May 27, 2011

Yucatán: Largest Ever Congregation of Whale Sharks

Take a boat off the Yucatán Peninsula this week and you will see the most astounding sight. The water is filled with the gentle giants of the sea, all meeting to feast on little tunny fish eggs. Whale sharks are there in their hundreds, with an estimated 420 of them forming the biggest aggregation. A second group are even further out to sea.

Aggregation of Whale Sharks

The Mexican Caribbean is home to the whale sharks, which can stray as far north as the Gulf of Mexico and the Southern coast of the USA. While sightings are rare up there, a glimpse of them off the Yucatán can be guaranteed, if you know where to look.

Yet their numbers this year have taken locals and scientists by surprise. Usually they are solitary creatures, meandering their way through the ocean alone or in schools no more numerous than a dozen. The hundreds in the Yucatán Afuera aggregation have brought researchers flocking to record this amazing event.

Flyovers have taken in the scale, with aerial footage and measurements; while scientists in boat are weaving amongst the whale sharks, collecting samples of food in nets.

Whale Shark

This is the world's largest fish, with adults reaching lengths of 40 feet (12 meters); yet they are utterly harmless to human beings. Their diet consists mainly of plankton, plants or very small fish. Though, as the recent feeding frenzy shows, mackerel eggs are apparently a favourite.

Meanwhile, over in the second aggregration, in the Yucatán Cabo Catoche, it appears that shrimp and small crustaceans were there main draw on the menu.

Whale sharks swim with their mouths open wide. As water funnels through, they filter out the good stuff and keep it in their stomachs. The rest is channeled out through their gills.

Whale Shark

Despite their huge size, whale sharks are not aggressive. They have a reputation for being incredibly docile and moving extremely slowly through the ocean. They will generally ignore human beings, as we aren't food; though well-fed ones are more inclined to be playful. They will happily allow people to swim alongside them and will even give them a 'ride', towing them through the water.

They live up to 100-150 years. Each one has a unique pattern of spots on its back, acting like fingerprints to identify them.

Aggregation of Whale Sharks

Mike Maslanka, biologist at the USA's Smithsonian Conservation Biology Institute, explained the significance of this find. "With two significant whale shark aggregation areas and, at the very least, one active spawning ground for little tunny, the northeastern Yucatán marine region is a critical habitat that deserves more concerted conservation effort."

His colleague, Lee Weigt, head of the Laboratories of Analytical Biology, added, "Having DNA barcoding is an incredibly valuable resource for this research. It not only allowed us to know what exactly this huge aggregation of whale sharks were feeding on, not readily done from only physical observations of eggs, but it also revealed a previously unknown spawning ground for little tunny."

It is worth noting that whale sharks are considered 'vunerable' by the International Union for Conservation of Nature. This is due largely to over-fishing and trophy hunting. The greatest predator for whale sharks being, of course, humans.

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