Sardine run shoals off South Africa are often more than 7 kilometers long. The spectacular shoals form during the annual KwaZulu-Natal sardine run, when Southern African pilchards move northward along South Africa’s eastern coast.
A typical shoal can also be about 1.5 kilometers wide and 30 meters deep, making it visible from aircraft and sometimes from the sea surface. The immense concentration attracts dolphins, sharks, whales, seals, seabirds and commercial or small-scale fishers, producing the famous feeding frenzy.
The migration is linked to cool coastal water moving north from the Agulhas Bank. Sardines prefer temperatures below roughly 21°C, while the warm Agulhas Current offshore can restrict their movement to a narrow inshore corridor. In unusually warm or unfavorable years, the run may be weak, offshore or apparently absent.
The event is not guaranteed every year, and climate change and fishing pressure have raised conservation concerns. “More than 7 kilometers” describes the length of the shoals, not the total distance traveled by the migrating fish.