Responses of African penguins to regime changes of sardine and anchovy in the Benguela system
Regional trends in numbers of African penguins Spheniscus demersus conform with an altered distribution of sardine Sardinops sagax and anchovy Engraulis capensis prey. In the 1950s, sardine dominated the pelagic fish component of the Benguela system. Abundance of this fish decreased in the 1960s and early 1970s and it was replaced by anchovy. Beginning in the early 1980s, sardine started to increase and anchovy to decrease in abundance. The decrease of the sardine resulted in collapses of colonies of African penguins between Lüderitz and Table Bay. Although colonies east of Table Bay increased, the overall population of African penguins fell by 25%. As the Benguela system started to revert to one dominated by sardine, penguin colonies between Lüderitz and Table Bay stabilized. Three new colonies were established in the vicinity of Table Bay, but the large colony at Dyer Island underwent a massive decrease. As a result, overall numbers of African penguins decreased by a further 19%. During shifts between regimes dominated by sardine and anchovy, African penguins that are breeding for the first time immigrate to colonies where food is plentiful. Inability of African penguins to cope with recent shifts between regimes may have resulted from increased competition for food with fishermen and seals during the 20th century.