Large numbers of free ranging salmon are being killed by parasitic sea lice in European waters every year, an international study has suggested.
The research involved the release of 280,000 tagged salmon smolts into 10 rivers in Ireland and Norway.
Sea lice were responsible for 39% of deaths among the young fish, according to the study's newly-published results.
Scientists from University of St Andrews' Scottish Oceans Institute worked on the research.
Also involved were the Department of Zoology at the University of Otago in New Zealand; Atlantic Veterinary College at the University of Prince Edward Island in Canada; Inland Fisheries in Ireland; the Institute of Marine Research in Norway; and the Norwegian Institute for Nature Research.
The scientists said natural mortality of wild salmon during their ocean migration could be as high as 90-95%, with deaths caused by a variety of factors including sea lice.
Prof Christopher Todd, of the Scottish Oceans Institute, said it was important that the industry continued to give control measures high priority.
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