Virulent disease at Marine Harvest salmon farms raises concerns over potential impacts on wild fish

Salmon & Trout Conservation UK


Integrity of Special Area of Conservation for wild salmon on Harris under threat. Other important wild fisheries also at risk.

Integrity of Special Area of Conservation for wild salmon on Harris under threat. Other important wild fisheries also at risk

Salmon and Trout Conservation Scotland calls on Scottish Government to intervene to protect wild fish

Marine Harvest salmon farms in the Hebrides and Wester Ross are currently host to rampant Amoebic Gill Disease (AGD), which can cause severe losses amongst affected fish. At least four sites are impacted including West Loch Tarbert and East Loch Tarbert on Harris, Loch Greshornish on Skye and the Isle of Ewe in Wester Ross. Up to 25 per cent of the fish at the afflicted sites are understood to have been lost, with hundreds of thousands of mortalities transported to Wigan (Greater Manchester) for incineration.

Marine Harvest is struggling to manage the situation and has been slow to admit the extent of the problems. AGD is a very unpleasant disease which causes asphyxia; many fish then suffocate to death. Salmon and Trout Conservation Scotland (S&TCS) is adamant that the Scottish Government should act now to protect wild fish.

Whilst Scotland’s Fish Health Inspectorate ( states that AGD is “occasionally recorded on wild salmon without causing significant pathology”, it concedes that there is a “difficulty of obtaining samples for disease diagnosis in wild fish”. Juvenile wild salmon (smolts) migrate from their rivers in the spring, passing through the coastal zone, before heading out to sea. If they are infected as they swim past disease-harbouring farms, it is impossible to monitor their fate.

Paul Hopper, Senior Biologist at the Outer Hebrides Fisheries Trust (OHFT), explained:

“If AGD is still present next spring, wild salmon smolts on their outward migration to sea could be put at risk. Unlike with fish farms it is very difficult to obtain samples of wild fish at sea and hence gauge any impact on wild populations. Incidents of the disease have been recorded in Scotland at water temperatures as low as 7.5°C and accordingly we cannot rely on a drop in sea water temperature to help alleviate the situation imminently.”

Mr Hopper added:

“We are extremely concerned about AGD in West Loch Tarbert as well as the earlier lack of communication on this outbreak from the company involved. Having now held meetings with the local fish farmers, we have been reassured that the industry is working hard to improve the situation through treatments and careful management of their stocks. We cannot emphasise enough how important it is for the aquaculture industry to report incidences of diseases like AGD without delay so that all stakeholders can immediately work together to protect both farmed and already threatened wild fish stocks.”

Marine Harvest’s West Loch Tarbert farm is adjacent to the North Harris Special Area of Conservation (SAC) for Atlantic salmon.

Innes Morrison, Clerk to the Western Isles Fishery Board and Factor at Amhuinnsuidhe Castle Estate (with the fishings in the North Harris SAC), noted:

“We are very concerned that, if the disease is not eradicated by the spring, the migrating juvenile salmon from our SAC rivers will be vulnerable to deadly infection. In the meantime our sea trout, which remain in coastal waters, will surely be prone to infection. The salmon farming industry in the Western Isles seems to lurch from crisis to crisis – with both disease and sea lice epidemics – and yet virtually all applications for new farms or expansions are still being rubber-stamped by the local council with little if any concern for the environmental impact.”

Major mortalities due to AGD have now also been confirmed by the Fish Health Inspectorate at Marine Harvest’s site at Isle of Ewe in Wester Ross.

Bill Whyte, Chairman of the Wester Ross Area Salmon Fishery Board, said:

“The cloak of secrecy surrounding the presence of AGD at Marine Harvest’s farm in Loch Ewe is inexcusable. This outbreak of AGD must surely prompt further questions as to the suitability and viability of Loch Ewe for salmon farming. Prior to the arrival of the industry in Loch Ewe, the Loch Maree system was an iconic fishery for both wild salmon and sea trout.”

Andrew Graham-Stewart, Director of Salmon & Trout Conservation Scotland (S&TCS), said:

“If any terrestrial farming industry was beset by a similarly rampant and highly contagious disease, the authorities would step in immediately and ruthlessly cull all affected stocks. But because the tens of thousands of fish affected by and dying from AGD are unseen beneath the waves, the Scottish Government adopts a laissez-faire approach. Leaving aside the suffering caused to the fish in the cages, given the potential risks identified by local wild fish experts and the apparent inability of Marine Harvest to eradicate the disease, surely the Government now has a responsibility to intervene and order the immediate slaughter of the farmed stocks in question.”

A further concern amongst wild fish experts – with implications for wild salmon and sea trout – is the reluctance of salmon farm managers to treat AGD-affected fish against sea lice as the chemicals used may cause additional stress and thus exacerbate the incidence of AGD.

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