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Thread: Revealed: How sea lions make mega-dives

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    Revealed: How sea lions make mega-dives

    Revealed: How sea lions make mega-dives

    AFP
    Wednesday, Sep 19, 2012
    PARIS - 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 study published on Tuesday.
    Formally known as depression sickness, the bends occur when nitrogen gas, compressed in the bloodstream 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 sea lion (Zalophus californianus), anaesthetised the animal and fitted it with loggers to record oxygen pressure in its main artery 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 radio transmitter.
    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.
    Lung collapse in diving mammals is a natural action, in which air-processing alveoli - 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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    Re: Revealed: How sea lions make mega-dives

    Just think, these animals are approaching depths close to 1 mile underwater. Also, I had the pleasure of meeting Pipin Ferreras ( http://en.wikipedia.org/wiki/Francisco_Ferreras ) many years agao and we chatted about what deep freedivers do when they dive at deep depths (300 feet plus)- he mentioned that they open their noses and flood their sinus cavities with seawater to avoid the extreme pressure which would collapse these cavities (try doing this in your pool and see how uncomfortable it makes you feel!)

    A good movie on the subject is the Big Blue directed by Luc Besson. Kind of a sappy story line but the main character Jacques Mayol is based on a real-life person (now dead) who pioneered freediving in the Med...

    Plus 1 for my alma mater Scripps, yet again... thanks for posting.

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    I think I will use this the next time someone uses the "there is nothing to see past 130ft anyway."

    That's impressive although the dropping lung thing scares me a bit. I don't think I would want to try that...


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    Re: Revealed: How sea lions make mega-dives

    The surface intervals are important of course.
    The DCS risks while freediving are very low when you do your surface intervals. It only becomes an issue when you make lot's of dives with too short surface intervals.

    The sea lion apparently had other evolutionary selection pressures.

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    Re: Revealed: How sea lions make mega-dives

    Quote Originally Posted by Jantje  View Original Post
    The surface intervals are important of course.
    The DCS risks while freediving are very low when you do your surface intervals. It only becomes an issue when you make lot's of dives with too short surface intervals.

    The sea lion apparently had other evolutionary selection pressures.
    I've had freediving DCS over a dozen times and while most often it happens due to excessively rapid ascents (combined with insufficient surface intervals), it can also happen on single dives. I had DCS after a single dive to 104m/341ft (despite going back down on O2 at 6m for 5:00). Herbert Nitsch is three months into a slow recovery from severe DCS after a single no-limits freedive to 250m (820ft), and he even did a breath-hold deco stop on the ascent, which wasn't enough.

    From 2005-2010 I experimented with exhaling before beginning each dive (to take less air and N2 with me), but this method did not stop me from getting DCS.

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    Re: Revealed: How sea lions make mega-dives

    Quote Originally Posted by tdzao  View Original Post
    I've had freediving DCS over a dozen times and while most often it happens due to excessively rapid ascents (combined with insufficient surface intervals), it can also happen on single dives. I had DCS after a single dive to 104m/341ft (despite going back down on O2 at 6m for 5:00). Herbert Nitsch is three months into a slow recovery from severe DCS after a single no-limits freedive to 250m (820ft), and he even did a breath-hold deco stop on the ascent, which wasn't enough.

    From 2005-2010 I experimented with exhaling before beginning each dive (to take less air and N2 with me), but this method did not stop me from getting DCS.
    Really? Didn't know that incidents occurred that often. Good to know.
    Interesting. Thanks for the info. *reading about the Herbert Nitsch case*

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    Re: Revealed: How sea lions make mega-dives

    Quote Originally Posted by tdzao  View Original Post
    I've had freediving DCS over a dozen times and while most often it happens due to excessively rapid ascents (combined with insufficient surface intervals), it can also happen on single dives. I had DCS after a single dive to 104m/341ft (despite going back down on O2 at 6m for 5:00). Herbert Nitsch is three months into a slow recovery from severe DCS after a single no-limits freedive to 250m (820ft), and he even did a breath-hold deco stop on the ascent, which wasn't enough.

    From 2005-2010 I experimented with exhaling before beginning each dive (to take less air and N2 with me), but this method did not stop me from getting DCS.
    Thanks for sharing this information. I learned something new today.
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    Re: Revealed: How sea lions make mega-dives

    This is very interesting. I learnt something new too. Great info.

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    Re: Revealed: How sea lions make mega-dives

    Good stuff, now if could just collapse my lung at 800 feet.

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