Conservationists have discovered a cluster of rare and endangered crayfish at a nature reserve in Hampshire that were thought to have died out from the site over 30 years ago.  

The remarkable finding at Winnall Moors Nature Reserve comes more than three decades since white-clawed crayfish – the UK’s only native crayfish species – were thought to have vanished from the area in 1991 after a deadly plague wiped out local populations. 

For decades, conservationists have worked to recover white-clawed crayfish populations given their numbers have declined by about 70% in the UK since the 1970s due to pollution, habitat loss and the introduction of non-native crayfish. 

A group of reserves officers and volunteers for Hampshire & Isle of Wight Wildlife Trust made the discovery while carrying out routine habitat management at the reserve in Winchester. 

The team were removing a willow tree from the water to improve river flow, and as they hauled out the tree’s root ball – which was about the size of a large pumpkin – a group of what looked like ‘mini lobsters’ tumbled off it. 

The team’s first – and major – concern, however, was whether they had just unearthed a group of signal crayfish, an invasive species from North America that are now widespread in UK rivers. 

Signal crayfish carry a disease called crayfish plague, which they are largely resistant to but is lethal to white-clawed crayfish and has been the primary cause of our native species’ demise. 

Rachel Remnant, Reserves Officer for the Trust, and who was part of the team who discovered the crayfish, said: “Signal crayfish are known to occur roughly one kilometre away from where we were, so initially our worry was they had moved into the area and that’s what we’d found. 

“After a closer inspection, we couldn’t see any obvious red on the underside of the claws that signal crayfish typically have so we grew enticingly confident they were white-clawed crayfish but were still not 100% confident. 

“I video called my colleague, Dr Ben Rushbrook, who is the principal ecologist at the Trust and our resident crayfish expert, to show him what we’d found. He sounded excited but hesitant from what he saw, so said he would rush over.” 

While the team waited for Ben, Rachel used her upturned chainsaw helmet to hold the crayfish. This worked initially but eventually a larger container was needed, so one of the volunteers gave up his lunch box to hold the crustaceans. 

Once Ben arrived, he confirmed the crustaceans, the largest of which was about the length of a forefinger, were indeed white-clawed crayfish – a protected species in the UK. 

Ben, who has studied crayfish for over 13 years, said: “Finding this cluster of white-clawed crayfish is incredibly exciting, especially as we found some juveniles which suggests they are well established at this location. 

“It’s a bit of a mystery whether the crayfish have somehow managed to hang on undetected since the plague outbreak in the early 90s or whether they have since recolonised this stretch of river.” 

The ecologist added that the Trust are currently working on establishing several ‘ark sites’ across Hampshire to secure the long-term survival of this species. 

Ark sites are isolated, self-contained areas of rivers, lakes and ponds that have an absence of non-native crayfish. The Trust will continue to monitor this group of white-clawed crayfish to better understand how they are distributed across the reserve. 

The presence of white-clawed crayfish indicates a healthy ecosystem as the freshwater crustaceans require clean, well oxygenated and nutrient-rich waters.  

Rachel, who has worked at Winnall Moors Nature Reserve for almost 13 years, added: “This discovery was completely unexpected and the whole team has been buzzing about it ever since. 

“Life is tenacious, and this shows wildlife can come back if given the right conditions – it makes all the hard work over the years worth it. 

“Good news stories like this don’t come along too often, so we need to celebrate them when they do.”  

Over ten years ago the Trust embarked on an ambitious floodplain restoration programme, reconnecting relict water meadow carriers and improving river and stream habitat. This will have increased the amount of preferable habitat for white clawed crayfish and [we hope] contributed to their survival on site. Find out more about the Wildlife Trusts’ efforts to support the long-term survival of white-clawed crayfish at hiwwt.org.uk/southern-chalkstreams