Abstract

The spread of the invasive spinycheek crayfish, Orconectes limosus, was assessed for the period 1994 – 2008. This species was found in Lithuanian waters for the first time in 1994 and range expansion was discovered in 1995. In Lithuania, the noble crayfish, Astacus astacus, is the only native species, and at the end of the 19th century, Astacus leptodactylus began spreading, and in 1972 Pacifastacus leniusculus was introduced. The dispersal of A. leptodactylus was human-mediated, while the introduction of P. leniusculus was done in order to increase crayfish stocks. In 2000, the distribution of O. limosus covered an area delimited by the River Nemunas and the state boundary with Belarus, Poland and the Kaliningrad enclave of Russia. This crayfish was found to inhabit rivers and lakes of all trophic stages. The territory of Lithuania falls almost entirely within the catchment basin of the River Nemunas. This river, and its biggest tributaries, are suitable only for invasive O. limosus, and not native European species. Now O. limosus has invaded the entire territory of Lithuania. An abundant population of the invader was found in the River Venta, which runs from Lithuania to the Baltic Sea throughout the territory of Latvia. Long term monitoring studies were conducted in the river and at lake sites. The rate of expansion of O. limosus, as well as seasonal regularities in habitat occupation and abundance, were established.

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