Part 2: Visitors David discovers the creatures that visit the reef every year, from birds to whales, some travelling thousands of kilometres to get there. Using the latest technology, David dives into the shark-infested waters of Osprey Reef in the Triton submersible. Sixty years after his first visit to Raine Island, he returns to the nesting grounds of the green sea turtle and at Lady Elliot Island marvels at manta ray cleaning stations. New tracking technology allows David to follow the story of visitors like the dwarf minke whales. Stunning satellite imagery and computer animation reveal their journey and David discovers their surprising reasons for returning and why the reef is vital for their survival.