The Sardine Run: Enigma of the Sea
Every year, along the eastern coast of South Africa, something astonishing happens. A shimmering river of silver fish—millions strong—surges through the waters in a dense, pulsing mass. Behind them trail dolphins, sharks, gannets, whales and humans alike, all drawn to what is often called "The Greatest Shoal on Earth." This is the sardine run, one of nature’s most dramatic and least understood spectacles.
A living tidal wave
From May to July, the sardines—Sardinops sagax—migrate northward from the cool Agulhas Bank toward the warmer waters of KwaZulu-Natal. Shoals can stretch for kilometres, so dense they can be seen from aircraft. Divers who are lucky (and brave) enough to slip into the water encounter a surreal world: an endless blur of silver bodies, the electric hum of motion, and predators zooming among them.
Masses of common dolphins corral the sardines into tight bait balls. Cape gannets dive from the sky like missiles, plunging into the sea at dizzying speeds.
Copper sharks and dusky sharks slash through the fish from below, while Bryde’s whales lunge with open mouths to scoop up entire schools. It is a feast—and a frenzy.
But why do they run?
That is the mystery. The sardine run does not make a lot of sense—at least not from the sardines’ perspective.
The fish appear to be migrating from cold water into warmer waters that are near the upper limits of their tolerance. They spawn in both areas, so this long and risky journey is not strictly necessary for reproduction. Some scientists believe the sardine run might be a relic migration, left over from an ancient pattern when the waters were cooler, and the behaviour simply has not disappeared.
Others suggest that shifting currents and cold upwellings may trigger the run under very specific conditions. Some years, it does not happen at all—or is barely noticeable—leading researchers to question whether it is linked to climate variability or subtle shifts in ocean chemistry.
A feast for all—but for how long?
For predators, the sardine run is a once-a-year jackpot. For humans, it is a tourism bonanza and a dream for wildlife filmmakers. But for the sardines, it is a gauntlet.
And that is part of what makes the event so strange. The sardines are vulnerable and heavily targeted during the run—not just by wild predators but by commercial fisheries. Overfishing and ocean warming are threatening sardine populations throughout their range. If their numbers decline, the run may vanish altogether—leaving behind not only unanswered questions, but also entire food webs disrupted.
Mystery in motion
What drives these little fish to undertake such a perilous journey? Why only some years and not others? How long has this migration existed—and how much longer will it continue?
The sardine run is a reminder that even in our data-saturated age, the ocean holds on to its secrets. As divers and naturalists, we are witnesses to a story still being written—a shimmering epic of survival, strategy and sea-bound mystery. ■
Sources: Wikipedia.org
Ethologist Ila France Porcher, author of The Shark Sessions and The True Nature of Sharks, conducted a seven-year study of a four-species reef shark community in Tahiti and has also studied sharks in Florida with shark-encounter pioneer Jim Abernethy. Her observations, the first of their kind, have yielded valuable details about the reproductive cycles, social biology, population structure, daily behaviour patterns, roaming tendencies and cognitive abilities of sharks. Visit: ilafranceporcher.wixsite.com
