Porpoises are a group of fully aquatic marine mammals, similar in appearance to a dolphin, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). They are, however, closer related to narwhals and belugas than the true dolphins. There are seven extant species of porpoise, all among the smallest of the toothed whales. Porpoises are recognised from dolphins by their flattened, spade-shaped teeth distinct from the conical teeth of dolphins, and lack of a pronounced beak, although some dolphins (e.g. Hector's dolphin) also lacks a pronounced beak. Porpoises, and other cetaceans, belong to the clade Cetartiodactyla with even-toed ungulates, and their closest living relatives are the hippopotamuses, having diverged from them about 40 million years ago.
|The harbor porpoise (Phocoena phocoena)|
Porpoises range in size from the vaquita, at 1.4 metres (4 feet 7 inches) in length and 54 kilograms (119 pounds) in weight, to the Dall's porpoise, at 2.3 m (7 ft 7 in) and 220 kg (490 lb) . Several species exhibit sexual dimorphism in that the females are larger than males. They have streamlined bodies and two limbs that are modified into flippers. Porpoises use echolocation as their primary sensory system. Some species are well adapted for diving to great depths. As all cetaceans, they have a layer of fat, or blubber, under the skin to keep them warm in cold water.
Porpoises are abundant and found in a multitude of environments, including rivers (finless porpoise), coastal and shelf waters (harbour porpoise, vaquita) and open ocean (Dall's porpoise and spectacled porpoise), covering all water temperatures from tropical (Sea of Cortez, vaquita) to polar (Greenland, harbour porpoise). Porpoises feed largely on fish and squid, much like the rest of the odontocetes. Little is known about reproductive behaviour. Females may get one calf every year under favourabl conditions . Calves are typically born in the spring and summer months and remain dependent on the female until the following spring. Porpoises produce ultrasonic cliks, which are used for both navigation (echolocation) and social communication. In contrast to many dolphin species, porpoises do not form large social groups.
Porpoises were, and still are, hunted by some countries by means of drive hunting. The vaquita nearly became extinct in the twentieth century, with a predicted population of fewer than 100 individuals, and, since the extinction of the baiji, is considered the most endangered cetacean. Other threats to porpoises include extensive bycatch in gill nets, competition for food from fisheries, and marine pollution, in particular heavy metals and organochlorides. Some species of porpoises have been and are kept in captivity and trained for research, education and public display.
Taxonomy and evolutionEdit
Porpoises, along with whales and dolphins, are descendants of land-living ungulates (hoofed animals) that first entered the oceans around 50 million years ago (Mya). During the Miocene (23 to 5 Mya), mammals were fairly modern, meaning they seldom changed physiologically from the time. The cetaceans diversified, and fossil evidence suggests porpoises and dolphins diverged from their last common ancestor around 15 Mya. The oldest fossils are known from the shallow seas around the North Pacific, with animals spreading to the European coasts and Southern Hemisphere only much later, during the Pliocene.
- ORDER ARTIODACTYLA
- Infraorder Cetacea
- Parvorder Odontoceti toothed whales
- Superfamily Delphinoidea
- Family Phocoenidae – porpoises
- Genus †Haborophocoena
- Genus Neophocaena
- Genus †Numataphocoena
- Genus Phocoena
- Genus Phocoenoides
- P. dalli – Dall's porpoise
- Genus †Septemriocetus
- Genus †Piscolithax
- Family Phocoenidae – porpoises
- Superfamily Delphinoidea
- Parvorder Odontoceti toothed whales
- Infraorder Cetacea
Porpoises have a bulbous head, no external ear flaps, a non-flexible neck, a torpedo shaped body, limbs modified into flippers, and a tail fin. Their skull has small eye orbits, small, blunt snouts, and eyes placed on the sides of the head. Porpoises range in size from the 1.4 m (4 ft 7 in) and 54 kg (119 lb) Vaquita to the 2.3 m (7 ft 7 in) and 220 kg (490 lb) Dall's porpoise. Overall, they tend to be dwarfed by other cetaceans. Almost all species have female-biased sexual dimorphism, with the females being larger than the males, although those physical differences are generally small; one exception is Dall's porpoise.
Odontocetes possess teeth with cementum cells overlying dentine cells. Unlike human teeth, which are composed mostly of enamel on the portion of the tooth outside of the gum, whale teeth have cementum outside the gum. Porpoises, like other odontocetes, possess only one blowhole. Breathing involves expelling stale air from the blowhole, forming an upward, steamy spout, followed by inhaling fresh air into the lungs. All porpoises have a thick layer of blubber. This blubber can help with insulation from the harsh underwater climate, protection to some extent as predators would have a hard time getting through a thick layer of fat, and energy for leaner times. Calves are born with only a thin layer of blubber, but some species compensate for this with a covering of fine, downy hair known as lanugo.
Porpoises have two flippers on the front, and a tail fin. Although porpoises do not possess fully developed hind limbs, they possess discrete rudimentary appendages, which may contain feet and digits. Their flippers, for example, contain four digits. Porpoises are fast swimmers in comparison to seals, which typically cruise at 9–28 km/h (5–15 kn). The fusing of the neck vertebrae, while increasing stability when swimming at high speeds, decreases flexibility, making it impossible for them to turn their head. When swimming, they move their tail fin and lower body up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. Flipper movement is continuous. Some species log out of the water, which may allow then to travel faster, and sometimes they porpoise out of the water, meaning jump out of the water. Their skeletal anatomy allows them to be fast swimmers. They have a very well defined and triangular dorsal fin, allowing them to steer better in the water. Unlike their dolphin counterparts, they are adapted for coastal shores, bays, and estuaries.
The porpoise ear has specific adaptations to the marine environment. In humans, the middle ear works as an impedance equaliser between the outside air's low impedance and the cochlear fluid's high impedance. In whales, and other marine mammals, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, porpoises receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear. The porpoise ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater. Odontocetes send out high frequency clicks from an organ known as a melon. This melon consists of fat, and the skull of any such creature containing a melon will have a large depression. The large bulge on top of the porpoises head is caused by the melon.
The porpoise eye is relatively small for its size, yet they do retain a good degree of eyesight. As well as this, the eyes of a porpoise are placed on the sides of its head, so their vision consists of two fields, rather than a binocular view like humans have. When porpoises surface, their lens and cornea correct the nearsightedness that results from the refraction of light; their eyes contain both rod and cone cells, meaning they can see in both dim and bright light. Porpoises do, however, lack short wavelength sensitive visual pigments in their cone cells indicating a more limited capacity for colour vision than most mammals. Most porpoises have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a tapetum lucidum; these adaptations allow for large amounts of light to pass through the eye and, therefore, they are able to form a very clear image of the surrounding area.
Porpoises are not thought to have a good sense of taste, as their taste buds are atrophied or missing altogether. However, some have preferences between different kinds of fish, indicating some sort of attachment to taste.
Unlike most animals, porpoises are conscious breathers. All mammals sleep, but porpoises cannot afford to become unconscious for long because they may drown. While knowledge of sleep in wild cetaceans is limited, porpoises in captivity have been recorded to sleep with one side of their brain at a time, so that they may swim, breathe consciously, and avoid both predators and social contact during their period of rest.
Porpoises are fully aquatic creatures. Females deliver a single calf after a gestation period lasting about a year. Calving takes place entirely under water, with the foetus positioned for tail-first delivery to help prevent drowning. Females have mammary glands, but the shape of a newborn calf's mouth does not allow it to obtain a seal around the nipple— instead of the calf sucking milk, the mother squirts milk into the calf's mouth. This milk contains high amounts of fat, which aids in the development of blubber; it contains so much fat that it has the consistency of toothpaste. The calves are weaned at about 11 months of age. Males play no part in rearing calves. The calf is dependent for one to two years, and maturity occurs after seven to ten years, all varying between species. This mode of reproduction produces few offspring, but increases the probability of each one surviving.
Porpoises eat a wide variety of creatures. The stomach contents of harbour porpoises suggests that they mainly feed on benthic fish, and sometimes pelagic fish. They may also eat benthic invertebrates. In rare cases, algae, such as Ulva lactuca, is consumed. Atlantic porpoises are thought to follow the seasonal migration of bait fish, like herring, and their diet varies between seasons. The stomach contents of Dall's porpoises reveal that they mainly feed on cephalopods and bait fish, like capelin and sardines. Their stomachs also contained some deep-sea benthic organisms.
The finless porpoise is known to also follow seasonal migrations. It is known that populations in the mouth of the Indus River migrate to the sea from April through October to feed on the annual spawning of prawns. In Japan, sightings of small pods of them herding sand lance onto shore are common year-round.
Little is known about the diets of other species of porpoises. A dissection of three Burmeister's porpoises shows that they consume shrimp and euphausiids. A dissection of a beached Vaquita showed remains of squid and grunts. Nothing is known about the diet of the spectacled porpoise.
Interactions with humansEdit
–John Ray, 1671, the earliest description of cetacean airways
In Aristotle's time, the 4th century BCE, porpoises were regarded as fish due to their superficial similarity. Aristotle, however, could already see many physiological and anatomical similarities with the terrestrial vertebrates, such as blood (circulation), lungs, uterus and fin anatomy. His detailed descriptions were assimilated by the Romans, but mixed with a more accurate knowledge of the dolphins, as mentioned by Pliny the Elder in his “Natural history”. In the art of this and subsequent periods, porpoises are portrayed with a long snout (typical of dolphins) and a high-arched head. The harbour porpoise was one of the most accessible species for early cetologists, because it could be seen very close to land, inhabiting shallow coastal areas of Europe. Much of the findings that apply to all cetaceans were first discovered in porpoises. One of the first anatomical descriptions of the airways of the whales on the basis of a harbor porpoise dates from 1671 by John Ray. It nevertheless referred to the porpoise as a fish.
Harbour porpoises have historically been kept in captivity, under the assumption that they would fare better than their dolphin counterparts due to their smaller size and shallow-water habitats. Up until the 1980s, they were consistently short-lived. Harbour porpoises have a very long captive history, with poorly documented attempts as early as the 15th century, and better documented starting in the 1860s and 1870s in London Zoo, the now-closed Brighton Aquarium & Dolphinarium, and a zoo in Germany. At least 150 harbour porpoises have been kept worldwide, but only about 20 were actively caught for captivity. The captive history is best documented from Denmark where about 100 harbour porpoises have been kept, most in the 1960s and 1970s. All but two were incidental catches in fishing nets or strandings. Nearly half of these died within a month of diseases caught before they were captured or from damage sustained during capture. Up until 1984, none lived for more than 14 months. Attempts of rehabilitation seven rescued individuals in 1986 only resulted in three that could be released 6 months later. Very few have been brought into captivity later, but they have lived considerably longer. In recent decades the only place keeping the species in Denmark is the Fjord & Bælt Centre, where three rescues have been kept, along with their offspring. Among the three rescues, one (father of world's first harbour porpoise born in captivity) lived for 20 years in captivity and another 15 years, while the third (mother of first born in captivity) was still alive in 2018 after 20 years. This is older than the typical age reached in the wild, which is 14 years or less. Very few harbour porpoises have been born in captivity. Historically, harbour porpoises were often kept singly and those who were together often were not mature or of the same sex. Disregarding one born more than 100 years ago that was the result of a pregnant female being brought into captivity, the world's first full captive breeding was in 2007 in the Fjord & Bælt Centre, followed by another in 2009 in the Dolfinarium Harderwijk, the Netherlands. In addition to the few kept in Europe, harbour porpoise were displayed at the Vancouver Aquarium (Canada) until recently. This was a female that had beached herself onto Horseshoe Bay in 2008 and a male that had done the same in 2011. They died in 2017 and 2016 respectively.
Finless porpoises have commonly been kept in Japan, as well as China and Indonesia. As of 1984, ninety-four in total had been in captivity in Japan, eleven in China, and at least two in Indonesia. As of 1986, three establishments in Japan had bred them, and there had been five recorded births. Three calves died moments after their birth, but two survived for several years. This breeding success, combined with the results with harbour porpoise in Denmark and the Netherlands, proved that porpoises can be successfully bred in captivity, and this could open up new conservation options. The reopened Miyajima Public Aquarium (Japan) houses three finless porpoises. As part of an attempt of saving the narrow-ridged (or Yangtze) finless porpoise, several are kept in the Baiji Dolphinarium in China. After having been kept in captivity for 9 years, the first breeding happened in 2005.
Small numbers of Dall's porpoises have been kept in captivity in both the United States and Japan, with the most recent being in the 1980s. These animals consistently failed to thrive. Captive Dall's porpoises often repeatedly ran into the walls of their enclosures, refused food, and exhibited skin sloughing. Almost all Dall's porpoises introduced to aquaria died shortly after, typically within days. Only two have lived for more than 60 days: a male reached 15 months at Marineland of the Pacific and another 21 months at a United States Navy facility.
As part of last-ditch effort of saving the extremely rare vaquita (the tiny remaining population is rapidly declining because of bycatch in gillnets), there have been attempts of transferring some to captivity. The first and only caught for captivity were two females in 2017. Both became distressed and were rapidly released, but one of them died in the process. Soon after the project was abandoned.
Porpoises and other smaller cetaceans, mainly dolphins, are hunted in an activity known as drive hunting. This is accomplished by driving a pod together with boats and usually into a bay or onto a beach. Their escape is prevented by closing off the route to the ocean with other boats or nets. Porpoises are hunted this way in several places around the world, including the Faroe Islands, Peru, and Japan, the most well-known practitioner of this method. Porpoises are mostly hunted for their meat. Despite the controversial nature of the hunt resulting in international criticism, and the possible health risk that the high methylmercury levels impose, cetaceans are hunted at unsustainable levels. Dall's porpoises are the most targeted in Japan, and between the 1986 moratorium banning whaling worldwide and 2013, more than 400,000 had been killed.
Porpoises are highly affected by bycatch. Many porpoises, mainly the vaquita, are subject to great mortality due to gillnetting. Although it is the world's most endangered marine cetacean, the vaquita continues to be caught in small-mesh gillnet fisheries throughout much of its range. Incidental mortality caused by the fleet of El Golfo de Santa Clara was estimated to be at around 39 vaquitas per year, which is over 17% of the population size. Harbour porpoises also suffer drowning by gillnetting, but on a less threatening scale due to their high population; their mortality rate per year increases a mere 5% due to this.
Porpoises are very sensitive to anthropogenic disturbances, and are keystone species, which can indicate the overall health of the marine environment. Populations of harbor porpoises in the North and Baltic Seas are under increasing pressure from anthropogenic causes such as offshore construction, ship traffic, fishing, and military exercises. Increasing pollution is a serious problem for marine mammals. Heavy metals and plastic waste are not biodegradable, and sometimes cetaceans consume these hazardous materials, mistaking them for food items. As a result, the animals are more susceptible to diseases and have fewer offspring. Harbour porpoises from the English Channel were found to have accumulated heavy metals.
The military and geologists employ strong sonar and produce an increases in noise in the oceans. Marine mammals that make use of biosonar for orientation and communication are not only hindered by the extra noise, but may race to the surface in panic. This may lead to a bubbling out of blood gases, and the animal then dies because the blood vessels become blocked, so-called decompression sickness. This effect, of course, only occurs in porpoises that dive to great depths, such as Dall's porpoise.
Additionally, civilian vessels produce sonar waves in order to measure the depth of the body of water in which they are. Similar to the navy, some boats produce waves that attract porpoises, while others may repel them. The problem with the waves that attract is that the animal may be injured or even killed by being hit by the vessel or its propeller.
The harbour porpoise, spectacled porpoise, Burmeister's porpoise, and Dall's porpoise are all listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). 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. Their conservation statuses are either at least concern or data deficient.
As of 2014, only 505 Yangtze finless porpoises remained in the main section of the Yangtze, with an alarming population density in Ezhou and Zhenjiang. While many threatened species decline rate slows after their classification, population decline rates of the porpoise are actually accelerating. While population decline tracked from 1994 to 2008 has been pegged at a rate of 6.06% annually, from 2006 to 2012, the porpoise population decreased by more than half. Finless porpoise population decrease of 69.8% in just a 22-year span from 1976 to 2000. 5.3%. A majority of factors of this population decline are being driven by the massive growth in Chinese industry since 1990 which caused increased shipping and pollution and ultimately environmental degradation. Some of these can be seen in damming of the river as well as illegal fishing activity. To protect the species, China's Ministry of Agriculture classified the species as being National First Grade Key Protected Wild Animal, the strictest classification by law, meaning it is illegal to bring harm to a porpoise. Protective measures in the Tian-e-Zhou Oxbow Nature Reserve has increased its population of porpoises from five to forty in 25 years. The Chinese Academy of Science's Wuhan Institute of Hydrobiology has been working with the World Wildlife Fund to ensure the future for this subspecies, and have placed five porpoises in another well-protected area, the He-wang-miao oxbow. Five protected natural reserves have been established in areas of the highest population density and mortality rates with measures being taken to ban patrolling and harmful fishing gear in those areas. There have also been efforts to study porpoise biology to help specialize conservation through captivation breeding. The Baiji Dolphinarium, was established in 1992 at the Institute of Hydrobiology of the Chinese Academy of Sciences in Wuhan which allowing the study of behavioral and biological factors affecting the finless porpoise, specifically breeding biology like seasonal changes in reproductive hormones and breeding behavior.
Because vaquitas are indigenous to the Gulf of California, Mexico is leading conservation efforts with the creation of the International Committee for the Recovery of the Vaquita (CIRVA), which has tried to prevent the accidental deaths of vaquitas by outlawing the use of fishing nets within the vaquita's habitat. CIRVA has worked together with the CITES, the Endangered Species Act, and the Marine Mammal Protection Act (MMPA) to nurse the vaquita population back to a point at which they can sustain themselves. CIRVA concluded in 2000 that between 39 and 84 individuals are killed each year by such gillnets. In order to try to prevent extinction, the Mexican government has created a nature reserve covering the upper part of the Gulf of California and the Colorado River delta. They have also placed a temporary ban on fishing, with compensation to those affected, that may pose a threat to the vaquita.
- Read, A.J.; Hohn, A.A. (1995). "Life in the fast lane: the life history of harbour porpoises from the Gulf of Maine". Marine Mammal Science. 11: 423–440.
- Sørensen, T.B.; Kinze, C.C. (1994). "Reproduction and reproductive seasonality in Danish harbour porpoises, Phocoena phocoena". Ophelia. 39: 159–176.
- Gaskin, David E. (1984). Macdonald, D. (ed.). The Encyclopedia of Mammals. New York: Facts on File. pp. 196–199. ISBN 978-0-87196-871-5.
- Ichishima, H.; Kimura, M. (2005). "Harborophocoena toyoshimai, a new early Pliocene porpoise (Cetacea, Phocoenidae) from Hokkaido, Japan". Journal of Vertebrate Paleontology. 25 (3): 655–664. doi:10.1671/0272-4634(2005)025[0655:htanep]2.0.co;2.
- Ichishima, H.; Kimura, M. (2000). "A new fossil porpoise (Cetacea; Delphinoidea; Phocoenidae) from the Early Pliocene Horokaoshirarika Formation, Hokkaido, Japan". Journal of Vertebrate Paleontology. 20 (3): 561–576. doi:10.1671/0272-4634(2000)020[0561:ANFPCD]2.0.CO;2. JSTOR 4524127.
- Lambert, O. (2008). "A new porpoise (Cetacea, Odontoceti, Phocoenidae) from the Pliocene of the North Sea". Journal of Vertebrate Paleontology. 28 (3): 863–872. doi:10.1671/0272-4634(2008)28[863:ANPCOP]2.0.CO;2.
- Willis, Pamela; Crespi, Bernard; Dill, Lawrence; Baird, Robin; Hanson, M. (2004). "Natural hybridization between Dall's porpoises (Phocoenoides dalli) and harbour porpoises (Phocoena phocoena)" (PDF). Canadian Journal of Zoology. 82 (5): 828–834. doi:10.1139/Z04-059. Retrieved 22 November 2015.
- World Wildlife Fund. "Vaquita". WWF Global. Archived from the original on 8 December 2015. Retrieved 3 December 2015.
- Reeves, Randall; Stewart, Brent; Clapham, Phillip; Powell, James (2002). National Audubon Society Guide to Marine Mammals of the World (1st ed.). Knopf. ISBN 978-0-375-41141-0.
- Katherine Ralls; Sarah Mesnick. Sexual Dimorphism (PDF). pp. 1005–1011. Archived from the original (PDF) on 25 July 2019. Retrieved 29 August 2015.
- Reidenberg, Joy (2007). "Anatomical adaptations of aquatic mammals". The Anatomical Record. 290 (6): 507–513. doi:10.1002/ar.20541. PMID 17516440.
- Reeves, Randall; Stewart, Brent; Clapham, Phillip; Powell, James (2002). National Audubon Society Guide to Marine Mammals of the World. ISBN 978-0-375-41141-0.
- Frandsen, Marie; Galatius, Anders (2013). "Sexual dimorphism of Dall's porpoise and harbor porpoise skulls". Mammalian Biology. 78 (2): 153–156. doi:10.1016/j.mambio.2012.04.005.
- Scholander, Per Fredrik (1940). "Experimental investigations on the respiratory function in diving mammals and birds". Hvalraadets Skrifter. 22.
- Klinowska, Margaret; Cooke, Justin (1991). Dolphins, Porpoises, and Whales of the World: the IUCN Red Data Book (PDF). pp. 87–120. ISBN 978-2-88032-936-5. Retrieved 29 August 2015.
- Stevens, C. Edward; Hume, Ian D. (1995). Comparative Physiology of the Vertebrate Digestive System. Cambridge University Press. p. 317. ISBN 978-0-521-61714-7.
- Tinker, Spencer (1988-01-01). "The Vertebrae of the Cervical Region". Whales of the World. p. 37. ISBN 978-0-935848-47-2.
- "How is that whale listening?". EurekAlert. 4 February 2008. Retrieved 30 August 2015.
- Nummela, Sirpa; Thewissen, J.G.M; Bajpai, Sunil; Hussain, Taseer; Kumar, Kishor (2007). "Sound transmission in archaic and modern whales: Anatomical adaptations for underwater hearing". The Anatomical Record. 290 (6): 716–733. doi:10.1002/ar.20528. PMID 17516434.
- Thomas, Jeanette A.; Kastelein, Ronald A., eds. (2002). Sensory Abilities of Cetaceans: Laboratory and Field Evidence. NATO ASI Series A: Life Sciences. 196. doi:10.1007/978-1-4899-0858-2. ISBN 978-1-4899-0860-5.
- Thewissen, J. G. M. (2002). "Hearing". In Perrin, William R.; Wirsig, Bernd; Thewissen, J.G.M. (eds.). Encyclopedia of Marine Mammals. Academic Press. pp. 570–2. ISBN 978-0-12-551340-1.
- Ketten, Darlene R. (1992). "The Marine Mammal Ear: Specializations for Aquatic Audition and Echolocation". In Webster, Douglas B.; Fay, Richard R.; Popper, Arthur N. (eds.). The Evolutionary Biology of Hearing. Springer. pp. 725–727.
- Mass, Alla M.; Supin, Alexander, Y. A. (21 May 2007). "Adaptive features of aquatic mammals' eyes". Anatomical Record. 290 (6): 701–715. doi:10.1002/ar.20529. PMID 17516421.CS1 maint: multiple names: authors list (link)
- Sekiguchi, Yuske; Arai, Kazutoshi; Kohshima, Shiro (21 June 2006). "Sleep behaviour". Nature. 441 (7096): E9–E10. Bibcode:2006Natur.441E...9S. doi:10.1038/nature04898. PMID 16791150.
- E. J. Slijper (1966), "Functional morphology of the reproductive system in Cetecea", in Kenneth Stafford Norris (ed.), Whales, Dolphins, and Porpoises, University of California Press, p. 310, ISBN 978-0-520-03283-5
- Conrad Gesner. Historiae animalium. Archived from the original on 6 September 2008. Retrieved 4 September 2015.
- J. Ray (1671). "An account of the dissection of a porpess". Philosophical Transactions of the Royal Society of London. 6 (69–80): 2274–2279. Bibcode:1671RSPT....6.2274R. doi:10.1098/rstl.1671.0048.
- Susanne Prahl (2007). "Studies for the construction of epicranialen airway when porpoise (Phocoena phocoena Linnaeus, 1758)". Dissertation for the Doctoral Degree of the Department of Biology of the Faculty of Mathematics, Computer Science and Natural Sciences at the University of Hamburg: 6.
- Collet, A. (1984). "Live-Capture of Cetaceans for European Institutions". Rep. Int. Whal. Comm. 34: 603–607.
- "North Atlantic Harbour porpoise". Zootierliste. Retrieved 3 July 2018.
- "Dødsfald på Fjord&Bælt: Sif blev 15 år". fyens.dk. 1 February 2018. Retrieved 3 July 2018.
- "Tab for forskningen: Marsvinet Eigil er død". tv2fyn.dk. 28 April 2016. Retrieved 3 July 2018.
- Read, A.; Hohn, A.A. (1995). "Life in the fast lane: The life history of harbor porpoises from the Gulf of Maine". Marine Mammal Science. 11 (4): 423–440. doi:10.1111/j.1748-7692.1995.tb00667.x.
- "Phocoena phocoena, harbor porpoise". animaldiversity.org. Retrieved 3 July 2018.
- "Porpoise is 2nd to give birth in captivity". phys.org. 8 May 2009. Retrieved 3 July 2018.
- Vancouver Aquarium. "Spotlight on Porpoises". Vancouver Aquarium.
- "Porpoise rescued in Horseshoe Bay now a permanent resident of aquarium". North Shore News. 16 May 2012. Retrieved 3 July 2018.
- "Harbour porpoise Daisy, rescued in 2008, dies at Vancouver Aquarium". Vancouver Sun. 16 June 2017. Retrieved 3 July 2018.
- "Jack the harbour porpoise dies at Vancouver Aquarium". CBC. 13 August 2016. Retrieved 3 July 2018.
- Goldfarb, B. (2016). "Can captive breeding save Mexico's vaquita?". Conservation Biology. 353 (6300): 633–634. doi:10.1126/science.353.6300.633. PMID 27516576.
- Bunnel, Wade. "Hiroshima revamps its aquarium". Japan Times.
- Ding Wang; Yujiang Hao; Kexiong Wang; Qingzhong Zhao; Daoquang Chen; Zhuo Wei; Xianfeng Zhang (2005). "The first Yangtze finless porpoise successfully born in captivity". Environmental Science and Pollution Research. 12 (5): 247–250. doi:10.1065/espr2005.08.284.
- "Wayback Machine: Dall's Porpoises in Captivity". dolphinproject.com. Retrieved 3 July 2018.
- "Captivity: Last hope for saving the vaquita?". Deutsche Welle. 16 December 2016. Retrieved 3 July 2018.
- "The Plan to Rescue a Nearly Extinct Porpoise Goes Terribly Awry". The Atlantic. 9 November 2017. Retrieved 3 July 2018.
- "Update: After death of captured vaquita, conservationists call off rescue effort". Science Magazine. 9 November 2017. Retrieved 3 July 2018.
- "Spectacled Porpoise". porpoise.org. Retrieved 3 July 2018.
- Toxic: Japan's Unsustainable and Irresponsible Whale, Dolphin, and Porpoise Hunts (PDF), Environmental Investigation Agency, 2013, pp. 1–23
- Endo, Tetsuya; Haraguchi, Koichi; Hotta, Yohei; Hisamichi, Yohsuke; Lavery, Shane; Dalebout, Merel; Baker, Scot (2005). "Total Mercury, Methyl Mercury, Selenium Levels in the Red Meat of Small Cetaceans Sold for Human Consumption in Japan". Environmental Science and Technology. 39 (15): 5703–5708. Bibcode:2005EnST...39.5703E. doi:10.1021/es050215e. PMID 16124305.
- D'agrosa, C.; Lennert-Cody, C. E.; Vidal, O. (2000). "Vaquita Bycatch in Mexico's Artisanal Gillnet Fisheries: Driving a Small Population to Extinction". Conservation Biology. 14 (4): 1110–1119. doi:10.1046/j.1523-1739.2000.98191.x.
- Caswell, Hal; Brault, Solange; Read, Andrew; Smith, Tim (1998). "Harbor Porpoise and Fisheries: an Uncertainty Analysis of Incidental Mortality" (PDF). Ecological Applications. 8 (4): 1226–1238. doi:10.1890/1051-0761(1998)008[1226:hpafau]2.0.co;2. Retrieved 30 October 2015.
- Croft, Chris. "America's Favorite Fish Tainted by Porpoise Deaths". Retrieved 30 October 2015.
- Mahfouz, C; Henry, F; Courcot, L; Pezeril, S; Bouveroux, T; Dabin, W; Jauniaux, T; Khalaf, G; Amara, R (2014). "Harbour porpoises (Phocoena phocoena) stranded along the southern North Sea: an assessment through metallic contamination". Environmental Research. 133: 266–73. Bibcode:2014ER....133..266M. doi:10.1016/j.envres.2014.06.006. PMID 24981825.
- Siebert, Ursula; Pozniak, Blazej; Hansen, Kirstin; Anderson; Nordstrom, Gwyneth; Teilmann, Jonas; Van Elk, Niels; Vossen, Ardnt; Dietz, Rune (2011). "Investigations of Thyroid and Stress Hormones in Free-Ranging and Captive Harbor Porpoises (Phocoena phocoena): A Pilot Study". Aquatic Mammals. 37 (4): 443–453. doi:10.1578/am.37.4.2011.443.
- Cara E. Miller (2007). Current State of Knowledge of Cetacean Threats, Diversity, and Habitats in the Pacific Islands Region (PDF). Whale and Dolphin Conservation Society. ISBN 978-0-646-47224-9. Archived from the original (PDF) on 8 September 2015. Retrieved 5 September 2015.
- M. Andre; T. Johansson; E. Delory; M. van der Schaar (2005). Cetacean biosonar and noise pollution. Europe Oceans 2005. 2. Oceans 2005–Europe. p. 1028. doi:10.1109/OCEANSE.2005.1513199. ISBN 978-0-7803-9103-1.
- Kastelein, R. A., Schop, J., Gransier, R., Steen, N., & Jennings, N. (2014). "Effect of Series of 1 to 2 kHz and 6 to 7 kHz Up-Sweeps and Down-Sweeps on the Behavior of a Harbor Porpoise (Phocoena phocoena)". Aquatic Mammals. 40 (3): 232–242. doi:10.1578/AM.40.3.2014.232.CS1 maint: uses authors parameter (link)
- Culik, B.; von Dorrien, C.; Muller, V.; Conrad, M. (2015). "Bioacoustics". The International Journal of Animal Sound and Its Recording. 24 (3). ISSN 0952-4622.
- ""Appendix II 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". 5 March 2009.
- HELCOM (2013). "HELCOM Red List of Baltic Sea species in danger of becoming extinct" (PDF). Baltic Sea Environmental Proceedings (140): 92. Archived from the original (PDF) on 2014-10-07.
- "Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia" (PDF). Convention on the Conservation of Migratory Species of Wild Animals. pp. 1–6.
- IUCN, ASCOBANS, WWF, CMS, ACCOBAMS. "Odontocetes: The Toothed Whales" (PDF). IUCN, ASCOBANS, WWF, CMS, ACCOBAMS. Archived from the original (PDF) on 2015-12-08.CS1 maint: multiple names: authors list (link)
- Hashimoto, M.; Shirakihara, K.; Shirakihara, M.; Hiramatsu, K. (2013). "Estimating the rate of increase for the finless porpoise with special attention to predictions for the inland sea population in japan". Population Ecology. 55 (3): 441–449. doi:10.1007/s10144-013-0374-5.
- Mei, Zhigang; Zhang, Xinqiao; Huang, Shiang-Lin; Zhao, Xiujiang; Hao, Yujiang; Zhang, Lin; Qian, Zhengyi; Zheng, Jinsong; Wang, Kexiong; Wang, Ding (2014). "The Yangtze Finless Porpoise: On an Accelerating Path to Extinction?". Biological Conservation. 172: 117–23. doi:10.1016/j.biocon.2014.02.033.
- Krchnak, Karin (30 September 2014). "Saving the Finless Porpoise". World Wildlife Fund. Retrieved 25 October 2015.
- Wang, D.; Hao, Y.; Wang, K.; Zhao, Q.; Chen, D.; Wei, Z.; Zhang, X. (2005). "the first yangtze finless porpoise successfully born in captivity". Environmental Science and Pollution Research International. 12 (5): 247–250. doi:10.1065/espr2005.08.284.
- Barlow, J. (2014). "Vaquita (Phocoena sinus)". Edge of Existence programme. Zoological Society of London. Retrieved 25 October 2015.
- "Gulf of California Harbor Porpoise / Vaquita / Cochito (Phocoena sinus)". Species Information. NOAA Fisheries–Office of Protected Resources. 2013-07-08. Retrieved 20 January 2014.
- Gill Braulik (24 April 2015). "President of Mexico launches plan to save the vaquita". IUCN SSC–Cetacean Specialist Group. Retrieved 25 October 2015.
|Wikispecies has information related to Phocoenidae|
- Media related to Phocoenidae at Wikimedia Commons
- Whale Trackers – An online documentary series about whales, dolphins and porpoises.