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Grey whale (Eschrichtius robustus). There are two populations of this whale, one in the eastern north Pacific and one in the western north Pacific. It is found in coastal waters. It undertakes the longest known migration of any mammal. For the winter it migrates from Arctic waters to tropical equatorial waters, a round trip of up to 20,400 kilometres. It can grow up to 15 metres in length and weigh 16 tonnes, with females being larger than males. It has up to 180 large bristly baleen plates hanging down from its jaws. It feeds by swallowing sediment from the sea floor and then pressing its tongue against the plates, pushing the water out and trapping crustaceans and worms. Photographed in the Pacific Ocean. (KEYSTONE/SCIENCE PHOTO LIBRARY/CHR 366 CHRISTOPHER SWANN/SCIENCE PHOTO LIBRARY) === ===