Crayfish predator

Crayfish predator

Observation - Crayfish predator. Description: Thornton Beck, a tributary of the River Nidd, flows through my garden near Harrogate and supports a thriving population of American crayfish. I came across this smaller specimen on the rocks and wondred who attacked it. I discount herons, since it was wit

Thornton Beck, a tributary of the River Nidd, flows through my garden near Harrogate and supports a thriving population of American crayfish. I came across this smaller specimen on the rocks and wondred who attacked it. I discount herons, since it was within 3 metres of the kitchen window and was partly sheltered by overhanging vegetation - the hole in the carapace is too neat. There are reports of otter (?) and mink in the area - or was it simply rats?