Current view: Text account
Site description (2001 baseline):
Site location and context
This complex wetland system, located at the southern tip of the African continent, 25 km south of Bredasdorp, consists of the Nuwejaarsrivier and its associated marshes, Soetendalsvlei and the Heuningnes river and its estuary (the southernmost estuary in Africa). The area of interest extends from 5 km upstream of the Nuwejaarsrivier–Soetendalsvlei confluence to the mouth of the Heuningnes river. The vlei acts as a reservoir, and when it overflows, the run-off spills over into the Heuningnes river, which feeds the estuary. The primary wetland area is found between Heuningrug and Wiesdrif. Vegetation includes mixed and monospecific stands of tall to short sedges, reeds and grasses (
Eleocharis,
Cyperus,
Scirpus,
Typha,
Phragmites), open mud patches, shallow water,
Isolepis mats, deep pools and shallow pan-like pools. A second wetland area is the 5 km stretch of the Nuwejaarsrivier close to Moddervlei. The Wiesdrif pan on the farm is a shallow flooded depression in grassland, with much emergent vegetation. Many of the river channels are poorly defined and drainage into the estuary occurs via vleis and marshes, which constitute large areas of wetland.The estuary mouth comprises an extensive bay with sand, mudflats and tidal saltmarsh, dominated by
Limonium,
Salicornia and
Sarcocornia. Heavily grazed and degraded flood-plain vegetation is found between the saltmarsh and the sandbanks. Patches of reed
Phragmites occur at places along the riverbanks. The terrestrial vegetation adjacent to the estuary consists of dune scrub (coastal fynbos). The estuary is important as a nursery ground for marine fish.
See Box for key species.
Larus dominicanus regularly nests in the dunes a few kilometres to the north-east of Heuningnes mouth. The pebble slacks behind the beach are one of only two protected, confirmed breeding sites for
Sterna balaenarum in South Africa, holding 15% of the national breeding population, and
Sterna caspia,
Haematopus moquini,
Charadrius pecuarius and
Plectropterus gambensis all breed regularly.
Rostratula benghalensis, of the isolated and declining Western Cape breeding population, is also present in good numbers.
Grus paradisea occasionally roosts and feeds at open pools in the middle of the wetland.
Circus maurus and
C. ranivorus have been recorded at the site.
Pelecanus onocrotalus occasionally occurs in large numbers.The Nuwejaarsrivier marshes are excellent for secretive rails and crakes.
Porzana pusilla is numerous and probably breeds,
Sarothrura rufa has been recorded at a density of one pair/0.25 ha in excellent habitat, and
Rallus caeruleus and
Amaurornis flavirostris are widespread and abundant. Small numbers of migrant Palearctic and resident waders regularly use the site, including
Charadrius hiaticula,
C. pecuarius,
Calidris ferruginea and
C. minuata.
Non-bird biodiversity: The reptile Bradypodion pumilum (CR) is thought to occur in the area.
Pressure/threats to key biodiversity
De Mond State Forest was established in 1975 to preserve the Heuningnes estuary and the adjoining coastal fynbos vegetation. The estuary and dunes on either side form a Ramsar Site, designated in 1986. The remainder of the site, including the highly sensitive Nuwejaarsrivier marshes, is privately owned and unprotected.This site is worthy of the maximum possible protection. Detailed vegetation surveys would yield interesting information on plant-species composition and habitat diversity. Most of the catchment (upstream from the site) is on privately owned farmland, and several irrigation dams and weirs have been constructed on the Karsrivier. Any further damming of the tributaries could have serious implications for freshwater input to the estuarine system. A causeway in the intertidal zone 1.3 km upstream of the mouth is a considerable obstruction to tidal exchange, which has altered the character of the upper estuary, which now resembles a slackish turbid river. In its natural state water would dam up behind the dune barrier; during floods, the barrier would be periodically breached and the mouth would open up. An elongated lagoon about 2.5 km long used to form between the dune-ridges. The estuary mouth probably moved considerably, shifting by up to 2 km along the beach. However, whenever the mouth closed, extensive flooding occurred in the hinterland, which had been developed for farming; crops were destroyed and extensive topsoil was lost. In 1937 the Department of Agriculture and Forestry took steps to keep the river mouth open to reduce backsliding and appease local farmers.
The sand-dunes on either side of the estuary and to the north are now stabilized by non-native marram grass
Ammophila. The mouth width has also been reduced and confined artificially by brushwood barriers and dune afforestation. The barriers prevent large-scale migration of the mouth or the formation of a natural sand-spit. The considerable stabilization of the area and alteration of the natural flux may have affected the functioning of this estuary. The construction of road-protection levees has reduced tidal activity, resulting in areas of saltmarsh becoming colonized by coastal dune plants. Above the saltmarsh, the flood-plain vegetation is heavily grazed. A major threat to
Sterna balaenarum is the extensive disturbance caused by careless off-road vehicle drivers who insist on driving in the sensitive areas where the birds breed, despite signs prohibiting such activities.
Recommended citation
BirdLife International (2024) Important Bird Area factsheet: Agulhas Plain - Heuningnes Estuary (South Africa). Downloaded from
https://datazone.birdlife.org/site/factsheet/agulhas-plain--heuningnes-estuary-iba-south-africa on 23/11/2024.
