Once you dive headfirst into the water, all the sounds from above the water sound muffled. But it is never quiet under water: waves and precipitation, wind and currents are part of the natural background noise in the sea, as are the communication sounds of many sea creatures. In addition, there are sounds caused by humans, so-called underwater noise.
For the International Noise Awareness Day On April 28, 2021, we took a closer look at and listened to this underwater noise. What is underwater noise and where does it come from? What consequences does it have for the oceans and marine animals and what solutions are there to combat it?
About Underwater Noise
First: What actually is noise?
Sure, we all know the noisy street, the drilling machine or the construction site around the corner. But why do we perceive these sounds as “noise”? According to the World Health Organization Noise is “any type of sound that is disturbing, annoying or may have a detrimental effect on health”.
At higher volumes and at certain frequencies, we are more likely to perceive a noise as unpleasant. If this noise persists over a longer period of time or occurs regularly, it can affect our well-being and quality of life.
And what is underwater noise?
The same is true for underwater animals. In 2008, researchers, environmentalists and nature conservationists in the European Marine Strategy Framework Directive Underwater noise defined: sounds “that have the potential to cause adverse effects on the marine environment”.
Where does the underwater noise come from?
Quiet corners are becoming increasingly rare in our seas. According to the International Fund for Animal Welfare (IFAW), man-made underwater noise has in every decade of the last 40 years in some places in the world's oceans. This is due, for example, to the continuous noise from the increasing global shipping traffic, impulse noise such as from the construction of wind farms and explosions, as well as from sonar devices and seismic surveys.
Shipping traffic is a cause of underwater noise.
Continuous sound
Continuous noise from shipping traffic is increasing every year. In addition to the increasing number of larger container ships, the number of cruise passengers has increased over the last 20 years – with 28.5 million per year – and thus almost five times the number of cruise ships. Their propellers and engines constantly generate noise. Many ships use echo sounders to determine the water depth and continuously send out sound waves. This constant noise covers all natural sounds and often has the same pitch as many sea creatures use to communicate. Tourism near the coast also causes more noise under water, for example from motorboats, jet skis or water skis.
impulse sound
Impulse sound means the occurrence of short sound events. For example, depending on the design, piles for wind turbine supports are rammed into the seabed with thousands of hammer blows. Something similar happens when oil and gas platforms are built. Here you can listen to this once.
Sound or compressed air cannons used to search for oil and gas also produce pulsed sound. Ships can pull up to 40 compressed air cannons behind them and fire explosive bangs with great pressure every 15 seconds towards the sea floor. The resulting echoes collect information about the nature of the bottom and the raw materials found underneath. These devices are among the loudest used underwater.
No less loud are underwater explosions. These are used to blow up old ammunition. In the North and Baltic Seas, for example, about 1.6 million tons old explosive devices, which slowly rust and can become dangerous for marine animals, shipping and fishing. In addition, poison from the ammunition pollutes the marine environment. A quieter alternative would be to recover the ammunition.
sonars
Sonars help to explore the marine environment and make schools of fish, shallows or even submarines visible. military sonars With their particularly high sound pressure, they pose a mortal threat to whales and dolphins. They are mostly used for exercises or routine military activities to detect enemy objects in the water. Long sound pulses of 100 seconds each are emitted over a longer period of time, filling large areas under water with sound.
Source: Ocean Care: Knowledge, Focus Special 06, 2018.
One thing is clear: underwater noise is varied and constant. It is particularly bad when it occurs cumulatively, that is, when many sources of noise come together. Between so-called “ship highways”, sonar devices, sound cannons and explosions, many animals have no chance of escape.
The consequences of underwater noise: hearing-impaired whales and stressed fish
Many marine animals use sound for orientation, communication, finding partners and food, and avoiding enemies. All of these aspects are influenced by man-made underwater noise. Effects Depending on the duration, intensity and context, they range from changes in behavior to injuries and even death.
All animals are affected
Research into these effects is complex, but it is clear that almost all marine animals are affected. In general, increased noise exposure leads to Stress . Without the animal actively noticing it, the breathing rate can increase or the metabolic rate can change. Stress hormones are also released - and why shouldn't long-term stress lead to illness, as it does in humans. Sudden noise can trigger a reflexive startle reaction in animals, which is embodied in a protective posture. When an animal flees, the search for food is stopped and reserves are used up at the same time. In addition to individual animals, noise pollution can also affect entire animal populations - this depends on whether they can escape the noise and colonize new habitats.
fish, mussels and shrimp
Loud sound waves can fishing to internal injuries and, in the long term, to physical deformities and increased infertility. Shrimps and mussels are also affected, resulting in growth disorders, reduced fertility and the associated low reproduction rates.
Whales are particularly affected by underwater noise.
Underwater noise and whales
Increased, permanent noise can lead to, for example, whales leave or temporarily avoid the habitats in which they normally reside. This affects their hunting, diving and escape behavior and is reflected in reduced food intake and the resulting weakness. Impulse noise in the form of explosions can irritate whales, causing them to surface much too quickly, which can lead to fatal embolism (high nitrogen content in the blood and other tissues, also known as decompression sickness in humans). This also often manifests itself in the form of mass strandings, although there are many reasons for this.
Porpoises use sonar to orient themselves, as they have very poor eyesight. If this is disturbed, there is a risk that they will not be able to find any food at all and will die.
dolphins
Dolphins often try to be heard by their peers despite the noise and therefore scream even louder. This in turn leads to stress. Long-term noise can also lead to temporary or permanent hearing loss.
invertebrates
At squid and other invertebrates can experience changes in their cell structure when exposed to constant noise. This means that the hair cells change, which leads to their sense of balance being disturbed. Powerful sound waves can also kill the animals instantly with their pressure.
These are just some of the effects of noise pollution. They prove that the consequences for wildlife can be as diverse as they are serious - and research is still in its early stages. But one thing is already certain: something has to change if we don't want to endanger the marine ecosystem even further.
The path to more peace
In 2005, the United Nations Underwater noise is recognized as one of the five greatest threats to marine mammals and one of the ten greatest threats to the oceans as a whole. In theory, the solutions to underwater noise are simple: quieter ship propellers, speed limits, marine protected areas as refuges, technically improved and more economical engines - all of this would contribute to less noise and at the same time to a reduction in pollutant emissions. But in practice, progress is slow.
What solutions to underwater noise already exist?
For the German North Sea there is a soundproofing concept for offshore wind farms. The Federal Maritime and Hydrological Agency (BSH) coordinates this and ensures that the rules are adhered to. For example, two farms may not be built at the same time, so that porpoises can flee to quieter areas. In addition, the volume of the ramming may not exceed a certain decibel level and interference signals are sent beforehand to warn the animals.
Another means of reducing ramming noise are so-called Bubble curtains that dampen the sound. A kind of perforated bicycle tube is placed around the ramming point on the seabed and air is pressed in using compression. This then flows out of the holes and rises to the surface in the form of bubbles, thereby forming a curtain that dampens the sound. However, even after the construction of offshore wind farms or platforms, the noise in their vicinity remains due to supply trips.
One approach to reducing noise during seabed exploration is to use vibration instead of sound. Military However, it is not particularly cooperative when it comes to refraining from using sound. It is argued that the activities serve national security.
Need for Political Action
In general, however, in addition to technical means, there is still a lack of political decisions and cross-border solutions, which are essential to combat the massive problem of noise pollution in our oceans. These are also a focus of the UN Decade in the field of marine research for sustainable development, which began this year.
Currently, various environmental associations, including BUND and IFAW, are calling on the Federal Government in a open letter to the Environment Minister for continuous funding of long-term measuring stations in order to be able to better identify the sources and implement targeted measures, a reduction in noise at the source and Europe-wide noise reduction strategies. The hook is that they accuse the EU states of having completely failed to achieve the goals of the EU Marine Strategy Framework Directive agreed in 2008 - to achieve a good environmental status of our seas by 2020.
The good news at the end
We still have a long way to go before the noise pollution in the sea is significantly reduced. But there is a glimmer of hope: if the cause of the noise is eliminated, the pollution will stop immediately. There is still a lot to do, but there is great hope that in the long term we will be able to give marine animals a quieter environment. After all, we are also happy when we can just close the door on everything.
If you want to learn more about the problem, we recommend watching the documentary Sonic Sea . Here You can also sign the BUND petition against underwater noise directly.