Abstract

Between mid-April and September each year, large numbers of whale sharks (Rhincodon typus) visit continental shelf waters off Mexico’s Isla Holbox and Isla Contoy where the northwestern Caribbean Sea meets the southeastern Gulf of Mexico. Biological studies of these huge, pelagic planktivores to document their distribution, number, size, sex, behavior and migration began off Quintana Roo in August 2003, and have continued through 2006. Research methods comprise a combination of on-water and aerial surveys, tagging and tracking with visual and satellite tags, and logbook data collection by local guides and fishermen. Genetic tissue samples also have been collected for collaborating institutions. All data indicate at least several hundred whale sharks visit the area every summer to feed on plankton associated with a seasonal upwelling. Approximately 400 individual sharks have been tagged primarily in the summers of 2004-2006. Estimated size of observed sharks ranges 2-13 m TL; tagged animals range 3-12 m TL, with an average size of 6.7 m TL. Sex ratio is approximately one female for every 2-3 males. Mature and immature animals of both sexes are present. Resightings of tagged animals have been reported over 300 nm away from the tagging site and in subsequent years back at the site. Pop-off (PAT) satellite-tagging has confirmed migrations of nearly 900 km in one month and dives to at least 980 m when the sharks move off the Campeche Bank. Based on the number of animals documented to date, this area where the Gulf of Mexico meets the Caribbean Sea appears to be one of the world’s most important population centers for the whale shark

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