Contributing to hybrid governance to protect and manage remarkable areas on the high seas: the Thermal Dome and the Sargasso Sea


With SARGADOM, we want to improve the protection of biodiversity and to maintain ecosystem services in these two sensitive high seas areas and facilitate the design of hybrid ocean governance models. We think that is the only way to make the BBNJ treaty not simply a goodwill declaration, but a real and productive tool to govern and protect the high seas. We want to contribute to the UN negotiations – but, more than that, we want to be ready to contribute to the implementation phase of the BBNJ treaty.

The high seas represent 64% of the world’s ocean. It is governed by the United Nations Convention on the Law of the Sea (UNCLOS). It has an international status based on two distinct legal regimes: i) the seabed located beyond the continental shelf, the mineral resources of which are governed by the International Seabed Authority as part of the Common Heritage of Mankind and ii) the water column above the seabed, that is governed by the principle of Freedom of the High seas.


The economic activities taking place there are regulated by States, primarily under the responsibility of the flag State. However, at this stage there is no international legal basis for establishing protection zones that are binding on  all users. UNCLOS includes the principle of non-appropriation of the high seas and this makes it impossible for one State to restrict access from one area to another State. The sustainable management of the high seas therefore poses a number of major challenges.


UNCLOS provides a framework for the governance of areas beyond national jurisdiction (ABNJ), however, the existing system has been described as an “unfinished agenda”. To date, the existing international legal framework and existing regional and/or sectoral management regimes are incomplete and often ineffective. The need to reflect on global action for the governance and management of these areas, that would envisage  the establishment of conservation and management measures, or the limitation of human activities in order to conserve biodiversity there, has been discussed in the UN General Assembly since 2004. 

In this context, in 2017, after a process lasting more than a decade, the United Nations General Assembly (UNGA) established an intergovernmental conference to negotiate an International Legally Binding Instrument (ILBI) on the conservation and sustainable use of biodiversity beyond national jurisdiction (BBNJ). At the end of the fourth round of negotiations in March 2021, ILBI negotiators seem to accept that some form of global governance structure – through a Conference of the Parties (COP) – is needed.


“The treaty must balance the dual objectives of conservation and sustainable use,” Serge Segura, former French Ambassador for Oceans says, “there will be a sort of revolution if we succeed.”

The Thermal Dome and the Sargasso Sea are two sites representative of the diversity and importance of high seas ecosystems. They perfectly illustrate the fact that ecological limits (such as the interconnectivity of ecosystems) do not correspond to the legal delimitations established by UNCLOS. They are dynamic systems, which move, shrink, and expand with currents and winds. The two sites are mainly located beyond national jurisdiction on the high seas, but may “encroach” permanently, regularly or from time to time on EEZs that are under the jurisdiction of States.


The strategy proposed by the project is based on a DPSIR (Driving Force-Pressure-State-Impact-Response) analysis for each site, and an analysis of the current governance of the two sites and potential improvements, which will lead to the development of proposals to improve the governance and to agree to the establishment of appropriate conservation and management measures for the sites. It is hoped that the results of this work will help inform the implementation of future agreements on other high seas areas that wish to design area-based management tools (ABMTs). The knowledge gained will also support the development of agreements and action plans for the Thermal Dome and the Sargasso Sea.


Thermal Dome and the Sargasso Sea are two unique ecosystems that serve as pilot cases to advance the conservation of the high seas and also to test and reflect on the concept of hybrid governance, combining global and regional approaches. 

These two sites were chosen because of the relatively advanced state of knowledge of these two high seas ecosystems and the ongoing involvement of stakeholders in discussions about potential governance mechanisms. Other factors include the particular ecological importance of these areas, the quality of the teams already in place and their involvement at the global level. For these reasons they can bring a great deal to the table to inform the discussion of the BBNJ treaty, the effectiveness of which will depend heavily on a good understanding of the issues at stake.


Thermal Dome​

The Thermal Dome is located within and beyond the Exclusive Economic Zones (EEZs) of Central American countries in the Eastern Tropical Pacific. It is a phenomenon formed by the convergence of trade winds and sea currents that cause deep, cold and nutrient-rich waters to rise (upwelling). The thermocline is thus “lifted” up to about 15 meters from the surface, giving, through its bell shape, its name of “dome”. The size and location of the Thermal Dome is dynamic. Its average surface area is 530,000 km2. Its central zone is located around 9°N and 90°W, more than 65 km west of the borders of the EEZs of Costa Rica and Nicaragua, i.e. beyond their respective national jurisdictions.

The Thermal Dome area does not benefit from a strong and established framework of regional governance. However, the presence of the Central American Commission on Environment and Development (CCAD) should be noted. The CCAD, an organization belonging to the SICA (Central America Integration System), was created in 1989. Its role is to enhance the natural heritage of the region through the reasonable use of resources and the control of pollution. Through its competent committee on marine issues, it shows a strong interest in the governance and management of the Thermal Dome. Since 2014, the regional NGO MarViva, with the support of the government of Costa Rica and other Central American governments, has been leading an initiative to improve the governance of the Thermal Dome


Sargasso Sea​

Stretching over 5 million km2, the Sargasso Sea is a unique ecosystem found within the North Atlantic subtropical gyre. It takes its name from the golden seaweed that populates its surface, Sargassum, the  two dominant species are : Sargassum natans and S. fluitans. The Sargassum forms vast mats and windrows on the surface of the Sargasso Sea and acts as the foundation of the high seas ecosystem.

The Sargasso Sea is bordered by the flow of major ocean currents – the Gulf Stream forms its Western limit and the North Atlantic Current forms its northern limit, the Canary Current acts as a more diffuse eastern limit, and the Northern Equatorial Current together with the Caribbean Current, form the southern limit. Only the small islands of Bermuda have a direct coastline on the Sargasso Sea.

Since 2010, the Sargasso Sea Project, developed in association with IUCN and other partners and led by the Government of Bermuda, has been working with a wide range of stakeholders from government, academia and the private sector, as well as interested collaborators, to bring the importance of the Sargasso Sea ecosystem to the attention of the international community. It seeks to use existing competent international organizations to implement conservation measures for the Sargasso Sea, and to use this process as a model for other regions. In 2014, governments met in Bermuda to sign the Hamilton Declaration on Collaboration for the Conservation of the Sargasso Sea, which as of 2022 has a total of ten government signatories. It is a non-binding political agreement between interested governments located in the wider Sargasso Sea region or with an interest in the conservation of the high seas. The Sargasso Sea Commission, an independent body established by a political declaration, has been described as a new paradigm for governance on the high seas.


The expected outcomes of the project are different for the two study sites. 

For the Thermal Dome, it is a multisectoral proposal for the governance and regulation of the high seas, with emphasis on fisheries and navigation, which will be submitted to the UN stakeholders by the Central American Commission for Environment and Development (CCAD). For the Sargasso Sea Commission, it will be a Strategic Action Programme submitted for approval to key stakeholders including the Signatories of the Hamilton Declaration.

Through the process of developing innovative governance structures for the Thermal Dome and the Sargasso Sea, the project will aim to gain insight and knowledge that will aid in making recommendations for other sites or future global agreements on the high seas in general

Through the process of developing innovative governance structures for the Thermal Dome and the Sargasso Sea, the project will gain insight and knowledge that will aid in making recommendations for other sites or future global agreements on the high seas in general. The University of Brest will help to collect these lessons learned, and share them through the development of a massive open online course (MOOC) on the governance of the high seas.

Key Numbers

About high seas

0 %
of the world's ocean
0 M
of unidentified species
0 %
of the occupied habitat of Earth.

SARGADOM is the result of an international collaboration between research institutes, NGOs, marine area managers and public funders.

Implementing partners

Bermuda Institute of Ocean Sciences

Duke University Marine Lab – Nicholas School of the Environment

Imperial College

Neptune and company

OFB French Biodiversity Agency

With the support of

Fonds français pour l’environnement mondial
Global Fishing Watch

The National Aeronautics and Space Administration

University of Edinburgh

Global Environment Facility

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