Crayfish in the River Cherwell have caused the partial collapse of a wall belonging to Magdalen College. The wall, located alongside Addison Walk and near Magdalen Bridge, has been damaged by crayfish burrowing into it. The position of the wall on a bend in the river has made it suitable for the crayfish to take root there over a period of several years, causing severe structural damage.
Magadalen College have told Oxford City Council that the damage poses risk to the Grade-I listed Water Meadow, a popular area for riverside walks in Oxford. It is believed that the cost of repairing the damage will amount to thousands of pounds.
Proposed repair works include inserting underwater concrete supports and lining the wall with a trench sheet that will reduce future burrowing. Documents lodged with the city council by Magdalen College say, “The works will sensitively reinstate and stabilise the bank and ensure these grounds continue to remain in use.
Owing to the seriousness of the bank erosion – much of which is caused by burrowing crayfish and high flows over slumped clay – the professional advice received is that proposals put forward represent the only viable options.”
The American species of crayfish, Pacifastacus leniusculus, has invaded many British rivers and has been identified as a threat to the ecosystem of UK waterways by the Environment Agency and the Great British Non-Native Species Secretariat (NNSS). Pacifastacus Ieniusculus, also known as Signal Crayfish, were introduced to Britain in the 1970s after disease decimated the native population.
However, they have been identified as problematic due to their predatory behaviour and rapid breeding. Although a spokesperson from the Environment Agency said that cases of structural damage caused by the fish are rare, they have been known to burrow deep into river banks in order to hibernate during winter.
Attempts to reduce the population of Signal Crayfish by marketing them as a health food are yet to be successful.
