Closing the fishery for a month to save dolphins: the measure was imposed in 2024 after a ruling by the Conseil d’État, contested by part of the industry and defended by conservation groups. What remained to be seen was whether it works. The Pelagis observatory published the assessment of the first full season on 27 November 2025. The answer comes with figures.
What the assessment says
| Winter 2024-2025, with the closure | 1,900 common dolphins killed as bycatch |
|---|---|
| Average for the winters of 2017 to 2023 | 4,700 |
| Reduction during the month of closure | 60% |
| Period closed | 22 January to 20 February |
The closure is renewed from 22 January to 20 February 2026, for the third consecutive year. It applies to all European vessels in the area, and not to French boats alone.
How animals that sink are counted
The figure deserves an explanation of where it comes from, because it is not a direct count.
Common dolphins caught in fishing gear die at sea. Only some of the bodies drift ashore, and among those only some carry identifiable gear marks. The Réseau national échouages, the French stranding network, records these cases, and a drift model then works back to the total number of deaths, taking account of winds, currents and the buoyancy of carcasses.
The estimate therefore depends on the quality of that model, which is why the figures are given as orders of magnitude rather than to the unit. But the method is the same from one year to the next: the comparison between seasons remains valid, even though the absolute value carries an uncertainty. That is what makes it possible to speak of a 60% reduction.
Why this population, and why winter
The concentration of catches into a few weeks is not an accident of the calendar. In winter, common dolphins move closer to the continental shelf and gather there, following pelagic prey that aggregate on it. At the same moment, several fisheries target those same fish, with towed gear whose opening is measured in tens of metres.
The result is an overlap in space and in time, between animals that have gathered and gear that sweeps large volumes of water. It is this overlap that the closure removes for a month, and that is why its effect is so marked. Our page on fishing and ship strikes in the Bay of Biscay sets out this configuration.
It should be stressed that the measure did not reduce mortality by making the gear more selective. It reduced it by separating the two. It is a blunt lever, effective, and costly for the industry, which explains why it was imposed through litigation rather than negotiated.
The limits of a one-month closure
A month of closure does not cover the whole period of risk. The assessment covers four months, from 1 December to 31 March, and 1,900 deaths remain across that window. Mortality has not disappeared, it has been sharply reduced where the closure applied.
The sustainability threshold is in addition a matter of debate. European scientific advice places the acceptable removal for this population well below the current level, which explains why the question is not closed despite the result. Our pages on bycatch and on fishing and ship strikes in the Bay of Biscay set out this framework.
The other levers, and why they were not enough
The closure is not the first measure to have been tried. Three others have been deployed or tested, and are worth distinguishing.
Acoustic deterrents, known as pingers, emit a signal that keeps dolphins away from nets. Their effectiveness is established on certain gear, but it is uneven depending on the configuration, and the question of the animals becoming habituated to the signal arises over the long term. A device that works in the first year does not necessarily work in the fifth.
On-board cameras reduce no catches at all: they serve to measure them. Their value is to provide a catch rate per gear and per trip, and so a denominator, where stranding monitoring gives only a reconstructed total. They are an instrument for putting the debate on an objective footing, not for reducing mortality.
Gear modifications, finally, seek to leave a way out for an animal that has become caught. They are making progress, but none has demonstrated to date an effect comparable to that of a temporary closure.
The threshold, and why the debate is not closed
One question remains behind these figures: how many dolphins can be killed without the population declining. The answer is expressed as a fraction of the estimated population, and therefore presupposes that this population is known, which is what the aerial survey campaigns provide, and whose distribution maps we have published.
European scientific advice places this sustainable removal well below the level recorded, including after the 60% fall. In other words, the closure has produced a considerable improvement without bringing mortality below the threshold sought. That is the reason why the measure is being renewed, and why the discussion about extending it continues.
Two unknowns also remain open. The first is effort displacement: a fleet tied up for a month may fish more before and after, shifting part of the problem rather than removing it. The second is the share of catches attributable to gear or to fleets not covered by the closure. The 2025 assessment settles neither one nor the other.
What this result demonstrates beyond the dolphins
There is a more general lesson here, and it is a rare one. A contested management measure was applied, then assessed on the evidence with a public method, and the result is clear. That is not so frequent in environmental policy, where many measures are renewed without anyone measuring their effect.
This kind of evaluation presupposes long-term monitoring of strandings, carried out without interruption for decades. Our sighting maps for the Bay of Biscay give the context of this area.
Sources: report of the Pelagis observatory published on 27 November 2025, co-signed by Hélène Peltier; rulings of the Conseil d’État and the European Commission regulation framing the closure; data from the Réseau national échouages.
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