The long-term effects and detection ranges of passive integrated transponders in white-clawed crayfish

Individual identification of the endangered white-clawed crayfish (Austropotamobius pallipes) can provide valuable information when assessing long-term survival of animals released into the wild; currently the most effective method is the use of passive integrated transponders (PIT) tags. A 360 days ex situ experiment was undertaken on 20-month, captive-born A. pallipes of carapace length (CL): 22–31 mm, to assess growth and survival after PIT-tagging. Thirty crayfish, matched for sex and size, were PIT-tagged, with 30 untagged crayfish as a control. All crayfish survived for the first 60-day post-tagging, indicating that there was no short-term survival effect of the procedure, in controlled conditions. There was no significant difference in survival or growth over the year between tagged and untagged crayfish, indicating that A. pallipes (≥22 mm CL) can be PIT-tagged safely. A second ex situ experiment investigated the detection range of adult, wild-caught, PIT-tagged A. pallipes. Eighteen A. pallipes were tagged with either 8 mm or 12 mm tags and added to different treatments (bare tank, tank with substrate, brick refuge, pipe refuge, pipe refuge plus slate), and the distance to detection was measured. Throughout all treatments the A. pallipes tagged with 12 mm PIT tags were detected significantly further away (35.6 ± 3.8 mm) than the 8 mm PIT-tagged crayfish.