Once a year, South Africa is home to a stunning natural event that allows people to see thousands of marine and seabird species up close—pods of dolphins, flocks of gannets, and much more—as they descend upon millions of fish in a performance that only Mother Nature can provide.
It’s known as the KwaZulu-Natal sardine run, or the greatest shoal on Earth. (Read more about it.)
The run typically happens in May through June, when huge schools of sardines, or shoals, head north along South Africa’s KwaZulu-Natal province, located on the country’s eastern seaboard. During the Southern Hemisphere’s winter months, the waters near the coast begin to cool off to temperatures that dip below 22 degrees Celsius, or 71.6 degrees Fahrenheit, expanding the areas of suitable habitats for sardines to swim.
As a result, these cooler waters lure the sardines in to swim close to the shore in large, dark masses. For large predators like sharks and whales that feed on sardines, this large migration is Thanksgiving dinner.
The seasonal shoals offer a rare opportunity to “witness this incredible spectacle, which we don't usually see as they are offshore,” says Carl van der Lingen, a research associate at the Marine Research Institute at the University of Cape Town. “We can see the incredible predation pressure that these fish are under and the sardine/predator interactions,” van der Lingen adds.
The run is a magnet for a variety of species, says Christina Hagen, a Pamela Isdell Fellow of Penguin Conservation at Birdlife South Africa. Among the animals that come out to prey are albatross, Cape gannets, African penguins, humpback whales, Cape fur seals, dolphins, and sharks.
Van der Lingen estimates hundreds of millions of fish participate in the run.
“We have done three surveys up the east coast during the run, and each time estimated about 30,000 tons of sardines,” says van der Lingen. Assuming each fish weighs about 70 grams, that translates to 430 million fish.
He also estimates there are nearly 10,000 common dolphins and thousands of gannets associated with the KZN run.
It’s the incredible amount of fish in a comparatively small area that draws so many predators, Hagen says.
“It is remarkable because of the sheer numbers of fish and their predators that gather in one place,” she says. “In terms of biomass, it is larger than the wildebeest migrations of East Africa.”
The KwaZulu-Natal sardine run is more than just a yearly show that people flock to the coast to see; it is a phenomenon that fascinates scientists like van der Lingen. The “what” isn’t the only intriguing question.
“We think we have the answer,” van der Lingen says. The run “is most likely the spawning migration of a genetically distinct subpopulation of sardine,” he says.