Chondrichthyes (cartilaginous fish, including sharks, rays and chaemeras) >

Habitats of cartilaginous fish off the coast of southern Africa

The seas of southern Africa support a varied and diverse fauna of cartilaginous fishes, which can be roughly classified by habitat relative to the continental land mass. The majority of species occur on and around the edges of the continental shelves, from the seaside to approximately 200 m, but the area also has a varied upper continental slope fauna of deepwater sharks, rays (mostly skates), and chimaeras ranging from 200 to over 1000 m depth, and a less diverse oceanic fauna of widespread sharks and rays, which occur in the great ocean basins mostly in the top few hundred meters, but in some species reach the ocean floor. Southern Africa features a large number of cartilaginous fishes found nowhere else, the endemics. Others, particularly tropical shelf, oceanic, and deep-slope species, are wide-ranging, and occur in the Atlantic, western Indian Ocean, Indo-Pacific, or are circumtropical; some cool-water sharks are amphitemperate, and are absent from the tropics although widespread in temperate waters of the northern and southern hemispheres. Some rays have a more limited amphitemperate range, and occur in the north Atlantic and off the west coast of southern Africa.

Shelf cartilaginous fishes have a complex composition off southern Africa: the temperate-water species divide into wide-ranging amphitemperates, Atlantic amphitemperates, and restricted endemic species; the tropical species have major components from the Western Indian Ocean, Indo-West Pacific, and circumtropical species, and additional components from the Eastern Atlantic and Eastern Hemisphere. A few sharks and rays have a wide range from European seas through tropical West Africa to southern Africa. Several species show a bicoastal distribution, and are present off Namibia and the east coast but are missing from off the western Cape.

Shelf and oceanic cartilaginous fishes are much influenced by the two major current systems off southern Africa. The west coast, washed by the cold Benguela current, supports a temperate, depauperate fauna. The southern and southeast Cape coast has a richer temperate fauna with most of the west coast species and additional temperate endemic cartilaginous fishes. Mozambique and Natal are washed by the warm Agulhas current and have many tropical shelf sharks and rays, but southern Natal and Transkei are a transitional zone to the temperate eastern Cape fauna. In the summer, particularly in years with an "el Nin~o" flux of warm water, Natal sharks and rays follow the current to the eastern and southwestern Cape. A tropical shelf species, the Zambezi shark, has a broad salinity tolerance and regularly ascends tropical rivers and occurs in tropical lakes; it has been taken in rivers in Kruger Park and in Mozambique. Only one chimaera, the St Joseph, occurs on the shelf in temperate waters in southern Africa, but also extends onto the uppermost slope.

The oceanic cartilaginous fish fauna is dominated by tropical sharks, with lesser numbers of South Atlantic temperate-tropical sharks and a minor amphitemperate component. Oceanic sharks are wide-ranging and have no local endemics; some visit the shelf but normally occur far out at sea. Some of these give birth to their young offshore, which then migrate outwards to the open ocean. They include both the smallest and largest of sharks, as well as a variety of near-surface and deep-water species. Tropical oceanic sharks show a similar tendency to shelf sharks and rays in ranging southwestwards in the summer, and some of these turn up as far south as Cape Point. Oceanic rays are few, and include the unique pelagic stingray and possibly the manta. No chimaeras are oceanic.
The deep slope cartilaginous fishes include wide-ranging bottom species that cross the temperate-tropical boundary because of the generally cold waters of the slope in both temperate and tropical areas. There are, however, numerous slope endemics, and important differences between the deep-slope cartilaginous fish fauna of Natal and southern Mozambique and that off the western Cape. Some slope species are virtually circumglobal in all temperate and tropical seas, others are broadly shared with other regions, while some are endemic. Off the southwestern Cape there is a broad faunal transition zone at 200 to 600 m depth on the hake fishing grounds, with an intermediate cartilaginous fish fauna between the outer shelf and deep slope faunas. The slope ray fauna is dominated by skates, with a few species of stingrays (east coast) and electric rays. Most southern African chimaeras occur on the continental slope.

Text by Leonard J.V. Compagno, David A. Ebert and Malcolm J. Smale

  Iziko Museums of Cape Town, 2008

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