This first episode celebrates the amazing and diverse wildlife living in the seas around us, as Chris pairs up with scientists at the world's biggest whale nursery in Mexico. As around 300 mothers and calves arrive we gain a unique view of this spectacle from the air, and discover in real time how their condition and the population is faring.

Liz joins scientists on the Great Barrier Reef to witness baby turtles taking their first steps and carries out a live weigh in on young shearwater chicks. Steve finds himself surrounded by stingrays as a team attempt to ultrasound some pregnant females, and over in Mexico's Seat of Cortez, Chris hooks up with whale experts in search for the return of a long lost visitor to these waters, the sperm whale.