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Marine mammals and offshore industries

UK waters are home to several marine mammal species, all of which are protected under national and international legislation. Of the 28 cetacean species recorded in UK waters, twelve can regularly be seen, including minke, fin and sperm whales, harbour porpoise and four species of dolphin – bottlenose, common, Risso’s and white beaked. In addition, grey seals and harbour seals forage and breed in the UK.

Human activities in offshore waters such as those related to commercial fisheries, oil and gas and renewables, have the potential to impact these species if not managed appropriately. Pressures on marine mammals from offshore industries include bycatch, prey depletion, underwater noise, habitat degradation, and collision with static or moving objects. 

JNCC's role

JNCC provides quality-assured advice to Government, regulators, industry, consultants and others on the potential impacts to marine mammals from offshore industries. Advice covers multiple levels of planning, from national marine plans and strategic environmental assessments to individual operations' environmental impact assessments. It covers all stages of a development's life cycle.

We provide advice on potential impacts to offshore protected sites including on noise management measures for Special Areas of Conservation (SACs) designated for harbour porpoise. In addition, we provide advice on European Protected Species (EPS) regulations and licensing. 

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We have developed a suit of mitigation guidelines for industry to follow in order to reduce potential impacts to marine mammals from impulsive noise sources. We also developed, host and manage the UK Marine Noise Registry (MNR) to record human activities that produce loud, low to medium frequency impulsive noise in UK waters.

JNCC chairs an inter-agency working group on marine mammals and industries in order to share knowledge across the four countries' nature conservation agencies and facilitate a joined-up approach to advice.

We provide specialist marine mammal advice to support the  UK's Overseas Territories and contribute our expertise as part of our marine pollution role, including advice during pollution events and post-event monitoring.


Marine mammals are protected in UK offshore waters under a series of regulations. Cetaceans are covered by a system of strict protection from injury, killing and disturbance. In addition, grey and harbour seal, harbour porpoise and bottlenose dolphin are species for which the designation of Special Areas of Conservation (SACs) is required.

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The term European Protected Species (EPS) originates from the Habitats Directive and refers to species listed in Annex IV. For these species, member states are required to implement measures to prevent their capture, killing or disturbance throughout their natural range. 

The Directive was transposed into UK law through The Conservation of Habitats and Species Regulations 2017 and The Conservation of Offshore Marine Habitats and Species Regulations 2017. Similar legislation exists for Scottish and Northern Irish inshore waters. EPS whose natural range includes UK waters consist of cetaceans (whales, dolphins and porpoises), marine turtles and Atlantic sturgeon. In UK waters, the latter two are at the limit of their natural range and only occur in low numbers around the UK. UK Regulations make it an offence to kill, injure or disturb marine EPS. 

JNCC, Natural England and Natural Resources Wales (formerly the Countryside Council for Wales) provided guidance regarding the protection of cetacean EPS from injury and disturbance. This guidance* provides a useful resource for marine users, regulators, advisers and enforcement authorities when considering whether an offence of deliberate disturbance or injury/killing a cetacean EPS is likely to or has occurred as a result of an activity. Similar guidance is available from Scottish Natural Heritage for Scottish inshore waters.

JNCC has also developed marine mammal mitigation guidelines covering key activities, adherence to which is considered to minimise the risk of committing an injury offence.

* Note: the auditory injury thresholds and mitigation guidelines for geophysical surveys referred to in this document have since been updated.

Marine protected areas (MPAs) contribute to the long-term conservation of marine habitats and species. To date 355 marine MPAs have been designated, covering 25% of UK waters. Of these, 23 Special Areas of Conservation (SAC) have been designated for marine mammals, and three MPAs have been proposed for Scottish waters which include marine mammal features. 

JNCC provides conservation management advice for offshore sites in the form of site-specific conservation objectives and advice on operations, all of which can be found on our Site Information Centres. The majority of sites with marine mammal features are within territorial waters, however five sites for harbour porpoise extend into offshore waters. Sites which cover inshore and offshore waters are jointly managed by JNCC and the relevant country nature conservation body. The responsibility for MPAs within territorial waters sits with the relevant country nature conservation body:

When proposing activities within an MPA, potential impacts to the site and its features must be considered. Some activities outside sites, for example those that result in underwater noise, can still impact sites.


Assessing impacts to marine mammals

When submitting applications to undertake operations at sea, it is a requirement to consider all potential impacts from the proposal, including those to the environment. This is usually in the form of an environmental impact assessment (EIA), which assesses the environmental consequences (positive and negative) of a plan or project. An Environmental Statement (ES) is the written material submitted to a regulator or planning authority and will contain the results of the EIA. The size of the assessment and level of detail required will depend on the scale of the project, what and where it is, and any environmental sensitivities.

When considering potential impacts to marine mammals, a key consideration is whether there might be any impacts from noisy activities, for example piling, explosive use or geophysical surveys. A noise risk assessment is undertaken, which considers how loud the noise could be, at what distance from the activity could marine mammals be injured or disturbed, what could be done to reduce the level of noise and animal exposure and whether impacts could have an effect at the population level.

Typically, noise propagation modelling is undertaken to estimate distances at which hearing damage may occur. Depending on the results, mitigation may be required to ensure no marine mammals are in the vicinity before the activity begins. Regulators review these assessments and consult with country nature conservation bodies (CNCBs) including JNCC before deciding whether to consent the project.

Consideration should also be given to supporting habitats and processes important to marine mammals including those that relate to the seabed, water column and prey, particularly in protected areas. For example, activities that directly impact the seabed, such as dredging/burial, sweeping and deposits, could potentially affect a preferred prey species such as sandeel, making them unavailable to marine mammals as a food source.

Marine mammal management units (MUs) for the seven most common cetacean species in UK waters have been agreed by the UK country nature conservation bodies. These provide an indication of the spatial scales at which impacts of plans and projects need to be assessed. 

Baseline data

Before an impact assessment can be undertaken, it is important to identify which marine mammals species may be in the area where the activity will take place. This provides a baseline against which potential impacts can be assessed. However collecting such data for marine mammals can be technically difficult and expensive. For some projects, project specific data collection may be required, while for others a review of existing information may be sufficient. Examples of such information include:

  • Seal usage maps 2017: These maps have been produced by the Sea Mammal Research Unit (SMRU) on behalf of Marine Scotland and are based on tagging data for harbour and grey seals collected between 1991 and 2016. The estimates of usage, which have been scaled to estimated populations sizes in 2015, are presented as the mean number of seals within 5 x 5 km grid squares. However, they do not distinguish between year, season or types of usage (e.g. foraging or travelling). The confidence intervals reflect confidence in the estimated mean usage in each cell, rather than uncertainty in distribution across the maps.
  • SCANS III: A large-scale ship and aerial survey to study the distribution and abundance of cetaceans in European Atlantic waters. A continuation of the Small Cetacean Abundance in the North Sea and Adjacent Waters surveys (SCANS), the first survey was undertaken in July 1994, the second in July 2005 and the third (phase III) in July/August 2016. The phase III report contains density estimates for 19 cetacean species. It should be noted, however, that the primary purpose of these surveys was to determine abundance of the most common cetacean species at a large scale, not to derive densities at a smaller scale. In addition, the densities are based on a single survey in a single month of a single year, therefore do not consider seasonal or inter-annual variation.
  • Joint Cetacean Protocol (JCP) Phase III: The JCP was a collaborative project providing information on the distribution, abundance and population trends of cetacean species in the North Sea and adjacent sea regions. Phase III of the project used effort-linked sightings data to estimate patterns of abundance for seven cetacean species over a 17-year period (1994–2010). The data associated with the phase III report is available and the density surfaces have been scaled to the SCANS III abundance estimates for the marine mammal management units. JNCC recommends the guidance in Appendix 7 of the report is reviewed before using these data. 
  • Joint Cetacean Data Programme: This new programme aims to work with data providers to find solutions to collating and storing data long-term for continued use to improve the UK capacity for analysing and understanding cetaceans using our waters. Data is not yet available under the project, however Phase I is now complete.


Underwater noise

Marine mammals use sound for a number of biologically important behaviours, including foraging, avoiding predators, breeding, socialising, parental care and travelling. Man-made underwater noise has the potential to hamper or prevent marine mammals from undertaking these key behaviours. For example:

  • an animal could stop hunting for food;
  • noise could prevent an animal from hearing other important sounds, such as the approach of a predator or communications from mates or their young; 
  • noise may force animals away from important areas such as key foraging grounds (i.e. cause displacement). 

In addition, some loud sounds may cause physical injury, such as hearing loss or tissue damage, and in some cases may cause death.

Effects may be temporary and be of little consequence to an individual animal or conversely, they could directly impact an individual’s ability to survive or breed, particularly if an animal is subjected to repeated exposures to noise. If many individuals are affected, this could result in population-level impacts (i.e. a reduction in population size).

Sources of noise

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How noise propagates through the marine environment will depend on several factors, including water depth, substrate type, temperature and salinity. It is recognised that sound generated by certain activities, such as geophysical surveys, piling and explosive operations, have the potential to cause injury (e.g. hearing damage) and disturbance to marine mammals. 

Construction works in or near the sea, such as those involved in building harbours, offshore oil and gas facilities and offshore wind farms, may involve the use of pile driving, explosives and geophysical survey equipment including seismic air guns. Mitigation measures are routinely employed before these activities begin to reduce risks of injury to marine mammals.

Pile driving involves forcing a supporting or retaining structure into the seabed using a hydraulic hammer. This can result in substantial levels of underwater noise being transmitted directly into the water column and the seabed. The level of noise generated will vary depending mainly on the pile diameter and length, hammer energy and seabed conditions. Although no direct evidence exists for a causal link between pile driving sound and physical injury to marine mammals, data on auditory sensitivities and comparison with human and other terrestrial mammal data suggests that pile driving in the marine environment without mitigation could result in injuries to marine mammals in very close proximity (JNCC et al. 2010). There is also evidence for prolonged avoidance reactions. Projects that include piling over a prolonged period could constitute disturbance under UK Regulations (JNCC et al. 2010).

Explosive use in the marine environment can result in higher sound levels than any other man-made source (Richardson et al. 1995) and can produce shock waves at close distances. Subsequently their use has the potential to cause injury or death to marine mammals and without mitigation could constitute an injury offence under UK regulations. Small charges are widely used, for example during salvage operations, decommissioning, harbour clearance, harbour bottom alterations, and rock and concrete blasting.

Military ordnance have been detonated during war and peace (e.g. testing) and many unexploded ordnance (UXO) remain on the seabed. These are often removed by detonating a small charge next to the device, forcing the larger device to detonate. While the noise level produced by explosives is very loud, it is over very quickly, so subsequently any disturbance to marine mammals resulting from a single explosion is generally considered temporary. However, multiple detonations conducted over a prolonged period could constitute a disturbance offence under UK Regulations.

Geophysical surveys are undertaken to determine characteristics on or below the Earth’s surface by sending acoustic pulses into the seabed and recording the time taken for each energy wave to bounce back. Sound sources can be produced by a variety of different means including electromagnetic (echosounders, side-scan sonar, pingers, boomers, CHIRP, sonar), electrical dischargers (sparker) and pressurised airguns (seismic).

The depth at which pulses penetrate the seabed depends on why the data are being collected and the equipment being used. For example, large seismic airguns are used when exploring for oil and gas reserves as these surveys require deep penetration and can cover large areas, however the required resolution may be low.

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Other activities (e.g. site clearance before offshore wind farm construction, inter-connector cable installation or aggregate extraction), require more detailed, higher resolution information of a smaller area at shallower depths. These surveys may use small airguns and/or electrical/electromagnetic means (sometimes referred to as sub-bottom profiling or high-resolution survey equipment).

As with piling, there is no direct evidence for a causal link between geophysical survey noise and physical injury to marine mammals, however data on auditory sensitivities and comparison with human and other terrestrial mammal data suggests that source levels emitted by airguns could result in hearing damage to animals close to the source (JNCC et al. 2010) and there is evidence for short-term behavioural responses (Southall et al. 2007; Stone and Tasker 2006; Gordon et al. 2004; Thompson et al. 2013, Sarnocińska et al. 2020). Subsequently, their use without mitigation could constitute an offence under UK Regulations.

A review of other potential sources of underwater noise, (e.g. acoustic deterrents, military sonar and shipping), can be found in the EPS guidance published by the country nature conservation bodies (JNCC et al. 2010)

Auditory injury thresholds

Criteria to help predict potential auditory injury to marine mammals were first considered in 2002 when the US National Marine Fisheries Services (NMFS) brought together a panel of scientists to consider the problem of how to assess impacts from noise on marine mammals. This resulted in the publication of auditory exposure criteria in 2007 (Southall et al. 2007). 

The criteria introduced the concept of marine mammal frequency weighted hearing groups. This involved categorising marine mammals into groups based on what was known about their hearing. The criteria also presented auditory injury thresholds, representing levels of noise above which it is thought auditory injury may begin to occur. These criteria have been adopted in the UK for assessing impacts to marine mammals from noise (see SNCB guidance on EPS).

These criteria were updated in 2016 (NMSF, 2018) and most recently in 2019 (Southall et al. 2019). They reflect the most comprehensive and up-to-date scientific knowledge relating to the risk of auditory injury to marine mammals. JNCC requires these new thresholds and functional hearing groups to be used for any marine mammal noise assessment. It is worth noting that while the hearing groups and thresholds are the same in these two documents, the terminology used to identify the hearing groups does differ (e.g. harbour porpoise would be referred to as high frequency in NMSF 2018, but very high frequency in Southall et al. 2019). Assessments should be clear as to which reference and associated terminology they are using.

Noise management within harbour porpoise SACs

In June 2020, JNCC together with Natural England (NE) and the Department of Agriculture, Environment and Rural Affairs in Northern Ireland (DAERA) published advice to competent authorities on what could constitute Significant Disturbance within harbour porpoise SACs in England, Wales and Northern Ireland marine areas. In addition, guidance was provided on a noise management approach to keep underwater noise within levels that do not affect a site’s integrity. The advice and guidance are the culmination of several years of inter-agency discussion as well as consultation with regulators, industry and Non-Governmental Organisations. JNCC, NE and DAERA are committed to periodically reviewing this advice to ensure it remains workable, effective and takes account of best-available evidence.   

Harbour porpoise SACs noise guidance and supporting documents



Marine mammal bycatch refers to the capture or entanglement of marine mammals in fishing gear such as nets, lines, traps or hooks.

UK and EU legislation require the monitoring and mitigation of bycatch. Additionally, the UK has commitments under international agreements and conventions such as ASCOBANS and OSPAR. JNCC supports UK Governments and Devolved Administrations in addressing bycatch through the provision of technical advice on monitoring and mitigation. JNCC also provide technical expertise on this issue through ICES working groups.

Monitoring of bycatch of sensitive species, including marine mammals, is undertaken in the UK via the Bycatch Monitoring Scheme (PSBMS), implemented by the Sea Mammal Research Unit (SMRU). This programme deploys dedicated observers on board commercial fishing vessels to monitor levels of bycatch, and works with industry to investigate ways to reduce the impact. The UK Cetacean Strandings Investigation Programme (CSIP) also provides data regarding the prevalence of bycatch through monitoring causes of death of stranded marine mammals around the UK.


Collision risk

Death or injury by collision can result from the introduction of physical objects, mobile or immobile, that may collide with or result in potential collision of marine mammals. Traditionally this has been associated with vessels, with ship strikes of large whales being an issue of growing concern worldwide (Flynn & Calambokidis 2019). Concerns have also been raised regarding collision with underwater turbines (Sparling et al. 2013).

Post-mortem investigations in the UK have revealed some deaths caused by trauma could potentially be linked with vessel strikes, however, evidence of risk is limited (Deaville 2015). Mitigation to reduce risks includes reducing traffic, reduced speed limits and having marine mammal observers on vessels when travelling through areas with high marine mammal abundance.


Supporting habitats

When planning offshore activities, consideration should also be given to supporting habitats and processes important to marine mammals including those that relate to the seabed, water column and prey.

The links between habitat-prey-predator are poorly understood and more research is needed to provide the evidence required to properly assess the risk of certain activities. However, species such as harbour porpoise are highly dependent on year-round proximity to food sources and its distribution. An individual’s body condition may strongly reflect the availability and energy content of its prey (Santos & Pierce 2003). Displacement of animals from a preferred area, for whatever reason, can impact an individual’s ability to survive, breed or raise their young.

The seabed is not considered sensitive to noise disturbance, however, underwater sound has the potential to affect prey fish species, for example noise could disturb fish away from a specific area where marine mammals hunt. Noise can also cause hearing damage to some fish prey species (e.g. herring).


In addition, activities that directly impact the seabed, such as dredging/burial, sweeping and deposits, could potentially impact preferred prey species that rely on the seabed as part of their life cycle, such as sandeel, making them less available to marine mammals as a food source. 


JNCC have helped develop a number of tools to assist in assessing potential impacts to marine mammals in UK waters and developing mitigation protocols:

Other useful links include:



Brandt, M.J., Diederichs, A., Betke, K. & Nehls, G. 2011. Responses of harbour porpoises to pile driving at the Horns Rev II offshore wind farm in the Danish North Sea. Marine Ecology Progress Series, 421: 205-2016

Dähne, M., Gilles, A., Lucke, K., Peschko, V., Adler, S., Krügel, K., Sundermeyer, J. & Siebert, U. 2013. Effects of pile-driving on harbour porpoise (Phocoena phocoena) at the first offshore wind farm in Germany. Environmental Research Letters, 8: 025002 (16pp)

Deaville, R. 2015. UK Cetacean Stranding Investigation Programme Annual report for the Period 1st January - 31st December 2015

Flynn, K.R. & Calambokidis, J. 2019. Lessons from placing an observer on commercial cargo ships off the US west coast: utility as an observation platform and insight into ship strike vulnerability. Frontiers in Marine Science, Brief Research Report.

Gordon, J. G., Gillespie, D., Potter, J., Frantzis, A., Simmonds, M., Swift, R. J. & Thompson, D. 2004. A review of the effects of seismic survey on marine mammals. Marine Technology Society Journal, 37, pp. 14-34.

JNCC 2010. Joint nature Conservation Committee, Natural England and Countryside Council for Wales. October 2010. The protection of marine European Protected Species from injury and disturbance: guidance for the marine area in England and Wales, and the UK offshore marine area.

Richardson, W.J., Greene, C.R., Malme, C.I. and Thomson, D.H. 1995 Marine mammals and noise. Academic Press, San Diego, California.

Santos, M.B. & Pierce, G.J. 2003. The diet of harbour porpoise (Phocoena phocoena) in the northeast Atlantic. Oceanography and Marine Biology, 41:355-390

Sarnocin´ ska J, Teilmann J, Balle JD, van Beest FM, Delefosse M and Tougaard J (2020), Harbor Porpoise (Phocoena phocoena) reaction to a 3D seismic airgun survey in the North Sea. Marine Science, 6:824.

Southall, B. L., Bowles, A. E., Ellison, W. T., Finneran, J. J., Gentry, R. L., Greene, C. R., Kastak, D., Ketten, D., Miller, J. H., Nachtigal, P. E., Richardson, W. J., Thomas, J. A. and Tyack, P. 2007 Marine mammal noise exposure criteria: initial scientific recommendations. Aquatic Mammals, 33: 411-521.

Southall, B.L., Finneran, J.J., Reichmuth, C., Nachtigall, P.E., Ketten, D.R., Bowles, A.E., Ellison, W.T., Nowacek, D.P., and Tyack, P.L. 2019. Marine mammal noise exposure criteria: updated scientific recommendations for residual hearing effects. Aquatic Mammals, 45: 125-232.

Sparling, C.R., Coram, A.J., McConnell, B., Hawkins, K.R. & Northridge, S.P. 2013. Marine Mammal Impacts.  Wave & Tidal Consenting Position Paper Series, Paper 3. Natural Environment Research Council.

Stone, C.J. and Tasker, M.L. 2006 The effects of seismic airguns on cetaceans in UK waters. Journal of Cetacean Research and Management, 8: 255-264.

Thompson, P.M., Brookes, K.L., Graham, I.M., Barton, T.R., Needham, K., Bradbury, G. & Merchant, N.D. 2013. Short-term disturbance by a commercial two-dimensional seismic survey does not lead to long-term displacement of harbour porpoise. Proceeding of the Royal Society B, 280: 20132001 

NMFS 2018. 2018 Revision to Technical guidance for assessing the effects of anthropogenic sound on marine mammal hearing. National Marine Fisheries Service, U.S. Dept. of Commerce, NOAA Technical Memorandum NMFS-OPR-59, 167 p.


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