Trends in numbers of Kelp Gulls Larus dominicanus off western South Africa, 1978–2007

Abstract

The number of Kelp Gulls Larus dominicanus breeding at 11 islands in South Africa's Western Cape province increased during the period 1978 to 1999–2000 and then decreased. The increase came after removal of controls on gulls and was associated with supplementary food provided by fish factories and rubbish tips. The decrease resulted from predation of gull chicks at some colonies by an increased population of Great White Pelicans Pelecanus onocrotalus. At Dassen Island, the density of gull nests remained constant as the colony doubled, but decreased by 50% as the colony decreased. At Dassen and Schaapen islands, the clutch size increased after pelicans started eating chicks. Numbers of gulls at two southern colonies where pelicans are seldom encountered have increased recently. This may have been influenced by shifts to the south and east of several fish stocks and their associated fisheries.