RISK ASSESSMENT OF GENETIC IMPACT OF ESCAPED FARMED SALMON ON WILD POPULATIONS IN NORWAY

The aquaculture production of fish, crustaceans and molluscs is increasing globally. For marine fish, open water production in net pens has proved to be the best system in terms of cost-effective production. However, culture facilities, and especially cages deployed at sea, are prone to fish escapes. These escapees represent a threat to the genetic integrity of wild populations.

In 2014, aquaculture production of Atlantic salmon in Norway was more than 1.2 million tonnes, while the capture of wild salmon was less than 500 tonnes. Annually, several hundred thousand Atlantic salmon are reported escaped from fish farms. In order to assess the risks of escapes on the wild populations of Atlantic salmon, and other environmental impacts, the Institute of Marine Research have conducted a yearly risk assessment since 2011 (Taranger et al. 2015).

The proportion of escaped farmed salmon (incidence) is monitored in a range of Norwegian salmon rivers, and these numbers are used as a proxy for measuring the probability for genetic impact. If the incidence of escapees in a population is higher than 10% it is classified as at high risk for genetic impact. The formal legislation required to plan mitigation efforts in rivers with more than 10% incidence of farmed fish passed the Norwegian government in 2015.  In 2014 140 rivers were monitored, of which 30 had more than 10% escaped salmon.

The proportion of escapees interbreeding in wild salmon was recently estimated using genetic methods in 20 salmon populations in Norway using diagnostic genetic markers (Glover et al. 2013). These results demonstrated strong variations in introgression among populations, ranging as high as 47% in one. However, there was only a modest correlation between estimated proportion of escaped salmon over the last 20 years and indices of temporal genetic stability in these rivers, demonstrating that genetic methods are required to validate genetic impact. Here we review the status of fish escapes and genetic impact from escaped fish in Norway.   

References

Taranger, G.L., Karlsen, O., Bannister, R.J., Glover, K.A., Husa, V., Karlsbakk, E., Kvamme, B.O., Boxaspen, K.K., Bjorn, P.A., Finstad, B., Madhun, A.S., Morton, H.C. & Svåsand, T., 2015. Risk ssessment of the environmental impact of Norwegian Atlantic salmon farming. ICES J. Mar. Sci. 72, 997-1021.

Glover, K.A., Pertoldi, C., Besnier, F., Wennevik, V., Kent, M. & Skaala, ø. 2013. Atlantic salmon populations invaded by farmed escapees: quantifying genetic introgression with a Bayesian approach and SNPs. BMC Genetics 14, 74.