Bottlenose dolphin
The bottlenose dolphin is a toothed whale in the genus Tursiops. They are common, cosmopolitan members of the family Delphinidae, the family of oceanic dolphins. Molecular studies show the genus contains three species: the common bottlenose dolphin, the Indo-Pacific bottlenose dolphin, and Tamanend's bottlenose dolphin. Others, like the Burrunan dolphin, may be alternately considered their own species or be subspecies of T. aduncus. Bottlenose dolphins inhabit warm and temperate seas worldwide, being found everywhere except for the Arctic and Antarctic Circle regions. Their name derives from the Latin tursio and truncatus for the truncated teeth.
Numerous investigations of bottlenose dolphin intelligence have been conducted, examining mimicry, use of artificial language, object categorization, and self-recognition. They can use tools and transmit cultural knowledge from generation to generation, and their considerable intelligence has driven interaction with humans. Bottlenose dolphins gained popularity from aquarium shows and television programs such as Flipper. They have also been trained by militaries to locate sea mines or detect and mark enemy divers. In some areas, they cooperate with local fishermen by driving fish into their nets and eating the fish that escape. Some encounters with humans are harmful to the dolphins: people hunt them for food, and dolphins are killed inadvertently as a bycatch of tuna fishing and by getting caught in crab traps.
Common bottlenose dolphins have an encephalization quotient of 5.26, which is even higher than chimpanzees. This more than likely contributes to their high intelligence.
Taxonomy
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, found in coastal and oceanic habitats of most tropical to temperate oceans, and the Indo-Pacific bottlenose dolphin, 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, 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, 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.
Much of the discussion and doubts about its taxonomy is related to the existence of two ecotypes of bottlenose dolphins in many part of its distribution. For example, the two ecotypes of the common bottlenose dolphin within the western North Atlantic are represented by the shallower water or coastal ecotype and the more offshore ecotype. Their ranges overlap, but they have been shown to be genetically distinct. In 2022, Costa et al. established morphologic, genetic, and evolutionary divergence between the two ecotypes in the western North Atlantic, resurrecting Tursiops erebennus for the coastal form while the offshore form was retained in T. truncatus.
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, Lahille's bottlenose dolphin, and the Eastern Tropical Pacific bottlenose dolphin. The IUCN, on their Red List of endangered species, currently recognises only two species of bottlenose dolphins. The American Society of Mammalogists also recognizes only two species. While acknowledging the studies describing T. australis, it classifies it within T. aduncus.
Some recent genetic evidence suggests the Indo-Pacific bottlenose dolphin belongs in the genus Stenella, since it is more like the Atlantic spotted dolphin than the common bottlenose dolphin. However, more recent studies indicate that this is a consequence of reticulate evolution and incomplete lineage sorting, and thus support T.'' truncatus and T. aduncus'' belonging to the same genus.
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 from the Piacenzian coastal mudstone, and Tursiops miocaenus 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 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 real, functional nose is the blowhole on top of its head; the nasal septum is visible when the blowhole is open.Bottlenose dolphins have 18 to 28 conical teeth on each side of each jaw.
The flukes 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 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
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. Most research in this area has been restricted to the North Atlantic Ocean. 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. To hear the returning echo, they have two small ear openings behind the eyes, but most sound waves are transmitted to the inner ear through the lower jaw. As the object of interest is approached, the echo becomes booming, and the dolphins adjust by decreasing the intensity of the emitted sounds. The interclick interval also decreases as the animal nears the target. Evidently, the dolphin waits for each click's echo before clicking again. Echolocation details, such as signal strength, spectral qualities, and discrimination, are well understood by researchers. 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.
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. Bottlenose dolphins are able to detect salty, sweet, bitter, and sour tastes, but this has not been well-studied. Anecdotally, some individuals in captivity have been noted to have preferences for food fish types, although it is not clear if taste mediates this preference.
In 2022, a study at the University of St Andrews in Scotland found that dolphins were able to identify their "friends" and family members by the taste of their urine in the water.