The African Penguin Spheniscus demersus has decreased markedly in numbers through the 20th Century. In the first half of the century its eggs were harvested commercially, probably at a rate of 48% of total eggs produced. In 1910, the number of birds aged two or older at Dassen Island was estimated to be 1.45 million. This decreased to 0.22 million in 1956, 0.14 million in 1967 and just 0.03 million in 1990 - a loss of 98%. A colony may take more than 50 years to recover from a catastrophic oiling event, even with rehabilitation. In the long term, low-level chronic oiling can have a greater impact than a once-off catastrophic event, especially if disturbance results in substantial losses of clutches.