Harbour porpoises are found in cold temperate to sub-polar waters of the Northern Hemisphere (Gaskin 1992, Read 1999). They are usually found in continental shelf waters, although they occasionally travel over deeper offshore waters. In the North Pacific, they range from central California and northern Honshu to the southern Beaufort and Chukchi Seas (including the Bering and Okhotsk Seas, and Sea of Japan). In the North Atlantic, they are found from the southeastern United States to southern Baffin Island (they apparently do not enter Hudson Bay) in the west, and from Senegal to Novaya Zemlya in the east. They also occur around southeast and western Greenland, Iceland, and the Faroe Islands, and this is the only cetacean species that currently regularly occupies the Baltic Sea. The species occurs in the Black Sea, Marmara Sea, and Sea of Azov, but with the exception of the adjacent northern Aegean Sea, they do not regularly occur in the Mediterranean Sea.