Initial investigations into serious fish kills at three fish farms in Inver Bay, Co Donegal, indicate a biological or chemical cause, according to the Department of the Marine
Scientists have ruled out disease and have found that at least 230,000 farmed salmon died when their gills were burned - in some cases, down to the cartilage.
Losses at the three fish farms in south Donegal may be much higher when the final count is taken and at least half the stock has already perished. Truckloads of dead fish were being taken away for rendering yesterday as a multi-disciplinary team tried to establish possible causes.
The Department said it was informed of the situation a week ago and immediately sent scientists to Donegal. The cages are owned by Ocean Farm, which experienced a substantial fish kill in the bay a year ago, Eany Fish Farm and Creevin Salmon.
The Irish Salmon Growers Association has suggested that bottom trawling for prawns close to the cages may have disrupted the seabed and stirred up hydrogen sulphide gas. It said a vet attached to the companies found hydrogen sulphide levels 30 times higher than normal "high-risk" levels. The association has written to the Department seeking its policy on trawling close to fish farm cages.
However, the Department said that initial reports from the Marine Institute suggested a "water-borne irritant" which was biological or chemical in nature and which had since disappeared.
It said grab samples were taken from the area and engineering advice indicated that dredging or trawling was not responsible. This has also been borne out by examination of sediments below cages undertaken by the Marine Institute.
Mr Harry Lloyd, manager of the Northern Regional Fisheries Board, said as of yesterday there appeared to be no impact on the Eany system, an important salmon and sea trout angling fishery. He said the board was supporting the Department in its efforts to deal with the kill.
The salmon growers association said the Inver mortalities highlighted once again the need for a coastal zone management policy, as promised in the Programme for Government.
Salmon-farming is going through a traumatic period, with prices having been forced down by cheaper imports from Norway and Scotland.
Last week, an environmental code of practice for aquaculture companies and traders, known as "Ecopact", was published by Bord Iascaigh Mhara.
It said the code represented a "powerful commitment" to environmentally sustainable fish farming. That commitment extended beyond "simple compliance with legal requirements", the board said.
The chief executive of Bord Iascaigh Mhara, Mr Pat Keogh, said fish farmers depended on a clean,unpolluted natural environment" and the Ecopact approach was designed to capitalise on this.