Report highlights massive threat to wild salmon and sea trout from Scottish salmon farms failing to control sea lice over the last two years. Industry-wide problem with sea lice not under control

Salmon & Trout Conservation Scotland calls for urgent action from Scottish Government

Salmon & Trout Conservation Scotland (S&TCS) today (14 December 2015) published a detailed report into the control of sea lice on fish farms in Scotland over the last two years, which brings into sharp focus the seriousness of the problem with sea lice and the need for urgent action from the Scottish Government to protect wild salmon and sea-trout populations that are already in trouble.

Fisheries scientists are increasingly firm in their conclusions that sea lice produced on fish-farms harm wild salmonids, both at an individual and at a population level.

However, the S&TCS report shows that these threats are not being addressed by effective regulation and control of sea lice numbers on fish-farms in Scotland, which are essential to protect wild fish populations which are already significantly reduced (Notes 1 and 2).

Andrew Graham-Stewart, Director of S&TCS, commented:

"The Scottish Government is aware that wild salmonids in the "aquaculture zone" on the west coast are already in deep trouble. The shocking findings of the S&TCS report mean that the current "business as usual" approach of Scottish Government towards salmon farming is no longer sustainable.

Quite apart from the obligation the Scottish Government should feel to protect wild salmon and sea trout, as iconic wild species, Scotland has international responsibilities to comply with European law and to meet its commitments that it has made to other North Atlantic nations to protect Atlantic salmon.

We believe that the Scottish Government has no choice now but to act to increase the protection of wild salmonid species of international significance and take a lead among fish-farming nations.

Let"s hope it can raise its game to do just that."

What the report shows

Although analysis of the actual control of sea-lice on Scottish fish-farms is severely hampered by the lack of farm-specific sea lice data, S&TCS has analysed the available data published by the Scottish Government"s own Fish Health Inspectorate, the Scottish Environment Protection Agency and the Scottish Salmon Producers" Organisation covering 2013 to 2015.

This shows that between 2013 and 2015, the number of fish-farming regions failing to keep adult female sea lice numbers below the industry"s voluntary Code of Good Practice (CoGP) threshold is on an upward trend.

The industry-wide problem with sea lice appears to be increasing and is certainly not under control.

As the graph below illustrates, the proportion of the total Scottish farmed salmon production in regions over CoGP thresholds shows a similar upward trend, with regions representing almost 60% of Scottish production being over the CoGP threshold of 0.5 adult female lice per fish in May 2015, at the peak of the wild smolt migration run, when wild fish are at their most vulnerable to infestation with sea lice emanating from fish-farms.

Mr Graham-Stewart continued:

"What is concerning is that the data shows that in much of the production of farmed salmon in Scotland and the Western Isles, adult female sea lice counts per farmed fish have risen often to levels well above industry thresholds, where they often remain for many months.

This is a disaster for wild salmon and sea trout.

Nor does the use of wrasse as cleaner fish on some of the fish farms appear to be the panacea it is often held up to be. A number of regions appear to have experienced sea lice numbers persistently above CoGP thresholds, despite the use of wrasse as cleaner fish".

Recommendations for Scottish Government action

The S&TCS report makes a number of recommendations for action from the Scottish Government, including:

  • requiring the immediate publication of farm-specific sea-lice data;
  • tougher regulation and inspection of fish farms;
  • a Government-led review of the current voluntary code of practice, replacing it with a statutory code, as provided for in the Aquaculture Act 2007;
  • introducing an "upper-tier" sea lice threshold above which an immediate cull or harvest of farmed fish is required by law;
  • amending Scottish legislation to protect wild fish from potential damage caused by fish-farms, with inspectors given a legal duty to control sea lice on fish-farms in order to protect wild fish populations;
  • ordering the closure and / or relocation or persistently poorly-performing fish farms; and
  • signalling that the fish farming industry will be required eventually to move to full closed containment, to ensure a complete "biological separation" of wild and farmed fish.

Andrew Graham-Stewart, Director of S&TCS, concluded:

"Next year, Scotland will be in the spotlight.

At the Special Session at the 2016 Annual Meeting of North Atlantic Salmon Conservation Organisation next June, the Scottish Government will be required to justify to the Norwegians, Irish, Canadians and others, the actions it has taken to avoid the impacts of aquaculture on wild salmonid populations and to ensure both the recovery and conservation of the wild salmonid stocks of Scotland.

Action is required now, if Scotland is to be able to live up to its international obligations".


1) In 2015, the Scottish Government published its classification of the country"s rivers" salmon populations. This places all the rivers in the west Highlands and inner Hebrides in the worst-performing category, with wild salmon stocks not reaching their conservation limits, which are a measure of the overall health of the population. No river within salmon farming"s heartland of the west Highlands and inner Hebrides has, according to the Scottish Government"s own scientists, a sufficient stock of wild salmon.

Sea trout populations too are under considerable threat with the number of sea trout returning to Scottish rivers in decline, with the 2013 rod catch being the lowest on record according to Marine Scotland Science. The west Highlands has in recent decades lost all of its formerly prolific loch fisheries for sea trout.

2) The negative impact of sea lice, produced in huge numbers by fish farms, on wild salmonids (salmon and sea trout) is widely accepted by fisheries scientists including the Scottish Government's own Marine Scotland Science.

See Marine Scotland Science (2013) Summary of information relating to impacts of sea lice from fish farms on Scottish sea trout and salmon – 4th April 2013 – available at

A paper published in 2013 by a group of fisheries experts from Norway, Canada and Scotland re-analyses data from various Irish studies and shows that the impact of sea lice on wild salmon causes a very high loss (34%) of those returning to Irish rivers – see M Krkosek, C W Revie, B Finstad and C D Todd (2013) Comment on Jackson et al. Impact of Lepeophtheirus salmonis infestations on migrating Atlantic salmon, Salmo salar L., smolts at eight locations in Ireland with an analysis of lice-induced marine mortality – Journal of Fish Diseases.

Most importantly, there is clear evidence that both wild salmon and sea trout are in decline in Scotland's 'aquaculture zone', whereas, generally, populations have stabilized on the east and north coasts where there is no fish-farming see

This year, fisheries scientists from Norway, Scotland and Ireland reviewed over 300 scientific publications on the damaging effects of sea lice on sea trout stocks in salmon farming areas, and examined the effect of sea lice on salmon, concluding that sea lice have a potential significant and detrimental effect on marine survival of Atlantic salmon with potentially 12-29% fewer salmon spawning in salmon farming areas.

The researchers concluded that:

"Salmon lice in intensively farmed areas have negatively impacted wild sea trout populations by reducing growth and increasing marine mortality. Quantification of these impacts remains a challenge, although population-level effects have been quantified in Atlantic salmon by comparing the survival of chemically protected fish with control groups, which are relevant also for sea trout. Mortality attributable to salmon lice can lead to an average of 12?29% fewer salmon spawners.

Reduced growth and increased mortality will reduce the benefits of marine migration for sea trout, and may also result in selection against anadromy in areas with high lice levels. Salmon lice-induced effects on sea trout populations may also extend to altered genetic composition and reduced diversity, and possibly to the local loss of sea trout, and establishment of exclusively freshwater resident populations."

See Thorstad , E , Todd , C D , Uglem , I , Bjorn , P A , Gargan , P , Vollset , K , Halttunen , E , Kalas , S , Berg , M & Finstad , B 2015 , ' Effects of salmon lice Lepeophtheirus salmonis on wild sea trout Salmo trutta – a literature review ' Aquaculture Environment Interactions , vol 7 , no. 2 , pp. 91-113 . (at

Read open letter to Dr Aileen McLeod (Minister for Environment, Climate Change and Land Reform) from S&TCS.