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Dolphin
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This article is about the marine mammals. For other uses, see Dolphin (disambiguation).
Dolphins
Dolphins are an informal grouping of the infraorder Cetacea
Tursiops truncatus 01.jpg
Bottlenose dolphin
Information
Classification of
Cetacea
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetartiodactyla
Clade: Cetancodontamorpha
Suborder: Whippomorpha
Infraorder: Cetacea
Families thought
of as dolphins
Delphinidae
Iniidae
†Lipotidae
Platanistidae
Pontoporiidae
vte
Dolphins are a widely distributed and diverse group of aquatic mammals. They are an informal grouping within the order Cetacea, excluding whales and porpoises, so to zoologists the grouping is paraphyletic. The dolphins comprise the extant families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the new world river dolphins), and Pontoporiidae (the brackish dolphins), and the extinct Lipotidae (baiji or Chinese river dolphin). There are 40 extant species of dolphins. Dolphins, alongside other cetaceans, belong to the clade Cetartiodactyla with even-toed ungulates. Cetaceans' closest living relatives are the hippopotamuses, having diverged about 40 million years ago.

Dolphins range in size from the 1.7 m (5.6 ft) long and 50 kg (110 lb) Maui's dolphin to the 9.5 m (31 ft) and 10 t (11 short tons) killer whale. Several species exhibit sexual dimorphism, in that the males are larger than females. They have streamlined bodies and two limbs that are modified into flippers. Though not quite as flexible as seals, some dolphins can travel at 55.5 km/h (34.5 mph). Dolphins use their conical shaped teeth to capture fast moving prey. They have well-developed hearing which is adapted for both air and water and is so well developed that some can survive even if they are blind. Some species are well adapted for diving to great depths. They have a layer of fat, or blubber, under the skin to keep warm in the cold water.

Although dolphins are widespread, most species prefer the warmer waters of the tropic zones, but some, like the right whale dolphin, prefer colder climates. Dolphins feed largely on fish and squid, but a few, like the killer whale, feed on large mammals, like seals. Male dolphins typically mate with multiple females every year, but females only mate every two to three years. Calves are typically born in the spring and summer months and females bear all the responsibility for raising them. Mothers of some species fast and nurse their young for a relatively long period of time. Dolphins produce a variety of vocalizations, usually in the form of clicks and whistles.

Dolphins are sometimes hunted in places like Japan, in an activity known as dolphin drive hunting. Besides drive hunting, they also face threats from bycatch, habitat loss, and marine pollution. Dolphins have been depicted in various cultures worldwide. Dolphins occasionally feature in literature and film, as in the film series Free Willy. Dolphins are sometimes kept in captivity and trained to perform tricks. The most common dolphin species kept is the bottlenose dolphin, while there are around 60 captive killer whales.


Contents
1 Etymology
2 Taxonomy and distribution
2.1 Ocean dolphins
2.2 River dolphins
2.3 Hybridization
3 Evolution
4 Anatomy
4.1 Locomotive
4.2 Sensory
5 Behavior
5.1 Socialization
5.2 Reproduction and sexuality
5.3 Feeding
5.4 Vocalization
5.5 Jumping and playing
5.6 Intelligence
5.7 Sleeping
6 Threats
6.1 Humans
7 Relationships with humans
7.1 In history and religion
7.2 In captivity
7.2.1 Species
7.2.2 Controversy
7.2.3 Military
7.2.4 Therapy
7.3 Consumption
7.3.1 Cuisine
7.3.2 Health concerns
8 See also
9 References
10 Further reading
11 External links
Etymology
The name is originally from Greek δελφίς (delphís), "dolphin", dolphins 1 dolphins which was related to the Greek δελφύς (delphus), "womb". dolphins 1 dolphins The animal's name can therefore be interpreted as meaning "a 'fish' with a womb". dolphins 2 dolphins The name was transmitted via the Latin delphinus dolphins 3 dolphins (the romanization of the later Greek δελφῖνος – delphinos dolphins 1 dolphins ), which in Medieval Latin became dolfinus and in Old French daulphin, which reintroduced the ph into the word. The term mereswine (that is, "sea pig") has also historically been used. dolphins 4 dolphins

The term 'dolphin' can be used to refer to, under the parvorder Odontoceti, all the species in the family Delphinidae (oceanic dolphins) and the river dolphin families Iniidae (South American river dolphins), Pontoporiidae (La Plata dolphin), Lipotidae (Yangtze river dolphin) and Platanistidae (Ganges river dolphin and Indus river dolphin). dolphins 5 dolphins dolphins 6 dolphins This term has often been misused in the US, mainly in the fishing industry, where all small cetaceans (dolphins and porpoises) are considered porpoises, dolphins 7 dolphins while the fish dorado is called dolphin fish. dolphins 8 dolphins In common usage the term 'whale' is used only for the larger cetacean species, dolphins 9 dolphins while the smaller ones with a beaked or longer nose are considered 'dolphins'. dolphins 10 dolphins The name 'dolphin' is used casually as a synonym for bottlenose dolphin, the most common and familiar species of dolphin. dolphins 11 dolphins There are six species of dolphins commonly thought of as whales, collectively known as blackfish: the killer whale, the melon-headed whale, the pygmy killer whale, the false killer whale, and the two species of pilot whales, all of which are classified under the family Delphinidae and qualify as dolphins. dolphins 12 dolphins Though the terms 'dolphin' and 'porpoise' are sometimes used interchangeably, porpoises are not considered dolphins and have different physical features such as a shorter beak and spade-shaped teeth; they also differ in their behavior. Porpoises belong to the family Phocoenidae and share a common ancestry with the Delphinidae. dolphins 11 dolphins

A group of dolphins is called a "school" or a "pod". Male dolphins are called "bulls", females "cows" and young dolphins are called "calves". dolphins 13 dolphins

Taxonomy and distribution

Common dolphin

Bottlenose dolphin

Spotted dolphin

Atlantic spotted dolphin

Commerson's dolphin

Dusky dolphin

Killer whale

Amazon river dolphin
Parvorder Odontoceti, toothed whales
Family Platanistidae
Ganges and Indus river dolphin, Platanista gangetica with two subspecies
Ganges river dolphin (or Susu), Platanista gangetica gangetica
Indus river dolphin (or Bhulan), Platanista gangetica minor
Family Iniidae
Amazon river dolphin (or Boto), Inia geoffrensis
Orinoco river dolphin (the Orinoco subspecies), Inia geoffrensis humboldtiana
Araguaian river dolphin (Araguaian boto), Inia Araguaiaensis
Bolivian river dolphin, Inia boliviensis
Family Lipotidae
Baiji (or Chinese river dolphin), Lipotes vexillifer (possibly extinct, since December 2006)
Family Pontoporiidae
La Plata dolphin (or Franciscana), Pontoporia blainvillei
Family Delphinidae, oceanic dolphins
Genus Delphinus
Long-beaked common dolphin, Delphinus capensis
Short-beaked common dolphin, Delphinus delphis
Genus Tursiops
Common bottlenose dolphin, Tursiops truncatus
Indo-Pacific bottlenose dolphin, Tursiops aduncus
Burrunan dolphin, Tursiops australis, a newly discovered species from the sea around Melbourne in September 2011. dolphins 14 dolphins
Genus Lissodelphis
Northern right whale dolphin, Lissodelphis borealis
Southern right whale dolphin, Lissodelphis peronii
Genus Sotalia
Tucuxi, Sotalia fluviatilis
Costero, Sotalia guianensis
Genus Sousa
Indo-Pacific humpback dolphin, Sousa chinensis
Chinese white dolphin, Sousa chinensis chinensis
Atlantic humpback dolphin, Sousa teuszii
Genus Stenella
Atlantic spotted dolphin, Stenella frontalis
Clymene dolphin, Stenella clymene
Pantropical spotted dolphin, Stenella attenuata
Spinner dolphin, Stenella longirostris
Striped dolphin, Stenella coeruleoalba
Genus Steno
Rough-toothed dolphin, Steno bredanensis
Genus Cephalorhynchus
Chilean dolphin, Cephalorhynchus eutropia
Commerson's dolphin, Cephalorhynchus commersonii
Haviside's dolphin, Cephalorhynchus heavisidii
Hector's dolphin, Cephalorhynchus hectori
Genus Grampus
Risso's dolphin, Grampus griseus
Genus Lagenodelphis
Fraser's dolphin, Lagenodelphis hosei
Genus Lagenorhynchus
Atlantic white-sided dolphin, Lagenorhynchus acutus
Dusky dolphin, Lagenorhynchus obscurus
Hourglass dolphin, Lagenorhynchus cruciger
Pacific white-sided dolphin, Lagenorhynchus obliquidens
Peale's dolphin, Lagenorhynchus australis
White-beaked dolphin, Lagenorhynchus albirostris
Genus Orcaella
Australian snubfin dolphin, Orcaella heinsohni
Irrawaddy dolphin, Orcaella brevirostris
Genus Peponocephala
Melon-headed whale, Peponocephala electra
Genus Orcinus
Killer whale (Orca), Orcinus orca
Genus Feresa
Pygmy killer whale, Feresa attenuata
Genus Pseudorca
False killer whale, Pseudorca crassidens
Genus Globicephala
Long-finned pilot whale, Globicephala melas
Short-finned pilot whale, Globicephala macrorhynchus
Genus †Australodelphis
†Australodelphis mirus
Six species in the family Delphinidae are commonly called "whales", but genetically are dolphins. They are sometimes called blackfish.
Melon-headed whale, Peponocephala electra
Killer whale (Orca), Orcinus orca
Pygmy killer whale, Feresa attenuata
False killer whale, Pseudorca crassidens
Long-finned pilot whale, Globicephala melas
Short-finned pilot whale, Globicephala macrorhynchus
Ocean dolphins
Name Repartition Image
La Plata dolphin South America (east) PontoporiaBlainvillei.jpg
Long-beaked common dolphin cosmopolitan Delphinus capensis.JPG
Short-beaked common dolphin cosmopolitan Delphinus delphis with calf.jpg
Common bottlenose dolphin cosmopolitan Tursiops truncatus 01.jpg
Indo-Pacific bottlenose dolphin Indo-Pacific Tursiops aduncus, Port River, Adelaide, Australia - 2003.jpg
Burrunan dolphin Australia (south-east) Dauphin australie.jpg
Northern right whale dolphin Pacific (north) Anim1749 - Flickr - NOAA Photo Library.jpg
Southern right whale dolphin Southern Ocean Anim0796 - Flickr - NOAA Photo Library.jpg
Guiana dolphin South America (north & east) Descrição início ou comportamento.jpg
Indo-Pacific humpbacked dolphin Indo-Pacific Chinese white dolphin.jpg
Atlantic humpback dolphin Africa (west) Sousa teuszii1.jpg
Australian humpback dolphin Australia (north) & New Guinea Australian humpback dolphins, Tin Can Bay, 2016.jpg
Atlantic spotted dolphin Atlantic Atlantic spotted dolphin (Stenella frontalis) NOAA.jpg
Clymene dolphin Atlantic Clymenes.jpg
Pantropical spotted dolphin pantropical Schlankdelfin.jpg
Spinner dolphin pantropical Stenella longirostris.JPG
Striped dolphin cosmopolitan Stenella coeruleoalba.jpg
Rough-toothed dolphin cosmopolitan Rough toothed dolphin.jpg
Chilean dolphin South America (south-west) Tonino.jpg
Commerson's dolphin South America (south-east) CommersondolphinArgentina.jpg
Haviside's dolphin Africa (south-west) Dolphins at Lüderitz, Namibia (3144863196).jpg
Hector's dolphin New-Zealand (South Island) Hectors Dolphin near Akaroa.jpg
Risso's dolphin cosmopolitan Risso's Dolphin.jpg
Fraser's dolphin pantropical Frazer´s dolphin group.jpg
Atlantic white-sided dolphin Atlantic (north), North & Baltic Sea Atlantic white-sided dolphin.jpg
Dusky dolphin southern hemisphere DuskyDolphin.jpg
Hourglass dolphin Southern Ocean Hourglas dolphin.jpg
Pacific white-sided dolphin Pacific (north) Pacific white-sided dolphins (Lagenorhynchus obliquidens) NOAA.jpg
Peale's dolphin South America (south) Lagenorhynchus australis.jpg
White-beaked dolphin Atlantic (north), North & Baltic Sea Witsnuitdolfijn - Lagenorhynchus albirostris.jpg
Australian snubfin dolphin Australia (north) Snubfin-3.jpg
Irrawaddy dolphin Indo-Pacific Irrawaddy dolphin-Orcaella brevirostris by 2eight.jpg
Melon-headed whale pantropical Peponocephala electra Mayotte.jpg
Killer whale cosmopolitan Killerwhales jumping.jpg
Pygmy killer whale pantropical Feresa attenuata by OpenCage.jpg
False killer whale cosmopolitan False killer whale 890002.jpg
Short-finned pilot whale cosmopolitan Globicephala macrorhynchus Tenerife 2012 (cropped).jpg
Long-finned pilot whale Atlantic (north) & Southern Ocean Pilot whale spyhop.jpg
River dolphins
Name Repartition Image
Baiji Yangtze River Lipotes vexillifer.png
South Asian river dolphin Asia (south) GangeticDolphin.jpg
Amazon river dolphin Amazon Basin Inia geoffrensis Putumayo, Sucumbios, Ecuador 1.jpg
Araguaian river dolphin Amazon (east) Inia araguaiensis.jpg
Bolivian river dolphin Amazon (Bolivia) Dauphinrose bolivie.jpg
Tucuxi Amazon Basin Características físicas.jpg
Hybridization
In 1933, three strange dolphins beached off the Irish coast; they appeared to be hybrids between Risso's and bottlenose dolphins. dolphins 15 dolphins This mating was later repeated in captivity, producing a hybrid calf. In captivity, a bottlenose and a rough-toothed dolphin produced hybrid offspring. dolphins 16 dolphins A common-bottlenose hybrid lives at SeaWorld California. dolphins 17 dolphins Other dolphin hybrids live in captivity around the world or have been reported in the wild, such as a bottlenose-Atlantic spotted hybrid. dolphins 18 dolphins The best known hybrid is the wolphin, a false killer whale-bottlenose dolphin hybrid. The wolphin is a fertile hybrid. Two wolphins currently live at the Sea Life Park in Hawaii; the first was born in 1985 from a male false killer whale and a female bottlenose. Wolphins have also been observed in the wild. dolphins 19 dolphins

Evolution
Main article: Evolution of cetaceans

Dolphins display convergent evolution with fish and aquatic reptiles
Dolphins are descendants of land-dwelling mammals of the artiodactyl order (even-toed ungulates). They are related to the Indohyus, an extinct chevrotain-like ungulate, from which they split approximately 48 million years ago. dolphins 20 dolphins dolphins 21 dolphins

The primitive cetaceans, or archaeocetes, first took to the sea approximately 49 million years ago and became fully aquatic by 5–10 million years later. dolphins 22 dolphins

Archaeoceti is a parvorder comprising ancient whales. These ancient whales are the predecessors of modern whales, stretching back to their first ancestor that spent their lives near (rarely in) the water. Likewise, the archaeocetes can be anywhere from near fully terrestrial, to semi-aquatic to fully aquatic, but what defines an archaeocete is the presence of visible legs or asymmetrical teeth. dolphins 23 dolphins dolphins 24 dolphins dolphins 25 dolphins dolphins 26 dolphins Their features became adapted for living in the marine environment. Major anatomical changes include the hearing set-up that channeled vibrations from the jaw to the earbone which occurred with Ambulocetus 49 million years ago, a streamlining of the body and the growth of flukes on the tail which occurred around 43 million years ago with Protocetus, the migration of the nasal openings toward the top of the cranium and the modification of the forelimbs into flippers which occurred with Basilosaurus 35 million years ago, and the shrinking and eventual disappearance of the hind limbs which took place with the first odontocetes and mysticetes 34 million years ago. dolphins 27 dolphins dolphins 28 dolphins dolphins 29 dolphins The modern dolphin skeleton has two small, rod-shaped pelvic bones thought to be vestigial hind limbs. In October 2006, an unusual bottlenose dolphin was captured in Japan; it had small fins on each side of its genital slit, which scientists believe to be an unusually pronounced development of these vestigial hind limbs. dolphins 30 dolphins

Today, the closest living relatives of cetaceans are the hippopotamuses; these share a semi-aquatic ancestor that branched off from other artiodactyls some 60 million years ago. dolphins 31 dolphins Around 40 million years ago, a common ancestor between the two branched off into cetacea and anthracotheres; anthracotheres became extinct at the end of the Pleistocene two-and-a-half million years ago, eventually leaving only one surviving lineage: the hippo. dolphins 32 dolphins dolphins 33 dolphins

Anatomy

The anatomy of a dolphin showing its skeleton, major organs, tail and body shape
Dolphins have torpedo shaped bodies with generally non-flexible necks, limbs modified into flippers, non-existent external ear flaps, a tail fin, and bulbous heads. Dolphin skulls have small eye orbits, long snouts, and eyes placed on the sides of its head. Dolphins range in size from the 1.7 metres (5.6 ft) long and 50 kilograms (110 lb) Maui's dolphin to the 9.5 metres (31 ft) and 10 metric tons (11 short tons) killer whale. Overall, however, they tend to be dwarfed by other Cetartiodactyls. Several species have female-biased sexual dimorphism, with the females being larger than the males. dolphins 34 dolphins dolphins 35 dolphins

Dolphins have conical teeth, as opposed to porpoises' spade-shaped teeth. These conical teeth are used to catch swift prey such as fish, squid or large mammals, such as seal. dolphins 35 dolphins

Breathing involves expelling stale air from their blowhole, forming an upward, steamy spout, followed by inhaling fresh air into the lungs, however this only occurs in the polar regions of the oceans. Dolphins have rather small, unidentifiable spouts. dolphins 35 dolphins dolphins 36 dolphins

All dolphins have a thick layer of blubber, thickness varying on climate. This blubber can help with buoyancy, protection to some extent as predators would have a hard time getting through a thick layer of fat, and energy for leaner times; the primary usage for blubber is insulation from the harsh climate. Calves, generally, are born with a thin layer of blubber, which develops at different paces depending on the habitat. dolphins 35 dolphins dolphins 37 dolphins

Dolphins have a two-chambered stomach that is similar in structure to terrestrial carnivores. They have fundic and pyloric chambers. dolphins 38 dolphins

Dolphins' reproductive organs are located inside the body, with genital slits on the ventral (belly) side. Males have two slits, one concealing the dolphin penis and one further behind for the anus. dolphins 39 dolphins Females have one genital slit, housing the vagina and the anus, with a mammary slit on either side. dolphins 40 dolphins dolphins 41 dolphins dolphins 42 dolphins

Locomotive
Dolphins have two pectoral flippers, containing four digits, a boneless dorsal fin for stability, and a tail fin for propulsion. Although dolphins do not possess external hind limbs, some possess discrete rudimentary appendages, which may contain feet and digits. Dolphins are fast swimmers in comparison to seals which typically cruise at 9–28 kilometres per hour (5.6–17.4 mph); the killer whale (orca), in comparison, can travel at speeds up to 55.5 kilometres per hour (34.5 mph). The fusing of the neck vertebrae, while increasing stability when swimming at high speeds, decreases flexibility, which means they are unable to turn their heads. dolphins 43 dolphins dolphins 44 dolphins River dolphins, however, have non-fused neck vertebrae and are able to turn their head up to 90°. dolphins 45 dolphins Dolphins swim by moving their tail fin and rear body vertically, while their flippers are mainly used for steering. Some species log out of the water, which may allow them to travel faster. Their skeletal anatomy allows them to be fast swimmers. All species have a dorsal fin to prevent themselves from involuntarily spinning in the water. dolphins 35 dolphins dolphins 37 dolphins

Some dolphins are adapted for diving to great depths. In addition to their streamlined bodies, some can slow their heart rate to conserve oxygen. Some can also re-route blood from tissue tolerant of water pressure to the heart, brain and other organs. Their hemoglobin and myoglobin store oxygen in body tissues and they have twice the concentration of myoglobin than hemoglobin. dolphins 46 dolphins

Sensory

Biosonar by cetaceans
Diagram illustrating sound generation, propagation and reception in a toothed whale. Outgoing sounds are in red and incoming ones are in green
The dolphin ear has specific adaptations to the marine environment. In humans, the middle ear works as an impedance equalizer between the outside air's low impedance and the cochlear fluid's high impedance. In dolphins, and other marine mammals, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, dolphins receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear. The dolphin ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater. dolphins 47 dolphins Dolphins send out high frequency clicks from an organ known as a melon. This melon consists of fat, and the skull of any such creature containing a melon will have a large depression. This allows dolphins to produce biosonar for orientation. dolphins 35 dolphins dolphins 48 dolphins dolphins 49 dolphins dolphins 50 dolphins dolphins 51 dolphins Though most dolphins do not have hair, they do have hair follicles that may perform some sensory function. dolphins 52 dolphins Beyond locating an object, echolocation also provides the animal with an idea on an object's shape and size, though how exactly this works is not yet understood. dolphins 53 dolphins The small hairs on the rostrum of the boto are believed to function as a tactile sense, possibly to compensate for the boto's poor eyesight. dolphins 54 dolphins

The dolphin eye is relatively small for its size, yet they do retain a good degree of eyesight. As well as this, the eyes of a dolphin are placed on the sides of its head, so their vision consists of two fields, rather than a binocular view like humans have. When dolphins surface, their lens and cornea correct the nearsightedness that results from the refraction of light; they contain both rod and cone cells, meaning they can see in both dim and bright light, but they have far more rod cells than they do cone cells. Dolphins do, however, lack short wavelength sensitive visual pigments in their cone cells indicating a more limited capacity for color vision than most mammals. dolphins 55 dolphins Most dolphins have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a tapetum lucidum; these adaptations allow for large amounts of light to pass through the eye and, therefore, a very clear image of the surrounding area. They also have glands on the eyelids and outer corneal layer that act as protection for the cornea. dolphins 48 dolphins

The olfactory lobes are absent in dolphins, suggesting that they have no sense of smell. dolphins 48 dolphins

Dolphins are not thought to have a good sense of taste, as their taste buds are atrophied or missing altogether. However, some have preferences between different kinds of fish, indicating some sort of attachment to taste. dolphins 48 dolphins

Behavior

A pod of Indo-Pacific bottlenose dolphins in the Red Sea
See also: Cetacean surfacing behaviour
Dolphins are often regarded as one of Earth's most intelligent animals, though it is hard to say just how intelligent. Comparing species' relative intelligence is complicated by differences in sensory apparatus, response modes, and nature of cognition. Furthermore, the difficulty and expense of experimental work with large aquatic animals has so far prevented some tests and limited sample size and rigor in others. Compared to many other species, however, dolphin behavior has been studied extensively, both in captivity and in the wild. See cetacean intelligence for more details.

Socialization

Dolphins surfing at Snapper Rocks, Queensland, Australia
Dolphins are highly social animals, often living in pods of up to a dozen individuals, though pod sizes and structures vary greatly between species and locations. In places with a high abundance of food, pods can merge temporarily, forming a superpod; such groupings may exceed 1,000 dolphins. Membership in pods is not rigid; interchange is common. Dolphins can, however, establish strong social bonds; they will stay with injured or ill individuals, even helping them to breathe by bringing them to the surface if needed. dolphins 56 dolphins This altruism does not appear to be limited to their own species. The dolphin Moko in New Zealand has been observed guiding a female Pygmy Sperm Whale together with her calf out of shallow water where they had stranded several times. dolphins 57 dolphins They have also been seen protecting swimmers from sharks by swimming circles around the swimmers dolphins 58 dolphins dolphins 59 dolphins or charging the sharks to make them go away.

Dolphins communicate using a variety of clicks, whistle-like sounds and other vocalizations. Dolphins also use nonverbal communication by means of touch and posturing. dolphins 60 dolphins

Dolphins also display culture, something long believed to be unique to humans (and possibly other primate species). In May 2005, a discovery in Australia found Indo-Pacific bottlenose dolphins (Tursiops aduncus) teaching their young to use tools. They cover their snouts with sponges to protect them while foraging. This knowledge is mostly transferred by mothers to daughters, unlike simian primates, where knowledge is generally passed on to both sexes. Using sponges as mouth protection is a learned behavior. dolphins 61 dolphins Another learned behavior was discovered among river dolphins in Brazil, where some male dolphins use weeds and sticks as part of a sexual display. dolphins 62 dolphins

Forms of care-giving between fellows and even for members of different species dolphins 63 dolphins (see Moko (dolphin)) are recorded in various species - such as trying to save weakened fellows dolphins 64 dolphins or female pilot whales holding up dead calves for long periods.

Dolphins engage in acts of aggression towards each other. The older a male dolphin is, the more likely his body is to be covered with bite scars. Male dolphins can get into disputes over companions and females. Acts of aggression can become so intense that targeted dolphins sometimes go into exile after losing a fight.

Male bottlenose dolphins have been known to engage in infanticide. Dolphins have also been known to kill porpoises for reasons which are not fully understood, as porpoises generally do not share the same diet as dolphins and are therefore not competitors for food supplies. dolphins 65 dolphins The Cornwall Wildlife Trust records about one such death a year. Possible explanations include misdirected infanticide, misdirected sexual aggression or play behaviour. dolphins 66 dolphins

Reproduction and sexuality
See also: Bottlenose dolphin § Reproduction, Dusky dolphin § Social behavior and reproduction, and Short-beaked common dolphin § Reproduction

A skin-skeletal preparation
Dolphin copulation happens belly to belly; though many species engage in lengthy foreplay, the actual act is usually brief, but may be repeated several times within a short timespan. dolphins 67 dolphins The gestation period varies with species; for the small Tucuxi dolphin, this period is around 11 to 12 months, dolphins 68 dolphins while for the orca, the gestation period is around 17 months. dolphins 69 dolphins Typically dolphins give birth to a single calf, which is, unlike most other mammals, born tail first in most cases. dolphins 70 dolphins They usually become sexually active at a young age, even before reaching sexual maturity. dolphins 67 dolphins The age of sexual maturity varies by species and gender. dolphins 71 dolphins

Dolphins are known to display non-reproductive sexual behavior, engaging in masturbation, stimulation of the genital area of other individuals using the rostrum or flippers, and homosexual contact. dolphins 67 dolphins dolphins 72 dolphins dolphins 73 dolphins

Various species of dolphin have been known to engage in sexual behavior up to and including copulation with dolphins of other species. Sexual encounters may be violent, with male dolphins sometimes showing aggressive behavior towards both females and other males. dolphins 74 dolphins Male dolphins may also work together and attempt to herd females in estrus, keeping the females by their side by means of both physical aggression and intimidation, to increase their chances of reproductive success. dolphins 75 dolphins Occasionally, dolphins behave sexually towards other animals, including humans. dolphins 76 dolphins dolphins 77 dolphins

Feeding
Various methods of feeding exist among and within species, some apparently exclusive to a single population. Fish and squid are the main food, but the false killer whale and the orca also feed on other marine mammals. Orcas on occasion also hunt whale species larger than themselves. dolphins 78 dolphins

One common feeding method is herding, where a pod squeezes a school of fish into a small volume, known as a bait ball. Individual members then take turns plowing through the ball, feeding on the stunned fish. dolphins 78 dolphins Coralling is a method where dolphins chase fish into shallow water to catch them more easily. dolphins 78 dolphins Orcas and bottlenose dolphins have also been known to drive their prey onto a beach to feed on it, a behaviour known as beach or strand feeding. dolphins 79 dolphins dolphins 80 dolphins Some species also whack fish with their flukes, stunning them and sometimes knocking them out of the water. dolphins 78 dolphins

Reports of cooperative human-dolphin fishing date back to the ancient Roman author and natural philosopher Pliny the Elder. dolphins 81 dolphins A modern human-dolphin partnership currently operates in Laguna, Santa Catarina, Brazil. Here, dolphins drive fish towards fishermen waiting along the shore and signal the men to cast their nets. The dolphins' reward is the fish that escape the nets. dolphins 82 dolphins dolphins 83 dolphins

Vocalization

Spectrogram of dolphin vocalizations. Whistles, whines, and clicks are visible as upside down V's, horizontal striations, and vertical lines, respectively.
Dolphins are capable of making a broad range of sounds using nasal airsacs located just below the blowhole. Roughly three categories of sounds can be identified: frequency modulated whistles, burst-pulsed sounds and clicks. Dolphins communicate with whistle-like sounds produced by vibrating connective tissue, similar to the way human vocal cords function, dolphins 84 dolphins and through burst-pulsed sounds, though the nature and extent of that ability is not known. The clicks are directional and are for echolocation, often occurring in a short series called a click train. The click rate increases when approaching an object of interest. Dolphin echolocation clicks are amongst the loudest sounds made by marine animals. dolphins 85 dolphins

Bottlenose dolphins have been found to have signature whistles, a whistle that is unique to a specific individual. These whistles are used in order for dolphins to communicate with one another by identifying an individual. It can be seen as the dolphin equivalent of a name for humans. dolphins 86 dolphins These signature whistles are developed during a dolphin's first year; it continues to maintain the same sound throughout its lifetime. dolphins 87 dolphins In order to obtain each individual whistle sound, dolphins undergo vocal production learning. This consists of an experience with other dolphins that modifies the signal structure of an existing whistle sound. An auditory experience influences the whistle development of each dolphin. Dolphins are able to communicate to one another by addressing another dolphin through mimicking their whistle. The signature whistle of a male bottlenose dolphin tends to be similar to that of his mother, while the signature whistle of a female bottlenose dolphin tends to be more distinguishing. dolphins 88 dolphins Bottlenose dolphins have a strong memory when it comes to these signature whistles, as they are able to relate to a signature whistle of an individual they have not encountered for over twenty years. dolphins 89 dolphins Research done on signature whistle usage by other dolphin species is relatively limited. The research on other species done so far has yielded varied outcomes and inconclusive results. dolphins 90 dolphins dolphins 91 dolphins dolphins 92 dolphins dolphins 93 dolphins

Because dolphins are generally associated in groups, communication is necessary. Signal masking is when other similar sounds (conspecific sounds) interfere with the original acoustic sound. dolphins 94 dolphins In larger groups, individual whistle sounds are less prominent. Dolphins tend to travel in pods, upon which there are groups of dolphins that range from a few to many. Although they are traveling in these pods, the dolphins do not necessarily swim right next to each other. Rather, they swim within the same general vicinity. In order to prevent losing one of their pod members, there are higher whistle rates. Because their group members were spread out, this was done in order to continue traveling together.

Jumping and playing

Pacific white-sided dolphins porpoising
Dolphins frequently leap above the water surface, this being done for various reasons. When travelling, jumping can save the dolphin energy as there is less friction while in the air. dolphins 95 dolphins This type of travel is known as porpoising. dolphins 95 dolphins Other reasons include orientation, social displays, fighting, non-verbal communication, entertainment and attempting to dislodge parasites. dolphins 96 dolphins dolphins 97 dolphins

Dolphins show various types of playful behavior, often including objects, self-made bubble rings, other dolphins or other animals. dolphins 6 dolphins dolphins 98 dolphins dolphins 99 dolphins When playing with objects or small animals, common behavior includes carrying the object or animal along using various parts of the body, passing it along to other members of the group or taking it from another member, or throwing it out of the water. dolphins 98 dolphins Dolphins have also been observed harassing animals in other ways, for example by dragging birds underwater without showing any intent to eat them. dolphins 98 dolphins Playful behaviour that involves another animal species with active participation of the other animal can also be observed however. Playful human interaction with dolphins being the most obvious example, however playful interactions have been observed in the wild with a number of other species as well, such as humpback whales and dogs. dolphins 100 dolphins dolphins 101 dolphins

Juvenile dolphins off the coast of Western Australia have been observed chasing, capturing, and chewing on blowfish. dolphins 102 dolphins While some reports state that the dolphins are becoming intoxicated on the tetrodotoxin in the fishes' skin, dolphins 103 dolphins other reports have characterized this behavior as the normal curiosity and exploration of their environment in which dolphins engage. dolphins 104 dolphins

Intelligence
Main article: Cetacean intelligence
See also: Cetacean surfacing behaviour
Dolphins are known to teach, learn, cooperate, scheme, and grieve. dolphins 105 dolphins The neocortex of many species is home to elongated spindle neurons that, prior to 2007, were known only in hominids. dolphins 106 dolphins In humans, these cells are involved in social conduct, emotions, judgment, and theory of mind. dolphins 107 dolphins Cetacean spindle neurons are found in areas of the brain that are homologous to where they are found in humans, suggesting that they perform a similar function. dolphins 108 dolphins

Brain size was previously considered a major indicator of the intelligence of an animal. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks. Allometric analysis indicates that mammalian brain size scales at approximately the ⅔ or ¾ exponent of the body mass. dolphins 109 dolphins Comparison of a particular animal's brain size with the expected brain size based on such allometric analysis provides an encephalization quotient that can be used as another indication of animal intelligence. Killer whales have the second largest brain mass of any animal on earth, next to the sperm whale. dolphins 110 dolphins The brain to body mass ratio in some is second only to humans. dolphins 111 dolphins

Self-awareness is seen, by some, to be a sign of highly developed, abstract thinking. Self-awareness, though not well-defined scientifically, is believed to be the precursor to more advanced processes like meta-cognitive reasoning (thinking about thinking) that are typical of humans. Research in this field has suggested that cetaceans, among others, possess self-awareness. dolphins 112 dolphins The most widely used test for self-awareness in animals is the mirror test in which a temporary dye is placed on an animal's body, and the animal is then presented with a mirror; they then see if the animal shows signs of self-recognition. dolphins 113 dolphins

Some disagree with these findings, arguing that the results of these tests are open to human interpretation and susceptible to the Clever Hans effect. This test is much less definitive than when used for primates, because primates can touch the mark or the mirror, while cetaceans cannot, making their alleged self-recognition behavior less certain. Skeptics argue that behaviors that are said to identify self-awareness resemble existing social behaviors, and so researchers could be misinterpreting self-awareness for social responses to another individual. The researchers counter-argue that the behaviors shown are evidence of self-awareness, as they are very different from normal responses to another individual. Whereas apes can merely touch the mark on themselves with their fingers, cetaceans show less definitive behavior of self-awareness; they can only twist and turn themselves to observe the mark. dolphins 113 dolphins

In 1995, Marten and Psarakos used television to test dolphin self-awareness. dolphins 114 dolphins They showed dolphins real-time footage of themselves, recorded footage, and another dolphin. They concluded that their evidence suggested self-awareness rather than social behavior. While this particular study has not been repeated since then, dolphins have since passed the mirror test. dolphins 113 dolphins

Sleeping

Sleeping dolphin in captivity: a tail kick reflex keeps the dolphin's blowhole above the water
Further information: Sleep (non-human)
Generally, dolphins sleep with only one brain hemisphere in slow-wave sleep at a time, thus maintaining enough consciousness to breathe and to watch for possible predators and other threats. Earlier sleep stages can occur simultaneously in both hemispheres. dolphins 115 dolphins dolphins 116 dolphins dolphins 117 dolphins In captivity, dolphins seemingly enter a fully asleep state where both eyes are closed and there is no response to mild external stimuli. In this case, respiration is automatic; a tail kick reflex keeps the blowhole above the water if necessary. Anesthetized dolphins initially show a tail kick reflex. dolphins 118 dolphins Though a similar state has been observed with wild sperm whales, it is not known if dolphins in the wild reach this state. dolphins 119 dolphins The Indus river dolphin has a sleep method that is different from that of other dolphin species. Living in water with strong currents and potentially dangerous floating debris, it must swim continuously to avoid injury. As a result, this species sleeps in very short bursts which last between 4 and 60 seconds. dolphins 120 dolphins

Threats

Lesions in the dorsal fin of a bottlenose dolphin caused by lobomycosis, a fungal infection of the skin
Dolphins have few marine enemies. Some species or specific populations have none, making them apex predators. For most of the smaller species of dolphins, only a few of the larger sharks, such as the bull shark, dusky shark, tiger shark and great white shark, are a potential risk, especially for calves. dolphins 121 dolphins Some of the larger dolphin species, especially orcas (killer whales), may also prey on smaller dolphins, but this seems rare. dolphins 122 dolphins dolphins 123 dolphins Dolphins also suffer from a wide variety of diseases and parasites. dolphins 124 dolphins dolphins 125 dolphins The Cetacean morbillivirus in particular has been known to cause regional epizootics often leaving hundreds of animals of various species dead. dolphins 126 dolphins dolphins 127 dolphins Symptoms of infection are often a severe combination of pneumonia, encephalitis and damage to the immune system, which greatly impair the cetacean's ability to swim and stay afloat unassisted. dolphins 128 dolphins dolphins 129 dolphins A study at the U.S. National Marine Mammal Foundation revealed that dolphins, like humans, develop a natural form of type 2 diabetes which may lead to a better understanding of the disease and new treatments for both humans and dolphins. dolphins 130 dolphins

Dolphins can tolerate and recover from extreme injuries such as shark bites although the exact methods used to achieve this are not known. The healing process is rapid and even very deep wounds do not cause dolphins to hemorrhage to death. Furthermore, even gaping wounds restore in such a way that the animal's body shape is restored, and infection of such large wounds seems rare. dolphins 131 dolphins

The study, published in the journal Marine Mammal Science, suggests that at least some dolphins are up to the shark challenge with research finding that many dolphins survive attacks using everything from sophisticated combat moves to teaming up against the shark. dolphins 132 dolphins dolphins 133 dolphins dolphins 134 dolphins

Humans
See also: Dolphin drive hunting and Cetacean bycatch
Rows of dead dolphin lying on concrete
Dead Atlantic white-sided dolphins in Hvalba on the Faroe Islands, killed in a drive hunt
Some dolphin species are at risk of extinction, especially some river dolphin species such as the Amazon river dolphin, and the Ganges and Yangtze river dolphin, which are critically or seriously endangered. A 2006 survey found no individuals of the Yangtze river dolphin, which now appears to be functionally extinct. dolphins 135 dolphins

Pesticides, heavy metals, plastics, and other industrial and agricultural pollutants that do not disintegrate rapidly in the environment concentrate in predators such as dolphins. dolphins 136 dolphins Injuries or deaths due to collisions with boats, especially their propellers, are also common.

Various fishing methods, most notably purse seine fishing for tuna and the use of drift and gill nets, unintentionally kill many dolphins. dolphins 137 dolphins Accidental by-catch in gill nets and incidental captures in antipredator nets that protect marine fish farms are common and pose a risk for mainly local dolphin populations. dolphins 138 dolphins dolphins 139 dolphins In some parts of the world, such as Taiji in Japan and the Faroe Islands, dolphins are traditionally considered food and are killed in harpoon or drive hunts. dolphins 140 dolphins Dolphin meat is high in mercury and may thus pose a health danger to humans when consumed. dolphins 141 dolphins

Dolphin safe labels attempt to reassure consumers that fish and other marine products have been caught in a dolphin-friendly way. The earliest campaigns with "Dolphin safe" labels were initiated in the 1980s as a result of cooperation between marine activists and the major tuna companies, and involved decreasing incidental dolphin kills by up to 50% by changing the type of nets used to catch tuna. The dolphins are netted only while fishermen are in pursuit of smaller tuna. Albacore are not netted this way, making albacore the only truly dolphin-safe tuna. dolphins 142 dolphins Loud underwater noises, such as those resulting from naval sonar use, live firing exercises, and certain offshore construction projects such as wind farms, may be harmful to dolphins, increasing stress, damaging hearing, and causing decompression sickness by forcing them to surface too quickly to escape the noise. dolphins 143 dolphins dolphins 144 dolphins

Dolphins and other smaller cetaceans are also hunted in an activity known as dolphin drive hunting. This is accomplished by driving a pod together with boats and usually into a bay or onto a beach. Their escape is prevented by closing off the route to the ocean with other boats or nets. Dolphins are hunted this way in several places around the world, including the Solomon Islands, the Faroe Islands, Peru, and Japan, the most well-known practitioner of this method. By numbers, dolphins are mostly hunted for their meat, though some end up in dolphinariums. Despite the controversial nature of the hunt resulting in international criticism, and the possible health risk that the often polluted meat causes, thousands of dolphins are caught in drive hunts each year.

Relationships with humans
In history and religion

Fresco of Dolphins, ca. 1600 BC, from Knossos, Crete.

Vessel in form of killer whale, Nazca culture, circa 200 AD. American Museum of Natural History collections.
Dolphins have long played a role in human culture. Dolphins are sometimes used as symbols, for instance in heraldry.

In Greek myths, dolphins were seen invariably as helpers of humankind. Dolphins also seem to have been important to the Minoans, judging by artistic evidence from the ruined palace at Knossos. During the 2009 excavations of a major Mycenaean city at Iklaina, a striking fragment of a wall-paintings came to light, depicting a ship with three human figures and dolphins. Dolphins are common in Greek mythology, and many coins from ancient Greece have been found which feature a man, a boy or a deity riding on the back of a dolphin. dolphins 145 dolphins The Ancient Greeks welcomed dolphins; spotting dolphins riding in a ship's wake was considered a good omen. dolphins 146 dolphins In both ancient and later art, Cupid is often shown riding a dolphin. A dolphin rescued the poet Arion from drowning and carried him safe to land, at Cape Matapan, a promontory forming the southernmost point of the Peloponnesus. There was a temple to Poseidon and a statue of Arion riding the dolphin. dolphins 147 dolphins

The Greeks reimagined the Phoenician god Melqart as Melikertês (Melicertes) and made him the son of Athamas and Ino. He drowned but was transfigured as the marine deity Palaemon, while his mother became Leucothea. (cf Ino.) At Corinth, he was so closely connected with the cult of Poseidon that the Isthmian Games, originally instituted in Poseidon's honor, came to be looked upon as the funeral games of Melicertes. Phalanthus was another legendary character brought safely to shore (in Italy) on the back of a dolphin, according to Pausanias.

Dionysus was once captured by Etruscan pirates who mistook him for a wealthy prince they could ransom. After the ship set sail Dionysus invoked his divine powers, causing vines to overgrow the ship where the mast and sails had been. He turned the oars into serpents, so terrifying the sailors that they jumped overboard, but Dionysus took pity on them and transformed them into dolphins so that they would spend their lives providing help for those in need. Dolphins were also the messengers of Poseidon and sometimes did errands for him as well. Dolphins were sacred to both Aphrodite and Apollo.

When heraldry developed in the Middle Ages, not much was known about the biology of the dolphin and it was often depicted as a sort of fish. Traditionally, the stylised dolphins in heraldry still may take after this notion, sometimes showing the dolphin skin covered with fish scales.

Dolphins are present in the coat of arms of Anguilla and the coat of arms of Romania, dolphins 148 dolphins and the coat of arms of Barbados has a dolphin supporter. dolphins 149 dolphins dolphins 150 dolphins

A well-known historical example of a dolphin in heraldry, was the arms for the former province of the Dauphiné in southern France, from which were derived the arms and the title of the Dauphin of France, the heir to the former throne of France (the title literally means "The Dolphin of France").

"Dolfin" was the name of an aristocratic family in the maritime Republic of Venice, whose most prominent member was the 13th Century Doge Giovanni Dolfin.

In Hindu mythology the Ganges River Dolphin is associated with Ganga, the deity of the Ganges river. The dolphin is said to be among the creatures which heralded the goddess' descent from the heavens and her mount, the Makara, is sometimes depicted as a dolphin. dolphins 151 dolphins

The Boto, a species of river dolphin that resides in the Amazon River, are believed to be shapeshifters, or encantados, who are capable of having children with human women.

There are comparatively few surviving myths of dolphins in Polynesian cultures, in spite of their maritime traditions and relevance of other marine animals such as sharks and seabirds; unlike these, they are more often perceived as food than as totemic symbols. Dolphins are most clearly represented in Rapa Nui Rongorongo, and in the traditions of the Caroline Islands they are depicted similarly to the Boto, being sexually active shapeshifters. dolphins 152 dolphins

In captivity
Species

SeaWorld show featuring bottlenose dolphins and pilot whales
The renewed popularity of dolphins in the 1960s resulted in the appearance of many dolphinaria around the world, making dolphins accessible to the public. Criticism and animal welfare laws forced many to close, although hundreds still exist around the world. In the United States, the best known are the SeaWorld marine mammal parks. In the Middle East the best known are Dolphin Bay at Atlantis, The Palm dolphins 153 dolphins and the Dubai Dolphinarium. dolphins 154 dolphins


SeaWorld San Diego pilot whale with trainers
Various species of dolphins are kept in captivity. These small cetaceans are more often than not kept in theme parks, such as SeaWorld, commonly known as a dolphinarium. Bottlenose dolphins are the most common species of dolphin kept in dolphinariums as they are relatively easy to train, have a long lifespan in captivity and have a friendly appearance. Hundreds if not thousands of bottlenose dolphins live in captivity across the world, though exact numbers are hard to determine. Other species kept in captivity are spotted dolphins, false killer whales and common dolphins, Commerson's dolphins, as well as rough-toothed dolphins, but all in much lower numbers than the bottlenose dolphin. There are also fewer than ten pilot whales, Amazon river dolphins, Risso's dolphins, spinner dolphins, or tucuxi in captivity. dolphins 155 dolphins An unusual and very rare hybrid dolphin, known as a wolphin, is kept at the Sea Life Park in Hawaii, which is a cross between a bottlenose dolphin and a false killer whale. dolphins 156 dolphins

The number of killer whales kept in captivity is very small, especially when compared to the number of bottlenose dolphins, with 60 captive killer whales being held in aquaria as of 2017. dolphins 157 dolphins The killer whale's intelligence, trainability, striking appearance, playfulness in captivity and sheer size have made it a popular exhibit at aquaria and aquatic theme parks. From 1976 to 1997, 55 whales were taken from the wild in Iceland, 19 from Japan, and three from Argentina. These figures exclude animals that died during capture. Live captures fell dramatically in the 1990s, and by 1999, about 40% of the 48 animals on display in the world were captive-born. dolphins 158 dolphins

Organizations such as the Mote Marine Laboratory rescue and rehabilitate sick, wounded, stranded or orphaned dolphins while others, such as the Whale and Dolphin Conservation and Hong Kong Dolphin Conservation Society, work on dolphin conservation and welfare. India has declared the dolphin as its national aquatic animal in an attempt to protect the endangered Ganges River Dolphin. The Vikramshila Gangetic Dolphin Sanctuary has been created in the Ganges river for the protection of the animals. dolphins 159 dolphins

Controversy
See also: Captive killer whales

Shamu the killer whale, 2009, with a collapsed dorsal fin
There is debate over the welfare of cetaceans in captivity, and often welfare can vary greatly dependent on the levels of care being provided at a particular facility. In the United States, facilities are regularly inspected by federal agencies to ensure that a high standard of welfare is maintained. dolphins citation needed dolphins Additionally, facilities can apply to become accredited by the Association of Zoos and Aquariums(AZA), which (for accreditation) requires "the highest standards of animal care and welfare in the world" to be achieved. Facilities such as SeaWorld and the Georgia Aquarium are accredited by the AZA. Organizations such as World Animal Protection and the Whale and Dolphin Conservation campaign against the practice of keeping them in captivity. In captivity, they often develop pathologies, such as the dorsal fin collapse seen in 60–90% of male killer whales. Captives have vastly reduced life expectancies, on average only living into their 20s, although there are examples of killer whales living longer, including several over 30 years old, and two captive orcas, Corky II and Lolita, are in their mid-40s. In the wild, females who survive infancy live 46 years on average, and up to 70–80 years in rare cases. Wild males who survive infancy live 31 years on average, and up to 50–60 years. dolphins 160 dolphins Captivity usually bears little resemblance to wild habitat, and captive whales' social groups are foreign to those found in the wild. Critics claim captive life is stressful due to these factors and the requirement to perform circus tricks that are not part of wild killer whale behavior. Wild killer whales may travel up to 160 kilometres (100 mi) in a day, and critics say the animals are too big and intelligent to be suitable for captivity. dolphins 161 dolphins Captives occasionally act aggressively towards themselves, their tankmates, or humans, which critics say is a result of stress. dolphins 162 dolphins

Although dolphins generally interact well with humans, some attacks have occurred, most of them resulting in small injuries. dolphins 163 dolphins Orcas, the largest species of dolphin, have been involved in fatal attacks on humans in captivity. The record-holder of documented orca fatal attacks is a male named Tilikum, who has lived at SeaWorld since 1992. dolphins 164 dolphins dolphins 165 dolphins dolphins 166 dolphins Tilikum has played a role in the death of three people in three different incidents (1991, 1999 and 2010). dolphins 167 dolphins Tilikum's behaviour sparked the production of the documentary Blackfish, which focuses on the consequences of keeping orcas in captivity. There are documented incidents in the wild, too, but none of them fatal. dolphins 168 dolphins

Fatal attacks from other species are less common, but there is a registered occurrence off the coast of Brazil in 1994, when a man died after being attacked by a bottlenose dolphin named Tião. dolphins 169 dolphins dolphins 170 dolphins Tião had suffered harassment by human visitors, including attempts to stick ice cream sticks down her blowhole. dolphins 171 dolphins Non-fatal incidents occur more frequently, both in the wild and in captivity.

While dolphin attacks occur far less frequently than attacks by other sea animals, such as sharks, some scientists are worried about the careless programs of human-dolphin interaction. Dr. Andrew J. Read, a biologist at the Duke University Marine Laboratory who studies dolphin attacks, points out that dolphins are large and wild predators, so people should be more careful when they interact with them. dolphins 163 dolphins

Several scientists who have researched dolphin behaviour have proposed that dolphins' unusually high intelligence in comparison to other animals means that dolphins should be seen as non-human persons who should have their own specific rights and that it is morally unacceptable to keep them captive for entertainment purposes or to kill them either intentionally for consumption or unintentionally as by-catch. dolphins 172 dolphins dolphins 173 dolphins Four countries – Chile, Costa Rica, Hungary, and India – have declared dolphins to be "non-human persons" and have banned the capture and import of live dolphins for entertainment. dolphins 174 dolphins dolphins 175 dolphins

Military
Main article: Military dolphin

A military dolphin
A military dolphin is a dolphin trained for military uses. A number of militaries have employed dolphins for various purposes from finding mines to rescuing lost or trapped humans. The military use of dolphins, however, drew scrutiny during the Vietnam War when rumors circulated that the United States Navy was training dolphins to kill Vietnamese divers. dolphins 176 dolphins The United States Navy denies that at any point dolphins were trained for combat. Dolphins are still being trained by the United States Navy for other tasks as part of the U.S. Navy Marine Mammal Program. The Russian military is believed to have closed its marine mammal program in the early 1990s. In 2000 the press reported that dolphins trained to kill by the Soviet Navy had been sold to Iran. dolphins 177 dolphins

Therapy
Dolphins are an increasingly popular choice of animal-assisted therapy for psychological problems and developmental disabilities. For example, a 2005 study found dolphins an effective treatment for mild to moderate depression. dolphins 178 dolphins However, this study was criticized on several grounds. For example, it is not known whether dolphins are more effective than common pets. dolphins 179 dolphins Reviews of this and other published dolphin-assisted therapy (DAT) studies have found important methodological flaws and have concluded that there is no compelling scientific evidence that DAT is a legitimate therapy or that it affords more than fleeting mood improvement. dolphins 180 dolphins

Consumption
Cuisine

Plate of dolphin sashimi
In some parts of the world, such as Taiji, Japan and the Faroe Islands, dolphins are traditionally considered as food, and are killed in harpoon or drive hunts. dolphins 181 dolphins Dolphin meat is consumed in a small number of countries worldwide, which include Japan dolphins 182 dolphins and Peru (where it is referred to as chancho marino, or "sea pork"). dolphins 183 dolphins While Japan may be the best-known and most controversial example, only a very small minority of the population has ever sampled it.

Dolphin meat is dense and such a dark shade of red as to appear black. Fat is located in a layer of blubber between the meat and the skin. When dolphin meat is eaten in Japan, it is often cut into thin strips and eaten raw as sashimi, garnished with onion and either horseradish or grated garlic, much as with sashimi of whale or horse meat (basashi). When cooked, dolphin meat is cut into bite-size cubes and then batter-fried or simmered in a miso sauce with vegetables. Cooked dolphin meat has a flavor very similar to beef liver. dolphins 184 dolphins

Health concerns
There have been human health concerns associated with the consumption of dolphin meat in Japan after tests showed that dolphin meat contained high levels of mercury. dolphins 185 dolphins There are no known cases of mercury poisoning as a result of consuming dolphin meat, though the government continues to monitor people in areas where dolphin meat consumption is high. The Japanese government recommends that children and pregnant women avoid eating dolphin meat on a regular basis. dolphins 186 dolphins

Similar concerns exist with the consumption of dolphin meat in the Faroe Islands, where prenatal exposure to methylmercury and PCBs primarily from the consumption of pilot whale meat has resulted in neuropsychological deficits amongst children. dolphins 185 dolphins

The Faroe Islands population was exposed to methylmercury largely from contaminated pilot whale meat, which contained very high levels of about 2 mg methylmercury/kg. However, the Faroe Islands populations also eat significant numbers of fish. The study of about 900 Faroese children showed that prenatal exposure to methylmercury resulted in neuropsychological deficits at 7 years of age

— World Health Organization dolphins 185 dolphins