[21-12-2011 to 30-06-2012]
Deadly diving: how bubbles can drive marine mammals round ‘the bends’
A new study has found that whales and seals could suffer from the same sickness experienced by human divers.
The research, led by scientists at the University of St Andrews, compiled evidence showing that marine mammals displayed signs of suffering from the diving sickness known as ‘the bends’.
Until now, it has been contentious as to whether cetaceans could suffer from the disorientating sickness that can cause everything from skin rashes to death in extreme cases in humans.
The new study published today (Wednesday 21 December) provides evidence of bubble formation in the bodies of beached whales and seals that suggests the potential for decompression sickness, caused by the pressure experienced during deep sea diving.
The research also suggests that excessive human noise, such as exposure to military sonar, might cause disorientation in marine mammals, leading to them losing their natural defences and to succumb to the bends rather than avoid them.
Lead researcher Dr Sascha Hooker of the University of St Andrews commented, “Decompression sickness, commonly known as 'the bends' is a serious problem for human divers, but the jury has been out as to whether marine mammals could get the bends or if it would be as serious for them.
“Unfortunately the technology doesn’t yet exist to measure what is going on physiologically inside a free-living whale during its descent to depths of over 1000 metres.
“However, our review of recent work on marine mammal diving physiology leads us to the conclusion that there may be the potential for them to suffer from the bends in the same way that humans do.”
The clue to ‘the bends’ taking hold is the appearance of bubbles in the bodies of marine mammals that are caused by an increase in levels of nitrogen in the blood and body tissue.
The research involved a team of experts from diverse fields including human diving medics, veterinary pathologists and experts in comparative animal anatomy, physiology, ecology and behavior.
Dr Hooker and fellow researchers at Woods Hole Oceanographic Institution in Massachusetts, reviewed both acute and chronic cases of bubble formation, including bubbles in the major organs of beaked whales that had beached following exposure to sonar; bubbles in the kidney and liver region of mass stranded dolphins, and bubbles in the tissue of bycaught dolphins and seals.
Examining the mechanisms thought to prevent diving injury in marine mammals, Dr Hooker and her colleagues showed that these are likely to be much more changeable than previously thought.
Dr Hooker concluded, “Our findings change the way we think about how marine mammals manage the problems of pressure when deep sea diving. The textbooks tell us that seals and whales can tolerate deep dives and rapid ascent without developing the nitrogen load that might lead to the bends. We suggest that this is not the case for all species, and that they may balance their management of nitrogen against other physiological requirements, such as the need for oxygen or the need for circulation to keep warm.
“One concern is that these naturally evolving mechanisms may be stretched by human pressures. An apparent threat to these animals, such as sudden high-levels of noise, could cause them to react; altering their dive trajectory or eliciting a fight-or-flight response – that causes them to exceed their normal coping mechanisms for the prevention of the bends.
“While the bends is rare under normal circumstances, excessive human noise or disturbance may cause a marine mammal to change its diving behaviour in ways that result in serious illness or injury.”
The research is published in Proceedings of the Royal Society B.
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