16 September 2005

Mexico: Tracking the elusive whale shark

The biggest shark in the sea comes here for an all-you-can eat buffet. Just off this remote speck of land three hours north of Cancun, whale sharks mass by the hundreds each summer in a stunning spectacle only recently discovered by scientists.

This is where the fish that inspired the Georgia Aquarium — the biggest fish that ever lived — swims wild, stuffing itself with tons of olive-green plankton, which blooms profusely in the bathtub-warm waters between Cuba and the Yucatan Peninsula.

"The numbers of animals that gather here could be astounding," said Robert Hueter, director of the Center for Shark Research at Sarasota's Mote Marine Laboratory. "This could be the largest gathering of these sharks in the world."

Just last week, 53-year-old Hueter was swimming with the gentle filter-feeders as part of a research effort partially funded by the Georgia Aquarium, which opens Nov. 23 in downtown Atlanta. The largest aquarium in the world is being paid for by Home Depot co-founder Bernie Marcus, who was inspired to open his wallet for the $200-million-plus facility after being awed by whale sharks at a Japanese aquarium.

The Georgia Aquarium will be the only fish tank outside of Asia to display the huge fish, which feed by straining plankton through a mesh-like layer in the throat. They can grow to the size of a rail car. The two Atlanta whale sharks, which were imported from Taiwan and dubbed Ralph and Norton, are young and still growing, measuring about 16.5 and 15 feet, respectively.

Marcus, as part of the aquarium's research mission, is funneling about $50,000 a year to Mote and Mexican conservation officials to study and protect the sharks in the wild off Holbox (pronounced hole-bosh) Island. The aquarium is touting research and education as part of its mission.

A piece of that research began before sunrise three days last week as Hueter, National Geographic Explorer-in-Residence Sylvia Earle and a few assistants loaded their gear into a boat and headed northeast to the vast plankton beds where the big sharks feed. Their goal: to learn about the shark's movements and behavior. Right now, scientists like Hueter, one of the nation's foremost shark experts, view the whale shark as a big question mark.

"We don't know if they're one giant worldwide population, or if they're discreet subpopulations," he said. "We know almost nothing at all about their reproduction, about their courtship and mating. We don't even know where they give birth. We don't know how long they live. We know what they eat, but not how much they eat. We don't know how they navigate, or even if they do; they might just follow ocean currents."

Scientists, in fact, did not even know the sharks — usually solitary animals — massed off Holbox until a local fisherman casually mentioned it to Hueter three years ago. Hueter had been traveling to Holbox since 1995, studying blacktip sharks. He spoke a little Spanish. His guide spoke a little English.

One day, while sitting on a boat on a quiet lagoon, the leather-skinned fisherman matter-of-factly announced, "Every year, after you leave, we have these big sharks that come here." He described hundreds of giant fish that the locals call "tiburon ballena," or domino sharks (because of their spots), that mysteriously congregate in the waters off the island from May to September. Just like clockwork. They had come when the fisherman's father was a boy and when his father's father was a boy.

Hueter was speechless.

"The local fishermen had known about it for generations," he said. "But they see so many things out here. They didn't think of it as significant. They had no way to compare it to anything going on anywhere else in the world."

The fish are visually stunning. Scientists have officially measured whale sharks that are more than 45 feet long. Some are thought to reach almost 60 feet. They can weigh 10 tons or more. One scientist calls them "buses with tails."

"It's as heart-stopping an experience to see a whale shark as it is to see a whale — these huge creatures that are so much bigger than mere human beings and who have such grace, such a way of self-possession about them," said oceanographer Earle, who celebrated her 70th birthday on Holbox snorkeling with one of the giants.

Before Holbox, researchers knew of a few other documented gathering spots in the world — western Australia, Belize, Honduras, the Indian Ocean. But these areas attract far fewer whale sharks than Holbox.

"And in all these other places around the world where they gather, it's almost all males," Hueter said. "Off Holbox, about 25 percent of the animals are females. Something very special is going on out here."

Hueter immediately contacted Mexican conservation officials to see if anyone was conducting research on the Holbox whale sharks. To his surprise, no one was.

"To me it was a gold mine," he said. "I had wanted to work with this species for decades. It was the perfect living laboratory." He returned to Holbox that year to meet with Mexican officials and conservationists about what they were calling "project domino." A few local fishermen had begun taking tourists out to the whale sharks, and the government saw the ecotourism potential, as well as potential problems, since the area is outside government protection.

Hueter laid out his research recommendations and that summer was able to mark 20 whale sharks with bright yellow "visual" tags. The next year scientists were able to tag 200 animals. By this summer, they had tagged more than 320.

Scientists speculate that as many as 500 whale sharks could congregate in the area every year, but that is only a guess.

Last week, Hueter was doing double duty on the small island. He attended a whale shark conference on Holbox that brought together about 70 Mexican bureaucrats, conservationists, scientists and fishermen-tour guides to discuss ways to protect the big fish. He later donned a snorkel and fins to continue Mote's research on the elusive shark.

Hueter grimaced the first day on the water as he unfolded a satellite image of the plankton bloom off Holbox. It indicated that the outer bands of Hurricane Katrina had battered what should have shown up as a solid carpet of the greenish micro-organisms. It was already late in the season, and Hueter knew the ragged plankton meant whale sharks would be widely dispersed and difficult to locate.

A week before Hueter arrived, tour guides were spotting a dozen whale sharks each morning in pond-calm waters about five to 10 miles offshore where the Gulf of Mexico meets the Caribbean. This post-Katrina week would be different.

The first day out, it took five hours in choppy, stomach-churning water to spot the first big fish, which guide Rafael De La Parra pointed to as a huge shadow about 30 yards off the bow. Hueter and Mote senior biologist John Tyminski put on their fins.

They entered the water in front of the shark. This one was about 18 feet long and swimming just below the surface. It appeared oblivious to the presence of the 25-foot-long boat. As the shark approached, Hueter dove and with a 6-foot-long "pole spear" inserted an 8-inch-long satellite tag — it looked like a microphone on a short cord — just below the dorsal fin. He emerged smiling from below with his thumb held high.

The scientists also noted the shark's sex — this one was a male — and they took a tissue sample, a pencil-eraser-sized piece of flesh retrieved with a hollow spear. They measured the base of the dorsal fin and estimated the animal's size, and they photographed it.

If Hueter is lucky, the $3,500 satellite tag will break free of the shark in about a month and begin transmitting a wealth of data to indicate where the animal has been, its activity patterns, water temperature and how deep it dove. So far, it has been frustrating science. Mote scientists installed three satellite tags over the last two years, and have heard nothing from any of them.

On this trip, despite the bad weather and the lack of sharks, Hueter and Tyminski attached satellite tags to two animals. The weather worsened the last day as thunderstorms moved in and a 6-foot chop obliterated visibility on the water. The sharks are leaving, just as they have done for eons. No one knows where they are going, but then no one really knows where they came from in the first place.

Hueter is checking out stories by local fishermen that some of the Holbox whale sharks have been seen "fighting," which could indicate some type of courtship or mating behavior.

Scientist Rachel Graham told the whale shark conference back on Holbox that she has discovered that juvenile whale sharks off Belize, where she lives, will wait for hours for schools of snapper to spawn and then gobble up the eggs.

None of it surprised Hueter, who got the surprise of his life just three years ago talking to a local fisherman.

"We're just beginning to understand these animals," Hueter said.

Source: www.sharktrust.org


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