How seals play and snooze underwater
13 June 2013 Last updated at 17:45 BST
An international team of scientists has discovered how marine mammals store such vast amounts of oxygen in their muscles.
It is a key adaptation that lets them hold their breath for far longer than humans.
The oxygen-storing protein in their muscles has special properties allowing huge quantities of it to be packed into their muscles without it sticking together.
Aquarist and seal expert Kylie Warner from Blue Reef Aquarium in Tynemouth explains how seals are so well adapted for underwater life that they even sleep while holding their breath.