Any River with a Salmon Parr Density classed as "Poor" should be deemed "No Harvestable Surplus of Adult Salmon"

The Scottish Government / Marine Scotland should make their decision on whether a river has a harvestable surplus of adult Atlantic Salmon based on the popluation density of the river (or its tributaries) of its juvenille Atlantic Salmon population density, which is determined by electrofishing.

Each rivers juvenille Atlantic Salmon population density should use the SFCC National Rivers Classification scheme for juvenile salmon density to indicate how the river compares to other Scottish SAC rivers.

If the population density scores "Poor" or

In 2005, J.D.Godfrey compiled a report entitled "Site Condition Monitoring of Atlantic Salmon SACs, Report by the SFCC to Scottish Natural Heritage, Contract FA02AC608".

Section 3 of that report is entitled "A National River Classification Scheme". The SFCC were asked to develop a national river classification scheme for Scottish rivers, conceived as similar to the National Rivers Authority River Classification Scheme (1995). The NRA’s scheme attempts to determine the status of a fishery with reference to the population density and fishes it contains.

Table 22 from the above report explains the basic structure of the classification scheme. Essentially rivers are scored A, B, C, D, E, with A being the highest juvenille population density found in Scotland and E being the lowest (zero juvenilles found).

Table 3.3.1 in the report entitled "Absolute Classification" sets out the classification of each river based on the electrofished juvenille Atlantic Salmon population per 100m2 (1+, 1++ atlantic salmon).  From this the river is given a score A, B, C, D or E.

In my opinion, the SG/Marine Scotland should use this method to deterine the current carrying capacity of each river (or tributary) and only issue Kill Licences for Harvestable Surpluses where the juvenille population scores an "A" or a "B".

From juvenille fish densities current adult run size of Atlantic Salmon in each river system (or tributary) can be estimated, and this can used as a way of determining how many adult fish can be harvested or how many carcass tags should be issued.

 

Why the contribution is important

It is suitable method, and achievable now and in the future.  It is based on facts.

by Electrofisher on July 23, 2015 at 08:14PM

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Comments

  • Posted by devronmac July 23, 2015 at 21:20

    The flaw in this argument is that electrofishing is usually carried out on a number of sites in a main river and/or tributary and/or feeder burns. Some of these sites may produce a high rating of juveniles and other areas will produce a low rating. It is difficult to see how an average rating can accurately be applied for a whole river system, particularly a large river system with several tributaries and feeder streams.. In any event, whilst I agree that a poor rating for juveniles throughout a whole river system(if that can be scientifically proven) should generate a no kill situation, it is actually the number of juveniles that survive to return to the river as mature adults that is the critical factor in determining the real surplus( harvestable or not). Until this can be done with a realistic and believable formula it will be difficult to determine harvestable surpluses in any river system. Does Marine Scotland have a proven formula for arriving at such a figure for each river?
  • Posted by Electrofisher July 23, 2015 at 21:59

    Unfortunately at the moment very few rivers have adult fish counters, so the data does not exist for the SG/Marine Scotland to use adult numbers to calculate harvestable surpluses.

    However, there is huge amounts of data for most of Scotland's rivers for juvenile fish counts found by electrofishing. The Atlantic Salmon Trust have a formula for morality rates from egg to spawned so a formula could easily be predicted using the populations of juveniles to estimate the number of returning adults.

    The geographical limits of the harvestable surplus zone could be decided to match any parameter from full catchment average right down to beat or tributary level, which would be a decision for the SG/Marine Scotland, and would tie in at a level of who buys the carcass tags/kill licence.

    Most electrofishing sites are chosen to be representative of the average productive habitat of any given watercourse.

    Ultimately some watercourses will have a higher carrying capacity than others and will produce a harvestable surplus and some watercourses will have a poor carrying capacity due to many factors or pressures on the species to survive, and these "at risk" watercourses should receive higher protection at least until populations become sustainable.
  • Posted by devronmac July 24, 2015 at 16:34

    Perhaps Marine Scotland could attempt to answer the question in the last sentence of my response to this thread and if no realistic formula presently exists, comment on what action is actually being taken to address the issue as it seems that the question of 'harvestable surplus'in all rivers is a critical factor in the licencing scheme.
  • Posted by marinescotland1 July 27, 2015 at 17:24

    Marine Scotland is investigating options similar to those adopted in other countries that use information on the number of adult salmon returning to rivers from a combination of catch and counter data (e.g. Norwegian methods given here: http://www.nina.no/archive/[…]ntalConservation%202013.pdf). This approach is consistent with International best practise and the aim of Scottish Government to use the best available science methods to aid management. Inevitably, there will be a degree of uncertainty in the processes. However, this can be reduced as further useful biological information is collected in the future and accommodated by introducing a degree of caution and incorporating flexibility to take on board new findings and methods as they become available. It has been suggested that electrofishing results such as those in the Godfrey report might be used to identify areas where killing is allowed. Unfortunately, it is not plausible to use such data to derive a harvestable surplus for a number of reasons. For example, Godfrey classified each site in relation to others within a region. There is no way of determining whether a “good” site was simply relatively high within that region or high in relation to the carrying capacity of the habitat. Furthermore, a wide range of numbers of spawning fish can result in a similar number of fry and hence juvenile surveys cannot be used to infer the harvestable surplus.

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