Irish Times, Letter to Editor, 6 July 2013: Salmon and sea lice
Sir, – I wish to respond to the claim by the Marine Institute that the effect of sea lice on migrating salmon smolts is negligible (Home News, July 3rd).
This study looked at the returns of hundreds of thousands of salmon smolts over a period of years and from a number of locations in Ireland. Half were treated against the effects of sea lice and the other half not treated. All were tagged so that comparisons could be made.
The result was that 5 per cent of the treated smolts returned as mature adult salmon whereas 4 per cent of the untreated smolts returned as mature adults. The study concluded that this represented a 1 per cent effect by sea lice and was therefore negligible.
Let’s apply this in practice. The Corrib river needs approximately 7,500 mature salmon to maintain conservation levels. If we could treat all of the migrating smolts against sea lice, we would need 150,000 smolts to migrate and 5 per cent to return as mature adults. However, since this is impossible for all sorts of reasons, we would need 187,500 smolts to migrate so that 4 per cent would return and maintain minimum stocks. Finding an extra 37,500 healthy smolts to offset the effects of sea lice is not a negligible outcome.
The study by the Marine Institute to exonerate sea lice from harming migrating salmon should not give comfort to Minister for Agriculture Simon Coveney in the question of super salmon farms in Galway Bay.
The Marine Institute also concludes that the apparent recovery of salmon stocks in some rivers proves that sea lice are not a problem! Surely the recovery would be greater if the stocks were only dealing with background levels of sea lice? – Yours, etc,