Bottlenose dolphins communicate through burst pulsed sounds, whistles, and body language. Examples of body language include leaping out of the water, snapping jaws, slapping the tail on the surface and butting heads.[34] Sounds and gestures help keep track of other dolphins in the group, and alert other dolphins to danger and nearby food. Lacking vocal cords, they produce sounds using six air sacs near their blow hole. Each animal has a uniquely identifying, frequency-modulated narrow-band signature vocalization (signature whistle).
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The Bottlenose Dolphins Taxonomy
Scientists were long aware that Tursiops dolphins might consist of more than one species. Molecular genetics allowed much greater insight into this previously intractable problem. The consensus is there are two species, although a third distinct species was described in 2011:
The common bottlenose dolphin (T. truncatus), is found in most tropical to temperate oceans; color is grey, with the shade of grey varying among populations; it can be bluish-grey, brownish-grey, or even nearly black, and is often darker on the back from the rostrum to behind the dorsal fin.
The common bottlenose dolphin (T. truncatus)
The Indo-Pacific bottlenose dolphin (T. aduncus), lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa; the back is dark-grey and the belly is lighter grey or nearly white with grey spots
The Indo-Pacific bottlenose dolphin (T. aduncus) The Burrunan dolphin (T. australis), found in the Port Phillip and Gippsland Lakes areas of Victoria, Australia, was described in September 2011 after research showed it was distinct from T. truncatus and T. aduncus.
The Burrunan dolphin (T. australis)
The following are sometimes recognized as subspecies of T. truncatus:
- The Pacific bottlenose dolphin (T. gillii or T. truncatus gillii), lives in the Pacific, and has a black line from the eye to the forehead.
- The Black Sea bottlenose dolphin (T. truncatus ponticus), lives in the Black Sea.
The two ecotypes of the common bottlenose dolphin within the western North Atlantic are represented by the shallower water or coastal ecotype and the more offshore ecotype. In general, there is significant genetic variation between populations, even among nearby populations. The IUCN lists both species as data deficient on their Red List of endangered species because of this issue.
Some recent genetic evidence suggests the Indo-Pacific bottlenose belongs in the genus Stenella, since it is more like the Atlantic spotted dolphin (Stenella frontalis) than the common bottlenose. Dolphins belong to the suborder Odontocetae, which groups all toothed whale species, the largest of which is the sperm whale.
Bottlenose Dolphin Reproduction
Both genders have genital slits on the underside of their bodies. The male can retract and conceal its penis through its slit. The female's slit houses its vagina and anus. Females have two mammary slits, each housing one nipple, one on each side of the genital slit. The ability to stow their reproductive organs (especially in males) allows for maximum hydrodynamics.
The breeding season produces significant physiological changes in males. At that time, the testes enlarge, enabling them to hold more sperm. Large amounts of sperm allow a male to wash away the previous suitor's sperm, while leaving some of his own for fertilization. Also, sperm concentration markedly increases. Having less sperm for out-of-season social mating means it wastes less. This suggests sperm production is energetically expensive. Males have large testes in relation to their body size.
During the breeding season, males compete for access to females. Such competition can take the form of fighting other males or of herding females to prevent access by other males. In Shark Bay, male bottlenose dolphins have been observed working in pairs or larger groups to follow and/or restrict the movement of a female for weeks at a time, waiting for her to become sexually receptive. These coalitions will fight with other coalitions for control of females.
Mating occurs belly to belly. Dolphins have been observed engaging in intercourse when the females are not in their estrous cycles and cannot produce young, suggesting they may mate for pleasure. The gestation period averages 12 months. Births can occur at any time of year, although peaks occur in warmer months. The young are born in shallow water, sometimes assisted by a (possibly male) "midwife", and usually only a single calf is born. Twins are possible, but rare. Newborn bottlenose dolphins are 0.8–1.4 m (2.6–4.6 ft) long and weigh 9–30 kg (20–66 lb), with Indo-Pacific bottlenose dolphin infants being generally smaller than common bottlenose dolphin infants.
To accelerate nursing, the mother can eject milk from her mammary glands. The calf suckles for 18 to 20 months, and continues to closely associate with its mother for several years after weaning. Females sexually mature at ages 5–13, males at ages 9–14. Females reproduce every two to six years. Georgetown University professor Janet Mann argues the strong personal behavior among male calves is about bond formation and benefits the species in an evolutionary context. She cites studies showing these dolphins as adults are inseparable, and that early bonds aid protection, as well as in locating females.
Unique Characteristics of Bottlenose Dolphin
The dolphin is considered the most intelligent animal of the aquatic environment, and among the most intelligent animals on the planet.
A dolphin's dominant sense is echolocation. Acoustical "clicks" reverberate back to the dolphin, giving it a very clear picture of its surroundings. Echolocation allows a dolphin to locate food and detect obstacles and other creatures under almost any condition.
Social and Family Structure
Dolphins are very curious, strong and physically resilient. Bottlenose dolphins spend much of their time playing and interacting with their pod members. It is highly sociable and usually sighted in groups of 5, 7 or more. Pods are structured around a matriarchal system.
Distribution
Dolphins frequent bays and coastlines, usually in depths under 20 meters. While some pods take up permanent residence and establish home waters, others are migratory and swim considerable distances from coast to coast.
Threats
Man is the only known enemy of these animals. In particular, the tuna fishing industry has had a profoundly negative effect on the species' survival rates. Since dolphins usually accompany schools of yellow-fin tuna, they are often caught and perish in tuna nets.
Bottlenose dolphins are also hunted as food source, used as shark bait or taken alive to be trained for circus shows in some parts of the world, though there is a growing trend towards protective legislation for dolphins.
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