Works are under way on Scottish rivers to reverse the damage done by installing instream fisheries development features such as croys and bank armouring. On the River Dee Special Area of Conservation (SAC) a total of 24 croys are currently being removed reversing what was previously considered to be fisheries enhancement works. Croys are artificial instream features which aim to deflect and constrict flows, and allow anglers to walk out on to fish. They have been widely used on British and Irish rivers in the hope that they would create pools for salmon and so increase fish catches. They are usually constructed from lines of boulders and rocks, which are taken from other areas of the riverbed. However, it is now understood that these features are damaging to rivers as they interfere with natural fluvial geomorphological processes. They also actually reduce habitat for salmonids and other aquatic species. The current works on the River Dee aim to restore natural river process and improve habitats for fish and other aquatic life, such as Freshwater Pearl Mussels.
Meanwhile on the River South Esk SAC, a series of bank protection and bank armouring features are being removed. This bank protection was installed in the 1990s to limit riverbank erosion and channel movement. However, it is now understood that this reduced river habitat quality for salmon, Freshwater Pearl Mussels and other aquatic life. Bank armouring affects natural erosion and deposition processes in rivers and essentially results in channelization. Bank armouring increases the flow of energy in the river causing the compaction and coarsening (armouring) of the river bed which can reduce spawning areas for fish.
The modifications on the River Dee were modest compared to some of the features put into many Irish rivers, for example on the Lower River Shannon which is an extreme example of how we got it wrong with fisheries development works in Ireland
Irish Rivers have been highly modified with croys, weirs, deflectors, and armouring as part of a number of misguided river ‘enhancement’ programmes. Indeed, we are continuing to infill our rivers with rocks and gravel and armour their banks. Current river enhancement programmes in Ireland are focused exclusively on developing salmonid habitats and providing angling features, often to the detriment of other aquatic species. These works are also often undertaken during the bird nesting season (they are exempt from the provisions of the Wildlife Act, 2000), and during the lamprey spawning season (no protection in Ireland).
However, it is becoming increasingly clear that many of these works are counter-productive and will also damage salmonid populations in rivers. It is likely that many of the fisheries development works currently being implemented in Ireland will, in time, come to be widely viewed as being as damaging to our rivers as the original arterial drainage schemes which many of these enhancement programmes sought to reverse. As is happening now in Scotland, we will end up removing many of these instream development works when we adopt more holistic river management approaches. The modifications on the River Dee were modest compared to some of the features put into many Irish rivers, for example on the Lower River Shannon which is an extreme example of how we got it wrong with fisheries development works in Ireland.
Read the news reports for the River Dee at the links below.
- £3.5 million project to restore River Dee
- Aboyne Croys Removed to Restore the Dee
- Removing Banchory Croys on the River Dee
Also see the ‘River Dee restoration scoping study‘. Also this presentation entitled ‘Improving freshwater pearl mussel habitat though restoration of natural processes‘.
For information on works in the River South Esk see this media report entitled ‘Angus river works to protect pearls in peril‘ and also the ‘River South Esk catchment restoration scoping study‘.
For further reading also see these posts:
- Instream enhancement works in Ireland – what about lampreys?
- Reversing the damage due to fisheries “development” works
Also visit our YouTube channel to see videos our the surveys we have recently completed on the Lower River Shannon to highlight the impact of instream development works.