The ability helps them time their underwater dives
Gray Seals May Have a Hidden Survival Sense
Gray seals (Halichoerus grypus) might possess a remarkable ability that helps them navigate the challenges of deep-sea diving—the ability to sense their own blood oxygen levels.
A new study, published in Science on March 21, suggests that gray seals adjust their dive times based on how much oxygen they inhale before submerging. This unique adaptation prevents them from drowning, allowing them to stay underwater for up to an hour.
How Oxygen Awareness Helps Seals
Most mammals, including humans, can’t directly detect oxygen levels in their blood. Instead, they rely on carbon dioxide buildup as a warning sign of low oxygen, triggering shortness of breath or even unconsciousness. However, such a system would be dangerous for marine mammals that need to plan their dives carefully.
To understand how seals manage this, ecologist Chris McKnight and his team at the University of St. Andrews in Scotland tested six juvenile gray seals in a controlled swimming pool environment.
Seals alternated between diving to an underwater feeding station and surfacing to breathe from a controlled air chamber. Researchers tested four different gas mixtures:
- Normal air (21% oxygen, 0.04% carbon dioxide)
- High oxygen (~twice the normal amount)
- Low oxygen (~half the normal amount)
- High carbon dioxide (standard oxygen but with 200 times more CO₂ than normal air)
Over 510 dives, researchers noticed a clear pattern:
✅ More oxygen led to longer dives
❌ High carbon dioxide had no effect on dive duration
A Unique Adaptation for Survival
These findings suggest that gray seals have evolved to sense oxygen directly in their blood and adjust their dive times accordingly. Unlike humans, they don’t rely on rising CO₂ levels as a warning sign—possibly because their diving lifestyle causes CO₂ to build up naturally over time.
McKnight believes that seals may use the same biological sensors as other mammals to track blood gases, but their brains process the data differently, allowing them to manage oxygen more efficiently.
This discovery sheds light on how marine mammals survive in extreme underwater environments—and hints that other diving species may have similar hidden senses.