Marine conservation campaigners have called for trawlers to be banned from fishing within three miles of Scotland’s shoreline to help depleted fish stocks and seabeds to recover.

The Our Seas coalition, which includes angling bodies, ecotourism firms, scallop divers, coastal communities and salmon conservation boards, believe a ban on inshore fishing would also help prevent illegal scallop dredging and trawling inside existing protected areas.

The National Trust for Scotland (NTS), the country’s largest landscape conservation charity, broadly supports the proposal, which would affect 18,000km (11,185 miles) of mainland and island coastline and 13,790 sq km of sea.

It has called for ministers to investigate reinstating a ban on trawlers within three nautical miles of shore in a new marine policy paper, the first in its 89-year history. The document codifies the trust’s calls for much stricter policies on fish farms, offshore renewables and mitigating the impacts of climate change on the sea.

Stuart Brooks, the trust’s head of conservation and policy, said there should be a restriction of all mechanised fishing within that coastal zone, except for places where there was sufficient evidence inshore fishing was safe.

“Fundamentally, it’s about the sustainability of our fisheries, and the people and wildlife that depend on them,” he said. Marine tourism now employed more people than fishing, he added.

The coalition, which includes NTS, is launching a campaign later this month urging the Scottish government to impose a three-nautical-mile ban, which was in force in Scottish waters for nearly a century until it was lifted in 1984.

The policy would have a significant impact on the boats that primarily trawl for langoustine or dredge for scallops, which replaced the once-bountiful stocks of finfish such as cod and herring that collapsed in inshore waters from overfishing.

The campaigners acknowledge narrow sea lochs and many sea channels between the islands would be closed to all trawling, except where trawlers can prove their activities were safe. It would promote lower-impact creel fishing for langoustine, crab and lobster, and hand-dived scallop firms.

Lobster caught between Iona and the Ross of Mull, where creel fishing predominates. Photograph: Richard Baker/Corbis via Getty Images

Open Seas, a conservation charity in the Our Seas coalition, cites an expert study for the Scottish government that said a three-mile closure could produce up to 2,707 extra jobs after 20 years, and at least £1bn of additional income, because it would boost fish stocks and other industries.

Scottish ministers have so far resisted pressure to adopt this proposal and have instead offered to ban bottom-trawling or dredging in 11 types of sensitive or rare habitat known as priority marine features.

These include beds of flame shell, seagrass and maerl, cold-water coral reefs, Northern sea fan and sponge communities, and native oyster colonies. Scores of sites around Scotland containing these habitats and species would be closed off. Scotland already has an extensive network of marine protected areas, covering 25% of the Celtic seas along the west coast and islands, and 12% of the North Sea.

Campaigners argue this strategy of piecemeal designation has failed. They point to incidents where priority features have already been destroyed by illegally dredging or where trawlers have been fishing inside exclusion zones, without being caught or penalised.

Alistair Sinclair, of the Scottish Creel Fishermen’s Federation, a partner in the Our Seas coalition, said: “We need to look forward and think of the generations coming after us. We have to secure a future for the young folk and families in rural communities along our coastline.”

Elaine Whyte, executive secretary of the Clyde Fishermen’s Association, one of the UK’s main inshore fisheries organisations, said Our Seas was wrong to attack the current system. “It’s not what the majority of inshore fishermen want,” she said.

She said there was a Scotland-wide network of inshore fisheries groups that balanced local fishing and community interests, using voluntary closures and restrictions on conservation grounds. It was an inclusive system and each group tailored its policies to local needs and conditions.

“A little bit of everything is the way to go,” she said.