Bottlenose Dolphin

Introduction

The Bottlenose Dolphin is found right around the coast of Australia and can sometimes be seen catching waves with surfers in Sydney.

Identification

The Bottlenose Dolphin has a short rounded snout, described as bottle-shaped, a smooth rounded melon. The large dorsal fin is slightly hooked and set half way along the body. Overall the body colour is a series of grey tones with an indistinct paler grey wash on the flanks fading into an off-white belly.

Two forms of Bottlenose Dolphin are currently recognised - the 'inshore' form and the 'offshore' form, which could possibly be different species. The Bottlenose Dolphin is commonly seen in groups or pods, containing anything from two or three individuals to more than a thousand.

Habitat

The Bottlenose Dolphin lives in coastal waters and oceans. They are resident or frequent inhabitants of bays and coastal areas. In some areas populations will maintain defined home ranges within recognised coastal landforms. Others are pelagic animals, found well out to sea, often off or quite close to a continental shelf edge. This species occupies a broader range of habitats than any other marine mammal.

Distribution

The Bottlenose Dolphin is found worldwide in temperate and tropical waters.

Feeding and diet

The Bottlenose Dolphin occupies a wide range of habitats, giving it access to a huge variety of organisms including invertebrates, bottom-dwelling fish and squid, plus the full range of pelagic (oceanic) fish species. Bottlenose Dolphins are a very social species and feed together, although they are known to feed alone. They also take advantage of human-induced prey abundance and regularly approach fishing trawlers.

Other behaviours and adaptations

Dolphins and other toothed whales use echolocation to locate prey, as well as other dolphins, and to develop a picture of their surroundings. By making clicking sounds and waiting for the echo to return from surrounding objects, they can determine how far away the object is and how big it might be. Working together as a group, dolphins can trap schools of fishes or squids by rounding them up and diving into the middle to feed.

The Bottlenose Dolphin is sleek and streamlined and can travel at speeds of up to 35 km per hour.

Communication

Bottlenose Dolphins communicate using clicking sounds and echolocation.

Life history cycle

Bottlenose Dolphin calves are born in the water after a gestation period of one year and suckle for about 18 months. They remain with the mother for about four years. They are a long-lived species, with an extensive life span of up to 45 years.

This species' life history is well known from years of observation in the wild and from its long history as a captive animal. The social organisation of groups and their size varies greatly, to some extent depending on the habitat. Animals in bays form only small groups of maybe 15 individuals while those off shore may number in the hundreds. Birth of the young occurs after a gestation period of about a year.

Conservation status

The Bottlenose Dolphin is still an abundant species, despite incidental kills by the fishing industry. However, habitat degradation and pollution are of increasing concern for Bottlenose Dolphins. Pollution is thought to have resulted in some cases of mass die-offs which occurred off the coast of the United States of America and in the Gulf of Mexico.

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. Pp. 282-283. Chanticleer Press, Inc New York, USA.