"This report is the first global assessment of the impacts of fish farms on wild salmon populations, and the results are startling."
Jennifer Ford, lead author of the study
The study found that in rivers where juveniles passed by fish farms during migration, the number of wild salmon surviving and returning to spawn decreased by 50 per cent or greater, on average, when compared to similar rivers with no fish farms.
The study, funded by the Lenfest Ocean Program, was published this week in the online journal PLoS Biology, a peer-reviewed, open-access journal produced by the Public Library of Science.
"This report is the first global assessment of the impacts of fish farms on wild salmon populations, and the results are startling," said Jennifer Ford, lead author of the study.
"The findings from our analyses varied in different regions, but by combining them, we see that there is a negative impact on wild salmon that is highly significant."
"The sophisticated analyses in this study help people stand back and see the big picture when considering impacts of salmon farming on wild fish. It seems clear that salmon farming as currently practiced is not compatible with sustainability of healthy wild populations," said John Reynolds, who holds a research chair in salmon conservation at Simon Fraser University in Vancouver.
The scientists analysed data from rivers on the Atlantic and Pacific coasts of Canada and from the United Kingdom. The researchers chose rivers with fish farms and nearby rivers of comparable climate and levels of human development with no fish farms. The research sites also needed to have existing wild salmon populations.
"We need to start examining the link between fish farms and declining wild salmon populations carefully, especially in areas where wild salmon are already low in numbers," said Margaret Bowman, director of the Lenfest Ocean Program.
In December 2007, Ford was a co-author on another study that focused on aquaculture in British Columbia which found that sea lice became a serious threat to juvenile wild salmon in that area when fish farms were introduced. The study found that during infestations of sea lice, the exposed populations declined at such a high rate that scientists predicted the populations would be near extinction in two salmon generations (about four years). Although sea lice was a main factor in this area, other scientific studies have shown that interbreeding with escaped farm salmon and diseases such as Infectious Salmon Anemia have been factors in other areas.
"The reason wild salmon populations are suffering may be different from place to place, but it's evident that aquaculture often presents a combination of factors that reduces survival of wild salmon," concluded Ford.
For a summary of the research and a list of other studies on the relationship between aquaculture and wild fish populations, visit: http://www.lenfestocean.org
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