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||
Listed migratory - Bonn
|Adopted/Made Recovery Plans|
Australian National Guidelines for Whale and Dolphin Watching (Department of the Environment and Heritage, 2005e) [Information Sheet].
Federal Register of
List of Migratory Species (13/07/2000) (Commonwealth of Australia, 2000b) [Legislative Instrument].
|Non-statutory Listing Status||
|Scientific name||Lagenorhynchus obscurus |
This is an indicative distribution map of the present distribution of the species based on best available knowledge. See map caveat for more information.
The current conservation status of the Dusky Dolphin, Lagenorhynchus obscurus, under Australian Government legislation and under international conventions, is as follows:
National: Listed as a Cetacean, and a Migratory species, under the Environment Protection and Biodiversity Conservation Act 1999.
Scientific name: Lagenorhynchus obscurus
Common name: Dusky Dolphin
The Dusky Dolphin is considered to be a conventionally accepted, well-established species. The validity of the six species in the genus Lagenorhynchus was confirmed on morphological grounds by Miyazaki and Shikano (1997). Two named and one unnamed subspecies of Lagenorhynchus obscurus have been recognised: L. o. fitzroyi (Waterhouse 1838) present along coastal South America from Peru to the Falkland Islands; L. o. obscurus around southern Africa from Angola to Cape Agulhas, the Prince Edward Islands and Île Amsterdam; and an unnamed subspecies (L. obscurus subsp.) distributed along the east coast of New Zealand from Whitianga, North Island to Stewart Island, Campbell Island, Auckland Island and Chatham Island (Rice 1998; Van Waerebeek 1993a; Würsig et al. 1997). The subspecific status of Australian specimens is currently unknown (Gill et al. 2000).
Dusky Dolphins are a small, moderately robust species with a short rostrum (snout) clearly demarcated from the melon (forehead). The conspicuous dorsal fin is moderately falcate (sickle-shaped) and pointed. Flippers are moderately curved on the leading edge, with a blunt tip (Jefferson et al. 1993; Leatherwood & Reeves 1983). Dusky Dolphins can live for more than 21 years and reach a maximum length of 2.11 m for males, and 1.93 m for females (Perrin & Reilly 1984).
The body colouration of Dusky Dolphins is complex and is generally counter-shaded, dark grey to black above and white below. The sides are marked with blazes and patches of pale grey. In front of the dorsal fin, Dusky Dolphins bear a broad light grey thoracic patch that encompasses the face, most of the head and flanks, and then tapers towards the belly. A separate crescent-shaped flank patch reaches the top of the tail stock just in front of the flukes. The front of this flank patch splits into two blazes, a shorter ventral and a longer dorsal one. The longer dorsal blaze narrows and stretches up onto the back, almost to the blowhole (Jefferson et al. 1993).
The rostrum (snout) is grey-black around the tip, tapering back to darken the lips near the gape. The eye is set in a small patch of grey-black. A variable crescent of pale grey contrasts the trailing (backward-facing) half of the dorsal fin with the dark coloured front half. The flippers are pale grey but darken around the edges (Jefferson et al. 1993).
Dusky Dolphins occur in groups of hundreds of individuals in summer and less than 20 in winter (Wursig et al. 1997). In some cases, large schools of several hundred dolphins have been observed.
Dusky Dolphins tend to rest in shallow water. This species readily rides the bow-wave of vessels and indulges in spectacular aerial displays including full somersaults high in the air. Most aerial behaviour is associated with surface feeding, while the more acrobatic displays are associated with social behaviour (Leatherwood & Reeves 1983). Dusky Dolphins are known to dive to at least 150 m depth.
In Australia, Dusky Dolphins are known from only 13 reports since 1828, with two sightings in the early 1980s (DEW 2007). They occur across southern Australia from Western Australia to Tasmania (Gill et al. 2000), with unconfirmed sightings south of continental Australia but confirmed sightings near Kangaroo Island, South Australia, and off Tasmania, and a recent stranding in the latter State. The record of a Dusky Dolphin stranding in Tasmania includes photographs of the animal, but a specimen has yet to be collected to confirm the species. One Dusky Dolphin skull was collected from Kerguelen Island. Given the lack of understanding of the species' distribution in Australian waters, no key localities have yet been identified (Bannister et al. 1996).
The current extent of occurrence for the Dusky Dolphin is estimated to be greater than 20 000 km² (based on the Australian Economic Exclusion Zone (EEZ) (200 nautical miles (nm), south of 35º S) (Peddemors & Harcourt 2006, pers. comm.). No past declines in extent of occurrence are known, although increasing ocean temperatures predicted by climate change scenarios could potentially decrease the extent of occurrence, with warmer water extending southwards beyond 35° S.
The area of occupancy of the Dusky Dolphin cannot be calculated due to the sparsity of records for Australia. However, it is likely to be greater than 2000 km² (Peddemors & Harcourt 2006, pers. comm.).
Dusky Dolphins are considered to occur in one location, as there are no known fixed pelagic boundaries that would obstruct their movement.
Dusky Dolphins occur throughout the Southern hemisphere, mostly in temperate and sub-Antarctic zones. They are primarily found from about 55° to 26°S, with extensions well northwards in association with cold currents. Although they are presumed to be primarily an inshore species, Dusky Dolphins may also be pelagic at times, possibly related to a desire for colder waters (Gill et al. 2000; Ross 2006). They are believed to occur in the southeast and southwest regions of both the Atlantic and Pacific oceans (CSG 1996). Around New Zealand their distribution is believed to be related to the Subtropical Convergence, with numbers declining north and south of this feature (Wursig et al. 1997).
The populations centered in New Zealand, the west coast of South America, and southwestern Africa are genetically distinct, and it has been suggested that these populations may deserve at least subspecies status (Findlay et al. 1992; Rice 1998; Van Waerebeek 1993a; Würsig et al. 1997).
The Dusky Dolphin is considered moderately abundant within its range, including in New Zealand (Bannister et al. 1996; CSG 1996). However, in Peru recent catches in gillnets, and by illegal harpooning, have been large enough to cause concern (Van Waerebeek 1994, Van Waerebeek et al. 1997, 1999, 2002, in CSG 1996). Reported changes in the proportion of Dusky Dolphins caught suggest that the Peruvian population is depleted. The demand for dolphin meat and blubber in Peru to be used as shark bait may be driving this exploitation (Van Waerebeek et al. 1999, in CSG 1996). Incidental mortality in fishing gear also occurs in Patagonia, Argentina, South Africa and New Zealand (CSG 1996).
Although the subspecific status of Australian Dusky Dolphins has not been resolved, it is unlikely that they constitute a distinct population. The Dusky Dolphin is presumed to be able to move between Australia and other countries as deep water is not thought to be a barrier to dispersal in this species. Because of this ability to move across deep waters, incidental bycatch of animals in neighbouring countries and/or international waters may affect the Australian population (Peddemors & Harcourt 2006, pers. comm.).
Dusky Dolphins are not well surveyed in Australian waters. The distribution is primarily assumed from 13 records, including a few sightings on various vessels and some beach-cast animals (Gill et al. 2000).
No population size is known, however, the low stranding and sighting rates suggest Dusky Dolphins are uncommon in Australian waters (Bannister et al. 1996; Gill et al. 2000; Ross 2006).
The lack of abundance and distribution data does not allow definitive assessment of Dusky Dolphin populations, but elsewhere in the range the distribution is contiguous. It is therefore likely that the species occurs in one population within Australia.
The generation length of Dusky Dolphins may be around 15 years (Perrin & Reilly 1984, Ross 2006). This estimate is based on the age at sexual maturity for males and females (7 and 18 years respectively), while weaning is thought to occur at 18 months. Dusky Dolphins are likely to have a calving interval of three years, as per other small cetaceans (Perrin & Reilly 1984, Ross 2006).
All cetaceans are protected within the Australian Whale Sanctuary under the EPBC Act. The Sanctuary includes all Commonwealth waters from the 3 nautical mile State waters limit out to the boundary of the EEZ (out to 200 nm and further in some places). The Dusky Dolphin is also subject to International Whaling Comission regulations and protected within the Indian Ocean Sanctuary and Southern Ocean Sanctuary
Dusky Dolphins occur mostly in temperate and sub-Antarctic waters. They are considered to primarily inhabit inshore waters but may also be pelagic at times (Ross 2006).
All sightings of Dusky Dolphins in Australian waters have been correlated with abnormally warm sea surface temperatures (more than 0.5 °C above normal temperature) (Gill et al. 2000). It is postulated that such oceanographic changes may promote conditions suitable for aggregation of Dusky Dolphin prey species, thereby increasing abundance of the dolphins (Gill et al. 2000).
Dusky Dolphins are resident inshore for much of year but are known to seek out colder water (<18 C) as inshore temperatures rise in summer. Off Australia, the seasonal reports of Dusky Dolphin sightings suggest a causal link with changes in one or more oceanographic features in this region. The position of the Subtropical Convergence, a feature that results in cold surface waters, appears to coincide with the northern limit of distribution for Dusky Dolphins off eastern New Zealand (with numbers declining north and south of this feature) (Gaskin 1968; Wursig et al. 1997). Seasonal distribution of Dusky Dolphins may also coincide with El Niño Southern Oscillation (ENSO) events, which expand the extent of cold waters (Gill et al. 2000).
Dusky Dolphins may associate with Southern Right Whales, listed as threatened under the EPBC Act.
The age at sexual maturity of Dusky Dolphins is different for males and females. Males reach sexual maturity at seven years, while females may take as long as 18 years to reach maturity (size is usually greater thean 1.65 m). Dusky Dolphins are known to live for over 21 years (Bannister et al. 1996; Perrin & Reilly 1984).
Dusky Dolphin mating is inferred to occur in summer as the gestation period is estimated to be 11 months and calves are born mainly in summer (Bannister et al. 1996). The calving interval for Dusky Dolphins is unknown, but is probably between two and three years (Perrin and Reilly 1984; Ross 2006). No calving areas have been identified in Australian waters, although a female Dusky Dolphin stranded in Tasmania while giving birth (Gill et al. 2000). Based on available, non-Australian information, the length at birth of Dusky Dolphin calves is 0.9 m, with weaning occurring at about 18 months of age.
The suspected calving interval of two to three years leads to a slow reproductive capacity for Dusky Dolphins, making them vulnerable to population decline and threatening processes.
Dusky Dolphins eat a wide diversity of prey, including schooling fish, especially Southern Anchovy, and midwater and benthic prey such as squid and laternfishes. Examination of stomach contents suggests that Dusky Dolphins off southern Africa feed on deep water species at night and come inshore during the day (Sekiguchi et al. 1992). While a similar diurnal movement by Dusky Dolphins was also observed in Argentina, (and associated with inshore resting behaviour), it has been suggested that the timing of foraging may be seasonal, and be correlated with the movements of their prey (Bannister et al. 1996; Wursig & Bastida 1986; Wursig et al. 1997).
Dusky Dolphins are generally considered to be surface feeders, often found feeding in aggregations with sea birds. Dusky Dolphin feeding behaviours have primarily been described for Argentinean individuals (Wursig et al. 1997). After slow movements and short submergence times at night, foraging is initiated at dawn. This pattern holds for spring and summer, but is reversed in winter. However, nocturnal feeding has been recorded throughout their range.
Dusky Dolphins may dive to depths of 150 m off New Zealand. Leaps with splashing and headfirst re-entries are typical when Dusky Dolphin are chasing fish. During actual feeding noisy "body slams" appear to be used to prey and alert nearby groups to the presence of prey. Cooperative feeding is common.
Cetaceans such as Dusky Dolphins are thought to be particularly vulnerable to broad-scale changes in the marine environment because of their high positions in marine food chains (Bannister et al. 1996).
Limited information is available for seasonal movement patterns in Australia but suggest some patterns may be linked to the position of the Subtropical Convergence and/or ENSO events. Large distance movements have been recorded for Dusky Dolphins in Argentina (Wursig & Bastida 1986). Diel (within 24 hour) movement patterns have been ascribed to nocturnal offshore feeding and diurnal nearshore resting for South Africa and Argentina (Findlay et al. 1992; Sekiguchi et al. 1992, Wursig et al. 1997). Dusky Dolphin populations off Argentina also show seasonal variations in numbers associated with the movement patterns of their prey (Wursig & Bastida 1986; Wursig et al. 1997).
Although sighting data are insufficient to determine any local seasonal trends in abundance and distribution, in both Argentina and New Zealand, school sizes increased during the summer months, with less than 20 dolphins occurring per school during the winter. In New Zealand these seasonal increases were thought to be associated with reproduction.
Dusky Dolphins are seldomly reported to mass strand, but one mass stranding of six animals has been recorded (Bannister et al. 1996).
Distinctive features of Dusky Dolphins include:
Dusky Dolphins are highly social and gregarious, often forming groups of several hundred animals (Leatherwood & Reeves 1983). They are one of the most acrobatic dolphins, regularly leaping high out of the water and sometimes tumbling in the air. Dusky Dolphins readily approach vessels to engage in bow-riding, allowing their distinguishing features to be confirmed.
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 offshore dolphins have primarily been boat-based transects, although some aerial surveys have been conducted. Very few dedicated cetacean surveys have been conducted in southern Australian waters, but surveys associated with oil and gas exploration may be used as platforms of opportunity. During such non-dedicated surveys a minimum requirement should be to record all cetacean sightings encountered with corresponding GPS position, environmental data (sea conditions and habitat) and behavioural observations. From fishing vessels, all incidentally caught animals should be recorded with corresponding GPS position, and attempts should be made to obtain basic biological information from dead animals (V. Peddemors 2006, pers. comm.).
Past and current threats to Dusky Dolphins include incidental capture in pelagic drift-net fisheries operating in the Tasman Sea and outside Australian Territorial Waters. In one New Zealand port, incidental mortality of Dusky Dolphins was estimated to be 100 to 200 animals per year (Jefferson et al. 1993), but had dropped to within the range of 50 to 150 animals during the mid-1980s (Würsig et al. 1997).
Entanglement in lost or discarded netting are also threatening this species (Bannister et al. 1996). Entanglement in an unregulated gillnet fishery and specific targeting for food off Peru, and illegal fishing for Dusky Dolphin off Chile, are considered threats to the global population of this species (Reeves et al. 2003; Van Waerebeek & Reyes 1994; Van Waerebeek et al. 1997).
In addition, pollution, including increasing amounts of plastic debris at sea, oil spills and dumping of industrial wastes into waterways and the sea, are leading to bio-accumulation of toxic substances in body tissues of many marine species. These threats have the potential to cause population declines for Dusky Dolphins (Bannister et al. 1996; Ross 2006).
In particular, the low reproductive rate of Dusky Dolphins (one offspring every two to three years) suggests that population recovery may be a slow process.
Bannister and colleagues (1996) and Ross (2006) recommended the following measures to be taken to better understand the threats to Dusky Dolphins:
- Determine the distribution and monitor abundance of Dusky Dolphins in Australian waters to assess the 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 southern waters.
- Obtain information on Dusky Dolphin diet to determine their trophic level and assess any possible impact of the fishing industry on dolphin food resources.
- Obtain basic biological information (including diet and pollutant levels) by ensuring incidentally-caught and stranded animals are reported and are made available to appropriate scientific museums.
Current projects initiated to address these threats include a requirement to report all incidental catches made within the Australian Exclusive Economic Zone (Bannister et al. 1996). Disentanglement workshops have also been initiated, and may be particularly relevant for offshore fisheries.
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 overviews of the biological information, threats and threat abatement recommendations for this species. In addition, Australian National Guidelines for Whale and Dolphin Watching (DEH 2005c) have been published.
The following table lists known and perceived threats to this species. Threats are based on the International Union for Conservation of Nature and Natural Resources (IUCN) threat classification version 1.1.
|Threat Class||Threatening Species||References|
|Biological Resource Use:Fishing and Harvesting Aquatic Resources:Harvest by gill netting||Lagenorhynchus obscurus in Species Profile and Threats (SPRAT) database (Department of the Environment and Heritage, 2006oh) [Internet].|
|Biological Resource Use:Fishing and Harvesting Aquatic Resources:Illegal fishing practices and entanglement in set nets||Lagenorhynchus obscurus in Species Profile and Threats (SPRAT) database (Department of the Environment and Heritage, 2006oh) [Internet].|
|Pollution:Garbage and Solid Waste:Ingestion and entanglement with marine debris||Lagenorhynchus obscurus in Species Profile and Threats (SPRAT) database (Department of the Environment and Heritage, 2006oh) [Internet].|
|Pollution:Industrial and Military Effluents:Leakage of industrial waste|
|Pollution:Pollution:Deterioration of water and soil quality (contamination and pollution)|
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.
Bierman, W.H. & E.J. Slijper (1948). Remarks upon the Species of the Genus Lagenorhynchus I and II. Proceedings Koninklijke Nederlandsche Akademie van Wetenschappen. 51:127-133.
Cetacean Specialist Group (1996). Lagenorhynchus obscurus. IUCN 2006, ed. 2006 IUCN Red List of Threatened Species. [Online]. Available from: http://www.iucnredlist.org/search/details.php/11146/all. [Accessed: 02-Aug-2007].
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.
Department of the Environment and Water Resources (DEW) (2007). National Whale and Dolphin Sightings and Strandings Database. [Online]. Available from: http://aadc-maps.aad.gov.au/aadc/whales/species_sightings.cfm?taxon_id=58. [Accessed: 12-Jul-2007].
Findlay, K.P., P.B. Best, G.J.B Ross & V.G. Cockcroft (1992). Distribution of Small Odontocete Cetaceans off the Coasts of South Africa and Namibia. South African Journal of Marine Science. 12:237-270.
Gaskin, D.E. (1968). Distribution of Delphinidae (Cetacea) in relation to sea surface temperatures off eastern and southern New Zealand. New Zealand Journal of Marine and Freshwater Research. 2:527-534.
Gill, P.C., G.J.B. Ross, W.H. Dawbin & H. Wapstra (2000). Confirmed sightings of dusky dolphins (Lagenorhynchus obscurus) in southern Australian waters. Marine Mammal Science. 16:452-459.
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].
Klinowska, M. (1991). Dolphins, Porpoises and Whales of the World: The IUCN Red Data Book. IUCN, Gland and Cambridge.
Leatherwood, S. & R.R. Reeves (1983). The Sierra Club Handbook of Whales and Dolphins. San Francisco: Sierra Club Books.
Miyazaki, N. & C. Shikano (1997). Comparison of Growth and Skull Morphology of Pacific white-sided dolphin, Lagenorhynchus obliquidens, between the Coastal Waters of Iki Island and the Oceanic Waters of the western North Pacific. Mammalia. 61:561-572.
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.
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, eds. (2003). Dolphins, Whales and Porpoises: 2002-2010 Conservation Action Plan for the World's Cetaceans. Switzerland and Cambridge: IUCN/SSC Cetacean Specialist Group. IUCN, Gland.
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. (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.
Van Waerebeek K. & J.C. Reyes (1994). Post-ban small cetacean takes off Peru: a review. Report of the International Whaling Commission (Special Issue 15). Page(s) 503-519.
Van Waerebeek K., M.-F. Van Bressem, F. Félix, J. Alfaro-Shigueto, A. García-Godos, L. Chávez-Lisambart, K. Ontón, D. Montes & R. Bello (1997). Mortality of dolphins and porpoises in coastal fisheries off Peru and southern Ecuador in 1994. Biological Conservation. 81:43-49.
Van Waerebeek, K. (1993a). Geographic variation and sexual dimorphism in the skull of the dusky dolphin, Lagenorhynchus obscurus (Gray, 1828). Fishery Bulletin, US. 91:754-774.
Van Waerebeek, K. (1993b). Presumed Lagenorhynchus skull at Tasmanian Museum reidentified as Lissodelphis peronii. Australian Mammalogy. 16(1):41-43.
Van Waerebeek, K. (1994). A note on the status of the dusky dolphins (Lagenorhynchus obscurus) off Peru. Report of the International Whaling Commission (Special Issue 15). Page(s) 525-527.
Würsig B., F. Cipriano, E. Slooten, R. Constantine, K. Barr & S. Yin (1997). Dusky dolphin (Lagenorhynchus obscurus) off New Zealand: status of present knowledge. Report of the International Whaling Commission. 47:715-722.
Würsig, B. & R. Bastida (1986). Long-range movement and individual associations of two dusky dolphins (Lagenorhynchus obscurus) off Argentina. Journal of Mammalogy. 67:773-774.
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). Lagenorhynchus obscurus in Species Profile and Threats Database, Department of the Environment, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed Sun, 13 Jul 2014 08:18:01 +1000.