Porpoise

Porpoise, common name applied to six species of small whales closely related to dolphins. Porpoises are generally smaller than dolphins and have rounded conical heads that lack the dolphin's characteristic beak. Porpoises have triangular rather than hooked dorsal fins, and instead of vaulting completely out of the water like dolphins do, they make wheel-like rolls, surfacing about four times a minute to breathe.

The most frequently seen and most wide-ranging of the porpoises is the common, or harbor, porpoise, which inhabits cool and cold waters of the northern hemisphere, especially around tidal estuaries and inlets of large rivers. Unlike dolphins, these porpoises are rarely seen in the open ocean and do not play in the bow waves or wakes of ships. They grow from 1.2 to 2 m (4 to 6.6 ft) long and are usually bluish-black above and sometimes whitish below. They often travel in small schools that make explosive exhalations as they surface. After mating, which occurs between June and September, the female gives birth after about 11 months to a calf 0.7 to 1 m (2.3 to 3.3 ft) long.

Other porpoises have more restricted ranges. The Dall porpoise has distinctly white underbelly markings that rise high up the flank; it inhabits the cold waters of the North Pacific as far south as Japan. The black finless porpoise, which has no dorsal fin, inhabits estuarial waters of southern and eastern Asia.

Scientific classification: Porpoises make up the family Phocoenidae of the order Cetacea. The common porpoise is classified as Phocoena phocoena, the Dall porpoise as Phocoenoides dalli, and the finless porpoise as Neophocoena phocaenoides.

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