Impact of predation by Cape fur seals Arctocephalus pusillus on Cape gannets Morus capensis at Malgas Island, Western Cape, South Africa

Cape fur seals (Arctocephalus pusillus) were estimated to kill some 6 000 Cape gannet (Morus capensis) fledglings around Malgas Island in the 2000/01 breeding season, 11 000 in 2003/04 and 10 000 in 2005/06. This amounted to about 29%, 83% and 57% of the overall production of fledglings at the island in these breeding seasons, respectively. Preliminary modelling suggests this predation is not sustainable. There was a 25% reduction in the size of the colony, the second largest of only six extant Cape gannet colonies, between 2001/02 and 2005/06. There has been a large increase in predation by Cape fur seals on seabirds around southern African islands since the mid 1980s, coincidental with both an increase in the seal population and altered management of the islands. At Malgas Island, most gannet fledglings were killed between 10h00 and 18h00, the period when most are in the water around the island, from mid January to mid March, the main fledging period. The Cape gannet is classified as Vulnerable.