Zachary Quinto sets out to research the strangest creatures dug up from the depths of the ocean and to see how much they lend to the monsters that are depicted in myth and legend. Starting in Australia, he meets with a teenager who was savagely attacked by a swarm of mysterious flesh-eating monsters, only to jump into the water himself the next day amongst highly venomous sea creatures.
From the carnivorous fish of American rivers to the eyeless monsters of the Atlantic Ocean, Zachary finds some merit in these old monster stories and is starting to understand just what we mean when we say that we know less than 1% of what waits in the depths below.

In the last 50 years, we have doubled the amount of fish we consume. Globally, billions of people rely on seafood as their primary source of protein. But the oceans can't keep up with so much demand. Around the world, fish stocks have plummeted and fisheries are crashing. People lost out. There was an industry just completely ravaged.
As the global fish supply dwindles, the industry faces a crisis on all sides - including crooked moguls, dubious imports and divisive regulations.

Immense shoals of fish throng our shallow seas. Small fish, in turn, sustain bigger ones. The rich coastal seas are the fishing grounds of our planet and can provide an abundance of food for wildlife and humanity. The seas fringing land make up less than a tenth of the world's oceans but 90 percent of marine creatures live in coastal waters, from fearsome sharks to lowly urchins. Protecting these habitats is a battle humanity must win.

David Attenborough reveals the extraordinary ways that some animals use colour to hide and disappear into the background. New science reveals how the Bengal tiger in central India uses its orange-black stripes to hide from its colour-blind prey. In Kenya’s Masai Mara, the zebra’s black-and-white pattern confuses predators with an extraordinary effect called motion dazzle. And on the island of Cuba, a small snail uses colourful stripes in a surprising way to hide from its enemies.
Other animals use colour to trick and to deceive. On Australia’s Great Barrier Reef, a blue-striped blenny uses colours to mimic other fish and launch a sudden attack. In the grasslands of Zambia, the chick of a pin-tailed whydah mimics the patterns of its nest mates to ensure that it is not detected as an imposter. And specialist cameras reveal how a tiny crab spider uses bright ultraviolet colours to lure in its victims.

The story of Tilikum, a captive killer whale that has taken the lives of several people , including a top killer whale trainer, underscores the consequences of keeping these powerful animals in captivity, the problems within the sea-park industry, the man's relationship to nature, and how little has been learned about these highly intelligent and sentient mammals.
Tilikum was captured in the northern Atlantic Ocean in 1983 and taken to Sealand of the Pacific, a now-shuttered park near Victoria, British Columbia. Former Sealand trainers interviewed in 'Blackfish' say the park’s female killer whales would aggressively gang up on Tilikum, particularly when they were confined in a 20-foot-by- 30-foot pool overnight.

One extraordinary family of fish has achieved the ultimate form of gender equality. When it comes to breeding, seahorses do it like no other animal on the planet. Their fierce females refuse to be left holding the baby. So it's the males that carry their brood. In this episode we explore the world of mating seahorses which are the only animals in the world that have a major gender role reversal.