South Africa is home to 88% of the world’s colonies of African penguins (Spheniscus demersus). The species is classified as Critically Endangered by the International Union for Conservation of Nature. This means there is a high risk the birds could go extinct in the wild following rapid population declines.
This species was once abundant along the coasts of South Africa and Namibia. But the population has fallen by about 78% over the last 30 years, driven by food scarcity, oil spills and climate-related shifts in the marine environment. African penguins mainly feed on anchovy and sardine. Changes in ocean conditions and overfishing have made it more difficult for the penguins to get enough food. In recent years, conservation organisations, scientists and government agencies have escalated efforts to halt this decline.
One of the most significant developments was a March 2025 court ruling that supported the introduction of improved no-fishing zones around key breeding colonies, to protect the penguins’ foraging grounds. Robben Island (11km north-west of Cape Town) is one of the colonies.
Protecting waters adjacent to breeding colonies is essential for the species’ long-term recovery. Food shortages in these areas, driven in part by competition with the purse-seine fishery (which uses a large net to surround schooling fish), have been directly linked to declining chick survival and the ongoing population collapse.
The court case (led by the organisations BirdLife South Africa and the Southern African Foundation for the Conservation of Coastal Birds) concluded that fish can no longer be caught within a 20km radius of Robben Island.
We are penguin researchers from the University of St Andrews, University of Exeter, the South African Department of Forestry, Fisheries and the Environment, and BirdLife South Africa. Our work has examined the interactions between penguins and fishing operations in detail, and can offer insights to guide the management of their respective needs.
Overlap with the fishing industry
Previous research into the effects of fishing on penguin populations has mostly looked at metrics such as the amount of fish removed by the fishery. But technology to track fishing locations and animal movement now enables us to look at the picture on a fine spatial scale. We can see where and how intensely commercial fishing and penguins overlaps, helping us identify areas that should be protected.
Our recent research used tracking data from penguins on Robben and Dassen islands, in the Western Cape of South Africa. We measured population-level spatial overlap between penguins and the local fishery. A small proportion of penguins were tracked using GPS devices, then we were able to simulate where more of the colony were going.
Knowing where a large proportion of the penguin population is sharing a particular space with fishing vessels makes it easier to target which areas to protect and when. It provides benefits for the fishing industry (allowing fishing in areas which are of lower importance to the penguins) and for the penguins (limiting competition with the fishery during the breeding season).
We also developed a new metric, “overlap intensity”, which captures not only how much space penguins share with fishing vessels, but how many individual penguins are affected. Traditional measures of spatial overlap simply calculate the percentage of area shared between predators (penguins) and fishing vessels. But this can dramatically underestimate the actual degree of interaction, especially when only a few areas are shared but many animals use them.
It reveals insight into ecological pressure and competition that area overlap alone misses. For example, it suggests stronger competition for prey than spatial overlap metrics imply. This method can not only be expanded to other colonies but more broadly to other species and ecosystems.
Our findings show that overlap increases sharply in years when fish are scarce. During 2016, a year of low fish abundance, around 20% of penguins foraged in the same areas as active fishing vessels. In years with healthier fish stocks, however, overlap dropped to just 4%. This pattern indicates that competition between penguins and the fishery intensifies when prey is limited. It poses the highest risk during sensitive periods such as chick-rearing, when adults must forage efficiently to provide for their young.
A new tool for risk and management
By quantifying overlap intensity at the population level, our study offers a powerful new tool for assessing ecological risk and supporting ecosystem-based fisheries management. It also provides practical guidance for designing dynamic marine protected areas that respond to real-time changes in predator–prey interactions.
Our results further show that the new no-fishing zone around Robben Island will protect a key foraging area to the north-east of the colony. This was previously one of the regions with the highest overlap between penguins and fishing vessels.
Continued monitoring will be essential to determine how overlap changes in response to the new ten-year purse-seine closures around both colonies. Similar assessments should also be conducted at additional breeding sites, including other islands involved in the closures. Foraging ranges of the penguins and the areas covered by the no-take zones vary from colony to colony.
Meanwhile, over the past few years, weighbridges have been installed at some colonies (including Robben Island) collecting penguin weights when they leave to feed and when they return. Data from these large scales will tell us more about how the closures affect penguin foraging success.
