Tursiops truncatus

Bottlenose dolphins have widely spaced eyes, relatively long flippers, a rounded forehead (called a melon), a relatively short, broad snout, and a mouth that seems permanently twisted into a grin. Inside the mouth are as many as 100 teeth. Highly social, bottlenose dolphins often swim in groups of several hundred individuals, and are famous for racing alongside watercraft. Some stay in coastal waters and others swim offshore. In the Atlantic, the coastal dolphins feed mostly on sea trout, croakers, and spot. The offshore population follows the Gulf Stream and feeds on deep-water fish and squid. Three different populations have been identified in the North Pacific: a temperate-water group, a tropical-water group, and a coastal group.

Adaptation: Imagine the structural and functional changes involved in transforming the right forelimb of a general mammalian type, such this Hedgehog, Erinaceus europaeus, into that of a cetaceans flipper, such as we find in the Bottle-nosed dolphin, Tursiops truncatus.

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Mammal Species of the World

The bottlenose dolphin is one of the most well-known species of dolphin (2). There appear to be two main varieties; a smaller, inshore form and a larger, more robust form that lives mainly offshore (6). This stocky species has a torpedo-shaped body, a short beak and pointed flippers (2). They are usually dark grey on the back with paler grey flanks and a white or pinkish belly (7). The sickle-shaped dorsal fin is tall, and positioned centrally on the back; variations in the shape of the dorsal fin along with scars and other markings on the skin can help researchers to identify individuals (8).

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.

Biogeographic Regions: indian ocean (Native ); atlantic ocean (Native ); pacific ocean (Native ); mediterranean sea (Native )

Other Geographic Terms: cosmopolitan

circum-global, mostly between 45°N and 45°S

East Pacific; Eastern Atlantic Ocean; Indo-West Pacific; Western Atlantic Ocean

occurs (regularly, as a native taxon) in multiple nations

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Worldwide distribution primarily in coastal and inshore areas of tropical, subtropical, and temperate regions; most common near shore, but occurs also pelagically in the eastern tropical Pacific Ocean and some other areas; generally not poleward of 45 degrees latitude except off northwestern Europe (Jefferson et al. 1993).

The bottlenose dolphin is found in coastal waters of most temperate, tropical and subtropical areas (9). Around the UK, it occurs in the English Channel, around north-east Scotland and in the Irish Sea, particularly in Cardigan Bay and off south-east Ireland (5). It is also found off western Ireland (5), but is rare further north than the UK (6).

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.

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.

Range mass: 260 to 500 kg.

Average mass: 400 kg.

Range length: 228 to 381 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: male larger

Length: 3700 cm

Weight: 650 grams

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.

Average depth: 1 m.

Habitat Regions: temperate ; tropical ; saltwater or marine

Aquatic Biomes: pelagic ; coastal ; brackish water

Other Habitat Features: estuarine

inshore and offshore

tropical to temperate, coastal

Depth range based on 18684 specimens in 2 taxa.
Water temperature and chemistry ranges based on 7761 samples.

Environmental ranges
  Depth range (m): 0 - 0
  Temperature range (°C): 1.736 - 29.485
  Nitrate (umol/L): 0.000 - 23.025
  Salinity (PPS): 30.701 - 40.333
  Oxygen (ml/l): 4.253 - 7.718
  Phosphate (umol/l): 0.048 - 1.582
  Silicate (umol/l): 0.399 - 14.997

Graphical representation

Temperature range (°C): 1.736 - 29.485

Nitrate (umol/L): 0.000 - 23.025

Salinity (PPS): 30.701 - 40.333

Oxygen (ml/l): 4.253 - 7.718

Phosphate (umol/l): 0.048 - 1.582

Silicate (umol/l): 0.399 - 14.997
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

Habitat Type: Marine

Comments: Offshore form frequents pelagic waters, especially in tropics. Coastal form usually shoreward of 20 m contour, often in lagoons, bays, river mouths; ascends river in some areas; common near passes connecting large bays with ocean. Young are born in the water.

A coastal and oceanic species, the bottlenose dolphin occurs in a range of habitats from open water and lagoons to rocky reefs (10). It also occurs in large estuaries and even the lower reaches of rivers and harbours (6).

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: Yes. At least some populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.

Makes regular movements between inshore and offshore areas, and for distances up to 100 km linearly along coast. Much larger movements may occur (Wells et al. 1999), but whether these constitute migrations is uncertain.

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.

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.

Animal Foods: fish; mollusks; aquatic crustaceans

Primary Diet: carnivore (Piscivore , Eats non-insect arthropods, Molluscivore )

Comments: Very opportunistic feeder; prefers fishes (e.g., mullet), squid, crustaceans, and cephalopods. Sometimes drives fish ashore and comes out of the water in pursuit. Foraging by plunging the head into sandy bottoms has been observed in the Bahamas (Rossbach and Herzing 1997).

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.

Ecosystem Impact: keystone species

Commensal/Parasitic Species:

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

The most common predators of bottlenosed dolphins are larger sharks, such as bull (Carcharhinus leucas), tiger (Galeocerdo cuvier), and dusky sharks (Carcharhinus altimus). 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.

Known Predators:

• bull sharks (Carcharhinus leucas)
• tiger sharks (Galeocerdo cuvier)
• dusky sharks (Carcharhinus altimus)

Tursiops truncatus (porpoise shark) preys on:
Penaeidae
Mugilidae
Actinopterygii
Rajiformes
Archosargus probatocephalus

Based on studies in:
USA: Florida (Estuarine)

This list may not be complete but is based on published studies.

10,000 to >1,000,000 individuals

Comments: Population in the southeastern Pacific Ocean was estimated to be 588,000 in 1978. NMFS estimated in 1989 that the population off the Atlantic and Gulf coasts of the U.S. was 14,000-23,000 (see Nowak 1991).

Group size usually less than 10 (coastal form) or 25 (offshore form), though herds of several hundred sometimes are reported offshore. Individuals may segregate by age and sex.

Coastal form apparently has limited home range along segment of coast; for example, resident dolphins in a South Carolina estuary had home ranges over four years that averaged 51.3 square kilometers (95% adaptive kernel method; Gubbins 2002). However, in the Southern California Bight, dolphins are highly mobile within a relatively narrow coastal zone, extending from at least Santa Barbara to Ensenada, Mexico (Defran et al. 1999). Offshore form apparently is less restricted in movements and may move long distances over deep water (e.g., see Wells et al. 1999).

In Florida, mean mortality rate was 19% in first year, up to 3.8% annually thereafter (see IUCN 1991).

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.

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.

Communication Channels: visual ; tactile ; acoustic

Other Communication Modes: vibrations

Perception Channels: visual ; acoustic ; echolocation ; vibrations

Comments: Active day and night.

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.

Range lifespan
Status: captivity: 53 (high) years.

Average lifespan
Status: captivity: 45 years.

Average lifespan
Status: wild: 25.0 years.

Average lifespan
Status: captivity: 30.0 years.

Average lifespan
Status: wild: 25.0 years.

Average lifespan
Status: wild: 35.0 years.

Average lifespan
Status: wild: 25.0 years.

Maximum longevity: 51.6 years (captivity) Observations: Estimates suggest that males may live up to 39 years in the wild and females up to 49 years (Ronald Nowak 1999). One captive female was still alive at 51.6 years of age (Richard Weigl 2005).

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.

Mating System: polygynandrous (promiscuous) ; cooperative breeder

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.

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 gestation period: 12 months.

Range birth mass: 14 to 20 kg.

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.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); viviparous

Average gestation period: 365 days.

Average number of offspring: 1.

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.

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

Gestation lasts about 12 months. Produces one young every 2-6 years. Young are closely tended by adults for 1st several months, weaned in 12-18 months or more. Males are sexually mature in 8-12 years, females in 5-12 years; average age of sexual maturity is around 11-12 years; a few live up to at least 40 (males) to 50 (females) years (Leatherwood and Reeves 1983, IUCN 1991).

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.

US Federal List: no special status

CITES: appendix i; no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

Unknown; probably breeding.

United States

Rounded National Status Rank: N4 - Apparently Secure

Rounded Global Status Rank: G5 - Secure

Reasons: Widespread and common in many areas worldwide.

Classified as Least Concern (LC) on the IUCN Red List (1) and listed on Appendix II of CITES (3). Listed on Annex II and IV of the EC Habitats Directive. North and Baltic Sea populations, western Mediterranean and Black Sea populations are included in Appendix II of the Convention on Migratory Species (Bonn Convention), and Appendix II of the Bern Convention (4). All cetaceans (whales and dolphins) are listed on Annex A of EU Council Regulation 338/97; they are therefore treated by the EU as if they are included in CITES Appendix I, so that commercial trade is prohibited. In the UK all cetaceans are fully protected under the Wildlife and Countryside Act, 1981 and the Wildlife (Northern Ireland) Order, 1985 (5).

Global Short Term Trend: Relatively stable (=10% change)

Comments: Local declines have occurred but overall relatively stable.

Degree of Threat: C : Not very threatened throughout its range, communities often provide natural resources that when exploited alter the composition and structure over the short-term, or communities are self-protecting because they are unsuitable for other uses

Comments: Incurs low to moderate levels of direct exploitation and incidental take in fisheries (Leatherwood and Reeves 1983, Jefferson et al. 1993). See Duignan et al. (1996) for information on recurrent epizootics of morbillivirus infections in the western Atlantic and Gulf of Mexico.

The bottlenose dolphin faces a number of threats including human disturbance, entanglement in fishing nets, and hunting. Like all cetaceans it is vulnerable to chemical and noise pollution. The captivity industry that supplies the world aquarium trade is also a problem (8).

The bottlenose dolphin is a UK Biodiversity Action Plan (UK BAP) priority species (5). It is protected in UK waters by the Wildlife and Countryside Act 1981 and the Wildlife (Northern Ireland) Orders 1985; it is illegal to intentionally kill, injure, or harass any cetacean species in UK waters (5). The Agreement on the Conservation of Small Cetaceans in the Baltic and North Seas (ASCOBANS), has been signed by seven European countries, this includes the UK. Provision is made under this agreement to set up protected areas, promote research and monitoring, pollution control and increase public awareness (5). Under Annex II of the EC Habitats Directive, candidate marine Special Areas of Conservation (SACS) are being set up for this species in Cardigan Bay (Wales) and the Moray Firth (north-east Scotland) (5).

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.

Positive Impacts: ecotourism ; research and education

Comments: Most commonly displayed cetacean in marine aquaria. Historically has been harvested for meat, leather, oil, and meal. Today the main directed fishery is in Japanese waters, producing meat for human consumption; limited direct take occurs in many other parts of the range (IUCN 1991). Blamed for damage to fisheries and fishing gear in many areas (see IUCN 1991 for examples), but claims of damage are not always adequately substantiated.

Least Concern (LC)