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Planet Earth

Charting the Whale Shark Universe

The pattern of a shark's spots can serve as its distinctive fingerprint.

By Anne CasselmanJuly 1, 2006 5:00 AM

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What do whale sharks and the night sky have in common? An awful lot, it turns out.

They are both on the large side. Both are attractive, if a bit daunting. And they have the same complexion: a sprinkling of white spots against a dark background.

It is this last characteristic that grabbed the attention of Ecocean, an Australian marine conservation agency. Using a star-recognition algorithm developed by NASA, volunteers Jason Holmberg and Zaven Arzoumanian, and marine biologist Brad Norman from Murdoch University in Australia, have developed software that can assign a whale shark a "digital fingerprint" based on a photograph of the pattern of spots on its back.

The goal, Holmberg says, is to find out whether "whale sharks are suffering the same population loss that we're seeing in other sharks all around the world." Ecotourists send in snapshots, which are fed into a database called the Whale Shark Photo-Identification Library. This allows Ecocean to track the movements of individual sharks as well as the dwindling of the general population. Shark H-001, for instance, has been spotted 12 times moving through the dark water between Belize and Honduras. So far the library contains photos of 473 sharks from 1,871 encounters in 27 countries.

Early results are ominous. For instance, the number of whale sharks at Ningaloo Reef in Western Australia declined on average by 19 percent from 2001 to 2005. This species, the largest fish in the sea, may be swimming through its twilight.

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