Abstract

Signal crayfish, Pacifastacus leniusculus (Dana), were introduced into Finland in the late 1960´s to enhance crayfish populations after the devastation of native populations of noble crayfish, Astacus astacus (Linnaeus), by the crayfish plague, Aphanomyces astaci (Schikora). The signal crayfish has established its position over time, currently constituting a large part of the annual crayfish catch in Finland. The faster-growing and more aggressive signal crayfish is capable of replacing the noble crayfish when occurring in sympatric populations, and therefore threatens the local noble crayfish populations. Habitat requirements are quite similar between these two species, although recently it has been observed that signal crayfish introductions into river habitats have often been unsuccessful compared to lakes. This experimental study aims at determining the differences between the noble crayfish and signal crayfish according to their adaptation to flowing water conditions. PIT-tag technology was used to track the crayfish. We observed that the signal crayfish moves faster and is more capable of moving upstream than the noble crayfish. The signal crayfish moved upstream against higher stream velocities and with a higher percentage of success than the noble crayfish. However, no differences were detected between the species in relation to preference over certain stream conditions. Research was conducted in both winter and summer temperatures, revealing that both species appear more active during summer than during winter.

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