DAWNFRESH, Scotland's largest producer of farmed trout is being investigated by Scotland's environmental regulator over the unpermitted use of a lice-killing insecticide said to be highly toxic to birds, fish and crustaceans.

The Scottish Environmental Protection Agency has confirmed that there has been "a number of occasions" in the last three months of last year where it had breached its pollution licence by overuse of azamethiphos on one of Dawnfresh's Etive fish farms, north of Oban.

And it has emerged that official data recorded by SEPA shows there were around 54 tonnes of fish deaths on the farm over the three months, with 43 tonnes in November alone, leading to worries from Friends of Loch Etive, the charity that aims to preserve and protect the Highland sea loch, that the insecticide has been a contributory factor.

If an average weight of three kilogram kg per farmed fish is assumed, this would mean that some 18,000 fish died on the Etive 6 farm over the three months.

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Dawnfresh, while admitting there was an error which led to the "technical breaches" deny the spike in fish deaths was related to the insecticide, saying it was down to a problem in transferring fish from a wellboat in November. A spokesman said its fish mortality rate was "very low" and "I would say industry leading".

Friends of Loch Etive, the charity that aims to preserve and protect the Highland sea loch, said the non-permitted use of azamethiphos on Etive 6 "will have risked serious harm to wild crustaceans in Loch Etive - crabs, prawns and lobsters".

It warned that spikes in farmed fish deaths have been caused on other fish farms by a combination of sea lice damage and sea lice treatment losses, or fish killed by the treatments with azamethiphos.

A leaked email reveals that SEPA has asked Dawnfresh what steps it was taking to address the issues and to "ensure that the site is brought back into compliance".

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It added: "The need for further action by SEPA will be considered when we have their response".

Etive 6 is now classed as "poor' in its 2016 compliance assessment.

A spokesman for FoLE said: “We are appalled that Dawnfresh has breached its pollution licence, apparently on a number of occasions over three months last autumn.

"It isn’t that long ago, when Dawnfresh first applied for this new farm, that it was insisting that the new farm would not need to treat for sea lice at all. Now it appears, just a couple of years later, that they cannot treat for sea lice without breaching their pollution control licences, damaging the wildlife of Loch Etive.

"As Friends of Loch Etive will continue to point out to Dawnfresh - and will pursue with the full weight of the law - Loch "Etive belongs to the Etive community and not to one company seeking to expand its industrial fish farming operations to the overall detriment of the wildlife of the loch”.

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FoLE say that "despite the problems and mortalites" at Etive 6, Dawnfresh farms are understood to be certified by the RSPCA Assured scheme, which describes itself as “the only farm assurance scheme in the UK dedicated solely to improving farm animal welfare”.

Stewart Hawthorn, farming director for Dawnfresh, said: “In 2016, we recorded an historically low number of sea lice in Loch Etive thanks to taking a more proactive approach to the problem.  Unfortunately, there were six instances on one of our sites where we did not meet our usual high standards in the technical implementation of a treatment.

"This is particularly frustrating for us because SEPA has confirmed that without these very small number of errors, the site would have been rated as 'excellent' in environmental compliance. We will be working with SEPA and our own team to ensure we have the lowest possible impact on the environment in the future.”

“Overall we are proud of our record of environmental compliance. "Going forward into 2017 we remain committed to effectively controlling sea lice and are already in the process of putting in place new treatment methods which will further reduce our reliance on chemicals.”

A SEPA spokesman said "SEPA is in contact with Dawnfresh regarding occasions where consecutive bath treatments with azamethiphos were carried out at Etive 6 less than 24 hours after the first treatment.

"These treatments are not in compliance with the site's CAR licence.

"We will be undertaking further investigations into this matter with the company."