The "unique habit" of whale sharks that converge to feed from fishing nets in Indonesia has allowed them to be tagged with low-cost technology usually used on pets, conservationists said Tuesday.

Experts in June injected tiny pill-sized radio transmitters beneath the skin of 30 whale sharks in Cenderawasih Bay in the eastern province of Papua, conservation group WWF said.

And it was only made possible because the giant animals, which measure up to 45 feet (13.7 metres) but are harmless to humans, were gathered to feed on fish caught in fishermen's nets, WWF Indonesia project leader Beny Ahadian Noor told AFP.

A YouTube video by Conservation International (CI) showing a whale shark sucking fish from a hole in a net in clear blue waters has now attracted more than one million views (www.youtube.com/watch?v=71FLO_6JJVo).

"Radio-frequency identification (RFID) tags have been used on pets such as dogs, but this is the first time on whale sharks," Noor said.

Researchers would usually use a more sophisticated satellite method, at $4,000 a tag. But Noor said each radio-frequency tag used in Cenderawasih Bay cost only $4.

"It's good enough for a start since we have little information about the behaviour of whale sharks here," he said.

Marine biologist Mark Erdmann, who joined the expedition, said it was "fairly impractical to swim after the giants with a receiver wand under water".

"What makes this tagging possible in Cenderawasih Bay is the unique habit this population has of aggregating at... fishing platforms to feast upon the small silverside baitfish that the fishers are catching," he said.

Whale sharks, the world's largest fish, are classified as "vulnerable" by the International Union for the Conservation of Nature (IUCN.)