Signal Crayfish

The Signal crayfish Pacifastacus leniusculus is native to North America have been identified as a potential threat to Irish waterways. The Signal crayfish has been categorised as an invasive species which has a negative impact on watercourses throughout Britain and Europe. Our proximity to Britain and our trade interaction with Britain means that it is the most likely potential source of the Signal crayfish. If Ireland’s native White-clawed crayfish is to be conserved it is imperative that Irish watercourses remain free of Signal crayfish.

Signal crayfish grow to a length of 18cm and due to their large size the Signal crayfish is known to predate on fish species such as the Stone loach Barbatula barbatula. Signal crayfish vary in colour from reddish brown, brownish blue and a plain brown. Unlike its counterpart the White-clawed crayfish the Signal crayfish has large claws. The Signal crayfish is distinguished by the white oval patch at the base of the pincers

The Signal crayfish is impervious to the infamous ‘crayfish plagueAphanomyces astaci and is a known vector of the ‘plague’. Introduction of the Signal crayfish to regional waterways has coincided with the absolute decimation of native crayfish populations which are highly susceptible to the plague e.g. White-clawed crayfish populations in British and European watercourses which were subject to the introduction of the Signal crayfish. Furthermore, the introduction of Signal crayfish to British and European waterways has a negative impact on native fish. The invasion of waters such as the Clyde’s Burn in Scotland has resulted in a depletion of trout; primarily due to the fact that the multitude of Signal crayfish diet on the same invertebrates as trout.

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