The Indian Ocean bottlenose dolphin (scientific name: Tursiops aduncus) is one of 36 species of Oceanic Dolphins in the family Delphinidae. This cetacean was only recently recognized as a distinct and separate species from the Common bottlenose dolphin (Tursiops truncatus). Additional information on this related species can be found in the article Common bottlenose dolphin.
|Tursiops aduncus. Source: Liz Hawkins/New South Wales Marine parks Authority|
Size comparison of an average human against the Bottlenose dolphin. Source: Chris Huh
The Indian Ocean bottlenose dolphin is sometimes found in groups that include Common bottlenose dolphins or other oceanic dolphins.
Distribution and Movements
The Indo-Pacific Bottlenose Dolphin has a discontinuous distribution in the warm temperate to tropical Indo-Pacific, from South Africa in the west, along the rim of the Indian Ocean (including the Red Sea, Persian Gulf, South China Sea, Sulu Sea, Celebes Sea and other coastal parts of the Indo-Malay Archipelago as far east as the Solomon Islands and possibly New Caledonia) to the southern half of Japan and southeast Australia in the east (Wells and Scott 2002; Möller and Beheregaray 2001). It is also found around oceanic islands distant from major landmasses within this range. (IUCN Red List)
The Indian Ocean bottlenose dolphin is most often found in shallow coastal waters
Threats and Conservation Status
The IUCN Redlist reports that the species near-shore distribution makes it vulnerable to environmental degradation, direct exploitation, and fishery conflicts (Curry and Smith 1997, Wells and Scott 1999; Reeves et al. 2003). Until hunting was outlawed in 1990, this species was hunted in a large-scale drive fishery in Taiwan’s Penghu Islands. Some Indo-Pacific bottlenose dolphins are taken in the small cetacean fisheries of Sri Lanka.
Incidental catches occur in a number of fisheries throughout the range, including gillnets and purse seines. A Taiwanese shark gillnet fishery operated in northern Australian waters during the early 1980s and took up to 2000 per year (Harwood and Hembree 1987). Incidental catch in Taiwan continues to be a serious problem. For example, multiple individuals have been seen observed in single catches there and throughout most of the species’ range (J.Y. Wang pers. comm.). A large proportion of dolphins (~40%) off Bangladesh exhibit scars and mutilations consistent with rope and net entanglement in trawl and gill-net fisheries (Rubaiyat Mansur Mowgli and Brian D. Smith pers. comm.). In South Africa and Australia, Indo-Pacific Bottlenose dolphins also suffer considerable mortality in the large-mesh nets set to protect bathers from sharks (Peddemors 1999; Reeves et al. 2003).
Live-captures for oceanarium display have taken place in Taiwan, Indonesia and the Solomon Islands in recent years from unassessed populations; their preference as a captive display species makes them vulnerable to depletion from such catches (Wang et al. 1999, Reeves et al. 2003, Kahn).
Indo-Pacific bottlenose dolphins in coastal areas are exposed to a wide variety of threats in addition to direct and indirect takes. Threats that are cause for concern include: 1) the toxic effects of xenobiotic chemicals; 2) reduced prey availability caused by environmental degradation and overfishing (Jackson et al. 2001); 3) direct and indirect disturbance and harassment (e.g. boat traffic and commercial dolphin watching and interactive programs); 4) marine construction and demolition and 5) other forms of habitat destruction and degradation (including anthropogenic noise). Although these and other threats are technically challenging to quantify by comparison with takes, their cumulative impact is likely to result in longitudinal population declines. Lack of historical data in many cases hampers understanding of long-term population trends, possibly resulting in shifting baselines.
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