Survival in the open ocean is at the forefront of this week’s episode, which showcases creatures living in our remotest waters.

The hunt for food is often tough here, but there’s remarkable footage of spinner dolphins, mobula rays and tuna enjoying a rare feast after targeting a shoal of lantern fish.

The episode also looks at how ocean currents benefit some creatures, including the stunning but sinister Portuguese man-of-war jellyfish, which drifts along snaring fish in its deadly stinging threads.

The biggest threat in the open ocean could be man-made, however, and there are sad scenes of a pilot whale carrying around her dead baby who may have been poisoned by plastic contamination of her milk.