Los Islotes is the southernmost breeding site of the California sea lion (Zalophus californianus) in Northern Hemisphere and represents one of the most important economic activities for the city of La Paz, Mexico. The increasing tourism activity grew without any control until researchers and organizations started to be concerned about the perturbation to the reproductive and haul-out patterns of the sea lion. The International Conservation Program of The Nature Conservancy funded a research project, with the goal to determine the effect of tourism activities on the behavior of sea lions, in order to help design regulations to assure better use and conservation of the site. The nature and intensity of tourism activity and the effects to the sea lion behavior were determined based upon monthly sampling over a one-year period (May 2000-April 2001). The main result was that perturbations occurred mostly in autumn and winter coinciding with the highest frequency of tourism, large number of male sea lions, increasing suckling behavior of pups, and unfavorable environmental conditions for haul-out, such as high tide level and strong winds. Researchers, service tourism providers, and governmental personnel collaborated and participated in workshops organized by the regional office, CONANP-SEMARNAT, in order to develop a regulation plan with a buoy system and zoning specifications for tourism activities. Some of the former management strategies are in current force in conservation management plans in the area. Current needs for conservation physiology studies relative to changes in tourism and fishing activities will also be discussed.