Bottlenose Dolphin (Tursiops sp.)
What does it look like?
The bottlenose dolphin is one of the world’s most familiar animals. It is dark to light grey, fading to white on the belly, with a slightly hooked dorsal fin set midway along the body. It has a short rostrum containing 18–26 cone-shaped teeth, and a prominent melon (forehead) containing oily fat. It is thought the melon helps to produce and concentrate the high-frequency whistles, clicks and pulses used by the dolphin to find its food. (This hunting technique is called echolocation.) The melon also features the dolphin’s nostril, called a blowhole, which is closed with a valve when the dolphin submerges. The dolphin can grow to 4 m and 650 kg, but those in Australia tend to be smaller, about 2.6 m long and 120 kg.
Research suggests that there are two distinct species of bottlenose dolphin. The dolphins in Western Australia are currently considered Indian Ocean bottlenose dolphins (Tursiops aduncus
Where does it live?
The bottlenose dolphin is common in seas world-wide. It is found around the entire Australian coastline, from estuaries to the open ocean. More than 2,000 dolphins inhabit Shark Bay and about 200 reside in the Monkey Mia
region. The complex social behaviour of these dolphins has been studied for more than 20 years, the longest continuous study
of bottlenose dolphins in the world.
Want to see the dolphins of Monkey Mia in action?
Dolphins in the Monkey Mia population form small subgroups which live in a defined home range. Members of the group help each other rear their young, called calves, and to hunt for fish, squid and crustaceans. At times they cooperate to herd schools of fish close to the water’s edge, clocking speeds of up to 40 kph! In some places in Shark Bay the dolphins actually trap the fish on shore, and then deliberately beach themselves to grasp their prey! Bottlenose dolphins also use their rostrum to dig out fish buried on the sea floor or under seagrass beds. In Shark Bay some dolphins have been discovered using sea sponges like gloves to protect their sensitive rostrum from being injured while poking about the sea floor. This is the only known example of tool use by wild dolphins anywhere in the world.
How does it breed?
The bottlenose dolphin lifespan is 30 to 35 years for males and 35 to 40 years for females. Females begin to breed from about 10 to 12 years of age and have one calf every three to four years. In this sociable species, even mating is a group activity. The males take turns to mate with a female, and try to prevent rival groups from having access to her. A calf is born about 12 months later and drinks its mother’s milk until it is about three to four years old.
Any threats to its survival?
The bottlenose dolphin is common and abundant. It has largely escaped the fate of species such as the pantropical spotted dolphin and spinner dolphin, which have been decimated by the tuna-fishing industry. Nevertheless, the bottlenose dolphin is still affected by pollution, especially plastic bags and fishing line. In Shark Bay, there is also a risk that dolphins may be ‘killed by kindness’. Some dolphins have learned to beg for food rather than hunt it themselves. Feeding dolphins teaches them to rely on handouts, and calves that don’t learn to hunt soon starve to death. At Monkey Mia, only adult females are fed, under ranger supervision, and never more than a third of their daily requirement. They must hunt for the other two-thirds themselves! It is illegal to feed dolphins without authorisation anywhere in Western Australia. Information gained from research at Monkey Mia
is used worldwide to manage human impacts on dolphins.
For more information about Western Australian wildlife check out the WA Museum Fauna Base
to download a printable PDF of this fact sheet.