Science & technology | Deep divesWhy dont seals drown?They can time their dives to match their blood oxygenFeeling buoyantPhotograph: Reuters Mar 20th 2025FREE-DIVING IS a perilous sport. Divers, swimming underwater without oxygen tanks, frequently black out from low oxygen and put themselves at risk of drowning. Marine mammals such as seals, by contrast, can spend most of their lives below the surface without running such risks. A paper published in Science on March 20th explains why: seals can apparently sense how much oxygen they have in their blood and plan their actions accordingly.Explore moreScience & technologyThis article appeared in the Science & technology section of the print edition under the headline Deep divesFrom the March 22nd 2025 editionDiscover stories from this section and more in the list of contentsExplore the editionReuse this content