Eliminering av signalkräfta på Gotland : En redovisning av utförda åtgärder inom åtgärdsprogrammet för bevarande av flodkräfta under 2007-2009

• SummaryThe Noble crayfish,Astacus astacus (also called the European crayfish or the broad-fingeredcrayfish) used to be the most common crayfish species in Sweden and Europe. It issusceptible to the crayfish plague,Aphanomyces astaci, and since 1907, when the firstoutbreak of crayfish plague was noted in Sweden, the Swedish Noble crayfish population hasdecreased with 97 %. The pattern is the same in all of Europe. To compensate for thediminishing Noble crayfish populations, Signal crayfish, Pacifastacus leniusculus wasintroduced into Europe (in Sweden in 1960). However, despite its resistance to crayfishplague, it still acts as a carrier of the disease. Thus, the introduction of the Signal crayfish mayhave accelerated the extinction rate of native crayfish populations. In Europe, the IUCN RedList of Threatened Species classifies the Noble crayfish as vulnerable. In Sweden theprospects for the crayfish are even worse, and the Official Swedish Red List classifies theNoble crayfish as Critical Endangered (based on the IUCN Red List criteria), facing anextremely high risk of extinction in the wild in the immediate future.The Swedish island of Gotland, situated in the Baltic Sea, is the first protected area in Swedenfor the Noble crayfish. No known outbreaks of crayfish plague have been confirmed onGotland, and Gotland is considered one of the very few areas left in Sweden that are notexposed to the crayfish plague. However, on Gotland there are three confirmed water bodieswhere Signal crayfish has been illegally introduced. The County Administrative Board onGotland was given the formal commission to exterminate any occurring populations of theSignal crayfish, as they can be carriers of the crayfish plague. This report contains of theactions taken to eliminate the Signal crayfish populations on Gotland during the years 2007–2009.The three localities where Signal crayfish occurs, including the ponds and the surroundingenvironment, was firmly investigated concerning the physical property and the composition ofthe ecosystem. The ponds where then treated with a pesticide containing the active substancedeltamethrin, with the aim of extinguishing all Signal crayfish. Deltamethrin is a syntheticpyrethroid insecticide, widely used on crops, as it is stable, less volatile and environmentallycompatible. The toxicity on mammals, including humans, and bird is relatively low ascompared to other pesticides, while it has been shown to be lethal to arthropods in very lowconcentrations. The ponds were treated with a dose aimed to reach a concentration of 0.5 μgdeltamethrin/l to obtain lethal doses.The outcome of the extermination of the signal crayfish in the three localities on Gotland wassuccessful so far. No live crayfish was found after the treatment, and all crayfish that wereplaced in cages in the ponds to control for the effectiveness of the pesticide treatment died.The concentration of deltamethrin declined rapidly and reached values below 0.1 μg/l, theEuropean Union drinking water limit, within one or a couple of weeks. The final succes ofthese actions is still uncertain as surviving individuals may take several years to detect.Inspections at all sites during the following years need to be carried out in order to determineif the Signal crayfish was completely exterminated from Gotland. 

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NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Environmental Sciences (hsv//eng)

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