'Bends' study shows how mammals make mega-dives

Scientists are attempting to understand how diving mammals can swim to great depts and not get the 'bends'
A sea lion swims by at the Smithsonian National Zoo in Washington, DC in August 2012. Scientists in California have shed light on a marine mystery: how diving mammals can hunt for food at great depths without getting the "bends," according to a new study.

Scientists in California have shed light on a marine mystery: how diving mammals can hunt for food at great depths without getting the "bends," according to a new study.

Formally known as , the bends occur when , compressed in the at depth, expands during ascent, causing pain and sometimes death.

Researchers led by Birgitte McDonald at the Scripps Institution of Oceanography netted a female adult California (Zalophus californianus), anaesthetised the animal and fitted it with loggers to record oxygen pressure in its and the time and depths to which it dived.

The 82-kilo (180-pound) sea lion was then released, and the data from its movements—48 dives, each lasting around six minutes—was sent back by .

At a depth of around 225 metres (731 feet), there was a dramatic plunge in the sea lion's oxygen pressure, signalling that it had collapsed its lung to shut off additional air (and thus nitrogen) to its bloodstream.

Sea lions are known to be able to dive some 300 metres without getting the 'bends'
A sea lion sleeps at the zoo in Wuppertal, western Germany, on April 19, 2012. Study shows how some mammals, such as sea lions, collapse their lungs in order to avoid decompression sickness caused by nitrogen gas in the bloodstream.

Lung collapse in diving mammals is a natural action, in which air-processing —elastic, balloon-like structures attached to the bronchi—are depleted to reduce the size of the organ.

The sea lion kept on diving, reaching a depth of some 300 metres (994 feet) before beginning its ascent.

At around 247 metres (802 feet), the oxygen pressure rose again, pointing to a reinflation of the lung, and then fell off slightly before the sea lion breached the surface.

If the sea lion had collapsed its lung, where did it keep the precious reserve of air to help it survive the ascent?

The answer: in the upper airways—the large bronchioles and trachea whose tissues cannot dissolve air into the bloodstream.

During the ascent phase, the sea lion draws on this pocket of air to feed the alveoli, the study suggests.

At the end of the experiment, the scientists removed the gadgets from the sea lion before releasing it once more into the sea, according to the research, published in Britain's Biology Letters journal.

Impressive as the California sea lion is for diving skills, it is still outstripped by the emperor penguin, which can reach more than 500 metres (1,625 feet), and the elephant seal, which can forage at more than 1,500 metres (5,200 feet).

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More information: rsbl.royalsocietypublishing.or … .1098/rsbl.2012.0743
Journal information: Biology Letters

(c) 2012 AFP

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Sep 19, 2012
Speaking of diving ability, the economic pressures to make human divers reach new depths during the offshore oil boom in the seventies had a tragic consequence:
Many divers died when using untested diving technologies, and hundreds more got permanent brain injuies.
This week surviving Norwegian divers are finally getting their case heard at the European court of human rights, after the Norwegian government for decades has refused to accept moral responsibility for granting permission for unsafe diving technologies to be used during the offshore oil boom. Primates are simply not adapted for deep-sea diving, and shoddy technologies will kill them.

Sep 19, 2012
Converting metric units to imperial units is an thankless task. With all the screwy assumptions about precision, maybe even harmful. Please just omit them.

Regarding maximum depth, is that based on the speed of descent/ascent and the longest time an animal can hold its breath, or are there other (physiological) factors?

Sep 20, 2012
"forage at 1500 meters"... Amazing!

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