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Marine Mammals Thematic Assessment

Executive Summary

Marine mammals have been and are subject to significant pressure from both natural impacts and human activity, which results in many populations and species not being in good status. Many pressures still occur on a wide scale today, such as incidental by-catch, or are even increasing, such as noise and hazardous substances, habitat loss or degradation of habitat. Marine mammals tend to have wide distributional ranges and some species are very rare. This makes the monitoring of marine mammals challenging, leading to a concerningly poor understanding of the distribution and population size of many marine mammal species.

As a result, the quantitative and qualitative assessments for marine mammals in the Quality Status Report (QSR) 2023 have revealed many species and populations to be in not good status. Moreover, limited improvement has been observed compared with previous assessments. For many species it is simply not known with confidence how well they are faring. With the environment expected to change rapidly in the future, for example through climate change, and given the shifts in the structure of food webs, where marine mammals often sit at the top, the continuing exposure to pollutants and society's shifting of food and energy production, for example, from land to sea, the threats to marine mammals are likely to remain at a high level.

There is limited evidence that the measures implemented to protect and improve the condition of marine mammal populations have been effective. However, the opportunity exists for more tailored measures and to improve the implementation of management measures. Similarly, there is a need to capitalise on the amount of data gathered through regionally coordinated monitoring, which would not only allow for a better understanding of marine mammal populations but also help in evaluating the effectiveness of measures that have been applied.

Q1. Identify the problems? Are they the same in all OSPAR Regions?

Many marine mammals are (top) predators and very mobile. This means that they are particularly susceptible to disturbances lower in the food web affecting their food and energy resources, and many are impacted by pressures occurring at various places in their wide distribution areas. Indirect pressures, such as reproductive disruption due to bioaccumulation of pollutants, act in addition to direct pressures on marine mammals, such as incidental by-catch, entanglement, vessel strikes or hunting. 

There is a wide range of societal needs driving the human activities that exert pressure on marine mammals, both on the individual and at the population level. The complexity of impacts results in many challenges associated with successful protection and management of marine mammals; these challenges are compounded in the case of highly mobile species that also migrate outside the OSPAR Maritime Area. 
OSPAR's QSR 2010 identified climate change, noise pollution, loss of habitat and prey, as well as by-catch, as the largest threats to marine mammals in the OSPAR Maritime Area. It was noted that cetaceans were especially threatened, being in some cases nearly extinct and in some cases not recovering, despite a moratorium on whaling. Because marine mammals are very mobile, designation of Marine Protected Areas (MPAs) was not expected to be sufficient as a protection measure: these MPAs, the QSR 2010 states, need to form an ecologically coherent network so that mobile species are protected at multiple (critical) life stages. The 2017 OSPAR Intermediate Assessment did not report recovery of cetaceans, in part because of data scarcity. For seals, grey seal abundance was largely increasing across the area assessed and grey seal pup production was observed to increase in most assessment units.  However, it should not be forgotten that grey seals are still undergoing recovery and recolonization from massive declines in the past due to hunting and pollution. Harbour seal abundance was largely stable or increasing, but decreasing in some assessment units.

Climate change is expected to impact marine mammals directly by affecting habitat suitability and causing distribution shifts, owing to animals tracking preferred environmental (e.g., temperature) conditions. Further, climate change is expected to impact primary productivity and availability of prey (both in time and space), forcing marine mammals to track their prey. Climate change is also likely to lead to increased human activity and associated pressures in Arctic Waters. Measures to adapt to and mitigate climate change are likely to result in increasing noise pollution and disturbance, affecting marine mammals in nearly all regions.  The expansion of renewable energy technologies will result in high disturbance during construction and decommissioning as well as increased ship traffic during the operational phases, increasing both impulsive and continuous noise pollution and thus affecting marine mammals’ behaviour and habitat use, and also impairing their hearing and causing injury. The whole spectrum of threats to marine mammals is still present in the OSPAR Maritime Area.

Grey seal. © Stephanie Gross/TiHo-ITAW

Q2. What has been done?

OSPAR has identified four marine mammal species of particular concern: the bowhead whale, the harbour porpoise, the northern right whale and the blue whale. OSPAR has adopted recommendations for actions both at the national level (e.g. recommendations to adopt legislation regarding human activities affecting the status of the selected species) and collectively (related to coordination of monitoring and exchange of knowledge) in order to address the threats to these species. Another OSPAR response aimed at the protection of marine mammals is the designation of Marine Protected Areas (MPAs). There are, however, still gaps in OSPAR’s network of MPAs, and this lack of eco-coherence limits its effectiveness in protecting marine mammals. The OSPAR Noise Action Plan and the new OSPAR Marine Litter Regional Action Plan are positive developments for marine mammals.

Q3. Did it work?

It is not possible to answer if the existing measures are able to reduce the impact of the human activities and pressures that continue to undermine the status of marine mammal species in the North-East Atlantic. The assessment results do not give a clear indication of successful implementation of measures and environmental management. In some cases, such as the large whale species on the OSPAR List of Threatened and/or Declining Species and Habitats (OSPAR Agreement 2008-06), the current status is principally a consequence of historic whaling activities. These species remain in not good status, although at least for the blue whale there are some indications of improvement. Given the long generation time of many of the species involved it is important that a long view is taken when measures are evaluated. Also, the monitoring needs to be suitable for the (sometimes very) wide distribution and rarity of marine mammal species. Cooperation with other competent authorities, including the Convention on the Protection of the Marine Environment of the Baltic Sea Area – also known as the Helsinki Convention (HELCOM), the Agreement on the Conservation of Small Cetaceans of the Baltic, North-East Atlantic, Irish and North Seas (ASCOBANS), the North Atlantic Marine Mammal Commission (NAMMCO), the International Whaling Commission (IWC), the Conservation of Arctic Flora and Fauna (CAFF) Working Group of the Arctic Council and the relevant fisheries management organisations will be key to ensuring the coordinated responses result in an improved state for marine mammals.

For the blue whale there are some indications of improvement. © Shutterstock

Q4. How does this field affect the overall quality status?

The status of marine mammals is typically also an indicator of the health of the wider ecosystem. Given their ecologically important role in the food web, they strongly depend on the quality status of ecosystems and exert top-down control on lower trophic levels. Marine mammals provide many ecosystem services, and changes in their status have implications for the wider ecosystem. The decline of marine mammal populations would adversely affect the provision of ecosystem services, primarily through significant impacts on food web functionality; biodiversity loss; reduced nutrient cycling and carbon storage potential; and by reducing the benefits that society derives from experiencing marine mammals in the wild. The assessments presented in the QSR 2023 on the abundance and distribution of grey seals and harbour seals, on grey seal pup production, on the incidental by-catch of marine mammals and on the distribution and abundance of cetaceans indicate that many pressures on marine mammals persist and some are of increasing concern (e.g., noise and plastic pollution, hazardous substances). Small toothed cetaceans are not in good status in all the Regions where they were assessed: Greater North Sea (Region II), Celtic Seas (Region III) and Bay of Biscay and Iberian Coast (Region IV). The status of baleen whales and deep-diving toothed cetaceans is unknown because of a lack of data to inform the indicators. Grey seals, recovering from local extinctions in the past, were found to be in good status in both the Greater North Sea and in the Celtic Seas, whereas harbour seals were considered to be in not good status in the Greater North Sea. The status of harbour seals in the Celtic Seas is unknown because of a lack of data, though for sites where data are available, the abundance of the species is increasing. Data from Arctic Waters were too limited and/or patchy for holistic indicator assessments. The available data from Arctic Waters suggest positive trends for some species or populations and negative for others.

In the QSR 2023, the pilot assessment for persistent chemicals bioaccumulation in marine mammals from the OSPAR Regions (presented within the Hazard Substances Thematic Assessment ) concludes that small toothed cetaceans, especially from the Greater North Sea and the Celtic Seas, are still at high risk of toxicity from legacy pollutants such as Polychlorinated Biphenyls (PCBs). Large knowledge gaps and the heterogeneity of the data prevented the integration of this information into the overall status assessment of marine mammals, but this hints at the necessity of increasing future efforts to achieve OSPAR’s operational objectives of the 2030 North-East Atlantic Environmental Strategy (S2.O2 and S2.O3) in respect of marine pollution and the effects of climate change on chemicals bioavailability (strategic objectives 11, 12 and 13), since long-lived species at the top of the food web still exhibit extremely elevated levels of persistent organic pollutants.

Small toothed cetaceans are still at high risk of toxicity from legacy pollutants such as PCBs. © Shutterstock

Q5. What do we do next?

In the North-East Atlantic Environment Strategy (NEAES) 2030 OSPAR acknowledges the consensus among scientists that the health of the North-East Atlantic is at risk of further degradation and that urgent action is needed to address the loss of biodiversity and improve ecosystem functioning.

With regard to marine mammals, OSPAR has expressed its ambition to conserve marine biodiversity and ecosystems to achieve good status for marine mammal species (Strategic Objective 5), and to ensure sustainable use of the marine environment, with a special view to addressing cumulative impacts (Strategic Objective 7). Further, OSPAR commits itself to the regional coordination and implementation of the EU Marine Strategy Framework Directive (Council Directive 2008/56/EC) (MSFD) for those Contracting Parties that are also EU member states (SX.01) and to applying ecosystem-based management in coordination with fisheries management bodies and other competent organisations.

These Strategic Objectives (S) are to be achieved through several Operational Objectives (O). 

  • The MPA network is to be expanded to cover at least 30% of the OSPAR Maritime Area, making sure that it is ecologically coherent (S5.O1). 
  • MPA management is to be improved (S5.O2 and 3, S11.O2) and its resilience to climate change and ocean acidification increased (S11.O1).
  • Agreed measures that allow threatened and declining mammals to recover will be implemented (S5.O5).
  • The List of Threatened and/or Declining species will be revised to take climate change and ocean acidification impacts into account (S11.O3).
  • Pressure on marine mammals will be prevented or reduced to allow achievement of good environmental status (S5.O4).
  • Where the knowledge base needed to achieve OSPAR's objectives related to marine mammals is currently insufficient, OSPAR will undertake action to coordinate data collection and sharing (S5.O6).
  • Methods to analyse cumulative impacts on marine mammals are to be (further) developed and the resulting knowledge will be used to reduce and/or prevent the severity of cumulative pressures on marine mammals (S7.O1). 
  • OSPAR commits itself to working with relevant competent authorities and stakeholders so as to minimise and, where possible, eliminate incidental by-catch of marine mammals (S7.O6).

The effective implementation of many of these objectives will depend heavily on national actions, which should continue to be reported through, for example, the implementation reporting requirements in the Recommendations on threatened and declining species and habitats.

OSPAR recognises the need to increase its focus on identifying and implementing collective actions which add value both to existing national actions and to the efforts of other international organisations. Overall, the 2019 implementation reporting indicates that there is a good level of engagement to implement the national actions within the Recommendations, in particular within the areas where the species and habitats are considered to be under threat and/ or in decline. The level of engagement in collective actions is clearly at a lower level, with some of the more complex actions not having been progressed and implemented. Many of the actions focus on monitoring and assessment, relatively few on response, but in either case there has been only modest progress. OSPAR will therefore develop a series of biodiversity action plans, starting with marine birds and coastal shelf benthic habitats, to identify priority response measures which are well-defined, add value and can be delivered within the resources available to the OSPAR Contracting Parties.  

The QSR 2023 provides a powerful evidence base for action. OSPAR will strengthen its capacity to use this evidence base and all future assessments in order to support engagement with other international partners. Engagement cannot be an end in itself: the development of a practical approach to Ecosystem-Based Management (EBM) will provide the opportunity and the mechanism to share evidence and common objectives for more sustainable use of the marine environment. Working with interested partners and drawing on international best practice, OSPAR will design and implement a pilot project on EBM in one of the OSPAR Regions.

Progress against all of these challenging objectives for biodiversity will be tracked through OSPAR’s NEAES Implementation Plan. A planned review in 2025 will provide an opportunity to adjust OSPAR’s Strategy and, if necessary, take further action to protect and conserve biodiversity.

Marine Mammals Assessments


Lead authors: Anita Gilles, Matthieu Authier, Roma Banga, Marianna Pinzone

Supporting authors: Julia Carlström, Federico Cornacchia, Emily Corcoran, Janos Hennicke, Simone de Winter, Anders Galatius, Steve Geelhoed, Adrian Judd, Emily Martin, Nikki Taylor, Jos Schilder, Gro van der Meeren, Daniel Wood

Supported by: OSPAR Biodiversity Committee (BDC), Intersessional Correspondence Group on Coordination of Biodiversity Assessment and Monitoring (ICG-COBAM), Intersessional Correspondance Group on the Quality Status Report (ICG-QSR), Intersessional Correspondance Group on Ecosystem Assessment Outlook (ICG-EcoC), Intersessional Correspondance Group on Economic and Social Analysis (ICG-ESA), Climate Change Expert Group (CCEG), OSPAR Marine Mammal Expert Group (OMMEG), OSPAR Commission Secretariat


OSPAR, 2023. Marine Mammal Thematic Assessment. In: OSPAR, 2023: Quality Status Report 2023. OSPAR Commission, London. Available at: