| dc.description.abstract | In this surveillance program, environmental DNA (eDNA) monitoring of the water was used as an alternative method to the traditional cage experiments with live noble crayfish. Here, DNA from spores of Aphanomyces astaci are detected directly from water filtrates. The presence/absence of eDNA from noble crayfish (Astacus astacus) and signal crayfish (Pacifastacus leniusculus) was also determined to supplement the results and to gain the possibility to evaluate the habitat status in more detail, and as a part of the collaboration and coordination with the national surveillance program for noble crayfish. The main geographic focus of this surveillance program has been the Halden watercourse and neighbouring risk areas. Other covered geographic areas include the Mosse watercourse, Glomma watercourse, and selected areas in the Eidskog municipality including the Buåa watercourse, the Vrangselva watercourse and River Finnsrudelva. In total, 56, 35, 21 and 34 water samples were collected from selected sites in the Halden-, Mosse-, Glomma watercourse regions and in the Eidskog region, respectively. Locations for sampling water were strategically selected and focused on both control zones and the risk areas adjacent to crayfish plague control zones. The presence/absence of the three target species was determined simultaneously through screening with species-specific qPCR assays. In 2018, A. astaci spread upstream in the Mosse watercourse while no spread was observed in any of the other monitored areas. • In the control zone of the Halden watercourse, A. astaci eDNA was only detected in the southern part of Lake Rødenessjøen. Here, the known presence of signal crayfish was confirmed by eDNA detection. No sign of crayfish plague was observed in the northern part of Lake Rødenessjøen (Kroksund) up to the control zone border at Fosserdam. This result was supported by positive detections of noble crayfish eDNA in all water samples from River Hølandselva and upstream. All water samples in this risk area were negative for A. astaci and signal crayfish, while most samples were positive for noble crayfish eDNA. • In the Mosse watercourse, no eDNA of A. astaci or signal crayfish was detected. However, one dead crayfish found in Lake Langen was positive for A. astaci, demonstrating that crayfish plague has spread into Lake Våg and Lake Langen. Noble crayfish eDNA was detected at the inlet of Lake Langen. • In the Glomma watercourse, no sign of crayfish plague was found, and the samples were negative for all screened targets. • In Eidskog municipality, no samples were positive for either signal crayfish or A. astaci, while several were positive for noble crayfish eDNA in River Vrangselva and River Finnsrudelva. | |
