Cancun, Mexico - Skipper Jorge drops anchor 50 kilometres off the Mexican coastal resort of Cancun before shouting over to his partner Jose to usher two passengers with life-jackets, flippers and snorkels to the side of the vessel. Suddenly Jorge lets out a cry of "12 metres" and a huge fish, whose mouth stretches more than one-and-a-half metres across, looms into view. It approaches the boat slowly and swims alongside.
Jose and the two guests let themselves fall into the water before making their way towards the cavernous opening which could easily swallow up both of them. For its part, the whale shark seems to be ignoring the two colourful "objects" within its field of vision and it simply changes course.
The world's biggest fish - since whales are mammals and not fish- is far more interested in looking for plankton, its main source of nourishment. Meanwhile the snorkelers are filled with a sense of wonder at the huge, brown creature in front of them.
Its back is a checkerboard of pale yellow spots, its belly white and it has a pair each of dorsal and pectoral fins. The top fin of the whale shark is more than two metres high.
In the Indian Ocean, where the whale shark is often relentlessly hunted down for its meat, which is sold as a delicacy to Taiwan and other countries, snorkelers and divers have little chance of spotting the creature. In Southeast Asia the fish is an endangered species.
Close to Cancun, between the islands of Contoy and Holbox, the whale sharks are in their element. Every summer from June to September the world's largest number of whale sharks congregate with clockwork regularity.
"There are several hundred of them," said captain Jorge.
The summer months are marked by a huge aggregation of plankton off the northern end of Yucatan peninsula. It is believed the sharks come here to feed on the micro organisms which form the basis of their diet, but they also consume fish eggs and sometimes even small dolphins.
It is a fascinating spectacle as the animals swim for hours on the surface with their mouths agape to take in up to 6,000 litres of seawater an hour. They suck in the water near the surface before filtering the liquid to recover around four kilos of plankton at a time.
They use their sense of smell to help locate their prey, then the huge mouth opens and the water is actively pumped over the gills. Whatever gets caught on the gills is swallowed - mostly plankton but also small fish which do not manage to get out of the way.
Biologists have tagged many of the whale sharks and are able to follow their progress across thousands of miles of the world's oceans. One whale shark was found to have travelled nearly 900 kilometres in 31 days.
"We even came across one whale shark which had been tagged in Australia," said Jorge.
For officials in Cancun and the state of Quintana Roo, the whale sharks are more than just a lucrative source of tourist income in Mexico's most popular holiday area.
The entire area off Cancun is a national park where shipping movements are strictly limited. A maximum of 15 boats a day are allowed to travel out to the whale sharks.
"Tourism does represent a risk," admits biologist Ignacio Barat. "And we can only preserve nature if everyone adheres by the rules."
The enchanting island of Contoy is off-limits to the "whale shark boats." The nearly nine-kilometre-long island is largely uninhabited and has been set aside as an animal and nature reserve where no more than 200 visitors a day are permitted. It is also home to thousands of cormorants, frigate birds and pelicans who share the habitat with salt water crocodiles, iguanas and snakes.
The waters of the Caribbean Ocean around the shores of the island in the Gulf of Mexico are teeming with barracudas, sharks and dolphins. There is a small research station, a natural history museum and accommodation for four biologists who observe and carry out research.
Contoy's pristine beauty is protected by an organisation called "The friends of the Isla de Contoy" which is chaired by the German Honorary Consul in Quintana Roo, Rudolf Bittorf. Needless to say, only a few, carefully-chose tour companies have permission to land people on this unique island.
Internet: www.cancun.travel, www.islacontoy.org
