Our marine expert Will Fitter explores what the ‘High Seas Treaty’ means for ocean conservation.
The world’s oceans may be better mapped and understood than ever before, but the high seas – the vast areas beyond national jurisdiction that cover around two-thirds of the ocean – remain difficult to govern. Despite being subject to international law, these waters are often beyond the practical reach of enforcement, allowing illegal fishing, pollution, and other illicit activities to persist.
This governance gap is one reason why the new High Seas Treaty, formally known as the Agreement on the Conservation and Sustainable Use of Marine Biological Diversity of Areas Beyond National Jurisdiction (BBNJ Agreement), is attracting global attention.
Adopted by the UN in 2023 and entering into force this year following ratification by 60 countries, including the UK, the treaty aims to strengthen protection of marine biodiversity in international waters. Its headline measures include enabling Marine Protected Areas (MPAs) on the high seas and creating new requirements for Environmental Impact Assessments (EIAs) for activities that could significantly affect marine ecosystems.
While the treaty is a landmark achievement, important questions remain about how it will work in practice.
Marine Protected Areas: Protection without enforcement?
One of the treaty’s most significant powers is the ability to establish Marine Protected Areas (MPAs) in international waters. These protected areas are intended to conserve biodiversity and help address growing pressures from overfishing, resource extraction, and habitat degradation.
However, the details have yet to be determined. Existing MPAs vary considerably in their level of protection. In UK waters, for example, only a few (under 2% by number) are fully protected no take zones while the majority permit activities such as bottom trawling under certain conditions.
This reflects a wider reality: marine management decisions often require balancing environmental objectives with economic and social considerations. Eunomia has explored these challenges through work for the Scottish Marine Directorate, examining the social impacts of proposed fisheries management measures in Scottish MPAs and engaging directly with fishing communities affected by conservation policies.
A more fundamental challenge is enforcement, something stakeholders also discussed in the research. However, this challenge is particularly acute on the High Seas, which are vast, remote, and difficult to police. The treaty does not create a dedicated international enforcement body and instead relies largely on individual states to implement and uphold its provisions.
This creates a classic “Tragedy of the Commons” problem. Because no single country owns the resource, incentives to invest in enforcement to protect these waters can be weaker. As documented by Outlaw Ocean, non-governmental actors such as Sea Shepherd often play a significant role in monitoring and tackling illegal fishing activities. The treaty strengthens the legal framework for protection but does not fully resolve the challenge of enforcement.
Environmental Impact Assessments: A stronger framework, but unclear standards
The treaty also introduces a more structured approach to Environmental Impact Assessments (EIA) for activities on the high seas, including deep-sea mining, offshore energy development, and bioprospecting.
Whilst this represents a significant step beyond UNCLOS, a UN treaty adopted in 1982, which requires countries to assess environmental impacts on the ocean, the treaty provides limited guidance on how assessments should be conducted and further uncertainty remains. The treaty requires an EIA where activities may have “more than a minor transitory effect” on the marine environment. Yet crucial details are still undefined. What constitutes a “minor” impact? How long is “transitory”?
In addition, the treaty does not create an independent regulator with the authority to approve or reject projects. As a result, national political and economic interests are likely to continue influencing decision-making. The effectiveness of the EIA framework will therefore depend heavily on future guidance and implementation.
Better data will be critical
If the treaty is to deliver meaningful outcomes, robust evidence and better environmental data will be essential.
Improved understanding of the ecological, social, and economic value of high-seas ecosystems could strengthen decision-making and support more effective environmental assessments. While the treaty does not explicitly require ecosystem service valuation, many of its provisions relating to cumulative and long-term impacts lend themselves to this approach – a necessity recognised in the UK’s own impact assessment for implementing the treaty, which used ecosystem service valuation to assess potential benefits.
At Eunomia, our work in this area reinforces how valuable these frameworks can be. From examining the impacts of water quality on coastal economies to researching the costs and benefits of restoring marine habitats like kelp forests, oyster reefs, seagrass, and saltmarsh, we help turn high-level marine policy into actionable insight.
Eunomia are well placed to support a variety of UK stakeholders in EIAs requisite under The High Seas Treaty as well as assessment of potential socio-economic impacts. For wider policy work for the Defra Family, Eunomia is a lead supplier on numerous sublots of Defra’s Environmental Science Research, Development and Evidence (ESRDE) Framework, including sublot 6.5 (Marine & Fisheries: Society and the Sea), where we are supported by our strong network of partners, such as Poseidon, One Ocean, Middlesex University London, Imperial Consultants, IFF Research, CECAN, Paula Orr, Ric Eales Consulting Ltd and David Baxter Environmental.
Turning ambition into action
The High Seas Treaty is an important milestone in international environmental governance. For the first time, there is a global framework specifically designed to protect biodiversity across the vast ocean areas that lie beyond national borders.
Yet its success will depend not on ratification, but implementation. Questions around MPA design, enforcement, assessment standards and governance remain unresolved, and these issues will shape the treaty’s ultimate impact.
Addressing them will require better evidence, stronger assessment methodologies, and meaningful engagement with industries and coastal communities affected by change. Environmental protection and economic development do not have to be competing objectives, but achieving both will require careful planning and informed decision-making.
The treaty provides the framework. The challenge now is turning its ambition into action.