Dassen Island Nature Reserve
Dassen Island lies in the Atlantic Ocean approximately 55km north west of Cape Town and 9km off Yzerfontein. It is South Africa’s second largest Island, after Robben Island in Table bay. The Island was proclaimed a nature reserve in 1987 and Is managed by Cape Nature Conservation, primarily to protect its seabird colonies. Public visits are limited, because of the sensitive nature of the seabirds.
Ecology and History
The ecology of small island is often dynamic. Natural fluctuations of plant and animal populations, in addition to a long history of human disturbance, have so altered Dassen Island that there is uncertainty about its original species.
The island was named by Dutchman Van Spilbergen in 1601, after dassies which evidently occurred in abundance. Early records describe the island as covered in plants about two meters tall, and riddled with burrows in which penguins bred.
During the mid-17th century the island functioned as an outpost of the Dutch East India Company. Seals, birds and fish were caught to supply the settlement at the Cape. Sheep, pig and rabbit farming was also attempted, but was unsuccessful due to the shortage of fresh water. The Island still has a large population of now-wild rabbits which overgraze the spars vegetation, particularly during the summer months. Large numbers of Cape Fur seals used to breed on the island, but were hunted extensively for meat and fur from the 17th century until the mid-20th century and are now rarely seen.
During the mid 1840’s the island’s guano cover was removed for use in fertilisers. From 1870 until 1967 penguin eggs were exploited for public consumption. This practice reached a peak in 1919, when almost 600 000 fresh eggs were collected from the island. It is estimated that the penguin population had to have been about 400 000 to have produced this number of eggs. In the early 1990’s the penguin population had fallen to around 25 000 birds, demonstrating the devastating effect of egg collection. The penguin colonies have since been stabilised, aided by the Island’s status as a nature reserve.
House mice were accidentally introduced and later cats were brought to control the mice, but also fed on birds and rabbits. Angulate tortoises, originally from the mainland, and guinea fowl-brought as eggs from Robben Island – also occur on Dassen Island. Management of the Island includes control of these alien animal species.
The Cape’s west coast has been a busy shipping lane for several centuries and the rough seas have claimed countless ships and lives. Dassen Island’s lighthouse, reputedly the most isolated manned lighthouse on the South African coast, was built in 1893 and stands on the southern and highest point of the island. Nevertheless, the island remains a danger to ships and small craft, and several rusting and rotting shipwrecks litter its coastline. The 1994 sinking of the Apollo sea. A bulk ore carrier near Dassen Island and the resultant oil spill caused environmental damage to the island and threatened its penguin population.
Dassen Island’s most significant animals are the seabirds, particularly the large populations of African penguin, white pelican, African black oystercatcher, three species of cormorant, and kelp gull. In addition Egyptian geese, sacred ibis, Cape wagtail, Hartlaub’s gull and swift tern breed on the island in smaller numbers. Pelagic species, including Antarctic terns, Sabine’s gull skuas and white chinned petrel occasionally visit the island, and despite some human presence, the birds are far better protected than on the mainland.
The breeding seasons of the various seabird species are staggered through the year and their colonies are scattered over the entire island. The birds are extremely sensitive when breeding- even the slightest disturbance may cause the abandon their nests, giving marauding gulls and ibises to take eggs or small chicks. For this reason public access to the island is limited and strictly controlled.
(Cape Nature conservation 11/1997)