Straddling Fish Stocks and Highly Migratory Species: Legal Regimes and Governance

The ocean is a single physical system, yet international law has sliced it into zones of sovereign jurisdiction and areas beyond national jurisdiction. This juridical partitioning collides with the biological reality of the marine environment. Fish do not observe the equator, the coast, or the outer limit of the exclusive economic zone. They move, migrate, and interbreed across these artificial boundaries, creating a fundamental tension between national sovereignty and the need for cooperative conservation. This tension defines the modern law of the sea in relation to living resources. The legal regime must account for two distinct biological categories that demand specific governance: straddling fish stocks and highly migratory species. While they often overlap in the physical world, the legal treatment of each follows distinct trajectories within the United Nations Convention on the Law of the Sea and the supplementary agreements that followed.

Understanding this regime requires tracing the evolution from the open access era of the nineteenth and twentieth centuries to the zonal sovereignty system established by UNCLOS. It requires analyzing the inadequacies of the original treaty text and the political effort required to close those gaps through the 1995 Agreement. It also demands a critical look at the mechanisms of Regional Fisheries Management Organizations, the persistent problem of compliance on the high seas, and the emerging pressures of climate change. This article examines the architecture of that law, the obligations it imposes upon states, and the structural weaknesses that continue to threaten the sustainability of marine fisheries.

The Historical Shift from Open Access to Zonal Sovereignty

For much of recorded history, the high seas were regarded as res communis, a domain in which all nations enjoyed an equal freedom of fishing. There was no concept of exclusive rights over ocean resources beyond the territorial limits of a coastal state, which were historically narrow, usually restricted to the cannon shot range or three nautical miles. This freedom persisted despite growing concerns about overfishing. The technological revolution in fishing gear during the mid twentieth century, characterized by larger vessels and sonar technology, intensified extraction rates and triggered a race to fish. States responded to this pressure by unilaterally extending their claim over coastal fisheries.

The negotiation of the United Nations Convention on the Law of the Sea represented a compromise. Coastal states received sovereign rights over the living resources within a 200 nautical mile exclusive economic zone. This gave them the authority to determine allowable catches and manage conservation. However, this extension created a new problem. It transferred significant portions of high seas fishing grounds to coastal state jurisdiction, reducing the space available to distant water fishing nations. More importantly, it fragmented the management of fish populations that do not respect the new boundary. Stocks that spend part of their life cycle within the exclusive economic zone and part on the high seas became difficult to manage under a purely national or purely international regime.

The international community recognized early that the 200 mile claim was not a complete solution. The Convention itself contained provisions acknowledging that fish move. Yet the general language of the original text proved insufficient to force cooperation. It established a duty to cooperate but lacked the detailed procedural mechanisms and compliance obligations required to make that duty effective. The gap between the legal aspiration of cooperation and the reality of national interest left the high seas vulnerable to overexploitation. This failure is the context against which the 1995 Agreement must be understood.

The Jurisdictional Architecture of UNCLOS 1982

The 1982 Convention addresses marine living resources through a series of interconnected articles. The regime distinguishes between resources within the exclusive economic zone, where the coastal state has sovereign rights, and resources on the high seas, where the duty is one of cooperation. Article 63 deals with stocks occurring within the exclusive economic zone and extending onto the high seas. It requires the coastal state and the states fishing for such stocks on the high seas to seek either directly or through appropriate subregional or regional organizations to agree upon the measures necessary for conservation. Article 64 addresses highly migratory species listed in Annex One, which include various tunas, swordfish, and sharks. It obliges coastal states and states whose fishing vessels operate on the high seas, either directly or through appropriate international organizations, to coordinate measures for conservation.

Article 116 through 119 governs fishing on the high seas. Article 116 asserts the right of all states to fish, subject to treaties and the duties in Article 117. Article 117 imposes a duty on the flag state to adopt measures for the conservation of living resources. Article 118 reinforces the duty to cooperate for conservation. Article 119 sets out the principles for conservation within the exclusive economic zone, emphasizing the maintenance or restoration of populations at levels capable of producing maximum sustainable yield.

The weakness of the 1982 text lay in its generality. The duty to cooperate was framed as an obligation of conduct rather than an obligation of result. States could claim they were negotiating in good faith without achieving a binding management plan. There was no requirement to apply the precautionary approach, meaning states could wait for scientific certainty before acting, a standard that is often unattainable in marine ecology. There was no robust mechanism for dispute resolution specific to fisheries. These gaps allowed high seas fishing to continue despite scientific warnings about stock depletion.

What Legal Framework Governs Straddling Fish Stocks?

The United Nations Agreement for the Implementation of the Provisions of the Convention Relating to the Conservation and Management of Straddling Fish Stocks and Highly Migratory Fish Stocks, adopted in 1995, was designed to fill the void. It applies to fish stocks in two areas. First, stocks occurring within the exclusive economic zone and extending onto the high seas. Second, stocks occurring within the area of national jurisdiction as well as in an adjacent area of the high seas beyond that zone. This dual scope ensures that the management regime covers the entire biological range of the stock regardless of which legal zone it occupies at any given time.

The Agreement imposes stricter obligations than the Convention. It mandates that conservation and management measures be based on the best scientific evidence available. It requires the application of the precautionary approach, which shifts the burden of proof. Rather than waiting for definitive proof of overfishing, states must act to prevent harm when there is uncertainty. This is a significant doctrinal shift from the maximum sustainable yield approach of 1982, which was often interpreted as a target to harvest up to rather than a ceiling to respect.

The Agreement also emphasizes the role of regional fisheries management organizations. It requires that states become members of, or accede to, the relevant organization to exercise their rights to fish for these stocks. If no organization exists, states are obliged to establish one. This creates a gatekeeping mechanism. A state that does not cooperate with the regional organization cannot claim the benefit of fishing those stocks. This provision targets the practice of unreported or unregulated fishing, often referred to as illegal, unreported, and unregulated fishing, which has long plagued the high seas.

Despite its comprehensive design, the Agreement faces a ratification challenge. Many of the major distant water fishing nations did not ratify it initially. While participation has grown substantially over the last two decades, the universality of the regime remains incomplete. This partial adherence creates jurisdictional asymmetries. States party to the Agreement must comply with conservation measures agreed in regional organizations, while states that have not joined may operate under the looser standards of the Convention. This divergence complicates the creation of a truly uniform global standard.

The Compatibility Obligation and the Zone Interface

One of the most complex legal problems in fisheries management is the compatibility between the measures adopted for the exclusive economic zone and those adopted for the adjacent high seas. A coastal state may set a total allowable catch for a stock within its own waters. If it sets that catch too high, it may leave no stock for the high seas fishing of neighboring states. Conversely, if high seas harvest is too high, it may undermine the conservation measures applied inside the exclusive economic zone. The biological reality of the stock requires a single, coherent management strategy that spans the entire range of the species.

Article 7 of the 1995 UN Fish Stocks Agreement directly addresses this interface by establishing the principle of compatibility. It requires coastal states and distant water fishing nations to ensure that conservation and management measures established for the high seas and those adopted within areas under national jurisdiction do not undermine each other. In determining compatible measures, states must consider the biological characteristics of the stocks, the extent to which the stocks occur in areas under national jurisdiction versus the high seas, and the historical dependence of coastal states and high seas fishing nations on those resources.

However, achieving compatibility in practice remains politically contentious. Coastal states often argue that their sovereign rights within the exclusive economic zone give them primary authority over the management of the stock, demanding that high seas measures adjust to coastal preferences. Distant water fishing nations contend that compatibility requires equal compromise on both sides of the maritime boundary. When states fail to reach an agreement on compatible measures, the Agreement requires them to resort to provisional arrangements or dispute settlement mechanisms, but pending a resolution, the risk of unsustainable overexploitation persists.

Regional Fisheries Management Organizations: Institutional Architecture and Flaws Regional Fisheries Management Organizations (RFMOs) serve as the primary institutional mechanism for governing straddling and highly migratory fish stocks. These intergovernmental bodies bring together coastal states and flag states with fishing interests in specific ocean regions or targeted species, such as the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) or the Western and Central Pacific Fisheries Commission (WCPFC). RFMOs are empowered to conduct scientific assessments, set Total Allowable Catches (TACs), allocate national quotas, and establish technical measures such as gear restrictions, closed seasons, and spatial closures.

Despite their central role in ocean governance, RFMOs suffer from structural weaknesses that undermine their effectiveness. First, decision-making rules frequently rely on consensus or allow individual states to opt out of binding management measures through formal objections. This mechanism enables minority interests to block scientifically necessary catch reductions or exempt themselves from stringent rules. Second, allocation negotiations are notoriously fraught, as historical fishing nations and developing coastal states compete for quota shares based on conflicting equitable principles.

Furthermore, RFMOs have historically struggled with dynamic ecological shifts. Because these organizations were established on fixed geographical or species-specific mandates, they often operate in organizational silos, failing to account for ecosystem-wide interactions or cross-jurisdictional migration patterns.

Compliance, Enforcement, and the Flag State Responsibility Gap Under general international law and UNCLOS Article 92, the flag state exercises exclusive jurisdiction over ships flying its flag on the high seas. This fundamental doctrine creates a major enforcement loophole in high seas fisheries governance, commonly referred to as the flag state responsibility gap. When fishing vessels engage in illegal, unreported, and unregulated (IUU) fishing, the primary duty to investigate, prosecute, and sanction lies with the flag state. However, many flag states—particularly those operating as flags of convenience—lack the political will, financial resources, or regulatory capacity to effectively monitor and control their distant water fleets.

To counter this weakness, the 1995 UN Fish Stocks Agreement introduced groundbreaking exceptions to exclusive flag state jurisdiction. Articles 21 and 22 authorize inspecting states that are party to the Agreement to board and inspect fishing vessels of other state parties on the high seas to verify compliance with regional conservation measures. If serious violations are discovered—such as fishing without a license, failing to maintain accurate catch records, or using prohibited gear—and the flag state fails to respond, the inspecting state may secure evidence and require the vessel to proceed to the nearest port.

Beyond high seas boarding and inspection, modern governance relies heavily on Port State Measures. The 2009 FAO Port State Measures Agreement (PSMA) strengthens this secondary line of defense by allowing port states to deny port access, landing privileges, and port services to foreign vessels suspected of IUU fishing. Combined with mandatory Vessel Monitoring Systems (VMS), electronic observer coverage, and catch documentation schemes, port state controls reduce the economic incentives for illegal operations by cutting off access to commercial markets.

Emerging Pressures: Climate Change and Ocean Warming The legal architecture established by UNCLOS and the 1995 Agreement was built on the assumption that fish stocks occupy relatively stable geographical distribution ranges. Climate change directly undermines this assumption. Rising sea surface temperatures, ocean acidification, and shifting ocean currents are altering marine ecosystems and forcing species to migrate toward higher latitudes or deeper waters in search of optimal thermal conditions.

These climate-induced spatial shifts create severe jurisdictional disruptions:

• Jurisdictional Displacement: Fish stocks that were previously contained within the exclusive economic zone of one coastal state are moving into the zones of adjacent states or onto the high seas.

• Allocation Conflicts: Historical catch allocations and quota shares established by RFMOs become obsolete as species vacate traditional fishing grounds, sparking governance disputes between historical rights holders and emerging host states.

• Governance Voids: Species moving into high seas areas not governed by an existing RFMO face a regulatory vacuum where no binding conservation rules apply.

Current legal instruments lack flexible mechanisms to automatically adjust management regimes to shifting species distributions. RFMOs must adopt dynamic, climate-resilient governance frameworks that incorporate real-time spatial monitoring, adaptive quota allocations, and precautionary buffers to account for climate uncertainty.

Structural Weaknesses and the Path Toward Sustainable Governance The governance of straddling and highly migratory fish stocks sits at the intersection of public international law, sovereign rights, and marine ecology. While the legal regime has advanced significantly from the absolute freedom of the high seas toward a framework structured around cooperation and science-based management, major structural weaknesses remain:

1. Gaps in Universality: Incomplete ratification of the 1995 Agreement enables non-party states to claim rights under UNCLOS while avoiding stricter compliance duties.

2. Consensus and Opt-Out Rules: RFMO decision-making structures allow individual economic interests to override scientific recommendations.

3. Enforcement Limitations: Inadequate enforcement on the high seas and persistent reliance on flag state compliance perpetuate IUU fishing.

4. Institutional Rigidity: Existing legal structures lack the flexibility to adapt to rapid, climate-driven changes in marine ecosystems.

Addressing these weaknesses requires strengthening the binding nature of RFMO decisions, eliminating opt-out provisions, expanding non-flag state enforcement rights, and fully integrating the precautionary approach into quota allocations. Furthermore, implementing the 2023 Agreement on Biodiversity Beyond National Jurisdiction (BBNJ Treaty) will offer new tools—such as high seas marine protected areas and comprehensive environmental impact assessments—to complement RFMO management. Only through a legally binding, ecologically coherent, and internationally enforceable governance framework can the international community resolve the inherent conflict between national borders and the fluid reality of ocean life.