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reLAKSation no 1062

Sea trout data: As anticipated the Twittersphere abounded with abuse following my analysis of the Fishery Trust/FMS/Marine Scotland Science sea trout data in last week’s reLAKSation but more about this later.

There were also some more reasonable comments such as why had I not presented graphs of infestation over time to see if there had been any change. In time, I will be looking at the changes from year to year for each sampling site and will discuss my findings when that work is completed. However, I would mention again that I am not a paid researcher and I have a full-time job.  However, this data is published on the Scottish Government website, and anyone is free to undertake any analyses they like using this data. Alternatively, anyone can contact Marine Scotland Science directly for the data.

Someone else said that this data is taken out of context and doesn’t consider changes to habitat and feed, especially as the fish don’t seem to grow to the larger sizes seen elsewhere. I have in the past considered the wider issues affecting sea trout but have attracted the usual abuse in response. Despite this, I will revisit these issues in this commentary.

After embarking on my journey to investigate the relationship between salmon farms and wild fish, I used the official Scottish Government catch data as collected by Marine Scotland Science to produce a graph of sea trout catches from rivers within the area now called the Aquaculture Zone. This is the updated graph:

The SEPA consultation document about a risk framework for sea lice states in relation to sea trout that available catch data indicates a long-term decline on the west coast starting in the 1950s (pre-dating the development of finfish aquaculture) and continued until around the 1990s, from when catches appear to have stabilised or even increased. Since I produced my version of this graph, this is the first time that I have ever heard any confirmation of my own observation. I have previously distributed this graph throughout the wild fish sector asking for any alternative explanation to this long-term decline from the 1950s onwards. I have not received one single reply.

I have also tried to find out whether there was any attempt to discover what might have caused the decline prior to the arrival of salmon farming on the west coast. I have searched through reports at both Aberdeen and Pitlochry Marine Scotland Science libraries and found nothing. There didn’t seem to be any interest in why sea trout were in decline, at least until the arrival of salmon farming, when there was something tangible to blame.

And certainly, there were some who were very quick to blame salmon farming, even though they had never shown any interest in the decline leading up to that point. Salmon & Trout Conservation have published a response to the SEPA consultation. They say that the official catch data from the 1950s to the 1980s was notoriously unreliable especially as sea trout were so plentiful that they were not recorded. What this means is that although there was an obligation in place to record catches, S&TC say that it was ignored by anglers and proprietors. Clearly, they were considered so plentiful that they failed to notice that the fish stocks were in decline. Having stated that the data was notoriously unreliable (implying that the observations made by myself and SEPA are flawed), S&TC then say that the same catch data from the great sea trout fisheries of the west Highlands show a steep decline. S&TC refer to the collapse of the Loch Maree sea trout fishery, which they date round the time that a salmon farm opened in Loch Ewe and about which I have covered extensively in my book – Loch Maree’s Missing Sea Trout. Instead, I would refer to the sea trout fishery of Loch Stack, about which Andrew Graham Stewart of S&TC has previously waxed lyrical.

This graph of the collapse of the Loch Stack sea trout fishery is taken from the report of a symposium held in Oban in June 1987. The only salmon farm in the area was registered on the 22 August 1985. In his book about the rivers of the north-west Highlands (2005) Andrew Graham Stewart writes that sea trout catches in Loch Stack have shown a slight decline since the mid-1960s, but it was the advent of fish farms to Loch Laxford in the mid-1980s that was the body blow. This graph is of sea trout catches taken from Marine Scotland Science data. The question that the wild fish sector refuse to answer which applies to both Laxford/ Loch Stack as well as the wider Aquaculture Zone is could it be that whatever has cause the decline prior to the arrival of salmon farming, also have continued to cause the decline once salmon farming became established?

Interestingly, in their response to SEPA, S&TC include a graph of the decline of Loch Maree sea trout, which is similar to the above but then include the graph of sea trout declines across all of Scotland without any explanation. The two graphs look remarkedly similar which begs the question whether the declines of sea trout along the west coast are just part of a wider decline of sea trout across all of Scotland?

In fact, sea trout are not just in decline across Scotland but most of Europe too.

The only official comment on the state of sea trout stocks comes from the last report on sea trout fisheries for 2020. This states:

“This is the third lowest on record and 74% of the previous five-year average, although the impact of the coronavirus pandemic complicates direct comparisons with previous years.” There is no explanation for the long-term decline.

In 2016, shortly after I had started to promote the hundreds of graphs of catch data from every fishery district in Scotland that I had produced, Marine Scotland Science published a short report titled ‘Using catch data to examine the potential impact of aquaculture on salmon and sea trout’.  In this report, they state that ‘it is very important to note that analyses of fishery catches cannot be used to prove whether or not fish farming has an impact on wild fish as there are many other factors that may cause changes in fish populations.’  Strangely, Marine Scotland Science did not arrive at this conclusion after RAFTS and subsequently S&TC used catch data to ‘prove’ salmon farming was to blame for the declines of catches on the west coast back in 2011. Even now, Marine Scotland Science cite papers in their Summary of Science of sea lice that use catch data to show the negative impacts of salmon framing. It seems that it is acceptable to use catch data to prove salmon farms do have a negative impact on wild fish but can’t be used to show that they do not.

This Marine Scotland Science document continues that there are many other factors that may cause changes in fish populations, and these may differ between the regions of coast that were considered (east coast and AZ). For example, catches of sea trout have declined over recent decades on both farmed and non-farmed areas in Scotland and it is plausible that different factors are responsible in the two regions. This is despite stating that there was no obvious change in the relative contribution of farming and non-farming areas to the total Scottish catch of sea trout as salmon aquaculture expanded.

To summarise what Marine Scotland Science have said together with their data is that sea trout have been in decline on the west coast since well before the arrival of salmon farming and similar declines have also been seen across all of Scotland, yet according to Marine Scotland Science, it is plausible that the arrival of salmon farming supplanted the cause of the declines just in the Aquaculture Zone whilst whatever caused the declines elsewhere continued to do so. It’s not surprising that Marine Scotland Science make strenuous efforts to avoid having to answer my questions. In my opinion, the only aspect of this debate that is plausible is that Marine Scotland Science are so unfavourable to salmon farming, that they are unwilling to consider the extensive evidence that shows that they could be wrong.

You may remember that it was the sea trout data obtained from Marine Scotland Science that has prompted this commentary. It was the size of the sample that impressed me and enabled me to demonstrate that like all parasites sea lice exhibit an aggregated distribution. Whilst some fish have been found to carry large numbers of the parasite, their aggregated distribution means that they are not representative of the whole population. I have been repeatedly puzzled as to why those in sea lice research rarely mention this feature of sea lice biology and of course the answer is that it doesn’t support the claim that sea lice are negatively impacting wild fish populations. In this specific example, 72% of the fish were lice free, which means that 72% of the population cannot be impacted by the influence of salmon farms. Many other fish have very low numbers of the parasite and thus are equally unlikely to be impacted.

Even though the summary of the science fails to mention the aggregated distribution of sea lice, Marine Scotland Science have been aware of it for over twenty years if not longer. Alexander Murray of the then FRS Marine Laboratory gave a presentation at a meeting in 2001 and published a paper the following year in which he notes that a few hosts have large numbers of parasites, but most have low or zero parasite loads. He continues that this is referred to as an over-dispersed or aggregated distribution which means that the impact of parasites on their hosts is not uniform. Thus whilst average intensities of infection are low and tolerable some host individual will receive high and potentially damaging intensities. In the case of the Marine Scotland Science data discussed last week, this high and potentially damaging intensity affects just 8% of the sample.

Large samples of data of salmon and sea trout infestations with sea lice obtained from Norway, show exactly the same pattern of infection with most fish being lice free. Dr Murray cites a number of parasitology papers that support this view, so it is incredible that the mainstream science regarding the interaction between salmon farming and wild fish chooses to ignore this aspect of sea lice biology. Perhaps, if Marine Scotland Science highlighted the aggregated nature of sea lice distribution, then it would rather undermine their claim that salmon farms are damaging to wild fish populations.

Of course, the saddest part of this narrative is that whilst Marine Scotland Science continue to focus on sea lice on the west coast, numbers of wild fish elsewhere continue their downward spiral towards extinction.

Finally, I would just mention that it is also rather sad that certain individuals on Twitter prefer to issue abuse at anyone who doesn’t agree with their view. Again, I am accused of manipulating data to suit my cause. All the data I use is in the public domain so rather than continuing to criticise, I suggest that they examine the data themselves to support their own theory. I usually prefer to ignore these individuals, most of whom prefer to hide behind their keyboards, but one of my correspondents was so horrified by comments made by an account claimed to be run by someone called Robert Cameron who has accused me of being akin to a holocaust denier. My correspondent found this particularly offensive and disrespectful. This discussion is about salmon declines, not the awful atrocities that people have inflicted on others. Despite his abusive comments, I would still be willing to debate the issues with him or any other critic face to face. Of course, I will never hear from any of them because they don’t seem to have anything to contribute to the discussion other than to be critical and abusive.