Over 300 fish killed at Portavo Reservoir

I note the initial report recently received from government concerning recent fish kill at Portavo Reservoir in August 2013 and look forward to final report identifying why so many fish died. A total of at least 347 dead fish were recorded following this awful event plus small number of roach and an eel. 

Cllr Muir at Portavo Reservoir
I was baffled by the bureaucracy encountered when I initially tried to report the problem but am glad someone is finally taking the initiative to find out the cause and explore solutions. 

With routine scheduled maintenance due to take place at the Reservoir from November 2013 to March 2014 no more fish will be stocked until 2014 giving us time to sort the problem and help secure a viable long term future for this valuable environmental haven which should be saved not sold.

Response from Department for Culture, Arts and Leisure below.

I refer to your e-mail dated 29 August 2013 to Minister NI ChuilIn regarding correspondence you received, in relation to a fish kill at Portavoe Reservoir. The Minister has seen your email and I have been asked to respond on her behalf.

Following a report of dead fish at Portavoe reservoir on 30 August, DCAL Fisheries Protection Officers, working with Inspectors from the NIEA, carried out a joint investigation of the incident. Initial findings indicated no evidence of any introduced pollution in the reservoir, with natural causes the likely reason for the fish mortalities.

Some of the dead fish were found to be affected by fish lice and a fungus. The approximate fish mortalities total was 94 on Friday, 169 on Saturday and 84 on Sunday. It is important to note that while the majority of fish mortalities were trout, small numbers of other species have also been recorded including perch, eels and roach. A number of dead fish were passed to the Agri-Food and Biosciences Institute Veterinary Sciences Division for investigation of the lice and fungus. Unfortunately they require the fish to be still alive or recently dead and further analysis could not be carried out.

The reservoir was stocked with 750 rainbow trout from the Department's fish farm at Movanagher near Kilrea on 28 August. These were healthy takeable size fish, free from any parasites or infections. Had there been any signs that Portavoe was unsuitable to receive the fish on that date, the fish would not have been stocked.

Fish are sensitive to dissolved oxygen levels in the water and the NIEA staff have taken a number of samples from the reservoir. Dissolved oxygen levels recorded during the daytime were deemed adequate to sustain fish life, however it is at night that the dissolved oxygen levels will be at their lowest.

The NIEA subsequently positioned a water monitoring buoy in the centre of the reservoir to record dissolved oxygen levels over a number of days and information received has indicated that the lake is prone to periods of low oxygen levels. As such DCAL is currently reviewing it's stocking protocols for Portavoe Reservoir.

Significant aquatic weed growth has resulted from recent high temperatures and sunlight and this impacts on oxygen levels in the water. Consequently the Department moved a weed cutting vessel to Portavoe on 3 September and work on removing excess aquatic weed is underway.

When anglers and members of the public contact DCAL regarding such incidents staff will try to be as helpful as possible, but cannot speculate on causes of a fish kill. You will appreciate that until all the circumstances are assessed and investigations completed, staff would not wish to jeopardise any further action by making comments that are not fully informed.

I hope that this information is of assistance to you.

Yours sincerely,

Departmental Private Secretary to Carãl NI Chuilin MLA
Minister of Culture, Arts and Leisure