Bottlenose dolphin

Scientists have been long aware of the fact that the Tursiops dolphins might consist of more than one species, as there is extensive variation in color and morphology along its range. In the past, most studies used morphology to evaluate differences between and within species, but in the late 20th century, combining morphological and molecular genetics allowed much greater insight into this previously intractable problem. Since the late 1990s and early 2000s, most researchers acknowledged the existence of two species: the common bottlenose dolphin (T. truncatus), found in coastal and oceanic habitats of most tropical to temperate oceans, and the Indo-Pacific bottlenose dolphin (T. aduncus), that lives in coastal waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa. In 2011, a third distinct species was described, the Burrunan dolphin (T. (aduncus) australis), found in the Port Phillip and Gippsland Lakes areas of Victoria, Australia, after research showed it was distinct from T. truncatus and T. aduncus, both in morphology and genetics. Also, evidence has been accumulating to validate the existence of a separate species, Lahille's bottlenose dolphin, T. gephyreus, that occurs in coastal waters of Argentina, Uruguay and southern Brazil. Other sources accept the Pacific bottlenose dolphin (T. t. gillii or T. gillii), that inhabits the Pacific, and has a black line from the eye to the forehead. T. gillii, first described in 1873, is currently considered a junior synonym of T. truncatus. Additionally, T. nuuanu was described in 1911 for bottlenose dolphins along the Pacific coast in Central America. An analysis of T. gillii and T. nuuanu specimens supported T. gillii as a synonym of T. truncatus, while T. nuuanu was recognized as a subspecies. In general, genetic variation between populations is significant, even among nearby populations. As a result of this genetic variation, other distinct species currently considered to be populations of common bottlenose dolphin are possible. Their ranges overlap, but they have been shown to be genetically distinct. The Society for Marine Mammalogy's Committee on Taxonomy presently recognizes three species of bottlenose dolphin: T. truncatus, T. aduncus, and T. erebennus. They also recognize three subspecies of common bottlenose dolphin in addition to the nominotypical subspecies: the Black Sea bottlenose dolphin (T. t. ponticus), Lahille's bottlenose dolphin (T. t. gephyreus), and the Eastern Tropical Pacific bottlenose dolphin (T. t. nuuanu). However, more recent studies indicate that this is a consequence of reticulate evolution (such as past hybridization between Stenella and ancestral Tursiops) and incomplete lineage sorting, and thus support T. truncatus and T. aduncus belonging to the same genus. Kawili'Kai at the Sea Life Park in Hawaii|alt=Photo of left side of dolphin head at surface Hybrids Bottlenose dolphins have been known to hybridize with other dolphin species. Hybrids with Risso's dolphin occur both in the wild and in captivity. The best known hybrid is the wholphin, a false killer whale–bottlenose dolphin hybrid. The wholphin is fertile, and two currently live at the Sea Life Park in Hawaii. The first was born in 1985 to a female bottlenose. Wholphins also exist in the wild. In captivity, a bottlenose dolphin and a rough-toothed dolphin hybridized. A common dolphin–bottlenose dolphin hybrid born in captivity lives at SeaWorld California. Other hybrids live in captivity around the world and in the wild, such as a bottlenose dolphin–Atlantic spotted dolphin hybrid. Fossil species Bottlenose dolphins appeared during the Miocene. Known fossil species include Tursiops osennae (late Miocene to early Pliocene) from the Piacenzian coastal mudstone, and Tursiops miocaenus (Miocene) from the Burdigalian marine sandstone, all in Italy. ==Description==

The bottlenose dolphin weighs an average of , but can range from . It can reach a length of just over . Its color varies considerably, is usually dark gray on the back and lighter gray on the flanks, but it can be bluish-grey, brownish-grey, or even nearly black, and is often darker on the back from the rostrum to behind the dorsal fin. This is called countershading and is a form of camouflage. Older dolphins sometimes have a few spots. Bottlenose dolphins can live for more than 40 years. Females typically live 5–10 years longer than males, with some females exceeding 60 years. This extreme age is rare and less than 2% of all bottlenose dolphins will live longer than 60 years. Bottlenose dolphins can jump to a height of 6 metres (20 feet) in the air. ==Anatomy==

Their elongated upper and lower jaws form what is called a rostrum, or snout, which gives the animal its common name. The flukes (lobes of the tail) and dorsal fin are formed of dense connective tissue and do not contain bone or muscle. The dorsal fin usually shows phenotypic variations that help discriminate among populations. The animal propels itself by moving the flukes up and down. The pectoral flippers (at the sides of the body) are for steering; they contain bones homologous to the forelimbs of land mammals. A bottlenose dolphin discovered in Japan has two additional pectoral fins, or "hind legs", at the tail, about the size of a human's pair of hands. Scientists believe a mutation caused the ancient trait to reassert itself as a form of atavism. Newborn dolphins are born with vibrissae, whisker-like tactile follicles mainly on the rostrum, as part of a sensory organ called the "follicle-sinus complex", which is present only during the postnatal period. The whiskers are possibly used to locate the mother's nipples. ==Physiology and senses==

at Dalkey Island In colder waters, they have more body fat and blood, and are more suited to deeper diving. Typically, 18–20% of their body weight is blubber. Bottlenose dolphins typically swim at , but are capable of bursts of up to . The higher speeds can only be sustained for a short time. Senses The dolphin's search for food is aided by a form of sonar known as echolocation: it locates objects by producing sounds and listening for the echoes. Clicking sounds are emitted in a focused beam in front of the dolphin. When the clicking sounds hit an object in the water, like a fish or rock, they bounce off and come back to the dolphin as echoes. Echolocation tells the dolphins the shape, size, speed, distance, and location of the object. Bottlenose dolphins are also able to extract shape information, suggesting they are able to form an "echoic image" or sound picture of their targets. They also have electroreception. The calves are born with two slender rows of whiskers along their snout, which fall off soon after birth, leaving behind a series of dimples known as vibrissal pits able to sense electric fields. Dolphins have sharp eyesight. The eyes are located at the sides of the head and have a tapetum lucidum, or reflecting membrane, at the back of the retina, which aids vision in dim light. Their horseshoe-shaped, double-slit pupils enable dolphins to have good vision both in air and underwater, despite the different indices of refraction of these media. When under water, the eyeball's lens serves to focus light, whereas in the in-air environment, the typically bright light serves to contract the specialized pupil, resulting in sharpness from a smaller aperture (similar to a pinhole camera). By contrast, a bottlenose's sense of smell is poor, because its blowhole, the analog to the nose, is closed when underwater and it opens only for breathing. Like other toothed whales, it has no olfactory nerves or olfactory lobe in the brain. Communication Bottlenose dolphins communicate through burst pulsed sounds, whistles, and body language. Examples of body language include leaping out of the water, snapping jaws, slapping the tail on the surface and butting heads. Signature whistles, which are in a higher frequency range than humans can hear, have an important role in facilitating mother–calf contact. In all 19 cases, the mother dolphin changed the same signature whistle when the calf was present, by reaching a higher frequency, or using a wider frequency range. Similarly, humans use higher fundamental frequencies and a wider pitch range to inflect child-directed speech (CDS). This has rarely been discovered in other species. The tonal whistle sounds (the most melodious ones) allow dolphins to stay in contact with each other (above all, mothers and offspring), and to coordinate hunting strategies. The burst-pulsed sounds (which are more complex and varied than the whistles) are used "to avoid physical aggression in situations of high excitement", such as when they are competing for the same piece of food, for example. The dolphins emit these strident sounds when in the presence of other individuals moving towards the same prey. The "least dominant" one soon moves away to avoid confrontation. ==Intelligence==

Cognition Cognitive abilities that have been investigated include concept formation, sensory skills, and mental representations. Such research has been ongoing since the 1970s. This includes: acoustic and behavioral mimicry, comprehension of novel sequences in an artificial language, memory, monitoring of self behavior, discrimination and matching, comprehension of symbols for various body parts, comprehension of pointing gestures and gaze (as made by dolphins or humans), mirror self-recognition, and numerical values. Tool use and culture At least some wild bottlenose dolphins use tools. In Shark Bay, off Western Australia, dolphins place a marine sponge on their rostrum, presumably to protect it when searching for food on the sandy sea bottom. This has only been observed in this bay (first in 1997), and is predominantly practiced by females. A 2005 study showed mothers most likely teach the behavior to their offspring, evincing culture (behavior learned from other species members). Mud plume feeding is a feeding technique performed by a small community of bottlenose dolphins over shallow seagrass beds (less than 1 m) in the Florida Keys in the United States. The behavior involves creation of a U-shaped plume of mud in the water column and then rushing through the plume to capture fish. Along the beaches and tidal marshes of South Carolina and Georgia in the United States, bottlenose dolphins cooperatively herd prey fish onto steep and sandy banks in a practice known as "strand feeding". Groups of between two and six dolphins are regularly observed creating a bow wave to force the fish out of the water. The dolphins follow the fish, stranding themselves briefly, to eat their prey before twisting their bodies back and forth in order to slide back into the water. While initially documented in South Carolina and Georgia, strand feeding has also been observed in Louisiana, Texas, Baja California, Ecuador, and Australia. Some Mauritanian dolphins cooperate with human fishermen. The dolphins drive a school of fish towards the shore, where humans await with nets. In the confusion of casting nets, the dolphins catch a large number of fish as well. Intraspecies cooperative foraging has also been observed. These behaviors may also be transmitted via teaching. Controversially, Rendell and Whitehead have proposed a structure for the study of cetacean culture. Similar cases have been observed in Laguna, Santa Catarina in Brazil since during 19th century as well. Near Adelaide, in South Australia, several bottlenose dolphins "tail-walk", whereby 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 via human training in dolphinaria. 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 copied it from her, and the behaviour has continued through generations until 2022. 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 functions like a name, allowing the marine mammals to keep close social bonds. The new research shows that dolphins have the longest memory yet known in any species other than humans. Cortical neurons Some researchers hypothesize that the number of nerve cells (neurons) in the cortex of the brain predicts intelligence in mammals. A 2019 study estimated the number of neurons in the cerebral cortex of three common bottlenose dolphins and found numbers ranging from 11.7 to 15.2 billion neurons. The human average being approximately 16 billion, this is likely within the range found in the human population. ==Life history==

Bottlenose dolphins have a lifespan of 40–60 years. Females can outlive males and live for 60 years or more. Dolphins start to reproduce aged 5 to 15 years. Respiration and sleep The bottlenose dolphin has a single blowhole located on the dorsal surface of the head consisting of a hole and a muscular flap. The flap is closed during muscle relaxation and opens during contraction. Dolphins are voluntary breathers, who must deliberately surface and open their blowholes to get air. They can store almost twice as much oxygen in proportion to their body weight as a human can: the dolphin can store 36 milliliters (ml) of oxygen per kg of body weight, compared with 20 ml per kg for humans. This is an adaptation to diving. The bottlenose dolphin typically 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 can breathe while "half-asleep". During the sleeping cycle, one brain hemisphere remains active, while the other hemisphere shuts down. The active hemisphere handles surfacing and breathing behavior. The daily sleeping cycle lasts for about 8 hours, in increments of minutes to hours. During the sleeping cycle, they remain near the surface, swimming slowly or "logging", and occasionally closing one eye. The female's slit houses her vagina and anus. Females have two mammary slits, each housing one nipple, one on each side of the genital slit. The ability to stow their reproductive organs (especially in males) allows for maximum hydrodynamics. The breeding season produces significant physiological changes in males. At that time, the testes enlarge, enabling them to hold more sperm. Large amounts of sperm allow a male to wash away the previous suitor's sperm, while leaving some of his own for fertilization. Also, sperm concentration markedly increases. Having less sperm for out-of-season social mating means it wastes less. This suggests sperm production is energetically expensive. Males have large testes in relation to their body size. During the breeding season, males compete for access to females. Such competition can take the form of fighting other males or of herding females to prevent access by other males. Male Sarasota Bay common bottlenose dolphins with the defensive advantages of male pair-bonding range more widely than unpaired males, and encounter more unrelated females. In Shark Bay, male Indo-Pacific 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, waiting for her to become sexually receptive. Humans and bottlenose dolphins are the only species that share this type of "gang formation" habit as a form of cooperation. Mating occurs belly to belly. The gestation period averages 12 months. Twins are possible, but rare. Newborn bottlenose dolphins are long and weigh , with Indo-Pacific bottlenose dolphin infants being generally smaller than common bottlenose dolphin infants. and continues to closely associate with its mother for several years after weaning. Female bottlenose dolphins have to expend additional energy in carrying out parental care, e.g., infant-carrying behavior. Dolphins do not physically hold their infants but line up in an echelon position with infants swimming beside them. This position creates a change of water flow pattern from the infant which minimizes separation between the mother and infant, but also increases the mother's surface area and creates a drag for the swimmer. This also leaves less energy to use in swimming speed, foraging, and predator evasion. Social interaction , Scotland|alt=Photo of one large and two small dolphins breaching together 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 animals. However, they live in fission-fusion societies of varying group size, within which individuals change associations, often on a daily or hourly basis. Group compositions are usually determined by sex, age, reproductive condition, familial relations and affiliation histories. In a dolphin community near Sarasota, Florida, the most common group types are adult 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 social strategies of marine mammals such as bottlenose dolphins "provide interesting parallels" with the social strategies of elephants and chimpanzees.{{Cite book Bottlenose dolphins studied by Bottlenose Dolphin Research Institute researchers off the island of Sardinia show random social behavior while feeding, and their social behavior does not depend on feeding activity.{{cite journal| last=Díaz López| first=Bruno|author2=Shirai J.B.| year=2008| pages=292–303| volume=212| title=Marine aquaculture off Sardinia Island (Italy):ecosystem effects evaluated through a trophic mass-balance model ==Ecology==

Feeding Fish is one of the main items in the dolphin diet. They also eat shrimps, squid, mollusks, and cuttlefish, and only swallow the soft parts. They eat 22 pounds of fish a day. When they encounter a shoal of fish, they work as a team to herd them towards the shore to maximize the harvest. "Strand feeding" is an inherited feeding technique used by bottlenose dolphins near and around coastal regions of Georgia and South Carolina. When a pod 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, consuming the fish they washed up on shore. This happens only during low tides. One type of feeding behavior seen in bottlenose dolphins is mud ring feeding. Bottlenose dolphins conflict with small-scale coastal commercial fisheries in some Mediterranean areas. Common bottlenose dolphins are probably attracted to fishing nets because they offer a concentrated food source. However, human-dolphin interactions extend beyond fisheries and can have significant negative consequences for dolphin behavior and survival. Research has shown that frequent interactions with humans such as feeding, can alter dolphins' natural behaviors. Such exposure often reduces their innate wariness, making them more vulnerable to intentional harm and predation, including shark attacks. Relations with other species at Chanonry Point, Scotland.|alt=Photo of two animals at surface surrounded by spray Dolphins can exhibit altruistic behaviour toward other sea creatures. On Mahia Beach, New Zealand, on March 10, 2008, two pygmy sperm whales, a female and calf, stranded on the beach. Rescuers attempted to refloat them four times. Shortly, a playful bottlenose dolphin known to local residents as Moko arrived and, after apparently vocalizing at the whales, led them along a sandbar to the open sea, saving them from imminent euthanasia. In 2019 a female was observed caring for a juvenile melon-headed whale, the first reported instance of a bottlenose dolphin adopting a non-conspecific infant. The bottlenose dolphin can behave aggressively. Males fight for rank and access to females. During mating season, males compete vigorously with each other through displays of toughness and size, with a series of acts, such as head-butting. They display aggression towards sharks and smaller dolphin species. At least one population, off Scotland, has practiced infanticide, and also has attacked and killed harbour porpoises. University of Aberdeen researchers say the dolphins do not eat their victims, but are simply competing for food. However, Dr. Read of Duke University, a porpoise expert researching similar cases of porpoise killings that had occurred in Virginia in 1996 and 1997, holds a different view. He states dolphins and porpoises feed on different types of fish, thus food competition is an unlikely cause of the killings. Similar behaviour has been observed in Ireland. In the first half of July 2014, four attacks with three porpoise fatalities were observed and caught on video by the Cardigan Bay Marine Wildlife Centre in the Cardigan Bay, Wales. 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 affiliative, they can also be hostile. A pod of bottlenose dolphins is capable of defending against most sharks by charging the predator; dolphin 'mobbing' behavior of sharks can occasionally prove dangerous for the shark, notably in smaller species. ==Relation to humans==

Interaction The species sometimes shows curiosity towards humans in or near water. Occasionally, they rescue injured divers by raising them to the surface. They also do this to help injured members of their own species. In coastal regions, dolphins run the risk of colliding with boats. Researchers of the Bottlenose Dolphin Research Institute first quantified data about solitary bottlenose dolphin diving behavior in the presence and absence of boats. Dolphins responded more to tourist than fishing vessels. Driving behavior, speed, engine type and separation distance all affected dolphin safety. However, dolphins in these areas can also coexist with humans. For example, in the town of Laguna in south Brazil, a pod of bottlenose dolphins resides in the estuary, 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. One dolphin then displays a unique body movement outside the water, which serves as a signal to the fishermen to cast their nets (the entire sequence is shown here,). In this unique form of cooperation, the dolphins gain because the fish are disoriented and because the fish 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' enterprises and tours operate in many countries. The documentary film The Cove documents how dolphins are captured and sold to some of these enterprises (particularly in Asia) while the remaining pod is slaughtered. In addition to such endeavors, the individuals swim with and surface near surfers at the beach. Bottlenose dolphins perform in many aquaria, generating controversy. Animal welfare activists and certain scientists have claimed that the dolphins do not have adequate space or receive adequate care or stimulation. However, others, notably SeaWorld, counter by claiming that the dolphins are properly cared for, have much 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 in the Gulf of Mexico and returned to captivity. to find mines and boobytraps underwater, leaping out of the water|alt=Photo of dolphin leaping clear of the water next to a man wearing a hat The military of the United States and Russia train bottlenose dolphins as military dolphins for wartime tasks, such as locating sea mines and detecting enemy divers. The U.S.'s program is the U.S. Navy Marine Mammal Program, located in San Diego. Tião was a well-known solitary male bottlenose dolphin that was first spotted in the town of São Sebastião in Brazil around 1994 and frequently allowed humans to interact with him. The dolphin became infamous for killing a swimmer and injuring many others, which later earned him 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, with a sequel, Flipper's New Adventure (1964), and was remade as a feature film in 1996, starring Elijah Wood and Paul Hogan, as well as a second TV series running 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 Secrets of the Bermuda Triangle (1996 Ian Toynton movie), a girl named Annie (played by Lisa Jakub) swims with dolphins. Human and dolphin interaction segments, shot on location in the Florida Keys with Dolphin Research Center, are featured on Sesame Street and on a Halloween episode of The Simpsons, Treehouse of Horror XI. 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 Winter, who was rescued from a crab trap in December 2005 and lost her tail, but learned to swim with a prosthetic one. Dolphin Tale 2, a sequel to the 2011 film, featured another rescued dolphin named Hope and an appearance by Bethany Hamilton. The sequel was released on September 12, 2014. The NFL's Miami Dolphins 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 Between 1950 and 2020, about four million of dolphins have drowned in fishing nets. Tuna fishing crews have been the most responsible for the largest number of deaths. In 1972, the U.S. government passed a law limiting the number of dolphins that could be killed yearly by tuna fishing crews. Dolphins in the United Kingdom have also been found to contain high levels of pollutants in their tissues. Heavy metals including mercury, PCBs and DDT are of great concern. These pollutants can cause harm in dolphins growth development, reproduction, and immunity. Since the mid-1990s, hundreds of dolphins have been trained to perform in shows presented by aquariums, zoos, and amusement parks. Scientists conduct various types of research to understand the dolphin's communication system. The man-made chemical perfluorooctanesulfonic acid (PFOS) may be compromising 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, levels which were later found to be associated with kidney malformations, indicating possible health effects of high heavy metal concentrations in dolphins. Conservation ) 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 around 190 individuals, and are under threat from harassment, traumatic injury, water pollution and reduction in food availability. Likewise, an isolated population in Doubtful Sound, New Zealand, is in decline due to calf loss coincident to an increase in warm freshwater discharge into the fiord. 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 mortality over time (Manlik et al. 2016). In United States waters, hunting and harassing of marine mammals is forbidden in almost all circumstances, from passage of the Marine Mammal Protection Act of 1972. ==See also==