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The Most Extraordinary Shoal on Earth

As an enormous shimmering mass appears along the South African coastline, gannets are sent torpedoing into the ocean, common dolphins are seen near shore, and breaching whales dance down the horizon. Yes, the most magnificent shoal on earth is here! The migration begins just off Cape Point, where the sardines leave the colder waters of the Agulas Bank after spawning.

They swim along the eastern coast of South Africa, towards the port of Durban. Their journey is approximately 2,000 kilometers (1,250 miles) long, and not only does it attract thousands of tourists, but also a large variety of predators that are all too eager to feast at the annual pilchard party.

Common Dolphins Working Together to Make a Bait Ball

The run usually includes around 10 million sardines and the shoal can often reach up to 7 kilometers (more than 4 miles) in length and about 1.5 km (up to 1 mile) in width, resulting in the largest fish migration on earth, rivaling that of east Africa’s Great Wildebeest migration across the Savannah.

The run occurs as a result of a current of cold water that drives millions of sardines north, towards Mozambique, where the shoal eventually moves away from the coastline, eastwards into the Indian Ocean.

The shoal brings together a diversity of predators, all trying to get their share of the shimmering buffet. The common dolphins steal the show in pods of up to 5,000 individuals, with snorkelers describing the event as completely “mind-blowing”.

Sharks Preying on Shimmering Mass of Sardines

By using bubbles and teamwork, they separate a portion of the sardines from the large shoal (sardines instinctively group together as a behavioral defense mechanism due to the increased chance of survival) and form bait balls that vary between 10-20 meters in diameter. The dolphins then force the bait ball towards the surface (up to 10 meters) where the sardines are easiest to catch.

The bait balls add fuel to the fire, as sharks like the bronze whaler sharks, spinner sharks, dusky sharks, grey nurse sharks, black tip sharks, and zambezi sharks gorge on the sardines once they've been rounded up. Other predators include game fish (bluefish, king mackerel, various kingfish species, garrick and geelbek), birds (Cape gannet, cormorrants, terns and gulls) that plummet into the ocean in massive numbers, penguins, seals, and finally the largest of the melee of predators, the humpback whale, also ‘drops in’ to take advantage of the opportunity.

Shark Feasting on Bait Ball

The whales also put on marvelous courtship displays on their migration route to the northern warmer waters to mate and calve, with pectoral and tail slapping leaving the onlookers in awe.

Why the second largest animal migration occurs is still a mystery, but it is believed to be temperature dependent, only occurring when the warmer ocean temperatures decrease to below 21°C. Although the reason for this extraordinary event remains unclear, it undoubtedly is one of nature’s most spectacular phenomenon and a dream come true for any photographer, underwater or above.

Common Dolphins Hunting Sardines


Further Reading

Overview of Scuba Diving in South Africa

Great White Shark Cage Diving - South Africa

No Cage - Diving with Tiger Sharks off South Africa

Published July 15,
2016





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