Porpoise
Porpoise Temporal range: Miocene to Recent
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The harbor porpoise (Phocoena phocoena)
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Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Artiodactyla |
Infraorder: | Cetacea |
Superfamily: | Delphinoidea |
Family: | Phocoenidae Gray, 1825 |
Type genus | |
Phocoena Cuvier, 1816
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Genera | |
Porpoises (
Porpoises range in size from the
Porpoises are abundant and found in a multitude of environments, including rivers (
Porpoises were, and still are, hunted by some countries by means of
Taxonomy and evolution
Porpoises, along with
- ORDER Artiodactyla
- Infraorder Cetacea
- Parvorder Odontocetitoothed whales
- Superfamily Delphinoidea
- Family Phocoenidae – porpoises
- Genus †Haborophocoena[5]
- Genus Neophocaena
- N. phocaeniodes – Indo-Pacific finless porpoise
- N. sunameri – East Asian finless porpoise
- N. asiaeorientalis – Yangtze finless porpoise
- Genus †Numataphocoena[6]
- 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
- S.ceruttii
- Genus †Septemtriocetus[7]
- Genus †Piscolithax
- Family Phocoenidae – porpoises
- Superfamily Delphinoidea
- Parvorder
- Infraorder Cetacea
Recently discovered hybrids between male harbour porpoises and female Dall's porpoises indicate the two species may actually be members of the same genus.[8]
Biology
Anatomy
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[9] to the 2.3 m (7 ft 7 in) and 220 kg (490 lb) Dall's porpoise.[10] Overall, they tend to be dwarfed by other cetaceans. Almost all species have female-based sexual dimorphism, with the females being larger than the males,[11][12] although those physical differences are generally small; one exception is Dall's porpoise.[13][14]
Odontocetes possess teeth with
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] 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.[17] 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 them 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.[12][18]
Senses
The porpoise ear has specific adaptations to the
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.[24] 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.[21]
The
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.[21]
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.[25]
Behaviour
Life cycle
Porpoises are fully aquatic creatures. Females deliver a single calf after a
Diet
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.[18]
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.[18]
Little is known about the diets of other species of porpoises. A dissection of three Burmeister's porpoises shows that they consume shrimp and
Interactions with humans
Research history
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.
–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] 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.[27] 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.[28][29] 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
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.[18][30] Harbour porpoises have a very long captive history, with poorly documented attempts as early as the 15th century,[18] and better documented starting in the 1860s and 1870s in London Zoo, the now-closed Brighton Aquarium & Dolphinarium, and a zoo in Germany.[30][31] At least 150 harbour porpoises have been kept worldwide, but only about 20 were actively caught for captivity.[18] 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.[18][30] Attempts to rehabilitate seven rescued individuals in 1986 only resulted in three that could be released 6 months later.[18] 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,[32][33] while the third (mother of first born in captivity) is the world's oldest known harbour porpoise, being 28 years old in 2023.[34] The typical age reached in the wild is 14 years or less.[33][2][35] 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.[18] Disregarding one born more than 100 years ago that was the result of a pregnant female being brought into captivity,[18] 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.[36] 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.[37][38] They died in 2017 and 2016 respectively.[39][40]
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.[18] 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.[18][41] The reopened Miyajima Public Aquarium (Japan) houses three finless porpoises.[42] 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.[43]
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 Catalina Island in southern California.[44] 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.[18][45] 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.[45]
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.[41][46] 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.[47][48] Soon after the project was abandoned.[48]
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.[18][49]
Threats
Hunting
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
Fishing
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.[55] 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.[56]
The fishing market, historically has always had a porpoise bycatch. Today, the
Environmental hazards
Porpoises are very sensitive to
The military and geologists employ strong
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.[63]
Conservation
The harbour porpoise, spectacled porpoise, Burmeister's porpoise, and Dall's porpoise are all listed on Appendix II of the
As of 2014, only 505
Because
See also
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External links
- Media related to Phocoenidae at Wikimedia Commons
- Whale Trackers – An online documentary series about whales, dolphins and porpoises.