Three species of dolphin are found in South Australia: the Indo-Pacific bottlenose dolphin (Tursiops aduncus), found in coastal waters such as those of the the Adelaide Dolphin Sanctuary; the common bottlenose dolphin (Tursiops truncatus), which live along oceanic coasts and in the deep water off South Australia; and the short-beaked common dolphin (Delphinus delphis), which may be seen in the gulfs but usually inhabit deeper waters.
In the Adelaide Dolphin Sanctuary there are approximately 40 Indo-Pacific bottlenose dolphins that are frequently observed, with more than 300 of various species recorded as visitors. Extensive research has been undertaken by the Whale and Dolphin Conservation, and Dr Mike Boseley, on the behaviour and life-cycle of the sanctuary animals and the adverse effects of human interference.
Indo-Pacific bottlenose dolphins grow to around 2.5 metres in length, and weigh about 160 kilograms. They live for up to 40 years. Like whales, dolphins breathe through a blowhole on the top of their heads.
Dolphins can dive to depths of more than 500 metres, but they must surface for air every few minutes. Dolphins have excellent vision above and below the water.
Most bottlenose dolphins are highly sociable and often can be observed as part of a group known as a pod. These pods of up to 15 dolphins hunt, play and help protect each other. Most members of the pod are unrelated, although mothers may stay with their offspring for up to eight years. Adult males generally form separate bachelor groups of two or three, forming bonds that may last a lifetime.
Females usually become sexually mature between the ages of five and 12 and males usually become sexually mature between the ages of 10 and 12. Bottlenose dolphins may breed throughout the year, but they usually give birth to their calves in late summer. A female may be pregnant for up to 12 months and a calf may suckle for as long as 18 months, remaining with the mother for many years. Local females usually produce offspring once every three to four years.
A natural bond is formed between female dolphins and those pregnant or with calves. These groupings are called “maternity pods”. When dolphins are first born they are usually about 1 metre in length and dark in color. They tend to be born tail first and are able to swim and breathe within minutes of birth.
Human activities are threatening the survival of dolphins. Pollution, stormwater and rubbish represent a major threat affecting food supplies. Sanctuaries like the Adelaide Dolphin Sanctuary are vital to ensure the continued survival of these wonderful creatures.