Gray seals may sense their own blood oxygen levels

The ability helps them time their underwater dives

A gray seal pops its head up above the water.

Gray seals (one shown) are aware of their blood oxygen levels and make diving decisions accordingly, a new study suggests.

Sea Mammal Research Unit, University of St. Andrews

Gray seals may possess a secret sense that helps them survive at sea.

The marine mammals adjusted their time spent underwater based on the amount of oxygen in the air they breathed before diving, researchers report in the March 21 Science.