After initiatives to encourage the mammal on Thames, Windrush, Evenlode and Cherwell rivers, efforts turn to the Great Ouse, writes PETER BARRINGTON

If Kenneth Grahame had written The Wind in the Willows in more recent times he might well have cast the villians of the tale away from the weasels, those adolescent delinquents living in the Wild Wood, to the mink that have been making a meal of Ratty and his water vole friends.

Grahame could well have cast otters as among the heroes of his yarn of the Thames riverbank at Moulsford and Wallingford.

For it transpires that otters are playing a part in the revival of water voles — remember Ratty was really a water vole, not a water rat — by becoming an enemy of the rapacious mink.

Initiatives to encourage otters to thrive again are being undertaken on several rivers, including the Great Ouse River that rises in Northamptonshire in the Brackley/Buckingham region and flows eastwards to the Wash at King's Lynn.

Earlier other projects were carried out in the Upper Thames catchment area upstream of Oxford and taking in such tributaries as the Windrush, Evenlode and Cherwell.

While otters, and indeed water voles, are indicators of the health of rivers, both have suffered in recent years.

Matt Dodds, green spaces biodiversity officer for Aylesbury Vale District Council, explained that water vole numbers have been badly hit over the years by mink that have multiplied after escaping from commercial mink farms.

"Mink have munched their way through the water vole population. However, otters are the friends of water voles as they are enemies of mink. Otters are from the same family as mink but are bigger. Otters mainly eat fish but they do prey on mink and so they can help the growth of the water vole population," said Matt.

He explained that there was a better chance of water voles recovering if the mink population was reduced.

"Otters are largely nocturnal animals and water voles are diurnal or day-time creatures and so they have some protection from otters. Mink are also small enough to go down water vole burrows, but otters cannot," he said.

So to encourage otters into the Great Ouse where it flows through North Buckinghamshire and the Aylesbury Vale, a number of otter spotting groups have been set up, each with a length of river.

One of the surest signs to indicate the arrival of otters is their spraints or droppings.

In addition to spotting and recording otters, the groups have been building otter holts or homes with the assistance of the British Trust for Conservation Volunteers and the Vale Countryside Volunteers.

"We have also been able to enlist the help of landowners in encouraging otters and water voles. Farmers can assist by ensuring their cows do not break down riverbanks and so destroy water vole burrows," said Matt.

Apart from keeping a weather eye on otters, landowners and volunteers have been able to take the fight against mink by having mink traps on land and on specially designed mink rafts that are anchored on the riverbank.

The rafts have a cover or hood and the floor is lined with plasticine or other similar material on which mink leave their paw or footprints.

"While mink traps have to be monitored daily, the rafts can be checked weekly. Once mink prints are found on the raft then a humane trap is put on the raft, which then has to be monitored every day. A captured mink is disposed of quite humanely," said Matt.

Mink traps have been made by inmates of Spring Hill open prison at Grendon Underwood, between Bicester and Aylesbury.

"Otters have been gradually returning to this region. In the past they were decimated by being hunted and the use of certain pesticides in agriculture. Otters maintained a presence in the west and are now spreading eastwards," said Matt.

Projects to assist otters were undertaken in the Upper Thames region for about ten years from the early 1990s to 2002 by the Environment Agency and Berkshire, Buckinghamshire and Oxfordshire Wildlife Trust.

Graham Scholey, conservation team leader for the Environment Agency based at Wallingford, said: "Up to the beginning of the 1990s, there were virtually no otters in the Upper Thames catchment region. But their numbers have been recovering. While we cannot put an exact figure on the population, it is in double figures, though I doubt if it is in three figures yet."

The project was divided up into four areas: upstream of Oxford on the Thames; the Windrush and Evenlove; the Cherwell and, in the south, the River Kennet in the Hungerford/Newbury area.

"We monitored the riverside habitats for the presence of otters and also bankside scrubland cover where female otters can lay up during the day," said Grahm.

Otters have re-colonised the region probably through natural migration from the Severn and Avon rivers which, with their tributaries, are relatively close to the Upper Thames and the Cotswolds.

Graham explained: "Otters are very good travellers and they are territorial. So young otters will move out of locations where otters are already established."

Otters have a mainly fish diet, but it could also take in mink and water vole.

"The biggest threat to otters now is road kill as there are many more vehicles on our roads than in the past," said Graham.