Abstract

Switzerland has three native crayfish species, Austropotamobius torrentium, Austropotamobius pallipes and Astacus astacus and four introduced species: Astacus leptodactylus from Turkey and three North American species, Orconectes limosus, Pacifastacus leniusculus and Procambarus clarkii. To investigate the life history of the native and introduced crayfish species, I monitored 11 crayfish populations between 1996 and 1999. Activity, moulting, reproduction, fecundity, egg development and growth of the juveniles were recorded monthly by SCUBA diving and by sampling either by traps or by hand. Orconectes limosus and P. clarkii showed a different life cycle and activity pattern than the other species. Both species spawned during warmer periods of the year and had a much shorter egg carrying time than the other species which carried eggs during winter. In contrast to the native species and P. leniusculus, which were active only during the night, O. limosus, P. clarkii and A. leptodactylus were active during the day and night. Orconectes limosus and P. clarkii had high numbers of small eggs whereas A. astacus, A. leptodactylus and P. leniusculus had high numbers of large eggs. Austropotamobius torrentium and A. pallipes had a few and large eggs. The females of the American species became sexually mature in their second year. The females of the European species matured in their third year. Growth of juveniles in their first year was fastest in A. leptodactylus, P. leniusculus and P. clarkii and slowest in A. torrentium. The introduced crayfish species displayed a great potential for colonizing further waterbodies in Switzerland. The characteristics of life history indicate that these species will be strong competitors of the native Swiss crayfish fauna.

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