Native Crayfish Rediscovered in Berkshire!

The native or white-clawed crayfish is one of our rarest invertebrates. At the start of the 20th century, it was widespread and common in the small chalk and limestone streams in Berkshire and Oxfordshire. Indeed, it was so common that Thomas Henry Huxley recommended that all budding students of invertebrate life should catch some to study and dissect. His 1879 book about crayfish is titled “The Crayfish: An introduction to Zoology” which emphasises the fact that he wanted to use this common and ubiquitous species that anyone could get hold of as a starting point in the study of zoology. Fast forward a little over 100 years and the situation could not be more different.

The native crayfish had long been fished in a sustainable way by country people to supplement their diet and to sell to market in the cities. When the stream habitats started to suffer run-off from the intensification of agriculture after the second world war, these small scale fisheries started to decline. The solution, or so it was thought, was to start farming American or signal crayfish. These were a more robust and generalist species of crayfish from the Pacific NW of America, more suitable for commercial farming than the native crayfish which is more of a niche species. Unfortunately the American crayfish proved to be both very adaptable and very good at escaping and before long started to appear in our native streams and rivers. This might not have been so bad except that they also carry a fungal plague. This has co-evolved with them and although it is endemic, does not cause them any problem. This was not the case for our native crayfish and the crayfish plague (as it is known) proved 100% fatal. As soon as American crayfish appeared upstream of a native population, the fungal spores wash downstream and that’s that. The result is that native crayfish are now present only in a few streams in the north and west of Oxfordshire, OR SO WE THOUGHT till ecologists working on a project to improve a bridge on the River Loddon this summer surprised themselves by catching one! It’s the first record of native crayfish in Berkshire for over 20 years, and the first record on the River Loddon for 30 years! This gives us some hope that there may be other small surviving pockets of population still left to be discovered in our area.

Posted: October 8, 2020