Exposing Scottish Government’s ludicrously inflated adult salmon estimates

Scottish Government first introduced classifications for the country’s salmon rivers in September 2015. These applied for the 2016 season. The classifications put all the rivers in the west Highlands and inner Hebrides in the worst-performing category (no 3), with wild salmon stocks not reaching what are known as ‘conservation limits’ – a measure of the overall health of the population.

The categories and criteria are as follows:

Category 1 rivers: “exploitation is sustainable therefore no additional management action is currently required”.

Category 2 rivers: “Management action is necessary to reduce exploitation; mandatory catch and release will not be required in the first instance, but this will be reviewed annually”.

Category 3 rivers: “Exploitation is unsustainable therefore management actions required to reduce exploitation for 1 year i.e. mandatory catch and release”.

Scottish Government has recently re-classified 22 west coast rivers to Category 1 and 35 west coast rivers to Category 2 on the basis of adult salmon population estimates, which are the product of Marine Scotland Science’s (MSS) new (flawed) methodology. The agency’s output relating to this methodology is available here

In response to major concerns about the veracity of MSS’s approach and population estimates, S&TCS recently commissioned Professor Colin Adams, the leading fisheries academic from Glasgow University, “to examine the science that lies behind the methodology being used and provide an analysis of the strengths, weaknesses and assumptions of the resulting procedures.” Professor Adams report is accessible here.

Professor Adams’ conclusions include:

  • There is little doubt that the assumptions and simplifications used combined with a lack of empirical data are resulting in estimates of salmon abundances which differ significantly from the reality in a number of rivers
  • We advise that the outputs of this assessment are used with considerable caution until higher quality empirical data become available

It is becoming increasingly evident that where other data is available to test the MSS model, it is failing hugely.

Craig MacIntyre, Director of the Argyll Fisheries Trust, said:

“When we compare our survey data of several Argyll rivers with the MSS salmon abundance estimates, we conclude that MSS has overestimated the number of salmon present by up to a factor of ten. Grossly inflating salmon numbers risks setting back local conservation efforts, such as catch and release, as well as misleading local authorities and regulators when they are making decisions about aquaculture expansion.”

Bill Whyte, Chairman of the Wester Ross Area Salmon Fishery Board, added:

“The highly questionable recategorisation of many of our rivers will serve as a green light for the salmon farming industry to push for unjustifiable expansion.”

Andrew Graham-Stewart, Director of Salmon & Trout Conservation Scotland (S&TCS), noted:

“It is clear that the methodology used falls far short of an acceptable standard for providing reliable estimates of salmon numbers. The model needs radical refining before it can be relied upon.”

The only fish counter in the west Highlands is on the River Morar. It shows an annual count of some 500 salmon – approximately one third of MSS’s estimate.

The Argyll Fisheries Trust has just carried out a snorkel survey of one its rivers. 30 adult salmon were counted. MSS’s estimate is 1500.

The overestimates are not limited to the west coast. For example, the River Helmsdale is given an adult salmon population by MSS of over 30,000 annually. MSS itself operates a fish counter three miles upstream of the river mouth. The annual count is generally between 4,000 and 5,000. It is hardly plausible that this huge discrepancy can be explained by tens of thousands of salmon spawning below the counter.

Similarly the River Shin is given an adult salmon population of over 35,000 annually. The fish counter in the dam at Loch Shin records less than 200 migrating each year upstream into the loch. It is simply not credible to suggest that tens of thousands of salmon spawn in the five miles of river between the dam and the river mouth.

(Sunday Herald coverage on 6 November)