By Rebecca Morelle

Science reporter, BBC News

Please turn on JavaScript. Media requires JavaScript to play. Advertisement A sardine feeding frenzy has been captured on camera in remarkable detail. A BBC crew filmed thousands of sharks and dolphins, as well as elusive Bryde's whales, feasting on shoals. The footage also revealed gannets' deft underwater hunting skills as they dived to catch sardines. Each winter, cool ocean currents drive millions of the small fish northwards along the eastern coast of South Africa. These immense shoals, squeezed into this narrow cold-water corridor, provide an incredible feeding opportunity for the predators that live in and around these waters. You have to be on the water, waiting and waiting and waiting for the ideal conditions

Hugh Pearson The sardine run forms part of the BBC Natural History Unit series: Nature's Great Events. However, despite the epic scale of this spectacle, filming it was not easy. Hugh Pearson, who produced The Great Tide, said: "It is an annual event, but by its nature it is not predictable and it is very difficult to find - the shoals are found over such a vast expanse of sea." The team used microlites to track down the sardines, allowing helicopter, boat-based and underwater crews to capture the feeding frenzy in extensive detail. Mr Pearson said: "You have to be on the water, waiting and waiting and waiting for the ideal conditions. "But when it happens, and you have the best action and the best predators in clean water - once you get all of those in one place, you can just clean up. "It happened to be the best year for baitballs in a long time." Underwater cameraman Didier Noirot, who has worked with Jacques Cousteau for more than a decade, managed to capture armies of sharks, dolphins and seabirds as they gorged on the swirling shoals. Please turn on JavaScript. Media requires JavaScript to play. Advertisement His footage also helped to reveal more about they way that gannets hunt. Mr Pearson said: "Rather than simply diving, catching a fish and bringing it back up to the surface, Didier found that the gannets were 'arrowing down' to a depth of 10m (30ft), then swimming down a further 20m (60ft), and then charging around like penguins to catch the sardines." The crew also managed to film the elusive Bryde's whale. "These are very secretive ocean hunters, and they are difficult to find - but we got some very cool shots of them both above and below the water, taking some huge bites of sardines," explained Mr Pearson. Although the crew managed to capture 2008's sardine run on film, they fear recent changes to the ocean's currents may be affecting this annual event. Mr Pearson said: "The changing climate seems to be making it even more unpredictable. "We first went there to film in 2007, but there was no sardine run that year. "In fact, three of the last five years were very poor for the sardine run, which is probably linked to climate change. "The sardines need to have cool water to swim up, and the water has just not got cool enough in the last few years." Nature's Great Events: The Great Tide is on Wednesday 4 March on BBC One at 2100 GMT and is repeated on Sunday at 1800 GMT



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