Biodiversity

Species Profile and Threats Database


For information to assist proponents in referral, environmental assessments and compliance issues, refer to the Policy Statements and Guidelines (where available), the Conservation Advice (where available) or the Listing Advice (where available).
 
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].
 
Information Sheets Australian National Guidelines for Whale and Dolphin Watching (Department of the Environment and Heritage, 2005e) [Information Sheet].
 
Non-statutory Listing Status
IUCN: Listed as Least Concern (Global Status: IUCN Red List of Threatened Species: 2013.1 list)
Scientific name Stenella attenuata [51]
Family Delphinidae:Cetacea:Mammalia:Chordata:Animalia
Species author (Gray,1846)
Infraspecies author  
Reference  
Distribution map Species Distribution Map

This is an indicative distribution map of the present distribution of the species based on best available knowledge. See map caveat for more information.

Illustrations Google Images

The current conservation status of the Pantropical Spotted Dolphin, Stenella attenuata, under Australian Government legislation and under international conventions, is as follows:

National: Listed as Cetacean under the Environment Protection and Biodiversity Conservation Act 1999.

International: Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES): Listed on Appendix II.

International Union for Conservation of Nature and Natural Resources (IUCN): Classified as Lower Risk - Conservation dependent.

Scientific name: Stenella attenuate

Common name: Pantropical Spotted Dolphin

Other names: Spotters

The taxonomy of Spotted Dolphins was revised by Perrin and colleagues in 1987. Two species are currently recognised: the Atlantic Spotted Dolphin, Stenella frontalis, described by G. Cuvier in 1829, and Stenella attenuata Gray 1846, termed the Pantropical Spotted Dolphin. The latter species occurs off Australia (Gilpatrick et al. 1978; Perrin et al. 1987), but is highly variable (with age and geographically) in size, colour pattern and skeletal characteristics. Three subspecies are currently recognised in the Pacific Ocean (Reeves et al. 2003; Rice 1998). The few available Australian specimens have not been compared with specimens from other regions.

Pantropical Spotted Dolphins are generally slender and streamlined. They have a long thin beak that is separated from the melon by a distinct crease. The tip of the rostrum is often white in colour. The dorsal fin is narrow, falcate (sickle-shaped) and usually pointed at the tip (Jefferson et al. 1993). Colouration in the Indo-Pacific form is complex and varies substantially between geographic areas. They are unspotted at birth, but are spotted by adulthood, with varying degrees of white mottling on the dark cape. This dark cape is narrow on the head and sweeps low on the flank and in front of the dorsal fin (Jefferson et al. 1993). A dark eye patch, eye band, mouth border and gape-to-flipper band are present. It is unknown whether the coastal and oceanic forms off Australia differ in colour patterning, as with the eastern tropical Pacific where they are better studied.

Physical maturity occurs after 15 years, with sexual dimorphism leading to different maximum lengths for males (2.57 m) and females (3.4 m). The maximum weight of Pantropical Spotted Dolphins is 119 kg and the maximum age is approximately 50 years (Perrin & Hohn 1994). They are gregarious, and although the average group size is less than 100 dolphins, group size ranges from a few individuals to over 1000 animals. Offshore groups are usually larger than coastal ones (Ross 2006). Pantropical Spotted Dolphins are often seen with other dolphins (including Spinner Dolphins), tuna and sea birds, probably in feeding aggregations. Their home range is several hundred kilometres or more and daily movements of 30–50 km are made (Ross 2006). Pantropical Spotted Dolphins can swim very rapidly and are often very acrobatic, leaping high into the air. They also ride bow waves.

In Australia, Pantropical Spotted Dolphins have been recorded off the Northern Territory, Western Australia down south to Augusta, Queensland and NSW. The record for Victoria is believed to be erroneous (Ross 2006).

The current extent of occurrence for Pantropical Spotted Dolphins is estimated to be greater than 20 000 km² (based on the Australian Economic Exclusion Zone (200 nautical miles (nm), north of 34° S and generally deeper than 200 m but also on the continental shelf) (Peddemors & Harcourt 2006, pers. comm.). Increasing ocean temperatures predicted by climate change scenarios could potentially increase the extent of occurrence of the species, with warmer water extending beyond 34° S.

The area of occupancy of Pantropical Spotted 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 (Peddemors & Harcourt 2006, pers. comm.). 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.

Pantropical Spotted Dolphins occur in one location as deep water does not appear to be a barrier to movement in this species, and there are no known unsurpassable fixed pelagic boundaries in the Australian region.

Pantropical Spotted Dolphins are mostly found in oceanic tropical zones between about 40° N and 40° S, inhabiting both near-shore and oceanic habitats. They therefore occur in both the northern and southern hemispheres in the Pacific, Atlantic and Indian oceans.

Pantropical Spotted Dolphin populations have primarily been assessed in areas where they were extensively hunted or caught in fisheries. In particular, the offshore Spotted Dolphins in the eastern tropical Pacific (ETP) bore the brunt of the large dolphin kills by tuna seiners between the late 1950s and 1980s. It is estimated that nearly five million dolphins were killed between 1959 and 1972, three million of which were Pantropical Spotted Dolphins (Reeves et al. 2003). Abundance estimates in the late 1980s totalled about two million Pantropical Spotted Dolphins in the eastern tropical Pacific (Wade & Gerrodette 1993). In 1998, the northeastern offshore stock was estimated at between 600 000–1 million, and the coastal stock between 70 000–100 000 (Reeves et al. 2003). Recent assessments suggest that populations are not recovering at the expected rate (Southwest Fisheries Science Centre 1999 in Reeves et al. 2003).

In the Gulf of Mexico, Pantropical Spotted Dolphins were determined to be the most abundant cetacean species (Hansen et al. 1995), while in the Western Indian Ocean it ranked as the sixth most abundant species (Ballance & Pittman 1998). Estimated abundance in Japanese waters (where thousands have been taken in drive and harpoon fisheries) was about 440 000 in the early 1990s (Miyashita 1993).

Other areas where large numbers have been killed for food or bait include the Solomon Islands, Sri Lanka, Lesser Antilles, Indonesia and the Philippines. Although the species is not considered threatened, there is a need for improved understanding of regional stock differences, abundance and take levels.

Pantropical Spotted Dolphins are believed to be common throughout their range, although there is no reliable estimate for numbers that occur in Australian waters. Therefore the global percentage occurring in Australian waters is unknown. It is likely that Pantropical Spotted Dolphins move between Australia and other countries due to the lack of any deep water barriers. The threats posed to this species in neighbouring countries have the potential to affect the Australian population.

Pantropical Spotted Dolphins are not well surveyed in Australian waters. The distribution is primarily assumed from incidental sightings, plus beach-cast and bycatch reports. However, these methods are believed to result in reliable distributional information for the species.

No population size is known for Pantropical Spotted Dolphins, although they are not considered rare. In each ocean surveyed, they are amongst the most abundant cetaceans, numbering several hundred thousand animals. The species is therefore potentially abundant in Australian waters and certainly likely to exceed 10 000 mature individuals (Peddemors & Harcourt 2006, pers. comm.).

Lack of abundance and distribution data do not allow definitive assessment of the potential for sub-populations of Pantropical Spotted Dolphins in Australia. However, elsewhere in the range their distribution appears split into near-shore and oceanic populations (Wade & Gerrodette 1993). It is possible that a similar separation may occur in Australian territorial waters. Limited data suggests there may be large scale stock differentiation within the species in the eastern tropical Pacific, but this requires further research of dolphins in Australian waters.

There have been no population trends identified for Australian Pantropical Spotted Dolphin due to a paucity of survey data. The population of Pantropical Spotted Dolphins 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, little quantitative data is available.

No extreme fluctuations are known to occur in populations of Pantropical Spotted Dolphins. There is some evidence of seasonal range extensions, especially noted in Japanese waters where they seasonally follow the northern edge of the warm Kuroshio Current (Miyazaki et al. 1974), but these are unlikely to be at the scale of one order of magnitude of the total population size of Pantropical Spotted Dolphins.

All cetaceans are protected within The Australian Whale Sanctuary under the EPBC Act. The Sanctuary includes all Commonwealth waters from the three nm State waters limit out to the boundary of the EEZ (out to 200 nm and further in some places).

Pantropical Spotted Dolphins inhabit both near-shore and oceanic habitats in tropical and warm temperate seas. They have also been found on the shelf and along the continental slope, indicating that they may use neritic (over the continental slope) habitat as well.

Multi-species aggregations of Pantropical Spotted Dolphins in the eastern tropical Pacific were correlated with a shallow, mixed layer and a thick, oxygen-minimum layer, creating a well-defined, shallow, 100 m deep pelagic habitat. Preferred water temperatures are warmer than 22 °C, but Pantropical Spotted Dolphins are also occasionally found in temperate waters (Bannister et al. 1996).

Pantropical Spotted dolphins reach sexual maturity at between 12 and 15 years for males (1.9–2.0 m in length) and 10 to 12 years for females (1.8–2.0 m in length). Maximum age has been estimated at 50 years (Perrin & Hohn 1994). Predators include humans, sharks and several other cetaceans, including the Killer Whale, False Killer Whale, and Pygmy Killer Whale (Leatherwood & Reeves 1983). Sharks are known to take dolphins in association with purse-seining operations (Bannister et al. 1996).

Due to a general lack of Australian data, this overview of Pantropical Spotted Dolphin reproductive parameters is based on non-Australian information (Ross 2006). Calves are born at 0.8–0.9 m in length, and wean at between one and three years. The interval between calves is between two and four years, depending on calf survivorship. The mating season for Pantropical Spotted Dolphins is diffuse, with peaks in spring and autumn. Gestation lasts 11.2–11.5 months. The calving season is therefore equally diffuse, with peaks in spring and autumn. No calving areas are known in Australian waters (Bannister et al. 1996; Myrick et al. 1986; Perrin & Hohn 1994; Perrin & Reilly 1984; Ross 1984).

There are no known reproductive behaviours that may make Pantropical Spotted Dolphins particularly vulnerable to a specific threatening process, however a suspected calving interval of two to four years leads to a slow reproductive capacity.

Pantropical Spotted Dolphins feed mainly on small epipelagic and mesopelagic fish, and squids. Some other foods are taken, such as nemertean worms and crab larvae (Sekiguchi et al. 1992; Würtz et al. 1992). Diet varies with region and reproductive state. Lactating females eat a greater proportion of fish than squid, presumably because the former is higher in calorific value (Ross 2006).

The Pantropical Spotted Dolphin diet overlaps greatly with that of Yellowfin Tuna and a close association has been noted between these species and sea birds in the eastern tropical Pacific (Bannister et al. 1996; Peddemors 1999). Unfortunately, this association has led fishers to target tuna by searching for dolphin groups. Seine nets are then set to target the tuna swimming below the dolphins, which has historically resulted in large numbers of dolphins taken as bycatch. This has been a major threatening process in the eastern tropical Pacific, and it is likely that similar fishing practices (and resulting threatening processes) occur in other oceans where this association between the dolphins and tuna exists.

Seasonal north-south movements are known off Japan and inshore/offshore movements have been recorded in the eastern tropical Pacific (Bannister et al. 1996; Leatherwood & Reeves 1983). However, no such seasonal changes in distribution are known for Australian waters.

Distinctiveness
The slender streamlined shape with characteristic spotting and distinct dark dorsal cape make Pantropical Spotted Dolphins readily identifiable at sea. The lips and tip of the beak are often white in colour, a particularly noticeable feature as the dolphins swim towards the observer and the beaks break the surface at initiation of the breathing roll.

Detectability
Pantropical Spotted Dolphins are vigorous swimmers, often leaping clear of the water. They will readily bow-ride in front of vessels, except in the eastern tropical Pacific where they have learnt to avoid boats (Leatherwood & Reeves 1983).

Recommended methods
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. There are almost no dedicated cetacean surveys conducted in Australian waters, but surveys associated with petro-chemical exploration may be used as platforms of opportunity. During such non-dedicated surveys, a minimum requirement is 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, plus attempts should be made to obtain basic biological information from dead animals (Peddemors 2006, pers. comm.).

A number of threats facing the Pantropical Spotted Dolphin have been identified. Past threats to Pantropical Spotted Dolphins include:

  • Incidental bycatch in the Taiwanese gill-net fishery in the Arafura and Timor Seas, northern Australia, between 1974–86, in which an estimated 560 Pantropical Spotted Dolphins were caught (comprising 4% of the total dolphin bycatch) (Harwood & Hembree 1987).
  • Live captures during the 1970s for a NSW oceanarium (Ross 2006).
  • Directed fisheries and incidental catch that killed large numbers of Pantropical Spotted Dolphins in Indonesia, the Philippines and the Solomon Islands, where they hunted for human consumption (Dawbin 1966a; Reeves et al. 2003).
  • Capture in inshore shark nets in low numbers in Queensland and New South Wales.

The current threats to the species include:

  • Direct catches in areas adjacent to Indonesia, Philippines and Solomon Islands.
  • Illegal catches within the Australian EEZ by fishers from nearby countries.
  • Possible illegal and incidental catches by fishers in northern Australian waters.
  • Incidental capture in pelagic gill-net fisheries off Sri Lanka.
  • Entanglement in drift-nets 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).

Pantropical Spotted Dolphins have a low reproductive rate, producing one offspring every two to three years. This means that population recovery is a slow process.

Bannister and colleagues (1996) and Ross (2006) recommended the following actions be taken to better understand the threats to Pantropical Spotted Dolphins:

  • Determine the distribution and monitor abundance of Pantropical Spotted 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 northern waters.
  • Obtain information on Pantropical Spotted Dolphin diet to determine their trophic level and assess any possible impact of the fishing industry on dolphin food resources.
  • Determine the taxonomic relationships within and outside the Indo-Pacific region to assess the likely impact of threats on possible individual populations of Pantropical Spotted Dolphins.
  • Obtain basic biological information (including diet and pollutant levels) from incidentally-caught and stranded Pantropical Spotted Dolphin specimens, especially from the Arafura and Timor Seas. This should include 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 the Australian National Parks and Wildlife Service
  • surveys of the Queensland coast by researchers at 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). Disentanglement workshops have been initiated which may be particularly relevant for offshore fishers and suitable action plans developed.

The impact of the gill-net fishery on the Pantropical Spotted Dolphin in the Arafura and Timor Seas is likely to have eased, as available information indicates that such activities have all but ceased in that region (Ross 2006).

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 Spotted 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 2005e) have been published.

No threats data available.

Ballance, L.T. & R.L. Pitman (1998). Cetaceans of the western tropical Indian Ocean: Distribution, relative abundance, and comparisons with cetacean communities of two other tropical ecosystems. Marine Mammal Science. 14(3):429-459.

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.

Dawbin, W.H. (1966a). Porpoises and porpoise hunting in Malaita. Australian Natural History. 15:207-211.

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.

Hansen, L.J., K.D. Mullin & C.L. Roden (1995). Estimates of cetacean abundance in the northern Gulf of Mexico from vessel surveys. Southeast Fisheries Science Center, Miami Laboratory Contribution No. MIA-94/5-25 (unpublished). 20.

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.

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.

Miyazaki N, T.Kasuyo & M. Nishiwaki (1974). Distribution and migration of two species of Stenella in the pacific coast of Japan. Scientific Reports of the Whales Research Institute, Tokyo. 26:227-243.

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. (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. & A.A. Hohn (1994). Pantropical Spotted Dolphin Stenella attenuata. In: Ridgway, S.H. and R. Harrison, eds. Handbook of Marine Mammals Vol. 5: The First Book of Dolphins. Page(s) 71-98. Academic Press.

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.

Perrin, W.F., E.D. Mitchell, J.G. Mead, D.K. Caldwell, M.C. Caldwell, P.J.H. van Bree & W.H. Dawbin (1987). Revision of the Spotted Dolphins, Stenella spp. Ridgway, S.H. & R. Harrison, eds. Marine Mammal Science. 3:99-170.

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.

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.

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.

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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). Stenella attenuata in Species Profile and Threats Database, Department of the Environment, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed Wed, 23 Jul 2014 13:58:16 +1000.