Sea trout swimming close to salmon farms in Ireland and in Scotland have been found to be carrying significantly higher levels of sea lice infestation than those swimming further away from such farms.

Research carried out by scientists at Inland Fisheries Ireland and Argyll Fisheries Trust in Scotland also found sea trout swimming close to salmon farms had reduced weight.

The study saw the team of researchers examine sea lice levels of more than 20,000 sea trout from 94 rivers and lakes here and in Scotland over a period of 25 years.

The infestation levels were worse during years where rainfall was lowest. During such periods, an average sea trout caught within 10kms of a farm weighed up to 10g less than similar sized fish caught over 40kms from a farm.

Sea trout are considered to be particularly vulnerable to sea lice because they spend extended periods in waters close to coasts, where salmon farms can typically be found.

Sea lice infestation is considered bad for sea trout because it impacts negatively on the condition of their bodies, causes them to change their migration patterns and has been linked to increased death. 

Between 1974 and 2014 18 Connemara fisheries reported a collapse in rod catch of seat trout over the 1989/1990 period linked to lice infestation from salmon farms.

Since then the level of sea trout rod catches has not recovered to the level it was at before the collapse. 

Angling is worth €836 million to the Irish economy every year and supports upwards of 11,000 jobs.

The research was published in the international journal Aquaculture Environment Interactions.