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Theory and research

  • Assessment of natural and anthropogenic sound sources and acoustic propagation in the North Sea (English)
  • Reactions of North Sea fish species to underwater sounds in a wide frequency range (Dutch)
  • Review of literature for the UK Offshore Operators Association (English)
  • Underwater noise and mammals (English)
  • Sources and their impacts (English)
  • Report of MSFD Task Group 11 (English)

 

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Descriptor 11: Energy incl. Underwater Noise

“Introduction of energy, including underwater noise, is at levels that do not adversely affect the marine environment”

The introduction of energy is quite difficult to explain and grasp. It changes the physical systems. Simply put, when we speak about introduction of energy, we refer to light, electricity, heat, noise, electromagnetic radiation, radio waves or vibrations. Building the foundations of an offshore platform using pile driving for instance is the source of a lot of energy releases, whether in the form of noise or vibrations.

Although energy is a natural process, it does not always have a positive effect on other natural processes. Human activities can take a disproportional amount of energy out of a system or add to it. This can have a negative impact on the marine environment.

Why should we pay attention to the introduction of energy?

Generally, the strongest effects from these activities on the marine environment are caused by underwater noise. Heat can also be an issue in the case of cooling water systems. Finally, electromagnetic radiation can be expected in the case of activities related to electricity. Yet, there is very little information on the effects of electromagnetic fields on marine life. Most studies have dealt with underwater noise. 

Impacts of man-made energy on the marine environment are related to the prevalence and timing of any activity as well as the distribution and abundance of sensitive marine life. For instance, in the case of offshore construction, shipping activities and pile driving (i.e. foundation building) add noise to the already established ambient noise levels. The disturbance from shipping (from fishing and recreational vessels) lies in particular in the fact that the noise input from these activities can be continuous. Loud impulse noise and ambient (continuous) noise should therefore be distinguished.

What kind of damage does underwater noise cause?

Attention has been raised on the topic of underwater noise and its effects on marine life. Yet, the effects of underwater noise are not fully understood. One reason for this is that only for a few species of mammals and fish, tests have been performed to identify hearing range and sensitivity.

But even if an individual hears the noise, we are not sure how it will react or what damage will be done. It could avoid the source and be chased out of important areas, for example spawning grounds. It might influence its ability to detect food. Its hearing could get damaged at close ranges with further effects on communication about food, danger and reproduction. Research proved that marine fauna certainly do experience effects from noise exposure. It has been established for example that stranding incidents in beaked whales were caused by underwater noise from military activities. The graph shows some hearing curves of toothed whales.

Audiogram for odontocetes © Reynolds and Rommel 1999)
Audiogram for odontocetes © Reynolds and Rommel 1999

Some underwater noise can be heard by marine life over distances of dozens of kilometres. For example pile driving sound can be as loud as 250 decibels* at the source and can potentially be picked up by a harbour porpoise over distances of at least 80 km under certain circumstances. Although, we cannot compare these levels to in-air values without some corrections, we can say that that pile driving is quite loud!

*relative to 1 micropascal

Overcraft in UK © iStockphoto
 
Submarine cables in the OSPAR Maritime area © OSPAR 2009a
Submarine cables in the OSPAR Maritime area © OSPAR 2009

What  are the main sources of energy in the marine environment?

Human sources of energy in the marine environment are commonly related to transport, mining and fishing and construction. The effects of recreation and industries can also be experienced in coastal waters.

Sources of energy include:

  • Shipping for trade or tourism, like ferries or cruise ships, recreation boats and fishing boats, which all produce noise;
  • The use of sonar systems by all kinds of vessels;
  • Construction (especially through piling) of offshore oil and gas platforms and wind parks;
  • Dredging for shipping lanes, sand mining and for laying pipes and cables;
  • Operation of platforms and their lights; 
  • Cable connections between offshore activities, the main land and between power stations, causing electromagnetic radiation;
  • Cooling water systems for industry, which raise water temperature;
  • Military activities, which produce noise.

 

What can be done?

Monitoring underwater energy

Measuring underwater energy is now part of the Environmental Impact Assessment (EIA) that is necessary for new activities to obtain proper licences. Through these EIAs, companies are under the obligation to perform monitoring or to mitigate the effects of the energy input from their activities.

Registration or monitoring of energy generally occurs at a limited level and often a simple measurement of energy is performed. However, setting up a proper study of the different energy parameters, to understand how the energy is spread and subsequently what the effects on the environment are, is far more complex. The distribution of heated water can be modelled quite well thanks to knowledge about local currents. The propagation of underwater noise can also be modelled in computer programmes.

The adoption of the Marine Directive and specifically of Descriptor 11 has given a great impulse to the market of underwater sound equipment, engineering and advice. There is also more interest for research in this field and governments, companies and institutes have already performed a great amount of studies on the topic.

As a follow up to the Commission Decision on criteria and methodological standards on good environmental status (GES) of marine waters (Commission Decision 2010/477/EU), the Marine Directors requested the Directorate-General for the Environment (DG ENV) in 2010 to establish a technical subgroup under the Working Group on GES (WG GES) in relation to the Marine Strategy Framework Directive 2008/56/EC (MSFD) for further development of Descriptor 10 Marine Litter and Descriptor 11 Noise/Energy. For practical reasons the work was carried out by two separate groups. The reports compile the recommendations regarding Descriptor 10 (Marine Litter) and Descriptor 11 (Noise).

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