Angling Notes: Lice infestation of sea trout worst close to marine salmon farms, research finds
Sea trout infested with sea lice. Photograph: Bengt Finstad
NEW research by scientists from Inland Fisheries Ireland (IFI) and Argyll Fisheries Trust (AFT, Scotland) have found that sea trout carry significantly higher levels of sea lice infestation and reduced weight closer to marine salmon farms.
Scientists examined levels from more than 20,000 sea trout from 94 river and lake systems in Ireland and Scotland at varying distances from salmon farms over 25 years. Sea trout are known to remain for extended periods in near-coastal waters and are therefore vulnerable to sea lice impact.
The research paper entitled Aquaculture and environmental drivers of salmon lice infestation and body condition in sea trout was authored by Dr Samuel Shephard and Dr Paddy Gargan of IFI alongside Craig MacIntyre of AFT. It was published in the journal Aquaculture Environment Interactions in October.
Studies have shown that the impact of lice in farmed areas on sea trout is substantial, with increased mortality, reduced body condition and a change in migratory behaviour.
Heavily liced sea trout return to freshwater prematurely to rid themselves of lice and exhibit very poor marine growth and greatly reduced marine survival. In fact, the most heavily lice infested sea trout die at sea, the study found.
Data from 18 Connemara fisheries (1974 to 2014) show a collapse in rod catch over the 1989/1990 period. This collapse is linked to lice infestation from salmon farms while recovery of sea trout rod catches to pre-collapse levels did not occur.
Dr Gargan, said: “While there had been some improvement in sea lice control in recent years, lice control on salmon farms was still not sufficient in certain west of Ireland bays during the spring migration period for sea trout to avoid heavy lice infestation and increased marine mortality.”
IFI’s Head of Research and Development, Dr Cathal Gallagher, added: “This research will inform coastal zone planning of aquaculture in the future and contribute towards the avoidance of potential impact on sea trout stocks.”
Salmon Watch conference
The review, he said, “must ensure all stakeholders can participate in a transparent licensing process and have confidence that any licensing decision complies with all EU and national legal requirements and protects our oceans for future generations”.
Regrettably, his statement makes no mention of how all those legal requirements are going to be enforced. That is the focus of the conference.
Stocks of wild Atlantic salmon continue to decline. The causes are multiple, some having an impact on parts of the salmon population, such as climate change, and salmon farming having a more local effect.
There is general consensus among salmon conservationists that the impact over which man has some influence, eg freshwater and inshore environments, water quality, exploitation, by-catch at sea and the impact of salmon farms, need to be addressed with urgency.
Where salmon farms are concerned, the settled view has to be as rapid as possible a transition to recycling and closed containment systems. There are now sufficient examples of such systems operating in Europe and North America to confirm they are viable methods for producing high quality farmed salmon economically.
But the vast open cage salmon farming industry is not going to change to closed containment overnight; it is vital that it be regulated so as to mitigate its negative environmental impacts, including on wild salmonids.
The conference will examine the following issues: Current state of wild salmon stocks; Environmental impact of salmon farming; Current legal structure for regulation of salmon farming; Case study – the Faroe Islands; Is a consensus on salmon farming regulation possible?; What needs to be done to regulate Irish salmon farms?
Lismore angling courses
The second course on Saturday, May 27th, will focus on techniques for low water fishing such as stripping micro trebles and large flies, nymphing for salmon and furrowing flies. The cost of both courses is €150 (which includes fishing and lunch) and both are confined to six participants.
Contact Glenda at 00353 (0) 872 351 260 or firstname.lastname@example.org.