Mote Marine Laboratory

One Big Fish

By: Patrick Maggard

Dr. Bob Hueter’s first encounter with a whale shark, more than 30 years ago, was exciting, a little scary and ichthyologically incorrect.

These days, when he swims with the spotted giants off Isla Holbox, Mexico, as part of a multi-year study, the director of Mote’s Center for Shark Research, plays strictly by the book, which means no touching, because too much physical contact with humans could change whale shark behavior.

But in 1975, when Hueter was a graduate student at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, there was no book to play by. Hueter, who was working on a master’s degree under the legendary Samuel “Sonny” Gruber, learned that a large whale shark appeared to be in distress in Florida Bay, so he and doctoral student Joel Cohn drove to the Keys, took a boat out and found the fish. Getting in the water, they measured it with a rope (it was 32 feet long) and determined that it was, indeed, in distress: It would lie on the bottom in 10 feet of water for a few minutes, facing into the current, then move 100 to 200 yards.

“Back then, we didn’t have all the conservation concerns we do now — we didn’t worry about altering behavior,” Hueter said. “So what did I do? I just latched onto its dorsal fin, and when it got up and moved, I went for a ride. It was a feeling of amazing power, all muscle. I thought, ‘This animal can go anywhere it wants.
I particularly remember reaching down under the shark to see if it had claspers — she didn’t; she was a female — and worrying that if she rolled over, I was dead meat.”

Hueter also tapped around its eyes and determined that, unlike shark species with nictitating membranes (a kind of third eyelid) to protect their eyes, whale sharks retract their eyeballs into their heads.

Flash forward to 2005. Hueter’s most recent whale shark encounter was in August and September off Holbox (pronounced hole-BOSCH) as the leader of a team of Mote researchers and their counterparts from Mexico’s Project Domino, a group of Mexican scientists and tour guides who study the animals and regulate tourist activities around them. Locals call whale sharks “dominos” because of the animals’ spots.

Mote has been studying whale sharks off Holbox since 2003. Why this isolated, difficult-to-get-to spot off the northeast tip of the Yucatan Peninsula?

Because it’s one of the most important whale shark feeding areas in the world.
Every summer, nutrient-rich water from deep in the Caribbean Sea wells up and flows west through the Yucatan Strait and over the shallow continental shelf off Holbox. All those nutrients trigger plankton blooms, which, in turn, attract hundreds of the plankton-eating whale sharks. During the 2005 season, scientists tagged 164 whale sharks and tour operators reported 1,627 sightings, with animals ranging in size from 6 to 42 feet.

Mote got interested in the whale sharks of Holbox in 2003, after years of studying blacktip sharks in Laguna de Yalahau, the estuary between Holbox and the mainland. Holbox had become a tourist destination for whale-shark watchers the previous year, and Project Domino scientists contacted Mote for help studying the animals. “Through 30 years of studying sharks, I’d always wanted to work on the whale shark,” Hueter said. “But off Florida, they’re just not that common and predictable. Off the Yucatan, we have them by the hundreds every summer.”

While at Holbox, Mote and Domino scientists spend up to eight hours a day on the water looking for whale sharks. When they spot one, they put on snorkel gear and get in the water following all the Holbox whale shark eco-tourism rules, which include only three people in the water, no touching, no scuba diving and no flash photography.

Swimming with a whale shark is nothing less than an awe-inspiring experience. Ideally, the captain stops the boat a few hundred feet in front of the shark, rather than beside it, so the fish swims toward the snorkelers. At first, the shark appears as a shadowy, oblong blur in the distance. As it gets closer, cruising at about 2 knots, snorkelers can distinguish its trench-size mouth, then the silver-dollar spots as sunlight ripples across its massive body. Finally the whole fish comes into view, beautiful and graceful beyond description, huge beyond the size of any sea creature snorkelers or scuba divers commonly see, and no more concerned with the inconsequential humans than with the hundreds of fish swimming around it.

But scientists don’t have time to marvel at the fish: They have science to do. Among their tasks:

•  Take tissue samples for DNA tests to determine whether whale sharks are genetically the same population around the world. So far, the animals appear to be mixed into one worldwide population, which indicates long migrations and a lot of intermingling.

•  Measure the base of the whale shark’s dorsal fin. Measuring the length of a whale shark in the wild is impossible, unless the animal is in distress and lying on the bottom, so the scientists estimate the animal’s length and measure the base of the dorsal fin. Then they compare their estimates and measurements to whale sharks killed and accurately measured in Taiwan’s commercial fishery. In this way, the scientists test the accuracy of their estimations.

•  Attach an external tag at the base of the dorsal fin with a Hawaiian sling. Mote and Domino scientists have put external tags on more than 300 whale sharks since 2003. These tags are a way of getting a handle on the whale shark population. If someone sees a tagged whale shark and reports the number, scientists can get a sense of whale shark movements. So far, two tagged Holbox whale sharks have been reported off Utila, in the Honduras Bay Islands, and whale sharks tagged off Belize and Utila have been spotted at Holbox. These returns indicate that whale sharks feeding at Holbox travel long distances during the rest of the year.

•  Attach a satellite “pop-off” tag. These $3,500 tags are programmed to detach after a specified length of time, float to the surface and beam data to a satellite, which then passes it on to Mote scientists. While a tag is on the shark, it records such information as water temperature, pressure, which indicates depth, and approximate location.

Before the 2005 trip, Hueter and his team had attached satellite tags to three whale sharks, but none reported back. In 2005, they put tags on two 18-foot immature males and set them to pop off one month later. Data from both tags started streaming in right on time. One tag surfaced 65 miles south of Cozumel, which means one of the fish headed south and traveled at least 155 miles in one month. The other tag surfaced 197 miles south-southeast of Brownsville, Texas, so that fish headed northwest and traveled at least 551 miles. These findings indicate that Holbox is an important feeding site for whale sharks from different areas, not just the Caribbean or Gulf of Mexico. The tags also showed that the southbound shark dove to 997 feet, and the westbound shark went to at least 3,200 feet, the tag’s depth-recording limit. Scientists don’t yet know why the plankton-eating fish make such deep dives. It could be for food: Some plankton are vertical migrators, spending part of the day at the surface and part in deep water. Another possible reason for deep dives is that the big animals, which build up a lot of body heat, seek colder water to regulate their body temperature.

Mote’s work with the Holbox whale sharks would be impossible without Project Domino. “We can only be there a very small part of the year, so having their biologists and observers document whale shark movements throughout the season is critically important,” Hueter said. “They also monitor tags. If any tags come up, they get them. And they’re doing aerial surveys. We couldn’t do this work in Mexico without the involvement of the local biologists and resource managers.”

Working with Project Domino, Mote scientists are gaining insight into the whale sharks of the Caribbean Basin. “We’re learning that Holbox is a very special place in the lives of whale sharks,” Hueter said. “It’s the most concentrated number of whale sharks anywhere in the world. Nobody else has seen the numbers we’ve seen at Holbox.

“We’ve learned that these animals come to Holbox in the summer to feed and leave in the fall. This area attracts the full size range, from pre-teens all the way up to very large animals of both sexes. In many other areas, it’s almost exclusively males. At Holbox, one out of every four whale sharks is a female.”

Unfortunately, Holbox was devastated by Hurricane Wilma in October 2005: A 12-foot storm surge rolled over the island, whose highest point is 3 feet above sea level. But Mote scientists are planning to return to the tiny island in 2006 to continue their work with Project Domino. Hueter also hopes to expand the lab’s whale shark work by teaming up with biologists around the world. The idea is to attach 100 satellite tags to whale sharks at Holbox, the Sea of Cortez, Kenya, the Maldive Islands, and Djibouti.

In July, Mote scientists plan to travel to another whale shark hot spot: the Persian Gulf off the United Arab Emirates. “A corporation is building a mega-resort with an aquarium in Dubai, and we hope to work with them,”Hueter said. “There are also whale sharks swimming along the coast, coming into marinas and getting trapped in there. We need to learn what’s going on to see if conservation measures are in order.

“I’m anxious to get going. Dubai is no desert camp. It’s an extremely wealthy, cosmopolitan, bustling city. They’re building like crazy, and they’re concerned with the impacts of development. They’re tied to the sea, and they’ve got to understand what’s happening with these animals.”

More than 30 years ago, when little was known about whale sharks, a young graduate student had his first encounter with one of the huge animals, rode its dorsal fin, went eye-to-eye with its mysteries. Thirty years later, Hueter is still trying to unlock the secrets of the largest fish in the sea.

And that’s one big fish story. 

Big sharks need big collaborations

In addition to his work with whale sharks in Mexico, Dr. Robert Hueter is working with Georgia Aquarium officials to create a research plan for Ralph and Norton, the only whale sharks living in a U.S. aquarium. “We know very little about the sensory biology or vision of the whale sharks — or even how fast they grow,” said Dr. Bruce Carlson, Georgia Aquarium vice president. “It’s very hard to get out in the ocean and study something this size. Having them here opens up great opportunities to learn more about whale sharks and help in their conservation.”

Learn more about: Dr. Hueter's Research

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