Giving Whales and Dolphins 'the bends'
17 December, 2001 [ABC]
US research suggests that underwater explosions and sonar tests used in research and exploration might be causing haemorrhaging and 'the bends' in marine mammals.
This week's New Scientist reports on the research from the US Navy Marine Mammal Program in San Diego and Harvard Medical School.
The US Navy regularly uses sonar signals to track submarines, and conducts controlled underwater explosions, writes New Scientist's James Hrynyshyn. Commercial shipping, seismic exploration for oil, and scientific experiments that use sound to measure ocean temperature add to the noise.
Researchers have long suspected that noise pollution could disrupt the hearing and behaviour of marine creatures and be responsible for whale beachings. The new findings, by Dorian Houser and team of the Navy Marine Mammal Program, have identified a further problem.
Houser and colleagues developed a mathematical model that shows low-frequency sound waves can interfere with the ability of whales and dolphins to safely store nitrogen gas, which gets squeezed out of their lungs into their bloodstream when they dive.
The longer and deeper they dive, the more dissolved gas accumulates in their bodies, saturating the surrounding tissue. As they surface, they get rid of this potentially dangerous build-up of nitrogen bubbles from their blood.
The research team has found that sound waves can cause the microscopic gas bubbles in the cetaceans' tissue to expand, eventually becoming so big that they block blood vessels or rupture tissue. The bubbles may even crush nerves, leading to joint pain and disorientation - classic symptoms of decompression sickness, known in humans as 'the bends'.
The researchers argue that 'beaked' whales, such as bottlenose and sperm whales, are likely to be particularly susceptible because of their diving behaviour and their levels of dissolved gas.
That may explain why beaked whales seem to beach themselves more often than other species in areas with high naval activity, Hauser said.
In separate research, Darlene Ketten of the Harvard Medical School exposed the carcasses of beached dolphins to controlled underwater blasts and assessed damage to their ears, heart, lungs, liver, and spleen.
"We're seeing classic symptoms of blast lung and gut haemorrhage," she told a recent meeting of the Society for Marine Mammology in Vancouver, adding that smaller dolphins were particularly at risk.
The conference also heard Ken Balcomb of the Center for Whale Research in Washington report that 16 whales and dolphins were washed up on an island in the Bahamas on one day, following Naval exercises the previous day. All the whales showed signs of unusual haemorrhaging, he said.
According to Wendy Dunn, Research Director of the Dolphin Research Institute, the impact of such tests in Australia is yet to be fully assessed.
"A lot of people have issues with exploration drilling and seismic testing for oil and gas, and I believe the industry has been trying to address these," she said.
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