First evidence of bidirectional exchange between distant humpback whale breeding populations in eastern Australia and Brazil

Abstract Movements between humpback whale (Megaptera novaeangliae) breeding stocks are exceedingly rare, and exchange between distant breeding grounds in both directions has not previously been documented between eastern Australia and Brazil. Using 19 283 curated photo-identification images from eastern Australia (breeding stock E1 (BSE1)) and Brazil (breeding stock A (BSA)) collected between 1984 and 2025, we identified two individuals photographed in both areas, representing the first recorded exchange in both directions between BSE1 and BSA. The breeding grounds are separated by minimum great-circle distances of 14 200 km and 15 100 km, respectively, distances that reflect the separation between sighting locations rather than actual distances travelled, as photo-identification records only the endpoints of each individual’s travel. Resighting intervals of 6 and 22 years suggest that these are rare, possibly single-lifetime events rather than regular migratory shifts. These findings extend the known spatial limits of inter-basin connectivity for Southern Hemisphere humpback whales and support the ‘Southern Ocean Exchange’ hypothesis, whereby population recovery and environmental variability may create opportunities for exceptional exchange between ocean basins. Although such events occurred in only 0.01% of identified whales, continued global collaboration through photo-identification platforms will be essential for detecting and quantifying these rare exchanges.