Reintroducing the white-clawed crayfish to the River Lathkill. Conserving Natura 2000 Rivers. Conservation Techniques Series No 8.
Published source details
(2003) Reintroducing the white-clawed crayfish to the River Lathkill. Conserving Natura 2000 Rivers. Conservation Techniques Series No 8. English Nature report.
Published source details (2003) Reintroducing the white-clawed crayfish to the River Lathkill. Conserving Natura 2000 Rivers. Conservation Techniques Series No 8. English Nature report.
In Britain, the native white-clawed crayfish Austropotamobius pallipes is becoming increasingly scarce since the introduction of the larger North American signal crayfish Pacifastacus leniusculus, which kill and eat or displace native crayfish. Furthermore they carry a fungal disease which has wiped out several populations of white-clawed crayfish.
In 1993, the River Lathkill in western England lost its entire population of white-clawed crayfish in a mass mortality (this was not due to signal crayfish – instead it was thought to be due to an outbreak of crayfish plague). The UK LIFE project “Safeguarding Natura 2000 rivers in the UK” aims to expand the range or increase populations of white-clawed crayfish where suitable habitat is available but not presently occupied due to past historical impacts that had resulted in their extirpation. As part of this project a pilot crayfish reintroduction in 1999/2000 demonstrated that conditions in the River Lathkill were such that it could once again support white-clawed crayfish.
English Nature and David Rogers Associates conducted an experimental reintroduction and looked at methods of rearing large numbers of white-clawed crayfish from relatively small numbers of imported stock (of UK origin). A particular aim was to experimentally develop methods for rearing captive crayfish for reintroduction. A summary of preliminary attempts to raise juveniles in captivity during 2000, is outlined.
Study site: In April 2000, ten ovigerous (egg-carrying) female white-clawed crayfish Austropotamobius pallipes (transferred via a quarantine facility from a donor population at Bestwood ponds, Nottinghamshire) were held for re-introduction purposes within a large holding tank adjacent to the River Lathkill in Derbyshire, western England.
Crayfish cages Individual crayfish cages within the holding tank measured 15 cm x 10 cm x 10 cm (rigid 8 mm square mesh. These cages were surrounded by a one cubic metre fine meshed cage (mesh dimensions: 2 mm diameter circular). This mesh was fine enough to retain hatchling juveniles which were able to disperse through the 8 mm mesh of the brood cages, thus reducing the potential for their mother to predate them. The individual cages were also supported above the bottom of the holding tank to reduce the potential for bacterial and fungal infections.
The ten females and resulting eggs / juveniles were monitored for the remainder of the year.
Summary of results:
1) On 1 April 2000, the average number of eggs held by each female was estimated at 40.
2) On 20 June 2000, the eggs were observed hatching and there did not appear to be any losses.
3) On 10 July 2000, the number of Stage 2/3 juveniles was estimated at 40 per adult.
4) On 31 July 2000, it was observed that the juveniles had left their parent.
The adults in their individual cages were removed, leaving the juveniles in the fine mesh cage. Only 13 juvenile crayfish could be found.
The fate of the majority of potentially free-living juvenile crayfish (400) was not known.
Possibilities included: heavy predation by the adult females; and escape of juveniles through the 2 mm mesh of the 1m³ fine mesh cage into the main holding tank.
The juvenile crayfish were monitored on four further occasions until 20 May 2001. Full details of the number of surviving juveniles are given in Table 1 (attached). No juveniles survived beyond 10 months.
Conclusions: Initially, this method yielded similar numbers of eggs and Stage 2/3 juveniles to wild populations. However, the rearing of juveniles hatched in 2000 was not successful so in 2001 several new methods were trialled in an attempt to increase productivity (for a summary please see: www.conservationevidence.com/ViewSummary.aspx?ID=10523)
Note: If using or referring to this published study, please read and quote the original report, this is available at: http://www.english-nature.gov.uk/LIFEinUKRivers/publications/lathkill-crayfish.pdf