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Weighing up to several tons, whale sharks are also notable for their markings. Each pattern of spots is unique and scientists identify individual fish using computer programs first developed to study star constellations. (Brian Skerry)

Swimming With Whale Sharks

Wildlife researchers and tourists are heading to a tiny Mexican village to learn about the mystery of the largest fish in the sea

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At the moment, Rafael de la Parra has but one goal: to jump into water churning with whale sharks and, if he can get within a few feet of one, use a tool that looks rather like a spear to attach a plastic, numbered identification tag beside the animal’s dorsal fin. De la Parra is the research coordinator of Proyecto Dominó, a Mexican conservation group that works to protect whale sharks, nicknamed “dominoes” for the spots on their backs.

He slips off the fishing boat and into the water. I hurry in after him and watch him release a taut elastic band on the spear-like pole, which fires the tag into the shark’s body. De la Parra pops to the surface. “Macho!” he shouts, having seen the claspers that show it’s a male.

The biggest fish in the sea, a whale shark can weigh many tons and grow to more than 45 feet in length. It’s named not only for its great size but its diet; like some whale species, the whale shark feeds on plankton. A filtering apparatus in its mouth allows it to capture tiny marine life from the vast amount of water it swallows. But it is a shark—a kind of fish with cartilage rather than bone for a skeleton—a slow-moving, polka-dotted, deep-diving shark.

De la Parra and a group of American scientists set out this morning from Isla Holbox off the Yucatán Peninsula. The sleepy tourist island, whose primary vehicles are golf carts, has become a research center where scientists study whale sharks. The animals spend most of their lives in deep water, but they congregate seasonally here off the coast of the Yucatán, as well as off Australia, the Philippines, Madagascar and elsewhere. No one knows for sure how many whale sharks are in these waters, but the best estimate is 1,400. The global whale shark population may number in the hundreds of thousands.

Researchers have fastened IDs to about 750 whale sharks here since the scientists started studying them in earnest in 2003, and they hasten to say the procedure does not seem to hurt the animal. “They don’t even flinch,” says Robert Hueter, a shark biologist at the Sarasota, Florida-based Mote Marine Laboratory, which collaborates with Proyecto Dominó. The researchers have outfitted 42 sharks with satellite tags, devices that monitor water pressure, light and temperature for one to six months, automatically detach and float to the surface, then transmit stored information to a satellite; scientists use the data to recreate the shark’s movements. Another type of electronic tag tracks a shark by transmitting location and temperature data to a satellite every time the animal surfaces.

Despite all the new information, says Ray Davis, formerly of the Georgia Aquarium, “there are a lot of unanswered questions out there. Everyone’s admitting they don’t know the answers, and everybody’s working together to get the answers.”

Eugenie Clark is Mote’s founding director and one of the pioneers of shark research. The first whale shark she observed, in 1973, was a dead one caught in a net in the Red Sea. Once she began studying live ones, in the 1980s, she was hooked. On one occasion, she grabbed the skin under a whale shark’s first dorsal fin as it cruised by. She held on, going ever deeper underwater until, at some point, it occurred to her she’d better let go.

“It was incredible,” Clark remembers. “When I finally came up, I could barely see the boat, I was so far away.”

Clark, who is 89 and continues to do research, recalls the ride with impish delight. At one point, as we sit in her Florida office, she casually mentions a recent dive, then catches herself. “Don’t mention how deep I went,” she whispers. “I’m not supposed to do that anymore.” Then she explodes in laughter.

As she studied feeding behavior in whale sharks, she noticed that juveniles, less than 35 feet long, fled from humans, but larger animals didn’t seem to mind nearby divers.

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