Bottlenose dolphin

The famous dolphins at Monkey Mia are bottlenose dolphins (Tursiops truncatus). Although they are wild, they regularly visit the shore to interact with people. Bottlenose dolphins can also be seen riding on the bow wave created by boats, surfing waves or leaping playfully in the air.

Photo: Bottlenose Dolphins

Description

Bottlenose dolphins have prominent dorsal fins, which are seen slicing through the water. The fin is slightly hooked and set midway along the body. This frequently photographed mammal is also easily recognised by its well-formed melon and short, wide and rounded beak. The species has a medium grey back above a pale or light grey flank or belly. The flippers are broad at the base and taper to a point.

Bottlenose dolphins are very variable in size, ranging from between two and four metres as adults, depending on where they are found. The Shark Bay population, for example, is quite small compared with animals seen in Perth waters. The average length for adults is three metres and calves are about a metre in length when born.

Status and distribution

Bottlenose dolphins are common in cold, temperate and tropical seas and estuaries all over the world. They are often seen close inshore in estuaries, even entering rivers. An offshore form is found in the open ocean. In some parts of the world, bottlenose dolphins are killed for food.

Life history

Bottlenose dolphins have a fascinating social structure. Within a population, they form small subgroups that inhabit a defined home range. However, members of the group change from time to time and they assist each other in activities such as fish herding and calf rearing.

Even mating is a group activity - the males cooperate to herd a femal in reproductive condition to take turns to mate with her. They also try to prevent rival groups from having access to her. A calf is generally born 12 months later and lives for up to 30 years.

Females begin to breed from about six years of age, calving every two or three years. The calves suckle for up to 18 months.

Bottlenose dolphins eat a wide variety of fish, squid and octopuses. The offshore form may be able to dive to depths of more than 600 metres to catch fish.

Stranding history

Bottlenose dolphins often strand, either singly or in small groups. In October 1990, eleven bottle nose dolphins were returned to the Peel Inlet, south of Perth, Western Australia, after becoming trapped in a shallow inland lake and shallow rivers near the coastal town of Mandurah. A major concern when they strand is the risk of sunburn, and many animals can be seen with scars from burning.