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Bottlenose dolphin facts for kids

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Bottlenose dolphin
Tursiops truncatus 01-cropped.jpg
Bottlenose Dolphin breaching in the bow wave of a boat
Bottlenose dolphin size.svg
Size comparison against an average human
Scientific classification
Kingdom:
Phylum:
Class:
Order:
Family:
Genus:
Tursiops
Species:
T. truncatus
Binomial name
Tursiops truncatus
Montagu, 1821
Cetacea range map Bottlenose Dolphin.png
Bottlenose Dolphin range (in blue)

A bottlenose dolphin is a kind of dolphin that gets its name because its snout is shaped like a bottle. Its real nose for breathing is just a hole on top of its head. Bottlenose dolphins are quite intelligent. They are skilled and accurate hunters that eat mostly small-sized fish.

Description

Bottlenose dolphins are various shades of gray, with the darkest gray at the top and almost white shades at the underside. This countershading makes them hard to see while they are swimming both from above and below. Adults can range from 6.6 to 13.1 feet (2.0 to 4.0 m) and 330 to 1,430 pounds (150 to 650 kg). Males are usually larger than females. Except in the eastern Pacific, dolphins in warmer, shallower waters tend to be smaller than those in cooler, pelagic (open) waters.

Bottlenose dolphins can live for more than 40 years. Females typically live 5 to 10 years longer than males. Less than 2% of all bottlenose dolphins will live longer than 60 years. Bottlenose dolphins can jump up to 20 feet (6.1 m) in the air. They use these jumps to communicate with each other.

Anatomy

See also: Dolphin#Anatomy

The bottlenose dolphin's long upper and lower jaws form what is called a rostrum, or snout. They have 18 to 28 cone-shaped teeth on each side of the jaws. The real, functional nose is a blowhole on top of its head, almost centered between the eyes. The nasal septum is visible when the blowhole is open.

Bottlenose Dolphin KSC04pd0178 head only
Bottlenose dolphin head, showing rostrum and blowhole

The dorsal fin and flukes (lobes of the tail) do not contain bone or muscle. They are formed of dense connective tissue. The flukes propel the dolphin when it moves them up and down. The pectoral flippers (at the sides of the body) are used for steering.

Physiology and Senses

Dolphin at Dalkey Island
Dolphin and a paddler at Dalkey Island

In colder waters, they have more body fat and blood, which help them to dive more deeply than those that live in warmer waters. Typically, 18%–20% of a cold water-dwelling bottlenose dolphin's body weight is blubber. Most research in this area has been restricted to the North Atlantic Ocean. Bottlenose dolphins typically swim at 3 to 7 miles per hour (4.8 to 11.3 km/h). They are also able to swim in short bursts of speed ranging from 18 to 22 miles per hour (29 to 35 km/h).

Senses

Bottlenose dolphins use a form of sonar called echolocation to search for their food. They send out a burst pulse of clicking sounds in a focused beam and listen for the echo. When the clicking sounds hit an object in the water, like a fish or rock, they bounce back to the dolphin, telling it the shape, size, speed, distance, and location of the object. The dolphins hear this echo (and locate the objects) in two ways: the sound waves are sent to the inner ear through the lower jaw and through two small ear openings behind the eyes. As the dolphin gets closer to an object, it decreases two things: the intensity of sounds and the time between the sounds it releases.

Bottlenose dolphins have sharp eyesight. The eyes are located at the sides of the head and have a reflecting membrane, called a tapetum lucidum, at the back of the retina. This helps them to see well in dim light. Their horseshoe-shaped, double-slit pupils help the dolphins to have good vision both in air and underwater.

Since bottlenose dolphins have no olfactory (smelling) nerves or lobe in the brain and because they have a blowhole that closes when it is underwater, they have a poor sense of smell.

Researchers believe that bottlenose dolphins are able to detect salty, sweet, bitter (quinine sulphate), and sour (citric acid) tastes. Some dolphins in captivity have been known to have preferences for fish types. However, not enough research has been done to show whether the fish is preferred because of taste or some other reason.

Communication

Bottlenose dolphins communicate through burst pulsed sounds, whistles, and body language. Their body language can include leaping out of the water, snapping the jaws, slapping the tail on the surface, and butting heads. Sounds and gestures help keep track of other dolphins in the group and tell other dolphins of danger and nearby food. Because bottlenose dolphins do not have vocal cords, they produce sounds using six air sacs near their blowhole. Each dolphin has its own unique whistle (signature whistle). Researchers from the Bottlenose Dolphin Research Institute (BDRI), based in Sardinia, Italy, have now shown whistles and burst pulsed sounds are important for dolphins.

The tonal whistle sounds (the most melodious ones) allow dolphins to stay in contact with each other and to coordinate hunting strategies. The burst-pulsed sounds, which are more complex and varied than the whistles, are used when there is a possible confrontation. Each dolphin produces these sounds, and the least dominant dolphins move away.

Intelligence

Military-trained-dolphin
Bottlenose dolphin responding to human hand gestures.

Cognition

Since the 1970s, scientists have been studying the bottlenose dolphins' cognitive abilities (the ability to think). This research includes the dolphins' ability to copy sound and behaviors, understand the order of occurrences, understand artificial language, remember things, monitor self-behavior, identify likenesses and differences, show knowledge of symbols for various body parts, understand pointing gestures and gazing (as made by dolphins or humans), recognize themselves in a mirror, and show recognition of numbers.

Tool Use and Culture

At least some wild bottlenose dolphins use tools. In Shark Bay, dolphins have been seen placing a marine sponge on their rostrum, probably to protect it when the dolphin for food on the sandy sea bottom. In 2005, a study was done that showed that mothers were most likely to teach this behavior to their offspring.

In the Florida Keys, a small community of bottlenose dolphins performs a feeding technique called mud plume feeding. They create a U-shaped cloud of mud in the water column and rush in to capture fish.

Along the beaches and tidal marshes of South Carolina and Georgia in the United States, groups of bottlenose dolphins practice strand feeding. They separate into groups of two to six dolphins and create a bow wave to force fish out of water. The dolphins follow the fish, eat their prey, and then twist their bodies back and forth in order to slide back into the water.

Dolphins who live off the coast of Mauritania cooperate with fishermen because they know that they will benefit from this cooperation. The dolphins drive a school of fish toward the shore where the humans await with nets. While the fishermen are casting their nets, the dolphins are able to catch some of the fish as well.

Near Adelaide, in South Australia, three bottlenose dolphins can tail-walk. They elevate the upper part of their bodies vertically out of the water and propel themselves along the surface with powerful tail movements. Tail-walking mostly arises because of human training in dolphinariums. In the 1980s, a female from the local population was kept at a local dolphinarium for three weeks, and the scientist suggests she copied the tail-walking behavior from other dolphins. Two other wild adult female dolphins have now copied it from her.

A study conducted by the University of Chicago showed that bottlenose dolphins can remember whistles of other dolphins they had lived with after 20 years of separation. Each dolphin has a unique whistle that acts as a name, allowing them to keep close social bonds. New research shows that dolphins have the longest memory known in any species other than humans.

Life History

Respiration and Sleep

The bottlenose dolphin has a single blowhole on the top of its head consisting of a hole and a muscular flap. The flap is closed during muscle relaxation and opens during contraction (tightening of the muscles). Dolphins are voluntary breathers, which means that they have to choose to go to the surface and open their blowholes to get air. Typically, dolphins surface two to three times per minute, but a dolphin can stay underwater for up to 20 minutes. Although it sounds like dolphins would not be able to sleep, they sleep differently than humans. A dolphin rises to the surface to breathe through its blowhole two to three times per minute, although it can remain submerged for up to 20 minutes.

Dolphins have a sleep cycle that lasts for about 8 hours total, in sections of minutes to hours. During the sleep cycle, they remain near the surface, and half of their brain (the part that controls surfacing and breathing) remains active. They swim slowly (called logging) and occasionally close one eye.

Reproduction

See also: Dolphin#Reproduction and sexuality
Bottlenose dolphin mother and juvenile
Mother and juvenile bottlenose dolphins head to the seafloor

During the breeding season, males compete for access to females. This competition can take the form of fighting other males or of herding females to prevent access by other males. In Shark Bay, male bottlenose dolphins have been observed working in pairs or larger groups to follow and/or restrict the movement of a female for weeks at a time. These alliances, also known as male reproductive alliances, will fight with other alliances for control of females.

Mating occurs belly to belly. The gestation period averages 12 months. Births can happen at any time of year, but more births happen during warmer months. The young (called calves) are born in shallow water, sometimes assisted by a (possibly male) "midwife," and usually only a single calf is born. Twins are possible but rare. Newborn bottlenose dolphins are 2.6 to 4.6 ft (0.79 to 1.40 m) long and weigh 20 to 66 lb (9.1 to 29.9 kg). Calves born in the Indo-Pacific are usually smaller than common bottlenose dolphin infants. The mother can eject milk from her mammary glands to help her calf start nursing sooner. The calf suckles for 18 months to up to 8 years, and continues to stay close to its mother for several years after weaning. Females are ready to become mothers between the ages of 5 and 13; males are ready to become fathers between the ages of 9 and 14. Females reproduce every two to six years. Georgetown University professor Janet Mann explains that males develop strong bonds at a young age.

Social Interaction

Bottlenose dolphin with young
An adult female bottlenose dolphin with her young, Moray Firth, Scotland

Adult males live mostly alone or in groups of two to three, and join pods for short periods of time. Adult females and young dolphins normally live in groups of up to 15. This group size, and even the members within the group change from time to time, often on a daily or hourly basis. In a dolphin community near Sarasota, Florida, the most common group types are adults females with their recent offspring, older subadults of both sexes, and adult males - either alone or in bonded pairs. Smaller groups can join to form larger groups of 100 or more and occasionally exceed 1,000. The way they live can be compared to the way elephants and chimpanzees live.

Bottlenose dolphins studied by Bottlenose Dolphin Research Institute researchers off the island of Sardinia show random group behavior while feeding, and their behavior does not depend on feeding activity. In Sardinia, there are more dolphins around a floating fin-fish farm.

Ecology

Feeding

A dolphin's diet consists mainly of small fish, crustaceans, and squid. Although this differs by location, many populations share an appetite for fish from the mullet, the tuna and mackerel, and the drum and croaker families. Its cone-like teeth serve to grasp but do not chew food.

Here is a list of the different ways that dolphins hunt:

  • When some dolphins encounter a shoal of fish, they work as a team to herd them toward the shore so that they can catch more fish for one meal.
  • Other dolphins hunt alone, often targeting bottom-dwelling animals.
  • Sometimes a dolphin will hit a fish with its fluke, knocking it out of the water. This strategy is called "fish whacking".
  • "Strand feeding" is an inherited feeding method used by bottlenose dolphins near and around coastal regions of Georgia and South Carolina. When a pod (group) finds a school of fish, they will circle the school and trap the fish in a mini whirlpool. Then, the dolphins will charge at the school and push their bodies up onto a mud-flat, forcing the fish on the mud-flat as well. The dolphins then crawl around on their sides, eating the fish they washed up on shore. Finally, they flip their bodies back into the water.
  • Mud plume feeding is a method that some dolphins use to confuse fish. They create a U-shaped mud ring into which the fish swim. When the fish are disoriented, the dolphins swim in and eat the fish.
  • In some Mediterranean areas, bottlenose dolphins use human fisheries. They go to the nets because they know that many fish are located there.

Relations with Other Species

2005-05-n2-2550
A bottlenose dolphin attacks and kills a harbour porpoise at Chanonry Point, Scotland

Dolphins can show kind behavior toward other sea creatures. On Mahia Beach, New Zealand, on March 10, 2008, two pygmy sperm whales, a female and calf, were stranded on the beach. Rescuers, including Department of Conservation officer Malcolm Smith, attempted to help them four times. Soon, a playful bottlenose dolphin known to local residents as Moko arrived and, after apparently vocalizing to the whales, led them 660 ft (200 m) along a sandbar to the open sea, saving them from certain death.

Bottlenose dolphins can also behave aggressively. Males fight for rank and access to females. During mating season, males compete powerfully with each other through displays of toughness and size, with acts like head-butting. They display aggression toward sharks and smaller dolphin species. At least one population, off Scotland, has attacked and killed harbor porpoises. Some researchers believe that dolphins do not always eat their victims but compete for the food to show their power.

The bottlenose dolphin sometimes forms mixed-species groups with other species from the dolphin family, particularly larger species, such as the short-finned pilot whale, the false killer whale, and Risso's dolphin. They also interact with smaller species, such as the Atlantic spotted dolphin and the rough-toothed dolphin. While interactions with smaller species are sometimes friendly, they can also be hostile.

Predators

Some large shark species, such as the tiger shark, the dusky shark, the great white shark, and the bull shark, prey on the bottlenose dolphin, especially calves. The bottlenose dolphin can defend itself by charging the predator; dolphin "mobbing" behavior can occasionally kill the shark. Targeting a single adult dolphin can be dangerous for a shark of similar size. Killer whale populations in New Zealand and Peru have been seen preying on bottlenose dolphins, but this seems rare, and other orcas may swim with dolphins. Swimming in pods allows dolphins to better defend themselves against predators. Bottlenose dolphins either use complicated evasive maneuvers to out-swim their predators or mobbing techniques to either batter the predator to death or force it to flee.

Relation to Humans

Interaction

Bottlenose Dolphin -Notojima Aquarium -Ishikawa -Japan-8a
At Notojima Aquarium, Japan

Bottlenose dolphins sometimes show curiosity towards humans in or near water. Sometimes they rescue injured divers by raising them to the surface. They also do this to help injured members of their own species. In November 2004, it was reported that dolphins worked together to help four lifeguards in New Zealand. The lifeguards were swimming 330 ft (100 m) off the coast near Whangarei and were approached by a shark (reportedly a great white shark). Bottlenose dolphins herded the swimmers together and surrounded them for 40 minutes, preventing the shark from attacking, as they slowly swam to shore.

When dolphins swim near the shore, they run the risk of colliding with boats. Researchers at the Bottlenose Dolphin Research Institute studied the behavior of bottlenose dolphins' diving behavior when boats were both present and absent. Dolphins responded more to tourist boats than fishing boats. Driving behavior, speed, engine type, and separation distance of boats all affect dolphin safety.

Dolphins in these areas can also coexist with humans. For example, in the town of Laguna in south Brazil, a pod of bottlenose dolphins lives near the shore, and some of its members cooperate with humans. These cooperating dolphins are individually recognized by the local fishermen, who name them. The fishermen typically stand up to their knees in the shallow waters or sit in canoes, waiting for the dolphins. Now and then, one or more dolphins appear, driving the fish towards the line of fishermen. When a dolphin displays a unique body movement outside the water, like slapping its tail on the water, the fishermen know it is time to cast their nets (the entire sequence is shown here, and a detailed description of the signal's characteristics is available here). In this unique form of cooperation, the dolphins benefit because the fish are disoriented and cannot escape to shallow water where the larger dolphins cannot swim. Likewise, studies show that fishermen casting their nets following the unique signal catch more fish than when fishing alone, without the help of the dolphins. The dolphins were not trained for this behavior; the collaboration began before 1847. Similar cooperative fisheries also exist in Mauritania, Africa.

Commercial "dolphin encounter" businesses and tours operate in many countries. The documentary film The Cove documents how dolphins are captured and sold to some of these companies (particularly in Asia) while the remaining pod is slaughtered. Bottlenose dolphins perform in many aquaria, which has brought about arguments from both animal activists and scientists. Animal welfare activists and certain scientists have claimed that the dolphins do not have enough space or receive good care or stimulation. However, others, notably SeaWorld (backed by different scientists), show that the dolphins are properly cared for, have lots of environmental stimulation, and enjoy interacting with humans.

Eight bottlenose dolphins that lived at the Marine Life Aquarium in Gulfport, Mississippi were swept away from their aquarium pool during Hurricane Katrina. They were later found and returned to captivity from the Gulf of Mexico.

NMMP dolphin with locator
K-Dog, trained by the US Navy to find mines and boobytraps underwater, leaping out of the water

The military of the United States and Russia train bottlenose dolphins as military dolphins for wartime tasks. The jobs of the dolphins include locating sea mines and detecting enemy divers. The program in the United States, called the U.S. Navy Marine Mammal Program, is located in San Diego.

Tião was a well-known female bottlenose dolphin who lived by herself that was first spotted in the town of São Sebastião in Brazil around 1994. She frequently allowed humans to interact with her. The dolphin became infamous for killing a swimmer and injuring many others, which later earned her the nickname "killer dolphin."

Cultural Influence

The popular television show Flipper, created by Ivan Tors, portrayed a bottlenose dolphin in a friendly relationship with two boys, Sandy and Bud. A seagoing Lassie, Flipper understood English and was a hero: "Go tell Dad we're in trouble, Flipper! Hurry!" The show's theme song contains the lyric "No one you see / is smarter than he". The television show was based on a 1963 film and was remade as a feature film in 1996, starring Elijah Wood and Paul Hogan. A second TV series ran from 1995 to 2000, starring Jessica Alba.

Other television appearances by bottlenose dolphins include Wonder Woman, Highway to Heaven, Dolphin Cove, seaQuest DSV, and The Penguins of Madagascar, in which a dolphin, Doctor Blowhole, is a villain. In the HBO movie Zeus and Roxanne, a female bottlenose dolphin befriends a male dog, and in Bermuda Triangle, a girl named Annie (played by Lisa Jakub) swims with dolphins. Many human and dolphin interaction segments are shot on location in the Florida Keys with Dolphin Research Center.

Dolphin Tale, directed by Charles Martin Smith, starring Nathan Gamble, Ashley Judd, Harry Connick Jr., Morgan Freeman, Cozi Zuehlsdorff and Kris Kristofferson, is based on the real-life story of the dolphin named Winter, who was rescued from a crab trap in December 2005 and lost her tail. The movie tells the story of the rescue and how she has learned to swim with a prosthetic tail. Dolphin Tale 2, a sequel to the 2011 film, featured another dolphin named Hope and an appearance by Bethany Hamilton. The sequel was released on September 12, 2014.

Bottlenose dolphins have appeared in novels. In The Hitchhiker's Guide to the Galaxy and one of its sequels, So Long, and Thanks For All the Fish, the dolphins try to warn humans of Earth's impending destruction, but their behavior was misinterpreted as playful acrobatics. Bottlenose dolphins are primary characters in Anne McCaffrey's Dragonriders of Pern series, especially The Dolphins of Pern. Bottlenose dolphins are incorporated into the science fiction video game series Ecco the Dolphin. Delphineus, a dolphin, is a character in the video game EcoQuest: The Search for Cetus. He helps the boy, Adam, to find the sea king Cetus (a sperm whale) and clean up the underwater environment where he lives. Bottlenose dolphins were mentioned in various Star Trek novels and other materials. Their job was to serve as navigation specialists onboard various Federation starships.

T.D., the Miami Dolphins' mascot, uses the bottlenose dolphin as its mascot and team logo.

Factual descriptions of the dolphins date back into antiquity – the writings of Aristotle, Oppian, and Pliny the Elder all mention the species.

Threats

Bottlenose dolphins are still captured or killed in dolphin drive hunts for their meat, to eliminate competition for fish, and for capture for marine parks. Bottlenose dolphins (and several other dolphin species) often travel with tuna and can get caught in tuna nets, which can kill the dolphins. Because people were concerned about the safety of the dolphins, many stopped buying tuna. This is called a boycott. These boycotts led to the idea of "dolphin-safe" labeling for fishing practices that do not endanger dolphins.

The man-made chemical perfluorooctanesulfonic acid (PFOS) may be harming the immune system of bottlenose dolphins. PFOS affects the immune system of male mice at a concentration of 91.5 ppb, while PFOS has been reported in bottlenose dolphins in excess of 1 ppm. High levels of metal contaminants have been measured in tissues in many areas of the globe. A recent study found high levels of cadmium and mercury in bottlenose dolphins from South Australia. These levels were later shown to be associated with kidneys that were not formed correctly, showing that higher heavy-metal concentrations can be bad for a dolphin's health.

Conservation

Dolphinjf
Bottlenose dolphin (at Hundred Islands National Park).

Bottlenose dolphins are not endangered. Their future is stable because of their abundance and adaptability. However, specific populations are threatened due to various environmental changes. The population in the Moray Firth in Scotland is estimated to consist of about 190 dolphins that are under threat from harassment, traumatic injury, water pollution, and less food. Likewise, an isolated population in Doubtful Sound, New Zealand, is in decline due to calf loss because of an increase in warm freshwater flow into the fjord. Less local climate change, such as increasing water temperature may also play a role but has never been shown to be the case. One of the largest coastal populations of bottlenose dolphins in Shark Bay, Western Australia, was forecast to be stable with little variation in deaths over time.

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