The official investigation into last year's major fish kill at Inver Bay and McSwyne's Bay in Donegal has found that the cause was "probably" the result of a combination of natural events, Lorna Siggins, Marine Correspondent, reports.
The report by the Marine Institute has found "no evidence" that the fish kill was caused by dredge spoil dumped during the Government's development of Killybegs harbour.
The report says it "appears most likely" that the initial trigger for the mortalities was a "biological event", such as a bloom of jelly or siphonophores (small jellyfish-like organisms), which coincided with an "intrusion" of offshore water in early July 2003.
This was followed by a protracted period of high water temperatures in July and August of last year which, together with secondary infections, increased stress on the fish.
The report's authors refer to other major fish kills by jellyfish, such as the Isle of Lewis in the outer Hebrides where a jellyfish "invasion" killed about 900,000 salmon at two fish farms in 2002. A similar event occurred on the Norwegian west coast in the same year.
However, the Marine Institute scientists state in the body of their report that they found no physical evidence of jellyfish on the gills of either batch of samples taken from the site of the three affected fish farms in south Donegal. Nor were there any jellyfish in the fish stomachs.
Mr Richie Flynn, chief executive of the Irish Salmon Growers' Association (ISGA), said that he was disappointed that an "inconclusive" report could take eight months to produce.
Three farms employing 120 people and producing €15 million worth of fish annually had gone out of business as a result of this event, and the ISGA was now consulting its legal advisers, Mr Flynn said.
Over 850,000 fish reared by three fish farms in Inver Bay and McSwyne's Bay perished over a period of weeks last summer at three farms - the largest being Ocean Farm, which had no insurance to cover the mortalities. Immediately after the fish kill was confirmed, the Department of Communications, Marine and Natural Resources issued a statement in which it denied that dredging of Killybegs harbour was the cause.
The ISGA had originally maintained that trawling for prawns was the culprit, when mud or silt was disturbed and released hydrogen sulphide.
This in turn suffocated fish, which showed substantial damage to their gills. However, the association subsequently identified the sea site where upwards of 200,000 tonnes of dredge spoil from Killybegs harbour was disposed of last year,about five miles west of the fish farms.
The ISGA said that the dumping produced the black silting mud which appeared on fish farm nets, and was also found on gear owned by inshore fishermen in the area. This has been dismissed by Marine Institute scientists.
The Marine Institute said that copies of its report have been presented to the Minister for Communications, Marine and Natural Resources, and have been issued to local producers in Inver Bay and McSwynes Bay, Co Donegal.