The majority of blue whales migrate to colder waters to feed, but a BBC film crew have filmed an exceptional group that live off the coast of Sri Lanka year round. The whales are thought to take advantage of a cold water upswelling in the area that delivers large numbers of krill, their preferred food. Specialist cameramen Doug Allan and Didier Noirot got up close and personal with the world's underwater record breakers for the BBC One series Ocean Giants. Here Didier filmed the aggressive mating displays of male humpback whales off the coast of Hawaii. Bowhead whales are the fattest animals in the world. Living in arctic waters, the whales have up to 50 tonnes of body fat to keep them warm. The whales are also thought to be the longest-lived mammals on earth as their low body temperature helps them to live for up to 200 years. Grey whales undertake the longest annual migration of any known mammal, travelling from warm breeding grounds at the equator to their summer feeding grounds in the Arctic. Researchers have suggested that these epic journeys could also be driven by the threat of predation from killer whales.