Crayfish plague outbreaks are threatening to destroy Yorkshire’s last remaining strongholds of native white-clawed crayfish.

Devastating declines in Yorkshire’s native crayfish populations

The River Ure in North Yorkshire is home to the third largest population of crayfish in England, but large numbers of the species were found dying in August 2020. Samples confirmed they had crayfish plague. Devastatingly, it is estimated that around three million native crayfish will eventually succumb to the plague.

In the same month, crayfish plague was also confirmed in South Yorkshire, in one of the last surviving populations in the region at Barlow Brook near Chesterfield. What’s more, a previously healthy population of white-clawed crayfish have also disappeared from Wyke Beck, in North Leeds, with none found in 2019 or 2020. A single American signal crayfish was found at the top of the Wyke Beck catchment.

We are concerned that the plague may spread into adjacent river catchments which are home to extensive native populations, such as the Kent & Eden catchments. The transfer of plague from the Ure to other crayfish populations would be devastating.

Yorkshire’s story is sadly similar to most other areas of the UK. Large parts of southern England are now devoid of white-clawed crayfish. Read more about impacts of Crayfish plague in southern England

Origins of crayfish plague

White-clawed crayfish are our largest native freshwater invertebrate but they are now increasingly rare. Crayfish plague is spread by American signal crayfish, who are resistant to the disease. They were introduced into the UK in the 1970s and 80s in an effort to diversify farming within the Aquaculture industry (the farming of  fish, crustaceans, molluscs ect.) However, they soon began to escape from these ponds into our rivers.

Our native white-clawed crayfish have no natural resistance to the fungal infection, and populations exposed to it quickly disappear. The disease is spread through spores in the water, and through interactions between crayfish.

The effects of American signal crayfish on our rivers

Even if the American signal crayfish don’t have the plague, they quickly out-compete and kill native populations. They also have a wider detrimental impact on our rivers, killing other invertebrates, eating fish eggs and smothering fishing bait – they pose a real risk to our fishing industries.

Human causes behind the decline

Yorkshire currently finds itself on the front line of various expanding American signal crayfish populations. It’s particularly concerning to see American signal crayfish appearing in new areas, far away from existing populations. We have recently discovered populations in Roundhay Lake (Wyke Beck) and Wortley Beck in Leeds, which aren’t linked to any existing populations.  They have been moved either purposefully or accidentally by human activity.

We are aware of at least one example of people deliberately transferring American signal crayfish into ponds in Yorkshire. A fishing club bailiff confronted a young couple who admitted they had just emptied a bucket of crayfish into a pond before they fled the scene. The assumption is that they had plans to return to “forage” for the crayfish once established.

While fishing for American signal crayfish to eat is allowed in some areas of the country, it is illegal in Yorkshire. We often see recipes using American signal crayfish, which suggest that by catching them people can stop their spread. Unfortunately, catching them is not enough to stop their expansion, and by advertising this there are often unintentional negative consequences, which cause further spread.

Another way that humans contribute to the spread of crayfish plague is via wet clothing and equipment. The Ure crayfish plague outbreak was identified following surveys commissioned by the Environment Agency. We have not found any American signal crayfish in the area of the plague outbreak, so it appears that the plague was transferred into the catchment by human action.

Protecting our native white-clawed crayfish populations

The Environment Agency is working hard to establish emergency Ark sites where native white-clawed crayfish can be transported. Ark sites are locations which are safe from plague and other pressures posed by American signal crayfish.

How you can help

We need help from everyone, but especially water-users, to ensure crayfish plague is contained. There are a number of things you can do to help stop the spread of crayfish plague. Most importantly, any officials who enter rivers or ponds should follow good biosecurity measures, namely ‘Check, Clean, Dry’.

Clothing and equipment should be thoroughly dried and free of organic debris before entering a river or watercourse. A suitable disinfectant such as Virkon aquatic should be used on boots and equipment after entering a watercourse. Learn more about biosecurity

Report your sightings

Members of the public can help to alert us to the presence of native white-clawed crayfish – please report any sightings to Tim Selway: tim.selway@environment-agency.gov.uk.

Photo Credits

White-Clawed Crayfish with eggs, Wyke Beck – Tim Selway. Fatal impacts on White-Clawed Crayfish – Tim Selway. American Signal Crayfish – Trevor Renals. American Signal Crayfish Wortley Beck – Tim Selway. Ark sites act as refuges for native crayfish – Tim Selway. Cleaning clothing and equipment can reduce spread of Crayfish Plague -Tim Selway