A family of 27 water voles that set up home in a sewage farm have been rescued at a cost of £400,000.
Click to view image: '783920a8f950-water_vole.jpg'colonised three disused sludge lagoons and a ditch within the Crossness sewage treatment works in Abbey Wood, southeast London. Because the animals have full legal protection Thames Water had to relocate them if it was to go ahead with plans to increase the sewage capacity at the plant.
The operation is estimated to have cost more than £14,800 per vole. Just capturing them is estimated to have cost £100,000, with 150 traps being set on floating polystyrene rafts and checked every eight hours for six weeks. Another £100,000 was spent on preparing the operation and about £200,000 on creating a hectare of fresh habitat to meet the animals’ needs.
Apples are a traditional favourite of water voles, but failed as a lure for them at Crossness. Instead the traps had to be baited with stronger-smelling grated carrots to attract them. Some 50kg of carrots were grated and placed in the traps.
The captured voles
Click to view image: '8bdb23ad8571-water_vole_2_dean_heward.jpg' were placed in empty Pringles tubes and transported to the Wildwood captive breeding centre in Herne Bay, Kent.
They and their offspring will stay in Kent for the next two years until suitable habitat can be created for them at the Crossness nature reserve owned by Thames Water and adjacent to the sewage works. The removal operation is one of the first to be licensed since water voles were afforded full legal protection last year, barring any form of disturbance or harm to them or their burrows. The once common animals are Britain’s fastest declining mammal.
Jonathan Benge, an ecologist at Scott Wilson, a design and engineering consultancy, was in charge of the operation and said that the water voles had colonised the sewage farm along a ditch from the neighbouring nature reserve. Despite the smell associated with sewage from hundreds of thousands of homes, the water voles found the location perfect.
“The sludge lagoons hadn’t been used for 12 years and had developed into a reed bed habitat. It was a perfect water vole habitat,” he said.
“The smell is always there. But the smell of the sewage isn’t going to deter them from superb habitat.”
Crossness deals with sewage equivalent to that produced by two million people. Each day it treats 777,600 cubic metres and when it has been expanded its capacity will have increased 44 per cent to 1,117,900 cubic metres per day.
When the replacement habitat is ready the water voles, or at least their descendants, are expected to be transported back to southeast London.
Dr Benge said: “Our biggest problem will be preventing it being colonised naturally by the water voles already in the nature reserve before we can put our captive-bred ones there.”
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