Plans to scrap limits on the amount of salmon that can be kept at fish farms around the coast would increase disease, worsen pollution and harm wild fish, campaign groups are warning.

The Scottish Environment Protection Agency (Sepa) is about to propose abandoning long-established limits on the mass of salmon that can be farmed in cages at particular locations in order to support the industry’s “growth agenda”.

The limits help reduce salmon overcrowding and seabed contamination from pesticides and waste, as well as controlling infestations by sea lice, which can affect wild fish. But they have been breached over 800 times at Scottish fish farms since 2002.

In October the fish farming industry announced a plan to double its business from £1.8 billion in 2016 to £3.6 billion by 2030. The plan was backed by the Scottish Government, which promised to set up an “industry leadership group”.

In the next few weeks Sepa is due to launch a public consultation on how it regulates fish farming. According to a recent submission it made to the Scottish Parliament on the government’s draft budget, this will include a plan to drop salmon “biomass” limits.

The aim was to ensure that “the regulatory framework more closely matches the growth agenda pursued by the industry by removing imposition of a limit on biomass,” Sepa said.

This would enable operators “to increase biomass where environmental monitoring demonstrates that the location is able to cope,” it argued. It would put responsibility for day-to-day management of sites into the hands of “responsible fish farmers”.

But the proposal has run into fierce criticism. According to the animal welfare group, Compassion in World Farming, it would benefit the industry but be “disastrous” for fish.

“Squeezing ever more fish into a set amount of space will have damaging effects on their well-being, with crowding leading to increased stress and potentially higher incidence of disease,” said the group’s chief executive, Philip Lymbery.

“Scrapping the limit on maximum biomass would be a seriously retrograde move which would have repercussions on the welfare of both farmed and wild fish.”

Lymbery argued that the higher the concentrations of fish farms, the higher the incidence of sea lice. Lice cause suffering and death for caged and wild fish, and their treatments can kill fish and cause pollution.

“We should be reducing biomass,” he said. “Until we find a humane and sustainable way of dealing with the sea lice issue the industry should not be seeking to grow at all.”

Don Staniford from the Global Alliance Against Industrial Aquaculture attacked Sepa for “cravenly kowtowing” to the industry and ignoring environmental concerns. “Sepa is bending over backwards to accommodate the relentless expansion of salmon farming,” he said.

“Salmon farms, even at current capacity, are causing widespread benthic impacts with dead zones under cages. Increasing production will effectively wipe out whole swathes of the seabed.”

Staniford pointed out that the industry already had to deal with escalating sea lice infestation, chemical resistance and disease. “Removing what few controls there are in favour of unrestricted expansion is a recipe for ruin,” he argued.

According to industry data, there have been 858 breaches of salmon biomass limits since 2002 at 170 fish farms, amounting to over 74,000 tonnes. Sepa pointed out that on average there had been five sites a month over the limit.

Salmon & Trout Conservation Scotland, which represents anglers, was also opposed to the removal of biomass limits. By restricting the number of salmon, they provided wild fish a little protection against sea lice.

“If the Scottish Government is to strip even that modicum of protection away, in this precipitous dash for growth at all costs, it is the wider environment that will suffer,” said the group’s fish farming campaigner, Guy Linley-Adams.

“It is simple maths. More fish on a farm means more lice on the farm and more lice leaving the farm to infect wild fish.”

Sepa confirmed that it was intending to launch a new licensing framework for fish farms “in the coming weeks”. The proposals had not been finalised but were likely to include fewer restrictions on salmon numbers.

Fish farms would be given a biomass limit to start with but that could rise if the environment wasn’t being unduly harmed, according to Sepa’s area manager, Stuart Baird.

“If the results of seabed monitoring show that impacts from the fish farm comply with seabed standards then the farmer will be able to increase the biomass held at that site incrementally,” he said.

“Increases above the fixed starting biomass will only be allowed where environmental monitoring demonstrates that it is safe to make such increases. At sites which fail to meet environmental standards, further stocking will not be permitted until conditions come back into compliance with seabed standards.”

Baird added: “This method will allow for growth but only where environmental monitoring shows the site is able to cope with this growth.”

The Scottish Salmon Producers Organisation, which represents fish farmers, declined to comment because it did not have “up to date information” on biomass proposals.

A version of this story was published in the Sunday Herald on 8 January 2017.

Photo thanks to John Allan licensed for reuse under this Creative Commons Licence.