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Signal Crayfish found in the Derwent Catchment
A member of the public has reported to the Environment Agency in Penrith seeing a crayfish
in the St Johns Beck (Derwent Catchment) near Threlkeld. No crayfish (native or
non-native) were previously known to occur in this catchment.
Environment Agency staff from fisheries and FRB (Fisheries, Recreation and Biodiversity)
have confirmed that non-native signal crayfish are present. Over thirty individuals have
been recovered so far and it is confirmed that the population occupies at least 600m of St
Johns Beck which is an important salmon spawning area. Further investigations are ongoing
into the extent of the infestation and the source.
This is the first time signal crayfish have been recorded in Cumbria and anyone who thinks
they may have seen a crayfish in any of the tributaries of the River Derwent is urged to
contact the Environment Agency immediately (0800 807060).
Cumbrian rivers and becks support some of the last remaining populations of the native
white clawed crayfish. Crayfish plague (caused by the fungus Aphanomyces astaci) has
caused drastic losses of native crayfish in rivers in England. It is believed that this
disease was introduced and is spread by the most frequently farmed species, the signal
crayfish a carrier of the disease.
Crayfish plague is spread by spores that are specific to crayfish but can be transferred
between rivers not only by crayfish but also by fish, water, mud or equipment that has
been in water where signals crayfish are present.
 |
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| Native white-clawed crayfish up to 12cm
long, underside of claws = dirty white/pink |
Signal Crayfish
up to 30cm long, underside of claws = red. |
Preventing the spread of crayfish plague.
As the spores remain viable only when damp, complete drying of equipment that has been in
contact with water or sediments is an effective way of killing them.
(This is probably the easiest and best way to help / prevent spread of crayfish plague
– wash boats with tap water and allow to completely dry out (UV kills plague spores).
Also please consider the order of rivers paddled. Please paddle the Derwent Catchment
rivers last (Eden, Leven and Kent rivers first) and then wash all kit thoroughly.)
Spores can also be killed by Iodine-based (iodophors) disinfectants.
Disinfection of Equipment and Tackle.
Typical iodophor products are Wescodyne/Iosan CCT and FAM 30/Iofarm, generally available
from farm or dairy suppliers. Label information and manufacturers instructions should
always be adhered to, but as a broad guide, Wescodyne/Iosan CCT should be diluted 1.5
parts in 100 with water, and FAM 30/Iofarm 1 part in 100 with water. Disinfection is best
achieved by first clearing off all mud etc. followed by immersion/exposure for 5 minutes,
or by application to surfaces using a spray, or pad soaked in disinfectant.
Disinfectants can be applied using a spray applicator, although it may be necessary to use
a bowl to dip paddles and other equipment. Iodophors are inactivated by prolonged exposure
to light. When active they are a dark brown solution, becoming colourless when
inactivated. Inactivated disinfectant should not be used.
Always read product labels and follow the manufacturers instructions.
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