What Is the Sardine Run, and Why Is It Called the Greatest Shoal on Earth?
Each winter, along the wild eastern coast of South Africa, the sea does something almost unbelievable. Billions of sardines gather into shoals so vast they can stretch for kilometres, dark rivers of fish visible from the air, moving north through the cold coastal water. And behind them, above them plus beneath them comes everything that eats them: dolphins in their thousands, sharks, whales plus seabirds diving like spears from the sky. For a few weeks, a stretch of ocean becomes the scene of one of the largest gatherings of marine predators on the planet. People call it the greatest shoal on Earth.
If you were floating in the water in the middle of it, you would understand why. But the sardine run is more than a spectacle. It is a genuine natural puzzle, driven by ocean currents that are still not fully understood, and increasingly shadowed by a real question about whether it will continue at all. So what exactly is the sardine run, why does it happen, plus why does it deserve its extraordinary reputation?
Before reading this article, see if you can answer these three questions. By the end, you should be able to answer all three in your own words.
What actually happens during the sardine run, and when?
Why do billions of sardines make this journey at all?
What is uncertain about the run, including whether it will keep happening?
Keep them close. We will return to them at the end.
Quick Answer
The sardine run is a mass migration of billions of sardines north along South Africa's east coast each winter, roughly between May and July, trailed by enormous numbers of predators: common dolphins, sharks, whales plus diving Cape gannets. It is called the greatest shoal on Earth for its sheer scale, among the largest gatherings of marine life anywhere. It is driven by a band of cold coastal water, though the full picture is still debated, and its future is genuinely uncertain. POV Travel runs an expedition into the heart of it.
What actually happens
To grasp why the sardine run is so famous, you first need to picture what unfolds, because the scale is hard to overstate.
Each southern winter, very large numbers of sardines move northward along the eastern coast of South Africa, following a band of cooler water close to the shore. When conditions are right, they form shoals of staggering size, sometimes kilometres long and many metres deep, so dense that from above they look like vast dark stains spreading through the sea. And this concentration of prey draws an equally staggering response. Common dolphins arrive in their thousands and work together to herd portions of the shoal towards the surface, corralling the fish into swirling "bait balls." Once a bait ball forms, the assault comes from every direction: sharks slicing through, Cape gannets folding their wings and plunging from the sky like a hail of arrows, whales rising from below with mouths agape plus seals darting through the chaos. The dolphins behave almost like sheepdogs working a flock, pushing and turning the sardines into a tight, panicked mass that the other predators then tear into. For a few weeks, this drama repeats along the coast, and to be in the water beside a bait ball is to sit at the centre of one of the ocean's most intense events.
Why the sardines make the journey
Behind the spectacle lies a genuine question: why do billions of sardines undertake a journey that turns them into a moving feast? And the honest answer is that it is not fully settled.
The broad driver is temperature. Sardines favour cooler water, and the run is closely tied to a band of cold water that moves up the coast in winter, allowing the fish to push north into areas they could not otherwise tolerate. In that sense, the sardines are following a temporary cold corridor along the shore. But the finer details, exactly why the migration takes the form it does, why the numbers vary so dramatically from year to year plus what precisely triggers it, are still debated by researchers. Some questions remain about whether the run is a genuine population level migration or the movement of a particular cooler water group of sardines, and about how the various currents and temperature bands interact to produce it. What is clear is that this is not random. It is a phenomenon tightly linked to the physical oceanography of the coast. What is less clear, and genuinely interesting, is the full mechanism behind it. The sardine run is a case where a spectacle everyone can see rests on causes scientists are still working to pin down.
The greatest shoal, and its uncertain future
POV's approach is to be honest about the whole picture, and part of that picture is a real and growing question mark over the run itself.
The reputation as the greatest shoal on Earth rests on scale: in a strong year, the biomass of fish and the number of predators involved make it one of the largest marine gatherings anywhere. But the run is famously unpredictable. Some years it is spectacular; other years it is weak, late or barely materialises. And beneath that natural variability sits a deeper concern. Because the run depends so closely on cool water, warming seas raise a genuine question about its long term future. If the band of cold coastal water that drives the migration shrinks or shifts, the sardine run as we know it could weaken or change. Researchers are watching this closely, and it is fair to say the future of the run is genuinely uncertain rather than assured. This does not make the phenomenon any less extraordinary. If anything, it adds urgency and meaning to witnessing it: the greatest shoal on Earth is also a barometer of a changing ocean, and how it fares in the coming decades is a real open question.
Why This Question Matters
The sardine run is a vivid lesson in how the ocean actually works, and why its rhythms are worth understanding rather than just watching.
It shows how a single physical factor, a band of cool water, can orchestrate one of the planet's greatest wildlife events, linking currents, fish plus predators into one connected drama. It reveals the ocean as a tightly interdependent system, where a shift in temperature ripples all the way up to whales and seabirds. And it stands as a living indicator of ocean change, its unpredictability and uncertain future making it a phenomenon to understand and value now. To watch the sardine run with this understanding is to see not just a feeding frenzy but a window into the machinery of the sea, and into the questions we still cannot fully answer about it.
What Researchers Still Don't Know
Genuine uncertainties surround the sardine run, which is part of what makes it so compelling.
The precise triggers and mechanisms of the migration are not fully understood, and researchers continue to debate exactly why the run takes the form it does and why its scale varies so much between years. Whether it represents a broad population migration or the movement of a specific cool water group of sardines is still discussed. The full way in which currents, temperature bands plus the sardines' behaviour interact remains an active area of study. And the run's long term future under warming seas is genuinely uncertain, with real questions about how a phenomenon so dependent on cold water will fare. These gaps are not weaknesses in the story. They are the frontier of understanding one of the ocean's greatest events.
What Travellers Can Actually Experience
The remarkable thing about the sardine run is that, in a strong year, you can be right in the middle of it, in the water beside the action.
Along South Africa's Wild Coast in winter, expeditions head out by boat in search of activity, using diving birds, splashing plus other signs to locate the bait balls where predators are working the sardines. When a bait ball is found, snorkellers can enter the water nearby to witness dolphins, sharks, gannets plus sometimes whales converging on the same swirling mass of fish, one of the most intense wildlife encounters in the ocean. The run is unpredictable, so patience and flexibility are part of the experience, and no two days are the same. Responsible operators keep a respectful distance from the animals and let the natural behaviour unfold around you rather than interfering with it. Encountering the sardine run this way, with an understanding of the currents and predators involved, turns raw spectacle into something you can genuinely read and comprehend.
How POV Travel Approaches This Topic
We treat the sardine run as both an unforgettable spectacle and a genuine natural phenomenon worth understanding, not just filming.
So we set the drama in its context. We explain what drives the run, why the predators gather plus why the whole event hinges on a band of cool water. And we are honest about what remains uncertain, from the finer mechanics of the migration to the real question of how it will fare as the ocean warms. We would rather you understand the sardine run as a connected, fragile system than treat it as a simple thrill.
We show you the evidence and the open questions, then put you in the water to see it for yourself. The aim is that you leave not just having witnessed the greatest shoal on Earth, but understanding it.
Experience It Yourself
POV Travel runs the South Africa Sardine Run, a six day small group expedition along the Wild Coast in search of the bait balls and the predators that gather on them, in the heart of the run's May to July season. Groups are kept small, to a maximum of six, and the days are spent out on the water, reading the signs and entering the sea alongside the action when a bait ball forms. You can find the dates and details here: South Africa Sardine Run.
Frequently Asked Questions
What is the sardine run?
The sardine run is a mass migration of billions of sardines northward along the east coast of South Africa each winter, roughly between May and July. The enormous shoals draw huge numbers of predators, including common dolphins, sharks, whales plus diving Cape gannets, creating one of the largest gatherings of marine life on the planet. It is often called the greatest shoal on Earth. POV Travel runs an expedition into the heart of the run each season.
When is the sardine run in South Africa?
The sardine run typically takes place during the southern winter, broadly between May and July, though the exact timing varies from year to year and the run is famously unpredictable. It is closely tied to a band of cool water moving up the coast, so its timing and strength depend on ocean conditions. POV Travel's South Africa Sardine Run expedition is scheduled within this window to give the best chance of encountering the action.
Where is the best place to see the sardine run?
The sardine run is best experienced along South Africa's Wild Coast, in the Eastern Cape and KwaZulu-Natal region, where the shoals and their predators move north close to shore. Expeditions head out by boat to locate the bait balls where the feeding happens. POV Travel organises sardine run expeditions along this coast, taking small groups out on the water to find and, conditions permitting, snorkel near the action.
Can you swim with the sardine run?
Yes, in a strong year you can snorkel near the bait balls where dolphins, sharks, gannets plus whales gather to feed, one of the most intense wildlife encounters in the ocean. This is done responsibly, entering the water near the action while keeping a respectful distance from the animals. POV Travel's South Africa Sardine Run expedition is built around exactly this, taking small groups out to witness the feeding frenzy up close when conditions allow.
What animals can you see on the sardine run?
The sardine run draws a remarkable range of predators. Common dolphins arrive in their thousands and herd the sardines into bait balls; Cape gannets dive from the sky in huge numbers; several shark species move in to feed; whales, including Bryde's and migrating humpbacks, may appear; plus seals join the chaos. Together they make the run one of the greatest concentrations of marine predators anywhere, which is why it is such a sought after wildlife experience.
Why does the sardine run happen?
The run is driven mainly by temperature. Sardines prefer cooler water, and each winter a band of cool water moves up the coast, allowing the fish to push north into areas they could not otherwise tolerate. The finer details, including exactly why the migration takes its particular form and why its scale varies so much between years, are still debated by researchers. So while the broad cause is understood, the full mechanism remains an active area of study.
Is the sardine run disappearing?
Its future is genuinely uncertain. Because the run depends so closely on cool coastal water, warming seas raise a real question about its long term prospects: if the band of cold water that drives it shrinks or shifts, the run could weaken or change. It is already famously unpredictable, strong some years and weak in others. Researchers are watching it closely, and how it fares under a warming ocean is an open and important question.
Now, Can You Answer Them?
You held three questions at the start. Before you move on, take a moment with each, in your own words.
What actually happens during the sardine run, and when?
Why do billions of sardines make this journey at all?
What is uncertain about the run, including whether it will keep happening?
If you can work through all three, you understand why this is called the greatest shoal on Earth: a cold water migration of billions of fish that orchestrates one of the planet's largest predator gatherings, driven by causes researchers are still refining, and facing a genuinely uncertain future.
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