White Clawed Crayfish

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 I went for a walk yesterday that took me along the Scandal Beck (a tributary of the River Eden). On the banks of the river was a stone that had obviously been used as a picnic table by an otter and the remains of his meal were strewn about. A recognisable part of the leftovers is shown below.


It's clear that this claw comes from a white clawed crayfish. These animals are not common in the UK as they need the water to be rich in calcium. This requirement is fulfilled in the Eden valley by the limestone substrate. I think that the River Eden is as far North as theses animals get. I know that there are crayfish in this part of the system because for a number of years I have volunteered with the Eden Rivers Trust to survey them. It was not uncommon to find a couple of hundred animals in a 300m stretch of river. The following images give an indication of scale.


In recent years the population of the native white clawed crayfish has been threatened by the arrival of the invasive signal (red clawed ) crayfish from North America. The non native species seem to have escaped from ornamental ponds (the crayfish can walk short distances overland) and they are much more aggressive than the native species and carry a different set of diseases.
We have a small stream next to the house but as this runs dry in the summer it does not support a population of crayfish. One problem is that crayfish don't move far and if the river suffers from a pollution incident , or dries up the crayfish can't easily repopulate the system.

Diary Notes
With the ground thawing after the snow the lapwing and common gull have returned to feed. Perhaps they had to go to the coastal areas whilst the snow was here? I repositioned the trail cams last night to a different area which was an unsuccessful experiment and produced three rabbits and nothing else. I saw one brown hare on my walk, and we caught a glimpse of our local neighbourhood stoat in the garden.



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