ICES: Introgression of escaped farmed Atlantic salmon harmful to wild species
July 25, 2016
The escape of farmed Atlantic from net pens to rivers to spawn may result in genetic introgression and reduced fitness of wild salmon, according to new research published by the International Council for the Exploration of the Seas (ICES).
The ICES study, "Widespread genetic introgression of escaped farmed Atlantic salmon in wild salmon populations", quantifies genetic introgression of farmed to wild salmon, using molecular genetic markers, in populations from 147 salmon rivers -- representing three-quarters of the total wild salmon spawning population in Norway.
For 109 rivers with adult modern samples and sample sizes of 20 or more, the average level of farmed genetic introgression was 6.4% (the median was 2.3%), with a range between 0.0% and 42.2%.
Fifty-one of these rivers showed significant farmed genetic introgression when compared with historical reference samples, while "a highly significant correlation" was spotted between estimated farmed introgression and average proportion of escaped farmed salmon.
A generally lower level of introgression was found in national salmon rivers and national salmon fjords subjected to formal protection by parliament, leading researchers to the conclusion that "wild genetic introgression is high in a large proportion of Norwegian salmon rivers, with the highest levels found in the most intensive areas of salmon farming."
"The extensive genetic introgression documented here poses a serious challenge to the management of farmed and wild Atlantic salmon in Norway and, in all likelihood, in other regions where farmed-salmon escape events occur with regularity," wrote the authors Sten Karlsson, Ola Diserud, Peder Fiske and Kjetil Hindar.