The Common Dolphin Delphinus delphis

Introduction

Australia’s waters are the home of several groups of marine mammals. These include seals (Order Carnivora), which spend much of their time on land, dugongs (Order Sirenia) in the north of the continent, and the Order Cetacea, which includes whales and dolphins, such as the Common Dolphin, Delphinus delphis.

Common Dolphins
Photographer / Source: Mark Norman

Where do they occur?

Common Dolphins are found world wide in tropical to temperate seas and in shallow and oceanic waters. They are recorded widely in Australian and Victorian waters and are often found stranded on beaches. D. delphis seems to be a casual visitor to Port Phillip Bay. Large herds observed offshore are possibly linked with fish migrations

What do they eat?

Common dolphins are predators of fish and cephalopods (squid and octopus) and take whatever is in season. There is no information on their feeding preferences in Victoria, although small school species such as anchovies and mackerel are likely to be important.

What is their breeding cycle and social organisation?

Common Dolphins are social animals and in Victorian waters occur in small herds of five to fifty throughout the year. In summer, larger groups of many thousands have been reported in Bass Strait. In all well-studied populations, males are larger than females, but there are no representative measurements for Victoria. From studies in the eastern North Pacific, we know that females are three to four years old at sexual maturity and that males mature between seven and twelve. Gestation takes 10-11 months in northern hemisphere populations and although births occur year round, they peak in summer and autumn. Size at birth is around 0.8 m to 0.9 m, and there is a Victorian record of a 0.9 m new born calf stranded in January. Calves are probably weaned by 18 months.

What is their conservation status?

The species has not been surveyed, but it is considered to be common in Victoria. Common Dolphins are protected by both Federal and State laws.