State bodies at loggerheads over proposed salmon farm
Marine Institute and IFI cite scientific evidence for opposing views on effect of sea lice on wild stock mortality rates
Were David Attenborough to visit the west coast of Ireland in search of natural drama, he couldn’t select two more controversial species for study than Caligus elongatus or Lepeoptheirus salmonis.
Long before fish farm cages were ever imagined on this island’s coastline, sea lice larvae were the bane of wild salmon and sea trout, attaching themselves and grazing on the mucus, skin and blood of the fish.
The same lice were regarded as a good sign for the restaurateur, indicating the freshness of a returning wild fish.
However, the role that aquaculture might play in elevating lice levels – transferred from adult wild to farmed fish and from there to juvenile wild fish leaving river mouths – came into sharp focus over two decades ago when there was a much publicised collapse of sea trout stocks in the western game fisheries.
Nine years ago, two marine scientists, Martin O’Farrell and Neil Bass, came to the conclusion that there was little or no evidence to support fish farms being the major culprit. They noted that an erratic decline in stocks of both salmon and sea trout was charted in Scotland, and much of it predated salmon farming by up to 30 years.
Human factors, such as catching sea trout as a by-catch in drift nets, installation of upstream and downstream traps by private fishery owners, and acidification caused by afforestation were more likely culprits, they said.
Still, serious differences over the issue have surfaced again in relation to Bord Iascaigh Mhara’s plans for a 15,000-tonne organic salmon farm in Galway Bay. While there is no effective anti-lice vaccine, there is a national sea lice monitoring and control programme which the European Commission has expressed satisfaction with.
Yet several State bodies are at odds over the issue. A recently completed Marine Institute-led study of returns of Atlantic wild salmon to river basins says pollution and poor water quality, rather than fish farms, are the main cause of stock mortality, and suggests that the State’s own scientific data indicates rivers in districts with salmon farms “have performed best in terms of meeting their conservation limits” and ability to support a commercial catch.
The study for the peer-reviewed Agricultural Sciences journal says there is a “steady and sustained improvement in the overall status of Irish salmon stocks”. The paper followed a previous nine-year study which concluded that infestation of outwardly migrating Atlantic salmon smolts by sea lice was only a “minor component of overall marine mortality” .
The study, led by David Jackson, analysed the return rates of fish treated to protect against sea lice with untreated “control” fish – reviewing data on 352,142 migrating salmon from 28 releases at eight locations along Ireland’s south and west coasts from 2001 to 2009.
Data published by Inland Fisheries Ireland (IFI), the State body responsible for wild salmon, and previously unpublished data from the Burrishoole and Bundorragha (Delphi) fisheries in the west was included in the review.
A similar study conducted in Norway, published this year in the Journal of Fish Diseases, came to a similar conclusion. The study led by Ove Skilbrei involved 650,000 salmon smolts released in “paired experiments” across 16 rivers over a 10-year period.
However, Inland Fisheries Ireland begs to differ. It says the basis on which the status of salmon populations in each river has been assessed for the Marine Institute-led study is fundamentally flawed and that the categorisation techniques deployed “totally misrepresent salmon numbers in Irish rivers”.
It says the study has drawn “blanket conclusions regarding fish stock numbers in rivers currently designated as ‘Open’ which fail to recognise that fish populations would vary significantly within this category, depending on the specific river concerned”.