Ocean Noise: Turning down the Volume
The oceans are noisy places
Many marine species use sound in some way including hunting, finding mates and offspring, navigation, locating an appropriate habitat, avoiding predators and communication. Sound moves faster in water than in air and can travel long distances alerting ocean dwellers to changes in their surroundings.
Coral reefs are one of the loudest natural ocean habitats with the healthiest reefs producing the most noise! Many fish species spend their early lives as pelagic larvae drifting through the ocean, when they reach the late larval stage they need to find a suitable habitat where they can safely develop as juvenile fish. Sound is one of the key indicators that enable these late stage larvae to locate healthy reefs or other suitable coastal habitats. Each habitat produces a distinct sound array.
Other marine species, most notably cetaceans use sound as a means of navigation, communication and hunting. Echolocation is the production of focused sound beams that enable the toothed whales and dolphins to hunt effectively in low visibility. It also allows them to determine the location, size and movement of objects around them which aids them in navigation. Other cetaceans such as humpback whales use sound to communicate within populations, reinforcing emotional relationships as well as ensuring the group remains together.
What happens when these natural ocean noises are disturbed or interrupted?
Increases in human activities such as shipping, recreation, underwater construction and ocean exploration in many habitats has changed ocean sound. Researchers have estimated that ship traffic doubled between 1950 and 2000. Increasing noise intensity by 3 decibels per decade, this translates to a doubling of sound intensity within the same time frame. Other human induced sounds such as a blast from a seismic air gun, which are used to map the sea floor for gas/oil, can sound as loud as a rocket launch and will be audible for hundreds of kilometres.
The increase in ocean noise can reduce the efficacy of communication between individuals and/or groups. It can reduce an animal’s ability to navigate through the ocean and can inhibit it from finding a suitable habitat. Changes in ocean noise can also hinder an animal’s ability to hear environmental cues disrupting feeding and breeding behaviours. Some human induced noise can even cause a stress response in aquatic species, particularly if it is sudden and extremely loud.
The first major indicator of the problem of ocean noise was the discovery of masses of dead beaked whales. It is thought that loud sounds triggered a panic response in these animals causing them to dive suddenly, this led to physiological complications including decompression sickness and haemorrhages. Between 1900 and 1950 only seven mass strandings had been recorded, however since the introduction of high-power sonar in naval operations in 2004 more than 120 mass stranding events have been observed.
Further studies have indicated the impact of ongoing, background noise such as that caused by shipping and transport. In 2001 following the attack on the twin towers, commercial transport dropped significantly. A long-term study of right whale faeces that was running at the time noted a reduction in the amount of stress-related metabolites. Several other studies have led to similar conclusions, for example stress-hormone level increased in fish and crabs when exposed to boat noise leading to changes in nursing behaviour.
Can we turn down the Volume?
Ocean noise is a hot topic in the ocean science community. Hundreds of research projects being undertaken to understand the impact that sound has on marine life. The negative impacts of noise in the oceans are finally being recognized and a lot of work is being done to reduce it. Many solutions and mitigation programs are being developed to combat the problem. Seismic air guns could be replaced by vibration mechanisms which produce less sound. That will reduce the risk of injury to marine organisms. Noise limits are being placed on pile driving for the installation of offshore wind farms. Some companies are now working on ways of sinking piles rather than hammering them into place. Shipping noise can be reduced by raising engines off the ship floor. Propellers that create only very small bubbles also helps. Many cruise ships are now using electric motors, thus reducing both noise pollution and carbon emissions!
Research into the severity of ocean noise is something that has gained a lot of momentum in recent years. Several Campaigns calling for the reduction of ocean noise have been heard. Scientists are working to better understand and reduce the impacts on marine life. With a lot of hard work and a bit of patience I am hopeful for a quieter ocean in the future!