" We used photo-identification data collected from 2003 through 2009 to estimate population structure, site fidelity, abundance, and movements of this species along the west coast of the Gulf of California to make recommendations for effective conservation and management. Of 251 whale sharks identified from 1784 photographs, 129 sharks were identified in Bahía de Los Ángeles and 125 in Bahía de La Paz. Only juveniles (mostly small) were found in these 2 bays. At Isla Espíritu Santo, we identified adult females; at Gorda Banks we identified 15 pregnant females. High re-sighting rates within and across years provided evidence of site fidelity among juvenile sharks in the 2 bays. Though the juveniles were not permanent residents, they used the areas regularly from year to year. A proportion of the juveniles spent days to a month or more in the coastal waters of the 2 bays before leaving, and periods of over a month outside the study areas before entering the bays again. Additionally, 26 juveniles migrated between Bahía de Los Ángeles and Bahía de La Paz. Pregnant females aggregated for a few days in oceanic waters at Isla Espíritu Santo and Gorda Banks, but no re-sightings occurred between years. The presence of pregnant females and small juveniles (2 m) suggests the presence of a nursery near the 2 far offshore areas. These 4 localities are important for conservation of this endangered species."