Atlantic humpbacked dolphin (Sousa teuszii)
|French:||Dauphin À Bosse De L'Atlantique, Dauphin Du Cameroun|
|Spanish:||Bufeo Africano, Delfín Blanco Africano, Delfín Jorobado Del Atlántico|
|Size||Maximum length: 2.5 – 2.8 m (2)|
|Weight||up to 284 kg (3)|
Classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix I of CITES (4).
The most distinctive feature of this rather elusive cetacean is its distinctive humped appearance when it breaks the ocean’s surface to breathe (2). This is caused by the wide hump or ridge on the dolphin’s back, from which the dorsal fin emerges (3). The Atlantic humpbacked dolphin is a robust-bodied marine mammal (2), typically slate grey on the sides and back and light grey on the underside (3). It has a long, narrow, distinct beak (2) (3), broad flippers that are rounded at the tip, and a broad tail fin, deeply notched in the centre (2). It is thought that, like the better known and closely related Indo-Pacific humpbacked dolphin (Sousa chinensis), male Atlantic humpbacked dolphins are larger than females (2) (3).
The Atlantic humpbacked dolphin occurs in the eastern Atlantic Ocean (1), from Western Sahara, south to southern Angola (5).
Shallow, tropical, coastal waters, less than 25 metres deep, are the preferred habitat of the Atlantic humpbacked dolphin. This includes the often murky waters of bays, river deltas and mangrove channels (2). This dolphin has also been observed entering large rivers, although it rarely travels far upstream, remaining within salty water (5).
The Atlantic humpbacked dolphin is a slow swimming species, which typically moves at about five kilometres per hour, surfacing briefly every minute or so. Typically occurring in groups of four to seven individuals, the Atlantic humpbacked dolphin, unlike many other dolphins, will avoid boats and is rarely seen bow riding (2).
Humpbacked dolphins are known to feed on fish, including bream, mullet and herring, and cephalopods. Off the coast of Senegal, the Atlantic humpbacked dolphin has been observed moving inshore with the incoming tide to feed on prey within mangrove channels, and then returning to the ocean as the tide retreats (2). It is thought to use echolocation when foraging; a series of clicks are produced which reflect off objects and help the dolphin locate its prey in the often murky habitat. This dolphin may also emit whistles and screams, vocalisations which may be important in communication with other dolphins (2).
Very little is known about reproduction in this dolphin; breeding has been recorded in March and April, and the calves are thought to be about one metre long at birth (2).
As an inhabitant of coastal waters, the Atlantic humpbacked dolphin is highly vulnerable to the effects of human activities (2). Fisheries impact the dolphin, firstly, by causing incidental mortality when the dolphin becomes entangled in fishing gear (6). This is currently considered to be the greatest immediate threat to this species (1), and may be the reason behind the rarity of this species in the coastal waters of Senegal and Gambia, and in Dakhla Bay in Western Sahara, two areas in which the Atlantic humpbacked dolphin was once common (6). Secondly, fisheries may impact this dolphin by reducing the availability of prey (6). In certain areas, the Atlantic humpbacked dolphin is also captured intentionally for food by local people (5), although the numbers that are caught, and what impact this has on the population, is not known (1).
In addition to the threat of fisheries, the Atlantic humpbacked dolphin is potentially being affected by boat strikes and habitat degradation. For example, mangroves are being converted to rice cultivation in some areas, destroying an important foraging habitat of this dolphin (1) (5). A high human population density within its range, and the associated development of agriculture and industry, will undoubtedly continue to have an impact on the shallow coastal waters in which the Atlantic humpbacked dolphin is found (1) (5).
The Atlantic humpbacked dolphin is listed on Appendix II of the Convention on Migratory Species (CMS). This indicates that this is a species that would benefit from international co-operation, with regards to its conservation, and the Convention encourages the relevant countries to implement suitable conservation measures (7). Considering its specific habitat preferences, estimated low abundance and the threats it faces, the Atlantic humpbacked dolphin is likely to be in great need of further research and conservation measures (6).
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- 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.
- Cetacean: cetaceans are a group comprising all whale species, therefore including dolphins and porpoises.
- Dorsal fin: the unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.
- Echolocation: detecting objects by reflected sound. Used by bats and odontocete cetaceans (toothed whales, dolphins and porpoises) for orientation and to detect and locate prey.
IUCN Red List (December, 2007)
- Ross, G.J.B. (2002) Humpback dolphins. In: Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (Eds) Encyclopedia of Marine Mammals. Academic Press, London.
- Jefferson, T.A., Leatherwood, S. and Webber, M.A. (1993) FAO Species Identification Guide. Marine Mammals of the World. FAO, Rome.
CITES (December, 2007)
- Van Waerebeek, K., Barnett, L., Camara, A., Cham, A., Diallo, M., Djiba, A., Jallow, A.O., Ndiaye, E., Bilal, A.S. and Bamy, I.L. (2004) Distribution, status, and biology of the Atlantic humpback dolphin, Sousa teuszii. Aquatic Mammals, 30(1): 56 - 83.
- 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.
Convention on Migratory Species (November, 2008)