A female humpback whale has astonished marine biologists by swimming over 9,800 kilometres from breeding areas in Brazil to those in Madagascar, setting a record for the longest mammal migration ever documented.

According to Peter Stevick, a biologist at the College of the Atlantic in Bar Harbor, Maine, and his colleagues, the journey is unusual not just for its distance but also because it spanned an ocean basin, multiple breeding zones and almost 90 degrees of longitude.