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
