Indo-Pacific bottlenose dolphins look very similar to common bottlenose dolphins, with a relatively robust body, moderate-length beak, and tall falcate dorsal fin. However, they tend to be somewhat more slender than common bottlenose dolphins, and the beak is relatively longer and more slender.
Coloration (although variable) tends to be somewhat lighter than in most common bottlenose dolphins. The cape is generally more distinct, and there is often a light spinal blaze extending to below the dorsal fin. The most distinctive feature is generally the presence of prominent black spots or flecks on the bellies of adults of this species (these are very rarely present on common bottlenose dolphins). However, not all Indo-Pacific bottlenose dolphins necessarily have ventral spotting.
The teeth number 23-29 in each upper and lower jaw. They are a bit more slender than those of common bottlenose dolphins.
Although maximum size is geographically variable, Indo-Pacific bottlenose dolphins grow to lengths of only about 2.7 m and 230 kg. Length at birth is about 85-112 cm.
Can be Confused With
This species can be difficult to distinguish from the common bottlenose dolphin in sightings at sea. The best field characters to look for are the length and slenderness of the beak, and the presence/absence of black spots on the belly.
These animals are found only in the warm temperate to tropical Indo-Pacific, from South Africa in the west to southern Japan and north-central Australia in the east. They occur almost exclusively over the continental shelf, mostly in very shallow coastal and inshore waters. There are also populations around some oceanic islands in southern Japan.
Ecology and Behavior
Indo-Pacific bottlenose dolphins occur in groups ranging in size up to the low hundreds, but groups of less than 20 are much more common. They sometimes occur in mixed groups with common bottlenose dolphins and other delphinid species. Off western Australia, where this species’ behavior has been most intensively studied, male Indo-Pacific bottlenose dolphins often band together to garner young females from the group.
Although reproductive activity occurs throughout the year, breeding peaks in spring and summer months. The gestation period is about 12 mos, and calves are weaned after 18-24 months of lactation.
Sharks often prey on these animals, at least in areas where they have been well-studied, such as South Africa and eastern and western Australia.
Feeding and Prey
Feeding is on a large variety of schooling, demersal and reef fishes, as well as cephalopods. Most prey items are less than 20 cm in length. Off eastern Australia dolphins feed behind trawlers, often in association with sympatric humpback dolphins.
Threats and Status
Some Indo-Pacific bottlenose dolphins are taken in the small cetacean fisheries of Sri Lanka and possibly in Indonesia as well. Live-captures for oceanarium display have taken place in Taiwanese and Indonesian waters in recent years. Until it was outlawed in 1990, this species was involved in a large-scale drive fishery in Taiwan’s Penghu Islands.
Incidental catches occur in a number of fisheries throughout the range, including gillnets and purse seines. The largest known of these includes up to 2,000 per year taken in the Taiwanese driftnet fishery operating in Indonesian waters (this fishery formerly operated in northern Australian waters). In addition, Indo-Pacific bottlenose dolphins are killed in anti-shark gillnets in South Africa and Australia. Since it is a coastal species, it is subjected to a number of other human threats – including habitat destruction/degradation, vessel collisions, and environmental contamination.
Currently, the conservation status of Indo-Pacific bottlenose dolphins is ‘Not Listed’ (IUCN and ESA).
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