Recreational capacity is a function of the natural and social environment, the activity concerned, and the management regime. Indo-Pacific surf destinations with cheap and open access and no capacity management have experienced crowding, crime, pollution and price collapses. Many island surf breaks can handle only a few surfers at once because of the shape of the reefs. A crowding factor may be conceptualised as the proportion of rideable waves each surfer is forced to cede to another boardrider. Quota management systems using operator permits need to incorporate the complexity of the environment and the industry, but be equitable enough to gain general acceptance, and simple enough to enforce without dispute. Siberut Island in the Mentawai chain near West Sumatra, Indonesia, is covered by dense tropical rainforest which supports a number of endangered species and has been proposed as a Biosphere Reserve. It is also home to indigenous village communities with traditional social and religious practices. This island is subject to commercial logging and plantation agriculture, and tourism seems to be the only politically realistic economic alternative at present. To provide infrastructure for long-term growth in nature and cultural tourism, an immediate source of tourism revenue is needed. The most immediate option seems to be surf lodges on some of the smaller Mentawai Islands, which have already been largely cleared and are already visited by boat-based surf tour operators. Operators will only invest in lodges if they can acquire preferential rights to particular surf breaks. Hence the recreational capacity of the islands for surf tourism must be determined, and allocated between operators through a management system. Relevant data and one management option are presented here.