The Caribbean spiny lobster, Panulirus argus, Latreille, is the main source of income for the communities in the Sian Ka'an Biosphere Reserve Mexico. The fishery has recently been certified as sustainable by the Marine Stewardship Council provided that further stock assessment is carried out. A total of 379 lobsters were tagged in an unfished area offshore from the Bahía del Espíritu Santo fishing grounds to assess whether lobsters remained within these areas and were thus fully protected. The lobsters recaptured in the shallow area (5.3%) were sufficient to develop a multistate mark recapture model, which takes into account fishing and natural mortality, tag reporting rate and tag loss. This estimated that between 15 and 20% of all adult lobsters dwelling in the unfished area moved into the fishery and were subjected to exploitation. This study suggests that the offshore unfished area provides protection to the majority of the stock in this area while adding to and maintaining fishing yields within the inshore commercial fishery.