NewsAnimalsGray seals may sense their own blood oxygen levelsThe ability helps them time their underwater dives 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. AndrewsBy McKenzie Prillaman1 hour agoGray 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. The finding suggests gray seals (Halichoerus grypus) perceive their own blood oxygen levels, an ability that prevents them from drowning on dives that can last up to an hour.Mammals need oxygen to live. But they usually cant detect its presence in their blood. Instead, most rely on the effects of elevated carbon dioxide as a proxy for low oxygen. In humans, an increase in circulating carbon dioxide, monitored via sensory organs in the carotid arteries, leads to shortness of breath, hunger for air and panic. A person will eventually pass out.