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The Western Regional Fisheries Board reports a serious fish kill on Lough Bofin, a lake on the island of Innishbofin Co. Galway. Inishbofin is located approximately 10km seawards from Cleggan Co. Galway.
Hundreds of dead eels were observed by Islander John Day last week and he became so concerned that he alerted the Fishery Board on Thursday last. The incident was also reported by Dr. John Mercer a marine biologist who lives on the island and is familiar with the area. Next morning, the scene was assessed by the Board’s Senior Environmental Officer Kevin Rogers who recovered dead eels and stickleback along a 250 metre zone of the north - west shoreline. It is thought to be the first ever fish kill ever recorded on any of the offshore islands in the western region.
Also large numbers of eels travelled overland in an attempt to escape from the lake towards the sea through the causeway and were found dead up to 50 metres from the lake boundary. Unusually, numerous live eels attempted to seek refuge underneath the rocks that form the causeway.
Fishery Officers are baffled by the incident particularly as oxygen levels are not seriously depleted. However, the fact that the lake is classified as a “shock lagoon” subject to tidal influence by “percolation and overwash” would seem to suggest that the fish died as a result of a sudden salinity change. Lough Bofin is therefore unusual in that is isolated from the sea by a narrow causeway though which sea water percolates during high tide conditions causing saline conditions to exist within the lake. The key question relates to whither there was a sudden and dramatic increase in salinity levels sufficient to cause acute impact on the fish populations which may not have had adequate time acclimatise to changing conditions.
Other causes are also being examined. The fact that eels ranged in size from 1metre downwards would indicate that the have survived in the lake for many years without being similarly affected. Samples have been recovered from the scene for further analysis and eels have been sent for pathological examination.
A preliminary report on the plankton in the samples which had been referred to Dr. Colin Pybus of GMIT was received on Monday evening last and he has identified the presence of a particular dinoflagellate organism which is known to produce toxins. This finding is thought to be highly significant and would indeed explain the eel mortalities which occurred in such a dramatic fashion.
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Greg Forde
Acting Chief Executive Officer
24th May 2004
For further information, contact;
Gregory Forde, Acting Chief Executive Officer
Tel 091 563110 or
Kevin Rogers, Senior Environmental Officer
Tel 091 563110 or 087 2527397.
Photo: fishkillinishbofin2004.pdf
Photo Caption: Fig. 1 Lough Bofin, Inishbofin Island
Fig. 2 Shingle causeway through which sea water percolates.
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