by Alan Waterman
This meeting was led by John Field ably assisted by his son Henry. The group met up at the small car park for Buckholt Woods and John went through the preliminaries, not only health and safety for ourselves but also the Crayfish. We had all been advised that our footwear (wellies) had to be scrupulously clean and disinfectant spray was on hand to make doubly sure. John apologised for the initial ambiguity over the date for this meeting (although that was not necessary) but explained that the Crayfish are fully protected from any interference until July 1st as they are breeding, and the females are carrying eggs and young and that if they are captured, they will release the eggs or young which is obviously not beneficial. Also, that Crayfish do not refer to the calendar so depending on the local conditions the safe date to catch and observe them is of necessity variable.
John works for GWT and is involved with their efforts to conserve the White-clawed crayfish, this involves providing refugia for the Crayfish and natural flood management structures that have been installed in the Painswick Stream at Cranham Scout Centre and Buckholt Woods.
The work is quite complex and involves various operations, initially we were shown stream management which has become more untidy and more natural over the years, mostly trees that are close to the stream are felled ( usually Ash with dieback) and allowed to fall across the steam and other branches etc are introduced to provide a natural barrier. Also, the Crayfish are detritivores so they will feed on rotting bark and other dead plant material that collects in these natural dams. In addition to helping the Crayfish the water retention helps reduce the risk of flooding lower down in places like Stroud.
As most of us are aware that the White-clawed Crayfish is our native crayfish but in recent years the Signal Crayfish has been introduced and has widely replaced the native species. Signal Crayfish are bigger, more resistant to pollution and disease and they are more able to spread from place to place. Even if there were no disease or pollution John said that the Signal Crayfish would gradually out compete and replace the White-clawed Crayfish.
The main disease of crayfish is a fungus called Aphanomyces astaci , both species are vulnerable to it, but the Signal Crayfish has a slightly thicker exoskeleton so is more resistant. Transport of signal crayfish, and infected native European freshwater crayfish between waters is the main cause of contamination, though the disease can also be spread via items that have been in contact with contaminated water, such as a fishing tackle and footwear. The spores are sensitive to high or low temperatures. ( pour boiling water over you wellingtons). They also suffer from another disease called Porcelain disease, where the under sides of their abdomen appears white. Its tough being a White-clawed Crayfish.
Another aspect of the GWT’s work is to capture and relocate adults to areas where the crayfish were once found but have recently disappeared from. John explained that they aim to move 200 individuals at a time but they each have to be checked so that 50% are male and 50% are female also that they are the right size, so no small young ones and no large old ones and then they are checked to see that they are not showing any signs of disease. Also that they are the right species and no Signal Crayfish slip through.
Apart from managing the flow of the streams they also provide little microhabitats for the crayfish, these are called refugia, it may be a bundle of coppiced twigs ( faggots) laid into the water or a good layer of stones and rocks for them to hide in and to search for food. Prior to our visit John deployed artificial refuge traps, these resemble overgrown pan pipes and the crayfish use them to hide in. This was where John’s son came in, he had waders on and his task was to retrieve the trap and tip out any crayfish into a white inspection tray. The first trap had two crayfish, both males and the second one had just one, we did not inspect other traps leaving the occupiers in peace. The unfortunates that were caught were duly photographed and John used them to explain to us how to tell the White-clawed from the Signal which is largely to do with sharp little forward facing spines on their carapace that you can feel with your finger as you run it over them. The signal Crayfish lacks these and is quite smooth.
Johns main message was that prevention is key to reducing the spread of crayfish plague. Everybody who enjoys the countryside can play their part in helping to stop the spread of crayfish plague and therefore help to save our native White-clawed Crayfish. Crayfish plague is water-borne and is spread very easily on contaminated kit – wellies, canoes, fishing tackle, etc. It’s really important that people check that their wellies, and other kit, are clean and dry before moving between watercourses so as to prevent the spread of Crayfish Plague. On a practical level this means washing, ideally disinfecting, your boots and other kit at the end of your walk or paddle and allowing them to fully dry before being used on your next wet adventure – that pair of half-forgotten damp wellies or waders in the back of the shed could be harbouring the fungal spores that cause Crayfish Plague. Preventing the spread of non-native crayfish is also vitally important – crayfish must not be removed from, or moved between, watercourses. The trapping of non-native Signal Crayfish for human consumption requires a permit from the Environment Agency, but the activity is discouraged unless part of an authorised eradication scheme. Please note that the native White-clawed Crayfish is a Protected Species and can only be handled by licensed persons.
John imparted a huge amount of knowledge to us during our meeting and answered vast numbers of questions indicating how interested his audience was. Many thanks and keep up the good work.