When whales are killed or die of natural causes, their carcasses can feed marine life for days and even weeks. The blood leaking from the dead whale can be detected by sharks for miles around. The sharks will then swim to the carcass and have a free meal, often feeding many creatures at a time. Here is an example of over seventy sharks feeding on a dead whale carcass at once while onlookers watch from boats. Two boats full of tourists circle the carcass and film while dozens of sharks swim just meters below them. If a boat sprung a leak or a person fell over it would mean almost certain death.