Risso's Dolphin
Encyclopedia
Risso's dolphin is the only species
of dolphin
in the genus
Grampus.
, 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.
, while the posterior tapers to a relatively narrow tail. The bulbous head has a vertical crease in front.
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 non-white 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 2-7 pairs of teeth, all in the lower jaw.
Length is typically 10 feet (3 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 kg (661.4–1,102.3 lb) making it the largest species called "dolphin".
, Pacific
and Atlantic Ocean
s, Rissos are also found in the Persian Gulf
, Mediterranean
and Red Sea
s, 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 400–1000 m (1,312.3–3,280.8 ft) and water temperature 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 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 exists.
, mostly nocturnally. Predation does not appear significant. Mass strandings are infrequent.
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 whale
s as well as ocean swells.
who 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, and the species is recognised as abundant and safe.
Risso's have successfully been taken into captivity in the United States
, Japan
and Italy
, although not with the regularity of bottlenose dolphin
s or orca
. Hybrid Risso's-bottlenose dolphins have been bred in captivity.
), 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).
's Goto Islands
has been associated with parasitic neuropathy of the VIIIth cranial nerve by a trematode in the genus Nasitrema.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of dolphin
Dolphin
Dolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in 17 genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating...
in the genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Grampus.
Taxonomy
Risso's dolphin is named after Antoine RissoAntoine Risso
Giuseppe Antonio Risso , called Antoine Risso, was a Niçard naturalist.Risso was born in Nice, County of Nice, a part of the Duchy of Savoy, and studied under Giovanni Battista Balbis. He published , and . Risso's dolphin was named after him...
, whose description formed the basis of the first public description of the animal, by Georges Cuvier
Georges Cuvier
Georges Chrétien Léopold Dagobert Cuvier or Jean Léopold Nicolas Frédéric Cuvier , known as Georges Cuvier, was a French naturalist and zoologist...
, 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
Orca
The killer whale , commonly referred to as the orca, and less commonly as the blackfish, is a toothed whale belonging to the oceanic dolphin family. Killer whales are found in all oceans, from the frigid Arctic and Antarctic regions to tropical seas...
. The etymology of the word grampus is unclear. It may be an agglomeration of the Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
grandis piscis or French
French language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
grand poisson both meaning big fish. The specific epithet griseus refers to the mottled (almost scarred) grey colour of its body.
Description
Risso's have a relatively large anterior body and dorsal finDorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
, while the posterior tapers to a relatively narrow tail. The bulbous head has a vertical crease in front.
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 non-white 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 2-7 pairs of teeth, all in the lower jaw.
Length is typically 10 feet (3 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 kg (661.4–1,102.3 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 than close to land. As well as the tropical parts of the IndianIndian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, Pacific
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
and Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
s, Rissos are also found in the Persian Gulf
Persian Gulf
The Persian Gulf, in Southwest Asia, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.The Persian Gulf was the focus of the 1980–1988 Iran-Iraq War, in which each side attacked the other's oil tankers...
, Mediterranean
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
and Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
s, but not the Black Sea
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
. They range as far north as the Gulf of Alaska
Gulf of Alaska
The Gulf of Alaska is an arm of the Pacific Ocean defined by the curve of the southern coast of Alaska, stretching from the Alaska Peninsula and Kodiak Island in the west to the Alexander Archipelago in the east, where Glacier Bay and the Inside Passage are found.The entire shoreline of the Gulf is...
and southern Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
and as far south as Tierra del Fuego
Tierra del Fuego
Tierra del Fuego is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of a main island Isla Grande de Tierra del Fuego divided between Chile and Argentina with an area of , and a group of smaller islands including Cape...
.
Their preferred environment is just off the continental shelf
Continental shelf
The continental shelf is the extended perimeter of each continent and associated coastal plain. Much of the shelf was exposed during glacial periods, but is now submerged under relatively shallow seas and gulfs, and was similarly submerged during other interglacial periods. The continental margin,...
on steep banks with water depths varying from 400–1000 m (1,312.3–3,280.8 ft) and water temperature at least 10 °C (50 °F) and preferably 15–20 °C (59–68 F).
The population around the continental shelf of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
is estimated 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 exists.
Ecology
They feed almost exclusively on neritic and oceanic squidSquid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
, mostly nocturnally. Predation does not appear significant. Mass strandings are infrequent.
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 whale
Gray Whale
The gray whale, Eschrichtius robustus, is a baleen whale that migrates between feeding and breeding grounds yearly. It reaches a length of about , a weight of , and lives 50–70 years. The common name of the whale comes from the gray patches and white mottling on its dark skin. Gray whales were...
s as well as ocean swells.
Reproduction
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.Human interaction
Risso's dolphins generally do not approach boats, but occasionally surf bow waves. A notable exception was an individual named Pelorus JackPelorus Jack
Pelorus Jack was a Risso's dolphin that was famous for meeting and escorting ships through a stretch of water in Cook Strait, New Zealand, between 1888 and 1912...
who accompanied boats in Admiralty Bay
Admiralty Bay, New Zealand
Admiralty Bay is a large indentation in the northern coast of New Zealand's South Island. It lies close to the northernmost mainland point of the Marlborough Sounds, immediately to the south of D'Urville Island....
in New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
's Marlborough Sounds
Marlborough Sounds
The Marlborough Sounds are an extensive network of sea-drowned valleys created by a combination of land subsidence and rising sea levels at the north of the South Island of New Zealand...
for more than 20 years. Hunting of this species has never been particularly widespread, and the species is recognised as abundant and safe.
Risso's have successfully been taken into captivity in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, although not with the regularity of bottlenose dolphin
Bottlenose Dolphin
Bottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin , instead of one...
s or orca
Orca
The killer whale , commonly referred to as the orca, and less commonly as the blackfish, is a toothed whale belonging to the oceanic dolphin family. Killer whales are found in all oceans, from the frigid Arctic and Antarctic regions to tropical seas...
. Hybrid Risso's-bottlenose dolphins have been bred in captivity.
Conservation
The Risso's dolphin populations of the North Sea, Baltic Sea and Mediterranean Sea are listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMSBonn Convention
The Convention on the Conservation of Migratory Species of Wild Animals aims to conserve terrestrial, marine and avian migratory species throughout their range...
), 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
ASCOBANS
ASCOBANS is a regional agreement on the protection of small cetaceans that was concluded as the “Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas” under the auspices of the UNEP Convention on Migratory Species, or Bonn Convention, in September 1991 and came into force...
), the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS
ACCOBAMS
ACCOBAMS, the Agreement on the Conservation of Cetaceans in the Black Sea,Mediterranean Sea and contiguous Atlantic area is ‘a cooperative tool for the conservation of marine biodiversity in the Mediterranean and Black Seas’....
), 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).
Strandings
At least one case report of strandings in JapanJapan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
's Goto Islands
Goto Islands
The are Japanese islands in the East China Sea, off the western coast of Kyūshū. The islands are a part of Nagasaki Prefecture.- Geography :There are 140 islands in total, including five main islands:,,,, and....
has been associated with parasitic neuropathy of the VIIIth cranial nerve by a trematode in the genus Nasitrema.
External links
- Risso's Dolphin Photos
- Whale and Dolphin Conservation Society
- ARKive Photographs, video
- Convention on Migratory Species page on the Risso's dolphin
- Official website of the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area
- Official webpage of the 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
- Official website of the Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas