Researchers Matched Whale’s Tail From Brazil To Australia and Confirmed a Record 15,100-Kilometer Journey

Two humpbacks crossed between Brazil and Australia, redrawing whale migration maps.

A humpback whale photographed in Brazil in September 2003 appeared again in September 2025 off eastern Australia, so far from its first sighting that researchers first had to make sure the whale was really the same.

It was. The match links two breeding grounds about 15,100 kilometers apart—the longest confirmed geographic distance between sightings of a single humpback. A second whale made the reverse crossing, from Australia to Brazil, showing that even populations long treated as separate can occasionally cross into each other’s range.

Familiar Fluke

Humpbacks often expose the underside of their tails, or flukes, when they dive. Each fluke carries a unique mix of black-and-white markings, notches, and scars. Researchers use those patterns like fingerprints.

The team analyzed 19,283 high-quality fluke photographs from eastern Australia and Latin America, collected between 1984 and 2025. Scientists and citizen photographers contributed many of the images through Happywhale, a global platform that uses image-recognition software to find matching whales. Researchers then visually checked the matches.

“Every photo contributes to our understanding of whale biology and, in this case, helped uncover one of the most extreme movements ever recorded,” lead researcher Dr. Cristina Castro of Pacific Whale Foundation said in a statement.

One whale was photographed in Hervey Bay in 2007 and again in 2013. In 2019, it appeared off São Paulo, Brazil, swimming alone toward the humpback nursery at Abrolhos Bank. The minimum distance between the sightings was about 14,200 kilometers.

The other whale first appeared in 2003 at Abrolhos Bank, in a competitive group of nine adults. In 2025, it was spotted alone in Hervey Bay, 22 years and one month later.

“It was extraordinary to photograph a whale that’s gone this distance—it has never happened before,” study co-author Stephanie Stack told The Guardian.

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Wherever They May Roam

Humpbacks make some of the longest migrations of any mammal. They feed in cold waters, often near Antarctica, then migrate to warmer breeding grounds. East Australian humpbacks usually move between Antarctic feeding grounds and breeding waters near the Great Barrier Reef.

The two whales mentioned by the new study broke this pattern. They appeared to cross between breeding populations that scientists had treated as largely separate: eastern Australia’s breeding stock E1 and Brazil’s breeding stock A.

But the photographs probably reveal only two points of a bigger trajectory.

“We know where it started, and we know where it ended up, but we don’t know anything about what happened in between,” Stack said.

The whales may have traveled farther than the straight-line distances suggest. They may have mixed with other humpbacks on shared Antarctic feeding grounds, then followed a different migration route north. The study says the finding supports the Southern Ocean Exchange idea: whales from different breeding populations can meet in southern feeding areas, and a few may later join another population’s route.

Widening the Map

The crossings were extraordinarily uncommon. Out of more than four decades of data and nearly 20,000 identified whales, researchers found only two animals in both regions—about 0.01%. The long gaps between sightings suggest these were rare, perhaps once-in-a-lifetime movements, not regular migrations.

Still, if whales breed after switching regions, they may carry genes between populations. Male humpbacks may also transmit songs, which can spread across ocean basins similar to a musical fad.

“Finding not one but two individuals that have crossed between Australia and Brazil challenges what we thought we knew about how separate these populations really are,” Stack told the Associated Press.

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Climate change adds urgency to the question. Humpbacks depend on krill, the small crustaceans that swarm in Antarctic waters. As sea ice and krill distributions shift, whales may alter where they feed and which routes they take. The study does not show climate change is responsible for these unusually long journeys, but it suggests researchers need to watch for future changes.

“These whales were photographed decades apart, by different people, in opposite parts of the world, separated by two different oceans, and yet we can connect their journey,” Stack concluded.

The study was published in the journal Royal Society Open Science.