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Verlorenvlei is one of the most important estuarine systems in the Western Cape and one of the largest natural wetlands along the west coast of South Africa. It is also one of the few coastal fresh water lakes in the country. The system comprises a coastal lake and reedswamp connected to the sea by a small estuary. Situated amid dramatic topography, the lake is approximately 13.5 km long and 1.4 km wide and occurs in the zone of transition between the karroid and fynbos vegetation types. This results in the region displaying a high species diversity typical of an ecotone area. (RAMSAR)
Verlorenvlei IBA (Important Bird Area) Information
|Status: Global IBA (A1, A4i)
||Province: Western Cape|
|Protection: Unprotected||Size: 29 600 ha|
Verlorenvlei is a partially closed coastal estuarine lake and marsh system fed by an intermittent allogenic river. The estuary mouth lies along the Atlantic Ocean at the town of Elands Bay, which is located 25 km south of Lambert’s Bay. This is one of the largest natural wetlands along southern Africa’s west coast, and it is one of the few coastal freshwater lakes in South Africa. Its catchment covers some 1 890 km2 and consists of four main tributaries: the Kruis, Bergvallei, Hol and Krom Antonies rivers, which have their sources in the Olifantsrivierberge and Swartberge in the east and the Piketberge in the south. Three of the four rivers drain the extensive flatlands of the sandy coastal plain, and the Krom Antonies River drains the Moutonshoek Valley. All four flow into the 30-km-long Verlorenvlei River.
Verlorenvlei can be regarded as a coastal lake and reed-swamp system due to its intermittent connection with the ocean. The main body of the lake is c. 13.5 km long and 1.4 km wide, and has an average depth of 3 m and a maximum depth of c. 4.5 m during the wet season. Extensive low-lying sand flats occur to the north and east of the lake, sloping up to a series of low hills that form the catchment boundary. On the southern side, the lake lies against the base of a continuous range of low sandstone hills averaging some 120 m a.s.l., with Muishoekberg (300 m a.s.l.) forming the only prominent peak. Towards the west and closer to the sea, the ridge becomes rugged, with high cliffs ending in the ocean at Baboon Point (200 m a.s.l.).
The system lies in a winter-rainfall area and given sufficient rain inland it fills and overflows into the sea at Eland’s Bay. In summer, however, it gradually desiccates, reaching its lowest levels at the end of the dry season. Generally the lake never dries up completely, although in very dry years the water level can become extremely low. The fluctuations in water level influence the distribution patterns of the flora and fauna, so the wetland’s variable nature is critical to the functioning of the system. A shallow, narrow, 2.5-km-long channel runs from Verlorenvlei to the sea, but a rocky sand-covered bar at the mouth and other artificial obstructions make it a virtually closed system. Usually, the mouth is blocked and the channel is reduced to a series of stagnant saline pools. During good rains, however, the lake spills into the channel and some tidal exchange takes place. The lake is regarded as oligotrophic, but the nutrient status varies, depending on the water level. Salinity levels can reach as high as 40 parts per thousand on the eastern side of the railway bridge (hypersaline conditions) to 0.5 parts per thousand at Redelinghuys.
The terrestrial vegetation surrounding the vlei is transitional between karroid and fynbos vegetation, resulting in a high diversity of ecotonal communities. The coastal dunes support strandveld, comprising clumps of succulent or evergreen shrubs interspersed with smaller shrubs and restios. Saline marshy areas with a dense cover of halophytic vegetation are found immediately inland of the seaward dunes and around the mouth of Verlorenvlei, whereas dry mountain fynbos grows on surrounding sandstone outcrops.
Verlorenvlei supports more than 189 bird species, of which 75 are waterbirds. The wetland occasionally hosts more than 4 000 birds; the highest number recorded in a single count was 11 891, according to the data from counts undertaken by CapeNature since 1990. At least 26% of the Western Cape’s Great White Pelican Pelecanus onocrotalus population congregates at this site at times. Greater Flamingo Phoenicopterus roseus and Lesser Flamingo Phoeniconaias minor also occur here occasionally, when conditions at Rocher Pan (35 km south) or Wadrifsoutpan (13 km north) are unsuitable or water levels in the lake are very low, as occurred in the 2004–2005 season. Relatively large numbers of Little Bittern Ixobrychus minutus and Caspian Tern Sterna caspia occur regularly in the wetland.
Historically an important moulting ground and summer refuge for Anatidae, the area supported large numbers of Yellow-billed Duck Anas undulata, Cape Shoveler A. smithii and South African Shelduck Tadorna cana. However, many of these species have declined over the past decades, as data from CapeNature illustrate. Large numbers of Great Crested Grebe Podiceps cristatus, Red-knobbed Coot Fulica cristata and White-breasted Cormorant Phalacrocorax lucidus can also be found at this wetland. There is a high density of African Marsh Harrier Circus ranivorus, which forages over the marsh and reedbed areas. Black Stork Ciconia nigra breeding in the Olifantsrivierberge and Swartberge to the east and Piketberge to the south very occasionally forages in the vlei. The site also holds 4–5 pairs of African Fish Eagle Haliaeetus vocifer, and Verreauxs’ Eagle Aquila verreauxii occurs on the cliffs around the vlei.
African Black Oystercatcher Haematopus moquini and Chestnut-banded Plover Charadrius pallidus are recorded at the estuary mouth from time to time. The palustrine habitats are diverse and rich and hold populations of secretive Rallidae such as African Rail Rallus caerulescens and Baillon’s Crake Porzana pusilla. Red-chested Flufftail Sarothrura rufa may occur, but has not been confirmed. Rallid species are particularly abundant between Matjiesgoeddrif and Redelinghuys, where the composition and structure of the palustrine vegetation are diverse and the area has extensive and excellent habitat for them and for waders. The diverse ecotonal terrestrial vegetation around Verlorenvlei’s fringes supports several restricted-range and biome-restricted assemblage species. In recent years, a pair of Goliath Herons seems to have been resident in the area and may be breeding.