All Tursiops species were initially included in the species Tursiops truncatus. It is now recognized that there are at least three species, including Tursiops truncatus (found in all oceans except polar waters), Tursiops gillii (found in the eastern North Pacific), and Tursiops aduncus (found in the Indian, South Pacific, and western and southern North Pacific oceans). Tursiops aduncus was identified in 1883 by Christian Ehrenberg. Indo-Pacific bottlenosed dolphins are differentiated from common bottlenosed dolphins by genetic and morphological differences. Some have suggested that Indo-Pacific bottlenosed dolphins are more closely related to Stenella and Delphinus species than to Tursiops truncatus. This is an area of active research.
It has been argued that the large and convoluted brain of Indo-Pacific bottlenosed dolphins allows for greater intelligence and higher-order learning. They communicate via auditory perception. While their sense of sight is not well-developed, their sense of hearing is keen and important in echolocation. Indo-Pacific bottlenosed dolphins generate ultrasonic clicks and interpret the returning signals to perceive objects in their environment. Each dolphin also uses a characteristic whistle that helps other identify them individually. Indo-Pacific bottlenosed dolphins also communicate via tactile signals. Most often, flippers are rubbed over the flippers or bodies of other dolphins of the same sex and age. Flipper rubbing is observed between opposite sexes around mating and between mothers and calves.
Communication Channels: visual ; tactile ; acoustic
Perception Channels: visual ; tactile ; acoustic ; ultrasound ; echolocation ; vibrations ; chemical
Hunting and shark nets have historically threatened populations of bottlenosed dolphins because these dolphins, especially Indo-Pacific bottlenosed dolphins, prefer shallow coastal waters. These dolphins are killed for meat, fertilizer, cooking oil, and machine lubrication.
US Federal List: no special status
CITES: appendix ii
State of Michigan List: no special status
There are no known adverse effects of Tursiops aduncus on humans.
At some sites, Indo-Pacific bottlenosed dolphins have been habituated to the presence of human swimmers. At Mikura Island, Japan, there is a dolphin swim program in the summer that began in the 1990’s. Bottlenosed dolphins are common in marine exhibits and zoos. They can be easily trained to perform agile displays and to play with and locate objects. However, Indo-Pacific bottlenosed dolphins are generally more shy and less inquisitive than other bottlenosed dolphins. Like other marine mammals, the lifespan of these dolphins in captivity is significantly shorter than in the wild and there are significant ethical concerns with keeping such large, intelligent mammals in captive conditions.
Positive Impacts: food ; ecotourism ; research and education
Indo-Pacific bottlenosed dolphins are predators of many species of bony fish and squid in coastal tropical waters. Indo-Pacific bottlenosed dolphins are prey of many species of sharks. They often act as hosts for parasites and barnacles. Semi-parasitic barnacles can attach to their skin, causing irritations and drag as they swim.
Ecosystem Impact: keystone species
Commensal/Parasitic Species:
Indo-Pacific bottlenosed dolphins have a diet consisting of mainly bony fish and, to a lesser degree, cephalopods. While they eat a wide variety of fish species, the majority of their diet is composed of just a few species, which varies regionally. In captivity these dolphins eat 6 to 7 kg of food per day. They hunt cooperatively and foraging behavior is characterized by shallow dives multiple times per minute. In shallow water they hunt by using several methods, including “kicking” fish into the sand with their tails and chasing small fish up on to the shore. While feeding and traveling they leap from the water regularly. Hunting and feeding occur most frequently in the morning and afternoon.
Animal Foods: fish; mollusks
Primary Diet: carnivore (Piscivore )
Indo-Pacific bottlenosed dolphins tend to live in shallow water near the shore at depths of less than 300 m. The habitat of some Indo-Pacific bottlenosed dolphins is estuarine but spatial distribution of dolphins varies depending on season and tidal state. These variables influence water temperature and prey distribution.
Biogeographic Regions: indian ocean (Native ); pacific ocean (Native )
Indo-Pacific bottlenosed dolphins tend to live in shallow water near the shore at depths of less than 300 m. With rapid gas exchange at the capillaries, double the amount of erythrocytes, and about 2 to 9 times the amount of myoglobin of land animals, dolphins are able to alternate between no breathing while deep diving and normal breathing while swimming along the surface.
Range depth: 2 to 300 m.
Habitat Regions: tropical ; saltwater or marine
Aquatic Biomes: reef ; coastal ; brackish water
Other Habitat Features: estuarine
The average lifespan of the Indo-Pacific Bottlenose dolphin in the wild is more than 40 years, while the average age of adult males and females in the wild is 19 years and 26 years, respectively. The oldest known dolphins in the wild are a 39 year old male and a 49 year old female.
Range lifespan
Status: wild: 39 for male, 49 for female (high) years.
Average lifespan
Status: wild: 40+ years.
Tursiops aduncus are similar to Tursiops truncatus in form with a fusiform body, dorsal fin, and beak. The dorsal surface is slate blue or dark gray, with darker flippers and extremities and lighter, often pink-tinted, undersides. Patterning and ventral spotting vary by age and geographic location. A recent study has claimed that ventral spotting may be a sign of reproductive maturity, especially in females.
Adult Indo-Pacific bottlenosed dolphins have a head and body length between 175 and 400 cm, a pectoral fin length of about 23 cm, and a tail fluke expanse of 60 cm. Their weight is about 230 kg. Adult female Tursiops aduncus have been measured to be 200 cm in length in certain regions, while adult males are usually longer and heavier than females. Females have a single external opening and males have distinct anal and genital openings.
Like most bottlenosed dolphins, Indo-Pacific bottlenose dolphins have conical, single-rooted, unicuspid, homodont teeth that are about 1 cm in diameter. However, tooth counts alone usually cannot be used to differentiate T. aduncus and T. truncatus. In general, bottlenosed dolphins have between 20 and 28 teeth on each side of the jaw. Another cranial feature is the concavity of the top of the rostrum between the anterior edge of the nares and the distal tip of the premaxillae.
There are a number of physical differences between T. truncatus and T. aduncus. Indo-Pacific bottlenosed dolphins can be distinguished from T. truncatus by ventral spotting in adult specimens which increases with age, a longer, better-defined rostrum, a smaller melon, and, in some cases, more teeth. Indo-Pacific bottlenosed dolphins also have a smaller body, a smaller head, and larger flippers than T. truncatus. They have a more slender rostrum that is tapered more abruptly near the base and taller and broader-based dorsal fins relative to other bottlenosed dolphins. However, these differences are variable, which can make it difficult to distinguish them in areas of overlap.
With rapid gas exchange at the capillaries, double the amount of erythrocytes, and about 2 to 9 times the amount of myoglobin of land animals, dolphins are able to alternate between no breathing while deep diving and normal breathing while swimming along the surface.
Average mass: 230 kg.
Range length: 175 to 400 cm.
Other Physical Features: endothermic ; homoiothermic; bilateral symmetry
Sexual Dimorphism: male larger
Indo-Pacific bottlenosed dolphins are hunted by at least 10 species of sharks. These predators may have played an important role in the evolution of social behavior in bottlenosed dolphins. By traveling in groups, they are less vulnerable to predators. Humans are also predators because bottlenosed dolphins are hunted and captured for food and entertainment. Their countershaded color pattern also helps to make them harder to see in marine environments.
Known Predators:
Anti-predator Adaptations: cryptic
Indo-Pacific bottlenosed dolphins are one of the few mammal species in which males cooperate with other males to allow for easier mating with females. Males form alliances with one to three other , potentially unrelated, males. These male groups herd females for mating, sometimes called “mate guarding.” Single males may also attempt to guard females for mating. Breeding females also form groups. Smaller female groups are easier to defend, whereas larger groups of females are difficult to defend. Male and female dolphins tend to mate with more than one partner. Copulation usually occurs when the dolphins are positioned belly to belly in the same direction.
Mating System: polygynandrous (promiscuous) ; cooperative breeder
Female reproductive success depends on the depth of the water; shallow water allows for easier detection of predators and reduced predation overall by sharks. Females reach reproductive maturity between 7 and 12 years of age, this maturation is communicated to males by freckling on the ventral region. Males reach reproductive maturity between 9 and 13 years. The gestation period is about 12 months.
At birth, Indo-Pacific bottlenosed dolphins are between 0.8 and 1.1 m in length and between 9 and 21 kg. Young are born tail first and are able to swim immediately. The highest rates of births are from October to December. The lactation period lasts for about 18 months in captivity and about 32 months in the wild. The teats are enclosed in slits along the urogenital opening. The mean weaning age is 3.5 years. However, a study in Australia found a weaning age ranging from 2.7 to 8 years. Adult females, in a sample population off the coast of Mikura Island, Japan, give birth once every 3 to 4 years.
Breeding interval: Female Indo-Pacific bottlenosed dolphins breed every 4 to 6 years.
Breeding season: The breeding season typically ranges from September to January. However, breeding may occur throughout the year.
Average number of offspring: 1.
Average gestation period: 12 months.
Average weaning age: 42 months.
Average time to independence: 4 years.
Range age at sexual or reproductive maturity (female): 7 to 12 years.
Range age at sexual or reproductive maturity (male): 9 to 13 years.
Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous
Adult female Indo-Pacific bottlenosed dolphins invest a great deal of time and attention in their calves. Even after weaning, calves stay with their mothers for another one to three years.
Adult male Indo-Pacific bottlenosed dolphins provide little or no parental care, instead maximizing their mating opportunities. Males sometimes cooperate to defend groups of females.
Parental Investment: precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female, Protecting: Female); pre-independence (Provisioning: Female, Protecting: Female); post-independence association with parents
Red Sea.
Unknown, probably accidental.
The Indo-Pacific bottlenose dolphin (Tursiops aduncus) is a species of bottlenose dolphin. This dolphin grows to 2.6 m (8.5 ft) long, and weighs up to 230 kg (510 lb).[4] It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa.[4] Its back is dark grey and its belly is lighter grey or nearly white with grey spots.[4]
The Indo-Pacific bottlenose dolphin is generally smaller than the common bottlenose dolphin, has a proportionately longer rostrum, and has spots on its belly and lower sides.[5][6] It also has more teeth than the common bottlenose dolphin — 23 to 29 teeth on each side of each jaw compared to 21 to 24 for the common bottlenose dolphin.[6]
Much of the old scientific data in the field combine data about the Indo-Pacific bottlenose dolphin and the common bottlenose dolphin into a single group, making it effectively useless in determining the structural differences between the two species. The IUCN lists the Indo-Pacific bottlenose dolphin as "near threatened" in their Red List of endangered species.[2]
Until 1998, all bottlenose dolphins were considered members of the single species T. truncatus. In that year, the Indo-Pacific bottlenose dolphin was recognized as a separate species.[5][7] Both species are thought to have split during the mid-Pleistocene, about 1 million years ago.[8]
Some evidence shows the Indo-Pacific bottlenose dolphin may actually be more closely related to certain dolphin species in the genera Stenella and Delphinus, especially the Atlantic spotted dolphin (S. frontalis), than it is to the common bottlenose dolphin.[5][9] 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.[8]
The Burrunan dolphin (T. (aduncus) australis) has been alternately considered its own species, a subspecies of T. truncatus, or a subspecies of T. aduncus. Following the results of a 2020 study, the American Society of Mammalogists presently classifies it as a subspecies of T. aduncus.[8][10] The same study delineated 3 distinct lineages within T. aduncus which could each be their own subspecies: an Indian Ocean lineage, an Australasian lineage, and the Burrunan dolphin.[8] The Society for Marine Mammalogy does not recognize the Burrunan dolphin as a distinct species or subspecies, citing the need for further research.[11]
Indo-Pacific bottlenose dolphins are very similar to common bottlenose dolphins in appearance. Common bottlenose dolphins have a reasonably strong body, moderate-length beak, and tall, curved dorsal fins; whereas Indo-Pacific bottlenose dolphins have a more slender body build and their beak is longer and more slender.[12] The Indo-Pacific population also tends to have a somewhat lighter blue colour and the cape is generally more distinct, with a light spinal blaze extending to below the dorsal fin. However, although not always present, the most obvious distinction can be made with the presence of black spots or flecks on the bellies of adults of Indo-Pacific bottlenose dolphins, which are very rare in common bottlenose dolphins.[12] Their teeth can number between 23 and 29 in each upper and lower jaw, and are more slender than those of common bottlenose dolphins.[12] Size of Indo-Pacific bottlenose dolphins can vary based on geographic location; however, its average length is 2.6 m (8.5 ft) long, and it weighs up to 230 kg (510 lb).[4] The length at birth is between 0.84 and 1.5 m (2.8 and 4.9 ft).[4]
The local population centering Mikura-jima is claimed to be a distinct form or species.[13]
Indo-Pacific bottlenose dolphins feed on a wide variety of fish and cephalopods (particularly squid).[14]
In one study,[14] researchers looked at the feeding ecology of Indo-Pacific bottlenose dolphins by analyzing the stomach contents of ones that got caught in the gillnet fisheries off Zanzibar, Tanzania. The prey items found in the stomach contents included 50 species of bony fish and three species of squid. From their results, the researchers concluded the most important prey group was fish, which accounted for 87% of the total number of prey items consumed and occurred in 24 of 26 stomachs examined. Cephalopods comprised the other 13% of prey items and were found in 13 of the 26 stomachs.[14] The remains of some crustaceans were also found; they hypothesize, however, they were consumed secondarily, since a number were found intact in the fish prey stomachs and therefore were not included in the diet analysis.[14]
Indo-Pacific bottlenose dolphins live in groups that can number in the hundreds, but groups of five to 15 dolphins are most common.[6] In some parts of their range, they associate with the common bottlenose dolphin[6] and other dolphin species, such as the humpback dolphin.[6]
The peak mating and calving seasons are in the spring and summer, although mating and calving occur throughout the year in some regions. Gestation period is about 12 months. Calves are between 0.84 and 1.5 m (2.8 and 4.9 ft) long, and weigh between 9 and 21 kg (20 and 46 lb). The calves are weaned between 1.5 and 2.0 years, but can remain with their mothers for up to 5 years. The interbirth interval for females is typically 4.5 to 6 years.[4]
In some parts of its range, this dolphin is subject to predation by sharks;[6] its lifespan is more than 40 years.[4]
Indo-Pacific bottlenose dolphins located in Shark Bay, Australia, have been observed using sponges as tools in a practice called "sponging". A dolphin breaks a marine sponge off the sea floor and wears it over its rostrum, apparently to probe substrates for fish, possibly as a tool.[15][16]
The first report and footage of spontaneous ejaculation in an aquatic mammal was recorded in a wild Indo-Pacific bottlenose dolphin near Mikura Island, Japan, in 2012.[17]
A tribe of Austral indigenous people on the Mornington Island have been communicating with wild dolphins for millennia. They are said to have "a medicine man who calls the dolphins and "speaks" to them telepathically. By these communications he assures that the tribes' fortunes and happiness are maintained."[18]
Indo-Pacific bottlenose dolphins have been observed to swim near and rub themselves against specific types of corals and sponges. A team of scientists followed up on this behavior and discovered metabolites with antibacterial, antioxidative, and hormonal activities in the corals and sponges, suggesting that they might be used by the dolphins to treat skin infections.[19]
The species is not considered to be endangered; its near-shore distribution, though, makes it vulnerable to environmental degradation, direct exploitation, and problems associated with local fisheries.[20]
The major predators of this species are typically sharks, and may include humans, killer whales (Orcinus orca), and sting rays. In the early 1980s, many were deliberately killed in a Taiwanese driftnet fishery in the Arafura Sea, off northwestern Australia.[21] Large-mesh nets set to protect bathers from sharks in South Africa and Australia have also resulted in a substantial number of deaths.[22] Gillnets are also having an impact, and are a problem throughout most of the species' range.
These small cetaceans are commonly found in captivity,[14] causing conservation concerns, including the effects of removing the animals from their wild populations, survival of cetaceans during capture and transport and while in captivity, and the risks to wild populations and ecosystems of accidentally introducing alien species and spreading epizootic diseases, especially when animals have been transported over long distances and are held in sea pens.[23]
Bottlenose dolphins are the most common captive cetaceans on a global scale.[23] Prior to 1980, more than 1,500 bottlenose dolphins were collected from the United States, Mexico, and the Bahamas, and more than 550 common and 60 Indo-Pacific bottlenose dolphins were brought into captivity in Japan.[23] By the late 1980s, the United States stopped collecting bottlenose dolphins and the number of captive-born animals in North American aquaria has increased from only 6% in 1976 to about 44% in 1996.
In the South Korea, in the 2010s, environmental groups and animal protection groups led a campaign (2013년 대한민국 남방큰돌고래 방사) to release southern bottlenose dolphins illegally captured by fishermen and trapped in Jeju Pacific Land[24] and Seoul Zoo.[25]
In a study on three populations of Indo-Pacific bottlenose dolphins in Japan,[26] the characteristics of acoustic signals are believed to be affected by the acoustic environments among habitats, and geographical variation in animal acoustic signals can result from differences in acoustic environments; therefore, the characteristics of the ambient noise in the dolphins' habitats and the whistles produced were compared. Ambient noise was recorded using a hydrophone located 10 m below the surface and whistles were recorded by using an underwater video system.
The results showed dolphins produced whistles at varying frequencies with greater modulations when in habitats with less ambient noise, whereas habitats with greater ambient noise seem to cause dolphins to produce whistles of lower frequencies and fewer frequency modulations. Examination of the results suggest communication signals are adaptive and are selected to avoid the masking of signals and the decrease of higher-frequency signals. They concluded ambient noise has the potential to drive the variation in whistles of Indo-Pacific bottlenose dolphin populations.
Small, motorized vessels have increased as a source of anthropogenic noise due to the rise in popularity of wildlife viewing such as whale watching. Another study[27] showed powerboat approaches within 100 m altered the dolphin surface behaviour from traveling to milling, and changed their direction to travel away from the powerboat. When the powerboat left the area and its noise ceased, the dolphins returned to their preceding behaviour in the original direction.
Another study[28] in Shark Bay, Western Australia, on dolphin behavioural responses showed significant changes in the behaviour of targeted dolphins were found when compared with their behaviour before and after approaches by small watercraft. Dolphins in the low-traffic site showed a stronger and longer-lasting response than dolphins in the high-traffic site. These results are believed to show habituation of the dolphins to the vessels in a region of long-term vessel traffic. However, when compared to other studies in the same area, moderated responses, rather, were suggested to be because those individuals sensitive to vessel disturbance left the region before their study began.
Although these studies do show statistical significance for the effects of whale-watching boats on behavior, what these results mean for long-term population viability is not known. The Shark Bay population has been forecast to be relatively stable with little variation in mortality over time (Manlik et al. 2016).[29]
The Indo-Pacific bottlenose dolphin populations of the Arafura and the Timor Sea are listed on Appendix II[30] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). They are listed on Appendix II[30] as they have an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.[31]
The Indo-Pacific bottlenose dolphin is also covered by Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region (Pacific Cetaceans MoU).[32]
The Adelaide Dolphin Sanctuary is a marine protected area in the Australian state of South Australia located on the east coast of Gulf St Vincent, which was established in 2005 for the protection of a resident population of Indo-Pacific bottlenose dolphins.[33]
The Indo-Pacific bottlenose dolphin (Tursiops aduncus) is a species of bottlenose dolphin. This dolphin grows to 2.6 m (8.5 ft) long, and weighs up to 230 kg (510 lb). It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa. Its back is dark grey and its belly is lighter grey or nearly white with grey spots.
The Indo-Pacific bottlenose dolphin is generally smaller than the common bottlenose dolphin, has a proportionately longer rostrum, and has spots on its belly and lower sides. It also has more teeth than the common bottlenose dolphin — 23 to 29 teeth on each side of each jaw compared to 21 to 24 for the common bottlenose dolphin.
Much of the old scientific data in the field combine data about the Indo-Pacific bottlenose dolphin and the common bottlenose dolphin into a single group, making it effectively useless in determining the structural differences between the two species. The IUCN lists the Indo-Pacific bottlenose dolphin as "near threatened" in their Red List of endangered species.
