The sardine run along the cape coast of South Africa is one of the largest marine-life migrations on earth. Masses of sardines traveling north form large shoals, resulting in a feeding frenzy for predators and a captivating show for divers and snorkelers
Every year between May and August, billions of sardines spawn in the cool waters of the Agulhas Bank and travel along the east coast of South Africa. They follow a cool current heading from Agulhas Bank to Mozambique.
Many environmentalists opine that the sardine run could easily rival the great wildebeest migration in East Africa in terms of biomass. Some shoals span over 4 miles (7 km) long, with a width of around .3 miles (1.5 km) and a depth of around 98 feet (30 m).
Sardines are extremely sensitive to even the slightest change in water pressure, so when one fish in a shoal moves, the rest react. Predators use this to their advantage to move some of the fish into concentrated balls. Dolphins sometimes blow bubbles toward the ball to concentrate the fish even more before launching an attack. Sharks and Cape gannets join in the feast and the fish become lethargic as the oxygen in the surrounding water decreases, making them easy prey.
Humpback whales traveling from Antarctica to Mozambique accompany the sardines on their run. Instead of joining in the run, the whales join the sardines on their way to their summer breeding grounds in the warmer waters of Mozambique.
Sardines prefer cooler water, between 57 and 68 F, (14 and 20 C) . Scientists think that the water temperature must drop below 70 F (21 C) for the migration to take place. Water along the southeastern coast of South Africa drops down to these temperatures during the country’s winter months. The warm Agulhas Current relaxes between May and August, allowing cooler water to move north from Agulhas Bank toward South Africa’s Wild Coast and KwaZulu-Natal.