Traffic Lights: Some readers experienced difficulty in downloading my review of the Traffic Light System, so it is now available from the ‘Reports’ section of the website. The link is https://www.callandermcdowell.co.uk/reports/traffic-light-system-review/
Textbook: Those who might have read my report of my analysis of the Norwegian NALO sea lice data will have read a short account of parasite ecology within the first few pages. This was taken directly from a textbook titled ‘An Introduction to Animal Parasitology’ (third edition) written by J.D. Smyth, Emeritus Professor of Parasitology at the University of London and published by the Cambridge University Press in (1994) (Previous editions were published in 1962 and 1979). This textbook is said to appeal to all students with an interest in parasitology as well as being of interest to research workers in the field.
The very first page of this 548-page textbook is headed Chapter 1 – Parasitism, what is a parasite? This page is reproduced as follows but for the ease of reading, the many references have been omitted:
“1.1 Animal associations
The majority of animals live independently in their natural habitats, seeking their own food materials and utilising free water and oxygen for their metabolic processes. Between some animals, however a variety of patterns of association have developed and these may be broadly divided into two groups: homogenetic associations – those between individuals of the same genotype; and heterogenetic associations – those between individuals of different genotype.
Individuals of the same species may form loosely united communities such as herds of cattle or flocks of sheep whilst others such as some species of ants or bees may form elaborately organised communities in which individual members exhibit considerable division of labour or specialisation.
Heterogenetic associations are in general much more complex, and a number of terms have been developed to describe them. Like many terms used in biology, these are essentially operational words which are definable only within broad limits and not in absolute terms.
They do, nevertheless, serve a useful role in enabling us to file data into convenient though not watertight compartments. Terms such as commensalism, phoresis, symbiosis, mutualism, and parasitism have been widely used for various types of heterogenetic association and their definition – which has always been controversial has been much discussed by early workers in the field. These terms were developed in a period when little data on the possible physiological and/or mathematical basis of such an association were available.
Within recent years, the situation has changed somewhat, and although information is still meagre, the general increase in knowledge of animal physiology, biochemistry, and population dynamics enables these associations to be considered on a broader basis. In particular it is increasingly recognised that Parasitology is essentially a branch of Ecology, and the phenomenon of parasitism can be considered as an ecological relationship between two populations of different species and much attention has been paid to the quantitative aspects of this relationship.
An important conclusion that has emerged from such studies is instead of parasites being randomly distributed within the host population (as might be expected) they tend to be over-dispersed i.e. a few hosts harbour large numbers of parasites and many hosts harbour only a few. That this type of frequency distribution is a major characteristic of parasitism was first postulated by Crofton (1971) and has since been confirmed by numerous studies on many host-parasite systems.
A negative binomial has proved to be a good empirical description of this pattern of infection and an example is shown.
This shows the distribution of the metacercaria of the trematode Displostomum spathaceum which commonly occurs in the eyes of fish throughout the world. The lens of a few fish are found to be infected with enormous numbers of larvae (over 400 in one fish) but most only contain relatively few and its distribution closely follows a negative binomial pattern.”
Th example given shows the classic aggregated distribution, although because the few fish with many parasites are grouped together, the graph appears to show an increased number of host fish with the parasite. This is drawn simply to save space given that over 400 parasites were found in one fish. Much is made of the wild fish sector of fish caught with high numbers of sea lice claiming that this is only the result of the presence of salmon farming. The reality is that such high numbers of parasites are actually a normal occurrence. It is simply that most people have very little idea of parasite ecology and consequently make completely wrong assumptions.
The same can also be said about the scientific community. I have repeatedly asked which of the scientists working on sea lice is a parasitologist. I am still waiting for an answer.
An Introduction to Animal Parasitology is an enormous textbook covering a wide range of issues concerning parasites, yet on the very first page, it details the simple fact that the distribution of parasites including sea lice amongst their hosts is that the majority of hosts carry no or very few parasites whilst a few hosts carry many. If sampling does not show this distribution, then the sampling is wrong. At the same time and with regard to sea lice, if the majority of hosts carry no or very few sea lice, then they cannot be at risk of mortality.
Over the years, the salmon farming industry has been accused of twisting the science to suit its cause. This is not about salmon farming. This is about parasite ecology. Sea lice are parasites and if those who claim sea lice are detrimental to wild fish bothered to look at the science relating to parasites then perhaps, they would turn their attention to finding the real cause why wild salmon are under threat.
What frustrates me most about the understanding of Parasite Ecology in relation to salmon farming in Scotland is that I first learnt about aggregation or overdispersion from an internal report written by a scientist working for the Fisheries Research Services (now the Marine Directorate) in 2006. Although an internal report, it was posted on the web (now removed) where I found it several years ago. At the time I was searching for a particular aspect of sea lice infestation so wasn’t immediately drawn to the relevant piece.
The report is titled – A review of research and field data on relative louse infection levels on wild salmon smolts and sea trout and the proximity of fish farms to river estuaries. It is numbered as report 12/06.
The report states that:
Overdispersion, or aggregation, is a situation where only a few hosts in a population have a large parasite burden and the majority of the host population have few or no parasites.
It goes on to say that:
The overdispersion of lice on hosts creates serious difficulties in interpreting data, particularly that from wild fish. In an over-dispersed distribution, most of the lice are on a few fish with very high loads. This makes obtaining a representative sample difficult, making estimates of mean abundance and intensity unreliable.
Clearly, Government scientists were aware of the natural distribution of parasites and the difficulty that sampling of infested hosts eighteen years ago but seemingly chose to ignore their own research review for reasons best known to themselves. However, it is never too late to rediscover this ignored science.
Canada Lice: Recently, the BC Salmon Farmers Association published a new 617- page report – Modern Salmon Farming in BC. This is a major work covering every aspect of salmon farming in BC. Of special interest was chapter 10 about sea lice which runs for about 85 pages.
However, one graph sums up all that anyone needs to know about sea lice in relation to infestation of wild salmon. This is figure 10 which is a pie chart showing the analysis of sea lice infestation of 320,177 Pacific salmon sampled between 2001 and 2022. This is probably the largest data set of sea lice infestation gathered from any salmon farming area.
The data set includes samples from all five Pacific salmon species (the report also details all of these separately). The data set includes all salmon sampled, including those sampled by groups opposed to salmon farms including that of Alexandra Morton’s Salmon Coast Field Station.
The data set identified that 72.6% (243,334) of the fish sampled carried no lice at all. This means that 72.6% of the fish sampled had no contact with any lice and therefore could not be at any risk of mortality. A further 13.4% (42,904) of the fish carried just one louse with just 3% (9,605) of the fish had over five lice.
A larger image of the various data sets used in this analysis and the number of salmon each analysed is below.
The Canadian industry prefer to use pie charts to describe the level of infestation, however as such aggregate distribution are usually illustrated by a negative binomial graph, I have expressed the data in that way too.
The column at the end of the graph is larger because it includes all those fish that carry more than 5 sea lice. If this was broken down, the tail of the graph would be much longer with columns that hardly register on the graph because they would be so small.
I have previously analysed the data from the Salmon Coast Field Station, and they follow a similar pattern, despite Alexandra Morton’s claims that sea lice from salmon farms are responsible for the declines in Pacific salmon numbers.
I suspect that the publication of Canadian data will make no difference to those who object to salmon farming, whether in the America’s or in Europe, because those objectors are not interested in hearing the facts, preferring to rely on their own preconceptions as justification why salmon farms should be closed down.
Tracking: A new paper has been published by researchers from the University of Glasgow’s Centre for Ecology and the Natural Environment in the Journal of Fish Biology. This has tracked the migration route of 1914 smolts from 25 rivers in four countries. This was a collaborative project between 22 agencies and organisations. Of special interest was that four of the 45 authors are from the Atlantic Salmon Trust.
The AST have been running a three-year project to track smolts from rivers on the Scottish west coast running from 2021 to 2023 and thus their work is clearly included in this new paper. The AST say on their website that the valuable information gained from their project will help inform ongoing adaption of the SEPA sea lice risk framework. The AST project has always been about the interaction between wild smolts and salmon farms and their view that salmon farming is harming wild salmon as declared in the AST’s position statement on aquaculture.
Interestingly, this new paper mentions salmon farming just once.
“Moriarty et al. (2023) showed that post-smolts passing through the Minch could be expected to acquire an increased load of the parasitic sea louse Lepeoptherius salmonis emanating from salmon farming units, which are relatively more dense in this area. One working conclusion from the pathway information in this study is that the general risk of exposure to sea louse infection likely differs between populations, with populations from rivers draining into the Solway, Clyde, Foyle, and Bush marine areas likely to be less exposed to the risk of infection than post-smolts from the other regions examined here (Linnhe, Torridon, Eireasort, and Laxford), where post-smolts do migrate through the Minch.”
The problem here is the Moriarty paper is about the dispersal model and simulates smolt migration. It is an assumption not fact. There is still no evidence to support the claim that migrating salmon smolts pick up enough sea lice as they migrate past salmon farms and then subsequently die from such infestation. It is all conjecture based on an outdated and unproven narrative from the wild fish sector. Sadly, the AST are no different to any other wild fish group in their reluctance to discuss the science about salmon farming, sea lice and wild fish.
https://onlinelibrary.wiley.com/doi/10.1111/jfb.15760