Porpoise

Porpoise

Taxobox
name = Porpoises
fossil_range = Mid Miocene to Recent


image_width = 225px
image_caption = "Phocoena phocoena", Harbour Porpoise at the Fjord & Bæltcentret in Denmark
regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Cetacea
subordo = Odontoceti
familia = Phocoenidae
familia_authority = Gray, 1825
subdivision_ranks = Genera
subdivision = "Neophocaena" - Finless porpoise
"Phocoena" - Harbour porpoise "et al."
"Phocoenoides" - Dall's porpoise

Porpoises are small cetaceans of the family Phocoenidae; they are related to whales and dolphins. They are distinct from dolphins, although the word "porpoise" has been used to refer to any small dolphin, especially by sailors and fishermen. The most obvious visible difference between the two groups is that porpoises have flattened, spade-shaped teeth distinct from the conical teeth of dolphins, and shorter beaks.

The name derives from French "pourpois", originally from Medieval Latin "porcopiscus" ("porcus" pig + "piscus" fish).

Porpoises, divided into six species, live in all oceans, mostly near the shore. Freshwater populations of the Finless Porpoise also exist. Probably the best known species is the Harbour Porpoise, which can be found across the Northern Hemisphere. Like all toothed whales, porpoises are predators, using sounds to locate prey and to coordinate with others. They hunt fish, squid, and crustaceans.

Porpoises apparently diverged from dolphins about 15 million years ago in the northern Pacific, then spread across the globe much later.

Taxonomy and evolution

Porpoises, along with whales and dolphins, are descendants of land-living ungulates (hoofed animals) that first entered the oceans around 50 million years ago. During the Miocene (23 to 5 MYA), mammals were fairly modern. The cetaceans diversified, and fossil evidence suggests that porpoises diverged from dolphins and other cetaceans 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.cite book |editor=Macdonald, D.|author= Gaskin, David E.|year=1984 |title= The Encyclopedia of Mammals|publisher= Facts on File|location=New York|pages= 196-199|isbn= 0-87196-871-1]

* Sub-order Odontoceti: toothed whales
**Family Phocoenidae: Porpoises
***Genus "Neophocaena"
****Finless Porpoise, "Neophocaena phocaeniodes"
***Genus "Phocoena"
****Harbour Porpoise, "Phocoena phocoena"
****Vaquita, "Phocoena sinus"
****Spectacled Porpoise, "Phocoena dioptrica"
****Burmeister's Porpoise, "Phocoena spinipinnis"
***Genus "Phocoenoides"
****Dall's Porpoise, "Phocoenoides dalli"

Recently-discovered hybrids between male Harbour porpoises and female Dall's Porpoises indicate that the two species may actually be members of the same genus.

Physical characteristics

Porpoises tend to be smaller but stouter than dolphins. They have small, rounded heads and blunt jaws instead of beaks. While dolphins have a round, bulbous "melon", porpoises do not. Their teeth are spade-shaped, whereas dolphins have conical teeth. In addition, a porpoise's dorsal fin is generally triangular, rather than curved like that of many dolphins and large whales. Some species have small bumps, known as tubercles, on the leading edge of the dorsal fin. The function of these bumps is unknown. cite book| author=Read, Andrew |title= "Porpoises"|year=1999|publisher=Voyageur Press |location=Stillwater, MN, USA|ISBN=0-89658-420-8]

These animals are the smallest cetaceans, reaching body lengths up to 2.5 metres (8 ft); the smallest species is the Vaquita, reaching up to 1.5 m (5 ft). In terms of weight the lightest is the Finless Porpoise at 30-45 kilograms (65-100 lb) and the heaviest is Dall's Porpoise at 130-200 kg (280-440 lb). Because of their small size, porpoises lose body heat to the water more rapidly than other cetaceans. Their stout shape, which minimizes surface area, may be an adaptation to reduce heat loss. Thick blubber also insulates them from the cold. The small size of porpoises requires them to eat frequently, rather than depending on fat reserves.

Life history

Porpoises are relatively r-selected compared with dolphins: that is, they rear young more quickly than dolphins. Female Dall's and Harbour Porpoises often become pregnant with a single calf each year, and pregnancy lasts for about 11 months. Porpoises have been known to live 8-10 years although there are some that lived to be 20.

Behavior

Porpoises are predators of fish, squid, and crustaceans. Although they are capable of dives up to 200 m, they generally hunt in shallow coastal waters. They are found most commonly in small groups of fewer than ten individuals. Rarely, some species form brief aggregations of several hundred animals. Like all toothed whales they are capable of echolocation for finding prey and group coordination. Porpoises are fast swimmers—Dall's porpoise is said to be one of the fastest cetaceans, with a speed of 55 km/h (34 mph). Porpoises tend to be less acrobatic and more wary than dolphins.

Human impact

Accidental entanglement (bycatch) in fishing nets is the main threat to porpoises today. One of the most endangered cetacean species is the Vaquita, having a limited distribution in the Gulf of California, a highly industrialized area. [cite web| url=http://www.theporpoisepage.com/vaquita.php|title=The Porpoise Page - Information on Porpoises | accessdate=2006-11-03]

In some countries, porpoises are hunted for food or bait meat.

Porpoises are rarely held in captivity in zoos or oceanaria, as they are generally not as capable of adapting to tank life nor as easily trained as dolphins.

ee also

*Dolphin
*Whale

References

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Look at other dictionaries:

  • Porpoise — Por poise, n. [OE. porpeys, OF. porpeis, literally, hog fish, from L. porcus swine + piscis fish. See {Pork}, and {Fish}.] 1. (Zo[ o]l.) Any small cetacean of the genus {Phoc[ae]na}, especially {Phoc[ae]na communis}, or {Phoc[ae]na phoc[ae]na},… …   The Collaborative International Dictionary of English

  • porpoise — c.1300, from O.Fr. porpais (12c.), lit. pork fish, from porc pork (see PORK (Cf. pork)) + peis fish, from L. piscis fish. The Old French word is probably a loan translation of a Germanic word, Cf. O.N. mar svin, O.H.G. meri swin, M.Du. mereswijn …   Etymology dictionary

  • porpoise — [pôr′pəs] n. pl. porpoises or porpoise [ME porpoys < OFr porpeis, lit., swine fish < L porcus, pig (see FARROW1) + piscis, FISH] 1. any of a family (Phocoenidae) of small, usually gregarious toothed whales found in most seas, with a torpedo …   English World dictionary

  • porpoise — is pronounced paw pǝs, in preference to a second syllable as in poise …   Modern English usage

  • porpoise — ► NOUN ▪ a small toothed whale with a blunt rounded snout. ORIGIN Old French porpois, from Latin porcus pig + piscis fish …   English terms dictionary

  • porpoise — porpoiselike, adj. /pawr peuhs/, n., pl. (esp. collectively) porpoise, (esp. referring to two or more kinds or species) porpoises, v., porpoised, porpoising. n. 1. any of several small, gregarious cetaceans of the genus Phocoena, usually blackish …   Universalium

  • porpoise — n. 1) a school of porpoises 2) a young porpoise is a calf 3) a female porpoise is a cow 4) a male porpoise is a bull * * * [ pɔːpəs] a female porpoise is a cow a male porpoise is a bull a school of porpoises a young porpoise is a calf …   Combinatory dictionary

  • porpoise — /ˈpɔpəs / (say pawpuhs) noun (plural porpoises, porpoise) 1. any of several small, gregarious cetaceans of the genus Phocoena, usually blackish above and paler underneath, and with a blunt, rounded snout, especially the common porpoise, P.… …  

  • porpoise — I. noun Etymology: Middle English porpoys, from Anglo French porpeis, from Medieval Latin porcopiscis, from Latin porcus pig + piscis fish more at farrow, fish Date: 14th century 1. any of a family (Phocoenidae) of small gregarious toothed… …   New Collegiate Dictionary

  • porpoise — [14] The porpoise is etymologically the ‘pig fish’. The word comes via Old French porpois from Vulgar Latin *porcopiscis, a compound formed from porcus ‘pig’ (source of English pork) and piscis ‘fish’ (a relative of English fish) and based on the …   The Hutchinson dictionary of word origins

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