Improving trapping effectiveness for controlling the red swamp crayfish Procambarus clarkii

In Tuscany (Central Italy), a population of the invasive alien red swamp crayfish Procambarus clarkii is present in Lake Romena, close to a national park, and threatens the conservation of the native white-clawed crayfish Austropotamobius pallipes complex. A field study was conducted to reduce the abundance of the P. clarkii population through intensive trapping activities and improve the effectiveness of catches using three different types of traps: two wire mesh traps (cylindrical and rectangular) and artificial refuge traps. The study also aimed at assessing the composition of the lake animal community, particularly the presence of crayfish predators (using eDNA), and the potential spread of P. clarkii outside the lake. The control activities conducted over two trapping seasons in 2022–2023 led to a decrease of at least 50% in the abundance index (Catch Per Unit Effort) of the crayfish population. Cylindrical traps caught more individuals, especially larger ones and males, with artificial refuge traps capturing relatively more females and smaller individuals. eDNA sampling highlighted the presence of a diversified community, mainly composed of alien species, and some crayfish predators (e.g. fish). The surveys conducted in the surrounding areas revealed the presence of P. clarkii downstream of the lake. Control activities using different types of traps should be maintained to decrease further the P. clarkii population abundance, while additional management activities should be carried out to halt the spread of the species outside the lake in order to prevent its further ecological impacts.