The harbour porpoise has a global population of at least 700,000. In 2016, a comprehensive survey of the Atlantic region in Europe, from Gibraltar to Vestfjorden in Norway, found that the population was about 467,000 harbour porpoises, making it the most abundant cetacean in the region, together with the common dolphin. Based on surveys in 1994, 2005 and 2016, the harbour porpoise population in this region is stable. The highest densities are in the southwestern North Sea and oceans of mainland Denmark; the latter region alone is home to about 107,000 harbour porpoises. The entire North Sea population is about 335,000. In the Western Atlantic it is estimated that there are about 33,000 harbour porpoises along the mid-southwestern coast of Greenland (where increasing temperatures have aided them), 75,000 between the Gulf of Maine and Gulf of St. Lawrence, and 27,000 in the Gulf of St. Lawrence. The Pacific population off mainland United States is about 73,000 and off Alaska 89,000. After sharp declines in the 20th century, populations have rebounded in the inland waters of Washington State. In contrast, some subpopulations are seriously threatened. For example, there are less than 12,000 in the Black Sea, and only about 500 remaining in the Baltic Sea proper, representing a sharp decrease since the mid-1900s.
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