THE CRAYFISH OF NOTTINGHAMSHIRE

Transcription

1 153 Species Survival: Securing white-clawed crayfish in a changing environment THE CRAYFISH OF NOTTINGHAMSHIRE David M Holdich 1 and Chris Jackson 2. 1 Crayfish Survey & Research, Peak Ecology Ltd., Arden House, Deepdale Business Park, Bakewell, Derbyshire DE 45 1GT, UK. 2 Biodiversity Officer, Nottinghamshire Biodiversity Action Group, c/o Conservation, Nottinghamshire County Council, Trent bridge House, Fox Road, West Bridgford, Nottingham NG2 6BJ, UK. Corresponding author: David M Holdich. david.holdich@ntlworld.com ABSTRACT All the information available on the distribution of crayfish in Nottinghamshire has been gathered together for the first time. Substantial populations of white-clawed crayfish exist north of the River Trent in the midsouth-west of the county, especially in the R. Leen catchment. The signal crayfish is largely confined to the mid-south-east of the county, both south and north of the R. Trent, although single live individuals have been found at two separate locations in the R. Leen catchment in 2009 and A large population of spinycheek crayfish has inhabited Clifton Pond in the Attenborough Nature Reserve since the 2000s but does not appear to have spread further. No outbreaks of crayfish plague have been reported in the county, although a number of white-clawed populations have been lost south of the R. Trent, in the mid-southeast of the county, and most recently in the far north-west. Field surveys carried out in 2010 and 2011 by a core group of individuals who attended a crayfish training course have confirmed a number of old records. The R. Leen below Newstead Abbey down to Papplewick and Bestwood Country Park contain excellent populations of white-clawed crayfish. An educational leaflet informing the public of the crayfish resources in Nottinghamshire has been produced including advice on the importance of conserving its white-clawed crayfish populations. It is hoped that this paper will encourage those interested in crayfish in other counties to join forces to produce an up-to-date picture of the situation in their region. Keywords: crayfish, Nottinghamshire, distribution, conservation INTRODUCTION There are currently seven species of crayfish in Britain (Holdich and Sibley 2009), but only two have a widespread distribution, i.e. the indigenous or native white-clawed crayfish, Austropotamobius pallipes (Lereboullet 1858) (Figures 1, 6), and the North American signal crayfish, Pacifastacus leniusculus (Dana 1852) (Figure 3). The former has declined rapidly in its range over the last few decades, whilst the latter has dramatically increased its range (see Rogers and Watson, this volume (a), (b)). This is mainly due to the impact of signal crayfish through competitive exclusion and a disease they carry, commonly known as crayfish plague (caused by the fungus-like organizm, Aphanomyces astaci (Schikora1903)), to which white-clawed crayfish are extremely susceptible. Despite having the most stringent legislation in Europe concerning nonindigenous crayfish species (NICS) (Holdich and Pöckl 2005) this has not worked in stopping their spread. This process is continuing to the present day with SW England (Holdich and Sibley 2009, Sibley et al. 2009) and Scotland (Gladman 2009) feeling the brunt of the signal crayfish invasions.

2 Crayfish of Nottinghamshire (Holdich and Jackson) 154 Of the other five species the noble crayfish, Astacus astacus (Linnaeus 1758), from continental Europe is restricted to a small area of SW England (although none have been recorded in recent times, Sibley 2011, pers. comm.); the narrow-clawed crayfish, Astacus leptodactylus (Eschscholtz 1823), from Eastern Europe, has scattered populations in England (mainly in the south-east) and Wales, but none in Scotland; the North American red swamp crayfish, Procambarus clarkii (Girard 1852), is restricted to SE England; the North American spiny-cheek crayfish, Orconectes limosus (Rafinesque 1817) (Figure 2), occurs at single localities in the East and West Midlands, Lincolnshire and SE England; and the North American virile crayfish, Orconectes virilis (Hagen 1870), is only known from NW London. In addition, the Australian redclaw crayfish, Cherax quadricarinatus (von Martens 1868), which is the only non-european crayfish that can be legally kept in aquaria in England and Wales, has occasionally been found in the wild but no populations are known. Risk assessments have been carried out on the NICS in Britain and some of these have been published (Peay et al. 2010, Defra 2011). It is clear that of all the NICS currently in Britain the signal crayfish has the most potential to cause damage to the freshwater environment, a situation that is mirrored in many European countries (Tricarico et al. 2010). It has been estimated that the annual economic cost of signal crayfish in Britain is over , which includes costs for management, river bank restoration, angling and research (Williams et al. 2010). In order to protect vulnerable populations of white-clawed crayfish a number of ark sites are being set up where part of the population can be translocated to (Peay 2009; O Neill and Whitehouse, this volume; Robbins, this volume). An ark site can be defined as a discrete site, comprising running water and/or stillwater components, that supports a healthy recruiting population of white-clawed crayfish and, without significant management intervention, can reasonably be expected to sustain a population in favourable condition for the foreseeable future (Sibley et al. 2009). One of the first modern assessments of the distribution of the white-clawed crayfish in Britain was made in the early 1970s and showed a widespread distribution (Thomas and Ingle 1971). In the 1980s and 1990s most records for crayfish in Britain were collated by research staff (David Holdich, David Jay, Ian Reeve and David Rogers) at the University of Nottingham, the resulting database being one of the first entries for the National Biodiversity Network s Gateway scheme ( ). Papers and reports published in the 1980s and 1990s (e.g. Jay and Holdich 1981, Goddard and Hogger 1986, Holdich and Reeve 1991, Holdich et al. 1995a) followed the trends of white-clawed and signal crayfish distribution, i.e. a decline in the range of white-clawed crayfish and expansion in the range of signals. Sibley (2003a) and Holdich et al. (2004) provided an overview of the situation, and data collated by Sibley from the national and Environmental Agency (EA) databases was used for Britain s contribution to the Atlas of Crayfish in Europe (Souty-Grosset et al. 2006). Recently, a thorough review of the distribution of crayfish in Britain has been undertaken (Rogers and Watson, this volume (a)). Interestingly, there is very little written evidence that the white-clawed crayfish existed in Britain before 1500, although Holdich et al. (2009a) have managed to show that it appears to have been fairly widespread before then, and has thus been accepted by the IUCN as an indigenous crayfish species (ICS), albeit an endangered one. This endangered status not only applies to white-clawed crayfish in Britain but elsewhere in Europe (Füreder et al. 2010, Sibley and Holdich, this volume). Grandjean et al. (1997), using molecular methods, have shown that the white-clawed crayfish may have been introduced into England from Brittany (France), but as to when is not known. At a county level few details have been published that highlight the decline in white-clawed crayfish and the increase in signal crayfish populations, the exceptions being the counties of SW England (see Holdich and Sibley 2009) and Hampshire (Hutchings 2009). In the early 2000s Peter Sibley of the EA used the available data to form a database of the occurrence of the white-clawed crayfish and NICS in England and Wales on a county basis. Despite the large number of records for Nottinghamshire these have never been mapped in any detail (except for internal reports) so that an overall picture could be seen. In order to manage

3 155 Species Survival: Securing white-clawed crayfish in a changing environment white-clawed crayfish in any region it is important that their distribution is known so that any threats to their survival can be clearly seen and the information followed up on a detailed up-to-date database to find the exact locality. Whilst such information can be used to highlight the threat from NICS, it is also useful when considering planning applications that might impact on white-clawed crayfish populations. Interest in crayfish in Nottinghamshire was heightened by the discovery of spiny-cheek crayfish in a lake on the Attenborough Nature Reserve in 2002 (Holdich and Black 2007) (Figure 2), and a short film of the research being carried out was shown on East Midlands TV as a local contribution to the Saving Planet Earth series ( or you can watch the video). The reasoning behind this was that the spiny-cheek crayfish might pose a threat to the local endangered white-clawed crayfish. Further interest was raised when Lee Scudder found a live adult signal crayfish in 2009 (Figure 3) in a pond near the R. Leen, which is the main source of white-clawed crayfish in Nottinghamshire (see below). The authors of this paper have tried to obtain as much information as possible about the crayfish situation in Nottinghamshire and represent it in mapped form for three time periods. In addition, a detailed database has been compiled. Figure 1. Front view of a male white-clawed crayfish, Austropotamobius pallipes, from the River Leen showing the granulate nature of the claws (below left).

4 Crayfish of Nottinghamshire (Holdich and Jackson) 156 Figure 2. A male spiny-cheek crayfish, Orconectes limosus, from Church Pond, Attenborough showing the characteristic maroon stripes across the abdomen and the spiny cheeks. Figure 3. A male signal crayfish, Pacifastacus leniusculus, from Moor Pond Wood, Papplewick showing the smooth nature of the claws and the white patch at the junction of the fingers of the claw.

5 157 Species Survival: Securing white-clawed crayfish in a changing environment METHODS The county of Nottinghamshire is located in the East Midlands region of England, and extends to approximately hectares. Most urbanized areas are found towards the west of the county with the city of Nottingham located in the south-west. North of Nottingham are the towns of Hucknall, Kirkby in Ashfield, Sutton in Ashfield, Mansfield and Worksop. Running north to south down the centre of the county are the towns of Retford, Ollerton and Southwell. The east of the county is largely rural in nature with Newark-on-Trent the only notable urban centre. The geology of the county is predominantly arranged in a north-south formation. In the west, the coal measures and magnesian limestone form two narrow bands, before giving way to a broad central swathe of sandstone in Sherwood. To the east of this, and dominating the centre of the county, are the mercia mudstones. The eastern part of the county is characterized by alluvial sand and gravel associated with the major river floodplains, whilst lias and boulder clay occur in the south-east. One of England s major rivers, the R. Trent, which rises to the west in Staffordshire, runs through the county from the south-west to the north-east (Figures 8-10), before joining the R. Ouse at the head of the Humber Estuary. It is fed by a number of major tributaries in the county: draining the west of the county are the R. Erewash and the R. Leen, running southwards and entering the R. Trent at Nottingham; in the centre of the county, the R. Maun, R. Meden, R. Ryton and R. Poulter run west to east, forming the R. Idle near Retford before entering the Trent in the far north of the county; the R. Greet enters the R. Trent from the north-west near Southwell; the R. Soar enters the R. Trent from the south upstream of Nottingham; and the R. Smite, which becomes the R. Devon, enters the R. Trent at Newark from the south-east. There are crayfish records for Nottinghamshire held in various contract reports, unpublished dissertations, the database developed by crayfish researchers at the University of Nottingham, and databases held by the local EA and the county Natural History Museum. Most of these records are also held in the National Biodiversity Network s Gateway database ( These were all accessed and the information put into a new database for Nottinghamshire. The data was used to produce distribution maps for three time periods; pre-1991, and 2002 to 2011 (August) (Figures 8-10). Where spurious records cropped up, i.e. apparently incorrect grid references, these were checked against other records for the locality where possible. Additional records were obtained by internet searches. Crayfish records for surrounding counties were also accessed from the national database for possible threats from NICS to Nottinghamshire s whiteclawed crayfish. During 2010 and 2011 a number of field surveys were carried out in the R. Leen catchment in order to check on previous records and to survey new sites. Between six and 15 people were involved as part of a training programme for potential crayfish surveyors that was a follow on from a Crayfish Training Day organized by Chris Jackson and given by David Holdich. The event was funded by Ashfield District Council and the 6C s Strategic Green Infrastructure fund. As a result of the training day a group of volunteers was set up - The Nottinghamshire (Notts) Crayfish Group, with a view to studying crayfish in the county in more detail (Figure 4). Additional localized surveys were carried out by the Environment Agency and EMEC Ecology. Field methods involved hand and pond net searches both in the daytime and by torchlight at night. In addition, crayfish Trappy TM traps were set overnight by the EA at a number of sites. As crayfish are known to occupy a wide range of habitats (Holdich and Rogers 2000, Holdich 2003a), including muddy ones, as long as the water is clean (Holdich et al. 2006), all possible habitats were sampled, although on most occasions they were only found in leaf litter, in submerged macrophytes, and under waterlogged logs and rocks. On one occasion in September 2010 Peay s (2002) standard method for estimating population abundance was carried out on the R. Leen and Japanese Water Gardens downstream of the Garden Lake at Newstead Abbey. In this method the average number of crayfish per ten refuges is calculated. A number of >5 indicates

6 Crayfish of Nottinghamshire (Holdich and Jackson) 158 a very high abundance (grade A); >=3, <=5 indicates high abundance (grade B); >=1, <3 indicates moderate abundance (grade C); 0, <1 indicates low abundance (grade D); and 0 indicates absent or undetected (grade E). Work was carried out under Natural England (NE) licences (nos and ) accredited to David Holdich. Sampling was carried out in summer after the young had been released from their mothers at juvenile stage 3 and before breeding started again in the winter (Reynolds 2002) (a condition of the NE licence). In some of the initial surveys stage 3 juveniles were collected, which are only about 1.5 cm long (Figure 5). As these look rather like juvenile signal crayfish due to their colouration a method was explained to separate the two species, i.e. the presence of very sharp spines in the sides of the groove running over the top and sides of the carapace in white-clawed crayfish both juveniles and adults, but which are absent in signal crayfish (Holdich 2009). Figure 4. The Nottinghamshire (Notts) Crayfish Group volunteer training day. Figure 5. Stage 3 white-clawed crayfish juvenile.

7 159 Species Survival: Securing white-clawed crayfish in a changing environment RESULTS AND DISCUSSION Nottinghamshire The earliest record uncovered was for the River Trent at Trent Bridge (Walker 1925). This is of particular interest as it is dated 1641 from an anonymous manuscript in Bromley House Library. Two records of Potamobius pallipes (as it was then known) are mentioned in Stebbing (1906) both come from the north of the county, i.e. for the River Maun at Mansfield (Carr 1904) and Shireoaks near Worksop (Stebbing 1906). Stebbing quotes a Rev. J Walker of Averham Rectory, Newark-on-Trent for 1903, whom stated that as far as he was aware crayfish did not occur in the R. Trent catchment, although they occurred at Shireoaks, near Worksop (R. Ryton catchment). This was confirmed by two local people, one of who was of the opinion that Shireoaks was the only place where crayfish occurred in the county. However, Carr (1904) states that they are fairly common in the R. Maun and the mill-dams of Mansfield. Stebbing was in fact sent specimens in London from a cascade that ran from one pond to another in the park at Shireoaks Hall, where they had apparently been for at least 50 years. A record for 2004 from the Nottinghamshire Wildlife Trust confirms that they are still present at Shireoaks Hall in pools of an overgrown cascade in the water garden. This is the most northerly record in the county. This led the authors to believe that a 1992 EA record for a location north of Worksop was probably in the wrong place as the name given for the observer was that of the family that own Shireoaks Hall. It therefore seems likely that white-clawed crayfish have been continuously present there at least since the 1850s. Thomas and Ingle (1971) were the first workers to try and list all the crayfish records for Britain. Although they came up with an impressive list they only gave two records for Nottinghamshire, i.e. R. Maun and Shireoaks, as mentioned in Stebbing (1906). Anecdotal evidence suggests that white-clawed crayfish were present in the R. Leen as far down as Lenton in Nottingham City before it was channelized there in the middle of the 20 th C. Jay and Holdich (1981) compiled a national list and for Nottinghamshire they gave: Pitt House (SK ; R. Leen (SK , , 51-52; Fairham Brook (SK ); Kingston Brook (SK ); Dover Beck (SK ), Grassmore Dyke (SK ), Grassthorpe (SK ), Newton Solney (SK ), and Bretby Park (SK ). Mees (1983) made an extensive study of the ecology of white-clawed crayfish in the R. Leen around Papplewick. The population studied had high abundance as was found upstream at Newstead Abbey in 2010 (see below), but the results were never published. In 1987 and 1989 Holdich and Reeve produced a series of reports for the Joint Nature Conservation Committee (JNCC), which for the first time mapped all known crayfish records in Britain on large-scale maps. This information was summarized by Holdich and Reeve (1991) but on a catchment basis. For the R. Trent catchment they only gave: R. Leen, Woodhall Farm and Bullwell Hall as having white-clawed crayfish populations in Nottinghamshire. Holdich et al. (1995a) list white-clawed crayfish for the R. Leen and its tributaries, and from Bullwell Hall and Woodhall Farm. In 1999 the local EA commissioned a M.Sc. student to collate the crayfish records for Nottinghamshire and to carry out surveys for some of the sites where old records existed. He found no white-clawed crayfish at sites on the R. Ryton (Blyth, Hodsock House) north of Worksop, or to the west of Worksop at Bondhay Dyke (Castle Hill Farm), or at Grassthorpe (R. Trent tributary) and The Beck (Caunton) north of Southall and Newark. To the north-east of Nottingham no crayfish were found in the Oxton Dumble (a small, steep-sided, wooded stream) or a tributary of Dover Beck (Calverton), and to the north-west none were found at

8 Crayfish of Nottinghamshire (Holdich and Jackson) 160 Westville (Hucknall). No crayfish were found south of the R. Trent in Polser Beck (Normanton) and Kingston Brook (Wysall and West Leake). This survey showed that some of the records listed by Jay and Holdich (1981) were probably no longer present, particularly those to the south of the R. Trent. Positive records for white-clawed crayfish were for Cauldwell Brook south of Mansfield, the R. Maun downstream of this brook in Mansfield, and to the north-west of Nottingham at Nethergreen Brook downstream of Moorgreen Reservoir and in Nethergreen Brook at Eastwood, as well as at Underwood north of the reservoir. A positive record was also obtained for the R. Leen at Linby. In 2002 part of the population of white-clawed crayfish in Nanpantan Reservoir near Loughborough (Leicestershire) were translocated by the EA to Kingston Brook (Wysall) in south-west Nottinghamshire (Figure 10). Crayfish were kept in cages in the brook but did not survive for more than a few months. Kingston Brook had previous records for white-clawed crayfish, but none have been recorded since Nanpantan Reservoir is connected to Wood Brook, where a population of signal crayfish was detected in a tributary in Recent surveys in relation to a mortality of signal crayfish (see below) have shown that the signals have migrated downstream in the tributary into Wood Brook from where they have migrated both downstream and upstream towards the reservoir. This reservoir used to have a substantial population of white-clawed crayfish but its present status is unknown. A mortality of white-clawed crayfish was recorded in Nethergreen Brook below Moorgreen Reservoir in 2001 (Sibley 2001, pers. comm.), but the population has recovered as there have been a number of positive sightings since then. In 2010 an ovigerous white-clawed crayfish was found in the upper reaches of the R. Erewash at Jacksdale by the EA (Rippon 2010, pers. comm.): an unusual record for a river that has a history of pollution. However, the record was confirmed with more individuals being found in May 2011 (Winter 2011, pers. comm.), as well as in the adjacent Cromford Canal in early June (Randeria 2011, pers. comm.). Another unusual record is from Baker Lane Brook in Hucknall. The EA reported records for this brook for 1990 and 1992 and in 2009, 22 individuals were found in a survey by EMEC Ecology (Sharkey 2009, pers. comm.). This population is the only one found in the R. Leen catchment that is in a completely urbanized area. Bestwood Duck Ponds in the R. Leen catchment contain large populations of white-clawed crayfish in a number of the fishing ponds (see Rogers and Watson, this volume (b)). Some ponds associated with Cauldwell Brook (Mansfield) also contain white-clawed crayfish. During a visit by the Notts Crayfish Group to Shireoaks Hall (Worksop) in September 2011, the owner (Godleweski 2011, pers. comm.), informed us that white-clawed crayfish occurred in his fishing ponds. A survey of a lake at the end of the water gardens also revealed white-clawed crayfish in the marginal vegetation. These are the only static bodies of water in Nottinghamshire with current records for white-clawed crayfish. In all the above surveys no mention is made of any signal crayfish populations in Nottinghamshire. Two occurrences had in fact been recorded by the National Rivers Authority the R. Greet in Southall in 1984 and the R. Trent at Kelham near Newark in Since the mid-1980s the R. Greet around Southall and Kirklington seems to have been the centre for expansion of the signal crayfish. They have also been recorded for Maythorne Fishery (near Southall) and Halam Beck (north of Southwell), as well north of the R. Trent at Rollerston (Upton Mill, south-west of Newark), and two sites south of the R. Trent at Systerton and in the R. Devon (Hawton, just south of Newark). Closer to Nottingham City, signals have been recorded from Dover Beck at Gonaldson and Cocker Beck at Lowdham. In April 2011 some very large signals were reported from Dover Beck just north of Calverton, and subsequent trapping nearer to Calverton by the EA confirmed their presence (Figure 10) (Hughes 2011, pers. comm.). Few studies have been carried out on signal crayfish in Nottinghamshire. Sibley (2003b) attempted a multiple recapture exercise to try and eliminate them from an irrigation pond near Newark. This was quite successful, but it seems likely that the population will have recovered by now as there were undoubtedly some left. One male had a carapace length of 95 mm and a weight of 200 g, making it one of the largest ever recorded,

9 161 Species Survival: Securing white-clawed crayfish in a changing environment with 70 mm and 110 g being the norm (Lewis 2002). A study was carried out in on the population of signals over a 1200 m length in the R. Greet at Southall (Taylor 2010). A total of 549 were caught, marked and released (370 males, 179 females of which 95 were ovigerous). The mark and recapture exercise recovered 14 individuals, which was too low to calculate a population estimate, but the population was obviously large. The largest individual caught was female with a carapace length of 77.9 mm. Apparently signals caught by rod and line from the R. Greet are sold cooked in the market at Melton Mowbray (Rhodes 2010, pers. comm.). In 2009 a single adult male was found under a tree stump in Moor Pond Wood (50 m from but not connected to the R. Leen) just south of Papplewick (Figure 3), but surveys in late 2009 and early 2010 by the EA (including trapping) and Chris Jackson and Lee Scudder (including night searches), of the pond and R. Leen yielded no further signals, but did yield large individuals of white-clawed crayfish from the R. Leen (Hughes, 2009, pers. comm.). A survey undertaken by Cresswell Associates at Grange Farm (200 m downstream from Moor Pond Wood) in August 2010 also identified a healthy population of white-clawed crayfish. In early August 2011, during a survey of the R. Leen just upstream of the Mill Lakes (Bestwood Country Park), a single large male signal was found (see Figure 10). This was sent to Cefas by the EA to see if it was carrying crayfish plague but the results came back negative (Stebbing 2011, pers. comm.). In the same vicinity 15 white-clawed crayfish were found. Further surveys in mid-august failed to detect any more signals. The various databases mentioned above have been added to from records held by individuals and the county records centre, and corrected by Chris Jackson. The corrected database for Nottinghamshire gives 160 records for white-clawed crayfish since 1973 (one of these records is unfortunately not dated), 44 records of signal crayfish since 1984, and three records of spiny-cheek crayfish since This does not represent the number of populations but the number of records over time, e.g. the spiny-cheek crayfish was recorded from the same site in 2002, 2005 and 2007, although they were probably present before 2002 (Holdich and Black 2007). From the available data maps for three time periods for the three crayfish species present in the county were produced (Figures 8-10). The spiny-cheek crayfish (Figure 2) was introduced by a carp angler to Clifton Pond in the Attenborough Nature reserve round about 2000, although it is not known how many or where they came from as he died soon after (Holdich and Black 2007). A study of the life history and distribution of the crayfish in the pond was carried out over a year. All stages were found, including ovigerous females, and they were widespread in the pond and at all depths. They were also found to be burrowing into the pond banks. Coots were found to be feeding on them in the shallows. As seen by the number of exoskeletal remains on the pond shores spinycheek crayfish are still present, although there is no evidence they have spread to other ponds (Langtree 2010, pers. comm.). Field surveys in 2010 and 2011 A Nottinghamshire (Notts) Crayfish Group was formed in 2010 with the following aims: 1) To establish whether or not signal crayfish have a breeding populations within the R. Leen catchment. (None were found in the 2010 or 2011 surveys, although two males were found at separate locations). 2) Collate all existing records for crayfish species in Nottinghamshire. (This has been achieved). 3) Try to establish an active survey/monitoring effort within Nottinghamshire for the future. (This is on-going). 4) Seek to identify potential ark sites within the county and research how these could be created. (No ark sites have been identified so far).

10 Crayfish of Nottinghamshire (Holdich and Jackson) 162 Early in 2010 David Holdich was invited to visit Hollinwell Golf Club to assess the site as a possible ark site. The site has a series of ponds and pools that are spread throughout the valley bottom. In one of these pools is the Hollin Well, which is the main source of the R. Leen that begins downstream (Figure 7). Most of the site is found on the sandstones upstream of the sections of the R. Leen known to support white-clawed crayfish. However, an examination of the possible ark sites did not reveal any that were suitable. Fifteen white-clawed crayfish records were collected during 2010, mainly by the Notts Crayfish Group for the R. Leen catchment. In 2011 a further 19 records for white-clawed crayfish have been collected again mainly through the work of the Notts Crayfish Group. White-clawed crayfish records were confirmed in 2010 for Annesley Brook running through the Linby Quarries SSSI; and for the Garden Lake, Venetia Gardens, Japanese Water Gardens and R. Leen below Newstead Abbey. Records were also confirmed for Bestwood Duck Ponds, R. Leen in Bestwood Country Park, R. Leen at Papplewick Dam (Figure 6), and downstream to Papplewick. No sign of white-clawed crayfish burrows as seen in the R. Witham in Lincolnshire (Tero et al. 2003) were found. In March 2011, white-clawed crayfish were seen in three out of four of the Bestwood Duck Ponds surveyed for amphibians by Chris Jackson and Lee Scudder. In August 2011, during a survey of the R. Leen just upstream of the Mill Lakes (Bestwood Country Park),15 white-clawed crayfish were found. In August 2011, Alison Sharkey (EMEC Ecology) found 14 white-clawed crayfish in a dam at the bottom end of the Mill Lakes, the most southerly record so far for the river itself (Figure 10). On the 26 th of September 2010 the relative abundance of white-clawed crayfish in the R. Leen below Newstead Abbey was calculated using Peay s (2002) method. All six habitat patches sampled by pairs of surveyors had five or more crayfish per ten refuges, with an overall average of nine. This indicated that a very high population is present, despite this stretch of the R. Leen being smothered in sediment from the Lower Lake in In August 2011 a number of dead crayfish were reported from the River Ryton close to Shireoaks Hall (to the west of Worksop) to the EA by a member of the public. An officer from the EA visited the site and confirmed the reports and identified the crayfish as the white-clawed crayfish. Possible causes for the mortality were examined by scientists at Cefas and crayfish plague was ruled out (Hill 2011, pers. comm.). A survey by the Notts Crayfish Group in September 2011 found no crayfish over a 100 m stretch of the R. Ryton adjacent to Shireoaks Hall, but they were found in a lake in the grounds of the Hall and an overgrown canal. A number of potential sites north of Nottingham were examined for crayfish in August-October 2010 but none were found, i.e. Mosley Spring Brook, Annesley and Newstead Pit Top Lagoons, Dob Park (north) and Farley s Lane Brook. Crayfish records Figure 10 shows the distribution of crayfish in Nottinghamshire for the period 2002 to White-clawed crayfish records are mainly concentrated in the R. Leen catchment, but also exist for the R. Erewash and R. Maun catchments to the west and north respectively of the R. Leen. White-clawed crayfish appear to have been present at Shireoaks Hall near Worksop for at least 150 years, and due to the recent mortality (see above) are now known to occur in the R. Ryton itself. The single record in the south-west of the county represents a translocation from Nanpantan Reservoir in Leicestershire, but it is unlikely that any crayfish have survived. It can clearly be seen that other than the two records for the R. Leen catchment all the signal crayfish records are centred in the mid-south-east of the county, both north and south of the R. Trent. The spiny-cheek crayfish in Clifton Pond at Attenborough have been present for at least ten years and surprisingly have not apparently spread further.

11 163 Species Survival: Securing white-clawed crayfish in a changing environment Figure 6. A large male white-clawed crayfish from the River Leen at Papplewick Dam, showing the typical brown coloration and the triangular shaped rostrum between the eyes (compare with Figures 2 and 3).

12 Crayfish of Nottinghamshire (Holdich and Jackson) 164 Figure 7. The senior author drinking River Leen water from a silver cup at the 9th hole of the Hollinwell Golf Club close to the source of the River Leen. Surrounding counties The Gateway national database and the EA database indicate that the counties surrounding Nottinghamshire all have crayfish populations. Derbyshire has two species (A. pallipes and P. leniusculus), Leicestershire has three species (A. pallipes, A. leptodactylus and P. leniusculus), Lincolnshire has three species (A. pallipes, O. limosus and P. leniusculus), Rutland has one species (P. leniusculus), Staffordshire has three species (A. pallipes, O. limosus, and P. leniusculus) and Yorkshire (East and South) has two species (A. pallipes and P. leniusculus). Although A. leptodactylus does not carry crayfish plague it would probably outcompete A. pallipes for resources due to its faster growth, higher fecundity and larger adult size, if the two species occupied the same habitat (Holdich et al. 1995b). A population is established in a brook in Leicestershire, where previously white-clawed crayfish had been recorded (Holdich 2009, pers. obs.). Continental Europe has five ICS and at least ten NICS established in the wild, which are a potential threat to their survival as eight are capable of harbouring crayfish plague (Holdich et al. 2009b). Britain by contrast has a single ICS and six NICS established in the wild the worst ratio in Europe (Holdich and Sibley 2009). Currently Nottinghamshire has one ICS and two NICS, which are fairly well separated both geographically and hydrologically from each other (Figure 10). However, surrounding counties also have populations of NICS. Whilst none of the NICS in the surrounding counties pose an immediate threat to Nottinghamshire s whiteclawed crayfish they could easily be transported into the county by anglers and other members of the public, by natural migration, as well as by predators such as birds. In fact, mid-south-west Nottinghamshire where most of the white-clawed crayfish records come from is surrounded by threats from NICS. The lower

13 165 Species Survival: Securing white-clawed crayfish in a changing environment reaches of the R. Leen are heavily channelized and it is unlikely that NICS could make their way very far upstream from the R. Trent due to the present nature of the river. However, signal crayfish in particular are very invasive and are known to be able to climb up concrete walls over weirs (Holdich 2003b), so this pathway into the R. Leen catchment should not be ruled out. The spiny-cheek crayfish population at Ancaster in Lincolnshire is relatively close to Nottinghamshire s eastern border (Maunsell 2008). The population in the Attenborough Nature Reserve (Holdich and Black 2007) occurs upstream of the R. Leen, but is within a very short distance of the R. Trent. Signal crayfish have not been reported from the R. Erewash, which drains into the R. Trent just south of Nottingham. However, the R. Derwent, which also drains into the R. Trent just south of Nottingham, has a number of records for the catchment, including the main river at Matlock. Environment Agency records date back to There were mass mortalities of white-clawed crayfish in the R. Derwent and the associated R. Wye in 1991 that may well have been caused by crayfish plague (Alderman 1993). Signal crayfish are present in the R. Wye below Buxton as well as various ponds in the area. A mortality in the R. Lathkill, south of Bakewell (Derbyshire) prompted Rogers and Watson (2007, this volume (b)) to undertake a reintroduction programme using stock from Nottinghamshire, but this has recently been hit by a mortality. The recent report (August 2011) of dead white-clawed crayfish on the River Ryton has identified another threat to white-clawed crayfish populations in Nottinghamshire. Peay (2008) has recorded signal crayfish from two sites near Eckington on the River Moss in Derbyshire. She suggests that it is possible that the signal crayfish have already reached the confluence with the River Rother, beyond Eckington. Despite having poor water quality she considers that if the R. Rother can support coarse fish then signal crayfish should be able to colonize it. The River Rother is linked to the River Ryton by the Chesterfield Canal and tributaries of the R. Rother are within a kilometre of tributaries of the R. Ryton in South Yorkshire. Thankfully, specimens from the R. Rother mortality sent to Cefas for analysis in August 2011 were found to be free of crayfish plague (Stebbing 2011, pers. comm.). Other potential threats come from further up the R. Trent as the R. Dove, R. Hamps, R. Churnet, all of which have established populations of signal crayfish, are connected to it upstream of Nottinghamshire; signal crayfish also occur in the R. Trent itself at Burton-on-Trent (Cyster 2010, pers. comm.). In addition, a number of signal crayfish infested watercourses drain into the R. Soar, which itself drains into the R. Trent upstream of Nottingham, e.g. Gaddesby Brook via the R. Wreake (Harris and Young 1996, Sibley 2000) and Wood Brook (Loughborough). A significant mortality of signal crayfish occurred in a stretch of Wood Brook in 2010, although there are still live signals upstream and downstream of the mortality site (Holdich and Jackson 2010, pers. obs.). Possible causes for the mortality have been examined by scientists at Cefas but none have been found (Stebbing 2011, pers. comm.). It is not clear if signal crayfish are in the R. Trent between Nottingham and Newark, but dead individuals have been found at Farndon south of Newark and at Kelham (presumably alive) north-west of Newark. They are common in much of the R. Greet downstream to the confluence with the R. Trent, and large crayfish were reported from the Trent nearby by anglers in 2009, but trapping by the EA failed to find any individuals (Firkins 2010, pers. comm.). A single male was found by trapping in the R. Devon (south of Newark), this could have entered the river from the R. Trent or from some other source. Downstream of Nottingham rivers such as the Wharfe in Yorkshire, which joins the R. Trent via the R. Ouse, contain substantial numbers of signal crayfish (Peay and Rogers1999). There is also a threat from escapees from aquarium tanks. In the 1980s a living red swamp crayfish was discovered in a churchyard in Nottinghamshire and was donated to the University of Nottingham crayfish

14 Crayfish of Nottinghamshire (Holdich and Jackson) 166 researchers! This most probably was an escaped aquarium pet as there was no water in the immediate area. It is possible that the signal crayfish (Figure 3) discovered in a pond near the R. Leen at Papplewick in 2009 was an escaped pet or a deliberate discard. It looked to be quite an old specimen that had not moulted recently as evidenced by the calcareous algal growths on its exoskeleton (Figure 3). The signal crayfish found in the R. Leen in 2011 may also have had one or the other origin. So far no potential ark sites have been identified in Nottinghamshire. However, the R. Leen downstream of Newstead Abbey and Bestwood Duck Ponds could be considered as existing ark sites as they contain significant numbers of white-clawed crayfish. However, the areas are frequently visited by the members of the public, and in the case of Bestwood Duck Ponds, by anglers, so, as ark sites, they would be vulnerable to crayfish plague carried by a number of vectors. In addition, two signal records have been found in the R. Leen catchment. The current distribution of crayfish in Nottinghamshire indicates that there are strong populations of whiteclawed crayfish in the R. Leen catchment, especially upstream from below the Mill Lakes to Newstead Abbey. Good populations also occur in Cauldwell Brook in the R. Maun catchment, and in Nethergreen Brook south of Moorgreen Reservoir. The presence of white-clawed crayfish in fishing ponds and a lake at Shireoaks Hall near the R. Ryton to the north of the county has been confirmed recently, and the mortality in the R. Ryton indicates that they are probably also present there. Some white-clawed populations appear to have been lost from the county, notably south of the R. Trent and to the east of Nottingham. The cause for this is probably due to pollution from agriculture rather than crayfish plague. What is clear is that despite the large number of rivers and streams in Nottinghamshire very few have populations of crayfish. The extent of the distribution of signal crayfish in the mid-south-east of the county, both south and north of the R. Trent, has not been studied, although new records are often reported, such as for Dover Beck in The population of spiny-cheek crayfish in Clifton Pond at Attenborough has, so far as is known, not spread, which is surprising as a variety of birds are feeding on them and could transfer them to other ponds or to the nearby R. Trent. A question arises as what to do with NICS if they are caught. Trapping them in Nottinghamshire is illegal except by licence for scientific purposes (Hughes 2010, pers. comm.). (This is because of the presence of white-clawed crayfish in the county and the risk of spreading crayfish plague. Trapping out the larger individuals in a population can also lead to an explosion of smaller individuals). This question arose out of a volunteer work task, pulling Himalayan Balsam from the Potwell Dyke (a tributary of the R. Greet in Southwell) in 2010, which as a result revealed some crayfish. The group involved asked the Environment Agency (EA) for advice and was told to put them back as they had not been identified. Given the location of the site they were almost certainly signal crayfish. One of us (CJ) asked the EA for clarification about this and the advice given was again to put them back in case they were white-clawed crayfish, but if they were sure they were NICS, then they could be destroyed, but that there was an issue of humane disposal to consider (Renals 2010, pers. comm.). Renals also added that removing signals would have no significant impact on the population, but killing a white-clawed crayfish may impact small populations. With the advent of mobile phone cameras it should be possible to photograph specimens and send them to the EA for identification. Specimens that need destroying should be taken away securely and killed by freezing.

15 167 Species Survival: Securing white-clawed crayfish in a changing environment Figure 8. All crayfish records in Nottinghamshire for the period pre-1990 (inclusive). It should be noted that only two records for signal crayfish were recorded for this time period, and that six white-clawed crayfish records existed outside the River Leen catchment, including three south of the River Trent.

16 Crayfish of Nottinghamshire (Holdich and Jackson) 168 Figure 9. All crayfish records in Nottinghamshire for the period The white-clawed crayfish records south of the River Trent and to the east of Nottingham were not verified during this time period, but many more signal crayfish records were collected.

17 169 Species Survival: Securing white-clawed crayfish in a changing environment Figure 10. All crayfish records in Nottinghamshire for the period Signal crayfish records increased during this time period, including two south of the River Trent and two in the River Leen catchment. The white-clawed crayfish record south of the River Trent is for a translocation, but this did not survive. The spiny-cheek crayfish record is for Clifton Pond at the Attenborough Nature Reserve, which is very close to the River Trent.

18 Crayfish of Nottinghamshire (Holdich and Jackson) 170 CONCLUSION Knowledge of crayfish distribution in Nottinghamshire has increased recently and this has been greatly helped by the production of detailed maps of their distribution and field surveys. However, there are still a number of waters that have not had their records confirmed for many years or where the distribution limits are not known. So far the surveys have concentrated on the white-clawed crayfish, but there is an urgent need to survey more of the county, especially in the east, in order to assess the spread of signal crayfish. In summary: For the time period pre-1991 there are 46 white-clawed crayfish records and two records for signals crayfish at Southall and Kelham (Figure 8). For the time period there are 47 white-clawed crayfish records and 21 signal crayfish records (Figure 9). For the time period (August) there are 68 white-clawed crayfish records and 21 signal crayfish records (Figure 10). At the present time the white-clawed crayfish populations in the mid-south-western part of Nottinghamshire are not under any immediate threat, but potential threats are relatively close by. The finding of two separate male crayfish in the R. Leen catchment gives rise for concern, but at the time of writing there have been no known mortalities amongst white-clawed crayfish in the river. To help inform the public of the potential threats an educational leaflet has been prepared by the authors. This can be accessed through the Nottinghamshire Biodiversity Action Group website ( In addition the Local Wildlife Sites Partnership have developed criteria for the selection of local wildlife sites (locally known as Sites of Importance for Nature Conservation or SINC sites), based on the presence of white-clawed crayfish. This offers these sites a degree of protection through the planning system. It is hoped that this paper will encourage those interested in crayfish in other counties to join forces to produce an up-to-date picture of the situation in their region. ACKNOWLEDGEMENTS Thanks are due to members of the Notts Crayfish Group who carried out the field surveys, notably Kathy Hughes (Environment Agency) who also set the traps, and Lee Scudder (Nottinghamshire County Council Green Estates Team); and those who have provided extra records and information, particularly Rebecca Brunt (Environment Agency), Louise Hill (Environment Agency), the Nottingham Biological & Geological Records Centre, and Alison Sharkey (EMEC Ecology). Special thanks are due to Ashfield District Council and the 6C s Strategic Green Infrastructure Fund for funding the training session and some of the surveys, and to Karen Taylor (Nottinghamshire County Council) for assistance with the mapping. REFERENCES Alderman DJ (1993). Crayfish plague in Britain, the first twelve years. Freshwater Crayfish 9: Carr JW (1904). Nottinghamshire Crustacea and Arachnida. Report of the Transactions of the Nottingham Nature Society : 61. Cyster G (2010). Environment Agency, Midlands Region. Personal communication.

19 171 Species Survival: Securing white-clawed crayfish in a changing environment Defra (2011). The invasive non-native species strategy for Great Britain: protecting our natural heritage from invasive species. GB Non-native Species Secretariat. Defra, London, UK. Publ. Internet. Firkins I (2010). Environment Agency, Midlands Region. Personal communication. Füreder L, Gherardi F, Holdich D, Reynolds J, Sibley P and Souty-Grosset C (2010). Austropotamobius pallipes. In: IUCN IUCN Red List of Threatened Species. Version Publ. Internet. [accessed 10 March 2011]. Gladman Z, Adams C, Bean C, Sinclair C and Yeomans W (2009). Signal crayfish in Scotland. In: Crayfish Conservation in the British Isles. (J Brickland, DM Holdich and EM Imhoff, eds.), pp Proceedings of a conference held on 25th March 2009 in Leeds, UK. Goddard JS and Hogger JB (1986). The current state and distribution of freshwater crayfish in Britain. Field Studies 6: Godlewski L (2011). Shireoaks Hall, Worksop, Nottinghamshire. Personal communication. Grandjean F, Souty-Grosset C and Holdich DM (1997). Mitochondrial DNA variation in four British populations of the white-clawed crayfish Austropotamobius pallipes pallipes: implications for management. Aquatic Living Resources 10: Harris RR and Young HJ (1996). Distribution, densities and population characteristics of signal crayfish, Pacifastacus leniusculus (Dana), in the Gaddesby Brook, Leicestershire. Report for the National Rivers Authority. Hill L (2011). Environment Agency. Personal communication. Holdich D, Sibley P and Peay S (2004). The white-clawed crayfish a decade on. British Wildlife 15(3): Holdich DM (2003a). Ecology of the White-clawed Crayfish. Conserving Natura 2000 Rivers. Ecology Series No. 1. English Nature, Peterborough. Holdich DM (2003b). Crayfish in Europe an overview of taxonomy, legislation, distribution, and crayfish plague outbreaks. In: Management & Conservation of Crayfish. (DM Holdich and PJ Sibley, eds.), Proceedings of a conference held in Nottingham on 7 th November, Environment Agency, Bristol. Holdich DM (2009). Identifying crayfish in British waters. In: in the British Isles. (J Brickland, DM Holdich and EM Imhoff, eds.), pp Proceedings of a conference held on 25th March 2009 in Leeds, UK. Holdich DM and Black J (2007). The spiny-cheek crayfish, Orconectes limosus, digs into the UK. Aquatic Invasions 2(1): Holdich DM, Palmer M and Sibley PJ (2009a). The indigenous status of Austropotamobius pallipes (Lereboullet) in Britain. In: in the British Isles. (J Brickland, DM Holdich and EM Imhoff, eds.), pp Proceedings of a conference held on 25th March 2009 in Leeds, UK.

20 Crayfish of Nottinghamshire (Holdich and Jackson) 172 Holdich DM, Peay S, Foster, J, Hiley P and Brickland J. (2006). Studies on the white-clawed crayfish (Austropotamobius pallipes) associated with muddy habitats. Bulletin Français de la Pêche et de la Pisciculture : Holdich DM and Pöckl M (2005). Does legislation work in protecting vulnerable species? Bulletin Français de la Pêche et de la Pisciculture : Holdich DM and Reeve ID (1991). The distribution of freshwater crayfish in the British Isles with particular reference to crayfish plague, alien introductions and water quality. Aquatic Conservation 1(2): Holdich DM Reynolds JD, Souty-Grosset C and Sibley PJ (2009b). A review or the everincreasing threat to European crayfish from non-indigenous crayfish species. Knowledge and Management of Aquatic Ecosystems : 46pp. DOI: /kmae/ Holdich DM and Rogers D (2000). Habitat requirements of the white-clawed crayfish, Austropotamobius pallipes. In: Crayfish Conference Leeds, pp (D Rogers and J Brickland, eds.). Environment Agency, Leeds. Holdich DM, Rogers WD and Reader JP (1995a).. Final Project Record for National Rivers Authority R&D contract 378/N&Y. Holdich DM, Rogers WD, Reader JP and Harlioglu M (1995b). Interactions between three species of freshwater crayfish (Austropotamobius pallipes, Astacus leptodactylus and Pacifastacus leniusculus). Freshwater Crayfish 10: Holdich DM and Sibley PJ (2009). ICS and NICS in Britain in the 2000s. In: in the British Isles. (J Brickland, DM Holdich and EM Imhoff, eds.), pp Proceedings of a conference held on 25th March 2009 in Leeds, UK. Hughes K (2009, 2010, 2011). Environment Agency, Midlands Region. Personal communications. Hutchings A (2009). Monitoring Austropotamobius pallipes (Lereboullet) in a chalk stream in southern England. In: in the British Isles. (J Brickland, DM Holdich and EM Imhoff, eds.), pp Proceedings of a conference held on 25th March 2009 in Leeds, UK. Jay D and Holdich DM (1981). The distribution of the British freshwater crayfish, Austropotamobius pallipes (Lereboullet). Freshwater Biology 11: Langtree C (2010). Southern Reserves Officer, Nottinghamshire Wildlife Trust. Personal communication. Lewis SD (2002). Pacifastacus. In: Biology of freshwater crayfish. (DM Holdich, ed.), pp Blackwell Science Ltd, Oxford. Maunsell F (2008). Ancaster. Wet Fens in Lincolnshire; Crayfish Project. ECOM. Mees CC (1983). Ecological and pollution studies of the British crayfish. PhD thesis. University of Nottingham, UK. Peay S (2002). A Standardised Monitoring Protocol for White-clawed Crayfish, Austropotamobius pallipes in the UK SAC Rivers. Life in UK Rivers Project. Contract LIF English Nature, Peterborough. 58 pp.

21 173 Species Survival: Securing white-clawed crayfish in a changing environment Peay S (2008). Wingerworth Lido and River Moss Crayfish Survey Report to Derbyshire County Council. Peay S (2009). Selection criteria for ark sites for white-clawed crayfish. In: in the British Isles. (J Brickland, DM Holdich and EM Imhoff, eds.), pp Proceedings of conference held in Leeds on 25 th March 2009 in Leeds, UK. Peay S, Holdich DM and Brickland J. (2010). Risk assessments of non-indigenous crayfish in Great Britain. Freshwater Crayfish 17: Peay S and Rogers D (1999). The peristaltic spread of signal crayfish (Pacifastacus leniusculus) in the River Wharfe, Yorkshire, England. Freshwater Crayfish 12: Randeria A (2011). Environment Agency. Personal communication. Renals T (2010). Technical Advisor for Invasive Species. Environment Agency. Personal communication. Reynolds JD (2002). Growth and reproduction. In: Biology of freshwater crayfish. (DM Holdich, ed.), pp Blackwell Science Ltd, Oxford. Rhodes J (2010). Private contractor. Personal communication. Rippon L (2010). Environment Agency, Midlands Region. Personal communication. Sharkey A (2009, 2011). EMEC Ecology, The Old Ragged School, Brook Street, Nottingham NG1 1EA. Personal communications. Sibley PJ (2000). Signal crayfish management in the River Wreake catchment. In: Crayfish Conference Leeds. (D Rogers and J Brickland, eds.), pp Environment Agency, Leeds. Sibley PJ (2001, 2011). Environment Agency. Personal communication. Sibley PJ (2003a). The distribution of crayfish in Britain. In: Management & Conservation of Crayfish. (DM Holdich and PJ Sibley, eds.), pp Proceedings of a conference held in Nottingham on 7th November, Environment Agency, Bristol. Sibley PJ (2003b). Signal crayfish in Britain with reference to the Tweed catchment. In: Proceedings of a seminar held in December, 2001: Publ. Internet. [accessed 10 January 2010]. Sibley PJ, Holdich DM and Lane M-R (2009). Invasive crayfish in Britain management and mitigation. International Urban Ecology Review 4: Stebbing P (2010). Co-ordinator for Crustacean Diseases, National Reference Laboratory, Fish Health Inspector, Cefas, Barrack Road, The Nothe, Dorset DT4 8UB, Weymouth. Personal communication. Stebbing P (2010, 2011). Co-ordinator for Crustacean Diseases, National Reference Laboratory, Fish Health Inspector, Cefas, Barrack Road, The Nothe, Dorset DT4 8UB, Weymouth. Personal communications. Stebbing TRR (1906). Zoology, Crustaceans. In: The Victoria History of the country of Nottingham, Vol. 1. (W Page, ed.), pp Constable & Co., London.

22 Crayfish of Nottinghamshire (Holdich and Jackson) 174 Souty-Grosset C, Holdich DM, Noël PY, Reynolds JD. and Haffner P (eds.) (2006). Atlas of Crayfish in Europe. Muséum national d Histoire naturelle, Paris, (Patrimoines naturels, 64). ISBN: Taylor S (2010). Signal crayfish (Pacifastacus leniusculus) movements on the River Greet. Student dissertation. Brackenhurst College, Nottinghamshire. Tero, C, Holdich DM, Smith P, Kite N, Longfield R and Smith P (2003). White-clawed crayfish Austropotamobius pallipes in the River Witham. In: Management & Conservation of Crayfish. (DM Holdich and PJ Sibley, eds.), pp Proceedings of a conference held in Nottingham on 7 th November, Environment Agency, Bristol. Thomas WJ and Ingle R (1971). The nomenclature, bionomics and distribution of the crayfish, Austropotamobius pallipes (Lereboullet) (Crustacea, Astacidae) in British waters. Essex Naturalist 32: Tricarico E, Vilizzi L, Gherardi F and Copp GH (2010). Calibration of FI-ISK, an invasiveness screening tool for non-native freshwater invertebrates. Risk Analysis 30 (2): Walker JH (1925). An itinerary of Nottingham: Trent Bridge. Transactions of the Thoroton Society 29 (1925). Williams F, Eschen R, Harris A, Djeddour D, Pratt C, Shaw RS, Varia S, Lamontagne-Godwin J Thomas SE and Murphy ST (2010). The economic cost of invasive non-native species on Great Britain. Publ. Internet. [accessed 13 March 2011]. Winter M (2011). Environment Agency. Personal communication. Rees M, Nightingale J, Holdich D (eds.) (2011). Species Survival: Securing