The sea's largest fish has been a mystery until recent decades. Thanks to electronic tags, researchers are uncovering some of the secrets of the whale shark (Rhincodon typus Smith, 1828). One tagged animal, dubbed "Rio Lady," swam some 5,000 miles during a span of 150 days. Another dove to a depth of 6,324 feet in the Gulf of Mexico. These sharks are attracting scientists and tourists alike to places like the Yukatan Peninsula. Environmental journalist Juliet Eilperin traveled to one Mexican island to swim with the whale sharks and writes about her journey in the June 2011 issue of Smithsonian Magazine. Spoiler alert: Eilperin was a bit too slow for the spotted sharks.