dolphin

Dolphins are highly intelligent aquatic mammals closely related to whales and porpoises. The name is from Ancient Greek δελφίς delphis meaning "with a womb", viz. "a 'fish' with a womb". A group of dolphins can be called a "school" or a "pod".

The word is used in a few different ways. It can mean:

1. Any member of the family Delphinidae (oceanic dolphins),
2. Any member of the families Delphinidae and Platanistoidea (oceanic and river dolphins),
3. Any member of the suborder Odontoceti (toothed whales; these include the above families and some others),
4. Used casually as a synonym for Bottlenose Dolphin, the most common and familiar species of dolphin.

In this article, the second definition is used. Porpoises (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. There are almost forty species of dolphin in seventeen genera. They vary in size from 1.2 m (4 ft) and 40 kg (88 lb) (Maui's Dolphin), up to 9.5 m (30 ft) and ten tonnes (the Orca). However, the average length for most North American species is 13.89 feet in length. Most species weigh about 50 to 200 kg (110 to 440 lb). They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly eating fish and squid. The family Delphinidae is the largest in the Cetacea, and relatively recent: dolphins evolved about ten million years ago, during the Miocene.

Taxonomy

• Suborder Odontoceti, toothed whales
  • Family Delphinidae, oceanic Dolphins
    • 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, 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 Dolphins
    • Genus Inia
      • Boto (Amazon River Dolphin), Inia geoffrensis
    • Genus Lipotes
      • Chinese River Dolphin (Baiji), Lipotes vexillifer
    • 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, Orcinus orca
• Pygmy Killer Whale, Feresa attenuata
• False Killer Whale, Psudoorca crassidens
• Long-finned Pilot Whale, Globicephala melas
• Short-finned Pilot Whale, Globicephala macrorhynchus

Hybrid dolphins

In 1933, three abnormal dolphins were beached off the Irish coast; these appeared to be hybrids between Risso's Dolphin and the Bottlenose Dolphin. 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. Normally, Spinner Dolphins have sometimes hybridised with Spotted Dolphins and Bottlenose Dolphins. Bands of males of one dolphin species often mate with lone female Spinners. Blue Whales, Fin Whales and Humpback Whales all hybridize normally. Dall's Porpoises and Harbour Porpoises also commonly hybridized. There has also been a reported hybrid between a beluga and a narwhal. See also wolphin.

Genetic evolution and anatomy of dolphins

Dolphins, along with whales and porpoises, are thought to be descendants of terrestrial mammals, most likely of the Artiodactyl order. Modern dolphin skeletons have two small rod shaped pelvic bones thought to be vestigial hind legs. They entered the water roughly fifty million years ago. See evolution of cetaceans for the details.

Dolphins have a fusiform body, adapted for fast swimming. The head contains the melon, a round organ used for echolocation. In many species, the jaws are elongated, forming a distinct beak; for some species like the Bottlenose, there is a curved mouth that looks like a fixed smile. Teeth can be very numerous (up to two hundred and fifty) in several species. The dolphin brain is large and has a highly structured cortex, which often is referred to in discussions about their advanced intelligence. A recent theory however disputes the existence of a neural basis for dolphin intellect, suggesting instead that the large brain is only an adaptation to living in cold water. ^[1] This theory has not found widespread acceptance. Their teeth are arranged in a way that works as an array or antenna focusing the incoming sound, making it easier for them to pinpoint the exact location of an object. The basic coloration patterns are shades of gray with a light underside and a distinct dark cape on the back. It is often combined with lines and patches of different hue and contrast. See individual species articles for details.

Dolphin behavior

See also: Whale behavior

Dolphins are often regarded as one of Earth's most intelligent species, though it is hard to say just how intelligent dolphins are as straightforward 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 that could meaningfully be done still have not been carried out, or have been carried out with inadequate sample size and methodology. See the "cetacean intelligence" article for more details.

Dolphins often leap above the water surface, sometimes performing acrobatic figures (e.g. the spinner dolphin). Scientists are not quite certain about the purpose of this behavior, but it may be to locate schools of fish by looking at above water signs, like feeding birds. They could also be communicating to other dolphins to join a hunt, attempting to dislodge parasites, or simply doing it for fun. Play is a very important part of dolphins' lives and they can often be observed playing with seaweed or play-fighting with other dolphins. They even harass other locals, like seabirds and turtles. Dolphins also seem to enjoy riding waves frequently 'surf' coastal swells and the bow waves of boats.

They are also willing to occasionally approach humans and playfully interact with them in the water. In return, some human cultures such as the Ancient Greeks treated them with welcome; a ship spotting dolphins riding in their wake was considered a good omen for a smooth voyage. There are many stories of dolphins protecting shipwrecked sailors against sharks by swimming circles around them.

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 fellows for support.

Because of their capacity for learning, dolphins have been employed by humans for any number of purposes. Dolphins trained to perform in front of an audience have become a favorite attraction in dolphinaria, for example SeaWorld. Such places may sometimes also provide an opportunity for humans to interact very closely with dolphins. Dolphin-human interaction is also employed in a curative sense at places where dolphins work with autistic or otherwise disabled human children. The military has 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 to kill Vietnamese skin divers. Reports of cooperative human-dolphin fisheries date back to Pliny. A modern human-dolphin fishery was reported in Laguna, Santa Catarina, Brazil in 1990.

In May 2005, researchers in Australia discovered a cultural aspect of dolphin behaviour: Some dolphins (Tursiops aduncus) teach their children to use tools. The aquatics break sponges off and put them onto their mouths thus protecting the delicate body part during their hunt for fish on the sea bed. This knowledge of how to use a tool is mostly transferred from mothers to daughters, unlike simian primates, where the knowledge is generally passed onto all the young, irrespective of sex. The technology to use sponges as mouth protection is not genetically inherited but a taught behaviour.

Dolphins are one of the few animals other than humans known to mate for reasons other than reproduction. Sex does not appear to be consensual in all cases however, with male Bottlenose Dolphins even being known to molest females of other dolphin species.^[2] There have even been cases of dolphins cavorting with humans.^[3]

Senses

Most dolphins have acute eyesight, both in and out of the water, and their sense of 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 echolocation, which seems to be an ability all dolphins have. The dolphin's sense of touch is also well-developed. However, dolphins lack an olfactory nerve and thus have no sense of smell, 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.

Feeding

Dolphins are predators, chasing their prey at high speed. The dentition is adapted to their prey: Species with long beaks and many teeth forage on fish, whereas short beaks and lesser tooth count are linked to catching squid. Some dolphins may take crustaceans. Usually, the prey is swallowed whole. The larger species, especially the orca, are capable of eating marine mammals, even small whales. There are no known reports of cannibalism amongst dolphins.

Individual species may employ a number of methods of hunting:

• Herding - where a superpod will control a school of fish while individual members take turns plowing through the herd, feeding.
• Corralling - where fish are chased to shallow water where they are more easily captured.
• Fish Wacking - where the dolphin uses its fluke to strike the fish, stunning it and sometimes sending it clear out of the water.
• Stunning - using the echolocation melon (organ), very loud clicks are directed at prey, stunning them.
• Foraging - A recent study reported that wild bottlenose dolphins (Tursiops) in Western Australia use sponges to forage in the sea bed for food.^[4]
• Mudding - Coastal bottlenose dolphins in South Carolina have been observed to drive fish onto mud banks and retrieve them from there.

Threats to dolphins

Some dolphin species face an uncertain future, including pink dolphins, black dolphins, Amazon River dolphins, and Yangtze River dolphins, all of which are critically or seriously endangered. For example, only seventeen Yangtze River dolphins are known to exist.^[5]

Contamination of environment - the oceans, seas, and rivers - is an issue of concern, especially pesticides, heavy metals, plastics, and other industrial and agricultural pollutants that do not disintegrate rapidly in the environment are reducing dolphin populations, resulting in dolphins building unusually high levels of contaminants. Injuries or death due to collisions with boats, especially their propellors, are also not uncommon.

Various hunting methods, most notably purse seine fishing for tuna and the use of drift and gill nets, results in a large amount of dolphins being killed. In some parts of the world dolphins are actively hunted and killed, usually in drive hunts.

Dolphins in human culture

Dolphins have long played a role in human culture. Dolphins are common in Greek mythology and there are many coins from the time that feature a man or boy riding on the back of a dolphin. 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, the deity of the Ganges river.

In more recent times, the 1963 Flipper movie and the subsequent popular Flipper television series, contributed to the popularity of dolphins in 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. Flipper, a Bottlenose Dolphin, understood English unusually well and was a marked hero. A 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 1990's science fiction television series seaQuest DSV in which the animal, named Darwin, could communicate with English speakers using a vocoder, an invention that translated the clicks and whistles to English and back. More well known from this time period is probably the movie Free Willy however, which made famous the Orca playing Willy, Keiko. The 1977 horror movie Orca paints a less friendly picture of the animal. Here, a male Orca takes revenge on fishermen after the killing of his mate.

The renewed popularity of dolphins in the 1960's resulted in the appearance of many dolphinariums 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 large amount of visitors. In the United States, best known are the SeaWorld marine mammal parks, and their common Orca stage name Shamu, which they have trademarked, is used as a synonym for Orca by some Americans. Southwest Airlines, an American airline, has even painted three of their Boeing 737 aircraft in Shamu colors as an advertisement for the parks and have been flying with such a livery on various aircraft since 1988.

Dolphins are also common in contemporary literature, especially science fiction novels. For example, in the Pern novels by Anne McCaffrey, human colonists of the fictional planet Pern bring genetically-engineered dolphin volunteers as additional colonists. In the second book of the Rifters trilogy, Maelstrom, by Peter Watts, enhanced Bottlenose Dolphins are used as underwater hunter-killers by a private military. An other 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. In the book Startide Rising by author David Brin, a spaceship named Streaker is also manned by enhanced dolphins, whose intelligence matches that of humans. More humourus is The Hitchhiker's Guide to the Galaxy, in which dolphins are the second most intelligent creatures on Earth, after mice, and tried in vain to warn humans of the impending destruction of the planet. However, their behavior was misinterpreted as playful acrobatics. Their story is told in So Long, and Thanks for All the Fish. In the science fiction comic The Ballad of Halo Jones, dolphins are a respected species that are the best at piloting spacecraft, and are very peaceful and anti-war. Similarly, The Illuminatus! Trilogy features a dolphin with a mature and very educated attitude as a significant supporting character.

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 biologist struggling to crack the code of 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.

Occasionally, dolphins make an appearance in computer games. Best known is the Ecco the Dolphin game series for the Sega Genesis/Mega Drive, Game Gear, Sega Dreamcast and PlayStation 2. 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. In Command and Conquer: Red Alert 2, the Allied side can train dolphins equipped with a sonar weapon.

Dolphins are also featured in several comic animated television series. In a Halloween episode of The Simpsons, dolphins reveal the ability to speak, walk on land, and their taste for humans while in a King of the Hill episode, Hank is molested by an aroused dolphin. South Park character Eric Cartman believes dolphins live in igloos.

An American National Football League (NFL) team is named the Miami Dolphins. Their logo depicts an aqua-colored Bottlenose Dolphin wearing an American football helmet and jumping in front of a coral-colored sunburst.

See also

• Dolphins in mythology
• List of dolphin species
• Wolphin
• John C. Lilly – Dolphin intelligence researcher
• Louis Herman– Scientist studying dolphin cognition and sensory processes
• Cetacean intelligence – Article about dolphin intelligence
• Dolphin drive hunting – A still practiced method of hunting dolphins
• The Day of the Dolphin, a fictional movie about dolphins being used for assassination

References

1. ^ An examination of cetacean brain structure with a novel hypothesis correlating thermogenesis to the evolution of a big brain, article by Paul Manger, 2006
2. ^ National Geographic's Dolphins: The wild side documentary (1999), IMDb. "Sex is as frequent as it is casual, a social tool used to strengthen and maintain bonds. But beneath the harmony lies a darker side of dolphins. Gangs of strong males pick on younger or smaller dolphins.", quote from National Geographic website
3. ^ "Male dolphins often become aggressive and endanger swimmers because of dominant and sexual behaviour.", quote from Managing of solitary and sociable male dolphin behaviour off Cherbourg in Normandy, France, and in the Channel Islands, U.K.
4. ^ http://www.pnas.org/cgi/content/abstract/0500232102v1
5. ^ BBC article on the Yangtze River dolphin

External links

• Cetacea News and Educational Articles, in English, French, and Spanish
• Dolphins help lifeguards from sharks
• Cetacea.org site
• Facts and Information on Dolphins
• Protect Dolphins While on a Volunteer Vacation
• Red Sea Spinner Dolphin - Photo gallery
• Tursiops.org: Current Dolphin-related news
• Wild Dolphin Foundation; Hawaiian Spinner Dolphin pictures, videos, information and conservation
• PBS NOVA: Dolphins: Close Encounters
• Common dolphin prey species in the eastern Ionian Sea
• OM Place A pictorial comparative chart.
• Project website on Dolphins which discusses the different Types of Dolphins, Dolphin Behavior, as well as a Fact File about Dolphins and images.
• Dolphins and their significance in world mythology.
• The Whale & Dolphin Conservation Society (WDCS)
• The Guardian: "Deep thinkers" - about the inteligence od Dolphins