An aggressive species of crayfish which has been invading England’s waterways is being tracked with radio transmitters in a bid to better understand them.
The Environment Agency said non-native virile crayfish prey on native wildlife and spread crayfish plague, a disease deadly to native white clawed crayfish.
The North American predators have recently been spotted in waterways in east London after first being found on the River Lee near Enfield in 2004.
They have since colonised more than 17km (10.6m) of the river and connected waterways, spreading into Hertfordshire.
The Environment 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 (1,640ft) per 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 River Lee following the invasion of the signal crayfish in the 1980s and the associated spread of crayfish plague.
Adam Ellis, environmental monitoring officer at the Environment 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.
It is believed that virile crayfish arrived in the UK after an aquarium owner released them into an east London pond.