Avian Demography Unit
Department of Statistical Sciences
University of Cape Town
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Seabird Islands of South Africa

Seal Island, False Bay

Bruce Dyer and Les Underhill
Marine and Coastal Management and Avian Demography Unit

Seal Island, False Bay, aerial view
Photo B.M. Dyer
Aerial view of Seal Island in False Bay

Seal Island in False Bay consists essentially of a huge granite rock 2 ha in area, with no beaches or vegetation. It lies almost centrally in the northern part of False Bay, 5.7 km offshore. A radio mast, built on the island during World War II, was a conspicuous landmark in the bay until it was blown over in a winter storm in 1970. All that remains of this is some rusty, twisted metal. There are also ruins of some huts and a few structures from the sealing and guano-collection era. Some rock inscriptions made by sealers in the 1930s are still evident. Guano collection ceased in 1949.

About 100 years ago (ie about 1880), the great voyage of the HMS Challenger brought the naturalist Moseley to the Cape. The following extract from his notes brings out the changes that have taken place since then - or at least one of them. "I paid a visit to an island in False Bay, called Seal Island. It is a mere shelving rock, on which it is only possible to land on very favourable occasions. The whole place is a rookery of the Jackass Penguin".

Nowadays, this island supports the largest Cape Fur Seal Arctocephalus pusillus colony in the Western Cape; up to 75 000 seals occur. The growth of the population of seals was held in check by a quota system until the early 1980s. The market for fur seal products crashed in 1983 and seal harvesting no longer occurs on Seal Island. As a result, the seal population has increased dramatically in recent decades. The seals attract Great White Sharks Charcharadon charcharius, and an ecotourism industry to view the sharks is slowly developing.

Rock
inscriptions, Seal Is
Photo B.M. Dyer
Sealers' rock inscriptions on Seal Island

Seal Island continues to support a small population of African Penguins. The penguins have been provided with artificial nest sites, and this has increased their breeding success. In spite of the increasing seal population, the number of penguins has remained stable since the 1980s, and about 80 pairs breed each year.

Other bird species which breed regularly on the island are Whitebreasted Cormorants and Bank Cormorants. Cape Cormorants bred for the first time in 2000; there were 30 nesting pairs. A handful of Cape Wagtails almost certainly breed on the island. There are a few Turnstones in summer, but no African Black Oystercatchers.

Cape Gannets bred on the island in the 17th century, but it is not documented when this colony folded. Kelp Gulls last bred in the 1950s. They remain common scavengers on the island, though.

Seal Island
Photo B.M. Dyer
Seals, seals and more seals...

The Western Cape population of Great White Pelicans bred on Seal Island from about 1930 until 1954. Before 1930, they were breeding at Dyer Island and at Quoin Rock. They left Dyer Island as a result of disturbance by guano-scrapers. They were displaced from Quoin Rock because of competition for space by a growing population of Cape Fur Seals. About 20-30 pairs of pelicans bred at Seal Island. However, they were subjected to considerable disturbance from sealers and guano collecters. By 1950, competition for space with seals forced them to move off the ground and breed on the roofs of the huts on the island. The final straw was the destruction of these nests when the roofs were repainted. The last breeding was recorded in 1954, and non-breeding birds visited the island until 1956. From 1955, Great White Pelicans have bred on Dassen Island, and continue to do so. The population there has grown to about 800 pairs.

Seal Island is a nature reserve of the Western Cape Nature Conservation Board. It has no visitor access facilities. As observed by Moseley, landing on the island is difficult. It is dependent on sea conditions and usually requires a leap onto mussel- or barnacle-covered rocks.

The island has a bird list totalling 24 species, which have been seen either on the island or in the immediate vicinity.


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Last updated 8-March-2003