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Series 1: 2. Open Ocean

The open ocean is the largest wilderness on earth. Covering more than half of the planet's surface, it appears at first glance to be an endless blue desert. Yet hidden here are some of the most extraordinary animals.\n\nWe uncover the surprising strategies, epic journeys and remarkable resilience that allows life to thrive here. From wandering predators and drifting castaways to giant whales and tiny turtle hatchlings, it is a world where life survives against the odds.\n\nThe journey begins far beyond the sight of land, where California sea lions travel miles into the Pacific in search of seasonal, rich fishing grounds. Here, they join one of the open ocean's great feeding spectacles as black skipjack tuna, mahi-mahi and seabirds converge on vast schools of fish in a dramatic battle for a meal.\n\nSome animals aren’t just visitors here; they spend their entire lives in this immense expanse. Rough-toothed dolphins have roamed the oceans since before woolly mammoths walked the earth, and yet we know very little about them. To help find food, they use sophisticated teamwork and ingenious hunting techniques that have rarely been witnessed.\n\nAlthough the open ocean seems like a featureless expanse, it is shaped by powerful currents that flow across the globe like invisible rivers. These currents transport animals, nutrients and entire ecosystems across immense distances. For ocean drifters such as Smith's swimming crabs, the currents are both a lifeline and a gamble, carrying them through a world where danger can appear without warning.\n\nCurrents also drive one of the largest floating ecosystems on the planet. Today, the Great Atlantic Sargassum Belt stretches over 5,000 miles across the ocean. But changing conditions are sweeping unprecedented amounts of this seaweed onto coastlines throughout the Caribbean. On the beaches of Mexico, turtle hatchlings emerging from their nests face a daunting new obstacle as mountains of sargassum block their path to the sea. Their struggle reveals how changes in the open ocean can have profound consequences far beyond the horizon.\n\nIn the Pacific, we follow one of nature's greatest aerial pirates, a frigatebird mother raising her chick alone. Unable to dive for fish herself, she employs thievery to survive in a world where food is often scarce. But this isn’t easy, and eventually she turns to fishing boats for a meal. Our activities have the power to change the balance of life here, and in the Atlantic Ocean, a fish farm attracts turtles from far and wide.\n\nIn a breathtaking finale, we witness an extraordinary encounter between the largest animal ever to have lived and one of the ocean's most formidable predators. A team of killer whales attempt to bring down an adult blue whale. It’s a dramatic contest of endurance, intelligence and power that reveals both the vulnerability and resilience of these ocean giants.\n\nAcross a realm larger than all the continents combined, the open ocean remains one of the least understood places on our planet. As the hidden dramas and astonishing wildlife are revealed, we discover that this vast, blue wilderness still holds countless secrets - and that its future depends increasingly on the choices we make today.

Source: BBC 1