Indo-Pacific bottlenose dolphin

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File:Aerial view of a pod of Indo-Pacific bottlenose dolphins (Tursiops aduncus) with calves at Gordon's Bay, Sydney, 27 December 2020.webm

The Indo-Pacific bottlenose dolphin (Tursiops aduncus) is a species of bottlenose dolphin. This dolphin grows to Template:Convert long, and weighs up to Template:Convert.<ref name=princeton>Template:Cite book</ref> It lives in the waters around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa.<ref name=princeton/> Its back is dark grey and its belly is lighter grey or nearly white with grey spots.<ref name=princeton/>

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.<ref name="encyc">Template:Cite book</ref><ref name=audubon>Template:Cite book</ref> 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.<ref name=audubon/>

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 the Indo-Pacific bottlenose dolphin as "near threatened" in their Red List of endangered species.<ref name="iucn status 19 November 2021" />

Taxonomy

Until 1998, all bottlenose dolphins were considered members of the single species T. truncatus. But in that year, the Indo-Pacific bottlenose dolphin was recognized as a separate species.<ref name="encyc" /><ref>Template:Cite journal</ref> Both species are thought to have split during the mid-Pleistocene, about 1 million years ago.<ref name=":0">Template:Cite journal</ref>

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.<ref name="encyc" /><ref>Template:Cite journal</ref> 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.<ref name=":0" />

The Burrunan dolphin (T. (aduncus) australis) has been alternately considered its own species, a subspecies of T. truncatus, or a subspecies of T. aduncus. Following the results of a 2020 study, the American Society of Mammalogists presently classifies it as a subspecies of T. aduncus.<ref name=":0" /><ref>Template:Cite web</ref> 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.<ref name=":0" /> The Society for Marine Mammalogy does not recognize the Burrunan dolphin as a distinct species or subspecies, citing the need for further research.<ref name="mammalogy">Template:Cite web</ref>

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.<ref name="Worlds">Worlds Creatures. (2004) Indo-Pacific bottlenose dolphin Template:Webarchive.</ref> 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.<ref name="Worlds"/> Their teeth can number between 23 and 29 in each upper and lower jaw, and are more slender than those of common bottlenose dolphins.<ref name="Worlds"/> Size of Indo-Pacific bottlenose dolphins can vary based on geographic location; however, its average length is Template:Convert long, and it weighs up to Template:Convert.<ref name="princeton"/> The length at birth is between Template:Convert.<ref name="princeton"/>

The local population centering Mikura-jima is claimed to be a distinct form or species.<ref>Template:Cite web</ref>

Diet

Indo-Pacific bottlenose dolphins feed on a wide variety of fish and cephalopods (particularly squid).<ref name="Amir">Template:Cite journal</ref>

In one study,<ref name="Amir"/> 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 Zanzibar, 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.<ref name="Amir"/> 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.<ref name="Amir"/>

Behavior

Socializing dolphins in the Red Sea

Indo-Pacific bottlenose dolphins live in groups that can number in the hundreds, but groups of five to 15 dolphins are most common.<ref name=audubon/> In some parts of their range, they associate with the common bottlenose dolphin<ref name=audubon/> and other dolphin species, such as the humpback dolphin.<ref name=audubon/>

The peak mating and calving seasons are in the spring and summer, although mating and calving occur throughout the year in some regions. The gestation period is about 12 months. Calves are between Template:Convert long, and weigh between Template:Convert. The calves are weaned between 1.5 and 2.0 years, but can remain with their mothers for up to 5 years. The interbirth interval for females is typically 4.5 to 6 years.<ref name=princeton/>

In some parts of its range, this dolphin is subject to predation by sharks;<ref name=audubon/> its lifespan is more than 40 years.<ref name=princeton/>

Indo-Pacific bottlenose dolphins located in Shark Bay, Australia, have been observed using sponges as tools in a practice 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.<ref name="Smolker 1997">Template:Cite journal</ref><ref name="Mann 2008">Template:Cite journal</ref>

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.<ref name=spontaneous>Template:Cite journal</ref>

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.<ref>Template:Cite web</ref>

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.<ref>Curry, B.E. and Smith, J. (1997) "Phylogeographic structure of the bottlenose dolphin (Tursiops truncatus): stock identification and implications for management", pp. 227–247 in: A.E. Dizon, S.J. Chivers, and W.F. Perrin (eds) Molecular Genetics of Marine Mammals. Society for Marine Mammalogy, Special Publication No. 3, Allen Press, Lawrence, Kansas.</ref>

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<ref>Tursiops aduncus (Indo-Pacific bottlenose dolphin). Animal Diversity Web. https://animaldiversity.org/accounts/Tursiops_aduncus/</ref>) 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.<ref>Template:Cite journal</ref> Large-mesh nets set to protect bathers from sharks in South Africa and Australia have also resulted in a substantial number of deaths.<ref>Template:Cite journal</ref> 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,<ref name="Amir"/> causing conservation concerns, including the effects of removing the animals from their wild populations, survival 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.<ref name="Fisher">Template:Cite journal</ref>

Bottlenose dolphins are the most common captive cetaceans on a global scale.<ref name="Fisher"/> 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.<ref name="Fisher"/> By the late 1980s, the United States stopped collecting bottlenose dolphins and the number of captive-born animals in North American aquaria has increased from only 6% in 1976 to about 44% in 1996.

In the South Korea, in the 2010s, environmental groups and animal protection groups led a campaign (2013년 대한민국 남방큰돌고래 방사) to release southern bottlenose dolphins illegally captured by fishermen and trapped in Jeju Pacific Land<ref>Template:Cite news</ref> and Seoul Zoo.<ref>Template:Cite news</ref>

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.<ref>Template:Cite news</ref>

Japan

In a study on three populations of Indo-Pacific bottlenose dolphins in Japan,<ref>Template:Cite journal</ref> 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<ref>Template:Cite journal</ref> 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

Dolphin in shallow water at Monkey Mia, Shark Bay, Western Australia

Another study<ref>Template:Cite journal</ref> 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).<ref name="Manlik et al. 2016">Template:Cite journal</ref>

Conservation

The Indo-Pacific bottlenose dolphin populations of the Arafura and the Timor Sea are listed on Appendix II<ref name="Appendices">"Appendix II Template:Webarchive" of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). As amended by the Conference of the Parties in 1985, 1988, 1991, 1994, 1997, 1999, 2002, 2005, and 2008. Effective: 5 March 2009.</ref> of the Convention on the Conservation of Migratory Species of Wild Animals (CMS). They are listed on Appendix II<ref name="Appendices" /> as they have an unfavourable conservation status or would benefit significantly from international co-operation organised by tailored agreements.<ref>Convention on Migratory Species page on the Indo-Pacific bottlenose dolphin Template:Webarchive. cms.int</ref>

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).<ref>Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region. pacificcetaceans.org</ref> The population of the Menai Bay Conservation Area in the Zanzibar Archipelago of Tanzania has been researched.<ref>Temple, Andrew J., et al. "Spatial and temporal variations in the occurrence and foraging activity of coastal dolphins in Menai Bay, Zanzibar, Tanzania." PloS one 11.3 (2016): e0148995.</ref>

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.<ref name=mp>Template:Cite book</ref>

See also

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References

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Further reading

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