Sea lice and sea trout in "perfect" partnership

NEW research identifying a "perfect partner" relationship between sea lice and sea trout has been welcomed by fish farmers and questioned by anglers. Both sea creatures evolved a parasite/ host relationship over "eons" - that is, long before fish farming became a culprit for their connection - a seminar in University College, Dublin (UCD) heard at the weekend.

The research by a Galway based consultancy, Aquafact International, appears to break the link between sea lice, fish farms and sea trout decline.

It adds a significant piece to the ecological jigsaw which the salmon farming industry is attempting to put together", Mr Diarmuid Mulcahy, chairman of the Irish Salmon Growers Association (ISGA), said in a statement.

The findings, based on three years' scientific work, were presented to the Sixth Environmental Researchers' Colloquium at UCD on Saturday. The study of the interaction between larval sea lice and sea trout ecology related to Killary Harbour.

The working hypothesis is that spring salmon, mature sea trout or slob trout move into the estuary and act as a source of infestation for sea lice, while the fish farm does not.

"What Aquafact has proven is that before fish farms were heard of in Ireland, sea lice and sea trout had developed a highly dependent and complex relationship which ensures that the parasite always takes advantage of its host's natural habits," Mr Mulcahy said.

A great deal of scientific work had been commissioned by fish farmers over the last five years on this issue, he added.

"Our fledgling industry, the most legislatively and environmentally scrutinised sector in Ireland, has made the first significant steps towards identifying the facts about the life cycles and habits of sea lice and sea trout."

Dr Graham Shaw, chairman of the Save Our Sea Trout (SOS) campaign, said that he had no problem with the hypothesis; where it related to the background infestation of sea trout with sea lice prevalent in sea trout rivers throughout Ireland.

However, it failed to explain the huge increase in infestation, accompanied by premature return of sea trout to fresh water and the population collapse, witnessed in virtually every sea trout river within 20 kilometres of a salmon farm - and in no other location.