Researchers map out the crayfish conflict in our rivers

Researchers are monitoring Norfolk's rivers for invasive signal crayfish

Researchers are monitoring Norfolk's rivers for invasive signal crayfish (inset) which are threatening native white-clawed crayfish - Credit: Jack Greenhalgh

An aquatic research effort is under way across Norfolk's rivers to help protect an endangered native crayfish from foreign invaders.

The white-clawed crayfish is the UK’s only native freshwater crayfish, but its numbers are declining due to habitat loss, pollution and competition from invasive species such as the North American signal crayfish.

So researchers are mapping out the populations of both species to help inform conservation efforts.

Jack Greenhalgh, a PhD student from the University of Bristol, is working with the Norfolk Rivers Trust and a team of volunteers who have been sifting through riverbanks with pond nets in search of crayfish.

Researchers collected 165 water samples from 50 sites in 10 Norfolk rivers

Researchers collected 165 water samples from 50 sites in 10 Norfolk rivers - Credit: Google Maps

They also collected 165 water samples from 50 sites in 10 rivers, which will be analysed for DNA traces which can indicate the presence of different species.

It is hoped the results will give a greater understanding of where remaining native crayfish populations are clinging on, and where invasive signal crayfish are advancing.

Mr Greenhalgh said: "The goal is to map the distribution of the native white-clawed crayfish, which is really quite endangered.

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"It has lost about 90pc of its population across the UK. So we really wanted to identify the last remaining strongholds in Norfolk so we can protect and conserve them. 

"The other aim is to identify where new populations of invasive signal crayfish are - if we can catch them in the act of colonising a new place then we have a greater chance of being able to slow them down or stop them.

"I am using environmental DNA - when you take a sample of the water, floating in there is the DNA released by the crayfish when they swim or when the females are heavy with eggs.

"By capturing the DNA we can use a genetic finger-print to identify various species of crayfish. It is like a crime scene, where you might brush for fingerprints or send off strands of hair for sampling."

Ursula Juta, catchment and education manager for the Norfolk Rivers Trust, said the county is one of the last strongholds for white-clawed crayfish - the largest invertebrates in our rivers.

Ursula Juta, catchment and education manager for the Norfolk Rivers Trust

Ursula Juta, catchment and education manager for the Norfolk Rivers Trust - Credit: Archant

"We have got 15 of the world's 200 chalk streams, so the water quality is beautiful, but also the rivers lack access because there is so much private land ownership, so there are less opportunities for people moving invasive species or their eggs," she said.

"We can use Jack's data to enhance the habitat for white-clawed crayfish to make sure there is enough vegetation, and to protect them from pollution events. If the landowners know they have got a population of white-clawed crayfish they are much more likely to manage their land and rivers sensitively to protect them."

The study has been part-funded by the Environment Agency.

Researchers searching for crayfish in Norfolk's rivers

Researchers searching for crayfish in Norfolk's rivers - Credit: Jack Greenhalgh

FUNDING FOR CRAYFISH HATCHERY

A hatchery for white-clawed crayfish is to be built in Norfolk thanks to a £95,300 grant from the government’s Green Recovery Challenge Fund.

Banham Zoo, which is run by the Zoological Society of East Anglia (ZSEA), was awarded the grant in collaboration with the Norfolk Rivers Trust to build an on-site hatchery which could help restore the population of the endangered native white-clawed crayfish.

Sarah Lee, living collections coordinator at the ZSEA, said: “Sadly our native crayfish face local extinction throughout the county unless urgent action is taken.

"Over the next few months we will be building the on-site hatchery which will enable us to successfully rear and then release these endangered native freshwater invertebrates back into the wild with integral collaboration with the Norfolk Rivers Trust.”

Researchers searching for crayfish in Norfolk's rivers

Researchers searching for crayfish in Norfolk's rivers - Credit: Jack Greenhalgh

An invasive signal crayfish

An invasive signal crayfish - Credit: Jack Greenhalgh

Researchers searching for crayfish in Norfolk's rivers

Researchers searching for crayfish in Norfolk's rivers - Credit: Jack Greenhalgh

Norfolk's chalk rivers are among the few remaining strongholds for white-clawed crayfish

Norfolk's chalk rivers are among the few remaining strongholds for white-clawed crayfish - Credit: Jack Greenhalgh


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