Key Antarctic food source moves south

A keystone prey species in the Southern Ocean is retreating towards the Antarctic because of climate change. Krill are small, shrimp-like creatures that swarm in vast numbers and form a major part of the diets of whales, penguins, seabirds, seals and fish. Scientists say warming conditions in recent decades have led to the krill contracting poleward. Simeon Hill from the British Antarctic Survey spoke with our science correspondent Jonathan Amos.