The sound of silence would be a welcome change for the world’s marine life as they battle the intrusion of maritime shipping. Noise pollution, as well as physical danger from propellers and monster vessels, is a growing concern as the world’s marine commerce is ever expanding. Many of us have read about the effect of shipping noise on whales and dolphins, but for organisms living below 1000 meters, where vision is irrelevant, there is almost total reliance on acoustic signals to find food, and each other, in the pitch blackness of those depths. Noise from human marine traffic conflicts with those signals to a level we are only just realizing. Add to that that some estimates suggest that shipping-noise emissions are doubling every 11.5 years, and we have a potential marine environmental disaster on out hands. The fact that it is so remote from human activity amplifies the need to publicize and address the issue before irrevocable harm is done without much awareness from those of us on the surface of the oceans.
Reducing marine traffic is not a practical consideration as a solution, when roughly 90% of all traded goods currently travel by sea. Putting a speed limit on commercial shipping would also work, but the cost of enforcement would be prohibitive and the additional cost on the products shipped would be significant – again, probably a non-starter in trying to solve this problem. Technology, however, offers some hope of reducing this human-generated noise pollution on marine life.
Cavitation from propellers is a major source of extraneous noise for marine life. The rotation of the propellers produces pressure differentials around the propeller, which produces bubbles of air, which, when they collapse, produce noise. That low frequency noise can travel thousands of meters underwater and can disrupt the communications among blue and humpback whales, for example. They use the same noise frequencies to talk to each other and find food.
A new technology, which incorporates flexible polymers into the metal propeller blades allowing the propeller tips to flex could reduce cavitation considerably. Another possibility is to create a “bubble-screen” around the stern of ships, which would reduce the transmission of engine and machinery noises into the surrounding water.
It occurred to me as I was writing this piece that the U.S. Navy, and others, have invested huge amounts of money in reducing the cavitation noise generated by the propellers of nuclear submarines. Their purpose has been to produce more stealth capability, but there would appear to be no reason why that noise reduction technology couldn’t be used by commercial shipping. The only reasons for not doing that would be national defense considerations and cost – I can’t begin to imagine the cost differential between a commercial oil tanker’s propeller and that of a nuclear “Boomer”. However, commitment and ingenuity could possibly take what we already know and make it more commercially viable.
Tom Smith, a researcher in naval architecture at University College, London, says that technological solutions for reducing ocean noise pollution abound. What is missing, however, is funding to test them at sea, and a willingness on the part of shipbuilders and ship owners to commit to using them. Again, the remoteness of the problem from normal human activity probably contributes as much to the lack of interest and priority in solving the problem as does cost.
There are some indications of change, which is encouraging. Some seaports, such as the Vancouver Fraser Port Authority, now offer discounts, equivalent to thousands of dollars, for ships that meet the highest level of noise reduction. There is also some research that suggests that quieter ships may also turn out to be more efficient. Now that the International Marine Organisation has pledged to reduce carbon emissions from international shipping by 70% relative to 2008 levels, by 2040, this may prove to be too good a deal to resist. Marine life will be cautiously applauding.
