Over 60,000 African penguins starved to death between 2004 and 2011 after sardine stocks collapsed

Overexploitation of sardines off southern Africa led to the deaths of over 60,000 African penguins, new research suggests, with scientists linking the die-off to chronic food shortages during the birds’ annual moult.

The study, published in the journal Ostrich: Journal of African Ornithology, found that nearly 62,000 penguins died between 2004 and 2011, largely around Dassen and Robben islands. The period coincided with a collapse in sardine (Sardinops sagax) populations, which were estimated to have fallen to about 25 per cent below their maximum recorded abundance.

African penguins (Spheniscus demersus), which were uplisted to ‘critically endangered’ on the IUCN Red List in 2024, undergo an annual moult lasting about 21 days. During this period, the birds come ashore, shed their feathers and cannot enter the water to feed. They must therefore accumulate sufficient fat beforehand — and regain body condition quickly afterwards — or risk dying of starvation before new feathers grow in.

“At both islands, annual survival rates of adult penguins, and proportions of breeders that failed to return to their colonies to moult, were significantly related to an index of prey availability developed for the region,” the study reported. “Although some adults moulted at a colony to the southeast, where food may have been more plentiful, much of the mortality likely resulted from failure of birds to fatten sufficiently to moult.”

Pre-moult penguins typically require around 35 days to build up fat reserves and are about 31 per cent heavier than breeding adults. During the moult itself, the birds lose almost half their body mass (47 per cent), including muscle, and their swimming speed drops from about 19 kilometres per hour (kmph) to 10 kmph. This severely reduces their ability to catch prey once they return to sea.

After moulting, African penguins need reliable access to food for roughly 42 days to recover body condition. Without this, their energy reserves are rapidly depleted, often fatally.

The researchers noted that fishing pressure on sardines was particularly intense west of Cape Agulhas between 2005 and 2010, with exploitation rates remaining above 20 per cent and peaking at 80 per cent in 2006.

“High regional exploitation rates give rise to the potential for localised fisheries impacts on dependent predators,” the authors wrote in the paper. “For example, 70,000 tonnes of sardine were caught within 30 km of Dyer Island in 2004 and, when the size of that African penguin colony was over 3,500 pairs, numbers breeding were negatively related to sardine catches made within 20 nautical miles of it.”

They added that climate change is already reshaping the distribution and abundance of sardines, further threatening the species, and that broader spatial management of fishing pressure, as recommended by the African-Eurasian Migratory Waterbirds Agreement, 2020 may be required.

Long-term recovery of sardine biomass within key penguin foraging grounds will be essential for the species’ survival, the study concluded.