In addition, proponents and land managers should refer to the Recovery Plan (where available) or the Conservation Advice (where available) for recovery, mitigation and conservation information.
|EPBC Act Listing Status||Cetacean|
|Adopted/Made Recovery Plans|
|Policy Statements and Guidelines||
Marine bioregional plan for the North-west Marine Region (Department of Sustainability, Environment, Water, Population and Communities (DSEWPaC), 2012y) [Admin Guideline].
Australian National Guidelines for Whale and Dolphin Watching (Department of the Environment and Heritage, 2005e) [Information Sheet].
|State Listing Status||
|Scientific name||Grampus griseus |
This is an indicative distribution map of the present distribution of the species based on best available knowledge. See map caveat for more information.
Scientific name: Grampus griseus
Common name: Risso's Dolphin
Other names: Grey Dolphin, Grampus (French)
Described as Delphinus griseus by Cuvier in 1812 from a stuffed specimen stranded at Brest in Brittany. Subsequently, in 1928 Gray created the genus Grampus for a number of species including the Brest specimen. Risso's Dolphin is now accepted as single species with a worldwide distribution (Rice 1998). Morphological differences between regions suggest several races exist, but the potential for sub-specific taxonomy is unresolved. The few available Australian specimens have not been compared with other regions, so it is currently unknown whether they represent a discrete stock or subspecies.
Risso's Dolphins are robust, blunt-headed animals lacking a distinct beak. A distinctive deep crease runs up the forehead. The flippers are recurved, long and pointed. The dorsal fin is tall and falcate (sickle-shaped). The mouthline slopes upward and there are typically no more than seven pairs of peg-like mandibular teeth that are often badly worn in older individuals. No maxillary teeth are present. The colouration and markings of adults are conspicuous, the body being very light grey to white with a narrow cape sometimes being visible. Extensive scarring appears to be primarily from aggressive encounters with conspecifics. There is a large anchor-shaped light grey patch on a dark ventrum. Newborns are also light grey in colour.
The maximum weight known for Risso's Dolphins is greater than 230 kg. There is no known sexual dimorphism, although males may be slightly heavier.
Risso's Dolphin is usually gregarious, living in groups of 25 to several hundred individuals, although they may also be solitary (Leatherwood & Reeves 1983). They sometimes swim in 'echelon formation', lined up abreast at evenly spaced intervals. This formation is speculated to be a useful prey-hunting tactic. Dives are long and deep. Risso's Dolphins display most of the usual delphinid behaviour patterns, including aerial activities, but are not regular bow-riders. "Pelorus Jack" was a Risso's Dolphin that 'led' ships into harbour in Pelorus Sound, New Zealand for many years (Baker 1974). This species has been seen in the company of Striped Dolphins, Pilot Whales, Common Dolphins and other pelagic cetaceans. The few Australian strandings were all single animals, but mass strandings are known elsewhere (Bannister et al. 1996).
In Australia, Risso's Dolphins have been recorded from all states except Tasmania and the Northern Territory (Bannister et al. 1996; Ross 2006). Stranding records range from about 23° S to 39° S, although there is at least one stranding from further north, on Croker Island in the Northern Territory (NT Government 2013). No estimates of abundance are available but this species is believed to be reasonably abundant throughout the main part of its range, with depths from the limited sighting data ranging from 180 m to 1500 m (Corkeron & Bryden 1992). Fraser Island has the only suspected 'resident' population in Australia (Corkeron & Bryden 1992).
The current extent of occurrence of Risso's Dolphins in Australian waters is estimated to be greater than 20 000 km² (based on the Australian Exclusive Economic Zone (EEZ) to 200 nautical mile (nm), north of 45º S and in waters generally deeper than 200 m) (Peddemors & Harcourt 2006, pers. comm.). There have been no known past declines in extent of occurrence. There are no anticipated future changes in the extent of occurrence of Risso's Dolphin, although increasing ocean temperatures predicted by climate change scenarios could potentially increase the extent of occurrence with warmer water extending beyond 45° S.
The area of occupancy of Risso's Dolphins cannot be accurately calculated due to the sparsity of sighting records for a large proportion of the range. However, the area of occupancy is likely to be greater than 2000 km² (V. Peddemors & R. Harcourt 2006, pers. comm.). There have been no known past declines in the area of occupancy. No future changes are currently anticipated, although future expansion of pelagic gillnet fisheries may result in increased incidental catches, potentially depleting local waters and leading to a decrease in area of occupancy.
Risso's Dolphin is considered to occur in one location, as there are no known boundaries to dispersal in this species' pelagic habitat.
Risso's Dolphins have been successfully kept in captivity in Japan and the United States (Leatherwood & Reeves 1983), but no re-introductions have been attempted to date. No captive animals are kept in Australia.
Risso's Dolphin inhabits tropical, subtropical, temperate and subantarctic waters between 60° N and 60° S. It has been sighted both inshore and well offshore, although is generally considered pelagic and oceanic. South African records appear to be associated with the 1000 m isobath, but it appears to come into shallower water when the continental shelf is close to shore, and is frequently seen over continental slope (Bannister et al. 1996; Corkeron & Bryden 1992). Sea temperatures range from 1530 °C. Seasonal migration has been suggested, for example, off Japan, while searching for prey (Bannister et al. 1996).
Risso's Dolphin are abundant in tropical and temperate latitudes throughout the world's oceans (Kruse et al. 1999). There are an estimated 29 000 individuals off the eastern United States (Waring et al. 2001), 2700 in the northern Gulf of Mexico (Waring et al. 2001), 16 500 off the western United States (Carretta et al. 2001), 83 000 in three areas of concentrated occurrence off Japan (Miyashita 1993) and 175 000 in the Eastern Tropical Pacific (Wade & Gerrodette 1993).
They are hunted off Japan, with recent reported catches ranging from 250 to 500 individuals (Reeves et al. 2003). They are also a major target of artisanal (traditional) hunting and often taken in Sri Lankan and Philippine fisheries (Reeves et al. 2003), but populations in these areas have not been sufficiently assessed.
There are no estimates of population size, either globally or for Australia, although they are believed to be common throughout their range. It is likely that Risso's Dolphins move between Australia and other countries due to the lack of any deep water barriers.
This species is not well surveyed in Australian waters, and the distribution is primarily assumed from beach-cast animals. However, this method is believed to result in reliable distributional information for the species.
No population size is known, however Risso's Dolphin are not considered rare. Approximately 175 000 individuals occur in the Eastern Tropical Pacific, with similarly high densities in all areas where surveys have been conducted. The species is therefore potentially abundant in Australian waters.
Lack of abundance and distribution data do not allow definitive assessment of the likelihood of sub-populations of Australian Risso's Dolphins, but elsewhere in the range the distribution appears contiguous. It is therefore likely that the species occurs in one population within Australia. Limited data suggests there may be large scale (oceanic basin) stock differentiation within the species, as South African specimens are significantly shorter in length than Mediterranean or North Atlantic specimens (Ross 1984, Peddemors 1999).
There are no known trends for Australian Risso's Dolphin populations, due largely to a paucity of survey data. However, the population can be assumed to have been nominally reduced due to human-induced mortalities. Ongoing incidental captures and directed takes are the most likely cause of potential future population decline, although no quantitative data are available.
No extreme fluctuations anticipated for Risso's Dolphin populations. However, there is some evidence of seasonal range extensions (Baird & Stacey 1990).
Risso's Dolphins have readily hybridised with Bottlenose Dolphins in captivity. Suspected hybrids, with characteristics of both Risso's Dolphins and Bottlenose Dolphins, were observed on the Irish coasts in the 1950s (Leatherwood & Reeves 1983).
All cetaceans are protected within the Australian Whale Sanctuary under the EPBC Act. The Sanctuary includes all Commonwealth waters from the 3 nm State waters limit out to the boundary of the EEZ (out to 200 nm and further in some places). The species is also subject to International Whaling Comission regulations and protected within the Indian Ocean Sanctuary and Southern Ocean Sanctuary.
Risso's Dolphin occur mainly on steep sections of the upper continental slope (Baumgartner 1997), usually in waters deeper than 1000 m (Ross 1984), in tropical and warm temperate latitudes.
Risso's Dolphins show a marked preference not only for water greater than 1000m deep, but also for warm temperate to tropical conditions, although they do sometimes extend their range into cooler latitudes in summer (Leatherwood & Reeves 1983). They are therefore generally found in waters with temperatures ranging between 1530 °C. Although they are primarily found in pelagic oceanic waters, Risso's Dolphin frequently move over the continental slope.
Risso's Dolphin is regularly seen with other oceanic cetaceans, particularly Pilot Whales (Leatherwood & Reeves 1983).
The biological data presented in this profile is largely based on non-Australian specimens. It should be noted that there may be regional variations in size, as highlighted for South African animals when compared with Risso's Dolphins from the northern hemisphere (Ross 1984).
Weight and length at birth is about 59 kg and 1.11.5 m in length. Age for the various life history stages is unknown. Lengths are therefore used to provide an indication of size categories for each stage: length at weaning is less than 2.12 m; length at sexual maturity ranges from 2.63.0 m. The calving interval and mating season are not known; however the gestation period is about one year. Calving possibly occurs in summer, although a Victorian newborn was recorded in June. No calving areas are known (Bannister et al. 1996; Perrin & Reilly 1984).
Age and length at physical maturity are not known, but maximum weight is greater than 230 kg; maximum age is more than 17 years and maximum length is recorded at 4.1 m (Baker 1974; Bannister et al. 1996; Ross 1984).
No calving areas are known in Australian waters.
There are no known behaviours that may make Risso's Dolphin particularly vulnerable to a specific threatening process, although a suspected calving interval of two to three years leads to a slow reproductive capacity.
Risso's Dolphin feeds in pelagic waters primarily on squid, some octopus and possibly fish. Squid species taken by Risso's Dolphin are both pelagic and neritic (Bannister et al. 1996). Recent studies in South Africa have inferred that it is inappropriate to consider the Risso's Dolphin as an opportunistic predator (Cockcroft et al. 1993; Sekiguchi et al. 1992). Off the south-east coast of South Africa, in Hawaiian waters and in the Spanish Atlantic, Risso's Dolphin feeds exclusively on cephalopods (Clarke & Young 1998; Cockcroft et al. 1993; Gonzalez et al. 1994). Similarly, a low presence of fish in stomachs on the west coast indicates that it targets cephalopods as prey. Although 17 cephalopod species were identified from stranded Risso's Dolphin stomachs, data suggested that there may be resource partitioning between subgroups of dolphins according to sex and size class (Cockcroft et al. 1993).
Very few behavioural observations have been reported. However, morphological data can provide insight into feeding. The dentition of Risso's Dolphin is peculiar, as there are no maxillary teeth and no more than seven pairs of peg-like mandibular teeth. The grooved palate probably facilitates grasping cephalopod prey. This cephalopod-biased diet may lead to increased interactions with fisheries (Peddemors 1999).
Over 70% of prey taken by Risso's Dolphin are luminous or have photophores (cells that emit a glowing light), suggesting this dolphin may rely extensively on eye-sight during feeding (Peddemors 1997).
Risso's Dolphin throughout South Africa appear to forage in both coastal and offshore waters (Peddemors 1999) and it is likely that similar foraging behaviour would occur in Australian waters.
Distinctiveness and detectability
The robust body, relatively tall falcate dorsal fin on mid-back, bulging face with square melon bisected by a deep crease, and a heavily scarred pale skin combine to make this species easy to identify at sea. The behaviour of Risso's Dolphin can also be characterised by occasional spyhops, breaches, lobtails and flipper slaps. Risso's Dolphin usually travels slowly, ignoring boats, but will occasionally swim alongside the vessel, either riding the wake or bow. Blows are very distinct between typically short dives. Risso's Dolphins surface at a 45° angle and will sometimes fluke when diving (Shirihai 2002).
Cetacean surveys are constrained by several important factors including weather (e.g. sea state and light conditions), area to be covered, aim of the survey (abundance estimate versus ecological studies), the activities of the animals themselves (e.g. travelling, resting, surface versus deep feeding), and the type of craft used for the survey.
Surveys for pelagic dolphins have primarily been boat-based transects, although some aerial surveys have been conducted in the Eastern Tropical Pacific. Almost no dedicated cetacean surveys are conducted in Australian waters, but surveys associated with petro-chemical exploration may be used as platforms of opportunity. The limited sighting data for Risso's Dolphin has come from aerial surveys off Fraser Island, Queensland (Corkeron & Bryden 1992).
The minimum recommended requirement for non-dedicated surveys is to obtain basic biological information and GPS position from incidentally-caught animals from fishing vessels. One biologist on fishing vessels for one year is recommended as the observer could also record all cetacean sightings encountered during fishing operations. In addition, the minimum recommended requirement for a sighting program operated from existing cruises is two observers on two appropriate vessels for one year (V. Peddemores 2006, pers. comm.).
There is no information on past threats to Risso's Dolphin. Current threats include direct catches in areas adjacent to Indonesia, with the likely potential for illegal catches within the Australian EEZ; direct fisheries captures in Solomon Islands, albeit in small numbers; possible illegal and incidental catches in northern Australian waters; and incidental capture in pelagic gill-net fisheries off Sri Lanka (where it comprises 25% of catch) and which is cause for concern (Ross 2006).
The potential threats to Risso's Dolphin includes: incidental and illegal captures within Australian waters of northern Australia (Harwood & Hembree 1987); entanglement in drift-nets set outside Australian Territorial Waters and in lost or discarded netting; and pollution (including increasing amounts of plastic debris at sea, oil spills and dumping of industrial wastes into waterways and the sea) leading to bio-accumulation of toxic substances in body tissues (Bannister et al. 1996).
The low reproductive rate of Risso's Dolphin (i.e. one offspring every 23 years) means that population recovery is a slow process for this species.
Bannister and colleagues (1996) recommended the following actions be taken to better understand the threats to Risso's Dolphin:
- Determine distribution and monitor abundance in Australian waters to assess possible impact of threats, particularly the effect of direct and indirect fishing activities. This should be done via a sighting program to monitor numbers, particularly in northern waters
- Obtain information on diet to determine trophic level and assess possible impact of fishing industry on food resources.
- Determine taxonomic relationships within and outside Indo-Pacific region to assess likely impact of threats on possible individual populations.
- Obtain basic biological information (including diet and pollutant levels) from incidentally-caught and stranded specimens, especially from Arafura and Timor seas, including ensuring specimens are made available to appropriate scientific museums to enable collection of life history data and tissue samples for genetic analysis.
Current projects initiated to address these threats include:
- a study of incidental catch in Arafura and Timor seas, 1981-1985, by Australian National Parks and Wildlife Service
- surveys off the Queensland coast by the James Cook University and the University of Sydney.
Additionally, there is now a requirement to report all incidental catches made within the Australian EEZ (Bannister et al. 1996).
Additional conservation actions recommended includes undertaking a behavioural and photo-identification study of the Fraser Island animals (Bannister et al. 1996). Disentanglement workshops have also been initiated, and may be particularly relevant for offshore fishers. Action plans for Risso's Dolphins may also need to be developed.
Marine bioregional plans have been developed for four of Australia's marine regions - South-west, North-west, North and Temperate East. Marine Bioregional Plans will help improve the way decisions are made under the EPBC Act, particularly in relation to the protection of marine biodiversity and the sustainable use of our oceans and their resources by our marine-based industries. Marine Bioregional Plans improve our understanding of Australia's oceans by presenting a consolidated picture of the biophysical characteristics and diversity of marine life. They describe the marine environment and conservation values of each marine region, set out broad biodiversity objectives, identify regional priorities and outline strategies and actions to address these priorities. Click here for more information about marine bioregional plans.
Risso's dolphin has been identified as a conservation value in the North-west (DSEWPaC 2012y) Marine Region. The "species group report card - cetaceans" for the North-west (DSEWPaC 2012y) Marine Region provides additional information.
The Action Plan for Australian Cetaceans (Bannister et al. 1996) and the Review of the Conservation Status of Australia's Smaller Whales and Dolphins (Ross 2006) provide brief biological overviews and management recommendations of this species. In addition, Australian National Guidelines for Whale and Dolphin Watching (DEH 2005c) have been published.
No threats data available.
Baird, R.W. & P.J. Stacey (1990). Status of Risso's Dolphin, Grampus griseus, in Canada. The Canadian Field Naturalist. 105:233-242.
Baker, A. (1974). Risso's Dolphin in New Zealand waters, and the Identity of 'Pelorus Jack'. Records of the Dominion Museum. 8:267-276.
Bannister, J.L., C.M. Kemper & R.M. Warneke (1996). The Action Plan for Australian Cetaceans. [Online]. Canberra: Australian Nature Conservation Agency. Available from: http://www.environment.gov.au/resource/action-plan-australian-cetaceans.
Baumgartner, M.F. (1997). The distribution of Risso's dolphin (Grampus griseus) with respect to the physiography of the northern Gulf of Mexico. Marine Mammal Science. 13(4):614 - 638.
Carretta, J.V., J. Barlow, K.A. Forney, M.M. Muto & J. Baker (2001). U.S. Pacific marine mammal stock assessments:. Page(s) 2001. NOAA Technical Memorandum.
Clarke, M. & R. Young (1998). Description and analysis of cephalopod beaks from stomachs of six species of odontocete cetaceans stranded on Hawaiian shores. Journal of the Marine Biological Association of the United Kingdom. 78(2):623-641.
Cockcroft, V.G., S.L. Haschick & N.T.W. Klages (1993). The diet of Risso's dolphin, Grampus griseus (Cuvier, 1812), from the east coast of South Africa. Zeitschrift fur S┐etierkunde. 58:286-293.
Corkeron, P.J. & M.M. Bryden (1992). Sightings of Risso's Dolphin, Grampus griseus (Cetacea: Delphinidae), off Fraser Island, Queensland. Australian Mammalogy. 15:129-130.
Department of the Environment and Heritage (2005e). Australian National Guidelines for Whale and Dolphin Watching. [Online]. Available from: http://www.environment.gov.au/resource/australian-national-guidelines-whale-and-dolphin-watching-2005.
Gonzalez A, F.Lopez A., A. Guerra & A. Barreiro (1994). Diets of marine mammals stranded on the northwestern Spanish Atlantic coast with special reference of Cephalopoda. Fisheries Research. 21(1-2):179-191. Amsterdam.
Harwood, M.B. & D. Hembree (1987). Incidental catch of small cetaceans in the offshore gill-net fishery in Northern Australian Waters: 1981-1985. Report of the International Whaling Commission. 37:363-367.
Klinowska, M. (1991). Dolphins, Porpoises and Whales of the World: The IUCN Red Data Book. IUCN, Gland and Cambridge.
Kruse, S., D.K. Caldwell & M.C. Caldwell (1999). Risso's dolphin Grampus griseus. In: Handbook of Marine Mammals; The Second Book of Dolphins and the Porpoises. Volume 6::183-212. Academic Press, San Diego.
Leatherwood, S. & R.R. Reeves (1983). The Sierra Club Handbook of Whales and Dolphins. San Francisco: Sierra Club Books.
Miyashita, T. (1993). Abundance of dolphin stocks in the western North Pacific taken by the Japanese drive fishery. Report of the International Whaling Commission. 43:417-437.
Northern Territory Government (NT Government) (2013). Community bands together to rescue stranded dolphin at Croker Island. [Online]. Available from: http://lrm.nt.gov.au/news-room/2013/community-bands-together-to-rescue-stranded-dolphin-at-croker-island.
Peddemors, V.M. (1997). Risso's Dolphin. In: Mills, G. and L. Hes (Eds.), eds. The Complete Book of Southern African Mammals. Page(s) 304. Struik Winchester Publishers, Cape Town.
Peddemors, V.M. (1999). Delphinids of southern Africa: a review of their distribution, status and life history. Journal of Cetacean Research. 1(2):157-165.
Peddemors, V.M. & R. Harcourt (2006). Personal Communication. Sydney: Graduate School of the Environment, Macquarie University.
Perrin, W.F. & S.B. Reilly (1984). Reproductive parameters of dolphins and small whales of the family Delphinidae. Reports of the International Whaling Commission (Special Issue 6). Page(s) 97-133.
Reeves, R.R., B.D. Smith, E.A. Crespo & G. Notarbartolo di Sciara (2003). Dolphins, Whales and Porpoises: 2002-2010 Conservation Action Plan for the World's Cetaceans. Page(s) 139. IUCN/SSC Cetacean Specialist Group.
Rice, D.W. (1998). Marine mammals of the world. Systematics and distribution. Special publication number 4. Kansas: Society for Marine Mammalogy.
Ross, G.J.B. (1984). The smaller cetaceans of the south-east coast of southern Africa. Annals of the Cape Provincial Museums (Natural History). 15:173-411.
Ross, G.J.B. (2006). Review of the Conservation Status of Australia's Smaller Whales and Dolphins. Page(s) 124. [Online]. Report to the Australian Department of the Environment and Heritage, Canberra. Available from: http://www.environment.gov.au/resource/review-conservation-status-australias-smaller-whales-and-dolphins.
Sekiguchi K, N.T.W. Klages & P.B. Best (1992). Comparative analysis of the diets of smaller odontocete cetaceans along the coast of southern Africa. South African Journal of Marine Science. 12:843-861.
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Würtz, M., R. Poggi & M.R. Clarke (1992). Cephalopods from the Stomachs of a Risso's Dolphin (Grampus griseus) from the Mediterranean. Journal of the Marine Biological Association of the United Kingdom. 72:861-867.
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Anonymous (undated). Report to the International Whaling Commission.:417-437.
This database is designed to provide statutory, biological and ecological information on species and ecological communities, migratory species, marine species, and species and species products subject to international trade and commercial use protected under the Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act). It has been compiled from a range of sources including listing advice, recovery plans, published literature and individual experts. While reasonable efforts have been made to ensure the accuracy of the information, no guarantee is given, nor responsibility taken, by the Commonwealth for its accuracy, currency or completeness. The Commonwealth does not accept any responsibility for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the information contained in this database. The information contained in this database does not necessarily represent the views of the Commonwealth. This database is not intended to be a complete source of information on the matters it deals with. Individuals and organisations should consider all the available information, including that available from other sources, in deciding whether there is a need to make a referral or apply for a permit or exemption under the EPBC Act.
Citation: Department of the Environment (2014). Grampus griseus in Species Profile and Threats Database, Department of the Environment, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed Thu, 24 Apr 2014 06:07:40 +1000.