Food, fishing and seabirds in the Benguela upwelling system

Abstract

The Benguela upwelling system off south-western Africa supports sardine Sardinops sagax and anchovy Engraulis encrasicolus that are harvested by purse-seine fisheries and are the main prey of three endemic seabirds: African Penguin Spheniscus demersus, Cape Gannet Morus capensis and Cape Cormorant Phalacrocorax capensis. There have been large, long-term changes in the abundance and distribution of the fish resources that have influenced seabird populations. After 1956/1957, the numbers of penguins and gannets breeding in Namibia decreased by 90% and 95%, respectively. After 1978/1979, the number of Cape Cormorants breeding in Namibia decreased by 76%. These decreases were significantly related to the biomass of sardine and anchovy in Namibia and are thought to result mainly from a greatly reduced availability of prey. In South Africa, when the sardine collapsed, it was replaced by anchovy. In the Western Cape, the numbers of Cape Gannets and Cape Cormorants were stable after the collapse of the sardine but African Penguins decreased. The sardine resource recovered in the 1980s and 1990s but, at the turn of the century, was displaced to the east, leading to increases and then decreases in the numbers of penguins and gannets in the Western Cape. In the Eastern Cape, there were long-term increases in the numbers of penguins and gannets, until a recent decrease in penguins. In South Africa, the models used to advise allowable catches for sardine and anchovy are being modified to incorporate a model of African Penguins and functional relationships linking penguins and fish stocks. Consideration is also being given to precluding fishing in areas around seabird breeding colonies.