By the late 1990s it had become apparent that one of the commonest mammals on our river - the Water Vole - had disappeared.
The reason became apparent through the increasing population of feral American Mink in the area. Many people had seen this bold mammal in broad daylight and on a visit to the River Stort above Bishops Stortford two Mink put in an appearance in front of officers from the Environment Agency, the Wild Trout Association and my late friend John Green who rented the Trout fishing. On asking what could be done, I was referred to the Game Conservancy website where instructions were given for the construction of a ‘Mink raft’. Using some of the funds from the Sawbridgeworth Marsh Nature Reserve a couple of rafts were constructed and deployed, this was in 2005. Because of the nature of what we were doing the initial trapping was carried out clandestinely and it was not until 2008 that a whole programme of Mink raft trapping was rolled out across the whole of Hertfordshire.
Catches in the first year over the whole catchment were spectacular and looking back it was quite remarkable that we alone caught nine animals in the first season. The lack of water birds as well as voles on the river was testament to the damage that mink were doing to our native wildlife. It was recognised that the most effective trapping programme was done on a regional basis and it was thus that the Eastern Counties Mink Control Group formed, meeting regularly at Cambourne to discuss results and strategies.
By 2012 catches of Mink had fallen drastically and some consideration was being given to reintroduction of Water Voles to the Stort Valley in areas where the habitat was considered to be suitable. Thus in the Autumn of 2014 it was learnt that some Water Voles were due to be made available from a coastal realignment project on the Essex coast at the River Colne. Tidal surges in line with the progress of global warming had led to the overtopping of the sea wall on several occasions at Fingringhoe. The Environment Agency were preparing to start a project to create new saltmarsh and this would have resulted in the voles living in the reedbeds in the borrow dyke at the back of the sea wall, being made homeless.
Thus it was on 23rd March 2015, 150 traps were brought up from the Derek Gow Consultancy in Cornwall, baited with apple and carrot and set out along the dyke at 10 m intervals. The traps were inspected twice daily at 8 AM and 4 PM, any catches removed and placed in secure cages with food and bedding. Only after there had been five clear days with no catches then it was deemed that the population had been captured.
The voles were taken back to Cornwall for health checking and also to be integrated with homeless voles from the dredging of the Rivers Parrett and Tone in Somerset. This was important to create a proper genetic mix and lessen the chances of inbreeding. In the meantime, preparations were made for the ‘soft release’ of the voles at the HMWT Thorley Wash Nature Reserve. Fencing was put in along the ditches to prevent access by cattle when they would be introduced for grazing the reserve at the end of June. Four mink rafts were either installed or made ready in case any Mink should appear. Finally, on Tuesday, 2nd June the voles were brought up from Cornwall and kept overnight in an old stable block at Tednambury Farm. The following day a large team of volunteers assembled to carry the release cages on to the reserve, these were placed at specified 40 m intervals. The release cages contained bedding as well as apple and carrot. ITV and Anglia both attended the day and news reports appeared on 11th June. On the same day a small number of excess males were ‘hard released ‘ i.e. let go into the backwater. Over the next week or so the animals were held captive but fed in the release cages and then wooden ‘baffles’ with holes in were installed, these would allow the voles to come and go as they pleased. Seven of the voles had radio collars fitted and these were tracked for the following fortnight once the release cages were removed on Friday 12th of June.
At the time of writing the voles are establishing themselves very well and have started to mark out their territories by making latrines. The voles were released in pairs and it is very likely that many of these will breed before the end of the season in September. Close monitoring of the population will take place at the same time and it is hoped that we shall find the new population in a healthy condition next Spring. From this release point it is hoped that the voles will recolonise the river especially down towards the Sawbridgeworth Marsh Nature Reserve where some habitat enhancement is taking place later in the year.