SUNDAY 19 NOVEMBER 2017
BBC One/RTE One
The big blue is a marine desert, far from shore, kilometres deep, with almost nothing to eat - and home to some of the largest and most spectacular creatures on Earth.
With special pressure-proofed cameras we witness record-breaking feats of endurance, as sperm whales hunt for squid a kilometre down in the abyss.
Until recently, no one knew how baby turtles survived in the vast open ocean. Big Blue reveals that they head to the centre of the ocean, where they use floating debris as life-rafts.
Jelly-like Portuguese man-of-war harness sail-power to trawl for fish. Thousands of dolphins herd vast shoals of Lanternfish to trap them against the surface. Unique aerial footage reveals a centuries-old legend: the savage feeding frenzy of the 'boiling seas'.
Whale sharks make an epic voyage across the Pacific to a spot where, scientists now think, it may be safest to give birth. And a pair of ageing albatrosses give their lives to raise their very last chick.
Yet even thousands of kilometres from land, there is evidence of human activity.
Globe-spanning currents carry plastic into the heart of every ocean, often with tragic consequences. - Could plastic be one challenge too far for the creatures of the Big Blue?