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American Signal Crayfish

Scientific name:Pacifastacus leniusculus
AKA: Cimwch dir Croyw (Welsh)
Native to: North America
Habitat: Most freshwater habitats

Crayfish prefer slow-flowing, clean water free of silt and filamentous algae. They love habitats where they can hide, submerged tree roots, crevices in stonework and stands of submerged aquatic plants.

Unfortunately, the American crayfish breed earlier, become larger, are more agressive and carry a disease to which they are immune but the native British white-clawed crayfish (Austropotamobius pallipes) is not. All these factors mean that where they occur, the foreign invader tends to outcompete and kill off the native species.

We received a licence from the Environment Agency to set traps to find out which crayfish we have in our stretch of the Severn. In our first sampling season, we caught only the American Signal Crayfish. The results of our sampling is summarised below.

 

Site No.

Coordinates Date No. caught Wet Weight (g) length to rostrum tip (mm) length to eye Gender
1 SO 09060 91092 0
2 SO 09025 91075 0
1 SO 09060 91092 02/09/2012 0
2 SO 09025 91075 02/09/2012 1 26 44 m
2 SO 09025 91075 03/09/2012 0
3 SO 09045 91087 03/09/2012 4 27 43 m
23 41 m
19 39 f
27 43 f
3 SO 09045 91087 04/09/2012 0
4 SO 09017 91068 04/09/2012 0
5 SO 12006 92308 07/09/2012 1 18 40 f
6 SO 12086 92348 07/09/2012 1 18 39 m
5 SO 12006 92308 08/09/2012 2 25 43 f
17 39 f
6 SO 12086 92348 08/09/2012 2 25 43 f
27 43 f
6 SO 12086 92348 09/09/2012 1 16 25 m
7 SO 12221 92391 09/09/2012 1 30 45 m
8 SO 11031 91807 14/09/2012 0
9 SO 11000 91759 14/09/2012 0
10 SO 11331 91582 06/09/2013 0
11 SO 11337 91584 06/09/2013 0
12 SO 12282 92301 06/09/2013 0
13 SO 12164 92400 06/09/2013 0
14 SO 12092 92347 07/09/2013 0
15 SO 12118 92355 07/09/2013 0
16 SO 09049 91082 14/09/2013 4 21 42 33 m
42 51 38 f
18 41 31 f
19 39 30 f
17 SO 09027 91068 14/09/2013 3 44 50 40 m
39 36 22 f
41 53 42 m
05/06/2014 0
05/06/2014 0
06/06/2014 0
06/06/2014 0
04/09/2014 0
04/09/2014 0
05/09/2014 0
05/09/2014 1 29 m
NA 2 7 m
16 41 30 f
N/A 2 26 43 33 m
16/09/2014 <1  15 12 juv
16/09/2014 6 19 40 30 f
16/09/2014 45 51 40 m
16/09/2014 16 37 27 m
16/09/2014 14 35 27 m
16/09/2014 9 33 25 m
16/09/2014 15 40 19 m 1 claw

Distribution

Sampling on our stretch of the river Severn we have found caught the American signal crayfish at virtually every site we have sampled. Sample sites are shown as red dots.

craysites