Duiker Island, named so after the Cormarants which inhabits the island (in Afrikaans it's called Duiker) – also known as Seal Island – is a place where thousands of Cape Fur Seals can be seen in their natural habitat. A boat trip provides beautiful views of the bay, the harbour, The Sentinel and Chapman’s Peak.

Seal Island is a small land mass so named because of the great number of Cape Fur Seals that occupy it. It is 5 acres (2.0 hectares) in area and home to 64,000 cape fur seals. It is home to seabirds too and it is likely that non-marine species (in no great number) fly there to breed as well.

The island is an outcrop of the Cape granite and rises no more than about four to six metres above the high tide mark. The island is long and narrow- 800 metres by 50 metres. There is no vegetation or soil of any significance and no beach.