MINISTERS are facing mounting pressure to ban trawlers from raking the seabed for prawns to help reverse the catastrophic collapse of fish populations in the mouth of the River Clyde.

A new report by Scottish Government scientists has concluded that past fishing has had "a major ecological impact" on the firth. As many of 90% of the fish are now smaller than the minimum landing size, and 72% of them are just one species – whiting.

One factor blamed for preventing the populations recovering is that bigger fish are taken as by-catch – unwanted fish thrown back into the sea – by the Clyde's £20 million prawn trawler industry.

Data from the Government's scientific observers suggests the trawlers "may be partly responsible for the current absence of older, larger fish in the Clyde", the report says.

The claim has been seized upon by conservationists, creel-fishers and anglers to boost their campaign for a ban on prawn trawling within three miles of the coast. But it has been fiercely rejected by the prawn trawling industry, which denies it is to blame.

The Clyde Ecosystem Review published by the Government's Marine Scotland Science, compares the Clyde to "used agricultural land in need of restoration". Without bigger fish, it will fail to meet the environmental standards required by the European Union's marine framework directive in 2020.

"The destructive impact of prawn trawling in terms of damage to the seabed and high levels of by-catch is now well understood by scientists," said Robert Younger, chairman of the Sustainable Inshore Fisheries Trust, which brings together conservationists and creel fishers.

"There is no prospect for the recovery of the Clyde fishery unless restrictions are placed on trawling by the Scottish Government."

According to Howard Wood, chairman of Community of Arran Seabed Trust, prawn trawling also damages the seabed and fish nursery grounds. "The Clyde has the potential to recover, but unless we curtail trawling and dredging, fish stocks will not recover," he said.

Steve Bastiman, chairman of the Scottish Sea Angling Conservation Network, described the Clyde as "a shameful embarrassment" for Scotland's politicians. "Rigorous controls on destructive commercial fishing practices are required if it is to stand any chance regaining its former glory," he said.

However, the firth's 40-plus prawn trawlers were strongly defended by Archie McFarlane, the secretary of the Clyde Fishermen's Association, who blamed the collapse of fish populations on seals. "These claims are made by people who do not understand what they are talking about," he said.

Fisheries Secretary Richard Lochhead has promised discussions with stakeholders to find a way forward. "I am optimistic that, with the right management in place, the Clyde can once again house a thriving and balanced ecosystem," he said.