Scientists disentangle the whale shark from a fishing net after tagging it. (Above) A sample of the tissue collected by the scientists

New Delhi, Dec. 18: A female whale shark caught in a fishing net in northern Arabian Sea near Verawal, Gujarat, has become the first to be tagged by Indian scientists for a study on the migration and genetics of the biggest known fish.

Marine biologists alerted by fishermen implanted a tiny tube with a unique identity number near the dorsal fin of the whale shark and released the fish. The tube will serve as a visual tag to allow the whale shark’s movements to be tracked if it is ever caught again.

During the implantation, the scientists also extracted a bit of surface tissue from the whale shark for genetic studies to be carried out at the Central Marine Fisheries Research Institute, Kochi, in collaboration with the University of Illinois in the US.

“The genetic analysis will help determine whether the whale shark population in the Arabian is an isolated population or interbreeds with whale sharks elsewhere in the world,” said Dhiresh Joshi, project co-ordinator with the Wildlife Trust of India.

The whale shark, the world’s largest fish, can grow up to 15 metres in length and is widely distributed across tropical and warm temperate waters. The Union environment ministry in 2001 assigned the whale shark maximum protection under the wildlife laws after a study by the World Wide Fund for Nature India found that more than 600 whale sharks were being caught by Gujarat fishermen each year.

“The catch prior to 2001 was almost exclusively for exports — there’s virtually no market for whale sharks in India,” Joshi said. “Fishermen are now aware of its protected status, but the large fish continues to get entangled in nets — and are released back into the sea.”

More than 200 whale sharks have been caught in nets and released in the northern Arabian Sea over the past three years. It is such whale sharks that the tagging project now hopes to assign unique identity tags.

Marine biologists say whale sharks zones have long been recognised as indicators of abundant fish. The whale sharks move to areas rich in plankton, and fishermen have known that where there is a whale shark, there must be plenty of other fish, Joshi told The Telegraph.

“Until now we’ve been trying to photo ID whale sharks,” said Manoj Matwal, a field officer with the Wildlife Trust of India, the non-government agency collaborating with the Gujarat Forest Department for the whale shark project supported by Tata Chemicals Limited.

Whale sharks have characteristic spots on their left sides and marine biologists believe the pattern of spots are unique on different whale sharks — something like fingerprints. “But capturing a photo of the spots is often difficult — the water can be turbid,” Matwal said.

Project biologists have asked fishermen to call them each time they find a whale shark in their nets. They hope to tag at least 50 to 60 whale sharks and wait for them to be sighted again. Only subsequent sightings will allow their movements to be tracked. Australia, Mexico, Philippines and Seychelles are among other countries that have already established similar whale shark tagging initiatives.