African penguins starving

African penguins along South Africa’s coast have likely starved in large numbers during their moulting season because of collapsing food supplies, a new study reveals.

At two key breeding colonies — Dassen Island and Robben Island — researchers estimate that about 95% of African penguins that bred in 2004 died over the next eight years because of food scarcity. 

The findings, published this week in Ostrich: Journal of African Ornithology, were produced by a team from the department of forestry, fisheries and the environment and the University of Exeter.

Between 2004 and 2011, sardine stocks off western South Africa were consistently below 25% of their peak abundance, said co-author and conservation biologist Richard Sherley from the Centre for Ecology and Conservation at the University of Exeter.

“This appears to have caused severe food shortage for African penguins, leading to an estimated loss of about 62 000 breeding individuals,” said Sherley, whose research focus is on using long-term data on animal populations to examine human impacts on — and interactions with — the oceans. 

The study highlights the urgent need to restore sardine populations in critical foraging areas. African penguins, classified as critically endangered last year, rely on these fish for survival.

The charismatic seabird, which is endemic to South Africa and Namibia, has lost 97% of its population. If current trends persist, the species will be extinct in the wild by 2035.  

Mass starvation during moult

African penguins undergo a major moult annually – usually soon after breeding – shedding and replacing all their worn-out feathers with fresh, new ones to keep up their insulation and water-proofing. 

During the period, they came ashore for about three weeks to shed and replace all their feathers at once, the study said, detailing how moult was essential because old feathers lose their insulation and swimming efficiency. 

Penguins with old plumage swim slower — about 14km/h compared to 19km/h with new feathers — and use more energy to move through the water.

While moulting on land, penguins also fast, losing nearly half their body weight. Much of the weight loss comes from the muscles used for swimming, so even with fresh feathers, their maximum swimming speed is temporarily reduced to about 10km/h, roughly the same as their main prey. 

To prepare for this, penguins must build up fat stores before moult and rebuild their strength afterward, a process that takes about 35 days before and 42 days after moulting. 

Pre-moult adults are on average 31% heavier than breeding adults. Failure to fatten properly or to recover afterward could be fatal, the study noted.

Moult is a critical stage in the penguin’s annual cycle. Penguins that need to prepare for moult may abandon breeding attempts, even leaving chicks behind, to feed and gain weight. This makes the timing and availability of food especially important for their survival.

The study noted how research showed a clear link between food availability and successful moulting. At Dassen and Robben islands, the proportion of penguins failing to moult rises when forage fish (sardine and anchovy) were scarce. 

Similarly, the number of adults successfully moulting predicted the number of breeding pairs in the following season, highlighting how essential good feeding conditions were for the population’s survival and reproduction.

Dangerously ‘underfed’

Since 2004, sardine biomass (the total weight of all sardines in an area used to track their population) off western South Africa has plunged below 25% of maximum abundance almost every year, leaving penguins dangerously underfed. 

Changes in the temperature and salinity of the spawning areas off the west and south coasts of South Africa made spawning in the historically important west coast spawning areas less successful and spawning off the south coast more successful, Sherley explained.

“However, due to the historical structures of the industry, most fishing remained to the west of Cape Agulhas, which led to high exploitation rates in that region in the early to mid 2000s,” he added.

Sherley and his colleagues analysed counts of the number of breeding pairs and moulting adult-plumaged penguins on Dassen and Robben islands from 1995 to 2015. 

The two sites are two of the most important breeding colonies historically, holding about 25 000 (Dassen Island) and 9 000 (Robben Island) breeding pairs in the early 2000s. 

“As such they are also the locations of long-term monitoring programmes,” said co-author  Azwianewi Makhado from the environment department. 

The authors factored in estimates of adult penguin survival rates based on capture-mark-recapture analysis for 2004 to 2011. 

Survival rates and the proportion of breeders that failed to return to their colonies to moult were compared with an index of prey availability developed for the region. Adult survival, principally through the crucial annual moult, was strongly related to the availability of prey, Sherley said. 

“High sardine exploitation rates — that briefly reached 80% in 2006 — in a period when sardine was declining because of environmental changes likely worsened penguin mortality,” he said.

Losses were not just confined to Dassen and Robben, the team noted. “These declines are mirrored elsewhere,” Sherley said, adding that the species had undergone a global population decline of nearly 80% in the past 30 years. 

The prey index, developed by the team in a previous study, is based on the proportions of anchovies and sardines, both of which are eaten by African penguins, in the diet of another bird, Cape gannets.  

“Cape gannet diet is thought to be a good ‘sampler’ of the availability of sardine and anchovy because they are the most wide-ranging of the seabirds in Southern Africa that feed on these species,” Makhado said. 

‘Difficult proposition’

Picking up the penguin population is a difficult proposition, as the required improvement in sardine spawning is fundamentally dependent on environmental conditions.  

Fisheries management approaches that reduced the exploitation of sardine when its biomass was less than 25% of its maximum and allowed more adults to survive to spawn, as well as those that reduced the mortality of juvenile sardines, could also help “although this is debated by some parties,” noted Sherley.

Ongoing conservation actions — such as artificial nests, predator management and the rehabilitation of adults and chicks — are crucial.

Commercial purse-seine fishing (large net) has recently been banned around the six largest breeding colonies, increasing penguins’ access to prey during critical life stages, including chick rearing and moulting, the authors said. 

In 2023, an international expert panel reviewing experimental fishing closures near breeding colonies concluded that such closures were likely to support population growth.

The panel emphasised, however, that while future closures could benefit penguin conservation, they would need to be part of a broader suite of conservation measures, as closures alone were unlikely to reverse the ongoing decline in penguin numbers.

Later that year, then minister of forestry, fisheries and the environment Barbara Creecy established no-take fishing zones around the six key penguin colonies, which together hold 76% of the global population. 

Initial assessments suggested that the spatial extent of these closures offered limited benefit to the penguins while imposing little to no cost on the purse-seine fishery. 

Following a settlement between conservation groups and the fishing industry, formalised by the high court earlier this year, Dion George, the former minister, revised the closures to better align with the penguins’ foraging ranges.

Hope for recovery

“It is hoped that the revised closures – which will operate year-round until at least 2033 – will decrease mortality of African penguins and improve their breeding success at the six colonies around which they have been implemented,” the authors said.

“In the face of the ongoing impact of climate change on the abundance and distribution of their key prey, other interventions are likely to be needed.” 

Fishing pressure should be managed carefully across different areas, taking into account that predators consume a larger share of fish when stocks are low, and that current procedures for allocating sardine and anchovy catches may not fully protect penguins’ foraging needs.

With the global African penguin population dropping below 10 000 breeding pairs in 2023, urgent action is needed to prevent further declines. 

The researchers said smaller colonies were at higher risk of extinction because low numbers reduced fitness and foraging efficiency. Penguins that fed in groups caught more prey, but very small colonies might not have enough birds to form effective foraging groups.

The fishing closures, along with wider management of sardine and anchovy fisheries, should help stabilise penguin colonies. These measures are also likely to benefit two other seabird species that rely on the same fish: the vulnerable Cape gannet and the endangered Cape cormorant.