It is a pity that the Google analytics tool is not working at the moment as it would be interesting to see how many hits the website had this weekend! However it is good to see that there are so many people with a great passion for the Spey.
This post concerns the 0+ parr stocking monitoring completed last week on the upper Conglass Water, a tributary of the Avon. Other monitoring results, including the Blye, Mulben, Knockando, Ringorm and the Burn of Brown will be presented later. This may be a lengthy post, and it will contain an insight into the mind of a biologist so maybe the reader should grab a coffee first.
The Conglass Water is a significant burn with a mean width of over 10m at the lower end. The length of accessible habitat is over 20km. It rises at over 500m in the hills around the Lecht and flows down to join the Avon at about 280m altitude. The geology in the upper reaches is mainly granite and mica-schists but in its lower reaches the Conglass flows through sandstone and even a small area of limestone. Known to be a very productive spawning and nursery burn, it is accessible to salmon and trout over almost its entire length.
The upper reaches were stocked with 160,000 0+ salmon parr in September 2011 as this part of the burn was considered beyond the natural reach of salmon, although the evidence below suggests otherwise. The stocked reach extended from the picnic site at the Iron Mine to Glenmullie, a distance of 5.4km. The stocking density was 5/m2 a very high rate for fish at such an advanced stage. We surveyed three sites last week, the Iron mine picnic site, Blairnamarrow confluence and at Glenmullie, covering the stocked area top, middle and bottom.
The middle site was surveyed with a three run electrofishing protocol and the other sites with a single run. The three run survey technique allows us to calculate the densities of fish present with a high degree of accuracy. For those unfamiliar with electrofishing I should point out that generally not all fish are captured during the first run, but by using consistent technique and effort during each succesive run through the site the number of fish captured should decrease allowing a depletion estimate to be calculated. Using the data from the three run site we could establish that 63% of the fry present were captured during the first run and 67% of the parr. These figures were then applied to the results from the sites where only a single run was completed to derive a good estimate of the minimum fish numbers at each site.
I have mentioned in previous posts the Scottish Fisheries Coordination Centre national classification scheme as I like to use it to put our local results into context. Colour coding the results allows easy visual interpretation. The table below shows the classification categories. The classification scheme also has refinements based on stream width but here I use the basic national classification. The scheme is based on one run electrofishings or the first run of multiple run surveys so the results from the survey sites below don’t show the absolute fish densities at each site, just the results from the first run. The table below shows that a salmon fry density greater than 42.1/100m2 is in the excellent, or “A” class band, equivalent to the top 20% of Scottish sites. For salmon parr a density between 9.1 and 15.8/100m2 means it is good or “B” class or in the 20-40% band of Scottish results. Green is best and amber/red not so good.
The tables below show the first run and SFCC classification for each of the three stocking monitoring sites.
Note that when the above site was stocked I have recorded it with yes in the stocked column. If the column is blank there was no stocking that year.
We have quite a history of surveying at the Glenmullie site and it can be seen that the salmon and trout densities there are generally in the good or excellent category. Salmon fry are present every year showing that salmon spawn naturally in the area. The Blairnamarrow site was a new site established this year for the stocking monitoring. Salmon fry were present here also, but not at the upper site, showing that the upper limit of salmon spawning in 2011/12 was a bit further upstream than thought. At the upper site salmon fry were present in 2003 and 2007, when the records show no stocking was done. However they were absent in 2012 although there was an excellent density of salmon parr present. It is quite likely that these were largely of stocked origin although as the fish were not marked in any way it is impossible to tell without genetic analysis. The trout parr densities at the upper site were also very high, so much so that it is quite likely the upper Conglass would be in the top 10% of Scottish burns for trout density, a good proportion of which will become sea trout smolts.
We also have a monitoring site in the lower Conglass Water at Ruthven Farm. It was surveyed regularly until 2007 but the 2012 survey found the current fish densities to be similar to those found in the earlier surveys. The results from this site are shown below.
It should be clear that the juvenile salmon densities at this site are fantastic, all from naturally spawned fish. Trout densities are much lower at the bottom end of the burn. This is a common occurrence with trout densities generally increasing in the upper reaches of most burns.
Using the data from the four electrofishing sites I have attempted to quantify the total parr production in the Conglass Water. As this is based on the results from four sites confidence levels are not sky high although I believe the figures produced won’t be far away from actual. The Conglass was split into three sections; the upper from Iron mine site to Blairnamarrow confluence, middle from Blairnamarrow to Glenmullie and lower from Glenmulliue down. Using the fish densities from the three run survey calculations and multiplying by the area of habitat in each stretch the following estimates were obtained.
I calculated that we may have a created a population of 2,500 -3,000 salmon parr by stocking but for me the most striking figure is the 57,000+ of salmon parr and the almost 23,000 trout parr that the burn supports. Over 95% of the salmon parr present will be from natural spawning. Based on these figures we have a survival from stocking to 1+ parr of 1.72%.
As a biologist this is really the crux of the stocking debate. Here we have a relatively modest Spey tributary, albeit an extremely productive one, which contains a large natural population of juvenile salmon and trout.
We have incorrectly defined the upper limit of salmon spawning and we have stocked the upper reaches of a tributary with hatchery salmon parr from Avon mainstem broodstock.
We have stocked very high densities of salmon into a burn containing some of the highest densities of trout (juvenile sea / brown trout) in Scotland.
We have established a population of stocked salmon parr, amounting to less than 5% of what the burn supports naturally
I guess some would view the results of the Conglass Water stocking a success. Others may view it as an ill-thought attempt to change the natural order of things, at the expense of the trout population and quite likely the existing salmon population.
So how come we are reduced to stocking such burns? As a biologist I consider that the scope for justifiable stocking in the Spey is limited. There is a huge area of accessible habitat in the Spey, granted much of it considerably less productive than the Conglass, but there is a huge area nevertheless. Maybe not the reputed 15% of the Scottish total found in the Tweed, but it may be in the region of 10%? Fish are present throughout the accessible area. Only 1% of the river is cut off to fish access by man-made structures, excluding the hydro structures at the top of the river, so obstructions are not a hugely significant factor. If we are to improve the Spey salmon population, and ultimately the fishery we should in my view be focussing our energies on making sure the all accessible habitat is functioning and producing smolts to its optimum.
Other monitoring results will follow.