Bottle-Nosed Dolphin

Bottle-Nosed Dolphin, best-studied and generally the best-known species of dolphin. It occurs along almost all tropical and temperate coasts to about latitude 40° south and to latitude 45° north, and around the British Isles it occurs up to latitude 60° north. Bottle-nosed dolphins are coastal in most areas and remain in groups of usually fewer than 20, although offshore varieties also exist in many places and, in deep water, groups can be as large as 200. Some populations make seasonal migrations.

Bottle-nosed dolphins are named for their snout, which is distinctly set off from the head, like the neck of a bottle. The animals are generally dark gray or black above, with a lighter belly. The length of adults varies, from about 2 m (about 6.6 ft) to about 4 m (about 13 ft). In general, males are slightly larger than females, and cold-water bottle-nosed dolphins are larger than their warm-water counterparts. Bottle-nosed dolphins have a prominent, curved dorsal fin with a thin trailing edge that readily tatters. This distinctive tattering has been used by researchers to identify and track individuals and groups.

Bottle-nosed dolphins feed on many different types of prey, including shrimp, squid, other invertebrates, and fishes. The dolphins feed by nosing into near-shore rocky crevasses, by chasing fish onto mudbanks and snapping them up while they are beached, or by cooperatively herding prey into dense clusters, sometimes against a shore or up to the surface of the water. The dolphins also take advantage of human fisheries, usually by following shrimp boats for the prey that they stir up and for the catch that is tossed overboard.

Bottle-nosed dolphins are gregarious and, at least in some near-shore societies, appear to stay together for life. Females come to sexual maturity after 5 to 12 years, and males after 9 to 13 years. There is some evidence for polygamous mating, in which there is no overt aggressive competition by either males or females for access to mates. After a gestation period of about 12 months, a single calf is born. Calves nurse for up to 18 months. The dolphins communicate by means of a rich repertoire of whistles and rasping sounds and, in at least some populations, individuals appear to have a signature whistle. Bottle-nosed dolphins are able to discriminate even small objects by echolocation—that is, they send out high frequency clicks that bounce off prey and other objects and use the returning echoes to distinguish the objects. For this reason most studies of echolocation in dolphins have used bottle-nosed dolphins as subjects.

Bottle-nosed dolphins are often considered the most adaptable of the cetaceans because they live amid industrial activity around harbors and ship channels in many parts of the world. They have recently become the subject of dolphin watching and other tourist activities, and they are the most commonly kept dolphins in zoos and marine aquaria. Bottle-nosed dolphins have been hunted for meat, fertilizer, and oil, but their numbers do not appear to have been significantly reduced except in the Black Sea, where pollution and overfishing of the dolphin's prey have caused as much damage to them as direct killing.

Scientific classification: The bottle-nosed dolphin belongs to the family Delphinidae in the suborder Odontoceti, order Cetacea. It is classified as Tursiops truncatus.

Contributed By:
Bernd G. Wursig

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