Located to the east of Port Elizabeth, in the large arc of Algoa Bay, this group of coastal islands is clustered in two groups of three islands each. One group comprises the large St Croix Island with the much smaller stacks of Jahleel and Brenton Rocks closer inshore. St Croix Island lies 4 km from the mainland and is situated between the Coega and Sundays river mouths, 21 km north-east of the harbour at Port Elizabeth. This rocky 12 ha island rises to 58 m and supports minimal vegetation. The second island group consists of Bird, Seal and Stag Islands, and lies some 40 km east of the first group (i.e. 53 km due east of Port Elizabeth) and 7 km from the nearest land fall at Woody Cape Nature Reserve (IBA ZA073). Bird Island (19 ha) is the largest of the Algoa Bay islands; it is relatively flat and rises to only 9 m. Seal Island is a small island (0.6 ha) lying 360 m north of Bird Island, and Stag Island is even smaller (0.1 ha), lying 320 m north-west of Bird Island. Much of the island group is covered by sparse growth of mixed vegetation dominated by the fleshy herb Mesembryanthemum. Tetragonia and Chenopodium form localized 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.
See Box for key species. Fourteen species of seabirds, several species of shorebirds and 33 species of terrestrial birds have been recorded on the island group. Eight seabird species currently breed on the Algoa Bay islands. These are the only islands off southern mainland Africa where Sterna dougallii breeds regularly. The Algoa Bay islands currently hold 43% of the global population of Spheniscus demersus, the majority of which are on St Croix. St Croix also holds a locally significant breeding population of Phalacrocorax capensis. Bird Island is one of only six breeding sites in the world for Morus capensis. Larus dominicanus and Haematopus moquini are found throughout the Algoa Bay complex. The island group is also known to hold large numbers of Sterna vittata, which in winter roost on the island in their thousands (regularly holding between 10% and 20% of the estimated total Afrotropical non-breeding population).
Non-bird biodiversity: St Croix Island holds significant populations of two lizards, the Algoa-Bay endemic Cordylus tasmani and Pachydactylus maculatus.
Pressure/threats to key biodiversity
The island group is administered as part of the Woody Cape Nature Reserve. In 1981 the St Croix Group, and a 300 m marine zone around each island, was proclaimed South Africa’s first island marine reserve. The Guano Islands section of the Division of Sea Fisheries formerly controlled the island group. Eastern Cape Nature Conservation, which subsequently became the Directorate of Nature Conservation of the Eastern Cape Province, has managed the islands since April 1992. A management plan was compiled in 1995. A proposed harbour and heavy-industry complex at the Coega river mouth, opposite Jahleel Island, poses a huge threat to the seabirds of the St Croix group. The development would result in increased pollution and shipping activity, which would affect all breeding seabirds negatively.The population of Spheniscus demersus at the Algoa Bay Islands has been increasing steadily during the last century. There are only a few growing colonies in the world, and it is thought that these birds may be relocating here from colonies that are in decline in the Western Cape or farther afield. 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 Sardinops sagax, has been implicated as one of the most significant factors causing seabird population declines, especially of Spheniscus demersus, Morus capensis and Phalacrocorax capensis. A recommendation has been made that marine reserves with a radius of 25 km be created around important breeding islands. Within these zones commercial fishing should be banned or restricted.An unpredictable threat, which is difficult to control, is chronic pollution by crude oil or other pollutants which spill into the ocean when tankers break open, wash their tanks, dump cargo or pump bilge. Spheniscus demersus is particularly susceptible to these events, and a single oil disaster has the ability to severely affect populations. It is believed that the breeding sites in Algoa Bay, at the eastern extremity of the species’s range, are at highest risk as they are closest to the major oil-shipping routes.
BirdLife International (2023) Important Bird Areas factsheet: Algoa Bay Islands: Addo Elephant National Park. Downloaded from
http://www.birdlife.org on 09/02/2023.