Influence of local and regional prey availability on breeding performance of African penguins Spheniscus demersus

Abstract

Population trends of African penguins Spheniscus demersus in the Western Cape, South Africa, and their breeding success have been linked to the abundance of their main prey, sardine Sardinops sagax and anchovy Engraulis encrasicolus. During the late 1990s and early 2000s, both fish species increased markedly in abundance, but after 2004, sardine biomass decreased to below average levels. In addition, adults of both stocks were principally located to the east of Cape Agulhas from 2001 to 2009 and were thus distant from seabird colonies on South Africa's West Coast. The number of African penguin pairs counted at Robben Island from 2001 to 2009 and the fledging period of chicks from successful nests increased and decreased in apparent response to the biomass of sardine prior to each breeding season, possibly linked through adult condition at the onset of breeding. Breeding success and chick-fledging rates increased during the study period and showed positive relationships with local food availability, indexed through the annual industrial catch of anchovy made within 56 km (30 nautical miles) of the colony. In addi- tion, chick-fledging rates were depressed in 2-chick broods during years when anchovy con- tributed <75% by mass to the diet of breeding birds. Previously reported relationships between the overall abundance of forage fish in South Africa and penguin breeding success were not sup- ported. Taken together, these results highlight the combined importance of ensuring adequate local food availability for seabirds during the reproductive cycle and safeguarding regional prey abundance during the non-breeding season.