Burrowing activity of the invasive red swamp crayfish, Procambarus clarkii, in fishponds of La Brenne (France)

In 2007, the invasive crayfish Procambarus clarkii (Girard 1852) was identified for the first time in the "Parc Naturel Regional de la Brenne" (Indre department, Centre region, France). Ten infestation sites were found in the park, with 62 fishponds colonised. To better understand how the fishponds could be affected, and changes in invaded ponds, we followed crayfish burrowing activity in recently drained fishponds in two areas. Weekly investigations of burrowing activity by analysing their density, occupation and location with respect to the banks, and micro-habitat features were carried out for 2 months in spring. Burrow densities of 1.16 and 1.05 burrows m(-2) were found at Le Terrier Blanc and Coudreau 3 respectively. Procambarus clarkii sought humid soil in a dry pond and preferred burrowing on silt substrates. While no statistical differences were found between sites, some differences were observed among weeks independently of the sites. The mean mouth diameter of burrows in the two sites was 5.7cm (SD=2.17, n=214; min. value: 1.2cm; max. value: 14cm). Notwithstanding the situation in the last weeks of the study (when most chimneys were built), there was a certain turnover between open and plugged burrows, and in occupancy. Given the scale and duration of the study and the number of fishponds surveyed, this study successfully quantified the dynamics of burrowing in these ponds and conclusions provide a useful basis for future studies and give suggestions of how other colonised fishponds may be affected.