Ocean Matters

Oceanic Noise Pollution

Causes of Oceanic Noise Pollution and Recommendations for Reduction

Usually when people think of pollution they conjure up images of sewage spilling into the oceans, massive oil spills, floating trash and maybe even toxic chemicals.  Noise pollution, however, is easily left out of such thoughts. Nevertheless, pollution from noise is likely as dangerous to many marine animals as any other type of pollution. So what exactly is noise pollution and what can we do to stop it from getting worse in the oceans?

Sources of Noise Pollution

We all know what noise pollution on land sounds like. Just imagine walking down a street in New York City with car horns blaring, and big trucks and buses continuously roaring by. Underwater noise pollution is similar except that it affects marine animals such as dolphins, whales, seals, etc. Undersea noise pollution comes from a variety of sources including large ships, underwater exploration and mining, and sonar. Below, we discuss a few common sources of noise pollution.

Historical Marine Noise Pollution

Humpback whales use their sonar abilities to communicate with other humpback whales and to find potential mates. If they were unable to communicate there is a chance that these whales would not be able to breed properly. As a side note, humpback whales sing very complex and hauntingly beautiful songs. Photo taken by Bill Lawton, National Marine Mammal Laboratory.

Sources of Marine Noise Pollution

Unfortunately for many marine species, boat traffic creates incredibly loud noises. Many of these loud signals are below the margin of 1000Hz. Modern day supertankers cruise the oceans creating a sound pulse of 190 decibels or more at or below the 500Hz range. Smaller boats such as tugs and ferries typically create a sound wave of 160-170 decibels. These ships create a virtual wall of "white noise" that has a constant loudness. This white noise can block communication attempts between cetaceans or limit them to very small areas. The following pictures indicate some of the animals affected by underwater noise.

These Stellar sea lions and California sea lions use sonar to echo-locate in the water and to communicate with each other. Underwater noise pollution makes it harder for these amazing animals to find food and communicate. Other species such as Gray Whales also use sound for similar purposes and suffer the same problems. Sound pollution sometimes even causes Gray Whales to break away from their normal migration routes. Pictures taken by Rolf Ream and Jeffrey L. Laake, National Marine Mammal Laboratory.

Gray Whale photo taken by Dave Withrow, National Marine Mammal Laboratory.

 
The pictures above indicate some of the sources of underwater noise.

In addition to boats and ships, there are several other sources of underwater noise pollution in the oceans, such as noise caused by oceanic exploration for oil and minerals. While searching for oil, oil companies use air-guns to explore the ocean bottom for potential oil reserves. These air-guns fire a pulse of sound at 250 decibels that bounces off the ocean floor and returns to the ship. Once the company finds oil it constructs drilling platforms and so forth that only add to the noise pollution in the oceans.

Another source of noise pollution in the ocean is from a scientific process known as acoustic thermometry, which uses pulses of low frequency sound (at 195 decibels) to try to determine the average temperature of the oceans. Sound waves travel differently through warm and cold water so it is hoped that this technique can help monitor the advance of global warming. In the process of obtaining temperature measurements, acoustic thermometry can do damage to marine species exposed to the high sound levels associated with its operation.

So called "Pingers" and "Ringers" are two other major sources of noise pollution in the oceans. Pingers are devices that emit a shrill 130-decibel sound to scare away marine mammals (and other species) from fishing boats. Pingers are not loud enough to cause any physical harm to the exposed animals but scientists do not know enough information about their overall effects. The first use of these devices in 1994 was to reduce by-catch of harbour porpoises. The devices actually worked quite well, though repeated heavy usage was not expected to be as effective as the porpoises could possibly habituate to the noise. To help reduce cetacean bycatch, the European Union made pingers compulsory in all areas in 2007. 

Ringers may be harmful to species such as Harbour Seals, pictured above.

Recommendations to Decrease Underwater Noise Pollution

There are many things we can do to decrease ocean noise. The first method would be to simply recognize that there is a noise problem in the oceans, which some governments have begun to do. With formal recognition, it may be possible for national and international agencies to work together to help reduce this problem. Moreover, marine mammal protection laws/acts in coastal nations across the planet need to be updated (or even created) to address this issue. Allocating more power to the environmental protection agencies that monitor and manage marine mammals would also help to regulate oceanic noise pollution. For any new policies regarding ocean noise, scientists should follow the pre-cautionary principal to ensure that no further harm will come to marine mammals. From this perspective, governments should adopt legislation with the habitats of marine mammals in mind, ensuring that important areas would receive the least impact possible.

For the time being, however, there needs to be serious noise mitigation efforts from the various oceanic noise polluters. In terms of shipping, major shipping routes should be moved away from important marine mammal habitats. For areas past the territorial limit allotted to each coastal nation, shipping authorities would need to establish proper routes away from important marine mammal areas. In terms ship design, isolating engines from hulls would help reduce noise output. There also has to be regular acoustic maintenance of ships such as cleaning the propeller of debris (this reduces noise considerably), general maintenance such as repairing bearings, loose plates and so forth. For mineral exploration, once acoustic hotspots such as whale breeding grounds are identified, exploration in these areas should be stopped. Another great idea would be to have third-party mineral surveys instead of letting companies survey on their own. Currently, different companies survey the same areas individually creating a lot of excess noise pollution. As for acoustic thermometry, this technology should be avoided in biologically sensitive areas such as whale sanctuaries. Lastly, we need to further study Pingers and Ringers to see what their long-term impacts are.
If we do nothing to mitigate oceanic noise pollution, the problem will likely worsen. Over time, noise pollution may compromise marine mammals’ ability to hear to the point where species survival may be threatened. With global cooperation and effort it may be possible to tackle the marine noise pollution problem before it is too late.

For more information go to:
Georgia Strait Alliance - acoustic impacts on marine life

Whales On-line - noise pollution

Ocean Mammal Institute - Underwater Noise Pollution

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