Tursiops Truncatus – Common Bottlenose Dolphin –
| Conservation status |
|---|
 Least Concern (IUCN 3.1)[2] |
 Data Deficient (IUCN 3.1)[2] (Europe) |
| Scientific classification |
Tursiops truncatus (Montagu, 1821)
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Infraorder: | Cetacea |
| Family: | Delphinidae |
| Genus: | Tursiops |
| Species: | T. truncatus |
The common bottlenose dolphin or Atlantic bottlenose dolphin (Tursiops truncatus) is the most well-known species of the family Delphinidae.
Common bottlenose dolphins are the most familiar dolphins due to the wide exposure they receive in captivity in marine parks and dolphinaria, and in movies and television programs.[4] The common bottlenose dolphin is the largest species of the beaked dolphins.[5] They inhabit temperate and tropical oceans throughout the world, and are absent only from polar waters.[4][5][6][2][7] Until recently, all bottlenose dolphins were considered as a single species, but now the Indo-Pacific bottlenose dolphin[2][7] and Burrunan dolphin have been split from the common bottlenose dolphin.[3][8] While formerly known simply as the bottlenose dolphin, this term is now applied to the genus Tursiops as a whole.[1][9][10] These dolphins inhabit warm and temperate seas worldwide. As considerable genetic variation has been described among members of this species, even between neighboring populations, many experts consider that additional species may be recognized.[3][9]
Description
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The common bottlenose dolphin is grey in color and may be between 2 and 4 m (6.6 and 13.1 ft) long, and weighs between 150 and 650 kg (330 and 1,430 lb).[8] Males are generally larger and heavier than females. In most parts of the world, the adult’s length is between 2.5 and 3.5 m (8.2 and 11.5 ft) with weight ranging between 200 and 500 kg (440 and 1,100 lb).[5][9] Dolphins have a short and well-defined snout that looks like an old-fashioned gin bottle, which is the source for their common name.[11]
The muzzle is short, and comes as an extension of a head forming a “melon” – term used because of the sphericity – rather pronounced. The upper jaw is shorter than the lower jaw. They have 20 to 26 pairs of teeth. The dorsal fin, located in the middle of the back, has a shape which can vary slightly between individuals, but it always presents a well marked concavity of its rear edge.The color of the back of individuals is quite variable: almost black or dark gray-brown, it decreases in intensity on the flanks to become whitish on the belly.
Morphological variations occur according to geographic distribution.
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Like all whales and dolphins, though, the snout is not a functional nose; the nose has instead evolved into the blowhole on the top of their heads. Their necks are more flexible than other dolphins’ due to five of their seven vertebrae not being fused together as is seen in other dolphin species.[12]
Intelligence
The common bottlenose dolphin has a bigger brain than humans.[13] Numerous investigations of bottlenose dolphin intelligence include tests of mimicry, use of artificial language, object categorization, and self-recognition.[14][15][16][17][18][19] This intelligence has driven considerable interaction with humans. Common bottlenose dolphins are popular in aquarium shows and television programs such as Flipper.[20] They have also been trained for military uses such as locating sea mines or detecting and marking enemy divers, as for example in the U.S. Navy Marine Mammal Program.[21][22] In some areas, they cooperate with local fishermen by driving fish toward the fishermen and eating the fish that escape the fishermen’s nets.[23]
Ecology and Behavior
K-Dog, trained by the US Navy to find mines and boobytraps underwater, leaping out of the water
As a very social animal, common bottlenose dolphins live in groups called pods that typically number about 15 individuals, but group size varies from pairs of dolphins to over 100 or even occasionally over 1,000 animals for short periods of time.[9] The types of groups include: nursery groups, juvenile groups, and groups of adult males.[5]
Alimentation
Their diets consist mainly of eels, squid, shrimp and a wide variety of fishes.[1][6] They do not chew their food, instead swallowing it whole. Dolphin groups often work as a team to harvest schools of fish, though they also hunt individually. Dolphins search for prey primarily using echolocation, which is a form of sonar.
The diet of common bottlenose dolphin varies depending on area. Along the U.S. Atlantic coast, the main prey includes Atlantic croakers (Micropogonias undulatus), ‘spot’ fish (Leiostomus xanthurus), and American silver perch (Bairdiella chrysoura), while dolphins in South Africa typically feed on African massbankers (Trachurus delagoa), olive grunters (Pomadasys olivaceus), and pandora (Pagellus bellottii).[5]
Research indicates that the type and range of fish in a dolphin’s diet can have a significant impact on its health and metabolism.[24]
Communication
Dolphins also use sound for communication, including squeaks emitted from the blowhole, whistles emitted from nasal sacs below the blowhole, and sounds emitted through body language, such as leaping from the water and slapping their tails on the water. Their heads contain an oily substance that both acts as an acoustic lens and protects the brain case. They emit clicking sounds and listen for the return echoes to determine the location and shape of nearby items, including potential prey.[25]
Reproduction
Mating behavior of bottlenose dolphin is polygamous. Although they can breed throughout the year, it mostly occurs in spring.[5][26] Males form alliances to seek an estrous female. For a chance to mate with the female, males separate the female from her home range.[5] Females bear a calf every three to six years.[5][27] After a year-long gestation period, females bear a single calf.[5] Newborn calves are between 0.8 and 1.4 m (2 ft 7 in and 4 ft 7 in) long and weigh between 15 and 30 kg (33 and 66 lb).[9] They can live as long as 40–50 years.[28] The calf suckling lasts between 18 and 20 months.[5] Sexual maturity varies by population, and ranges from 5–14 years of age;[28] sexual maturity occurs between 8 to 13 years for males and 5 to 10 years for females.[5]
Reproduction occurs at different times of the year depending on the geographic distribution: in summer along the European coasts, in spring and in autumn along the Florida coasts. Sexual maturity is different according to the sexes: 10 years for females, 13 years for males. The gestation lasts 12 months and the breastfeeding period 12 to 18 months. There is a baby every two or three years. Love games, social events, cries and “songs” participate in the reproduction process.
The dolphin’s feces would contain substances that induce sexual arousal in a partner.
Life Expectancy
The average life expectancy of common bottlenose dolphins is about 17 years old,[29][30][31][32] but in captivity they have been known to live to up to 51 years old.[33]
Distribution
The common bottlenose dolphin can be found in the temperate, subtropical and tropical oceans worldwide.[34] Its habitat is mainly coastal, but it also enters estuaries and rivers. A few groups of individuals from tropical seas may be pelagic. The global population has been estimated at 600,000.[35] Some bottlenose populations live closer to the shore (inshore populations) and others live further out to sea (offshore populations). Generally, offshore populations are larger, darker, and have proportionally shorter fins and beaks. Offshore populations can migrate up to 4,200 km (2,600 mi) in a season, but inshore populations tend to move less. However, some inshore populations make long migrations in response to El Niño events.[9] The species has occurred as far as 50° north in eastern Pacific waters, possibly as a result of warm water events.[36] The coastal dolphins appear to adapt to warm, shallow waters. It has a smaller body and larger flippers, for maneuverability and heat dispersal. They can be found in harbors, bays, lagoons and estuaries. Offshore dolphins, however, are adapted to cooler, deeper waters. Certain qualities in their blood suggest they are more suited to deep diving. Their considerably larger body protects them against predators and helps them retain heat.[37]
Similar Species
A fairly close species Tursiops aduncus (Ehrenberg, 1833), from the coast of South Africa, has been identified by some authors and seems to be validated at present. This dolphin is darker than Tursiops truncatus and its belly may have punctuation.
There are subspecies for Tursiops truncatus , they are:
– Tursiops truncatus truncatus
– Tursiops truncatus ponticus present in the Black Sea
Morphological adaptations of this species are possible depending on ecological conditions, which may have led to the distinction of different questionable species …
Various Biology
The average age that can be reached by bottlenose dolphins is 30 years old. It is a very common species which is the “benchmark” in terms of dolphins for the general public, popularized by a television series and by dolphinariums.
A particularity of the Delphinidae, particularly studied in the bottlenose dolphin, is to have a sonar system allowing by echolocation * to have a great knowledge of the surrounding organisms and structures without the use of sight. Waves are emitted, their echo is received and gives very precise information on the environment.
Oral communication has also been studied and demonstrated in bottlenose dolphins, it allows a relatively elaborate exchange of information without, however, really understanding the exact meaning of the messages exchanged.
Some scientists believe that local populations of bottlenose dolphins (Molène-Ouessant, Pertuis Breton, Arcachon, etc.) occupy ecological niches left free by the rarity of the porpoise.
Bottlenose dolphins form groups that live in specific areas of our coastline.
Dolphins have already been seen chasing a school of fish along with sharks. Likewise, a common coastal fishery exists between bottlenose dolphins and Imragen fishermen, people of the coast of Mauritania. The same school of mules is surrounded by men and dolphins who each benefit from the work of the other party.
When it performs apnea for food, the bottlenose dolphin can dive to about 200 m and remain in immersion for about fifteen minutes.
Other Human Interactions
Some interactions with humans are harmful to the dolphins. Dolphin hunting industry exists in multiple countries including Japan, where common bottlenose dolphins are hunted for food annually in the town of Taiji,[38] and the Faroe Islands. Also, dolphins are sometimes killed inadvertently as a bycatch of tuna fishing.[39][40]
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 later became infamous for killing a swimmer and injuring many others, which earned it the nickname of killer dolphin.
Fungie is another solitary male bottlenose, living in close contact with humans in Dingle harbour, Ireland, since 1983. He has become a symbol of the town, although some doubt exists over whether he is a single dolphin.[41]
Conservation
The North Sea, Baltic, Mediterranean and Black Sea populations of the common bottlenose dolphin are listed in Appendix II[42] to the Convention on the Conservation of Migratory Species of Wild Animals (CMS) of the Bonn Convention, since they have an unfavorable conservation status or would benefit significantly from international cooperation organized by tailored agreements.[43]
Estimated population of a few specific areas are including:[2]
| Area | Population |
|---|---|
| Northern Gulf of Mexico | 97,964 |
| Eastern coast of North America | 110,000 |
| Eastern Tropical Pacific | 243,500 |
| Hawaiian Islands | 3,215 |
| Coastal of California | 345 |
| Japan | 36,791 |
| Eastern Sulu Sea | 2,628 |
| Western European continental shelf | 12,600 |
| Mediterranean Sea | fewer than 10,000 |
| Black Sea | least several thousands |
The species is covered by the Agreement on Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS), the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS), the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region,[44] and the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia.[45]
Marine Pollution
Common bottlenose dolphins are the most common apex predators found in coastal and estuarine ecosystems along the southern coast of the US,[46] thus serve as an important indicator species of bioaccumulation and health of the ecosystem.
It is believed that some diseases commonly found in dolphins are related to human behaviors, such as water pollution. Water pollution is linked to point and non-point source pollution. Point source pollution comes from a single source such as an oil spill[47] and/or chemical discharge from a specific facility. The environmental impact of the Deepwater Horizon oil spill caused a direct impact and still serves as a long term impact of future populations. Common bottlenose dolphins use these important habitats for calving, foraging, and feeding. Environmental impacts or changes from chemicals or marine pollution can alter and disrupt endocrine systems, affecting future populations. For example, oil spills have been related to lung and reproductive diseases in female dolphins. A recent study[48]suggested signs of lung disease and impaired stress in 32 dolphins that were captured and assessed in Barataria Bay, Louisiana, US. Out of these 32 dolphins, 10 were found pregnant and, upon a 47-month check up, only 20% produced feasible calves, compared to a previous success rate of 83%, in the same area. It is believed that a recent oil spill in this area is partially to blame for these severely low numbers.
Dense human development along the eastern coast of Florida and intense agricultural activity have resulted in increased freshwater inputs, changes in drainage patterns, and altered water quality (i.e. chemical contamination, high nutrient input, decreased salinity, decreased sea grass habitat, and eutrophication.[49] High nutrient input from agriculture chemicals and fertilizers causes eutrophication[50] and hypoxia, causing a severe reduction in water quality. Excess of phosphorus and nitrogen from these non-point sources deplete the natural cycle of oxygen by overconsumption of algae. Harmful algal blooms are responsible for dead zones and unusual mortality events of common bottlenose dolphins consuming these toxic fish from the brevetoxin produced by the dinoflagellate Karenia brevis.[51] Brevetoxins are neurotoxins that can cause acute respiratory and neurological symptoms, including death, in marine mammals, sea turtles, birds, and fishes.[52]
Further Information
The Tursiops are one of those dolphins that are frequently observed taking advantage of the bow wave of ships, which allows them to move forward at high speed (10 to 25 knots on average) without having to exert much effort.
In the Red Sea, a group of about ten bottlenose dolphins has already been observed, very compact, just below the surface, swimming at low speed and uttering a lot of calls while a silky shark ( Carcharhinus falciformis ) wandered in the area in sometimes drawing circles around this group of dolphins (personal observation). Did this shark detect that a female was close to giving birth and were the other dolphins surrounding her to protect her?
Many anecdotes are related to dolphins in ancient history and in mythology (mainly Greek), and many certainly relate to the bottlenose dolphin; many representations show animals with well-marked melons and short beaks. Some of these anecdotes are linked to rescues that dolphins allegedly carried out from men who fell at sea. A mythological account claims that dolphins are the reincarnation of repentant pirates. In tribute to the services rendered by certain dolphins, they were represented on the arms of certain warriors of antiquity, and this habit was perpetuated later, in particular among the lords of the region of Vienne, in Isère. Their extended domain took the name of Dauphiné and they named their eldest son “Dauphin”.
Today it is not uncommon for bottlenose dolphins, most often isolated, or sometimes in pairs, to approach the coasts to the point of staying a long time in contact with human populations.
An animal which adopts this behavior is called an “ambassador dolphin”. It is not without asking the question: are these individuals who have been rejected by their group of origin?
On the French coasts (and elsewhere too!), Some have become stars:
– Jean-Louis, Pointe du Van, Brittany, years 1976 to 1988.
“Jean-Louis” is a name used by sailors to usually refer to sharks! The dorsal fin does not excuse everything anyway… In fact, it was more about “Jeanne-Louise”, since this individual was a female. Buses of divers came from very far sometimes to immerse themselves with this star which was particularly attracted by the curious who knew how to interest and respect it. Indeed, certain gestures, certain noises (friction of a knife on a chain…) interested her a lot, but it was not necessary to try to touch her, which these animals with sensitive skin do not generally appreciate.
– Fanny et Marine, Fos-sur-Mer, years 1987 and 1988 in an environment which was not very attractive (industrial port).
– Françoise, Arcachon, between 1983 and 2000 (year of her death), she lived in a group (“semi-solitary” dolphin) but sometimes came to join the human race!
– Dolphy, between Banyuls and Rosas (Spain), years 1990 to 1995, very playful, with men or with dogs.
– Jean-Floch has been visible since 2003 at Cap Sizun and seems particularly energetic.
Unfortunately for him, the bottlenose dolphin endures life in captivity more than other cetaceans and, as a result, it has been captured a lot for use as a show animal. This undoubtedly contributed to its popularity and paradoxically to a certain awareness of the general public in favor of the defense of marine mammals.
Some bottlenose dolphins in captivity are used therapeutically for children with psychological disorders. Others, in captivity, have been trained to help with the work of professional divers or even combat divers …
Anthropomorphic behavior made us see in the appearance of the mouth of this animal an eternal “smile”! Even if we know that this is fictitious, we must know how to recognize in this animal, without excess of sentimentality, enough qualities to deserve the attention and the protection that it is entitled to expect from us …
