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International Journal of Biodiversity Science and Management 3 (2007) 209–216 Increasing the chances of successful reintroduction of white-clawed crayfish (Austropotamobius pallipes) in the Peak District National Park, UK David Rogers and Elizabeth Watson David Rogers Associates, 9 The Moat, Castle Donington, Derby, UK Key words: Austropotamobius pallipes, reintroduction, captive breeding, Peak District National Park, UK Biodiversity Action Plan, conservation strategy SUMMARY The current strategy for conserving white-clawed crayfish, Austropotamobius pallipes, contained in the United Kingdom Biodiversity Action Plan includes reintroduction to isolated water, free of signal crayfish, Pacifastacus leniusculus. The purpose of this project was to improve the chances of successful reintroduction of white-clawed crayfish into the River Lathkill in the Peak District National Park and to demonstrate how the method might be applicable to other reintroduction and captive breeding schemes. The method focussed on the habitat requirements of white-clawed crayfish, in particular the need of younger crayfish to conceal themselves from predators. Cages were built which provided juvenile crayfish with hides. The cages were tested in the river and juvenile growth and survival were recorded. Adult crayfish survival was only 50% annually whilst survival of juveniles was much less. Despite this, the habitat within the cages protected crayfish during moult and is thought to have increased their survival rate. The project has provided evidence for development of a successful reintroduction and captive breeding programme for white-clawed crayfish that will enable the conservation strategy to be undertaken more effectively. INTRODUCTION The white-clawed crayfish (Austropotamobius pallipes to encourage measures to reverse the previous Lereboullet) has become locally extinct from many losses, but despite this, the trend of decline has con- river systems in the United Kingdom (UK) over the tinued (Rogers 2003; Holdich et al. 2004). White- past 150 years (Holdich et al. 1999a, 2004) and if no clawed crayfish has an ‘unfavourable conservation action is taken, it is predicted to become virtually status’ in Wales, and indications are that this is the extinct (except in isolated pockets) in Britain with- case throughout the UK (Rogers and Watson 2004, in 35 years (Figures 1, 2 and 3). The white-clawed 2005). To achieve favourable conservation status, crayfish was identified as a priority species in the UK more active management is required, particularly Biodiversity Action Plan (UK BAP) (HMSO 1995) in two areas: conservation (including appropriate Correspondence: David Rogers, David Rogers Associates, 9 The Moat, Castle Donington, Derby, DE74 2PD. Email: firstname.lastname@example.org 209 Reintroducing white-clawed crayfish Rogers and Watson Figure 1 Areas where white-clawed crayfish have been Figure 2 Areas where signal crayfish have been recorded in the UK (open circles) compared with areas recorded in the UK (open circles) compared with areas occupied at present (filled circles); each dot represents occupied in 1980 (filled circles); each dot represents a a 10-km square 10-km square re-introduction) of native stocks, and containment and reduction of alien invasive crayfish species, e.g. No. Natives Signals of 10- 500 km signal crayfish, Pacifastacus leniusculus. The Euro- sq uar es occ pean Union Water Framework Directive 2000/60/ upi ed EC aims to achieve good ecological status in water bodies by 2015 (DEFRA 2003), but it alone will not prevent the demise of white-clawed crayfish. 100 Indeed, European astacologists consider reintro- 0 197 198 199 200 201 202 203 204 0 0 0 0 0 0 0 0 Year duction to be a ‘crucial part of management and conservation strategies’ (Schultz et al. 2002). Figure 3 Trend of expansion of signal crayfish and One action in the UK BAP for the white-clawed decline of white-clawed (native) crayfish; projected to crayfish is ‘if feasible, instigate and support reintro- 2040 duction programmes to selected sites’ (UK BAP 2005). To support this aim, the ecological require- addition, a practical project, the results of which are ments of white-clawed crayfish have been identified presented in this paper, has been undertaken on (Holdich 2003) and a protocol for reintroducing the River Lathkill, Derbyshire, to try to increase the them has been prepared (Kemp et al. 2003). In chances of success of reintroduction. The Lathkill 210 International Journal of Biodiversity Science and Management Reintroducing white-clawed crayfish Rogers and Watson crayfish project is part of the ‘Life in UK Rivers’ provide crayfish food. Shelter is also essential project (David Rogers Associates 2003). One of the because they moult many times in the first few aims was to develop practical techniques to expand years of life but also moult annually when they are the range or increase populations of white-clawed adult. During moult, they have soft bodies and are crayfish. The project rationale put forward a strong particularly vulnerable to cannibalism and preda- argument for reintroducing crayfish to suitable tion by eels Anguilla anguilla, pikes Esox Lucius, carp sites from which they had been lost, where non- Cyprinius carpio, mink Mustela vison, otter Lutra native species were not present and where factors lutra, and herons Ardea cinerea (Holdich 2003). such as instream obstructions made natural re- Typically, they occupy habitats under rocks, tree colonisation unlikely. This project explored how roots, macrophytes, dense algae, overhanging best to improve the chances of success. banks or any material that can provide conceal- Following international guidelines, the aim of ment from predators. Juvenile crayfish are very reintroduction is to establish a viable, free-ranging vulnerable to predation (from each other, adult population in the wild of a species that has become crayfish and predators) when they first become locally extinct (The International Union for the independent (they normally leave the adult in Conservation of Nature and Natural Resources July), especially during moulting, which is a regu- (IUCN) 1998). A captive breeding programme lar ordeal during the first summer of their life; established before a species is reduced to critically moulting occurs up to seven times during the first low numbers, with a view to re-establishing popula- summer (Pratten 1980). The requirement for tions in the wild, is an important element of overall each individual to find regularly a secluded and strategy (IUCN 1987). The Lathkill crayfish project secure habitat is of paramount importance for used both these conservation measures (reintro- survival. duction and captive breeding) to help improve the chances of success. BACKGROUND The native, white-clawed crayfish was once wide- spread in Britain and Ireland (Figure 1). It mainly The strategy for conservation of the white-clawed occurs in waters with good quality water, large crayfish in the UK has changed considerably over populations favouring relatively hard waters. It can the past 30 years. White-clawed crayfish, which was withstand intermittent organic pollution events, widely consumed in the 18th, 19th and early 20th such as from sewage treatment works, particularly if century, declined in favour as a food item in the UK there is incomplete mixing of the waters allowing it during the late 19th and 20th century as rivers to seek out higher oxygen concentrations (Holdich became more polluted by industrialisation. and Rogers 2000). The white-clawed crayfish is Signal crayfish were introduced to the British particularly susceptible to a virulent pathogen, cray- Isles in the 1970s and were cultivated for the food fish plague (Aphanomyces astaci). Signal crayfish industry. However, having escaped the farm (Pacifastacus leniusculus), which have been spread- ponds, they now thrive in British streams, lakes and ing throughout the UK since the early 1970s rivers (Hogger 1986). This exotic pest has led to (Figure 2), are the main agent for distribution of the depletion of plant life and fish eggs (www. crayfish plague. Figure 3 shows the relationship environment-agency.gov.uk), and has had a parti- between the distribution of the two species and, by cularly adverse effect on the native white-clawed extrapolation, shows that the native crayfish will be crayfish (Holdich et al. 1999b). In addition to the all but extinct in the UK by 2040, broadly concur- signal crayfish out-competing native crayfish with ring with predictions by Holdich et al. (2004) and regard to habitat space and food, they also act Sibley (2003). Although crayfish plague has been as vectors for a crayfish ‘plague’ (Aphanomyces the main cause of the demise of white-clawed cray- astaci), which kills infected natives (Schikora 1903; fish since 1970, habitat destruction, pollution and Alderman et al. 1990). When signal crayfish were competition with introduced species have also been first introduced, little was known about the distribu- contributing factors. tion of native, white-clawed crayfish in the UK White-clawed crayfish require suitable water (Thomas and Ingle 1971; Jay and Holdich 1981). quality conditions and associated plant, macro- Prospective signal crayfish farmers were able to invertebrate and detritus assemblages, which foster the notion that white-clawed crayfish were all International Journal of Biodiversity Science and Management 211 Reintroducing white-clawed crayfish Rogers and Watson but extinct because there were so few records of BACKGROUND TO THE RIVER their distribution. LATHKILL CRAYFISH PROJECT The ravages of crayfish plague were first docu- The River Lathkill contained a good population of mented in the UK by Bowler (1979), but at this time white-clawed crayfish until a mass mortality, prob- the government were supporting the expansion of ably due to crayfish plague, occurred in 1993. The the signal crayfish farming industry by subsidising entire population on the Lathkill and adjacent the British Crayfish Marketing Association (a signal catchments was wiped out and surveys showed that crayfish producers co-operative) through the no crayfish (native or alien) were present in the Ministry of Agriculture Fisheries and Food. In the Lathkill between 1993 and 1998 (Rogers 1998). In 1990s, the ministry even published an information 1999/2000, a small-scale study involving a release of leaflet on crayfish culture (Alderman and Wickins white-clawed crayfish into a protected area of the 1990). In the 1980s, conservation measures for the Lathkill demonstrated that the river could again white-clawed crayfish were virtually non-existent. It support this species; the present project aimed to was listed in Appendix III of the Bern Convention improve the success of such releases. in 1982, but only in 1986 was it legally protected in The project looked at methods of rearing suit- Britain, when it was included on Schedule 5 of the ably large numbers of white-clawed crayfish from Wildlife and Countryside Act 1981. This only pro- relatively small numbers of imported stock, which tected the species from ‘taking’ (Section 9 (1)) or would increase the potential for success whilst limit- ‘sale’ (Section 9(5)); it had little effect on conserva- ing impacts on donor populations. Introduced tion of the species, and its habitat was not protected stock was taken from local sources, as genetic dis- at all (as is still the case). The damage caused by the similarity is a possible problem in reintroduction spread of signal crayfish and the associated crayfish programmes. The project had a limited timetable plague was belatedly recognised in the 1990s and, so the reintroduction was primed by introduction in 1992, signal crayfish were added to Part I of of numbers of older stock. The Haddon Estate, Schedule 9 (effectively a list of pest species) of the which owned the river rights, was a partner in this Wildlife and Countryside Act 1981. Research project. River keepers were involved and existing focused on eradication of signal crayfish but no facilities adjacent to the river were utilised so that method proved successful. There have been when the project ended the opportunity to con- further legislative efforts to limit the spread of tinue breeding and reintroducing crayfish was signal and other non-native species of crayfish by available if funds permitted. trying to control the use of traps and the keeping of It is difficult to assess if reintroductions of these species. These are the Prohibition of Keeping white-clawed crayfish have been successful because, of Live Fish (Crayfish) Order 1996, the inclusion of after release, wild crayfish are hard to find again crayfish in the definition of ‘fish’ by the Depart- and it is not always possible to know if those found ment for Environment, Food and Rural Affairs and are introduced or from a relic source. To overcome its agencies under the Salmon and Freshwater this, Reynolds et al. (2000) released adults into Fisheries Act 1975 and the introduction of a raft black plastic mesh enclosures where survival was of byelaws by the Environment Agency in 2005. monitored for 3 months before full release from The consensus amongst experts is that signal the enclosures to the wild; results indicated 25% crayfish will continue to spread in the UK at the survival over the 3 months in the enclosures, expense of white-clawed crayfish, and provision suggesting that survival of white-clawed crayfish should be made to protect white-clawed crayfish in introduced to a semi-wild environment (preda- those areas that can be isolated from signal crayfish. tor-free enclosure) is very poor. For the Lathkill The Lathkill project is one such attempt to protect project, adult white-clawed crayfish were put into a white-clawed crayfish. It reintroduces crayfish to a protected environment (concrete tanks) alongside small catchment and focuses on improving the river the river. Adult survival and growth over a summer environment in line with known ecological require- and winter period were monitored. As the crayfish ments. The project, as well as being described as were individually marked by clipping of the cara- reintroduction, could also be described as ‘catch- pace, their success (in terms of survival and growth) ment-based captive breeding’. could be monitored. 212 International Journal of Biodiversity Science and Management Reintroducing white-clawed crayfish Rogers and Watson A previous study (LeBas and Rogers 2000) had this lasted for at least 2 moults (Rogers 1996), so shown that it was not possible to rear newly- would allow monitoring over the duration of the independent juvenile crayfish for a full year, even field study. Survival and growth in carapace length in a protected wild environment (cage in the was monitored over one winter period (25/10/00 concrete tank). The present project experimented to 15/05/01) and the subsequent summer period with three different protected habitats, created in (15/05/01 to 17/10/01). Survival results are pre- an attempt to improve survival. Having established sented in Table 1 and growth results appear in in laboratory trials the most successful habitat for Figure 4. juvenile survival, a field version was constructed and the trials extended for a further 2-year period. Juveniles Three different juvenile environments were created as laboratory trials to improve survival: a METHODS titanium mesh cage, an aquarium, and a flexible Monitoring adult survival and growth folded net cage (Photos 1–3). The aquaria also Sixty-two adult white-clawed crayfish (30 males, 32 provided the opportunity to observe the juveniles females) were introduced into concrete tanks con- leaving the adult. taining numerous short pipe shelters, adjacent to The flexible folded net was found to be a success- the River Lathkill and supplied with water from the ful environment for rearing juvenile white-clawed river. These crayfish were individually marked crayfish, whereas the titanium mesh cage and the using pleural and uropodal clipping (Chien and aquarium were less successful. Of 17 indepen- Avault 1979). Previous experience had shown that dent juveniles (June 2001) introduced to the Photo 1 Photo 2 Photo 3 Photo 4 Photos 1–4 Different juvenile environments tested in laboratory trials to improve white-clawed crayfish survival. Photo 1: titanium mesh cage to be placed in a large tank. Photo 2: aquarium. Photo 3: flexible folded net cage (partially covered with a roof tile) held in a large tank [the most successful experimental facility]. Photo 4: flexible cage, large version International Journal of Biodiversity Science and Management 213 Reintroducing white-clawed crayfish Rogers and Watson laboratory flexible folded net cage, 11 survived there was better survival in the winter period until November 2001, undergoing several moults, compared with the summer. The average and range and reaching an average carapace length of 10 mm. of growth of adult white-clawed crayfish during Therefore a larger field version of this cage was winter and summer, as measured by increase in constructed (Photo 4) for use in concrete tanks carapace length, is shown in Figure 4. Most adjacent to the River Lathkill, and survival and growth occurred in the summer period. Based on growth of juveniles from the stage when they first records of individually-marked crayfish, average become independent was measured over a two-year annual adult growth of 5 mm (9.1%) in females period (Table 2). and 7 mm (21.9%) in males was recorded over the complete year. For juveniles, the larger ver- sion of the flexible folded net cage proved to be a RESULTS successful environment for rearing crayfish. Survival and growth results are summarised in Monitoring adult survival and growth Table 2. Annual survival was approximately 50%: for males, survival was roughly the same during the summer and winter periods, whilst for females Summer Table 1 Survival of adult white-clawed crayfish from 25/10/00 to 17/10/01 Survival over period (%) Winter Summer Annual 4 Winter Males 70 71 50 2 Females 75 63 50 Males and females 73 67 48 Male Female Male Female No. of crayfish in experiment = 62 crayfish; 30 male, 32 Figure 4 Average and range of growth of adult female white-clawed crayfish in summer and winter Table 2 Summary of survival and growth of juvenile white-clawed crayfish in the large version of the flexible folded net cage No. of crayfish Average carapace in cage length in mm Average weight Date (Stage/age in years) (range) (g) Notes 26/10/02 66 12.8 1.1 (Juveniles) (8–17) 30/01/03 17 12.5 0.8 The small crayfish were difficult to (Juveniles) (10–15) find in the folds of the net and it was thought that some were not caught 10/7/03 34 16.7 – Two dead crayfish also found (Summerlings) (9–23) 04/11/03 14 24 4.9 (1+ crayfish) (18–30) 13/02/04 12 24 4.8 (1+ crayfish) (19–28) 30/06/04 9 28 5.8 (2+ crayfish) (22–34) 214 International Journal of Biodiversity Science and Management Increase in carapace length Reintroducing white-clawed crayfish Rogers and Watson The present project managed to reduce this risk, CONCLUSIONS thus giving a small population more chance of Increasing understanding and knowledge of white- survival. clawed and signal crayfish populations has influ- The Lathkill project has provided evidence to enced changes in the strategy for conservation of support conservation measures that could enable the white-clawed crayfish in the UK. There is no some of the conservation objectives for the white- known method of stopping the spread of signal clawed crayfish to be met successfully. The methods crayfish and associated crayfish plague, so the focus fulfil the IUCN Guidelines for Re-introductions of the conservation strategy is shifting towards the and the IUCN Policy Statement on captive breed- creation of populations of white-clawed crayfish in ing. Guidelines would have to be adapted on a areas isolated from signal crayfish. Although the case-by-case basis for other white-clawed crayfish crayfish in the present project were not introduced reintroductions, but they do provide a basis for directly to the wild, the survival and growth of 62 development of a reintroduction and captive individually-marked adults was traced over a 1-year breeding strategy. This project has shown that, in period in a semi-wild environment; indications are the wild, mortality of adult white-clawed crayfish that annual survival is 50% and that adult growth appears to be at least 50% per annum and is much only occurs in the summer period. A study of higher in juveniles and pre-adults. Captive rearing juvenile and pre-adult crayfish found that mortality of juvenile and pre-adult white-clawed crayfish in a was much higher than 50%, and the best material favourable habitat has provided a method for found to provide cover for protection from preda- reducing mortality, particularly during moult, due tion was loosely hung net curtain. Although, in the to predation, thus increasing the chances of long term, a self-sustaining population in the wild successful reintroduction. It is recommended must be able to withstand at least 50% annual that further work be undertaken to boost white- mortality, in the short term, a small-reintroduced clawed crayfish survival rates. population could be easily eliminated by predation. REFERENCES Alderman DJ, Holdich D and Reeve I. Signal crayfish HMSO. Biodiversity: The UK Steering Group Report – acting as vectors in crayfish plague in Britain. Volume II: Action Plans Tranche 1. London: HMSO; Aquaculture 1990;86:3–6 1995:157 pp. Alderman DJ and Wickins JF. Crayfish Culture. Ministry Hogger JB. Aspects of the introduction of “signal of Agriculture Fisheries and Food. Laboratory crayfish”, Pacifastacus leniusculus (Dana), into the Leaflet 1990;62:16pp. southern United Kingdom. Aquaculture 1986;58: Bowler K. Plague that has raged Europe. Fish Farmer 27–44 1979;2:34–5 Holdich D, Sibley P and Peay S. The white-clawed cray- Chien YH and Avault JWJr. Double cropping rice, fish – a decade on. 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International Journal of Biodiversity Science & Management – Taylor & Francis
Published: Dec 1, 2007
Keywords: AUSTROPOTAMOBIUS PALLIPES; REINTRODUCTION; CAPTIVE BREEDING; PEAK DISTRICT NATIONAL PARK; UK BIODIVERSITY ACTION PLAN; CONSERVATION STRATEGY
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