Monitoring a Norwegian freshwater crayfish tragedy - eDNA snapshots of invasion, infection and extinction

1.The European Noble crayfish (Astacus astacus) is threatened by crayfish plague caused by the oomycete Aphanomyces astaci, which is spread by the invasive North American crayfish (e.g. signal crayfish, Pacifastacus leniusculus). Surveillance of crayfish plague status in Norway has traditionally relied on the monitoring survival of cage‐held noble crayfish, a method of ethical concern. Additionally, trapping is used in crayfish population surveillance. Here we test whether environmental DNA (eDNA) monitoring could provide a suitable alternative to the cage‐method, and a supplement to trapping.

2.We took advantage of an emerging crayfish plague outbreak in a Norwegian watercourse following illegal introduction of disease‐carrying signal crayfish, and initiated simultaneous eDNA‐monitoring and cage‐based surveillance, supplemented with trapping. A total of 304 water samples were filtered from several sampling stations over a four year period. eDNA data (species‐specific qPCR) for the p...