Humpback dolphins are members of the genus Sousa. They are most often found very close to the shore, typically in small schools of less than 10 dolphins. They are medium sized dolphins, measuring up to 2.5m long, characterized by the conspicuous hump and elongated dorsal fin found on their backs. The pectoral fins are considerably small and the tail flukes have a well-defined median notch.
Taxonomy and Distribution
There is strong support for the recognition of 4 species of humpback dolphin: Sousa teuszii (Atlantic humpback dolphin) occurring in the Atlantic Ocean of West Africa, S. sahulensis (Australian humpback dolphin) occurring from North Australia throughout Southeast New Guinea, S. chinensis (Indo-Pacific humpback dolphin) occurring from Myanmar (Burma) throughout Southeast Asia, and S. plumbea (Indian Ocean humpback dolphin) occurring in the Indian Ocean from South Africa to Myanmar (Burma).
In South Africa, there are two populations of humpback dolphins with some level of genetic differentiation; one occuring between the eastern side of False Bay up to Algoa Bay and another on the Kwazulu Natal coast eastward of Mzamba.
Currently the IUCN Red List still considers S. chinensis and S. plumbea as one species and lists them as 'Near threatened' because globally they are thought to number only 10,000 adult individuals. However, when considering S. plumbea separately, the species is considered internationally ‘Vulnerable’.
Within South African waters, rough estimates indicate the presence of less than 1,000 individuals. Consequently, and based on a number of other criteria, they were recently listed as ‘Endangered’ during the South African National Red List Assessment. They are considered the country’s most endangered marine mammal.
As humpback dolphins inhabit a narrow strip of shallow, inshore water and remain mostly within 400 meters of the shore and/or in waters less than 15m deep, their habitat often overlaps with human activities making them particularly vulnerable to human induced pressures such as habitat loss, pollution, shark nets and fishing activities.
Adapted from Mendez et al. 2013
Featured illustration by Uko Gorter
Picture copyright R. Logston