New summer surveys to try to identify cause of crayfish deaths
Source: gov.uk (2025-08-07)

The Environment Agency is carrying out a series of summer surveys to try to identify the cause of unusual symptoms in an endangered native species.

Last autumn around 100 native white clawed crayfish were found dead in the River Wansbeck catchment in Northumberland.

The subsequent investigation determined crayfish displaying similar symptoms - unusual orange patches on their shell – were widespread across the Wansbeck catchment as well as areas of the neighbouring rivers Tyne and Blyth catchments.

Now the Environment Agency is carrying out surveys across Northumberland and the North East through the summer to determine current populations of the native species.

The surveys will also be identifying locations where crayfish are displaying the unusual symptoms.

Intensive surveys on the Hart Burn, where the initial deaths were reported, as well as at some other sites, will help the Environment Agency understand the mortality rates in the population.

Working closely with experts

The team is working with both the Centre for Environment, Fisheries and Aquaculture Science (Cefas) and experts at Teesside University in efforts to understand more about the situation.

Sarah Jennings, Area Environment Manager at the Environment Agency said:

After a pause during winter and spring while the river levels were high we are now back out at rivers right across the North East to carry out widespread crayfish surveys.

We are working closely with experts at Cefas and Teesside University on sampling and analysis in efforts to understand more about what is happening to this important species.

There’s a lot we still don’t know but we hope this new work sheds some light as we continue efforts to safeguard the future of the white clawed crayfish.

Early surveys indicate that healthy populations of the native white clawed crayfish still remain in the North East – including in the Wansbeck catchment - but symptoms persist in some areas.

Surveys also show populations of the invasive American signal crayfish are also affected by the same symptoms.

Potential novel pathogens

Dr Jamie Bojko, Associate Professor in Disease Ecology (Research and Innovation), Teesside University, said:

We are applying metagenomic and metatranscriptomic methods, in combination with histology, to uncover potential novel pathogens that may be the cause of the shell abnormalities seen in the white claw population.

At the end of September last year, it was discovered that around 100 of the endangered native species had been found dead in the River Wansbeck catchment, one of the last remaining strongholds of the species.

Testing carried out by Cefas returned negative results for the listed disease white spot syndrome virus, in addition to Bunya-like brown spot virus, crayfish plague, and no evidence for any significant bacterial infection was identified.

The Environment Agency continues to be supported by the Northumberland Crayfish Partnership, which as well as the National Trust and Zoo, also includes Northumberland Rivers Trust and Northumberland Wildlife Trust.

The public and especially river users are being urged to follow Check, Clean, Dry advice to prevent the spread of symptoms:
- Check clothing and equipment for mud, aquatic animals or plant material. Remove anything found and leave it at the site.
- Clean everything thoroughly as soon as possible, paying attention to areas that are damp or hard to access and using hot water if possible.
- Dry for at least 48 hours, or if this is not possible use a suitable disinfectant before using elsewhere.
More information on check, clean, dry can be found on the invasive non-native species website. (https://www.nonnativespecies.org/what-can-i-do/check-clean-dry/)

If people see any crayfish, alive or dead, leave it where it is and report it immediately to the Environment Agency on xx-xxxx-xxxx. It is illegal to handle or remove crayfish from the water without the correct licences

Background information

Latest update:
- The symptoms seen in crayfish includes unusual orange patches on their upper shell and in some cases opaque-white muscles in the tail.
- The total number of confirmed mortalities last winter was around 100. The Environment Agency is working to understand more about mortality rates and the long-term impact on the species. Most known deaths so far have been in the Wansbeck catchment.
- Porcelain disease, caused by the microsporidian parasite Astathelohania contejeani, is known to infect and cause mortalities in freshwater crayfish and has previously been identified in crayfish around the country. This was present in some samples and is the only potentially relevant finding identified that could explain some of the mortalities observed.
- However, many affected crayfish are not showing any signs of porcelain disease, suggesting there is a wider issue which is not yet fully understood. The Environment Agency is continuing to work with Cefas.
- Water quality testing carried out by the Environment Agency ruled out pollution.
November 2024 rescues and quarantine:
- In November the Environment Agency joined forces with partners at the National Trust and Northumberland Zoo to rescue visibly healthy crayfish from the River Wansbeck at the Trust’s Wallington Estate.
- Females carrying eggs – known as ‘berried’ females – were kept in tanks at Northumberland Zoo, which has the facilities to rear the young and release them in the future.
- The berried females’ eggs hatched in April this year and the offspring are thriving in the zoo’s hatchery, which is on-show to the public. The plan will be to release these young crayfish locally in 2026, once they meet the release requirements.
- Males and females were also quarantined for three months by the National Trust in tanks at Wallington in the hope that the crayfish could be released into an ark site on the Estate.
- Ark sites are contained water bodies that are isolated from the risks commonly affecting white-clawed crayfish where they can live, breed, and be reintroduced into rivers. Unfortunately, approximately one fifth of the crayfish displayed symptoms after this quarantine period, which meant all of the crayfish were returned to the river.
White clawed crayfish:
- The endangered white-clawed crayfish are the UK’s only native, freshwater crayfish. They play a vital role in keeping our waterways clean and as a source of food for other native species.
- They have struggled to survive since the increase of the invasive American signal crayfish in the 1970s. The signals spread crayfish plague, which isn’t harmful for them but is fatal for the native species and are also bigger and out-compete the white clawed crayfish.
- There are no known signal crayfish in the River Wansbeck catchment and crayfish plague was ruled out as a cause for the River Wansbeck mortalities.
- Breeding takes place in autumn and ‘berried’ females can carry around 80 eggs through winter and spring. These hatch into juveniles in early summer.