Tursiops aduncusIndo-Pacific bottlenose dolphin

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Geographic Range

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. (Fury and Harrison, 2008; Fury and Harrison, 2011; Kogi, et al., 2004; Kurihara and Oda, 2007; Nowak, 2003; Saayman, et al., 1973; Shirihai and Jarrett, 2006)

Habitat

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. (Fury and Harrison, 2011; Kogi, et al., 2004; Martin, et al., 2001; Nowak, 2003; Vaughan, et al., 2011)

  • Range depth
    2 to 300 m
    6.56 to 984.25 ft

Physical Description

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. (Krzyszczyk and Mann, 2012; Nowak, 2003; Shirihai and Jarrett, 2006; Vaughan, et al., 2011)

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. (Kogi, et al., 2004; Mann, et al., 2000; Nowak, 2003; Shirihai and Jarrett, 2006; Vaughan, et al., 2011)

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. (Kurihara and Oda, 2007; Martin, et al., 2001; Nowak, 2003)

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. (Kogi, et al., 2004; Kurihara and Oda, 2007; Shirihai and Jarrett, 2006)

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. (Martin, et al., 2001)

  • Sexual Dimorphism
  • male larger
  • Average mass
    230 kg
    506.61 lb
  • Range length
    175 to 400 cm
    68.90 to 157.48 in

Reproduction

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. (Möller, et al., 2001; Reynolds, et al., 2000)

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. (Krzyszczyk and Mann, 2012; Mann, et al., 2000; Nowak, 2003; Shirihai and Jarrett, 2006)

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. (Kogi, et al., 2004; Mann, et al., 2000; Nowak, 2003; Shirihai and Jarrett, 2006; Vaughan, et al., 2011)

  • 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

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. (Mann, et al., 2000; Reynolds, et al., 2000; Shirihai and Jarrett, 2006)

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. (Möller, et al., 2001)

  • 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

Lifespan/Longevity

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. (Klinowska and Cook, 1991; Nowak, 2003; Shirihai and Jarrett, 2006)

  • Range lifespan
    Status: wild
    39 for male, 49 for female (high) years
  • Average lifespan
    Status: wild
    40+ years

Behavior

Indo-Pacific bottlenosed dolphins are socially and behaviorally similar to common bottlenosed dolphins and occasionally form pods with common bottlenosed dolphins and less often with Indo-Pacific humpback dolphins. Most Indo-Pacific bottlenose dolphins spend their lives in schools or pods of between 5 and 15 dolphins to help with hunting, predator avoidance, and reproduction. They have been observed, in the wild and in captivity, playing by chasing and splashing each other and some have linked this behavior with learning. In these pods, there is a social hierarchy where the largest dolphin is usually the most dominant. In the wild there are also same sex groups, especially in subadult groups, that later join larger pods. They are usually less social and more shy than common bottlenosed dolphins. They are less frequently observed at the surface and make less frequent leaps from the water. (Nowak, 2003; Reynolds, et al., 2000; Shirihai and Jarrett, 2006; Vaughan, et al., 2011)

  • Range territory size
    15 to 85 km^2

Home Range

Indo-Pacific bottlenosed dolphins exhibit site fidelity and have well-established home ranges. Most males and females remain in their natal home range until maturity. In the Pacific, home ranges tend to be found around an island. Home ranges can be up to 85 square km, however the range depends on gender and may change seasonally. Density estimates are reported to range from 0.06 to 4.80 per sq km. (Möller, et al., 2001; Nowak, 2003)

Communication and Perception

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. (Martin, et al., 2001; Nowak, 2003; Sakai, et al., 2006; Vaughan, et al., 2011)

Food Habits

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. (Amir, et al., 2005; Nowak, 2003; Shirihai and Jarrett, 2006; Vaughan, et al., 2011)

  • Animal Foods
  • fish
  • mollusks

Predation

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. (Heithaus, 2001; Mann, et al., 2000; Reynolds, et al., 2000)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

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. (Amir, et al., 2005; Heithaus, 2001; Perrin, et al., 2008)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

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. (Kogi, et al., 2004; Martin, et al., 2001; Nowak, 2003; Shirihai and Jarrett, 2006)

Economic Importance for Humans: Negative

There are no known adverse effects of Tursiops aduncus on humans.

Conservation Status

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. (Hammond, et al., 2008; Lipscomb, et al., 1994; Nowak, 2003; Reynolds, et al., 2000; Van Bressem, et al., 2001)

Other Comments

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. (Nowak, 2003; Reynolds, et al., 2000; Rice, 1998; Shirihai and Jarrett, 2006)

Contributors

Kelly Diaz (author), Yale University, Rachel Racicot (editor), Yale University, Eric Sargis (editor), Yale University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

Glossary

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

brackish water

areas with salty water, usually in coastal marshes and estuaries.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cooperative breeder

helpers provide assistance in raising young that are not their own

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

echolocation

The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

estuarine

an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.

food

A substance that provides both nutrients and energy to a living thing.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

keystone species

a species whose presence or absence strongly affects populations of other species in that area such that the extirpation of the keystone species in an area will result in the ultimate extirpation of many more species in that area (Example: sea otter).

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

piscivore

an animal that mainly eats fish

polygynandrous

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

social

associates with others of its species; forms social groups.

tactile

uses touch to communicate

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

ultrasound

uses sound above the range of human hearing for either navigation or communication or both

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

young precocial

young are relatively well-developed when born

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