Explore the vast range of titles available.

The invasive alien ectoparasite Gyrodactylus salaris is one of the greatest threats to wild Atlantic salmon (Salmo salar) in Norway. Since its introduction in the 1970s the Norwegian Environmental Authorities have applied a piscicide based eradication strategy, using rotenone to eradicate the host species, Atlantic salmon and the parasite. After refining the methods and techniques following several unsuccessful treatments, the program has become a success and a total eradication of G. salaris from Norway now seems possible. This paper describes the methods and techniques used in this program during a large eradication operation conducted in the Rauma infection zone in central Norway using different land based peristaltic and boat mounted pumps in combination with continuous drip stations and gardening cans. The eradication was performed in 2013 and 2014 and involved six infected rivers. The largest river, the river Rauma has an anadromous section of 42 kilometers and consists of both rugged fast flowing areas and slow flowing parts characterized by laminar water currents. The piscicide, CFT-Legumine®, containing 3.3% active rotenone was applied at a dose of 1 mg/l using a range of application methods aiming to achieve concentrations of 0.033 mg/l rotenone. To ensure target concentrations were met, rotenone concentrations were monitored using liquid chromatography with UV detection in all treated river in an on-site lab on a daily basis. Target concentration was reached in all treated rivers and while investigations are ongoing, to date they indicate eradication has been effective.

The introduced monogenean Gyrodactylus salaris (Malmberg, 1957) is categorized as one of the most severe threats against Atlantic salmon (Salmo salar Linnaeus, 1758) in Norway and has almost eradicated salmon populations in the Skibotn and Signaldalen Rivers in northern Norway. The parasite was unintentionally introduced to the Skibotn River in 1976 via release of infested Atlantic salmon smolt from Sweden. The parasite is restricted to freshwater, and survives at most a few days without its host. Therefore, eradication of all hosts in the infected river systems has been the preferred strategy to eliminate the parasite. After two failed eradication attempts in 1988 and 1995, the parasite spread further to neighbouring rivers. This, along with several other failed rotenone treatments in Norway in the 1990s, resulted in severe criticism of the national eradication strategy for G. salaris. Still, the eradication program continued, and the failed eradication attempts were analysed for possible improvements. Arctic char (Salvelinus alpinus Linnaeus, 1758) has proved to be a potential long-term host for the parasite and infested char were documented to have survived in small, groundwater-fed tributaries and ponds during the first two eradication attempts in the Skibotn River. Low limits on allowed rotenone concentrations set by the pollution control authorities might also have contributed to the failures. A third attempt at eradicating the parasite from River Skibotnelva was made in 2015 and 2016, using new knowledge about the parasite and its hosts, renewed strategies to map and deal with dilution from groundwater intrusion and an official acceptance of increased concentrations of rotenone. Treatments for two consecutive years was the main strategy improvement from previous eradication attempts. Water samples showed sufficient levels of rotenone concentrations at all sample points during the treatment periods. Significant efforts in collecting all possible surviving fish from the first-year treatment and screening them for G. salaris revealed no surviving parasites at the time of the second-year treatment. The national G. salaris eradication campaign includes a surveillance programme for eradication confirmation. The results so far are positive for the Skibotn Region, but the earliest an eradication confirmation can be issued earliest is 2021.

Roach (Rutilus rutilus) is indigenous to south-eastern Norway and alien to the rest of the country. In Trondheim municipality, in the middle part of Norway, roach was introduced into the Ila watercourse in 1881. Roach has a great potential to alter the ecosystem when introduced to new locations. The potential negative impact on potable water source quality and the prospect of permanently eradicating an alien species resulted in rotenone treatment of six lakes in Trondheim municipality. The rotenone concentration in the lakes was surveyed by water sampling until it could no longer be detected. A lethal concentration of rotenone at all test points was measured in all lakes during the survey period. Fourteen days after treatment, a near homogenous concentration was reached. The concentration reduction was similar in the lakes and relatively quicker during the first weeks after treatment. It was also consistent between depths except for the surface, where the concentration degraded more quickly. Rotenone degradation is a key factor when planning eradication efforts, and reports on this varies considerably between different locations. Despite application of rotenone in different depth strata, it took several days to reach homogenous concentration and several months and a fall turnover for the rotenone to break down and dilute below the detection limit in the lakes described.

A fast, accurate and simple method using liquid chromatography (LC) with UV detection was used for the on-site determination of the piscicide rotenonein water during fish control treatments. Sample volumes of 10 to 40 µL were loaded onto a Waters XBridge™ C18 2.5 µm 3.0 x100 mm analytical column usinga mobile phase of water–acetonitrile (45:55) at a flow-rate of 0.5 mL/min. The method was evaluated using river and estuarine water spiked with rotenone(0.1–330 µg/L) and various preservation methods. The within-assay precision measured as relative standard deviation (RSD, n = 12) was 5.5 to 6.5% andthe between assay precision (RSD, n = 4) was 6.5 to 7.5%. The limit of quantification was 1 µg/L, below normal piscicidal treatment rates (5 to 200 µg/L)and regulatory limits (< 2 µg/L) generally considered safe. The analysis time was 6 min/sample allowing for real-time adjustment of rotenone dosages duringfish control treatments. The relatively small size (75×60×50 cm) of the LC system made it ideal for transportation and installation in remote treatment areas;it can be operated out of a small trailer in the field with electricity. Our studies indicate that the preservation of water samples with equal quantitiesof acetonitrile stabilizes rotenone indefinitely (> 170 days) if kept cool (4 °C) and in the dark. Although increased salinity decreased the recoveryof rotenone, sample filtration with Spin-X filter membranes negated the effect.