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FALLOW DEER

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THE DISCOVERY OF A NATIVE WHITE-CLAWED CRAYFISH POPULATION IN SUFFOLK GEN BROAD Ecology of White-clawed crayfish White-clawed crayfish Austropotamobius pallipes are Britain’s only native freshwater crayfish and one of our largest freshwater invertebrates (Plate 3). They prefer clean well-oxygenated calcareous streams, rivers and lakes with a hard substrate of cobbles and stones and plenty of crevices, submerged plants, tree roots to provide refuges during the day. Crayfish are nocturnal, emerging at night to feed on a wide variety of plants, other invertebrates and detritus. They have a range of predators, such as fish, birds, rats, mink and otter and the young are also eaten by carnivorous insect larvae and nymphs such as beetles and dragonflies. As in most crayfish species, they are cannibalistic, for example, feeding on recently moulted individuals (Suffolk Biodiversity Action Plan). White-Clawed Crayfish were once common across Suffolk. However, the accidental introduction of the North American Signal Crayfish Pacifastacus leniusculus into the wild from crayfish farms since the 1970s has devastated the native population. They are larger and more aggressive than our native species and produce more young (Joint Nature Conservation Committee). They also carry a disease caused by the fungus Aphanomyces astaci known as crayfish plague against which they are immune, but which is deadly to White-clawed Crayfish. Affected animals die rapidly, often within a few days. Signal Crayfish therefore pose a serious threat to our native species through competition, predation and disease. White-clawed Crayfish are legally protected under the Wildlife & Countryside Act 1981, listed in the IUCN Red Data List and appear in Appendix III of the Bern Convention and Annexes II and V of the European Habitats Directive. They are a national (and Suffolk) Biodiversity Action Plan Species. Background to the study The last known Suffolk colony of White-clawed crayfish at Chad Brook near Long Melford was decimated by crayfish plague in July 2011 (Suffolk Biodiversity Partnership, Environment Agency). This devastating event hastened investigation of informal reports that an isolated population of native crayfish existed in the Haughley Watercourse, a tributary of the River Gipping near Stowmarket. A baseline survey was carried out in the autumn of 2011 to determine if a population existed and, if so, its extent along the river. In 2009, a pioneering native crayfish ‘ark’ site was established by the Environment Agency, Suffolk FWAG, Suffolk Wildlife Trust and Suffolk Biodiversity Partnership as a way to conserve some of Suffolk’s last remaining native crayfish (Environment Agency). Individuals were successfully translocated from the River Chad to form the basis of a new population in an isolated lake on a private farm, a site free of non-native crayfish. This conservation technique has since become more widely used and promoted (Buglife).

Trans. Suffolk Nat. Soc. 47 (2012)


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Suffolk Natural History, Vol. 47

Methods Haughley Watercourse was surveyed for evidence of the presence of native White-clawed crayfish by Diane Ling (Suffolk FWAG) and Genevieve Broad on 27 and 30 September 2011. The river length of 7 km was divided into 30 × 230 m lengths and a survey site randomly chosen from each 230 m length. The ‘standard’ survey method was used, during which all potential refuges at each site were searched by hand, using a net, for 10 minutes. The length of river searched at each site varied due to the different habitats present. Approximately 800 m of the Haughley Watercourse was surveyed. Environmental conditions were recorded including the strength of river flow, water temperature, depth, water clarity and channel width. Habitat features were also noted, such as the type and size of channel and bank refuges, the main substrate, siltation level, adjacent land use, amount of shading and the presence of species indicative of high water quality, such as bullhead. Sites were assessed for suitability as crayfish habitat. Each crayfish caught was sexed (if possible) and the carapace measured (Plate 4). Each individual was also assessed for signs of disease and breeding / moulting condition before being returned as quickly as possible to the same refuge. Results The weather conditions were warm and sunny on each day of survey. The river flow was low to normal; water depth varied between a few centimetres to over a metre. The water temperature at most sites was 14oC. All sites had a silt or clay substrate and the water clarity was poor to moderate. Most sites had no suitable bank refugia, although some had tree roots, and a few had with cobbles, rubble and other ‘hard’ shelter suitable for crayfish. The habitats along the river are highly variable, with pockets of suitable habitat bounded by unsuitable areas which are heavily shaded or overgrown with vegetation. Approximately half of the sites had emergent vegetation. No signs of alien crayfish were found. White-Clawed crayfish burrows were found at four sites and individuals caught at three sites. The abundance of individuals is probably under-recorded as efforts were made to disturb the animals as little as possible. No signs of disease were seen on any individuals. Table 1 shows the details of the individuals (seven live and one dead) caught at each site and the associated habitat. Unfortunately, severe pollution was recorded from field drains and from a private house mid-way along the watercourse survey. This appears to have had a highly detrimental effect on the downstream river for some considerable distance. Discussion It was established that a small population of native White-clawed crayfish exists at the lower end of the Haughley Watercourse, although it is not known how far the population extends downstream and upstream. Five sites upstream were considered to provide potentially suitable habitat and should be re-surveyed at a later date.

Trans. Suffolk Nat. Soc. 47 (2012)


WHITE-CLAWED FALLOW DEER CRAYFISH

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Table 1. White-clawed Crayfish individuals caught and the habitats at each site. Site No 26

27

29

Habitat

Individuals

Notes

Depth: between 6cm and over 1 m. 2 juveniles Found under alder Substrate: cobbles, gravel, silt. (4 mm each) tree roots. Large complex refugia of tree 1 juvenile roots, woody debris and (3 mm) vegetation. Bullhead present. Depth: over 1 m. 1 adult female Found in glass jar. Substrate: cobbles, gravel, silt. (22 mm) Found under a small Complex refugia. Bullhead 1 juvenile rock. present. (4 mm) Found in complex tree root system. 1 juvenile Found in same tree (5 mm) root system as above juvenile. 1 dead crayfish half grown (15 mm) Depth: over 1 m 1 adult female Found under a tree Substrate: gravel, clay, silt. (19 mm) root. A few cobbles, many tree roots. Bullhead present.

There is, at present, no means of eliminating crayfish plague or eradicating Signal (or other non-native) Crayfish (Environment Agency). To protect this population, and any others remaining in Suffolk, it is therefore essential to prevent the spread of the disease as far as possible by thoroughly cleaning equipment such as nets and waders and raising awareness of the problems amongst those who work in waterways, with landowners and with the general public, for example anglers. The discovery of this previously undocumented population of WhiteClawed Crayfish has shown that pockets of individuals may still exist, although they are likely to be few and far between due to the rapid and widespread rise of Signal Crayfish. The study recommends that further work should be undertaken to a) establish the level of immediate threat to this native crayfish population; b) consider designating the stretch of river where crayfish were found as a County Wildlife Site; c) providing neighbouring landowners / managers with information about native crayfish conservation; d) consider translocating some individuals from this population to an ‘ark’ site; e) source funding for more detailed surveys.

Trans. Suffolk Nat. Soc. 47 (2012)


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Suffolk Natural History, Vol. 47

Acknowledgements Thank you to all the landowners who made access to the watercourse possible and to Suffolk Biodiversity Partnership and Suffolk Naturalists’ Society for funding the study. References Buglife Selecting ark sites for White-lawed crayfish. Retrieved 23 January 2012 from: http://www.buglife.org.uk/conservation/currentprojects/Species+Action/ Conserving+our+Crayfish/Crayfish+Ark+Site+Selection+Criteria Environment Agency Suffolk’s last remaining native crayfish hit by plague 26 Sep 2011. Retrieved 23 January 2012 from: www.environment-agency.gov.uk/news/133536.aspx Joint Nature Conservation Committee 1092 White-clawed (or Atlantic stream) crayfish Austropotamobius pallipes Retrieved 23 January 2012 from: http://jncc.defra.gov.uk/protectedsites/sacselection/species.asp? featureintcode=s1092 Suffolk Biodiversity Partnership White-Clawed Crayfish species action plan (2003). Retrieved 23 January 2012 from: http://www.suffolkbiodiversity.org/content/suffolkbiodiversity.org/PDFs/ action-plans/whiteclawedcrayfish000.pdf Suffolk Biodiversity Partnership Newsletter June 2011. Retrieved 23 January 2012 from: http://www.suffolkbiodiversity.org/news.aspx

Trans. Suffolk Nat. Soc. 47 (2012)


G. Broad G. Broad

Plate 3: White-clawed crayfish Austropotamobius pallipes, Britain’s only native freshwater crayfish and one of our largest freshwater invertebrates (p. 15 ).

Plate 4: Each crayfish caught was sexed (if possible) and the carapace measured (p. 16).

THE DISCOVERY OF A NATIVE WHITE-CLAWED CRAYFISH POPULATION IN SUFFOLK  

Gen Broad

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