Tursiops truncatus
bottlenosed dolphin

Tursiops truncatus typically occupies waters with surface temperatures between 50 and 90 degrees Fahrenheit. Although some bottlenosed dolphins migrate seasonally (for example, populations along the Atlantic coast), they are typically found in tropical, subtropical, and warm temperate waters. (Jefferson, Webber, and Pitman, 2008; Klinowska, 1991; Reynolds, III, and Wells, 2003; Reynolds et al., 2000)

Bottlenosed dolphins are found everywhere except polar waters. They do not usually dive deeper than 1 meter, although deep water bottlenosed dolphins typically dive deeper than inshore members of the species. Deep water bottlenosed dolphins come up to take breaths every 1 to 2 minutes, whereas inshore bottlenosed dolphins take breaths two times per minute. Bottlenosed dolphins have been known, however, to dive deep enough to go 4 ½ minutes without taking a breath. Bottlenosed dolphins are found in bays, estuaries, sounds, open shorelines and in some instances in rivers. (Reynolds, III, and Wells, 2003; Reynolds et al., 2000; Ridgway and Harrison, 1999)

Bottlenosed dolphins have a fusiform body that lacks many external characteristics of terrestrial mammals, including hair, external ears and hind limbs. A fusiform body reduces turbulence and allows bottlenosed dolphins to cruise underwater at high speeds. Dolphins have front flippers, a dorsal fin and flukes, which are used in swimming. The dorsal fin is tall, curved and set near the middle of the back. These dolphins are typically black to a light gray on their sides, and their bellies are white, sometimes with a slight pink hue. Bottlenosed dolphins are typically 84 to 140 cm at birth, and typically weigh between 14 and 20 kg. Adult males are usually between 244 and 381 cm long, and weigh about 500 kg. Adult females are typically between 228 and 366 cm, and weigh about 250 kg. This sexual dimorphism may be a result of females using energy to achieve sexual maturity at a earlier age than males, while males continue to grow. (Jefferson, Webber, and Pitman, 2008; Reeves et al., 2002; Reynolds, III, and Wells, 2003; Reynolds et al., 2000; Ridgway and Harrison, 1999)

As is true of all modern cetaceans, the skulls of bottlenosed dolphins are telescoped; that is, the rostra are elongated and tapered anteriorly and the nostrils are moved dorsally. This allows dolphins to breathe more easily during swimming. Bottlenosed dolphins are homeotherms and endotherms. They use insulation, in the form of blubber, a relatively small surface area due to their large body sizes, and vascular shunts that allow selective cooling of certain organs and tissues to help thermoregulate. Bottlenosed dolphins have a thermoneutral zone of 13 to 28 degrees Celsius. If the temperature of their environment drops below 13 degrees Celsius or rises above 28 degrees Celsius, their metabolic rate increases. (Jefferson, Webber, and Pitman, 2008; Reeves et al., 2002; Reynolds, III, and Wells, 2003; Reynolds et al., 2000; Ridgway and Harrison, 1999)

Bottlenosed dolphins are threatened by a variety of factors, both natural and of human origin. Natural mortality is due to injury, disease, and predation. Male bottlenosed dolphins typically live about 40 to 45 years and female dolphins can live over 50 years (the oldest female documented lived to be 53 years old). Because in many cases dolphins are found in shallow waters, they encounter many humans and human activities. Recreational fishing gear causes many deaths when dolphins become entangled in nets or swallow fishing hooks. Dolphins are sometimes preyed upon by sharks, although this is may be less of a problem now than in the past due to declining shark populations. One of the largest and most serious threats to bottlenosed dolphins is environmental contamination, caused mainly by the increase of human development along shorelines. Chemicals of human origin find their way into coastal ecosystems through runoff from agriculture, residential, and industrial sources. (Reynolds, III, and Wells, 2003; Reynolds et al., 2000)

Bottlenosed dolphins are very social animals. They typically live in groups that range in size from a few individuals to over 100. They participate in fission-fusion societies in which subgroups frequently join or leave the main group. They are very active animals and can swim up to speeds of 30 km/hr, although on average they swim between 3 and 6 km/hr. They form several kinds of groups, including nursery groups (mothers and calves), juvenile groups (young dolphins of both genders up to their mid teens), and adult males (can be found individually or more commonly as strongly bonded pairs). Bottlenosed dolphins engage in aggressive behavior including biting, ramming, and tail slaps; and bonding and acceptance behavior, including stroking and rubbing. Captive dolphin groups are characterized by a dominance hierarchy based on age, size and gender. Large adult males are dominant over other group members. In the absence of males, the largest female assumes dominance. (Jefferson, Webber, and Pitman, 2008; Reynolds, III, and Wells, 2003; Reynolds et al., 2000)

Bottlenosed dolphins are very intelligent animals. In captivity this intelligence is demonstrated by their ability to solve problems in experimental trials as well as during their everyday lives. Their cognitive skills are reflected by the speed and effectiveness by which they acquire and perfect behaviors. One may wonder how dolphins, as marine animals that must surface to breathe every few minutes, sleep. It turns out that they rest one side of their brains while decreasing their activity level. This allows them rest and yet remain ‘conscious’ to breathe and carry on basic survival behaviors. Bottlenosed dolphins also participate in epimeletic behavior, that is, they aid in the recuperation of injured dolphins. This behavior may include protecting the injured dolphin from threats as well as holding the injured dolphin at the surface. Epimeletic behavior is most commonly found among mothers of calves that have died. (Jefferson, Webber, and Pitman, 2008; Reynolds, III, and Wells, 2003; Reynolds et al., 2000)

Home Range

Density estimates of bottlenosed dolphins range from 0.06 to 1.22 dolphins per square kilometer. A group's home range is typically 125 square kilometers. (Jefferson, Webber, and Pitman, 2008; Reynolds, III, and Wells, 2003)

Bottlenosed dolphins use sound to communicate with other members of their groups. They use both audible sounds and high frequency echolocation. Each dolphin is believed to possess its own signature whistle and, once it is developed, it is retained for the duration of the dolphin’s life. Kin recognize one another by their whistles and these sounds help maintain group cohesion. Signature whistles develop in calves as young as one month, allowing them to maintain contact with their mother. Surprisingly, the signature whistle of a male calf tends to resemble its mother's more than that of a female calf. The signature whistle also gives the location and emotional state of each dolphin. Bottlenosed dolphins also navigate with echolocation, used to detect bottom topography, prey, and the presence of predators. It is even sometimes used to stun prey. Echolocation calls pass through the melon and intramandibular fat body, which contain acoustic lipids; these structures serve as acoustic lenses to focus sound. The intramandibular fat bodies focus sound to each ear, while the melon is used as a lens to focus outgoing sound. (Reynolds, III, and Wells, 2003; Reynolds et al., 2000)

Bottlenosed dolphins also use vision to perceive their surroundings. Like those of humans, their eyes contain rods and cones, but they are not used in the same way as humans. Cones, for example, are used to provide good acuity when light levels are high. These and other adaptations allow dolphins to use their vision at different times of the day and at different depths. (Reynolds, III, and Wells, 2003; Reynolds et al., 2000)

The diet of bottlenosed dolphins is broad and varies from one place to another. Inshore bottlenosed dolphins typically feed on fish and invertebrates found near the shoreline, while deep water bottlenosed dolphins typically feed on squid and pelagic fish. Bottlenosed dolphins found along the U.S. Atlantic coast typically feed on Atlantic croakers (Micropogonias undulatus), ‘spot’ fish (Leistomomus xanthurus), and silver perch (Bairdiella chrysoura), while dolphins in South Africa typically feed on African massbankers (Trachurus delagoae), olive grunters (Pomadasys olivaceum), and pandora (Pagellus bellotti). Bottlenosed dolphins typically choose prey between 5 and 30 cm in length. They eat between 4.5 and 16 kg per day, depending on the size of the individual and if it is lactating. Most of the time, bottlenosed dolphins feed individually. At times, however, dolphins participate in cooperative feeding with other dolphins, especially when feeding on a school of prey. They have also been known to trap their prey on the shore, stranding themselves in order to feed on stranded prey ("strand feeding"). And in some cases dolphins use echolocation calls to stun their prey. Some bottlenosed dolphins use passive listening rather than echolocation to locate prey. When prey is detected, these dolphins either rush in or alert others of the prey’s presence. (Reynolds et al., 2000; Ridgway and Harrison, 1999)

The sharp teeth of these dolphins allow them to grasp prey while the tongue maneuvers prey down the throat. Dolphins teeth are not used to chew and prey is typically swallowed whole. They may break up their prey by shaking it in the air and striking it with their tails, called fish-whacking. Bottlenosed dolphins in Australia may mount a sponge on their rostrum to protect their snouts as they forage on the bottom. They have also been known to follow the boats of fisherman and catch discarded prey or bait. (Reynolds et al., 2000; Ridgway and Harrison, 1999)

The most common predators of bottlenosed dolphins are larger sharks, such as bull (Carcharhinus leucas), tiger (Galeocerdo cuvier), and dusky sharks (Carcharhinus obscurus). These sharks prey on smaller dolphins, calves and female dolphins more than larger dolphins. It is not uncommon to observe dolphins with shark bites, demonstrating their survival of an attack. Blubber may provide some protection against predators. Many shark populations have decreased up to 80 percent since 1970, so some populations of dolphins may be experiencing lower predation by sharks. More recently, stingrays have been recognized as causing deaths in bottlenosed dolphin populations. (Reynolds, III, and Wells, 2003; Reynolds et al., 2000)

Bottlenosed dolphins feed on small fish and squid. They are hosts for a few species of parasites including the fluke Braunina cordiformis, tapeworms such as Monorygma delphini, roundworms (Anisakis marina), and thorny-headed worms (Corynosoma cetaceum). It has been said that healthy bottlenosed dolphin populations indicate a healthy marine ecosystem. (Reynolds et al., 2000; Ridgway and Harrison, 1999)

There are no known adverse effects of Tursiops truncatus on humans.

Humans receive a considerable amount of economic gain from bottlenosed dolphins. They are often used in captivity to swim with humans and perform. Dolphins are used in tours in which participants are educated about the lives of dolphins and encouraged to preserve their livelihood and habitat. Bottlenosed dolphins have also been known to fish cooperatively with humans, letting Brazilian fishermen, for example, know when and where to drop their nets. Bottlenosed dolphins are even used for research by the U.S. Navy on echolocation and thermoregulation. These research dolphins have also helped navy divers to find submerged objects in the ocean. Research on bottlenosed dolphins has contributed substantially to our understanding of social communication and behavior and the nature of intelligence. (Reynolds et al., 2000)

Bottlenosed dolphins in the United States are protected under the Marine Mammal Protection Act of 1972. The goal of this Act is to allow marine species to obtain optimum sustainable population levels keeping in mind the carrying capacity of the habitat. Anyone who removes a marine animal (e.g., a dolphin) without proper procedure faces fines up to $20,000 or periods of incarceration up to one year. Bottlenosed dolphins are also protected under the Environment Protection and Biodiversity Conservation Bill of 1998 in Australia. This bill is applied to waters up to 200 miles from the shores of Australia. It involves environmental impact assessments, conservation of biodiversity and endangered species as well as management of protected areas. Bottlenosed dolphins are found in most waters and so are protected by many different laws in a large number of countries. Although there are laws that protect bottlenosed dolphins, humans need to become more aware of the way our daily lives affect the livelihood of dolphins. Much of the environmental contamination found in the habitats of bottlenose dolphins are caused by humans. Common pollutants found in the tissues of dolphin are polychlorinated biphenyls (PCB), used as dielectric fluids in coolants, lubricators and transformers, and pesticide DDTs (1,1-bis-(4-chlorophenyl)-2,2,2-trichloroethane). Eighty percent of the total amount of these toxins in a female dolphin may be transferred through breast milk to its calf, causing suppression of the immune system or in some cases death. It is one thing to make sure that we are not removing dolphins from their habitats but it is also important to make sure their habitats are not being destroyed by our negligence. (Jefferson, Webber, and Pitman, 2008; Reynolds et al., 2000; Ridgway and Harrison, 1999)

Fossil remains of several Tursiops species have been found in Pliocene (2 to 5 million years old) and Pleistocene (less than 2 million years old) deposits. It has been suggested that Tursiops originated in the Mediterranean region. The teeth of bottlenosed dolphins are flattened at the tips, which caused them to be placed in the genus Tursio, but because Tursio is a synonym of Physeter, the genus name was changed to Tursiops. Tursio in Latin means dolphin, and the suffix -ops means appearance, hence the name, Tursiops. Trunco is the Latin term for truncated, which makes reference to the flattened teeth of bottlenosed dolphins. There are three synonyms of Tursiops truncatus: Tursiops gephyreus, Tursiops gillii and Tursiops nuuanu. Tursiops has recently been separated into two species: Tursiops truncatus and Tursiops aduncus. (Jefferson, Webber, and Pitman, 2008; Reynolds, III, and Wells, 2003; Reynolds et al., 2000)