France has announced a temporary ban on almost all commercial fishing in the Bay of Biscay to protect dolphins, reports BBC News.
It will start on Monday and run until 20 February affecting fishing grounds off the country's Atlantic coast.
French marine experts CIEM estimate around 9,000 dolphins die in the bay each year after being accidentally caught in fishing gear.
Local fishermen say the ban is "absurd" and fear losing money - but the government has promised compensation.
Last year the country's top administrative court, the State Council, ordered the move after environmentalists called for better protection for the marine mammals.
The ban, lasting about a month, is the first since the end of the World War Two, according to news agency AFP. Fishing will cease almost entirely during the ban covering an area from Finistere in Brittany to the Spanish border.
Boats longer than 8m (26.2ft) will be affected with reports suggesting this could mean around 450 French vessels are out of action.
Some in the industry estimate they could lose millions of euros in revenue but the French government has promised compensation.