Big Mac: We have previously written about the theory put forward by Jens Christian Holst that mackerel stocks are significantly much larger than estimated and these fish are not only competing with migrating salmon smolts for food but also likely to be predating on them.

Last week, both the Times newspaper and the Sunday Times published articles about Dr Holst’s theory. He says that the population of mackerel has exploded to at least 57 billion fish, which is six times the 9 billion fish estimated by the International Council for the exploration of the Sea (ICES).  EU Governments seek advice from ICES when setting the fishing quotas for mackerel.

In a new review, Dr Holst says that there is strong evidence that the northeast mackerel stocks have grown totally out of proportion due to gross underestimation and cautious fishing quotas that has led to underfishing. Dr Holst says that his theory has been hard to sell because it challenges the widely held notion that sea lice and escaped farmed salmon are the biggest threat to wild salmon.

The Scottish Government told the Sunday Times that ‘The concerning decline in wild salmon numbers is due to a complex range of factors including pressures on the marine environment. We recently announced a package of investment to help qualify and mitigate potential pressures on salmon stocks and will continue to engage with and support the sector.’

However, the Sunday Times suggested that the Scottish Government’s £700,000 investment to identify the causes of a decline in wild salmon stocks including the effects of aquaculture, hydro and illegal poaching, could be misguided.

Certainly, the impression we get from people we have spoken to is a belief that if mackerel stocks were so high then ICES would know about it and thus this theory should be considered with caution. This is despite the fact that a new survey conducted by ICES late year suggested that stocks were now at a record high of 10.3 million tonnes, even though this is still well short of Dr Holst’s estimation.

Although Dr Holt’s review has been the subject of much Twitter activity, the only written comment appears to come from the Atlantic Salmon Trust on their Facebook page ( They mention that they had invited Dr Holst to speak at a meeting in 2011 when he was still working at Norway’s Institute of Marine Research. The AST say that following on from their meeting, they had hoped to see some experimentation to test the hypothesis and the subsequent publication of a paper in the scientific literature. They say that they are unaware that this happened. This is presumably because Dr Holst and IMR parted company.

The AST say that their Honorary Scientific Advisory Panel have discussed the hypothesis and are unanimously of the view that in order to assess its merits, it needed to be developed and tested through the normal research channels. They have invited Dr Holst to contribute to their ‘Likely Suspects Framework’ and have said that it is important that the hypothesis is published as a scientific paper and submitted to ICES for appraisal.

We, at Callander McDowell are interested to see that at least one member of the AST’s Scientific panel has produced a hypothesis about the impacts of aquaculture on wild fish which has not been tested in the scientific literature, yet seems to have been widely accepted as proven. Meanwhile, the AST are spending £1 million on a tracking project even though the problems for wild salmon appear to occur after the fish have left the coastal waters, which are the limit of the AST’s investigations. We might be more impressed if the AST were to divert some of their funding towards researching the issues for wild salmon out on the high seas.

Dr Holst is now an independent researcher and we would imagine the demands for further research are well beyond his means. The AST are much better placed than Dr Holst to initiate the sort of collaborative research that this theory demands. In our view, Dr Holst has not only come up with the best explanation as to what might be happening to wild salmon; It is the only explanation. As we have regularly pointed out, it is easier for some to blame aquaculture for the decline in wild salmon, than actually address issues such as competition and predation from mackerel stocks.

It would therefore now seem that there is something of an impasse with an expectation of further research yet a lack of resources to undertake such work. We might therefore expect Dr Holst’s theory to be pushed aside in favour of more accessible research as to what happens to wild fish in Scotland’s rivers and near seas. However, this week, IntrafIsh published an article detailing a report published in Fiskeribladet in Norway.

The Intrafish article is entitled ‘The researchers do not believe in their own mackerel research’. This suggests that research showed a mackerel stocks of 2015 million tonnes in 2016 whilst the actual stock was set at 3.1 million tonnes when the fishing quotas were fixed.

The big question is why is there such a discrepancy? After all, IMR employs skilled scientists who regularly publish their work in the scientific literature. A significant amount of the work on the impact of sea lice on wild salmon comes from the same institution.

Stock assessments are made using a variety of parameters but one of the most influential is tagging and recapture. This has its origin in Norway and was driven through the work of Norwegian fishermen who returned tagged fish. A tagging programme was initiated in 1969 using steel tags and this ran until 2007. The last three years of this programme involved a change of tagging method to eliminate some of the mortality caused by actually tagging the fish.

We are not clear as to the reasons why the tagging programme using steel tags came to an end, but the tagging programme was reinstated in 2011 using electronic tags. As more data became available, researchers have become increasingly concerned about a conflict in the data collected using steel tags and that from the new electronic tags. It seems that that the fishing mortality from steel tag research was around 62% whilst the electronic tags suggested a mortality of 92%. This meant a huge discrepancy between the size of the stocks subsequently estimated from the two tagging methods.

Aril Slotte from IMR told Fiskeribladet that it is better to use the new data that they have today, and this is why the stock estimate is so low. Dr Slotte said that he does not have the skills to explain how the data is weighted into a statistical model for the stock assessment, but he said other researchers will provide clarification in time for the ICES meeting later this year.

Meanwhile, Johannes Hamre, a former researcher at IMR said that he had previously conducted an experimental tank trial in which he found that tagging mortality was between 20-25%. At this level, the current stock of mackerel could be as high as 40 million tonnes, which suggests that Dr Holst’s theory might be justified. Dr Hamres told Fiskeribladet that the original method of using steel tags produced reliable results that were reflected in quota recommendations set by ICES.

Clearly, changing the method of stock assessment over the last ten years has impacted greatly on the size of the stock. It may be that the best way to protect wild salmon may not be to invest in more and more research but simply to increase the fishing quota for mackerel. We suspect that an admission that researchers have got it wrong may be slow in coming, but we hope that remedial action may be quicker. Perhaps then the aquaculture industry may be removed from the list of ‘Likely Suspects’. The AST say that they hope to soon publish the conclusions and recommendations of the International Likely Suspects Framework Workshop held last year In Edinburgh. We will be interested to see how much representation the salmon farming industry had at this workshop or whether it was just ‘fait accompli’.


Latest fashion: It seems that the latest fashion for scientific papers is work based on some form of modelling or other. The mackerel stock research previously discussed involves a form of population model that requires, according to Aril Slotte of IMR, complex maths and statistics that even he doesn’t understand. Most of the research that implicates sea lice in the decline of wild salmon stocks is based on statistical models, which are built using assumptions – usually an assumption that sea lice do have a detrimental impact on wild fish stocks.

Now a Scottish Government funded study has identified that the growth of Scottish salmon aquaculture from 1979 to 2016 fits a simple two-phase logistic population model. We wonder where this predilection for using models will lead.

We are not even sure as to what the point or purpose of modelling the growth of the salmon industry is. The paper states that in order to understand the pressures likely to shape the future of Scottish salmon production, the past must be investigated. The authors say that the model is deliberately simple, describing the growth rather than explaining it.  As far as we are concerned, the history of the salmon industry is well documented, so this description adds nothing of consequence. What the paper lacks is the explanation of why the industry grew as it did, but we, at Callander McDowell are more than happy to fill in the gaps. Even with our explanation, we are not convinced that the two -phase model will provide any answers for the future because the Scottish salmon industry has already entered a third phase which the authors of the paper have failed to identify.

The paper describes a fundamental change that affected the salmon farming industry around 1992. Prior to then, the authors describe the industry growth as extensive in nature with the number of farms increasing exponentially (35% per year) whilst productivity per farm increased slowly (11% per year). After 1992, the number of farms fell, but productivity increased.

The authors do not appear to explain what happened in or around 1992, but clearly something did that forced a change on salmon production. We would argue that understanding this event is much more important than simply describing the changes that occurred on farms.  The changes around 1992 involved a fundamental rethink as to how salmon were farmed. Readers of reLAKSation from the early days may remember that we have previously described these events in quite some detail. However, we are happy to reminisce about the days of the salmon Klondike.

The salmon farming industry was born out of an interest to help supplement the harvest of wild fish stocks, but salmon became a species of choice because the large size of the eggs meant that newly hatched fish would take a dry feed from the outset. Marine fish species posed many more challenges. At the same time, there was a market demand for salmon and thus the fish would not require a hard sell to consumers. After the initial difficulties were overcome and it was shown that the fish could be farmed relatively easily, salmon farming became the subject of great interest in the west coast communities. There was a rush to invest in this new form of aquaculture fuelled by the relatively high price of salmon in the London markets. Every fish that could be harvested achieved a premium price for the farmer. Issues such as mortality and feed conversion were not that important since the pioneering companies reaped the rich rewards. These rewards attracted more and more people to the industry and hence production grew rapidly.

Then sometime from 1989 to 1992, the market changed almost overnight. The increased production saturated the existing market for salmon and as a result, the price collapsed. We have previously described this change as a move from being low volume, high margin to an industry of high volumes and low margins.

We have often compared salmon farming to the automotive industry to explain what happened. If Lexus or Jaguar stated to produce their cars in the same numbers as say the Ford Fiesta, they would not command Lexus or Jaguar prices instead, consumers would be looking to pay a price more in line with a mass-produced car. This is what happened to salmon.

Salmon had been perceived as a premium product served at special occasions and top restaurants, but farming made it more widely available. It started to appear on the fish counters in ever greater volume, but this volume had to be reflected in a lower price.

For the farmer, lower prices meant lower margins and to offset the lower returns, farming had to change. This meant production costs had to be reduced, hence better health care management and improved feed conversions, but more importantly production had to increase. Farmers looked to producing more fish at a smaller margin.

Not all farmers liked this new scenario so decided to sell. This meant that the number of farms declined but the remaining farms increased in size as they consolidated their operations.  At the time, we predicted that the future Scottish salmon industry would consist of a handful of salmon farming companies producing much larger quantities of fish. We also said that these companies would become more integrated especially producing consumer ready products.

This has not quite happened as we saw it, and this is because the industry has more recently gone through another change which is linked to the stock market.

Salmon has become a widely available consumer-oriented product so is unlikely to undergo the massive change that we saw in the early nineties. This change is not reversible and therefore is now history. It is unlikely that even a complex model of the events then will help us understand how the industry will develop in the future.

Salmon farming, as with all forms of agriculture is not something that can be conducted in isolation. There are many factors that affect the way production will develop, not least the marketplace. Without the market, the industry has no future at all. We certainly don’t need a model to tell us this.

(The growth of Scottish salmon aquaculture. Murray AG & L A Munro 2018. Aquaculture 496 146-152).


Scots apart: Scotland, it seems, remains an unhealthy place. The Times and Scotsman newspapers report that the Scottish public have largely ignored health advice extolling the importance of eating fresh fruit, vegetables and oily fish. 65% of Scottish adults are overweight and 29% are obese. Consumption of cakes, sweet biscuits and confectionary and other foods that are high in sugar and fat has been constant over the last fifteen years. Although people are knowledgeable about the Five-a-day that relates to the number of portions of fruit and vegetables that should be eaten daily, this knowledge does not translate into changes in dietary behaviour.

Equally, knowledge that consumption of fish can be good for human health has not registered with consumers as overall fish consumption, specially of oily fish, has remained static. Karen Barton of Abertay University who conducted the research said that the situation was much worse in areas classed as deprived. However, she said that even in the least deprived areas, intakes of healthy foods were much lower than recommended.

The Scottish Government say that too many people face serious health risks linked to poor diet. They aim to tackle this with a new health plan beginning with childhood obesity.

It comes as little surprise that fish consumption has not changed in Scotland. Although it is responsible for most of the fish produced in the UK, most is sent south or exported. Although SeaFish has their 2040 strategy aiming to stimulate fish consumption in the UK, it is clear that more drastic action is needed. The Scottish Government clearly now recognise this, and we would hope that the fish sector is already in discussion with Ministers to discuss how fish consumption can be increased in Scotland.

We, at Callander McDowell have closely watched the market for many years and it doesn’t take much to see that even in the UK as a whole, consumers are buying less fish to cook and eat themselves. Perhaps, these latest findings could be the catalyst for more radical action.


Insolvent: We hope that our readers might remember that a couple of weeks ago we described how we were disappointed to see the absence of fish from the Manchester Eats Food Festival. We did mention that one of the chef demonstrations was provided by Ed Bains of Randall & Aubin fish restaurant with two outlets, one in Soho in London and the other in Manchester.

Randall & Aubin seemed to have bucked the trend in relation to the longevity of fish restaurants in Manchester. Dedicated fish restaurants do not seem to last for long, which might indicate that the local restaurant-goers prefer other foods and cuisines to eating fish.

This week the Manchester trend continued as Randall & Aubin announced that their Manchester branch is up for sale as it is now insolvent.

We think that this news is yet another indication that the fish message is not getting through to consumers. In our opinion, we don’t think that restaurant-goers who may be spending £40 a head are that interested in how healthy their food is. What they want is tasty food and a good time. Unfortunately, we tend to hear too much about the health benefits and sustainability rather than how good fish is to eat and that deters consumers from a fish experience.