South Africa’s Sardine Run occurs between May and July when billions of sardines – or more specifically the Southern African pilchard Sardinops sagax – spawn in the cool waters of the Agulhas Bank and move northward along the east coast of South Africa past the beaches of KwaZulu-Natal. The run, containing millions of individual sardines, occurs when a current of cold water heads north from the Agulhas Bank up to Mozambique where it then leaves the coastline and goes further east into the Indian Ocean.
In terms of biomass, researchers estimate the sardine run could rival East Africa’s great wildebeest migration, and as a spectacle it is equally amazing. Little, however, is known of the phenomenon. It is believed that the water temperature has to drop below 21°C in order for the migration to take place.
Sardines group together when they are threatened. This instinctual behaviour is a defense mechanism, as lone individuals are more likely to be eaten than large groups. This creates huge shoals which are often more than 7 km long, 1.5 km wide and 30 meters deep!
These shoals are clearly visible from spotter planes or from the surface – but they also attract huge numbers of predators who close in on the swirling silvery masses of tightly packed fish.
The Cape Fur Seal follows the shoals up the Eastern Cape coastline as far as Port St Johns, but they are just one of the marine creatures who turn up for the feast. About 18,000 Dolphins (mostly the common dolphin but also the bottlenose dolphin) divide the shoals into smaller bait balls. These, as the name suggests, are masses of fish swimming in a spherical formation about a common centre. It is a last ditch defensive measure adopted by schooling fish when they are threatened by predators. These balls can be 10–20 metres in diameter and extend to a depth of 10 metres.
Once the bait ball has been formed the dolphins rush in and gorge themselves, scattering the sardines in all directions before the ball swiftly re-forms itself. The bait balls are short lived, seldom lasting longer than 10 minutes. That’s because all this activity attracts a wide range of other predators.
Sharks arrive in huge numbers – primarily the Bronze Whaler, but also Dusky Shark, Grey Nurse Shark, Blacktip Shark, Spinner Shark, Hammerheads, Great Whites and Zambezi Shark. They are joined by game fish such as shad/elf a.k.a. Bluefish, King Mackerel, various Kingfish species, Garrick, Geelbek and Eastern Little Tuna. Cape Gannets dive from the sky like black and white arrows, scything into the balls from above. Cormorants, Terns and Gulls all get in on the action too. Even Whales cruise through the clouds of fish gulping down huge numbers. The term “feeding frenzy” hardly does the spectacle justice!
Not surprisingly this breath taking phenomenon, one of the world’s greatest natural wonders, attracts spectators from all over the world. Even from a boat it is a magnificent sight, but many venture into the blue seas to snorkel or dive in the boiling waters.
Words alone cannot do the occasion justice – but have a look at these video clips and you’ll see why so many people find the experience totally unforgettable.