With information from Judy Mann, South African Association for Marine Biological Research
Images by Steve Woods
As the winter wind begins to bite, hordes head to the beaches of South Africa’s east coast with nets, fishing rods or scuba gear in hand. The coastline is washed silver with millions of sardines fighting furiously for survival. This is the sardine run.
WHAT CAUSES THE SARDINE RUN?
The bulk of the South African sardine (Sardinops sagax) population is found in the upper layers of the ocean between the Western Cape coast and the Agulhas Bank area, off the Southern Cape coast, where these fish spawn. They are cold-water fish that live in areas of cold upwellings (where deeper, cooler, nutrient-rich water surges to the surface as it reaches shallow coastal areas).
There are many theories as to why, each winter, large shoals of sardines make the one-way trip from the cooler waters of the Cape to the warmer waters of KwaZulu-Natal. The most popular one is that the penetration of cooler water eastwards along the Eastern Cape effectively expands the suitable habitat available for sardines. A small proportion therefore spills over into the narrow band of cool, northerly-flowing water that is created between the coast and the warm Agulhas Current. This upwelling of cool water is aided by south-westerly winds which likely also influence the movement of the sardines northwards.
However, the sardine run is increasingly unpredictable, due to overfishing and changing environmental conditions. The cool band of water close to shore is critical to the run; if the water is too warm (over 20°C), the sardines remain in the cooler water further south or move northwards further offshore and at greater depths where the water is cooler.
Aside from expanding their habitat, it is not clear what advantage the sardines gain by entering KwaZulu-Natal waters. In fact, these waters contain less food than Cape waters, the cooler conditions there are only temporary and, to top it all, the sardines are decimated by the many predators which follow hot on their heels. Because the fish become concentrated at the surface in the narrow band of cool water, they are quickly found by predators that feast on this unexpected meal in these otherwise less productive waters.
WHY IS THE RUN SO IMPORTANT BIOLOGICALLY?
The extraordinary productivity of sardines sustains the populations of many larger marine species. As they “run”, the sardines are followed by a great concentration of predators. Sharks such as copper, dusky, blacktip and spinners compete for a share of the bounty. Gamefish such as shad, garrick and geelbek are in hot pursuit of the shimmering mass of sardines. Marine mammals such as Cape fur seals and even humpback and minke whales have been known to join the feeding frenzy. Seabirds such as cormorants, terns, gulls and the endangered African penguin gorge themselves on the band of silver fish. Other opportunistic predators attracted by the commotion can appear, including tunas, sailfishes, sea lions and lunging Bryde’s whales. Orcas have also been known to show up, hoping to snatch a dolphin.
It is estimated that around 20 000 dolphins (mostly common dolphins) take advantage of the run, appearing in super pods of up to 5 000 individuals. They have developed special hunting techniques using their sonar skills and bubble streams to locate and isolate a ball of sardines. They “herd” part of the shoal away from the rest by working together underwater. The dolphins twist and turn below the isolated shoal, driving it upwards. The sardines are then rounded up into densely packed groups, called “bait balls”, at the surface. These bait balls can be up to 20m in diameter and reach a depth of 10m, but are short-lived, seldom lasting longer than 10 minutes. This is natural, given the multitudes of predators below as well as the onslaught of the seabirds above.
About 100 000 Cape gannets are part of this spectacle. These birds time their breeding to coincide with the arrival of the sardines. With remarkable eyesight, the gannets can see the sardines from the air and are able to target their dive precisely. Once the target is locked, the gannets dive from 30-40m above the ocean’s surface, piercing it head-first at speeds of up to 120km/h. Luckily, these amazing birds have air pockets in their joints which act as shock absorbers to cushion the blow; their nostrils also have flaps which prevent water from being pushed into their brains. Once they are immersed, they continue to dive as deep as 15m for around 20 seconds to get their fill of sardines.
WHY DIVING THE RUN IS A DIVER’S DREAM
This is a phenomenon that everyone must witness at least once, whether from a boat, while snorkelling, or – should you be lucky enough – on a dive. While snorkelling allows you to jump into the water with a moment’s notice, ensuring you do not miss any of the action, diving allows you a front-row seat to “the greatest show on earth”. If you are a freediver, you can combine the best of both worlds and slip into the water with less restrictions and time wasted. Nothing beats the diver’s perspective of all the incredible activity underwater. The ocean is full of energy and sound; the mass of sardines boils at the surface. As wheeling squadrons of gannets mount an unrelenting aerial assault, the frantic screeches from the vortex become deafening. If you are underwater during such an assault, your ears will be battered by a barrage of artillery fire. The explosions of each bird’s impact with the water goes right through you. This noise and vibration attracts dolphins and sharks from kilometres away. Soon, you will hear the clicks and whistles of schools of hundreds of dolphins as they streak past you into the sardines. As things heat up, you might just hear the haunting song of a whale as it looms below you, opening a cavernous mouth in anticipation, large enough to swallow you whole. Everything happens all around you, at lightning-fast speed; what an adrenaline rush.
During the run, the sardine shoals are often more than 7km long, 1.5km wide and 30m deep. They are clearly visible from spotter planes and even from space! Keep in mind, though, that sardine run diving is hard work; be prepared to spend hours at sea every day and sometimes, see very little. Conditions can be miserable with a winter chill in the air. Finding the sardines every day is not guaranteed, though with time, patience and a little luck, your efforts might just be rewarded beyond your wildest imagination. Remember that, on the quiet days, there is still plenty more to see and do; not the least of which is the chance to dive with humpback whales, also migrating up this coastline at this time of the year. In essence, keep in perspective that this is a wild adventure; seize every opportunity and make the most of your time both above and below the water. Watch the horizon for the gannets and other seabirds, read the signs and just celebrate being out on the ocean. If you are fortunate enough to join an experienced sardine run team, you will have the best chance of success. All that remains is for you to react!
The sardine run is surely one of the most amazing wildlife experiences out there – a marine spectacle beyond comprehension. Divers have a unique opportunity to get right up close and personal with one of nature’s unexplained mysteries. Make sure you take advantage of the once-in-a-lifetime opportunity to be in the thick of what many of the world’s top marine biologists, wildlife photographers and filmmakers call the most intense wildlife event in the world.
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