A dramatic crash in food availability off South Africa’s west coast may have pushed African penguins into a years-long starvation crisis and one that wiped out the vast majority of breeders at two of the species’ most important colonies.

A new study published today in Ostrich: Journal of African Ornithology reports that roughly 95% of penguins that bred on Dassen Island and Robben Island in 2004 died within the following eight years, a period marked by chronically depleted sardine stocks.

Researchers from South Africa’s Department of Forestry, Fisheries and the Environment and the University of Exeter have suggested that the losses occurred largely during the birds’ annual moult, when penguins must remain on land and cannot feed.

“Between 2004 and 2011, the sardine stock off west South Africa remained below 25% of its peak abundance,” said Dr. Richard Sherley of the University of Exeter’s Centre for Ecology and Conservation. “This appears to have caused severe food shortage for African penguins, leading to an estimated loss of about 62,000 breeding individuals.”

African penguins undergo a 21-day moult each year, shedding their waterproof plumage and emerging with new insulation. The trade-off, however, is a severe one. The birds cannot enter the water and must rely entirely on fat reserves. If they cannot bulk up beforehand – or recover quickly afterward – many simply don’t survive.

“They are evolved to build up fat and then to fast,” Sherley explained. “If food is too hard to find before they moult or immediately afterwards, they will have insufficient reserves to survive the fast.”

That scenario appears to have unfolded repeatedly since 2004. With sardine biomass collapsing off the west coast – due both to environmental shifts and intensified fishing pressure – penguins found themselves caught in a nutritional bottleneck.

Warming temperatures and shifting salinity in historically important west-coast spawning grounds reduced sardine reproduction there, pushing much of the spawning activity farther south. Yet, fishing fleets continued to concentrate effort west of Cape Agulhas, resulting in what the authors describe as “high exploitation rates”, at times approaching 80%.

These environmental and industrial pressures combined to leave penguins with little to eat at the very moments they needed energy most.

The research team analysed two decades of monitoring data from Dassen and Robben islands – once home to roughly 34,000 breeding pairs combined. Capture-mark-recapture data from 2004 to 2011 showed that adult survival during the moult was tightly linked to prey availability, as measured by a regional prey index based on Cape gannet diets.

“These declines are mirrored elsewhere,” Sherley added, noting that the species has fallen nearly 80% globally over the past 30 years.

The authors warn that recovery will be challenging. Sardine spawning success depends heavily on environmental conditions, and improved fisheries management remains a subject of debate.

However, recent conservation measures offer glimmers of hope. These include artificial nests, predator control, and expanded rescue and rehabilitation programs. In a major policy shift, South Africa has also banned purse-seine fishing around the six largest penguin colonies, a move intended to improve penguin access to prey during their most vulnerable life stages.

“In 2024, African penguins were classified as Critically Endangered,” Sherley said. “Restoring sardine biomass in key foraging areas will be essential for their long-term survival.”

The team continues to track penguin foraging behaviour, breeding success and overall population trends. “We hope that the recent conservation interventions, together with reduced exploitation rates of sardine when its abundance is less than the 25% threshold, will begin to arrest the decline,” Sherley said. “We are looking for the first signs of recovery.”

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