Bottlenose Dolphin

Tursiops truncatus
Scientific classification
Binomial name
Tursiops truncatus

The Bottlenose Dolphin (Tursiops truncatus) is the most common and well known dolphin species. They inhabit warm and temperate seas worldwide and may be found in all but the Arctic and the Antarctic Oceans.

Table of contents
1 Description
2 Subdivision
3 Conservation
4 Bottlenoses in human culture
5 References


Bottlenose Dolphins are grey; dark at the top near the dorsal fin, very light and almost white at the underside. This way, they are hard to see both from above and below when swimming. The elongated upper and lower jaws give the animals their name; the nose however is located elsewhere: it's the blowhole on top of the head. Their face shows a characteristic "smile". Adults range in length from 2 to 4 meters and in weight from 150 to 650 kilograms, with males being slightly longer and considerably heavier than females on average.

The flukes (lobes of the tail) and dorsal fin are formed of dense connective tissue and don't contain bones or muscle. The animal propels forward by moving the flukes up and down. The pectoral flippers (at the sides of the body) serve for steering; they contain bones clearly homologous to the forelimbs of land mammals (from which dolphins and all other whales evolved some 50 million years ago).

Bottlenose Dolphins normally live in groups called pods, containing up to 12 animals. These are long-term social units. Typically, a group of females and their young live together in a pod, and juveniles in a mixed pod. Several of these pods can join together to form larger groups of one hundred dolphins or more. Males live mostly alone or in groups of 2-3 and join the pods for short periods of time.

Bottlenose Dolphins typically swim at a speed of 5-11 kilometers per hour; for short times, they can reach peak speeds of 35 kilometers per hour.

The species is commonly known for its friendly character and curiousity. It is not uncommon for a diver to be investigated by a group of them. Occasionally, dolphins have rescued an injured diver by raising them to the surface, a behavior they also show towards injured members of their own species.

Dolphins are predators however, and they also show aggressive behaviors. This includes fights among males for rank and access to females, as well as aggressions towards sharks and other smaller species of dolphins.

Female Bottlenose Dolphins live for about 40 years; the more stressful life of the males apparently takes its toll, and they rarely live more than 30 years.

Their diet consists mainly of small fish, occasionally also squid, crabs and similar animals. Their peg-like teeth serve to grasp but not to chew food. When a shoal of fish has been found, the animals work as a team to keep the fish close together and maximize the harvest. They also search for fish alone, often bottom dwelling species.

The search for food is aided by their echolocation system: they locate objects by producing sounds and listening for the echo. The clicking sounds are emitted in a focused beam towards the front of the animal. They have two small ear openings behind the eyes, but most sound waves are transmitted to the inner ear through the lower jaw. As the object of interest is approached, the echo grows louder; the dolphins protect themselves by turning down the volume of the emitted sounds. This is in contrast to the technique used by bat echolocation and human sonar: here the sensitivity of the sound receptor is turned down.

They also have sharp eyesight. The eyes are located at the sides of the head and have a tapetum lucidum which aids in dim light.

Bottlenose Dolphins communicate with body movements and with sounds they produce near their blow hole (they lack vocal cords). Each animal has a characteristic signature sound with which it identifies itself to others. Other communication uses about 30 distinguishable sounds, but a "dolphin language" has not been found. See also the article on the dolphin brain for some general information about the intelligence of dolphins.

Every 5-8 minutes, the dolphins have to rise to the surface to breathe through their blowhole. (On average, they breathe more often however, several times per minute.) Their sleep is thus very light; some scientists have suggested that the two halves of their brains take turns in sleeping and waking.

The gestation period is 12 months. The young are born in shallow water, sometimes assisted by a "midwife" (which may be male). The calves are about 1 meter long at birth. To speed up the nursing process, the mother can eject milk from her mammary gland. The calve is nursed for 12 to 18 months. The young live closely with their mother for up to 6 years; the males are not involved in the raising of their offspring. The females become sexually mature at age 5-12, the males a bit later, at tage 10-12.

Large shark species such as Tiger sharks, Dusky Sharks, and Bull Sharks prey on Bottlenose Dolphins. Killer Whales may also prey on them, but this seems rare. Humans kill Bottlenose Dolphins for food or because they compete for fish; the dolphins also sometimes die when caught in fishing nets.


Scientists have long been aware of the possibliity that the Bottlenose Dolphins might divide into more than one species. The advent of molecular genetics has allowed much greater insight into a previously untractable problem. The consenus amongst scientists (and reported in Rice's 1998 standard reference on the taxonomy of cetaceans [1]) is that there are two species:

  • the Bottlenose Dolphin (T. truncatus), found in in most warm to tropical oceans, color sometimes almost blue, a dark line from beak to blowhole
  • the Indo-Pacific Bottlenose Dolphin (T. aduncus), lives in the waters around India, Australia and South-China, back is colored dark-gray and belly is white with gray spots.

  • the Pacific Bottlenose Dolphin (T. gillii), lives in the Pacific, has a black line from the eye to the forehead.

is commonly recognised as a subspecies of T.truncatus.

Unfortunately much of the old scientific data in the field combines data about the two species into a single group - making it effectively useless in determining the structural differences between the two species. Indeed the IUCN lists both species as data deficient in their Red List of endangered species precisely because of this issue. See [1].

Some recent genetic evidence suggests that the Indo-Pacific Bottlenose in fact belongs in the genus Stenella - the species being more similar to the Atlantic Spotted Dolphin than the Common Bottlenose ([3]). The taxonomic situation of these animals is likely to remain in flux for some time to come.


Bottlenose Dolphins are not endangered. Their future is currently foreseen to be stable because of their abundance and high adaptability. In U.S waters, hunting and harassing of marine mammals is forbidden in almost all circumstances. The international trade in dolphins is also tightly controlled.

Bottlenoses in human culture

Bottlenose Dolphins (as well as other dolphins) are often trained to perform in dolphin shows. Some animal rights activists claim that the dolphins there are not adequately challenged and that the pools are too small; others maintain that the dolphins are well cared for and enjoy performing.

Direct interaction with dolphins is used in the therapy of severely handicapped children.

The eponymous hero of the television series Flipper was a Bottlenose Dolphin living in the waters off the Florida Keys.

The military of the U.S and Russia train Bottlenose Dolphins for wartime tasks such as attaching mines to enemy ships, locating sea mines, or fighting off enemy divers.


  1. "Marine Mammals of the World. Systematics and Distribution", by Dale W. Rice (1998). Published by the Society of Marine Mammalogy as Special Publication No. 4,
  2. Hale, P.T., Barreto, A.S. and Ross, G.J.B. (2000). Comparative morphology and distribution of the aduncus and truncatus forms of bottlenose dolphin Tursiops in the Indian and Western Pacific Oceans. Aquatic Mammals 26(2): 101-110. Discussing distinguishing features between Bottlenose Dolphin species
  3. LeDuc R.G., Perrin W.F. and Dizon A.E. (1999). Phylogenetic relationships among the delphinids cetaceans based on full cyctochrome b sequences. Marine Mammal Science Vol 15, pages 619-648.