Wild Salmon Survival in the Balance – 1% may be the Crucial Tipping Point
Inland Fisheries Ireland (IFI) notes the recent Marine Institute (MI) publication which identifies that sea lice emanating from aquaculture facilities can cause mortality to wild Atlantic salmon. In this regard, the recent publication (Jackson et al, 2012) concurs with previously published international research (Krkosek et al, 2012 & Gargan et al, 2012). IFI welcomes the fact that there is now a clear acceptance of the negative impact of sea lice on juvenile salmon and the debate can now progress to identify the best methodologies to reduce or eliminate this impact. IFI would also like to see similar progress in relation to the issue of escaped farmed salmon.
In recent years approximately 5% of all juvenile salmon going to sea return back to their native rivers as adults to spawn. Precisely because natural mortality rates of salmon are high, even a proportionally small additional mortality from sea lice can amount to a large loss in salmon returning. To put this average 1% reduction in return rates, as reported by the MI, in context, if 3,000 salmon return to a river, and this represents a 5% return rate, a reduction in the return rate to 4% translates into a reduction of 1/5 (20%) of the adult salmon or 600 fewer fish returning. The Board of IFI is concerned that this level of additional mortality has the potential to curtail commercial or recreational salmon fisheries and impact on individual river salmon conservation limits and may be the tipping point between having an open or closed fishery.
