North American predators move upstream at 500m a month, spreading disease to native species, Environment Agency finds
Members of an aggressive species of crayfish which have been invading England's waterways are being tracked with radio transmitters in an attempt to better understand them.
The Environment Agency said virile crayfish (Orconectes virilis), which are non-native, prey on native wildlife and spread crayfish plague, a disease deadly to native white clawed crayfish. The north American predators have recently been seen in waterways in east London after first being found on the river Lea near Enfield in 2004.
They have since colonised more than 10 miles of the river and linked waterways, spreading into Hertfordshire.
The agency has fitted small radio transmitters on the backs of the unwelcome guests, with preliminary results showing that virile crayfish are moving upstream at a rate of 500 metres a month.
This is substantially faster than their cousin, the signal crayfish, which is also non-native.
The UK's only native crayfish, the white clawed crayfish, was wiped out along the Lea after an invasion of the signal crayfish in the 1980s and the associated spread of crayfish plague. The plague is a fungal infection that can be easily spread between rivers on wet angling gear and water sports equipment.
Adam Ellis, environmental monitoring officer at the agency, said: "Whilst rivers in England and Wales are cleaner than they have been for decades, there is still a lot to be done in order to return them to full health. This includes the control of invasive species like virile crayfish.
"By tracking the colonisation of the river Lea by virile crayfish, we will better understand how this species impacts the environment and our native wildlife.
"However, one of the most important ways to protect our wildlife is to stop the spread of non-native invasive species. We're appealing to the public not to release unwanted pets into the wild."
Anyone who catches a crayfish must follow strict guidelines on how to handle them to prevent their spread and the transmission of crayfish plague.
It is believed that virile crayfish arrived in the UK after an aquarium owner released them into an east London pond.
The rise of invasive species is a challenge in meeting tough new EU targets on the ecology of rivers and lakes. They cost the UK economy an estimated £1.7bn a year, according to the agency.