Olifants River Estuary

Site description

Lying approximately 250 km north-west of Cape Town, the Olifants River estuary is one of only four perennial estuaries on the west coast of southern Africa and covers an area of c. 2 000 ha. The nearest towns are Lutzville and Vredendal, 23.5 km and 42 km east of the estuary respectively. The small subsistence village of Papendorp lies along the estuary’s western bank. The Olifants River catchment, which spans some 46 625 km², is the second largest in South Africa; only the Orange River catchment is larger. The Olifants River rises in the Agter Witzenberg, a plateau lying between the Winterhoek (2 100 m a.s.l.) and the Skurweberg (1 850 m a.s.l.) mountains. As the river runs north it is flanked by the Cedarberg (IBA SA101) to the east and the Olifantsrivierberge and Swartberge to the west. It passes through an intensively irrigated fruit-farming district before it is joined by the Doring River, which contributes much of the flow and silt that enter the estuary. Jointly this catchment is referred to as the Olifants–Doring river system.

The extent and salinity of the estuary are highly variable. The catchment lies within a winter-rainfall area and in winter the freshwater flow is strong, with plumes of red water extending into the ocean for several hundred metres. In summer, however, sea water penetrates the estuary, and saline water has been recorded nearly 32 km upstream. A point 10.5 km upstream is normally regarded as the upper limit of the estuary. Adjacent to Papendorp, an island is encompassed by two estuarine arms that re-join to form the permanently open mouth.

Extensive salt marshes flank the estuary on both sides. On the northern bank of the mouth a steep rocky shoreline rises to form a gravel terrace. The southern bank consists of sandy beach and vegetated dunes, and can shift with floods and high seas. This movement is mitigated to a small degree by the vegetated dunes. Aquatic and semi-aquatic vegetation covers relatively large areas near the mouth. Floodplain vegetation, which is occasionally inundated, grows on the river terraces above the salt marshes. Reedbeds consisting predominantly of Scirpus littoralis and Phragmites australis line the banks of the river upstream of Olifantsdrif. The terrestrial vegetation on higher ground is of considerable interest, as it is one of the few areas on the west coast where karroid vegetation reaches the shoreline. After spring rains the veld breaks out in mass displays of flowers.

Birds

Approximately 127 bird species have been recorded at the Olifants River estuary and its environs, at least 60 of which are waterbirds. The estuary may regularly support more than 15 000 waterbirds, but this is difficult to determine as the current regular counts do not include the large mud banks exposed on the northern bank of the estuary at the mouth or the backwater on the northern bank opposite Ebenhauser. Current data show the highest count to be just over 2 500 birds.

The estuary frequently holds threatened species such as Lesser Flamingo Phoeniconaias minor, Greater Flamingo Phoenicopterus roseus, Caspian Tern Sterna caspia, African Marsh Harrier Circus ranivorus, Black Harrier C. maurus (a pair of which breeds regularly at the estuary) and African Black Oystercatcher Haematopus moquini. Great White Pelicans Pelecanus onocrotalus that breed at Dassen Island IBA (SA109) use the estuary as a primary foraging and roosting area during the non-breeding season. Young African Black Oystercatchers probably also use the estuary as a staging post when they move between the south-western Cape and Namibia. Damara Tern Sterna balaenarum occasionally forages in the estuary. Large numbers of South African Shelduck Tadorna cana, Curlew Sandpiper Calidris ferruginea and Hartlaub’s Gull Chroicocephalus hartlaubii use the estuary when conditions are suitable. Although waterbird numbers are not exceptional, the estuary acts as a vital staging point for both Palearctic migrants and flamingos between the Orange River mouth (IBA SA030) and the important wetlands to the south and east, such as the Berg River wetlands (SA104), Langebaan Lagoon (SA105), Rietvlei (SA111) and the Wilderness–Sedgefield Lakes Complex (SA114).

The vegetation surrounding the estuary is suitable for many Namib-Karoo biome-restricted assemblage and other arid-zone species, including Karoo Korhaan Eupodotis vigorsii, Grey Tit Parus afer, Karoo Lark Calendulauda albescens, Tractrac Chat Cercomela tractrac, Karoo Chat C. schlegelii, Sickle-winged Chat C. sinuata and Black-headed Canary Serinus alario. These species do not occur in large enough numbers to meet the IBA criteria and have been removed from the trigger species list. Namaqua Warbler Phragmacia substriata occurs in the acacia thickets and the reedbeds along the river margin, and Cape Long-billed Lark Certhilauda curvirostris is also found here, particularly along the rocky northern bank of the estuary.

IBA trigger species

Globally threatened species are Lesser Flamingo (177 individuals), Ludwig’s Bustard Neotis ludwigii, Southern Black Korhaan Afrotis afra, Black Harrier, African Black Oystercatcher (21 individuals) and Chestnut-banded Plover Charadrius pallidus (69 individuals). Regionally threatened species are Caspian Tern (8 individuals), Great White Pelican (430 individuals), Greater Flamingo (209 individuals) and African Marsh Harrier.

Common biome-restricted species include Cape Spurfowl Pternistis capensis and Cape Bulbul Pycnonotus capensis, while Southern Black Korhaan is locally common in specific habitats. Uncommon species in this category include Ludwig’s Bustard and Karoo Lark. Congregatory species of which more than 1% of the population is present at this site is Hartlaub’s Gull (450 individuals); and 0.5% of the population is present are South African Shelduck (93 individuals) and Curlew Sandpiper (1 108 individuals).

The individual figures have been extracted from CWAC data and indicate the maximum number of birds of a species encountered in a single count. It must be noted that this count covers only the southern shore of the estuary. Substantial mud-flat habitat occurs on the northern shore, so the above numbers may grossly underestimate the abundance of certain species, notably the two flamingos.

Other biodiversity

The Olifants River system has a remarkable incidence of endemism among freshwater fish. It is the only river system in southern Africa to have more than six taxa restricted to its catchment; eight species are found only in the Olifants River catchment. None of these endemics occur in the estuary, although it does hold a rich assemblage of aquatic invertebrates, numbering more than 45 species. It is a vital nursery area for fish such as white steenbras Lithognathus lithognathus and southern mullet Liza richardsonii.

The IBA lies in the centre of the ranges of many reptiles endemic to Namaqualand, most of which have been recorded in the vicinity and are probably present in the terrestrial Succulent Karoo vegetation matrix surrounding the wetland. These species include speckled padloper Homopus signatus, Namaqua dwarf adder Bitis schneideri, many-horned adder B. cornuta, coastal legless skink Acontias litoralis, Cuvier’s blind legless skink Typhlosaurus caecus, striped dwarf burrowing skink Scelotes sexlineatus, Knox’s desert lizard Meroles knoxii, large-scaled girdled lizard Cordylus macropholis, Namaqua plated lizard Gerrhosaurus typicus, Namaqua dwarf chameleon Bradypodion occidentale and Austen’s thick-toed gecko Pachydactylus austeni.

More widespread southern African endemics that have been recorded in the district may also occur at the site. They include Karoo toad Bufo gariepensis, angulate tortoise Chersina angulata, tent tortoise Psammobates tentorius, Cape cobra Naja nivea, striped legless skink Acontias lineatus, spotted sand lizard Pedioplanis lineoocellata, Karoo girdled lizard Cordylus polyzonus, southern rock agama Agama atra, southern spiny agama A. hispida, giant ground gecko Chondrodactylus angulifer, western Cape thick-toed gecko Pachydactylus labialis, Weber’s thick-toed gecko P. weberi and Marico thick-toed gecko P. mariquensis.

In 2012 a brown hyaena Hyaena brunnea was found killed on the main road just east of the estuary. It is likely that a small population still exists in this area, especially towards the north of the estuary.

Conservation issues

Threats

Like many of South Africa’s estuaries, the Olifants River estuary is threatened primarily by changes to water-flow regimes and water quality as a result of water abstraction and pollution. Incorrect water- and sediment-flow dynamics can destabilise the estuary, while pollution can reduce habitat quality for the bird species. The Bulshoek and Clanwilliam dams, built in 1919 and 1932 respectively, are already in place on the Olifants River. If additional dams were to be built, river flow in summer would be further attenuated, resulting in greater penetration of sea water upstream and changes to the river ecology. The Clanwilliam Dam is due to be raised in 2015 to address water needs in the area, and the consequent changes to water-flow regimes and water volumes could negatively impact the ecology of the estuary. Flow rates and flow regimes are currently being monitored to acquire a baseline for comparison once the dam wall has been raised.

Mineral exploitation, particularly sand mining for manganese and the commercial production of salt, also poses a significant threat to the estuary. These practices can lead to an irreversible loss of habitat or reduction in habitat quality. Marine diamond mining occurs north of the estuary, both at sea and on land. The salt flats to the south of estuary are being mined by means of traditional salt-mining techniques, which have been identified as the least detrimental to the area and are the preferred methods for the local community. An additional threat further upstream is the transporting of minerals from mines down to Saldanha Bay. There have been incidents of trucks overturning and losing their loads on the Lutzville low-level bridge, which lead to the pollution of the Olifants River and estuary downstream.

Disturbance of the sensitive estuarine habitat, foredunes and beach areas by the driving of quad bikes and 4x4s off-road, as well as illegal camping on the mudflats and other sensitive areas, can disturb feeding birds and lead to loss of habitat or reduction in habitat quality due to the destruction of the sensitive vegetation. The expansive floodplain is criss-crossed with vehicle tracks, and off-road vehicles have already damaged the vegetation extensively. The terrestrial vegetation has become drastically overgrazed in places, mainly by goats and sheep. The passage of vehicles and pedestrians should be severely restricted, especially on the floodplain and salt marshes. A number of government agencies and other partners are working together during the tourist season to try to reduce the number of vehicles driving on the sensitive vegetation.

Conservation action

There is limited conservation action at the estuary due to the lack of a formal conservation designation, such as a nature reserve; such formal protection status should be pursued. Although the mouth meets the criteria for recognition as a Ramsar wetland of international importance, the site does not currently have Ramsar status, and this should also be pursued.

The Olifants Estuary Management Forum, an active group comprising stakeholders with links to the estuary, is addressing the key threats to the estuary. It is also lobbying government to gain formal protection status for the site. The Olifants River estuary currently enjoys good flow volumes and water quality and this should be maintained in order to provide the habitat necessary for the IBA trigger bird species.

CapeNature in conjunction with the local community and relevant departments are looking at the feasibility of establishing a formal nature reserve in the area. This could be achieved by transferring some of the existing State land to CapeNature for formal protection, as well as incorporating community land along the southern boundary of the estuary in some form of Biodiversity Stewardship agreement. The process is under way and will need buy-in from various partners to make it a reality.

Related webpages

None.

Contact

If you have any information about the IBA, such as a new threat that could impact on it, please send an e-mail to iba@birdlife.org.za or call BirdLife South Africa +27 (11) 789 1122.

Page last updated

Wednesday, 11 February 2015