Fish dominate the planet's waters through their astonishing variety of shape and behaviour. The beautiful weedy sea dragon looks like a creature from a fairytale, and the male protects their eggs by carrying them on his tail for months. The sarcastic fringehead, meanwhile, appears to turn its head inside out when it fights. Slow-motion cameras show the flying fish gliding through the air like a flock of birds and capture the world's fastest swimmer, the sailfish, plucking sardines from a shoal at 70 mph. And the tiny Hawaiian goby undertakes one of nature's most daunting journeys, climbing a massive waterfall to find safe pools for breeding.
In Herne Bay in Kent, Steve makes a jaw-dropping discovery of sharks teeth on the beach. Looking at how bad fatbergs are for the arteries of our seas. Plus we soar high over Mull with Sea eagles, and Chris meets a photographer who believes we have the best marine life in the world.
The first programme shows how sharks are the ocean's great predators, living in every ocean and hunting in every way. Blacktip sharks hunt in huge packs and herd fish into baitballs, tasselled wobbegongs are ambush hunters, Greenland sharks live under the arctic ice, and whitetip reef sharks are the masters of hunting at night. The finale shows the great white in its hunt for fur seals off the coast of South Africa.