The 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.
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. Probably best known is the Harbour Porpoise, which can be found across the Northern Hemisphere.
Taxonomy and evolution
- See also: Evolution of
cetaceans
Porpoises, along with whales and dolphins, are descendants of land-living mammals and are related to hoofed animals. Evolutionary philosophy teaches they entered the water roughly 50 million years ago.
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.[1]
Physical characteristics
A
Harbour Porpoise at an aquarium. In the wild, porpoises rarely jump out of the
water.
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. [1]
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.[1]
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. Although the lifespan of most species is not known, specimens older than in their mid-teens
have rarely been found.[1]
Behaviour
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.[2]
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.
In popular culture
In the 1966 Batman film, Batman and Robin are rescued by a "Noble Porpoise" who
intercepted a torpedo that was headed in their direction.
In the BBC comedy series, Blackadder The Third, the Prince Regent, played by
Hugh Laurie, confuses the title of the story The Prince And The Pauper with The Prince And The Porpoise.
See also
References
External links
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