A marine expert has revealed why an orca targeted a great white shark in an "unprecedented" killing caught on camera off the coast of South Africa. Footage showed a killer whale striking the shark on its pectoral fin before extracting the fish’s nutrient-rich liver - the organ is an incentive for the killing, according to experts. Shark biologist Alison Towner told Sky News: "Shark livers are huge... they are packed full of oils and lipids. "Killer whales are so specialised and so efficient at what they do - they often take a specific portion of their prey and discard the rest."