In this episode we see why marine species are drawn to the coasts of Australia and discover that the country's three surrounding oceans - the Southern Sea, the Pacific and The Indian Ocean create a unique environment for ocean voyagers of all types. In the clean waters of Pearson Island off South Australia Sealions, once a rare sight are now protected from hunting and are thriving. Meanwhile in the shallows of Spencer Gulf, June is the time for a midwinter gathering of spectacularly colourful giant cuttlefish who battle for mates. The cold Southern Ocean also brings humpback whales from Antarctica to give birth and triggers the breath-taking spectacle of thousands of Australian spider crabs, the largest crustaceans in the world, congregating under the piers of Port Philip Bay to moult. It's a grisly time as the first to reveal their soft shells are cannibalised by their neighbours. Still, there's safety in numbers as bigger predators, smooth stingrays, sweep over the congregation sucking them from the seabed. A hundred miles up the coast from Sydney, Cabbage Tree Island is home to one of only two breeding colonies of Gould's petrel in the world. Chicks must find their way across rocky ground, scale the vertical trunks of giant cabbage tree palms and overcome their vicious spines in order to capture the breeze to become airborne. They will spend the next five to six years at sea. Off the west coast the Lacepede Islands are bathed in the warm currents of the Indian Ocean. 18,000 pairs of brown boobies build makeshift nests here whilst further south Shark Bay lives up to its ominous name as tiger sharks sweep in to prey on a whale carcass.