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Australian snubfins usually group together in schools of up to fifteen dolphins. Unlike the Irrawaddy dolphins, Australian snubfins can be found traveling alone. Usually the average school of Australian snubfins consists of five dolphins.<ref>Parra, G.J. (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. Ph.D. Thesis. Townsville: James Cook University. Referenced on: http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=81322
Australian snubfins usually group together in schools of up to fifteen dolphins. Unlike the Irrawaddy dolphins, Australian snubfins can be found traveling alone. Usually the average school of Australian snubfins consists of five dolphins.<ref>Parra, G.J. (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. Ph.D. Thesis. Townsville: James Cook University. Referenced on: http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=81322
</ref> These groups of Australian snubfins are found along Australia’s north coast from the Kimberley National Marine Park in Western Australia to the Gladstone region of Queensland. They are also found in the waters around Papua New Guinea. <ref>Case, A. (2011, June 8). Snubfin dolphins face extinction . Retrieved from Australian Geographic: http://www.australiangeographic.com.au/journal/snubfin-dolphins-face-extinction.htm</ref>
</ref>


==Conservation==
==Conservation==

Revision as of 23:00, 24 October 2013

Snubfin dolphins
Orcaella brevirostris
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Mammalia
Order:
Cetacea
Family:
Delphinidae
Genus:
Orcaella

Gray, 1866
Species

Orcaella brevirostris
Orcaella heinsohni

Distribution of genus Orcaella

The snubfin dolphins (Orcaella) are a genus of Cetaceans containing two members: the Irrawaddy Dolphin (Orcaella brevirostris) and the Australian Snubfin Dolphin (Orcaella heinsohni). The genus was long believed to be monotypic with the only species being the Irrawaddy Dolphin; however, in 2005, supposed Irrawaddy Dolphin populations inhabiting the Australian/New Guinean regions were found to be significantly different and were declared a separate new species named the Australian Snubfin Dolphin.

Taxonomy and Evolution

Until 2005, Orcaella brevirostris was the only recognized species in the genus Orcaella. However, comparisons within the populations of Orcaella inhabiting the Asia region and populations inhabiting the Australia/New Guinea region show distinctions in habitat, morphology, and genetics [1]. Morphological differences include height of dorsal fin, skull shape, presence or absence of a median dorsal groove in front of the dorsal fin, and coloration. Genetic analysis constitutes a 5.9% difference between the two populations. [2] In 2005, these significant distinctions considered by Beasley, Arnold and Robertson warranted a taxonomic split of Orcaella into two separate species, Orcaella brevirostris and Orcaella heinsohni . Orcaella brevirostris known as the Irrawaddy Dolphin consists of the Asian population. The newly recognized species, known as the Australian Snubfin Dolphin, consists of the Australian/New Guinea population [3].

The Snubfin Dolphins (Orcaella) contain two of the 35 species of Oceanic dolphins that make up the Cetacean family of Delphinidae.[4] The phylogenetic status of Orcaella has long been confused. Although the Snubfin Dolphins are externally similar to the Monodontidae (narwhal)[1], a genetic study conducted by Arnason and Gretarsdottir identified the 'Irrawaddy Dolphin' as a Delphinid. In their study, phylogenetic information obtained from a highly repetitive DNA (hrDNA) component characteristic of all cetaceans show that Orcaella share close affinities with the Delphinidae and did not support a close relationship to the Monodontidae[5]

Recent molecular analyses indicate that the genus Orcaella is closely related to the Orca of the genus Orcinus, the two of them together forming the subfamily Orcininae[6][7]

Characteristics

Irrawaddy Dolphin

The Irrawaddy dolphin’s body length is about 180-275 centimeters long. Its color can range from a slate blue to a slate gray while its under parts tend to be paler. It has a bulging forehead with a short beak and has about 12 to 19 teeth on each side of each jaw. The pectoral fin is broad and triangular shaped and the small dorsal fin appears on the posterior end of its back. The Irrawaddy dolphins are rarely found by themselves. They usually remain in groups of no more than ten dolphins. The Irrawaddy dolphins eat fish and crustaceans. [8]

Australian Snubfin Dolphin

Australian snubfin dolphins are very similar to the Irrawaddy dolphins, however, while the bodies of Irrawaddy dolphins are two-colored, the bodies of Australian snubfins are three-colored. The snubfin has a small “snubby” dorsal fin, giving them the name “snubfin”. They are dark on the dorsal side, and transition to a light brown on the flanks while having a white belly. Australian snubfins are shy and tend to stay away from boats. The skulls and fins of Australian snubfins also have slight variations from the Irrawaddy dolphins. Similar to the Irrawaddy, the Australian snubfins feed on fish and fish eggs, crustaceans, and cephalopods. [9]

The Australian snubfin dolphin reaches 2.3 meters in length in females and 2.7 meters in length in males. Body weight of the Australian snubfin can reach 130 kg. [10]

Australian snubfins usually group together in schools of up to fifteen dolphins. Unlike the Irrawaddy dolphins, Australian snubfins can be found traveling alone. Usually the average school of Australian snubfins consists of five dolphins.[11] These groups of Australian snubfins are found along Australia’s north coast from the Kimberley National Marine Park in Western Australia to the Gladstone region of Queensland. They are also found in the waters around Papua New Guinea. [12]

Conservation

Irrawaddy Dolphin

In 2008, the IUCN Red List changed its assessment of the Irrawaddy Dolphin (Orcaella brevirostris) from Data Deficient to Vulnerable. Currently five subpopulations of the Irrawaddy dolphin are Critically Endangered. The species was given the status due to the low sizes of subpopulations, significant range declines, and threats to the species have been well documented and remain unsustainable, severe, and pervasive[13].

Threats

Irrawaddy Dolphins inhabit freshwater environments making them subject to anthropogenic threats. They include mortality from bycatch (specifically gillnets); habitat degradation caused by: dams, deforestation, and mining; vessel strikes; and capture for live aquarium display. Irrawaddy dolphin have also been hunted in the past in certain areas including the Mekong and Mahakam Rivers[13]. Other potential threats include noise pollution in nearby cities and the possibility of mass pathogen induced mortalities.[1]

Conservation Actions

The Action Plan for the Conservation of Irrawaddy Dolphins provides detail on strategies to alleviate bycatch and takes note that protection of certain areas of freshwater Irrawaddy Dolphin populations can be an effective method of conservation.[13]

Australian Snubfin Dolphin

After the species of Australian Snubfin Dolphin (Orcaella heinsohni) was declared a new species in 2005, the species was categorized as Near Threatened on the IUCN Red List in 2008. Although data of population structure and population trends is limited, the categorization of Near Threatened rather than Data Deficient is more appropriate. This is due to species' population size (fewer than 10,000 mature individuals), limited range, low densities in surveyed areas, and its continuing vulnerability to bycatch. After more conclusive data is collected, a reassessment of the species has the potential to be categorized as either Vulnerable or Endangered.[14]

Threats

Due to its occurrence in the close proximity to the Australian/New Guinean shore, the Australian Snubfin Dolphin is threatened by anthropogenic causes. A significant number of Australian Snubfin Dolphins are killed by anti-shark nets used to protect bathers and inshore gill-nets embedded across creeks and rivers used to catch threadfin salmon and barramundi.[14]

Conservation Actions

Although enforcement has been inadequate, regulations, including net attendance rules and gear modifications, have been set in order to reduce bycatch.[14]


References

  1. ^ a b c Ross, G. J. (2006). Review of the conservation status of Australia's smaller whales and dolphins. Department of the Environment and Water Resources.
  2. ^ Beasley, I., Robertson, K. M. and Arnold, P.. 2006. DESCRIPTION OF A NEW DOLPHIN, THE AUSTRALIAN SNUBFIN DOLPHIN ORCAELLA HEINSOHNI SP. N. (CETACEA, DELPHINIDAE). Marine Mammal Science 21: 365 -400
  3. ^ Beasley, Isabel L. (2007). Conservation of the Irrawaddy dolphin, Orcaella brevirostris (Owen in Gray, 1866) in the Mekong River: biological and social considerations influencing management. PhD thesis, James Cook University.
  4. ^ Evans, Peter G.H. (1984). Macdonald, D., ed. The Encyclopedia of Mammals. New York: Facts on File. pp. 180–185. ISBN 0-87196-871-1.
  5. ^ Arnason U., Gretarsdottir S.. 1992. Evolution of the common cetacean highly repetitive DNA component and the systematic position of Orcaella brevirostris. Journal of Molecular Evolution 34: 201-208.
  6. ^ LeDuc, R.G., Perrin, W.F., Dizon, A.E. (1999). Phylogenetic relationships among the delphinid cetaceans based on full cytochrome b sequences. Marine Mammal Science 15, 619–648.
  7. ^ May-Collado, L., Agnarsson, I. (2006). Cytochrome b and Bayesian inference of whale phylogeny. Molecular Phylogenetics and Evolution 38, 344-354.
  8. ^ World Wildlife Fund. (2013). Irrawaddy dolphin. Retrieved from wwf.panda.org: http://wwf.panda.org/what_we_do/endangered_species/cetaceans/about/irrawaddy_dolphin/
  9. ^ "Australian Snubfin Dolphins, Orcaella heinsohni ~ MarineBio.org." MarineBio Conservation Society. Web. Thursday, October 24, 2013. <http://marinebio.org/species.asp?id=1320>.
  10. ^ Robertson KM, Arnold PW (2009) Australian snubfin dolphin Orcaella heinsohni. In: Encyclopedia of marine mammals (Perrin WF, Würsig B, Thewissen JGM, eds.) Academic Press, Amsterdam, pp. 62-64.
  11. ^ Parra, G.J. (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. Ph.D. Thesis. Townsville: James Cook University. Referenced on: http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=81322
  12. ^ Case, A. (2011, June 8). Snubfin dolphins face extinction . Retrieved from Australian Geographic: http://www.australiangeographic.com.au/journal/snubfin-dolphins-face-extinction.htm
  13. ^ a b c Reeves, R.R., Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K. 2008. Orcaella brevirostris. IUCN Red List of Threatened Species. Version 2013.1. International Union for Conservation of Nature. Retrieved 23 October 2013.
  14. ^ a b c Reeves, R.R., Jefferson, T.A., Karczmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E.R., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K. 2008. Orcaella heinsohni. IUCN Red List of Threatened Species. Version 2013.1. International Union for Conservation of Nature. Retrieved 23 October 2013
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