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Sea Lice Pose Significant Threat to Wild Salmon Says New Research

15th November 2012
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Sea Lice Pose Significant Threat to Wild Salmon Says New Research

#ATLANTIC SALMON - About 39% of salmon mortalities were attributable to the impact of sea lice on wild salmon fisheries, according to a new international study.

The research, published in Proceedings of the Royal Society B, involved experts from Inland Fisheries Ireland collaborating with the Scottish Oceans Institute at the University of St Andrews, the Department of Zoology at the University of Otago in New Zealand, the Atlantic Veterinary College at the University of Prince Edward Island in Canada and the Institute of Marine Research in Norway.

In a statement on the report, IFI says: "In previously published studies, groups of salmon smolts were treated to protect them against sea lice infestation and other groups were untreated and both groups released to sea into 10 areas of Ireland and Norway. A proportion of these released fish were recaptured as adult salmon one or more years later.

"Analysis of the results of all previously published studies together provide experimental evidence from a large marine ecosystem that sea lice can have large impacts on salmon recruitment, fisheries, and conservation. The sea lice were likely acquired during early marine migration in areas with salmon farming, which elevate local abundances of sea lice."


IFI says the results "indicate that parasite-associated mortality may cause the closure of some fisheries when conservation targets of return adult abundances are not being met. However, the implications of these results may be most serious for small populations in small river systems."

The inland fisheries body explains that the high natural mortality rate of both treated and untreated salmon groups was accounted for, which revealed "a large effect of parasites".

"Precisely because natural mortality rates are high, even a proportionally small additive mortality from parasites can amount to a large loss in adult salmon recruitment," it adds.

Minister of State for Natural Resources Fergus O'Dowd welcomed the report, stating:  “From the results of this detailed study, it is crucial that sea lice levels are maintained below [designated] protocol levels, particularly in spring when wild salmon smolts are migrating to sea to avoid increased marine mortality.

Minister O'Dowd added that the results of this study "augment our knowledge in the context of proposals for aquaculture development".

The news comes in the wake of IFI's dispute with Bord Iascaigh Mhara over the exclusion of a report critical of the proposed new deep sea wild salmon farm in Galway Bay from the statutory consultation.

The scheme has faced opposition from local salmon anglers who fear the new facility would pose a threat to wild salmon stocks in Irish rivers by increasing the risk of sea lice infection.

Published in Inland Waterways
MacDara Conroy

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MacDara Conroy

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MacDara Conroy is a contributor covering all things on the water, from boating and wildlife to science and business

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