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reLAKSation no 885

Waiting and waiting: There has been a lot of conjecture about the REC Committee report with some observers arguing that the Committee should discuss the report in public, whilst others are giving hints of leaks. We notice that all this conjecture comes from the anti-salmon farming lobby.

In our opinion, everyone should simply sit back and allow the Committee to continue their deliberations without any distraction. The fact that the discussions are taking so long is just an indication that the issues are being given full consideration.

To this end, it is disappointing that Mark Ruskell MSP has placed a motion before the Parliament. We think he could have waited until the REC Committee report is published so he can see what they recommend before taking this action.

Mark Ruskell is the Green’s environment spokesman and it was interesting to see that despite an active Twitter account, he has made no comment about the BBC TV’s programme – Drowning in Plastic. This was the TV special about the state of plastic pollution in the world’s seas and oceans including both large pieces and microplastic. It was only a few months ago that a study of mussels sold in the UK found they all contained some form of plastic contamination. The plastic tide reaches even to Scotland which is surely why Mr Ruskell should be calling for stricter controls on plastic, improved recycling and encouraging innovative ways to deal with this issue that might help communities throughout the world. He should be demanding immediate action by the Scottish Parliament rather than his unnatural focus on aquaculture.


Shot in the foot: The latest issue of Shooting Times magazine includes a feature about Don Staniford. It reports that Don has formed an unlikely alliance with those from Field Sports against salmon farming. As we know Mr Staniford has repeatedly raised the issue of seals and the fact sometimes seals have to be shot as a last resort, which he says must stop.

Yet, here is Mr Staniford featured in the magazine for shooting enthusiasts, who kill animals for sport and pleasure. The Shooting Times says that Mr Staniford is now working alongside a strong advocate of shooting – Andy Richardson. It seems that Mr Richardson is keen to see seals returned to general licence so that their numbers can be controlled.

It seems that seals only matter to Mr Staniford if they are killed to protect salmon farms. He appears equally unconcerned about the huge numbers of pheasant, grouse, snipe, pigeons, partridges, geese, woodcock, deer, mountain hares and who knows what else are shot for the pleasure of his new friends.


Second look:  We previously mentioned that Marine Scotland have updated their ‘Summary of Science’ on the Scottish Government website. This is the science relating to impacts of salmon lice from fish farms on wild Scottish sea trout and salmon.

We expected this update because Marine Scotland had written to us that:

We have therefore reached a consensus based on international research data that there is a relationship between salmon farming and wild migratory salmonids.

We were keen to see which international research has influenced their decision. Certainly, the list of scientific papers cited has increased but a quick perusal of the new text left us unsure of what new research proves the relationship between sea lice from salmon farms and wild fish. We therefore compared the text of the 2018 summary with that of the 2016 version. The previous version was not dated but as it includes a reference to a paper published in 2016, it is safe to assume that the previous summary was written just two years ago.

A comparison of the two summaries highlights some interesting points. The first is that whilst new scientific papers have been included, one has been removed. This is the paper by Morton et al. 2011. This is a paper from Alexandra Morton, the Canadian based anti-salmon farm campaigner.

The new summary includes fourteen references to fourteen additional scientific papers. What is of most interest is that half of them are papers that were published before 2016 and therefore could have been included in the previous summary. None of these add anything new to the debate.

Of the remaining seven papers, only one brings a new finding to the debate. The remainder are simply added confirmation of existing conclusions. Some of these papers have already been discussed in past issues of reLAKSation as in our opinion, they do not support the arguments been put forward by Marine Scotland. As they are simply confirmatory works, we won’t discuss them at this time.

The one paper of interest appears in the section of the summary that asks whether salmon lice have an effect on wild fish at population level. The paper is by Shephard and Gargan (2017). The summary states:

Shephard & Gargan (2017) estimated that returns of salmon after one year at sea were 50% lower in the river Errif, Ireland, in years following high sea lice levels on nearby salmon farms during smolt migration than in other years.  A declining trend in marine survival of salmon remained when the predicted impact of sea lice was removed, suggesting multiple factors affecting survival. The authors considered that the reduction in returning salmon numbers due to sea lice could affect the viability of the salmon population in the long term.’

After this paper was published, the Irish Times published an editorial that said that the Shephard & Gargan paper envisages an ‘extinction vortex’ for wild fish in salmon farming areas. The editorial stated:

Any doubt about the devastating impact sea lice levels can have on wild salmon and sea trout stocks will have been swept away by a report from Inland Fisheries Ireland that envisages an “extinction vortex” in salmon farming areas in the absence of remedial action. Published by Samuel Shephard and Patrick Gargan and based on 26 years of statistics from the Erriff River that flows into Killary harbour on the Mayo/Galway border, the report finds that elevated lice levels have reduced annual returns of wild fish by some 50 per cent. Rising sea temperatures and other factors are also limiting survival rates but salmon farms are the biggest threat. Initially, it was thought that lice infestation on salmon farms only affected sea trout stocks. But falling wild salmon numbers, in spite of a ban on drift netting, tells a different story.

Interestingly a different view was expressed by Jon Gibb, from the River Lochy, who wrote in Fish Farmer in 2017 that:

Several rivers in the Loch Linnhe region are currently experiencing the worst salmon run for many years (after a near record MSW salmon run last year) and the papers have been quick to blame fish farms. But tracing back to May 2015, when this year’s smolt cohort went to sea, one finds that local farms had some of the lowest lice levels ever recorded. Something doesn’t add up.

Furthermore, over the last three years, Marine Scotland Science has been trapping thousands of migrating wild salmon smolts from two tributaries of the river Lochy and treating half against sea lice infestation and leaving half untreated. Far from the treated group outperforming the other (as might be expected if sea lice are the issue) not a single fish from either group has yet to be recorded back to the river. This suggest that something far larger and more sinister is at play than simply sea lice from fish farms.

Even the latest peer reviewed paper currently being used extensively by fiery wild fish campaign groups (Shepard & Gargan 2017) would agree. It concludes that while fish farming impacts may have reduced individual adult returns on the studied river, ‘salmon lice impact does not explain a declining trend in this population’.

Whilst Marine Scotland Science’s interpretation of the paper as it is appears in the science summary is one way of expressing this work, we prefer to look at the abstract summary as written by the authors (the bold highlights are ours).

ABSTRACT: Atlantic salmon Salmo salar has shown declines in abundance associated with reduced survival during marine life stages. Key impacts on survival may include a changing ocean environment and salmon louse Lepeophtheirus salmonis infestation from aquaculture. A 26 yr record from the Erriff River (Western Ireland) was used to evaluate the contribution of sea lice from salmon aquaculture to declining returns of wild 1 sea-winter (1SW) salmon. Statistical models suggested that returns were >50% lower in years following high lice levels on nearby salmon farms during the smolt out-migration. The long-term impact of salmon lice was explored by applying predicted annual loss rates as a multiplier to observed 1SW salmon returns. This produced a ‘lice-corrected’ return time series, i.e. an estimate of how returns might have looked in the absence of a serious aquaculture lice impact. The corrected time series was adjusted to account for some reduction in recruitment due to lost spawners. Comparing observed and lice-corrected time series suggested that salmon lice have strongly reduced annual returns of 1SW Erriff salmon, but that the salmon lice impact does not explain a declining trend in this population.

We would therefore conclude that whilst this paper might suggest that sea lice might have an impact on wild salmon populations, the authors do stress that sea lice are not the real issue for wild salmon populations. This view seems to agree with that of Jackson et al (2013) who says that sea lice are a minor component of wild fish mortality.

Having looked closely at the research, we are having some difficulty in understanding how the 2015 summary remains inconclusive whilst the 2018 update provides sufficient extra evidence to enable Marine Scotland Science to conclude that there is a relationship between sea lice from salmon farming and wild fish.

What makes their conclusion even more difficult to accept are the scientific papers that they have failed to include. We would like to provide one example and that is the paper from Emily Nelson from the Canadian Government’s Department of Fisheries & Oceans and others. The paper describes the distribution of sea lice in and around farms in the Bay of Fundy. The paper was first presented at the international conference, Sea Lice 2016, in Ireland. Members of Marine Scotland Science attended the conference so were definitely aware of this paper.

The main finding of this research which was founded on the collection of larval lice from the water using a plankton net, was that whilst they did find examples of high densities of lice within the farm, these high densities dropped away within one hundred metres of the cages. The researchers concluded that if the rate of depletion continued to one kilometre from the cages, then wild fish would have to swim through 1×1010  cubic metres of water to encounter one infectious larvae. This contradicts the view that the waters around salmon farms are a soup of infectious sea lice.

Instead of including reference to this paper, Marine Scotland Science include reference to their own work in the summary. Using mathematical modelling, they estimate that larval sea lice could spread up to 30km from farm cages. It is quite a difference.

We have included the full text of the 2018 Summary of Science update in this commentary. The changes to the 2018 version as compared to that of 2015 are highlighted in bold. Standard bold text represents additions whilst italicised bold text has been removed.



Summary of Science (as curently found on the Scottish Governement website).


Summary of information relating to impacts of salmon lice from fish farms on wild Scottish sea trout and salmon

The salmon louse is a native parasite that infests both farmed and wild salmonids to the potential detriment of aquaculture and angling interests (Torrissen et al. 2013). Recent reviews have considered information concerning interactions between salmon farms and wild salmonids (e.g. Taranger et al. 2015; Thorstad et al. 2015, Vollset et al.2016). Here, the evidence available to assess the likelihood and scale of impact of salmon lice from salmon farms on Scottish wild salmonids is summarised. The aim is not to repeat existing reviews but to focus on key issues relevant to locating fish farms in the Scottish coastal zone.

Are salmon farms a significant source of salmon lice?

Yes, salmon farms have been shown to be a more important contributor than wild fish to the total numbers of salmon lice in the environment (Morton et al 2011. Butler 2002; Penston & Davies 2009).

Is there an association between levels of lice on salmon farms and in the surrounding environment?

Yes, environmental larval lice concentrations relate to local farm lice loads (McKibben & Hay 2004; Penston & Davies 2009; Harte et al. 2017).  The distribution of lice depends on hydrodynamic conditions and so the relationship may be highly variable at any specific location (Salama et al. 2013).

Is there an association between levels of lice on salmon farms and on wild sea trout?

Yes, analysis of data from Norway highlights a significant relationship between infection potential from farms and settlement on wild sea trout (Hellend et al. 2015).   Data collected throughout the west coast of Scotland showed that the proportion of individual sea trout with sea louse burdens above a level known to cause physiological stress increased with the mean weight of salmon on the nearest fish farm (a measure of where they are in their production cycle), and decreased with distance from that farm (Middlemas et al. 2013). A similar pattern was noted in a study of farms in a loch on the Isle of Skye (Moore et al. 2018), and analysis of Irish and Scottish sea trout data (Shepherd et al. 2016).

Is there an effect of salmon lice on wild sea trout at the individual level?

Individual wild sea trout sampled on the west coast of Scotland have been shown to have salmon louse infestations above a level known to cause physiological harm (Middlemas et al. 2010, 2013).  Studies in Norway have also indicated changes in behaviour of sea trout, with them spending more time in freshwater environments when sea lice infestation levels were high (Halttunen et al. 2018).

Is there evidence of an effect of salmon lice on wild sea trout at the population level?

No such direct evidence for a Scottish situation has been published.

An experiment in Norway, comparing survival of anti-lice treated sea trout smolts with non-treated smolts, indicated an increased survival rate of 3.41% over 1.76% , this is about a 50% reduction in the stock returning to the river, suggesting that salmon lice can negatively affect sea trout populations (Skaala et al. 2014).

Is there an association between levels of lice on salmon farms and on wild salmon?

No information is available for wild salmon in Scotland. An association between lice levels on  farms with louse settlement on hatchery reared salmon held short distances away has been noted. However it is inconclusive as to whether it is possible to estimate infection pressure from salmon farms at specific points in time (Pert et al. 2014).  In Scotland and Norway, salmon lice abundance on farmed fish is lowest in early spring and peaks during autumn (Jansen et al. 2012; Murray 2016a). This seasonal change in lice infestation levels is comparable to those observed on wild salmonids in Norway (Serra-Llinares et al. 2014).

Is there an effect of salmon lice on wild salmon at the individual level?

No information is available for Scotland.

In Norway, an experiment examining returning wild and hatchery reared salmon that had been treated with an anti-lice medicine indicated that non treated salmon returning after one winter at sea tended to be smaller than the treated fish (Skilbrei et al. 2013).

Is there an effect of salmon lice on wild salmon at the population level?

No empirical information exists on impacts of lice on wild populations of salmon in Scotland. Declines in catches of wild salmon have been steeper on the Scottish west coast than elsewhere in Scotland and Norway (Vøllestad et al. 2009) although the authors stressed that this did not prove a causative link with aquaculture. Ford & Myers (2008) compared indices of salmon abundance on the east and west coasts of Scotland together with farm production data. They found a reduction in the catches and counts of salmon on the west coast correlating with increased production of farmed salmon. In addition Butler & Watt (2003) showed that rivers with farms had significantly lower abundances of juvenile salmon than those without farms.

Shephard & Gargan (2017) estimated that returns of salmon after one year at sea were 50% lower in the river Errif, Ireland, in years following high sea lice levels on nearby salmon farms during smolt migration than in other years.  A declining trend in marine survival of salmon remained when the predicted impact of sea lice was removed, suggesting multiple factors affecting survival. The authors considered that the reduction in returning salmon numbers due to sea lice could affect the viability of the salmon population in the long term.

Experiments comparing survival of smolts treated or untreated with anti-sea lice medicines have shown that sea lice adversely affect certain salmon populations in Norway and Ireland (e.g. Vollset et al. 2014; 2016). There is a great deal of year-to-year and site-to-site variability in the magnitude of such impacts and the reduction in numbers of returning salmon associated with lice infestations is in the range of 0-39% (Jackson et al. 2011; Krkošek et al. 2013; Skilbrei et al.2013; Vollset et al. 2016). A meta-analysis of all available Norwegian studies showed anti-lice treatment increased returns of adult salmon by an average of 18% (Vollset et al. 2016).  It is not clear in these studies how much of the estimated impact of lice is due to baseline natural levels in the environment and how much is associated with an additional effect caused by salmon aquaculture.  No information exists on impacts of lice on wild salmon populations in Scotland, However The estimated mean effect size of lice seen in other countries is of a similar magnitude to the difference between the aquaculture zone and east coast of Scotland in the reduction in abundance of wild salmon determined using data from fish counters (Ford & Myers 2008). It is not clear how much of this regional variation may be due to factors besides aquaculture.

Over what distance do farms influence environmental lice levels?

Salmon lice transport modelling in a Scottish system reports that >97.5% of sea lice are transported within 15 km of fish farms (Salama et al. 2016).  However, site-specific factors, such as prevailing wind and currents, and local topography can have a large impact on the direction and distance of lice dispersal (Salama et al. 2013, 2018; Adams et al. 2012).

Middlemas et al. (2013) found a significant relationship between sea lice infestations on sea trout and the distance to the nearest salmon farm. Infestation levels were highest when sea trout were sampled near to a salmon farm and reduced as the distance to the nearest farm increased. There is considerable scatter around the general relationship found by Middlemas et al. (2013) which likely reflects unknown site-specific factors and unaccounted fish movements.

Do we understand the dispersal patterns of sea trout and salmon?

Salmon smolts depart rapidly from home rivers but there is no knowledge of their subsequent distribution in relation to the Scottish coast. In general sea trout remain near shore for their first two months at sea and then disperse more widely. There is no understanding of the scale of sea trout dispersal or whether it is uniform in direction relative to the home river (Middlemas et al. 2009, Malcolm et al. 2010).

Can fish farmers reduce numbers of lice released into the environment?

There are a number of control strategies that farms can use to reduce salmon lice infestation. These include chemical, physical and biological methods. Historically chemical treatments have been favoured, reduced efficacy of treatments has been documented (Lees et al. 2008; Aaen et al. 2015) as has increased frequency of treatment (Murray 2016b). This has encouraged alternative control methods to be investigated. One of these is the use of cleaner fish, such as wrasse, as a biological control. These fish are introduced into pens to directly eat lice off salmon (Leclercq et al. 2013). This adds an additional method to control sea lice as part of integrated pest management; other methods include functional feeds (Jensen et al. 2015), cage design to control salmon swimming depth or source of cage intake water (Stein et al. 2016; Nilsen et al. 2017), thermal removal of sea lice (Grøntvedt et al. 2015), freshwater treatment (Powell et al. 2015) and selective breeding (Gharbi et al. 2015).


Salmon aquaculture can result in elevated numbers of sea lice in open water and hence is likely to increase the infestation potential on wild salmonids.  This in turn could have an adverse effect on populations of wild salmonids in some circumstances. The magnitude of any such impact in relation to overall mortality levels is not known for Scotland.  However Concerns that there may be a significant impact of aquaculture have been were raised initially due to declines in catches of both salmon and sea trout on the Scottish west coast. There is scientific evidence that individual Scottish sea trout can experience physiologically detrimental burdens of salmon lice in areas with salmon aquaculture but the effects on populations in different areas is not known. International scientific evidence from Norway and Ireland indicates that early protection against salmon lice parasitism results in reduced absolute marine mortality, increasing recapture rates of experimental salmon and reduces the time spent at sea,  indicating that salmon lice can influence the population status of wild salmon.  Marine Scotland Science  is completing a pilot project to investiagte feasibility of addressing this data gap for Scottish salmon. Further information on this project can be found on the SARF website. The interim findings, combined with other data from rod catches and counters, suggest that survival of wild salmon at sea on the west coast of Scotland is too low for the approach at present to be expanded into a network of experimental sites.



Cupcake week:  By the time you read this reLAKSation, the UK will have celebrated National Cupcake Week (September 14th).  This is according to a comprehensive list of National Food Days in the UK that is posted on the food blogging website It is surprising what foods us Brits are prepared to celebrate. The list is a never-ending surprise however the biggest surprise is the absence of Seafood Week 2018, which actually began on Friday.

According to Seafish, this year’s Seafood Week will consist of eight themes; one for each day of the week-long celebration. These themes revolve around specific species including: ‘Memorable mackerel’, ‘Crazy about crab’, ‘Mad about mussels’, ‘Fish and Chip fanatic’, ‘Sensational scallops’, ‘Loving langoustines’, ‘Pick up some plaice’ and ending the week with ‘It’s time for tuna’.

The latest report on the state of fisheries and aquaculture from the FAO states that 47% of fish and seafood consumed is now farmed. The high proportion of farmed fish and seafood is not just a FAO statistic but is reflected in the offerings in many UK supermarkets. Fish counters are dominated by farmed fish such as salmon, sea bass, sea bream, Rainbow trout, and basa. Wild caught fish include cod, haddock, tuna, monkfish, plaice, lemon sole, hake, mackerel and sardines. Of course, there are other species available, but their availability depends on the store and the counter. Some counters also offer shellfish such as mussels and large prawns, both of which are farmed.

Farmed might now make up for nearly half the fish and seafood on the fish counter but it seems Seafood Week is mainly about the wild. The only day devoted to a farmed fish or seafood is ‘Mad about mussels.’ Seafood Week therefore doesn’t really seem to reflect the makeup of the fish and seafood market in the UK. Part of the reason is historical. We seem to remember that Seafish was established through the amalgamation of the Herring Board and the White Fish Board, under the terms of the Fisheries Act 1981. The intention was to include all fish and seafood, but one member of the House of Lords objected as he didn’t want salmon to be included in their remit and consequently, Seafish are now not involved in the marketing of salmon. We also heard that the then Scottish Salmon Board also objected to joint promotion. Whichever one is correct means that salmon are thus effectively excluded from the Seafood Week campaign. This is a shame because salmon is the UK’s favourite fish.

In addition, most of the other popular farmed species, such as sea bass, sea bream, basa and warm-water prawns are not farmed in the UK and thus may not be considered part of the promotion of the UK fish industry. However, tuna, which is featured in the forthcoming promotion, is not a UK species. According to the UK Government, Seafish supports the seafood industry to work for a sustainable profitable future. It offers regulatory guidance and services to all parts of the seafood industry including catching and aquaculture, processors, importers, exporters and distributors of seafood as well as restaurants and retailers. Thus, as an imported species tuna would earn its place, especially as consumer demand ensures that sufficient volumes are imported to help contribute to the industry coffers.

We are sure that the promoters of National Cupcake Week have little problem of encouraging consumers to eat a cupcake whatever day it is. By comparison, Seafood Week presents many challenges. In theory, the idea of promoting a different species on each day offers a range of choices. However, anyone spending any time in supermarkets will see that few shoppers opt to buy fish during an average week. Prompted by the tradition of ‘Fish on Friday’, many fish counters seem to do the bulk of their business on a Thursday and Friday and possibly Saturday too but for the rest of the week, fish counters are largely a no-go zone. It will be a hard sell to persuade shoppers to buy crab on a Saturday, mussels on a Sunday, scallops on a Tuesday and langoustines on a Wednesday. The Monday of the promotion is dedicated to fish and chips, but as Friday is a big day for fish and chips and it might have made more sense to build on this strength.

Of course, there is more to Seafood Week than retail sales as Seafish encourage restaurants and fish and chip shops to get involved. We have never been to a restaurant during Seafood Week to see how they promote fish dishes, but we hope to do so this year. We just hope that there is salmon on the menu.