Posted on 19 September 2012

How many spotted sharks have been spotted? In Donsol at least, 377.

High-tech satellite tags, waterproof cameras and hefty lungs are the tools of Dave David’s trade. As the head researcher of WWF’s Donsol-based whale shark photo-identification programme, Dave has spent the past six years holding his breath – literally – to swim with the world’s largest fish.

Strikingly-spotted whale sharks (Rhincodon typus) can grow longer than a passenger bus and weigh a whopping 10 tonnes. With unblinking golf ball-sized eyes, they wolf down wafting clouds of plankton and the occasional, unlucky small fish. Together with basking and megamouth sharks, they are one of just three planktivorous or filter-feeding sharks and have cruised the world’s seas for some 50 million years. Little is known of their habits, with fewer than 350 sightings recorded prior to the 1980s.

Through the support of WWF-Denmark, WWF-Philippines allied with Australia-based ECOCEAN, the Hubbs Sea World Research Institute (HSWRI) and Banco de Oro Unibank (BDO) to catalogue the country’s whale sharks. The partnership provides researchers with both population pegs and migratory data to guide conservation efforts not just for whale sharks – but for all migratory pelagic species.

Sporting waterproof digital cameras, trained WWF skin divers snap photos of a spot right above each shark’s pectoral fins, behind its gill slits. The photos are fed into a computer which uses a program to triangulate each shark’s unique spot configuration. Data is then uploaded to the web-based ECOCEAN library.

Unless it is a new individual, the library shows researchers when and where the shark was last encountered. Since 2003, ECOCEAN has catalogued 3822 individual sharks from places as far as Mexico, Mozambique and the Galapagos Islands.

“Photo-identification is a non-invasive approach for identifying sharks,” explains David. “The library uses the whale shark’s distinct patterns, plus information on scars, sex and size to identify individuals.”

Since WWF-Philippines began implementing the programme in 2007, 458 individual whale sharks have been identified – 377 in Donsol, 54 in Cebu, 14 in Leyte and the rest in Bohol, Palawan, Albay and Batangas.

To complement the photo-identification drive, 29 whale sharks were affixed with detachable GPS satellite tags designed to pop to the surface after several months of data collation. Four sharks were tagged in May 2007, 10 more in May 2009 and 15 in April 2010.

The results suggest that most tagged whale sharks keep to 200 kilometers of Donsol. Three however, swam east to the Philippine Sea, with one more swimming as far north as Taiwan. All spent most of their time below 50 meters, rarely rising to the surface to feed.

“The results suggest that whale sharks are highly-mobile, transient foragers which recognize no country or territorial boundary as their own. The distribution of whale sharks and other large filter-feeders also indicate the presence of plankton and the overall health of our oceans,” expounds David.

For years, Donsol has been identified as a whale shark hotspot, hosting one of the largest aggregations of whale sharks on Earth. Other large aggregations include Ningaloo Reef in Australia with 808, Mexico with 812 and Mozambique with 624. Through continued research, Dave and other WWF volunteers hope to generate an accurate peg of the country’s migratory and resident whale shark population.

“Long days at sea are worth it, considering the immense scientific, ecological and economic value that whale sharks bring people,” adds David. “Even after years of research, there’s still so much we have to discover – where they feed, mate and give birth. Our work continues, which is just as well because diving with these gentle giants is pure magic.”

After six years of swimming with the world’s largest fish, it seems that each shark encounter still leaves Dave breathless. 

For further information:

Dave David
Whale Shark Researcher, WWF-Philippines
ddavid@wwf.org.ph

Gregg Yan
Communications & Media Manager, WWF-Philippines
gyan@wwf.org.ph