Rough-toothed dolphin  (Steno bredanensis)

Classified as Least Concern (LC) on the IUCN Red List (1) and listed on Appendix II of CITES (3).

With a head that slopes smoothly down into a long beak, and large flippers that are set fairly far back on the body (2), this rather primitive-looking dolphin is sometimes said to be somewhat reptilian in appearance (4). Named for the subtle ridges and wrinkles on the teeth (4), the body of the rough-toothed dolphin is patterned black, white and grey. It has a white underside, mid-grey sides, and a black to dark grey back. A darker region on the back, called a cape, runs narrowly from the top of the head to behind the tall, curved-back dorsal fin, where it widens (2). The body often bears the scars of bites from cookie-cutter sharks, leaving behind white patches, splotches and spots (2). Young rough-toothed dolphins often lack these white marks, and are more subdued in colour (2).

The rough-toothed dolphin is found in all three major oceans of the world (the Atlantic, Pacific and Indian) (2), typically between 40 degrees north and 35 degrees south (4).

This dolphin inhabits tropical and warm temperate waters (2), usually measuring over 25 degrees Celsius (5), where it is generally found in deep, offshore waters (2).

Although widespread, the rough-toothed dolphin is not frequently encountered, and thus few studies have been conducted on its ecology and biology (2). Like many other dolphins, it is a sociable animal, commonly moving in groups of 10 to 20 individuals, although larger groups have also been observed, such as one consisting of up to 300 dolphins in Hawaii. In these groups, the rough-toothed dolphin has been seen with other dolphin species, as well as often associating with flotsam, the rubbish and debris found floating in the ocean (2).

Often described as a sluggish or lethargic creature, the rough-toothed dolphin often swims with its chin and head above the water’s surface, skimming along with a distinctive splash (2) (4). It is not the most acrobatic of dolphins, but will occasionally leap and ride the bow waves of boats (2).

It feeds on a range of fish and cephalopods, with its robust, rough teeth suggesting that some particularly large fish may be eaten. Algae have also been found in the stomachs of rough-toothed dolphins, although this may have been eaten accidentally (2). It is known to dive to 70 metres to capture its prey and remain underwater for 15 minutes, although evidence suggests that this dolphin is actually capable of undertaking much deeper dives. With males reaching sexual maturity at 14 years, and females at 10 years, the rough-toothed dolphin is known to live for up to 32 to 36 years (2).

The greatest threat to the rough-toothed dolphin is likely to be incidental capture in fishing nets (2). While this dolphin is directly hunted in several areas for its meat (5), including Japan, Sri Lanka, Indonesia, the Solomon Islands and Papua New Guinea (2), relatively small numbers are taken (6), and as it inhabits offshore waters, it is unlikely to be affected by habitat degradation and pollution to the same extent that coastal-dwelling dolphins are (2).

The rough-toothed dolphin is listed on Appendix II of the Convention on International Trade in Endangered Species (CITES), meaning that any trade in this species should be carefully monitored (3). This dolphin is also held in captivity in a number of countries where, incidentally, they have been found to be bold and inventive animals (2). Studies of the rough-toothed dolphin in captivity may allow knowledge of this species’ biology to be furthered (5).

For further information on the conservation of dolphins see:

• Whale and Dolphin Conservation Society:
  www.wdcs.org

• Algae: simple plants that lack roots, stems and leaves but contain the green pigment chlorophyll. Most occur in marine and freshwater habitats.
• Cephalopods: from the Greek for ‘head-foot’, a class of molluscs that occur only in marine habitats. All species have grasping tentacles, and either an internal or external shell. Includes nautiloids, cuttlefish, squids, octopuses, and extinct ammonites and belemnites.
• Dorsal fin: the unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.

1. IUCN Red List (June, 2008)
   http://www.iucnredlist.org
2. Jefferson, T.A. (2002) Rough-toothed dolphin. In: Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (Eds) Encyclopedia of Marine Mammals.Academic Press, London.
3. CITES (October, 2008)
   http://www.cites.org
4. Jefferson, T.A., Leatherwood, S. and Webber, M.A. (1992) FAO Species Identification Guide. Marine Mammals of the World.FAO, Rome.
5. Klinowska, M. and Cooke, J. (1991) Dolphins, Porpoises and Whales of the World: The IUCN Red Data Book.IUCN, Gland, Switzerland.
6. Reeves, R.R., Smith, B.D., Crespo, E.A. and Notarbartolo di Sciara, G. (2003) Dolphins, Whales and Porpoises: 2002–2010 Conservation Action Plan for the World’s Cetaceans.IUCN/SSC Cetacean Specialist Group, IUCN, Gland, Switzerland and Cambridge, UK.