Species: Indian Ocean Bottlenose Dolphin
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Indian Ocean Bottlenose Dolphin (Tursiops aduncus)
DescriptionThe bottlenose dolphin is the most well known of all dolphin species, due to their abundance in coastal waters, their regular interactions with humans and they are the commonest dolphin species found in captivity. Bottlenose dolphins show great variation is size, colour and physical characteristics depending on location although until recently, they were still considered a single species. Advances in research technology has changed this opinion and two species of bottlenose dolphin are currently recognised, the pan-tropical and temperate Tursiops truncatus and the endemic Indian Ocean Tursiops aduncus. Generally, bottlenose dolphins are dark grey in colour with a pale underside. They have a prominent beak and a large, sickle shaped dorsal fin in the centre of the back. In some areas they can grow up to 4m in length (150-650kg). The T. aduncus tend to be smaller than T. Tursiops, with proportionally longer beaks and more teeth. They also develop ventral spotting around sexual maturity (Rice 1998; Wang et al., 2000a; 2000b; Wells & Scott 2002; Culik 2004; Perrin et al., 2007). Some research has suggested that the T. aduncus may in fact be more closely related to the common or spotted dolphin and not T. truncatus (LeDuc et al., 1999).
Distribution:Bottlenose dolphins are found in most of the worlds warm temperate to tropical waters and can be found both offshore and in coastal waters. T. aduncus is the species predominantly sighted in Singapore waters and this species range is more limited than the T. trucatus, covering from the east coast of Africa eastwards through the Persian Gulf, Arabian Sea and Bay of Bengal to Taiwan and Australia. In the Indian Ocean, T. aduncus is the predominant coastal species while T. truncatus is usually seen offshore (Wells & Scott, 2002).
Distribution of T. aduncus, reproduced from Culik 2004, Wells & Scott, 2002. Behaviour:Bottlenose dolphins in general are highly active animals, frequently bow-riding and breaching. They typically show their forehead when surfacing but not the beak (unlike the humpback dolphin).
Primarily considered a coastal species, they are also often seen in pelagic waters (Wells & Scott 1999). They often frequent river mouths, bays and lagoons. Coastal dolphins generally form groups of 6-8 animals, with pelagic (offshore) groups being much larger. They are active throughout the day and night, with their time divided between periods of feeding, socialising, resting and travelling (Shane et al., 1986; Wells et al., 1999). The length of time spent on each of these activities can be dependant on time of day, season, tidal state and reproductive season. They feed on a wide variety of fish species, depending on the location and are also known to take squid and crustacean species. Indian Ocean dolphins seem to show a preference for prey species that inhabit reefs or sandy areas and some inshore schooling fish (Wells & Scott, 2002). Bottlenose dolphins primarily feed by themselves but are known on occasion to form co-operative groups to catch schools of prey. Bottlenose dolphins in the wild are thought to live to more than 50 years of age (Hohn et al., 1989; Wells & Scott 1999). Females reach sexual maturity at an earlier age than males although the actual age varies with region (female between 5-13 years and males 9-14 years; Wells et al., 1999). Births have been reported in all months of the year but tend to vary with region and to be associated with the warmer months (Connor et al., 1999). The interval between calves appears to be longer for T. aduncus with calves being born every 4-6 years compared to the 3-6 year interval for T. truncatus (Connor et al., 1999). More research is needed to distinguish between the sub-species of Tursiops and to establish their importance in different areas. Tursiops aduncus is not listed separately by the IUCN, but Tursiops truncatus is listed as “data deficient”. Both species are listed on Annex II of CITES. |
