While not proven it is a promising technique to aid in lessening the impact that human-made underwater noise has on marine life. In 2003 and 2004 the California Department of Transportation deemed it necessary to drive new pilings in the seabed, but were concerned that the pressure of the waves they created while hammering the pilings into the sea floor would affect the seals nearby. The consulting marine biologist for this project, Bud Abbott, warned the waves might kill the fish as well.
During an early test quite a few dead fish were found on the surface. After collecting the fish for testing Abbott found that the swim bladders of the fish has burst and their kidneys were greatly damaged as well. As alarming as this was it helped scientists discover ways to lessen the harsh effect of sound waves.
During an early test quite a few dead fish were found on the surface. After collecting the fish for testing Abbott found that the swim bladders of the fish has burst and their kidneys were greatly damaged as well. As alarming as this was it helped scientists discover ways to lessen the harsh effect of sound waves.
"When a pressure wave hits an air bubble, it will compress the bubble, then it will expand again, so energy is lost," Abbott explained. Although scientists disagree on the amount of energy lost in this process, Abbott said, there is no doubt that the air bubble actually changes the shape of the wave.
"Sound travels faster through water than air," said Abbott. "It slows down as it hits the air bubble." This creates a much smoother wave, altering it from a brief percussive bang to a longer, weaker wave.
For the Bay Bridge project, Caltrans placed a wall of air bubbles directly against each pile as it was being driven. This attenuated the waves caused by the pile driving. Overall fish deaths were reduced and delayed mortalities did not occur beyond 69 meters (226 feet) from the piling.
In Germany offshore wind farms are becoming increasingly important in the nation's plans for renewable energy but are becoming concerned that marine life may be affected by the construction and placement of these wind turbines. A government study found that porpoises avoided swimming within 20 kilometers of wind farms and because of this Germany has set a limit of 160-decibels allowed in wind farm construction 750 metres from the source. The government has even listed bubble curtains as an option to lessen the noise level.
Shell is another name that is looking into bubble curtains for protect the marine life from the noise pollution it creates. It is a very important issue because Shell works in the Arctic where the marine life are among the most diverse in the world. Unfortunately, Shell's research on bubble curtains is still at an early stage so it will not be included in their 2012 season of exploratory drilling.
This method does not show signs of being prefect however as Karl-Heinz Ehlmer, who was involved in the first study of bubble curtains in Germany, says that are bubbles may be sensitive to tide currents and larger bubbles can show a chaotic behaviour. He also mentioned how expensive this technology is and mentions other alternatives. One that he is working on is called Hydro Sound Dampers, uses only fishing nets and foams. He finds that this is better than bubble curtains because is is more effective in lowering noise and is less costly. Other scientists are thinking of instead masking the noise, lowering it altogether by anchoring the turbines to the sea floor in a less noisy way.
So, unfortunately it does not seem that they will be a definite way to lower noise pollution any time soon but it is slightly reassuring that there are methods and experiments by scientists taking place to lower the noise.
Source and Direct Citation: http://news.nationalgeographic.com/news/energy/2012/02/120207-bubble-curtains-to-protect-whales/?source=gecfeatures
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