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Risso's dolphin

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Risso's dolphin[1]
Size compared to an average human
CITESAppendix II(CITES)[3]
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Delphinidae
Genus: Grampus
Gray,1828[4]
Species:
G. griseus
Binomial name
Grampus griseus
(G. Cuvier,1812)
Distribution of Risso's dolphin

Risso's dolphin(Grampus griseus) is adolphin,the onlyspeciesof thegenusGrampus.Some of the closest related species to these dolphins include:pilot whales(Globicephalaspp.),pygmy killer whales(Feresa attenuata),melon-headed whales(Peponocephala electra), andfalse killer whales(Pseudorca crassidens).[5]

Taxonomy

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Risso's dolphin is named afterAntoine Risso,whose study of the animal formed the basis of the recognized description byGeorges Cuvierin 1812.[6]The holotype referred to specimen at theMuséum National d'Histoire Naturelle,an exhibit using preserved skin and skull obtained atBrest, France.[7]

The type and sole species of the genusGrampusrefers toDelphinus griseusCuvier 1812. A proposition to name this genusGrampidelphisin 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 exilisIredale, T. & Troughton, E. le G. 1933).[8]These were recognised as synonyms after publication of theCatalog of Whales(Hershkovitz, 1966).[7]

Another common name for the Risso's dolphin is grampus (also the species' genus), although this common name was more often used for theorca.The etymology of the word "grampus" is unclear. It may be an agglomeration of theLatingrandis piscisor Frenchgrand poisson,both meaning big fish. The specific epithetgriseusrefers to the mottled (almost scarred) grey colour of its body.

Description

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Illustrations byEdward Drinker Copein 1876
3d model of skeleton

Risso's dolphin has a relatively large anterior body anddorsal fin,while the posterior tapers to a relatively narrow tail. The bulbous shape of the head has a vertical crease in front.[9]

A calf bears no scars, in contrast to its mother behind it.

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.[10]Older individuals appear mostly white. Most individuals have two to seven pairs of teeth, all in the lower jaw.[9]

The scar patterns are so pronounced and persistent in this species that they can be used to distinguish individuals over a lifetime.

Length is typically 10 feet (3.0 m), although specimens may reach 13 feet (4.0 m).[11]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".[12][13]

Range and habitat

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A Risso's dolphin swims offMorro Bay.
A Risso's dolphin in the Gulf of Genoa

Risso's dolphins are found nearly worldwide, from cold and temperate to tropical waters, in theIndian,PacificandAtlantic Oceans,as well as parts of theBaltic Sea,thePersian Gulfand theMediterranean,NorthandRed Seas(excepting theBlack Sea;however, a rare stranding was recorded in theSea of Marmarain 2012).[14]). There have been several documented sightings inRoskilde Fjord,in the waters of Lejre Vig, just off of the coast of Skjoldungernes Land National Park,Denmark.

In the Pacific, they range fromFrench Polynesiawest toSamoa,north to theHawaiian Islands,as far as theGulf of Alaska.However, they are absent from the waters of the western Pacific (off of Asia) beyondFutuna.They are quite common along the western coasts ofBritish Columbia,theUnited StatesandMexico,continuing their range to the southern tip ofTierra Del Fuego.In the eastern Atlantic, they have been sighted as far south as the offshore waters ofLiberia,GuineaandWestern Africanorth through theCanary Islandsand theAzoresto southernGreenland.On the western Atlantic side, Risso’s dolphins have been seen as far south asGuyanaandMartinique;they can be found throughout much of theCaribbean Seaand theGulf of MexicotoFloridaand theBahamas,and all along the AmericanEastern Seaboardand the CanadianMaritime Provinces.[9]

Their preferred environment is just off thecontinental 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).[9]They have been recorded diving to depths of up to 600 m (2,000 ft) in pursuit of prey.[15]

The population around the continental shelf of the US is estimated[by whom?]to be 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.

Since at least 2017, Risso's dolphins have begun to appear off of the subarctic Norwegian coast,as far north as Bleik's Canyon,off ofAndøya.The repeated, regular sightings imply an expansion of their natural range. Possible explanations for this movement are a changing climate or varying water currents, as well as a northward migration of prey species or competition with other cetaceans, such aspilot whales.

Ecology

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Risso's dolphin off Port San Luis, Harford Pier, atAvila Beach, California

They feed almost exclusively onneriticand oceanicsquid,mostly nocturnally. Predation does not appear significant. Massstrandingsare infrequent.[9]Analysis carried out on the stomach contents of stranded specimens in Scotland showed that the most important species preyed on in Scottish waters is thecurled octopus(Eledone cirrhosa).[16]

A population is found offSanta Catalina Islandwhere they aresympatricwithshort-finned pilot whales(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.[17]They also travel with other cetaceans. They surf thebow wavesofgray whales,as well as ocean swells.[9]

Risso's dolphins have a stratified social organisation.[18]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.[19]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,[18]but it is unclear whether or not these females stay together after their calves leave or remain in their natal pods.

Behavior

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Natural Resources Waleswork on the conservation of Risso's dolphins aroundBardsey Island,Wales

Feeding

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Like many dolphin species, they use echolocation to target cephalapods and fish that are feeding below. Tagging of a population in the Azores revealed thatGrampus griseusplan 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 m (2,000 ft) 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.[15]

Social behavior

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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.[10]

Reproduction

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See also:Dolphin § Reproduction and sexuality

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.[9]

Risso's dolphins have successfully been taken into captivity in Japan and the United States, although not with the regularity ofbottlenose dolphinsororcas.HybridRisso's-bottlenose dolphins have been bred in captivity.[citation needed]

Human interactions

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Like other dolphins and marine animals, there have been documentations of these dolphins getting caught inseine-netsandgillnetsacross the globe.[5]Many of these incidents have resulted in death.[19]Smallwhalingoperations 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.[5]

InIreland,though not apparently inEngland,Risso's Dolphin was one of theroyal fishwhich by virtue of the royal prerogative were the exclusive property of theEnglish Crown.[20]

A famed individual namedPelorus Jackwas widely reported between 1888 and 1912, travelling with ships navigating theCook Straitin 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.[21]

Conservation

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The Risso's dolphin populations of the North, Baltic, and Mediterranean Seas are listed on Appendix II[22]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.[23]

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),[24]the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS),[25]the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU)[26]and the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia (Western African Aquatic Mammals MoU).[27]

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.[19]

Strandings

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At least one case report of strandings in Japan'sGoto Islandshas been associated withparasiticneuropathyof the eighthcranial nerveby atrematodein the genusNasitrema.[28]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.[29]

References

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  1. ^Mead, J. G.; Brownell, R. L. Jr. (2005)."Order Cetacea".InWilson, D. E.;Reeder, D. M. (eds.).Mammal Species of the World: A Taxonomic and Geographic Reference(3rd ed.). Johns Hopkins University Press. pp. 723–743.ISBN978-0-8018-8221-0.OCLC62265494.
  2. ^Kiszka, J.; Braulik, G. (2018)."Grampus griseus".IUCN Red List of Threatened Species.2018:e.T9461A50356660.doi:10.2305/IUCN.UK.2018-2.RLTS.T9461A50356660.en.Retrieved19 November2021.
  3. ^"Appendices | CITES".cites.org.Retrieved14 January2022.
  4. ^William Perrin (2014). Perrin WF (ed.)."GrampusGray, 1828 ".World Cetacea Database.World Register of Marine Species.Retrieved16 March2015.
  5. ^abcBaird, Robin (2008).Encyclopedia of Marine Mammale 2nd edition.Academic Press. pp. 975–976.ISBN9780123735539.
  6. ^Cuvier, L.C.F.D. (1812)."Rapport sur divers cétacés pris sur les côtes de France".Annales du Muséum National d'Histoire Naturelle. Paris.19:1–16 [13].Delphinus griseus Cuvier, 1812.
  7. ^abHershkovitz, P. (1966)."Catalog of living whales".Bulletin of the United States National Museum(246): viii 1–259.doi:10.5479/si.03629236.246.
  8. ^Iredale, Tom; Troughton, Ellis Le G. (1933)."The correct generic names for the Grampus or Killer Whale, and the so called Grampus or Risso's Dolphin".Records of the Australian Museum.19(1): 28–36.doi:10.3853/j.0067-1975.19.1933.689.
  9. ^abcdefgBaird, Robin W. (2009). Perrin, William F.; Wursig, Bernd; Thewissen, J. G. M. (eds.).Encyclopedia of Marine Mammals(2nd ed.). Burlington Ma.: Academic Press. p. 975.ISBN978-0-12-373553-9.Archived fromthe originalon 9 November 2009.
  10. ^abMacLeod, Colin D. (January 1998). "Intraspecific scarring in odontocete cetaceans: an indicator of male 'quality' in aggressive social interactions?".Journal of Zoology.244(1): 71–77.doi:10.1111/j.1469-7998.1998.tb00008.x.ISSN0952-8369.
  11. ^"Grampus griseus – Risso's dolphin".Animal Diversity Web.
  12. ^American Cetacean Society Fact Sheet –Risso's DolphinArchived11 July 2007 at theWayback Machine
  13. ^Risso's Dolphin.Whale Web. Retrieved 22 September 2015.
  14. ^First stranding record of a Risso’s Dolphin (Grampus griseus) in the Marmara Sea, Turkey(pdf). Retrieved 6 September 2017
  15. ^abVisser Fleur, Keller Onno A., Oudejans Machiel G., Nowacek Douglas P., Kok Annebelle C. M., Huisman Jef and Sterck Elisabeth H. M. 2021Risso's dolphins perform spin dives to target deep-dwelling preyR. Soc. open sci.8:202320
  16. ^MacLeod, C.D.; Santos, M.B.; Pierce, G.J. (2014).Can habitat modelling for the octopusEledone cirrhosahelp identify key areas for Risso's dolphin in Scottish waters?(PDF)(Report). Scottish Natural Heritage Commissioned Report. Vol. 530. Scottish Natural Heritage. Archived fromthe original(PDF)on 24 December 2016.Retrieved24 December2016.
  17. ^Shane, Susan H. (1995)."Behavior patterns of pilot whales and Risso's dolphins off Santa Catalina Island, California"(PDF).Aquatic Mammals.21(3): 195–197 – via Aquatic Mammals Issue Archives.
  18. ^abHartman, K. L.; Visser, F.; Hendriks, A. J.E. (14 March 2008). "Social structure of Risso's dolphins (Grampus griseus) at the Azores: a stratified community based on highly associated social units".Canadian Journal of Zoology.86(4): 294–306.doi:10.1139/Z07-138.ISSN0008-4301.
  19. ^abc"Risso's dolphin, Open Waters, Marine mammals, Grampus griseus at the Monterey Bay Aquarium".montereybayaquarium.org.Retrieved27 April2018.
  20. ^Ball, F. Elrington (1917).History of Dublin.Vol. 5. Dublin: Alexander Thom and Co. p. 49.
  21. ^Hutching, Gerard (1 September 2015)."The story of Pelorus Jack".Te Ara – the Encyclopedia of New Zealand.Archivedfrom the original on 14 June 2020.Retrieved14 June2020.... Pelorus Jack....was so named because he would meet boats near the entrance to Pelorus Sound, in the Marlborough Sounds....'
  22. ^"Appendix IIArchived11 June 2011 at theWayback Machine"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.
  23. ^Convention on Migratory Species page on the Risso's dolphin.Cms.int (25 June 1998). Retrieved 22 September 2015.
  24. ^Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas.Ascobans.org. Retrieved 22 September 2015.
  25. ^Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area.Accobams.org. Retrieved 22 September 2015.
  26. ^Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region.Pacificcetaceans.org. Retrieved 22 September 2015.
  27. ^Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia.Cms.int. Retrieved 22 September 2015.
  28. ^Morimitsu, T; Kawano, H; Torihara, K; Kato, E; Koono, M (1992). "Histopathology of eighth cranial nerve of mass stranded dolphins at Goto Islands, Japan".Journal of Wildlife Diseases.28(4): 656–8.doi:10.7589/0090-3558-28.4.656.PMID1474668.
  29. ^Câmara, Nakita; Sierra, Eva; Fernández, Antonio; Arbelo, Manuel; Bernaldo de Quirós, Yara; Arregui, Marina; Consoli, Francesco; Herráez, Pedro (29 January 2020)."Capture Myopathy and Stress Cardiomyopathy in a Live-Stranded Risso's Dolphin (Grampus griseus) in Rehabilitation".Animals.10(2): 220.doi:10.3390/ani10020220.ISSN2076-2615.PMC7070958.PMID32013196.

Further reading

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