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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.
BirdLife International (2019) Important Bird Areas factsheet: Algoa Bay Islands: Addo Elephant National Park. Downloaded from http://www.birdlife.org on 22/07/2019.