Greenpeace UK activists have placed giant boulders on the seabed in the Southern North Sea Marine Protected Area (MPA) to stop bottom trawlers fishing there, in what the group calls an underwater “boulder barrier”.

The campaigners laid the boulders, each weighing up to two tonnes, over the weekend off England’s east coast. Greenpeace says the barrier effectively closes 116 sq km of the MPA to bottom trawling. The protest coincided with the first episode of Blue Planet III on BBC One on Sunday.

The MPA was designated to protect harbour porpoises. Yet according to Greenpeace analysis of Global Fishing Watch data, bottom trawlers logged at least 37,200 hours of fishing there in 2025, far more than in any other UK offshore MPA.

The Southern North Sea supports nearly 20% of the UK North Sea harbour porpoise population. The site was designated to prevent “significant disturbance” of the species and to keep prey available, but there are no fishing restrictions across most of it. The group says trawling depletes fish stocks leaving porpoises with less food, while the noise disrupts their ability to hunt.

Across all the UK’s offshore MPAs, Greenpeace says bottom trawlers and dredgers dragged gear over a cumulative 55,600 sq km of seabed in 2025, an area 58 times the size of Dartmoor National Park. They spent at least 115,000 hours towing gear along the seabed in these areas, equivalent to more than 13 years of non-stop fishing. 

The group has declared the area an “ocean park” and will patrol it in its ship, the Arctic Sunrise, to deter other destructive fishing, including mid-water gear that affects porpoises.

The group notes that the area figure counts every pass of the gear, so seabed trawled more than once is counted each time. It measures the total amount of trawling, not the area of seabed affected. 

Will McCallum, co-executive director of Greenpeace UK, said: “Imagine a bulldozer tearing through a treasured national park like Dartmoor or the Peak District. Out of sight, destruction on that scale is happening near our own shores in places we’re told are ‘Marine Protected Areas’.” He said the group had warned in June that it would take direct action if the government did not act, and challenged ministers to ban destructive fishing across all protected waters.

The actor Simon Pegg and the actor Benedict Cumberbatch have signed boulders, as have six MPs: Ellie Chowns, Carla Denyer, Barry Gardiner, Kerry McCarthy, Dr Simon Opher and Dr Roz Savage. McCarthy, a former climate minister, said less than 1% of UK seas were protected from industrialised fishing and called for a ban on bottom trawling. The UK has signed up to protect 30% of land and sea for nature by 2030. 

About 11% of the UK’s MPAs (43 of 378) are fully protected by law from bottom trawling, Greenpeace says. In 2025 the government announced plans to ban the practice in parts of a further 42 MPAs, but the consultation closed over a year ago and no results or decision have been published. The Southern North Sea is due to be covered by a later consultation, with no date set.

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