June 22, 2024

Distribution, Status, and Biology of the Atlantic Humpback Dolphin, Sousa teuszii (Kükenthal, 1892)


Koen Van Waerebeek, Linda Barnett, Almamy Camara, Anna Cham, Mamadou Diallo, Abdoulaye Djiba, Alpha O. Jallow, Edouard Ndiaye, Abdellahi O. Samba Ould Bilal, and Idrissa L. Bamy


Abstract: The distribution, status, and biology of the Atlantic humpback dolphin (Sousa teuszii) is critically reviewed, and results of recent research are discussed. The species’ known distribution limits are, in the north, Dahkla Bay (23º50’N), Western Sahara, and in the south, Tombua (15º47’S), southern Angola. Its habitat is predominantly inshore coastal and estuarine, over soft-sediment bottoms. There is no evidence that it might occur beyond the brackish waters of estuaries into a riverine, fresh-water habitat. There are no records for the Senegal, Casamance, and Niger Rivers. A total of eight stocks are provisionally discerned for management purposes. Six of these are confirmed-contemporary (based on recent records), including Dahkla Bay, Banc d’Arguin, Saloum-Niumi, Canal do Gêba-Bijagos, South Guinea, and Angola. Two stocks, the Cameroon Estuary and Gabon, are historical, and new field-work needs to confirm their current presence. No inference is made on degree of reproductive isola- tion and biological population status of any named stock. The potential existence of a western Togo stock is currently under study. Nine coastal states, including Morocco (Western Sahara), Mauritania, Senegal, The Gambia, Guinea-Bissau, Guinea-Conakry, Cameroon, Gabon, and Angola are confirmed range states. While historically distribution may have been quasi-continuous over the species’ range, indications of contemporary distribution gaps are emerging. Ongoing monitoring of cetacean takes in coastal fisheries off western Ghana, and experimental whale-watching sorties in Bénin have not yielded a single record. The species has either become rare through human-related pressures or, less likely, it never lived there. For most other areas there is little, if any, information due to the lack of research. No abundance estimates are available for any stock. The smallest extant stock may be the northernmost, Dahkla Bay. The aggregated number of individuals seen in four sightings was 28 individuals. The healthiest known stock seems to be Canal do Gêba-Bijagos (in Guinea-Bissau), which may number at least several hundred, if not more. How extensively humpback dolphins range in-between core areas is unclear, but only a few individuals have been encountered. There is no evidence for seasonality in presence, nor for seasonal movements. Regular cross-border movements between the Saloum Delta (Senegal) and Niumi National Park (The Gambia) technically qualifies S. teuszii as a “migratory species” under the Conservation of Migratory Species (CMS) Convention. Fisheries-related mortality is thought to be significantly higher than the few recorded takes suggest because it is very rarely reported. Combined with habitat encroachment, such losses may threaten the long-term survival of some stocks.


Document Type: Research Article

DOI: 10.1578/AM.30.1.2004.56

Page Numbers: 56-83

Info SKU: Vol__30__Iss__1__VanWaerebeek Category: