A remarkable video of gannetts, sharks, dolphins & divers diving on the sardine run on the Agulhas Bank off South Africa.

Shark Explorers – Sardine Run 2013

From Scuba Diver Life — Gearing Up For South Africa’s Sardine Run

Exactly why and how the sardine run takes place is still a subject of some debate among experts. It is an unpredictable event that depends upon a delicate balance of simultaneous factors; while some years produce shoals of sardines so dense that they can be seen from the air, in other years the sardines do not run at all. It is certain that South Africa’s complex oceanography plays a key role, and that the opening up of a corridor of cool, inshore water along the country’s eastern coast between May and July is the main facilitator of the phenomenon. At this time of year, great shoals of sardines spawn in the frigid waters of the Agulhas Bank and then follow the cool current north. Sardines can only tolerate temperatures below 69 degrees Fahrenheit, and their presence in the typically warmer waters of South Africa’s east coast depends on the existence of the temporary cool-water corridor pushing from the south. Because the sardines are restricted to such a narrow channel by their inability to survive in warmer offshore water, they are effectively penned against the coastline by the millions.

The real stars of the show are not the sardines themselves, but the incredible number of predators that trail in their wake. The shoals make easy pickings, corralled into shallow water with no escape, a circumstance exploited by both resident and visiting predators. The two most important indicator species for the arrival of the sardine run are the Cape gannet and the common dolphin, both of which follow the migration in their multitudes. It is not unusual for the common dolphins that arrive on the South African coast in conjunction with the beginning of the run each year to travel in pods of over 1,000 individuals. Predators from the temperate waters to the south meet with those from the tropical waters of the north in a shared effort to gorge themselves on the sardines, creating a unique environment where penguins rub shoulders with sailfish. Similarly, pelagics are drawn inshore by the glut of readily available prey — tuna, oceanic blacktip sharks and dusky sharks are all common sights on the run. From orcas to great whites, from Cape fur seals to bronze whaler sharks, the possibilities for predator sightings on the trail of the sardines are endless. Perhaps the most impressive visitor of all is the Bryde’s whale, a 45-foot-long giant, capable of decimating entire bait balls in a single mouthful.