Norway's wild salmon owe part of their genetic make-up to escapees from salmon farms, which could compromise the fitness of the wild population.

Credit: NPL/Alamy

Wild Atlantic salmon (Salmo salar; pictured) are more genetically diverse and generally better adapted to the environment than are their farmed counterparts. Sten Karlsson and his colleagues at the Norwegian Institute for Nature Research in Trondheim looked at genetic markers in 21,562 wild salmon from 147 locations around Norway. They found significant genetic material from farmed salmon in wild fish from about half of these locations, with the average wild population showing 6% farmed genetic heritage. In some locations, this rose to 42%.

Wild populations in areas with many salmon farms contained higher levels of farmed salmon DNA than did those in regions with less farming. Managers of both wild and farmed animals should work to minimize mating between the two populations, the authors say.

ICES J. Mar. Sci. (2016)