Management of Ecoparasite Gyrodactylus Salaris on Atlantic Salmon in Norway

The invasive ectoparasite Gyrodactylus salaris first appeared in Norway in 1975 and is considered one of the worst threats to native Atlantic Salmon Salmo salar, causing epidemics that have reduced parr density and returning adults by 86–87% in 49 rivers.  The goal of the management program is to eradicate the parasite through host removal wherever possible and reduce their numbers where eradication isn’t possible.   Prior to host removal in affected drainages, representative individuals of salmon and other species of interest are removed, treated, artificially spawned, and the progeny raised in a hatchery for eventual reintroduction into the parasite-free drainage.  Although it is difficult to eradicate a pathogenic parasite in the wild, the obligatory dependence of the parasite on host salmonids and the requirement that the parasite must live on the host in freshwater makes it susceptible to localized eradication through host removal.  Since 1981, management efforts have improved with effective preventative measures, a better understanding of parasite life-history, fast and accurate parasite surveillance, detailed habitat characterization studies of infested sites, and the use of the fish toxicant rotenone in conjunction with barriers to limit treatment size and complexity.