Tonight, David Attenborough describes the annual surge of more than 100 million sardines along South Africa's east coast as inshore waters cool with the arrival of winter. This is the Sardine Run: an underwater Armageddon, the greatest gathering of predators anywhere on the planet, and the most spectacular event in the world's oceans. From intimate moments of the creatures caught up in the run, to the dramatic finale of this spectacular event, The Great Tide is an action-packed feeding-frenzy, filmed underwater, on the ocean's surface, and in the air. However, in recent years the sardine run has become less predictable, perhaps due to the warming effects of climate change. If the sardine run does not happen, the lives of the animals caught up in the drama, including a mighty army of dolphins, sharks, whales, seals and gannets, hang in the balance.