South Africa's population of Kelp Gulls (Larus dominicanus vetula) numbered about 10,000 pairs during 1976/1977–1980/1981, increased to 21,000 pairs from 2000/2001–2004/2005 and then decreased to 17,500 pairs from 2009/2010–2013/2014. The increase in the late 20th century and the decrease in the early 21st century were mainly attributable to large increases and decreases in numbers breeding at islands off the west coast of South Africa. The increases followed cessation of controls on Kelp Gulls at the islands in the 1970s and were associated with supplementary food provided by fisheries and landfill sites, whereas the decreases were influenced by substantial predation of chicks by Great White Pelicans (Pelecanus onocrotalus). The decreases of Kelp Gulls at islands off the west coast of South Africa in the early 21st century were offset to some extent by an increase in numbers breeding on mainland sites, especially around greater Cape Town and along the south coast. The proportion of Kelp Gulls breeding on the south coast increased from 15% in 2000/2001–2004/2005 to 44% in 2009/2010–2013/2014. As there are fewer islands off the south coast than the west coast of South Africa, the proportion of Kelp Gulls breeding at mainland sites as opposed to island localities increased from 12% in 2000 to 31% in 2014. Mainland colonies are more susceptible to disturbance by humans and predation by mainland carnivores, but, in spite of this, the generalist Kelp Gull has performed better in recent years than several specialist, endemic seabirds. At Dyer Island and Bird Island (Algoa Bay), where Kelp Gull numbers increased, predation by Kelp Gulls on eggs and chicks of threatened seabirds is thought to have contributed to decreases in these seabirds, and controls on Kelp Gulls have been reintroduced.