Tagging whale sharks in the Maldives

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Somewhere around us in the incredible turquoise and blue-black waters of the Maldives, the planet’s biggest fish is swimming by.

Reaching lengths of up to 20m and sporting a dramatic checkerboard pattern of bright polka dots, you’d think that spotting a whale shark would be easy.

But we’ve been peering into the water for three hours now and so far, nothing.

We’re cruising up and down a known shark aggregation zone, a stretch of the Indian Ocean outside the island necklace of South Ari atoll, one of 26 coral formations that make up the Maldives archipelago.

On board are conservation biologists Richard Rees and Adam Harman from the Maldives Whale Shark Research Programme and the tagging expert accompanying them, Brent Stewart, of Hubbs-SeaWorld Research Institute in San Diego, US.

Brent has tagged everything from seals to sea birds to learn more about their lives, and he’s also tagged a group of whale sharks off Kenya.

This project, which began last year, is the first attempt to tag whale sharks in the Maldives and the team is hoping it will reveal precious information about the little-studied fish.

Spot the difference

Whale sharks (Rhincodon typus ), first discovered in the 1800s, are found throughout the tropical oceans, but relatively little is known about their behaviour, how long they live, their breeding habits, or their migratory routes – or indeed whether they migrate.

The group is keeping an open-access database of the sharks. This means that each time one is found, one of the researchers will free-dive down to take a picture of it between the fifth gill and the side fin on both left and right sides.

Using software similar to fingerprint-matching technology, the snaps of the shark’s spot patterns are compared to see if it has previously been photographed or is a new find. So far they have recorded 106 on the database, all but two of which are male.

But before they can be snapped, we need to find them, and we’re not the only ones searching.

Speedboats frequently whiz past us carrying resort tourists on whale shark-spotting trips.

The activity is increasingly popular and has become big business here, which Richard thinks may be related to the number of boat impact injuries sustained by the sharks.

In a survey Richard’s team recently completed, more than 75% of whale sharks recorded in the area had scars or wounds from boat damage.

They are especially vulnerable because they swim slowly and close to the surface.

His organisation is campaigning for a large Marine Protected Area to be established here to protect the sharks from boat damage and fin-poaching.

Tag tools

While the others keep a lookout for sharks, Brent talks me through the tagging procedure and shows me some of the formidable equipment they’ll be using, including a harpoon and a spear gun.

The sharks are tagged just beneath the dorsal fin into a thick layer of fat – they rarely even bleed. The group is using two types of tag, one of which is programmed to release after a few days.

This records data including temperature, depth and light level, before bobbing to the surface where it will transmit its data via Argos satellites.

The other, smaller, type of tag stays on the shark indefinitely and needs to be cut off at a later date by researchers.

Brent is also collecting skin samples from the fish for mitochondrial DNA analysis and other studies. This, he hopes, will help to reveal how closely related the sharks in the Maldives are to each other and to sharks elsewhere in the world.