Blue whales are increasingly being hit by ships, especially off the coast of California. As whale numbers recover from hunting and the number of ships that ply the oceans increases this is a growing problem. What can be done? Monty Don explores this little known threat to whales, a threat that is found in all oceans all over the world and effects most species of whale. It seems that the welcome news that whale numbers are slowly rising is being countered by concern over ship strikes, most of which are fatal. A simple solution is to slow the speed of ships down to around 10 knots, but this has financial implications for the shipping industry, so a balance has to be struck. Technology could help, but it is expensive, not reliable in choppy seas and in the case of sonar could fill the ocean with more noise. How can we share the oceans with giants and still move 90% of traded goods by boat?