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In the spring of 2024, the United Kingdom quietly closed the book on a small, silvery fish.
It was a conservation move, ostensibly. The government, with support from devolved administrations, banned fishing for sand-eels in English and Scottish waters. If you’ve never heard of sand-eels—well, you’re not alone. They’re not the kind of fish you’d find on a dinner plate. They’re skinny, unassuming, and mostly known for their importance to other creatures—especially seabirds like puffins and kittiwakes. And yet, that ban would go on to trigger the first full-blown legal arbitration under the post-Brexit EU–UK Trade and Cooperation Agreement (TCA), finalized in the Permanent Court of Arbitration in The Hague in April 2025.
An environmental dispute, yes. But also a trade disagreement. A sovereignty story. A diplomatic test. All rolled into one.
The Sand-Eel, the Puffin, and the Fine Print of Brexit
Let’s start with the basics. Sand-eels are forage fish—meaning, they exist largely to be eaten by others. In northern marine ecosystems, they are foundational. Puffins, in particular, rely on them during breeding season. Without sand-eels, puffin chicks starve. That’s not exaggeration; it’s just… biology.
Now, by early 2024, ecological pressures—warming seas, overfishing, changing currents—were already stressing these ecosystems. Seabird numbers, especially in the North Sea, had been falling for years. Scientists began sounding the alarm about sand-eel stocks too. In response, the UK banned industrial fishing for them in both Scottish and English waters (Marine Management Organisation, 2024). It was described as a science-led, precautionary measure to preserve biodiversity. A decision that—at first glance—seemed uncontroversial, even commendable.
But then came the fine print.
Under Annex 38 of the EU–UK TCA, EU vessels—particularly Danish ones—retained access to certain UK waters for fishing until 2026. Denmark, it turns out, operates one of the largest sand-eel fisheries in Europe. So, when the UK shut its waters, citing ecological urgency, it did more than close a fishing ground. It closed a door on existing EU economic rights, without—at least according to Brussels—due process.
And so, what began as a biodiversity protection measure morphed into a legal case. The EU invoked the dispute resolution provisions of the TCA and hauled the UK before a tribunal. The first such case since Brexit.
Law, Science, and the Scramble for Justification
Here’s where things got thorny.
The EU’s core argument was simple: the UK had acted unilaterally, without adequate consultation or justification, and therefore had breached the agreement. They weren’t challenging the idea of conservation per se—but rather the method, the manner, the… timing.
The UK countered that it had every right to take urgent environmental action, especially when backed by strong science. And in fairness, there was a mountain of ecological data pointing to the vulnerability of sand-eel populations and the cascading risks to puffins and other birds (Marine Management Organisation, 2024).
But law is not just about having the facts on your side. It’s about process. About balance. About framing the facts in a way that doesn’t trample existing obligations—particularly to others.
The tribunal thus found itself asking some deceptively simple questions:
- Was the ban science-based?
- Did it discriminate against EU vessels?
- Was it proportionate?
- And—crucially—had it respected EU access rights under the TCA?
Each of these questions required parsing not just the legal text of the TCA, but the motivations and methods behind the UK’s decision.
The Tribunal Speaks: A Judgment in Shades of Grey
The tribunal’s ruling, delivered in April 2025, was neither a victory lap for the UK nor a vindication for the EU. It was nuanced—almost to a fault.
On the one hand, the UK won some important points. The tribunal found that the sand-eel ban was based on credible scientific evidence and applied equally to UK and EU vessels. There was no discriminatory intent, no favoritism toward domestic fleets (Permanent Court of Arbitration, 2025b, pp. 120–160). That’s not insignificant—many environmental measures fail precisely because they mask protectionism under the guise of ecology.
But on proportionality, things got trickier.
While the Scottish ban was upheld as proportionate and legally sound, the English ban was found wanting. The tribunal concluded that the UK had not fully considered the impact on EU access rights in English waters, nor demonstrated why less trade-restrictive alternatives were unavailable (pp. 128–136).
So: a partial breach. A procedural lapse, rather than a condemnation of the policy itself.
Importantly, the tribunal didn’t strike the ban down. It merely ordered the UK to revisit its justification, improve consultation, and ensure future decisions meet the standards of the TCA (pp. 148–152). The ban stayed, but with conditions.
Legal Process as Environmental Pathway?
One could see this as a technicality—a split verdict about a fishing ban few people had even heard of. But there’s a deeper significance here.
This was the first test of the legal machinery underpinning the TCA. And that machinery worked. There were no screaming headlines, no retaliatory tariffs, no threat to walk away from the deal. Just lawyers, scientists, hearings, and—eventually—a reasoned ruling that both sides accepted. No small feat, given the combative tone of much of the post-Brexit relationship.
More subtly, the case drew a map for future environmental policy within trade frameworks. The tribunal affirmed that countries can enact conservation measures—even unilaterally—if they follow proper process: use good science, avoid discrimination, consult meaningfully, and weigh the economic impacts on others. In that sense, the decision supports environmental ambition—but demands legal discipline (European Commission, 2024).
Trade Deals Meet Climate Reality
This case also speaks to a broader tension shaping international law today: how do you balance ecological urgency with economic predictability?
Trade agreements are traditionally designed to reduce barriers and create certainty. Environmental regulation, by contrast, often thrives on the ability to act fast—to respond to emerging threats, shifting baselines, and evolving science. Sometimes, the very concept of “proportionality” can feel like a straitjacket when species are in decline or ecosystems are near collapse.
And yet… the law doesn’t disappear just because a policy feels righteous. That’s the hard part. Environmental urgency, no matter how heartfelt, does not exempt governments from international obligations. The puffins may be in trouble—but that doesn’t give Whitehall carte blanche to rewrite the rules unilaterally.
Or, to flip it: legal frameworks can accommodate urgent conservation—if those crafting the policies take the time to respect the procedural scaffolding. The case offers a template: not perfect, but workable.
Quiet Diplomacy, Unfolding in Courtrooms
There’s also something oddly reassuring about the tone of the entire episode. Unlike earlier Brexit disputes—fishing quotas, Northern Ireland protocol, vaccine exports—this case never spilled into tabloid fury. It wasn’t the subject of parliamentary shouting matches or pointed threats across the Channel.
It was… professional. Procedural. Even a little boring, in the best way.
Both sides used the tools they had agreed to. Both made their cases. And when the ruling came, neither side stormed out. The UK government acknowledged the result and promised to revise its justification (UK Government, 2025). The EU, for its part, welcomed the legal clarity. Conservation groups like the RSPB cautiously praised the tribunal’s affirmation of science-based policy, while reminding governments not to skip the legal homework next time (The Guardian, 2025).
In a world awash with flashpoints, this sort of low-drama legalism might feel underwhelming. But it’s precisely what makes it important.
A Final Reflection: Why the Small Stuff Matters
At the end of the day, this was a dispute about a small fish, in a patch of sea that few people ever think about. But sometimes, the small cases are the most revealing.
They test systems not at their extremes, but in the margins—in the murky in-between where principles meet practice. That’s where treaties are truly judged. Not in the pomp of signing ceremonies, but in the quiet grind of enforcement.
And perhaps there’s a lesson in the outcome. The puffins, of course, don’t care much for trade law. They just need food. But in 2025, the legal system—slow, flawed, deliberative—spoke on their behalf. And more importantly, it did so in a way that acknowledged both ecological need and economic fairness.
That balance is hard to strike. But it might just be the kind of balance we need more of—if we’re serious about governing a world where nature, politics, and trade are no longer separate categories, but overlapping realities.
References
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European Commission (2024) EU requests consultations under Trade and Cooperation Agreement over UK’s permanent closure of the sandeel fishery. Press release, 16 April. Available at (Accessed: 3 May 2025).
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Marine Management Organisation (2024) Variation issued: Tuesday 26 March 2024 – Sandeel closure within English waters of ICES Area 4. GOV.UK. Available at (Accessed: 3 May 2025).
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Permanent Court of Arbitration (2025a) Case Summary: EU v UK – Sandeel Dispute. Available at (Accessed: 3 May 2025).
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Permanent Court of Arbitration (2025b) Final Award in EU–UK Sandeel Arbitration. 28 April. Available at (Accessed: 3 May 2025).
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The Guardian (2025) UK sandeel ban partially upheld despite EU legal challenge. 2 May. Available at (Accessed: 3 May 2025).
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UK Government (2025) Response to arbitration tribunal final report: UK‑Sandeel (The European Union v. the United Kingdom of Great Britain and Northern Ireland). Cabinet Office & Department for Environment, Food & Rural Affairs, 2 May. Available at (Accessed: 3 May 2025).