|Scientific Name:||Sousa teuszii|
|Species Authority:||(Kükenthal, 1892)|
|Taxonomic Notes:||The validity of this species has been questioned in the past few years, but recent studies on skull morphology have made it apparent that the species is indeed valid and separate from the Indo-Pacific Humpback Dolphin (see Jefferson and Van Waerebeek 2004). Further studies on molecular genetics of the genus are underway and preliminary results support this conclusion (H. Rosenbaum pers. comm. to T. Jefferson 2006). The Atlantic Humpback Dolphin appears to be isolated from other humpback dolphins by a gap in distribution of at least 2,000 km on the southwestern coast of Africa, an area dominated by cold upwelling associated with the Benguela Current System (see Jefferson and Van Waerebeek 2004).|
|Red List Category & Criteria:||Vulnerable C2a(i) ver 3.1|
|Assessor/s:||Reeves, R., Collins, T., Jefferson, T.A., Karkzmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K.|
|Reviewer/s:||Brownell Jr., R.L. & Cooke, J.|
This species is considered Vulnerable C2a(i) because of an inferred or suspected continuing decline, where the total number of mature individuals is considerably fewer than 10,000, and each of the defined subpopulations is estimated to contain fewer than 1,000. In a comprehensive assessment of available information, Van Waerebeek et al. (2004) identified eight possible “management stocks” but acknowledged that not all were likely to prove to be biologically distinct populations (subpopulations). It is inferred from the available information summarized above that the total population (all ages) is only a few thousand, and almost certainly fewer than 10,000. Of those, only about half would be mature (Taylor et al. 2007). Although there have been no quantitative studies of trends, the ongoing threats – particularly bycatch in fisheries, which almost certainly has been increasing in recent decades – support the suspicion of a continuing decline in population size.
|Range Description:||The Atlantic Humpback Dolphin is endemic to the eastern tropical Atlantic, where it is limited to coastal and inshore waters (Ross 2002, Van Waerebeek et al. 2004). It occurs in nearshore waters off tropical to subtropical West Africa, from Western Sahara south to at least southern Angola (Notarbartolo di Sciara et al. 1998, Van Waerebeek et al. 2004).
The map shows where the species may occur based on oceanography. The species has not been recorded for all the states within the hypothetical range as shown on the map. States for which confirmed records of the species exist are included in the list of native range states. States within the hypothetical range but for which no confirmed records exist are included in the Presence Uncertain list.
Native:Angola (Angola); Congo; Gabon; Gambia; Guinea; Guinea-Bissau; Mauritania; Senegal; Western Sahara
|FAO Marine Fishing Areas:||
Atlantic – eastern central; Atlantic – southeast
|Range Map:||Click here to open the map viewer and explore range.|
Little information on population size is available, as this is one of the least-known delphinids. Although there has been no assessment in most areas of their overall range, the population of Atlantic Humpback Dolphins appears fragmented, with subpopulations separated by areas of low or zero density (Van Waerebeek et al. 2004). Eight “management stocks” have been provisionally identified. Six of them are identified on the basis of “sightings, or other contemporary records, clustered around a confirmed habitat” (Van Waerebeek et al. 2004) – Dahkla Bay, Banc d’Arguin, Saloum-Niumi, Canal do Gêba-Bijagos, South Guinea, and Angola. The other two – Cameroon Estuary and Gabon – are based on “historical evidence.” The continued presence of Humpback Dolphins in the Estuaire de Gabon was recently confirmed (Tim Collins pers. comm. to R. Reeves, 8 January 2008). A ninth management stock is suspected to exist off western Togo (Van Waerebeek et al. 2004).
Rough “estimates” for the Saloum River delta, Senegal, were 100 animals, and there were thought to be at least several hundred in Guinea Bissau several decades ago (Ross et al. 1994, Reyes 1991). A small group of at least 20 dolphins resides in the Rio Grande de Buba (a fjord-like sea arm rather than a river) and upstream to the confluence of the Rio Sahol (Van Waerebeek et al. 2004). Although the species often has been reported as common (Reyes 1991, Culik 2004), there are no other numerical data on abundance. Considering the relatively small numbers observed, and even taking account of the many areas of the species’ range where there has been little or no assessment, the total population probably numbers only a few thousand.
|Habitat and Ecology:||
Atlantic Humpback Dolphins are found primarily in estuarine and shallow (< 20 m) coastal waters with soft sediment bottoms (Van Waerebeek et al. 2004). They have been observed as far as about 50 km up the Saloum River and are known to enter the Niger and Bandiala rivers, but they rarely travel far upstream and usually remain within the range of tidal influence (Van Waerebeek et al. 2004). There is no evidence to suggest the existence of separate freshwater subpopulations. In at least some areas (e.g., Gabon and Mauritania), these dolphins occur in the surf zone just offshore of the breakers (Busnel 1973; Tim Collins pers. comm. to T. Jefferson, 2007). There are no reports from offshore waters. Among the features that have been described as aspects of preferred habitat are proximity to sandbanks, brackish, mangrove-lined estuaries, and turbid waters with temperatures ranging between 17°C and 28°C (Maigret 1980, Ross et al. 1994).
There is little information on the diet of Atlantic humpback dolphins. They appear to feed on nearshore schooling fishes such as mullet (Mugil spp.) and, contrary to some descriptions, are not thought to eat vegetable matter (see Van Waerebeek et al. 2004). Stomach contents have included grunts (Pristipoma jubelini) and bongo fish (Ethmalosa fimbriata) (Van Waerebeek et al. 2004).
Incidental mortality in fishing nets and lines is known from at least Morocco, Mauritania, Senegal and Guinea Bissau (Van Waerebeek et al. 2004). Although such mortality has not been assessed properly anywhere in the species’ range, it probably occurs in most or all areas and is considered the most serious immediate threat to the species.
Some Atlantic Humpback Dolphins are probably taken directly for food by local people (Van Waerebeek et al. 2004). The fishing communities of Joal and Fadiouth in Senegal have a tradition of hunting cetaceans, and others in the Petite Côte were known to hunt dolphins until at least 1996 (Van Waerebeek et al. 2004). Past and present levels of these captures, and their potential impacts on subpopulations, remain unknown (Reyes 1991). The most recently documented interaction in Senegal was in November 1996, when three dolphins were found together, each with a piece of netting tied around the tailstock on a beach of Sangomar Island in the Saloum delta (Van Waerebeek et al. 2004).
Habitat destruction, boat strikes, and environmental contamination are additional potential threats, although generally little is known about them. In Senegal there has been a permanent reduction of mangrove areas to facilitate the extension of rice culture and exploitation of forests, especially in the Fathala area. Habitat destruction and degradation may be significant factors affecting the species’ status given its nearshore distribution and the high human population densities, associated with agricultural and industrial development, in some areas. These problems will contribute to fragmentation of the dolphin population. Offshore oil exploration and development are underway in at least Gabon and Angola. Excessive fishing of neritic fish stocks in parts of West Africa also may have reduced food availability for these dolphins (Van Waerebeek et al. 2004).
The species is listed in Appendix I of CITES and Appendix II of CMS.
These dolphins are a high priority for research and conservation because of their restricted and apparently fragmented range, narrow ecological niche, apparently low numbers, and continuing threats (IWC 2003, Reeves et al. 2003, Van Waerebeek et al. 2004).
|Citation:||Reeves, R., Collins, T., Jefferson, T.A., Karkzmarski, L., Laidre, K., O’Corry-Crowe, G., Rojas-Bracho, L., Secchi, E., Slooten, E., Smith, B.D., Wang, J.Y. & Zhou, K. 2012. Sousa teuszii. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 10 December 2013.|
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