A single whale shark has swum all the way from Madagascar to the Seychelles, in what researchers say is the first documented instance of the species making this journey. The discovery hints that whale sharks may regularly cross national boundaries in the western Indian Ocean, highlighting the need for international collaboration to help monitor and protect this endangered species.
"We've been recording whale sharks since 2015 and to see an individual travelling between Madagascar and Seychelles is astounding,” says Stella Diamant of the Madagascar Whale Shark Project. “This first-of-its-kind event is what we were waiting for.”
Whale sharks are the biggest fish in the ocean. They can grow up to 20 metres long and weigh up to 20 tonnes, but they are gentle giants. They swim sedately, at speeds of around 3 miles per hour, with their enormous mouths wide open, so they can filter their food – plankton, krill and small fish – directly from the water.
More than half of all whale sharks have been lost over the last 75 years. Climate change and pollution are problems, but so are collisions with ships, accidental bycatch and deliberate hunting. Now, the whale shark is listed as endangered on the IUCN’s Red List, but whilst it has been protected in the Seychelles since 2003, it currently lacks formal protection in Madagascar.
Like a human fingerprint, every whale shark has a unique pattern of spots. This enabled researchers from the Madagascar Whale Shark Project and the Marine Conservation Society Seychelles to identify hundreds of individuals and track one of them 746 miles (1,200 kilometres) across the Indian Ocean.
Photo-identification confirmed that a juvenile male first recorded off Nosy Be, Madagascar, in 2019, was resighted off Mahé in the Seychelles, in August 2025. This is the first verified sighting of a whale shark moving from Madagascar to another country in the region, adding rare evidence that whale sharks form a shared, transboundary population.
“This discovery underscores the importance of long-term monitoring and international collaboration. Without shared photo-identification databases, this movement would have gone unnoticed,” says Diamant.
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The finding comes amid declining sightings in Madagascar and increasing sightings in the Seychelles, suggesting that the whale sharks’ feeding grounds could be changing.
Now, the two conservation organisations are working together to monitor the whale sharks. “This record highlights the significant gaps that remain in our understanding of the spatial ecology and migratory behaviour of the world’s largest fish,” says Christophe Mason-Parker from Marine Conservation Society Seychelles.
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Top image: Volunteer photographs a whale shark in Madagascar. Credit: Stella Diamant
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