Sardine run
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The Sardine Run occurs between May and July along the East coast of South Africa when millions of sardines move up northwards. The sheer numbers create a feeding frenzy along the coastline in what is one of the largest marine events in the world. This has been dubbed "the greatest shoal on earth" by the Kwazulu-Natal tourist board.
The sardines spawn in the cool waters of the Agulhas Bank through spring and early summer. Most of the fish stay in the cooler waters of the Atlantic Ocean and end up along the west coast of Africa.
It is thought that 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 coast line and goes further East out into the Indian Ocean.
In terms of biomass, researchers estimate the sardine run could rival East Africa's great wildebeest migration[1]. However, little 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. In 2003, the sardines failed to 'run', the 3rd time in 23 years [2]. While 2005 saw a good run, 2006 marked another non-run. [3]
The shoals are often more than 7 km long, 1.5 km wide and 30 meters deep and are clearly visible from spotter planes or from the surface.
Sardines group together when they are threatened. This instinctual behaviour is a defense mechanism as individuals are more likely to be eaten than large groups. These bait balls can be 10-20 metres in diameter and extend to a depth of 10 metres. The bait balls are short lived and seldom last longer than 10 minutes.
It is thought that dolphins (eastimated as being up to 18,000 in number, mostly the common dolphin but also the bottlenose dolphin) are largely responsible for rounding up the sardines into bait balls. Once the sardines are rounded up, sharks (primarily the bronze whaler, but also dusky shark, blacktip shark, spinner shark and zambezi shark), game fish (like shad or elf, king mackerel, various kingfish species, garrick, geelbek and eastern little tuna) and birds (like the Cape gannet, cormorants, terns and gulls) take advantage of the opportunity.
The Cape Fur Seal follows the shoals up the Eastern Cape coastline as far as Port St Johns.
