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.
- Biogeographic Regions
- indian ocean
- pacific ocean
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.
- Habitat Regions
- tropical
- saltwater or marine
- Aquatic Biomes
- reef
- coastal
- brackish water
- Other Habitat Features
- estuarine
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.
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.
- Other Physical Features
- endothermic
- homoiothermic
- bilateral symmetry
- Sexual Dimorphism
- male larger
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.
- 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.
- 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
-
provisioning
-
pre-weaning/fledging
-
provisioning
- female
-
protecting
- female
-
provisioning
-
pre-independence
-
provisioning
- female
-
protecting
- female
-
provisioning
- 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.
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.
- Key Behaviors
- natatorial
- diurnal
- motile
- sedentary
- social
- dominance hierarchies
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.
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.
- Perception Channels
- visual
- tactile
- acoustic
- ultrasound
- echolocation
- vibrations
- chemical
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.
- 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.
- 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.
- Ecosystem Impact
- keystone species
- barnacles ( Xenobalanus )
- nematodes ( Nematoda )
- flukes ( Braunina cordiformis )
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.
- Positive Impacts
- food
- ecotourism
- research and education
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.
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.
Additional Links
Contributors
Kelly Diaz (author), Yale University, Rachel Racicot (editor), Yale University, Eric Sargis (editor), Yale University, Tanya Dewey (editor), University of Michigan-Ann Arbor.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- tropical
-
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
- saltwater or marine
-
mainly lives in oceans, seas, or other bodies of salt water.
- 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.
- coastal
-
the nearshore aquatic habitats near a coast, or shoreline.
- brackish water
-
areas with salty water, usually in coastal marshes and estuaries.
- estuarine
-
an area where a freshwater river meets the ocean and tidal influences result in fluctuations in salinity.
- 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.
- 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.
- polygynandrous
-
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
- cooperative breeder
-
helpers provide assistance in raising young that are not their own
- 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).
- year-round breeding
-
breeding takes place throughout the year
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- young precocial
-
young are relatively well-developed when born
- natatorial
-
specialized for swimming
- diurnal
-
- active during the day, 2. lasting for one day.
- motile
-
having the capacity to move from one place to another.
- sedentary
-
remains in the same area
- social
-
associates with others of its species; forms social groups.
- dominance hierarchies
-
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- visual
-
uses sight to communicate
- tactile
-
uses touch to communicate
- acoustic
-
uses sound to communicate
- ultrasound
-
uses sound above the range of human hearing for either navigation or communication or both
- 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.
- vibrations
-
movements of a hard surface that are produced by animals as signals to others
- chemical
-
uses smells or other chemicals to communicate
- 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.
- 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).
- food
-
A substance that provides both nutrients and energy to a living thing.
- 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.
- carnivore
-
an animal that mainly eats meat
- piscivore
-
an animal that mainly eats fish
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