Ranging behaviour of a large freshwater invertebrate, the white-clawed crayfish Austropotamobius pallipes

1. Radio-telemetry and mark-recapture methods were used to study the summer movements of adult and juvenile white-clawed crayfish, Austropotamobius pallipes from a wild population in a small braided stream, Dalton Beck, North Yorkshire, U.K. Radio-transmitters were attached to the chelae of 18 large (> 35 mm carapace length) crayfish and individuals were subsequently located to within 0.15 m. Additionally a total of 888 crayfish were marked with carapace brands, and 83 were recaptured. 2. Radio-tracked crayfish exhibited significantly greater local activity at dusk (21.00-00.00) than at dawn (03.00-06.00), or during morning (09.00-12.00) and afternoon (15.00-18.00) monitoring periods. 3. The greatest movements of radio-tracked crayfish occurred within 2 days of release. After this time, periods of residence were interspersed by movements to new locations, interpreted as establishment of ephemeral home areas. It is suggested that the initial large movements were the result of a 'fright response' following capture. 4. Movements varied widely between individuals, some moving more than 300 m in 10 days, while others showed little movement over an equivalent time period. Mean (+/- SE) daily movements were 4.6 +/- 3.0 m for males and 1.5 +/- 1.0 m for females. Although crayfish often used specific home sites for in excess of 7 days, displaced animals did not return to home sites. 5. The total distances travelled and the mean distance travelled per day by individual radio-tagged crayfish did not differ significantly between upstream or downstream directions or between males and females. This was also the case for marked crayfish used in mark-recapture studies. 6. Positive correlations between distance moved per day and size (carapace length) were found for downstream movements by male and female crayfish, but not for upstream movements. 7. Some preliminary observations of the response of crayfish to flood events suggested that these could be catastrophic with two out of five tracked crayfish found dead after a high stream-discharge event.