Taking care of our white-clawed crayfish
Native white-clawed crayfish used to be widespread across England and Wales but have been in severe decline since the 1970’s and at least 80% of the original populations have been wiped out. The main cause of this is the introduction of signal crayfish in the 1970’s and 80’s. They carry a disease called crayfish plague which is fatal to white-clawed crayfish and out-compete and predate their smaller and less aggressive cousins. Native crayfish also have to deal with other threats such as siltation and pesticide pollution associated with declining water quality. In Devon we have just two white-clawed crayfish populations left and one of those is in the river Culm in the Blackdown Hills AONB. Believed to have died out in the 1980’s, I was lucky enough to ‘rediscover’ them at Culmstock bridge in 2005. Surveys since then have found white-clawed crayfish between Culmstock and Hemyock along the Culm, but also a population of signal crayfish spreading up and downstream from Whitehall.
In 2018, Blackdown Hills AONB was lucky enough to get Heritage Lottery funding for the Culm Community Crayfish Project. As well as raising awareness of our special crayfish amongst the local community we organised a comprehensive survey of the Culm catchment. With the help of some amazing volunteers, we surveyed the Culm from Uffculme nearly to its source, plus two tributaries, the Madford and Bolham rivers, and several pond sites. We found that white-clawed crayfish are present from Hemyock all the way downstream to Five Fords near Uffculme, but signal crayfish are present in the Madford and Bolham rivers and downstream of our white-clawed crayfish at Uffculme. Even worse, the crayfish on the Madford river tested positive for crayfish plague which could easily spread to our white-claws downstream.
Discovering that our native crayfish are in an even more precarious position than we thought, Blackdown Hill AONB started to look for ways of helping our special River Culm residents. In 2019 we teamed up with Paignton Zoo who set up a facility to house and breed captive-bred Culm white-claws, descendants of animals that I collected in 2015 and 2016 for the Bristol Zoo breeding programme. James Maben from the AONB and some of our regular volunteers located some potential ‘ark sites’ – safe places where we can release and nurture captive bred crayfish – and carried out initial tests and surveys. In the meantime, Paignton Zoo secured funding for a two-year Devon ark site project. This means we can develop this work and extend it to the other Devon white-clawed crayfish population on the Creedy/Yeo river near Crediton. Sadly, due to Covid-19, we were unable to make a start on the ark-site work this year, but things are back on track ready for 2021.
With careful planning and social distancing, we have managed to get out ‘crayfishing’ this year, surveying the Sheldon stream, a tributary running northward entering the Culm at Five Fords. It’s great to see many of our brilliant volunteers from 2018 – I think some of them may have caught my crayfish ‘bug’! We survey using a combination of searching under rocks, kick sampling, and setting artificial refuge traps which mimic the natural places a crayfish would hide. It’s sometimes challenging – like when the forecast heavy rain arrives three hours early – or when the river more closely resembles the Amazon jungle than the Blackdown Hills! – but we always enjoy the unique outlook on the local countryside seen from the river. Unfortunately, this year we haven’t found any white-clawed crayfish and have found yet another signal crayfish population, making the need for ark sites even more pressing.
Over the last three years we have managed to do a huge amount of work to find out more about our special crayfish and the threats they face. None of this could be achieved without the assistance of our volunteers and I for one am eternally grateful. As this year’s crayfishing season comes to a close, I will look back on a challenging but nonetheless productive and rewarding year and be grateful that there are so many lovely people out there who share my interest and enthusiasm from these enigmatic and fascinating creatures.