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Gill disease kills salmon by the tonne

SHETLAND’S biggest salmon producer lost one third of its predicted harvest during the last three months of 2012 due to the impact of a new disease which only arrived in the islands last summer.

Amoebic gill disease (AGD) is the main cause for Grieg Seafood Hjaltland to write down 2,400 tonnes of salmon during the quarter, costing the company more than £5 million.

The losses include a combination of dead fish and salmon which have had or will have to be harvested early before they have reached their expected average weight of 4.5kg.

The Shetland salmon industry is planning a pre-emptive strike over six weeks from next month with every salmon farm in the isles being treated.

David Sandison, general manager with the trades body Shetland Aquaculture, said AGD is carried by a sea-borne amoeba and was first found in Tasmania and Chile.

It is believed the northern hemisphere outbreak began at a fish farm in northern France, from where it travelled via Ireland to the west of Scotland.

There it grew extensively during the dry summer experienced in that part of the world. How it came to Shetland remains unknown, but it could have been transported in ballast water, Sandison said.

“AGD has been widespread throughout Scotland and was first confirmed in the north of Shetland in August last year and between August and November it has been recorded at quite a number of different sites in different areas at varying degrees,” he said.

“It is going to mean there will be a dent in the outturn in production and most companies will be affected to a greater or lesser extent, but there are one or two companies in Scotland that have reported no problem at all.

“We will be treating every single site in Shetland from the second week of February until the end of March on an area by area basis.”

Despite the scale of the problem, Sandison said it would be wrong to describe this as a “crisis”.

“I think the fact that we have managed through collective action of the industry to get control of the situation is the main thing and the fact that we now have a plan in place to do a pre-emptive treatment this year should ensure it doesn’t happen again.

“But we can’t deny it’s had a big impact on the industry’s performance at the tail end of the year.”

Farmed salmon is Shetland’s biggest industry valued at around £140 million a year.