Berg River Estuary

Site description

Covering an area of c. 6 621 ha, the Berg River Estuary IBA is located 140 km north of Cape Town. The town of Laaiplek lies directly north of the river mouth, and 6 km upstream is the town of Velddrif. The Berg River forms one of only four perennial estuaries on the arid west coast of southern Africa. The IBA includes only the lower Berg River, but this system is reliant on the management of its catchment, which extends c. 160 km upstream from the river mouth to its source in the Franschhoek and Drakenstein mountains. From its source, the river flows through the towns of Paarl and Wellington before arching west and meeting the Atlantic Ocean at Laaiplek. The lower reaches of the river meander over very flat country so that, on average, the riverbed falls only 1 m in the last 50 km.
The ecological functioning of the estuary is determined by seasonal changes in river discharge and consequent changes in salinity and turbidity. In winter, when the estuary is flooded by muddy, fresh river water, most of the marine species disappear. As the floods recede in spring, the salinity increases and the system shifts back to a predominantly marine environment. When the shallow pools on the floodplain start to dry out, also in spring, there is a marked increase in the number of birds the wetlands support.

The floodplain encompasses eight major wetland types in addition to the river channel: ephemeral pans, commercial salt pans, reed marsh, sedge marsh, salt marsh, halophytic floodplain, xeric floodplain and intertidal mudflats. The ephemeral pans comprise monospecific stands of Juncus maritimus in summer. After winter rains, abundant Aponogeton distachyos appears, along with other species. The commercial salt pans comprise a salt desert generally lacking macrophytes.

The reed marsh is based on saturated, silt-rich soils, mainly on inner riverine beds. Although the sedge marsh is dominated by Juncus kraussii, smaller sedge species are also present in a varied mosaic that includes non-sedge species. The salt marsh experiences tidal flooding by saline water twice a day and is dominated by fleshy-leaved salt-tolerant species. Halophytic floodplain vegetation consists primarily of Sarcocornia pillansii, which may be interspersed with open patches that are colonised by ephemeral growth in spring. The xeric floodplain vegetation comprises a great diversity of xerophytes. The floodplain can be inundated for up to two weeks at a time when the Berg River floods. The terrestrial vegetation within the catchment has been altered dramatically and consists primarily of an agricultural matrix, with patches of Strandveld near the coast and a mosaic of invasive alien Acacia species and indigenous fynbos in the mountainous interior.

Birds

Since 1975, approximately 250 bird species have been recorded on and adjacent to the lower Berg River, 127 of which are waterbirds. The most important habitats for foraging birds are the estuarine mudflats and ephemeral floodplain pans, while for breeding the riparian marshes and the commercial salt pans are key. On average, more than 12 000 non-passerine waterbirds occur at the estuary during summer and 6 000 non-passerine waterbirds during winter. In combination, the estuary and floodplain regularly support more than 20 000 birds; in December 1992 a count of both habitats yielded 46 234 waterbirds.

Total waterbird numbers are strongly influenced by the influx of Palearctic migrants and more than 8 000 migrant waders, especially Curlew Sandpiper Calidris ferruginea and Little Stint C. minuta, are regularly present in summer. Among resident waders, Kittlitz’s Plover Charadrius pecuarius is most abundant, but large numbers of the Afro-tropical resident population of Pied Avocet Recurvirostra avosetta are also present when conditions are favourable. The open mudflats support a small population of African Black Oystercatcher Haematopus moquini.

The commercial salt pans hold many breeding species, including very large numbers of Caspian Tern Sterna caspia, incorporating up to 13% of the South African breeding population. Greater Flamingo Phoenicopterus roseus and Lesser Flamingo Phoeniconaias minor have attempted to breed at the salt pans in recent years and Chestnut-banded Plover Charadrius pallidus breeds here regularly. Kelp Gull Larus dominicanus and Hartlaub’s Gull Chroicocephalus hartlaubii are resident at the Berg River and occur in large numbers, breeding in mid-summer and early winter respectively. Swift Tern Thalasseus bergii breeds here sporadically. Large mixed-tern roosts are occasionally seen on the floodplain and the small islands in the middle estuary. Substantial numbers of Great White Pelican Pelecanus onocrotalus occur regularly on the lower Berg River, which is a key foraging and roosting area for the Dassen Island (IBA SA109) breeding population during the non-breeding season.

Great Crested Grebe Podiceps cristatus and Black-necked Grebe P. nigricollis breed occasionally. South African Shelduck Tadorna cana uses the estuary in large numbers as a moulting site and also breeds regularly. Yellow-billed Duck Anas undulata, Cape Teal A. capensis, Cape Shoveler A. smithii and Red-knobbed Coot Fulica cristata breed in the inundated salt marshes in the upper estuary. This area is also one of the few remaining breeding sites for Greater Painted-snipe Rostratula benghalensis in the Western Cape.

A large heronry c. 1 km west of the Kersefontein farmhouse is known to have existed for the past 300 years. It holds 13 breeding species, including substantial numbers of Grey Heron Ardea cinerea, Black-headed Heron A. melanocephala, Western Cattle Egret Bubulcus ibis, Yellow-billed Egret Egretta intermedia and African Spoonbill Platalea alba, as well as Glossy Ibis Plegadis falcinellus, which appears to be increasing. The reed marsh immediately adjacent to the floodplain is important for breeding African Marsh Harrier Circus ranivorus, especially below Die Plaat. African Fish Eagle Haliaeetus vocifer and an isolated European Bee-eater Merops apiaster population occasionally breed along the river. There is a significant roosting site for four of South Africa’s cormorant species – Crowned Phalacrocorax coronatus, Cape P. capensis, Bank P. neglectus and White-breasted P. lucidus – in the area, which also provides a night roost for certain species, with estimates of up to 60 000 Cape Cormorants coming in to roost in the evenings, as well as significant numbers of different tern species.

The numbers of Cape, Bank and Crowned cormorants have reduced significantly and it is suggested that the density of wader species using the area is also decreasing year on year due to alterations in habitat quality and other disturbances. Of particular concern is the number of species that no longer meet the population limits for the congregatory category of the IBA criteria.

IBA trigger species

Globally threatened species are Cape Cormorant (maximum 1 787 individuals), Crowned Cormorant (maximum 70 individuals), Lesser Flamingo, African Black Oystercatcher, Black Harrier Circus maurus and Chestnut-banded Plover. Regionally threatened species are Greater Flamingo, Great White Pelican, Caspian Tern, African Marsh Harrier, Lanner Falcon Falco biarmicus and Greater Painted-snipe. Biome-restricted species common in the IBA include Cape Spurfowl Pternistis capensis and Cape Bulbul Pycnonotus capensis, while Karoo Lark Calendulauda albescens is locally common.

Red-knobbed Coot (maximum 1 400 individuals) meets the 1% or more congregatory threshold, and African Spoonbill and Chestnut-banded Plover meet the 0.5% or more congregatory threshold. Species that have not met the 1% or more threshold but should be on probation and reviewed in future assessments are Cape Shoveler, Kittlitz’s Plover, Curlew Sandpiper, Pied Avocet, Kelp Gull, Hartlaub’s Gull, Swift Tern, Sandwich Tern Thalasseus sandvicensis and White-winged Tern Chlidonias leucopterus. Species that should be reviewed for the 0.5% or more threshold are Great Crested Grebe, Black-necked Grebe, Little Stint and South African Shelduck.

Other biodiversity

Three endemic, highly localised and threatened reptiles occur on the xeric floodplain of the Berg River: the west coast endemic Gronovi’s dwarf burrowing skink Scelotes gronovii, Kasner’s dwarf burrowing skink S. kasneri and large-scaled girdled lizard Cordylus macropholis. A fourth threatened reptile, Cape sand snake Psammophis leightoni, is also found on the floodplain. The South African endemic sand toad Bufo angusticeps and Namaqua dwarf chameleon Bradypodion occidentale occur along the fringes of the wetland.

Conservation issues

Threats

The principal threat to this estuary stems from inadequate water flow volumes and an unnatural flow regime of fresh water coming down the Berg River from its catchment, due to high levels of water abstraction along the river’s course and to the Berg River Dam. In 1998, water supplied to the Greater Cape Town metropolitan area from the Berg River and additional abstraction for agricultural use had reduced the mean annual run-off of water by 23%. Further reductions are likely to have occurred as a result of the construction of the Berg River Dam, which stores water and supplies it to the growing population of Cape Town. Abstraction at the dam and increased, unregulated abstraction of water along the river’s length have a major impact on the water levels and flow regime of the estuary.

The dam was built so that specific volumes of water could be released at certain intervals in order to maintain the natural flow regime of the river. However, these flow regimes will not entirely mimic a natural system. Winter inundation of the floodplain, either naturally or through controlled releases, is essential for the continued ecological functioning of the floodplain and estuary. Lack of winter flooding may result in the development of hyper-saline conditions and consequent biological sterility on the floodplain. The most important threat to this wetland is therefore further reduction in the mean annual run-off, which would significantly affect seasonal water flow patterns and volumes.

The mean annual run-off may also be reduced by a proposed impoundment upstream of the estuary. In addition, water volumes will almost certainly be diminished by the construction of the Corex steel smelter (Saldanha Steel) and the associated spin-off industries near Saldanha Bay, which will require considerable quantities of water for their operation. It has been proposed that water be abstracted from the Berg River for these purposes. The Saldanha Bay Industrial Development Zone and the associated industries planned for the area may further exacerbate water abstraction issues in this system.

A second threat is hyper-salinity in the estuary, which occurs when the sediments at the river mouth are dredged to allow boats access to what has become a fully constructed harbour in place of the natural estuary and river mouth. Dredging increases the velocity of the tidal flow, the turbidity of the water and the penetration of salt water upstream, and intensifies erosion within the system. The increased penetration of salt water – a result of reduced freshwater flow as well as dredging – changes the ecological character of the estuary, impacting primarily on the vegetation types and invertebrate fauna of the area. Alterations in the plant and invertebrate community in turn impact on the foraging wader and other waterbird species.

Eutrophication of the estuary and wetlands due to the run-off of excess fertilisers and other chemicals from agricultural activities along the Berg River’s course to the sea can have a major negative impact on the ecology of the wetland system. Greater nutrient loading may be another cause of the increase in algal and plant material that seems to be affecting wader foraging habitat. Light, noise and other pollutants from upstream activities, the harbour, salt-mining operations and the urban area can lead to further degradation of the sensitive estuarine environment.

Human activities, such as boating on the river, and disturbance factors from the nearby towns, harbour and factories also pose a threat to the birds of this site. Birds breeding and foraging in the wetlands are likely to be affected and may be forced out of highly disturbed areas. Proposed developments in certain parts of the estuary will also lead to an irreversible loss of habitat and increased disturbance in adjacent areas.

In the terrestrial environment, the occurrence of alien vegetation such as Sesbania punicea and Australian Eucalyptus and Acacia species constitute further threats as they transpire more than indigenous vegetation does and thus use substantially more water. The aquatic water hyacinth Eichhornia crassipes has invaded and poses a significant threat to the open-water system and floodplain, changing the character of the tidal mudflats that provide essential foraging habitat for migratory and resident shorebirds and waders.

Conservation action

The permanent waterbody and intertidal mudflats are owned by the State and managed by CapeNature in conjunction with the local municipality. The salt marshes, salt works and most of the floodplain and catchment area are privately owned. Previously, little to no conservation action was being taken at this site, but this has been remedied by the appointment of a marine estuary ranger, through CapeNature. As well as conducting regular patrols on the river and estuary, the ranger carries out law enforcement duties, biodiversity monitoring and environmental education and public awareness work. He is supported by the Berg River Estuary Forum, which also provides a platform for certain issues to be raised with the relevant departments.

Restricted access to private land and the commercial salt pans reduces the impact of human activities to some extent. The Western Cape DEADP is carrying out a large-scale Berg River improvement and rehabilitation project, which should ultimately enhance the state of the estuary as freshwater flow and cycles are improved and levels of pollution decreased. This project is also removing alien vegetation species, including Eucalyptus species and water hyacinth, in the IBA and upstream of it. The salt works provide foraging habitat for certain bird species, as they are able to maintain the correct salinity to support the birds’ prey base.

In providing habitat for waterbirds in both high numbers and great diversity, the Berg River estuary is sufficiently important to satisfy the criteria for registration with the Ramsar Convention. However, the DEA requires a site to have a designated management authority and a management plan before Ramsar registration can proceed. Although registration is desirable, attention should rather be focused on acquiring formal conservation protection and sustained conservation management for the estuary. To this end, the proclamation of a Protected Environment, or a similar Biodiversity Stewardship option, is being investigated for this and other Western Cape estuaries. This is being done through a project to be managed by BirdLife South Africa. A Protected Environment is a form of stewardship in which local landowners establish a collective and include portions of their properties in a designated area. The landowners receive some benefits from this arrangement, while legislation restricts the kinds of activities that can take place within the area. A landowner’s conservancy that has been formed by farmers within the IBA could be the beginning of such a stewardship initiative.

The Berg River estuary’s rich birdlife offers substantial tourism potential if managed appropriately. Recognising this, the local municipality is becoming involved in the management of the site. In addition, the lower floodplain is vital as a nursery area for juvenile fish, many species of which form the basis of employment for hundreds of families living on the west coast. Any negative impacts on commercially valuable fish species – and many are already in decline – will have a knock-on effect on the well-being of many human communities in the area. Protection of the lower estuary, and the waters that inundate its floodplain, is therefore imperative. The site is monitored regularly and bird counts are carried out by members of the West Coast Bird Club. There are also a number of registered CWAC sites along the length of the estuary that can provide the data required for the motivation for formal protection, Ramsar status or the avitourism potential.

Related webpages

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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

Friday, 13 February 2015