required between traditional and national fisheries leaders to develop mutually-acceptable policies that augment and share the power of management.