Sea lice mortality in salmon link to if fisheries are open or closed
ANGLILNG NOTES: A 1 per cent reduction in salmon returning to their native rivers because of sea lice mortality may be the crucial tipping point between having an open or closed fishery, according to Inland Fisheries Ireland (IFI) following a Marine Institute publication, which notes that sea lice emanating from aquaculture facilities can cause mortality in wild Atlantic salmon.
To put this in context, if 3,000 salmon return to a river and this represents a 5 per cent return rate, a further reduction of one per cent means that 600 fewer adult fish return. This, says IFI, has the potential to curtail commercial or recreational salmon fisheries and impact on river conservation limits.
The study identifies that approximately 40 per cent of released juvenile salmon show a significant difference in return rate between sea lice “treated” and “non-treated” groups, indicating that mortality from sea lice is significant in 40 per cent of releases in the study.
If wild salmon stocks are not to be adversely impacted, the location of salmon farms in relation to salmon rivers also comes under scrutiny in the publication, as does the critical importance of sea lice control prior to and during migration.
Development of resistance to chemical treatment of sea lice and other fish husbandry problems, such as pancreas disease and amoebic gill disease, are likely to make sea lice control even more difficult in future years, the study deduces.
As one of the world’s largest producers of farmed salmon, Norway is seriously concerned about the impact of sea lice arising from aquaculture facilities on wild salmon stocks and the issue of escaped farmed salmon.
In its strategy portfolio, the Norwegian authorities point out that if delousing in fish farming fails to yield the desired effect on lice figures for wild fish, it may be necessary to consider a reduction in the biomass of farming facilities in the worst-affected areas.
On the issue of escaped farm salmon, they say “scientific comparisons of wild and farmed salmon, and their cross-breeds, has shown that gene transfer from farmed to wild salmon can reduce the latter’s ability to survive”. The IFI is keen to echo these views from an Irish perspective.
Inland Fisheries Ireland is supportive of the development of a sustainable aquaculture industry and welcomes all advances in research that will underpin the sustainability of this industry and safeguard wild salmon and sea trout stocks into the future.