In Mexico, Chris pairs up with scientists at the world's biggest whale nursery to witness the arrival of gray whale mothers and their babies. Steve drops anchor in the Bahamas to take the plunge with some enormous ocean predators including Tiger sharks.

Liz joins scientists to find out how temperature increases are impacting the reef, and how plastic is putting the future of the planet's turtles at risk.

Steve, Chris and Liz join scientists to further understand the importance of migrations, long and short, and understand how human demands have impacted the oceans.

Steve, Chris and Liz try to understand what the future holds for all life within the blue planet, and the extraordinary efforts scientists are making to protect the seas.