A recent Canadian study shows that wild salmon are mating with farmed salmon, and it may be to the detriment of the wild gene pool.
Along the rivers of Newfoundland, wild salmon are interbreeding with escaped farmed salmon, with around a third of the fish testing positive for the hybrid strain. An extensive research effort under the Canadian Department of Fisheries and Oceans (DFO) has found thousands of interbred fish in 17 of the 18 rivers targeted during the survey.
DFO scientist Ian Bradbury had this to say about how widespread the issue is:
“It was widespread across a suite of the rivers that we looked at. I think there was only one river where we didn’t see evidence of hybridization.”
With an estimated 750,000+ salmon having escaped over the years from fish farms in Newfoundland, interbreeding was not totally unexpected, and studies have revealed similar trends in Scotland and Norway. Although aquaculture fish farms do use sterilization methods, these do not work 100 percent of the time, and fish capable of breeding with wild salmon periodically escape.
Concerns that this is having an impact on the long-term health of wild salmon populations are increasing. Though the subject requires more study, early indicators are not good.
“The consensus seems to be that the more interbreeding and introgression we see, the more population productivity goes down. So, we do see an impact on population size, and we really need to better understand what these impacts are,” indicated Bradbury.
The potential impacts on wild salmon has drawn the attention of some conservation groups, such as the Atlantic Salmon Federation (ASF), who see this interbreeding as damaging to wild salmon populations and have expressed concerns over proposals to further expand aquaculture in Newfoundland.
Steve Sutton, a representative of the ASF, voiced concerns around aquaculture farming expansion:
“We have seen already in Newfoundland the entire south coast salmon populations have been assessed as threatened and aquaculture has been named as one of the threats to those populations. We’ve seen those populations decline and now we are finally starting to see the mechanism around those reductions.”
Studies will continue to examine the impacts of interbreeding between farmed and wild salmon to better define strategies moving forward.