Indo-Pacific Bottlenose Dolphins

Taxobox
name = Indo-Pacific Bottlenose Dolphin
status =
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regnum = Animalia
phylum = Chordata
classis = Mammalia
ordo = Cetacea
familia = Delphinidae
genus = "Tursiops"
species = "T. aduncus"
binomial = "Tursiops aduncus"
binomial_authority =
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Indo-Pacific Bottlenose Dolphin ("Tursiops aduncus") is a species of dolphin.

Recent molecular studies that analyzed the external morphology and osteology of Bottlenose Dolphins have shown that the common bottlenose dolphin ("Tursiops truncatus") is a distinct species from the Indo-Pacific bottlenose dolphin ("Tursiops aduncus"). [Moller Luciana M., Beherega Luciano B. 2001. Coastal bottlenose dolphins from southeastern Australia are "Tursiops aduncus" according to sequences of the mitochondrial DNA control region. Marine Mammal Science 17(2): 249-263.] This page looks at the general characteristics of the Indo-Pacific bottlenose dolphin which are listed in the contents.

Description of the Species

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 are have a more slender body build and their beak is longer and more slender.Worlds Creatures. 2004. Indo-Pacific Bottlenose Dolphin. Retrieved March 28, 2008 from the website: http://www.worldscreatures.com/water-species/dolphins/indo-pacific-bottlenose-dolphin.htm.] The Indo-Pacific population also tends to be somewhat lighter in colour and the cape is generally more distinct with a light spinal blaze extending to below the dorsal fin.2 However, although not always present, the most obvious distinction came 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. Their teeth can number between 23 and 29 in each upper and lower jaw and are more slender than those of common bottlenose dolphins. Size of Indo-Pacific bottlenose dolphins can vary based on geographic location however their average length is about 2.7 m and typically weigh 230 kg. Their length at birth is about 85-112 cm.

Diet

Indo-Pacific bottlenose dolphins feed on a wide variety of fish and cephalopods (particularly squid).Amir Omar A., Per Berggren, Simon Ndaro G.M., Narriman Jiddawi S. 2005. Feeding ecology of the Indo-Pacific bottlenose dolphin (Tursiops aduncus) incidentally caught in the gillnets fisheries off Zanzibar, Tanzania. Estuarine, Coastal and Shelf Science 63(3): 429-437.]

Geographic distribution

It is found from from southern Japan, southward to Australia and along the entire rim of the Indian Ocean (including the Indo-Malay archipelago) to Cape Agulhas in southeastern Africa, including the Red Sea.Cetacean Specialist Group. 1996. Tursiops aduncus. International Union for Conservation of Nature and Natural Resources (IUCN). 2007 IUCN Red List of Threatened Species. Retrieved March 18, 2008 from the website: http://www.iucnredlist.org/search/details.php/41714/ref.]

Case study:

In a recent study conducted by Amir et al. (2005) 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 Zanibar, Tanzania. The prey items found in the stomach contents comprised of 50 species of bony fish and 3 species of squid. From their results the researchers concluded that 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. The remains of some crustaceans were also found however they hypothesize that they were consumed secondarily since a number were found intact in the fish prey stomachs and therefore were not included in the diet analysis.

Possible symbiosis:

Indo-Pacific bottlenose dolphins located in Shark Bay, Australia are thought to have a symbiotic relationship with sponges by doing what is called “sponging”. What happens is a dolphin breaks a marine sponge off the sea floor and wears it over its rostrum. It is thought that the reason they do this is to probe substrates for fish however it is still not completely understood if it is used for a tool or simply for play.

tatus and Threats

Indo-Pacific bottlenose dolphins are not considered to be endangered as a species however, it has a near-shore distribution which makes it vulnerable to environmental degradation, direct exploitation, and problems associated with local fisheries. [Curry, B.E. and Smith, J. 1997. Phylogeographic structure of the bottlenose dolphin (Tursiops truncatus): stock identification and implications for management. In: A.E. Dizon, S.J. Chivers, and W.F. Perrin (eds) Molecular Genetics of Marine Mammals, pp. 227-247. Society for Marine Mammalogy, Special Publication No. 3, Allen Press, Lawrence, Kansas.]

The major predators of this species are typically sharks however some others may include humans, killer whales (Orcinus orca) and sting rays. Just recently large numbers of these dolphins were deliberately killed in a Taiwanese drive fishery which greatly impacted the species.Fact|date=May 2008 It is now prohibited however, gillnets are still having an impact and are a problem not only here but throughout most of the species’ range. In the early 1980s many were killed in a Taiwanese driftnet fishery in the Arafura Sea, off northwestern Australia. [Harwood, M.B. and Hembree, D. 1987. Incidental catch of small cetaceans in the offshore gillnet fishery in northern Australian waters: 1981-1985. Report of the International Whaling Commission 37: 363-367.] Large-mesh nets set to protect bathers from sharks in South Africa and Australia has also resulted in a substantial number of deaths in the Indo-Pacific bottlenose dolphins. [Peddemors, V.M. 1999. Delphinids of southern Africa: a review of their distribution, status and life history. Journal of Cetacean Research and Management 1: 157-165.]

Captivity and Implications for Conservation

Indo-Pacific dolphins are one of many small cetaceans commonly found in captivity. Some of the conservation concerns for animals in captivity include: the effects of removing the animals from their wild populations, survivorship 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.Fisher Sue J., Reeves Randall R. 2005. The Global Trade in Live Cetaceans: Implications for Conservation. Journal of International Wildlife Law and Policy 8: 315-340]

History and Development:

Bottlenose dolphins are the most common captive cetaceans on a global scale. 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. By the late 1980s, the United States stopped collecting bottlenose dolphins and the number of captive-born animals in North American aquariums has increased from only 6 percent in 1976 to about 44 percent in 1996.

Conservation Concerns:

The expansion of live-capture operations could be “contributing to the depletion of some local populations” in Southeast Asia, especially those in nearshore and riverine waters. Because the Indo-Pacific bottlenose dolphins are a popular display animal and because they have small, disjunct populations they are vulnerable and are of great concern.

Effects of Whale-watching

Not much is known about the impact of whale-watching on cetaceans however; a lot of research is being conducted in an attempt to fill in the knowledge gaps. Listed below are some examples of current research on the effects of whale-watching boats and the Indo-Pacific bottlenose dolphins:

Japan

Morisaka et al. (2005) [Morisaka Tadamichi, Shinohara Masanori, Nakahara Fumio, Akamatsu Tomonari. 2005. Effects of Ambient Noise on the Whistles of Indo-Pacific Bottlenose Dolphin Populations. Journal of Mammalogy 84(3): 541-546.] conducted a study on three populations of Indo-Pacific bottlenose dolphins in Japan. It is believed that characteristics of acoustic signals are 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 dolphin's habitats and the whistles produced were compared. Ambient noise was recorded using a hydrophone located 10m below the surface and whistles were recorded by using an underwater video system.

Results showed that 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 that communication signals are adaptive and are selected to avoid the masking of signals and the decrease of higher-frequency signals as Tadamichi et al. states in the paper. They concluded that 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. Lemon et al. (2006) [Lemon Michelle, Lynch Tim P., Cato Douglas H., Harcourt Robert G. 2006. Response of traveling bottlenose dolphins (Tursiops aduncus) to experimental approaches by a powerboat in Jervis Bay, New South Wales, Australia. Biological Conservation 127:363-372] carried out a study in Australia on bottlenose dolphins to look at whether powerboats are in fact a significant source of disturbance for these animals. The surface behaviour and acoustic response of traveling dolphins to approaches by a powerboat were assessed by a series of experimental trials. Dolphin behaviour was monitored continuously from an independent research boat before, during, and after a powerboat approached. Once a group of traveling dolphins was located, the group was randomly assigned to either a control or treatment condition. During each experimental trial the dolphin's acoustic and surface behaviour were recorded "pre-exposure" with the powerboat stationary and engine off, "on-approach" with the powerboat approaching the focal group, "exposure" with the power boat moving slowly alongside the group, and "post-exposure" when the powerboat had departed from the area. For the control trials the surface and acoustic behaviours were recorded from the research vessel where only the electric motor was used.

Results of the study showed that powerboat approaches altered the surface behaviour and direction of traveling dolphins when exposed to vessels within 100m. Their whistles and echolocation click bouts however, were not affected when approached. When powerboats approached the dolphins they changed their surface behaviour from traveling to milling and changed their direction to travel away from the powerboat. It was not until the powerboat left the area and its noise ceased that the dolphins returned to their preceding behaviour in the original direction.

hark Bay, Australia

Another study was carried out by Bejder et al. (2006) [Bejder Lars, Samuels Amy, Whitehead Hal, Gales Nick. 2006. Interpreting short-term behavioural responses to disturbance within a longitudinal perspective. Animal Behaviour 72: 1149-1158] in Shark Bay, Western Australia on the behavioural responses of Indo-Pacific bottlenose dolphins to experimental vessel approaches in regions of both high and low vessel traffic. Data was collected from two different sites that had different histories of vessel activity: high vessel activity classified as the impact site and low vessel activity classified as the control site. A team of researchers evaluated group-level, non-vocal, behavioural responses of dolphins 15 minutes before, during and after approaches by an experimental vessel.For each experiment observers selected a focal dolphin group based on the group's proximity to the shore station and the absence of any vessels within 300m. After the focal group was selected, observers on the shore recorded behavioural data for 15 minutes. Then vessel-based observers were directed towards the focal group and collected data once within 50m of the group. Throughout the 15 minute period, shore observers continued to record behavioural data while the vessel maintained a distance of 10-50m from the focal group. Observers aboard the experimental vessel identified individual dolphins in the focal group taking dorsal fin photographs. When the experimental vessel was beyond 300m of the focal group, the shore team continued to monitor the behaviour and movements of the focal group for another 15min. Tour vessel movements were also tracked using GPS to show focal group movements during the experiment.

Results show that there were significant changes in the behaviour of targeted dolphins when compared with their behaviour before and after approaches. Dolphins in the control site showed a stronger and longer-lasting response than dolphins in the impact site. It is believed that these results 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, it is suggested that this study documented moderated responses not because of habituation occurring but 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 it is important to note that these results do not have biological significance and needs to be researched further.

References

Further reading

Cockcroft VG, Ross GJB. 1990. Age, growth, and reproduction of bottlenose dolphins Tursiops truncatus from the east coast of southern Africa. Fishery Bulletin 88(2): 289-302.

Moller Luciana M., Beheregaray Luciano B., Allen Simon J., Harcourt Robert G. 2006. Association patterns and kinship in female Indo-Pacific bottlenose dolphins (Tursiops aduncus) of southeastern Australia. Behavioural Ecology Sociobiology 61: 109-117.

Nowacek Stephanie M., Wells Randall S., Solow Andrew R. 2001. Short-term effects of boat traffic on bottlenose dolphins, Tursiops truncatus, in Sarasota Bay, Florida. Marine Mammal Science 17(4): 673-688.

Schroeder, J. Pete. Breeding Bottlenose Dolphins in Captivity. In The Bottlenose Dolphin, edited by Stephen Leatherwood and Randall R. Reeves, pp. 435-446. San Diego: Academic Press, Inc., 1990.

Shane Susan H., Wells Randall S., Wursig Bernd. 1986. Ecology, behaviour and social organization of the bottlenose dolphin: a review. Marine Mammal Science 2(1): 34-63.

Urian, K.W., Duffield D.A., Read A.J., Wells R.S., Shell E.D. 1996. Seasonality of Reproduction in Bottlenose Dolphins, Tursiops truncatus. Journal of Mammalogy, 77(2): 394-403.

Wells, Randall S., Scott Michael D., Irvine Blair A. The Social Structure of Free-ranging Bottlenose Dolphins. In Current Mammalogy, Volume 1, edited by H.H. Genoways, pp. 247- 305. New York: Plenum Press, 1987.