An international team of scientists has documented, for the first time, humpback whales travelling between breeding grounds in eastern Australia and Brazil, crossing more than 14,000 kilometres of open ocean.

The findings set new records for the greatest distances ever confirmed between sightings of individual humpback whales anywhere in the world.

“Discoveries like this are only possible because of investment into long-term multi-decadal research programmes and international collaboration,” Griffith University Phd Candidate and co-author Stephanie Stack said.

“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.”

By comparing tens of thousands of photographs of whale tails, also known as “flukes”, the team identified two individual whales that had been photographed in both eastern Australia and Brazil.

One whale was first photographed in Hervey Bay, Queensland in 2007, and was seen again in the same area in 2013 before turning up off the coast of São Paulo, Brazil in 2019.

These two breeding grounds are separated by a minimum straight-line ocean distance of about 14,200km – roughly the distance from Sydney to London.

Because only the start and end points of the whale’s journey were documented, the actual route taken, and therefore the true distance swum, remains unknown.

The other whale was first photographed in 2003 at the Abrolhos Bank – Brazil’s main humpback whale nursery off the coast of Bahia – in a large, boisterous group of nine adults.

Twenty-two years later, in September 2025, it was spotted alone in Hervey Bay, Australia, representing a travel distance of 15,100km, making this the longest distance ever documented between sightings of the same individual humpback whale on record.

The study drew on 19,283 high-quality fluke photographs collected between 1984 and 2025 from eastern Australia and Latin America, contributed by both scientists and citizen scientists through the global platform Happywhale.

By running these photographs through an automated image-recognition algorithm, and then independently verifying every potential match by eye, the team found the two humpback whales that had been photographed in both regions.

“This kind of research highlights the value of citizen science,” said lead researcher Dr Cristina Castro from Pacific Whale Foundation.

“Every photo contributes to our understanding of whale biology and, in this case, helped uncover one of the most extreme movements ever recorded.”

The researchers said these findings highlighted these crossings were very rare: in more than four decades of data covering nearly 20,000 individual whales, only two such animals were found, representing just 0.01 per cent of identified individuals.

“Despite their rarity, these exchanges matter for the long-term health of whale populations,” Ms Stack said.

“Occasional individuals moving between distant breeding grounds can help maintain genetic diversity across populations and may even carry new song styles from one region to another – humpback whale songs are known to spread culturally across ocean basins, much like music trends in human populations.”

The team added these findings also supported what scientists called the “Southern Ocean Exchange” hypothesis: the idea that humpback whales from different breeding populations occasionally met on shared Antarctic feeding grounds, and that some individuals then followed a different migration path home – ending up, perhaps for the rest of their lives, in an entirely new breeding region.

Climate-driven changes to the Southern Ocean, including shifts in sea ice and the distribution of Antarctic krill (the whale’s main prey), may be making such crossings more likely over time.

The study ‘First evidence of bidirectional exchange between distant humpback whale breeding populations in eastern Australia and Brazil’ has been published in Royal Society Open Science.