SEPA have a number of invertebrate monitoring sites and recently they kindly supplied us with the monitoring results covering the last decade or more. In 2012/13 we spent some time sampling invertebrates ourselves; all very informative, but also very time consuming. As regular blog readers will know we have focussed much time and effort trying to understand the impact of extreme flows on the fish population but of equal relevance are their impacts on the invertebrate population.
I have now had a chance to do a full analysis of the new SEPA data with some summary graphs shown below.
The decision was made to concentrate primarily on the results from autumn samples as the recent large spates have occurred in August (2014) and September (2009). The graph above shows the British Monitoring Working Party (BMWP) scores from autumn samples at a range of sites across the Spey. There is no trend apparent from this set of results; no surprise as the BMWP scoring system was established to assess water quality and reflects the range and type of species present with no account taken of abundance.
When the results are presented as average score per taxon (BMWP score divided by the number of scoring invertebrate families), the results were similar.
Perhaps of more interest are the results for invertebrate abundance at the monitoring sites. Compared to the 2013 monitoring results there was a large reduction in invertebrate abundance in the 2014 autumn samples (all taken after the Bertha spate) although when compared with the longer term series the reduction is not quite so dramatic. The results from the 2013 samples appear to have been particularly good, although that was after a warm, and low water, summer, which had been preceded by an extended period of benign flows.
When the average abundance figure for these sites for each year are compared it can be seen that the 2009 and 2014 scores were the lowest in the series. Of note though is the recovery in invertebrate abundance in 2010 and 2015. In the words of the SEPA ecologist “Natural events, where there is not another significant pollution pressure, do have an effect, but with nothing holding back recovery and good invertebrate recolonisation sources in tributaries and upstream, a quick recovery is possible“.
This graph show the results from the Fochabers monitoring site. The abundance results have been variable with 2013 producing the two highest counts. The 2009 and 2014 autumn survey points are highlighted in red. Whilst the 2014 sample was one of the lowest abundance counts in the sequence the 2009 figure was about average.
The equivalent results from the Feshie are shown in the graph above. In this case the autumn 2009 and 2014 were the lowest in the sequence, although in both cases the counts in the following samples recovered quickly to typical levels.
The results from the Garva Bridge site have been included for comparison. There seems to have been a step change in abundance between 2009 and 2011 with almost all subsequent results higher than the earlier years. As with the Feshie site the samples taken after the recent large spate events were the lowest in the comparable sequence. Invertebrate abundance in the river upstream of Spey Dam is higher than in the Feshie, which is very interesting – not quite the barren stream implied by some. SEPA also responded to my query about acidification in the Spey above Spey Dam as follows ” site 207131, River Spey upstream from Garva Bridge does not have acid monitoring on it, which suggests it was previously screened and found to be without risk from acidification“. This is my assessement also, as our own invertebrate sampling has found mayflies and large stoneflies; of species known to be intolerant of acidic conditions, to be present.
As far as fish are concerned there is much more too it than just invertebrate abundance. Not all invertebrates are equally accessible to fish, and most are seasonal in their availability but nevertheless abundance does provide a useful measure of food availability. From the above it appears that an impact from the recent large spates was recorded, particularly in the more mobile stretches of the river but equally a rapid recovery was also noted.
More topically over the last week there have been large hatches of grannon on the river, and this week the large stonefly hatch has commenced. The grannom is a type of caddis which makes a distinctive square section case from silk. As they are attached to the surface of the riverbed fishers often find them impaled on their hooks. On the drive back from Grantown the other day you could tell when the road and river converged by sound alone; the pitter patter of grannoms hitting the windscreen was very audible.
A grannom splattered number plate.
Two large stoneflies resting under the lid of the Avon smolt trap this morning. These are females, the males of this species have stunted wings and limited flying ability,