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Orcaella heinsohniAustralian snubfin dolphin

By Maureen Hanzel

Geographic Range

Australian snubfin dolphins, Orcaella heinsohni, are native to Australian and Oriental coastal waters surrounding the Sahul shelf. They are found as far north as Manokwari, Indonesia and as far south as the Brisbane River in Australia. Their range in Australia is from Broome in Western Australia to Brisbane in Queensland. (Beasley, et al., 2005)

Habitat

Australian snubfin dolphins inhabit shallow coastal waters up to 30 m deep and 23 km from the coast. They are rarely seen in waters deeper than 20 m. Groups of Australian snubfin dolphins are often found adjacent to river and creek mouths. They exhibit preferential habitat selection for shallow areas with seagrass, over dredged channels, and areas with coral reefs. (Parra, et al., 2002; Parra, 2006)

  • Range depth
    0 to 30 m
    0.00 to 98.43 ft

Physical Description

Australian snubfin dolphins are fusiform in body shape with round, highly mobile heads and small dorsal fins. It has been suggested they are sexually dimorphic but this has not been documented well. Adults are relatively small, varying in length from 2.1 to 2.3 m and weighing 114 to 133 kg. Australian snubfin dolphins are gray to blue gray with a white abdominal field between their flippers and genital region. This tri-partite coloration is the easiest way to distinguish them from their close relatives, Irrawady dolphins (Orcaella brevirostris). The dorsal fin is a crescent shape measuring 9.59 cm high, significantly higher than Irrawady dolphins. Their flippers are 16% of their body length with a smoothly curved anterior margin. These dolphins exhibit homodont dentition with up to 20 teeth in the upper right, 22 in the upper left, 18 in the lower right and 19 in the lower left. Beyond coloration, Australian snubfin dolphins have distinctive skeletal characteristics that separate them from Irrawady dolphins, including the number of bony ossicles, temporal fossa height, and pterygoid depth. Australian snubfin dolphins have three bony ossicles and nasal bones, while Irrawady dolphins only have two. Australian snubfin dolphins have a temporal fossa height of 61.2 mm compared to 45.8 mm in Irrawady dolphins. Australian snubfin dolphin pterygoid depth ranges from 19.4 to 31.2 mm, whereas Irrawady dolphin pterygoid depth, which ranges from 30.7 to 48.6 mm. (Beasley, et al., 2005; Marsh, et al., 1989)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    114 to 133 kg
    251.10 to 292.95 lb
  • Range length
    2.1 to 2.4 m
    6.89 to 7.87 ft

Reproduction

Reproduction is understudied in this species. It is suggested that they are a monogamous species. This is based on the strong and temporally stable association patterns within groups. Groups range from 1 to 8 individuals, but groups of 5 are most common. (Parra, 2005)

A breeding season in Australian snubfin dolphins has not been identified. However, the number of juveniles in groups is generally higher during the dry season from May through November than the wet season of December through April. A gestation length of 14 months suggests that more mating occurs during the wet season. Generally a single offspring is born. Birth mass is 10 to 12 kg. Due to their tight social structure, it is believed that the young are reared communally. Juveniles follow their mothers for as long as they are reliant on her for milk and protection. Adult size is reached between 4 and 6 years of age. It is suspected that once these dolphins reach adult size, they leave their mothers' social group. (Marsh, et al., 1989; Parra, et al., 2002; Parra, 2006)

  • Breeding interval
    Breeding intervals in Australian snubfin dolphins are not reported.
  • Breeding season
    Breeding seems to occur mainly in the wet season, from December to April.
  • Range number of offspring
    1 to 2
  • Average number of offspring
    1
  • Average gestation period
    14 months
  • Average weaning age
    24 months

Australian snubfin dolphins are born able to swim. They are weaned at about two years old and remain near their mother in their natal group until they are adult sized, between 4 and 6 years old. (Beasley, et al., 2005)

  • Parental Investment
  • precocial
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • post-independence association with parents

Lifespan/Longevity

Australian snubfin dolphins can live for more than 20 years, but generally do not survive past 28 years of age. (; Marsh, et al., 1989)

  • Range lifespan
    Status: captivity
    18 to 28 years
  • Average lifespan
    Status: captivity
    20 years

Behavior

Australian snubfin dolphins are most frequently observed foraging and traveling in small groups during the dry season. Australian snubfin dolphins live sympatrically with Indo-Pacific humpback dolphins and dugongs. The majority of behavioral interactions between Indo-Pacific humpback dolphins and Australian snubfin dolphins are aggressive sexual behaviours. Male Indo-Pacific humpback dolphins will chase Australian snubfin dolphin females to make physical contact, females with juveniles are particular targets. Females react with submissive fleeing behavior or resistance using their rostrum. Interactions between Australian snubfin dolphins and dugongs are generally of an impartial nature. (Parra, et al., 2002; Parra, 2005; Parra, 2006)

Home Range

Home range sizes in Australian snubfin dolphins are not reported in the literature.

Communication and Perception

Australian snubfin dolphins produce broadband clicks, three different types of pulsed sound, and two different types of whistles to communicate with one another. During foraging, Australian snubfin dolphins produce click trains, which are also used to a lesser extent during socializing. During social behavior, Australian snubfin dolphins often produce squeak sounds. The two whistle types are both short in duration and relatively low in frequency (1 to 8 kHz) and occur during socialization and foraging. There is also evidence of ultrasonic sound communication among Australian snubfin dolphins. (Parijs, et al., 2000)

Food Habits

Australian snubfin dolphins are opportunistic and generalist feeders. They feed on a variety of fish and invertebrates found in their coastal and estuarine habitat. They have been recorded eating anchovies, sardines, eels, halibut, breams, and grunters. Squid, cuttlefish, and other cephalopods are also important in the diet. They occasionally eat decapod crustaceans, and isopods. (Parra and Jedensjö, 2009)

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

Predation

Humans pose the greatest predation risk to Australian snubfin dolphins. Other important predators are sharks, particularly tiger sharks (Galeocerdo cuvier). Australian snubfin dolphins are also at risk of death by Indo-Pacific humpback dolphin (Sousa chinensis) aggression. They escape predation through social behavior, grouping to improve vigilance, agility in the water, and their countershaded color pattern. (Parra, 2005)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Australian snubfin dolphins are dominant predators of fish and cephalopod species in coastal areas of Australia and Indonesia. There is little else known about their ecosystem roles. (Parra and Jedensjö, 2009)

Economic Importance for Humans: Positive

Australian snubfin dolphins are an endemic species and their level of importance within the ecosystem has not been determined. Australian snubfin dolphins and Irrawady dolphins are an interesting example of allopatric speciation. (Beasley, et al., 2005)

Economic Importance for Humans: Negative

There is no negative impact of Australian snubfin dolphins on humans.

Conservation Status

The International Union for Conservation of Nature and Natural Resources categorize Australian snubfin dolphins as near threatened. There are currently less than 10,000 mature individuals. The major threats include entanglement in gill nets set in shallow waters for fishing, entanglement in shark nets set for human protection, and habitat degradation (coastal zone development, pollution, boat traffic, and overfishing of prey resources). (Gribble, et al., 1989; Reeves, et al., 2009)

Other Comments

Orcaella heinshoni was separated from Orcaella brevirostris in 2005 after genetic research and other evidence suggested that they are evolutionarily significant populations. (Beasley, et al., 2005)

Contributors

Maureen Hanzel (author), University of Manitoba, Jane Waterman (editor), University of Manitoba, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

female parental care

parental care is carried out by females

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

molluscivore

eats mollusks, members of Phylum Mollusca

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nomadic

generally wanders from place to place, usually within a well-defined range.

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

piscivore

an animal that mainly eats fish

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born

References

Beasley, I., P. Arnold, G. Heinsohn. 2002. Geographical variation in skull morphology of the Irrawaddy dolphin, Orcaella brevirostris (Owen in Gray, 1866). Raffles Bulletin of Zoology, 10: 15-34.

Beasley, I., K. Robertson, P. Arnold. 2005. Discription of a New Dolphin, The Australian Snubfin Dolphin Orcaella Heinsohni Sp. N. (Cetacea, Delphinidae). Marine Mammal Science, 21/3: 365-400.

Gribble, A., G. McPherson, B. Lane. 1989. Effect of the Queensland Shark Control Program on non target species: whale, dugong, turtle and dolphin: a review. Marine and Freshwater Research, 49: 645-651.

Heinsohn, G. 1979. Biology of small cetaceans in north Queensland waters.. Townsville, Queensland: Unpublished report to the Great Barrier Reef Marine Park Authority. 23 pp.

Marsh, H., R. Lloze, G. Heinsohn, Kasuya. 1989. Irrawaddy dolphin Orcaella brevirostris (Gray, 1866). Pp. 101-118 in S Ridgway, R Harrison, eds. Handbook of Marine Mammals, Vol. 6. New York: Academic Press.

Parijs, S., G. Parra, P. Corkeron. 2000. Sounds produced by Australian Irrawaddy dolphins, Orcaella brevirostris. Journal of Acoustical Society of America, 108/4: 1938-1940.

Parra, G., M. Jedensjö. 2009. Feeding habits of Australian Snubfin (Orcaella heinsohni) and Indo-Pacific humpback dolphins (Sousa chinensis). The Great Barrier Reef Marine Park Authority, Townvsille and Reef & Rainforest Research Centre LImitred, Cairns: 1-22.

Parra, G. 2005. Behavioural ecology of Irrawaddy, Orcaella brevirostris (Owen in Gray, 1866), and Indo-Pacific humpback dolphins, Sousa chinensis (Osbeck, 1765), in northeast Queensland, Australia: A comparative study. Cairns: James Cook University.

Parra, G. 2006. Resource partitioning in sympatric delphinids: space use and habitat preferences of Australian snubfin and Indo-Pacific humpback dolphins. Journal of Animal Ecology, 75: 862-874.

Parra, G., P. Corkeron, H. Marsh. 2006. Population sizes, site fidelity and residence patterns of Australian snubfin and Indo-Pacific humpack dolphins: Implications for conservation. Biological Conservation, 129: 167-180.

Parra, G., A. Preen, P. Corkeron, H. Marsh. 2002. Distribution of Irrawaddy dolphins, Orcaella brevirostris, in Australian waters. Raffles Bulletin of Zoology, 10: 141-154.

Reeves, R., M. Dalebout, A. Jefferson, L. Karczmarski, K. Laidre, G. O'Corry-Crowe, L. Rojas-Bracho, E. Secchi, E. Slooten, B. Smith, J. Wang. 2009. "Orcaella heinsohni" (On-line). IUCN Red List of Threatened Species. Accessed October 20, 2011 at www.iucnredlist.org.

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