We discovered this American signal crayfish whilst working on restoring the beck. These were introduced into the wharfe over 20yrs ago and have spread everywhere. Unfortunately they brought a virus with them that our native crayfish are very vulnerable to and are now locally extinct.  I believe this is a large male. It is an offence to remove them from the river as its been discovered that they eat smaller signal crayfish and thereby keep the overall numbers down. They are also a popular food source for our local otters