Animal Diversity Web

Ge­o­graphic Range

Gram­pus griseus has an ex­ten­sive dis­tri­b­u­tion. The species can be found in tem­per­ate, sub­trop­i­cal and trop­i­cal wa­ters of oceans world­wide. ("NOAA fish­eries", 2010; Amano and Miyazaki, 2004; Nuno, 2008; Pawloski, et al., 2003; Stew­art, et al., 2002)

• Biogeographic Regions
• indian ocean
• atlantic ocean
• pacific ocean
• mediterranean sea

• Other Geographic Terms
• cosmopolitan

Habi­tat

Risso's dol­phins are pelagic, but pre­fer habi­tat on steep slopes, rang­ing from 400 to 1,200 me­ters. They are often seen near the edges of con­ti­nen­tal shelves, or near ba­thy­met­ric fea­tures such as seamounts and sub­ma­rine canyons. They are most com­monly found in wa­ters rang­ing in tem­per­a­ture from 59 to 68 de­grees F, but will in­habit wa­ters cold as 50 de­grees F. ("NOAA fish­eries", 2010; Leather­wood, et al., 1980; Nuno, 2008; Pawloski, et al., 2003; Tay­lor, et al., 2010)

Risso’s dol­phins are pre­sent year round through­out most of their ge­o­graphic range. Res­i­dents of the north­ern-most parts of their range mi­grate sea­son­ally be­tween sum­mer­ing and win­ter­ing grounds For ex­am­ple, pop­u­la­tions off the coast of north­ern Scot­land dur­ing the sum­mer, mi­grate to the Mediter­ranean dur­ing the win­ter, and pop­u­la­tions off the coast of Cal­i­for­nia dur­ing the sum­mer, mi­grate to Mex­i­can wa­ters dur­ing win­ter. (Culik, 2010)

• Habitat Regions
• temperate
• tropical
• saltwater or marine

• Aquatic Biomes
• pelagic
• benthic
• coastal

• Range depth

  400 to 1,200 m

  1312.34 to ft

Phys­i­cal De­scrip­tion

Risso's dol­phins have blunt, squar­ish heads and lack the beak typ­i­cal of other del­phinids. The dor­sal fin is tall and fal­cate, and their flip­pers are long, pointed, and re­curved. The an­te­rior part of the body is very ro­bust, ta­per­ing to a nar­row tail­stock. Adults range from 2.6 to 4 m in length, with an av­er­age body mass around 400 kg. The sexes are sim­i­lar in size. New­borns range from 1.1 to 1.5 m in length and av­er­age 20 kg at birth. Along the body axis on the melon (i.e., beak, eyes, blow­hole) there is a slight con­cave groove which is a unique char­ac­ter­is­tic of this species. Sex­ual di­mor­phism has not been re­ported in this species. ("NOAA fish­eries", 2010; Jef­fer­son, et al., 1993; Pawloski, et al., 2003; Stew­art, et al., 2002)

The youngest calves range in colour from iri­des­cent gun­metal grey to fawn-brown dor­sally and are creamy-white ven­trally. Pale ochre-yel­low high­lights ac­cen­tu­ate the muz­zle. A white an­chor-shape patch be­tween the flip­pers re­sem­bles the chest chevron seen on pilot whales but is typ­i­cally brighter and more ex­ten­sive. Calves be­come sil­ver-grey, then darken to nearly black, re­tain­ing the ven­tral patches of white. As an­i­mals age fur­ther, their heads, ab­domens, and flanks lighten. (Nishi­waki 1972, Kruse et al. 1999, MMSC 1996, ("NOAA fish­eries", 2010; Jef­fer­son, et al., 1993; Stew­art, et al., 2002)

This species dis­plays highly vari­able col­oration. The youngest calves range in colour from iri­des­cent gun­metal grey to fawn-brown dor­sally and are creamy-white ven­trally. Pale ochre-yel­low high­lights ac­cen­tu­ate the muz­zle. A white an­chor-shape patch be­tween the flip­pers re­sem­bles the chest chevron seen on pilot whales but is typ­i­cally brighter and more ex­ten­sive. Calves be­come sil­ver-grey, then darken to nearly black, re­tain­ing the ven­tral patches of white. In older an­i­mals, lip colour fre­quently con­trasts with the sur­round­ing back­ground. Col­oration fades with age, and some adults ap­pear al­most com­pletely white due to the lin­ear scar­ring that ac­cu­mu­lates on in­di­vid­u­als over time. These dis­tinc­tive scars ac­cu­mu­late pri­mar­ily on the an­i­mals' dor­sal and lat­eral sur­faces and have been hy­poth­e­sized to re­sult from the com­bined ef­fects of lack of repig­men­ta­tion of dam­aged tis­sue and a slower heal­ing process than that ob­served in an­i­mals such as bot­tlenose dol­phins. Scar­i­fi­ca­tion can be caused by other Risso's dol­phins, preda­tors (e.g., cookie cut­ter sharks), prey, or by par­a­sites like sea lam­prey. In­traspe­cific, tooth rake, scars tend to be long and par­al­lel and may act as an in­di­ca­tor of male fit­ness dur­ing ag­gres­sive so­cial in­ter­ac­tions. ("NOAA fish­eries", 2010; Hart­man, et al., 2008; Jef­fer­son, et al., 1993; MacLeod, 1998)

Risso's dol­phins lack teeth in their upper jaws, but have 2 to 7 pairs of sharp peg-like teeth in their lower jaw, which are spe­cial­ized for cap­tur­ing prey, fight­ing preda­tors, and com­pet­ing with con­spe­cific for mates and re­sources. Evo­lu­tion­ary re­ten­tion of these teeth may be partly due to their sig­nif­i­cance in male-male in­ter­ac­tions. ("NOAA fish­eries", 2010; Jef­fer­son, et al., 1993; MacLeod, 1998; Stew­art, et al., 2002)

Risso's dol­phins may be con­fused with bot­tlenose dol­phins, false killer whales, and killer whales due to the shape and size of their dor­sal fin. How­ever, their blunt heads and ex­ten­sive scar­ring make them un­mis­tak­able. ("NOAA fish­eries", 2010)

• Other Physical Features
• endothermic
• homoiothermic
• bilateral symmetry

• Sexual Dimorphism
• sexes alike

• Range mass

  300 to 500 kg

  660.79 to 1101.32 lb

• Range length

  2.6 to 5 m

  8.53 to 16.40 ft

• Average length

  2.8 m

  9.19 ft

Re­pro­duc­tion

There is no in­for­ma­tion re­gard the mat­ing sys­tem of Gram­pus griseus. How­ever, other Cetaceans tend to be ei­ther polyg­y­nous and polyan­drous. (Stew­art, et al., 2002)

There is lit­tle in­for­ma­tion avail­able re­gard­ing re­pro­duc­tive be­hav­ior in Gram­pus griseus. Most fe­males are sex­u­ally ma­ture by 8 to 10 years old, how­ever, size is often a bet­ter in­di­ca­tor of sex­ual ma­tu­rity than age in ma­rine cetaceans. Most males reach sex­u­ally ma­tu­rity at a length of 2.6 to 2.8 m. Ges­ta­tion lasts 13 to 14 months, and av­er­age mass of new­borns calves is 20 kg. Wean­ing is com­plete by 12 to 18 months after par­tu­ri­tion. Breed­ing and calv­ing occur year-round, but peak dur­ing sum­mer and win­ter in the north At­lantic and east­ern Pa­cific, re­spec­tively. ("NOAA fish­eries", 2010; Nuno, 2008)

• Key Reproductive Features
• year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual
• fertilization
• viviparous

• Breeding season

  Grampus griseus breeds year round, but peaks seasonally depending on hemisphere.

• Average number of offspring

  1

  AnAge

• Range gestation period

  13 to 14 months

• Range weaning age

  12 to 18 months

• Range age at sexual or reproductive maturity (female)

  8 to 10 years

Fe­male Risso's dol­phins are the pri­mary care givers to calves, and pa­ter­nal care, which is rare in other cetaceans, has not been doc­u­mented in this species. New­borns are pre­co­cial and begin swim­ming im­me­di­ately after birth. Mother-calf pods form, and young usu­ally do not leave the group until a few years be­fore sex­ual ma­tu­rity. Al­lo­parental care has been recorded amongst fe­males. Often, while a calve's mother is for­ag­ing for food, an­other fe­male pro­vides care. (Hart­man, et al., 2008)

• Parental Investment
• precocial
• female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female
• pre-weaning/fledging
  • provisioning
    • female
  • protecting
    • female
• post-independence association with parents

Lifes­pan/Longevity

On av­er­age Risso's dol­phins live at least 30 years. ("NOAA fish­eries", 2010)

• Average lifespan
  Status: wild

  30 years

• Average lifespan
  Status: wild

  20.0 years

  Max Planck Institute for Demographic Research

Be­hav­ior

Un­like most cetaceans, which tend to have ei­ther a fu­sion-fis­sion or ma­tri­lin­eally based so­cial sys­tem, Risso's dol­phins dis­play a strat­i­fied so­cial sys­tem. Clus­ters are formed based on age and sex class, with strongest as­so­ci­a­tions oc­cur­ring be­tween adult fe­males and adult males. Fe­male re­pro­duc­tive suc­cess is pos­i­tively in­flu­enced by the in­creased so­cial sup­port and for­ag­ing ben­e­fits of larger pods. For ex­am­ple, while a given fe­male is search­ing for food, she is able leave her calf in the care of other fe­males in the group. As a re­sult, fe­male pods tend to be much larger than those of males. Male for­ma­tions ex­pe­ri­ence a trade off in re­la­tion to size, as for­ag­ing ben­e­fits and habi­tat de­fense in­crease with pod size, but re­pro­duc­tive ben­e­fits de­crease due to in­creased com­pe­ti­tion for mates. Risso's dol­phins are very so­cial, and as many as 4,000 in­di­vid­u­als have been doc­u­mented in a sin­gle pod. Al­though es­ti­mates for the av­er­age pod size have var­ied over the years, re­cent stud­ies sug­gest a mean pod size of 3 to 12 in­di­vid­u­als. (Hart­man, et al., 2008; Kruse, et al., 1999; Nuno, 2008; Stew­art, et al., 2002)

Risso’s dol­phins spend 77% of their time trav­el­ing, 13% en­gaged in so­cial ac­tiv­ity, 5% feed­ing, and about 3.7% rest­ing. They feed at night, as that is when their pri­mary prey, cephalopods, travel to the ocean sur­face. Risso's dol­phins use a va­ri­ety of be­hav­iors to com­mu­ni­cate with con­specifics, such as chas­ing, bit­ing, aer­ial ac­ro­bat­ics, lob-tail­ing, and breach­ing. Males are often found ha­rass­ing other species, such as false killer whales and bot­tlenose dol­phins. Ag­gres­sive phys­i­cal con­tact has been doc­u­mented, such as flip­per slap­ping be­tween in­di­vid­u­als, stik­ing with flukes and dor­sal fins, and body blows (Kruse 1999, MMSC 1996). ("NOAA fish­eries", 2010; Hart­man, et al., 2008; Kruse, et al., 1999; Nuno, 2008; Stew­art, et al., 2002)

Risso’s dol­phins have been recorded as­so­ci­at­ing and form­ing groups with other cetaceans, in­clud­ing bot­tlenose dol­phins and Pa­cific white-sided dol­phins. Hy­brid off­spring be­tween bot­tlenose dol­phins and Risso’s dol­phins have been known to occur, both in cap­tiv­ity and in the wild. ("NOAA fish­eries", 2010; Kruse, et al., 1999)

• Key Behaviors
• natatorial
• diurnal
• nocturnal
• motile
• social

Home Range

There is no in­for­ma­tion re­gard­ing home-range size in Risso’s dol­phins.

Com­mu­ni­ca­tion and Per­cep­tion

Risso’s dol­phins use echolo­ca­tion to lo­cate, iden­tify, and de­ter­mine the dis­tance of var­i­ous ob­jects in their en­vi­ron­ment. One of the most well-known sounds of del­phinids are clicks. The clicks of Risso's dol­phins have a peak fre­quency of 65 kHz, 3-dB band­widths of 72 kHz, and du­ra­tions of 40 to 100 Ms, all of which are con­sis­tent with other del­phinids. Risso’s dol­phins are also able to emit sonar clicks in the water while the ma­jor­ity of their fore­head is above water, a char­ac­ter­is­tic unique to this species. In ad­di­tion to broad­band clicks, Risso's dol­phins make a num­ber of dif­fer­ent vo­cal­iza­tions, in­clud­ing barks, buzzes, grunts, chirps, whis­tles, and si­mul­ta­ne­ous whis­tle and pulse sounds. Whis­tle and burst-pulse vo­cal­iza­tions have not been re­ported in other cetaceans and are thought to be unique to this species. (Corkeron and Van Par­ijs, 2001; Pawloski, et al., 2003)

• Communication Channels
• visual
• acoustic

• Perception Channels
• visual
• tactile
• acoustic
• echolocation
• chemical

Food Habits

Risso's dol­phins are known to prey on a mix of ner­itic, oceanic, and oc­ca­sion­ally bot­tom dwelling or­gan­isms. Their diet con­sists of fish, krill, crus­taceans, and cephalopods. Their most im­por­tant prey item is the greater arg­onaut, which is also known as the paper nau­tilus. They often fol­low prey into shal­low wa­ters along the con­ti­nen­tal shelf, and pre­fer to feed be­tween 600 and 800 m below the sur­face of the sea. ("NOAA fish­eries", 2010; Jef­fer­son, et al., 1993; Kruse, et al., 1999; Raga, et al., 2006; Stew­art, et al., 2002)

• Primary Diet
• carnivore
  • molluscivore

• Animal Foods
• fish
• mollusks
• aquatic crustaceans

Pre­da­tion

There is no in­for­ma­tion avail­able re­gard­ing preda­tors spe­cific to Risso's dol­phin. (Stew­art, et al., 2002)

Ecosys­tem Roles

Risso's dol­phins con­sume large amounts of fish, krill, crus­taceans, and cephalopods and likely have a sig­nif­i­cant in­flu­ence on the abun­dance of these an­i­mals. Risso's dol­phins are one of many hosts for sea lam­prey, which is com­mon in shore­line habi­tat through­out north At­lantic. ("NOAA fish­eries", 2010; Stew­art, et al., 2002)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

In In­done­sia and the Caribbean, Risso’s dol­phins are hunted for their meat and oil. In Japan, they are taken pe­ri­od­i­cally for food and fer­til­izer. Small num­bers are some­times col­lected for live ex­hi­bi­tions. ("NOAA fish­eries", 2010; Kruse, et al., 1999)

• Positive Impacts
• food
• body parts are source of valuable material

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Risso’s dol­phins are some­times a by-catch in the U.S. tuna purse seine in­dus­try, and are taken oc­ca­sion­ally in coastal gill net and squid sein­ing in­dus­tries off the U.S. coast. They are some­times a con­sid­ered a nui­sance to fish­er­man. Risso’s dol­phins are high trophic level con­sumers. As a re­sult, their tis­sues ac­cu­mu­late pol­lu­tants that are preva­lent through­out their ge­o­graphic range, a process known as bioac­cu­mu­la­tion, and con­sum­ing the meat of this species could be harm­ful. (Stew­art, et al., 2002; Storelli and Macrot­ri­giano, 2000)

Con­ser­va­tion Sta­tus

Risso's dol­phins are abun­dant and have a broad ge­o­graphic range. As a re­sult, they are clas­si­fied as a species of "least con­cern" on the IUCN's Red List of Threat­ened Species. How­ever, be­cause lit­tle is known of cur­rent pop­u­la­tion trends, it is dif­fi­cult to es­ti­mate po­ten­tial con­ser­va­tion needs. Po­ten­tial threats in­clude di­rect killings for meat and oil in the In­dian Ocean, and by-catch in the north At­lantic, the Mediter­ranean Sea, the south­ern Caribbean, the Azores, Peru, and the Solomon Is­lands. Be­cause this species re­lies on echolo­ca­tion to hunt, it is also thought that an­thro­pogenic sounds may in­flu­ence local pop­u­la­tions. Re­cent cli­mate change may also in­flu­ence their range and abun­dance, how­ever, po­ten­tial ef­fects are cur­rently un­clear. (Stew­art, et al., 2002)

• IUCN Red List

  Least Concern
  More information

• IUCN Red List

  Least Concern
  More information

• US Federal List

  No special status

Other Com­ments

The word "gram­pus" is Latin for "a kind of whale" and the word "griseus" is Latin for "gray". Pelorus Jack, a fa­mous Risso's dol­phin, had the habit of play­ing about ships and seemed to guide them into Pelorus Sound. It was ob­served for 24 years (around the turn of the cen­tury) es­cort­ing ships. (Kruse, et al., 1999)

Con­trib­u­tors

Kelsey Hans (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Phil Myers (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor, John Berini (ed­i­tor), An­i­mal Di­ver­sity Web Staff.

Ref­er­ences

2010. "NOAA fish­eries" (On-line). Of­fice of Pro­tected Re­sources. Ac­cessed March 12, 2011 at http://​www.​nmfs.​noaa.​gov/​pr/​species/​mammals/​cetaceans/​rissosdolphin.​htm.

Amano, M., N. Miyazaki. 2004. Com­po­si­tion of a school of Risso's dol­phins, Gram­pus griseus. Ma­rine and Fresh­wa­ter Bi­ol­ogy, Zo­ol­ogy, 20/1: 152-160.

Corkeron, P., S. Van Par­ijs. 2001. Vo­cal­iza­tions of eatern Aus­tail­ian Risso's dol­phins, Gram­pus griseus. Cana­dian Jour­nal of Zo­ol­ogy, 79/1: 160-164.

Culik, B. 2010. "Gram­pus griseus" (On-line). CMS (Con­ven­tion on Mi­gra­tory Spe­ices). Ac­cessed April 16, 2011 at http://​www.​cms.​int/​reports/​small_​cetaceans/​data/​g_​griseus/​g_​griseus.​htm.

Gas­pari, S., S. Airoldi, A. Hoelzel. 2007. Risso's dol­phins (Gram­pus griseus) in UK wa­ters are dif­fer­en­ti­ated from a pop­u­la­tion inte Mediter­ranean Sea and ge­net­i­cally less divers. Con­ser­va­tion Ge­net­ics, 8: 727-732.

Hart­man, K., F. Visser, A. Hen­driks. 2008. So­cial struc­ture of Risso's dol­phin (Gram­pus Griseus) at the Azores: a strat­i­fied com­mu­nity based on highly as­so­ci­ated so­cial units. Cana­dian Jour­nal of Zo­ol­ogy, 86/4: 294-306.

Jef­fer­son, T., S. Leather­wood, M. Web­ber. 1993. Ma­rine Mam­mals of the World. Rome: United Na­tions En­vi­ron­ment Pro­gramme. Ac­cessed March 31, 2011 at http://​books.​google.​com/​books?​id=W4Cbz0WphN0C&​printsec=frontcover&​cd=1&​source=gbs_​ViewAPI#​v=onepage&​q&​f=false.

Jef­fer­son, T., M. Web­ber, R. Pit­man. 2008. Ma­rine Mam­mals of the World, A Com­pre­hen­sive Guide to their Iden­ti­fi­ca­tion. San Diego, Cal­i­for­nia: El­se­vier. Ac­cessed March 12, 2011 at http://​books.​google.​com/​books?​id=TwFUimDtz7sC&​printsec=frontcover&​dq=Jefferson+Marine+mammals+of+the+world&​source=bl&​ots=B_​gBRRyj9B&​sig=KkGU24VxRGp6-Nzwapy63vJfXEs&​hl=en&​ei=Xmp-TabEIcLlrAHXnIXVBQ&​sa=X&​oi=book_​result&​ct=result&​resnum=3&​ved=0CCkQ6AEwAg#​v=onepage&​q&​f=false.

Kruse, S., D. Cald­well, M. Cald­well. 1999. Risso's Dol­phin. Pp. 183-212 in S Ridg­way, R Har­ri­son, eds. Hand­book of Ma­rine Mam­mals, Vol 6. Lon­don: Aca­d­e­mic Press.

Leather­wood, S., W. Per­rin, V. Kirby, C. Hubb, M. Dahlheim. 1980. Dis­tri­b­u­tion and move­ments of Risso's dol­phin, Gram­pus griseus, in the east­ern north Pa­cific. Fish­ery Bul­letin, 77/4: 951-963.

MacLeod, C. 1998. In­trasp­cific scar­ring in odon­to­cete cetaceans: and in­di­ca­tor of male 'qual­ity' in agres­sive so­cial in­ter­ac­tions?. Jour­nal of Zo­ol­ogy, 244: 71-77.

Mooney, T., P. Nachti­gall, M. Yuen. 2006. Tem­po­ral res­o­lu­tion of the Risso's dol­phin, Gram­pus griseus, au­di­tory sys­tem. Jour­nal of Com­par­a­tive Phys­i­o­log­i­cal Anatomy, 192: 373-380.

Nuno, J. 2008. Field Notes on the Risso's Dol­phin (Gram­pus Griseus) Dis­tri­b­u­tion, So­cial Ecol­ogy, Be­haious, and Oc­curence in the Azores. Aquatic Mam­mals, 34/4: 426.

Pawloski, J., P. Nachti­gall, W. Au, J. Philips, H. Roit­blat. 2003. Echolo­ca­tion in Risso's dol­phin, Gram­pus griseus. The Jour­nal of the Acousti­cal So­ci­ety of Amer­ica, 113/1: 605-616.

Raga, J., M. Rad­uan, C. Blanco. 2006. Diet of Risso's dol­phin (Gram­pus Griseus) in the west­ern Mediter­ranean Sea. Sci­en­tia Ma­rina, 70/3: 407-411.

Stew­art, B., P. Clapham, J. Pow­ell, R. Reeves. 2002. Na­tional Au­dobon's Guide to Ma­rine Mam­mals of the World. New York: Al­fred A. Knopf.

Storelli, M., G. Macrot­ri­giano. 2000. Per­sis­tent Or­ganchlo­rine Residues in Risso's Dol­phins (Gram­pus griseus) from the Mediter­ranean Sea. Ma­rine Pol­lu­tion Bul­letin, 40/6: 555-558.

Tay­lor, B., R. Baird, J. Bar­low, S. Daw­son, J. Ford, J. Mead, G. No­tar­bar­tolo di Sciara, P. Wade, R. Pit­man. 2010. "Gram­pus griseus" (On-line).

The IUCN Red List of Threat­ened Species

Wur­sig, B., J. Thewis­sen. 2009. En­cy­clo­pe­dia of Ma­rine Mam­mals. Lon­don: Aca­d­e­mic.