Marine Mammals - Marine online assessment tool

The extent to which Good Environmental Status has been achieved

Marine mammals overall are not achieving Good Environmental Status (GES) across both the Celtic Seas and Greater North Sea sub-regions (Figure 1).

Data availability limits our capacity to confidently assess status of each component in the regional seas, but evidence suggest that bycatch is a significant contributor to poor GES, particularly for cetaceans. Grey seals are stable or increasing across their range while harbour seals remain in decline despite stable populations in the west of Scotland. A pilot indicator assessment also highlighted that small, toothed cetaceans continue to be at high risk of toxicity from legacy pollutants such as polychlorinated biphenyls (PCBs) (Jepson and others, 2016).

Figure showing marine mammals indicators divided between Celtic and North seas. Small toothed cetaceans have a not good environmental status in both Celtic and north seas. Deep diving toothed cetaceans and Baleen whales have an unknown status in both Celtic and north seas. Seals have unknown status in Celtic seas and a not good status in the north sea.

Figure 1. Outcome of GES for marine mammals by UK Marine Strategy (UKMS) region. Outcomes utilise the integrated assessment of status using the OSPAR Common Indicators for Seal Abundance and Distribution , Abundance and Distribution of Cetaceans , Grey Seal Pup Production and Marine Mammal By-catch. These Common Indicators cover 13 species of cetacean, and both grey and harbour seals. The comparatively small number of marine mammal species available for an integration led to the one-out-all-out (OOAO) rule the only appropriate option (OSPAR Biodiversity Committee 2022: BDC 22/9/1 §3.7c). OOAO necessitates that if one assessed threshold is not met at the Common Indicator level, then all in that group are considered to not meet the threshold at the integrated level. For this reason, integrated GES outcomes for UKMS, at the regional sea level in this figure, may differ from those shown in Table 1 (which presents outcomes according to individual indicators).

Progress since previous assessments

There is no clear evidence of improvement in relation to GES compared to previous assessments although advances in methodologies have been made through the Convention for the Protection of the Marine Environment of the North-East Atlantic (OSPAR) commission, which will improve capacity to identify change in future assessments.

Grey seals continue to increase in abundance across the UK. Harbour seals in the Greater North Sea are in a further state of decline compared to previous assessments due to the continued decline of the species in north-east Scotland, and a more recent sustained decline in the south-east of England. Harbour seal abundance is stable on the west coast of Scotland, but their status in other parts of the Celtic Seas remains uncertain.

Bycatch estimates for harbour porpoise, the only species to be assessed in previous assessments, remain broadly similar, although further exploration of bycatch estimates in relation to population trends is required to understand whether risk has proportionally changed. The underlying methods for assessment of the state of marine mammal bycatch has been further developed since 2019 with the agreement of threshold-setting methods which should now enable clear review of progress in future (Taylor and others, 2022).

How progress has been assessed

Assessment overview

The extent to which GES for marine mammals has been achieved under the 2024 UK Marine Strategy (Table 1) has been determined using outputs from the OSPAR Quality Status Report (QSR) 2023 Integrated Marine Mammal Thematic Assessment.

Table 1. Overview of the indicator status for Marine Mammals (2024) 

Criteria 1	Bycatch mortality
UKMS 2019 Target	The long-term viability of marine mammal populations is not threatened by incidental bycatch.
Corresponding OSPAR QSR 2023 Common Indicator	Marine mammal bycatch
Greater North Sea	Partially met (seals)
Greater North Sea	Not met (cetaceans)
Celtic Seas	Partially met (seals)
Celtic Seas	Not met (cetaceans)
Criteria 2	Population demographic characteristics
UKMS 2019 Target	Population abundance and distribution are consistent with favourable conservation status.
Corresponding OSPAR QSR 2023 Common Indicator	Seal abundance and distribution
Greater North Sea	Partially met
Celtic Seas	Partially met
Corresponding OSPAR QSR 2023 Common Indicator	Abundance and distribution of cetaceans
Greater North Sea	Not met
Celtic Seas	Not met
Criteria 3	Population demographic characteristics
UKMS 2019 Target	Grey seal pup production does not decline substantially in the short or long-term.
Corresponding OSPAR QSR 2023 Common Indicator	Grey seal pup production
Greater North Sea	Met
Celtic Seas	Met

Table 1 describes whether GES has been met for the individual UKMS Descriptors for seals and cetaceans at the scale of Regional Seas. These outcomes consider cetaceans and seals independently, at the scale of the individual descriptor (bycatch, abundance & distribution, pup production), and are different to the integrated outcome shown in Figure 1.

A Descriptor status of ‘Partially Met’ has been used in scenarios where some elements of the Descriptor are meeting threshold values under the corresponding OSPAR Common Indicator assessments, but not all. The purpose of this has been to has to provide a more accurate summary of status to support Actions required to move Descriptor status towards GES.

While bycatch of grey seals in both the Greater North Sea, and Celtic Seas are below the threshold values calculated as part of the OSPAR Marine Mammal Bycatch Common Indicator; harbour seals are not presently assessed as part of the indicator. Therefore, it is not possible to report that GES has been met for seals overall in UK Regional Seas. Furthermore, results within OSPAR Marine mammal bycatch note caveats in accounting for potential regional impacts of bycatch of grey seals, particularly in the southern portion of the Celtic Seas where the population is lower, but the estimated bycatch levels may be higher.

The ‘Partially Met’ status of seals (Abundance and Distribution) in the Greater North Sea and Celtic Seas acknowledges the mixed picture for both seal species across the UK. While grey seal abundance, and distribution is largely increasing above threshold values across all areas where sufficient data is available to carry out an assessment. The picture for harbour seals is more mixed; harbour seals remain in decline across much of the east coast of Scotland and England (Greater North Sea), but stable populations remain in the west of Scotland (Celtic Seas).

Detailed assessments

Four OSPAR Common Indicator Assessments were integrated following agreed methods to generate an overarching status assessment for marine mammals in the OSPAR North-East Atlantic. Status for marine mammals was assessed as ‘Not good’ if at least one Common Indicator outcome failed. These assessments and their associated Coordinated Environmental Monitoring Programme (CEMP) documents describe in detail the background, methods, results, and conclusions from which the assessments are drawn:

Marine Mammal Thematic Assessment | CEMP

Seal Abundance and Distribution | CEMP

Abundance and Distribution of Cetaceans | CEMP

Grey Seal Pup Production | CEMP

Marine Mammal Bycatch | CEMP

A further Pilot Assessment of Status and Trends of Persistent Chemicals in Marine Mammals is also considered as additional information to inform on the status of marine mammals.

The appropriate scale for the assessment of GES for some of the more highly mobile and widespread marine mammals is larger than that of the UKMS regional seas. Through applying the outputs from the OSPAR QSR (2023), assessment scales for some species extend into the wider Northeast Atlantic regions used by OSPAR (e.g. Region IV: Bay of Biscay and Iberian Coast) which is more representative of the natural population ranges of these species. Where this is the case, the UK outlook for the species within the wider OSPAR QSR 2023 assessment outputs is described in further detail.

Bycatch is a key contributor to the ‘not good’ status of cetaceans across the Greater North Sea and Celtic Seas (Table 2). Both common dolphin and harbour porpoise bycatch estimates exceed OSPAR thresholds for bycatch in all UK-relevant Assessment Units (AU) (Taylor and others, 2022 Table D). To ascertain the significance of calculated UK bycatch estimates (Kingston and others, 2021) in relation to the threshold limits for bycatch across the OSPAR area, Table 2 focuses the outputs from the OSPAR Marine Mammal Bycatch Common Indicator across the three species assessed; as well as the most recent published UK bycatch estimates (2019) which are then illustrated as a percentage of the OSPAR threshold value for each species. Bycatch estimates for harbour porpoise, in particular, are significant when considered against the threshold values.

Table 2. Summary of UK bycatch estimates in relation to the calculated threshold limit for bycatch across the OSPAR area. Table illustrates the most recent UK bycatch estimates for common dolphin, harbour porpoise and grey seal (Kingston and others, 2021) as a percentage of the bycatch thresholds calculated for the relevant OSPAR assessment units (AU) within the QSR Marine Mammal Bycatch common indicator (M6). Note that there is some variation in spatial extent between OSPAR and UK Marine Strategy and bycatch estimates, and therefore these percentages are indicative only.

Species	UK Marine Strategy Region(s)	UK bycatch estimate (2019 data) (Kingston and others, 2021)	Associated OSPAR AU bycatch threshold value (Taylor and others, 2022)	UK estimated bycatch as a percentage of the OSPAR AU threshold value
Common dolphin (Delphinus delphis)	Celtic Seas; Greater North Sea	278 95% confidence limit (CL) range 165-662	985 (Northeast Atlantic AU)	28%
Harbour porpoise (Phocoena phocoena)	Greater North Sea	833 (95% CL range 502-1560) – (Assuming full Acoustic Deterrent Device (ADD) compliance) 1061 95% CL range 599-1922 - Assuming no ADD use	1622	47% (ADD compliance) 60% (No ADD use)
Harbour porpoise (Phocoena phocoena)	Celtic Seas		160*	47% (ADD compliance) 60% (No ADD use)
Grey seal (Halichoerus grypus)	Greater North Sea	488 95% CL range 375-872	7171 (North Sea AU)	5%
Grey seal (Halichoerus grypus)	Celtic Seas	488 95% CL range 375-872	3647	5%

* Value is the OSPAR Irish and Celtic Seas, and West Scotland and Ireland AU threshold values combined

Achievement of targets and indicators used to assess progress in 2024

Grey seal pup production

Seal Abundance and distribution

Marine Mammal Bycatch

Abundance and distribution of Cetaceans

Photographic credits: Grey seal pup production © Graeme Duncan. Seal Abundance and distribution © John Weinberg. Marine Mammal Bycatch © JNCC. Abundance and distribution of Cetaceans © Nikki Taylor.

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

The drivers of increased pressures on the state of marine mammals derive from social and economic needs for sustained and increased food, energy and national security, as well as health and well-being.

The need for fishing, aquaculture and agriculture to maintain the UK’s food supply increases the risk of bycatch, entanglement, further exposure to chemical pollutants and habitat degradation, and prey depletion in the marine environment.

Priorities to both decarbonise and grow UK-based power sources under the Net Zero Strategy and British Energy Security Strategy drive much of the UK’s increasing offshore renewable power activities, resulting in an increase of pressures that can impact marine mammals using the areas.

Marine mammals are important for both tourism and recreation in the UK, supporting coastal economies and communities. The risk of incidences of disturbance, harassment and injury to marine species is likely to rise with increases in marine tourism and recreational activities.

Impact of pressure on ecosystem services

The impacts of increasing pressures on the ecosystem services provided by marine mammals closely reflects the position of the OSPAR QSR 2023 Marine Mammal Thematic Assessment, with the exception of references to their value as a food and material source, which is not part of UK culture. The pressures and impacts identified reflect the increasing anthropogenic use of our marine environment. Reduced abundance or significant displacement of marine mammals resulting from these pressures would adversely affect the provision of services. Impact concerns include Regulation and Maintenance Services (regulation and functionality of food webs, carbon sequestration, nutrient cycling) and Cultural Services (wildlife recreation, coastal economy, wellbeing).

Impacts of climate change on pressures and state

Climate change is impacting the availability of suitable habitats, the phenology of primary production and key life history events and the prevalence of disease in marine mammals (Martin and others, 2023)

Although grey seal, bottlenose dolphin and harbour porpoise distribution has expanded southwards, there is some evidence that UK marine animal distributions may be shifting northwards, with some dolphin species previously observed in warmer, more southern waters being recorded more frequently further north. This corroborates with increasing average sea surface temperatures and northward shifts in commercial fish species, of which several feature in the diet of various marine mammal species.

Increased occurrence of harmful algal blooms, exposure to novel pathogens and thermal stress in marine mammals, as a result of higher temperatures and stronger stratification of the water column, intensify the prevalence and susceptibility to disease and negative impacts on reproductive success in marine mammals.

Increased storm frequency and sea level rise have also resulted in higher mortalities of grey seals at breeding sites around the UK. More regular occurrences of these events have the potential to impact future trends in abundance.

Management actions taken

Measures for achieving GES for marine mammals can be found in the UK Marine Strategy Part 3 2025: Programme of Measures. The UK’s management actions contribute to a wider OSPAR-level strategic response and are largely reflected within the 2023 OSPAR marine mammal thematic assessment.

The UK Cetacean Conservation Strategy is being developed collaboratively to better deliver effective management, research, monitoring and communication to achieve and/or maintain good environmental status.

The Bycatch Mitigation Initiative lays out how the UK intends to minimise, and where possible, eliminate the bycatch of marine species.

Marine Protected Areas (MPAs) are presently designated for grey seal, harbour seal, harbour porpoise, bottlenose dolphin, Risso’s dolphin and minke whale. The development of appropriate management plans by appropriate authorities is underway.

Assessments of English MPAs designated for harbour porpoise are being undertaken to determine if fishing activity is causing an adverse effect on the integrity of the sites. Gear specific assessments have also been carried out for Welsh fisheries.

Research into the drivers of seal population declines in Scotland and the south-east of England is on-going. Monitoring action to improve understanding of seal abundance in Wales and the southwest of England has been supported by UK and devolved administrations.

Industrial activities which may impact protected marine mammals within MPAs are managed through the implementation of Habitats Regulation Assessment (HRA) and Environmental Impact Assessment (EIA). Cetacean Management Units have been developed by UK statutory nature conservation bodies (SNCBs) and support the assessment of impacts on species from marine developments. Guidance supports the management of impulsive noise activities within English, Irish and Welsh MPAs to ensure levels do not affect site integrity and mitigation to reduce both noise propagation through the marine environment and the risk of injury to marine mammals.

Fisheries byelaws in four English Special Areas of Conservation (SACs) designated for benthic habitats, and area-based gear restrictions in Welsh waters respectively have been implemented.

Fisheries Management Plans are being developed for a number of commercial stocks to ensure their sustainable management. Wider ecosystem benefits and protected species are considered as part of these Plans and may bring added benefits to marine mammals outside of MPAs.

Marine wildlife watching codes and best practice guidance has been produced by all devolved UK administrations to inform members of the public on how to minimise disturbance to wildlife when using the coastal and marine environment.

Next steps

Evidence challenges

Seals

Evidence gaps are primarily being addressed collectively through coordinated research and management actions including:

Exploring the likely impacts of climate change on seals, to clarify how management may need to adapt as changes in the environment occur.

Developing a methodology that enables us to assess the cumulative impacts of human-induced threats to seals.

Understanding the causes of declines in harbour seal populations across the UK.

Cetaceans

As with seals, evidence gaps are primarily being addressed collectively through coordinated research and management actions set out in a range of initiatives, including driven by:

The UK Cetacean Conservation Strategy.

The Marine Wildlife Bycatch Mitigation Initiative (BMI) and others.

Northeast-Atlantic Small Cetaceans in European Atlantic waters and the North Sea (SCANS) surveys.

Initiatives such as the Joint Cetacean Data Programme which support the standardising and collating of marine mammal datasets to strengthen the evidence base available for strategy and management decisions.

We will also consider:

Mechanisms to evaluate the cumulative impacts of human-induced pressures.

The likely impacts of climate change on cetaceans.

Engagement with the EU Life CIBBRiNA international bycatch programme to coordinate efforts to mitigate pressures across shared seas.

Operational objectives

Outside of formal measures (in the programme of measures), to help us continue progress toward meeting GES, the following operational activities will be undertaken.

We will consider management of marine mammals in the wider ecosystem context, with a view to taking an ecosystem approach to management where applicable.

Seals

Agreed objectives include:

• Continue research investigating potential causes of the harbour seal declines in Scotland and the south-east of England.

• Prioritise research investigating life history parameters (e.g. survival and birth rates) and population dynamics of seals to improve understanding of their status.

• Identify appropriate mitigation measures and, where required, develop strategies to manage identified risks to seal populations.

• Explore collaborative partnerships and technologies to develop a better understanding of drivers of change and population resilience (e.g. bycatch, disease).

Cetaceans

Continue existing monitoring of cetacean bycatch and entanglement, using new technology (such as Remote Electronic Monitoring) where possible.

Coordinate and streamline monitoring to deliver efficiencies and improve evidence-bases for cetaceans, including stranding post-mortem analyses and tissue biopsies to explore the implications of PCBs and other chemical contaminants on cetacean health.

Seek appropriate opportunities for innovation and investment in technologies and methodologies to improve cetacean monitoring capacity and improve utilisation of existing data e.g. Joint Cetacean Data Programme (JCDP).

Continue to support Marine Protected Area condition monitoring to enable effective reporting on status.

Maintain, and where required, explore new measures to reduce bycatch. Each Devolved Government is at a different phase of development of bycatch policies.

Technical Detail: Good Environmental Status for the next cycle

Table 3 and 4 show the overarching targets (characteristics) for GES for seals and cetaceans respectively, along with their criteria, individual GES targets and associated indicators for the next assessment cycle (subject to change following the UK Marine Strategy Part 1 public consultation (HM Government, 2012)  

Table 3. GES criteria and targets for seals for the next assessment cycle. 

Criteria	2024-2030 GES targets	Comment	Indicators
Bycatch mortality	The long-term viability of seal populations is not threatened by bycatch, and the trend in bycatch estimates is decreasing.	Changed to reflect improved ability to detect and assess trends	D1.3 Marine mammal bycatch
Population abundance and distribution	Abundance and distribution trends are stable where good status is established or improving where species or populations are not achieving GES.	Changed to reflect improved ability to detect and assess trends	D1.2 Changes in abundance and distribution of seals
Grey seal pup production	Grey seal pup production remains stable where good status is established or improves where populations are not achieving GES.	Changed to reflect improved ability to detect and assess trends	D1.3 Grey seal pup production

Table 4. GES criteria and targets for cetaceans for the next assessment cycle. 

Criteria	2024-2030 GES targets	Comment
Bycatch mortality	The long-term viability of cetacean populations is not threatened by bycatch, and the trend in bycatch estimates is decreasing.	Changed to reflect improved ability to detect and assess trends	D1.3 Marine mammal bycatch
Population abundance and distribution	Abundance and distribution trends are stable where good status is or improving where species or populations are not achieving GES.	Changed to reflect improved ability to detect and assess trends	D1.2 Abundance and distribution of coastal bottlenose dolphins;

Additional indicators:

There is potential to consider the outputs from the UK indicator on impulsive and continuous noise, and how this might contribute to assessment of GES of marine mammals. Similarly, as the OSPAR Pilot Assessment of Status and Trends of Persistent Chemicals in Marine Mammals develops, there is potential to consider further development from a UK perspective with appropriate experts. There is scope to consider the development of an indicator specifically designed to highlight trends likely linked to climate change to support identification of resilience of species to climate change impacts.

References

OSPAR (2023). Marine Mammal Thematic Assessment. In: OSPAR, 2023: Quality Status Report 2023. OSPAR Commission, London. Available at: oap.ospar.org/en/ospar-assessments/quality-status-reports/qsr-2023/thematic-assessments/marine-mammals/

Jepson, P., Deaville, R., Barber, J. and others (2016). PCB pollution continues to impact populations of orcas and other dolphins in European waters. Sci Rep 6, 18573 (2016). https://doi.org/10.1038/srep18573

Kingston, A., Thomas, L and Northridge, S. (2021). UK Bycatch Monitoring Programme Report for 2019. https://randd.defra.gov.uk/ProjectDetails?ProjectID=19943andFromSearch=YandPublisher=1andSearchText=ME6004andSortString=ProjectCodeandSortOrder=AscandPaging=10#Description

Martin, E., Banga, R. and Taylor, N.L. Climate change impacts on marine mammals around the UK and Ireland. MCCIP Science Review 2023, 22pp. https://www.mccip.org.uk/sites/default/files/2023-02/Climate%20Change%20Impacts%20on%20Marine%20Mammals%20around%20the%20UK%20and%20Ireland.pdf

Taylor, N., Authier, M., Banga, R., Genu, M., Macleod, K., Gilles, A. (2022). Marine Mammal By-catch. In: OSPAR, 2023: The 2023 Quality Status Report for the Northeast Atlantic. OSPAR Commission, London. Available at: https://oap.ospar.org/en/ospar-assessments/quality-status-reports/qsr-2023/indicator-assessments/marine-mammal-bycatch

Contributors

Roma Banga, Nicola L Taylor

Acknowledgements: Emily Martin, Nichola Clear, Poppy Cooney

Supported by: HBDSEG Marine Mammal Subgroup; OMMEG; OSPAR BDC; ICG-COBAM; ICG-POSH.