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Risso's dolphin (''Grampus griseus'') is a
dolphin A dolphin is an aquatic mammal within the infraorder Cetacea. Dolphin species belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontoporiidae (the ...
, the only
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of the
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''Grampus''. Some of the closest related species to these dolphins include:
pilot whale Pilot whales are cetaceans belonging to the genus ''Globicephala''. The two extant species are the long-finned pilot whale (''G. melas'') and the short-finned pilot whale (''G. macrorhynchus''). The two are not readily distinguishable at sea, ...
s (''Globicephala'' spp.),
pygmy killer whale The pygmy killer whale (''Feresa attenuata'') is a poorly known and rarely seen oceanic dolphin. It is the only species in the genus ''Feresa''. It derives its common name from sharing some physical characteristics with the orca also known as t ...
s (''Feresa attenuata''),
melon-headed whale The melon-headed whale (''Peponocephala electra''), also known less commonly as the electra dolphin, little killer whale, or many-toothed blackfish, is a toothed whale of the oceanic dolphin family (Delphinidae). The common name is derived fro ...
s (''Peponocephala electra''), and
false killer whale The false killer whale (''Pseudorca crassidens'') is a species of oceanic dolphin that is the only extant representative of the genus '' Pseudorca''. It is found in oceans worldwide but mainly in tropical regions. It was first described in 184 ...
s (''Pseudorca crassidens'').


Taxonomy

Risso's dolphin is named after
Antoine Risso Giuseppe Antonio Risso (8 April 1777 – 25 August 1845), called Antoine Risso, was a Niçard and natural history, naturalist. Risso was born in the city of Nice in the Duchy of Savoy, and studied under Giovanni Battista Balbis. He published ' (1 ...
, whose study of the animal formed the basis of the recognised description by
Georges Cuvier Jean Léopold Nicolas Frédéric, Baron Cuvier (; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French natural history, naturalist and zoology, zoologist, sometimes referred to as the "founding father of paleontology". Cuvier ...
in 1812. The holotype referred to specimen at the
Muséum National d'Histoire Naturelle The French National Museum of Natural History, known in French as the ' (abbreviation MNHN), is the national natural history museum of France and a ' of higher education part of Sorbonne Universities. The main museum, with four galleries, is loc ...
, an exhibit using preserved skin and skull obtained at
Brest, France Brest (; ) is a port city in the Finistère department, Brittany. Located in a sheltered bay not far from the western tip of the peninsula, and the western extremity of metropolitan France, Brest is an important harbour and the second French mi ...
. The type and sole species of the genus ''Grampus'' refers to ''Delphinus griseus'' Cuvier 1812. A proposition to name this genus ''Grampidelphis'' in 1933, when the taxonomic status of 'blackfish' was uncertain, and conserving the extensive use of "''Grampus''" for the 'killer' ''Orcinus orca''", also suggested renaming this species (''Grampidelphis exilis'' Iredale, T. & Troughton, E. le G. 1933). These were recognised as synonyms after publication of the ''Catalog of Whales'' (Hershkovitz, 1966). 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 orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus '' Orcinus'' and is recognizable by its black-and-white ...
. The etymology of the word "grampus" is unclear. It may be an agglomeration of the
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
''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.


Description

Risso's dolphin has a relatively large anterior body and
dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...
, while the posterior tapers to a relatively narrow tail. The bulbous shape of the head has a vertical crease in front. Infants are dorsally grey 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; scarring is a common feature of male to male competition in toothed whales, but Risso's dolphin tend to be unusually heavily scarred. The pronounced appearance of these scars results from the lack of repigmentation, which may be advantageous as a display that reduces further challenges from other males. Older individuals appear mostly white. Most individuals have two to seven pairs of teeth, all in the lower jaw. Length is typically , although specimens may reach . Like most dolphins, males are typically slightly larger than females. This species weighs , making it the largest species called "dolphin".American Cetacean Society Fact Sheet 
Risso's Dolphin


Range and habitat

Risso's dolphins are found worldwide in temperate and tropical waters, in the
Indian Indian or Indians may refer to: Peoples South Asia * Indian people, people of Indian nationality, or people who have an Indian ancestor ** Non-resident Indian, a citizen of India who has temporarily emigrated to another country * South Asia ...
,
Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
and Atlantic Oceans, also the
Persian Gulf The Persian Gulf ( fa, خلیج فارس, translit=xalij-e fârs, lit=Gulf of Persis, Fars, ), sometimes called the ( ar, اَلْخَلِيْجُ ٱلْعَرَبِيُّ, Al-Khalīj al-ˁArabī), is a Mediterranean sea (oceanography), me ...
,
Mediterranean The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the e ...
and
Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...
s, but not the
Black Sea The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Roma ...
(a stranding was recorded in the
Sea of Marmara The Sea of Marmara,; grc, Προποντίς, Προποντίδα, Propontís, Propontída also known as the Marmara Sea, is an inland sea located entirely within the borders of Turkey. It connects the Black Sea to the Aegean Sea via the ...
in 2012). They range as far north as the
Gulf of Alaska The Gulf of Alaska (Tlingit: ''Yéil T'ooch’'') 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, ...
and southern Greenland and as far south as
Tierra del Fuego Tierra del Fuego (, ; Spanish for "Land of the Fire", rarely also Fireland in English) is an archipelago off the southernmost tip of the South American mainland, across the Strait of Magellan. The archipelago consists of the main island, Isla ...
. Their preferred environment is just off the
continental shelf A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...
on steep banks, with water depths varying from and water temperatures at least and preferably . They are recorded diving to depths of 600 metres in pursuit of prey.Visser Fleur, Keller Onno A., Oudejans Machiel G., Nowacek Douglas P., Kok Annebelle C. M., Huisman Jef and Sterck Elisabeth H. M. 202
Risso's dolphins perform spin dives to target deep-dwelling prey
R. Soc. open sci.8:202320
The population around the continental shelf of the United States is estimated 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 exists.


Ecology

They feed almost exclusively on
neritic The neritic zone (or sublittoral zone) is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth. From the point of view of marine biology it forms a relatively stable and well-illuminate ...
and oceanic
squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
, mostly nocturnally. Predation does not appear significant. Mass strandings are infrequent. Analysis carried out on the stomach contents of stranded specimens in Scotland showed that the most important species preyed on in Scottish waters is the curled octopus (''Eledone cirrhosa''). A population is found off Santa Catalina Island where they are
sympatric In biology, two related species or populations are considered sympatric when they exist in the same geographic area and thus frequently encounter one another. An initially interbreeding population that splits into two or more distinct species sh ...
with
short-finned pilot whale The short-finned pilot whale (''Globicephala macrorhynchus'') is one of the two species of cetaceans in the genus '' Globicephala'', which it shares with the long-finned pilot whale (''G. melas''). It is part of the oceanic dolphin family (Del ...
s (''Globicephala macrorhynchus'') and both species feed on the squid population. Although these species have not been seen to interact with each other, they take advantage of the commercial squid fishing that takes place at night. They have been seen by fishermen to feed around their boats. They also travel with other cetaceans. They surf the
bow wave A bow wave is the wave that forms at the bow of a ship when it moves through the water. As the bow wave spreads out, it defines the outer limits of a ship's wake. A large bow wave slows the ship down, is a risk to smaller boats, and in a harbor ...
s of gray whales, as well as ocean swells. Risso's dolphins have a stratified social organisation. These dolphins typically travel in groups of between 10 and 51, but can sometimes form "super-pods" reaching up to a few thousand individuals. Smaller, stable subgroups exist within larger groups. These groups tend to be similar in age or sex. Risso's experience fidelity towards their groups. Long-term bonds are seen to correlate with adult males. Younger individuals experience less fidelity and can leave and join groups. Mothers show a high fidelity towards a group of mother and calves, but it is unclear whether or not these females stay together after their calves leave or remain in their natal pods.


Behavior


Feeding

Like many dolphin species, they use echolocation to target cephalapods and fish that are feeding below. Tagging of a population in the Azores revealed that ''Grampus griseus'' plan whether to make a shallow or deep dive, with different strategies that create profitable foraging for the considerable expenditure in time and energy. Risso's can achieve depths over 600 metres by exhausting their lungs and using several spins to rapidly descend, almost vertically, and increase the time spent foraging. This allows the species to exploit a deep and dispersed layer of prey such as squid, those taking refuge during daylight when they become more vulnerable to predation.


Social behavior

Risso's dolphins do not require cutting teeth to process their cephalopod prey, which has allowed the species to evolve teeth as display weapons in mating conflicts.


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 39.6 years. Risso's dolphins have successfully been taken into captivity in Japan and the United States, although not with the regularity of
bottlenose dolphin Bottlenose dolphins are aquatic mammals in the genus ''Tursiops.'' They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus definitively contains two species: the common ...
s or
orcas The orca or killer whale (''Orcinus orca'') is a toothed whale belonging to the oceanic dolphin family, of which it is the largest member. It is the only extant species in the genus ''Orcinus'' and is recognizable by its black-and-white pat ...
.
Hybrid Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two dif ...
Risso's-bottlenose dolphins have been bred in captivity.


Human interactions

Like other dolphins and marine animals, there have been documentations of these dolphins getting caught in seine-nets and
gillnets Gillnetting is a fishing method that uses gillnets: vertical panels of netting that hang from a line with regularly spaced floaters that hold the line on the surface of the water. The floats are sometimes called "corks" and the line with corks is ...
across the globe. Many of these incidents have resulted in death. Small
whaling Whaling is the process of hunting of whales for their usable products such as meat and blubber, which can be turned into a type of oil that became increasingly important in the Industrial Revolution. It was practiced as an organized industry ...
operations have also been cause of some of these deaths. Pollution has also affected many individuals who have ingested plastic. Samples from these animals shows contamination within their tissue. In
Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
, though not apparently in
England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
, Risso's Dolphin was one of the
royal fish Under the law of the United Kingdom, whales (mammal) and sturgeons are royal fish, and when taken become the personal property of the monarch of the United Kingdom as part of his or her royal prerogative. In England and Wales According to Willia ...
which by virtue of the royal prerogative were the exclusive property of the English Crown. A famed individual named
Pelorus Jack Pelorus Jack (fl. 1888 – April 1912) was a Risso's dolphin (''Grampus griseus'') that was famous for meeting and escorting ships through a stretch of water in Cook Strait, New Zealand. The animal was reported over a 24 year period, from ...
was widely reported between 1888 and 1912, travelling with ships navigating the
Cook Strait Cook Strait ( mi, Te Moana-o-Raukawa) separates the North and South Islands of New Zealand. The strait connects the Tasman Sea on the northwest with the South Pacific Ocean on the southeast. It is wide at its narrowest point,McLintock, A H, ...
in New Zealand. A law protecting the animal was passed after a public outcry, renewed twice more, but suggested be invalid by its reference to Fisheries acts that did not concern marine mammals.


Conservation

The Risso's dolphin populations of the North, Baltic, and Mediterranean Seas are listed on Appendix IIAppendix 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.
of the Convention on the Conservation of Migratory Species of Wild Animals (
CMS CMS may refer to: Computing * Call management system * CMS-2 (programming language), used by the United States Navy * Code Morphing Software, a technology used by Transmeta * Collection management system for a museum collection * Color manag ...
), 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 Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas, often abbreviated to ASCOBANS, is a regional agreement on the protection of small cetaceans that was concluded as the Agreement on the Con ...
), 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. Currently, Japan, Indonesia, the Solomon Islands, and The Lesser Antilles hunt Risso's dolphins.


Strandings

At least one case report of strandings in Japan's
Goto Islands GoTo (goto, GOTO, GO TO or other case combinations, depending on the programming language) is a statement found in many computer programming languages. It performs a one-way transfer of control to another line of code; in contrast a function ca ...
has been associated with
parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
neuropathy Peripheral neuropathy, often shortened to neuropathy, is a general term describing disease affecting the peripheral nerves, meaning nerves beyond the brain and spinal cord. Damage to peripheral nerves may impair sensation, movement, gland, or o ...
of the eighth
cranial nerve Cranial nerves are the nerves that emerge directly from the brain (including the brainstem), of which there are conventionally considered twelve pairs. Cranial nerves relay information between the brain and parts of the body, primarily to and ...
by a
trematode Trematoda is a class of flatworms known as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is usually a snail. The definitive host ...
in the genus ''Nasitrema''. There was a recent reporting of a juvenile male Risso's dolphin that was stranded alive on the coast of Gran Canaria on 26 April 2019. This was the first documented case of capture myopathy and stress cardiomyopathy in a male juvenile Risso's dolphin that has received rehabilitation.


References


Further reading

*''National Audubon Society Guide to Marine Mammals of the World'' *''Encyclopedia of Marine Mammals'' *''Whales, Dolphins and Porpoises'', Mark Carwardine,


External links


Whale and Dolphin Conservation SocietyARKive
Photographs, video

* {{Taxonbar, from=Q203897
Risso's dolphin Risso's dolphin (''Grampus griseus'') is a dolphin, the only species of the genus ''Grampus''. Some of the closest related species to these dolphins include: pilot whales (''Globicephala'' spp.), pygmy killer whales (''Feresa attenuata''), melon ...
Cosmopolitan mammals
Risso's dolphin Risso's dolphin (''Grampus griseus'') is a dolphin, the only species of the genus ''Grampus''. Some of the closest related species to these dolphins include: pilot whales (''Globicephala'' spp.), pygmy killer whales (''Feresa attenuata''), melon ...
Risso's dolphin Risso's dolphin (''Grampus griseus'') is a dolphin, the only species of the genus ''Grampus''. Some of the closest related species to these dolphins include: pilot whales (''Globicephala'' spp.), pygmy killer whales (''Feresa attenuata''), melon ...