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Significant Electro Fishing Survey Work Completed

By the end of June, MulkearLIFE has usually completed a full catchment wide electrofishing survey. This was the case in 2010 and 2011. The third stock survey was scheduled for June 2012. But unlike previous years a weather window never presented. Flood conditions or near flood conditions continued from early June throughout much of June. One day’s eelectrofishing of the Annagh River was achieved on the 27th June and it was almost a month later that work recommenced when the main tributaries rivers of the Mulkear River (Annagh, Newport Bilboa Rivers) were surveyed last week. The relatively good conditions last week, the first prolonged dry spell in seven weeks, also allowed the project to undertaken a catchment wide rapid assessment survey for otter.


The crew of two boats work towards downstream net (Image: Ruairí Ó Conchúir)

What is Electrofishing?
Electrofishing involves the use of specifically designed equipment which passes an electric current through the water in a river. This temporarily stuns the fish within the radius of the electrode (usually no more than a few meters in diameter) and causes the fish to float to the surface (turn) where they are then collected with a net. MulkearLIFE uses both backpack equipment and equipment which can be placed in a boat. The sites are surveyed to the Water Framework Directive (WFD) standard so that ecological status can be assigned to each site. The entire basis on the work is to assess fish stocks throughout the catchment. To get a snap shot of the stability or otherwise of fish stock and to assess what beneficial impact the instream works undertaken as part of the work programme of MulkearLIFE is having on fish stocks and especially what impact have such works have had on salmon numbers.

How Does MulkearLIFE Carry Out Electrofishing Survey Work?
All sites used by MulkearLIFE are different. Hence the recourse requirements (staff, boats, nets, electrofishing packs) differ also. The basic elements of the work consist of the installation of nets across the width of a river channel. These nets are secured at locations upstream and downstream of the selected site (section of river channel) which forms part of MulkearLIFE’s network of sites throughout the catchment in which annual electrofishing takes place? In a two boat survey, as indicated in the images, the electrofishing equipment is placed in the boats and used by MulkearLIFE / IFI staff in that section of river channel between the nets. Fish are drawn towards the electrode net and are collected with nets as they turn in the water. The fish are quickly captured, transferred by net into larger temporary holding tanks and fully recorded before being immediately released.


Assessing fish stocks in the catchment – July 2012 (Image: Ruairí Ó Conchúir)

Why Does MulkearLIFE Electrofish?
MulkearLIFE is required to undertake annual electrofishing surveys to assess the status of fish stocks at selected sites throughout the catchment. Having established a baseline in previous years, the electrofishing survey allows MulkearLIFE to calculate the total number of fish species that are present in a particular site or river channel. The catchment wide survey allows the project to build up a picture across the entire catchment. The analysis of the data allows the project to assess the condition of the fish, together with their size and age. This is an extremely useful indicator of the quality of the water courses in the catchment and their importance in supporting fish and aquatic life in general.

MulkearLIFE’s Instream Works
All of MulkearLIFE’s instream works (on the Newport, Clare- Annagh, Bilboa and Mulkear rivers) consists of measures to restore degraded habitats. The need for such instream measures arises from the arterial drainage work carried out on the Mulkear which altered the pre-existing natural riffles. Rubble mats in particular, on the main channel of the Mulkear River, mimic the natural riffle habitat which were present pre-drainage. The rubble mat reduces the cross-sectional area of the river thereby increasing flow velocities at low summer flows. The faster flowing area on top of the rubble mat is quickly colonised by a range of aquatic vegetation. In addition, a considerable variety of invertebrates favour such conditions and colonise the rubble mat in significant numbers. This level of colonisation happens within months and is indeed already taking place. The fast flowing water also provides exceptional habitat for young salmon and trout and with invertebrate colonisation having taken place will provide them with an adequate food supply.


As fish float to the surface they are quickly collected (Image: Ruairí Ó Conchúir)

Summary on Partial Electrofishing Survey 2012
While the full catchment wide electrofishing survey is yet to be completed, in general, brown trout numbers were comparable with previous surveys in 2010 and 2011. Initial findings on Atlantic salmon numbers would indicate lower total numbers at all sites surveyed. This may be a reflection on the continual flooding since 1st June but a full picture will not emerge until such time as MulkearLIFE manages to complete surveying of the main channel of the Mulkear River.

As the month of July closes out, MulkearLIFE is delighted that it has managed to electrofish all of its survey sites bar those on the main stem of the Mulkear River. As water levels again rise this week and with continued unsettled wet weather, it is uncertain when MulkearLIFE will manage to complete its electrofishing survey work for 2012.


The power behind the crews, Noel Sheehan / Flan Ryan (IFI) (Image: Ruairí Ó Conchúir)

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Mulkear LIFE, Inland Fisheries Ireland, Ashbourne Business Park, Dock Road, Limerick, Ireland
Phone: +353 (0)61 300 238   Email: limerick@fisheriesireland.ie