Indo-pacific humpbacked dolphin

April 19, 2011, 11:42 pm
Content Cover Image

Indo-Pacific humpacked dolphin. Source: Creative Commons


The Indo-Pacific humpacked dolphin (Sousa chinensis), a marine mammal, is a member of the family of oceanic dolphins within the order of cetaceans. The species is also known as the pink dolphin, named after members of the species who have a characteristically bright pink color, are found on the coasts of east Africa, Asia, and Australia.  Depending on location, the dolphins are known to vary in their shape and colors, leading to a debate as to whether the four distinctively different dolphins are all a part of Sousa chinensis, or whether all four are a different species of their own. The four argued species are:

  • Sousa plumbea (Indian humpback dolphin or Plumbeous humpback dolphin) - Indian Ocean east to the Malay Peninsula
  • Sousa lentiginosa  (Speckled dolphin) - waters around India and Sri Lanka.
  • Sousa chinensis (Indo-Pacific humpack dolphin)
  • Sousa borneensis (Malayan dolphin) - around the island of Borneo

  caption Indo-Pacific humpback dolphins (Sousa chinensis) in Hong Kong. The mother is dumping heat through dilated capillary vessels. Source:Thomas Jefferson

caption Size comparison of an average human against the Humpback dolphins. Source: Chris Huh

 Conservation Status:
caption Indo-pacific hump-backed dolphin distribution in the world. Source: IUCN

 

Scientific Classification

Kingdom: Animalia (Animals)
Phylum:--- Chordata
Class:------ Mammalia (Mammals)
Order:-------- Cetacea (Cetaceans)
Family:-------- Delphinidae       
Genus:----------Sousa
Species:----------- Sousa chinensis (Osbeck, 1765)

Common names

Bornean dolphin
Borneo white dolphin
Chinese white dolphin
Indian humpback dolphin
Indo-Pacific hump-backed dolphin
Indo-Pacific Humpback Dolphin
Indo-Pacific humpbacked dolphin
Lead-colored dolphin
Pacific humpback dolphin
Plumbeous dolphin
Ridge-backed dolphin
Speckled dolphin
White dolphin

However, at this time, only the Indo-Pacific humpack dolphin is recognized. The only other recognized humpback dolphin under the genus Sousa is the Atlantic humpback dolphin (Sousa teuszii).

Physical description

The Indo-Pacific humpback dolphin has a typically streamlined body and a long slender beak. Populations differ in both shape and color, with those in the west of the range possessing a 'double-step' dorsal fin with a fatty hump upon which the dorsal fin sits. Although usually dark grey on their back and lighter underneath, white and pink variations are also known; the most famous of these are the 'pink dolphins' of Hong Kong Bay.

Also, colour can vary greatly between different ages and individuals. For example, calves are typically darker than adults. 

Given the wide morphological differences, there is some disagreement as to whether the Indo-Pacific humpback dolphin does in fact represent four different species: S. plumbea, S. lentiginosa, S. chinensis and S. borneensis respectively

Indo-Pacific humpbacked dolphins range from 220 to 230 cm in length, and  females may be slightly smaller. 

Reproduction

Little is known about the reproductive habits of Indo-Pacific humpbacked dolphins.  Studies have shown that peak months of birth are between December and February.  Courtship may involve chasing in circles at higher speeds, turning on one side and waving a flipper in the air, or somersaulting. There is little data on maturation and mortality. 

Behavior

Indo-Pacific humpbacked dolphins are gregarious animals. They typically live in groups of three to seven, although groups of up to 20 have been observed. These dolphins have been known to chase off and kill sharks.

Indo-Pacific humpacked dolphins are slow swimmers, moving an average of 4.8 km/hr.  Despite this sluggishness, many aerial displays are seen; including breaching, when the dolphin leaps out of the water, lob-tailing (slapping the surface of the water with the tail) and spyhopping, when the dolphin raises its head vertically out of the water and then sinks below the surface quietly. They surface for long intervals of between 40 and 60 seconds.

The humpback dolphin has an unusual diving posture, first lifting its beak out of the water and arching its back, and then pausing before dipping below the surface or flipping its tail to dive. 

Aggression appears to serve a useful purpose in predator defense and in a social context as aggression appears to affect dominance rank within the group.

Distribution

Indo-Pacific humpbacked dolphins, Sousa chinensis, are found in the Indian and Pacific Oceans. They are found in the Eastern hemisphere along the coasts of Asia, east Africa, and Australia. 

Habitat

Sousa chinensis inhabit in coastal waters such as rivers, estuaries, and mangrovesInhabits coastal tropical and subtropical waters.. Their distribution coincides with the distribution of coastal mangrove areas in the Indian and Pacific Oceans. This dolphin is usually found in shallow waters that are less than 20 metres in depth in warm waters ranging from 15 to 36 degrees Celsius.

Food habits

Sousa chinensis feed in shallow waters on fish, mollusks and crustaceans. When searching for food they use echolocation and hunt either singly or in small groups. Whether or not the dolphin is hunting in small groups, the tend to feed independently, and this may reflect on the density of their prey and the schooling behavior of the dolphins themselves. Although gregarious, these dolphins can be aggressive and require some distance separating themselves from others when feeding.

Conservation status

IUCN Red list: Near Threatened

Threats

Indo-Pacific humpback dolphins are at risk from factors that also threaten all other cetaceans, such as entanglement in fishing nets, pollution and the depletion of fish stocks worldwide. These coastal dolphins are also threatened by boat traffic, a factor that is especially pertinent in Hong Kong where this dolphin's habitat is also the busiest harbour in the world. In South Africa, shark nets may be an important cause of mortality but more data on this potential threat is required. Destruction of coastal mangrove habitats throughout Asia is believed to be causing a decline in the numbers of Indo-Pacific humpbacked dolphins as well.

This species is occasionally hunted for meat, but not on a commercial scale. A few individuals have been captured alive for display at marine parks. One population of a related species on the west coast of Africa actually cooperate with local fishermen. 

References and further reading

  • Encyclopedia of Life, Sousa chinensis (Osbeck, 1765) [[1]] [accessed December 7, 2009]
  • IUCN Redlist, Sousa chinensis [[2]] [accessed December 7, 2009]
  • Carwardine, M., Hoyt, E., Fordyce, R.E. and Gill, P. (1998) Whales and Dolphins. HarperCollins Publishers, London.
  • Macdonald, D.W. (2001) The New Encyclopedia of Mammals. Oxford University Press, Oxford.
  • CITES (July, 2002)
  • Animal Diversity Web (July, 2002)
  • Whale and Dolphin Conservation Society (July, 2002)
  • Our World (July, 2002)
  • Richards Bay Humpback Dolphins (July, 2002)
  • Atkins, S. (2002) Pers. Comm. Search. Carwardine, M. 1995. Whales, Dolphins, and Porpoises. New York, NY: DK Publisher Inc..
  • Ellis, R. 1982. Dolphins and Porpoises. New York, NY: Alfred A. Knopf, Inc..
  • Evans, P. 1987. The Natural History of Whales and Dolphins. New York, New York: Facts on File, Inc..
  • Frère, Céline H., Peter T. Hale, Lindsay Porter, Victor C. Cockcroft, and Merel L. Dalebout. 2008. Phylogenetic analysis of mtDNA sequences suggests revision of humpback dolphin (Sousa spp.) taxonomy is needed. Marine & Freshwater Research, vol. 59, no. 3. 259-268
  • IUCN (2008) Cetacean update of the 2008 IUCN Red List of Threatened Species
  • Jefferson, T.A., S. Leatherwood and M.A. Webber. 1993. Marine mammals of the world. FAO Species Identification Guide. Rome. 312 p.
  • Jefferson, Thomas A., and Leszek Karczmarski. 2001. Sousa chinensis. Mammalian Species, no. 655. 1-9
  • May, J. 1990. The Greenpeace Book of Dolphins. New York, NY: Sterling Publishing Company, Inc..
  • Mead, James G., and Robert L. Brownell, Jr. / Wilson, Don E., and DeeAnn M. Reeder, eds. 2005. Order Cetacea. Mammal Species of the World: A Taxonomic and Geographic Reference, 3rd ed., vol. 1. 723-743
  • Perrin, W. (2010). Sousa chinensis (Osbeck, 1765). In: Perrin, W.F. World Cetacea Database. Accessed through: Perrin, W.F. World Cetacea Database
  • Rice, Dale W. 1998. Marine Mammals of the World: Systematics and Distribution. Special Publications of the Society for Marine Mammals, no. 4. ix + 231
  • Richard Weigl (2005) Longevity of Mammals in Captivity; from the Living Collections of the World. Kleine Senckenberg-Reihe 48: Stuttgart.
  • UNESCO-IOC Register of Marine Organisms
  • Wilson, Don E., and DeeAnn M. Reeder, eds. 1993. Mammal Species of the World: A Taxonomic and Geographic Reference, 2nd ed., 3rd printing. xviii + 1207
  • Wilson, Don E., and F. Russell Cole. 2000. Common Names of Mammals of the World. xiv + 204
  • van der Toorn, J. 1999. "Indo-Pacific hump-backed dolphin" (On-line). Jaap's Marine Mammal Pages. Accessed 11/07/04
Glossary

Citation

Life, E. (2011). Indo-pacific humpbacked dolphin. Retrieved from http://www.eoearth.org/view/article/153812

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