Whale Sharks Protected From...Deadly Swimmers?

Dec. 26, 2007 -- Based on thousands of remarkable underwater images, marine scientists have concluded that the world's largest shark is thriving in western Australia, thanks to well-managed ecotourism that appears to benefit both people and ocean wildlife there.

The 5,100 images represent the most extensive photo survey ever conducted of whale sharks, with nearly 10 times more data than any other previous study. Marine scientist Brad Norman took many of the photographs himself while swimming alongside the 20-ton ocean giants, which can be over 65 feet long.

"It really is a privilege to be able to swim alongside the largest fish in the ocean, given the fact that this species is so rare and vulnerable to extinction," Norman told Discovery News. "They are so graceful -- a true gentle giant. And it's not only the great length that is awesome, it's also their girth. Literally the size of a bus underwater!"

Norman and computer programmer colleague Jason Holmberg are both members of ECOCEAN, a research, education and conservation organization. They, along with NASA astronomer Zaven Arzoumanian, teamed up for the project, which used Hubble space telescope software to analyze the sharks.

The high-tech software was needed to pick out minute differences among the photographed sharks so the researchers could track individuals. Each whale shark has speckles and stripes on its skin that, like fingerprints, are believed to appear in unique patterns.

The study, published in the January issue of Ecological Applications, the journal for the Ecological Society of America, determined more and more whale sharks are returning to the northern area of Ningaloo Marine Park in western Australia from April to June each year, when the krill, jellyfish and other small prey that the whale sharks feed upon are plentiful.

Although the sharks are enormous creatures with 6,000 teeth, they're relatively peaceful fish that feed by simply opening their mouths. Finely meshed gill-rakers keep prey in while filtering water out. The only real danger to humans is an accidental slap from the shark's gigantic tail. Such a hit could probably knock a diver out cold.

Two thirds of the whale sharks that come to the reef, which meets the beach of Australia's North West Cape, are repeat visitors, providing further evidence that a series of "Code of Conduct" rules are working at Ningaloo.