thumb|Aerial view of a pod of Indo-Pacific bottlenose dolphins (Tursiops aduncus) with calves at Gordon's Bay, Sydney.

The Indo-Pacific bottlenose dolphin (Tursiops aduncus) is a species of bottlenose dolphin. This dolphin grows to long, and weighs up to . It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa. 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. Both species are thought to have split during the mid-Pleistocene, about 1 million years ago.

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. 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. 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.

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.

Diet

Indo-Pacific bottlenose dolphins feed on a wide variety of fish and cephalopods (particularly squid).

In one study,

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.

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.

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 (such as great white sharks, tiger sharks, bull sharks, bluntnose sixgill sharks, broadnose sevengill sharks, dusky sharks, oceanic whitetip sharks, shortfin mako sharks, Pacific sleeper sharks, and Greenland sharks) and may include humans, killer whales (Orcinus orca), and stingrays. 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,

Bottlenose dolphins are the most common captive cetaceans on a global scale. and Seoul Zoo.

In 2019, Canada banned the trade, possession, capture, and breeding of whales, dolphins, and porpoises for entertainment through passing Bill-203, also known as the Ending the Captivity of Whales and Dolphins Act.

Japan

In 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 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.

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. Another study 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.

Shark Bay, Australia

thumb|Dolphin in shallow water at [[Monkey Mia, Shark Bay, Western Australia]]

Another study 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).

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 (CMS). They are listed on Appendix II

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). The population of the Menai Bay Conservation Area in the Zanzibar Archipelago of Tanzania has been researched.

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.

See also

  • List of cetaceans
  • Marine biology

References

Further reading

  • 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.
  • Save Solomon Dolphins