Risso's Dolphin
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  Size comparison against an average human
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| Grampus griseus (G. Cuvier, 1812) |
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 Risso's Dolphin range
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The Risso's Dolphin (Grampus griseus) is the only species of dolphin in the genus Grampus.
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[edit] Taxonomy
Risso's Dolphin was first described by Cuvier in 1812. The species' common name is from Mr. Risso who described a specimen to Cuvier on which Cuvier made his first description. Another common name for Risso's Dolphin is the Grampus (also the species genus), although as a common name this was historically used for the Orca. The etymology of the word grampus is unclear. It may be an aglomeration of the Latin grandis piscis or French grand poisson both meaning big fish. The specific epithet griseus refers to the mottled (almost scarred) grey colour of the dolphin's body.
Length is typically 10 feet (3 m), although animals have been recorded up to 12.5 feet (3.8 m). Like most dolphins, males are typically slightly larger than females. Weight averages about 650 pounds (300 kg), and large individuals may weigh up to 1100 pounds (500 kg).[1]
[edit] Population and distribution
It is found worldwide in temperate and tropical waters, usually in deep waters rather than close to land. As well as the tropical parts of the Indian, Pacific and Atlantic Oceans, Rissos are also found in the Mediterranean and Red Seas, though are absent from the Black Sea. Their preferred environment is just off the continental shelf on steep banks (with water depths varying from 400-1000m) with water temperature at least 10°C and preferably in excess of 15°C.
The population around the continental shelf of the United States has been recorded to be in excess of 60,000. In the Pacific a census recorded 175,000 individuals in eastern tropical waters and 85,000 in the west. No global estimate of population exists.
[edit] Human interaction
Risso's Dolphins generally do not approach boats. A notable exception was an individual named Pelorus Jack who accompanied boats in Admiralty Bay in New Zealand's Marlborough Sound for more than 20 years. Whaling of this species has never been particularly widespread though operations off Sri Lanka may be significantly damaging the local population.[citation needed] Globally the species is recognised as abundant and safe.
Risso's have been taken into capitivity successfully in the United States and Japan, though with nowhere near the regularity of Bottlenose Dolphins or Orca. Hybrid Risso's-Bottlenose Dolphins have been bred in captivity.
[edit] Strandings
At least one case report of strandings in the Goto Islands (Japan) has been associated with parasitic neuropathy of the VIIIth cranial nerve by a trematode in the Nasitrema spp. genus. (See Morimitsu et al. 1992. J Wildl Dis 28:656-658).
[edit] References
- Cetacean Specialist Group (1996). Grampus griseus. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 10 May 2006. Database entry includes justification for why this species is listed as data deficient
- National Audubon Society Guide to Marine Mammals of the World ISBN 0-375-41141-0
- Encyclopedia of Marine Mammals ISBN 0-12-551340-2
- Whales, Dolphins and Porpoises, Mark Carwardine, ISBN 0-7513-2781-6
- Grampus griseus (TSN 180457). Integrated Taxonomic Information System.
- Risso's Dolphin Photograph, Jens Kuhfs Photography
- ^ American Cetacean Society Fact Sheet - Risso's Dolphin
[edit] External links
- Whale and Dolphin Conservation Society
- ARKive Photographs, video
