reLAKSation no 840

Hark the Herald: Another week, another attack on the salmon farming industry. Given the amount of relentless press coverage, it would seem that salmon farming is perceived to be the source of major environmental problems in UK waters, yet salmon are extremely intolerant to any pollution or poor water quality so salmon farmers are extremely wary of any actions that might cause issues within the waters they farm.

The latest revelation in the Sunday Herald is that the Scottish Government colluded with the salmon industry to prevent the Scottish Environmental Protection Agency from implementing a ban in 2018 of the anti-lice treatment marketed as Slice, containing the active ingredient emamectin. Talk of a ban resulted from new scientific evidence suggesting that emamectin is also damaging other wildlife in Scottish sea lochs.

This latest attack on salmon farming comes after the release of emails between SEPA, the Scottish Government and the salmon farming industry. This has prompted critics of the salmon industry to accuse the Government of a cover-up and misleading the public. One campaigner has said that SEPA has been ‘lobotomised’ by civil servants acting on behalf of the industry.

In its defence, SEPA has said that it has moved to tighten up conditions on the use of Slice and is launching a public consultation on strengthening the conditions of use including a review of the environmental quality standard of emamectin, to help inform on future regulation of all treatments used in the marine environment.

Salmon farming has had a negative environmental image for many years. It can be traced back to a campaign launched in the US aimed at persuading consumers to avoid imported farmed salmon and to choose American wild salmon instead. The campaign, run by some of the largest US charitable foundations paid tens of millions of dollars to 30 environmental organisations to spread negative messages about farmed salmon and to push wild salmon from Alaska. Ultimately, the campaign failed in the US, but the environmental groups began to believe their own propaganda, and this has spread from the US to Europe and continues to dominate environmental policies about salmon farming to this day. That’s not to say that the salmon farming industry is perfect but everything humankind does has some impact on the environment.

Sea lice are an ongoing problem. Sea lice are a natural parasite and have been the subject of complaint for many years mainly from the angling sector, who blame sea lice from salmon farms for declines in wild salmon and sea trout stocks. The Salmon & Trout Association, renamed themselves as Salmon & Trout Conservation to spread their conservation message but they don’t seem sufficiently concerned about the threat to wild salmon to tell their members to stop killing wild salmon for sport. Instead, it is easier to blame others for the declines, including the salmon farming industry. The problem is that the evidence linking salmon farming to a decline in wild salmon stocks is still circumstantial although some ground-breaking research will shortly show that salmon farming is just a scapegoat for much wider problems.

In the case of emamectin, there has been some research suggesting that the active ingredient does have some impact of some other crustaceans in the locality of salmon farms. However, this comes from one unpublished study and it would be unreasonable to expect SEPA to implement a ban based on just this one piece of work.  After all, there have been hundreds of research paper about the effects of sea lice and there is still no firm agreement as to its impact on wild fish. Slice is a licensed product for which the manufacturer has had to demonstrate its environmental credentials. It must be used according to its license and its local approvals. It is right that SEPA should review emamectin use, just as it should review all inputs into salmon farming, before deciding if any action is required. It is also right that they should discuss the future of emamectin with all those who are involved in its use. SEPA have extended these discussions to include a public consultation.

At the same, time, the salmon industry has been keen to find solutions to sea lice that do not involve any medicinal treatment. The use of cleaner fish and mechanical removal have increased significantly and other novel methods for keeping lice at bay are under evaluation. It is already anticipated that emamectin use will diminish in future and this was always on the cards before these latest revelations. Unfortunately, the small number of very vocal critics are not interested in solutions but rather prefer to pick up on any issue they think might undermine the image of farmed salmon to consumers. SEPA should not be making knee jerk decisions based on the views of this vocal minority and the press coverage they generate. Nor should they be criticised for taking a measured view.

It is worth considering the impacts of salmon farming against the use of diesel cars. It is estimated the 7.500 people in the UK and 38,000 people worldwide die prematurely due to the use of diesel engines. No Government has instituted an immediate total ban on diesel cars preferring to look how they can be phased out. The salmon industry is already looking to reduce its use of emamectin regardless of any alleged impacts on the environment. This is because they have found better ways of dealing with lice. However, an immediate ban is impractical just as it would be impractical to ban diesel cars overnight.


Lice: Anyone reading the national press might believe that salmon farms are riddled with lice. It was therefore interesting to read a tweet from the West Sutherland Fisheries Trust. They simply say – “Out for a morning trip to the fish farm cages to see routine monitoring and check for sea lice. Good to see such large lice free fish and a wee lump sucker for good measure.” Unfortunately, there are some critics who wish to portray a different picture.


Selective selection: Intrafish reports that a group of researchers from NINA, IMR, NTNU, the Sea Lice Centre and Pathogen have published a report in Nature – Scientific Reports, which states that salmon farms are the main source for the spread of sea lice. This is the conclusion of a study looking at a gene mutation in sea lice that makes it resistant to organophosphates. They found that sea lice on wild fish caught in areas where fish farms operate also have this mutation. They therefore concluded that the only good explanation is that the mutation must have spread to wild fish from salmon farms. Given that the sea lice infectious stages are spread in the water by currents and winds, this is not at all surprising.

The research group say that it will now not be possible to get rid of this problem and that reducing the use of the treatments will not bring about a return to lice that are sensitive to the treatments. This might not happen immediately, but it is possible. Hopefully, the move to non-medicinal treatments will continue to accelerate so that such mutations will not be an issue.

Whilst this scientific paper concerned selection of a mutation in sea lice, we, at Callander McDowell, were more interested in its list of references. We think that this illustrates another form of selection; one which governs the thrust of sea lice research.

Sea lice research is undertaken by a small group of researchers, mainly based in Norway, but also in Scotland and Ireland as well as in North America. Inevitably, there is a great deal of interaction and collaboration and this helps re-enforce current views.

We, at Callander McDowell, have bene taking a new look at sea lice and the interactions with wild fish. We began again at the time when the first epizootics of sea lice were initially identified and have tried to uncover the thinking at that time.  As we pass through history, what has become more apparent to us is that as perceptions have developed this has been reflected in the thinking and a reliance on a choice of papers that would reflect that thinking. This is a type of selection in which papers and studies that do not fit in with the current thinking are ignored. This doesn’t mean the information in these papers is wrong, they simply do not support the established view and hence they disappear from sight. Inevitably, the salmon industry is left with a scientific picture of sea lice that has been distorted by active selection over many years. The references in this latest paper would not be quoted in our own work because we have followed a different pathway. Whether we will be accused of similar selection remains to be seen.

We recently came across a paper from 2004 by Dr Alasdair McVicar entitled Management actions in relation to the controversy about sea lice infections in fish farms as a hazard to wild salmonid populations. The paper appeared in Aquaculture Research Vol 35.

Alasdair used to work for the fish disease section at the Government Marine Laboratory in Aberdeen, but he may just have retired when he gave this paper at Sea Lice 2003.

Dr McVicar makes many points which are still relevant. These include:

-Confidence in a conclusion depends on the strength of supportive information available and not on the frequency of its repetition.

-There is a common failure to recognise that correlation between two sets of data does not necessarily indicate a cause-effect relationship and therefore the existence of a hazard.

-It is known that the size of a salmonid fish stock is the result of an interaction of many biological and physical factors and therefore meaningful studies should be multidisciplinary. From a fish disease perspective alone, the focus on sea lice has diverted attention away from other important diseases. For example, there have been over 80 infectious conditions recorded in Atlantic salmon, several of which have known pathogenic potential.

– Although sea lice have been extensively considered in the scientific literature, considerable debate continues to be generated. There have been a series of meetings of international experts over the last seven years making sea lice one of the most intensively reviewed topics in aquatic biology. In 1996, ICES commissioned a special 5-day workshop which was attended by 31 scientists from 6 countries, who could not reach agreement on some basic issues. It is therefore hardly surprising that non-specialists, the media and the public are confused.

-It is notable that this and other meetings have been able to conclude that that there is a cause-effect relationship between sea lice on farms and variations in wild salmon populations.

-It is accepted that there are serious declines in wild salmonid populations in the general areas of salmon farming in Scotland, Ireland and Norway coinciding with high levels of lice infection in wild salmon populations. However, significant declines in stocks have also occurred in areas where there is no salmon in sea water.

-Official statistics for catches of sea trout are available in Scotland since 1952 and it is apparent that the decline of the stock has occurred at a roughly constant rate for all that period. Approximately, 50% of the stocks that was present in the 1950’s had disappeared by 1980 prior to the main development of salmon farming. Clearly, salmon farming cannot be implicated in the widespread decline in these salmonid populations. If there had been an effect on farms in the last 20 years, this would be superimposed on the influence of these other factors that are still operating and relative contribution difficult to apportion.

-There is a considerable body of evidence and widespread international agreement that salmon lice are pathogenic and dangerous to farmed and wild salmonids. However, many discussions on this topic often ignore basic epizootic principles and make major leaps of faith from superficial findings in small numbers of fish to a whole wild fish population.

-If some fish from a wild fish population are compromised by lice from salmon farms this does not necessarily translate on a pro rata basis to the whole wild population. The popular perception that every fish in each life cycle stage is important to the size of the spawning stock is not supported by classic fish stock assessments studies. One study concluded that the majority of fish in the juvenile phase were destined to die and whether disease hastens the process may not influence the outcome. It was concluded that the availability of food was a main limiting factor in the early stages of development.

We, at Callander McDowell, are not surprised that this paper is now rarely quoted even though it is just as relevant today as it was nearly fourteen years ago.


Down from the lice: Kyst reported from the recent Sustainable Growth Summit in Bergen where one of the speaksers was Ole Erik Lerøy, Chairman of Marine Harvest Group. Mr Lerøy told the audience that sea lice were one of the main reasons limiting production growth. However, he still believes that a solution will be found to control lice soon. He said that there are serval initiatives underway hoping to seek a solution. Mr Lerøy said that sea lice were the elephant in the room and it makes the salmon industry vulnerable to everything else.

We, at Callander McDowell, remain puzzled as to why feeding the fish from the bottom of the cage has never been thoroughly investigated as a solution. It makes sense that if surface feeding can be avoided then the fish will not be attracted up to the surface layers where the infectious lice stages congregate.

We ran a simple trial back in 1994 and the results were encouraging. There was no interest to take it further at the time but now lice are such an issue, all options are surely worth consideration.