A7.5 Desmoulin’s Whorl Snail Survey Baseline Conditions English Heritage

NEW 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.

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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, , 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,

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Desmoulin's whorl snail is locally distributed across southern and eastern England from 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 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. 5 Site under water. Entire sampling site in standing or flowing water over 5 cm deep.

3.2.7 Information regarding the vegetation and moisture is supplied in Appendix I.

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4.0 RESULTS

4.1 Desk Study

4.1.1 Wiltshire and Swindon Biological Records Centre provided six records for Desmoulin’s whorl snail, four within the Desk Study Area and two just to the north. All were recorded in 1996 and were recorded as ‘rare’ and ‘occasional’ in locations 5 and 4 respectively to ‘frequent and locally abundant’ at location 3. The closest record to the Survey Area was location 2 where they were recorded as ‘common in wetter areas’ (see Figure 2).

4.1.2 The River Avon catchment was described by Killeen (1997a) as being of national importance for the snail after surveying suitable habitat and finding the snail in 29 out of 76 locations. Of the 29 sites, 24 were on the Avon itself. Killeen states that it is very likely that Desmoulin’s whorl snail is living in every suitable area of habitat along the stretch of the Avon surveyed.

4.1.3 An ecological assessment undertaken in 2000 failed to find the snail during extensive searches of the flood plain area adjacent to the Countess East Site (AERC, 2000) although the area of ungrazed swamp/marshy vegetation adjacent to the River Avon was identified as providing ideal habitat. It was assessed that should Desmoulin’s whorl snail be present it would be living at low density or in isolated pockets.

4.2 Survey Results

4.2.1 Within the Survey Area of 1km of river upstream from the A303 survey, only small fragments of potentially suitable riparian habitat existed. A total of 21 sites were sampled. The locations are shown on Figure 3, and the descriptions given in Appendix I. These locations were surveyed in detail for the Desmoulin’s whorl snail.

4.2.2 The snail composition at each site is shown in Table 1.

4.2.3 Desmoulin’s whorl snail was found only at two sites (sites 10 and 18) along the River Avon. Both sites comprised relatively broad (2-3 m) riparian fringes vegetated mainly by grasses and sedges. However, only two adult specimens were found at each location from a total of 16 samples taken at these two locations. On the basis of these very low numbers, these cannot be regarded as populations, but more likely represent individuals that have been deposited from upstream locations.

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Table 1: Molluscan Composition Recorded

Species Site 123456789101112131415161718192021 Vertigo moulinsiana ------x ------x - - - Succinea/Oxyloma xxxxx-xxxxxxx-xxxxxxx Cochlicopa lubrixca ----x------x-x--x Vallonia pulchella ------x -- Discus rotundatus --x-x----x-----x-- -xx Punctum pygmaeum ----x----x------x--- Arion subfuscus --x-x------Zonitoides nitidus -x-xx----x--x---x---- Deroceras laeve xxxxx- -x-xx-x--xxxx- - Deroceras reticulatum --x-x--x-x--x-xxxx-xx Monacha cantiana ----x--x------x Ashfordia granulata --x-x--x-x- - - -x-xxxxx Trichia striolata ------x------xx Trichia hispida --x-x------x-xx Arianta arbustorum --x----x-x------x Cepaea spp. --xxx--xxx--x---xx-xx

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5. EVALUATION

5.1 Suitable Desmoulin’s whorl snail habitat along the river banks was discontinuous. Marginal strips with grasses and sedges occurred principally around the northern part of the survey area, especially around the bend in the river. The absence of Desmoulin’s whorl snail may be attributed to a number of factors:

x Most of these riparian margins were very small in area (mostly only a few square metres); x The banks have been revetted at several places, or were otherwise rather steep, such that the riparian plants were either standing in water or were on dry banks, and therefore the soggy conditions favoured by Desmoulin’s whorl snail were absent. Where there was no revetting, the narrow marginal habitat was subject to the effect of varying water levels, which may be too unstable an environment for the snail; and x The riparian margins were cut as part of river management and for angler's access. The adjacent field was used for cereals, therefore the riverbank may be subject to effects of herbicides, pesticides and fertilisers;

5.2 A summary of the findings is shown in Table 2 including the numbers recorded and the habitats available. The absence of Desmoulin’s whorl snail from the field drain (Sites 1-4) is rather surprising. Whilst the eastern half of the drain was rather dry and heavily poached by cattle, the western half was fenced off and contained ideal conditions for the snail, it was wetter and supports dense fen vegetation. Similar favourable habitat also existed within the boundary of the water treatment works (Site 5).

5.3 Although it should not be expected that every area of suitable habitat to be populated, in light of the number of other nearby populations in the River Avon corridor, it is unclear why such suitable habitats do not support the snail. It is possible that previous management affected these areas and they have only become suitable in recent years. Records of Desmoulin’s whorl snail occur upstream in four locations within the Desk Study Area including to the south east of Milston (location 3 of Desk Study) where they were recorded as frequent and locally common. It is thought that the snail disperses by waterborne transportation (Killeen, 2003) and it is therefore possible that where habitats have only recently become suitable for Desmoulin’s whorl snail, these habitats may in time become colonised from populations upstream.

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5.4 Allied with the ability to disperse into novel habitats Desmoulin’s whorl snail are Hermaphrodite. The ability to self fertilise makes it possible for a single coloniser to establish a new population and Killeen (2003) states that there is ‘no doubt regarding the species’ capacity to establish and rapidly spread into ideal habitat and increase in abundance’. The individuals present may represent initial colonisers of suitable habitat and may establish a population at these sites.

5.5 Within the Survey Area only two locations produced Desmoulin’s whorl snail records and only discontinuous suitable habitat was identified (figure 3b).

5.6 The area downstream from the New Visitor Centre Survey Area, included within the A303 survey found populations of the Desmoulin’s whorl snail. Most of the records were for the area upstream of the A303 road bridge, immediately adjacent to Countess East Site in the marginal fringe of the river and in the floodplain fen area. Relatively high numbers of the snail were recorded here comparing favourably with other component parts of the Avon cSAC (NPA, 2003). An estimate of approximately 140 snails/sample equivalent to 280 snails/m2 was recorded. The marginal vegetation both on the eastern bank of this area and down stream found low numbers of the snail and supported little suitable habitat.

5.7 The area of marshy fen where the number of individuals were high at 345 adults and 198 juveniles and two areas of river edge supporting 127 and 76 adults respectively and 69 and 38 juveniles were assessed as being of International Importance whilst other areas

5.8 Upstream and on the eastern bank where smaller numbers of snails were found, the A303 survey assessed these populations as being of Medium Importance: Regional with Potential for Substitution with areas assessed as being of Lower Importance.

5.9 For the purposes of the New Visitor Centre the evaluation of the importance of the sample sites are shown on Figure 5. The floodplain fen area sample sites A11, A12, A13, A14 and A15 are assessed as being of International Importance. It is possible that Areas A9 and A10 which contain dense nettle Urtica dioica and patches of Phragmites, Phalaris arundinacea and Glyceria maxima don’t currently support suitable conditions for the Desmoulin’s whorl snail. This northern area of the floodplain fen is drier than the south.

5.10 Two riverbank areas upstream, A4 and A8 support smaller numbers of the snail which are unlikely to be viable in their own right. These areas are valued as being of County Importance. No areas of International Importance were found upstream in the Survey Area.

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No specific assessment of importance has been given for the sites where only two individual animals were found as these are unlikely to be viable populations and are quite probably individuals washed downstream as in area A17 south of the A303 bridge. Instead areas with potential for Desmoulin’s whorl snail based on their current habitat and conditions are shown on Figure 5.

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6. CONCLUSIONS

6.1 The highest density of Desmoulin’s whorl snail is in the flood plain fen and the adjacent riparian habitat which is of International Importance. The northern part of the floodplain fen habitat adjacent to Countess East Site did not support any Desmoulins whorl snail, and the habitat was deemed unsuitable, possibly due to the drying out of this habitat. Two other areas were identified as being of County Importance, supporting relatively few animals in smaller areas of suitable habitat.

6.2 Only four animals were found during the New Visitor Centre Survey upstream of Countess East Site although some areas of suitable habitat were identified particularly around the Pumping Station. These areas have been identified but have not given a value.

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REFERENCES

AERC 2000. Ecological Assessment Countess East. Ref D5801. English Heritage.

Bratton, J.H. (ed), 1991. British Red Data Books: 3. Invertebrates other than insects. JNCC, Peterborough.

Drake, C.M. 1999. A review of the status, distribution and habitat requirements of Vertigo moulinsiana in England. Journal of Conchology 36: 63-79.

Highways Agency. June 2003. A303 Stonehenge Improvement Environmental Statement.

HMSO 1995. Biodiversity: The UK Steering Group Report – Volume II: Action Plans. HMSO, .

Kerney, M.P. 1999. Atlas of the land and freshwater molluscs of Britain and Ireland. Harley Books, Colchester.

Killeen, I.J. 1997a. A survey of the River Avon and tributaries (Wiltshire/) and associated wetland habitats to assess their importance for the snail Vertigo moulinsiana. In: Vertigo moulinsiana: Surveys and studies commissioned in 1995-96. English Nature Research Reports. 217. Ed. C.M. Drake, pp. 25-41.

Killeen, I.J. 1997b. Further survey of the River Avon and tributaries (Wiltshire/Hampshire) and associated wetland habitats to assess their importance for the snail Vertigo moulinsiana. In: Vertigo moulinsiana: Surveys and studies commissioned in 1995-96. English Nature Research Reports. 217. Ed. C.M. Drake, pp. 42-43.

Killeen, I.J. 1997c. A survey to determine boundaries of pSSSI for Vertigo moulinsiana on the River Bourne, Wiltshire. In: Vertigo moulinsiana: Surveys and studies commissioned in 1995-96. English Nature Research Reports. 217. Ed. C.M. Drake, pp. 44-45.

Killeen, I.J., in press. Surveys of EU Habitats Directive Vertigo species in England: 3. Vertigo moulinsiana. English Nature Research Reports, Peterborough.

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Chris Blandford Associates A7.5 Desmoulins whorl snail report.doc The New Stonehenge Visitor Centre English Heritage

Killeen, I.J. 2003 Ecology of Desmoulin’s whorl snail. Conserving Natura 2000 Rivers Ecology Series No. 6. English Nature, Peterborough,

Nicholas Pearson Associates 2003 Desmoulin’s whorl snail Baseline Survey Results. For and on behalf of the Highways Agency.

Chris Blandford Associates A7.5 Desmoulins whorl snail report.doc TABLES Table 2 - Summary of Desmoulin’s whorl snail results

Site Number of Comments number Desmoulin’s whorl snail found Adults/uvJ New Visitor Centre Survey 1 0 Potentially suitable habitat although rather dry and poached by cattle. 2 0 Potentially suitable habitat although rather dry and poached by cattle. 3 0 Potentially suitable habitat 4 0 Potentially suitable habitat 5 0 Potentially suitable habitat 6 0 No suitable habitat 7 0 Some potentially suitable habitat 8 0 Some potentially suitable habitat although rather dry 9 0 Some potentially suitable habitat 10 2 Adults Some potentially suitable habitat 11 0 Small area suitable habitat 12 0 Small area suitable habitat 13 0 Small area suitable habitat 14 0 No suitable habitat 15 0 Discontinuous suitable habitat 16 0 Discontinuous suitable habitat, much in standing water. 17 0 Discontinuous suitable habitat 18 2 Adults Some potentially suitable habitat 19 0 Discontinuous suitable habitat 20 0 Discontinuous suitable habitat 21 0 Some potentially suitable habitat A303 Survey A1 0 Occasional suitable habitat A2 0 Potentially suitable habitat A3 0 Potentially suitable habitat A4 22/12 Few individuals found. Discontinuous suitable habitat A5 0 No suitable habitat A6 0 No suitable habitat A7 0 Small area suitable habitat A8 34/28 Present in low numbers. Discontinuous suitable habitat A9 0 Little suitable habitat A10 0 Little suitable habitat A11 76/38 Low numbers throughout. Discontinuous suitable habitat. A12 0 Little suitable habitat A13 208/135 Present throughout wetter areas and locally common. Extensive area of fen with suitable habitat. A14 127/69 Very occasional. Discontinuous suitable habitat. A15 137/63 Present throughout wetter areas and locally common. Extensive area of fen with suitable habitat. A16 0 No suitable habitat A17 2 2 specimens probably washed downstream. Discontinuous suitable habitat A18 0 Potentially suitable habitat A19 0 No suitable habitat A20 0 Potentially suitable habitat APPENDICES APPENDIX I The New Stonehenge Visitor Centre English Heritage

APPENDIX I: Habitat Descriptions Site Habitat Description & Vegetation Composition Vegetation height (m) Moistureg 1 Field drain Unfenced field drain amongst cattle-grazed pasture. Damp depression with Carex and Glyceria < 0.2 2 (heavily poached) and marginal Juncus. 2 Field drain Section c. 40 m long within electric fence, relatively open in middle of ditch with grasses & 0.8 2 Ranunculus. Margins with sparse Carex, Glyceria & Juncus. 3 Field drain Fen in course of drain within barbed wire fence. Dense Carex, Glyceria, Phalaris, Iris, Mentha, up to 1.4 2-3 at E, Urtica and other herbs. Tree shade at western end. 3-4 at W 4 Field drain Permanently filled ditch with Lemna. Dense, mostly, Glyceria surrounds. 1 - 1.3 3-5 5 Marsh Within boundary of water treatment works. Diverse marsh with Glyceria, Carex, Phragmites, up to 1.9 2 or less Epilobium etc. 6 River, Right bank More or less tree-lined along entire section, no suitable V. moulinsiana habitat. - - 7 River, Right bank Steep banks with occasional Sparganium, Carex and herbs. up to 1.4 4-5 8 River, Right bank Broad (2-3 m) fringe of Glyceria with Urtica and other herbs. <1.2 2 9 Drain Drain alongside woodland with marginal Carex riparia. 1.3 4-5 10 River, Right bank Relatively wide margin (3-5 m) with Glyceria, Solanum, Phragmites. up to 1.4 2-4 11 River, Right bank Small marginal lens of Glyceria and Iris. 1.2 3 12 River, Right bank Small marginal lens of Glyceria and Iris. 1.1 2 13 River, Right bank Small marginal lens of Glyceria and Carex. 0.9 3 14 River, Left bank Riverside path backed by trees, only patches of herbs along bank, no suitable V. moulinsiana 1.3 4-5 habitat. 15 River, Left bank Patchy riparian fringes of Carex and Sparganium, mostly standing in water. 1.3 4-5 16 River, Left bank Discontinuous riparian fringes of Carex, Sparganium and herbs, mostly standing in water. 1.3 4-5 17 River, Left bank Discontinuous riparian fringes of Carex, Sparganium and herbs. up to 1.3 2-5 18 River, Left bank Broader margin with Glyceria, Iris, Sparganium etc. up to 1.3 2-5 19 River, Left bank Margins with patches of Glyceria. <1.1 2 20 River, Left bank Patchy riparian fringes of Carex and herbs. <1.3 2 21 River, Left bank Adjacent to field. River with steep banks with fringe of Epilobium, Urtica, willows, and up to 1.4 1-2 occasional patches of Carex riparia and Phalaris. g Moisture levels determined using arbitrary scale described in Section 3.4

Chris Blandford Associates A7.5 Desmoulins whorl snail report.doc FIGURES