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. These cases represent the first recorded exchange in both directions between BSE1 and BSA. The breeding grounds in which these individuals were photographed are separated by minimum great-circle distances of 14,200 km and 15,100 km, respectively. These distances represent the separation between sighting locations rather than the actual distance travelled by each whale, because photo-identification records only the endpoints of each individual’s travel. Time intervals of 12 and 22 years between sightings suggest that these represent rare, possibly single-lifetime events rather than regular migratory shifts. These findings significantly extend the known spatial limits of inter-basin connectivity for Southern Hemisphere humpback whales and provide direct evidence supporting the “Southern Ocean Exchange”, 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, they highlight the potential for rare individual movements to influence population structure, cultural transmission, and connectivity across ocean basins. Continued global collaboration through photo-ID platforms will be essential for detecting these extreme exchange events.

Citation: Castro Ayala, C., Stack, S.H., Marcondes, M.C.C., Cardoso, J., Cheeseman, T., Currie, J.J., Francisco, A., Olio, M., Righi, B., Stuckenbrock, S., & Sousa-Lima, R.S. (2026). First evidence of bidirectional exchange between distant humpback whale breeding populations in eastern Australia and Brazil. Royal Society Open Science, 13(5), 260251. 

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