Grampus griseus

Risso's dolphins are often covered with scars. The older the dolphin, the more scratches on its body. These scars are probably caused by the teeth of other Risso's dolphins, made during fights or while playing. Squid can also leave scars, when they are caught and eaten by the animal.

"Much of what we know about Risso's dolphin, also called grampus, comes from studying stranded animals. They inhabit deep tropical and warm-temperate waters worldwide, usually where the water is deeper than 180 m, making them hard to study. The remains found in stomachs show they prey upon squid exclusively. Scars are often found on their skin, which may be the results of wounds produced by squid beaks and tentacles. Some researchers believe these marks may also reflect the highly physical ways these dolphins interact - by slapping, splashing, and leaping on one another. Risso's dolphin is highly social. Hundreds of them have been seen swimming on the surface, leaping clear of the water, and ""bow-riding"" on waves, sometimes with Pacific white-sided dolphins and northern right whale dolphins."

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Risso's dolphin feeds largely on squid, although other cephalopods are also taken, as well as fish and crustaceans (2). Like most dolphins, this species is a highly social animal, typically occurring in groups of between 3 to 50 individuals (2), and may mix with different species of cetaceans (whales and dolphins) (8). When groups are hunting they spread out into a long line (5). This species tends to ride alongside or in the wake of boats, and young individuals often breach (clear the water), slap their flippers on the surface of the water or 'spyhop' (lift their heads clear of the water) (5). A number of sounds are produced, including characteristic 'signature whistles' (6), many of these vocalisations are important in detecting prey through echolocation (8).

Risso's dolphin is a large, stocky species with a blunt head (2). They are easily recognised as they are heavily scared and become whiter with age as the number of scars increases (2). Calves are born with grey skin that turns chocolate brown as they age (5), eventually they take on the adult colouring of a grey back and white underside with darker flippers and tail (5). The scars are thought to be caused by the teeth of other Risso's dolphins, due to playing or fighting, however it is also thought that some of the scars are the result of squid bites (2). The tall, centrally positioned sickle-shaped dorsal fin is even taller and more erect in adult males than in females (7).

 Grampus griseus has a robust body up to 4 meters in length and weighs up to 600 kg. Males of the species are larger than females. Colouration varies individually and with age. Generally adults are medium to dark grey on the back, paler on the flanks with a marked border and a white anchor shaped patch on the belly. Dorsal fin, flippers and flukes are dark grey. This species has a large blunt head, no beak and a characteristic crease on its forehead from the blowhole to the upper 'lip'. The mouth line is straight and slants upwards slightly. There are 3-7 pairs of strong oval teeth at the tip of the lower jaw and, only occasionally are there one or two vestigial teeth on the upper jaw. Grampus griseus has a tall dorsal fin up to 60 cm high with a pointed or rounded tip. Its flippers are also pointed and up to 60 cm long. The pointed tail flukes have an expanse of up to 76 cm.Grampus griseus is one of the largest members of the Delphinidae family. 'Grampus' meaning 'grand fish', and 'griseus' referring to its grey colouration. At birth this species has a muted anchor shaped patch on its belly, and is uniformly gray becoming lighter with age. This is due to the extensive teeth scarring caused by Grampus griseus during play, aggression and sexual behaviour, as well as confrontations with cephalopod species (to a lesser degree) (Carwardine, 2000). The white colouration in older species may confuse it with Beluga whales (Delphinapterus leucas), however Risso's tall dorsal fin is the main distinguishing feature (Martin, 1990; Carwardine, 2000). Gestation is 13-14 months, and sexual maturity around 3-4 years for both sexes. Calves can be up to 1.7 meters long and weight approximately 20 kg. Grampus griseus dives for 1-2 minutes but can stay submerged for up to 30 minutes. It also takes a dozen breaths every 15-20 seconds, and seldom bow-rides. Full breaching occurs in the young and half breaching in adults (Carwardine, 2000). This species occurs in groups of about 12, and can aggregate into large of herds, up to 4000 individuals has been recorded. This species feeds on pelagic fish and cephalopods, favouring squid. Hybrids of Grampus griseus and Bottlenose dolphin, Tursiops truncatus, have also been reported in the wild (Kinze, 2002). 

This species is subject to by-catch, and is included in the UK Biodiversity Action Plan list of species of conservation concern (Biodiversity Steering Group, 1995). All species of cetaceans are given protection under the Wildlife and Countryside Act 1981 and the Wildlife (Northern Ireland) Order 1985. All cetacean species are listed on Annex A of EU Council Regulation 338/97 and therefore treated by the EU as if they are on CITES Appendix I therefore prohibiting their commercial trade. Risso's dolphin is also listed on Annex IV of the EC Habitats Directive, which prohibits all killing, capture, disturbance, sale, exchange or keeping of the animials. The directive requires that all accidental killing and capture be monitored by all member states. Also this species is listed under Appendix II of the Bonn Convention (North and Baltic Sea populations), and Appendix II of the Bern Convention. The Bonn Convention is the parent Convention to the 'Agreement on the Conservation of Small Cetaceans in the Baltic and the North Seas' (ASCOBANS) formulated in 1992. The UK is one of seven European countries which have signed the agreement which includes the protection of specific areas, monitoring, research, information exchange, pollution control and heightened public awareness. Measures included are specifically aimed at protecting dolphins and porpoises in the North Baltic Seas (Anon, 1999e).

Grampus griseus has an extensive distribution. The species can be found in temperate, subtropical and tropical waters of oceans worldwide.

Biogeographic Regions: indian ocean; atlantic ocean ; pacific ocean ; mediterranean sea

Other Geographic Terms: cosmopolitan

in all oceans

Georges Bank, on the continental shelf and shelf edge waters

Mediterranean and Red Sea.

occurs (regularly, as a native taxon) in multiple nations

Global Range: Not uncommon worldwide in tropical, subtropical, and warm temperate oceans. In the North Atlantic: Newfoundland to Lesser Antilles in the west, Sweden to the Mediterranean in the east. South to Argentina and South Africa in the south Atlantic. In the Pacific Ocean: Alaska and the Kuiles south to central Chile, Australia, and New Zealand. Occurs also in the Indian Ocean and Red Sea. May wander into cooler waters in summer. See Leatherwood et al. (1980) for information on distribution in the eastern Pacific Ocean.

Widely distributed, inhabiting tropical and warm temperate waters of both hemispheres (6). In UK waters the main concentration is around the Hebrides, but the species also occurs around the Northern Isles and in the Irish Sea. It is also quite common in south-east and western Ireland (4).

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.

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,

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.

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.

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.

Range mass: 300 to 500 kg.

Range length: 2.6 to 5 m.

Average length: 2.8 m.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes alike

Length: 400 cm

Sexual Dimorphism: None

Length:
Range: 2.8-3.8 m

Weight:
Average: 500 kg
Range: 400-600 kg

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.

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.

Range depth: 400 to 1,200 m.

Habitat Regions: temperate ; tropical ; saltwater or marine

Aquatic Biomes: pelagic ; benthic ; coastal

temperate to tropical, oceanic

Depth range based on 3009 specimens in 1 taxon.
Water temperature and chemistry ranges based on 2342 samples.

Environmental ranges
  Depth range (m): 0 - 2200
  Temperature range (°C): 3.515 - 29.261
  Nitrate (umol/L): 0.037 - 28.479
  Salinity (PPS): 30.381 - 37.318
  Oxygen (ml/l): 3.182 - 7.195
  Phosphate (umol/l): 0.055 - 1.881
  Silicate (umol/l): 0.746 - 26.702

Graphical representation

Depth range (m): 0 - 2200

Temperature range (°C): 3.515 - 29.261

Nitrate (umol/L): 0.037 - 28.479

Salinity (PPS): 30.381 - 37.318

Oxygen (ml/l): 3.182 - 7.195

Phosphate (umol/l): 0.055 - 1.881

Silicate (umol/l): 0.746 - 26.702
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

Habitat Type: Marine

Comments: Pelagic waters; generally in water >180 m deep (>1000 m deep according to IUCN 1991). In the northern Gulf of Mexico, occurs mainly in steep sections of the upper continental slope, where water depth is 350-975 m and gradient is greater than 24 m per 1.1 km (Baumgartner 1997).

 Grampus griseus is a deep water species sighted close to shore where the continental shelf is narrow and around oceanic islands. It prefers tropical and warm temperate water migrating north in the summer months.

Shows a preference for deep, warm temperate and tropical waters in offshore areas (6). Risso's are fairly abundant, with wide distribution. They prefer deep off shore waters, but can be seen close to shore around oceanic islands. In Britain and Ireland most records are within 11 km of the coast (9).

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

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.

Animal Foods: fish; mollusks; aquatic crustaceans

Primary Diet: carnivore (Molluscivore )

Comments: Diet mainly squid, occasionally small fishes.

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.

Commensal/Parasitic Species:

• sea lamprey (Petromyzon marinus)

There is no information available regarding predators specific to Risso's dolphin.

Usually occurs in groups; off California, groups averaged usually between 30-50, sometimes over 200; in the eastern tropical Pacific, groups averaged 15-26; in the northeastern Atlantic and Mediterranean, average group size was 6-7, with maximum of 20-30 (Leatherwood et al. 1980, IUCN 1991). Commonly associates with pilot whales.

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.

Communication Channels: visual ; acoustic

Perception Channels: visual ; acoustic ; echolocation

Comments: Active day/night.

On average Risso's dolphins live at least 30 years.

Average lifespan
Status: wild: 30 years.

Average lifespan
Status: wild: 20.0 years.

Maximum longevity: 42.5 years (captivity) Observations: One captive specimen lived for 42.5 years (Richard Weigl 2005).

There is no information regard the mating system of Grampus griseus. However, other Cetaceans tend to be either polygynous and polyandrous.

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.

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

Range gestation period: 13 to 14 months.

Average birth mass: 20 kg.

Range weaning age: 12 to 18 months.

Range age at sexual or reproductive maturity (female): 8 to 10 years.

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

Average number of offspring: 1.

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.

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

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.

US Federal List: no special status

IUCN Red List of Threatened Species: least concern

Accidental?

Rounded Global Status Rank: G5 - Secure

Classified as Least Concern (LC) on the IUCN Red List (1). Listed on Annex IV of the EC Habitats Directive, and Appendix II of the Bonn Convention (North and Baltic Sea populations), and Appendix III of the Bern Convention (3). All cetaceans (whales and dolphins) are listed on Annex A of EU Council Regulation 338/97; they are therefore treated by the EU as if they are included in CITES Appendix I, so that commercial trade is prohibited. In the UK all cetaceans are fully protected under the Wildlife and Countryside Act, 1981 and the Wildlife (Northern Ireland) Order, 1985 (4).

Comments: Hunted only incidentally in small cetacean fisheries throughout the world (Leatherwood and Reeves 1983). The only known substantial threat is local--incidental take that occurs in association with the Sri Lankan gillnet fishery in the Indian Ocean (IUCN 1991).

This dolphin is vulnerable to hunting (5) and environmental change, chemical and noise pollution (8), and entanglement in fishing nets, which results in drowning (5).

A UK Biodiversity Action Plan priority species, Risso's dolphin is protected in UK waters by the Wildlife and Countryside Act 1981 and the Wildlife (Northern Ireland) Orders, 1985; it is illegal to intentionally kill, injure, or harass any cetacean (whale or dolphin) species in UK waters (4). The Agreement on the Conservation of Small Cetaceans in the Baltic and North Seas (ASCOBANS) has been signed by seven European countries, including the UK. Provision is made under this agreement to set up protected areas, promote research and monitoring, pollution control and increase public awareness (4).

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.

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.

Positive Impacts: food ; body parts are source of valuable material

Comments: Sometimes maintained in marine aquaria. Meat is used locally for human consumption (IUCN 1991).