Why Marine Mammals Don’t Get the Bends

California sea lion

AIR-BREATHING MARINE MAMMALS LIKE WHALES AND DOLPHINS routinely dive to great depths – measured in thousands of feet – and return to the surface at high speed without experiencing the decompression sickness that we human mammals have to be extremely careful about.

How can they do this, while we humans can’t? Scientists have long suspected that they limit nitrogen absorption and decrease the risk of decompression sickness by collapsing their lungs during the dives. Researchers at the Scripps Institution of Oceanography in La Jolla, CA, have demonstrated this process by tracking the partial pressure of oxygen in the arterial bloodstream of a California sea lion (Zalophus californianus) during repeated deep dives.

In a study published in The Royal Society’s online journal Biology Letters they reported that they tracked the sea lion over a course of 48 deep dives, reaching depths of nearly 3,000 feet and returning, on average, in about six minutes. During the dives, the sea lion’s lungs collapsed at a depth of 225 meters/738 feet and re-expanded at that depth during ascent.

During the dives, a pulmonary oxygen reservoir was preserved that supplemented blood oxygen during the ascent. As she rose, the oxygen expanded into the lungs, avoiding blackout. Published online September 19, 2012, doi: 10.1098/rsbl.2012.0743 Biol. Lett.