Harbour porpoise
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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.<ref name=shirihai>Template:Cite book</ref>
Taxonomy
The English word porpoise comes from the French Template:Lang (Old French Template:Lang, 12th century), which is from Medieval Latin Template:Lang, which is a compound of porcus (pig) and Template:Lang (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 Template:Cvt long at birth, weighing Template:Cvt. Adults of both sexes grow to Template:Cvt. The females are heavier, with a maximum weight of around Template:Cvt compared with the males' Template:Cvt. 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.<ref>Template:Cite journal</ref><ref>Template:Cite web</ref><ref>Template:Cite web</ref>
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.<ref>Template:Cite news</ref> 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.<ref>Template:Cite journal</ref>
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.<ref name="Schevill">Template:Cite journal</ref>
Distribution
The harbour porpoise species is widespread in cooler coastal waters of the North Atlantic, North Pacific and the Black Sea.<ref name="Bjorge2018">Template:Cite book</ref> 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.<ref name="Audubon">Template:RefAudubonMarineMammals</ref><ref name="Bjorge2018" /> 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.<ref name="Audubon" /><ref name="Bjorge2018" />
The populations in these regions are not continuous<ref name="Audubon" /> 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.<ref name="shirihai" /><ref name="Bjorge2018" />
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.<ref>Template:Cite tech report</ref>
Population status
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The harbour porpoise has a global population of at least 700,000.<ref name=Bjorge2018/> 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.<ref name=StAndrewsTotal>Template:Cite news</ref> Based on surveys in 1994, 2005 and 2016, the harbour porpoise population in this region is stable.<ref name=StAndrewsTotal/> The highest densities are in the southwestern North Sea and oceans of mainland Denmark;<ref name=StAndrewsTotal/> the latter region alone is home to about 107,000-300,000 harbour porpoises.<ref name=FyensS>Template:Cite news</ref><ref>Template:Cite web</ref> The entire North Sea population is about 335,000.<ref>Template:Cite journal</ref> 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),<ref name=Bjorge2018/> 75,000 between the Gulf of Maine and Gulf of St. Lawrence, and 27,000 in the Gulf of St. Lawrence.<ref name="iucn" /> The Pacific population off mainland United States is about 73,000 and off Alaska 89,000.<ref name="iucn" /> After sharp declines in the 20th century, populations have rebounded in the inland waters of Washington state.<ref>Template:Cite news</ref> In contrast, some subpopulations are seriously threatened. For example, there are less than 12,000 in the Black Sea,<ref name="iucn" /> and only about 500 remaining in the Baltic Sea proper, representing a sharp decrease since the mid-1900s.<ref name=StAndrewsBaltic>Template:Cite web</ref>
Natural history
Ecology
Harbour porpoises prefer temperate and subarctic waters.<ref name= "Audubon"/> They inhabit fjords, bays, estuaries and harbours, hence their name.<ref name= "Audubon"/> They feed mostly on small pelagic schooling fish, particularly herring, pollack, hake, sardine, cod,<ref>Template:Cite web</ref> capelin, and sprat.<ref name=Bjorge2018/> They will, however, eat squid and crustaceans in certain places.<ref name=Bjorge2018/> This species tends to feed close to the sea bottom, at least for waters less than Template:Convert deep.<ref name=Bjorge2018/> However, when hunting sprat, porpoise may stay closer to the surface.<ref name=Bjorge2018/> When in deeper waters, porpoises may forage for mid-water fish, such as pearlsides.<ref name=Bjorge2018/> A study published in 2016 showed that porpoises off the coast of Denmark were hunting 200 fish per hour during the day and up to 550 per hour at night, catching 90% of the fish they targeted.<ref name=sn>Template:Cite web</ref><ref name=diet>Template:Cite journal</ref> Almost all the fish they ate were very small, between Template:Convert long.<ref name=sn/><ref name=diet/>
A study (2024) shown that prey availability is an important driver of seasonal and diel dynamics of harbour porpoise acoustic activity in the Black Sea. In the southeastern region, porpoise activity was primarily nocturnal, with a peak from January to May, aligned with anchovy migration. On the northwestern shelf, porpoises were more active during daylight from April to October, reflecting the migration patterns of sprat.<ref name="Ivanchikova_et_al_2024">Template:Cite journal</ref>
Harbour porpoises tend to be solitary foragers, but they do sometimes hunt in packs and herd fish together.<ref name=Bjorge2018/> Young porpoises need to consume about 7% to 8% of their body weight each day to survive, which is approximately 15 pounds or 7 kilograms of fish. Significant predators of harbour porpoises include white sharks and killer whales (orcas). Researchers at the University of Aberdeen in Scotland have also discovered that the local bottlenose dolphins attack and kill harbour porpoises without eating them due to competition for a decreasing food supply.<ref name=read>Template:Cite book</ref> An alternative explanation is that the adult dolphins exhibit infanticidal behaviour and mistake the porpoises for juvenile dolphins which they are believed to kill.<ref name=infanticide>Template:Cite journal</ref> Grey seals are also known to attack harbour porpoises by biting off chunks of fat as a high energy source.<ref>Template:Cite journal</ref>
Behaviour, reproduction and life-span
Some studies suggest porpoises are relatively sedentary and usually do not leave a certain area for long.<ref name=Bjorge2018/> Nevertheless, they have been recorded to move from onshore to offshore waters along the coast.<ref name=Bjorge2018/> Dives of Template:Convert by harbour porpoises have been recorded.<ref name=Bjorge2018/> Dives can last five minutes but typically last one minute.<ref>Template:Cite journal</ref> A rarely occurring parabolic dive type has been hypothesized to represent a state of unihemispheric slow-wave sleep, during which the porpoise engages in largely automated swimming behavior and very little vocalization. These episodes make up only a small proportion of all dives, but the animal may also engage in periods of sleep during other undemanding manoeuvers, such as slow surfacing from depth.<ref>Template:Cite journal</ref>
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The social life of harbour porpoises is not well understood. They are generally seen as a solitary species.<ref name= "Audubon"/> Most of the time, porpoises are either alone or in groups of no more than five animals.<ref name= "Audubon"/> Porpoises mate promiscuously.<ref name=Bjorge2018/> Males produce large amounts of sperm, perhaps for sperm competition.<ref name=Bjorge2018/> Females become sexually mature by their third or fourth year and can calve each year for several consecutive years, being pregnant and lactating at the same time. The gestation of the porpoise is typically 10–11 months.<ref name= "Audubon"/> Most births occur in late spring and summer.<ref name=Bjorge2018/> Calves are weaned after 8–12 months.<ref name= "Audubon"/> Their average life-span in the wild is 8–13 years, although exceptionally individuals have reached up to 20,<ref name=Bjorge2018/><ref name=ADWHarbourPorpoise>Template:Cite web</ref> and in captivity up to 28 years.<ref>Template:Cite news</ref> In a study of 239 dead harbour porpoises in the Gulf of Maine–Bay of Fundy, the vast majority were less than 12 years old and the oldest was 17.<ref>Template:Cite journal</ref>
Threats
Hunting
Harbour porpoises were traditionally hunted for food, as well as for their blubber, which was used for lighting fuel. Among others, hunting occurred in the Black Sea, off Normandy, in the Bay of Biscay, off Flanders, in the Little Belt strait, off Iceland, western Norway, in Puget Sound, Bay of Fundy and Gulf of Saint Lawrence.<ref name="iucn" /><ref>Template:Cite web</ref><ref>Template:Cite book</ref> The drive hunt in the Little Belt strait is the best documented example. Thousands of porpoises were caught there until the end of the 19th century (it was banned in 1899), and again in smaller scale during the shortages that occurred in World War I and World War II.<ref>Template:Cite book</ref> A similar, short-lived re-emergence of hunting during the world wars happened in Poland and the Baltic countries.<ref name=NAMMCO>Template:Cite web</ref> Currently, the species is only hunted as part of the traditional Inuit hunt in the Arctic, notably in Greenland.<ref name="iucn" /><ref name=NAMMCO/> In prehistoric times, harbour porpoises were also hunted in many areas, for example by the Alby People of the east coast of Öland, Sweden.
Interactions with fisheries
The main threat to porpoises is static fishing techniques such as gill and tangle nets. Bycatch in bottom-set gill nets is considered the main anthropogenic mortality factor for harbour porpoises worldwide. Several thousand die each year in incidental bycatch, which has been reported from the Black Sea, the Baltic Sea, the North Sea, off California, and along the east coast of the United States and Canada.<ref name="iucn" /> Bottom-set gill nets are anchored to the sea floor and are up to Template:Convert in length. It is unknown why porpoises become entangled in gill nets, since several studies indicate they are able to detect these nets using their echolocation.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> Porpoise-scaring devices, so-called pingers, have been developed to keep porpoises out of nets and numerous studies have demonstrated they are very effective at reducing entanglement.<ref>Template:Cite journal</ref><ref>Larsen, F (1999). The effect of acoustic alarms on the by-catch of harbour porpoises in the Danish North Sea gill net fishery. Paper SC/51/SM41 presented to the IWC Scientific Committee</ref> However, concern has been raised over the noise pollution created by the pingers and whether their efficiency will diminish over time due to porpoises habituating to the sounds.<ref name=Teilmann2006/><ref>Template:Cite journal</ref>
Mortality resulting from trawling bycatch seems to be less of an issue, probably because porpoises are not inclined to feed inside trawls, as dolphins are known to do.
Overfishing
Overfishing may reduce preferred prey availability for porpoises. Overfishing resulting in the collapse of herring in the North Sea caused porpoises to hunt for other prey species.<ref>Template:Cite journal</ref> Reduction of prey may result from climate change, overfishing, or both.
Noise pollution
Noise from ship traffic and oil platforms is thought to affect the distribution of toothed whales, like the harbour porpoise, that use echolocation for communication and prey detection. Noise from shipping traffic, particularly busy sea lanes, appears to instigate evasive behavior, with predominantly lateral movements during the day and deeper dives during the night.<ref>Template:Cite journal</ref> The construction of thousands of offshore wind turbines, planned in different areas of North Sea, is known to cause displacement of porpoises from the construction site,<ref>Template:Cite journal</ref> particularly if steel monopile foundations are installed by percussive piling, where reactions can occur at distances of more than Template:Convert.<ref>Template:Cite journal</ref> Noise levels from operating wind turbines are low and unlikely to affect porpoises, even at close range.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>
Pollution
Marine top predators like porpoises and seals accumulate pollutants such as heavy metals, PCBs and pesticides in their fat tissue. Porpoises have a coastal distribution that potentially brings them close to sources of pollution. Porpoises may not experience any toxic effects until they draw on their fat reserves, such as in periods of food shortage, migration or reproduction.
Climate change
An increase in the temperature of the sea water is likely to affect the distribution of porpoises and their prey, but has not been shown to occur. Reduced stocks of sand eel along the east coast of Scotland, a pattern linked to climate change, appears to be the main reason for the increase in malnutrition in porpoises in the area.<ref>Template:Cite journal</ref>
Conservation status
Overall, the harbour porpoise is not considered threatened and the total population is in the hundreds of thousands.<ref name="iucn" />
The harbour porpoise populations of the North Sea, Baltic Sea, western North Atlantic, Black Sea and North West Africa are protected under Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS).<ref name="Appendices">"Appendix II Template:Webarchive" of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As amended by the Conference of the Parties in 1985, 1988, 1991, 1994, 1997, 1999, 2002, 2005 and 2008. Effective: 5 March 2009.</ref> In 2013, the two Baltic Sea subpopulations were listed as vulnerable and critically endangered respectively by HELCOM.<ref>Template:Cite journal</ref> Although the species overall is considered to be of Least Concern by the IUCN,<ref name="iucn" /> they consider the Baltic Sea and Western African populations critically endangered, and the subspecies P. p. relicta of the Black Sea endangered.<ref>Template:Cite iucn</ref><ref>Template:Cite iucn</ref><ref>Template:Cite web</ref>
In addition, the harbour porpoise is covered by the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS), the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS) and the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU).
See also
References
Further reading
External links
- ARKive - images and movies of the harbour porpoise (Phocoena phocoena)
- Whale & Dolphin Conservation Society (WDCS)
- Convention on Migratory Species page on the Harbour porpoise
- Official website of the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area
- Official website of the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas
- Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia
- Voices in the Sea - Sounds of the Harbour Porpoise
Template:Cetacea Template:Taxonbar Template:Authority control
- Pages with broken file links
- Phocoena
- Cetaceans of Europe
- Mammals of North America
- Cetaceans of the Atlantic Ocean
- Fauna of the North Sea
- Fauna of the Baltic Sea
- Fauna of the Black Sea
- Cetaceans of the Pacific Ocean
- Mammals described in 1758
- Cetaceans of the Arctic Ocean
- Animal taxa named by Carl Linnaeus
- Fauna of the Holarctic realm
- Habitats Directive species