Difficult to deal with: attempts for eradication of marbled crayfish from a small urban pond

The marbled crayfish is an emerging invasive species, mainly due to parthenogenetic reproduction and high adaptability.Its successful eradication seems to be possible only in early detected populations and under favourable conditions.The population of marbled crayfish was discovered in a small urban pond in Prague, Czech Republic, in August 2020.Shortly afterwards, management was initiated with the aim of complete eradication.The pond was harvested and drained twice in November 2020 and October 2021.The crayfish were collected, the exposed pond bottom was treated by liming and left dry over winter.Predatory fish were stocked in the pond after refilling.Survival of the crayfish after the pond draining in 2021 was likely facilitated by up to 40 cm deep burrows found under large boulders.No specimens were observed in the nearby stream and marbled crayfish presence was not detected by environmental DNA screening in the stream and three other standing waters in the vicinity.The combined efforts resulted in a reduction in crayfish densities by an order of magnitude between successive harvests, but complete eradication of marbled crayfish was not achieved by 2023, as individual juveniles were captured during monitoring in the following two years.The perch-dominated fish stock apparently exerts a strong predation pressure that may control the crayfish population, as no marbled crayfish were captured during monitoring in 2024.The current status of the population is unclear, and further monitoring is warranted.Effective cooperation between different institutions and stakeholders has been successfully established, and the public and stakeholders have been educated about the risks of invasive species.However, with prolonged activities aiming to eradicate the crayfish, we also experienced decrease of public support for further radical actions.This experience provides a solid basis for future invasive crayfish management activities at sites with similar conditions.