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South Africa

Seal Island, False Bay

Bruce Dyer1 and Les Underhill2
1Marine and Coastal Management; 2Animal 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.

  Seals at 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.

Bruce Dyer
Marine and Coastal Management

Bank cormorants at Seal Island, False Bay
Photo B.M. Dyer
Bank cormorants breeding at Seal Island
 
Artificial nest of African penguin
Photo B.M. Dyer
Artificial nest of African penguin

This bird list is based on historic records and on irregular official visits to Seal Island made during the period 1987-2000. It includes species seen on the island and in the immediate vicinity.

    • African Penguin - breeds
    • Cory's Shearwater - seen close by
    • European Storm Petrel - seen close by
    • Wilson's Storm Petrel - seen close by
    • Blackbellied Storm Petrel - seen close by
    • Great White Pelican - bred from about 1930 to 1954. Last seen 1956
    • Cape Gannet - used to breed, seen close by
    • Whitebreasted Cormorant - breeds
    • Cape Cormorant - bred in 2000 for the first time
    • Bank Cormorant - breeds
    • Crowned Cormorant - visits, and would breed if there were suitable habitat
    • Turnstone - a few in summer
    • American Sheathbill - vagrant
    • Arctic Skua - seen close by
    • Pomerine Skua - seen close by
    • Subantarctic Skua - seen close by
    • Kelp Gull - used to breed, common scavanger on island
    • Hartlaub's Gull - visits
    • Sabine's Gull - seen close by
    • Swift Tern - visits
    • Sandwich Tern - visits
    • Common Tern - visits
    • Feral Pigeon - vagrant
    • Cape Wagtail - probably breeds