A scientific report by Inland Fisheries Ireland has found that no specific factors could be conclusively established as the cause of death of nearly 1,100 salmon at Ballisodare Bay.
However, extensive investigations undertaken by IFI and partners have identified a number of contributory factors that may have potentially been involved.
In total, 1,079 mortalities were recorded (587 below lower falls; 470 in the stretch above the lower falls and 22 in the fish pass).
A report into the investigation into killings has been published by Inland Fisheries Ireland, the details of which have been published today.
The IFI say they were first made aware of initial reports of mortalities of the salmon in early July with the first records of small numbers of mortalities from the 28th June.
It was observed that certain dead and moribund fish presented with varying combinations of Saprolegnia-like fungal infections around the gills and dorsal region, haemorrhaging and some minor abrasive damage on the underside and apparent gill abnormalities which included paleness, excess mucous and damaged gill filaments.
The first records of mortalities are from the 28th June.
Up to the end of June, 14 mortalities were recorded. Between the 1st and 7th July, 55 mortalities were recorded.
There was a significant increase in recorded incidences of mortalities and observations of diseased fish from the 8th July.
However, no new mortalities were evident after the 19th July with the sole mortality removed from the river on 21st July considered to be dead for at least a few days based on its degraded condition.
It should be noted that the records are of recovered fish mortalities observed in the river.
They may not reflect all mortalities that occurred. In addition, an unknown proportion of the mortalities below the lower falls may have been ‘fall back’ from the stretch above.
There is some evidence to suggest that a proportion of the affected salmon could have had exposure to the excessive levels of the Chaetocerous diatom present at sea in the vicinity of the Ballisodare estuary on their return journey to the river.
As a result of this, the gills would have negatively affected normal gill function and therefore, hampered normal oxygen uptake.
The IFI have issued a number of recommendations following the conclusion of the investigation.
These include a risk analysis to assess all aspects of the river environment that may have contributed to the mortalities observed and identify where any precautionary and mitigation measures could be considered and implemented.
