The large-scale migration of sardines during winter in South Africa is a breathtaking spectacle eagerly anticipated each year, especially by the coastal communities in the KwaZulu-Natal province. However, researchers warn that climate change and overfishing are putting this species at risk.
According to a correspondent in South Africa, as winter begins in the Southern Hemisphere, cold waters rise. Off the coast of South Africa, silver-colored masses emerge from the ocean depths. These are massive schools of sardines, consisting of tens to hundreds of millions of sardines swimming densely, covering an area longer than 7 km, wider than 1.5 km, and deeper than 30 m. Following the nutrient-rich cold currents, sardines embark on their annual migration from Cape Agulhas to KwaZulu-Natal.
The large-scale migration of sardines during winter in South Africa. (Photo: AFP).
As they move north, schools of sardines become trapped between the eastern coast of South Africa and the warm waters of the Agulhas current flowing southwards. According to expert Peter Teske from the University of Johannesburg, sardines are trying to avoid the Agulhas current because they dislike the warm waters and prefer to move towards the cooler shallows near the coast. However, in the Eastern Cape province, the Agulhas current is too close to the shore, trapping them.
Additionally, sardine fishing activities become bustling, peaking in June each year, when up to 18,000 dolphins herd sardines into bait balls with diameters reaching up to 20 meters. At this time, sardines also become an easy target for other predators such as sharks, whales, seals, and various seabirds that participate in this oceanic feast. For the few sardines that survive the onslaught of predators, their future remains bleak. The schools continue to move northwards along the cold waters until the upwelling ceases. According to expert Teske, they keep moving into warmer waters – the worst possible habitat.
These cold-water sardines become trapped in a subtropical habitat that is too warm for their survival. This long journey of thousands of kilometers for these small fish ends in an “ecological trap” – making sardines a rare example of a mass migration that offers no clear benefits for the species’ survival. However, it is certain that this is part of the food web for endangered species such as African penguins, Cape cormorants, Cape gannets, and sharks. Experts warn that current overfishing practices and rising ocean temperatures are causing sardine stocks to decline, putting the world-renowned sardine migration at risk of extinction within the next few decades.
Currently, sardines are gradually appearing towards the end of the year, if at all. A 2019 study indicated that since the sardine migration was first documented in the press nearly a hundred years ago, the first appearance date of sardines has been delayed by 1.3 days each decade between 1946 and 2012, coinciding with the shift of warm ocean currents.
According to the findings of one study, changes in the migration timing of sardines have caused their predators and prey to no longer be in the same place at the same time. This has shown severe repercussions for top predators like Cape gannets and African penguins, which primarily feed on sardines. Marine biologist Stephanie Plön from Stellenbosch University suggests that disruptions in such events can cause a cascading effect, breaking down entire ecosystems following relatively small climate changes. However, experts note that there is very little research exploring the temporal shifts in migratory species like sardines and that more studies are needed to understand the relationship between atmospheric and ocean warming and what humans can do to mitigate the impacts of this phenomenon.
Sardines are an important commercial fish species in South Africa. Following the rapid decline in sardine catch yields in the mid-1960s, the industry changed its fishing strategy to use smaller mesh nets to catch juvenile anchovies in an effort to help restore sardine populations.
