with its whalemen stranded in their lifeboats after a sperm whale attack is used to illustrate the difficulty of surviving in the open ocean. The currents that circle the South Pacific support huge shoals and an incredible variety of life, but much of the centre is an ocean desert. Nutrients are trapped at depth by the thermocline, making the windless surface clear but barren. Life can be tough for large predators. Some, including short-finned pilot whales, can dive to great depths to hunt squid. Others, such as rare oceanic whitetip sharks, track the whales hoping for scraps or a chance to seize a young calf. The waters around the Galápagos teem with life thanks to the cool, nutrient-rich Antarctic current. Underwater footage shows penguins, manta rays, and sea lions feeding. The sea lions work together to divide shoals into smaller bait balls, and blow bubbles into the reef to scare fish out. Seabirds are great ocean wanderers, but all must return to land to breed. On French Frigate Shoals, frigatebirds take sooty tern chicks from their nests, whilst offshore a dozen tiger sharks snatch any unfortunate black-footed albatross chicks that get their maiden flight wrong. Dusky dolphins and bull sperm whales are filmed in the waters off New Zealand, where rescue boats guide an exhausted whale beached in a shallow bay back out to sea. 4. "Ocean of Volcanoes" UK broadcast 31 May 2009, 2.29 million viewers (9.9% audience share) The fourth episode opens with rare footage of Kavachi, an undersea volcano, erupting. The South Pacific islands are typically volcanic in origin, and those of Hawaii are among the youngest. Kilauea's rivers of lava flow directly into the sea, where they cool rapidly and release steam explosively. Pioneering species such as ōhia lehua colonise new land, putting roots down through the cracks into lava tubes where strange troglobites eke out their existence. In the Galápagos Islands, penguins take advantage of the cool shade of lava tubes to raise their chicks, but predatory Sally Lightfoot crabs lie in wait in the shadows. On the Solomons, megapodes bury their eggs in the warm ash of an active volcano, a natural incubator. Aerial photography of Mauna Kea, the Society Islands, Bora Bora and Rangiroa shows how erosion changes the character of volcanic islands over time. Eventually they sink back into the sea, leaving behind coral atolls and sheltered lagoons. Channels between ocean and