African Penguins compete for food with seals and commercial fisheries. Commercial fisheries off South African and Namibia catch large quantities of sardine (Sardinops sagax) and anchovy (Engraulis capensis), important prey for African penguins. Sardine stocks off South African collapsed in the 1960's and off Namibia in the 1970's. The reduced availability of prey was probably the main reason for the large decrease in numbers of penguins from Cape Town to Lüderitz. For example, penguins at Possession Island declined from 23 000 pairs in 1956 to fewer than 500 pairs in 1987.
In addition to fishing, greatly expanded herds of Cape Fur Seals (Arctocephalus pusillus) have decreased availability of food to African Penguins.
Five of the world's 50 largest oil spills in history have occurred off the coast of South Africa. Oil spills have a major impact on African Penguins, especially when the oil washes ashore at breeding areas (Underhill et al. 1999). Contrary to experience elsewhere, the cleaning of oiled penguins in southern Africa is relatively effective and has been demonstrated to make a contribution to conservation efforst (e.g. Underhill et al. 1999). Catastrophic oil spills occur irregularly, but there is also persistent chronic oiling which accounts for steady high levels of mortality. For example, of 689 dead penguins found at St. Croix Island over a 10-year period, oil pollution accounted for more deaths (44%) than any other factor.