Penguins living off the coast of South Africa are likely to starve en masse during the molting season as a result of the collapse of food supplies, according to work led by the University of Exeter in the UK, in collaboration with an international team of researchers from the South African Department of Forestry, Fisheries and Environment. The work has been published in the peer-reviewed Journal of African Ornithology.
In fact, at two of the most important breeding colonies of the African penguin (Spheniscus demersus) – Dassen Island and Robben Island – it is estimated that about 95% of birds bred in 2004 died over the next eight years as a result of food shortages.
“Between 2004 and 2011, sardine populations off the west coast of South Africa consistently remained below 25% of maximum abundance, and this appears to have caused severe food shortages for African penguins, resulting in an estimated loss of 62,000 penguin individuals,” reports co-author and conservation biologist Richard Shirley of the Center for Ecology and Conservation, a world-leading research and education centre, based at the University of California. Exeter.
The researchers say the findings could have important relevance to management strategies aimed at helping to ensure the birds’ long-term survival.
In 2024, African penguins are classified as critically endangered, and restoration of sardine biomass in key foraging areas appears essential for their long-term survival. It is worth noting that African penguins shed their feathers annually, shedding them and replacing them with new feathers to maintain their insulation and water resistance. However, the temporary loss of this protection means that the birds must remain on the ground and cannot hunt during the molting process, which lasts about 21 days.
To prepare for this period without food, penguins must first fatten up. “They have evolved to store fat and then rapidly as their body metabolizes those stores and the proteins in their muscles to cope with molting,” explains Dr. Shirley, whose research focuses on using long-term data on animal populations to study human impacts on and interactions with the oceans.
“Then, they need to be able to quickly regain their fitness. So, if it’s too difficult to find food before or right after molting, they won’t have enough reserves to survive the fast.” This is exactly the danger penguins have faced over the past two decades.
Since 2004, the biomass of Sardinops sagax, a major food for African penguins, has fallen in all but three years to less than 25% of its maximum abundance on the west coast of South Africa.
Dr Shirley said: “Changes in temperature and salinity in breeding areas off the western and southern coasts of South Africa have reduced breeding success in areas of historical significance on the west coast, while breeding has increased off the southern coast. “However, due to historic industrial structures, most of the fishing remained west of Cape Agulhas, resulting in high rates of exploitation in that area in the early and mid-2000s.”
In their study, Dr. Shirley and his colleagues analyzed the numbers of breeding penguin pairs and adult penguins on Dassen and Robben Islands between 1995 and 2015. “These two sites are historically important breeding colonies, hosting approximately 25,000 dass and approximately 9,000 robin pairs in the early 2000s. They are home to long-term monitoring programs.” Adds Dr Azwiani Makhado, co-author of the study, from the Department of Forestry, Fisheries and Environment.
The authors looked at estimates of adult penguin survival rates based on capture mark and recapture analysis for the period 2004-2011.
Survival rates and the proportion of breeders who did not return to their colonies to molt were compared with a prey availability index developed for the region.
“Adult survival, especially through crucial annual molting, was closely linked to prey availability,” insists Dr. Shirley. “High rates of sardine exploitation – briefly reaching 80% in 2006 – during a period when their populations were declining due to environmental changes likely exacerbated penguin mortality.”
The team points out that the losses are not limited to Dasen and Robin only. “These declines are mirrored elsewhere,” Shirley says, adding that the species has seen a global population decline of about 80% in the past 30 years.
The prey index, which the team developed in a previous study published in the ICES Journal of Marine Science, is based on the proportions of anchovies and sardines, both of which are consumed by African penguins, in the diet of another bird, the gannet (Morus capensis). “The diet of the gannet is thought to be a good example of the availability of sardines and anchovies, as they are the most widespread seabirds in southern Africa that feed on these species,” explains Dr Makhado.
The team points out that restoring penguin numbers in the future is a difficult task, because the necessary improvement in sardine hatching depends mainly on environmental conditions. However, there are measures we can take.
“Fisheries management approaches that reduce exploitation of sardines when their biomass is below 25% of maximum and allow more adults to survive to spawn, as well as those that reduce mortality of recruits (juvenile sardines), can also help, although this is debated by some parties,” explains Shirley.
At the same time, several conservation measures have been taken to directly protect the penguins, including providing artificial nests, managing predators, as well as rescuing, rehabilitating and raising adult penguins and chicks.
In addition, commercial purse seine fishing has recently been banned in the six largest breeding colonies in South Africa. According to Dr. Makhado, this is expected to increase penguins’ access to prey at critical stages of their life cycle, such as chick rearing and pre- and post-molting.
With this study completed, researchers continue to monitor the reproductive success, condition of the chicks, foraging behavior, population trajectory, and survival of the African penguins.
“We hope that recently implemented conservation interventions, combined with lower rates of exploitation of sardines when their abundance is below 25% of maximum, will begin to halt the decline and that the species will show some signs of recovery,” Dr. Shirley concludes.