ORIGINAL PAPER The first record of the non-indigenous signal crayfish Pasifastacus leniusculus in Norway Stein I. Johnsen Æ Trond Taugbøl Æ Oddgeir Andersen Æ Jon Museth Æ Trude Vra ˚ lstad Received: 3 January 2007 / Accepted: 3 January 2007 Ó Springer Science+Business Media B.V. 2007 Abstract The non-indigenous signal crayfish Pasifastacus leniusculus was registered for the first time in Norway in October 2006. The location represents an isolated pond about 100 km in air line from the nearest known signal crayfish population in the neighbouring country Sweden without any connecting watercourses. The occurrence is therefore undoubtedly caused by human introduction. Molecular analyses con- firmed that tested individuals from the signal crayfish population were carriers of the crayfish plague agent Aphanomyces astaci. Disease carry- ing signal crayfish represents a severe threat to the indigenous and endangered noble crayfish Astacus astacus. Norwegian authorities are cur- rently considering actions for the eradication of the signal crayfish population. Keywords Aphanomyces astaci Á First record Á Non-indigenous Á Norway Á Signal crayfish Introduction The noble crayfish Astacus astacus is the only indigenous species of freshwater crayfish in Scan- dinavia, and is an endangered species according to the Norwegian red list 2006 (Ka ˚la ˚ s et al. 2006). Since the 1960’s, the non-indigenous North– American signal crayfish Pasifastacus leniusculus has been introduced and spread at a large scale in Sweden, and is now the dominating freshwater crayfish species in Swedish waterbodies (Souty- Grosset et al. 2006). Signal crayfish are natural hosts for the oomycete Aphanomyces astaci (Unestam 1972) and consequently also chronic carriers of the agent that since the 1930’s has been known to cause the crayfish plague, a disease lethal to European freshwater crayfish (Alderman and Polglase 1988; Alderman et al. 1990). North- American freshwater crayfish therefore pose a great threat to indigenous European species of freshwater crayfish. Despite the massive intro- duction of signal crayfish in Sweden, this species has until now not been recorded in the neigh- bouring country Norway. However, it is expected to appear soon in the Norwegian part of the lake Store Le, a bordering lake between Norway and Sweden where signal crayfish has been observed in the Swedish part of the lake (Taugbøl 2004). In this paper, we report the first record of signal crayfish in Norway. The discovery was unexpected, as the locality is situated far away S. I. Johnsen (&) Á O. Andersen Á J. Museth Norwegian Institute for Nature Research, Fakkelga ˚ rden, 2624 Lillehammer, Norway e-mail: stein.ivar.johnsen@nina.no T. Taugbøl Glommen’s and Laagen’s Water Management Association, 2605 Lillehammer, Norway T. Vra ˚ lstad Section for Feed and Food Microbiology, National Veterinary Institute, 0033 Oslo, Norway 123 Biol Invasions DOI 10.1007/s10530-007-9092-2