At the start of every winter, the coast of South Africa sees billions of little fish converge in the biggest biomass migration on the planet. It’s the annual sardine run – a literal force of nature that feeds an entire coastline. Strangest of all – they don’t have to go. The sardines ride a cold current, through a gauntlet of predators, against all odds of survival, but the purpose of the journey remains a mystery. They race past a hungry seal colony, endure an aerial assault by gannets and face hungry sharks. When dolphins show up, the feast kicks into even higher gear, before orcas arrive with a final surprise.