In Norway, the Atlantic salmon parasite Gyrodactylus salaris was introduced through transfers of salmon and trout from Sweden in the 1970’s and quickly became the most acute threat to wild salmon in the country, capable of extirpating entire river populations in four to six years.
The parasite eventually spread to 50 rivers and Norwegian authorities began a campaign to eradicate the parasite by denying it a host. Live gene banks and milt banks were established and entire rivers were treated with rotenone, removing all wild salmon. Among the largest was the Rauma River, which was treated in 2014 and subsequently declared parasite free.
Gyrodactylus salaris is a flesh eating parasite that has devastating effects on wild Atlantic Salmon. In Norway, it brought 50 populations to the verge of extirpation before authorities launched a campaign to deny the parasite a host by using rotenone in rivers. Photo Jannicke Wiik Nielsen Veterinaerinstituttet
To date, of the 50 rivers infected with Gyrodactylus salaris, 32 have been declared parasite free and salmon have been reintroduced, 11 others have been treated and are awaiting final analysis while seven rivers remain infected. Through the use of rotenone, the eradication of Gyrodactylus salaris in Norway is possible.
Norway's prolific wild Atlantic Salmon rivers faced an existential threat from Gyrodactylus salaris, yet following a multi-year rotenone campaign, nearly all infected rivers are now parasite free. Photo ASF/Christoper Buckley