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The Harnham Water Meadows Framework Management Plan - Annexes
Annex VII. Water Vole Survey information
Supplied by Beth Nightingale, formerly Water Vole Recovery Project Officer WWT
Water voles have partial protection under the Wildlife & Countryside Act (1981, as amended). In order to inform restoration plans, the Harnham Water Meadows Trust requested a water vole survey; this was undertaken 3 rd May 2006. Three main ditches were surveyed along with a small section of the River Nadder. These sites are marked on the map below. A full account is given under XVII, the site Management statement.
Standard water vole survey methodology was used whereby the vegetation along the ditches was hand searched for field signs. Field signs include burrows, latrines and single droppings, footprints and feeding stations with cut vegetation. These were recorded on a standard survey form included in the Water Vole Conservation Handbook (Strachan, 1998). Habitat information and other wildlife, such as water birds, otter, and brown rat as well as the non-native species American Mink, were also recorded.
Water voles were found to be present on Site 1 (refer to the map below) the Town Path ditch at the northern end and on Site 3 a feeder ditch on the eastern side of the water meadows. A total of 16 and 14 latrines were found on each site respectively with 37 and 19 burrows respectively. Rat droppings were found on Site 1 toward the southern end and a pair of mallard was also noted. A pair of mute swan was recorded on Site 3. No mink or otter signs were found during the survey.
The habitat is currently dry semi-improved and unimproved grassland that is grazed by sheep. During the survey a high density of sheep were present in the meadows on the western side of the site. Bank side trees are frequent on the town path on the far bank. Reeds/sedges are also present having been turned over following dredging works on this ditch. The near bank is a red brick and concrete causeway, although some small areas of soft bank edge remain. Site 2 with the ditch on the western side has very little diversity of vegetation with small pockets of soft rush. The main carriage running west from the town path is overgrazed and poached by sheep. The eastern ditch has patches of sedges and soft rush, where the water voles are present. The northern bank is most suitable where it has been fenced off, with tall herbs established behind the sedges. The water quality across the site appeared to be locally poor with evidence of partial and historical algal blooms and high sediment loading.
The predictive equation to estimate water vole population density can be applied using the latrine numbers. This is y = 1.48+0.638x, where y = water voles and x =latrines (Morris et al, 1998). If applied to these sites, Site 1 would have 12 individuals, Site 3 has 11. These small colonies would appear to have dispersal barriers and are not interacting due to the lack of vegetation cover, causeway along the Town Path and sluices with concrete walls. Although the survey was carried out early on in the breeding season and the population density would be expected to increase by the end of the summer, their distribution is very restricted. The primary cause of this is a lack of wetland plants and herbs, which would provide both a food source and cover to escape predators. This lack of vegetation diversity on the ditches also impacts on habitats for aquatic macro-invertebrates, dragonflies and birds.
In order to enhance the site for water voles and other wildlife it is recommended that a more sensitive ditch management regime be adopted. This would include dredging with a long reach excavator, so as to avoid compaction and collapse of water vole burrows, from one bank only. Previous reports of in-channel dredging are damaging to water vole habitat and other wildlife. Although the centre of a channel will need to be dredged to keep it open, a fringe (between 20 and 30cm) of wetland plants should be left on each edge. Plants removed from the centre of the channel should be relocated if possible to the edges of channels elsewhere. Re-profiling work on banks should avoid burrows; if this were not possible water voles would need to be excluded from a particular area before the works take place. Work should be undertaken outside the breeding season (i.e. between October and March) including d redging. The protocol should be undertaken on a case-by-case basis advised by Natural England, and should follow a rotational pattern as far as possible with the dredgings disposed away from the bank face or immediate bank top, in conjunction with EA best practice.
Construction works such as the installation of sluices would also need to avoid water vole burrows. Other main issues for the ditches are overgrazing and poaching of the banks by sheep. This is detrimental to wildlife and potentially to water quality causing nutrient enrichment from faecal input, as well as increased sedimentation from the sheep poaching and trampling the banks. It is recommended that fewer sheep are grazed in the western meadows; if this is not possible then temporary electric fencing be used to exclude animals from all but designated drinking points along the ditches.
If rat control is undertaken then steps to avoid accidentally catching water voles is essential. Discouraging rats from the ditch alongside the Town Path would benefit water voles and nesting water birds; it would also prevent risks to human health. Encouraging the public not to feed the ducks is desirable, otherwise feeding with grain is preferable.
Morris, P.A., Morris, M.J., MacPhearson, D., Jefferies, D.J., Strachan, R. and Woodruff, G. L. (1998). Estimating numbers of the Water Vole Arvicola terrestris: a correction to the published method. Journal of Zoology, 246: 61-62.
Strachan, R. (1998). Water Vole Conservation Handbook. English Nature, Environment Agency and the Wildlife Conservation Research Unit.
Water Vole Survey Results Harnham Water Meadows (May 2006)
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