Dolphin, Dolphin

There are almost forty species of dolphin in seventeen genera. They vary in size from and (Maui's Dolphin), up to and (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 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.

Dolphin Safari (2006) sightings log , page retrieved December 17 2006.

In captivity, a Bottlenose Dolphin and a Rough-toothed Dolphin produced hybrid offspring. Texas Tech University (1997), Mammals of Texas - Rough-toothed Dolphin , article retrieved December 8 2006.

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. Louis Herman, interviewed for Associated Press, article by Jeanette J. Lee (2005), Livescience.com - Whale-Dolphin Hybrid Has Baby Wholphin , article retrieved April 26 2007.

The ancestors of the modern day dolphins entered the water roughly fifty million years ago, in the Eocene epoch.

Associated Press / FOX news (2006), Japanese Researchers Find Dolphin With 'Remains of Legs' , article retrieved November 6 2006.

Teeth can be very numerous (up to two hundred and fifty) in several species. Dolphins breathe through a blowhole located on top of their head, with the trachea being anterior to the brain. The dolphin brain is large and highly complex and is different in structure from that of most land mammals.

The Institute for Marine Mammal Studies (IMMS), Dolphin Frequently Asked Questions: Why is a dolphin a mammal and not a fish? , article retrieved February 21 2008.

VirtualExplorers.org, All About Dolphins - Amazon River Dolphin fact sheet , article retrieved February 21 2008.

Hearing is also used for 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. 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 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, SeaWorld, Bottlenose Dolphins - Senses , article retrieved December 17 2006.

Bjorn Mauck, Ulf Eysel and Guide Dehnhardt (2000), Selective heating of vibrissal follicles in seals (Phoca Vitulina) and dolphins (Sotalia Fluviatilis Guianensis) , article retrieved March 11, 2007.

Laurie Stepanek (1998), Amazon River Dolphin (Inia geoffrensis) , article retrieved March 11, 2007.

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. Compared to many other species however, dolphin behaviour has been studied extensively by humans, both in captivity and in the wild. See the cetacean intelligence article for more details.

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. Davidson College, biology department (2001) Bottlenose Dolphins - Altruism , article retrieved March 12 2008.

The dolphins break sponge 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 on to both sexes. The technology to use sponges as mouth protection is not genetically inherited but a taught behaviour. Rowan Hooper for New Scientist (2005), Dolphins teach their children to use sponges , article retrieved December 17 2006.

Nic Fleming, Science correspondent for the Telegraph (2008), Dolphins woo females with bunches of weeds , article retrieved February 11 2008.

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.

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.

Herzing D.L., Rogers C.A., for the Wild Dolphin Project, Directionality of sexual aggression in mixed-species encounters between Atlantic Spotted dolphins and Bottlenose dolphins in the Bahamas (2005), article retrieved September 18 2007.

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.

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.

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.

Dolphin echolocation clicks are amongst the loudest sounds made by animals in the sea. W. W. L. Au, The Sonar of Dolphins (Springer, NY, 1993).

At times they also harass other local creatures, like seabirds and turtles. 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.

If not needed to keep the blowhole above the water, the tail kick reflex may subside. Dolphins kept unconscious using anesthetics initially show a similar tail kick reflex. James G. McCormick (PhD), Department of Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, North Carolina (2007), Behavioral Observations of Sleep and Anesthesia in the Dolphin: Implications for Bispectral Index Monitoring of Unihemispheric Effects in Dolphins , article retrieved February 11 2008.

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 diseases and parasites.

A 2006 survey found no individuals of the Yangtze River Dolphin, leading to the conclusion that the species is now functionally extinct. Douglas Williams for Shanghai Daily (2006), Yangtze dolphin may be extinct . Article retrieved December 9 2006.

Ebury Press, London. ISBN 0-09-189780-7 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.

CBC news (2003), Navy sonar may be killing whales, dolphins , article retrieved October 27, 2008.

The Ancient Greeks treated them with welcome; a ship spotting dolphins riding in their wake was considered a good omen for a smooth voyage. In Hindu mythology, the Ganges River Dolphin is associated with Ganga, the deity of the Ganges river.

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 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.

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. In the 1973 movie The Day of the Dolphin trained dolphins are kidnapped and made to perform a naval military assassination using explosives.

For example, a 2005 study with 30 participants found it was an effective treatment for mild to moderate depression. Christian Antonioli and Michael A. Reveley, (2005), Randomised controlled trial of animal facilitated therapy with dolphins in the treatment of depression.

PBS - Frontline, The Story of Navy dolphins. , article retrieved June 8, 2008.

Dolphins are still being trained by the United States Navy 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. BBC News (2000), Iran buys kamikaze dolphins , article retrieved June 7, 2008.

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 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 chimpanzees) in David Brin's 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.

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.

Examples include the Triton Fountain by Bernini and depictions of dolphins in the ruined Minoan palace at Knossos and on Minoan pottery.

Source: Wikipedia > Dolphin