Are you sitting down? I have something shocking to tell you. The people who run our fisheries have been struck down by an unprecedented attack of good sense. I expect them to recover soon, but while the sickness persists, anyone who values the ecosystem has something to celebrate.

On 1 November, the fleet of nomadic scallop dredgers that moves around the country trashing the sea floor was due to resume its assault on Cardigan Bay off the Welsh coast, near where I live. Partly because it harbours one of the only two large populations of bottlenose dolphins in the UK, most of the bay's coastal waters are classified as special areas of conservation – the strictest protection available under EU law.

But until now, dredgers from all over the country have been allowed to drag their steel hooks and chain mats over the seabed between November and May, trashing everything that lives there: all the sessile animals, the fish, their spawn, and any features that might harbour life. The damage they inflict is out of all proportion to the catch, and they probably cost other fisheries far more money than they make themselves. Banned from other sensitive areas, they have poured into Cardigan Bay, where as many as 70 boats have been working at once.

Until now, the regional fisheries committee, which is supposed to defend the marine ecosystem, has wrung its hands and claimed there is nothing it can do. But a vocal campaign by local people, led by the Friends of Cardigan Bay, has prompted it at last to act. This month, the county's Fisheries Committee announced it has banned scallop dredging in the bay indefinitely, pending the results of an ecological assessment by scientists at Lancaster University.

There are two remaining problems. The first is that, amazingly, an assessment hasn't yet been conducted. The dredgers have been the subject of huge controversy for years, but the fisheries committee has allowed them to keep operating without bothering to discover how much damage they are doing. Divers' photos and research from other parts of the UK suggests it is likely to be horrendous. But the scallop dredgers might challenge the ban on the grounds that their impact hasn't yet been assessed. Why wasn't this research carried out before?

The other problem is that the dredgers aren't going to give up: they will just move to another part of the UK, where they haven't yet been banned, and start trashing the marine ecosystem there. Isn't it time this practice is banned all around the UK, and even throughout Europe?

But don't let me spoil this rare moment, in which a concern for the health of the ecosystem has been allowed to trump raw greed and plunder. Enjoy it while it lasts.

www.monbiot.com