What is Noise Pollution?

Noise in the Ocean

The ocean is a constant cacophony of noise - both natural and anthropogenic.  Waves, cracking ice, reefs and even weather such as lightning provide a continual source of background noise for our animals. Alongside that, many animals rely on vocalisations and other noises to communicate, hunt, or survive. In recent years however, science has begun to focus its attention on man-made noises, and how that affects our underwater population. Sound travels roughly 5 times faster and 60 times further in water than in air, which is around 1,500 metres per second, so it is vital we understand the effects our actions are having on marine animals.

Noise Pollution Examples

Man-made noise contributes more and more every day to the sound heard under the water. Some examples of this are:

• Airguns

  • Used for seismic exploration - A compressed air supply creates a rapidly expanding bubble that lets off a high-level impulsive sound. During a seismic survey, airguns are fired every 10 to 15 seconds as the vessel moves along, sometimes for weeks or months on end. Once the sound enters the seabed, the reflected sound is picked up by hydrophones.
  • Oil and gas exploration vessels use airguns 7 orders of magnitude louder than the loudest ship sounds. At frequencies similar to cetaceans' communications, this runs the risk of confusing or harming marine mammals.

• Pile Driving

  • Used to construct turbines, bridges and other structures, the pile generates sound in multiple ways. First, upon contact with the water, but as the hydraulic hammer repeatedly pushes the pile into the seabed, compression waves are also generated throughout the seabed. 

• Wind Turbines

  • Once running, wind turbines generate much less noise than during construction. The operational sound of a turbine has been recorded as not much higher than the natural background noise, and so isn't a major worry for scientists.

• Sonar

  • Sonar is used by many companies to detect fish schools, survey the seabed, and for military purposes. Regular sonars include echo sounders, side-scanners, and fish-finders - and operate at around 20-800 kHz. The real issue occurs when it comes to naval sonars. These sonars are high-power, low and mid frequency that use several hundred to several thousand hertz, and have been proven to be a cause of mass strandings of cetaceans.

• Vessels

  • Most vessels produce low-frequency sounds from onboard machinery, the hull, propellers etc., which is a predominant source of noise for the ocean. 90% of all goods travel by ship, and there are 60,000 commercial vessels are on the seas at any time, with traffic set to only increase in the coming years.
  • Ice-breaking ships in the Artic are even louder, as decibel levels rise when ice breaks.

Effects on Marine Life:

Loss of hearing

In some cases close to the source of sound, injuries such as tissue and organ damage are found, along with permanent and temporary hearing loss (known as PTS and TTS). TTS has been recorded in odontocetes and pinnipeds, and PTS has been found in wild odontocetes, though the causes were unknown.

Acoustic Masking

Acoustic masking occurs when noise interferes with an animals communication and detection of acoustic signals. An example is Beluga whales, who responded to icebreaker ships that were tens of kilometres away, and were expected to be barely audible.

Ship collisions

Some cetaceans cannot accurately locate ships when the noise pollution is too great, and may accidentally swim towards them rather than away.

Documented Behavioural Changes

Sonar: 

• Humpback whales increased the length of their song
• Beaked whales ceased echolocation
• Long-finned pilot whales increased their call rate

Boat noise:

• Killer whales increased their call duration and level
• Beluga whales increased their call level, reduced their call rate and shifted the mean frequency up
• Bottlenose dolphins increased their whistle rate
• Fin whales decreased their call duration and band width