A remarkable new story is unfolding in the Arctic. As the ice melts and polar bears struggle to survive in a fast-warming world, another animal is taking over the polar bear's once dominant role as top predator. An ever-increasing number of killer whales - or orcas - are appearing in Arctic waters in the summer months, attracted to these huge hunting grounds by the growing expanses of open water and attacking the same prey animals polar bears once survived on: seals, narwhal, belugas, and bowhead whales. Polar bears may be classified as marine mammals, but they are not adapted to hunting in the water despite being able to swim huge distances. They need the ice to hunt and as it vanishes they can no longer reach their traditional prey. And they are certainly no match for the world's greatest aquatic hunter - the killer whale. As the polar bear's world is shrinking, the orca's is growing.