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Tursiops truncatusbottlenosed dolphin

By Jessica Jenkins

Geographic Range

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, et al., 2008; Klinowska, 1991; Reynolds, III and Wells, 2003; Reynolds, III, et al., 2000)

Habitat

Bottlenosed dolphins are found everywhere except polar waters. 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 4.5 minutes without taking a breath. Bottlenosed dolphins are found in bays, estuaries, sounds, open shorelines and large, estuarine rivers. (Reynolds, III and Wells, 2003; Reynolds, III, et al., 2000; Ridgway and Harrison, 1999)

  • Average depth
    1 m
    3.28 ft

Physical Description

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, et al., 2008; Reeves, et al., 2002; Reynolds, III and Wells, 2003; Reynolds, III, 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, et al., 2008; Reeves, et al., 2002; Reynolds, III and Wells, 2003; Reynolds, III, et al., 2000; Ridgway and Harrison, 1999)

  • Sexual Dimorphism
  • male larger
  • Range mass
    260 to 500 kg
    572.69 to 1101.32 lb
  • Average mass
    400 kg
    881.06 lb
  • Range length
    228 to 381 cm
    89.76 to 150.00 in

Reproduction

Bottlenosed dolphins are polygamous. They engage in mating behavior in either of two ways, in alliances or individually. Males that form alliances look for females that are in estrous. When males find a female in estrous they separate her from her home range for a chance to mate with her. Sometimes they flank the female to prevent access by other males to insure that only they have the opportunity to mate with her. Waiting for a female to become receptive can take several weeks. Some males do not engage in alliances, instead remaining in their home ranges. When an estrous female enters the home range of such a male, he attempts to attract her to mate. During courtship, a male postures by arching his back. He strokes and nuzzles the female, and he may clap his jaws or yelp. Bottlenosed dolphin copulation typically occurs belly-to-belly with both animals facing the same direction, although an animal facing the opposite direction is not uncommon. Intromission lasts only around 10 seconds and involves vigorous pelvis thrusts. (Jefferson, et al., 2008; Reynolds, III and Wells, 2003; Reynolds, III, et al., 2000)

Female dolphins typically reach sexual maturity between 5 and 10 years of age, while males reach sexual maturity between 8 and 13 years old. Sexual maturity is usually achieved years before reproduction; males that reach sexual maturity at age 10 don’t typically breed until they are at approximately 20 years old. Reproductive seasons vary from region to region. Typically, females ovulate at a particular time of year while males are active throughout the year (but with a peak of testosterone production when females ovulate). Gestation lasts about 12 months and each pregnancy produces one calf. Females nurse their young from nipples on each side of their genital slit until the calf is between 18 and 20 months. Bottlenosed dolphins reproduce every 3 to 6 years, with females usually becoming pregnant soon after their calf is weaned. Calves can be born at any time of the year but with a peak in birthing during warmer months. Females can reproduce well into their late forties. (Jefferson, et al., 2008; Reynolds, III and Wells, 2003; Reynolds, III, et al., 2000)

  • Breeding interval
    Female bottlenosed dolphins breed once every 3 to 6 years.
  • Breeding season
    Breeding may occur throughout the year but is often concentrated in the warmer months.
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Average gestation period
    12 months
  • Average gestation period
    365 days
    AnAge
  • Range weaning age
    18 to 20 months
  • Average time to independence
    5 years
  • Range age at sexual or reproductive maturity (female)
    5 to 10 years
  • Range age at sexual or reproductive maturity (male)
    8 to 13 years

Females provide the bulk of parental investment, investing especially heavily during lactation. Lactation in bottlenosed dolphins typically lasts 18 to 20 months. Lactating females require 88 to 153 cal/kg as opposed to non-lactating females that typically require 34 to 67 cal/kg. Bottlenosed dolphins participate in allomaternal care, that is, all of the females within a group help care for each others' offspring. When a bottlenosed dolphin calf is born, it learns to ride the pressure waves alongside its mother during its first few days. The mother assists the calf to keep it alongside her body. Females also protect calves from predators. (Jefferson, et al., 2008; Reynolds, III and Wells, 2003; Reynolds, III, et al., 2000)

  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female
  • post-independence association with parents

Lifespan/Longevity

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, III, et al., 2000)

Behavior

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, et al., 2008; Reynolds, III and Wells, 2003; Reynolds, III, 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, et al., 2008; Reynolds, III and Wells, 2003; Reynolds, III, et al., 2000)

  • Average territory size
    125 km^2

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, et al., 2008; Reynolds, III and Wells, 2003)

Communication and Perception

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, III, 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, III, et al., 2000)

Food Habits

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 olivaceus), 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, III, 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, III, et al., 2000; Ridgway and Harrison, 1999)

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

Predation

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, III, et al., 2000)

Ecosystem Roles

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, III, et al., 2000; Ridgway and Harrison, 1999)

Commensal/Parasitic Species
  • flukes (Braunina cordiformis)
  • tapeworms (Monorygma delphini)
  • roundworms (Anisakis marina)
  • thorny-headed worms (Corynosoma cetaceum)

Economic Importance for Humans: Positive

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, III, et al., 2000)

  • Positive Impacts
  • ecotourism
  • research and education

Economic Importance for Humans: Negative

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

Conservation Status

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, et al., 2008; Ridgway and Harrison, 1999; Jefferson, et al., 2008; Ridgway and Harrison, 1999; Jefferson, et al., 2008; Ridgway and Harrison, 1999; Jefferson, et al., 2008; Reynolds, III, et al., 2000; Ridgway and Harrison, 1999)

Other Comments

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, et al., 2008; Reynolds, III and Wells, 2003; Reynolds, III, et al., 2000)

Contributors

Jessica Jenkins (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor, Tanya Dewey (editor), Animal Diversity Web.

Glossary

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cooperative breeder

helpers provide assistance in raising young that are not their own

cosmopolitan

having a worldwide distribution. Found on all continents (except maybe Antarctica) and in all biogeographic provinces; or in all the major oceans (Atlantic, Indian, and Pacific.

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

keystone species

a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).

migratory

makes seasonal movements between breeding and wintering grounds

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

piscivore

an animal that mainly eats fish

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born

References

Jefferson, T., M. Webber, R. Pitman. 2008. Marine Mammals of the World. Burlington, MA: Academic Press.

Klinowska, M. 1991. Dolphins, Porpoises and Whales of the World. Gland, Switzerland and Cambridge, UK: International Union for Conservation of Nature and Natural Resources.

Reeves, R., B. Stewart, P. Clapham, J. Powell. 2002. Sea Animals of the World. New York: A & C Black Publishers.

Reynolds, III, J., R. Wells. 2003. Dolphins, Whales, and Manatees. Gainesville, Florida: University Press of Florida.

Reynolds, III, J., R. Wells, S. Eide. 2000. The Bottlenosed Dolphin. Gainesville, FL: University Press of Florida.

Ridgway, S., S. Harrison. 1999. Handbook of Marine Mammals. London: Academic Press.

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