Mote Marine Laboratory

A Whale Shark of a Summer

By: Hayley Rutger

Whale sharks gather each year for a summer plankton feast near Mexico in the largest aggregation of this species known to science. This year, more than four times the usual crowd has dropped in for dinner, according to Mote Marine Laboratory scientists who recently returned from their annual whale shark research expedition.

Mote scientists have been studying whale sharks in conjunction with Proyecto Domino, Mexico's Comisión Nacional de Áreas Naturales Protegidas, the University of South Florida, the Georgia Aquarium and ecotourism guides and fishermen from Quintana Roo, Mexico, since 2003. Past surveys have shown that an estimated 1,400 whale sharks — the Earth's largest fish — visit Gulf of Mexico and Caribbean Sea waters near Isla Holbox, Mexico, to feed from May to September. Scientists are just beginning to map their world travels and favorite hangouts.

Mote researchers and our collaborators have discovered that the sharks come and go throughout summer at Holbox, often in groups of several sharks up to 100 or so in one place. But this July, Mote researchers swam among a group of about 200 whale sharks, and Proyecto Domino researchers counted a group of 420 sharks during aerial surveys.

In another twist, these mega-clusters were east of their usual haunt, closer to Isla Mujeres. To scientists' knowledge, Isla Mujeres waters have only hosted groups of sharks in late summer, not all summer long.

"This year, we're seeing a tremendously dense aggregation of hundreds of whale sharks that scientists have never observed before, and it seems to be lasting all summer," said Dr. Robert Hueter, director of Mote's Center for Shark Research.

The throng gives Hueter and his team a great selection of animals to study and track. Mote scientists outfit sharks with satellite tags, which send location and environmental information via satellite. So far, Hueter's group has mapped the travels of 22 whale sharks. Click here to read more about past findings.

This year, Mote scientists satellite-tagged three females with lengths of 23, 25 and 26 feet and one 23-foot male. Each tag is programmed to pop off the shark after six months and transmit its information from the ocean surface back to the lab via satellite.

Mote scientists hope to return to Mexico in the next few weeks to attach a more precise type of satellite tag and to use accelerometers — instruments that reveal sharks' behaviors by measuring small body movements. But they don't know how long the mass gathering of whale sharks will last or what caused it.

"It could be that an upwelling of unusually cold water is herding these animals together to the northeast and keeping them from spreading over their usual area north of Holbox," Hueter said. "Or, it could be that an unusually productive spawning of fish eggs is keeping them at the buffet table northeast of Isla Mujeres."

Whatever the reason, he says that seeing the huge group is "wonderful to experience — like diving in a fish bowl of whale sharks."

Florida Gulf Coast residents and visitors may also be lucky enough to spot a whale shark in our coastal waters.

• Please report any new whale shark sightings immediately by calling Mote’s Center for Shark Research at 941-388-1827.  Please note the number of whale sharks you saw along with the time, date and location (GPS coordinates if possible). Please provide your phone number and/or e-mail and note whether you can provide photos.
  (Please do not report old/historical sightings unless you have precisely documented the sighting, including date, specific location and number of whale sharks.)

Whale sharks — gentle plankton-eaters — are deemed vulnerable by the International Union for the Conservation of Nature.

Learn more about: Shark Reseach at Mote

Unfortunately, sharks need more than crustaceans to thrive. As a species, they need the world to be aware of their plight. They need scientists working 'round the clock on their behalf. We need your support to make that happen. Please donate to shark research today.