The southern African region is bounded in the north by the watershed of the Cunene, Okavango and Zambezi River systems and by the African coast for the rest. Physiographically there is a low-lying coastal band extends around the region, broadest in Mocambique, and bounded on the interior by an escarpment that varies in nature from abrupt and steep mountains to broken ranges and hills. The interior forms an extensive plateau, elevated around the edges and basin-like in the central parts.
The rivers of southern Africa are broadly divided into two classes – a few large complex basins draining the interior that break through the escarpment in defined gorges and tracts, with a large number of smaller systems draining from the escarpment to the coast. Major basins include, from east to west, the Zambezi, Save, Limpopo, Incomati, Phongolo, Thukela, Kei, Sundays, Gamtoos, Berg, Olifants, Orange and the Cunene. The Okavango is an endorheic system that terminates in a large inland Delta with a single outlet into the Magadigadi Pans of the Kalahari basin. At various times in the past there existed a large shallow inland lake in this basin. Apart from a few small coastal lakes there are no major lakes other than Lake Malawi in the region.
Several major man-made lakes occur on the large river systems including Lake Kariba, Lake Cahorra Bassa on the Zambezi, and Lake Gariep and Lake Vanderkloof on the Orange. Most rivers are highly regulated by dams and a recent estimate indicates that only 4% of the river reaches in South Africa are "free-flowing". Two over-arching climate systems ‚Äì in the northern sectors a warm tropical or warm temperate summer rainfall system and in the south-west and southern extremities a temperate winter rainfall belt. Rainfall varies from as high as 1400mma–¬π in the extreme north-west and south west, to under 250mma–¬π in the western Namib and Kalahari basins.
With a wide variety of habitats and ecoregions, southern Africa is remarkably rich in plant, invertebrate and vertebrate biodiversity. The Cape Floral Kingdom is a distinctive and spectacular component of the coast and mountains of the southern and south-west areas. Afromontane forests occur in patches along the eastern montane archipelago from Malawi to the Cape. Grass and shrublands dominate the more southerly and high-altitude inland plateaus with savannah bush and woodlands found around the eastern coastal and tropical inland belts.
Recent estimates of freshwater dependent invertebrates include few molluscs (45) and crustaceans (27), and around 200 insects from southern Africa. The aquatic dependent vertebrate fauna of the region includes 197 frogs, 7 reptiles, around 428 waterbirds and 15 mammals, all relatively well described in field guides and other specialized books.
The current estimate of freshwater fishes from the region (excluding Lake Malawi/Nyassa) is around 350, including those tolerant of brackish water. The tropical fauna is richest and the temperate fauna restricted by a broad continental-peninsular effect. The long isolation of the temperate fauna results in a high endemicity and range restrictions that increase vulnerability considerably.
The Mormyridae, Cyprinidae, Alestidae, catfishes of various families (siluriforms), Poeciliidae, Nothobranchiidae and the Cichlidae dominate the tropical families with a number of other families, such as the kneriids, anabantids, mastacembelids and Protopteridae but contributing to the character of the biodiversity.
Cyprinidae, Austroglanididae, Anabantidae and Galaxiidae are the only primary freshwater fish families from the temperate far south (Cape). Although this diversity is comparatively depauperate, it is none-the-less of considerable scientific interest because of its high endemicity and unique character. For example the temperate African cyprinids are 80% polyploid including hexaploids (the genus Labeobarbus) tetraploids (Pseudobarbus and a lineage of barbine species currently still in the genus "Barbus" ). The genus Pseudobarbus is under revision and several undescribed species have been exposed through genetic analysis.
The African Galaxiidae are currently being extensively revised and indications are of a far greater diversity than the single species currently reported. Much of this diversity is highly restricted in distribution and many species are threatened. The phylogenetic relationships of the small catfish family Austroglanididae is proving hard to define. Likewise the anabantid genus Sandelia is now known to be more diverse than the two species recognized for many years.
The IUCN assessment of southern Africa completed in 2009 indicated that 40 (11%) species out of 355 assessed are globally threatened (i.e. either Critically Endangered, Endangered or Vulnerable). 235 (66%) are of Least Concern and 71 (19.6%) are Data Deficient. The main threats to freshwater fishes are alien fish, and habitat destruction, with a lesser extent of impact arising from pollution, utilization and erosion of genetic integrity.
Most focused conservation activities have taken place in South Africa but actions to improve fisheries knowledge and practice and to protect certain specific sites such as Aigamas cave and the Lake Guinas sinkhole in Namibia as well as research and faunal surveys have also occurred in other countries in the region. Active conservation efforts have naturally focused on the threat from alien fishes whilst indirect efforts, aimed at habitat and catchment environmental conservation that positively improves fish status, have probably been of considerably greater affect. Conservation policies have been developed and in a few cases translated into legislation. The South African Water Act (1998) was completely revised to include provisions for water for river functioning for the first time. Efforts to mitigate the impact of alien fishes have also been made by both government departments and the private sector.
Especially noteworthy has been the effort to provide alternative fishing of indigenous species in place of alien trout and bass. Research on the biology and ecology of potential indigenous angling species and threatened species also has improved approaches to the conservation of fishes. A research programme on fish passways has resulted in much improved understanding of the movement of indigenous fishes and the role and design of fish passways as conservation tools. The pressures on water resources from a rapidly increasing urban population in the various countries of the region is aggravating aquatic environmental degradation in many places. Mining and the long-term impacts of mining of water quality is a great concern in South Africa. A recently published atlas of freshwater ecosystem priority areas summarises graphically the state of rivers in the country. The Atlas provides maps to support sustainable development of water resources and is an important step towards the long-term conservation of freshwater ecosystems in South Africa.
Darwall, W.R.T., Smith, K.G., Tweddle, T. and Skelton, P. (eds) 2009. The Status and Distribution of Freshwater Biodiversity in Southern Africa. Gland, Switzerland: IUCN and Grahamstown, South Africa: SAIAB. viii+120pp. Available here
Marshall, B. 2011.The Fishes of Zimbabwe and their Biology. (Smithiana Monograph 3). The South African Institute for Aquatic Biodiversity, Grahamstown, South Africa.
Skelton, P. 2001. A Complete Guide to the Freshwater Fishes of Southern Africa. Struik Publishers, Cape Town.
Paul recently retired as Managing Director of South African Institute for Aquatic Biodiversity after 16 years in the position. Prior to that (1984-1995) he served as Curator of Freshwater Fishes at the JLB Smith Institute of Ichthyology (before it became SAIAB), and also as Curator of Fishes at the Albany Museum from 1972-1983. His research career mostly concerned the taxonomy of southern African freshwater fishes and their conservation. He evaluated the threatened species and wrote the South African Red Data Book for fishes in 1977 and 1987.
He has conducted fieldwork and projects throughout southern Africa, and has travelled extensively to the major international museums with African freshwater fish holdings. He has been a member of the IUCN SSC/WI Freshwater Fish Specialist Group since its beginnings and was the project leader for the recent southern African assessment as part of the Pan-African assessment completed in 2011.