|Size compared to an average human|
(G. Cuvier, 1812)
|Risso's dolphin range|
Risso's dolphin is named after Antoine Risso, whose description formed the basis of the first public description of the animal, by Georges Cuvier, in 1812. Another common name for the Risso's dolphin is grampus (also the species' genus), although this common name was more often used for the orca. The etymology of the word "grampus" is unclear. It may be an agglomeration 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 its body.
Infants are dorsally gray to brown and ventrally cream-colored, with a white anchor-shaped area between the pectorals and around the mouth. In older calves, the nonwhite areas darken to nearly black, and then lighten (except for the always dark dorsal fin). Linear scars mostly from social interaction eventually cover the bulk of the body. Older individuals appear mostly white. Most individuals have two to seven pairs of teeth, all in the lower jaw.
Length is typically 10 feet (3.0 m), although specimens may reach 14.1 feet (4.3 m). Like most dolphins, males are typically slightly larger than females. This species weighs 300–500 kilograms (660–1,100 lb), making it the largest species called "dolphin".
Range and habitat
They are found worldwide in temperate and tropical waters, usually in deep waters rather, but close to land. As well as the tropical parts of the Indian, Pacific and Atlantic Oceans, they are also found in the Persian Gulf and Mediterranean and Red Seas, but not the Black Sea. They range as far north as the Gulf of Alaska and southern Greenland and as far south as Tierra del Fuego.
Their preferred environment is just off the continental shelf on steep banks, with water depths varying from 400–1,000 m (1,300–3,300 ft) and water temperatures at least 10°C (50°F) and preferably 15-20°C (59-68°F).
The population around the continental shelf of the United States is estimated[by whom?] in excess of 60,000. In the Pacific, a census[which?] recorded 175,000 individuals in eastern tropical waters and 85,000 in the west. No global estimate exists.
These dolphins typically travel in groups of 10–51, but that may reach 400. Smaller, stable subgroups exist within larger groups. They also travel with other cetaceans. They harass and surf the bow waves of gray whales, as well as ocean swells.
Gestation requires an estimated 13–14 months, at intervals of 2.4 years. Calving reaches seasonal peaks in the winter in the eastern Pacific and in the summer and fall in the western Pacific. Females mature sexually at ages 8–10, and males at age 10–12. The oldest specimen reached 34.5 years.
Risso's dolphins generally do not approach boats, but occasionally surf bow waves. An exception, named Pelorus Jack, accompanied boats in Admiralty Bay in New Zealand's Marlborough Sounds for more than 20 years. Hunting of this species has never been particularly widespread, though complete pods are often netted and killed in Taiji, Japan.
Risso's dolphins have successfully been taken into captivity in the United States and Japan, although not with the regularity of bottlenose dolphins or orcas. Hybrid Risso's-bottlenose dolphins have been bred in captivity.
The Risso's dolphin populations of the North, Baltic, and Mediterranean Seas are listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMS), since they have an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.
In addition, Risso's dolphin is covered by the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS), the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS), the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU) and the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU).
Risso's dolphins are protected in the United States under the Marine Mammal Protection Act of 1992. The only country known to actively hunt Risso's dolphin is Japan. On November 20, 2013 - volunteer activists, Cove Guardians, live-streamed a slaughter of an entire pod of Risso's dolphins in Taiji, Japan. To this day, Japan continues to hunt them using the practice of slaughtering entire pods. In fact, the fishermen of Taiji, Japan captured a pod of 9 Risso's on February 4, 2014 and slaughtered all of them. One or two may have been taken into captivity the same day from the pod of 9, as skiffs were seen preparing slings to take some into captivity while the other pod members were killed in the shallows of the infamous 'Cove.' This is documented on the Sea Shepherd website.
- Mead, J. G.; Brownell, R. L., Jr. (2005). "Order Cetacea". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. pp. 723–743. ISBN 978-0-8018-8221-0. OCLC 62265494.
- Taylor, B.L., Baird, R., Barlow, J., Dawson, S.M., Ford, J., Mead, J.G., Notarbartolo di Sciara, G., Wade, P. & Pitman, R.L. (2008). Grampus griseus. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 7 October 2008.
- Baird, Robin W. (2009). Perrin, William F.; Wursig, Bernd; Thewissen, J. G. M., eds. Encyclopedia of Marine Mammals (2 ed.). Burlington Ma.: Academic Press. p. 975. ISBN 978-0-12-373553-9.
- "Grampus griseusRisso's dolphin". Animal Diversity Web. Retrieved February 2013.
- American Cetacean Society Fact Sheet – Risso's Dolphin
- Ball, F. Elrington History of Dublin (1917) Alexander Thom and Co Vol.5 p.49
- "Appendix II" of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As amended by the Conference of the Parties in 1985, 1988, 1991, 1994, 1997, 1999, 2002, 2005 and 2008. Effective: 5 March 2009.
- Convention on Migratory Species page on the Risso's dolphin
- Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas
- Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area
- Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region
- Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia
- See Morimitsu et al. 1992. J Wildl Dis 28:656–658
- 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