The study, released Feb. 11, found that in rivers where juvenile salmon passed by fish farms during migration, the number of wild salmon surviving and returning to spawn decreased by 50 percent or greater, on average, when compared to similar rivers with no fish farms.

The study, funded by the Lenfest Ocean Program, and managed by the Pew Environment Group of the Pew Charitable Trusts, was based on research data gathered over several decades, said Jo Knight, a spokesperson for Pew Environment.

“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.

Scientists analyzed data from rivers on the Atlantic and Pacific coasts of Canada and from the United Kingdom. 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.

The lead author of the study, Jennifer Ford, said the report constitutes the first global assessment of the impacts of fish farms on wild salmon populations, and the results are startling.

“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,” Ford said.

Her research included use of data gathered from 1970 through 2005 on all the mainland rivers inside of Vancouver Island on pink, coho and chum salmon, as well as the central coast of British Columbia. Other research involved Atlantic salmon in Eastern Canada, Scotland and Ireland, and sea trout in Ireland, she said.

British Columbia still has commercial and recreational salmon fisheries, but on the eastern coast, all commercial fisheries for Atlantic salmon are closed and recreational fishing is allowed only on some rivers, she said.

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Margaret Bauman can be reached at