Dolphin
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RedHeron
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/* Mythology */ Changed the link to "Ganga" for disambiguation purposes.
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{{otheruses}}
{{Taxobox
| name = Dolphins
| image = Bottlenose_Dolphin_KSC04pd0178.jpg
| image_width = 250px
| image_caption = [[Bottlenose Dolphin]] breaching in the bow wave of a boat
| fossil_range = Early [[Miocene]] - Recent
| regnum = [[Animal]]ia
| phylum = [[Chordate|Chordata]]
| classis = [[Mammal]]ia
| ordo = [[Cetacea]]
| subordo = [[Odontoceti]]
| familia = '''Delphinidae''' and '''Platanistoidea'''
| familia_authority = [[John Edward Gray|Gray]], 1821
| subdivision_ranks = [[Genus|Genera]]
| subdivision =
See article below.
}}
'''Dolphins''' are [[marine mammal]]s that are closely related to [[whale]]s and [[porpoise]]s. There are almost forty species of dolphin in seventeen [[genus|genera]]. They vary in size from 1.2 metres (4 ft) and 40 kilograms (88 [[pound (unit of weight)|lb]]) ([[Maui's Dolphin]]), up to 9.5 m (30 ft) and ten [[tonne]]s (the [[Orca]] or Killer Whale). They are found worldwide, mostly in the shallower seas of the [[continental shelves]], and are carnivores, mostly eating [[fish]] and [[squid]]. The [[Family (biology)|family]] [[Oceanic dolphin|Delphinidae]] is the largest in the Cetacea, and relatively recent: dolphins evolved about ten million years ago, during the [[Miocene]]. Dolphins are considered to be amongst the most intelligent of animals and their often friendly appearance and seemingly playful attitude have made them popular in [[human culture]].
==Origin of the name==
The name is originally from [[Ancient Greek]] {{polytonic|'''''δελφίς'''''}} (''delphís''; "dolphin"), which was related to the Greek {{polytonic|''δελφύς''}} (''delphys''; "womb"). The animal's name can therefore be interpreted as meaning "a 'fish' with a womb".<ref>The American Heritage® Dictionary of the English Language, Fourth Edition, [http://dictionary.reference.com/browse/Dolphin online entry at Dictionary.com], retrieved [[December 17]] [[2006]].</ref> The name was transmitted via the [[Latin]] ''delphinus'', [[Middle Latin]] ''dolfinus'' and the [[Old French]] ''daulphin'', which reintroduced the ''ph'' into the word.
The word is used in a few different ways. It can mean:
* Any member of the family [[Delphinidae]] (oceanic dolphins),
* Any member of the families Delphinidae and [[Platanistoidea]] (oceanic and river dolphins),
* Any member of the suborder Odontoceti (toothed whales; these include the above families and some others),
* Used casually as a synonym for Bottlenose Dolphin, the most common and familiar species of dolphin.
In this article, the second definition is used. [[Porpoise]]s (suborder Odontoceti, family [[Phocoenidae]]) are thus not dolphins in this sense. Orcas and some closely related species belong to the Delphinidae family and therefore qualify as dolphins, even though they are called whales in common language. A group of dolphins can be called a "school" or a "pod". Male dolphins are called "bulls", females "cows" and young dolphins are called "calves".<ref>[http://dictionary.reference.com/writing/styleguide/animal.html Dictionary.com - Style guide, animal names], page retrieved [[November 4]] [[2007]].</ref>
==Taxonomy==
[[Image:Comdolph.jpg|thumb|right|250px|[[Common Dolphin]]]]
[[Image:Dolphintursiops.jpg|thumb|right|250px|[[Bottlenose Dolphin]]]]
[[Image:Spotteddolphin1.jpg|thumb|right|250px|[[Spotted Dolphin]]]]
[[Image:Commdolph01.jpg|thumb|250px|right|[[Commerson's Dolphin]]]]
[[Image:DuskyDolphin.jpg|thumb|right|250px|[[Dusky Dolphin]]]]
[[Image:Killerwhales jumping.jpg|thumb|right|250px|[[Killer Whales]], also known as [[Orcas]]]]
[[Image:Inia.jpg|thumb|right|250px|The [[Boto]], or [[Amazon River Dolphin]]]]
* Suborder Odontoceti, toothed whales
** Family Delphinidae, [[oceanic dolphin]]s
*** Genus ''Delphinus''
**** [[Long-Beaked Common Dolphin]], ''Delphinus capensis''
**** [[Short-Beaked Common Dolphin]], ''Delphinus delphis''
*** Genus ''Tursiops ''
**** [[Bottlenose Dolphin]], ''Tursiops truncatus''
**** [[Indo-Pacific Bottlenose Dolphin]], ''Tursiops aduncus''
*** Genus ''Lissodelphis''
**** [[Northern Rightwhale Dolphin]], ''Lissodelphis borealis''
**** [[Southern Rightwhale Dolphin]], ''Lissiodelphis peronii''
*** Genus ''Sotalia''
**** [[Tucuxi]], ''Sotalia fluviatilis''
*** Genus ''Sousa''
**** [[Indo-Pacific Hump-backed Dolphin]], ''Sousa chinensis''
***** [[Chinese White Dolphin]] (the Chinese variant), ''Sousa chinensis chinensis''
**** [[Atlantic Humpbacked 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 ''Cephalorynchus''
**** [[Chilean Dolphin]], ''Cephalorhynchus eutropia''
**** [[Commerson's Dolphin]], ''Cephalorhynchus commersonii''
**** [[Heaviside's Dolphin]], ''Cephalorhynchus heavisidii''
**** [[Hector's Dolphin]], ''Cephalorhynchus hectori''
*** Genus ''Grampus''
**** [[Risso's Dolphin]], ''Grampus griseus''
*** Genus ''Lagenodelphis''
**** [[Fraser's Dolphin]], ''Lagenodelphis hosei''
*** Genus ''Lagenorhyncus''
**** [[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''
** Family Platanistoidea, [[river dolphin]]s
*** Genus ''Inia''
**** [[Boto]] (Amazon River Dolphin), ''Inia geoffrensis''
*** Genus ''Lipotes''
**** [[Chinese River Dolphin]] (Baiji), ''Lipotes vexillifer'' (considered [[functionally extinct]])
*** Genus ''Platanista''
**** [[Ganges River Dolphin]], ''Platanista gangetica''
**** [[Indus River Dolphin]], ''Platanista minor''
*** Genus ''Pontoporia''
**** [[La Plata Dolphin]] (Franciscana), ''Pontoporia blainvillei''
Six species in the family Delphinidae are commonly called "whales" but are strictly speaking dolphins. They are sometimes called "blackfish".
* Melon-headed Whale, ''Peponocephala electra''
* Killer Whale (Orca), ''Orcinus orca''
* Pygmy Killer Whale, ''Feresa attenuata'' [[Image:Baby wolphin by pinhole.jpeg|thumb|right|250px|[[Wolphin]] Kawili'Kai at the Sea Life Park in Hawaii.]]
* False Killer Whale, ''Psudorca crassidens''
* Long-finned Pilot Whale, ''Globicephala melas''
* Short-finned Pilot Whale, ''Globicephala macrorhynchus''
===Hybrid dolphins===
In 1933, three abnormal dolphins were beached off the [[Ireland|Irish]] coast; these appeared to be [[Hybrid (biology)|hybrid]]s between Risso's Dolphin and the Bottlenose Dolphin.<ref>Dolphin Safari (2006) [http://www.dolphinsafari.com/sightingslog.html sightings log], page retrieved [[December 17]] [[2006]].</ref> This mating has since been repeated in captivity and a hybrid calf was born. In captivity, a Bottlenose Dolphin and a Rough-toothed Dolphin produced hybrid offspring.<ref>Texas Tech University (1997), [http://www.nsrl.ttu.edu/tmot1/stenbred.htm Mammals of Texas - Rough-toothed Dolphin], article retrieved [[December 8]] [[2006]].</ref> A Common-Bottlenose hybrid lives at [[SeaWorld]] California <ref>Robin's Island [http://www.robins-island.org/dolphins_database.php?filter=Sea_World_California Dolphins at SeaWorld California], page retrieved [[December 17]] [[2006]].</ref> and another one lives at [[Discovery Cove]] in [[Orlando, Florida|Orlando]]. Various other dolphin hybrids have also been reported in the wild, such as a Bottlenose-Atlantic Spotted hybrid.<ref>Denise L. Herzing, Kelly Moewe and Barbara J. Brunnick (2003), [http://www.trustedpartner.com/docs/library/000059/Herzing%20Moewe%20Brunnick%20final.pdf Interspecies interactions between Atlantic spotted dolphins, Stenella frontalis and bottlenose dolphins, Tursiops truncatus, on Great Bahama Bank, Bahamas], article retrieved on [[December 17]] [[2006]].</ref> The best known hybrid however is the [[Wolphin]], a False Killer Whale-Bottlenose Dolphin hybrid. The Wolphin is a fertile hybrid, and two such Wolphins currently live at the Sea Life Park in [[Hawaii]], the first having been born in 1985 from a male False Killer Whale and a female Bottlenose. Wolphins have also been observed in the wild.<ref>[[Louis Herman]], interviewed for Associated Press, article by Jeanette J. Lee (2005), [http://www.livescience.com/animalworld/ap_050415_wolphin.html Livescience.com - Whale-Dolphin Hybrid Has Baby Wholphin], article retrieved [[April 26]] [[2007]].</ref>
==Evolution and anatomy==
[[Image:Dolphin anatomy.png|thumb|360px|right|The Anatomy of a Dolphin showing its skeleton, major organs and body shape.]]
===Evolution===
{{seealso|Evolution of cetaceans}}
Dolphins, along with whales and porpoises, are descendants of terrestrial mammals, most likely of the [[Artiodactyl]] [[order (biology)|order]]. The ancestors of the modern day dolphins entered the water roughly fifty million years ago, in the [[Eocene]] epoch.
[[Image:Dolphin embryo.jpg|thumb|left|'''Hind Limb Buds on Dolphins''' An embryo of a Spotted Dolphin in the fifth week of development. The hind limbs are present as small bumps (hind limb buds) near the base of the tail. The pin is approximately 1 inch (~2,5 cm) long.]]
[[Image:Bottlenose dolphin hind.jpg|thumb|left|Bottlenose Dolphin with vestigial hind flippers, captured 2006 in Japan.]]
Modern dolphin [[skeleton]]s have two small, rod-shaped pelvic bones thought to be [[vestigial]] hind legs. In October 2006 an unusual Bottlenose Dolphin was captured in [[Japan]]; it had small [[fin]]s on each side of its genital slit which scientists believe to be a more pronounced development of these vestigial hind legs.<ref>[[Associated Press]] / [[FOX news]] (2006), [http://www.foxnews.com/story/0,2933,227572,00.html Japanese Researchers Find Dolphin With 'Remains of Legs'], article retrieved [[November 6]] [[2006]].</ref>
===Anatomy===
Dolphins have a streamlined [[fusiform]] body, adapted for fast swimming. The tail fin, called the [[fluke]], is used for [[propulsion]], while the [[pectoral fin]]s together with the entire tail section provide directional control. The [[dorsal fin]], in those species that have one, provides stability while swimming.
Though it varies per species, basic colouration patterns are shades of grey usually with a lighter underside. It is often combined with lines and patches of different hue and contrast.
The head contains the [[melon (whale)|melon]], a round organ used for [[animal echolocation|echolocation]]. In many species, the jaws are elongated, forming a distinct beak; for some species like the Bottlenose, there is a curved mouth which looks like a fixed smile. Teeth can be very numerous (up to two hundred and fifty) in several species. Dolphins breathe through a [[blowhole (biology)|blowhole]] located on top of their head, with the [[Vertebrate trachea|trachea]] being [[anterior]] to the brain. The [[dolphin brain]] is large and highly complex and is different in structure from most land mammals.
Unlike most mammals, dolphins do not have hair, but they are born with a few hairs around the tip of their [[rostrum (anatomy)|rostrum]] which they lose shortly after birth, in some cases even before they are born.<ref>The Institute for Marine Mammal Studies (IMMS), [http://www.dolphinsrus.com/dolphinfaq.php Dolphin Frequently Asked Questions: Why is a dolphin a mammal and not a fish?], article retrieved [[February 21]] [[2008]].</ref> The only exception to this is the Boto river dolphin, which does have some small hairs on the rostrum.<ref>VirtualExplorers.org, [http://www.virtualexplorers.org/ARD/Dolphin/bkgd.htm All About Dolphins - Amazon River Dolphin fact sheet], article retrieved [[February 21]] [[2008]].</ref>
Their reproductive organs are located on the underside of the body. Males have two slits, one concealing the [[penis]] and one further behind for the [[anus]]. The female has one genital slit, housing the [[vagina]] and the anus. A [[Mammary gland|mammary slit]] is positioned on either side of the female's genital slit.
===Senses===
Most dolphins have acute [[eyesight]], both in and out of the water, and their sense of [[Hearing (sense)|hearing]] is superior to that of humans. Though they have a small ear opening on each side of their head, it is believed that hearing underwater is also if not exclusively done with the lower jaw which conducts the sound vibrations to the [[middle ear]] via a fat-filled cavity in the lower jaw bone. Hearing is also used for [[Animal echolocation|echolocation]], which seems to be an ability all dolphins have. It is believed that their teeth are arranged in a way that works as an array or antenna to receive the incoming sound and make it easier for them to pinpoint the exact location of an object.<ref>Goodson, A.D. and M. Klinowska. "A Proposed Echolocation Receptor for the Bottlenose Dolphin (''Tursiops truncatus''): Modelling the Receive Directivity from Tooth and Lower Jaw Geometry", in Thomas and Kastelein, eds, ''NATO ASI Series A: Sensory Abilities of Cetaceans'', vi.196:255-267 (Plenum NY, 1990) ISBN 0-30-643695-7</ref> The dolphin's sense of touch is also well-developed, with free nerve endings being densely packed in the skin, especially around the snout, pectoral fins and genital area. However, dolphins lack an [[olfactory nerve]] and lobes and thus are believed to have no [[sense of smell]],<ref>SeaWorld, [http://www.seaworld.org/animal-info/info-books/bottlenose/senses.htm Bottlenose Dolphins - Senses], article retrieved [[December 17]] [[2006]].</ref> but they can [[taste]] and do show preferences for certain kinds of fish. Since dolphins spend most of their time below the surface normally, just tasting the water could act in a manner analogous to a sense of smell.
Though most dolphins do not have any hair, they do still have [[hair follicle]]s and it is believed these might still perform some sensory function, though it is unclear what exactly this may be.<ref>Bjorn Mauck, Ulf Eysel and Guide Dehnhardt (2000), [http://jeb.biologists.org/cgi/reprint/203/14/2125.pdf Selective heating of vibrissal follicles in seals (Phoca Vitulina) and dolphins (Sotalia Fluviatilis Guianensis)], article retrieved [[March 11]], 2007.</ref> The small hairs on the rostrum of the Boto river dolphin are believed to function as a [[somatosensory system|tactile sense]] however, possibly to compensate for the Boto's poor eyesight.<ref>Laurie Stepanek (1998), [http://www.tmmsn.org/mmgulf/inia_geoffrensis.html Amazon River Dolphin (Inia geoffrensis)], article retrieved [[March 11]], 2007.</ref>
==Behaviour==
{{seealso|Whale surfacing behaviour}}
[[Image:Dolphins gesture language.jpg|right|thumb|250px|A pod of Indo-Pacific Bottlenose Dolphins in the [[Red Sea]] ]]
Dolphins are often regarded as one of Earth's most intelligent animals, though it is hard to say just how intelligent dolphins are, as comparisons of species' relative intelligence are complicated by differences in sensory apparatus, response modes, and nature of cognition. Furthermore, the difficulty and expense of doing experimental work with large aquatics means that some tests which could yield meaningful results still have not been carried out, or have been carried out with inadequate sample size and methodology. Dolphin behaviour has been studied extensively by humans however, both in captivity and in the wild. See the [[cetacean intelligence]] article for more details.
===Social behaviour===
[[Image:Dolphinsurfresize.jpg|left|thumb|250px|Dolphins surfing at [[Snapper Rocks]], [[Queensland]], [[Australia]].]]
Dolphins are social, living in pods (also called "schools") of up to a dozen individuals. In places with a high abundance of food, pods can join temporarily, forming an aggregation called a ''superpod''; such groupings may exceed a thousand dolphins. The individuals communicate using a variety of clicks, whistles and other vocalizations. They also use ultrasonic sounds for echolocation. Membership in pods is not rigid; interchange is common. However, the cetaceans can establish strong bonds between each other. This leads to them staying with injured or ill individuals, even actively helping them to breathe by bringing them to the surface if needed.<ref>Davidson College, biology department (2001) [http://www.bio.davidson.edu/people/vecase/behavior/Spring2001/Spring01/Ewart/Altruism.html Bottlenose Dolphins - Altruism], article retrieved [[March 12]] [[2008]].</ref> This [[altruism|altruistic]] behaviour does not appear to be limited to their own species however. A dolphin in [[New Zealand]] that goes by the name of ''Moko'' has been observed to seemingly help guide a female [[Pygmy Sperm Whale]] together with her calf out of shallow water where they had stranded several times.<ref>Ray Lilley for Associated Press (2008), [http://ap.google.com/article/ALeqM5gd1AJMmldYiTtyFHmMzp1vIPdppgD8VBPTPG0 Dolphin Appears to Guide Whales to Sea], article retrieved [[March 12]] [[2008]].</ref> They have also been known to seemingly protect swimmers from sharks by swimming circles around the swimmers.<ref>CBC News (2004), [http://www.cbc.ca/world/story/2004/11/24/dolphin_newzealand041124.html Dolphins save swimmers from shark], article retrieved [[March 11]], 2007.</ref><ref name="">{{cite web
| last =Celizic
| first =Mike
| title =Dolphins save surfer from becoming shark’s bait
| publisher =MSNBC
| date =2007-11-08
| url =http://today.msnbc.msn.com/id/21689083/?GT1=10547
| accessdate = 2007-11-08 }}</ref>
Dolphins also show [[culture|cultural]] behaviour, something long believed to be a quality unique to humans. In May 2005, a discovery was made in Australia which shows this cultural aspect of dolphin behaviour: Some dolphins, such as the [[Indo-Pacific Bottlenose Dolphin]] (''Tursiops aduncus'') teach their young to use tools. The dolphins break [[sea sponge|sponge]]s off and cover their [[snout]]s with them thus protecting their snouts while foraging. This knowledge of how to use a tool is mostly transferred from mothers to daughters, unlike [[simian]] [[primate]]s, where the knowledge is generally passed on to both sexes. The technology to use sponges as mouth protection is not genetically inherited but a taught behaviour.<ref>Rowan Hooper for New Scientist (2005), [http://www.newscientist.com/article.ns?id=dn7475 Dolphins teach their children to use sponges], article retrieved [[December 17]] [[2006]].</ref> Another such behaviour was discovered amongst river dolphins in Brazil, where some male dolphins apparently use objects such as weeds and sticks as part of a sexual display.<ref>Nic Fleming, Science correspondent for the Telegraph (2008), [http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2007/12/05/eadolphin105.xml Dolphins woo females with bunches of weeds], article retrieved [[February 11]] [[2008]].</ref>
Dolphins are known to engage in acts of aggression towards each other. The older a male dolphin is, the more likely his body is covered with scars ranging in depth from teeth marks made by other dolphins. It is suggested that male dolphins engage in such acts of aggression for the same reasons as humans: disputes between companions or even competition for other females. Acts of aggression can become so intense that targeted dolphins are known to go into exile, leaving their communities as a result of losing a fight with other dolphins.
Male Bottlenose Dolphins have been known to engage in [[infanticide (zoology)|infanticide]]. Dolphins have also been known to kill [[porpoises]] for reasons which are not fully understood, as porpoises generally do not share the same fish diet as dolphins and are therefore not competitors for food supplies.<ref>Dr. George Johnson (date unknown), [http://www.txtwriter.com/Onscience/Articles/Flipper.html Is Flipper A Senseless Killer?], article retrieved [[December 17]] [[2006]].</ref>
===Reproduction and sexuality===
Dolphin [[copulation]] happens belly to belly and though many species engage in lengthy [[foreplay]], the actual act is usually only brief, but may be repeated several times within a short timespan. The [[gestation period]] varies per species; for the small Tucuxi dolphin, this period is around 11 to 12 months, while for the Orca the gestation period is around 17 months. They usually become sexually active at a young age, even before reaching [[sexual maturity]]. The age at which sexual maturity is reached varies per species and gender.
Dolphins are known to have sex for reasons other than reproduction, sometimes also engaging in acts of a [[homosexual]] nature.<ref name="sexagg">Herzing D.L., Rogers C.A., for the Wild Dolphin Project, [http://www.univ-lr.fr/Labo/lbem/ecs2005/Abstract%20book.pdf Directionality of sexual aggression in mixed-species encounters between Atlantic Spotted dolphins and Bottlenose dolphins in the Bahamas] (2005), article retrieved [[September 18]] [[2007]].</ref> Various dolphin species have been known to engage in sexual behaviour with other dolphin species,<ref name="sexagg"/> this also having resulted in various hybrid dolphin species as mentioned earlier. Sexual encounters may be violent, with male dolphins sometimes showing aggressive behaviour towards both females and other male dolphins.<ref name="sexagg"/><ref>Scott et. al,[http://www.monkeymiadolphins.org/Pdf/Scott%20et%20al%202005.pdf Aggression in bottlenose dolphins: evidence for sexual coercion, male-male competition, and female tolerance through analysis of tooth-rake marks and behaviour] (2005), article retrieved [[September 18]] [[2007]].</ref> Occasionally, dolphins will also show sexual behaviour towards other animals, including humans.<ref>Amy Samuels, Lars Bejder, Rochelle Constantine and Sonja Heinrich (2003), [http://whitelab.biology.dal.ca/lb/Samuels%20Bejder%20et%20al%202003.pdf Marine Mammals: Fisheries, Tourism and Management Issues, chapter 15], pages 266 to 268, Cetaceans that are typically lonely and seek human company. Retrieved [[December 17]] [[2006]].</ref>
===Feeding===
Various methods of feeding exist, not just between species but also within a species. Various methods may be employed, some techniques being used by only a single dolphin population. Fish and squid are the main source of food for most dolphin species, but the False Killer Whale and the Killer Whale also feed on other marine mammals.
One feeding method employed by many species is herding, where a pod will control a school of fish while individual members take turns plowing through the school, feeding. The tightly packed school of fish is commonly known as a bait ball. Coralling is a method where fish are chased to shallow water where they are more easily captured. In [[South Carolina]], the Atlantic Bottlenose Dolphin takes this one step further with what has become known as strand feeding, where the fish are driven onto mud banks and retrieved from there.<ref>[http://www.nmfs.noaa.gov/pr/pdfs/species/coastalbottlenosestock.pdf "Coastal Stock(s) of Atlantic Bottlenose Dolphin: Status Review and Management,"] Proceedings and Recommendations from a Workshop held in Beaufort, North Carolina, [[13 September]]-[[14 September]] [[1993]]. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service. pp. 56-57.</ref> In some places, Orcas will also come up to the beach to capture [[sea lion]]s. Some species also whack fish with their fluke, stunning them and sometimes sending fish clear out of the water.
Reports of cooperative human-dolphin fisheries date back to the [[ancient Rome|ancient Roman]] author and [[natural philosophy|natural philosopher]] [[Pliny the Elder]].<ref>M.B. Santos, R. Fernández, A. López, J.A. Martínez and G.J. Pierce (2007), [http://journals.cambridge.org/production/action/cjoGetFulltext?fulltextid=703604 Variability in the diet of bottlenose dolphin, Tursiops truncatus, in Galician waters, north-western Spain, 1990 – 2005] (.pdf), article retrieved [[April 3]] [[2007]].</ref> A modern human-dolphin fishery still takes place in [[Laguna, Brazil|Laguna]], [[Santa Catarina (state)|Santa Catarina]], [[Brazil]]. Here, dolphins drive fish towards fishermen waiting along the shore and give them a signal when they can cast their nets. The dolphins then feed off the fish that manage to escape the nets.<ref>The Telegraph (2006), [http://www.telegraph.co.uk/travel/main.jhtml?xml=/travel/2006/03/09/etbrazil09.xml&page=1 Brazil's sexiest secret], article retrieved [[March 11]], 2007.</ref><ref>Dr. Moti Nissani (2007) [http://www.youtube.com/watch?v=ECk0yMifmzw Bottlenose Dolphins in Laguna Requesting a Throw Net] (video). Supporting material for Dr. Nissani's presentation at the 2007 International Ethological Conference. Video retrieved [[February 13]] [[2008]].</ref>
===Vocalizations===
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 however; [[frequency modulated]] sounds which are usually just called whistles; burst-pulsed sounds and clicks. Whistles are used by dolphins to communicate, though the nature and extent of their ability to communicate in this way is not known. Research has shown however that at least some dolphin species are capable of sending identity information to each other using a signature whistle; a whistle that refers specifically to the identity of a certain dolphin. The burst-pulsed sounds are also used for communication, but again the nature and extent of communication possible this way is not known.<ref>[http://www.dolphincommunicationproject.org/DissPDFs/Chapter4.pdf Atlantic Spotted Dolphin vocalizations, chapter Delphinid vocalizations.], the dolphin communication project, article retrieved [[August 7]] [[2007]].</ref> The clicks are directional and used by dolphins for echolocation and are often in a short series called a click train, the rate increasing when approaching an object of interest. Dolphin echolocation clicks are amongst the [[Whale song#Toothed Whale Sound Levels|loudest sounds made by animals]] in the sea.<ref>W. W. L. Au, The Sonar of Dolphins (Springer, NY, 1993).</ref> [[Image:PacificWhiteSidedDolphine.jpg|right|thumb|250px|Pacific White-Sided Dolphins breaching]]
===Jumping and playing===
Dolphins occasionally leap above the water surface, sometimes performing acrobatic figures (e.g. the [[Spinner Dolphin]]). Scientists are not always quite certain about the purpose of this behaviour and the reason for it may vary; it could be to locate schools of fish by looking at above-water signs like feeding birds, they could be communicating to other dolphins to join a hunt, attempting to dislodge parasites, or simply doing it for fun.
Play is a fairly important part of dolphins' lives, and they can be observed playing with [[seaweed]] or play-fighting with other dolphins. At times they also harass other local creatures, like [[seabird]]s and [[turtle]]s. Dolphins also seem to enjoy riding waves and frequently 'surf' coastal swells and the bow waves of boats. Occasionally, they're also willing to playfully interact with human swimmers.
===Sleeping===
Because dolphins need to come up to the surface to breathe and have to be alert for possible predators, they do not [[sleep]] in the same way land mammals do. Generally, dolphins sleep with only one brain [[Cerebral hemisphere|hemisphere]] in [[slow-wave sleep]] at a time, thus maintaining some amount of consciousness required to breathe and keeping one eye open to keep a watch out for possible threats. The earlier stages of sleep can be observed in both hemispheres of the brain, however.<ref>{{cite conference | last = Mukhametov | first = L. M. | coauthors = Supin, A. Ya. | title = Sleep and vigil in dolphins | booktitle = Marine mammals | location= [[Moscow]]| publisher=[[Nauka]]|year=1978}}</ref><ref name="Mukhametov, 1984">{{cite journal| last=Mukhametov| first=Lev| coauthors=| year=1984| title=Sleep in marine mammals| journal=Experimental Brain Research| volume=8 (suppl.)| pages=227–238}}</ref><ref>Dallas Grasby (1994) [http://www.bio.net/bionet/mm/neur-sci/1994-August/003910.html Excerpts from "Sleep in marine mammals", L.M. Mukhametov, Experimental Brain Research Supplement 8], article retrieved [[February 11]] [[2008]].</ref>
However, in captivity, dolphins have been observed to seemingly enter a fully asleep state where both eyes are closed and the animal does not respond to mild external stimuli, respiration being automatic with a tail kick [[reflex]] keeping the blowhole above the water. If not needed to keep the blowhole above the water, the tail kick reflex may subside. Dolphins kept [[unconscious]] using [[anesthesia|anesthetics]] initially show a similar tail kick reflex.<ref>James G. McCormick (PhD), Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina (2007), [http://www.anesthesia-analgesia.org/cgi/content/full/104/1/239#F199 Behavioral Observations of Sleep and Anesthesia in the Dolphin: Implications for Bispectral Index Monitoring of Unihemispheric Effects in Dolphins], article retrieved [[February 11]] [[2008]].</ref> Though a similar state has been observed with wild [[Sperm Whale]]s, it is not known if this state is ever reached in the wild amongst any dolphin species.<ref>BBC (2008), [http://news.bbc.co.uk/1/hi/scotland/edinburgh_and_east/7254522.stm Sperm whales caught 'cat napping'], article retrieved [[April 9]] [[2008]].</ref>
==Threats to dolphins==
===Natural threats to dolphins===
Except for mankind (discussed below), dolphins have few natural enemies, some species or specific populations having none at all making them [[apex predator]]s. For most smaller species of dolphins, only a few larger species of shark such as the [[bull shark]], [[dusky shark]], [[tiger shark]] and [[great white shark]] are a potential risk, especially for calves. Some of the larger dolphin species such as Orcas may also prey on some of the smaller dolphin species, but this seems rare. Dolphins may also suffer from a wide variety of [[disease]]s and [[parasite]]s.
===Human threats to dolphins===
{{seealso|Dolphin drive hunting}}
[[Image:Whaling in the Faroe Islands.jpg|thumb|right|250px|Dead Atlantic White-Sided Dolphins in [[Hvalba]] on the [[Faroe Islands]], killed in a drive hunt. ]]
Some dolphin species face an uncertain future, especially some of the river dolphin species such as the Amazon River Dolphin, and the Ganges and [[Baiji|Yangtze River Dolphin]], all of which are critically or seriously endangered. A 2006 survey found no individuals of the Yangtze River Dolphin, leading to the conclusion that the species is now [[functionally extinct]].<ref>Douglas Williams for Shanghai Daily (2006), [http://www.shanghaidaily.com/art/2006/12/04/298862/Yangtze_dolphin_may_be_extinct__researchers_say.htm Yangtze dolphin may be extinct]. Article retrieved [[December 9]] [[2006]].</ref>
Contamination of environment - the oceans, seas, and rivers - is an issue of concern, especially [[pesticides]], heavy metals, plastics, and other industrial and agricultural pollutants which do not disintegrate rapidly in the environment are reducing dolphin populations, and resulting in dolphins building up unusually high levels of contaminants. Injuries or deaths due to collisions with boats, especially their [[propeller]]s, are also common.
Various fishing methods, most notably [[Seine (fishing)|purse seine]] fishing for [[tuna]] and the use of drift and gill nets, results in a large amounts of dolphins being killed inadvertently.<ref>Clover, Charles. 2004. ''The End of the Line: How overfishing is changing the world and what we eat''. Ebury Press, London. ISBN 0-09-189780-7 </ref> Accidental by-catch in gillnets and incidental captures in antipredator nets used in marine fish farms are common and poses a risk for mainly local dolphin populations.<ref name="Díaz López, 2006">{{cite journal| last=Díaz López| first=Bruno| coauthors=Shirai J.A.| year=2006| title=Bottlenose dolphin (''Tursiops truncatus'') presence and incidental capture in a marine fish farm on the north-eastern coast of Sardinia (Italy)| journal=Journal of Marine Biological Ass. UK| volume=87| pages=113–117| doi=10.1017/S0025315407054215}}</ref><ref name="Díaz López, 2006b">{{cite journal| last=Díaz López| first=Bruno| year=2006| title= Interactions between Mediterranean bottlenose dolphins (''Tursiops truncatus'') and gillnets off Sardinia, Italy| journal= ICES Journal of Marine Science| volume=63|pages=946–951|doi=10.1016/j.icesjms.2005.06.012}}</ref> In some parts of the world such as [[Taiji, Wakayama|Taiji]] in Japan and the Faroe Islands, dolphins are traditionally considered as food, and killed in [[harpoon]] or [[dolphin drive hunting|drive hunts]].
However, a number of organizations rescue and [[Wildlife rehabilitation|rehabilitate]] sick, wounded, stranded or orphaned dolphins, or work on dolphin conservation and welfare.
==Human–dolphin relationships==
===Mythology===
[[Image:Ganga.jpg|thumb|A sketch of the goddess Ganga on her [[Vahana]] (mount) [[Makara (Hindu mythology)|Makara]] ]]
{{seealso|Dolphins in mythology}}
Dolphins have long played a role in human culture. Dolphins are common in [[Greek mythology]] and there are many coins from the time which feature a man or boy riding on the back of a dolphin. The [[Ancient Greece|Ancient Greeks]] treated them with welcome; a ship spotting dolphins riding in their wake was considered a good omen for a smooth voyage. Dolphins also seem to have been important to the [[Minoans]], judging by artistic evidence from the ruined palace at [[Knossos]]. In [[Hindu mythology]], the Ganges River Dolphin is associated with [[Ganga_in_Hinduism|Ganga]], the deity of the [[Ganges]] river.
===Entertainment===
{{seealso|Dolphinarium}}
[[Image:Keiko-weighing.jpg|thumb|right|150px|The famous Orca Keiko from the Free Willy movies being prepared for transport.]]
In more recent times, the [[Flipper (1963 film)|1963 ''Flipper'' movie]] and the subsequent popular ''[[Flipper (1964 TV series)|Flipper television series]]'', contributed to the popularity of dolphins in [[Western World|Western society]]. The series, created by [[Ivan Tors]], portrayed a dolphin in a friendly relationship with two boys, Sandy and Bud; a kind of seagoing ''[[Lassie (1954 TV series)|Lassie]]''. Flipper, a Bottlenose Dolphin, understood English commands unusually well and was a marked hero. A [[Flipper (1996 film)|second ''Flipper'' movie]] was made in 1996, which was based on the story of the original movie. A Bottlenose Dolphin also played a prominent role in the 1990s [[science fiction television]] series ''[[seaQuest DSV]]'' in which the animal, named Darwin, could communicate with English speakers using a vocoder, a fictional invention which translated the clicks and whistles to English and back.
[[Image:OceanWorld DolphinPhoto.jpg|left|thumb|220px|A young couple being entertained by a trained Bottlenose Dolphin in [[Puerto Plata]], [[Dominican republic]].]] More well known from this time period is probably the movie ''[[Free Willy]]'' however, which made famous the Orca playing Willy, [[Keiko (orca)|Keiko]]. The 1977 [[horror movie]] ''[[Orca (film)|Orca]]'' paints a less friendly picture of the animal. Here, a male Orca takes revenge on fishermen after the killing of his mate. In the 1973 movie ''[[The Day of the Dolphin]]'' trained dolphins are kidnapped and made to perform a naval military [[assassination]] using explosives.
[[Image:Dolphin0071.JPG|thumb|right|150px|Bottlenose Dolphin with a fish at [[The Mirage]] ]]
The renewed popularity of dolphins in the 1960s resulted in the appearance of many [[dolphinarium]]s around the world, which have made dolphins accessible to the public. Though criticism and more strict [[animal welfare]] laws have forced many dolphinariums to close their doors, hundreds still exist around the world attracting a large amount of visitors. In the [[United States]], best known are the SeaWorld [[marine mammal park]]s, and their common Orca [[stage name]] ''[[Shamu]]'', which they have [[trademark]]ed, has become well known. [[Southwest Airlines]], an American airline, has painted three of their [[Boeing 737]] aircraft in ''Shamu'' colours as an advertisement for the parks and have been flying with such a livery on various aircraft since 1988.
''[[Ecco the Dolphin]]'' is a well known [[Ecco the Dolphin (series)| video game series]]. The games are named after their main character, Ecco, a young Bottlenose Dolphin. The ''Ecco the Dolphin'' games hinge on the idea that cetaceans are sapient beings and have their own underwater society.
A well known American [[National Football League]] (NFL) team is named the [[Miami Dolphins]]. Their logo depicts an aqua-coloured Bottlenose Dolphin wearing an [[American football]] helmet and jumping in front of a coral-coloured sunburst.
===Therapy===
Dolphins are an increasingly popular choice of [[animal-assisted therapy]] for psychological problems and developmental disabilities. For example, a 2005 study with 30 participants found it was an effective treatment for mild to moderate [[clinical depression|depression]].<ref>Christian Antonioli and Michael A. Reveley, (2005), [http://bmj.bmjjournals.com/cgi/content/full/bmj;331/7527/1231 Randomised controlled trial of animal facilitated therapy with dolphins in the treatment of depression].</ref> However, this study was criticized on several grounds; for example, it is not known whether dolphins are more effective than common pets.<ref>{{cite journal |journal= BMJ |volume=331 |issue= 7529 |pages=1407 |date=2005 |author= Biju Basil, Maju Mathews |title= Methodological concerns about animal facilitated therapy with dolphins |url= http://www.bmj.com/cgi/content/full/331/7529/1407 |doi= 10.1136/bmj.331.7529.1407 |pmid= 16339258}}</ref> [[Review]]s 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 any more than fleeting improvements in mood.<ref>{{cite journal |journal=Anthrozoos |volume= 20 |issue= 3 |pages= 239–49 |date= 2007 |doi= 10.2752/089279307X224782 |author= Lori Marino, Scott O. Lilienfeld |title= Dolphin-Assisted Therapy: more flawed data and more flawed conclusions |url=http://www.marineconnection.org/docs/DAT%20Paper%202007.pdf |format=PDF |accessdate = 2008-02-20}}</ref>
===Military===
{{seealso|Military dolphin}}
A number of militaries have employed dolphins for various purposes from finding mines to rescuing lost or trapped humans. Such [[military dolphins]], however, drew scrutiny during the Vietnam War when rumors circulated that dolphins were being trained by the [[United States Navy]] to kill Vietnamese divers.<ref>PBS - Frontline, [http://www.pbs.org/wgbh/pages/frontline/shows/whales/etc/navycron.html The Story of Navy dolphins.], article retrieved [[June 8]], [[2008]].</ref> Dolphins are still being trained by the United States Navy however 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]].<ref>BBC News (2000), [http://news.bbc.co.uk/2/hi/world/middle_east/670551.stm Iran buys kamikaze dolphins], article retrieved [[June 7]], [[2008]].</ref>
===Literature===
Dolphins are also common in contemporary literature, especially [[science fiction novel]]s. A military role for dolphins is found in [[William Gibson]]'s short story ''[[Johnny Mnemonic]]'', in which [[cyborg]] dolphins are used in war-time by the military to find submarines and, after the war, by a group of revolutionaries to decode encrypted information. Dolphins play a role as sentient patrollers of the sea enhanced with a deeper empathy toward humans in [[Anne McCaffrey]]'s ''[[Dragonriders of Pern|The Dragonriders of Pern]]'' series. In the ''[[Known Space]]'' universe of author [[Larry Niven]], dolphins also play a significant role as fully-recognised "legal entities". More humorous is ''[[The Hitchhiker's Guide to the Galaxy]]'', in which dolphins are the second most intelligent creatures on Earth (after mice, and followed by humans) and tried in vain to warn humans of the impending destruction of the planet. However, their behaviour was misinterpreted as playful [[acrobatics]]. Their story is told in ''[[So Long, and Thanks for All the Fish]]''. Much more serious is their major role (along with [[chimpanzee]]s) in [[David Brin]]'s [[Uplift Universe|Uplift]] series. A talking Dolphin called "Howard" helps [[Hagbard Celine]] and his submarine crew fight the evil [[Illuminati]] in Robert Shea and [[Robert Anton Wilson]]'s [[Illuminatus Trilogy]].
Dolphins also appear frequently in non-science fiction literature however. In the book ''[[The Music of Dolphins]]'' by author [[Karen Hesse]], a girl is raised by dolphins from the age of four until she is discovered by the [[coast guard]]. Fantasy author [[Ken Grimwood]] wrote dolphins into his 1995 novel ''Into the Deep'' about a [[marine biology|marine biologist]] struggling to crack the code of [[cetacean intelligence|dolphin intelligence]], including entire chapters written from the viewpoint of his dolphin characters. In this book, humans and dolphins are capable of communicating via [[telepathy]].
===Art===
Dolphins are a popular artistic motif, dating from ancient times. Examples include the Triton Fountain by Bernini.
==References==
{{reflist|2}}
==External links==
{{Commons|Dolphin}}
{{wikispecies|Delphinidae}}
{{wiktionary}}
{{cetaceaportal}}
'''Further information:'''
*[http://digitalcollections.fiu.edu/wild/contents/dolphins/index.htm Weekly Radio Segments from ''With the Wild Things'': Dolphins]
* [http://www.omplace.com/omsites/discover/DOLPHINS/ OM Place - pictorial comparative chart of various dolphin species.]
* [http://www.ancientspiral.com/dolphin1.htm Dolphins and their significance in world mythology.]
'''Dolphin conservation and research:'''
* [http://www.wdcs.org The Whale & Dolphin Conservation Society (WDCS)]
* [http://www.dolphin-institute.org/ The Dolphin Institute]
* [http://www.dolphins.org/ The Dolphin research center]
* [http://www.neoucom.edu/DLDD/ Digital Library of Dolphin Development], Cetacean origins, Thewissen Lab
* [http://www.thebdri.com/ The Bottlenose Dolphin Research Institute]
*[http://www.oceania.org.au/ The Oceania Project, Caring for Whales and Dolphins]
'''Dolphin news:'''
* [http://www.tursiops.org/ Tursiops.org: Current Cetacean-related news]
'''Dolphin photos:'''
* [http://www.robertosozzani.it/Delfini/cont.html Red Sea Spinner Dolphin - Photo gallery]
* [http://www.pbs.org/wnet/nature/dolphins/index.html PBS NOVA: Dolphins: Close Encounters]
* [http://neptune.atlantis-intl.com/dolphins/preview_root.html David's Dolphin Images]
* [http://www.terranomada.com/dolphins/dolphins.html Images of Wild Dolphins in the Red Sea]
* [http://www.nationalgeographic.com/kids/creature_feature/0108/dolphins.html National Geographic]
[[Category:Toothed whales]]
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[[Category:Cetaceans]]
[[Category:Marine mammals]]
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