Segregation and foraging ecology of whale sharks, Rhincodon typus, in the southwestern Gulf of California

Sharks segregate by sex and size, but few studies have attempted to explain such behaviors. To address this, we examined aggregations and the foraging ecology of whale sharks in Bahía de La Paz (BLP) with aerial and ship surveys and direct observation. Zooplankton abundance and composition, and hydrographic conditions were analyzed in relation to whale shark occurrence to explore underlying factors causing segregations. We observed large aggregations of juveniles (<9 m total length, TL) inshore, comprised by 60 % male individuals, and small aggregations of adults (>9 m TL) offshore, composed of 84 % females. Juvenile sharks were associated to turbid shallow waters in BLP, where they performed stationary and dynamic suction feeding on dense copepod swarms. Adults occurred in oceanic waters and fed by ram-filtering on diffuse patches of euphausiids, with no association to oceanographic conditions. Such segregation may be advantageous to juvenile R. typus utilizing shallow coastal waters to find abundant preferred prey needed for their fast growth rates. Our studies suggest that the main driving forces of whale shark segregation by sex and size in BLP may be diet preference for juveniles and habitat preference for adult sharks.