The harbour porpoise (Phocoena phocoena) is one of eight extant species of porpoise. It is one of the smallest species of cetacean. As its name implies, it stays close to coastal areas or river estuaries, and as such, is the most familiar porpoise to whale watchers. This porpoise often ventures up rivers, and has been seen hundreds of kilometres from the sea. The harbour porpoise may be polytypic, with geographically distinct populations representing distinct races: P. p. phocoena in the North Atlantic and West Africa, P. p. relicta in the Black Sea and Sea of Azov, an unnamed population in the northwestern Pacific and P. p. vomerina in the northeastern Pacific.
Taxonomy The English word porpoise comes from the French pourpois (Old French porpais, 12th century), which is from Medieval Latin porcopiscus, which is a compound of porcus (pig) and piscus (fish). The old word is probably a loan-translation of a Germanic word, compare Danish marsvin and Middle Dutch mereswijn (sea swine). Classical Latin had a similar name, porculus marinus. The species' taxonomic name, Phocoena phocoena, is the Latinized form of the Greek φώκαινα, phōkaina, "big seal", as described by Aristotle; this from φώκη, phōkē, "seal". The species is sometimes known as the common porpoise in texts originating in the United Kingdom. In parts of Atlantic Canada it is known colloquially as the puffing pig, and in Norway 'nise', derived from an Old Norse word for sneeze, both of which refer to the sound made when porpoises surface to breathe.
Description
The harbour porpoise is a little smaller than the other porpoises, at about 67–85 cm (26+1⁄2–33+1⁄2 in) long at birth, weighing 6.4–10 kg (14–22 lb). Adults of both sexes grow to 1.4 to 1.9 m (4 ft 7 in to 6 ft 3 in). The females are heavier, with a maximum weight of around 76 kg (168 lb) compared with the males' 61 kg (134 lb). The body is robust, and the animal is at its maximum girth just in front of its triangular dorsal fin. The beak is poorly demarcated. The flippers, dorsal fin, tail fin and back are a dark grey. The sides are a slightly speckled, lighter grey. The underside is much whiter, though there are usually grey stripes running along the throat from the underside of the body. Many anomalously white coloured individuals have been confirmed, mostly in the North Atlantic, but also notably around Turkish and British coasts, and in the Wadden Sea, Bay of Fundy and around the coast of Cornwall. Although conjoined twins are rarely seen in wild mammals, the first known case of a two-headed harbour porpoise was documented in May 2017 when Dutch fishermen in the North Sea caught them by chance. A study published by the online journal of the Natural History Museum Rotterdam points out that conjoined twins in whales and dolphins are extremely rare. The vocalizations of the harbour porpoise is made up of short clicks from 0.5 to 5 milliseconds in bursts up to two seconds long. Each click has a frequency between 1000 and 2200 hertz. Aside from communication, the clicks are used for echolocation.
Distribution The harbour porpoise species is widespread in cooler coastal waters of the North Atlantic, North Pacific and the Black Sea. In the Atlantic, harbour porpoises may be present in a curved band of water running from the coast of West Africa to the coasts of Portugal, Spain, France, the United Kingdom, Ireland, Scandinavia, Iceland, Greenland, Nova Scotia and Newfoundland and the eastern seaboard of the United States. The population in the Baltic Sea is limited in winter due to sea freezing, and is most common in the southwest parts of the sea. There is another band in the Pacific Ocean running from the Sea of Japan, Vladivostok, the Bering Strait, Alaska, British Columbia, and California. The populations in these regions are not continuous and are classified as separate subspecies with P. p. phocoena in the North Atlantic and West Africa, P. p. relicta in the Black Sea and Sea of Azov, an unnamed population in the northwest Pacific and P. p. vomerina in the northeast Pacific. Concerning the North Atlantic, an international workshop co-organised by the North Atlantic Marine Mammal Commission and the Norwegian Institute of Marine Research reviewed the status of the species in 2018. It concluded that the harbour porpoise population structure is more complex than previously thought, with at least three genetically distinct subspecies in the North Atlantic. Given the structure of the harbour porpoise population, the workshop delineated 18 assessment areas for the North Atlantic.
Population status
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 107,000-300,000 harbour porpoises. As of 2022, the entire North Sea population (including the Danish waters of the Skagerrak) was about 339,000. 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.
Natural history
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