The Unseen Marine Animals Killer-2

周越

Sound emanating from ships is by far the most common culprit， so conservationists believe it should be addressed first. One of the easiest ways to do that is to simply get ship and boat traffic to slow down when moving through areas rich in marine life ＼| a strategy which could also help to cut carbon emissions from ships. Major ports in the US Pacific Northwest and Vancouver have already enacted slow＼|down programs， and a recent study found that the effort is making a significant difference.

Unlike other conservation efforts， which can require years of development， noise＼|reduction programs like these are relatively low＼|lift. And their impact can be felt right away.

Moving ship lanes away from areas populated by sensitive species like killer whales could also be beneficial. But in order for noise abatement endeavours to have a widespread effect on marine life， they will have to be backed by sweeping public policy.

And while slowing ships down is a good start， scientists agree ships ultimately need to be built and retrofitted with noise abatement in mind. A first step in that direction could be changing ship building requirements so the parts that make the most noise， like the engine and propeller， are designed to be quieter.

The International Maritime Organization has also made building quieter ships part of its mission， and in 2014 outlined simple guidelines for engineers and manufacturers to follow. That said， NGOs such as the World Wide Fund for Nature （WWF） have noted the voluntary guidelines put out by the IMO have been largely ineffective at curbing anthropogenic ocean noise， and are calling for mandatory limitations. Natasha Brown， an IMO spokesperson， says the IMO's guidelines are currently under review， providing an opportunity for member states and NGOs to submit proposals for further work and action on underwater noise.

Retrofitting ships would also help to reduce ocean noise. This tends to be more expensive than adjusting designs and parts for new ships， but it could be worth it if only the most problematic ships are targeted. One of Williams' studies on noise emanating from a fleet of 1，500 ships found 50% of the noise was coming from only 15% of the vessels. So retrofitting just those ships with new， noise＼|reducing propellers would make a significant difference in the fleet's overall sound impact.

Creating a financial incentive for private companies to build， buy and operate quieter ships could be another useful approach. Design adjustments already on the market， such as propellers which reduce cavitation， can also make ships more efficient and reduce carbon emissions. For companies looking to go greener， that added benefit may be what tips the scales.

While boat noise is the most common form of anthropogenic ocean noise， other sources also create problems.

The construction and operation of offshore wind farms is among them. Many major structures offshore are built using piledrivers， which can cause sudden bursts or pulses of loud underwater sound.Louder or higher frequency sounds like these may do more immediate damage to nearby marine life than the more chronic， lower＼|frequency sounds.

One way to reduce this noise is to create a bubble curtain around the sites， which form almost a wall and block some of the sound being emitted from a source.

Aircraft can also produce significant underwater noise， especially when they regularly take off and land at airports near bodies of water. Moving runways further away from areas that are home to sensitive marine life could help curb the problem.

Military sonar is another source of anthropogenic ocean noise that can sound so similar to whale calls that it confuses them， leading them to lose their sense of direction ＼| thought to be one reason why whales end up stranded on beaches. One potential solution is for the military to reduce the need for sonar by instead eavesdropping on natural sounds from marine animals as a way of detecting underwater threats.

Underwater mining for fuels like oil and gas can also produce bursts of ocean noise. Sometimes， excavation teams set off large explosions， or use seismic air guns in sharp bursts from a ship above to push through the ocean floor.

Restrictions that limits human exposure to high levels of noiseare needed for such noise exposure of marine animals. Such restrictions could include decibel limitations at certain points in bodies of water where vulnerable marine habitats exist， regulated by environmental government agencies like the Environmental Protection Agency （EPA） in the US.

These agencies could also provide guides for different industries to reduce their sound emissions. Seismic survey noise， for example， can be tempered by releasing the air in more continuous， lower frequency pushes over longer periods of time ＼| a process called marine vibroseis.

Focusing on one source of ocean sound pollution or one impacted species at a time won't make much of a difference on a global scale. But considering the overarching environmental impact， followed by the creation of a multipronged plan of action， might. In order to best assess what progress is being made and where work still needs to be done， monitoring soundscapes around the world must be part of that plan.

Hildebrand has called for a long＼|term， global ocean noise monitoring system that's accessible to anyone anywhere. Not only would researchers be able to better track changes this way， activists or politicians looking to push for policy change could also easily refer to real＼|time problem areas.

Ocean soundscape research is still a relatively new field， but scientists within it are always looking for ways to get more data， and better， more affordable listening technology. Scientists are also actively encouraging the development of low＼|cost， underwater recorders so that more research can be done， and more people can discover the fascinating sounds which can be heard underwater.

As long as humans are around， the noises they bring with them will likely remain a part of ocean soundscapes. But like any other type of harmful pollution， ocean noise needs to be regulated in a meaningful way if we are to keep marine animals' sound＼|driven worlds from shrinking away.