Common Dolphin

The Common Dolphin is a slender streamlined dolphin with a moderately long beak, tall dorsal fin and large tapering flippers.

Identification

The Common Dolphin has an attractively marked flank of yellow, buff and grey patches forms a sweeping hour glass shape brought into stark relief by the dark grey upper body and white belly. A number of bold dark stripes sweeping along the body further add to the dramatic appearance of this species. Like many widely distributed cetaceans, there appears to be a number of forms based on morphological differences and supported by genetic studies. A long beaked and a short beaked form are recognised.

Distribution

The possibility of potential confusion between the short and long beaked forms makes defining a clear distribution difficult. Common Dolphins appear to favour continental shelf and pelagic waters of the Atlantic and Pacific Oceans within the broad zones of the temperate and tropical latitudes. The presence of warm water influences the distribution of this species. Forming groups, which often number in the thousands the common dolphin travels at a fast and furious pace leaping clear of the water giving the appearance of a coordinated display.

Feeding and diet

The main prey of the Common Dolphin are squid and small school fish such as sardines, pilchards and anchovies. To take advantage of the movement of these organisms the dolphin will often feed at night, driving the swarming prey to the surface and feeding on the resultant confusion. This cooperative feeding strategy will often benefit surface feeding predators such as birds.

Life history cycle

In tropical waters, calving probably occurs all year round. Further towards the cooler latitudes, births are concentrated in late spring or early summer. The gestation period lasts for 11 to 12 months with the single young suckling for an additional period of at least a year. This extended period of infant care would mean that females maintain a minimum of at least two years between births.

Conservation status

In the past, this common species was directly targeted by fisheries in many parts of the world. It also was and continues to be one of the major casualties of some fishing industry practices. Before moratoriums forced modifications to these operations it was estimated that drift nets and purse seining in particular killed many thousands of animals each year. Current threats still include fishing industry activities along with habitat modifications and biological pollution.

References

• Baker, A. N. 1999. Whales and Dolphins of Australia and New Zealand: an identification guide. Allen & Unwin, St Leonards, Australia.
• Bryden, M., Marsh, H. and Shaughnessy, P. 1998. Dugongs, Whales, Dolphins and Seals. A guide to the sea mammals of Australasia. Allen & Unwin, St Leonards, Australia.
• Menkhorst, P. 2001. A Field Guide to Mammals of Australia. Oxford University Press, Melbourne, Australia.
• Reeves, R. R., Stewart, B. S., Clapham, P. J. and Powell, J. A. 2002. National Audubon Society Guide to Marine Mammals of the World. Chanticleer Press, Inc New York, USA.