Global IBA (A1, A4i, ii, iii)
2 680 ha
Located in the large arc of Algoa Bay and to the east of Port Elizabeth, this 40-ha collection of coastal islands is clustered in two groups of three islands each: the St Croix group, comprising St Croix, Jahleel and Brenton islands; and the Bird Island group, consisting of Bird, Seal and Stag islands, as well as Black Rocks. St Croix Island lies 4 km from the mainland and is situated between the mouths of the Coega and Sundays rivers, 21 km north-east of the harbour at Port Elizabeth. This rocky 12-ha island rises to 58 m a.s.l. and supports minimal vegetation. A high ridge runs from east to west across it, overlooking dwellings and a concrete landing jetty. The Bird Island group lies some 40 km east of the first group (53 km due east of Port Elizabeth) and 7 km from the nearest landfall at the Woody Cape Section of Addo Elephant National Park. Bird Island, at 19 ha, is the largest of the Algoa Bay Islands and is relatively flat, rising to only 9 m a.s.l. Seal Island is small (0.6 ha) and lies 360 m north of Bird Island, while Stag Island, located 320 m north-west of Bird Island, is even smaller (0.1 ha) and comprises a raised central shingle deposit covered with sparse vegetation and guano. Much of the island group is thinly covered with mixed vegetation and plants forming localised thickets that provide cover for some seabirds. The Algoa Bay Islands are of considerable importance as they are the only islands along a 1 777-km stretch of coastline between Cape Agulhas and Inhaca Island in Mozambique.
Fourteen seabird, several shorebird and 33 terrestrial bird species have been recorded on the Algoa Bay Islands and eight seabird species currently breed there. Certain of the seabird trigger species are showing declines similar to trends for the same species at other sites, whereas other species have been increasing at this IBA. These were regarded as the only islands in southern Africa where Roseate Tern Sterna dougallii bred regularly. However, the species has not been recorded nesting on St Croix Island since 2008, although there have been small increases in the number of breeding birds in South Africa over the past decade.
Although the number of African Penguins Spheniscus demersus has decreased by approximately 50% since Barnes (1998) was published, the Algoa Bay Islands still support almost 50% of the global population of this species, most of which are on St Croix Island. The decline here is similar to declines at all the other African Penguin colonies and urgent conservation action is being implemented by a number of partners.
With a locally significant breeding population of Cape Cormorants Phalacrocorax capensis, St Croix is one of the few breeding localities for this species in the warmer Agulhas Current. This population has remained fairly stable over the past few decades, except for a complete failure to breed in 2011.
Bird Island supports breeding Cape Gannets Morus capensis, one of only six such sites in the world. Gannet numbers here have increased by approximately 40% over the past 20 years, possibly in response to the eastward movement of the gannet’s primary prey, pilchard Sardinops sagax and anchovy Engraulis encrasicolus. Although this is positive for the species, the expansion of the colony has meant that gannets increasingly occupy space on the islands that could be utilised by other breeding seabirds and thus have a negative impact on these other species.
African Black Oystercatcher Haematopus moquini is found throughout the Algoa Bay complex. The exchange of birds between the islands within Algoa Bay is probably quite high, and the group should be treated as a single entity. The islands were also known to hold large numbers of Antarctic Tern Sterna vittata, which in winter roosted on them in their thousands.
IBA trigger species
Globally threatened species are African Penguin (11 304 breeding pairs; Crawford et al. 2012), Cape Cormorant (284 breeding pairs; Crawford et al. 2012), Cape Gannet (83 000 breeding pairs; Crawford et al. 2012) and African Black Oystercatcher (55 breeding pairs; SANParks census). Regionally threatened species are Caspian Tern Sterna caspia and Roseate Tern (90–100 breeding pairs; Crawford et al. 2012). The species reaching the 1% or more congregatory threshold are Kelp Gull Larus dominicanus and Antarctic Tern, while Swift Tern Thalasseus bergii (130 breeding pairs; Crawford et al. 2012) and Ruddy Turnstone Arenaria interpres are thought to reach the 0.5% or more congregatory threshold.
St Croix Island holds populations of the Algoa Bay endemic Tasman’s girdled lizard Cordylus tasmani and the spotted thick-toed gecko Pachydactylus maculatus.
It must be noted that although threats to this IBA do exist, SANParks is using all available resources to mitigate them wherever possible. The major threat to the islands and their seabird breeding colonies is the large-scale Coega Industrial Development Zone (IDZ) and the harbour and other industrial infrastructure associated with it. The direct and indirect threats arising from this industrial development include potentially catastrophic oil spills that could threaten the entire breeding colonies of certain IBA trigger bird species; chronic pollution; and disturbance and other negative impacts.
Between 1956 and 1980, the global Cape Gannet population declined by some 50%. The collapse was attributed to a decrease in pilchard stocks, the Cape Gannet’s primary food source. Despite the global decline, the Bird Island colony has been increasing since the late 1960s and continues to do so. In addition to being affected by overfishing, Cape Gannets are susceptible to oiling and human disturbance. During guano-scraping operations, which have now been banned for many years, high chick mortality was recorded. Chicks were either killed directly by displacement or, when excessive amounts of guano were removed, nesting areas became basin shaped and flooded after rain.
Certain factors are known to affect seabirds throughout their ranges. Competition with commercial fisheries, especially purse-seining for surface-shoaling fish such as anchovy Engraulis capensis and pilchard, has been implicated as one of the most significant factors causing seabird population declines, especially of African Penguin, Cape Gannet and Cape Cormorant. A recommendation has been made that marine reserves with a radius of 25 km should be created around important breeding islands and that commercial fishing should be banned or restricted within these zones.
Although the Cape fur seal Arctocephalus pusillus can be a threat to seabirds, through competition and displacement at breeding islands, the 4 000-strong seal population in Algoa Bay is decreasing and currently poses little threat to breeding seabirds in this region. Kelp Gulls and skuas, however, pose a more significant threat. The high number of gulls targeting penguin and gannet eggs can be a major issue, specifically on the smaller islands, and can lead to a decrease in reproductive success for these threatened species.
A threat that is both unpredictable and difficult to control is chronic pollution. Crude oil or other pollutants spill into the ocean when tankers break open, wash their tanks, dump cargo or pump bilge. African Penguins are particularly susceptible to these events, and a single oil disaster can severely affect populations. It is believed that the breeding sites in Algoa Bay, at the eastern extremity of the species’ range, are at highest risk as they are closest to the major oil-shipping routes.
As a South African National Park, this IBA has the highest form of legislative protection in South Africa, as well as the necessary management planning and conservation action required to maintain the site. Human access to the islands is highly restricted and only possible by means of a permit from SANParks for specific research activities.
SANParks implements all required conservation actions for this site, including the maintenance of infrastructure and the mitigation of threats. These actions are not limited by a lack of resources as much as by a lack of knowledge and best-practice required to address certain threats. An example of this is the breeding of African Penguins in artificial nests; although all the resources are available, the optimal construction material and other factors are still being determined.
Populations of seabirds in general and African Penguin in particular tend to go through periods of flux; within ten years large populations can dwindle to almost nothing. Because inter-island movements are poorly understood and seabird populations are relatively dynamic, it is vital that all southern African islands where birds breed, or could breed, are protected as a network.
If you have any information about the IBA, such as a new threat that could impact on it, please send an e-mail to email@example.com or call BirdLife South Africa +27 (11) 789 1122.
Page last updated
Friday, 16 January 2015
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