Indian Ocean Bottlenose Dolphin

## Description

The Indo-Pacific bottlenose dolphin (Tursiops aduncus ) is a species of bottlenose dolphin. This dolphin grows to 2.6 m (8.5 ft) long, and weighs up to 230 kg (510 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.

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. 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.

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.

## Appearance

The Indian Ocean bottlenose dolphin is a species of bottlenose dolphin. They are very similar to Common bottlenose dolphins in appearance. Indian Ocean bottlenose dolphins have a more slender body and their beak is longer and more slender. The Indian Ocean population also is somewhat lighter blue in colour. The cape is generally more distinct, with a light spinal blaze extending to below the dorsal fin. The most obvious distinction can be made with the presence of black spots or flecks on the bellies of adults of Indian Ocean bottlenose dolphins, although they are not always present. These black spots are very rare in Common bottlenose dolphins. The teeth can number between 23-29 in each upper and lower jaw, and are more slender than those of Common bottlenose dolphins.

## Distribution

Indian ocean bottlenose dolphins are found around India, northern Australia, South China, the Red Sea, and the eastern coast of Africa. They live in the warm temperate to tropical waters. These dolphins occur in shallow water near the shore at depths of less than 300 m.

## Behavior

Indian ocean bottlenose dolphins are very social animals. They live in groups that can number in the hundreds, but groups of 5-15 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 dolphin. Indian ocean bottlenose dolphins located in Shark Bay, Australia, have a symbiotic relationship with sponges. They do "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. These dolphins communicate via auditory perception and via tactile signals. They rub flippers over the flippers or bodies of other dolphins. As their sense of sight is not well-developed, their sense of hearing is very keen. Each dolphin uses a characteristic whistle that helps other dolhins identify them individually.

## Diet

Indian ocean bottlenose dolphins are carnivore (piscivore). They feed on a wide variety of fish and cephalopods (particularly squid).

## Reproduction

Indian ocean bottlenose dolphins have polygynandrous (promiscuous) mating system. Males form alliances with 1-3 other unrelated males. These male groups herd females for mating. It's called “mate guarding.” Breeding females also form smaller groups as they are easier to defend. 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 after which only 1 calf is born. The calves are weaned between 1.5-2 years but can remain with their mothers for up to 5 years. The interbirth interval for females is typically 4-6 years. Females reach maturity at 7-12 years of age, males reach reproductive maturity at 9-13 years.

## Population

### Population threats

Indian Ocean bottlenose dolphins are not considered to be endangered. Their near-shore distribution, though, makes them vulnerable to environmental degradation, direct exploitation, and problems associated with local fisheries. 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.

### Population number

According to the IUCN Red List, the total population size of the Indian Ocean bottlenose dolphin is unknown. However, there are estimated populations of the species in the following areas: off Zanzibar (Tanzania) - 136-179 dolphins; in the Persian Gulf - 1,200 dolphins; along the rim of the Swatch-of-No-Ground (Bangladesh) - 400 dolphins; off western Kyushu (Japan) - 218 dolphins; off Mikura Island (Japan) - 168 dolphins; northeastern Philippines - 50 dolphins; off Queensland (Eastern Australia) - 1,099 dolphins; in Shark Bay (Western Australia) - 2,000-3,000 dolphins. Currently, Indian Ocean bottlenose dolphins are classified as Data Deficient (DD) on the IUCN Red List.

## References

https://animalia.bio/indian-ocean-bottlenose-dolphin