Recently I was lucky enough to be invited along for some surveying by our friends @EnvAgencyMids We spent two sunny days in our waders with soggy sleeves, visiting different sites along the River Witham looking for white-clawed crayfish Austropotamobius pallipes.
Using a bathyscope to see below the water surface (see photograph to right) we searched pre-set survey areas for the very well camouflaged crustaceans.
Each crayfish we found was measured and inspected for any signs of disease or damage. Everything was recorded from siltation to shade and will be used to compare with previous and future data enabling the Environment Agency to track population changes and determine possible causes.
These amazing crustaceans are the only crayfish native to the British Isles but are sadly quite rare and continuing to decline due to several factors including habitat loss, pollution and the invasive North American signal crayfish Pacifastacus leniusculus. Their rarity affords them protected status and we were only allowed to catch and handle them under special licence.
The signal crayfish was introduced to UK commercial fisheries in the 1970s and has since escaped into our natural watercourses causing numerous problems. Not only does the signal crayfish carry the deadly crayfish plague which spreads to the native species, it is a voracious and aggressive predator, feeding on invertebrates, fish and frogs as well as smaller members of its own species and outcompeting the white-claws for food and habitat.
They also cause environmental issues through the creation of their extensive burrows, compromising the structural integrity of riverbanks, resulting in erosion, increasing flood risk and increased sedimentation. It is hard to see a positive – but I’m told they taste good ????
Conservation groups along with the Environment Agency are working hard to conserve the white-clawed crayfish by creating Ark Sites in the hope that they will be protected from the plague carrying invaders. These sites provide perfect crayfish habitat and are isolated from invasion. Finding suitable sites is challenging as the signal crayfish can travel hundreds of metres both up and down stream and over land.
The spread of invasive species and their disease put native crayfish and our rivers at risk but you can help Stop the Spread by following the Check, Clean Dry code and cleaning all your freshwater clothing and equipment thoroughly.
© 2019 Lincolshire Rivers Trust