WHALES blasted by military sonar signals appear to die of symptoms similar to the bends. The finding means the use of sound waves to detect submarines might need to be restricted.
Scientists from Spain and the UK have uncovered the first evidence that cetaceans exposed to sonar develop nitrogen bubbles in their vital organs. This is a classic symptom of decompression sickness suffered by divers who surface too quickly.
Lesions caused by bubbles were found in 14 beaked whales stranded in the Canary Islands after sonars were used in a major naval exercise in the area in September 2002. “Our findings suggest that naval sonar could be killing whales,” says Antonio Fernández, a veterinary pathologist from the University of Las Palmas in the Canary Islands.
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The military exercise was hosted by Spain and involved the navies of the UK and other European countries, and the US. The whales began washing up four hours after sonars were switched on, and were found to have bubbles in blood vessels in their brains and livers. Post-mortems also revealed clots of fat in blood in their brains, livers, lungs, kidneys and other tissues, along with widespread haemorrhaging. In humans, these are all signs of decompression trauma.
Fernández says the bubbles could have formed because the deep-diving whales were startled by the sonar and surfaced too quickly or changed their diving patterns. This would have caused the nitrogen dissolved in their tissues to come rapidly out of solution and create bubbles large enough to block arteries.
Another possibility, predicted by mathematical modelling, is that the sonar may repeatedly compress and expand tiny gas bubbles, enlarging them dangerously (91av, 15 December 2001, p 17).
Further evidence comes from analysis by London Zoo of 1401 dolphins and porpoises stranded around the UK between 1992 and 2003. Seven were found to have gas bubbles in their blood and livers. Lesions found in the cetaceans in Spain and the UK are new to marine mammal pathology, the researchers report (Nature, vol 425, p 575).
Marine conservationists are now demanding action. “There ought to be a complete re-evaluation of the threat to marine life from noise,” says Mark Simmonds, director of science at the Whale and Dolphin Conservation Society.