Antarctic fur seals (Arctocephalus gazella)
Subadult and adult males of Antarctic fur seals have been observed to prey on macaroni (Eudyptes chrysolophus) and king penguins (Aptenodytes patagonicus) at Marion Island (Prince Edward Islands).
Black rats (Rattus rattus)
Black rats, such as those found on Robben Island, may feed on bird eggs and possibly small chicks, especially those of the endangered African penguin (Spheniscus demersus). Bird Island (Lamberts Bay) is connected to the mainland by a causeway and thus seabirds may be susceptible to rats which come on the island via this causeway.
Canids
Bird Island (Lamberts Bay) is connected to the mainland by a causeway and thus seabirds are susceptible to dogs which may come onto the island via this causeway. Dogs on Robben Island may also have posed a threat to some seabirds.
Cape fur seals (Arctocephalus pusillus pusillus)
A small number of subadult and adult Cape males are known to prey on African penguins, Cape gannets (Morus capensis) and cormorants (bank (Phalacrocorax neglectus), Cape (P. capensis) and crowned (P. coronatus)) around some South African islands (e.g. Malgas, Dyer and Dassen Islands). It seems that this behaviour is learnt, and it is not a behaviour common to the entire seal population, e.g. seals at three large mainland breeding colonies in Namibia had negligible amounts of seabird prey items in their diet (0.1%). The individual seals which do predate on seabirds mainly take fledglings, especially those of cormorants and gannets. Most attacks occur at sea, although recently some seals have come on land to attack breeding gannets. Only part of the birds are consumed, and in some cases the predatory behaviour has been likened to play behaviour. Although only a few seals are responsible for this predation, their level of predation can significantly impact on local seabird populations, because an individual seal may kill numerous seabirds in one day. To manage this impact, individual seals responsible for the behaviour are shot and seals are chased off some islands where seabirds are breeding.
Cats (wild and feral)
Feral cats (Felis catus) have been found to predate on seabirds, especially on Robben, Dassen and Marion Islands. On Marion Island cats consumed vast numbers of birds and caused the extinction of some. On Dassen and Robben Islands, cats predated on the endangered African penguin. To conserve the various seabirds involved, the cats on Marion Island were eradicated by 1991 after an intensive erdication programme which lasted a number of years, and those on Dassen were eradicated by 2001. Cats on Robben Island are in the process of being removed. Feral cats also pose problems to penguins on the mainland, e.g. penguins at the boulders colony. Bird Island (Lamberts Bay) is connected to the mainland by a causeway and thus seabirds may be susceptible to cats which come on the island via this causeway. Leopards (Panthera pardus) may also predate on penguins at the mainland Stony Point colony.
Giant petrels (Macronectes spp.) Both northern and southern giant petrels on the Prince Edward islands scavenge from seabirds there, such as penguins.
Great white pelicans (Pelecanus onocrotalus)
The breeding colony of great white pelicans on Dassen Island has increased greatly recently. In the last decade pelicans have started predating on chicks of kelp gulls, Cape cormorants and swift terns (Sterna bergii), by walking in groups through the colonies and plucking chicks from nests. This behaviour is expanding to other islands around Saldanha Bay. The impact of this predation on the breeding success of affected seabirds may be substantial.
Humans Humans in South Africa don't prey on seabirds anymore. However, in the past, African penguin eggs were harvested unabatedly since the 18th century. At that time, penguins were also a source of food. Egg harvesting continued until the 1960s on Dassen Island. This may have led to the reduction of some colonies. Juvenile Cape gannets were also captured as food until the mid 20th century.
Kelp gulls (Larus (dominicanus) vetula) Kelp Gulls on South Africa's offshore islands rob eggs and small chicks from a variety of seabirds, namely African Penguins, Cape Gannets, cormorants, terns and Hartlaub's Gulls (Larus hartlaubii). This predation is of most concern for the penguin and the Roseate Tern (Sterna dougallii).
Killer whales (Orcinus orca)
Killer whales around Marion Island predate on penguins (e.g. king penguins (Aptenodytes patagonicus)). Some observations have shown that the whales can operate in groups, encircling a large number of penguins and then attacking the group. In South Africa, although the African penguin has been known to show anti-predatory behaviour towards killer whales, it is likely that these whales are not an important predator.
Mongooses & genets Bird Island (Lamberts Bay) is connected to the mainland by a causeway and thus seabirds are susceptible to mongooses which may come onto the island via this causeway. Mongooses and genets may also predate on penguins at the mainland Boulders and Stony Point penguin colonies.
Scared ibis (Threskiornis aethiopicus) Sacred Ibis historically bred on the off-shore islands of the Western Cape before colonizing the mainland and establishing breeding colonies primarily within reedbeds at freshwater wetlands. Birds at off-shore breeding colonies are known to predate on seabird colonies, feeding on eggs and young of African Penguin, terns, gulls and cormorants, with some birds observed pulling adult seabirds off nests to get to the nest contents.
Sharks
Circumstantial evidence exists of sharks preying on African penguins, and research has shown that some injuries on African penguins may possibly be attributable to sharks, great whites (Carcharadon carcharias) being the most important shark predator.
Snakes
Mole snakes (Pseudaspis cana) found on Robben Island have been seen in the area of seabird breeding colonies, where they on the eggs of seabirds breeding there, such as African penguins.
Subadult and adult males of Antarctic fur seals have been observed to prey on macaroni (Eudyptes chrysolophus) and king penguins (Aptenodytes patagonicus) at Marion Island (Prince Edward Islands).
Black rats, such as those found on Robben Island, may feed on bird eggs and possibly small chicks, especially those of the endangered African penguin (Spheniscus demersus). Bird Island (Lamberts Bay) is connected to the mainland by a causeway and thus seabirds may be susceptible to rats which come on the island via this causeway.
Bird Island (Lamberts Bay) is connected to the mainland by a causeway and thus seabirds are susceptible to dogs which may come onto the island via this causeway. Dogs on Robben Island may also have posed a threat to some seabirds.
A small number of subadult and adult Cape males are known to prey on African penguins, Cape gannets (Morus capensis) and cormorants (bank (Phalacrocorax neglectus), Cape (P. capensis) and crowned (P. coronatus)) around some South African islands (e.g. Malgas, Dyer and Dassen Islands). It seems that this behaviour is learnt, and it is not a behaviour common to the entire seal population, e.g. seals at three large mainland breeding colonies in Namibia had negligible amounts of seabird prey items in their diet (0.1%). The individual seals which do predate on seabirds mainly take fledglings, especially those of cormorants and gannets. Most attacks occur at sea, although recently some seals have come on land to attack breeding gannets. Only part of the birds are consumed, and in some cases the predatory behaviour has been likened to play behaviour. Although only a few seals are responsible for this predation, their level of predation can significantly impact on local seabird populations, because an individual seal may kill numerous seabirds in one day. To manage this impact, individual seals responsible for the behaviour are shot and seals are chased off some islands where seabirds are breeding.
Feral cats (Felis catus) have been found to predate on seabirds, especially on Robben, Dassen and Marion Islands. On Marion Island cats consumed vast numbers of birds and caused the extinction of some. On Dassen and Robben Islands, cats predated on the endangered African penguin. To conserve the various seabirds involved, the cats on Marion Island were eradicated by 1991 after an intensive erdication programme which lasted a number of years, and those on Dassen were eradicated by 2001. Cats on Robben Island are in the process of being removed. Feral cats also pose problems to penguins on the mainland, e.g. penguins at the boulders colony. Bird Island (Lamberts Bay) is connected to the mainland by a causeway and thus seabirds may be susceptible to cats which come on the island via this causeway. Leopards (Panthera pardus) may also predate on penguins at the mainland Stony Point colony.
Both northern and southern giant petrels on the Prince Edward islands scavenge from seabirds there, such as penguins.
The breeding colony of great white pelicans on Dassen Island has increased greatly recently. In the last decade pelicans have started predating on chicks of kelp gulls, Cape cormorants and swift terns (Sterna bergii), by walking in groups through the colonies and plucking chicks from nests. This behaviour is expanding to other islands around Saldanha Bay. The impact of this predation on the breeding success of affected seabirds may be substantial.
Humans in South Africa don't prey on seabirds anymore. However, in the past, African penguin eggs were harvested unabatedly since the 18th century. At that time, penguins were also a source of food. Egg harvesting continued until the 1960s on Dassen Island. This may have led to the reduction of some colonies. Juvenile Cape gannets were also captured as food until the mid 20th century.
Kelp Gulls on South Africa's offshore islands rob eggs and small chicks from a variety of seabirds, namely African Penguins, Cape Gannets, cormorants, terns and Hartlaub's Gulls (Larus hartlaubii). This predation is of most concern for the penguin and the Roseate Tern (Sterna dougallii). 
Killer whales around Marion Island predate on penguins (e.g. king penguins (Aptenodytes patagonicus)). Some observations have shown that the whales can operate in groups, encircling a large number of penguins and then attacking the group. In South Africa, although the African penguin has been known to show anti-predatory behaviour towards killer whales, it is likely that these whales are not an important predator.
On Marion Island, the diet of lesser sheathbills also includes food scavenged from penguin colonies.
Bird Island (Lamberts Bay) is connected to the mainland by a causeway and thus seabirds are susceptible to mongooses which may come onto the island via this causeway. Mongooses and genets may also predate on penguins at the mainland Boulders and Stony Point penguin colonies.
Sacred Ibis historically bred on the off-shore islands of the Western Cape before colonizing the mainland and establishing breeding colonies primarily within reedbeds at freshwater wetlands. Birds at off-shore breeding colonies are known to predate on seabird colonies, feeding on eggs and young of African Penguin, terns, gulls and cormorants, with some birds observed pulling adult seabirds off nests to get to the nest contents.
Circumstantial evidence exists of sharks preying on African penguins, and research has shown that some injuries on African penguins may possibly be attributable to sharks, great whites (Carcharadon carcharias) being the most important shark predator.
Mole snakes (Pseudaspis cana) found on Robben Island have been seen in the area of seabird breeding colonies, where they on the eggs of seabirds breeding there, such as African penguins.
Penguin eggs and chicks form an important part of the diet of skuas on the Prince Edward islands.