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Credit: Jennifer Schmidt, University of Illinois at Chicago.
Whale sharks are the largest fish species, ranging from 18 to 40 feet (5 to 12 m) in length. Though they live in warm waters across the globe, researchers usually get to study them only in coastal waters where young juvenile males cluster to feed. Much of the sharks' lives seem to occur in the open sea, where they're hard to observe, leaving chunks of their lives a mystery. For instance, no one has ever seen whale sharks mate.