Riding a Whale Shark

World’s Biggest Gathering of Whale Sharks

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To see a single whale shark — the world’s largest fish, a solitary behemoth that can grow to school-bus size — is a rare experience.

Seeing hundreds gathered in one place is unprecedented.

“It’s one of the most incredible gatherings of animals that’s ever been recorded. It’s mind-blowing,” said marine biologist Al Dove of the Georgia Aquarium. “As someone who studies whale sharks, which have a reputation of being something you see once in a blue moon, the idea of finding 400 in an area of the size of a couple football fields is unheard of.”

The so-called Afuera gathering, described April 29 in Public Library of Science One, took place in August 2009 off the northern tip of the Yucatan Peninsula, not far from the waters around Cabo Catoche. Dozens of whale sharks have converged there each summer since 2002, drawn by crustaceans that feed on massive plankton blooms fueled by upswellings of nutrient-rich deep-sea water.

‘It’s one of the most magnificent animals in the ocean, and we don’t know some of the most basic things about it.’

Rather than plankton, the Afuera gathering is sustained by the eggs of little tunny, a common species of tuna. In a blog post on Deep-Sea News, Dove notes that a spawning event capable of feeding 400 whale sharks eating constantly for an entire month is itself an ecological marvel. But it was naturally overshadowed by the whale sharks themselves, with the Afuera congregation representing a full fifth of all whale sharks believed to live in the Caribbean and western Atlantic.

“It’s the dog days of summer. It’s very, very hot. The water tends to be still and flat. You can hear the whispering of fins and tails cutting through the water,” said Dove. “People used to joke, in the old days of fisheries, ‘You could walk across the water on the backs of fishes.’ It’s not that far from the truth.”

In the new study, Dove and colleagues document the existence of this marvelous event. Once past the basic details, however, many questions emerge.

The Afuera whale sharks are just eating, not mating; the mating habits of whale sharks are a mystery to biologists. The gathering contained no juveniles, only adults; biologists don’t actually know where juvenile whale sharks live, where they’re born or even how they’re born. Whale sharks are literally a colossal mystery.

“It’s one of the most magnificent animals in the ocean, and we don’t know some of the most basic things about it,” said Dove. “It’s exciting and humbling. People are going to ask simple questions that you’re not going to be able to answer. But those huge gaps represent great opportunities to get out there and discover stuff.”