Underwater noise – the importance of mitigation

Underwater noise is a common side-effect of offshore energy industry activities. Noise produced during oil and gas, offshore wind, subsea cabling, and decommissioning operations can negatively impact marine mammals. Increases in dolphin numbers, recent sightings of orcas, and the revival of humpback whales in Scottish waters, means protection should be top of the agenda.

Noise can damage hearing and disrupt behaviour

Underwater sound can damage hearing and upset an animal’s ability to communicate, navigate, and forage for food. With energy industry activity increasing in the UKCS the potential for human-generated underwater sound is greater than ever. In the UK marine mammals are protected by law, and operators must take appropriate measures to ensure their safety.

Which activities cause concern?

A primary area of concern is seismic survey, and the harmful effects of this are well-recognised. Regulations are in place to protect cetaceans from what is classed as deliberate injury.

Another area of concern is pile-driving – piling is common during offshore windfarm construction, and potential behavioural disturbance can occur up to 50 km from source.

Additional activities with noise generating potential are underwater cutting and explosives, both likely to be used extensively during decommissioning. Operations such as rock-dumping and dredging also generate significant and sustained underwater noise, although this tends to be from the vessels dynamic positioning (DP) system however, rather than the operation itself.

Mitigation is easy and effective

Noise mitigation is most effective with a combined approach. This will include equipment and personnel, and will include Marine Mammal Observation (MMO), Passive Acoustic Monitoring (PAM), and depending on location, Acoustic Deterrent Devices (ADD).

Marine Mammal Observers (MMOs) detect marine mammals by visual observation from the client vessel or facility. The MMO accurately records sightings, and liaises with project teams to ensure compliance to guidelines. In the event that marine mammals enter an exclusion zone, the MMO will advise when operations should be delayed.

Passive Acoustic Monitoring (PAM) operators provide non-visual support using hydrophone cables, and monitor in-coming signals using specialised acoustic software. PAMs detect species such as sperm whales, which spend most of their time underwater, and provide cover during hours of darkness or reduced visibility.

Acoustic Deterrent Devices (ADD) are an additional safeguard, useful in some locations. Once deployed the ADD will emit a high frequency sound to deter the seals from entering operational areas.

MMO, PAM and ADD are complementary services, used simultaneously to provide full 24 hour coverage.

Choose the right personnel

In the UK, marine mammal monitoring and management guidelines set by the Joint Nature Conservation Committee (JNCC) are followed. MMO and PAM personnel should hold JNCC approved training certificates, and be familiar with JNCC reporting forms and reports. This ensures industry best practice, including accurate recording of data and consistent application of the correct procedures. In addition all MMO and PAM personnel should hold valid offshore survival training and offshore medical certification.

Planning a project? MES can help you comply with regulations concerning marine mammals during offshore operations. Contact our ops team.

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