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The Use of Earth Observation Tools for the Surveillance and Enforcement of Marine Protected Areas on the High Seas

Published online by Cambridge University Press:  14 November 2025

Efthymios Papastavridis
Efthymios Papastavridis*
Affiliation:
Assistant Professor of International Law, School of Law, National and Kapodistrian University of Athens , Athens, Greece
*
Email: epapast@law.uoa.gr
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Abstract

In the aftermath of the adoption of the Implementing Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biodiversity in Areas Beyond National Jurisdiction (BBNJ Agreement) and in view of the global target to protect at least 30 per cent of the ocean by 2030 (30×30), an issue that merits attention is the surveillance of marine protected areas (MPAs) on the high seas. The BBNJ Agreement is remarkably silent on how the relevant management measures in future MPAs will be implemented, despite the fact that enforcement challenges are prevalent in existing MPAs. This article discusses the potential use of maritime domain awareness (MDA) tools, including earth observation tools like satellites, in ensuring effective surveillance and subsequent enforcement of high seas MPAs. The article first introduces the concept of MDA and the use of earth observation tools in that context, highlighting the advantages that such tools may have in ensuring compliance in MPAs. It then explores the legal framework governing the employment of earth observation tools in high seas MPAs. The article argues that States are not merely permitted but also obligated to monitor their vessels’ activities in high seas MPAs. Furthermore, States are under a general obligation of cooperation, including the obligation to share information that is obtained by MDA tools. Finally, the article briefly discusses how evidence, like satellite imagery, could be used for enforcement purposes, including before domestic courts. It concludes that the use of earth observation tools would be instrumental to the effective surveillance and enforcement of high seas MPAs.

Keywords

marine protected areashigh seassurveillancemaritime domain awarenesssatellitesUNCLOSBBNJ Agreementmarine environment

Information

Type
Forum
Information
International & Comparative Law Quarterly , Volume 74 , Supplement S1: Law of the Sea: Present Challenges and Future Directions , July 2025 , pp. 27 - 45
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0), which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.
Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of British Institute of International and Comparative Law

1. Introduction

Areas Beyond National Jurisdiction (ABNJ), which comprise the high seas and the international seabed, make up 64 per cent of the oceans and seas and play an essential role in conserving marine living resources and biological diversity.Footnote 1 In this context, the use of marine protected areas (MPAs) as an integrated area-based management tool (ABMT) to regulate human activities and thus conserve biodiversity in ABNJ, has attracted increasing attention from the international community.Footnote 2

Notwithstanding the significance of ABMTs for protecting vulnerable marine ecosystems,Footnote 3 there is no central guidance under the United Nations Convention on the Law of the Sea (UNCLOS)Footnote 4 on their use, merely a series of fragmented and sectoral approaches.Footnote 5 Having acknowledged this gap in the protection of Marine Biodiversity in ABNJ, the Ad Hoc Open-ended Informal Working Group on Marine Biodiversity in ABNJ agreed in 2011 that ABMTs would be included in the ‘package deal’ to be addressed by a new Implementing Agreement under UNCLOS on the Conservation and Sustainable Use of Marine Biodiversity in Areas Beyond National Jurisdiction (BBNJ Agreement).Footnote 6 The BBNJ Agreement was finally adopted on 19 June 2023,Footnote 7 after long and arduous negotiations,Footnote 8 and is set to enter into force on 17 January 2026.Footnote 9 Having as one of its overriding aims the conservation of priority protection areas through the establishment of a comprehensive system of ABMTs, the adoption of the BBNJ Agreement marks a significant milestone towards the protection of marine biodiversity and a vital step towards achieving the Convention on Biological Diversity Kunming-Montreal Global Biodiversity Framework’s goal of protecting at least 30 per cent of marine habitats by 2030.Footnote 10

One of the principal achievements of the BBNJ Agreement is that it provides a global and cross-sectoral legal basis for the designation of MPAs in all marine ABNJ and across all sectors of human activities.Footnote 11 Also, the BBNJ Agreement offers a definition of MPA, something that to date has been missing from international law.Footnote 12 An MPA, for the purposes of the BBNJ Agreement, ‘means a geographically defined marine area that is designated and managed to achieve specific long-term biological diversity conservation objectives and may allow, where appropriate, sustainable use, provided it is consistent with the conservation objectives’.Footnote 13

Given the prominence of MPAs for the protection of marine biodiversity, one would expect that the BBNJ Agreement would have included detailed provisions on their implementation. Quite to the contrary though, the BBNJ Agreement sets forth only a general obligation for States Parties to ‘ensure that activities under their jurisdiction or control that take place in areas beyond national jurisdiction are conducted consistently with the decisions adopted under this Part’.Footnote 14 In addition, Article 26 stipulates that ‘[p]arties shall, individually or collectively, report to the Conference of the Parties on the implementation of area-based management tools, including marine protected areas, established under this Part and related measures’.Footnote 15 Apart from this reporting duty, there is no other mechanism for ensuring compliance with and enforcement of the BBNJ Agreement. It is thus uncertain how the effective implementation of the MPAs, or even the BBNJ Agreement itself, will be secured.Footnote 16 One option would be for measures concerning monitoring and implementation of MPAs to be set out in relation to a specific MPA as part of the proposed management plan submitted by the States Parties and decided by the Conference of the Parties (COP). Alternatively, such measures could form part of a decision or recommendation subsequently adopted by the COP on the implementation of the BBNJ Agreement.Footnote 17

These measures could include, among others,Footnote 18 the use of modern technologies, such as radars or satellites, for monitoring, control and surveillance (MCS) of MPAs.Footnote 19 Indeed, such tools are attaining increasing significance in providing for efficient Maritime Domain Awareness (MDA).Footnote 20 MDA is already instrumental to the fight against transnational organised crime at sea,Footnote 21 but can also provide, for present purposes, an important mode of MCS of MPAs. Apart from their paramount importance in reporting and raising awareness, earth observation tools, particularly satellite images, have significant evidentiary value in establishing the commission of illicit acts within MPAs.Footnote 22

There are already a number of high seas MPAs designated mainly by Regional Seas Arrangements:Footnote 23 eight in the North East Atlantic under the Convention for the Protection of the Marine Environment of the North East Atlantic (OSPAR Convention);Footnote 24 two in the Southern Ocean established by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR);Footnote 25 and one in the Mediterranean Sea under the Protocol to the Barcelona Convention Concerning Specially Protected Areas and Biological Diversity in the Mediterranean (SPAMIs Protocol) (Pelagos Sanctuary).Footnote 26 ABMTs, in the form of high seas bottom fishing closures, have also been designated by Regional Fisheries Management Organisations (RFMOs).Footnote 27 However, none of these MPAs systematically employ MDA tools for their surveillance and enforcement.

It is thus the purpose of this article, first, to demonstrate the utility of the use of earth observation tools for surveillance and enforcement of high seas MPAs and, second, to explore the legal framework governing the use of such tools for the said purposes, in particular the relevant rights and obligations of States in this regard. The article starts by introducing the concept of MDA and the use of earth observation tools in that context, highlighting the advantages that such tools may have in ensuring compliance in MPAs (Section 2). It then discusses whether States are permitted, or even obligated, to use such tools in relation to their vessels in high seas MPAs (Section 3). Next, it explores whether States are permitted to use such tools to monitor the activities of foreign-flagged vessels in high seas MPAs, and what measures can they take upon identifying an illegal activity therein (Section 4). Finally, it addresses the potential use of satellite data for enforcement purposes (Section 5). Section 6 concludes that the use of earth observation tools would be instrumental to the effective surveillance and enforcement of high seas MPAs.

2. MDA and earth observation tools in high seas MPAs

2.1. The concept of MDA

The concept of MDA is not included in UNCLOS; it arose in the context of increased maritime security concerns after the events of 9/11 in the United States and the ensuing fears about the potential impact of terrorist attacks on global trade if the maritime industry were targeted.Footnote 28 According to the definition provided by the International Maritime Organization (IMO), MDA is ‘[t]he effective understanding of any activity associated with the maritime environment that could impact upon the security, safety, economy or environment’.Footnote 29 Intelligence-gathering and information-sharing at sea are critical for ensuring maritime security.Footnote 30 In this light, MDA aims to provide an ample database of information, often in real time, against which maritime security activities—including interceptions of vessels at sea—can be planned and implemented, through centralised data-mining techniques.Footnote 31 In other words, MDA policies are an indispensable tool to gather and share information on who does what and where at sea.Footnote 32

The task of intelligence-gathering is particularly challenging in the maritime environment,Footnote 33 specifically with respect to large maritime areas, including MPAs on the high seas, since conventional assets like warships, coastguard vessels and State aircrafts or even drones lack the operational capacity for continuous and effective surveillance of such areas.Footnote 34 In this regard, an array of modern technologies have emerged over recent decades to facilitate MDA.

2.2. Earth observation tools

MDA policies and practices are heavily based on available technology. In view of rapid technological advancements, MDA tools have become more sophisticated over time. In an earlier era, MDA tools included oceanographic, marine geological, geophysical, chemical, biological and acoustic data and the use of equipment such as fathometers, swath bottom mappers etc.Footnote 35 Today, MDA tools may range from surface vessels and submarines, as well as remotely operated vehicles, autonomous underwater vehicles (AUVs) and seabed landers to satellites and radars.Footnote 36 Such MDA tools are prone to evolve in the future requiring an adaptive legal framework. Some of the most commonly used tools for MDA are as follows.

2.2.1. Vessel Monitoring Systems (VMS)

VMS is a ‘co-operative’ satellite-based system that monitors participating vessels.Footnote 37 Vessels using VMS must carry an operating a transmitter or transceiver, which sends the position of the vessel to the competent authorities of the flag State. Thus, VMS provides monitoring agencies with accurate locations of participating vessels at periodic time intervals. In fact, VMS has been a crucial tool for managing national and regional fisheries, as they provide a reliable source of vessel position and catch data. Indeed, they are generally mandated by coastal States or RFMOs.Footnote 38 Commercial fishers must have a VMS system as part of the licensing process by the flag State, the coastal States (as part of access conditions) and/or the RFMO(s) under which the vessel is to fish. However, the flag State or RFMO concerned owns the VMS data, which may not necessarily be shared with others.Footnote 39

2.2.2. Automatic Identification Systems (AIS)

Since 2004, the IMO requires AIS transponders to be installed on board all vessels of 300 gross tonnage and above engaged on international voyages, and all passenger ships irrespective of size.Footnote 40 AIS enable the automatic exchange of navigational information between vessels and shore stations. AIS data are continuously transmitted by vessels, thus enabling their real-time tracking identification.Footnote 41 The transmissions are received without permission.

AIS is therefore the largest and most significant source of geospatial ship movement data. However, since vessel tracking is not its core purpose, it is complex to analyse the relevant data. In this respect, the use of artificial intelligence (AI) models is attaining increasing prominence, since AIS is the only dataset to which one can apply strong AI models because it is continuously transmitted in real time.

However, AIS has its inherent limitations: first, it is not mandatory for small vessels that fall outside the requirements of the International Convention for the Safety of Life at Sea.Footnote 42 Second, the range for ship-to-ship communications is usually 20 miles and, for ship to shore communications, only 40 miles.Footnote 43 Third, and more importantly, the main deficiency of AIS, and VMS alike, is that they are cooperative in nature. This means that neither VMS nor AIS can track vessels which do not possess, or do not operate in a reliable fashion, the necessary transponders.Footnote 44 Further, they can be turned off or electronically subverted, thus rendering the vessel concerned ‘dark’.Footnote 45

2.2.3. Satellite surveillance technologies

In light of the deficiencies associated with the cooperative MDA tools, ‘non-cooperative’ tools involving earth observation tools through remote sensing satellites are increasingly used for vessel detection in vast areas.Footnote 46 The key operational difference between these two models is reported by an expert as follows:

AIS-based monitoring is dynamic, especially if you can apply AI models to it. Remote-sensing capabilities on the other hand can only provide static monitoring—it is very difficult to understand or have evidence of vessel behaviours (except for transshipment) based on remote-sensing data only with currently available technologies.Footnote 47

Satellite observations have the advantage that they can observe vast ocean areas repeatedly. However, all satellite sensors have specific limits on the size of the area that they can monitor.Footnote 48

The most common sensor that is used for vessel detection is a Synthetic Aperture Radar (SAR) system which, by transmitting microwave radiation, enables measurements to be made in all weather conditions, a significant advantage for most marine environments. In fact, SAR technology has been used since February 2004 in the French Antarctic territories to tackle illegal fishing for Patagonian toothfish.Footnote 49

The advantage of remote sensing tools is that they can cover large areas, they are not impeded by cloud cover or darkness, and they are much cheaper to acquire.Footnote 50 However, since SAR images contain a huge amount of information, the need for processing by automatic detection software or algorithms becomes imperative. However, there should be sufficient human resources with the expertise to interpret such data.Footnote 51 Although AI cannot completely substitute human operators, automated technologies can provide substantial support in analysing data collected from the maritime domain, thereby enabling the examination of vast quantities of surveillance footageFootnote 52 in a cost-effective manner that is affordable to most States.Footnote 53

2.2.4. Mind the gap: earth observation tools in high seas MPAs

Despite the unquestionable utility of earth observation tools for the surveillance of large maritime areas, to date there has been no satellite-based surveillance system operational over high seas MPAs. On the contrary, earth observation tools have been limited to use over MPAs or closed fishing areas within national jurisdiction. Notably, coastal States have increasingly resorted to private operators, like Skylight,Footnote 54 Ocean MindFootnote 55 or Global Fishing Watch,Footnote 56 to provide the requisite analytical tools. It remains to be seen whether and to what extent such tools will be used in high seas MPAs designated under the BBNJ Agreement. Their utility is self-evident in such remote and potentially vast maritime areas.

3. Surveillance in high seas MPAs as an assertion of flag State jurisdiction

Since the MPAs under consideration are located on the high seas, it is apparent that the implementation of MPAs and their related measures rests exclusively with flag States and, in particular, those flag States that are parties to the relevant instrument pursuant to which the MPA is established, be it—in the future—the BBNJ Agreement or another global or regional instrument. These States are under the obligation to ensure that their vessels are not acting in violation of the MPA and their related measures.Footnote 57

Third States, i.e. States not party to such an instrument, for example the BBNJ Agreement, are not bound per se by the MPA related measures (pacta tertiis principle).Footnote 58 It could be argued that the duty to respect those measures flows from such a protected area generating erga omnes effects as an ‘objective regime’.Footnote 59 Nevertheless, in view of the controversial nature of the ‘objective regime’ theory,Footnote 60 and the fact that high seas MPAs lack the territorial element with which such regimes are usually attached,Footnote 61 this argument is difficult to sustain.

As stated in Section 2.2.4, current high seas MPAs lack a detailed surveillance scheme providing for the use of earth observation tools. The BBNJ Agreement is also silent in this regard. Hopefully, in the future MPA management measures will include a detailed surveillance and enforcement mechanism, providing inter alia for the use of MDA tools.Footnote 62 Until then, and even in the absence of such mechanisms, this article argues that States are not only permitted but also obligated to conduct surveillance by all available MDA tools in relation to the activities of their vessels in high seas MPAs.

3.1. Permissibility of surveillance

On the high seas the predominant rule is freedom of navigation, which finds its expression in the exclusive jurisdiction of flag States over vessels flying their flag, enshrined in Article 92(1) UNCLOS.Footnote 63 Flag State jurisdiction, which includes the jurisdiction to enact laws (legislative or prescriptive jurisdiction) and enforce them (enforcement jurisdiction),Footnote 64 is exercised by the State whose flag the vessel in question is entitled to fly which, under the law of the sea, is the State of its nationality.Footnote 65 Flag State jurisdiction is thus the capacity of the State of nationality of a vessel to assert prescriptive and enforcement jurisdiction over that vessel under international law.Footnote 66

Since such jurisdiction is plenary in nature, it includes by necessary implication the capacity of the flag State to monitor its vessels’ activities as well as to take any necessary measures to ensure compliance with a high seas MPA. MCS measures fall clearly within the ambit of flag State jurisdiction, in particular its jurisdiction to enforce the MPA measures to which it has subscribed by being party to the relevant global or regional instrument or organisation. Hence, by virtue of their jurisdictional powers that they enjoy over their vessels on the high seas, flag States are entitled to monitor their activities in an MPA, including by resort to available earth observation tools.

3.2. Obligation of surveillance

Notably, the assertion of jurisdiction by the flag State under the law of the sea is in principle permissive, not mandatory. The assertion of jurisdiction is rendered compulsory only when the flag States concerned have assumed a relevant international obligation which requires them to exercise their prescriptive or enforcement jurisdiction. Thus, unless the flag States concerned have not assumed an obligation to this effect, it is within their discretion to conduct MCS over their vessels in a high seas MPA. This article contends that States are under such an obligation not only pursuant to specific regimes where applicable but, most importantly, under both UNCLOS and customary international law.

Briefly, by virtue of Part XII UNCLOS and customary international law, States are under certain specific obligations, including ‘to protect and preserve the marine environment’,Footnote 67 to take ‘all measures consistent with this Convention that are necessary to prevent, reduce and control pollution of the marine environment from any source, using for this purpose the best practicable means at their disposal’,Footnote 68 including those ‘necessary to protect and preserve rare or fragile ecosystems as well as the habitat of depleted, threatened or endangered species and other forms of marine life’.Footnote 69

As the International Tribunal for the Law of the Sea (ITLOS) has opined, all these obligations are obligations of conduct,Footnote 70 and thus of ‘due diligence’.Footnote 71 The crucial question of course is ‘what is the diligence that is due’?Footnote 72 In replying to this question in relation to climate change, ITLOS stated that:

the obligation of due diligence requires a State to put in place a national system, including legislation, administrative procedures and an enforcement mechanism necessary to regulate the activities in question, and to exercise adequate vigilance to make such a system function efficiently, with a view to achieving the intended objective.Footnote 73

The pronouncement of the International Court of Justice (ICJ) in Pulp Mills on the River Uruguay, which described an obligation to act with due diligence, is also pertinent:

It is an obligation which entails not only the adoption of appropriate rules and measures, but also a certain level of vigilance in their enforcement and the exercise of administrative control applicable to public and private operators, such as the monitoring of activities undertaken by such operators.Footnote 74

Consistent with the identification by the Seabed Disputes Chamber of ITLOS that ‘[t]he standard of due diligence has to be more severe for the riskier activities’, it is submitted that the standard of due diligence with respect to MPAs in vulnerable marine ecosystems should be ‘stringent’, given the high risks of serious and irreversible harm to the marine environment.Footnote 75

In light of this, there is room to argue that in order to meet this stringent standard of due diligence in implementing MPAs and related measures, and thus ‘protecting and preserving rare or fragile ecosystems’ under Article 194(5) UNCLOS, States should necessarily be guided by the ‘best available techniques’ and ‘best practicable means’, which include earth observation tools, including remote sensing. Such tools fall neatly into the scope of ‘best available techniques’ for the surveillance of MPAs on the high seas and their effective implementation, as dictated by the ‘due diligence’ obligations under Part XII, mainly Article 194 UNCLOS.Footnote 76 Hence, the use of such tools is instrumental in the discharge of all aspects of ‘due diligence’ duties by the flag State, namely: the introduction of policies, legislation and administrative controls; the exercise of vigilance and administrative controls in their implementation; and the employment of the ‘best available techniques’ to this end.

Thus, it is submitted that flag States are not only entitled but also obligated under UNCLOS to monitor their vessels on the high seas, including by all available tools, in accordance of course with their capabilities.Footnote 77 Importantly, the due diligence to be displayed by flag States in this regard would be even more rigid in high seas MPAs pursuant to Article 194(5) UNCLOS. Significantly, also, such monitoring obligations exist regardless of any pertinent obligation under the relevant MPA instrument, for example under future BBNJ Agreement MPA-related measures, which would be applicable to BBNJ Agreement States Parties, since the legal basis rests with Part XII UNCLOS, as explained in Section 1. It is argued that such due diligence obligations also form part of customary international law.Footnote 78

4. Surveillance and related actions in respect of foreign-flagged vessels in high seas MPAs

The next question concerns third States’ vessels. Are third States entitled to conduct any monitoring or surveillance over foreign flagged vessels in a high seas MPA? And what should they do if they spot any illicit activity from such vessels therein?

First, it is true that UNCLOS falls short of expressly providing for any right of States to request information from foreign-flagged vessels on the high seas or to monitor their activities. In the absence of such a permissive rule, it is questioned whether, on the contrary, international law contains any prohibition to this effect. As a corollary to the principle of the freedom of the high seas, all States enjoy the freedom of navigation on the high seas.Footnote 79 Such freedom, as ITLOS acknowledged in the M/V “Norstar” case, ‘would be illusory if a ship—a principal means for the exercise of the freedom of navigation—could be subject to the jurisdiction of other States on the high seas’.Footnote 80

In light of this, the pivotal question is whether the request for information from a foreign-flagged vessel on the high seas or, for the purposes of this article, the surveillance activities over such a vessel, amount to an interference with the freedom of navigation exercised by that vessel. If they do not, the surveillance activities would be in accordance with the law of the sea.Footnote 81 According to ITLOS:

any act of interference with navigation of foreign ships or any exercise of jurisdiction over such ships on the high seas constitutes a breach of the freedom of navigation, unless justified by the Convention or other international treaties. It goes without saying that physical or material interference with navigation of foreign ships on the high seas violates the freedom of navigation.Footnote 82

It follows that, in order not to violate the freedom of navigation and thus be permissible, the act in question, i.e. the surveillance of foreign vessels, should neither result in an interference with the navigation of the vessel, nor should it subject the vessel and its activities to the jurisdiction of the State concerned, unless such interference would be otherwise justified under international law. Provided that surveillance measures, including those conducted by earth observation tools, are not followed by any enforcement measures, it is submitted that they do not amount to an interference with the freedom of navigation, as construed by ITLOS in M/V “Norstar”.

This assertion also finds support in State practice, legal doctrine and treaty law.Footnote 83 Indeed, ‘it is a universally recognized customary rule of international law that warships of all nations, in order to maintain the safety of the high seas, have the power to require suspicious private vessels on the high seas to show their flag’.Footnote 84 The right to approach, or reconnaissance, is limited to the right to approach a ship to identify it, including by requesting it to ‘show her colours’, which is prima facie evidence of its nationality,Footnote 85 which today can be effected by modern technological means (e.g. AIS, Long-Range Identification and Tracking (LRIT)).Footnote 86 Thus, it is argued that the mere monitoring or surveillance of vessels on the high seas is well within the bounds of international law as a measure of general policing of the oceans.

Next, the question arises as to what subsequent measures should be taken regarding the vessel acting in violation of the MPA. As noted, absent the consent of the flag State there is no room for any enforcement against these vessels on the high seas. First, it is submitted that, albeit not mandatory on the face of UNCLOS, States shall report to the flag State concerned any violation of the MPAs and related measures. It is true that Article 94(6) UNCLOS stipulates that ‘a State which has clear grounds to believe that proper jurisdiction and control with respect to a ship have not been exercised may report the facts to the flag State’.Footnote 87 The term ‘may’ denotes a discretion on the part of the third State when it comes to such reporting and ‘it thus appears to provide, in formal terms, a relatively weak system of oversight’.Footnote 88

However, if one reads Article 94(6) UNCLOS in its context, in particular Part XII, in light of the object and purpose of the Convention,Footnote 89 which includes the protection of the marine environment,Footnote 90 and in line with the principle of effectiveness or effet utile in treaty interpretation (ut res magis valeat quam pereat),Footnote 91 there is room to argue that States are indeed under a duty to report any violations taking place in MPAs. Such a duty would be consistent with the general obligation of cooperation under Article 197 UNCLOS,Footnote 92 which is further elaborated upon in Articles 198, 199, 200 and 201.Footnote 93 Of particular relevance here is the duty of States to notify other States concerning imminent or actual damage to the marine environment.Footnote 94 As ITLOS opined in relation to climate change:

In the Tribunal’s view, the duty to cooperate is reflected in and permeates the entirety of Part XII of the Convention. This duty is given concrete form in a wide range of specific obligations of States Parties, which are central to countering marine pollution from anthropogenic GHG emissions at the global level.Footnote 95

In view of the urgent need to protect rare and fragile marine ecosystems, like those protected by high seas MPAs, it is submitted that whenever States become aware through MDA, including earth observation tools, of suspicious activities like dumping, illegal fishing or other illicit activities within an MPA, they are under the duty to notify, first, the flag State of the suspected vessel and, where appropriate, the competent international body (e.g. OSPAR, IMO, RFMOs etc).

Moreover, the duty to cooperate, as posited in UNCLOS and under customary international law,Footnote 96 denotes, in the view of the author, a duty to share information with the flag State concerned in case of a relevant request. Such information may, arguably, include satellite data that private operators within the respective States’ jurisdiction, such as Skylight or Global Fishing Watch, may hold. However, as the Arbitral Tribunal in The Enrica Lexie Incident stated, a duty to cooperate is ‘a duty of a continuing nature – an obligation of conduct rather than a one-time commitment or result’.Footnote 97 This means that while States are not obliged on each and every occasion to share information, including satellite data, they should nevertheless respond to any relevant request and, if they opt to deny the latter, justify this denial, for example on grounds of public security.Footnote 98 This would also be in accordance with the principle of good faith enshrined in Article 300 UNCLOS.Footnote 99

Noticeably, States would be under similar duties of cooperation, including sharing information on suspect vessels’ activities in high seas MPAs, by virtue of global and regional instruments, in particular related to fisheries. Suffice it to note Article 20(4) Fish Stocks Agreement provides that ‘States shall assist each other in identifying vessels reported to have engaged in activities undermining the effectiveness of subregional, regional or global conservation and management measures’.Footnote 100 Also, under paragraph 2 of the same Article:

[a] flag State conducting an investigation of an alleged violation of conservation and management measures for straddling fish stocks or highly migratory fish stocks may request the assistance of any other State whose cooperation may be useful in the conduct of that investigation. All States shall endeavour to meet reasonable requests made by a flag State in connection with such investigations.Footnote 101

It follows that if a State Party to the Fish Stocks Agreement becomes aware of illegal fishing activity using earth observation tools within an MPA, that State is obligated to notify the other States Parties, including the flag State, of this activity. Further, States Parties are required to provide such evidentiary material, including satellite images, to requesting parties, e.g. flag States.

Similar cooperation requirements, as well as various enforcement actions, are also prescribed by RFMOs, including in relation to high seas MPAs. For example, with respect to the Ross Sea MPA established by CCAMLR in 2016,Footnote 102 the relevant Conservation Measure sets forth that the ‘Members participating in the CCAMLR System of Inspection are encouraged to carry out surveillance and inspection activities within the MPA to verify compliance with this conservation measure and other applicable conservation measures’.Footnote 103 Also, more rigorous notification rules exist in relation to data obtained during inspections under RFMOs’ schemes.Footnote 104

5. The use of satellite data for enforcement of high seas MPAs

Having mapped out the rights and obligations of States concerning surveillance of high seas MPAs, including through the use of earth observation tools, this article next examines how these tools may be conducive to the exercise of enforcement jurisdiction in this regard. According to Article 73 UNCLOS, enforcement jurisdiction denotes ‘such measures, including boarding, inspection, arrest and judicial proceedings, as may be necessary to ensure compliance with the laws and regulations adopted [by the coastal] State in conformity with this Convention’.Footnote 105 Thus, enforcement jurisdiction in this regard would include not only the employment of the said tools for the surveillance of vessels, but also further enforcement measures over the vessels and the persons involved in their operation (unity of the vessel),Footnote 106 to punish any infringement of the MPA associated measures.

As noted in Section 3.1, in view of the principle of exclusive flag State jurisdiction on the high seas, no State can take any enforcement measures, apart from the abovementioned reporting requirements, in relation to the activities of foreign-flagged vessels on the high seas. Any enforcement measure shall be predicated upon the consent of the flag State either ad hoc or pursuant to an already existing agreement.Footnote 107

Should the flag State, or any other State permitted under international law to exercise enforcement jurisdiction in this regard,Footnote 108 decide to initiate proceedings against the vessel and the persons involved for the the infringement of the MPA-related measures (e.g. dumping, ship-to-ship transfer or fishing activity), earth observation tools may prove to be vital. Indeed, in order to corroborate the infringement under scrutiny, States may readily use evidence derived from, inter alia, satellite-based remote sensing technology. This MDA technology is of undisputed evidentiary value, since satellite evidence can provide information about locations that are too difficult to obtain directly. In fact, satellite evidence can often provide the only evidence that captures a particular event,Footnote 109 especially in remote maritime areas. Notably, satellite imagery and related spatial information, such as aerial photographs, geographic information systems and global positioning system data, have been used on a national level in environmental disputes, toxic torts, petroleum refinery class actions, chemical plant class actions, Hurricane Katrina-related damage claims and many others claims.Footnote 110

Satellite data is normally used in an evidential context in several ways. First, it can be used by a government or policing body to check compliance with specific legislation. Second, archives of satellite images can provide historical evidence where the temporal dimension of what happened is important.Footnote 111 Third, where satellites are used for regulatory monitoring, the images themselves are often not used as evidence in court but to provide advance notification to the authorities that something illegal might have taken place. The actual evidence of the illegal act is then ascertained from subsequent ground inspections, and the satellite data is merely used as an intelligence prompt.Footnote 112

Moreover, earth observation technology, including data acquired through satellites, has been used in international litigation as a means of evidence produced by the parties in support of their claims.Footnote 113 For example, satellite information as evidence has been presented inter alia before the ICJ,Footnote 114 ITLOSFootnote 115 and international arbitral tribunals.Footnote 116

Given the difficulties of successfully prosecuting environmental offences, especially in vast maritime areas where physical evidence is often unobtainable, earth observation tools are increasingly being incorporated into coastal State legislation as a way of not only detecting but also proving unlawful fishing activity, or more aptly, as a presumption of such activity.Footnote 117 For example, some coastal States in Africa have specifically incorporated remote detection techniques into their legislation, including electronic surveillance, satellite surveillance, videographic and photographic means, which constitute conclusive proof of the offence unless proven otherwise.Footnote 118 Also, a widely adopted approach is simply to acknowledge in legislation the evidentiary value of VMS data; for example, pursuant to section 176(1) of Kenya’s Fisheries Management and Development Act 2016, ‘[t]he readings of any mobile transceiver unit or other electronic location device integral to a [VMS] shall be admissible as evidence and may be used as prima facie evidence of the facts that they aver’.Footnote 119

Of relevance is that under some legislation, satellite data, amongst other relevant material, may be used to support statutory presumptions of an illegal activity at sea and as the sole evidence to prove such activity. The most striking example is clearly the legislation in the Pitcairn Islands, a United Kingdom overseas territory, which stipulates that remote tracking systems, including satellites and drones, may be used as evidence for fisheries prosecutions. As provided by the Pitcairn Marine Protected Area Ordinance 2016, for the purposes of any prosecution under the Ordinance or the applicable Marine Protection Regulations (updated in 2022), the means through which a fishing vessel may be found or observed:

include, but are not limited to: (a) remote satellite technology; (b) electronic monitoring by a Vessel Monitoring System (VMS); (c) an Automated Information System (AIS); (d) unmanned aerial, surface or underwater vehicle observations; (e) video, radar, acoustical and visual observations; (f) any other means that can reasonably be used to determine vessel activity historically or in real time.Footnote 120

To conclude, digital evidence, including satellite evidence obtained through remote sensing, is significant for the purposes of high seas MPAs’ enforcement. Indeed, satellite evidence may be used in court at a later stage to punish infringement of the MPA and its related measures, either in combination with physical evidence found during vessel inspection or autonomously. In this regard, the admissibility of satellite evidence depends largely on the procedural rules of the specific adjudicating court. Nevertheless, the extent to which such evidence would suffice for effective suppression is another question, which depends heavily on the national legislation in place but, more importantly, also on the quality of the evidence, e.g. the satellite imagery. Indeed, the probative value of satellite evidence will largely depend on its reliability as well as on its relevance to the adjudicated case.Footnote 121

6. Concluding remarks

The establishment of an effective network of high seas MPAs around the globe is instrumental to alter the trajectory of the oceans from one of degradation to one of recovery. This goal, however, cannot be achieved without ensuring that the MPAs and their protective measures will be implemented by all the relevant stakeholders. Admittedly, effective MDA, including the use of earth observation tools, could prove an invaluable asset for the surveillance and enforcement of MPAs, particularly in ABNJ. Thus, it must be one of the first priorities when planning and establishing MPAs and their associated protective measures. MDA may also furnish the necessary evidence to support further enforcement action, including criminal proceedings. Satellite evidence is, indeed, increasingly used by States to prove illicit activities in remote areas and their value as evidence depends on their authenticity, credibility and reliability.

Relatedly, States are under various duties in respect of the surveillance and enforcement of MPAs. Obviously, the key instrument in respect of the duty of surveillance of high seas MPAs is the one governing the MPA concerned. In the absence of any special provision to this effect, however, this article has argued that under UNCLOS States are not only permitted, but also obligated, to monitor their vessels in high seas MPAs, including through earth observation tools, in order to ensure that they are not acting in violation of the associated protective measures. Second, States are permitted to monitor the activities of foreign-flagged vessels as long as they do not interfere with their freedom of navigation without the consent of the respective flag State. Third, States are under a general obligation to cooperate with the view to protecting the marine environment, in particular vulnerable ecosystems such as those covered by an MPA, which includes the duty to share information on illicit activities of vessels therein. Finally, there are various global and regional instruments that may impose even more stringent duties on the respective States Parties.

Acknowledgements

The author would like to extend his gratitude to Professor Richard Barnes, Anna Riddell-Roberts, Dr Jack Kenny and Adaena Sinclair-Blakemore, for their valuable comments on a previous draft. The usual disclaimer applies.

References

1 See W Duan, The International Legal Regime Relating to Marine Protected Areas in Areas beyond National Jurisdiction (Brill 2022) 1.

2 See, inter alia, G Wright et al, ‘Marine Protected Areas in Areas beyond National Jurisdiction’ in R Rayfuse (ed), Research Handbook on International Marine Environmental Law (Edward Elgar 2015) 272, 273; H Thiel, ‘Approaches to the Establishment of Protected Areas on the High Seas’ in A Kirchner (ed), International Marine Environmental Law (Kluwer 2003)169.

3 See, e.g. UN, Sustainable Development Goals: Goal 14: Conserve and Sustainably Use the Oceans, Seas and Marine Resources, Goal 14 Target 14.5 <https://www.un.org/sustainabledevelopment/oceans/>.

4 United Nations Convention on the Law of the Sea (adopted 10 December 1982, entered into force 16 November 1994) 1833 UNTS 3 (UNCLOS).

5 See further D Freestone, ‘The UN Process to Develop an International Legally Binding Instrument under the 1982 Law of the Sea Convention: Issues and Challenges’ in D Freestone (ed), Conserving Biodiversity in Areas beyond National Jurisdiction (Brill 2019) 3, 9–16.

6 See ‘Letter dated 30 June 2011 from the Co-Chairs of the Ad Hoc Open-ended Informal Working Group to the President of the General Assembly’ (30 June 2011) UN Doc A/66/119 <http://www.un.org/depts/los/biodiversityworkinggroup/biodiversityworkinggroup.htm>. See UNGA Res 66/231 (24 December 2011) UN Doc A/RES/72/279.

7 See Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction (adopted 19 June 2023, not yet in force) (BBNJ Agreement) <https://treaties.un.org/doc/Treaties/2023/06/20230620%2004-28%20PM/Ch_XXI_10.pdf>.

8 See, inter alia, E Papastavridis, ‘The Negotiations for a New Implementing Agreement under the UN Convention on the Law of the Sea concerning Marine Biodiversity’ (2020) 69 ICLQ 585.

9 As of 20 September 2025, the BBNJ Agreement (n 7) has 61 States Parties and is set to enter into force on 17 January 2026; see UN Treaty Collection, Agreement under the United Nations Convention on the Law of the Sea on the Conservation and Sustainable Use of Marine Biological Diversity of Areas beyond National Jurisdiction <https://treaties.un.org/Pages/ViewDetails.aspx?src=TREATY&mtdsg_no=XXI-10&chapter=21&clang=_en>.

10 See COP to the CBD, Decision 15/4 on the Kunming-Montreal Global Biodiversity Framework (19 December 2022) UN Doc CBD/COP/Dec/15/4.

11 See V de Lucia, ‘After the Dust Settles: Selected Considerations about the New Treaty on Marine Biodiversity in Areas beyond National Jurisdiction with respect to ABMTs and MPAs’ (2024) 55 ODIL 115, 117.

12 ibid.

13 BBNJ Agreement (n 7) art 1(9).

14 ibid art 25(1). See also art 53 on the overall implementation of the BBNJ Agreement which is similarly vague and generic: ‘Parties shall take the necessary legislative, administrative or policy measures, as appropriate, to ensure the implementation of this Agreement.’

15 ibid art 26(1).

16 See, inter alia, International Union for Conservation of Nature, ‘Summit of the Future’ (Policy Brief, November 2023) 20 <https://iucn.org/sites/default/files/2023-11/iucn_policy-brief_summit-of-the-future_final.pdf>.

17 Under BBNJ Agreement (n 7) art 47(6), ‘[t]he Conference of the Parties shall keep under review and evaluation the implementation of this Agreement and, for this purpose, shall: (a) [a]dopt decisions and recommendations related to the implementation of this Agreement’.

18 Such as provisions on high seas boarding, mandatory port State jurisdiction or control of nationals. See Papastavridis (n 8) 609.

19 See, inter alia, M Kuruc, ‘Monitoring, Control and Surveillance Tools to Detect IUU Fishing and Related Activities’ in D Vidas (ed), Law, Technology and Science for Oceans in Globalisation: IUU Fishing, Oil Pollution, Bioprospecting, Outer Continental Shelf (Martinus Nijhoff 2010) 101, 105–06.

20 For definition and analysis of the concept of MDA, see Section 2.1.

21 On transnational organised crime at sea, see UN Office of Drugs and Crime (UNODC), ‘Combating Transnational Organized Crime Committed at Sea: Issue Paper’ (2013) <https://www.unodc.org/documents/organized-crime/GPTOC/Issue_Paper_-_TOC_at_Sea.pdf>.

22 For example, on 25 April 2025, France’s Court of Appeal in Rouen convicted the vessel Guardians of marine pollution off the coast of Le Havre based solely on satellite imagery, with no direct visual evidence. See ‘A Victory for the Oceans: CLE Expertise Establishes a Legal Precedent’ (CLS, 30 April 2025) <https://maritime-intelligence.groupcls.com/a-victory-for-the-oceans-marine-pollution-legal-precedent/>. See also the UK case of Maersk Kiera, in which satellite imagery was admitted as primary evidence in a maritime pollution prosecution. See European Maritime Safety Agency, ‘Satellite Images as Primary Evidence in UK Court’ (February 2012) <https://emsa.europa.eu/csn-menu/csn-service/oil-spill-detection-examples/286-oil-spill-detection-examples/1873-oil-spill-detection-examples-maersk-kiera-february-2012.html>.

23 See UN Environment Program (UNEP), UNEP Regional Seas Programme <https://www.unep.org/topics/ocean-seas-and-coasts/regional-seas-programme>; IMO, Regional Arrangements <https://www.imo.org/en/OurWork/Environment/Pages/Regional-Arrengements.aspx>.

24 See OSPAR Commission, Maps in Areas beyond National Jurisdiction <https://www.ospar.org/work-areas/bdc/marine-protected-areas/mpas-in-areas-beyond-national-jurisdiction>.

25 See CCAMLR, Marine Protected Areas (MPAs) <https://www.ccamlr.org/en/science/marine-protected-areas-mpas>.

26 See Pelagos Sanctuary <https://pelagos-sanctuary.org/>.

27 See, inter alia, R Caddel, ‘Deep-Sea Bottom Fisheries and the Protection of Seabed Ecosystems: Problems, Progress and Prospects’ in C Banet (ed), The Law of the Seabed (Brill 2020) 255, 270ff.

28 N Klein, Maritime Security and the Law of the Sea (OUP 2012) 2.

29 See IMO, ‘Amendments to the International Aeronautical and Maritime Search and Rescue (IAMSAR) Manual’ (25 May 2012) IMO Doc MSC.1/Circ. 1415, 11 <https://www.mardep.gov.hk/filemanager/en/share/msnote/pdf/msin1242anx1.pdf>.

30 Klein (n 28) 211–12. On intelligence-gathering on the high seas, see, inter alia, S Kaye, ‘Freedom of Navigation, Surveillance and Security: Legal Issues Surrounding the Collection of Intelligence from beyond the Littoral’ (2003) 24 AustYBIL 95.

31 C Bueger and T Edmunds, ‘Beyond Seablindness: A New Agenda for Maritime Security Studies’ in M Evans and S Galani (eds), Maritime Security and the Law of the Sea (Edward Elgar 2020) 25, 37.

32 D Guilfoyle, ‘Maritime Law Enforcement Operations and Intelligence in an Age of Maritime Security’ (2017) 93 ILS 300.

33 E Papastavridis, ‘Intelligence Gathering in the Exclusive Economic Zone’ (2017) 93 ILS 450.

34 Many remote MPAs require at least 15 hours of maritime surveillance, while manned patrol aircraft can only achieve about one to two hours of active surveillance in remote marine areas. See K Cremers, G Wright and J Rochette, ‘Strengthening Monitoring, Control and Surveillance in Areas Beyond National Jurisdiction’ (Partnership for Regional Ocean Governance, Strong High Seas Project, 2020) 34 <http://www.prog-ocean.org/wp-content/uploads/2020/01/Cremers-Wright-and-Rochette-2019.-Strengthening-Monitoring-Control-and-Surveillance-in-Areas-Beyond-National-Jurisdiction-1.pdf>.

35 JA Roach and RW Smith, Identification of Excessive Maritime Claims (Brill 1994) 248.

36 Papastavridis (n 33) 450.

37 UN Food and Agriculture Organization (FAO), ‘Fishing Operations: 1. Vessel Monitoring Systems’ (1998) <https://openknowledge.fao.org/bitstreams/6f0974dd-f3b5-4afd-a836-198f875d644c/download>.

38 Kuruc (n 19) 105.

39 See a detailed analysis of the benefits and the shortcomings of the use of VMS in comparison with other earth observation tools in K Cremers et al, ‘Options for Strengthening Monitoring, Control and Surveillance of Human Activities in the Southeast Atlantic Region’ (Partnership for Regional Ocean Governance, Strong High Seas Project, 2021) <http://www.prog-ocean.org/wp-content/uploads/2021/11/Cremers-K.-Bouvet-M.-Wright-G.-Rochette-J-Options-for-Strengthening-MCS-of-Human-Activities-in-the-Southeast-Atlantic-region.pdf>.

40 See Convention for the Safety of Life at Sea (adopted 1 November 1974, entered into force 25 May 1980) 1184 UNTS 278 (SOLAS Convention) ch V, regulation 19.

41 KA Sørensen et al, ‘RF, SAR and AIS Data Fusion for Improved Arctic Maritime Surveillance’ (SSRN, 21 June 2024) 2 <https://ssrn.com/abstract=4873035>.

42 Klein (n 28) 229.

43 ibid.

44 G Rowlands et al, ‘Satellite Surveillance of the Ascension Island Exclusive Economic Zone and Marine Protected Area’ (2019) 101 Marine Policy 40.

45 ibid. See also P Bunwaree, ‘The Illegality of Fishing Vessels “Going Dark” and Methods of Deterrence’ (2023) 73 ICLQ 179, 180ff.

46 Principle I of the UN Principles relating to Remote Sensing of the Earth from Outer Space defines the term ‘remote sensing’ as the activity of ‘sensing of the Earth’s surface from space by making use of the properties of electromagnetic waves emitted, reflected or diffracted by the sensed objects, for the purpose of improving natural resources management, land use and the protection of the environment’. UNGA Res 41/65 (3 December 1986) UN Doc A/RES/41/65.

47 Explanation provided by a Skylight expert (on file with the author).

48 M Lehmann and A Middleditch, ‘Satellite “Dark Vessel” Detection for MDA’ (Starboard Maritime Intelligence, 12 November 2022) <https://www.starboardintelligence.com/articles/satellite-dark-vessel-detection-for-maritime-domain-awareness>.

49 N Ansell, ‘Using Technology in Combating IUU Fishing: The Potential of Satellite Remote Sensing’ in Vidas (n 19) 197, 201–02.

50 ibid.

51 See Cremers et al (n 33) 30.

52 V Sakhuja, ‘Artificial Intelligence and Maritime Domain Awareness’ (Society for the Study of Peace and Conflict, 11 June 2018) <https://sspconline.org/opinion/artificial-intelligence-maritime-domain-awareness-vijay-sakhuja-110618>.

53 RA Eddin and S Guliyeva, ‘Bridging the Maritime Domain Awareness Gap: The Role of New Technologies in Promoting Equitable Surveillance Capabilities to Enact Environmental Obligations under the Law of the Sea’ (2023) 3 ASCOMARE Yearbook on the Law of the Sea 204.

54 Skylight provides operationally relevant information and insights for States pro bono. See Skylight <https://www.skylight.global>.

55 Ocean Mind is a UK-based non-profit organisation. Currently, as a contractor to the UK Government, it has been monitoring, among others, the Pitcairn Islands MPA (850,000 km2) to assess fishing activity and analyse compliance with MPA restrictions. See Ocean Mind <https://www.oceanmind.global>

56 Global Fishing Watch was founded in 2015 through a collaboration between three partners: Oceana, SkyTruth and Google. While initially focusing only on commercial fishing, it has worked on data and technology integration to support the effective design, management and monitoring of MPAs since 2020. See Global Fishing Watch <https://globalfishingwatch.org>.

57 See, e.g. BBNJ Agreement (n 7) art 25(1).

58 See Vienna Convention on the Law of Treaties (adopted 23 May 1969, entered into force 27 January 1980) 1155 UNTS 331 (VCLT) arts 34–38.

59 On objective regimes, see, inter alia, Free Zones of Upper Savoy and the District of Gex (France v Switzerland) [1932] PCIJ Ser A/B No 46, 96; MA Fitzmaurice, ‘Modifications to the Principles of Consent in relation to Certain Treaty Obligations’ (1997) 2 ARIEL 275, 299.

60 It is telling that during the drafting of the VCLT (n 58) Special Rapporteur Waldock had proposed a draft art 63 on objective regime. See H Waldock, ‘Third Report on the Law of Treaties’ in UNYBILC, vol II (1970) UN Doc A/CN.4/224, 26, which was later rejected by the International Law Commission (ILC). Ultimately, neither the ILC nor the VCLT retained the idea that objective treaties could be binding on third States. See E David, ‘Article 34’ in O Corten and P Klein (eds), The Vienna Conventions on the Law of Treaties (OUP 2011) 887, 891.

61 See Fitzmaurice (n 59) 300.

62 Other measures could include boarding powers, the assertion of port State jurisdiction or control of nationals. See, e.g. Agreement for the Implementation of the Provisions of the United Nations Convention on the Law of the Sea of 10 December 1982 relating to the Conservation; Management of Straddling Fish Stocks and Highly Migratory Fish Stocks (adopted 4 August 1995, entered into force 11 December 2001) 2167 UNTS 3 (Fish Stocks Agreement) pt VI (Compliance and Enforcement); Papastavridis (n 8).

63 ‘Ships shall sail under the flag of one State only and, save in exceptional cases expressly provided for in international treaties or in this Convention, shall be subject to its exclusive jurisdiction on the high seas’. See UNCLOS (n 4) art 92. See also D Guilfoyle, ‘Article 92’ in A Proelss (ed), UN Convention on the Law of the Sea: A Commentary (Beck/Hart/Nomos 2016) 700, 704.

64 On jurisdiction in general, see FA Mann, ‘The Doctrine of Jurisdiction in International Law’ (1964) 111 RCADI 1; M Akehurst, ‘Jurisdiction in International Law’ (1972–73) 46 BYIL 145.

65 See UNCLOS (n 4) art 91.

66 See also UNODC, ‘Flag State Jurisdiction and Transnational Organized Crime at Sea: Issue Paper’ (2023) <https://www.unodc.org/documents/Maritime_crime/UNODC_GMCP_Flag_State_Jurisdiction_and_transnational_organized_crime_at_sea.pdf>.

67 See UNCLOS (n 4) art 192.

68 ibid art 194(1).

69 ibid art 194(5).

70 As summarised by James Crawford, the distinction between obligations of conduct and result is that ‘obligations of result involve in some measure a guarantee of the outcome, whereas obligations of conduct are in the nature of best-efforts obligations, obligations to do all in one’s power to achieve a result, but without ultimate commitment’. See J Crawford, ‘Second Report on State Responsibility’ (19 July 1999) UN Doc A/CN.4/498, para 57.

71 See, e.g. in relation to UNCLOS (n 4) art 194(1), ITLOS stated that ‘[s]ince article 194, paragraph 1, of the Convention provides for an obligation of conduct, it requires States to act with “due diligence” in taking necessary measures to prevent, reduce and control marine pollution’. See Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law (Advisory Opinion) (21 May 2024) (Climate Change AO) para 233. As the ITLOS Seabed Disputes Chamber has stated, ‘[t]he notions of obligations “of due diligence” and obligations “of conduct” are connected’. See Responsibilities and Obligations of States with respect to activities in the Area (Advisory Opinion) ITLOS Reports 2011 (1 February 2011) para 111.

72 See generally I Papanicolopulu, ‘Due Diligence in the Law of the Sea’ in H Krieger et al (eds), Due Diligence in the International Legal Order (OUP 2020) 147.

73 Climate Change AO (n 71) para 235.

74 Pulp Mills on the River Uruguay (Argentina v Uruguay) (Judgment) [2010] ICJ Rep 14, 79, para 197.

75 Climate Change AO (n 71) para 241.

76 ibid para 239.

77 As Czybulka notes in this regard, ‘[best available techniques]’ takes account of the concerns of developing States that regulations requiring ‘best practical means’ could overburden them. Even if best means and technique are at the disposal of States, it may occur that, for example the technical personnel is not capable to apply them in a competent way’. D Czybulka, ‘Article 194’ in Proelss (n 63) 1296, 1304.

78 See the most recent examination of principles of international environmental law as part of customary international law in Obligations of States in respect of Climate Change (Advisory Opinion) (General List No 187, 23 July 2025) paras 217–315, 354 concerning the interrelationship between UNCLOS and customary international law.

79 See UNCLOS (n 4) art 87(1).

80 M/V “Norstar” (Panama v Italy) (Judgment) ITLOS Reports 2019 (10 April 2019) para 216.

81 According to the famous pronouncement of the Permanent Court of International Justice in the Lotus case, ‘[r]estrictions on the independence of States cannot … be presumed’; SS Lotus (France v Turkey) (Judgment) [1927] PCIJ Ser A No 10, 18. For a similar approach, see Accordance with International Law of the Unilateral Declaration of Independence in Respect of Kosovo (Advisory Opinion) [2010] ICJ Rep 403, paras 56, 84.

82 M/V “Norstar” (n 80) para 222.

83 See E Papastavridis, Interception of Vessels on the High Seas (Hart 2013) 57–59 and references therein.

84 R Jennings and A Watts, Oppenheim’s International Law (9th edn, Longmans 1992) 737.

85 See Y van der Mensbrugghe, ‘Le pouvoir de police des Etats en haute mer’ (1975) 11 RBDI 56, 61.

86 Under SOLAS Regulation 19-1, passenger ships, cargo ships of at least 300 gross tons and mobile offshore drilling units are required to automatically transmit information as to the identity of the ship, its position and the date and time of the position provided. The data centre selected by a flag State collects the information and ensures that the LRIT information is only sent to those entitled to receive it. See IMO, Long-Range Identification and Tracking (LRIT) <https://www.imo.org/en/OurWork/Safety/Pages/LRIT.aspx>.

87 UNCLOS (n 4) art 94(6) (emphasis added).

88 D Guilfoyle, ‘Article 94’ in Proelss (n 63) 700, 713.

89 See VCLT (n 58) art 31(1).

90 The object and purpose of a treaty is traditionally found in the preamble. See, e.g. Whaling in the Antarctic (Australia v Japan: New Zealand intervening) (Judgment) [2014] ICJ Rep 251, para 56. Suffice it to note that the preamble of UNCLOS sets out that ‘[r]ecognizing the desirability of establishing through this Convention with due regard for the sovereignty of all States, a legal order for … the equitable and efficient utilization of their resources, the conservation of their living resources, and the study, protection and preservation of the marine environment’: UNCLOS (n 4) preamble (emphasis added).

91 See C Braumann and A Reinisch, ‘Effet Utile’ in J Klingler, Y Parkhomenko and C Salonidis (eds), Between the Lines of the Vienna Convention? Canons and Other Principles of Interpretation in Public International Law (Kluwer 2018) 47–72.

92 See UNCLOS (n 4) art 197. See also the MOX Plant case in which the Tribunal underscored that ‘the duty to cooperate is a fundamental principle in the prevention of pollution of the marine environment under Part XII of the Convention and general international law’. MOX Plant Case (Ireland v United Kingdom) (Provisional Measures) ITLOS Reports 2001 (3 December 2001) para 82.

93 Climate Change AO (n 71) para 295.

94 UNCLOS (n 4) art 198: ‘When a State becomes aware of cases in which the marine environment is in imminent danger of being damaged or has been damaged by pollution, it shall immediately notify other States it deems likely to be affected by such damage, as well as the competent international organizations’. See also T Stephens, ‘Article 198’ in Proelss (n 63) 1333, 1338.

95 Climate Change AO (n 71) para 297.

96 See Mox Plant Case (n 92) para 82.

97 See The “Enrica Lexie” Incident (Italy v India) PCA Case No 2015-28, Award (21 May 2020) para 723, quoting S Lee and JW Kim, ‘UNCLOS and the Obligation to Cooperate: International Legal Framework for Semi-Enclosed Seas Cooperation’ in K Zou (ed), Maritime Cooperation in Semi Enclosed Seas (Nijhoff 2019) 11, 12.

98 Cf, e.g. OSPAR Convention (adopted 22 September 1992, entered into force 25 March 1998) 2345 UNTS 67, art 9(3) providing for grounds on refusal to access to environmental information; OSPAR Arbitration (Ireland v United Kingdom) PCA Case No 2001-03, Award (2 July 2003).

99 UNCLOS (n 4) art 300. See also Land and Maritime Boundary between Cameroon and Nigeria (Cameroon v Nigeria; Equatorial Guinea intervening) (Preliminary Objections) [1998] ICJ Rep 275, para 38.

100 Fish Stocks Agreement (n 62) art 20(4) (emphasis added).

101 ibid art 20(2) (emphasis added). See also Agreement to Promote Compliance with International Conservation and Management Measures by Fishing Vessels on the High Seas (adopted 24 November 1993, entered into force 24 April 2003) 2221 UNTS 91 (FAO Compliance Agreement) art V(1).

102 Technically speaking, CCAMLR is not a RFMO because it has the wider mandate to protect Antarctic marine living resources, even if most of its regulations to date concern the regulation of fishing. For CCAMLR MPAs, see, inter alia, M Haward, ‘Biodiversity in Areas beyond National Jurisdiction (BBNJ): The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) and the United Nations BBNJ Agreement’ (2021) 11 The Polar Journal 303.

103 CCAMLR, Conservation Measure 91-05 (2016) on the Ross Sea Region Marine Protected Area, art 23 <https://cm.ccamlr.org/measure-91-05-2016>.

104 See, e.g. North-East Atlantic Fisheries Commission Scheme of Control and Enforcement (2025) art 16(4) <https://www.neafc.org/system/files/New-ERS-Scheme-2025-corrected2.pdf>.

105 See UNCLOS (n 4) art 73(1).

106 As ITLOS held in M/V “Norstar”, ‘under the Convention (UNCLOS), a ship is to be considered a unit so that ‘[t]he ship, everything on it, and every person involved or interested in its operations are treated as an entity linked to the flag State’. M/V “Norstar” (Panama v Italy) (Preliminary Objections) ITLOS Reports 2016 (4 November 2016) 44. See also M/V “Saiga” (No 2) (Saint Vincent and the Grenadines v Guinea) (1999) 38 ILM 1323, para 106.

107 See, e.g. Fish Stocks Agreement (n 62) art 21. See generally Papastavridis (n 83).

108 For example, the State of the nationality of the master or the ship operator by dint of the nationality principle of international jurisdiction. See R O’Keefe, International Criminal Law (OUP 2015) 14.

109 RJ Rychlak, JI Gabrynovicz and R Crowsey, ‘Legal Certification of Digital Data: The Earth Resources Observation and Science Data Center Project’ (2007) JSpaceL 195, 202–03. See also ‘A Victory for the Oceans: CLE Expertise Establishes a Legal Precedent’ (n 22).

110 ibid.

111 R Purdy, ‘Evidence (Satellite Earth Observation)’ in M Hoffman and PJ Blount (eds), Elgar Concise Encyclopedia of Space Law (Edward Elgar 2025) 95, 95.

112 ibid 97.

113 See generally R Purdy and D Leung (eds.), Evidence from Earth Observation Satellites: Emerging Legal Issues (Brill 2012).

114 See, e.g. Certain Activities Carried Out by Nicaragua in the Border Area (Costa Rica v Nicaragua) and Construction of a Road in Costa Rica along the San Juan River (Nicaragua v Costa Rica) (Judgment) [2015] ICJ Rep 665, paras 202, 206.

115 See, e.g. Dispute concerning Delimitation of the Maritime Boundary Between Bangladesh and Myanmar in the Bay of Bengal (Bangladesh/Myanmar) (Judgment) ITLOS Reports 2012 (14 March 2012) para 244.

116 See, inter alia, South China Sea Arbitration (Republic of Philippines v People’s Republic of China) PCA Case No 2013-19, Award (12 July 2016) paras 322–326.

117 See P Flewwelling et al, Recent Trends in Monitoring, Control and Surveillance Systems for Capture Fisheries (FAO 2002) 26.

118 See, e.g. Law No 2015-017 Establishing the Code of Marine Fisheries (Mauritius) art 70 <http://extwprlegs1.fao.org/docs/pdf/Mau164733.pdf>; Code of Maritime Fishing 2015 (Senegal) art 91 <http://extwprlegs1.fao.org/docs/pdf/sen155049.pdf>.

119 See Fisheries Management and Development Act 2016 (Kenya) section 176(1) < http://extwprlegs1.fao.org/docs/pdf/ken160880.pdf>. See also, inter alia, Fisheries Act 2014 (Seychelles) sections 73–74 < http://extwprlegs1.fao.org/docs/pdf/sey143994.pdf>; Marine Living Resources Act 1998 (South Africa) sections 74, 76 <http://extwprlegs1.fao.org/docs/pdf/saf15984.pdf>.

120 See Pitcairn Marine Protected Area Ordinance 2016, section 24.3 <https://www.paclii.org/pn/legis/num_act/pimpao2016399/>. See also Pitcairn, Henderson, Ducie & Oeno Islands Marine Conservation Regulations 2022 <https://static1.squarespace.com/static/6526ff6fef608a3828c13d05/t/6558599e6255b43b78d3e4b2/1700288936433/2022-10-11+Marine+Conservation+Regulations+2022.pdf>.

121 P Marshall et al, ‘Recommendations for the Probity of Computer Evidence’ (2021) 18 DE&ESLR 20.