More frequently known as the Common Bottlenose Dolphin, Tursiops truncatus (literally, "dolphin with a cut-off face") is the most distinguished species of the family Delphinidae (dolphins). This is partially due to its characteristically short, rounded beak resembling a bottle - accounting for the informal name. However, the Common Bottlenose Dolphin is also the most familiar species of dolphin because of its wide range of exposure around the world through captivity in marine parks and dolphinariums. The following report outlines the extensive habitat of this species, as well as identifying five adaptations (structural, behavioural and physiological) that it has developed in order to maintain its status as the most prevalent dolphin species in the world.



Scientific Classification
  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Mammalia
  • Order: Cetacea
  • Sub-order: Odontoceti
  • Family: Delphinidae
  • Genus: Tursiops
  • Species: Truncatus


Diagram
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Habitat

Being the most prevalent dolphin species in the world, the Common Bottlenose Dolphin is widespread, active throughout both temperate and tropical waters worldwide. Despite this extensive range, it does not appear to be present in polar waters (pole-ward 45°) except in southern New Zealand and northern Europe, typically inhabiting waters with a surface temperature between 10 and 32 degrees celsius. The Common Bottlenose Dolphin is one of few species that expoits a wide array of habitats around the world, including both temperate and tropical inshore, coastal, shelf and oceanic waters.
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Due to the extensiveness of the species' population, it is understandable that the Common Bottlenose Dolphin has been separated into two varieties: coastal ecotypes and offshore ecotypes. Population density is much higher near shore than the more sparsely distributed offshore ecotype. Coastal ecotypes prefer shallow, warmer waters of less than 30 metres in depth. They inhabit near-shore water areas, such as harbours, lagoons, estuaries and bays, occassionally venturing far up into river mouths. They are unique to offshore ecotypes in that they mostly maintain long-term home ranges, difinitive to multiple generations; however, extremes of the species have also been found to be migratory in response to climatic patterns, such as the El-Niño Southern Oscillation.

Offshore ecotypes favour cooler, deeper waters and are largely migratory, subject to food availability and feeding habits, water temperature and potential threats. In one season, they are able to swim up to 4,200 kilometres. These ecotypes extend to the continental shelf, and are much less restricted in their range of movement than their coastal counterparts. They have been found to exist throughout all pelagic waters (sightings have been made extensively in the Pacific, Indian and Atlantic oceans), in particular showing preference for the waters along the continental shelf, as well as oceanic islands and atolls.
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The Common Bottlenose Dolphin is famed worldwide for its intelligence, friendliness and acrobatic activity, thereby contributing to its great prevalence in modern marine parks and dolphinariums worldwide. Laws and regulations are in place in order to ensure that all marine mammals (including the Common Bottlenose Dolphin) kept in captivity for both entertainment and educational purposes are provided with a safe, humane environment suitable to the species' otherwise natural habitat. For the Common Bottlenose Dolphin, this may be tailored to the specific animal's previous experience in the wilderness, and may include varying temperatures and depths of seawater, sand and some type of natural formations such as coral or rock.

Adaptations

Structural #1: Body Shape (Dorsal Fin, Flippers, Flukes)
All dolphins have a sleek, fusiform body shape. In addition to this, they possess a dorsal fin, flippers and a tail with flukes (refer to Fig. 1). These are vital components that maximum swimming efficiency, in order for them to be able to hunt and catch prey, as well as escape from potential predators and other threats. The dorsal fin, flippers and flukes work in conjunction with one another to allow the dolphin to move quickly and agilely, with reduced effort on its part. The dorsal fin and flipper contain neither bone nor muscle, but are made up of dense connective tissue. For this reason, they do not propel the animal but allow it to effectively steer and balance itself, enabling the dolphin to perform short, sharp movements as well as long, sweeping ones. The flukes of the tail act as the "propellor", and are comprised of extremely strong elastic muscles. The elasticity of these muscles remove the need for the dolphin to perform a downward stroke of the tail, as it "bounces" back automatically. This reduces the mammal's total energy consumption and allows for conservation. In addition, the tail is hinged to the body in such a way that it acts as a pivot. The "fulcrum" of this pivot (the hinge of the tail) is sufficiently located so that a small amount of effort is needed on the dolphin's part to produce a much larger, more powerful stroke, allowing a much higher propulsion than the muscles would ordinarily allow. These factors all contribute to a body that is incredibly adapted to its marine environment, allowing for maximum energy and swimming efficiency. Environmental pressures that may have lead to these adaptations include the nature of both predators and prey, as the Common Bottlenose Dolphin needs to be extremely quick and agile to escape and capture these elements, respectively; some large shark species prey on dolphins, and the Common Bottlenose Dolphin is customary to hunting and eating live prey.

Structural #2: Skin (Epidermis, Dermis, Hypodermis, Colouring)
The Common Bottlenose Dolphin has very smooth, rubbery skin, with no abrasions such as sweat glands or hair. This also allows it to move swiftly, as no drag is created by its movement. The Common Bottlenose Dolphin's skin is made up of three layers: the epidermis, the dermis and the hyperdermis. The epidermis is the outermost layer of skin. The skin layer beneath the epidermis is the dermis, which contains essential blood vessels, nerves and connective tissue. Beneath the dermis is the hypodermis, more commonly referred to as the "blubber" of the animal. Blubber is also found in whales and seals, and consists of a layer of fat reinforced by fibrous connective tissues. Blubber serves three predominant purposes. Firstly, the blubber in a dolphin additionally contributes to its streamlined shape, decreasing friction during activity. Secondly, like humans, it stores calories as an effective supply of energy when food is scarce. Lastly, it reduces heat loss - important for thermoregulation, which will be discussed further on in this report under 'Physiological Adaptations'. The colouring of the Common Bottlenose Dolphin is also essential in its adaptation to its environment - most are grey to dark grey on their backs, fading to a lighter colouring on its belly (refer to Fig. 1). This colouring is called countershading, and assists the dolphin by camouflaging it from both predators and prey. For instance, when viewed from above its back is invisible against the darkness of the water, whereas its lighter belly conceals it from those looking from below as it blends with the bright sea surface. The Common Bottlenose Dolphin's skin is essential for its survival, allowing it to move quickly and agilely, store energy, thermoregulate and become camouflaged. This adaptation maximised the dolphins' chances for survival throughout pressures such as predators, limited or fast-moving prey and water temperature fluctuations.

Behavioural #1: Echolocation
The Common Bottlenose Dolphin relies on sound rather than light in order to determine the location of the objects around it. This technique is called echolocation. Echolocation is similar to sonar in that it allows the location and size of objects to be measured based on the time it takes for a transmitted sound to return. Other animals that rely on echolocation are bats, whales and shrews. The Common Bottlenose Dolphin is able to send out high-frequency pulses that "bounce" back off of its surroundings, allowing it to create an acoustic image. These high-frequency pulses are created by cycling air through the nasal passages, which are below the blowhole. These pulses are then focussed into a beam by the anatomy of the dolphin's melon (refer to Fig. 1) and the oil reservoirs located there. The returning echoes are then channelled into similar oil-filled passages, this time located in the lower jaw, and into the inner ear. Through this behavioural technique, the dolphin is then able to deduce the location, size and shape of its surroundings. Echolocation is a crucial aspect of the Common Bottlenose Dolphin's survival, as it allows it to identify its environment. The Common Bottlenose Dolphin is dependent on echolocation as, due to the rapid absorption of sunlight in water and human pollutants, its aquatic surroundings are very hard to see through. These environmental pressures are the most likely causes for this behavioural adaptation, allowing the Common Bottlenose Dolphin to hunt, escape and breed without difficulty - essentially, allowing it to survive.

Behavioural #2: Social Interaction
Dolphins are known worldwide for their friendliness and inclination towards social interaction, both with humans and other animals. Common Bottlenose Dolphins are almost always found to be living in groups (called "schools" or "pods"), congregations that have a functionability that has been likened to a human family. Despite this comparison, living in a group provides not only warmth and comfort for the animals; it is essential for the youth of the group, for feeding, and for defence and safety. The younger generations of a pod are cared for constantly up until they are two years old. Naturally this presents difficulties, as the mother, the carer of her children, is unable to hunt and feed. Because of the close relationships wound through the entire group, an "aunt" is easily able to take over the nursing of the children while the mother feeds. This allows the mother to continue to survive whilst the children are still kept secure, something that would not be possible if dolphins lived individually. Another benefit of the dolphins' social behaviour is that it allows them to feed more efficiently and more often. Dolphins attack their prey in groups, surrounding large shoals of fish in a tight circle and swimming up and down while each dolphin takes its turn to feed. Feeding individually would be much more difficult as a dolphin would be forced to hunt constantly in order to survive. Lastly, teamwork is essential in the defence of the Common Bottlenose Dolphin against predators, in particular other marine animals such as sharks. An additional physical advantage of the Common Bottlenose Dolphin is its hard nose, strong tail and sharp, conical teeth, all ideal for attacking and battering an enemy. Alone, a dolphin would not be likely to survive an attack, but enough dolphins working together would have the strength to overcome a whale. The needs of a Common Bottlenose Dolphin mother, the need to feed regularly and efficiently and the need to defend against predators all contribute as foreign impacts that may have caused the Common Bottlenose Dolphin to form the behavioural habit of living in a group.

Physiological #1: Thermoregulation
All dolphins, including the Common Bottlenose Dolphin, practise thermoregulation: the maintenance of a constant body temperature. Dolphins, like humans, must keep their bodies at a stable temperature in order to function normally (for the Common Bottlenose Dolphin this is approximately 36 to 37 degrees celsius. The Common Bottlenose Dolphin uses several strategies in conjunction with one another in order to maintain its body temperature. These include a decreased surface-to-volume ratio; a fluctuating insulation system (their blubber, mentioned above, may thin or thicken depending on the amount of warmth needed); and a heat exchange system. The most important strategy is the heat exchange system. The heat exchange system is directly related to the dolphin's circulatory system, which is able to adjust in order to either conserve or expel body heat in order to achieve a constant body temperature. Arteries contained in the dolphin's flippers, flukes and dorsal fin are surrounded by veins. This means that the bodily heat contained in the arteries in the form of blood is transferred to the venous blood instead of the dolphin's external environment, conserving body heat. In colder waters, when a dolphin needs to conserve body heat further, circulation increases in the arteries but decreases in the veins, circulating more warm blood to the body's core. In warmer waters, or during prolonged exercise, the system is reversed; circulation decreases to the arteries and increases in the veins, circulating less warmth to the body core and shedding excess heat to the dolphin's environment (the water). An effective animation portraying this process may be found here near the bottom of the page under 'Thermoregulation'. As stated above, thermoregulation is critical to the Common Bottlenose Dolphin as it ensures that the animal does not overheat or freeze to death. The need to navigate varying temperatures of water for food and breeding, and the detrimental warming effects of climate change are the environmental pressures that have led to this particular physiological adaptation for the Common Bottlenose Dolphin.

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