Escaped farmed salmon have an impact on wild salmon stocks. Some of the escapees migrate up rivers and spawn with wild salmon. Interbreeding can genetically weaken the wild stocks, which in turn can reduce wild salmon production in the rivers.
In addition to putting genetic pressure on wild salmon, escaped farmed salmon also carry sea lice infestation and fish diseases. The Norwegian Government’s goal is that aquaculture will not contribute to permanent changes in the genetic characteristics of wild fish stocks.
Farmed production is 1 300 times greater than wild catches
In 2010 approximately 916 000 tonnes of salmon were produced in Norway. By comparison, sea and river catches totalled roughly 700 tonnes of salmon, including escaped farmed salmon.
Even without correcting for the proportion of escaped farmed salmon caught in the wild, production of farmed salmon was roughly 1 300 times greater by weight than the total catch of wild salmon.
Most Norwegian farmed salmon originate from a small number of wild salmon stocks. Producers selectively breed salmon for specific traits, increasing their genetic differentiation from wild stocks.
Farmed salmon are bred for traits such as rapid growth, delayed sexual maturity, disease resistance, meat colour and fat content. One impact of selective breeding is that farmed salmon have far less genetic variation than wild salmon. Wild salmon stocks need the greatest possible genetic diversity so that they can adapt to changes in the natural environment, such as climate change.
In Norway, there are 481 rivers that have or used to have their own stock of wild salmon. in 340 of these rivers (71 %), escaped farmed salmon are a critical factor when assessing and categorising the state of the wild stock. In addition, escaped farmed salmon are assessed to be putting pressure on the remaining 141 river stocks. The salmon stocks of 21 rivers are listed as threatened because the proportion of escapees is too high.
The Institute of Marine Research has published a risk assessment of the environmental impacts of Norwegian aquaculture, in which it concludes that there is a high probability that the Government’s goal of avoiding permanent changes in the genetic characteristics of wild stocks will not be met for Western Norway. For the rest of the country, there is a moderate probability that the goal will not be achieved.