Whales get the bends

December 12, 2001

Noise can bring on decompression sickness in whales and dolphins

UNDERWATER explosions and sonar tests may be giving whales and dolphins the equivalent of the bends.

The US Navy regularly booms out sonar signals across the ocean in a bid to track submarines, and conducts controlled explosions under water. Commercial shipping, seismic exploration for oil, and scientific experiments that use sound to measure ocean temperature add to the cacophony (New Scientist, 1 March 1997, p 30).

Biologists have long suspected that noise pollution is disrupting the hearing and behaviour of these inhabitants of the deep, compelling them to beach themselves. Now researchers believe that it could cause haemorrhaging and decompression sickness.

When whales and dolphins dive, nitrogen gets squeezed out of their lungs and into the bloodstream, saturating the surrounding tissue. The longer and deeper they dive the more dissolved gas accumulates in their bodies. As they surface, cetaceans exhale, washing this potentially dangerous build-up of nitrogen bubbles from their blood.

But Dorian Houser of the Navy Marine Mammal Program in San Diego and his team have devised a mathematical model which shows that low-frequency sound waves can interfere with a whale's ability to safely store the gas.

Sound waves rapidly compress and then expand microscopic bubbles of gas in the tissue, they say. With each cycle, each bubble absorbs more and more of the gas dissolved in the bloodstream. Eventually, the bubbles become so big that they can rupture tissues or block blood vessels.

They may also crush nerves, leading to classic symptoms of decompression sickness such as joint pain and disorientation.

Houser reviewed studies looking at the levels of dissolved gas in diving whales and dolphins. He found that the diving behaviour of beaked whales, such as bottlenose and sperm whales, makes them particularly susceptible, as nitrogen levels have often quadrupled by the end of a typical dive.

That may explain why beaked whales seem to beach themselves more often than other species in areas with high levels of naval activity, he says.

Darlene Ketten of the Harvard Medical School has also discovered that loud blasts, like those produced by military shells, can damage the heart, lungs, liver and spleen of dolphins, as well as the most sensitive organ, the ear.

She exposed the carcasses of beached dolphins to controlled underwater blasts. "We're seeing classic symptoms of blast lung and gut haemorrhage," she told a meeting of the Society for Marine Mammalogy in Vancouver last week. Smaller individuals are particularly at risk, she says.

The experience of one veteran whale researcher seems to back up the idea. Ken Balcomb of the Center for Whale Research in Washington state told the conference that in just one day in March, 16 whales and dolphins washed up around the island of Abaco in the Bahamas.

All the whales showed signs of unusual haemorrhaging. Sure enough, Balcomb later discovered that the US Navy had been conducting exercises in the area the day before.
-end-
Author: James Hrynyshyn

More at: Journal of Theoretical Biology (vol 213, p 183)

New Scientist issue: 15TH December 2001

PLEASE MENTION NEW SCIENTIST AS THE SOURCE OF THIS STORY AND, IF PUBLISHING ONLINE, PLEASE CARRY A HYPERLINK TO: http://www.newscientist.com

New Scientist

Related Nitrogen Articles from Brightsurf:

Chemistry: How nitrogen is transferred by a catalyst
Catalysts with a metal-nitrogen bond can transfer nitrogen to organic molecules.

Illinois research links soil nitrogen levels to corn yield and nitrogen losses
What exactly is the relationship between soil nitrogen, corn yield, and nitrogen loss?

Reducing nitrogen with boron and beer
The industrial conversion of nitrogen to ammonium provides fertiliser for agriculture.

New nitrogen products are in the air
A nifty move with nitrogen has brought the world one step closer to creating a range of useful products -- from dyes to pharmaceuticals -- out of thin air.

'Black nitrogen'
In the periodic table of elements there is one golden rule for carbon, oxygen, and other light elements.

A deep dive into better understanding nitrogen impacts
This special issue presents a selection of 13 papers that advance our understanding of cascading consequences of reactive nitrogen species along their emission, transport, deposition, and the impacts in the atmosphere.

How does an increase in nitrogen application affect grasslands?
The 'PaNDiv' experiment, established by researchers of the University of Bern on a 3000 m2 field site, is the largest biodiversity-ecosystem functioning experiment in Switzerland and aims to better understand how increases in nitrogen affect grasslands.

Reducing reliance on nitrogen fertilizers with biological nitrogen fixation
Crop yields have increased substantially over the past decades, occurring alongside the increasing use of nitrogen fertilizer.

Flushing nitrogen from seawater-based toilets
With about half the world's population living close to the coast, using seawater to flush toilets could be possible with a salt-tolerant bacterium.

We must wake up to devastating impact of nitrogen, say scientists
More than 150 top international scientists are calling on the world to take urgent action on nitrogen pollution, to tackle the widespread harm it is causing to humans, wildlife and the planet.

Read More: Nitrogen News and Nitrogen Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.