Sardine Run: The greatest marine festival on earth

South Africa has many tourist attractions and an annual attraction not to be missed is the spectacular marine festival occurring during May to August when the largest marine shoals on earth migrate along the east coast of South Africa to spawning sites where they release their eggs.

The ‘Sardine Run’ is a seasonal natural phenomenon that attracts a worldwide following of fish pilgrims, international sports divers and snorkelers. Scientists are still trying to unravel the enigma of the ‘Sardine Run’. Whilst research is ongoing, some hypothesis has been put forward to improve the understanding of the ‘Sardine Run’.

One hypothesis is that ocean currents allow for migration. Only a proportion of South African sardines break away from the main population of the Agulhas Bank along the southern Cape Coast where they habitat at temperatures lower than 21°C/ 70°F.

During winter, the water temperatures along eastern South Africa drop to below 20°C. The cold Benguela current pushing northwards from the Cape and the warm Agulhas current moving southwards create a narrow corridor within which the sardines swim to spawning sites along eastern Kwa Zulu Natal to release eggs.

Another hypothesis is that sardines return to their hatching place to reproduce, using sensory ability. In ancient times, sardines lived north off Kwa Zulu Natal, where the ocean was much colder. After the last de-glaciation, the seas got warmer and the fish had to migrate South.

In the annual reproductive season, sardines returned to their native place to scatter their eggs in the ancient spawning grounds. In spite of many dangers and high mortality suffered during the migration, sardines succeed in releasing their eggs in Kwa Zulu Natal waters, leaving them to drift back southwards, to the Agulhas Bank where they hatch the following year.

Confined to a narrow corridor, humongous shoals move together for protection. Shoals reach 7 km in length, 1.5 km in width and 30 m in depth. Silvery shoals can be seen from the shore or in the air. The mass migration attracts marine predators which include seabirds like Cape Gannets, sharks, seals, dolphins, and whales all pursuing their bountiful feast. Dolphins swimming at 40 km per hour use a hunting technique in an attempt to gather shoals for their gourmet buffet.

The sardines sensing danger instinctively group together forming a defense mechanism called ‘bait balls’. ‘Bait balls’ are one large evolving mass approximately between 10–20 metres in diameter, 10 metres in depth and lasting for 10 minutes.

Whales lunging through shoals devour mouthfuls whilst overhead mobs of surging seabirds cascade between 40 – 120 km per hour into the tumultuous waters to scoop off the bounty.

Called ‘The Greatest Shoal on Earth’, nature’s organised chaos of epic proportions enthralls from the air and beneath the sea. Underwater, divers and snorkelers delight in the grandeur.

Over the years, the ‘Sardine Run’ has become unpredictable and sometimes not occurring at all. Possible factors could be due to climate change causing high water temperatures or changes in the currents, illegal fishing, over fishing and loss of predator fish that don’t drive the shoals inshore or the migration may occur farther offshore.

But when sardine fever hits, Kwa Zulu Natal is alive with possibilities and tourism is boosted. Local tour operators plan diving expeditions, commercial fishing is undertaken where sardines are sold for human consumption or bait. Locals use seine nets to catch thousands of sardines as they enter the shallows in search of food. It is not unusual to find whole families catching sardines with washing baskets whilst gleefully filling their pockets. Its a fun-filled phenomenon that one must experience!