African penguins off the coast of South Africa are starving to death

At two historically important colonies of the species Spheniscus demersus - Dassen and Robben Islands - approximately 95 per cent of the birds nesting in 2004 are estimated to have died over the next eight years due to lack of food.

This was the conclusion reached by an international team of scientists from the South African Department of Forestry, Fisheries and Environment and the University of Exeter, UK. The study is published in Ostrich: Journal of African Ornithology.

Moult + starvation: a deadly combination

African penguins moult once a year, completely changing their feather cover to maintain the insulation and water-repellent properties of their plumage.

During the moult, they:

• lose their defences,

• they're forced to stay on land,

• theycan't hunt for about 21 days.

So the birds have to "fatten up" a lot before the moult, and quickly regain condition afterwards.

"They are evolutionarily adapted to store fat and then starve, using up reserves and muscle protein," explains co-author of the paper, environmental biologist Dr Richard Sherley (University of Exeter). - If prey is too hard to find before or immediately after the moult, there are simply not enough reserves to survive the moult".

This was the situation for penguins off the west coast of South Africa in the 2000s.

Sardine disappears - penguins die off

Since 2004, almost every year (except three) the biomass of sardine (Sardinops sagax) off the west coast of South Africa has fallen below 25 per cent of its peak. And it is sardine that is the key prey of African penguins.

According to Shirley, between 2004 and 2011, sardine stocks in the west of the country "consistently stayed below a quarter of peak levels," which led to an estimated loss of about 62 000 nesting adult birds.

Additionally, the situation has been made worse by:

• changes in temperature and salinity in traditional spawning areas,

• a shift in spawning success from the west coast to the south coast,

• while commercial fishing continued to be concentrated west of Cape Agulhas for historical reasons,

• this led to very high exploitation of the stock in the mid-2000s, with fishing pressure on sardine briefly reaching 80 per cent in 2006.

How the study was conducted

Scientists analysed monitoring data for Dassen and Robben Islands from 1995-2015:

• counts of nesting pairs,

• counts of moulting adult penguins in mating plumage,

• statistical estimates of adult survival (capture-mark-recapture method) for 2004-2011.

The resulting indices were compared with a foraging availability index developed previously for the region.

Results:

• adult bird survival, primarily during the annual moult period, was closely related to prey availability;

• high fishing pressure on sardine in years when stocks were already declining due to natural factors significantly increased penguin mortality.

Similar dynamics have been recorded at other colonies: overall, the species has declined by almost 80 per cent over the past 30 years. In 2024, the African penguin was officially categorised as Critically Endangered.

What can be done

Restoring the penguin population, the authors emphasise, is an extremely difficult task:

• a key factor is improving sardine spawning,

• which depends on marine conditions that humans have limited influence on.

Nevertheless, the researchers identify measures that could help:

• limiting sardine fishing when its biomass falls below 25 per cent of its maximum, so that more adults survive to spawn;

• reducing mortality of juvenile fish;

• tightening fisheries management approaches in key penguin feeding areas.

In parallel, direct bird conservation measures are already being implemented:

• installation of artificial nests,

• predator management,

• rescue, rehabilitation and feeding of adults and chicks.

In addition, purse seine fishing for finfish was recently banned around the six largest African penguin colonies in South Africa.

According to Dr Azwianewi Mahado (South Africa's Department of Forestry, Fisheries and Environment), these measures should improve access to food during critical periods of the life cycle, including chick rearing and preparation for moulting.

Scientists continue to monitor breeding success, chick condition, foraging behaviour, population dynamics and survival of African penguins.

"We are hopeful that the combination of recent conservation measures and reduced fishing pressure on sardine at low resource abundance will help arrest the decline in abundance and reverse at least part of the trend over time," Sherley concludes.