One Whale Shark’s Historic Indian Ocean Migration

The largest fish in the ocean just reminded us how small our (imaginary) borders really are. A juvenile male whale shark (Rhincodon typus) has completed a historic 746-mile (1,200 kilometer) journey from the clear azure waters of Madagascar to the sparkling turquoise ones of the Seychelles. It is the first documented movement of its kind between the two countries, with researchers from the Madagascar Whale Shark Project and the Marine Conservation Society Seychelles confirmed the match using photo identification. Although the starry constellations that adorn their bodies seem like they are all the same, much like fingerprints, each whale shark has a unique pattern. So by comparing photographs taken off Nosy Be in 2019 with images captured near Mahé in August 2025, scientists verified that it was the same individual.

Scientists in Madagascar have been recording whale sharks since 2015. In Seychelles, systematic monitoring began around the same time but was suspended after a marked decline in sightings. Then, in 2023, the sharks began reappearing in Seychelles waters, so surveys resumed and data were compared. “In 2015, MCSS suspended its long-term whale shark monitoring programme due to a marked decline in local sightings. With the species’ reappearance in Seychelles waters in 2023 and the subsequent recommencement of systematic surveys, it is incredibly exciting to document [this transboundary movement of a whale shark for the first time],” said Christophe Mason-Parker of MCSS.

Whale sharks are listed as Endangered on the International Union for Conservation of Nature Red List. Although their size can be imposing, these sharks are gentle filter feeders and are surprisingly vulnerable to human pressure. The species as a whole faces a suite of threats: fisheries bycatch, vessel strikes, targeted fishing in some regions, and climate driven changes that alter where plankton blooms occur. In Seychelles, whale sharks have been legally protected since 2003. In Madagascar, there is currently no formal national protection for the species (despite a recent study valuing Madagascar whale shark tourism at $1.5 Million USD amid calls for stronger protections). But the ocean — nor a whale shark — does not recognise these policy differences; it is doubtful that the young male cruising past dive boats in Nosy Be paused at an invisible maritime boundary before continuing toward Mahé. Yet its survival may depend on what happens on either side of that “line.”

The western Indian Ocean hosts significant tuna fisheries, and bycatch remains a persistent threat for large pelagic species. If a whale shark moves between jurisdictions with different levels of enforcement or protection, its risk profile changes mid journey. And while whale sharks have been known to migrate thousands of miles and kilometers in other parts of the world, this is the first verified case of a whale shark moving from Madagascar to another country in the western Indian Ocean, confirming that the animals using these waters form a shared, transboundary population. The single resighting poses more questions than answers, and the team is delving into the data to see if they can come up with some. One pressing question for the researchers is around climate change, which is reshaping where plankton blooms occur. These blooms are what whale sharks follow so if food availability shifts, the sharks will too. Is this a possible reason as to why sightings declined in Madagascar while increasing in Seychelles? Or are there fewer sharks overall in the region? Perhaps whale sharks are adjusting their feeding grounds in response to changing ocean productivity, or redistributing across the western Indian Ocean in response to a combination of environmental cues. Answering these questions will require more than observation alone: it will take coordinated monitoring and new technologies to truly understand what is driving these movements. That said, this does not diminish the power of photo identification. Accessible tools can still produce transformative insights, as has been highlighted here! “This discovery underscores the importance of long-term monitoring and international collaboration. Without shared photo-identification databases, this movement would have gone unnoticed,” says Stella Diamant of the Madagascar Whale Shark Project. A well maintained database, combined with collaboration between organisations, was key in this discovery. It makes you wonder how many similar journeys are unfolding right now, unrecorded and unseen.

The western Indian Ocean is a mosaic of cultures, economies and governance systems, yet its megafauna connects those pieces into a single ecological unit. We manage wildlife according to human boundaries, yet marine species operate on ecological ones. The two countries, with their differing policies, underscore just how fragmented our conservation frameworks can be. He’s oblivious to it, swimming through the blue waters and doing as he pleases, but the young whale shark has become an ambassador for interconnected conservation initiatives for his species in the region. The question now is whether we as a society will respond at the same scale at which he lives his life.