It’s difficult to sleep when you’re in the sea and you need to breathe air.

 

If you're asleep in a rough sea, you might drown. Humans breathe whether we think about it or not. Dolphins though are 'conscious' breathers, which means that they have to think before they breathe.

 

Dolphins have overcome this problem by resting just below the surface in a partially alert state.

 

It seems that dolphins shut down half their brain at a time, so that half the brain is ‘sleeping’ while the other half is still alert.

 

Dolphins probably spend a third of the day in this half sleeping, half waking state, which is much like the eight hours a night that humans spend snoozing in bed.

 

Do dolphins sleep at the surface then? Not always.

Depending on the choppiness of the sea, the dangers around them or how they feel, they might: 

 

• Swim slowly and come up to the surface every now to take a new lung of air before sinking back down again;

• Rest at the surface with their blowhole open to the air; 

• If they are in shallow water, they might rest at the bottom but then rise to the surface every few minutes to breath.