This is one of a series of bulletins that highlights some of the Trust and Board’s work on the River. No. 19

Those of you who have looked downstream whilst passing over Aboyne Bridge may have noticed some changes to the River since last year. There used to be three lines of boulders sticking out from the banks, which have now gone. The boulders themselves are still in the River but have been scattered, breaking up these structureswhich are known as ‘croys’.

So why were these croys here in the first place? Making croys in the 1990s was a common practice used to improve catches. The croys were supposed to create pools for the adult salmon and sea trout,so these fish would stay within the beat and be available to fishermen. It did not appear to improve the fishing, but did instead negatively impact the river flows, bed and banks, the fishing and its wildlife.

Through the changes to the riverbed and river flows, loss of large boulder habitat and increased erosion, it was clear that the croys at several locations in the River have damaged the habitat for both salmon and freshwater pearl mussels. So how could we fix the problem? The River Dee Trust and Dee DSFB are partners in the Pearls in Peril project, a European funded project aimed at improving and restoring habitat and conditions for salmon and freshwater pearl mussels in rivers across the UK. Consultants established the scale of the problem and recommended how it could be resolved and the River Dee team delivered the physical works,using funds awarded to this project.

The conclusion was that the boulders which were once throughout the River should be redistributed to create a natural bed, which would do three things -

  1. Generate ‘lies’ for adult salmon and sea trout
  2. Create suitable habitat for freshwater pearl mussels
  3. Restore the natural distribution of vital spawning gravels in the River

Achieving this without further damaging the River and its wildlife was essential. The solution for Aboyne was simple - a low cost, low tech approach using hand winches. The Dee DSFB team delivered what looked like an impossible feat over several weeks as they broke up the croys and spread the boulders out across the riverbed, using only physical labour to ensurenonegative impact to the River and its inhabitants.

Several spates have occurred since the work was delivered which will mobilise the spawning gravels trapped behind the croys and allow the boulders to settle. We will have to wait a few years for freshwater pearl mussels to use the habitat but will look for improvements in juvenile salmon populations from 2015.

Plans to address the Banchorycroysare underway and, after speaking to Colin Simpson, the Ghillie at Lower Blackhall & Kinneskie fishing beat in Banchory, it was clear how frustrated he was when croys were created at his beat in Banchory in 1995 -

“All the large boulders which made up the river bed were dragged out of the river by a large digger and heaped up to create the nine croys, others were used to reinforce the banksides, in the end the river had changed completely. The damage to the freshwater pearl mussels was devastating and the salmon fishing at the beat has never recovered, in fact the catches got worse.”

With the support of the two beats byBanchory Bridge practical work will start this summer to fix these structures.

This is one of a series of bulletins that highlights some of the Trust and Board’s work on the River. No. 19