• Latest Version, 2024 Assessment
• 2018 assessment

Underwater noise

The extent to which Good Environmental Status has been achieved

The achievement of Good Environmental Status (GES) for underwater noise in the UK is uncertain since threshold values for GES have yet to be defined. However, trends show an increase in both impulsive and continuous underwater noise across the assessment period. This suggests that further policy and management measures will be necessary if underwater noise levels are to be reduced. 

Progress since previous assessments

Impulsive noise reporting first began in 2015 with the launch of the UK Marine Noise Registry (MNR). After initial high reported noise levels due to exceptionally high levels of seismic survey activity in 2015, impulsive noise showed a decreasing trend between 2016 and 2017.  Since 2017, reported impulsive noise has increased in the Greater North Sea, whilst the Celtic Seas trend remains stable. This is due to relatively high levels of industrial activity in the Greater North Sea compared to Celtic Sea. Continuous noise monitoring began in 2018 and so data on trends prior to this are not available. 

How progress has been assessed

Assessment overview

GES for underwater noise is assessed using two indicators, against two criteria and targets (Table 1). These indicators look to measure impulsive noise and continuous noise across the Greater North Sea and Celtic Seas. The impulsive noise indicator measures the number of recorded Pulse Block Days (PDB) occurring each year. The continuous noise indicator uses models to assess the likely noise levels from shipping movements. There are not yet threshold values developed for GES to assess noise indicators against and so only trends can be assessed. As a longer timeseries of data becomes available over subsequent UK Marine Strategy (UKMS) assessment cycles, trend assessments will become more robust. 

Table 1. Summary overview of the status assessment for all Noise (D11) assessments 

Criteria 1	Safe levels of anthropogenic impulsive sound
2019 Target	Levels of anthropogenic impulsive sound sources are not increasing and do not exceed levels that adversely affect populations of marine animals.
Indicator	Impulsive sound in the sea  Uses data collated in the UK Marine Noise Registry, which primarily covers licensed activities.
Greater North Sea	Uncertain – increasing trend
Celtic Seas	Uncertain
Criteria 2	Safe levels of anthropogenic continuous sound
2019 Target	Levels of anthropogenic continuous low-frequency sound are not increasing and do not exceed levels that adversely affect populations of marine animals.
Indicator	Continuous low frequency sound (ambient noise) in UK seas  Modelled maps of shipping noise were used to assess the continuous noise indicator.
Greater North Sea	Uncertain – increasing trend
Celtic Seas	Uncertain – increasing trend

 

Detailed assessments

The impulsive noise indicator was assessed using data collated in the UK MNR, which primarily covers licensed activities. Activity is recorded in Pulse Block Days (PBD). A PBD occurs when at least one noise event has occurred within a UK oil and gas licensing block on a particular day. Since 2017, noise has increased, with a maximum of 4,974 PBDs recorded in 2021. Between 2017 and 2021, the average PBDs per year was 3933. The increase has been driven by activity in the Greater North Sea, since for the Celtic Seas total PBDs have remained stable over that period. The Greater North Sea accounts for 68% of total PBDs, even though the Celtic Sea has more than double the number of blocks, indicating relatively high levels of industrial activity in the Greater North Sea. Overall, seismic surveys accounted for 64% of PBDs, with 22% for sub-bottom profiler surveys, 7% for piling, 5% for unclassified military sonar, and less than 3% for Acoustic Deterrent Devices (ADD), explosives and multibeam surveys combined. Seismic surveys contributed the most PBDs in all years except 2020 when they were overtaken by sub-bottom profilers. 

Modelled maps of shipping noise were used to assess the continuous noise indicator. These maps are based on acoustic modelling combined with Automatic Identification System (AIS) ship-tracking data and have been validated using acoustic measurements. Between 2018 and 2022, shipping noise pollution became more prevalent in UK waters, with the area of the UK Exclusive Economic Zone (EEZ) exceeding 120 dB re 1 µPa (the noise level above which marine mammals are more likely to show behavioural response) increasing by 23%. A greater proportion of the Greater North Sea was affected by such noise levels (19.5% in 2022), compared to the Celtic Seas (15.2% in 2022). However, the increase in the prevalence of such noise levels across the assessment period was greater in the Celtic Seas, with a 39% increase between 2018 and 2022, compared to an 7% increase for the Greater North Sea. 

Achievement of targets and indicators used to assess progress in 2024

Impulsive noise

Continuous noise

 

Drivers, activities and pressures affecting the state of the marine environment

Underwater noise in the UK is generated by multiple human activities, including offshore energy production from oil, gas and offshore wind; coastal and offshore construction; military activities; detonation of unexploded ordnance (UXO) such as mines or munitions; shipping, fishing vessels and recreational boating; research activities; aggregates extraction; and aquaculture. These activities support societal needs for food, energy, materials, security, trade, communications, health and wellbeing. Pressure from anthropogenic noise can be continuous (mainly from shipping but also dredging and operational wind turbines) or impulsive (e.g., from seismic surveys, explosions and pile driving). 

The expansion in development associated with the increase in the installation of offshore windfarms is generating increasing levels of impulsive and continuous noise from construction, survey activity, operation and maintenance.  

There may also be an increase in geophysical / seismic surveys for Carbon Capture Use and Storage (CCUS) facilities, and noise associated with any decommissioning activity. 

Impact of pressure on ecosystem services

Underwater noise has the potential to cause behavioural disturbance, interfere with the hearing or physiology of marine animals and injury. Impacts associated with underwater noise can affect different marine ecosystem services. Specific ecosystem services include wild fish and other natural biomass and related raw materials; wild animals, plants and other biomass; water quality regulation; recreation related services; ecosystem and species appreciation; spiritual, artistic and symbolic services. 

Impacts of climate change on pressures and state

Climate change may affect levels of underwater noise and the impacts of this noise on marine environments. Changes in human activities driven by climate change include the expansion of offshore wind energy development, which is generating increasing levels of impulsive and continuous noise from construction, survey activity, operation and maintenance.  

Seismic surveys are the dominant source of impulsive noise. Any climate change driven reduction in North Sea oil and gas exploration and extraction is likely to reduce their contribution to impulsive noise activity as well as contributing to the UK Government’s Net Zero commitments. However seismic surveys used for Carbon Capture and Storage exploration may increase impulsive underwater noise. Other renewable offshore energy sources, such as tidal energy, are likely to generate underwater noise but their effect is unknown.  

Effects of climate change on the physical environment include ocean acidification, which results in a modest reduction in the sound absorption properties of seawater, although the effect may be negligible in the relatively shallow seas surrounding the UK. Sea temperature changes will also affect sound propagation (including via stratification), as will sea-level rise. 

Management actions taken

The actions we are taking to achieve GES for underwater noise are set out in the UK Marine Strategy Part 3 2025: Programme of Measures.  The collective management actions already in place contribute to the aim of reducing the environmental impacts of underwater noise. 

Key measures that directly manage noise from industrial activities include those applied via Marine Licence and planning consent conditions and/or requirements.  

The Joint Position Statement on unexploded ordnance clearance sets out that low noise methods of clearance should be the default method used to clear any type of UXO in the marine environment. High order clearance methods should only be used in extraordinary circumstances and always be the last resort. 

Noise disturbance thresholds have been set for impulsive noise in Special Areas of Conservation (SAC) for harbour porpoises in England, Wales and Northern Ireland. From January 2025 there is an expectation that all offshore wind pile driving activity in English waters should demonstrate they have utilised their best endeavours to deliver noise reductions, through the use of primary and/or secondary noise reduction methods in the first instance.  Further detail can be found in the January 2025 Reducing Marine Noise Policy Paper and associated  Cefas, JNCC, Natural England position on the use of quieter piling methods and noise abatement systems when installing offshore wind turbine foundations. 

Next steps

Evidence challenges

The status of impulsive and continuous noise is uncertain as thresholds values are yet to be defined. Headline challenges include: 

• Agreement of suitable noise exposure indicators for both impulsive and continuous noise in UK waters at population levels (noise is cross-boundary and affects mobile species), so that quantitative noise targets can be established. 

Operational objectives

• We will work nationally and with other countries, particularly in the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR) Commission, to establish threshold values for levels of impulsive and continuous anthropogenic sound.  

• We will continue to work collaboratively at the International Maritime Organisation to ensure that continuous underwater noise from shipping is robustly controlled at a global level. 

• The UK government intends to consult on an offshore wind piling noise limit which would significantly reduce the noise produced during the construction of offshore wind developments.  

• We will continue to develop the UK MNR to enable better planning, assessing, and managing of licensed activities in UK waters in accordance with agreed threshold values.  

• We will continue to coordinate direct measurement and modelling of ambient noise and the application of these outputs for management, such as through the UKMS monitoring network in England and Wales, the Scottish Passive Acoustic Network, the Scottish Marine Energy Research Programme, and ongoing monitoring undertaken by the Agri-Food and Biosciences Institute in Northern Ireland. 

Technical Detail: Good Environmental Status for the next cycle

Table 2 shows the overarching targets (characteristics) for GES, along with their criteria, individual GES targets and associated indicators for the next assessment cycle (subject to change following the UKMS Part 1 public consultation).

Table 2. GES criteria and targets for next assessment cycle.

Overarching target
Loud, low- and mid-frequency impulsive sounds and continuous low frequency sounds generated by human activities are reduced to the extent that they do not have adverse effects on marine ecosystems and animals at the population level.
Criteria	2024-2030 GES targets	Comment	Indicators
Impulsive noise	Levels of anthropogenic impulsive sound sources are not increasing and do not exceed levels that adversely affect populations of marine animals.	No change	Records of spatial and temporal data on impulsive sound.
Continuous noise	Levels of anthropogenic continuous low-frequency sound are not increasing and do not exceed levels that adversely affect populations of marine animals.	No change	Records of ambient "continuous" noise.

 

Work will also continue to develop noise exposure indicators for both impulsive and continuous noise in UK marine protected areas (such as marine mammal Special Areas of Conservation) and other sensitive habitats, consistent with the OSPAR Common Indicator for the risk of impact from impulsive noise. 

References

Contributors

Sónia Mendes (JNCC) and Nathan Merchant (Cefas). 

Acknowledgements: Manuel Nicolaus (Cefas), Adrian Judd (Cefas), Adrian Farcas (Cefas), Rosalyn Putland (Cefas), Rachel King (JNCC)