While the record is interesting, the findings help researchers understand the behaviors of the whales, which are endangered, Peter Stevick of the College of the Atlantic in Maine and an international team of colleagues reported. "It is unexpected to find this exceptional long-distance movement between breeding groups by a female," they wrote in the journal Biology Letters.

"While humpback whales regularly travel 5,000 km between breeding and feeding grounds, they are commuters, not adventurers," Stevick's team wrote in a summary of their work. The whale, identified by her natural markings and DNA, was first seen off Brazil in August 1999.

"The whale subsequently was photographed just over two years later on 21 September 2001 from a commercial whale watch tour vessel. It was one of a trio of whales seen between Ile Sainte Marie/Nosy Boraha and the east coast of Madagascar," they wrote.

"The minimum travel distance between these locations, via a great circle route rounding Cape Agulhas and Cap Ste Marie, is greater than 9,800 km (more than 6,000 miles). This is about 4,000 km (2,500 miles) longer than any previously reported movement between breeding grounds and more than twice the species' typical seasonal migratory distance."

The researchers cannot say why this whale traveled so far.

"It is the longest documented movement by a mammal, about 400 km (250 miles) longer than the longest seasonal migration that has been reported," they added.

Humpbacks rack up a lot of miles. They typically cover up to 25,000 kilometers (16,000 miles) going back and forth in a year.

"The severe depletion of humpback whales throughout the Southern Hemisphere, and apparent inconsistencies in the regional patterns of recovery, make understanding of regional movement patterns a considerable conservation concern," the researchers wrote.