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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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(Continued from page 1)

The fish have mostly been a mystery. Only in 1995 did scientists determine how whale sharks come into the world, after Taiwanese fishermen pulled up a dead female carrying 300 fetuses in various stages of development. These sharks are “aplacentally viviparous,” meaning the young develop inside eggs, hatch, then remain in the mother’s body until the pups are born. With the astonishing number of eggs, the whale shark became known as the most fecund shark in the ocean.

When two male whale sharks at the Georgia Aquarium died within several months of each other in 2007, scientists traveled to Atlanta to observe the necropsies. Analysis of the bodies helped researchers understand the 20 sieve-like pads the animals use for filter-feeding. Recent research by Hueter, De la Parra and others has shown that whale sharks primarily eat zooplankton in nutrient-rich coastal waters, like those near Isla Holbox; in other areas they seek out fish eggs, especially those of the little tunny. If they gulp something too big, they spit it out.

Rachel Graham, a conservation scientist at the Wildlife Conservation Society, was the first to attach a depth tag to one of the giants, in Belize in 2000. One of the 44 satellite tags she eventually deployed told her that a whale shark had dived 4,921 feet—nearly a mile. A marine biologist named Eric Hoffmayer recorded the deepest dive yet: in 2008, he monitored a shark in the Gulf of Mexico that descended 6,324 feet. “Their ability to adapt to all sorts of different environments is an important part of their survival,” says Graham, who’s tracking whale sharks in the Western Car­ibbean, Gulf of Mexico and Indian Ocean. Scientists don’t know why the animals go so deep. Sharks lack a swim bladder that keeps other fish buoyant, so one idea is that whale sharks free-fall toward the seafloor to rest.

In 2007, Hueter tagged a pregnant 25-foot-long female he nicknamed Rio Lady. Over the following 150 days, she traveled nearly 5,000 miles, from the Yucatán Peninsula through the Caribbean Sea to south of the Equator east of Brazil, ending up north of Ascension Island and south of St. Peter and St. Paul Rocks, roughly halfway between Brazil and Africa. No one is certain where whale sharks breed or give birth, but Hueter believes this area may be one of their elusive pupping grounds.

Legend has it that Isla Holbox, a former pirates’ hide-out, got its name from a deep lagoon on the southern part of the island: Holbox means “black hole” in Mayan. But fresh water bubbling up from a spring in another lagoon was the island’s real draw: the Maya viewed it as a fountain of youth, and Spanish ships stopped there to take on fresh water. Mangroves divide the island, which is less than two miles wide.

A tour guide describes islanders as “descendants of pirates, mestizos of several races, fishermen by trade.” Residents earned a living by trapping lobster until about 2000, when the excessively hunted crustacean grew scarce and fishermen wondered what to do next.

Willy Betancourt Sabatini was one of the first Holboxeños to realize that the massive sharks that congregated near the island to feed might be the answer. He and his sister, Norma, a local environmentalist who now serves as project director for the island’s Yum Balam Protected Area, along with researchers and local entrepreneurs, established rules for a new industry, shark tourism. Only two divers and one guide can be in the water with a single shark; flash photography and touching the sharks are forbidden. Islanders had learned from the lobster debacle that they needed to set limits. “They know if we don’t take care, all of us are going to lose,” Norma Betancourt Sabatini says.

“Conserve the whale shark,” says a sign on Isla Holbox. “It’s your best game.”

Shark tourism is growing. Graham, in a 2002 study of whale shark visitors to the small Belize town of Placencia, estimated revenues of $3.7 million over a six-week period. In the Philippines’ Donsol region, the number of whale shark tourists grew from 867 to 8,800 over five years. And a study found whale shark tourists spent $6.3 million in the area around Australia’s Ningaloo Marine Park in 2006.

“It’s simple and more predictable than fishing,” Willy Betancourt Sabatini says of shark watching. The 12 men who work for him as boat operators and guides earn twice as much as they did fishing, he adds. “We respect the rules. People understand it very well.”

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