Surveys for the Depressed River Mussel Pseudanodonta Complanata at Selected Locations in Staffordshire (July 2011)
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Surveys for the Depressed River Mussel Pseudanodonta complanata at selected locations in Staffordshire (July 2011) Fig. 1 Pseudanodonta complanata from the Llangollen Canal Dr. M. J. Willing A report for The Staffordshire Wildlife Trust Nick Mott (Project Officer) 1 REPORT CONTENTS: 1. SUMMARY 2. INTRODUCTION 3. METHODS 4. RESULTS 5. SITE ASSESSMENT SUMMARIES & DISCUSSION 6. ASIAN CLAMS CORBICULA FLUMINEA IN THE TRENT & MERSEY CANAL 7. FURTHER WORK 8. REFERENCES 9. ACKNOWLEDGEMENTS 10. APPENDICES • Appendix 10.1 Results • Appendix 10.2: Historic sites for Pseudanodonta complanata in Staffordshire and neighbouring Vice-counties • Appendix 10.3: Methods available for the survey of unionid mussels including Pseudanodonta complanata • Appendix 10.4: Unionid mussel identification 2 1. SUMMARY • Seven Staffordshire canal and river sites were visited on 5th and 6th July 2011 to try to locate populations of depressed river mussels Pseudanodonta complanata. • The surveys provided opportunities to provide training to Staffordshire Wildlife Trust and Environment Agency staff in identifying and sampling potentially suitable P. complanata habitat. • No P. complanata were located although low numbers of two other unionid mussels, Anodonta anatina and Unio pictorum were recorded at most sites. • Large numbers of the non-native Asian clam Corbicula fluminea were located at two sites on the Trent and Mersey Canal. These are new records for Vice-county 39: Staffordshire and the first finds of this species in the Midlands. • Suggestions are made for further work on P. complanata and C. fluminea in Staffordshire. • A unioid mussel identification key is attached to link with the laboratory based Pseudanodonta complanata training day. 2. INTRODUCTION The depressed (compressed) river mussel Pseudanodonta complanata inhabits medium to slow flowing hard water, lowland rivers and occasionally canals. It is locally distributed throughout England (Kerney 1999) where it has been recorded from at least 65 ten kilometre squares, whilst in Wales it is only known from a stretch of the lower River Wye (Willing 2009a). In Europe the species is widespread, occurring in the lowlands between south Scandinavia and the Alps. Throughout this range it is considered to be local (Kerney 1999) or regionally rare (McIvor & Aldridge 2007). Wells and Chatfield (1992) catalogued possible problems for the species in Austria, Germany, Poland, Sweden and Switzerland. In Germany the mussel is considered to be ‘threatened by extinction’ and has a high degree of legal protection (Der Bundesminister für Umwelt, Naturschutz und Reaktorsicherheit, 1996), although in the Netherlands, Gittenberger et al (1998) show a 50% increase in the number of known populations between 1970 – 1997 compared to pre-1970. On the IUCN Red List of Threatened Species (IUCN 2008) the species is placed at ‘Lower Risk – Near Threatened’. P. complanata was made a UK Biodiversity Steering Group (BAP) Priority Species in 1995 (Anon 1995) and an action plan for the mussel published in 1997 (Willing 1997). The Environment Agency has a statutory duty to promote the conservation of flora and flora dependent on aquatic habitats, and is the lead partner for the depressed river mussel SPA (species action plan in the UK. As part of the UK Biodiversity Action Plan (UKBAP), the main objective for the depressed river mussel is to maintain the present geographical distribution of the species. 3 The Conchological Society has three records of P. complanata for Vice-county 39: Staffordshire (10:2 Table 3) the most recent from Leek in 1933. In March 2010 N. Mott (freshwater ecologist with the Staffordshire Wildlife Trust) undertook a programme of P. complanata surveys at nine river and canal sites throughout the Canock Chase AONB (Mott 2010). Unfortunately no sites produced P. complanata, although several localities appeared to offer potentially suitable habitats for the mussel. The specific aims of this project were twofold. Firstly to survey a number of potentially suitable P. complanata sites on the rivers Tame, Mease, Trent and Dove and also the Coventry and Trent & Mersey canals. The second aim was to train a number of Staffordshire Wildlife Trust and Environment Agency staff to gain proficiency in field survey techniques for this and other large freshwater unionid mussels and also to be able separate and identify this group of mussels. 3. METHODS Pseudanodonta complanata can be surveyed in rivers and canals by a series of methods. No single approach is usually suitable in all parts of a river or canal and where one method fails to recover mussels then, on many occasions, another strategy is successful. The four main sampling options are with: 1. a long handled net (with a coarse mesh); 2. various dredges; 3. a hand collecting technique at river/canal margins whilst wading in the water; 4. the use of a ‘glass bottom bucket’ to visually search for mussels. Further details of these various sampling methods are discussed in Appendix 10.3. During these surveys the first technique was adopted as most sediments consisted of gravel deposits in only moderate water depths. The use of glass- bottomed buckets was trialled at sites 1a and 2a, but water turbidity and low mussel densities made this technique less useful than the use of a hand net. Sites were visited on 5th and 6th July 2011. Sites were also photographed using a digital camera and images are included in section 5. Survey locations were logged using a GPS device. 4. RESULTS Appendix 10.1 gives unionid mussel survey results including some records of other species). Molluscan naming throughout follows Anderson (2005) and site locations are displayed on Figs. 2 and 3. No live or dead Pseudanodonta complanata were found during the survey although two other unionid mussels, Anodonta anatina and Unio pictorum were recovered, the former species at all sites and the latter at four sites. A single dead Anodonta cygnea was also found at site 2a on the River Dove.The Asian clam Corbicula fluminea was found at two sites on the Trent 4 and Mersey Canal. Sampling in the canal at Newbold Quarry produced 73 individuals, whilst that at Stretton, 77 clams were recovered. Corbicula fluminea shell measurements are recorded in Table 2 (10.1) 5 Fig. 2 Survey sites 5th – 6th July 2011 Fig. 3 Survey locations on the Trent & Mersey Canal, 6th July 2011 5. SITE ASSESSMENT SUMMARIES & DISCUSSION Site 1 Wychnor: Two sites were visited. Site 1a lay in the Trent & Mersey Canal about 150m below a junction with the River Trent (Fig. 4). Small quantities of gravel at river margins gave way to loosely consolidated mud and silt. A search effort by 5 people totalling approximately 3 ‘man-hours’ only produced a low number of the two common unionid species Anodonta anatina and Unio pictorum (Fig. 5). The site appeared potentially suitable for Pseudanodonta complanata. Fig. 4 Wychnor: Site 1a 8 Fig. 5 Mussels from site 1a: Unio pictorum (left) & Anodonta anatina on (right) Site 1b lay immediately downstream the lock gates where the River Trent flows into the Trent & Mersey Canal (Fig 6). Loosely consolidated organic silt deposits produced the same two unionid species as site 1a (Fig. 7). 9 Fig. 6 Wychnor: Site 1b Fig. 7 Mussels from site 1a: Unio pictorum: two specimens to upper right & Anodonta anatina on right – specimen on lower left has two Dreissena polymorpha attached Site 2 River Dove: 10 Two sites were visited on the River Dove. The lower site 2a consisted of a stretch of fast water flow over a predominantly gravel bed with no fine marginal sediments. Large numbers of dead Anodonta anatina and a single A. cygnea (living at some point further upstream) were collected on exposed gravel bars amongst flood debris. Mussel sampling in this fast flowing stretch presented a few challenges. The use of a ‘glass-bottomed bucket’ was rendered difficult due to the part algal covering whilst the tightly packed gravel made the use of a net problematic. About 80m downstream the river widens to produce a slower water flow and a ‘bay’ where fine muddy sediments have accumulated grading into muddy-gravel nearer to the central channel. Hand netting by four surveyors produced about 30 – 40 live A. anatina, mostly juveniles. This site is potentially suitable for Pseudanodonta complanata although fine sediments are possibly rather too loosely consolidated to produce ‘ideal’ conditions for the mussel. Fig. Fig. 8 River Dove Site 2a About 300m upstream Site 2b lies at a weir in the river (fig. 9). A few live A. anatina were located in marginal shingle and finer sediments about 40m downstream of the weir. No live mussels were found amongst the boulders and cobbles lining the river bottom immediately upstream of the weir. 11 Fig. 9 River Dove Site 2b 12 Fig. 10 Site 2b: Anodonta anatina recovered about 40m below the weir Site 3 Croxall: Rivers Tame, Mease and Trent Site 3a: The River Tame was sampled about 100m upstream of its confluence with the River Trent (Fig. 11). Water turbidity prevented the use of a ‘glass- bottomed bucket’ and sampling was undertaken with hand nets. No live mussels were located although a few dead Anodonta anatina were found on the river margins. The predominantly gravel river channel was largely covered with a matt of filamentous algae and this would act to smother any large unionid mussels beneath1. One find of note was of a juvenile white-clawed crayfish Austropotamobius pallipes (Fig. 14). 1 M.J.W. observed similar unionid mortality assumed to be associated with algal mats blanketing river sediments in the New Bedford River in 2005 (Willing 2007) 13 Fig. 11 River Tame Site 3a Site 3b: The small River Mease (Fig. 12) lay further downstream from Site 3a. The predominance of muddy sediments produced a few live Anodonta anatina from fine muddy sediments; this is really a rather small river to support Pseudanodonta complanata.