The proposal, by Ayr-based firm Marine Biopolymers, would eventually see more than 30,000 tonnes of the seaweed gathered each year by specially adapted boats.
The harvesting method involves large toothed devices being trawled through kelp beds, removing entire plants over a certain size.
Seaweed has a number of uses, from pharmaceuticals to food, and the market for it is burgeoning.
But critics claim the move could damage the marine environment, deplete fish stocks, increase coastal erosion and drive climate change.
“Dredging our kelp forests is not dissimilar to clear-felling virgin rainforest,” said Nick Underdown, head of campaigns at sustainable fisheries charity Open Seas.
“It’s one of the few pristine habitats in our seas that remain unscathed by over-intensive exploitation. It provides a fundamental foundation to the way our seas work, providing habitat for many hundreds of species, and represents one of our best stores of blue carbon.
“On land we are trying to actively recover our native pine forests. Why repeat the mistake of deforestation at sea? The proposal is completely adrift from sensible, sustainable use of our seas and would drag us backwards.
“Our environment can sustain a vibrant Scottish seaweed industry, but allowing mechanical dredging in the way proposed will not only undermine the health of our sea, it will undermine other marine businesses and alternative harvesting methods.”
Ailsa McLellan, a mussel farmer and seaweed picker from Ullapool, said: “I’m concerned from an environmental point of view. Kelp is a significant absorber of carbon, it buffers ocean acidity caused by warming seas and prevents coastal erosion.
“It seems utterly bonkers to take that away at this stage in our planetary evolution. There is nothing green about dredging up kelp.”
Marine Biopolymers has submitted a scoping report to Marine Scotland, laying out its intention to apply for “one or more” licences to harvest kelp in waters from Mull up to Lochinver and across to the Outer Hebrides. The scheme would be a first for Scotland.
The company also aims to build a processing plant in Mallaig. The product will be used in heartburn medication.
A Scottish Government spokesman said: “Marine Scotland will consult fully on any forthcoming application and environmental assessments. Scottish ministers will then make a determination on a licence application, taking into account the effects on the environment and other uses of the sea.”
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