Damaging trawling of the seabed in a marine-protected area dropped 98% after a ban came into force, according to campaigners.
Dogger Bank in the North Sea is home to species such as sand eels, which are food for puffins and porpoises.
The government banned trawling in the area in June 2022, following a campaign by environment groups to ensure the bank is properly protected.
Now analysis by the Marine Conservation Society shows the amount of hours of bottom-towed fishing between June and October dropped.
It came down from an average of 623 hours in 2015-2019 to just 13 hours in 2022.
Before the ban was introduced, fishing with bottom-towed gear which drags over the sensitive seabed could still take place.
Campaign group Greenpeace dropped boulders into the sea to act as a barrier to fishing.
Jean-Luc Solandt, principal marine protection area (MPA) specialist at the Marine Conservation Society, said: "The huge reduction in seabed fishing we’ve identified shows how effective governments can be in protecting our ocean.
"This needs to be replicated across all offshore MPAs to help recover fish stocks, provide sanctuary for marine life, and protect sensitive habitats from destruction.
"Our ocean has an incredible ability to recover when it’s given a chance. The Government must meet its target to fully protect all English offshore MPAs before 2024.
"The sooner this happens, the sooner our seas can restore themselves."
Dogger Bank is one of four areas of English seas protected from this kind of fishing under government byelaws.
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