Porpoise

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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. ^[0]

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.^[0]

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.^[0]

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

• Dolphin
• Whale

References

•  • [ e] Cetaceans (whales, dolphins, and porpoises)
Suborder Mysticeti (baleen whales)	Eschrichtiidae (gray whales) Balaenopteridae (rorquals) Balaenidae (right whales) Neobalaenidae (pygmy right whales)
Suborder Odontoceti (toothed whales)	Platanistoidea (river dolphins) Delphinidae (oceanic dolphins) Phocoenidae (porpoises) Monodontidae (beluga and narwhal) Physeteridae (sperm whales) Kogiidae (pygmy and dwarf sperm whales) Ziphiidae (beaked whales)

External links

• Whale and Dolphin Conservation Society (WDCS)