Signal crayfish abundances (Spring 2019) — Sélune Observatory

The invasive crayfish Pacifastacus leniusculus, also known as California crayfish or Signal, has been present in the Selune basin for several years, but has been confined upstream by the dams’ reservoirs. Its potential habitat will be considerably expanded due to the renaturation of the Selune Valley. The purpose of this monitoring is to describe whether, and at what speed, the Pacifastacus colonise the downstream of the Selune as it returns to a lotic state (“current river”), and from there colonise the previously inaccessible tributaries as they flow directly into the water reservoirs. The follow-up is carried out through two annual follow-up campaigns, in spring and autumn. The presence of Pacifastacus is sought by trapping via the Ecrevisse IAE Abundance Index. The IAE is carried out on the most sensitive stations of the colonisation front and consists of laying 15 unbaited nasses for 24 hours, installed at least every 10 metres. Abundance in Pacifastacus is obtained by counting captured individuals and taking into account catch effort.