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Abstract

abstract

The occurrence of alien species on South African offshore islands is surveyed. Aliens (species not indigenous to the adjacent mainland of the Cape Province or Namibia, or, in the case of certain vertebrates, present by deliberate translocation), have been noted on 21 islands. It is probable that a more thorough search on Robben lsland, the islands of Algoa Bay and off the Namibian coast would reveal more species and more islands occupied. Sixteen alien vertebrate species are involved, 19 invertebrates and 50 seedbearing plants. The ecological history of the offshore islands is outlined and it is shown that in most cases arrival of aliens has taken place in the last 100 years, sometimes in the last 25 years. But for nearly all species there is no information available on how long they have been on each island, how they reached it and whether they have a detrimental impact on the rest of its biota. It is recommended that the feral cats Felis catus on Dassen and Robben islands be exterminated in the interest primarily of seabird conservation. The widespread presence of the skin beetle Dermestes maculatus is noted.