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A7.5 Desmoulin’s Whorl Snail Survey Baseline Conditions English Heritage NEW STONEHENGE VISITOR CENTRE & ACCESS ARRANGEMENTS Desmoulin’s Whorl Snail Survey Baseline Conditions Final February 2004 CHRIS BLANDFORD ASSOCIATES Environment Landscape Planning English Heritage NEW STONEHENGE VISITOR CENTRE & ACCESS ARRANGEMENTS Desmoulin’s Whorl Snail Survey Baseline Conditions Final Approved by: Dominic Watkins Signed: …………………… Position: Associate Technical Director Date: 16th February 2004 CHRIS BLANDFORD ASSOCIATES Environment Landscape Planning CONTENTS PAGE 1.0 INTRODUCTION 1 2.0 SCOPE OF 2003 SURVEY 3 3.0 METHODOLOGY 4 4.0 RESULTS 6 5.0 EVALUATION 8 6.0 CONCLUSION 11 7.0 REFERENCES 12 TABLES Table 1 – Snail Composition of Samples (within text) Table 2 – Summary of Desmoulin’s whorl snail findings and habitat survey APPENDICES Appendix I – Habitat descriptions FIGURES Figure 1 – Designated Sites and Survey Areas Figure 2 – Desk Study Area and Results Figure 3 – Location of Sample Sites Figure 4 – Results of Desmoulin’s whorl snail surveys Figure 5 – Evaluation of habitat for Desmoulin’s whorl snail The New Stonehenge Visitor Centre English Heritage SUMMARY As part of the Stonehenge New Visitor Centre Project, a survey was undertaken along the margins of the River Avon, to establish the presence/absence and distribution of Desmoulin’s whorl snail, Vertigo moulinsiana. The snail is listed as one of the qualifying interests of the River Avon cSAC. This species is listed as Nationally Rare in the British Red Data Book (RDB3) (Bratton 1991); it is scheduled on Annex II of the European Habitats & Species Directive and is included on the UK Biodiversity Action Plan (BAP) as a priority species (HMSO 1995). The survey, undertaken during September 2002, covered a 1 km stretch of the river and involved a beating technique to release snails adhering to riparian or wetland vegetation. Desmoulin’s whorl snail was recorded at two locations within the survey area in low densities. These were not thought to represent populations but individuals washed in from upstream populations. A survey undertaken in 2001, recorded a healthy population was recorded immediately upstream of the A303. Chris Blandford Associates A7.5 Desmoulins whorl snail report.doc The New Stonehenge Visitor Centre English Heritage 1.0 INTRODUCTION 1.1 As part of the development of current proposals for the New Stonehenge Visitor Centre Project, ecological surveys have been undertaken evaluate the ecological resource of the area. This report sets out the surveys conducted for Desmoulin’s whorl snail Vertigo moulinsiana along the River Avon undertaken for the Environmental Impact Assessment of the scheme. 1.2 Desmoulin’s whorl snail, is listed in the British Red Data Book (Bratton, 1991) as a Red Data Book 3 (Rare) species, is included within Annex II of the European Directive 92/43/EEC of 21st May 1992 on the Conservation of Natural Habitats and of Wild Fauna and Flora (also known as the Habitats Directive) and is a UK Biodiversity Action Plan (UKBAP) Priority Species (HMSO, 1996). It is also a Species of Principle Importance in the ‘List of habitats and species important to biological conservation in England’ prepared under Part 3, Section 74 of the Countryside and Rights of Way Act 2000. 1.3 The snail is a named feature in seven candidate Special Areas of Conservation (SAC) (designated under the habitats Directive, 1992) in England including the River Avon cSAC (Figure 1). The River Avon cSAC, which is also designated as a SSSI comprises the main river plus the tributaries: Till, Wylye, Nadder and Bourne. Desmoulin’s whorl snail is widespread and locally abundant in the Avon cSAC (Killeen, 1997a; 1997b; 1997c, in press). 1.4 Desmoulin’s whorl snail is an inhabitant of mainly calcareous fens and marshes. It occurs in swamps, fens and marshes usually bordering rivers and lakes. It lives on both living and dead stems and leaves of tall plants such as grasses, sedges and reeds including reed sweet- grass Glyceria maxima, greater pond-sedge Carex riparia, lesser pond-sedge C. acutiformis and great fen-sedge Cladium mariscus, common reed Phragmites australis and other plants such as yellow iris Iris pseudacorus and branched bur-reed Sparganium erectum. They are thought to graze on fungi and micro-algae and possibly on bacteria on marsh plants and decaying higher plants (Killeen, 2003). 1.5 The habitat requirements are determined by humidity and the snail maintains this by occupying different levels of the habitat (vertical movement). They climb above wet vegetation during warm periods and descends in cooler parts of the year and over-winter in plant litter following vegetation die back. They are found high on stems and leaves of monocotyledons throughout the summer active period (Kileen, 2003). In Britain, Chris Blandford Associates 1/15 A7.5 Desmoulins whorl snail report.doc The New Stonehenge Visitor Centre English Heritage Desmoulin's whorl snail is locally distributed across southern and eastern England from Dorset to north Norfolk with a few isolated colonies elsewhere (see Kerney, 1999; Drake, 1999). Chris Blandford Associates 2/15 A7.5 Desmoulins whorl snail report.doc The New Stonehenge Visitor Centre English Heritage 2.0 SCOPE OF 2003 SURVEY 2.1 Detailed surveys for Desmoulin’s whorl snail along the River Avon were undertaken in mid September 2001 as part of the Stonehenge A303 Environmental Impact Assessment (Highways Agency, 2003). The Study Area for these surveys extended to 1km upstream of the A303 bridge and 2km downstream. The length of River Avon adjacent to the Countess East Site was therefore included within the A303 Survey. As many of the A303 surveys extended into the Study Area for the New Visitor Centre EIA, an agreement was made to enable information collated for the A303 EIA to be utilised in the New Visitor Centre EIA 2.2 The Visitor Centre Survey Area extends 1 km upstream from the A303 survey (Nicholas Pearson Associates, 2003) (Figure 1) and was undertaken by a national expert in malacological studies. 2.3 The A303 survey (NPA, 2003) confirmed the presence of Desmoulin’s whorl snail at several locations along the Avon. The report found a ‘healthy population’ north of the A303, adjacent to the Countess East site. 2.4 The purpose of the New Visitor Centre Survey was to augment the earlier data and to provide comparable upstream information to provide a baseline against which future trends would be assessed. 2.5 The aim of the survey was to: x determine presence and numbers where present; x to assess the suitability of the area to act as a control site, upstream of any potential impacts from the proposed New Stonehenge Visitor Centre. Chris Blandford Associates 3/15 A7.5 Desmoulins whorl snail report.doc The New Stonehenge Visitor Centre English Heritage 3.0 METHODOLOGY 3.1 Desk Study 3.1.1 Records regarding Desmoulin’s whorl snail were sought from Wiltshire and Swindon Biological Records Centre within the Desk Study Area (Figure 2). Information was also gathered from the River Avon SSSI and cSAC citations. 3.2 Survey Methodology Site selection 3.2.1 The 1km section of the River Avon upstream from the A303 Survey Area (SU 154431 to 159434) was surveyed on foot on 3rd September, 2002. Descriptions of the habitat along the river bank and drains and ditches immediately adjacent to the river were made. Access was possible along the entire east bank, but much of the west bank comprises steep, wooded slopes. Only sites with suitable or potentially suitable habitat, as described in paras. 1.4 and 1.5, were sampled for Desmoulin’s whorl snail. Where this occurred on the west bank, it was accessed by wading across the river Snail Sampling 3.2.2 Experience elsewhere has revealed that close examination of the stems and leaves of sedges and reed sweet-grass in the field is both time consuming and not reliable at sites where Desmoulin's whorl snail populations are at low density. To maximise productivity of the survey snails were sought using only a beating technique. The optimum survey window for this technique extends from August-October. A large sheet of heavy duty, blue polythene was spread on the ground at the base of the vegetation. A strip of living and/or dead vegetation approximately 1.0 x 0.5 m was bent over the sheet and shaken vigorously to release adhering snails. At each location, five samples were examined. If Desmoulin's whorl snail was not recorded in 5 samples, it was presumed to be absent, and a new location was sampled. 3.2.3 Very wet, decaying litter at ground level was not sampled as this habitat has been found not to support Desmoulin's whorl snail during the active season (snails over-winter in plant litter following vegetation die back). Chris Blandford Associates 4/15 A7.5 Desmoulins whorl snail report.doc The New Stonehenge Visitor Centre English Heritage 3.2.4 All samples were analysed in the field. Specimens of Desmoulin's whorl snail were recorded as adults or juveniles. Specimens with a developed lip and aperture teeth were counted as adults and others as juveniles. All other mollusc species were identified, counted and recorded. Vegetation 3.2.5 Within each sampling site the dominant plant species were recorded, together with vegetation height, density and structure. Moisture 3.2.6 Ground moisture levels at each sampling site were recorded using an arbitrary scale from 1-5 given below: 1 Dry. No visible moisture on ground surface. 2 Damp. Ground visibly damp, but water does not rise under pressure. 3 Wet. Water rises under light pressure. 4 Very wet. Pools of standing water, generally less than 5 cm deep.