Researchers have documented two individual humpback whales that were sighted in both Australian and Brazilian breeding grounds, marking the first lifetime-recorded crossings of the Southern Ocean between these distant basins. The findings, published in Royal Society Open Science, were made possible by matching tens of thousands of whale tail, or fluke, photographs used for long-term photo-identification.
One whale was seen off Queensland in 2007 and 2013 and later near São Paulo in 2019, a separation of roughly 14,200 kilometers. The other was first observed off Bahia in Brazil in 2003 and then 22 years later off Hervey Bay in Queensland, about 15,100 kilometers apart. The reported distances reflect the separation between sighting locations rather than the actual path traveled, since photo-ID records only endpoints.
Authors say the observations extend the known spatial limits of inter-basin connectivity for southern hemisphere humpbacks and lend support to the Southern Ocean Exchange hypothesis: whales may meet on shared Antarctic feeding grounds and, in exceptional cases, return to different breeding areas. Humpbacks feed on krill and small fish in cold southern waters during summer and migrate to warmer tropical waters to breed in winter.
Such exchanges appear to be very rare. Of thousands of identified whales in the study, only 0.01% completed a cross-basin exchange in the photographic record. Resighting intervals of six and 22 years suggest these are likely sporadic, possibly single-lifetime events rather than regular migratory shifts. Still, researchers emphasize that even occasional movements between distant breeding grounds can help maintain genetic diversity and can introduce new songs and behaviors to populations.
Scientists warn that climate-driven changes to the Southern Ocean, including shifting sea ice and altered krill distributions, could make such long-distance crossings more likely over time. The study calls for continued global collaboration on photo-ID platforms to improve detection of rare movements and better understand connectivity between populations.
The research depended heavily on citizen scientists and volunteer spotters who submitted fluke photographs. Investigators thanked those contributors, noting that each image improves knowledge of whale biology and movements and helped reveal some of the most extreme individual migrations ever recorded.