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.
