Sites - Important Bird and Biodiversity Areas (IBAs)
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15o 52.00' East 27o 20.00' South
A1, A2, A3, A4i
0 - 1,488m
Year of IBA assessment
Site description The Sperrgebiet, or forbidden territory, lies in the south-western corner of Namibia. Famous for its diamonds, the area is bordered by the Orange river in the south and the Atlantic Ocean to the west. The northern boundary was established at the 26°S line of latitude, whereas the eastern boundary parallels the coast c.100 km inland. The IBA includes the Namibian side of the Orange river mouth (adjacent to IBA ZA030). Largely uninhabited, the only towns in the Sperrgebiet are Oranjemund on the southern coast and Lüderitz on the northern coast. The Sperrgebiet is an extremely arid zone, encompassing the northern extremity of the winter-rainfall portion of the Namib desert. It is the windiest region in southern Africa. The only permanent water in the area is the perennial Orange river. The northern coastal plain is rocky and holds various sandy bays; the southern shores, intensively mined for diamonds, are reconstituted sandy beaches. The major part of the remaining area comprises sand and gravel-plains with low isolated hills. In the centre and north of the park, dune sand and sand-sheets predominate, the most prominent area being Obib dune-field which rises to 500 m. Several rocky ranges, low mountains and inselbergs are found scattered throughout the park.
Various vegetation-types are found, including coastal zone vegetation, which consists of hummocks in sandy areas, which stabilize dunes and form barriers to sand movement. Lichens, such as Xanthoria, are found on the numerous rocky outcrops and on dead Salsola plants. The central sand-plains lie between 300 and 600 m and are covered by dune fields and coarse sands that are driven inland by southerly prevailing winds, which are a dominant feature of this region. The more elevated eastern sand-plains consist predominantly of gravel-plains with one permanent dune system north-east of the Klinghardtberg. The rocky outcrops and inselbergs receive higher precipitation and more fog moisture and have a more diverse flora than the surrounding areas. The Aurusberg supports the highest diversity and density of plants in the Sperrgebiet. The linear Orange river in the south supports dense riverine woodland.
Key Biodiversity See Box and Tables 2 and 3 for key species. This extremely arid area holds a depauperate avifauna of only some 110 bird species, many of which are restricted to the Namib–Karoo biome. However, the inclusion of the Orange river mouth boosts the species total to 251 bird species. The recently recognized Certhilauda barlowi is virtually restricted to the Sperrgebiet, which holds over 80% of its tiny 18,000 km² range. The newly recognized Certhilauda curvirostris just occurs in this region, in low numbers. Haliaeetus vocifer is common along the Orange river, where Phragmacia substriata and Francolinus capensis reach the northern limit of their distributions. The Orange river mouth is particularly species-rich (64 wetland species) and in the past has been the sixth most important wetland (for total abundance: 26,000 birds) in southern Africa. It is one of Namibia’s four Ramsar Sites. Bird numbers and species richness increase along its length from east to west, and the mouth alone holds four times as many birds as the total river along the Namibian border.
Several characteristic species of the Namib–Karoo biome occur in the Sperrgebiet, including Eupodotis vigorsii, Eremopterix australis, Cercomela schlegelii, C. sinuata, Euryptila subcinnamomea and Sylvia layardi. Other arid-zone species which are found within the area include Neotis ludwigii, Certhilauda erythrochlamys, Ammomanes grayi, Eremalauda starki, Cercomela tractrac and Serinus alario.
Non-bird biodiversity: The Sperrgebiet is characterized by high levels of endemicity in various taxa. At least 45 plant species are endemic to the Sperrgebiet and thus Namibia, but many more are endemic to the Sperrgebiet and Richtersveld of South Africa. The coastal zone holds the spectacular endemic plant Sarcocaulon patersonii. Aurusberg holds several endemic plants that are exclusive to this peak. In the Orange river valley, the inselbergs Skilpadberg and Swartkop hold several plants endemic to the lower Orange river, including Aloe ramosissima (VU) and A. gariepensis. Endemic and near-endemic amphibians include Breviceps macrops, B. namaquensis, Strongylopus springbokensis and a recently discovered, and as yet undescribed, toad Bufo. Endemic and near-endemic reptiles include Homopus sp., Bitis schneideri, B. xeropaga and two legless burrowing skinks. The Sperrgebiet comprises about 40% of the global range of the small mammal Bathyergus janetta. Cephalorhynchus heavisidii (DD), endemic to the south-west coast of Africa and probably one of the world’s rarest dolphins, is fairly common off the Sperrgebiet coast.