Why A Whale Shark's Spots Could Help Save Its Skin

Together with Australian marine biologist Brad Norman and JAVAprogrammer and software specialist Jason Holmberg, astrophysicist DrZaven Arzoumanian of the Universities Space Research Association andNASA's Goddard Space Flight Center in Maryland discovered that apattern-matching algorithm developed by astronomers to locate celestialobjects could be used to identify individual whale sharks. Whalesharks' spots are analogous to bright stars in the night sky, allowingthe trio of researchers to adapt the star pattern recognition techniqueto the characteristic markings found on the largest fish in the sea."This is an example of space technology finding an importantapplication here on Earth," says Arzoumanian.

According to Arzoumanian: "The contrast of white whale sharkspots on darker skin is well suited to a machine vision technique knownas 'blob extraction', which measures the locations and dimensions ofpixel groups of a single colour. The spatial relationships betweenthese groups, represented by a set of x, y coordinates, form the basisfor a unique identifier for each shark."

In the same way that individual whales can be identified by theshape and markings on their flukes, photographic identification ofindividual whale sharks through their spot pattern "fingerprints", aswell as other markers, has long been possible. However, the fullpotential of photographic identification has rarely been exploitedbecause of the unmanageable task of making visual identification inlarge data sets, so using pattern-matching to automate the process is amajor advance.

Once photographed, the technique means a whale shark has been"virtually tagged". According to Norman: "Identifying individualsrepeatedly through photography can also inform biological observationssuch as age of maturity, growth rate and foraging ecology."

The authors, devoting their own time and resources, have setup the ECOCEAN Whale Shark Photo-identification Library to act as asingle repository for whale shark photographs taken by divers andtourists as well as researchers. "The implications of thiscomputer-aided identification technique and web-based photo library formanagement and conservation of whale sharks may be profound," Normansays. Without knowing more about the population size, structure andevolution of migratory species like the whale shark, it is impossibleto know whether conservation efforts should be directed locally orinternationally, or whether marine reserves are effectively protectingthem.

Whale sharks are listed as "vulnerable to extinction" by theWorld Conservation Union (IUCN). Up to 20 metres long, the whale sharkis the world's largest fish and lives mainly in the warm water beltnorth and south of the equator. Whale sharks pose no danger to humansas they are filter-feeders.

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More information on ECOCEAN is available at www.ecocean.org.