Mote Marine Laboratory

The largest-ever scientific study of whale sharks — the world’s biggest fish — was published in the journal PLOS ONE Wednesday, Aug. 21 by Mote Marine Laboratory scientists and collaborators from Mexico. The study reveals the sharks’ international journeys and their relationship to the largest whale shark feeding hotspot known to science.

In short: This is big.

The nine-year study, entitled “Horizontal Movements, Migration Patterns, and Population Structure of Whale Sharks in the Gulf of Mexico and Northwestern Caribbean Sea,” is now available online in the peer-reviewed journal PLOS ONE.

This Mote-led study shows that whale sharks found at a major feeding hotspot near Mexico’s Yucatan Peninsula travel to many places throughout the Gulf of Mexico, the northwestern Caribbean Sea and the Straits of Florida. These findings highlight why the Mexican feeding site is a vital fueling station for whale sharks throughout the region and suggest that these wide-ranging fish need international protection. The study also documented the second-longest whale shark migration ever confirmed — a trail that may help researchers discover where the sharks give birth.

The project was centered off the Mexican state of Quintana Roo, on the northeastern Yucatan Peninsula. Coastal waters there host rich plankton blooms — a feast for the gentle filter-feeding whale sharks, which frequent the area from May through September. As many as 420 whale sharks have been observed during a single airplane survey, making this the largest known feeding aggregation of whale sharks on Earth.

From 2003-2012, project scientists studied these big eaters by fitting 813 sharks with ID tags and examining underwater photographs of  956 sharks to document their unique spot patterns, which serve as fingerprints and allow them to be individually identified. Both methods allowed scientists to recognize the sharks if they were found in other areas later. The researchers also attached electronic satellite tags to 35 whale sharks – the most whale sharks ever outfitted with satellite tags in one study. They were able to track the sharks’ movements beyond the feeding site, recording the temperatures and depths of the places the animals traveled. These tags released from the sharks anywhere from two to 190 days later, floated to the surface and sent data to the Mote scientists via satellite.

The results?

“They went all over the place,” said study leader Dr. Robert Hueter, director of the Center for Shark Research at Mote Marine Laboratory. “These sharks are coming and going from distant places around the ocean basin — this shows that the Quintana Roo feeding site is a very special place.”

Tagged sharks were re-sighted off Belize and Honduras, and an analysis of the satellite tracks by Mote biologist and co-author John Tyminski showed that some whale sharks spent several months in the Caribbean Sea. A large number of the sharks moved from the Yucatan Peninsula to other parts of the Gulf of Mexico, and at least three satellite-tagged sharks visited waters off Cuba.

When the project started, the researchers had no idea what they would find.

Whale shark image by Oscar Reyes.

"On our very first field trip in 2003, we were armed with a single satellite tag for deployment,” Tyminski recalled. “The Mexican government researchers brought us out with the promise of finding whale sharks in what was a vast expanse of water north of Cabo Catoche. We were very skeptical... despite the size of a whale shark, this still seemed like a needle in a haystack."

But after less than half an hour they spotted a 32-plus foot female whale shark. Later that day, they deployed the satellite tag on a different whale shark. Unfortunately, it failed to report — as did tags in 2004.

“But our luck changed in 2005,” Tyminski said. They deployed two tags that year; both reported in with one tag showing the shark traveled north into the Gulf of Mexico and the other tag showing the shark headed south into the Caribbean.

But one of the most thrilling finds from the nine years the research team has worked on this project has to have been their findings from a shark they nicknamed "Rio Lady."

Rio Lady was a 24-foot-long adult female whale shark. Her satellite tag showed a 150-day journey of nearly 5,000 miles through the Caribbean Sea and into the mid-Atlantic Ocean south of the equator. Her journey was probably even longer, considering that her satellite tag didn’t account for fine-scale meandering or deep dives, which the researchers found can be as deep as 1,928 meters — just over a mile.

As the study's data cruncher, Tyminski had the opportunity to see the results first. He checked and double checked his findings and, sure enough, Rio Lady had traveled past the Equator. "I was blown away," he said.

But the funnest part was sharing the news with Hueter. Tyminski printed out two maps — one zoomed in on the shark's position, the other zoomed out to show nearby land masses.

He handed Hueter the zoomed in one first. "He seemed to study it pretty carefully for a few seconds before looking back at me with a puzzled look. Then I handed him the other map and announced that it was in the middle of the Atlantic and south of the Equator.  He let out a big, 'hooray' and we high-fived to celebrate."

“Rio Lady’s trek was a huge finding for us,” Hueter said. “She undertook the second-longest migration ever confirmed for a whale shark, and she moved into an extremely remote area of open ocean where, we suspect, she gave birth to her young.”

Large females like Rio Lady are uncommon at the Yucatan Peninsula feeding cluster, which is 72 percent male. Feeding aggregations in other areas also have a male bias.

“We think mature females may be staying offshore and traveling to the open ocean so they can have their pups in areas with fewer predators,” Hueter said. “We hope Rio Lady’s migration has provided some clues for future studies. Whale shark reproduction is still a mystery.”

One thing’s for sure: These fish are international travelers — a fact that matters for conservation.

“Considering that these whale sharks wander in the Gulf of Mexico, the Caribbean and the Atlantic Ocean, it is fundamental to have regional collaboration in order to establish proper regional management,” said Rafael de la Parra, who co-authored the study while working with Mexico’s Proyecto Domino of the federal agency CONANP, and who now leads the nonprofit organization Ch'ooj Ajauil AC to continue his work on whale sharks.

Whale sharks are classified as Vulnerable by the International Union for Conservation of Nature’s Red List of Threatened Species™. This list is recognized as the most comprehensive, objective global approach for evaluating the conservation status of plant and animal species. Whale sharks worldwide face threats including boat strikes, net entanglement, habitat alterations and even too much pressure from well-intended ecotourism.

Whale sharks feeding near Mexico received new protection thanks in part to data gathered during the PLOS ONE study. In June 2009, the Mexican government established a Whale Shark Biosphere Reserve to extend a federally protected area to include most of the whale sharks’ summer feeding grounds.

“When we shared where the whale sharks were feeding off the north coast of Isla Holbox, on the Yucatan Peninsula, the Mexican government took action using data from our study and CONANP, a group we’ve been working closely with on this project,” Hueter said. “To their great credit, they moved quickly to get the area under official protection.”

The nine-year PLOS ONE study was funded by the Georgia Aquarium, Christopher Reynolds Foundation, National Geographic Society, Mote Marine Laboratory and an anonymous private foundation. Moving forward, Mote scientists and collaborators in the U.S. are beginning work with Mexican and Cuban colleagues to help establish a linked network of areas to protect whale sharks throughout the Gulf and Caribbean.

Mote scientists, who study marine life on six of the seven continents, emphasize that international collaboration is vital to sustaining marine resources.

“We hope our research leads to broad-scale protection of this truly unique and charismatic shark, the largest fish that has ever lived,” Hueter said. “We also hope such measures serve as a model for marine conservation action affecting numerous species that travel across international borders and into the waters of multiple nations.”