ZA082
Verlorenvlei Estuary


Year of compilation: 2001

Site description
Verlorenvlei is an estuary, fed by an intermittently flowing river, on the Atlantic Ocean, 3 km east of Elands Bay and 25 km south of Lambert’s Bay. It is connected to the sea via a shallow, narrow, 2.5-km-long channel, but a rocky sand-covered bar at the mouth and other artificial obstructions make Verlorenvlei a virtually closed system. Because of its intermittent connection with the ocean, Verlorenvlei can be regarded as a coastal lake and reed-swamp system. It 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.The lake is located north of a ridge of rugged hills with high krantzes near the sea. The main body of the lake is approximately 13.5 × 1.4 km, with an average depth of c.3 m and a maximum depth of c.4.5 m during the wet season. During winter the lake fills and overflows into the sea near Eland’s Bay, but during summer it gradually desiccates, reaching its lowest levels at the end of the dry season.

Large masses of filamentous green algae are common in the channel, where the water is often stagnant and hyper-saline. The vlei is dominated by aquatic vegetation, including Myriophyllum which, at times, occupies large areas, e.g. in the upper reaches below reedbeds. Marsh vegetation of Typha, Phragmites, Cyperus and Juncus is common and widespread on the fringes of the lake. The terrestrial vegetation surrounding the vlei is transitional between karroid and fynbos vegetation, resulting in a high diversity of ecotonal communities.

Key biodiversity
See Box for key species. Verlorenvlei supports over 189 bird species, of which 75 are waterbirds. The wetland regularly supports over 5,000 birds and occasionally it holds over 20,000, including more than 1,000 waders of at least 11 different species. Most importantly, the area is a moulting ground and summer refuge for ducks (Anatidae), and it regularly supports extremely large numbers of Anas undulata, A. smithii and Tadorna cana. Large numbers of Podiceps cristatus, Fulica cristata, Larus hartlaubii and Phalacrocorax carbo are also supported. There is a high density of Circus ranivorus, which forage over the marsh and reedbank areas. Haematopus moquini and Charadrius pallidus are recorded at the estuary mouth from time to time. The palustrine habitats are diverse and rich and hold populations of secretive rails (Rallidae), including large numbers of Sarothrura rufa, Rallus caerulescens and Porzana pusilla. The diverse ecotonal terrestrial vegetation around Verlorenvlei’s fringes supports several restricted-range and/or biome-restricted species, including the recently described Certhilauda curvirostris (see account for IBA ZA023).

Non-bird biodiversity: Rare plants include Ferraria foliosa, F. densepunctulata, Cerycium venoum (presumed extinct) and Cullumia floccosa. The fish Barbus burgi (CR) has a global range restricted to the Verlorenvlei system and some of the upper catchment streams of the Berg river. Among reptiles, the IBA lies in the centre of the ranges of several Namaqualand endemics, most of which have been recorded in the vicinity and may be present in the succulent Karoo terrestrial vegetation surrounding the wetland: Homopus signatus, Bitis schneideri (VU), B. cornuta, Acontias litoralis, Typhlosaurus caecus, Scelotes sexlineatus, Meroles knoxii, Cordylus cataphractus (VU), C. macropholis, Gerrhosaurus typicus (LR/nt), Bradypodion occidentale and Pachydactylus austeni.



Pressure/threats to key biodiversity

This wetland is of great significance, especially in terms of its large area, the diversity of its habitats, the large populations of waterbirds that it supports, and the relative scarcity of similar habitats in the Western Cape. Despite being one of the most important estuarine/lacustrine systems in South Africa, Verlorenvlei does not have any formal protection status and neither statutory control nor any form of management is currently in existence. The Ramsar-designated land is state-owned and is managed by Cape Nature Conservation.

Several man-made obstructions disrupt water flow in the system, a concrete causeway, a rubble causeway at the railway bridge, and road causeways (500 m, 1 km and 2.6 km upstream of the mouth) all prevent natural flow and disturb the sensitive ecological functioning of the system. These obstructions disrupt hydrological fluctuations within the wetland, causing flooding upstream, extensive siltation and reduction of freshwater load into the estuary, and also prevent fish migration. As such, urgent action is required to maintain free water movement in Verlorenvlei as a whole; unnecessary obstructions, especially the illegal causeway near the mouth, should be removed, while necessary crossing points should be modified to return the system to a natural state. Verlorenvlei may become irreparably damaged if conservation action is not rapidly forthcoming.

The land surrounding the lake is privately owned, and the vlei faces several threats from intensive farming practices in this area. The surrounding vegetation has become considerably degraded through extensive agricultural and grazing pressure. The introduction of mechanized irrigation systems, which use underground lake water, may impact the lake considerably. Non-native fish compete with indigenous freshwater species and alter the vegetation structure, potentially altering system dynamics. Similarly, the invasive non-native tree Acacia cyclops was introduced to stabilize the coastal dunes; it has now spread throughout the area where it threatens the indigenous vegetation.




Recommended citation
BirdLife International (2019) Important Bird Areas factsheet: Verlorenvlei Estuary. Downloaded from http://www.birdlife.org on 16/10/2019.