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The Marine & Freshwater Environment Publication
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February/March 2013 Vol 9 Issue 1
ONLINE EDITION
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‘Sea lice not a significant factor in decline of wild salmon’ - Marine Institute Gery Flynn
A
nine-year investigation by the Marine Institute into the possible causes of the steep decline in the survival rate of Atlantic salmon at sea concludes that sea lice infestation plays a relatively minor role - accounting for only 1% of overall marine mortality rate in the stocks studied, or ten fish in a thousand. Inland Fisheries Ireland, another State agency, but charged with responsibility for the protection, management and conservation of inland fisheries and sea angling resources however says that this 1% “maybe the crucial tipping point” (see page 13). Dr David Jackson who manages the Marine Institute’s Aquaculture Section and is in charge of the National Sea lice Monitoring and Control Programme confirmed to Inshore Ireland that the study, which involved over 350,000 migrating salmon from twenty-eight releases at eight locations on Ireland’s south and west coasts between 2001 and 2009, “provides clear evidence that while sea lice-induced mortality on outwardly migrating smolts can be significant, it is a minor and irregular component of marine mortality in the stocks studied and is unlikely to be a significant factor influencing conservation status of salmon stocks”.
“remains unclear” it was likely to be due to a variety of different factors. “The list of possible causes is long and could be due to a combination of these. Global warming; changes in locations or availability of prey species associated with the North Atlantic oscillation; increased fishing pressure and predation; habitat changes and the loss of post-smolts as
by-catch in pelagic fisheries; sea lice infestation and sea lice-induced mortality have all been suggested. However, the results of a thorough analysis of the combined data over nine years suggests that sea lice are unlikely to be a significant factor,” he declared. Standing firmly behind his findings, Jackson believes it is very important to realise that
his team’s conclusions are based “on large samples of fish” ― and over a significant time period. “We’ve been looking at sea lice on wild salmon for a number of decades now, and have published half-adozen scientific papers on our research. We’ve found that lice-induced mortality to be, on average, around 1% while over the same period the
average mortality in smolts is over 90%. Also, that level of mortality wasn’t found in all samples. In fact, it was only about 40% of samples where there was a significant level of mortality that could be attributed to sea lice.”
Research leaders
He added that Ireland is to »» page 12
Reason unclear
He added that while the cause for the alarming declining trend in sea survival of wild Atlantic salmon
Donal Maguire, Aquaculture Development Manager with BIM, speaking at the public meeting and debate on the proposed Galway Bay Salmon Farm held at the Nuns Island Theatre, Galway photo: Joe O’Shaughnessy, courtesy of The Connacht Tribune