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Dolphin

Encyclopedia : D : DO : DOL : Dolphin

For other uses, see Dolphin (disambiguation)}}}.
Dolphins are aquatic mammals related to whales and porpoises, famous for their intelligence, apparent compassion, and joy. 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 related species belong to the Delphinidae family and therefore qualify as dolphins, even though they are called whales in common language. There are almost 40 species of dolphin in 17 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 10 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 10 million years ago, during the Miocene.

Contents

Taxonomy

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

Hybrid dolphins

In 1933, three strange 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. In the wild, Spinner Dolphins have sometimes hybridised with Spotted Dolphins and Bottlenose Dolphins. In the wild, bands of males of one dolphin species have been observed to mate with lone female Spinners. Blue Whales, Fin Whales and Humpback Whales all hybridize in the wild. Dall's Porpoises and Harbour Porpoises have hybridized in the wild. There has also been a reported hybrid between a beluga and a narwhal. See also wolphin.

Evolution and anatomy of dolphins

Dolphins, along with whales and porpoises, are descendants of land-living mammals, most likely of the Artiodactyl order. Modern dolphin skeletons have two small rod shaped pelvic bones thought to be left-over hind legs. They entered the water roughly 50 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 250) in several species. The dolphin brain is large and has a highly structured cortex, which often is referred to in discussions about their high intelligence. 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

Bottlenose dolphin in the bow wave of a boat
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Bottlenose dolphin in the bow wave of a boat

Dolphins are widely believed to be amongst the most intelligent of all animals, 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 marine animals 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 Dolphin 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 playfighting with other dolphins. They have even been seen harassing other creatures, like seabirds and turtles. Dolphins also seem to enjoy riding waves and are frequently seen 'surfing' coastal swells and the bow waves of boats.

They are also famous for their willingness to occasionally approach humans and playfully interact with them in the water. In return, in some cultures like in Ancient Greece they were treated 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 the swimmers. A school of dolphins is also said to have pushed a fishing boat that was returning back out to sea after sensing the underwater disturbances generated by the 2004 Asian Tsunami.

Dolphins surfing at Snapper Rocks, Queensland, Australia.
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Dolphins surfing at Snapper Rocks, Queensland, Australia.

Dolphins are social animals, living in pods (also called "schools") of up to a dozen animals. In places with a high abundance of food, schools can join temporarily, forming an aggregation called a superpod; such groupings may exceed 1000 dolphins. The individuals communicate using a variety of clicks, whistles and other vocalizations. They also use ultrasonic sounds for echolocation. Membership in schools is not rigid; interchange is common. However, the animals can establish strong bonds between each other. This leads to them staying with injured or ill fellows for support.

A young couple being entertained by trained Bottlenose Dolphins in Puerto Plata, Dominican republic.
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A young couple being entertained by trained Bottlenose Dolphins in Puerto Plata, Dominican republic.

Because of their high 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 children. The military has employed dolphins for various purposes from finding mines to rescuing lost or trapped persons. 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 offspring to use tools. The animals break off sponges and put them onto their mouths thus protecting the delicate body part during their hunt for fish on the seabed. This knowledge of how to use a tool is mostly transferred from mothers to daughters in dolphins, unlike simian primates, where the knowledge is generally passed onto all the offsprings, irrespective of sex. The technology to use sponges as mouth protection is not genetically inherited but a taught cultural behaviour.

Dolphins are one of the few animals other than humans known to mate for reasons other than procreation. Even during infertile periods in the females menstral cycle dolphins have been observed mating for pleasure and to bond with one another. [BIRTH CONTROL, BISEXUALITY, DEATH BY CHOICE ...The dolphins have it all over us] - article by Bob Hunter, eye weekly

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 in the wild, 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 the animals they hunt: 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 large whales. There are no known reports of cannibalism amongst dolphins.

Individual species may employ a number of methods of hunting:

Dolphins in popular culture

See also

  1. redirect

References

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