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Dolphin

 

From Wikipedia, the free encyclopedia

 

 

Scientific classification

Kingdom:

Animalia

Phylum:

Chordata

Class:

Mammalia

Order:

Cetacea

Suborder:

Odontoceti

Family:

Delphinidae
Gray, 1821

 

 

Origin of the name

The name is from Ancient Greek δελφίς delphis meaning "with a womb" which can be interpreted as meaning "a 'fish' with a womb".[1]

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

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. A group of dolphins can be called a "school" or a "pod".

Taxonomy

 

Six species in the family Delphinidae are commonly called "whales" but are strictly speaking dolphins. They are sometimes called "blackfish".

 

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.[2] 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.[3] A Common-Bottlenose hybrid lives at SeaWorld California.[4] Various other dolphin hybrids have also been reported in the wild, such as a Bottlenose-Atlantic Spotted hybrid.[5]

 

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. Dolphins entered the water roughly fifty million years ago. Dolphins have a streamlined fusiform body, adapted for fast swimming. 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.

Modern dolphin skeletons have two small, rod-shaped pelvic bones thought to be vestigial hind legs. In October of 2006, an unusual Bottlenose Dolphin was captured in Japan that had small fins on either side of the genital slit, which scientists believe to be a more pronounced development of these vestigal hind legs.[6]

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.[7]

Unlike most mammals, dolphins do not have hair, but they are born with a few hairs around the tip of their rostrum which they lose after some time, in some cases even before they are born. River dolphins usually have them all their life and are believed to have a sensory function. Even in those species that lose the hair the hair follicles remain, and it is possible the nerves connected to them are still able to detect movements in the water.

 

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. 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.[8] The dolphin's sense of touch is also well-developed. However, dolphins lack an olfactory nerve and lobes and thus are believed to have no sense of smell,[9] 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.

The Anatomy of a Dolphin showing its skeleton, major organs and body shape.

The Anatomy of a Dolphin showing its skeleton, major organs and body shape.

 

 

Hind Limb Buds on Dolphins An embryo of a Spotten 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 long. Image used with permission, courtesy Thewissen LabSource [1]

Hind Limb Buds on Dolphins An embryo of a Spotten 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 long. Image used with permission, courtesy Thewissen LabSource [1]

 

Dolphin 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 and frequently 'surf' coastal swells and the bow waves of boats. Dolphins are also 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 agression can become so intense that targeted dolphins are known to go into exile: leave their communities as a result of losing a fight with other dolphins.

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 individuals 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 dolphins break sponges off and cover their snouts 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 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.[10]

Dolphins are one of the few animals other than humans known to mate for reasons other than reproduction and especially male Bottlenose Dolphins are known to engage in sexual acts with other dolphin species, which is not always consensual, though the Bottlenose may also be submissive in such encounters.[11] Occasionally, dolphins will also show sexual behaviour towards humans.[12]

Male dolphins have been known to engage in infanticide. Dolphins will also 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.[13]

Feeding

 

Individual species may employ a number of methods of hunting. One such method is herding, where a superpod will control a school of fish while individual members take turns plowing through the herd, feeding. The tightly packed school of fish is commonly known as bait ball. Coralling is a method where fish are chased to shallow water where they are more easily captured. In South Carolina, coastal Bottlenose Dolphins take this one step further with what has become known as mudding, where the fish are driven onto mud banks and retrieved from there. In some places, Orcas will also come up to the beach to capture Seals. Some species also whack fish with their fluke, stunning them and sometimes sending fish clear out of the water.

Threats to dolphins

 

Some dolphin species face an uncertain future, including pink dolphins, black dolphins, Amazon River dolphins, and the Ganges and Yangtze River dolphins, all of which are critically or seriously endangered. A 2006 survey found no individuals of the Yangtze River dolphin, leading to fears that the species may already be extinct.[14]

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, and resulting in dolphins building up unusually high levels of contaminants. Injuries or deaths due to collisions with boats, especially their propellers, are also not uncommon.

Various fishing methods, most notably purse seine fishing for tuna and the use of drift and gill nets, results in a large amounts of dolphins being killed inadvertently.[15] Accidental by-catch in trout nets is also not uncommon and poses a risk for mainly local dolphin populations. In some parts of the world, such as some areas in Japan and the Faroe Islands, dolphins are traditionally considered as food, and killed in harpoon or drive hunts.

2007: Year of the Dolphin

The year 2007 has been declared as (International) Year of the Dolphin by the United Nations and United Nations Environment Programme (UNEP).[16]

The UN Convention on Migratory Species, together with its specialized agreements on dolphin conservation ACCOBAMS and ASCOBANS and the WDCS (Whale and Dolphin Conservation Society) have proposed 2007 as the "Year of the Dolphin" ('YOD')).

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, a fictional 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 1973 movie The Day of the Dolphin also has a dark role for dolphins, which are trained to perform an assassination.

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 very educated dolphin with a mature attitude as a significant supporting character. A role for dolphins in Japanese manga is found in Triton of the Sea (or Blue Triton) created by Osamu Tezuka in the early 1970's. In this manga, dolphins aid the protagonists to fight an evil would-be dictator.

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.

In the music video for Guns N' Roses' 1993 single "Estranged", Axl Rose swims with dolphins after plunging into the water. They end up saving his life, and he swims with the dolphins and rides on top of one of them, and they carry him back to the top of the water.

Occasionally, dolphins make an appearance in computer games. Best known is the Ecco the Dolphin 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. In Command and Conquer: Red Alert 2, the Allied side can train dolphins equipped with a sonar weapon.

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.

 

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