Indo-Pacific Bottlenose Dolphin
Encyclopedia
The Indo-Pacific bottlenose dolphin (Tursiops aduncus) is a species of bottlenose dolphin
. The Indo-Pacific bottlenose dolphin grows to 2.6 metres (8.5 ft) long, and weigh up to 230 kilograms (507.1 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.
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. 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. The Indo-Pacific bottlenose dolphin also has more teeth than the common bottlenose dolphin — 23 to 29 teeth on each side of each jaw for the Indo-Pacific bottlenose dolphin, compared to 21 to 24 for the common bottlenose dolphin. There is evidence 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.
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 both species as data deficient in their Red List of endangered species because of this issue.
and cephalopod
s (particularly squid
).
In a recent study conducted by Amir et al. (2005), 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 Zanibar, 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. 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.
.
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 (19.8 and 46.3 lb). The calves are weaned between 1.5 and two years, but can remain with their mothers for up to five years. The interbirth interval for females is typically four to six years.
In some parts of its range, this dolphin is subject to predation by shark
s; its life span is more than 40 years.
Indo-Pacific bottlenose dolphins located in Shark Bay
, Australia are thought to have a symbiotic relationship with sponges by doing what is 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 or simply for play.
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. Large-mesh nets set to protect bathers from sharks in South Africa and Australia have also resulted in a substantial number of deaths. Gillnets are also having an impact, and are a problem throughout most of the species’ range.
Bottlenose dolphins are the most common captive cetaceans on a global scale. 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. By the late 1980s, the United States stopped collecting bottlenose dolphins and the number of captive-born animals in North American aquariums has increased from only 6 percent in 1976 to about 44 percent in 1996.
on cetaceans, but research is being conducted at several locations.
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.
Although these studies do show statistical significance for the effects of whale-watching boats, these results do not have biological significance and need to be researched further.
). They are listed on Appendix II as they have an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.
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).
Bottlenose Dolphin
Bottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin , instead of one...
. The Indo-Pacific bottlenose dolphin grows to 2.6 metres (8.5 ft) long, and weigh up to 230 kilograms (507.1 lb). It lives in the waters around India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, South China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
, the Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
, and the eastern coast of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. Its back is dark grey and its belly is lighter grey or nearly white with grey spots.
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. The Indo-Pacific bottlenose dolphin is generally smaller than the common bottlenose dolphin
Common Bottlenose Dolphin
Tursiops truncatus, commonly known as the Common Bottlenose Dolphin, is the most well-known species from the family Delphinidae.Common bottlenose dolphins are the most familiar dolphins due to the wide exposure they receive in captivity in marine parks, dolphinarias, in movies, and television...
, has a proportionately longer rostrum
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
, and has spots on its belly and lower sides. The Indo-Pacific bottlenose dolphin also has more teeth than the common bottlenose dolphin — 23 to 29 teeth on each side of each jaw for the Indo-Pacific bottlenose dolphin, compared to 21 to 24 for the common bottlenose dolphin. There is evidence the Indo-Pacific bottlenose dolphin may actually be more closely related to certain dolphin species in the genera Stenella
Stenella
Stenella is a genus of aquatic mammals in Delphinidae, the family informally known as the oceanic dolphins.Currently five species are recognised in this genus:*Pantropical Spotted Dolphin, S. attenuata*Atlantic Spotted Dolphin, S. frontalis...
and Delphinus
Delphinus
Delphinus is a constellation in the northern sky, close to the celestial equator. Its name is Latin for dolphin. Delphinus was one of the 48 constellations listed by the 2nd century astronomer Ptolemy, and it remains among the 88 modern constellations recognized by the International Astronomical...
, especially the Atlantic spotted dolphin
Atlantic Spotted Dolphin
The Atlantic Spotted Dolphin is a dolphin found in the Gulf Stream of the North Atlantic Ocean. Older members of the species have a very distinctive spotted coloration all over their body.-Taxonomy:...
(S. frontalis), than it is to 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 both species as data deficient in their Red List of endangered species because of this issue.
Description
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. 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. Their teeth can number between 23 and 29 in each upper and lower jaw, and are more slender than those of common bottlenose dolphins. Size of Indo-Pacific bottlenose dolphins can vary based on geographic location however its average length is 2.6 metres (8.5 ft) long, and it weighs up to 230 kilograms (507.1 lb). Their length at birth is between 0.84 and 1.5 m (2.8 and 4.9 ft).Diet
Indo-Pacific bottlenose dolphins feed on a wide variety of fishFish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
and cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s (particularly squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
).
In a recent study conducted by Amir et al. (2005), 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 Zanibar, Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
. 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. 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.
Behavior
Indo-Pacific bottlenose dolphins live in groups that can number in the hundreds, but groups of five to 15 dolphins are most common. In some parts of their range, they associate with the common bottlenose dolphin and other dolphin species, such as the humpback dolphinHumpback dolphin
Humpback dolphins are members of the genus Sousa. These dolphins are characterized by the conspicuous humps and elongated dorsal fins found on the back of adult members of the species...
.
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
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
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 (19.8 and 46.3 lb). The calves are weaned between 1.5 and two years, but can remain with their mothers for up to five years. The interbirth interval for females is typically four to six years.
In some parts of its range, this dolphin is subject to predation by shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s; its life span is more than 40 years.
Indo-Pacific bottlenose dolphins located in Shark Bay
Shark Bay
Shark Bay is a World Heritage listed bay in Western Australia. The term may also refer to:* the locality of Shark Bay, now known as Denham* Shark Bay Marine Park* Shark Bay , a shark exhibit at Sea World, Gold Coast, Australia* Shire of Shark Bay...
, Australia are thought to have a symbiotic relationship with sponges by doing what is 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 or simply for play.
Status and threats
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.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. Large-mesh nets set to protect bathers from sharks in South Africa and Australia have also resulted in a substantial number of deaths. Gillnets are also having an impact, and are a problem throughout most of the species’ range.
Captivity
These small cetaceans are commonly found in captivity, causing conservation concerns, including: the effects of removing the animals from their wild populations, survivorship 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.Bottlenose dolphins are the most common captive cetaceans on a global scale. 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. By the late 1980s, the United States stopped collecting bottlenose dolphins and the number of captive-born animals in North American aquariums has increased from only 6 percent in 1976 to about 44 percent in 1996.
Effects of whale watching
Not much is known about the impact of whale watchingWhale watching
Whale watching is the practice of observing whales and other cetaceans in their natural habitat. Whales are watched most commonly for recreation but the activity can also serve scientific or educational purposes. A 2009 study, prepared for IFAW, estimated that 13 million people went whale watching...
on cetaceans, but research is being conducted at several locations.
Japan
Morisaka et al. (2005) conducted a study on three populations of Indo-Pacific bottlenose dolphins in Japan. 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 dolphin's habitats and the whistles produced were compared. Ambient noise was recorded using a hydrophone located 10m 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.
Jervis Bay, Australia
Small, motorized vessels have increased as a source of anthropogenic noise due to the rise in popularity of wildlife viewing such as whale watching. Lemon et al. (2006)) showed powerboat approaches within 100m 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.Shark Bay, Australia
Another study by Bejder et al. (2006) in Shark Bay, Western Australia on dolphin behavioural responses showed there were significant changes in the behaviour of targeted dolphins 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, these results do not have biological significance and need to be researched further.
Conservation
The Indo-Pacific bottlenose dolphin populations of the Arafura and the Timor Sea are listed on Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals (CMSBonn Convention
The Convention on the Conservation of Migratory Species of Wild Animals aims to conserve terrestrial, marine and avian migratory species throughout their range...
). They are listed on Appendix II as they have an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.
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).
Further reading
- Cockcroft VG, Ross GJB. 1990. Age, growth, and reproduction of bottlenose dolphins Tursiops truncatus from the east coast of southern Africa. Fishery Bulletin 88(2): 289-302.
- Moller Luciana M., Beheregaray Luciano B., Allen Simon J., Harcourt Robert G. 2006. Association patterns and kinship in female Indo-Pacific bottlenose dolphins (Tursiops aduncus) of southeastern Australia. Behavioural Ecology Sociobiology 61: 109-117.
- Nowacek Stephanie M., Wells Randall S., Solow Andrew R. 2001. Short-term effects of boat traffic on bottlenose dolphins, Tursiops truncatus, in Sarasota Bay, Florida. Marine Mammal Science 17(4): 673-688.
- Schroeder, J. Pete. Breeding Bottlenose Dolphins in Captivity. In The Bottlenose Dolphin, edited by Stephen Leatherwood and Randall R. Reeves, pp. 435-446. San Diego: Academic Press, Inc., 1990.
- Shane Susan H., Wells Randall S., Wursig Bernd. 1986. Ecology, behaviour and social organization of the bottlenose dolphin: a review. Marine Mammal Science 2(1): 34-63.
- Urian, K.W., Duffield D.A., Read A.J., Wells R.S., Shell E.D. 1996. Seasonality of Reproduction in Bottlenose Dolphins, Tursiops truncatus. Journal of Mammalogy, 77(2): 394-403.
- Wells, Randall S., Scott Michael D., Irvine Blair A. The Social Structure of Free-ranging Bottlenose Dolphins. In Current Mammalogy, Volume 1, edited by H.H. Genoways, pp. 247- 305. New York: Plenum Press, 1987.