As many as 1,400 whale sharks, the world's largest species of fish, migrate through Cancun's warm coastal waters between mid-May to mid-September each year to feed on plankton in the Yucatan Peninsula.

Tourists with snorkelling gear take turns swimming alongside the gentle giants, which can reach up to 50 feet (15.2 meters) in length but pose no danger to humans.

"Swimming with the biggest fish in the world is certainly something unique. They won't hurt you. They're on their own business, just feeding themselves," said Kenneth Johnson, a marine biologist whose company, EcoColors, runs eco-adventure excursions in Mexico.

"They don't care if you swim alongside them. And if you happen to get in front of them, they'll just turn around and go the other way," he added.

Whale sharks, which are nicknamed "domino" for the spots on their back, have always summered in the area, but in recent years they have been discovered near Isla Mujeres, an island just eight miles (13 kms) northeast of Cancun.

Seasonal gatherings of the fish can also be seen near Australia, Indonesia and South Africa, but the largest recorded aggregation of whale sharks was off the coast of Isla Mujeres, according to the Smithsonian Conservation Biology Institute.

The location, which locals refer to as "The Cape" or "Blue Waters," is about only about a hour by boat from Cancun.

HUNDREDS OF WHALE SHARKS

During Mexico's whale shark season, which peaks during July and August, up to 50 boats a day carry adventurous tourists to the "Blue Waters" area. Depending on the weather, it is not uncommon for swimmers to be surrounded by 100-200 whale sharks.

"It's a very different experience, so if you're going to be in Cancun during the whale shark season, going on an excursion is a must-do," said Marina Colunga, director of marketing communications for the JW and CasaMagna Marriott resort, which help arrange tours, which cost from $120 - $200 per person for about a six-hour excursion.

"There aren't many places in the world you can do this," she added.

Rodrigo Friscione, a tour operator for his family-owned Solo Buceo, said no experience, or certification is needed to enjoy the creatures.

"You don't even need to know how to swim," he explained. "You just put on a life jacket, stick your face in the water and see the most beautiful, gigantic fish."

Unlike swims with dolphins which normally occur in enclosed areas, swimming with whale sharks is done in the wild.

"We don't own them. The sharks decided to come here and they will decide when to leave," said Colunga. "Those who experience them will never forget it for the rest of their lives."

(Reporting By Zorianna Kit. Editing by Patricia Reaney and Sofina Mirza-Reid)

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