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Dassen Island, South Africa’s second largest coastal island, lies 9 km from the mainland between Saldanha Bay and Cape Town. This island reaches 19.2 m at its highest point, and is generally flat or gently sloping, with extensive sandy areas and a few patches of exposed rock. It is richly covered with vegetation in winter. Several buildings occur in the north-east, as does a large manned lighthouse in the south-east. The island is partially enclosed by a low solid concrete wall. Hedges of non-native manitoka Myoporum occur near the buildings.
See Box for key species. Owing to its proximity to the mainland, comparative isolation, and suitable cover, the island offers sanctuary to a variety of land and seabirds. The most important resident is Spheniscus demersus. Numbers have been stable since 1989, following a 26% decrease during the late 1970s. Dassen Island also holds up to 4.6% of the global population of Haematopus moquini—the largest island population in South Africa. Dassen Island and Lake St Lucia (IBA ZA044) in KwaZulu-Natal are the only two sites in South Africa supporting breeding Pelecanus onocrotalus. Unlike most pelican populations, the Western Cape population has increased substantially during the twentieth century. The numbers on Dassen Island’s Boom Point have increased from less than 100 pairs in the mid-1970s to c.550 pairs in 1996. The island also supports healthy breeding populations of Phalacrocorax coronatus, P. capensis, Larus dominicanus, L. hartlaubii and Sterna bergii, as well as supporting many Arenaria interpres and other migratory waders during summer. Phalacrocorax neglectus, which used to breed in large numbers, has decreased dramatically over the last five years. Oceanodroma leucorhoa breeds on this island in very small numbers.
Non-bird biodiversity: Scelotes gronovii (LR/nt), a reptile endemic to the west coast, occurs on the island.
BirdLife International (2019) Important Bird Areas factsheet: Dassen Island. Downloaded from http://www.birdlife.org on 22/11/2019.