Risso's Dolphin OR Grampus

Grampus griseus


FIELD MARKS:
medium, to 4m (13 feet)
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blunt head
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all black body, extensively scarred
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falcate dorsal fin
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gregarious, often swims in chorus lines
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compare with False Killer Whale and Pilot Whale

Note

Body color varies with age, as does degree of scaring.

Description

This species is characterized by its blunt, bulbous and squarish head shape, indistinct beak, and characteristic white scarring. Tubular body that narrows rapidly behind the dorsal fin. Tall, dark dorsal fin that is distinctly falcate. Flippers are long, curved and pointed at tip. Body color is black above to grayish white on the chest and belly. Their skin scars easily; older adults' bodies may appear almost white due to extensive scarring from the teeth-raking of other Risso's dolphins during play, mating, or aggressive confrontations. Young are uniformly grey. Their bodies are stocky and range in length from 3 to 4 meters for adults.

Food

Squid seems to be their major prey, although they also will hunt fish and other cephalopods.

Habitat

Risso's dolphins are found mostly near the surface in deep water in tropical and warm temperate regions; outside the 100 fathom line, seaward from outer edge of continental shelf, possibly coastal waters where shelf edge is close to shore.

Range

Prefers warmer waters. In Atlantic from Eastern Newfoundland to Lesser Antilles, including North and East Gulf of Mexico. In Pacific from off Northern Washington to tropics.

Similar Species

From a distance, they can be confused with the Bottlenose Dolphin. However, the presence of a beak in the Bottlenose and the scarring of the Grampus quickly separates them.

Comments

Their pods are usually small, approximately a dozen or so, but they occasionally have been seen in large herds of several thousand. Occasionally solitary. Often swims in chorus lines, evenly spaced in chevron formation. Often accompanies Pacific White-sided Dolphins, Northern Right Whale Dolphins, and Pilot Whales. Occasionally rides bow waves or stern wakes but normally ignores ships. Will porpoise when swimming and slap the water with its tail. It occasionally breaches.

Also known as Grampus, Gray Grampus, White-headed Grampus, Mottled Grampus, White Blackfish, and Risso's Porpoise.



Copyright 1999-2003 - All Rights Reserved, By Norma Ranieri (EMail:Dolphintailz@oocities.com)



Credits

Much of the information found here has been adapted from the following sources:

"The Audubon Society Field Guide to North American Fishes, Whales & Dolphins", Copyright Chanticleer Press, Inc. 1983. All rights reserved.

"The Whale-Watchers Handbook: A Field Guide to the Whales, Dolphins, and Porpoises of North America", by David K. Bulloch, Copyright 1993, All rights reserved.

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