The experts say the female whale was first photographed off the coast of Brazil in August 1999. Just over two years later, someone aboard a whale watching vessel took a photograph of it off the east coast of Madagascar.
Experts who matched photos using the distinctive markings on the whale's tail were caught by surprise.
Humpback whales typically cover about 3,100 miles annually in their trips to and from the warmer waters in which they breed, but usually return to the same places.
Researchers said Wednesday this whale may have been bit more adventurous than its peers - or may have just gotten lost.
