What is a bottlenose dolphin? Bottlenose dolphins are actually small whales, and belong to the group known as 'toothed whales'. They are air breathing mammals so, even though they have adapted to the marine environment, they still must come to the surface to breathe through the blowhole on top of their heads. The common bottlenose dolphin (Tursiops truncatus) and Indo-Pacific bottlenose dolphin (Tursiops aduncus) are so named because they have a short rounded snout or 'beak' that resembles a bottle.
What do they look like? Bottlenose dolphins are sleek and streamlined and can travel at speeds of up to 35 kilometres per hour. They have a prominent dorsal fin, which can be seen slicing through the water. Bottlenose dolphins vary in size, shape and colour depending on where they are found. In general dolphins have a dark grey back and a light grey belly. This helps to camouflage the animal so when potential predators (such as killer whales or sharks) look up from the deep, the light grey belly blends in with bright surface waters. When seen from above, the grey back blends in with the deep dark waters below. Bottlenose dolphin calves weigh around 15-30 kilograms at birth and around 70-130 centimetres long. They will grow up to seven times their original body weight in their first year. An adult will reach 2-4 metres and weigh between 150-650 kilograms. Bottlenose dolphins can live to over 30 years of age.
Where do they live? Bottlenose dolphins are common in temperate and tropical seas all over the world. There is an inshore species that is often seen along the coast, in estuaries and even in rivers, and an offshore species that can be found in the open ocean. Bottlenose dolphins can be found in all of WA's marine parks but Shark Bay Marine Park is renowned for its friendly dolphins at Monkey Mia which regularly visit the beach to interact with people and accept fish from them (rangers supervise this to make sure the dolphins aren't given too much food so they continue to forage in the wild). Perhaps you have visited Monkey Mia and met these delightful animals!
What they eat and how: Bottlenose dolphins eat around 15 kilograms of food per day consisting of 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 food. Dolphins use echolocation for hunting and navigating. The clicking sounds they make travel through the water hitting objects up to 200 metres in front and echoing back to the dolphin, which allows them to work out the size, shape, speed, distance and direction of their prey. Working together as a group, dolphins can trap schools of fish or squid by rounding them up and diving into the middle to feed, swallowing their food whole and head first.
Vision courtesy of MIRG Australia (www.mirg.org.au)/Blue Office Productions
Threats: Natural predators include killer whales and sharks such as tiger sharks and dusky sharks. Other risks include entanglement in fishing nets (trawling, drift and gill nets), habitat destruction and degradation, pollution (organochlorines), disease (Morbillivirus) and illegal killing of dolphins. In some parts of the world bottlenose dolphins are killed for food. It is also possible that the dolphins' key prey species are being fished out, thus reducing the amount of food available to them.
Behaviour: Bottlenose dolphins are very social animals that live together in pods. Inshore pods may have around 12 members and offshore pods may number in the hundreds. Within the pod there is a strong sense of unity or bonding, with lots of interaction between the dolphins in the group (touching, chasing, making noises etc). Bottlenose dolphins are highly active and can be frequently seen tail slapping, riding on bow waves created by boats, surfing waves or leaping playfully into the air. They will chase one another, roll over each other and carry objects such as seaweed.
Breeding and caring for young: Dolphins have many partners over a lifetime and mate all year round. Females begin to breed from about six years of age, and have a calf every two to three years. Calves are born throughout the year, although most are born in spring and summer after a gestation period of 12 months. Calves are born tail first so that they do not drown and their mother quickly pushes them up to the surface for their first breath. Calves suckle their mother's milk for up to 18 months, although they begin eating fish at about 6 months of age and remain with their mother for about six years.
Conservation status: The bottlenose dolphin is common throughout the world's oceans.
How you can protect the bottlenose dolphin: You can care for them by helping to keep their environment clean. Take your rubbish home, and if you find any floating at sea or on the coast, please pick it up. Bottlenose dolphins often strand, either singly or in small groups. If you find a stranded or entangled dolphin you should report it to the Department of Environment and Conservation. While you are waiting for help to arrive, keep it wet and cool, and keep it shaded so it doesn't get sunburnt, but remember not to obstruct the blowhole, so the dolphin can breathe.
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