The Swartkops River estuary is located on the outskirts of Port Elizabeth, 15 km north of the harbour. The river flows from its catchment in the Groot Winterhoek Mountains west of Uitenhage and, like its tributary the Elands River, descends a relatively steep, narrow valley. The two rivers flow in parallel before joining shortly after they enter the floodplain. The estuary is tidal for c. 16 km upstream. Its upper reaches are narrow (c. 90 m wide) and channel-like, twisting their way through steep banks of muddy sand, and include a small intertidal area comprising a sandy substrata where sand prawn Callianassa kraussi is the most common invertebrate. The estuary widens slightly and becomes less convoluted between Bar None Salt Pans and Brickfields in the middle reaches. Below Brickfields, the steep banks flatten, the estuary broadens considerably (c. 350 m wide) and extensive open mudflats provide habitat for the estuarine mud prawn Upogebia africana. The mouth is permanently open and is covered with beds of the eelgrass Zostera capensis. When these beds disappeared in 1983, a large expanse of intertidal mudflats took their place. The eelgrass has since returned and the mudflats have receded.
Salt marsh comprising species such as Spartina maritima occurs commonly in the lower and middle reaches of the estuary, whose north and south banks are flanked by the Redhouse Salt Pans, operated by Cerebos. The Chatty Salt Pans lie south of the Swartkops–Redhouse railway line. Additional salt pans on the Motherwell side of the estuary are in the Zwartkops Valley Nature Reserve, near the brickfields. Three islands, of 9.9 ha, 1.3 ha and 0.5 ha, are located near these pans. The water depth over most of the pan is 0.6 m. The salinity of these salt-pan systems is highly variable, ranging between 30 and 50 parts per thousand; after heavy rain it may fall as low as nine parts per thousand.
The terrestrial vegetation surrounding the estuary can be divided into four primary types: coastal dune herbland, which grows along the coast near the mouth; floodplain scrubland, which comprises succulent scrub and herbs; grassland with species such as Themeda triandra; and thicket dominated by Portulacaria.
This IBA complex supports, on average, 14 500 birds each year and occasionally passes the 20 000 threshold. Redhouse Salt Pans and the Swartkops Estuary each regularly hold more than 4 000 birds a year; in the estuary, up to 3 300 of these are Palearctic migrants, present mainly in summer. At least 200 bird species occur regularly each year and of these, 77 species are waterbirds and three are raptors associated with wetlands (African Fish Eagle Haliaeetus vocifer, African Marsh Harrier Circus ranivorus and Western Osprey Pandion haliaetus). Of these 80 wetland species, 20 are Palaearctic migrants; of the remaining 60 non-migrant species, 37 have been recorded breeding in the IBA.
The intertidal mudflats near the river mouth support the greatest density of birds, including important numbers of African Black Oystercatcher Haematopus moquini, Grey Plover Pluvialis squatarola, Common Whimbrel Numenius phaeopus, Ruddy Turnstone Arenaria interpres and Terek Sandpiper Xenus cinereus. Thirteen species have been recorded breeding at Redhouse Salt Pans.
The estuary is considered the most important estuarine and salt-flats habitat on the Eastern Cape coast, and the most important site on the mainland of the Eastern Cape for breeding colonies of coastal birds, including African Black Oystercatcher, with up to 14 pairs annually. Kelp Gull Larus dominicanus breeds in large numbers and the pan has supported up to 683 nests. Two islands at Redhouse Salt Pans host the second largest coastal breeding colony of White-breasted Cormorant Phalacrocorax lucidus in southern Africa, with a maximum of 224 nests counted. Grey-headed Gull Chroicocephalus cirrocephalus, with up to 608 nests, and African Sacred Ibis Threskiornis aethiopicus also have regionally important breeding colonies here. Redhouse Salt Pans holds the second largest breeding colony of Caspian Tern Sterna caspia, with up to 58 nests, in South Africa; in some years 20% of the country's breeding birds nest here.
Important numbers of Black-necked Grebe Podiceps nigricollis, Greater Flamingo Phoenicopterus roseus, Lesser Flamingo Phoeniconaias minor, South African Shelduck Tadorna cana, Cape Teal Anas capensis, Cape Shoveler A. smithii, Pied Avocet Recurvirostra avosetta, Curlew Sandpiper Calidris ferruginea and Sanderling C. alba also occur on the salt pans. The Valley Bushveld in the surrounding Swartkops Valley Nature Reserve holds Cape Bulbul Pycnonotus capensis, Grey Tit Parus afer, Olive Bush-Shrike Chlorophoneus olivaceus, Southern Tchagra Tchagra tchagra, Karoo Scrub Robin Erythropygia coryphoeus, Cape Penduline-Tit Anthoscopus minutus, Black-bellied Starling Notopholia corrusca and Knysna Woodpecker Campethera notata.
Globally threatened species are Damara Tern Sterna balaenarum, African Black Oystercatcher, Cape Cormorant Phalacrocorax capensis, Lesser Flamingo, Martial Eagle Polemaetus bellicosus, Chestnut-banded Plover Charadrius pallidus and Knysna Woodpecker. Regionally threatened species are Caspian Tern, Roseate Tern Sterna dougallii, Greater Flamingo, Lanner Falcon Falco biarmicus, African Marsh Harrier, Half-collared Kingfisher Alcedo semitorquata and Greater Painted-snipe Rostratula benghalensis. Restricted-range and biome-restricted species common at the site include Cape Bulbul, while Olive Bush-Shrike, Black-bellied Starling and Knsyna Woodpecker are uncommon.
Species that have met the 1% or more congregatory population threshold are Black-necked Grebe (maximum 1 249 individuals; this and following data provided by Paul Martin), Greater Flamingo (maximum >1 000 individuals), South African Shelduck (maximum 422 individuals), African Black Oystercatcher (maximum 55 individuals), Ruddy Turnstone (maximum 601 individuals), Pied Avocet (maximum 490 individuals) and Kelp Gull (maximum 683 breeding pairs). Species meeting the 0.5% or more threshold are Caspian Tern (maximum 68 individuals), Cape Shoveler (maximum 315 individuals), Curlew Sandpiper (maximum 4 187 individuals), African Spoonbill Platalea alba (maximum 82 individuals) and Grey-headed Gull (608 breeding pairs).
Two Algoa Bay endemics, southern dwarf chameleon Bradypodion ventrale and Algoa dwarf burrowing skink Scelotes anguineus, are resident. The globally threatened loggerhead turtle Caretta caretta and green turtle Chelonia mydas are occasionally found in estuaries in the Eastern Cape, and may occur at Swartkops from time to time.
There are a number of major threats affecting this estuary and they stem mostly from its location within a major metropolitan municipality with associated development. However, expert opinion suggests that the estuary has maintained its ecological functioning and continues to provide important habitat for bird species despite the proximity of the metropolitan area.
The indirect effects of urbanisation and industrial development around the shores of the estuary include sewage run-off, solid waste pollution and litter, and people disturbing birds and their habitat. The adjacent land is used for various purposes, such as residential townships, industry and clay mining. As a result, substantial industrial sewage and organo-chlorine effluents enter the river. The Markman canal is a particularly serious source of pollution due to the multiple leaks along the sewage pipeline between Motherwell and the Fishwater Flats Waste Water Treatment Works. Pollution impacts the ecology of the estuary in a number of ways. Chemical effluents alter nutrient levels and may poison micro-organisms, leading to knock-on effects on the ecosystem, while solid waste can choke birds or other animals if swallowed. Storm-water canals that carry debris and pollutants into the estuary should be covered or re-directed into sewage networks. Heavy metals such as cadmium have recently been discovered in the sediments around the estuary, and traces that have been found in fish and invertebrates suggest that these could be accumulating higher up the food chain in birds.
Human disturbance from residential and other developments around the shores of the estuary, as well as boating and angling in the estuary itself, can negatively impact on birds and is especially harmful in a direct form, such as egg collection or predation by dogs. Bait collecting also causes considerable disturbance to breeding and foraging birds, and regulations to control it should be introduced to minimise its impact.
The construction of infrastructure such as roads and bridges has brought changes to the dynamics of the estuary, restricting and redirecting water flow and curbing the movement of sediments. The major dam at Groendal has also impacted on the broader flow dynamics and sediment load of the estuary. The restriction of the mouth to a single location at the sea has had a negative impact on the natural flooding and sediment deposition cycles along the coastline. Future water demands in and around this growing urban centre may result in the establishment of more impoundments, which will substantially reduce flow and potentially disrupt the ecological functioning of the estuary.
The Swartkops Estuary basin is administered mainly by the Nelson Mandela Bay municipality, although a number of other stakeholders are active at the site. One of these is the Zwartkops Conservancy, which has been in operation for a number of years (until 2010 under the name Zwartkops Trust). Its primary goal is the wise use and management of the estuary for both nature conservation and human recreation.
The Aloe Nature Reserve near Bluewater Bay protects the natural thicket vegetation and other biome types, but does not include parts of the estuary below the 5-m flood line. The Swartkops Valley Nature Reserve, along the northern border of the estuary, also conserves terrestrial vegetation, which forms a dense closed canopy up to 5 m high in places and serves to bind the shallow topsoil protecting the underlying clay. The natural vegetation is mostly intact, although prickly pear Opuntia species and jointed cactus O. aurantiaca have invaded 1% of the reserve's area. An application is being made for this reserve to become a Ramsar site.
The estuary itself needs to be formally protected, and stricter zonation and law enforcement with regard to its use should be applied. The staff previously employed at Aloe and Swartkops Valley nature reserves have been reassigned elsewhere, leaving a major management gap at this site. The Zwartkops Conservancy is addressing this issue and aims to raise funds to employ its own rangers at these reserves.
Although an integrated management plan for the estuary and associated nature reserves (Enviro-Fish Africa 2011) has been developed as part of the Swartkops River Valley Management Forum (established in terms of the Integrated Coastal Management Act) and C.A.P.E Estuaries Programme, it is not certain to what degree the plan has been implemented. The Nelson Mandela Bay municipality has a coastal and marine conservation office on the estuary at Swartkops, but it has insufficient capacity. Zwartkops Conservancy employs a part-time environmental officer, has a boat and supervises cleaners whose salaries are paid by the municipality's Expanded Public Works Programme. The conservancy also provides environmental education and holds regular classes for three busloads of schoolchildren per month. Seven honorary marine control officers, four of whom are qualified, are also present at the estuary.
Redhouse Salt Pans is still operated as a commercial venture, ensuring that adequate funds and manpower are available for the maintenance of the retaining walls and the continued operation of the water pump. These commercial functions are vital for waterbird management at the site, as the pans provide some of the most important waterbird habitat on the Eastern Cape coastline.
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