Ahuge ecological experiment begins today on Dogger Bank, part of the sunken landmass that once formed a bridge between Britain and mainland Europe. Trawling and dredging – fishing activities that not only scoop up fish and shellfish but also plough through plants and animals on the sea floor – are now banned, at least on the British part of this Atlantis of the North Sea. The protection of 12,000 sq km of seabed, 100km off eastern England, where early man hunted woolly mammoths, amounts to an act of rewilding thousands of times bigger than the “best in show” garden at this year’s Chelsea flower show. Covering an area almost the size of Northern Ireland, it marks a turning point in the health of our nearby seas. Until today, this officially designated marine protected area has been simply a “paper park” – a term used to describe somewhere protected in theory but not really in practice – hammered by dredgers targeting scallops and beam trawlers harrowing the seabed for sole. Nobody quite knows what will happen now, but history gives us an idea what Dogger Bank could be like again. In the 1830s, small sailing vessels could catch a ton of halibut a day. Today, vessels fishing across the whole bank – in UK, Danish, German and Dutch waters – land less than two tonnes of halibut a year. Slow-reproducing monsters such as halibut just are not given enough time to breed and grow before being caught. Halibut are not the only missing megafauna. There is a picture of a huge sturgeon caught on Dogger Bank in 1925 on the wall of a Lowestoft pub. One day sturgeon could be back, along with halibut and perhaps the oysters recorded along the south side of the bank in the 1880s. These communities of restored plants and animals will enhance the sea’s ability to soak up carbon. The possibilities are wildly exciting. What we do know from Lyme Bay on the English south coast, where trawling and dredging were banned in 2008, is that four times the number of commercially valuable fish came back, as did four times the overall number of species. The result of banning the most damaging fishing gear – not fishing per se – has been an economic and an ecological success. Why, you may ask, don’t we manage all our inshore waters that way? The success of Lyme Bay gives the lie to the moaning about “displacement” from the industrial side of the fishing industry, especially in the Netherlands. The reality is that the protection of Dogger Bank is likely to mean not the concentration of fishing in fewer places, but more fish to catch by “fishing the line” outside the protected area. The revival of fish habitat and fish stocks will spiral – provided the government gets on and properly protects the 70 or so other “paper parks” in UK offshore waters, which is by no means a certainty. The protection of Dogger Bank is that rare thing – a Brexit dividend. There are multiple ironies to it, though. The Dogger was theoretically protected a decade or so ago by the UK government under the EU habitats directive – written by the prime minister’s father, Stanley Johnson, when he was an EU official. Then nothing happened, because there is an unhelpful conflict in European law between nature conservation and the common fisheries policy that has yet to be resolved. When the common fisheries policy ended in UK waters after Brexit, ministers from the Department for Environment, Food and Rural Affairs were – our charity had to remind them – obliged to enforce the nature laws we had inherited from Europe. There was no longer any conflict in law. George Eustice, the environment secretary, has boasted that in protecting Dogger Bank, Britain was using its post-Brexit freedoms to protect the marine environment. But he then did something horrendous earlier this year, proposing in a green paper to remove all duties on ministers to protect nature sites, marine or terrestrial. Reassuringly, there is opposition to his ideas from all sides, and they are a long way away from becoming law. The protection of Dogger Bank nevertheless stands as a great achievement. It is a sign amid the prevailing gloom that we can begin to tackle the biodiversity crisis and the climate emergency by enhancing the power of the ocean to absorb carbon. Among these positive and hopeful developments are the creation of a “blue belt” of marine protected areas around some British overseas territories, the protection of the kelp belt off Sussex and the recovery of the bluefin tuna, now turning up off Britain, Ireland and Norway after decades of absence. I just wish we could rely on our government to follow the last example of ambitious science-based management. For, by contrast with the bluefin, two-thirds of fish stocks in UK and EU waters – including cod, the nation’s favourite fish – are currently harvested at levels in excess of scientific advice. Shockingly bad decisions continue to be taken every day, when we could be promoting the recovery of overexploited species and reducing carbon emissions at the same time. We need to look again at how we manage the oceans in a time of climate crisis. The ocean is the largest carbon sink on Earth, and it can help us by taking up far more carbon than it does at present. All we need to do is to load the dice against the smokestack industries of the sea – trawling, dredging and other industrial methods of fishing – that have already devastated our waters and which, scientists now tell us, cause as many carbon emissions as the global aviation industry. We can rewild the sea. It’s already being done, not just on Dogger Bank. It works and – here’s the thing – ultimately, everybody gains. Charles Clover is executive director of Blue Marine Foundation. His new book is Rewilding the Sea: How to Save our Oceans