Abstract
Humpback whales undertake one of the longest known migrations of any mammal. While their migration route generally extends between latitudes, the breeding stocks are longitudinally separated and display high site fidelity to their feeding grounds. While there is an indication of certain breeding stocks overlapping with each other, the current information on the migration routes of humpback whales within the Southern Hemisphere limits our understanding of the extent of this exchange. Presented here is the longest documented great-circle distance between sightings on wintering grounds of two different ocean basins of an adult male humpback whale, involving two breeding stocks in the eastern Pacific (stock G) and southwest Indian Ocean (stock C). These two stocks are separated by a minimum of 120° longitude, and a great-circle distance of 13 046 km. This extreme distance movement demonstrates behavioural plasticity, which may play an important role in adaptation strategies to global environmental changes and perhaps be an evolved response to various pressures, underlining the importance of consolidation of global datasets on wide-ranging marine mammals.