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].
|Scientific name||Steno bredanensis |
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: Steno bredanensis
Common name: Rough-toothed Dolphin
Other names: Steno
Originally described by Lesson in 1828 as Delphinus bredanensis. There are no recognised subspecies, although there is some evidence that Indo-Pacific animals differ from Atlantic animals. There is currently no information on taxonomic status of the few Australian specimens.
The Rough-toothed Dolphin is a relatively robust dolphin with a conical head and no demarcation between the melon and snout. The body is dark grey with a prominent narrow dorsal cape that dips slightly down onto the side below the dorsal fin (Jefferson et al. 1993). The ventral surface of the body is white, including the lower jaw and lips. The seemingly oversized flippers are set far back on the side, while the dorsal fin is also prominent and falcate. Scars and yellowish white to pink blotches occur on the side of the body, apparently the result of Cookie-cutter Shark bites.
Rough-toothed Dolphins grow to a maximum weight of about 155 kg. Males may be slightly larger than females, reaching maximum lengths of 2.65 m (compared to 2.55 m for females) (Miyazaki & Perrin 1994).
Groups may comprise up to several hundred individuals but usually number 1020. Rough-toothed Dolphins are known to occur with Pilot Whales, Bottlenose Dolphins, Spotted Dolphins and Long-snouted Spinner Dolphins (Ross 2006). They are thought to feed in groups (Leatherwood & Reeves 1983).
These dolphins ride bow waves but not as commonly as some other dolphin species. 'Skimming' swimming behaviour has also been reported. They may stay submerged for longer periods (up to 15 minutes) than other dolphins.
In Australia, the Rough-toothed Dolphin is recorded from Western Australia (Barrow Island), the Northern Territory, Queensland and southern New South Wales (Bannister et al. 1996).
The current extent of occurrence of the Rough-toothed Dolphin is estimated to be greater than 20 000 km² (based on the Australian Exclusive Econimic Zone (EEZ) (200 nm, north of 35º S and deeper than 200 m)) (V.M. Peddemors & R. Harcourt 2006, pers. comm.). There have been no known past declines in extent of occurrence, and no future changes are anticipated. However, increased ocean temperatures predicted by climate change scenarios could potentially increase the extent of occurrence with warmer water extending southward beyond 35° S.
The current area of occupancy of Rough-toothed Dolphins cannot be accurately calculated due to the sparsity of sighting records for a large proportion of the range. However, it is likely to be greater than 2000 km² (V.M. Peddemors & R. Harcourt 2006, pers. comm.). No past declines in area of occupancy have been identified, and no future changes are anticipated. However, 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.
The Rough-toothed Dolphin is anticipated to occur in one location as deep water is not a barrier to movement in this species, and there are no known fixed pelagic barriers in the Australian region.
Rough-toothed Dolphins have been successfully kept in captivity in Japan and Hawaii (Leatherwood & Reeves 1983), but no re-introductions attempted to date. No Rough-toothed Dolphins are held in captivity in Australia.
The Rough-toothed Dolphin is a tropical to subtropical species. It inhabits deep oceanic waters, rarely ranging north of 40° N or south of 35° S. Strandings in mid-latitudes outside these regions are probably vagrants. The species is known to infrequently wander into the Mediterranean Sea (Leatherwood & Reeves 1983).
No global population size estimates are available. Approximately 150 000 are estimated to occur in the eastern Tropical Pacific (Wade & Gerrodette 1993) and about 850 in the northern Gulf of Mexico (Waring et al. 2001). There may be some stock differentiation based on rostrum (snout) length, but this data is currently inconclusive (Leatherwood & Reeves 1983).
Off Japan they are occasionally taken for food in harpoon and drive fisheries, which may negatively affect the local population. Smaller numbers historically died in the tuna seine nets off the eastern Pacific (Leatherwood & Reeves 1983). However, these small reported mortalities probably had insignificant effects on the global population size. Their notoriety for stealing bait and fish off fishing lines makes them unpopular with many recreational and commercial fishers (Reeves et al. 2003).
There are no estimates of population size, either globally or for Australia, so the proportion of the global population in Australian waters is unknown. Rough-toothed Dolphins are believed to be uncommon throughout their range, but difficulties in identification could mean that abundance is underestimated. This species may therefore be more common in Australian waters than believed (Bannister et al. 1996). It is likely that Rough-toothed Dolphins move between Australia and other countries due to the lack of any deep water barriers.
The Rough-toothed Dolphin has not been well surveyed in Australian waters, and their 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, Rough-toothed Dolphins are not considered rare with approximately 150 000 individuals thought to occur in the eastern tropical Pacific. The species is potentially abundant in Australian waters, and certainly likely to exceed 10 000 mature individuals (V.M. Peddemors & R. Harcourt 2006, pers. comm.).
A lack of abundance and distributional data prohibit definitive assessment of the potential for subpopulations within the Australian range of the Rough-toothed Dolphin, 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.
No population trends have been calculated for Rough-toothed Dolphins, due 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. However, no quantitative data is available.
No extreme fluctuations in population size are anticipated as Rough-toothed Dolphins are not known to migrate.
The generation length of Rough-toothed Dolphins is believed to be around 20 years. This estimate is based on an age at sexual maturity of 14 years, a likely calving interval of three years, and a lifespan of approximately 32 years, as per other small cetaceans.
No cross-breeding is known for free-ranging wild animals. However, an apparently healthy calf, the result of a female Steno mating with a male Tursiops, survived for almost five years at Sea Life Park in Hawaii (Leatherwood & Reeves 1983), suggesting that some cross-breeding is possible in the wild.
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 Australian EEZ (i.e. out to 200 nm and further in some places). The Rough-toothed Dolphin is also subject to International Whaling Commission (IWC) regulations and protected within the Indian Ocean Sanctuary and Southern Ocean Sanctuary.
The Rough-toothed Dolphin inhabits pelagic and oceanic waters. All sightings have occurred in seas with surface temperatures exceeding 25 °C.
Rough-toothed Dolphins are regularly seen with Pilot Whales and Bottlenose Dolphins, and occasionally with Spotted and Spinner Dolphins (Leatherwood & Reeves 1983), all of which are listed cetaceans under the EPBC Act 1999.
The biological information presented in this profile is based primarily on limited and non-Australian information (Miyazaki & Perrin 1994; Perrin & Reilly 1984). Sexual maturity is achieved at about 14 years and 2.25 m for males, and 10 years and 2.20 m for females. Physical maturity is achieved at about 16 years. The maximum age and weight recorded for Rough-toothed Dolphins are 32 years and 155 kg respectively.
Group strandings have been recorded on several occasions outside Australia (Perkins & Miller 1983). Three animals stranded together on Barrow Island, Western Australia in 1971. Japanese specimens were found to have a high incidence of skeletal malformations. Very little is known about parasitology in these pelagic cetaceans (Bannister et al. 1996).
The length of Rough-toothed Dolphin calves at birth is about 1.0 m. There is no information on the age or length at weaning. Calving interval and season, mating season, and gestation period are all unknown (Ross 2006). No calving areas are known in Australian waters (Bannister et al. 1996; Perrin & Reilly 1984). There are no known behaviours that may make the Rough-toothed Dolphin particularly vulnerable to a specific threatening process. However, a suspected calving interval of two to three years leads to a slow reproductive capacity.
The limited data on feeding indicate that the diet of the Rough-toothed Dolphin includes pelagic octopus, squid and reef fish, with larger fish taken in deep water (Ross 2006).
The Rough-Toothed Dolphin feeds in groups of up to several hundred individuals, but usually group size is 10-20. When feeding, they may associate with Pilot Whales, Bottlenose Dolphins, and Spotted and Spinner Dolphins.
Their notoriety for stealing bait and fish off fishing lines makes them unpopular with many recreational and commercial fishers (Reeves et al. 2003). This may lead to both incidental captures and mortalities from fisher targeting. Additionally, their regular association with schools of Yellowfin and Skipjack Tuna, plus Dorado (Dolphinfish/Mahi Mahi), may make them susceptible to entanglement in purse-seine nets set for these fish species.
Distinctiveness and detectability
The narrow cape and cone-shaped head are the best clues for identifying Rough-toothed Dolphins. They are not especially wary, but show less propensity to bow-ride than other oceanic dolphins. They may swim rapidly for protracted periods with the snout continually near the surface and the dorsal fin continuously exposed, giving a skimming appearance to their movements. The tall falcate dorsal fin and distinctive colour pattern may enable rapid identification in mixed-species groups.
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 have been conducted in Australian northern waters, but surveys associated with petro-chemical exploration may be used as platforms of opportunity.
The minimum recommended requirement is to obtain basic biological information from incidentally-caught animals from fishing vessels. One biologist on fishing vessels for one year is recommended. The minimum recommendation is for a sighting program to be operated from existing cruises; two observers on two appropriate vessels (e.g. government) for one year is recommended. It may be possible to link observations with incidental catches by a biologist as outlined above (V.M. Peddemors 2006, pers. comm.).
No past threats to Rough-toothed Dolphins have been identified. The current threats include:
- Possible direct catches in areas adjacent to Indonesia, making illegal catches within Australian EEZ likely.
- Direct fisheries captures in Solomon Islands and Papua New Guinea, albeit in small numbers.
- Rare captures in purse-seine netting operations outside Australian waters.
- Incidental capture in pelagic driftnet and gillnet fisheries off Sri Lanka (Alling 1988; Ross 2006).
Potential or future threats to the species include:
- Incidental and illegal captures within Australian waters of northern Australia (Harwood & Hembree 1987).
- Entanglement in driftnets set outside Australian Territorial Waters and in lost or discarded netting.
- 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 Rough-toothed Dolphins (i.e. one offspring every two to three years) means that population recovery is a slow process.
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) recommended the following actions be taken to better understand the threats to Rough-toothed Dolphins:
- Determine distribution and monitor abundance in Australian waters to assess possible impact of threats, particularly the effect of direct and indirect fishing activities. This may 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. This should include ensuring specimens are made available to appropriate scientific museums (Bannister et al. 1996; Ross 2006).
Disentanglement workshops have been initiated to protect cetaceans caught in fishing nets, and may be particularly relevant for offshore fishers.
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.
The rough-toothed 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 for this species. In addition, Australian National Guidelines for Whale and Dolphin Watching (Department for the Environment and Heritage 2005e) have been published.
No threats data available.
Alling, A. (1988). Preliminary Report of the Incidental Entrapment of Odontocetes by Sri Lanka's Coastal Drift Net Fishery. Journal of the Bombay Natural History Society. 85(3):538-550.
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/coasts/publications/cetaceans-action-plan/pubs/whaleplan.pdf.
Department of the Environment and Heritage (2005e). Australian National Guidelines for Whale and Dolphin Watching. [Online]. Available from: http://www.environment.gov.au/coasts/publications/whale-watching-guidelines-2005.html.
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.
Jefferson, T.A., S. Leatherwood & M.A. Webber (1993). FAO species identification guide. Marine Mammals of the World. [Online]. Rome: United Nations Environment Programme, Food and Agricultural Organization. Available from: ftp://ftp.fao.org/docrep/fao/009/t0725e/t0725e00.pdf. [Accessed: 15-Aug-2007].
Leatherwood, S. & R.R. Reeves (1983). The Sierra Club Handbook of Whales and Dolphins. San Francisco: Sierra Club Books.
Miyazaki, N. & W.F. Perrin (1994). Rough-toothed dolphin Steno bredanensis (Lesson, 1828). In: Ridgeway & Harrison, eds. Handbook of Marine Mammals: The First Book of Dolphins. 5:1-21. Academic Press, London.
Peddemors, V.M. (2006). Personal Communications. Sydney: Graduate School of the Environment, Macquarie University.
Peddemors, V.M. & R. Harcourt (2006). Personal Communication. Sydney: Graduate School of the Environment, Macquarie University.
Perkins, J.S. & G.W. Miller (1983). Mass Stranding of Steno bredanensis in Belize. Biotropica. 15:235-236.
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.
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/coasts/publications/pubs/conservation-smaller-whales-dolphins.pdf.
Wade P. & T.Gerrodette (1993). Estimates of cetacean abundance and distribution in the eastern tropical Pacific. Report of the International Whaling Commission. 43:477-493.
Waring, G.T., J.M. Quintal & S.L. Swartz (2001). U.S. Atlantic and Gulf of Mexico marine mammal stock assessments - 2001. NOAA Technical Memorandum. NMFS-NE168.
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). Steno bredanensis in Species Profile and Threats Database, Department of the Environment, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed Mon, 10 Mar 2014 03:35:14 +1100.