Harbour Porpoise
Encyclopedia
The harbour porpoise is one of six species
of porpoise
. It is one of the smallest marine mammals. 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 miles 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 northwest Pacific and P. p. vomerina in the northeast Pacific.
porcopiscus, which is a compound of porcus (pig) and piscus (fish). The old word is probably a loan-translation of a Germanic word, cf. Danish
marsvin and Dutch
mereswijn (sea swine). Classical Latin had a similar name, porculus marinus (used by Pliny
), and the notion behind the name likely is a fancied resemblance of the snout to that of a pig or the sound of a porpoise breathing resembling a pig snort. The species is sometimes known as the common porpoise in texts originating in the United Kingdom
, though this usage appears to be dying out. It is also called a "puffer" or "puffer pig" by fishermen in New England and eastern Canada. The species' taxonomic name, Phocaena phocaena, is the Latin
ized form of the Greek
φώκαινα, phōkaina, "big seal", as described by Aristotle
; this from φώκη, phōkē, "seal".
. 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.
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 Spain
, France
, the United Kingdom
, Ireland
, Scandinavia
, Iceland
, Greenland
, Nova Scotia
and Newfoundland and the eastern seaboard of the United States
. There is a similarly-shaped band in the Pacific Ocean running from Sea of Japan
, Vladivostok
, the Bering Strait
, Alaska
and California
. The harbour porpoise has a global population of 700,000. Areas with sizable numbers include the North Sea
, where porpoises number at about 350,000; and well as the Gulf of Maine
/Bay of Fundy
area, the US west coast and Alaska.
, capelin
, and sprat. They will, however, also eat squid and crustaceans in some areas. The porpoises mostly forage near the sea bottom in waters less than 200m deep. They will also forage near the surface when feeding on sprat. When in deeper waters, porpoises may forage for mid-water fish, such as pearlsides.
Harbour porpoises tend to be independent foragers, but groups have been observed to collaborate to keep schools of fish closely together and herd them to the surface. 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 shark
s and killer whales (orcas). Researchers at the University of Aberdeen
in Scotland
have also discovered that the local bottlenose dolphin
s attack and kill harbour porpoises without eating them due to competition for a decreasing food supply.
Little is known about the social affiliation and interactions among harbour porpoises. They are generally seen as an asocial and solitary species. They are mostly seen alone or in small groups of two to five individuals. Porpoises have a promiscuous mating system, with each individual mating with several other individuals. Males produce large amounts of sperm which suggests they are sperm competitors
. Females, after reaching sexual maturity at around three to four years, can produce young annually for several years. With this they are over great nurtitional stress due to being pregnant and lactating at the same time. The gestation of the porpoise lasts 10 to 11 months. Most births tend to take places from May to August. Calves are nursed for eight to 12 months.
strait, Denmark
, is the best known example. Thousands of porpoises were caught there until the end of the 19th century and again in smaller scale during the world wars. Currently, however, this species is not subject to commercial hunting
, but it is hunted for food and sold locally in Greenland
. In prehistoric times, this animal was hunted by the Alby People of the east coast of Oland
, Sweden
.
The Harbour porpoise populations of the North Sea, Baltic Sea, western North Atlantic, Black Sea and North West Africa are listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS
). This listing means that these populations have an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.
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).
Currently, the total population is in the hundreds of thousands and the harbour porpoise is not under threat of extinction. There are, however, a number of threats that impact population distribution and numbers.
in bottom-set gill nets is considered the main anthropogenic mortality factor for harbour porpoises worldwide. Bycatch is reported from the Black Sea
, the Baltic Sea
, the North Sea
and the east coast of the United States
and Canada
. Bottom-set gill nets are anchored to the sea floor and are up to 12.5 miles (20 km) 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
. Porpoise-scaring devices, so-called pinger
s, have been developed to keep porpoises out of nets and numerous studies have demonstrated they are very effective at reducing entanglement. 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.
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.
along the east coast of Scotland seems to have been the main reason for the malnutrition in porpoises in the area.
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. Reduction of prey may result from climate change, or overfishing, or both.
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. 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, particularly if steel monopile foundations are installed by percussive piling, where reactions can occur at distances of more than 20 km. Noise levels from operating wind turbines are low and unlikely to affect porpoises, even at close range.
s and pesticide
s 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.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of porpoise
Porpoise
Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen...
. It is one of the smallest marine mammals. 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 miles from the sea. The harbour porpoise may be polytypic
Polytypic
In zoology, polytypic refers to a taxonomic unit with more than one subgroup at the next lower level.-See also:*Linnaean taxonomy*monotypic*monotypic habitat...
, 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 northwest Pacific and P. p. vomerina in the northeast Pacific.
Etymology
The English word porpoise comes from the French pourpois (old French porpais, 12th cent.), which is from Medieval LatinLatin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
porcopiscus, which is a compound of porcus (pig) and piscus (fish). The old word is probably a loan-translation of a Germanic word, cf. Danish
Danish language
Danish is a North Germanic language spoken by around six million people, principally in the country of Denmark. It is also spoken by 50,000 Germans of Danish ethnicity in the northern parts of Schleswig-Holstein, Germany, where it holds the status of minority language...
marsvin and Dutch
Dutch language
Dutch is a West Germanic language and the native language of the majority of the population of the Netherlands, Belgium, and Suriname, the three member states of the Dutch Language Union. Most speakers live in the European Union, where it is a first language for about 23 million and a second...
mereswijn (sea swine). Classical Latin had a similar name, porculus marinus (used by Pliny
Pliny the Elder
Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...
), and the notion behind the name likely is a fancied resemblance of the snout to that of a pig or the sound of a porpoise breathing resembling a pig snort. The species is sometimes known as the common porpoise in texts originating in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, though this usage appears to be dying out. It is also called a "puffer" or "puffer pig" by fishermen in New England and eastern Canada. The species' taxonomic name, Phocaena phocaena, is the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
ized form of the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
φώκαινα, phōkaina, "big seal", as described by Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...
; this from φώκη, phōkē, "seal".
Physical description
The harbour porpoise is a little smaller than the other porpoises, at about 67–85 cm (26–33 in) long at birth, weighing 6.4-10 kg. Adults of both sexes grow to 1.4 m to 1.9 m (4.6-6.2 ft). The females are heavier, with a maximum weight of around 76 kg (167 pounds) compared with the males' 61 kg (134 pounds). The body is robust, and the animal is at its maximum girth just in front of its triangular dorsal finDorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
. 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.
Populations and distribution
The harbour porpoise species is widespread in cooler coastal waters of the North Atlantic, North Pacific and the Black Sea. 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. Recent genetic evidence suggests the harbour porpoise population structure may be more complex, and they should be reclassified.In the Atlantic, harbour porpoises may be present in a curved band of water running from the coast of West Africa
West Africa
West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the UN definition of Western Africa includes the following 16 countries and an area of approximately 5 million square km:-Flags of West Africa:...
to the coasts of Spain
Spain
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...
, Scandinavia
Scandinavia
Scandinavia is a cultural, historical and ethno-linguistic region in northern Europe that includes the three kingdoms of Denmark, Norway and Sweden, characterized by their common ethno-cultural heritage and language. Modern Norway and Sweden proper are situated on the Scandinavian Peninsula,...
, Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
, Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
, Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...
and Newfoundland and the eastern seaboard of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. There is a similarly-shaped band in the Pacific Ocean running from Sea of Japan
Sea of Japan
The Sea of Japan is a marginal sea of the western Pacific Ocean, between the Asian mainland, the Japanese archipelago and Sakhalin. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific...
, Vladivostok
Vladivostok
The city is located in the southern extremity of Muravyov-Amursky Peninsula, which is about 30 km long and approximately 12 km wide.The highest point is Mount Kholodilnik, the height of which is 257 m...
, the Bering Strait
Bering Strait
The Bering Strait , known to natives as Imakpik, is a sea strait between Cape Dezhnev, Chukotka Autonomous Okrug, Russia, the easternmost point of the Asian continent and Cape Prince of Wales, Alaska, USA, the westernmost point of the North American continent, with latitude of about 65°40'N,...
, Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
and California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
. The harbour porpoise has a global population of 700,000. Areas with sizable numbers include the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
, where porpoises number at about 350,000; and well as the Gulf of Maine
Gulf of Maine
The Gulf of Maine is a large gulf of the Atlantic Ocean on the east coast of North America.It is delineated by Cape Cod at the eastern tip of Massachusetts in the southwest and Cape Sable at the southern tip of Nova Scotia in the northeast. It includes the entire coastlines of the U.S...
/Bay of Fundy
Bay of Fundy
The Bay of Fundy is a bay on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine...
area, the US west coast and Alaska.
Natural history
Ecology
Harbour porpoises are limited to northern or and subarctic waters. They are often found in fjords, bays, estuaries and harbours, hence the name. They feed mostly on small pelagic schooling fish, particularly herringHerring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
, capelin
Capelin
The capelin or caplin, Mallotus villosus, is a small forage fish of the smelt family found in the Atlantic and Arctic oceans. In summer, it grazes on dense swarms of plankton at the edge of the ice shelf. Larger capelin also eat a great deal of krill and other crustaceans...
, and sprat. They will, however, also eat squid and crustaceans in some areas. The porpoises mostly forage near the sea bottom in waters less than 200m deep. They will also forage near the surface when feeding on sprat. When in deeper waters, porpoises may forage for mid-water fish, such as pearlsides.
Harbour porpoises tend to be independent foragers, but groups have been observed to collaborate to keep schools of fish closely together and herd them to the surface. 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 shark
Great white shark
The great white shark, scientific name Carcharodon carcharias, also known as the great white, white pointer, white shark, or white death, is a large lamniform shark found in coastal surface waters in all major oceans. It is known for its size, with the largest individuals known to have approached...
s and killer whales (orcas). Researchers at the University of Aberdeen
University of Aberdeen
The University of Aberdeen, an ancient university founded in 1495, in Aberdeen, Scotland, is a British university. It is the third oldest university in Scotland, and the fifth oldest in the United Kingdom and wider English-speaking world...
in Scotland
Scotland
Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
have also discovered that the local bottlenose dolphin
Bottlenose Dolphin
Bottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin , instead of one...
s attack and kill harbour porpoises without eating them due to competition for a decreasing food supply.
Behavior and reproduction
Some studies suggest porpoises stay within an area for an extended period of time. Nevertheless, they have been recorded to make onshore/offshore movements parallel to the coast. Dives of 220m by harbour porpoises have been recorded. Extended dives tend to last a minute, but five-minute dives have been recorded.Little is known about the social affiliation and interactions among harbour porpoises. They are generally seen as an asocial and solitary species. They are mostly seen alone or in small groups of two to five individuals. Porpoises have a promiscuous mating system, with each individual mating with several other individuals. Males produce large amounts of sperm which suggests they are sperm competitors
Sperm competition
Sperm competition is a term used to refer to the competitive process between spermatozoa of two different males to fertilize an egg of a lone female. Competition occurs whenever females engage in promiscuous mating to increase their chances in producing more viable offspring...
. Females, after reaching sexual maturity at around three to four years, can produce young annually for several years. With this they are over great nurtitional stress due to being pregnant and lactating at the same time. The gestation of the porpoise lasts 10 to 11 months. Most births tend to take places from May to August. Calves are nursed for eight to 12 months.
Conservation
Harbour porpoises were traditionally hunted for food, as well as for their blubber, which was used for lighting fuel. The drive hunt in the Little BeltLittle Belt
The Little Belt is a strait between the Danish island of Funen and the Jutland Peninsula.The belt is about 50 km long and 800m to 28 km wide, the maximum depth is approximately 75 m, and contains numerous small Danish islands....
strait, Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
, is the best known example. Thousands of porpoises were caught there until the end of the 19th century and again in smaller scale during the world wars. Currently, however, this species is not subject to commercial hunting
Hunting
Hunting is the practice of pursuing any living thing, usually wildlife, for food, recreation, or trade. In present-day use, the term refers to lawful hunting, as distinguished from poaching, which is the killing, trapping or capture of the hunted species contrary to applicable law...
, but it is hunted for food and sold locally in Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
. In prehistoric times, this animal was hunted by the Alby People of the east coast of Oland
Öland
' is the second largest Swedish island and the smallest of the traditional provinces of Sweden. Öland has an area of 1,342 km² and is located in the Baltic Sea just off the coast of Småland. The island has 25,000 inhabitants, but during Swedish Midsummer it is visited by up to 500,000 people...
, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
.
The Harbour porpoise populations of the North Sea, Baltic Sea, western North Atlantic, Black Sea and North West Africa are listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS
Bonn Convention
The Convention on the Conservation of Migratory Species of Wild Animals aims to conserve terrestrial, marine and avian migratory species throughout their range...
). This listing means that these populations have an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.
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
ASCOBANS
ASCOBANS is a regional agreement on the protection of small cetaceans that was concluded as the “Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas” under the auspices of the UNEP Convention on Migratory Species, or Bonn Convention, in September 1991 and came into force...
), the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS
ACCOBAMS
ACCOBAMS, the Agreement on the Conservation of Cetaceans in the Black Sea,Mediterranean Sea and contiguous Atlantic area is ‘a cooperative tool for the conservation of marine biodiversity in the Mediterranean and Black Seas’....
) and the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU).
Currently, the total population is in the hundreds of thousands and the harbour porpoise is not under threat of extinction. There are, however, a number of threats that impact population distribution and numbers.
Interactions with fisheries
The main threat to porpoises is static fishing techniques such as gill and tangle nets. BycatchBycatch
The term “bycatch” is usually used for fish caught unintentionally in a fishery while intending to catch other fish. It may however also indicate untargeted catch in other forms of animal harvesting or collecting...
in bottom-set gill nets is considered the main anthropogenic mortality factor for harbour porpoises worldwide. Bycatch is reported from the Black Sea
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
, the Baltic Sea
Baltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...
, the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
and the east coast of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. Bottom-set gill nets are anchored to the sea floor and are up to 12.5 miles (20 km) 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
Animal echolocation
Echolocation, also called biosonar, is the biological sonar used by several kinds of animals.Echolocating animals emit calls out to the environment and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects...
. Porpoise-scaring devices, so-called pinger
Pinger
Pinger may refer to:*Ping'er, fictional character in Dream of the Red Chamber*Methylenedioxymethamphetamine*Underwater locator beacon...
s, have been developed to keep porpoises out of nets and numerous studies have demonstrated they are very effective at reducing entanglement. 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.
Mortality resulting from trawling
Trawling
Trawling is a method of fishing that involves pulling a fishing net through the water behind one or more boats. The net that is used for trawling is called a trawl....
bycatch seems to be less of an issue, probably because porpoises are not inclined to feed inside trawls, as dolphins are known to do.
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 eelSand Eel
Sand eel or sandeel is the common name used for a considerable number of species of fish. Most of them are sea fish of the genera Hyperoplus , Gymnammodytes or Ammodytes...
along the east coast of Scotland seems to have been the main reason for the malnutrition in porpoises in the area.
Overfishing
OverfishingOverfishing
Overfishing occurs when fishing activities reduce fish stocks below an acceptable level. This can occur in any body of water from a pond to the oceans....
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. Reduction of prey may result from climate change, or overfishing, or both.
Noise pollution
NoiseNoise pollution
Noise pollution is excessive, displeasing human, animal or machine-created environmental noise that disrupts the activity or balance of human or animal life...
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. 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, particularly if steel monopile foundations are installed by percussive piling, where reactions can occur at distances of more than 20 km. Noise levels from operating wind turbines are low and unlikely to affect porpoises, even at close range.
Pollution
Marine top predators like porpoises and seals accumulate pollutants such as heavy metals, PCBPolychlorinated biphenyl
Polychlorinated biphenyls are a class of organic compounds with 2 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings. The chemical formula for PCBs is C12H10-xClx...
s and pesticide
Pesticide
Pesticides are substances or mixture of substances intended for preventing, destroying, repelling or mitigating any pest.A pesticide may be a chemical unicycle, biological agent , antimicrobial, disinfectant or device used against any pest...
s 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.
Further reading
- Friel, D. and Sleeman, D.P. 2010. A neonate harbour porpoise (Phocoena phocoena (L.)) with damaged skin. Ir Nat. J. 31: 55.
External links
- ARKive - images and movies of the harbour porpoise (Phocoena phocoena)
- Whale & Dolphin Conservation Society (WDCS)
- The harbour porpoise in the southern North Sea: Abundance, threats and research- & management proposals by Jan Haelters & Kees C.J. Camphuysen for IFAW.
- 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