Inland Fisheries Ireland said it hoped any future applications for fish farms should take note of the findings of the research, which analysed sea lice levels over 25 years from more than 20,000 sea trout.
The sea trout were sampled from 94 separate river and lake systems in Ireland and Scotland at varying distances from salmon farms and one of the authors of the report, Dr Paddy Gargan, said the findings were the culmination of 25 years of study.
Dr Gargan, who is a Senior Research Officer at Inland Fisheries Ireland, said angling tourism in places like Connemara had been severely affected and that steps needed to be taken to limit the scale and effect of lice infestation on fish farms so as to protect wild fish.
The research, contained in international journal Aquaculture Environment Interactions, showed that sea trout captured closer to salmon farms had significantly higher levels of lice infestation and were found to be of reduced weight. It said sea trout was particularly vulnerable to sea lice.
According to the report, the effect of the increased lice infestation was most evident in years of less rainfall, when a sea trout of average length (180mm) caught within 10 kilometres of a farm could weigh up to 10g less than fish of similar length caught more than 40 kilometres from a farm. The study covered the entire coasts of west Ireland and Scotland and accounted for variability in temperature and rainfall.
Dr Gargan said the research “nails down the science” and showed that high lice levels were associated with fish farms, particularly every second year, just before large fish in fish farms are harvested.
“What we are saying is you need to ensure that in that second year that you have practically no lice on your farm to impact these [wild] fish going to sea,” he said.
Dr Gargan said regulations in the sector needed to be implemented “consistently” and that this was the responsibility of the Department of Agriculture, Food and the Marine.
He also said that areas such as Connemara had been “a mecca for angling tourism and that has much depleted since the 1990s.
“We have iconic species, like sea trout, that have suffered a collapse in Connemara.”
The issue of fish farms has proved controversial in recent years. Just last week it was reported that a West Cork salmon farm application will be considered at a hearing in Bantry next month.
Dr Cathal Gallagher, Head of Research and Development at Inland Fisheries Ireland, said: “This country is known as a unique angling destination as a result of its indigenous wild fish species and beautiful scenery. Continued investment in research is necessary to ensure the conservation and protection of our fisheries resource.”