Water Vole Translocation Project: Abberton ReservoirAbout Water Voles Measuring up to 24cm, water voles (Arvicola amphibius) are the largest of the British voles and at a quick glace, are often mistaken for the brown rat (Rattus norvegicus). Unlike the brown rat, water voles have a rounded face and appear distinctly furry. Ranging from sedges to rushes, grasses to flowering herbs, water voles are known to consume at least 227 varieties of plant. Water voles breed between March and September and produce two to five litters of three to eight young. Inhabiting river banks, canals, ditches, streams and ponds, water voles are typically found next to slow-flowing water. Forefeet have just four toes and hind feet have five like the brown rat, but toes of the water vole are less splayed. With practice, water vole tracks can be identified. Droppings are also used to monitor water vole presence and are cylindrical in shape, measuring from eight to twelve millimetres long and four to five millimetres wide. The rodent may be sighted swimming within the river channel or scurrying through the vegetated banks. Population Dynamics Loss of wetland habitats has been the primary cause of the decline of this rodent species. A habitat which has rapidly disappearing from British landscapes since the 1900s, wetlands are also becoming increasingly fragmented. Predation by American mink (Neovison vison), an non-native species brought to the Britain in 1929 for the fur trade, is also to blame for the decrease in numbers of the rodent. Belonging to the same family as badgers, otters and weasels, American mink prey on water voles and have no natural predators to bring down their population. In the South Eastern region, these threats have caused water voles to decline over 90% in the past twenty years. Water voles are therefore fully protected under Schedule 9 of the Wildlife and Countryside Act, 1981, under which it is an offence to: Intentionally kill, injure or take water voles Possess live or dead voles, or derivatives Intentionally or recklessly damage, destroy or obstruct any structure or place used for shelter or protection Intentionally or recklessly disturb water voles whilst occupying a structure or place used for that purpose. Sell water voles or offer or expose for sale or transport for sale Publish or cause to be published and advertisement which conveys the buying or selling of water voles.
The Abberton Water Voles In the fifteen years of planning for the Abberton Scheme (hyperlink to http://www.eswater.co.uk/arenhancement.aspx), water vole surveys were conducted by Essex Ecology Services Ltd (EECOS) along the surrounding ditches which were eventually to be flooded for the reservoir s expansion. Billett s ditch, located to the south of the reservoir, appeared unoccupied by the rodent for several years. 2008 was the first year that water vole signs were observed. Droppings on floating monitoring rafts within the ditch confirmed the presence of the species. The Abberton Water Vole Translocation Project, coordinated by the Essex Water for Wildlife Officer Darren Tansley, commenced in March of the following year after a successful application for a protected species licence from Natural England. Trapping The trapping and translocation effort was spread over two years. Each year, 53 humane water vole traps were baited with carrot and apple and placed at regular intervals along the length of Billett s ditch, initially without the doors in place to allow the animals to acclimatise to the traps. Two days later, the doors were set and for each water vole caught, the sex and weight were recorded. Traps were checked twice daily, once at 8am and once at 4pm by Essex wildlife Trust staff and volunteers and Essex & Suffolk Water s conservation team. Any water voles caught were then taken to Wild Wood in Kent, where they were vetted, sexed, micro-chipped and quarantined before release. Microchips were used to gain information on the dispersal of the water voles after release. More water voles were caught in the first year of trapping. A total of 22 water voles, eight males and 14 females, were caught in 2009. In 2010, just 16 individuals were caught, comprising nine males and seven females. Weighing each animal caught allowed data from 2009 and 2010 to be compared. There was no significant difference between the average weight of males caught in the first and second year. This was also true of the females. The difference in average weight between males and females was also compared within the same year and were found to differ significantly in 2009 (Figure 1a). In 2010 however, the average weight of males and females were similar (Figure 1b). This is because males weighed more on average in 2009 than in 2010, at 211g and 183g respectively.
Average Weight (g) Average Weight (g) 300 250 200 150 100 50 0 Sex Sex of Water Vole Male Female Figure 1a: Average weight of male and female water voles in 2009. 300 250 200 150 100 50 0 Sex Sex of Water Vole Male Female Figure 1b: Average weight of male and female water voles in 2010.
Translocation The water voles taken back to Abberton reservoir and released at the western end. Man-made scrapes were created at the Western End in autumn 2008 to act as refuges for wildlife during the construction of the enlarged reservoir. Close to the water voles original ditch and included in the mink monitoring programme, the western end scrapes were the ideal location for their release. Comprising six hectares of undisturbed wetland habitat, reedbed and diverse grassland flora, Layer Brook also flows through the area, providing the potential for the water voles to disperse upstream. Prior to release, the water voles were each marked with a Passive Integrated Transponder (PIT) tag, in order to determine their dispersal (Knight, 2009) Two suitable release areas were identified in 2009 in a field survey conducted by Darren Tansley. Both were separated by water and large enough to allow the water voles to establish their own territories. Water vole release pens, designed to give a soft release, were partially dug into the ground and the grid reference of each recorded. The voles entered their new environment by burrowing their way under the open bottom of the pens, creating a secure shelter to return to in the first few days of release. Figures 2a and 2b show the locations of the release pens for 2009 and 2010. Figure 1a: Location of water vole release pens at the western end in 2009.
Figure 1b: Location of the water vole release pens at the western end in 2010. Post-Translocation Monitoring Four separate trapping efforts were carried out between August and September 2009 to monitor the dispersal of the translocated water voles at the western end (Knight 2009). Of the PIT tagged voles, six female and 1 male were re-trapped. 16 untagged juveniles were also trapped, indicating that the water voles population had been successfully breeding. Statistical analysis showed voles trapped within different vegetation types to show habitat preferences. Most adult water voles were re-trapped in areas containing less grass cover and a greater cover of riparian reed. Numbers of water voles trapped within different vegetation types did not differ significantly for juveniles, suggesting that younger voles had not perceived differences in floristic composition (Knight, 2009). Surveys in 2010 have provided evidence that the water voles from the 2009 and 2010 trapping efforts have naturally expanded their range across the whole western end. All of the mink rafts installed to monitor the mink population were covered in water vole droppings and feeding signs. Two mink have been caught to date at the western end, hence monitoring for mink is continuing. References Knight, M. (2009). An investigation into the habitat preferences of a translocated water vole population: Abberton reservoir, pp. 91 Water for Wildlife (No date). Otter and Water voles: South East Otters and Rivers Partnership, pp14