View source for Porpoise

{{Short description|Small cetacean of the family Phocoenidae}}
{{About| the animal|other uses|text=Not to be confused with [[Phocidae]]}}
{{Good article}}
{{Use dmy dates|date=May 2021}}
{{Automatic taxobox
| name = Porpoise
| fossil_range = {{Fossil range|15.970|0}} <small>[[Miocene]] to Recent</small>
| image = Phocoena phocoena.2.jpg
| image_caption = The [[harbor porpoise]] (''Phocoena phocoena'')
| taxon = Phocoenidae
| authority = [[John Edward Gray|Gray]], 1825
| type_genus = ''[[Phocoena]]''
| type_genus_authority = [[Georges Cuvier|Cuvier]], 1816
| subdivision_ranks = [[Genus|Genera]]
| subdivision =
[[#Taxonomy and evolution|See text]]
}}

'''Porpoises''' ({{IPAc-en|ˈ|p|ɔː|r|p|ə|s|ɪ|z}}) are small [[Oceanic dolphin|dolphin]]-like [[cetacean]]s classified under the family '''Phocoenidae'''.  Although similar in appearance to [[dolphin]]s, they are more closely related to [[narwhal]]s and [[Beluga whale|beluga]]s.<ref name="McGoven2020">{{cite journal |last1=McGowen |first1=M.R. |last2=Tsagkogeorga |first2=G. |last3=Alvarez-Carretero |first3=G. |last4=dos Reis|first4=M.|title=Phylogenomic Resolution of the Cetacean Tree of Life Using Target Sequence Capture |journal=Syst Biol |date=2020 |volume=69 |issue=3 |pages=479–501 |doi=10.1093/sysbio/syz068|pmid=31633766 |pmc=7164366 |display-authors = 3|doi-access=free }}</ref> There are eight extant species of porpoise, all among the smallest of the [[toothed whales]]. Porpoises are distinguished 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 lack a pronounced beak. Porpoises, and other [[cetacea]]ns, belong to the [[clade]] [[Cetartiodactyla]] with [[even-toed ungulate]]s.

Porpoises range in size from the [[vaquita]], at {{convert|1.4|m|ftin|abbr=off}} in length and {{convert|54|kg|lb|abbr=off}} in weight, to the [[Dall's porpoise]], at {{convert|2.3|m|ftin|abbr=on}} and {{convert|220|kg|lb|abbr=on}}. 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 [[Animal echolocation|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 have one calf every year under favourable conditions.<ref name="Read&Hohn">{{cite journal |last1=Read |first1=A.J. |last2=Hohn |first2=A.A. |title=Life in the fast lane: the life history of harbour porpoises from the Gulf of Maine |journal=Marine Mammal Science |date=1995 |volume=11 |issue=4 |pages=423–440|doi=10.1111/j.1748-7692.1995.tb00667.x |bibcode=1995MMamS..11..423R }}</ref><ref name="Sorensen">{{cite journal |last1=Sørensen |first1=T.B. |last2=Kinze |first2=C.C. |title=Reproduction and reproductive seasonality in Danish harbour porpoises, ''Phocoena phocoena''. |journal=Ophelia |date=1994 |volume=39 |issue=3 |pages=159–176|doi=10.1080/00785326.1994.10429541 }}</ref> Calves are typically born in the spring and summer months and remain dependent on the female until the following spring. Porpoises produce ultrasonic clicks, which are used for both navigation ([[Echolocation (animal)|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 [[dolphin drive hunting|drive hunting]]. Larger threats to porpoises include extensive [[bycatch]] in [[gill net]]s, competition for food from fisheries, and [[marine pollution]], in particular heavy metals and [[organochlorides]]. The [[vaquita]] is nearly extinct due to bycatch in gill nets, with a predicted population of fewer than a dozen individuals. Since the extinction of the [[baiji]], the [[vaquita]] is considered the most endangered cetacean. Some species of porpoises have been and are kept in captivity and trained for research, education and public display.

==Taxonomy and evolution==
{{See also|Evolution of cetaceans}}
Porpoises, along with [[whale]]s and [[dolphin]]s, are descendants of land-living [[ungulate]]s (hoofed animals) that first entered the oceans around 50 million years ago (Mya). During the [[Miocene]] (23 to 5 [[Mya (unit)|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]].<ref name=EoM>{{cite book|editor= Macdonald, D.|author= Gaskin, David E.|year= 1984|title= The Encyclopedia of Mammals|publisher= Facts on File|location= New York|pages= [https://archive.org/details/encyclopediaofma00mals_0/page/196 196–199]|isbn= 978-0-87196-871-5|url= https://archive.org/details/encyclopediaofma00mals_0/page/196}}</ref>

*'''ORDER [[Artiodactyla]]'''
**Infraorder [[Cetacea]]
***Parvorder [[Odontoceti]] toothed whales
****Superfamily [[Delphinoidea]]
*****Family Phocoenidae – porpoises
******Genus †''[[Haborophocoena]]''<ref name="Ichishima2005">{{cite journal|author=Ichishima, H.|author2=Kimura, M.|year=2005|title=''Harborophocoena toyoshimai'', a new early Pliocene porpoise (Cetacea, Phocoenidae) from Hokkaido, Japan|journal=Journal of Vertebrate Paleontology|volume=25|issue=3|pages=655–664|doi=10.1671/0272-4634(2005)025[0655:htanep]2.0.co;2|s2cid=85421985 }}</ref>
*******''[[Harborophocoena toyoshimai|H. toyoshimai]]''
******Genus ''[[Neophocaena]]''
*******''N. phocaeniodes'' – [[Indo-Pacific finless porpoise]]
*******''N. sunameri'' – [[East Asian finless porpoise]]
*******''N. asiaeorientalis'' – [[Yangtze finless porpoise]]
******Genus †''[[Numataphocoena]]''<ref name="Ichishima2000">{{Cite journal | doi = 10.1671/0272-4634(2000)020[0561:ANFPCD]2.0.CO;2|jstor=4524127| title = A new fossil porpoise (Cetacea; Delphinoidea; Phocoenidae) from the Early Pliocene Horokaoshirarika Formation, Hokkaido, Japan| journal = Journal of Vertebrate Paleontology| volume = 20| issue = 3| pages = 561–576| year = 2000| last1 = Ichishima | first1 = H. | last2 = Kimura | first2 = M. |s2cid=131546796 }}</ref>
*******''[[Numataphocoena yamashitai|N. yamashitai]]''
******Genus ''[[Phocoena]]''
*******''P. phocoena'' – [[harbour porpoise]]
*******''P. sinus'' – [[vaquita]]
*******''P. dioptrica'' – [[spectacled porpoise]]
*******''P. spinipinnis'' – [[Burmeister's porpoise]]
******Genus ''[[Phocoenoides]]''
*******''P. dalli'' – [[Dall's porpoise]] 
******Genus †''[[Semirostrum]]''
*******''[[Semirostrum ceruttii|S. ceruttii]]''
******Genus †''[[Septemtriocetus]]''<ref name="Lambert2008">{{Cite journal | doi = 10.1671/0272-4634(2008)28[863:ANPCOP]2.0.CO;2| title = A new porpoise (Cetacea, Odontoceti, Phocoenidae) from the Pliocene of the North Sea| journal = Journal of Vertebrate Paleontology| volume = 28| issue = 3| pages = 863–872| year = 2008| last1 = Lambert | first1 = O. | s2cid = 84607782}}</ref>
*******''[[Septemtriocetus bosselaersii|S. bosselaersii]]''
******Genus †''[[Piscolithax]]''
*******''[[Piscolithax aenigmaticus|P. aenigmaticus]]''
*******''[[Piscolithax longirostris|P. longirostris]]''
*******''[[Piscolithax boreios|P. boreios]]''
*******''[[Piscolithax tedfordi|P. tedfordi]]''
Recently discovered [[Hybrid (biology)|hybrid]]s between male harbour porpoises and female [[Dall's porpoise]]s indicate the two species may actually be members of the same [[genus]].<ref>{{cite journal|first1=Pamela|last1= Willis|first2=Bernard|last2=Crespi|first3=Lawrence|last3=Dill|first4=Robin|last4=Baird|first5=M.|last5=Hanson|title=Natural hybridization between Dall's porpoises (''Phocoenoides dalli'') and harbour porpoises (''Phocoena phocoena'')|year=2004|access-date=22 November 2015|journal=Canadian Journal of Zoology|volume=82|issue= 5|pages=828–834|doi=10.1139/Z04-059|bibcode= 2004CaJZ...82..828W|url=http://www.cascadiaresearch.org/robin/WillisetalCJZ2004.pdf |archive-url=https://web.archive.org/web/20060625121801/http://cascadiaresearch.org/robin/WillisetalCJZ2004.pdf |archive-date=2006-06-25 |url-status=live}}</ref>

==Biology==

===Anatomy===
[[File:Cambridge Natural History Mammalia Fig 183.jpg|thumb|300px|Harbour porpoise skeleton]]
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 {{convert|1.4|m|ftin|abbr=on}} and {{convert|54|kg|lb|abbr=on}} [[vaquita]]<ref>{{cite web|url=http://wwf.panda.org/what_we_do/endangered_species/cetaceans/about/vaquita/|author=World Wildlife Fund|title=Vaquita|work=WWF Global|access-date=3 December 2015|archive-url=https://web.archive.org/web/20151208105912/http://wwf.panda.org/what_we_do/endangered_species/cetaceans/about/vaquita/|archive-date=8 December 2015|author-link=World Wildlife Fund}}</ref> to the {{convert|2.3|m|ftin|abbr=on}} and {{convert|220|kg|lb|abbr=on}} [[Dall's porpoise]].<ref>{{cite book|first1=Randall|last1=Reeves|first2=Brent|last2=Stewart|first3=Phillip|last3=Clapham|first4=James|last4=Powell|year=2002|title=National Audubon Society Guide to Marine Mammals of the World|publisher=Knopf|edition=1st|isbn=978-0-375-41141-0|url=https://archive.org/details/guidetomarinemam00folk}}</ref> 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,<ref>{{cite book |url=http://www.cetus.ucsd.edu/SIO133/PDF/Sexual%20Dimorphism.pdf |title=Sexual Dimorphism |author1=Katherine Ralls |author2=Sarah Mesnick |pages=1005–1011 |access-date=29 August 2015 |archive-url=https://web.archive.org/web/20190725004132/http://www.cetus.ucsd.edu/SIO133/PDF/Sexual%20Dimorphism.pdf |archive-date=25 July 2019  }}</ref><ref name="Cetacean anatomy">{{cite journal|first=Joy|last=Reidenberg|title=Anatomical adaptations of aquatic mammals|year=2007|journal=The Anatomical Record|volume=290|issue=6|pages= 507–513|doi=10.1002/ar.20541|pmid=17516440|s2cid=42133705|doi-access=free}}</ref> although those physical differences are generally small; one exception is Dall's porpoise.<ref name=r.reeves/><ref>{{cite journal|first1=Marie|last1=Frandsen|first2=Anders|last2=Galatius|title=Sexual dimorphism of Dall's porpoise and harbor porpoise skulls|year=2013|journal=Mammalian Biology|volume=78|issue=2|pages=153–156|doi=10.1016/j.mambio.2012.04.005|bibcode=2013MamBi..78..153F }}</ref>

Odontocetes possess teeth with [[cementum]] cells overlying [[dentine]] cells. Unlike human teeth, which are composed mostly of [[Tooth enamel|enamel]] on the portion of the tooth outside of the gum, whale teeth have cementum outside the gum. Porpoises have a three-chambered stomach, including a fore-stomach and fundic and pyloric chambers.<ref name=Qian1984>{{cite journal |last1= Qian |first1= L.Y. |last2= Shen |first2= W. |display-authors= etal |date= 1984 |title= The digestive organs of the finless porpoise |url= http://en.cnki.com.cn/Article_en/CJFDTotal-SLXX198404004.htm |journal= Acta Theriologica Sinica |volume= 1984-04 |access-date= 13 July 2020 |archive-date= 23 October 2020 |archive-url= https://web.archive.org/web/20201023035711/http://en.cnki.com.cn/Article_en/CJFDTotal-SLXX198404004.htm |url-status= dead }}</ref> Porpoises, like other odontocetes, possess only one blowhole.<ref name="Cetacean anatomy"/> Breathing involves expelling stale air from the [[blowhole (anatomy)|blowhole]], forming an upward, steamy spout, followed by inhaling fresh air into the lungs.<ref name="Cetacean anatomy"/><ref>{{cite journal |last=Scholander |first=Per Fredrik |title=Experimental investigations on the respiratory function in diving mammals and birds |year=1940 | journal=Hvalraadets Skrifter | volume=22 }}</ref> 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 rapidly gain a thick layer from the milk, which has a very high fat content.

===Locomotion===
Porpoises have two flippers on the front and a tail fin. Their flippers contain four digits. Although porpoises do not possess fully developed hind limbs, they possess discrete rudimentary appendages, which may contain feet and digits.{{citation needed|date=April 2022}} Porpoises are fast swimmers in comparison to seals, which typically cruise at {{convert|9|-|28|km/h|kn|0|abbr=on}}. 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.<ref>{{cite book|chapter-url=https://books.google.com/books?id=ASIVAAAAIAAJ&q=whales+have+a+fused+neck+vertebrae&pg=PA37|last=Tinker|first=Spencer|title=Whales of the World|chapter=The Vertebrae of the Cervical Region|page=[https://archive.org/details/whalesofworld00tink/page/37 37]|isbn=978-0-935848-47-2|date=1 January 1988|publisher=Brill Archive |url=https://archive.org/details/whalesofworld00tink/page/37}}</ref> 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 [[Cetacean surfacing behaviour|log]] out of the water, which may allow them to travel faster, and sometimes they [[Cetacean surfacing behaviour#Porpoising|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.<ref name="Cetacean anatomy"/><ref name="Porpoise">{{cite book |author1=Klinowska, Margaret |author2=Cooke, Justin |year=1991 |title=Dolphins, Porpoises, and Whales of the World: the IUCN Red Data Book |pages=87–120 |url=https://portals.iucn.org/library/sites/library/files/documents/RD-1991-001.pdf |archive-url=https://web.archive.org/web/20150509184324/https://portals.iucn.org/library/sites/library/files/documents/RD-1991-001.pdf |archive-date=2015-05-09 |url-status=live |access-date=29 August 2015| isbn=978-2-88032-936-5}}</ref>

===Senses===
[[File:Delfinekko.gif|thumb|right|[[Biosonar]] by cetaceans]]

The porpoise ear has specific adaptations to the [[Marine (ocean)|marine]] environment. In humans, the [[middle ear]] works as an impedance equaliser between the outside air's low [[Acoustic impedance|impedance]] and the [[cochlea]]r 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.<ref>{{cite web |title=How is that whale listening? |url=http://www.eurekalert.org/pub_releases/2008-02/iop-hit020108.php |date=4 February 2008 |access-date=30 August 2015 |publisher=EurekAlert}}</ref> The porpoise ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater.<ref>{{cite journal |author=Nummela, Sirpa |title=Sound transmission in archaic and modern whales: Anatomical adaptations for underwater hearing |journal=The Anatomical Record |volume=290 |issue=6 |pages=716–733 |year=2007 |doi=10.1002/ar.20528 |last2=Thewissen|first2=J.G.M |last3=Bajpai |first3=Sunil |last4=Hussain |first4=Taseer |last5=Kumar |first5=Kishor |pmid=17516434|s2cid=12140889 |author2-link=Hans Thewissen |doi-access=free }}</ref> Odontocetes send out high frequency clicks from an organ known as a [[melon (cetacean)|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.<ref name="Cetacean anatomy"/><ref name="Porpoise senses">{{cite book |editor1=Thomas, Jeanette A. |editor2=Kastelein, Ronald A. |title=Sensory Abilities of Cetaceans: Laboratory and Field Evidence |series=NATO ASI Series A: Life Sciences|volume=196 |isbn=978-1-4899-0860-5 |doi=10.1007/978-1-4899-0858-2 |year=2002 |s2cid=32801659 |url=https://books.google.com/books?id=VWz1BwAAQBAJ&q=cetacean+senses&pg=PA1 }}</ref><ref name="Thewissen-Hearing">{{cite book| last=[[Hans Thewissen|Thewissen]]| first=J. G. M.| chapter=Hearing| pages=[https://archive.org/details/encyclopediaofma2002unse/page/570 570–2]| title=Encyclopedia of Marine Mammals| editor1-last=Perrin| editor1-first=William R.| editor2-last=Wirsig| editor2-first=Bernd| editor3-last=[[Hans Thewissen|Thewissen]]| editor3-first=J.G.M.| year=2002| publisher=Academic Press| isbn=978-0-12-551340-1| chapter-url=https://archive.org/details/encyclopediaofma2002unse/page/570}}</ref><ref>{{cite book |last=Ketten |first=Darlene R.|chapter=The Marine Mammal Ear: Specializations for Aquatic Audition and Echolocation |title=The Evolutionary Biology of Hearing |editor1-last=Webster |editor1-first=Douglas B. |editor2-last=Fay |editor2-first=Richard R. |editor3-last=Popper |editor3-first=Arthur N. |year=1992 |publisher=Springer |chapter-url=https://www.researchgate.net/publication/230691464|pages=725–727}}</ref>

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 cell|rod]] and [[cone cell|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.<ref>{{cite journal |last1=Mass |first1=Alla M. |last2=Supin |first2=Alexander Y. A. |title=Adaptive features of aquatic mammals' eyes |journal=Anatomical Record |volume=290 |issue=6 |pages=701–715 |date=21 May 2007 |doi=10.1002/ar.20529 |pmid=17516421|s2cid=39925190 |doi-access=free }}</ref> 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.<ref name="Porpoise senses"/>

The [[olfactory lobes]] are absent in porpoises, suggesting that they have no sense of smell.<ref name="Porpoise senses"/>

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.<ref name="Porpoise senses"/>

===Sleep===
{{Further|Unihemispheric slow-wave sleep}}

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.<ref>{{cite journal |author1=Sekiguchi, Yuske |author2=Arai, Kazutoshi |author3=Kohshima, Shiro |title=Sleep behaviour |journal=Nature |volume=441 |issue=7096 |date=21 June 2006 | doi=10.1038/nature04898 |pmid=16791150 |pages=E9–E10 |bibcode=2006Natur.441E...9S|s2cid=4406032 }}</ref>

==Behaviour==
[[File:Two Dalls Porpoises.JPG|thumb|right|"Rooster tail" spray around swimming [[Dall's porpoise]]s]]

===Life cycle===
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.<ref>{{citation|editor=Kenneth Stafford Norris|author=E. J. Slijper|title=Whales, Dolphins, and Porpoises|chapter=Functional morphology of the reproductive system in Cetecea| chapter-url=https://books.google.com/books?id=x-iptRSGHIQC&pg=PA310|year=1966|publisher=University of California Press|isbn=978-0-520-03283-5|page=310}}</ref> 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 [[R/K selection theory|mode of reproduction]] produces few offspring, but increases the probability of each one surviving.<ref name=r.reeves>{{cite book|first1=Randall|last1=Reeves|first2=Brent|last2=Stewart|first3=Phillip|last3=Clapham|first4=James|last4=Powell|year=2002|title=National Audubon Society Guide to Marine Mammals of the World|publisher=Knopf Doubleday Publishing |isbn=978-0-375-41141-0|url=https://archive.org/details/guidetomarinemam00folk}}</ref>

===Diet===
Porpoises eat a wide variety of creatures. The stomach contents of harbour porpoises suggests that they mainly feed on [[Demersal fish#Benthic fish|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 [[cephalopod]]s and bait fish, like [[capelin]] and [[sardine]]s. Their stomachs also contained some deep-sea benthic organisms.<ref name="Porpoise"/>

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 [[prawn]]s. In Japan, sightings of small pods of them herding [[sand lance]] onto shore are common year-round.<ref name="Porpoise"/>

Little is known about the diets of other species of porpoises. A dissection of three Burmeister's porpoises shows that they consume shrimp and [[euphausiid]]s (krill). A dissection of a beached Vaquita showed remains of squid and [[grunt (fish)|grunts]]. Nothing is known about the diet of the spectacled porpoise.<ref name="Porpoise"/>

==Interactions with humans==

===Research history===
{{See also|Cryptid whale|Whale#In myth, literature and art}}
{{Quote box|width=30%|align=right|quote=The tube in the head, through which this kind fish takes its breath and spitting water, located in front of the brain and ends outwardly in a simple hole, but inside it is divided by a downward bony septum, as if it were two nostrils; but underneath it opens up again in the mouth in a void.|source=–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.{{Citation needed|date=December 2019|reason=removed citation to predatory publisher content}}  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 [[cetology|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.<ref>{{cite book|author= Conrad Gesner|url=http://etext.lib.virginia.edu/toc/modeng/public/AriHian.html|title=Historiae animalium |date=6 September 2008 |archive-url= https://web.archive.org/web/20080906090248/http://etext.lib.virginia.edu/toc/modeng/public/AriHian.html |archive-date=6 September 2008 |access-date=4 September 2015}}</ref> 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.<ref>{{cite journal|author=J. Ray|title=An account of the dissection of a porpess|journal=Philosophical Transactions of the Royal Society of London|volume=6|issue=69–80|year=1671|pages=2274–2279|bibcode = 1671RSPT....6.2274R|doi=10.1098/rstl.1671.0048|doi-access=free}}</ref><ref>{{cite journal|author=Susanne Prahl|title=Studies for the construction of epicranialen airway when porpoise (Phocoena phocoena Linnaeus, 1758)|journal=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|year=2007|page=6}}</ref> It nevertheless referred to the porpoise as a fish, most likely not in the modern-day sense, where it refers to a zoological group, but the older reference as simply a creature of the sea (cf. for example ''star-fish'', ''cuttle-fish'', ''jelly-fish'' and ''whale-fish'').

===In captivity===
{{Main|Cetaceans in captivity}}
[[File:Harbor Porpoise Fjord Baelt Denmark.JPG|thumb|[[Harbour porpoise]] in captivity]]

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.<ref name="Porpoise"/><ref name=Collet1984>{{cite journal| author=Collet, A. | year=1984 | title=Live-Capture of Cetaceans for European Institutions | journal=Rep. Int. Whal. Comm. | volume=34 | pages=603–607 }}</ref> Harbour porpoises have a very long captive history, with poorly documented attempts as early as the 15th century,<ref name="Porpoise"/> and better documented starting in the 1860s and 1870s in [[London Zoo]], the now-closed [[Brighton]] Aquarium & Dolphinarium, and a zoo in Germany.<ref name=Collet1984/><ref>{{cite web|url= http://www.zootierliste.de/en/?klasse=1&ordnung=114&familie=11403&art=1110105&subhaltungen=2|title=North Atlantic Harbour porpoise|work=Zootierliste|access-date=3 July 2018}}</ref> At least 150 harbour porpoises have been kept worldwide, but only about 20 were actively caught for captivity.<ref name="Porpoise"/> 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.<ref name="Porpoise"/><ref name=Collet1984/> Attempts to rehabilitate seven rescued individuals in 1986 only resulted in three that could be released 6 months later.<ref name="Porpoise"/> 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, another for 15 years,<ref>{{cite web|url=https://www.fyens.dk/kerteminde/Doedsfald-paa-FjordBaelt-Sif-blev-15-aar/artikel/3226969|title=Dødsfald på Fjord&Bælt: Sif blev 15 år|work=fyens.dk|date=1 February 2018|access-date=3 July 2018}}</ref><ref name=tv2fyn>{{cite web|url=https://www.tv2fyn.dk/artikel/eigil-er-doed|title=Tab for forskningen: Marsvinet Eigil er død|work=tv2fyn.dk|date=28 April 2016|access-date=3 July 2018}}</ref> while the third (mother of first born in captivity) is the world's oldest known harbour porpoise, being 28 years old in 2023.<ref>{{cite news| title=Marsvinet Freja bliver optaget i Guinness rekordbog | url=https://avisendanmark.dk/indland/marsvinet-freja-bliver-optaget-i-guinness-rekordbog | date=1 August 2023 | publisher=avisendanmark.dk | access-date=21 August 2023 }}</ref> The typical age reached in the wild is 14 years or less.<ref name=tv2fyn/><ref name="Read&Hohn"/><ref name=ADWHarbourPorpoise>{{cite web|url=http://animaldiversity.org/accounts/Phocoena_phocoena/|title=Phocoena phocoena, harbor porpoise|work=animaldiversity.org|access-date=3 July 2018}}</ref> 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.<ref name="Porpoise"/> Disregarding one born more than 100 years ago that was the result of a pregnant female being brought into captivity,<ref name="Porpoise"/> 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.<ref>{{cite web|url=https://phys.org/news/2009-05-porpoise-2nd-birth-captivity.html|title=Porpoise is 2nd to give birth in captivity|work=phys.org|date=8 May 2009|access-date=3 July 2018}}</ref> 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, West Vancouver|Horseshoe Bay]] in 2008 and a male that had done the same in 2011.<ref>{{cite web|url=https://www.vanaqua.org/experience/shows/porpoise|title=Spotlight on Porpoises|author=Vancouver Aquarium|work=Vancouver Aquarium|access-date=8 September 2015|archive-date=5 September 2015|archive-url=https://web.archive.org/web/20150905153432/http://www.vanaqua.org/experience/shows/porpoise|url-status=dead}}</ref><ref>{{cite web|url= http://www.nsnews.com/news/porpoise-rescued-in-horseshoe-bay-now-a-permanent-resident-of-aquarium-1.372119|title=Porpoise rescued in Horseshoe Bay now a permanent resident of aquarium|work=North Shore News|date=16 May 2012|access-date=3 July 2018}}</ref> They died in 2017 and 2016 respectively.<ref>{{cite web|url=https://vancouversun.com/news/local-news/harbour-porpoise-rescued-in-2008-dies-at-vancouver-aquarium|title=Harbour porpoise Daisy, rescued in 2008, dies at Vancouver Aquarium|work=Vancouver Sun|date=16 June 2017|access-date=3 July 2018}}</ref><ref>{{cite web|url=https://www.cbc.ca/news/canada/british-columbia/vancouver-aquarium-porpoise-1.3719481|title=Jack the harbour porpoise dies at Vancouver Aquarium|work=CBC|date=13 August 2016|access-date=3 July 2018}}</ref>

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.<ref name="Porpoise"/> 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.<ref name="Porpoise"/><ref name=Goldfarb2016>{{cite journal| author=Goldfarb, B. | year=2016 | title=Can captive breeding save Mexico's vaquita?| journal=Conservation Biology | volume=353 | issue=6300 | pages=633–634 | doi=10.1126/science.353.6300.633 | pmid=27516576 }}</ref> The reopened [[Miyajima Public Aquarium]] (Japan) houses three finless porpoises.<ref>{{cite news|url= http://www.japantimes.co.jp/culture/2011/08/05/events/events-outside-tokyo/hiroshima-revamps-its-aquarium/#.Ve4pN_lVhBc|title=Hiroshima revamps its aquarium|newspaper=Japan Times|first=Wade|last=Bunnel}}</ref> As part of an attempt of saving the [[Yangtze finless porpoise|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.<ref>{{cite journal | author1=Ding Wang | author2=Yujiang Hao | author3=Kexiong Wang | author4=Qingzhong Zhao | author5=Daoquang Chen | author6=Zhuo Wei | author7=Xianfeng Zhang | year=2005 | title=The first Yangtze finless porpoise successfully born in captivity | journal=Environmental Science and Pollution Research | volume=12 | issue=5 | pages=247–250 | doi=10.1065/espr2005.08.284 | pmid=16206715 | s2cid=37638759 }}</ref>

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. The first recorded instance of a Dall's taken for an aquarium was in 1956 captured off [[Santa Catalina Island (California)|Catalina Island]] in southern California.<ref>{{Cite web|date=2016-02-02|title=Wayback Machine: Dall's Porpoises in Captivity|url=https://www.dolphinproject.com/blog/wayback-machine-dalls-porpoises-in-captivity/|access-date=2021-09-17|website=Dolphin Project|language=en-US}}</ref> Dall's porpoises consistently failed to thrive in captivity. These animals 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.<ref name="Porpoise"/><ref name=DallsInCaptivity>{{cite web|url=https://dolphinproject.com/blog/wayback-machine-dalls-porpoises-in-captivity/|title=Wayback Machine: Dall's Porpoises in Captivity|work=dolphinproject.com|access-date=3 July 2018}}</ref> 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 Marine Mammal Program|United States Navy facility]].<ref name=DallsInCaptivity/>

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.<ref name=Goldfarb2016/><ref>{{cite web|url=https://www.dw.com/en/captivity-last-hope-for-saving-the-vaquita/a-36799824|title=Captivity: Last hope for saving the vaquita?|work=Deutsche Welle|date=16 December 2016|access-date=3 July 2018}}</ref> 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.<ref>{{cite web|url=https://www.theatlantic.com/science/archive/2017/11/vaquita-porpoise-mexico-extinction/545204/|title=The Plan to Rescue a Nearly Extinct Porpoise Goes Terribly Awry|work=The Atlantic|date=9 November 2017|access-date=3 July 2018}}</ref><ref name=ScienceMagVaquita>{{cite web|url=https://www.science.org/content/article/update-after-death-captured-vaquita-conservationists-call-rescue-effort|title=Update: After death of captured vaquita, conservationists call off rescue effort|work=Science Magazine|date=9 November 2017|access-date=3 July 2018}}</ref> Soon after the project was abandoned.<ref name=ScienceMagVaquita/>

Only a single [[Burmeister's porpoise]] and a single [[spectacled porpoise]] have been kept in captivity. Both were stranded individuals that only survived a few days after their rescue.<ref name="Porpoise"/><ref>{{cite web|url=http://porpoise.org/about-porpoises/spectacled-porpoise/|title=Spectacled Porpoise|work=porpoise.org|access-date=3 July 2018}}</ref>

===Threats===

====Hunting====
[[File:FMIB 35846 Porpoise Fishery.jpeg|thumb|Traditional catch of [[harbour porpoise]] by lancing in [[Bay of Fundy]]]]
Porpoises and other smaller cetaceans have traditionally been hunted in many areas, at least in Asia, Europe and North America, for their meat and blubber. A dominant hunting technique is drive hunting, where a pod of animals is driven 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. This type of fishery for [[harbour porpoise]]s is best documented from the [[Danish straits]], where it occurred until the end of the 19th century (it was banned in 1899), and again during the shortages in [[World War I]] and [[World War II]].<ref>{{cite book |last1=Petersen |first1=Åge |title=Marsvin og marsvinjægere |date=1969 |publisher=Middelfart By- og Egnshistoriske Museum |location=Middelfart, Denmark}}</ref> The [[Inuit]] in the Arctic hunt harbour porpoises by shooting and drive hunt for [[Dall's porpoise]] still takes place in Japan. The number of individuals taken each year is in the thousands, although a quota of around 17,000 per year is in effect today<ref>{{cite journal |last1=Jefferson |first1=TA |last2=Braulik |first2=G |title=''Phocoenoides dalli'' |url=https://www.iucnredlist.org/species/17032/50370912 |journal=IUCN Red List of Threatened Species|date=22 March 2017 }}</ref> making it the largest direct hunt of any [[cetacean]] species in the world<ref name="smm">{{cite web |title=''Phocoenoides dalli'' (Dall's porpoise, Dall porpoise) |url=https://www.marinemammalscience.org/facts/phocoenoides-dalli/ |website=The Society for Marine Mammalogy}}</ref> and the sustainability of the hunt has been questioned.<ref name="IWChunt">{{cite journal |title=Report of the Sub-Committee on Small Cetaceans |journal=International Whaling Commission |date=2008}}</ref><ref name="smm2">{{cite web |last1=Wells |first1=RS |title=Letter to Japanese Government Regarding Dolphin and Small Whale Hunts |url=https://www.marinemammalscience.org/letters/letter-to-japanese-government-regarding-dolphin-and-small-whale-hunts/ |website=The Society for Marine Mammalogy|date=29 May 2012 }}</ref>

====Fishing====
{{Main|Cetacean bycatch}}
[[File:Vaquita2 Olson NOAA.jpg|thumb|A [[vaquita]] swimming in the [[Gulf of California]].]]
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.<ref>{{cite journal|last1=D'agrosa|first1=C.|last2=Lennert-Cody|first2=C. E.|last3=Vidal|first3=O.|year=2000|title=Vaquita Bycatch in Mexico's Artisanal Gillnet Fisheries: Driving a Small Population to Extinction|journal=Conservation Biology|volume=14|issue=4|doi=10.1046/j.1523-1739.2000.98191.x|pages=1110–1119|bibcode=2000ConBi..14.1110D |s2cid=44057831}}</ref> 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.<ref>{{cite journal|url=https://www.umb.edu/editor_uploads/images/Caswell_etal_EcolAppl1998.pdf|first1=Hal|last1=Caswell|first2=Solange|last2=Brault|first3=Andrew|last3=Read|first4=Tim|last4=Smith|title=Harbor Porpoise and Fisheries: an Uncertainty Analysis of Incidental Mortality|journal=Ecological Applications|volume=8|issue=4|year=1998|access-date=30 October 2015|pages=1226–1238|doi=10.1890/1051-0761(1998)008[1226:hpafau]2.0.co;2|archive-date=8 December 2015|archive-url=https://web.archive.org/web/20151208132734/https://www.umb.edu/editor_uploads/images/Caswell_etal_EcolAppl1998.pdf|url-status=dead}}</ref>

The fishing market, historically has always had a porpoise bycatch. Today, the [[Marine Mammal Protection Act of 1972]] has enforced the use of safer fishing equipment to reduce bycatch.<ref>{{cite newsgroup|title=America's Favorite Fish Tainted by Porpoise Deaths|last=Croft|first=Chris|url=https://www.latimes.com/archives/la-xpm-1988-04-17-op-1956-story.html|access-date=30 October 2015}}</ref>

====Environmental hazards====
{{See also|Marine mammals and sonar}}
Porpoises are very sensitive to [[anthropogenic effect|anthropogenic]] disturbances,<ref name=":0">{{cite journal |title=Harbour porpoises (''Phocoena phocoena'') stranded along the southern North Sea: an assessment through metallic contamination |last1=Mahfouz |first1=C |last2=Henry |first2=F |last3=Courcot |first3=L |last4=Pezeril |first4=S |last5=Bouveroux |first5=T |last6=Dabin |first6=W |last7=Jauniaux |first7=T |last8=Khalaf |first8=G |last9=Amara |first9=R |year=2014 |journal= Environmental Research|doi=10.1016/j.envres.2014.06.006 |pmid=24981825 |volume=133 |pages=266–73|bibcode=2014ER....133..266M |hdl=2268/169176 |url=http://orbi.ulg.ac.be/handle/2268/169176 |hdl-access=free }}</ref> and are [[keystone species]], which can indicate the overall health of the marine environment.<ref name=":0" /> 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.<ref>{{cite journal |last1=Siebert |first1=Ursula |last2=Pozniak |first2=Blazej |last3=Hansen |first3=Kirstin |last4=Anderson |last5=Nordstrom |first5=Gwyneth |last6=Teilmann |first6=Jonas |last7=Van Elk |first7=Niels |last8=Vossen |first8=Ardnt |last9=Dietz |first9=Rune |year=2011 |title=Investigations of Thyroid and Stress Hormones in Free-Ranging and Captive Harbor Porpoises (''Phocoena phocoena''): A Pilot Study |journal=Aquatic Mammals |volume=37 |issue=4 |pages=443–453 |doi=10.1578/am.37.4.2011.443 |bibcode=2011AqMam..37..443S }}</ref> Increasing pollution is a serious problem for marine mammals. Heavy metals and [[plastic pollution|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.<ref name=wdcs>{{cite book |author=Cara E. Miller |title=Current State of Knowledge of Cetacean Threats, Diversity, and Habitats in the Pacific Islands Region |publisher=Whale and Dolphin Conservation Society |year=2007 |access-date=5 September 2015 |isbn=978-0-646-47224-9 |url=http://uk.whales.org/sites/default/files/whales-and-dolphins-in-the-pacific-islands.pdf |archive-url=https://web.archive.org/web/20150908003502/http://uk.whales.org/sites/default/files/whales-and-dolphins-in-the-pacific-islands.pdf |archive-date=8 September 2015  }}</ref> Harbour porpoises from the [[English Channel]] were found to have accumulated heavy metals.<ref name=":0" />

The military and geologists employ strong [[sonar]] and produce an increases in noise in the oceans. [[Marine mammal]]s 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]].<ref>{{cite book |author1=M. Andre |author2=T. Johansson |author3=E. Delory |author4=M. van der Schaar |title=Europe Oceans 2005 |chapter=Cetacean biosonar and noise pollution |publisher=Oceans 2005–Europe |year=2005 |volume=2 |pages=1028–1032 Vol. 2 |doi=10.1109/OCEANSE.2005.1513199 |isbn=978-0-7803-9103-1 |s2cid=31676969 }}</ref> This effect, of course, only occurs in porpoises that dive to great depths, such as Dall's porpoise.<ref>{{cite journal |author=Kastelein, R. A. |author2=Schop, J. |author3=Gransier, R. |author4=Steen, N. |author5=Jennings, N. |title=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'') |doi=10.1578/AM.40.3.2014.232 | volume=40 |issue=3 |journal=Aquatic Mammals |pages=232–242|year=2014 |bibcode=2014AqMam..40..232K }}</ref>

Additionally, civilian vessels produce sonar waves 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.<ref>{{cite journal |last1=Culik |first1=B. |last2=von Dorrien |first2=C. |last3=Muller |first3=V. |last4=Conrad |first4=M. |year=2015 |title=Bioacoustics |journal=The International Journal of Animal Sound and Its Recording |volume=24 |issue=3 |issn=0952-4622}}</ref>

===Conservation===
[[File:Porpoise Sculpture with Flowers and Fountains - Waterfront Park - Kelowna - British Columbia - Canada (8008022011).jpg|thumb|right|A porpoise sculpture in Kelowna, British Columbia, Canada]]

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).<ref name="Appendices">"{{cite web|url=http://www.cms.int/en/convention-text|title=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|date=5 March 2009}}</ref><ref>{{cite journal |author=HELCOM |author-link=HELCOM |year=2013 |title=HELCOM Red List of Baltic Sea species in danger of becoming extinct |journal=Baltic Sea Environmental Proceedings |issue=140 |page=92 |url=http://helcom.fi/Lists/Publications/BSEP140.pdf  |archive-url=https://web.archive.org/web/20141007002944/http://helcom.fi/Lists/Publications/BSEP140.pdf |archive-date=7 October 2014 }}</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 [[ACCOBAMS|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.<ref>{{cite web|url=http://www.cms.int/aquatic-mammals/sites/default/files/basic_page_documents/MoU_E.pdf |archive-url=https://web.archive.org/web/20150919134833/http://www.cms.int/aquatic-mammals/sites/default/files/basic_page_documents/MoU_E.pdf |archive-date=2015-09-19 |url-status=live|title=Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia|work=[[Convention on the Conservation of Migratory Species of Wild Animals]]|pages=1–6}}</ref> Their conservation statuses are either at [[least concern]] or [[data deficient]].<ref>{{cite web|url=http://www.cms.int/reports/small_cetaceans/img/Odontocete_poster.pdf|title=Odontocetes: The Toothed Whales |publisher=[[International Union for Conservation of Nature|IUCN]], [[ASCOBANS]], [[World Wide Fund for Nature|WWF]], [[Convention on the Conservation of Migratory Species of Wild Animals|CMS]], [[ACCOBAMS]]|archive-url=https://web.archive.org/web/20151208124558/http://www.cms.int/reports/small_cetaceans/img/Odontocete_poster.pdf |archive-date=8 December 2015}}</ref>

As of 2014, only 505 [[Yangtze finless porpoise]]s 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%.<ref>{{cite journal|last1=Hashimoto|first1=M.|last2=Shirakihara|first2=K.|last3=Shirakihara|first3=M.|last4=Hiramatsu|first4=K.|year=2013|title=Estimating the rate of increase for the finless porpoise with special attention to predictions for the inland sea population in japan|journal=Population Ecology|volume=55|issue=3|pages=441–449|doi=10.1007/s10144-013-0374-5|bibcode=2013PopEc..55..441H |s2cid=15843140}}</ref> 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]].<ref>{{cite journal | last1 = Mei | first1 = Zhigang | last2 = Zhang | first2 = Xinqiao | last3 = Huang | first3 = Shiang-Lin | last4 = Zhao | first4 = Xiujiang | last5 = Hao | first5 = Yujiang | last6 = Zhang | first6 = Lin | last7 = Qian | first7 = Zhengyi | last8 = Zheng | first8 = Jinsong | last9 = Wang | first9 = Kexiong | last10 = Wang | first10 = Ding | year = 2014 | title = The Yangtze Finless Porpoise: On an Accelerating Path to Extinction? | url = http://ir.ihb.ac.cn/handle/342005/19995 | journal = Biological Conservation | volume = 172 | pages = 117–23 | doi = 10.1016/j.biocon.2014.02.033 | bibcode = 2014BCons.172..117M | access-date = 27 January 2019 | archive-date = 29 May 2020 | archive-url = https://web.archive.org/web/20200529104049/http://ir.ihb.ac.cn/handle/342005/19995 | url-status = dead | url-access = subscription }}</ref> Some of these can be seen in damming of the river as well as [[illegal, unreported and unregulated fishing|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 Sciences]]' [[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.<ref>{{cite web|url=http://www.worldwildlife.org/stories/saving-the-finless-porpoise|title=Saving the Finless Porpoise|first1=Karin|last1=Krchnak|date=30 September 2014|access-date=25 October 2015|work=[[World Wildlife Fund]]}}</ref> 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.<ref>{{cite journal|last1=Wang|first1=D.|last2=Hao|first2=Y.|last3=Wang|first3=K.|last4=Zhao|first4=Q.|last5=Chen|first5=D.|last6=Wei| first6=Z.|last7=Zhang|first7=X.|year=2005|title=the first yangtze finless porpoise successfully born in captivity|journal=Environmental Science and Pollution Research International|volume=12|issue=5|pages=247–250|doi=10.1065/espr2005.08.284|pmid=16206715|s2cid=37638759}}</ref>

Because [[vaquita]]s 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.<ref>{{cite web|last1=Barlow|first1=J.|year=2014|title=Vaquita (Phocoena sinus)|url=http://www.edgeofexistence.org/mammals/species_info.php?id=78|work=Edge of Existence programme|publisher=Zoological Society of London|access-date=25 October 2015|archive-date=26 October 2016|archive-url=https://web.archive.org/web/20161026123310/http://www.edgeofexistence.org/mammals/species_info.php?id=78}}</ref> CIRVA has worked together with the [[CITES]], the [[Endangered Species Act]], and the [[Marine Mammal Protection Act of 1972|Marine Mammal Protection Act]] (MMPA) to nurse the vaquita population back to a point at which they can sustain themselves.<ref name="NOAA_Vaquita">{{cite web|title=Gulf of California Harbor Porpoise / Vaquita / Cochito (''Phocoena sinus'')|url=http://www.nmfs.noaa.gov/pr/species/mammals/cetaceans/vaquita.htm|publisher=NOAA Fisheries–Office of Protected Resources|work= Species Information|date= 8 July 2013|access-date=20 January 2014}}</ref> CIRVA concluded in 2000 that between 39 and 84 individuals are killed each year by such gillnets. 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.<ref>{{cite web|url=http://www.iucn-csg.org/index.php/2015/04/24/president-of-mexico-launches-plan-to-save-the-vaquita/|title=President of Mexico launches plan to save the vaquita|author=Gill Braulik|date=24 April 2015|access-date=25 October 2015|work=IUCN SSC–Cetacean Specialist Group|archive-date=18 October 2015|archive-url=https://web.archive.org/web/20151018131533/http://www.iucn-csg.org/index.php/2015/04/24/president-of-mexico-launches-plan-to-save-the-vaquita/|url-status=dead}}</ref>

==See also==
{{Portal|Cetaceans}}
* [[List of individual cetaceans]]

==References==
{{Reflist}}

==External links==
{{Wikispecies|Phocoenidae}}
{{Commons category}}
* [https://web.archive.org/web/20090130050016/http://www.whaletrackers.com/ Whale Trackers – An online documentary series about whales, dolphins and porpoises.]

{{Cetacea|O.}}
{{Odontoceti|D.}}
{{Taxonbar|from=Q10867}}
{{Authority control}}

[[Category:Porpoises| ]]
[[Category:Animals that use echolocation]]
[[Category:Delphinoidea]]
[[Category:Extant Miocene first appearances]]
[[Category:Langhian first appearances]]
[[Category:Taxa named by John Edward Gray]]