Sea lions dive deep by letting their lungs collapse on purpose
As a sea lion descends, water pressure squashes the tiny air sacs of its lungs, pushing air into stiff airways where it cannot dissolve into the blood. That sounds dangerous, but it protects the animal from decompression sickness. The catch is that every muscle must already hold enough oxygen for the whole dive.
Sea lions are eared seals, grouped with the fur seals in the family Otariidae. They have outer ear flaps, long front flippers, short coarse hair and bulky chests, and can walk on all fours on land. Six species survive; a seventh, the Japanese sea lion, died out in the 1950s. They range from subarctic to tropical seas in both hemispheres, except the northern Atlantic. A male California sea lion averages about 300 kg and 2.4 metres, while Steller sea lions can reach 1,000 kg. At a single meal they may eat 5 to 8 percent of their body weight.
Their family tree has been redrawn. Biologists once split sea lions from fur seals by the fur seals' dense underfur, but genetic work shows the northern fur seal is closer to some sea lions than to other fur seals, having branched off about 6 million years ago. Many taxonomies have dropped the old split, though the labels remain handy for describing body size and diet.
Diving relies on a suite of physiological tricks. Because collapsed lungs store no oxygen, the heart slows sharply, a response called bradycardia, and the body switches to oxygen held in muscle. Digestion can be throttled back by at least 54 percent to save oxygen, then resumes at full speed on surfacing. Sea lions also tolerate carbon dioxide far better than land mammals, but after repeated dives the build-up forces longer rests at the surface. On land they regulate heat by shifting blood flow to their flippers and hauling out.
Three species, the Australian, Galápagos and New Zealand sea lions, are endangered. In Galápagos, an eye fluke that multiplies in warmer water killed 70 of 91 monitored pups within two years. Hookworms strike Australian and New Zealand pups, and New Zealand researchers found treatment improved growth. Meanwhile, South American sea lions in Chile have been caught hunting introduced Chinook salmon as far as 160 km upriver.
Source: Sea lion
